Search

Background This phase 1 dose-escalation trial studied MM-302, a novel HER2-targeted PEGylated antibody–liposomal doxorubicin conjugate, in HER2-positive locally advanced/metastatic breast cancer. Methods Patients were enrolled in four cohorts: MM-302 monotherapy (8, 16, 30, 40, and 50 mg/m2 every 4 weeks [q4w]); MM-302 (30 or 40 mg/m2 q4w) plus trastuzumab (4 mg/kg q2w); MM-302 (30 mg/m2) plus trastuzumab (6 mg/kg) q3w; MM-302 (30 mg/m2) plus trastuzumab (6 mg/kg) and cyclophosphamide (450 mg/m2) q3w. Results Sixty-nine patients were treated. The most common adverse events (AEs) were fatigue and nausea. Grade 3/4 AEs of special interest included neutropenia, fatigue, mucosal inflammation, anemia, thrombocytopenia, febrile neutropenia, and palmar-plantar erythrodysesthesia. The MTD was not reached. With MM-302 ≥ 30 mg/m2, overall response rate (ORR) was 13% and median progression-free survival (mPFS) 7.4 months (95% CI: 3·5–10·9) in all arms. In 25 anthracycline-naïve patients, ORR was 28·0% and mPFS 10·9 months (95% CI: 1·8–15·3). Imaging with 64Cu-labeled MM-302 visualized tumor-drug penetrance in tumors throughout the body, including the brain. Conclusion MM-302 monotherapy, in combination with trastuzumab, or trastuzumab plus cyclophosphamide, was well tolerated and showed promising efficacy. The selected phase 2 MM-302 dose was 30 mg/m2 plus 6 mg/kg trastuzumab q3w.

This abstract was withdrawn by the authors.

Purpose Seribantumab is a fully human immunoglobulin G2 monoclonal antibody that binds to human epidermal growth factor receptor (HER) 3 (ErbB3), blocking heregulin (HRG) –mediated ErbB3 signaling and inducing ErbB3 receptor downregulation. This open-label randomized phase II study evaluated progression-free survival (PFS) with seribantumab in combination with once-per-week paclitaxel compared with paclitaxel alone in patients with platinum-resistant or -refractory ovarian cancer. A key secondary objective was to determine if any of five prespecified biomarkers predicted benefit from seribantumab. Patients and Methods Patients with platinum-resistant or -refractory epithelial ovarian, fallopian tube, or primary peritoneal cancer were randomly assigned at a ratio of two to one to receive seribantumab plus paclitaxel or paclitaxel alone. Patients underwent pretreatment core needle biopsy; archival tumor samples were also obtained to support biomarker analyses. Results A total of 223 patients were randomly assigned (seribantumab plus paclitaxel, n = 140; paclitaxel alone, n = 83). Median PFS in the unselected intent-to-treat population was 3.75 months with seribantumab plus paclitaxel compared with 3.68 months with paclitaxel alone (hazard ratio [HR], 1.027; 95% CI, 0.741 to 1.425; P = .864). Among patients whose tumors had detectable HRG mRNA and low HER2 (n = 57 [38%] of 151 with available biomarker data), increased treatment benefit was observed in those receiving seribantumab plus paclitaxel compared with paclitaxel alone (PFS HR, 0.37; 95% CI, 0.18 to 0.76; P = .007). The HR in patients not meeting these criteria was 1.80 (95% CI, 1.08 to 2.98; P = .023). Conclusion The addition of seribantumab to paclitaxel did not result in improved PFS in unselected patients. Exploratory analyses suggest that detectable HRG and low HER2, biomarkers that link directly to the mechanism of action of seribantumab, identified patients who might benefit from this combination. Future clinical trials are needed to validate this finding and should preselect for HRG expression and focus on cancers with low HER2 levels.

11042 Background: While the American Council on Graduate Medical Education (ACGME) set up a Planning Committee for Diversity in GME in 2018, no formalized milestones or training mandates have been announced. The nation-wide protests for racial justice following the senseless killings of Breonna Taylor, Ahmaud Arbery and George Floyd further brought to the forefront the need for immediate action to address widespread inequities across graduate medical education, our healthcare system and society as a whole. Therefore, the Johns Hopkins Hematology/Medical Oncology Fellowship Program focused on creating an anti-racism curriculum to foster dialogue on systemic racism and discrimination, grounded in the institutional and geographic context of our training program. Methods: Using the Kern six step curriculum development method, we created a comprehensive anti-racism initiative, which included virtual townhalls with Black alumni of the fellowship, book clubs, readings, and lectures. We sought to deepen the fellowship’s awareness of the impact of racism and inequity upon trainees, underrepresented minority oncologists and hematologists, and patients in order to develop initiatives to confront them productively. Trainees received a survey 6 months after the start of the curriculum to assess the impact of the initiatives upon trainees, and inform iterative changes to the curriculum. Results: 25 of 34 fellows across all post-graduate years (PGY) completed the survey. Fellows agreed that the curriculum was helpful (68%) and encouraging (60%). Collectively, fellows reported that the curriculum increased their awareness of instances of racism in medicine, caused them to think about next steps that the fellowship could take to address racism, and enabled them to identify available resources for support and further education. Respondents selected community engagement and recruitment of diverse fellowship classes as the most pressing priorities for the program. Conclusions: Social justice and anti-racism education belong in the formalized training of our hematology/medical oncology fellows. To this end, our ongoing curricular expansion is focusing on anti-racism training, diverse recruitment and youth mentorship. Collectively, a comprehensive yet program-specific approach facilitates opportunities for learning, engagement and development of the skills necessary to engage in this life-long work for ourselves, our communities and our patients.

3524 Background: The activity of pemetrexed is highly dependent on the intracellular enzyme folypolyglutamate synthase (FPGS) which adds glutamates to pemetrexed and yields very potent pemetrexed polyglutamates. Pemetrexed pentaglutamate (tetraglutamated pemetrexed) is 80-fold more potent than pemetrexed in inhibiting thymidylate synthase. Yet it is a poor drug candidate because it cannot readily cross the negatively charged cell membrane due to its own negative charge. We are developing LEAF-1401, a novel nanoliposomal encapsulation of gamma L-pentaglutamated pemetrexed. Because liposomes can readily be taken up by tumor cells, for its anti-tumor effect, LEAF-1401 can directly deliver pentaglutamated pemetrexed into tumor cells, bypassing the need for transmembrane folate carriers and FPGS which are both downregulated in resistant tumors. Methods: To measure drug levels in tumor, blood and various tissues (biodistribution), in vivo testing of LEAF-1401 and pemetrexed was conducted in a CT-26 murine colorectal carcinoma xenograft model. Animals were treated with a single dose of either LEAF-1401 (80mg/kg; equivalent to 32 mg/kg pemetrexed) or pemetrexed (118mg/kg). Tumor growth inhibition and clinical assessments were conducted. Animals were sacrificed: 5 mice per timepoint in each group and tumor, blood, liver, spleen and other tissues were harvested. Pentaglutamated pemetrexed levels were quantitatively analyzed by LC/MS/MS. Results: Compared to pemetrexed, LEAF-1401 treatment resulted in a 19-fold increase in exposure levels of pentaglutamated pemetrexed in the tumor and significant tumor growth inhibition. Plasma levels of pentaglutamated pemetrexed were high with LEAF-1401, but undetectable with pemetrexed. Like other liposomes, LEAF-1401 also resulted in accumulation of pentaglutamated pemetrexed in the liver and spleen (See Table below). Treatment appeared to be generally well tolerated. Conclusions: LEAF-1401, given at approximately a quarter of the equivalent pemetrexed dose, resulted in a 19-fold increase in pentaglutamate pemetrexed in tumor tissue compared to regular pemetrexed. LEAF-1401 represents a promising new class of novel nanoliposomal antifolates, that enhance the intratumoral delivery of potent polyglutamate antifolates, and improve antitumor activity while retaining an acceptable safety profile. [Table: see text]

Given the bulky nature of nanotherapeutics relative to small molecules, it is hypothesized that effective tumor delivery and penetration are critical barriers to their clinical activity. HER2-targeted PEGylated liposomal doxorubicin (MM-302, HER2-tPLD) is an antibody–liposomal drug conjugate designed to deliver doxorubicin to HER2-overexpressing cancer cells while limiting uptake into nontarget cells. In this work, we demonstrate that the administration and appropriate dose sequencing of cyclophosphamide can improve subsequent MM-302 delivery and enhance antitumor activity in preclinical models without negatively affecting nontarget tissues, such as the heart and skin. We demonstrate that this effect is critically dependent on the timing of cyclophosphamide administration. Furthermore, the effect was found to be unique to cyclophosphamide and related analogues, and not shared by other agents, such as taxanes or eribulin, under the conditions examined. Analysis of the cyclophosphamide-treated tumors suggests that the mechanism for improved MM-302 delivery involves the induction of tumor cell apoptosis, reduction of overall tumor cell density, substantial lowering of interstitial fluid pressure, and increasing vascular perfusion. The novel dosing strategy for cyclophosphamide described herein is readily translatable to standard clinical regimens, represents a potentially significant advance in addressing the drug delivery challenge, and may have broad applicability for nanomedicines. This work formed the basis for clinical evaluation of cyclophosphamide for improving liposome deposition as part of an ongoing phase I clinical trial of MM-302 in HER2-positive metastatic breast cancer. Mol Cancer Ther; 14(9); 2060–71. ©2015 AACR.

Background: Liposomal encapsulation of doxorubicin has addressed the cardiotoxicity of free doxorubicin, but has not achieved an improvement in anti-tumor activity in metastatic breast cancer. MM-302 is a HER2-targeted liposomal doxorubicin, specifically designed to target tumor cells overexpressing HER2 and minimize uptake into normal cells such as cardiomyocytes, which express low levels of HER2. MM-302 and MM-302 plus trastuzumab are being studied in patients as part of an ongoing Phase 1 clinical trial. Published reports indicate that deposition into solid tumors is a rate-limiting step in liposome-mediated delivery of drug to tumor cells. In order to understand drug deposition into solid tumors, we have radiolabeled MM-302 with 64Cu for imaging by PET/CT. Further, preclinical work has demonstrated that pretreatment with cyclophosphamide has the ability to improve liposomal drug delivery by making the tumor microenvironment permissive for deposition and retention of liposomes. This Phase 1 study evaluates the delivery of 64Cu-MM-302 to solid tumors and the ability of cyclophosphamide pretreatment to increase delivery of 64Cu-MM-302 to tumors. Methods: Patients aged ≥ 18 years with histologically confirmed HER2-positive advanced breast cancer that has progressed or recurred on standard therapy or for which no standard therapy exists, who have adequate performance status, bone marrow reserve and organ function, were eligible for the study. Patients received 30 mg/m2 of MM-302 plus 6 mg/kg trastuzumab, q3w and 400 MBq (10.8 mCi; 3-5 mg/m2, doxorubicin basis) of 64Cu-MM-302 (cycle 1 only) with or without pretreatment of 450 mg/m2 cyclophosphamide. Patients underwent PET/CT on the day of administration and on day 2, day 3 or both. The primary goal of this analysis was to study delivery of 64Cu-MM-302 and the effect of cyclophosphamide pretreatment. Other endpoints being studied include safety, dosimetry, and treatment response. Results: Combination of MM-302 with cyclophosphamide was well tolerated and no issues were reported related to 64Cu-MM-302 administration or imaging. Uptake of 64Cu-MM-302 in tumor lesions increased over time with significant deposition at 24 and 48 h while activity in the blood decreased over time. Median lesion deposition of 64Cu-MM-302 (as % i.d./kg) in the patients with cyclophosphamide pretreatment was higher than in those without pretreatment: 6.0 (n=5 patients/20 lesions) vs. 4.4 (n=7 patients/36 lesions) at 24 h and 7.6 (n=4 patients/16 lesions) vs. 4.0 (n=4 patients/17 lesions) at 48 h. Conclusions: PET/CT imaged 64Cu-MM-302 deposition into diverse tumor lesions, including liver, brain and bone metastases. Our preliminary data thus far suggest that cyclophosphamide pretreatment increases delivery of 64Cu-MM-302 to patient tumors, as predicted by preclinical models. Correlation between 64Cu-MM-302 tumor deposition and lesion/patient response is currently being investigated. Citation Format: Kathy Miller, Patricia M LoRusso, Pamela Munster, Ian Krop, Cynthia Ma, Helen Lee, Joe Reynolds, Karen Campbell, Victor Moyo, Bart Hendriks, Thomas Wickham, Barry A Siegel, Anthony F Shields. Effect of pre-treatment with cyclophosphamide on MM-302 (HER2-targeted liposomal doxorubicin) deposition in HER2-positive metastatic breast cancer patients assessed by 64Cu-MM-302 PET/CT [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-15-04.

The ErbB family of receptor tyrosine kinases comprises four members: epidermal growth factor receptor (EGFR/ErbB1), human EGFR 2 (HER2/ErbB2), ErbB3/HER3, and ErbB4/HER4. The first two members of this family, EGFR and HER2, have been implicated in tumorigenesis and cancer progression for several decades, and numerous drugs have now been approved that target these two proteins. Less attention, however, has been paid to the role of this family in mediating cancer cell survival and drug tolerance. To better understand the complex signal transduction network triggered by the ErbB receptor family, we built a computational model that quantitatively captures the dynamics of ErbB signaling. Sensitivity analysis identified ErbB3 as the most critical activator of phosphoinositide 3-kinase (PI3K) and Akt signaling, a key pro-survival pathway in cancer cells. Based on this insight, we designed a fully human monoclonal antibody, seribantumab (MM-121), that binds to ErbB3 and blocks signaling induced by the extracellular growth factors heregulin (HRG) and betacellulin (BTC). In this article, we present some of the key preclinical simulations and experimental data that formed the scientific foundation for three Phase 2 clinical trials in metastatic cancer. These trials were designed to determine if patients with advanced malignancies would derive benefit from the addition of seribantumab to standard-of-care drugs in platinum-resistant/refractory ovarian cancer, hormone receptor-positive HER2-negative breast cancer, and EGFR wild-type non-small cell lung cancer (NSCLC). From preclinical studies we learned that basal levels of ErbB3 phosphorylation correlate with response to seribantumab monotherapy in mouse xenograft models. As ErbB3 is rapidly dephosphorylated and hence difficult to measure clinically, we used the computational model to identify a set of five surrogate biomarkers that most directly affect the levels of p-ErbB3: HRG, BTC, EGFR, HER2, and ErbB3. Preclinically, the combined information from these five markers was sufficient to accurately predict which xenograft models would respond to seribantumab, and the single-most accurate predictor was HRG. When tested clinically in ovarian, breast and lung cancer, HRG mRNA expression was found to be both potentially prognostic of insensitivity to standard therapy and potentially predictive of benefit from the addition of seribantumab to standard of care therapy in all three indications. In addition, it was found that seribantumab was most active in cancers with low levels of HER2, consistent with preclinical predictions. Overall, our clinical studies and studies of others suggest that HRG expression defines a drug-tolerant cancer cell phenotype that persists in most solid tumor indications and may contribute to rapid clinical progression. To our knowledge, this is the first example of a drug designed and clinically tested using the principles of Systems Biology.

e14515 Background: Polyglutamation of antifolates by folylpolyglutamate synthase (FPGS) greatly enhances their activity, e.g. pentaglutamated pemetrexed is 80-fold more potent at inhibiting thymidylate synthase than pemetrexed. Polyglutamated antifolates however, do not readily cross the cell membrane, due to high negative charge and molecular mass. The resulting poor intracellular bioavailability greatly limits their therapeutic potential. Gamma glutamyl hydrolase (GGH) enzyme removes the glutamate residues from polyglutamates, which then are subject to efflux pumps. Resistance to pemetrexed has been linked to downregulation of both FPGS and folate transporters and upregulation of both GGH and the efflux pumps. We have been developing a novel class of nanoliposomal polyglutamated-antifolates including: LEAF-1401; nanoliposomal gamma-L pentaglutamated antifolate LEAF-1701; nanoliposomal alpha-L pentaglutamated antifolate These were designed to address key challenges of currently used antifolates namely: Bypassing the need for intracellular endogenous FPGS Direct delivery of the much more active polyglutamates through nanoliposome technology Minimizing toxicity to normal cells Mitigating against key antifolate resistance mechanisms such as downregulation of FPGS and folate transporters, and upregulation of GGH and efflux pumps Methods: In vitro testing in cell lines and in vivo testing in mice were performed using LEAF-1701 and LEAF-1401 in various tumor types. Results: Compared to pemetrexed: In vitro, LEAF-1701 and LEAF-1401 were more potent, in various cell lines while sparing normal neutrophils, colon and liver cells. In vivo, in H292 lung cancer xenografts, treatment with LEAF-1701 improved survival to 59 days vs 39 days for pemetrexed. In A549 lung cancer mouse orthotopic models, treatment with LEAF-1401 reduced metastatic tumor burden and prevented new metastases. In vivo, in mice doses of up to 80 mg/kg IV weekly were tolerated with little impact on blood counts and chemistry. Conclusions: LEAF-1701 and LEAF-1401 are innovative new chemical entities with promising preclinical activity and improved safety profiles and are now advancing to the clinic.

Background: MM-302 is a novel antibody drug conjugate (ADC) combining PEGylated liposomal doxorubicin with anti-HER2 scFvs. MM-302 was designed to overcome the limitations associated with using anthracyclines in the treatment of HER2-positive breast cancer. Anthracyclines have been an effective backbone of breast cancer therapies for decades. However, cardiotoxicity issues associated with free anthracyclines have limited their effective use. While liposomal doxorubicin formulations have succeeded in reducing cardiotoxicity, they have failed to demonstrate clear-cut efficacy advantages. MM-302 specifically targets tumor cells overexpressing HER2 with minimal uptake into normal cells such as cardiomyocytes which express low levels of HER2. This Phase 1 study evaluates the safety of MM-302 in patients with HER2+ advanced breast cancer. Methods: Patients aged ≥ 18 years with histologically confirmed HER2+ advanced breast cancer that have progressed or recurred on standard therapy or for which no standard therapy exists having measurable disease, adequate performance status, bone marrow reserve and organ function, were eligible for the study. A post-treatment biopsy was required. A 3 + 3 dose escalation design (8, 16, 30, 40 and 50 mg/m2 administered i.v. q4w) is used to identify a Phase 2 dose followed by expansion arms at 40 and 50 mg/m2 for a preliminary indication of activity. Secondary endpoints included determination of dose-limiting toxicity, adverse event(s), and PK of MM-302, as well as overall response and clinical benefit rates of MM-302. Results: We report data from MM-302 dose levels (30, 40 and 50 mg/m2 as monotherapy) that are expected to be therapeutically relevant. Eight patients dosed at presumed sub-therapeutic dose levels of 8 and 16 mg/m2 were excluded from the efficacy analysis. Patients had received a median of 9.5 prior agents (range 3-19) in all settings. All patients had been treated with trastuzumab, 96% with prior taxanes, 67% lapatinib, 54% anthracyclines and 33% T-DM1. At the time of this analysis (n = 27), overall response rate was 17% (4 out of 24 evaluable patients) and the estimated median Progression Free Survival (PFS) was 5.7 months, with six patients still receiving treatment. Eight patients (30%) had a PFS of greater than 6.0 months. Neutropenia was the most common treatment-related grade 3/4 toxicity and occurred in 15% of patients. The most common adverse events include fatigue, nausea, vomiting, and decreased appetite. Constipation, stomatitis, headache and rash were also observed in greater than 20% of patients. No patients discontinued treatment for toxicity. There was no protocol defined cardiotoxicity observed across all dose cohorts and five patients have had cumulative anthracycline exposure exceeding 550 mg/m2 without a reduction in left ventricular ejection fraction. Conclusion: Overall MM-302 appears to be well tolerated with promising activity in this ongoing trial. Further development is continuing combining MM-302 with trastuzumab and/or cyclophosphamide. In addition, we are evaluating the use of PET imaging to correlate liposomal tumor deposition as an additional potential patient preselection strategy. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-12-29.

Background: Anthracyclines have been an effective backbone of breast cancer therapies for decades. However, cardiotoxicity issues associated with free anthracyclines have limited their effective use in the clinic and ledto the exploration of anthracycline-free regimens, particularly with HER2- positive cancers that require treatment with another cardiotoxic agent, trastuzumab. While liposomal doxorubicin formulations have succeeded in reducing cardiotoxicity, they have failed to demonstrate clearcut efficacy advantages and can involve other toxicities. To address the safety and efficacy limitations of currently available anthracyclines, we have designed a new liposomal formulation, MM-302, that targets doxorubicin to HER2- overexpressing tumor cells. Antibody fragments that bind to HER2 without blocking HER2-mediated signaling are coupled to the outer surface of pegylated liposomal doxorubicin. MM-302 specifically binds and enters tumor cells overexpressing HER2 with minimal uptake into normal cells such as cardiomyocytes which express low levels of HER2. Materials and methods: MM-302, untargeted pegylated liposomal doxorubicin (PLD), and free doxorubicin were compared for their uptake into target and nontarget cells, pharmacokinetics, biodistribution, tumor microdistribution using FACS and confocal microscopy, and anti-tumor activity in BT-474 and NCI-N87 xenograft models. Results: Cellular uptake studies in tumor cell lines expressing various levels of HER2 demonstrate that MM-302 delivers significantly higher doxorubicin levels to HER2 over-expressing tumor cells compared to PLD as well as similar or higher levels than highly permeable free doxorubicin. However, in human cardiomyocytes, while free doxorubicin was again taken up at high levels, doxorubicin uptake was dramatically lower with both MM-302 and PLD. Pharmacokinetic studies in mice demonstrate that MM-302 has a similar half life, clearance, and organ distribution compared to PLD. In HER2-overexpressing BT-474 breast and NCI-N87 gastric tumor xenografts, MM-302 exhibits superior anti-tumor activity to both free anthracyclines and PLD. Tumor microdistribution studies further suggest that differences in the localization of doxorubicin in the tumor may be responsible for the enhanced activity of MM-302 compared to free doxorubicin and PLD. Discussion: These preclinical data suggest that MM-302 may provide in clinical practice a new opportunity to specifically deliver an anthracycline to HER2-overexpressing tumors with a potentially cleaner safety profile and improved efficacy over currently available free or liposomal doxorubicin. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-14-09.

BACKGROUND: Epoetin a (EPO) continues to be the initial treatment of choice for most anemic patients with myelodysplastic syndromes (MDS). Over the years, different therapeutic strategies have been adopted to optimize the clinical benefits of EPO in this setting. METHODS: In the current meta-analysis of published literature, erythroid response (ER) rates with EPO as a single agent versus its combination with granulocyte–colony-stimulating factor (G-CSF) or granulocyte-macrophage–colony-stimulating factor (GM-CSF) were compared. RESULTS: The assessment indicated that the ER rates were comparable between the 2 EPO-based therapeutic strategies. Furthermore, EPO monotherapy at a higher dose of 60,000 to 80,000 U weekly produced significantly higher ER rates (64.5%) compared with the standard oncology dose of 30,000 to 40,000 U weekly either as a single agent (49%; P < .001) or in combination with G-CSF/GM-CSF (50.6% P ¼ .007). In addition, when transfusion-dependent patients were assessed separately, both EPO monotherapy and its combination with G-CSF/GM-CSF produced comparable and appreciable levels of transfusion independence (28.8% and 24.8%, respectively). CONCLUSIONS: In the current meta-analysis, higher doses of EPO demonstrated better ER rates compared with EPO at standard doses alone or in combination with G-CSF/GM-CSF. Furthermore, the authors concluded that prospective clinical studies are warranted to evaluate the use of higher doses of EPO in anemic patients with MDS. Cancer 2009;115:706–15. V C 2009 American Cancer Society.

Heregulin-driven ERBB3 signaling has been implicated as a mechanism of resistance to cytotoxic and antiendocrine therapies in preclinical breast cancer models. In this study, we evaluated the effects of seribantumab (MM-121), a heregulin-blocking anti-ERBB3 monoclonal antibody, alone and in combination with the aromatase inhibitor letrozole, on cell signaling and tumor growth in a preclinical model of postmenopausal estrogen receptor–positive (ER+) breast cancer. In vitro, heregulin treatment induced estrogen receptor phosphorylation in MCF-7Ca cells, and long-term letrozole-treated (LTLT-Ca) cells had increased expression and activation levels of EGFR, HER2, and ERBB3. Treatment with seribantumab, but not letrozole, inhibited basal and heregulin-mediated ERBB receptor phosphorylation and downstream effector activation in letrozole-sensitive (MCF-7Ca) and -refractory (LTLT-Ca) cells. Notably, in MCF-7Ca–derived xenograft tumors, cotreatment with seribantumab and letrozole had increased antitumor activity compared with letrozole alone, which was accompanied by downregulated PI3K/MTOR signaling both prior to and after the development of resistance to letrozole. Moreover, the addition of an MTOR inhibitor to this treatment regimen did not improve antitumor activity and was not well tolerated. Our results demonstrate that heregulin-driven ERBB3 signaling mediates resistance to letrozole in a preclinical model of ER+ breast cancer, suggesting that heregulin-expressing ER+ breast cancer patients may benefit from the addition of seribantumab to antiendocrine therapy. Mol Cancer Ther; 14(11); 2642–52. ©2015 AACR.

Introduction: MM-302 is an antibody-liposomal drug conjugate designed specifically to target doxorubicin to HER2-overexpressing tumor cells. MM-302 is currently being evaluated in a Phase II trial in HER2 positive metastatic breast cancer (NCT02213744). HER2-positive breast cancer accounts for about 15-20% of breast cancer cases and is defined as IHC 3+ or 2+ and HER2 FISH amplified. A substantial percentage (∼30%) of breast cancer patients show positive HER2 IHC (1+/2+) without HER2 gene amplification (“HER2 intermediate”). This population is not eligible for treatment with currently approved HER2-targeted therapies. The purpose of this study is to investigate the in vitro and in vivo delivery/activity of MM-302 in the HER2 intermediate population. Methods: In vitro binding and viability studies were performed with MM-302, PEGylated liposomal doxorubicin (PLD) and T-DM1 with a panel of cell lines representing a range of HER2 expression. HER2-mediated cellular delivery of MM-302 was investigated in vivo in different HER2 expressing tumor models using a novel PEG immunofluorescent assay herein described. Frozen tumor tissues were stained for PEG, HER2 and cytokeratin, side-by-side with two cell standard arrays: A PEG array, obtained by cell incubation with increasing concentrations of MM-302, and a HER2 array, built with a panel of cell lines at different HER2 expression (from ∼50,000 to over 1,000,000 HER2). Image analysis and subsequent regression of the PEG and HER2 fluorescent intensities from the respective standards allowed for the quantification of the number of liposomes in individual tumor cells at distinct HER2 receptor numbers. Tumor cell apoptosis following MM-302 cellular delivery was measured by immunofluorescence followed by image analysis. Results: MM-302 efficiently bound to, and induced, tumor cell death across a panel of cell lines, with no significant distinction between cell lines expressing 300-400,000 HER2 or above 1,000,000 HER2 (IHC 3+). Conversely, T-DM1, used as control, significantly bound to and induced cell death only to cells above 1,000,000 HER2 (IHC 3+). In vivo evaluation of HER2-mediated cellular delivery via PEG immunofluorescent staining showed that MM-302 can be equally efficiently internalized in tumor cells above 1,000,000 HER2 (IHC 3+) and in the HER2 intermediate expression range. Preliminary analysis on post-treatment patient biopsies collected during a MM-302 Phase I study (NCT01304797) support clinical translation of these preclinical observations. Conclusions: Treatment with MM-302 results in efficient HER2 binding and liposome cellular delivery across a panel of HER2 models that extend beyond the traditional HER2 positive definition. This study suggests that MM-302 may be a promising candidate for the treatment of patients with intermediate HER2 expression who represent a significant unmet medical need. Citation Format: Elena Geretti, Christopher Espelin, Bambang Adiwijaya, Nancy Dumont, Silvia Coma, Zachary Koncki, Minh Pham, Gabriela Garcia, Troy Bloom, Victoria Rimkunas, Joe Reynolds, Karen Campbell, Victor Moyo, Istvan Molnar, Patricia LoRusso, Ian Krop, Kathy Miller, Cynthia Ma, Pamela Munster, Thomas Wickham. HER2-targeted PEGylated liposomal doxorubicin (MM-302) efficiently targets the HER2 intermediate cell population in vitro and in vivo. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-061.

Background: Nal-IRI (MM-398, nanoliposomal irinotecan) is designed for extended circulation relative to free irinotecan and to exploit leaky tumor vasculature for enhanced drug delivery to tumors. Tumor deposition of nal-IRI and subsequent conversion to SN-38 in both neoplastic cells and tumor associated macrophages (TAM) may positively correlate with response to therapy. In phase I studies of nal-IRI, activity has been shown in metastatic breast cancer (MBC), pancreatic and colorectal cancer. Ferumoxytol (FMX) is an iron-oxide superparamagnetic nanoparticle that has been used off-label for its MRI contrast properties. FMX has long-circulating pharmacokinetics and is taken up by TAMs with similar distribution patterns to nal-IRI in preclinical models. A single site pilot study established the feasibility of performing quantitative FMX MRI. Thirteen patients with advanced cancer (3 with ER/PR+ MBC) were imaged with FMX MRI and treated with nal-IRI. Median tumor lesion FMX uptake in the pilot study was 32.6 and 34.5 μg/mL at 1 h and 24 h, respectively. Lesions with FMX uptake above the median were associated with greater reductions in tumor size following treatment with nal-IRI as determined by CT lesion measurements. The relationship between FMX levels in tumor lesions and nal-IRI activity may serve as a potential biomarker for nal-IRI deposition and response in solid tumors. This study has been expanded to include additional MBC patients to further evaluate the technical feasibility of FMX MRI at multiple study sites, and to evaluate activity of nal-IRI in patients with MBC. Trial Design: Three cohorts of 10 patients with MBC in the following categories will be enrolled: ER and/or PR positive/HER2-negative, triple negative (TNBC) and MBC with brain metastases. An imaging phase will be followed by a treatment phase. The imaging phase consists of a baseline MRI scan, FMX infusion, and follow-up MRI scans at 1-4 and 24 h after infusion. The treatment phase begins 1-6 days after imaging and consists of nal-IRI 80 mg/m2 q2w. A pretreatment biopsy is required for correlative studies. Study Objectives: The primary objective of this multisite expansion is to investigate the feasibility of FMX quantitation in tumor lesions at multiple lesion sites in breast cancer. The secondary objective is to characterize the efficacy of nal-IRI in patients with metastatic breast cancer. Eligibility Criteria: The key inclusion criteria include patients with MBC, ECOG 0 or 1 with adequate bone marrow reserve and no prior topoisomerase 1 inhibitor or anti-VEGF treatment. ER and/or PR positive/HER2-negative and TNBC patients must have had 1-3 prior lines of chemotherapy in the metastatic setting and have at least 2 measurable lesions. Patients with brain metastasis must be neurologically stable and have new or progressive brain metastases after prior radiation therapy with at least one lesion measuring ≥ 1 cm in longest diameter on gadolinium-enhanced MRI. Status: This trial is currently recruiting patients. Citation Format: Sachdev JC, Ramanathan RK, Raghunand N, Anders C, Munster P, Minton S, Northfelt D, Blanchette S, Campbell K, Lee H, Klinz SG, Hendriks BS, Moyo V, Fitzgerald JB, Korn RL. A phase 1 study in patients with metastatic breast cancer to evaluate the feasibility of magnetic resonance imaging with ferrumoxytol as a potential biomarker for response to treatment with nanoliposomal irinotecan (nal-IRI, MM-398). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr OT3-02-14.

417 Background: NAPOLI-1 is a global, randomized Phase 3 study evaluating nal-IRI—a nanoliposomal irinotecan—with or without 5-FU/LV in 417 patients with mPAC previously treated with gemcitabine-based therapy. Primary survival analysis was based on 313 events. Nal-IRI+5FU/LV significantly improved overall survival (OS, primary endpoint), 6.1 months (mo) vs 4.2 mo; with 5-FU/LV (unstratified hazard ratio [HR] = 0.67; P = 0.012). Primary endpoint was supported by improved progression-free survival, time to treatment failure, objective response and CA19-9 tumor marker response rates, and manageable toxicities. An updated analysis of OS, 6- and 12-month-survival estimates, and safety is presented. Methods: The updated descriptive analysis of OS, based on 378 events (25 May 2015), includes data from all randomized patients across the 3 arms. Results: After 378 OS events, nal-IRI+5-FU/LV (n = 117) retained an OS advantage relative to 5-FU/LV (n = 119): 6.2 mo (95% confidence interval [CI], 4.8–8.4) vs 4.2 mo (95% CI, 3.3–5.3) with an unstratified HR of 0.75 (P = 0.0417). In contrast, there was no OS advantage with nal-IRI monotherapy (n = 151) vs 5-FU/LV (n = 149): 4.9 mo [95% CI, 4.2–5.6] vs 4.2 mo [95% CI, 3.6–4.9], HR = 1.08; P = 0.5. Six-month survival estimates were 53% (95% CI, 44–62%) for nal-IRI+5-FU/LV vs 38% (95% CI, 29–47%) for 5-FU/LV; 12-month survival estimates were 26% (95% CI, 18-35%) for nal-IRI+5-FU/LV vs 16% (95% CI, 10–24%) for 5-FU/LV. With events in nearly all patients, the OS curves converge at ~20 mo with 19 patients (16.2%) surviving beyond 20 mo. This is a reason for attenuation of the HR estimate and unstratified log rank p-value. The most common grade 3+ adverse events occurring at a ≥ 2% incidence in the nal-IRI-containing arms were neutropenia, diarrhea, vomiting, and fatigue. Conclusions: In an updated analysis, the median OS benefit for nal-IRI+5FU/LV over 5-FU/LV was maintained, with a similar safety profile. Nal-IRI+5-FU/LV may be a new standard of care for patients with mPAC previously treated with gemcitabine-based therapy. Clinical trial information: NCT01494506.

MM-398 is a stable nanotherapeutic encapsulation of the prodrug irinotecan (CPT-11) with longer plasma half-life and higher tumor deposition due to an enhanced permeability and retention effect. Pancreatic cancer has responded poorly to many therapeutics, largely because of inadequate drug penetration due to poor vascularization and the highly aggressive, hypoxic nature of the disease. We sought to better understand how MM-398, a relatively large (100nm) liposomal nanotherapeutic, could be used treat pancreatic cancer. We have tested MM-398 in several pancreatic xenograft models: BxPC3 (KRAS wild type), AsPC-1(KRAS G12D) , Panc-1 (KRAS G12D) and MiaPaCa (KRAS G12C). All models demonstrated complete tumor regression at 20 mg/kg or a human equivalent dose of 60-120 mg/m2. At this same dose, MM-398 suppresses tumor growth in a gemcitabine insensitive AsPC-1 xenograft. MM-398 functionally blocked AsPC-1 tumor cell proliferation as measured by ki-67 staining; however, gemcitabine administered at its maximum tolerated dose did not impact proliferation. MM-398 is currently in multiple clinical trials, including a phase 3 trial for patients with advanced gemcitabine-resistant pancreatic cancer (NAPOLI-1). In order to further understand mechanisms driving response to MM-398, we screened and ranked several cell lines for their ability to convert irinotecan into the active metabolite, SN38. BxPC3 and HT-29 tumors ranked highest in ability to convert irinotecan to SN-38, as measured by HPLC. In a BxPC3 pancreatic orthotopic model which spontaneously metastasizes, 10 mg/kg MM-398 significantly reduced both primary and metastatic tumor load as measured by ex vivo biophotonic imaging of BxPC3luc cells to spleen, lung, liver, diaphragm and GI associated lymph nodes (p In summary, MM-398 induces tumor regression in multiple mouse models of pancreatic cancer, including an orthotopic metastatic model. MM-398 activity may be driven in part by the ability to modify tumor microenvironment parameters, such as hypoxia and vascularization, both of which limit efficacy of chemotherapeutic agents in the treatment of pancreatic cancer. These data support the continued investigation of MM-398 in pancreatic cancer. Citation Format: Nancy Paz, Peter Laivins, Clet Niyikiza, Ulrik Nielsen, Jonathan Fitzgerald, Ashish Kalra, Milind Chalishazar, Stephan Klinz, Jaeyeon Kim, Daryl Drummond, Dmitri Kirpotin, Victor Moyo, Eliel Bayever. MM-398/PEP02, a novel liposomal formulation of irinotecan, demonstrates stromal-modifying anticancer properties. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Progress and Challenges; Jun 18-21, 2012; Lake Tahoe, NV. Philadelphia (PA): AACR; Cancer Res 2012;72(12 Suppl):Abstract nr A63.

BACKGROUND: Epoetin-α initiated once weekly, followed by once-every-3-weeks maintenance, was effective and well tolerated for chemotherapy-induced anemia. This study evaluated a starting dose of epoetin-α 120,000U once every 3 weeks for chemotherapy-induced anemia using early and late initiation regimens. METHODS: Patients with baseline hemoglobin 11.0-12.0 g/dL were randomly assigned to early intervention with immediate epoetin-α (n = 68) or to standard intervention with epoetin-α when hemoglobin decreased to

Background: MM-302 is an antibody drug conjugated HER2-targeted liposomal doxorubicin in development by Merrimack Pharmaceuticals. MM-302 is designed to deliver doxorubicin to HER2-overexpressing cancer cells with minimal exposure to healthy cardiomyocytes. Results of the MM-302 phase I study as a monotherapy, in combination with trastuzumab and trastuzumab plus cyclophosphamide, are presented. Methods: 69 patients with HER2-positive metastatic breast cancer (mBC) were treated with either MM-302 alone (8, 16, 30, 40 and 50 mg/m2, Q4W) (Arm 1), MM-302 (30 and 40 mg/m2, Q4W) plus trastuzumab (4 mg/kg, Q2W) (Arm 2), MM-302 (30 mg/m2, Q3W) plus trastuzumab (6 mg/kg, Q3W) (Arm 3), MM-302 (30 mg/m2, Q3W) plus trastuzumab (6 mg/kg, Q3W) and cyclophosphamide (450 mg/m2, Q3W) (Arm 4). Patients on Arms 3 and 4 received a single 3-7 mg/m2 (approximately 10.8 mCi) dose of 64Cu-MM-302 followed by PET/CT to assess for MM-302 tumor deposition. Results: Patients received a median of 4 prior regimens for mBC. The most common Grade 3/4 side effect was neutropenia observed in 8 patients with 1 patient experiencing febrile neutropenia. Adverse events of any grade occurring in >20% of the population were constipation, cough, decreased appetite, diarrhea, dyspnea, fatigue, nausea, neutropenia, stomatitis and vomiting. Alopecia and hand foot syndrome were observed in 10% and 4% of patients respectively. 1 patient experienced a dose limiting toxicity DLT (febrile neutropenia) and a MTD was not reached at 50 mg/m2. 11 patients received cumulative anthracycline (previous exposure plus MM-302) exposure >550 mg/m2. LVEF reductions below 50% or a >10 percentage point drop in LVEF from baseline occurred in 6 patients. 1 patient experienced Grade 1 cardiac failure resulting in treatment discontinuation. In patients treated with ≥30 mg/m2 MM-302 (n = 49), alone or in combination with trastuzumab, the response rate (RR) was 12% and median progression free survival (mPFS) was 7.6 months (95% CI: 3.6-11.0). mPFS was 10.6 months (95% CI: 1.8-10.6) in the 13 patients receiving MM-302 plus trastuzumab and cyclophosphamide in Arm 4. Conclusions: MM-302 had a manageable safety profile in this study as a monotherapy, in combination with trastuzumab and with trastuzumab and cyclophosphamide. RR and mPFS in this heavily pretreated mBC population suggest further study is warranted. MM-302 at a dose of 30 mg/m2 Q3W in combination with trastuzumab is currently being evaluated in a randomized phase II trial (HERMIONE) in anthracycline naïve HER2-positive locally advanced/mBC patients previously treated with trastuzumab, pertuzumab and T-DM1. Citation Format: Patricia LoRusso, Ian Krop, Kathy Miller, Cynthia Ma, Barry A. Siegel, Anthony F. Shields, Istvan Molnar, Thomas Wickham, Joseph Reynolds, Karen Campbell, Bart Hendriks, Ty McClure, Victor Moyo, Pamela Munster. A phase I study of MM-302, a HER2-targeted PEGylated liposomal doxorubicin, in patients with HER2+ metastatic breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT234. doi:10.1158/1538-7445.AM2015-CT234

234 Background: MM-398 is a nanoliposomal encapsulation of irinotecan. OS in the ITT population was significantly longer with MM-398+5FU/LV over 5FU/LV alone, and the most frequent grade 3+ AEs included neutropenia, fatigue, and GI effects (diarrhea and vomiting). Expanded, pre-specified analyses of the Phase 3 study are presented. Methods: Patients (n=417) with mPAC previously treated with gemcitabine-based therapy, were randomized 1:1:1 in an open-label study to receive: (A) MM-398 (120 mg/m2 IV over 90 min) q3w; (B) 5FU (2,000 mg/m2 over 24 h) plus racemic leucovorin (LV) (200 mg/m2 over 30 min) x 4w followed by 2w rest; or (C) combination of MM-398 (80 mg/m2 IV over 90 min) prior to 5FU (2,400 mg/m2 over 46 h) and racemic LV (400 mg/m2 over 30 min) q2w. The primary endpoint was OS. The Intent To Treat (ITT) population included all randomized patients; the Per Protocol (PP) population included patients who received at least 80% of the target dose in the first 6 weeks and did not violate any inclusion/exclusion criteria. Results: Analysis of the PP populations confirmed the favorable OS, which was also reflected by the PFS, ORR and CA19-9 levels, of the combination MM-398+5FU/LV arm over the control 5FU/LV arm. The MM-398 monotherapy arm did not show a statistically significant improvement in OS compared with the control arm. Analysis of subgroups, based on pretreatment characteristics including stage at diagnosis, time since initial histological diagnosis, prior lines of therapy, time since last prior therapy, and CA19-9 levels, consistently favored OS for the MM-398+5FU/LV arm over the 5FU/LV arm. Conclusions: Expanded analysis of the PP population and sensitivity analyses support the favorability of MM-398+5FU/LV over 5FU/LV, with a manageable safety profile. Clinical trial information: NCT01494506. [Table: see text]

BACKGROUND Patients with estrogen receptor (ER)-positive and ER-negative breast carcinomas differ in terms of disease progression, treatment regimens, and prognosis. The mechanism underlying the biologic differences of the two groups is understood poorly. Array comparative genome hybridization (CGH) on breast carcinoma subtypes demonstrated a consistent association between loss in regions of chromosome 5q and ER-negative tumors. It was shown previously that early growth response gene 1 (EGR1) on 5q acts like a tumor-suppressor gene, with its expression repressed in breast carcinomas. METHODS To test the hypothesis that EGR1 is deleted differentially in ER-negative versus ER-positive breast carcinomas, fluorescence in situ hybridization was employed in this study to determine the EGR1 deletion status in 50 breast carcinoma specimens. Deletion status was measured by the signal ratio of EGR1/chromosome 5. Linear regression was used to assess the results. RESULTS The mean EGR1/chromosome 5 ratio for the ER-negative group was significantly lower compared with the same ratio for the ER-positive group (P < 0.001). Although grade alone was not significant for predicting the ratio, the interaction between ER status and grade was significant (P < 0.01): For ER-negative specimens, the higher the grade, the lower the EGR1/chromosome 5 ratio. CONCLUSIONS The EGR1 gene appeared to be deleted in ER-negative human breast carcinomas. Egr-1 may contribute to the pathogenesis of ER-negative breast carcinomas versus ER-positive breast carcinomas. Cancer 2005. © 2005 American Cancer Society.

2518 Background: MM-151 is a novel oligoclonal anti-EGFR antibody combination designed to overcome key challenges of the EGFR network: ligand redundancy and signal amplification. Preclinical studie...

TPS4148 Background: HER2 overexpression occurs in ≤ 20% of GE cancers, and front-line fluoropyrimidine/platinum with TRAS increases survival in HER2+ GE junction/gastric cancer patients. Weekly PTX...

651 Background: MM-111 (111) inhibits ligand activated HER3 signaling in HER2+ tumors. This study evaluated the safety of 111 combined with standard of care (SOC) HER2-targeting regimens (Rx): cape...

Endocrine therapies directed against estrogen action are initially effective in estrogen-receptor positive (ER+) breast cancer, though most patients will eventually develop resistance to these treatments. It has recently been shown that growth factor signaling can activate ER through the AKT and MAPK signaling pathways. Moreover, both heregulin and ErbB3 signaling have been implicated as potential escape routes in the development of resistance to anti-estrogen therapies. Here we have used an in vivo model of ER+ breast cancer to investigate the activity of MM-121/SAR256212, alone and in combination with the aromatase inhibitor letrozole. Tumor xenografts of human breast cancer cells (MCF-7) engineered to express aromatase (MCF7-Ca) were generated in ovariectomized athymic nude mice. Mice were injected daily with androstenedione and randomized to treatment groups once the average tumor volume per group reached ∼300 mm3. Mice received vehicle, letrozole, MM-121, or both MM-121 and letrozole. Following development of resistance to letrozole, mice receiving letrozole alone were re-distributed into three treatment groups - letrozole, MM-121, or letrozole plus MM-121. Tumors were harvested at 24 h post-treatment initiation, at development of letrozole resistance, and at the end of study. Total and phosphorylated levels of certain signaling proteins in the ErbB network were measured by quantitative Western blotting. MM-121 in combination with letrozole significantly inhibited tumor growth (p In conclusion, MM-121 delayed the onset of resistance to letrozole in this in vivo model, and re-sensitized tumors to letrozole upon development of resistance. These data indicate a potential role for combining MM-121 with letrozole in first and second line treatment of ER+ breast cancer. Citation Format: Michael D. Curley, Gauri Sabnis, Lucia Wille, Gabriela Garcia, Victor Moyo, Armina Kazi, Gavin MacBeath, Angela Brodie. MM-121/SAR256212, an anti-ErbB3 antibody, restores sensitivity to letrozole and delays the onset of resistance in an ER+ breast cancer model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1072. doi:10.1158/1538-7445.AM2013-1072

MM-398 is a stable nanotherapeutic encapsulation of the pro-drug irinotecan with an extended plasma half-life and higher intratumoral deposition in animal models compared with free-irinotecan. MM-398 is currently in multiple clinical trials, including a Phase 3 trial for patients with advanced gemcitabine-resistant pancreatic cancer (NAPOLI-1). By using a systems pharmacology approach, we have previously identified the important determinants for MM-398 activity differentiating it from free irinotecan. One of the critical parameters identified in the model is activity of the tumor carboxylesterase (CES) as an important correlate to the MM-398 preclinical response. Our data also shows that tumor associated macrophages (TAMs) are the dominant cell type for phagocytosis of MM-398 in the tumor microenvironment. To validate these findings we used a perturbation strategy involving manipulation of TAMs with the anti-CSF1 antibody 5A1. Depletion of macrophages with 5A1 resulted in a strong size reduction of CD11b+F4/80+ mature macrophage populations in HT29, MC38 and LLC tumor models. Furthermore, other myeloid and non-myeloid cell populations showed tumor model and mouse strain-dependent changes in population size and liposome uptake. The overall impact of 5A1-mediated macrophage depletion was a reduction of the total cellular liposomal load within the tumors. Anti-CSF1 treatment also modulated the systemic clearance of MM-398 due to changes in the macrophage populations in the liver and spleen of the animals. To capture this complex interplay of systemic and local depletion events we have expanded our mechanistically-based PK model to include separate tumor macrophage and tumor cell compartments. The computational model also identified tumor permeability to MM-398 as a rate-limiting factor for drug deposition and in vivo activity. To assess the degree of variability in tumor permeability, we measured the levels of irinotecan and SN-38 using HPLC in six different xenograft models. A high degree of variability in irinotecan and SN-38 levels was seen across these models and between tumors from different mice bearing xenografts of the same cell lines. We then investigated the inter-relationship between tumor permeability, macrophage content, CES enzyme activity and SN-38 accumulation by assessing the levels of these markers in multiple human-derived primary xenograft models across different indications. In summary, we demonstrated the impact of TAM modulation on overall tumor levels of irinotecan and SN-38 following treatment with liposomally encapsulated irinotecan. We outline differences in permeability of xenografts to MM-398 and the capacity to convert irinotecan into SN-38. Citation Format: Ashish Kalra, Jaeyeon Kim, Stephan Klinz, Nancy Paz, Joseph Reutt, Daryl Drummond, Dmitri Kirpotin, Victor Moyo, Eliel Bayever, Peter Laivins, Clet Niyikiza, Ulrik Nielsen, Jonathan Fitzgerald. The tumor microenvironment modulates the delivery and activation of liposomal encapsulated irinotecan, MM-398. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5622. doi:10.1158/1538-7445.AM2013-5622

48 Background: ErbB2 (HER2) overexpression has been reported in 7-34% of gastric cancers. ErbB3 (HER3) is the preferred dimerization partner of ErbB2, and ErbB2/ErbB3 heterodimer activation is implicated in the progression and metastasis of ErbB2+ tumors. Activation of ErbB3 signaling is a postulated resistance mechanism to current ErbB2-directed therapies and select chemotherapies. In line with this research, ErbB3 levels are associated with poor prognosis in gastric cancers. MM-111 is a bi-specific antibody that docks to ErbB2 and inhibits ErbB3 signaling in cells that overexpress ErbB2. In this study, MM-111 was evaluated in ErbB2+ gastric cancer by testing the activity of MM-111 in ErbB2+ pre-clinical models of gastric cancer, and by assessing the prevalence of potentially predictive biomarkers in a panel of archived gastric and gastroesophageal junction (GEJ) tumors. Methods: MM-111 was tested in ErbB2+ gastric cancer xenografts that were either untreated or after tumors ceased to respond to trastuzumab/5-FU. Xenografts were analyzed at multiple time points for the expression of ErbB-receptor family members and their downstream signaling by Luminex -assays. Preclinical data indicate that ErbB2, ErbB3, and heregulin are predictive biomarkers for MM-111. In order to determine the prevalence of our potentially predictive biomarkers in gastric and GEJ cancers, we obtained commercially archived tumor tissue and assayed the tissue for ErbB2 and ErbB3 expression levels using quantitative IHC, and measured heregulin transcript levels by RT-PCR. Results: MM-111 synergizes with various treatment regimens in the 2nd line treatment setting in ErbB2+ gastric cancer xenografts. In our models, the combination of MM-111, trastuzumab, and paclitaxel is particularly effective after tumors progressed on trastuzumab/5-FU. MM-111 inhibits the activity of the ErbB –signaling axis in these models. In addition, 23% of GEJ tumor samples and 20% of gastric samples were positive for potentially predictive biomarkers. Conclusions: ErbB2+xenograft tumors that stop responding to trastuzumab-based therapies benefit from MM-111–based regimens.

MM-398 is a stable nanotherapeutic encapsulation of the prodrug irinotecan with an extended plasma half-life and higher intratumoral deposition compared with free-irinotecan. MM-398 is currently in multiple clinical trials, including a phase 3 trial for patients with advanced gemcitabine-resistant pancreatic cancer (NAPOLI-1). Pancreatic cancer has been described as being notoriously difficult to treat, potentially due to inadequate drug penetration through the dense stroma, or because the hypoxic tumor microenvironment suppresses cytotoxic activity. We sought to better understand how MM-398, a relatively large (100nm) liposomal nanotherapeutic, could potentially treat pancreatic cancer by determining the relative roles of systemic vs. local tumor activation of irinotecan in contributing to the activity of MM-398. Using a systems pharmacology approach, we developed a mechanistic pharmacokinetic (PK) model of MM-398 and free-irinotecan to predict both plasma and intratumoral levels of irinotecan and SN-38. The model was trained with PK and biodistribution data from mice bearing HT-29 xenografts, which were administered intravenously with varying doses of MM-398 or free-irinotecan. Model simulations predicted that MM-398 resulted in equivalent SN-38 exposure (area under curve, AUC) in tumor at a fivefold lower dose than free-irinotecan. However, an in vivo animal activity study showed that 15-fold lower dose of MM-398 was sufficient to yield equal growth inhibition of HT-29 xenografts, which reveals the limit of relating simple AUC-based exposure to in vivo tumor response. While intratumoral SN-38 exposure from free-irinotecan was limited to the first 48 hours after dosing, MM-398 maintained high levels of SN-38 throughout the week-long time window. Further analysis of the exposure-response identified that the duration of intratumoral SN-38 levels above the threshold was a valid predictive marker for xenograft tumor response. Identifying the source of intratumoral SN38 is confounded by the fact that the mouse species has an additional carboxylesterase (CES) that can convert irinotecan to SN-38 in serum. The serum SN-38/irinotecan ratio in mice is tenfold higher than that observed in humans. In order to translate this preclinical observation into the clinic, it is critical to identify the role of mouse-specific serum CES on intratumoral SN-38 exposure. Thus, we performed a PK study with knockout mice lacking the Ces1c gene, which encodes serum CES, and then retrained our mechanistic PK model. Serum SN-38 levels in the Ces1c knockout mice were measurably decreased by ˜85% in the central compartment. In contrast, simulating the effect of knock-out of either serum CES or tumor CES, predicts that the duration of intratumoral residence of SN-38 is significantly affected by tumor CES, rather than serum CES. This suggests that local activation to SN-38 by tumor CES as the main driver for SN-38 tumor residence, which in turn drives response. In summary, we applied a systems pharmacology approach to identify the importance of tumor CES (local SN-38 generation) as one of the determinants of MM-398 response. Liposomal encapsulation of irinotecan dramatically alters the pharmacokinetic profile of SN-38 in the tumor, as well as tumor response, by maintaining SN-38 levels above the response threshold. Local, sustained activity of this active irinotecan metabolite could result in prolonged cytotoxic and tumor microenvironment modifications with beneficial effects on treatment of pancreatic cancer and other solid tumors. Citation Format: Jaeyeon Kim, Eliel Bayever, Peter Laivins, Clet Niyikiza, Ulrik Nielsen, Jonathan Fitzgerald, Ashish Kalra, Milind Chalishazar, Stephan Klinz, Nancy Paz, Bart Hendriks, Daryl Drummond, Dmitri Kirpotin, Victor Moyo. Sustained intratumoral activation of MM-398 results in superior activity over irinotecan demonstrated by using a systems pharmacology approach [abstract]. In: Proceedings of the AACR Special Conference on Chemical Systems Biology: Assembling and Interrogating Computational Models of the Cancer Cell by Chemical Perturbations; 2012 Jun 27-30; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2012;72(13 Suppl):Abstract nr A6.

7556 Background: Erlotinib is effective in NSCLCs with wild-type EGFR and shows enhanced benefit in EGFR mutation-positive cancers. However, resistance invariably develops, often involving persistent ErbB3 signaling and activation of the PI3K/AKT survival pathway. We present the full results of the Phase 1 study evaluating the safety and tolerability of erlotinib plus MM-121 a fully human IgG2 monoclonal antibody (mAb) to ErbB3. Methods: Eligible patients had advanced stage NSCLC, and ECOG 0-2. Seven cohorts were enrolled, evaluating varying levels of the MM-121 and erlotinib, as well as alternate MM-121 infusion schedules. Tumor response was assessed every 8 weeks. Dose levels were determined by safety and pharmacokinetic (PK) data, and immunogenicity, efficacy endpoints and exploratory biomarker evaluations were performed. Results: From February 2010 – July 2011 32pts entered the study (median age 63y; 45% male; 18% ECOG 0, 82% ECOG 1. 56% had adenocarcinoma and 30% pts received 3 or more lines of prior therapies (range 0-7) with 91% having had prior platinum. 65% had wild-type EGFR status and were never treated or never responded to EGFR-TKIs (EGFRwt) and 28% had acquired resistance to erlotinib treatment (EGFRresist). The most common toxicities (any grade) observed were diarrhea (82%), rash (64%), and fatigue (64%). DLTs observed in different cohorts were diarrhea, mucositis, rash and failure to thrive. Clinical activity was observed including 1 PR (an EGFR TKI naïve EGFR mutant) and 14 SD. Average duration of disease stabilization was 21.6 wks (range 7.1 -89.3 wks). Median PFS is 8.1 weeks and the 16 week PFS rate was 41% in the overall population. For EGFRwt and EGFRresist pts the median PFS were 7.7 weeks and 15.1 weeks, and the 16 week PFS rates were 32% and 44%, respectively. 7/20 EGFRwt pts and 5/9 EGFRresist pts achieved SD. Conclusions: This study suggests that the combination of erlotinib and MM-121 has an acceptable safety profile in heavily pre-treated NSCLC patients with and without EGFR mutations. Early signals of patient benefit were seen and a large randomized phase II study is ongoing.

TPS663 Background: Anthracyclines have been an effective backbone of breast cancer therapies for decades. However, cardiotoxicity issues associated with free anthracyclines have limited their effective use in the clinic and led to the exploration of anthracycline-free regimens, particularly with HER2-positive cancers that require treatment with another cardiotoxic agent, trastuzumab. While liposomal doxorubicin formulations have succeeded in reducing cardiotoxicity, they have failed to demonstrate clear-cut efficacy advantages and can involve other toxicities. To address the safety and efficacy limitations of currently available anthracyclines, we have designed a new liposomal formulation, MM-302, that targets doxorubicin to HER2-overexpressing tumor cells. Antibody fragments that bind to HER2 without blocking HER2-mediated signaling are coupled to the outer surface of pegylated liposomal doxorubicin. MM-302 specifically binds and enters tumor cells overexpressing HER2 with minimal uptake into normal cells such as cardiomyocytes which express low levels of HER2. This first-in-human phase I study evaluates the safety of MM-302 in patients and provides preliminary efficacy data in HER-2+ advanced breast cancer (ABC). Methods: Patients aged > 18 years with histologically confirmed HER-2+ advanced breast cancer that have progressed or recurred on standard therapy or for which no standard therapy exists who have adequate performance status, bone marrow reserve, and organ function, are eligible for the study. Following a standard 3 + 3 dose escalation design, the maximum tolerated dose (MTD) or maximum feasible dose (MFD) is determined and up to 25 additional patients with HER-2+ ABC will be enrolled for a planned total of 40-49 patients. The primary endpoint is determination of the MTD/MFD. Secondary endpoints include determination of dose-limiting toxicity, adverse event(s), and pharmacokinetic and immunogenicity profiles of MM-302, as well as overall response and clinical benefit rates of MM-302. MM-302 is administered intravenously weekly in 4-week cycles. At the time of this submission, 8 patients have been enrolled in the dose escalation portion.

TPS3111 Background: The HER2/HER3 oncogenic heterodimer is a potent HER receptor pairing with respect to strength of interaction, receptor tyrosine phosphorylation, and downstream signaling through mitogen activated protein kinase and phosphoinositide-3 kinase pathways. MM-111 is a novel bispecific antibody fusion protein that inhibits ligand activated HER3 signaling through abrogation of ligand binding specifically in HER2 overexpressing tumors. In preclinical models of HER2+ solid tumors, MM-111 inhibits ligand-induced HER3 phosphorylation, cell cycle progression, and tumor growth. HER2 is a well-established target of anticancer agents such as trastuzumab and lapatinib, specifically in breast and gastric tumors. Preclinical data demonstrate that MM-111 potentiates the antitumor activity of both trastuzumab and lapatinib and this phase I study seeks to determine if MM-111 can be safely used in combination with various standard of care HER2 targeting regimens, namely; (1) trastuzumab, cisplatin and, capecitabine, (2) trastuzumab and lapatinib, and (3) trastuzumab and paclitaxel. Methods: This is a multi-arm phase I, open label, multicenter, dose-escalation study of MM-111 in an add-on design that evaluates the safety, pharmacokinetics (PK), and anti-tumor activity of MM-111 in combination. Each arm is designed to run as a separate phase I study to address safety and tolerability of each combination. For eligibility, patients are required to have documented advanced HER2-positive cancer, with adequate bone marrow, hepato-renal and cardiac function. The dose escalation for each arm utilizes a standard “3 + 3” design with MM-111 dosed initially at a moderate dose of 10 mg/kg and escalated up to 20 mg/kg to identify a phase II dose in combination with each regimen. Once the maximum tolerated dose or phase II dose is identified, expansion cohorts will accrue to further evaluate these combinations. The flexibility of the design allows additional combinations arms to be added. Key exploratory analyses will include an evaluation of safety, PK, and efficacy as evidenced by best overall response and duration of response.

MM-398 is a stable nanotherapeutic encapsulation of the pro-drug irinotecan (CPT-11). Irinotecan, a topoisomerase inhibitor is currently being used in clinical practice for treatment of several indications; however, associated toxicities, mainly, neutropenia and gastrointestinal toxicity, have limited its clinical utility. Previously, we have demonstrated that MM-398 treatment resulted in significantly higher intratumor concentrations of both irinotecan (142-fold) and SN-38 (9-fold), thereby exhibiting enhanced anti-tumor activity compared to free irinotecan in different xenograft models. Multiple phase 1 and 2 studies have established a pharmacokinetic and safety profile. Recent data support continued clinical development for the drug in various indications, including pancreatic, gastric, colorectal and potentially other solid tumors. In order to further understand the enhanced anti-tumor activity of MM-398 we developed a mechanism-based PK model of MM-398 and free irinotecan designed to predict intratumor levels of SN-38. Based on this model, we evaluated the role of various determinants of response of MM-398. Sensitivity analysis revealed that the local activation of MM-398 was important for obtaining higher SN-38 intratumor levels compared to free irinotecan. To identify cell types responsible for local activation of MM-398 we investigated cellular liposome phagocytosis ability. In vitro studies demonstrated preferential uptake of MM-398 by phagocytic macrophages compared to tumor cells. FACS analysis of tumor samples (from subcutaneous xenografts) highlighted higher uptake of labeled liposomes by CD11b + and F4/80+ cells as compared to tumor cells. We are developing in vivo systems using engineered cell lines overexpressing growth factors to recruit macrophages (CSF1) or overexpressing irinotecan conversion enzymes to further investigate the role of macrophagesin local tumor conversion of MM-398 and to validate the model prediction that local activation is critical to MM-398 mechanism of action. The extent of tumor vascularization and permeability were also highlighted in the sensitivity analysis. To determine the effect of MM-398 on these parameters, we treated mice bearing HT29 (colorectal cancer) xenografts with a single dose of MM-398 and measured hypoxic markers (CAIX) and microvessel density (CD31) by immunohistochemistry. Tumors treated with MM-398 showed a greater degree of CD31 staining and lower CAIX staining, indicating that MM-398 may be able to affect the tumor microenvironment. We are currently evaluating how the ability of MM-398 to alter the tumor microenvironment affects the activity of other chemotherapeutic agents in combination therapy. These findings could support the use of MM-398 as a combination modality against tumors that may have acquired resistance to traditional chemotherapeutic agents. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5696. doi:1538-7445.AM2012-5696

Background: The benefit of EGFR tyrosine kinase inhibitors (TKIs) is largely restricted to EGFR mutation-positive cancers and resistance invariably develops. A central theme of acquired resistance is persistent ErbB3 signaling, resulting in activation of the PI3K/AKT survival pathway. MM-121 is a fully human IgG1 monoclonal antibody (mAb) to ErbB3 with pre-clinical activity as a single agent and in combination with erlotinib in NSCLC, particularly in cancers with ligand-dependent activation of EGFR. This phase 1 study evaluated the safety and tolerability of MM-121 and erlotinib in NSCLC, as well as PK, immunogenicity, efficacy endpoints and exploratory biomarker evaluation. Methods: Patients with advanced NSCLC, good performance status and adequate organ function were enrolled. Patients were EGFR TKI-naïve, unless they were EGFR mutant, in which case acquired resistance was allowed. MM-121 was administered weekly and erlotinib was administered daily. Seven cohorts were enrolled, evaluating varying dose levels of the combination, as well as alternate MM-121 infusion schedules. Dose levels were determined by safety and pharmacokinetic (PK) data. Results: Between February 2010 and July 2011, 33 patients were enrolled. Median age was 64 years and there were 19 (57.5%) women. Twenty-four patients were erlotinib-naïve and 1 patient was an EGFR mutant. The most frequent adverse events were rash, diarrhea, nausea and fatigue. As of 31 July 2001, 16 patients remain on study. Full results will be presented at the meeting. Conclusions: In this phase 1 dose escalation study, MM-121 plus erlotinib was well tolerated by the majority of patients. A phase 2 study is planned. Reference: NCT00994123 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C27.

MM-398 (aka PEP02) is a stable, nanotherapeutic encapsulation of the pro-drug CPT-11 (irinotecan) that is currently in clinical development. In preclinical experiments, treatment with MM-398 resulted in significantly higher intratumoral concentrations of both irinotecan (142-fold) and its major metabolite, SN-38 (9-fold) and exhibited superior anti-tumor activity compared to free irinotecan in multiple tumor xenografts. Subsequently, multiple phase 1 and 2 studies have established a pharmacokinetic and safety profile that supports continued clinical development, including in pancreatic, gastric, colorectal and potentially other cancers. Because current evidence suggests that resistance to pancreatic cancer is driven largely by inadequate drug penetration into these often poorly vascularized, stromally dense and hypoxic tumors, we sought to better understand how this relatively large (100nm) liposomal nanotherapeutic could potentially result in increased efficacy in very advanced gemcitabine-resistant pancreatic cancer and other cancer types. We developed a mechanism-based PK model of MM-398 and free irinotecan designed to predict intratumor SN-38 levels. Sensitivity analysis revealed that for MM-398 local activation of irinotecan to SN-38 was a far more important parameter than systemic activation. Through cellular uptake studies, we demonstrated in vitro that MM-398 was preferentially internalized by phagocytic macrophage/monocyte cell lines and, to a far lesser extent, by tumor cell lines. Furthermore, tumor microdistribution studies by flow cytometry and IHC showed uptake of MM-398 liposomes in both tumor cells and tumor-associated macrophages with more liposomal material being present in the macrophages. This distribution also suggests that macrophages may contribute to the postulated rate limiting process of irinotecan activation. The sensitivity analysis also suggested that tumor permeability and vascularization are important determinants of tumor-associated SN-38 levels for both free irinotecan and MM-398. To determine the effect of MM-398 on these parameters we treated mice bearing HT29 (colorectal cancer) xenografts with a single dose of MM-398 and measured hypoxic markers (CAIX) and microvessel density (CD31) by IHC. Tumors treated with MM-398 showed a greater degree of CD31 staining and lower CAIX staining, indicating that MM-398 may be able to affect tumor characteristics that traditionally have contributed to therapy resistance and limited the delivery of cancer therapeutics and resistance. In summary, encapsulation of irinotecan alters rate-limiting processes that determine tumoral SN-38 levels. Delivery of MM-398 is believed to alter tumor microvessel density and decrease hypoxia. These intriguing mechanisms of action findings support the continued clinical development of MM-398 as a differentiated therapeutic for several cancer types. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C207.

TPS112 Background: Resistance to endocrine therapy (ET) is a common challenge in breast cancer. In treatment regimes involving exemestane, combination therapy employing MM-121 presents the potentia...

TPS119 Background: The ErbB2/ErbB3 oncogenic heterodimer is the most potent ErbB receptor pairing with respect to strength of interaction, receptor tyrosine phosphorylation, and downstream signaling through mitogen activated protein kinase and phosphoinositide-3 kinase pathways. MM-111 is a novel bispecific antibody fusion protein that specifically targets the ErbB2/ErbB3 heterodimer and abrogates binding of ErbB3’s ligand heregulin. In preclinical models of HER-2+ solid tumors, MM-111 inhibits ligand-induced ErbB3 phosphorylation, cell cycle progression, and tumor growth. ErbB2 (HER2) is a well established target of anticancer agents such as trastuzumab and lapatinib for HER2+ cancers, specifically breast and gastric. ErbB3 signaling has emerged as an important mechanism of resistance to ErbB2 (HER-2) targeted agents in clinical use, and preclinical data demonstrates that MM-111 potentiates the antitumor activity of trastuzumab. This first-in-human phase I/II study evaluates the safety and tolerability o...

TPS215 Background: Although EGFR tyrosine kinase inhibitors (TKIs) are very effective at treating EGFR-addicted cancers, resistance almost invariably occurs. It has been suggested that tumor cells may become resistant to EGFR TKIs by upregulating survival signaling via ErbB3 dependent activation of the PI3K/AKT pathway. In NSCLC tumors that harbor wildtype EGFR, simultaneous inhibition of EGFR and ErbB3 produces an additive effect on tumor growth inhibition preclinically. MM-121 is a monoclonal antibody (MAb) to ErbB3 that has pre-clinical activity in NSCLC, particularly in cancers with ligand-dependent activation of ErbB3. The current study will evaluate three distinct groups of NSCLC pts when treated with MM-121 and erlotinib. Methods: The following 3 pt groups will be studied:(Group A) EGFR wild type, EGFR-TKI naive pts, who have received at least 1 line of prior chemotherapy to assess whether MM-121 enhances intrinsic sensitivity of tumors to erlotinib; (Group B) EGFR mutated and EGFR TKI naive to ass...

Introduction: ErbB3 has been identified as a key driver of the PI3K/AKT signaling pathway, resulting in cell growth and survival. MM-121 is a fully human monoclonal antibody targeting ErbB3. By binding to ErbB3, MM-121 blocks heregulin, thereby inhibiting ligand-induced ErbB3 heterodimerization and activation of receptors. Binding of MM-121 also induces downregulation of ErbB3 from the cell surface. Methods: Patients ≥ 18 years with refractory advanced solid tumors were given MM-121 weekly in 4-week cycles at 6 dose levels. Dose escalation was based on dose limiting toxicities (DLTs) during cycle 1. Primary objectives were to determine the maximum tolerated dose (MTD) of MM-121 and describe any objective response and progression free survival. Secondary objectives were to describe the safety, pharmacokinetic (PK), and pharmacodynamic profile of MM-121. A dose expansion cohort at the highest dose cohort was also included for selected tumor types, with required pre- and post-treatment biopsies to assess MM-121 target effects, ErbB3 pathway markers, and guide dose schedule decisions. Results: Between July 2008 to January 2011, 38 patients have been enrolled in the study. Twenty-five patients were enrolled in the dose escalation part of the study and treated until unacceptable toxicity or progression. Six cohorts were completed and an MTD was not reached. Grade 1/2 nausea, diarrhea, fatigue and rash were the most commonly observed adverse events. Grade 1 hypomagnesemia was observed in 4 patients at different doses. One patient experienced a DLT of confusion at the lowest dose, considered possibly related to MM-121 treatment but confounded by other comorbidities. No other treatment related serious AEs were reported. An additional 13 patients have been enrolled to date in an expansion cohort. The overall safety profile for patients in the expansion cohort is similar to that observed for the dose escalation cohorts. Conclusion: In this single agent, first in human, dose escalation phase I study MM-121 was well tolerated with a favorable safety profile. Enrollment in the dose expansion cohort is ongoing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-410. doi:10.1158/1538-7445.AM2011-LB-410

TPS169 Background: The ErbB2/ErbB3 oncogenic heterodimer is the most potent ErbB receptor pairing with respect to strength of interaction, ligand–induced tyrosine phosphorylation, and downstream signaling through mitogen-activated protein kinase and phosphoinositide-3 kinase pathways. Recently, ErbB3 signaling has emerged as an important hypothesized mechanism of resistance to ErbB2 (HER2) targeted agents in clinical use (Sergina et al. Nature 2007; Garrett et al. SABCS 2009 abstract 63). MM-111 is a novel bispecific antibody fusion protein that specifically targets the ErbB2/ErbB3 heterodimer and blocks ligand binding to ErbB3. In HER2+ gastric, breast, ovarian, and lung cancer cell lines and xenografts, MM-111 inhibits ligand-induced ErbB3 phosphorylation, tumor cell cycle progression, and tumor growth. This first-in-human phase I-II study evaluates the safety and tolerability of MM-111 and provides preliminary efficacy data in HER-2+ advanced breast cancer (ABC). Methods: Patients (pts) aged ≥ 18 years...

In women, breast cancer is among the most common cancers and the fifth most common cause of cancer deaths. Due to the heterogeneity of the disease, 10-year progression free survival can vary widely with stage and type from 98% to 10%. We present data showing that MM-121, a fully human monoclonal anti-ErbB3 antibody, is efficacious in studies of both hormone dependent (ER+) and triple negative (ER-,PR-, Low Erb2) breast cancer lines that express the molecular profile consistent with MM-121 response (co-expression of ErbB3 and HRG). Using a combination of computational and experimental approaches, ErbB3 was identified as a critical transducer of oncogenic signaling leading to the development of MM-121, a first in class anti-ErbB3 antibody. We have previously demonstrated that MM-121, when used as a single agent, inhibits heregulin-induced signaling events in human cancer cell lines. Moreover, MM-121 caused dose-dependent inhibition of tumor growth in multiple xenograft models of human cancer, including ovarian, renal cell, pancreatic, lung, and prostate cancer. Estrogen dependent, or ER+ breast cancers, make up about 80% of breast cancers. A standard treatment for ER+ breast cancer includes hormone therapy; however a substantial number of ER+ breast cancers eventually develop resistance requiring additional treatments. Here we show that in ER+ breast cancer cells, MM-121 can block HRG induced ErbB3 activation and VEGF secretion as well as HGF induced pErbB3 in vitro. Additionally, in ER+ breast cancer xenograft models, MM121 is effective in combination with both chemotherapy agents and targeted therapies and may be effective in ER+ breast cancers that are refractory to hormone treatment. The triple negative breast cancers are characterized by poor prognosis, aggressiveness, and reduced responsiveness to standard treatments. MM-121 used as a single agent therapy was able to suppress tumor growth in triple negative primary human tumors, when grown as xenografts suggesting that MM-121 monotherapy may be clinically efficacious in triple negative breast cancers. Together, these data suggest that MM-121, when used as a single agent or in combination with other therapies, could offer significant clinical benefit to both ER+ and triple negative breast cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1806.

One of the challenges faced by targeted therapeutics currently in the clinic is the relatively small population of patients who derive significant benefit from their use. We report the development of a preclinical classifier which can correctly predict xenograft response to MM-121, an anti-ErbB3 antibody, based on the measurement of a few key biomarkers in cell lysates. Deregulation of the ErbB family receptors is common in many cancers. Using a combination of computational modeling and quantitative experiments we identified ErbB3 as a key mediator of mitogenic signaling downstream of the ErbB receptors. Based on these results, we developed MM-121, a first in class anti-ErbB3 monoclonal antibody that blocks heregulin-induced signaling and inhibits tumor growth in multiple xenograft models of human cancer. Here we present our efforts to derive a predictive biomarker signature that identifies tumors that are responsive to MM-121. Using our computational model of the ErbB signaling pathway we identified the five most critical proteins for predicting activation of phospho-AKT - a key mediator of cell survival and apoptosis. These proteins include MM-121's target, ErbB3, and its ligand, heregulin. We profiled these biomarkers in a large panel of cancer cell lines, and using the measured effect of MM-121 on inhibiting tumor growth in eight xenograft tumor models, we determined a classification rule for predicting xenograft response. We subsequently used this classification rule to correctly predict a priori MM-121 response in 11 xenograft models. These results suggest that our computationally-derived biomarker signature is sufficient for predicting response to MM-121 in xenografts, and could offer significant clinical benefit by helping select patients for MM-121 treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3756.

7094 Background: EPO+G/GM-CSF has been associated with higher ER rates vs EPO alone. Several non-ESAs have also been studied as single agents or in combination without growth factor. This meta-analysis compares ER rates achieved with EPO either as a single agent or in combination with G/GM-CSF or other agents vs non-ESA therapies (including thalidomide, azacytidine, all-trans retinoic acid, As2O3, etc). Methods: Data extraction was performed on studies from PubMed, ASCO/ASH proceedings in MDS pts treated with EPO±G/GM-CSF or other non-ESAs (search cutoff date 9/30/07). To allow cross comparison, only studies using IWG or IWG-like ER criteria and treatment-naive pts were selected. Pooled estimates of ER rates were calculated using random-effect (R- E) meta-analysis methods and results were stratified by: (i)EPO monotherapy (monotx), (ii)EPO+G/GM-CSF, (iii)EPO+non-ESAs, (iv)Non-ESA monotx, and (v)Non-ESA combinations. Results: Of 790 studies identified, 35 were included. Most pts (>59%) had RA/RARS, except ...

19589 Background: Reported here are the final Hb results for the group of patients enrolled under an amendment to a larger study that was the first to compare early vs standard intervention with EPO 120,000 U Q3W in patients with CIA and Hb of 11 to 12 g/dL. The amendment allowed for treatment of patients who had a Hb value 13.0 g/dL at any dosing visit; dose was reduced for Hb >12.0 g/dL or Hb increase >1.5 g/dL in a 3-week period (current prescribing information recommends target Hb not to exceed 12 g/dL). Hb response was analyzed using an observed case approach and Hb data following switch to 40,000 U QW were censored. Results: Fifty patients were enrolled under the amendment. BL characteristics were: mean age, 62.0 years; 67% female; mean Hb 10.1 g/dL. Mean Hb changes over time from BL for patients receiving Q3W dosing are shown in the table . PRBC transfusion rate after 4 weeks on treatment was 24.5%. 18.0% of patients had at least one dose withheld and 22.0% had at least one dose reduction. Five deaths and 6 clinically relevant TVEs were reported. Conclusions: This study shows that EPO is effective in raising Hb when initiated in patients with CIA and a Hb of No significant financial relationships to disclose. [Table: see text]

7082 Background: Recombinant human erythropoietin (EPO) is extensively used to improve erythropoiesis and reduce transfusions in anemic MDS pts. The addition of G/GM-CSF to EPO alfa or beta has been associated with higher erythroid response (ER) rates vs. EPO alone. Studies suggest higher ER rates could be achieved with EPO monotherapy if higher initiation doses were used. To study this question a meta-analysis was performed on studies of MDS pts treated with EPO alfa or beta + G/GM-CSF. Methods: Data extraction was performed on studies from PubMed, ASCO and ASH proceedings from 1990–2006 in MDS pts treated with EPO (alfa or beta) ± G/GM-CSF. To allow for cross comparisons, only studies including IWG or IWG-like ER criteria were selected for analysis. Pooled estimates of ER rates were calculated using fixed-effect (F-E) meta-analysis methods. Results were stratified by: (i) EPO-alfa at standard doses, (ii) EPO- alfa at high doses, (iii) EPO-alfa + G/GM-CSF, and (iv) EPO-beta + G/GM-CSF. Results: From 39 studies identified, 19 met inclusion criteria. Most pts (>55%) had RA/RARS. Studies using EPO-alfa at standard doses showed comparable ER rates to studies using EPO- alfa + G/GM-CSF (49.0% vs. 50.6%; p=0.731) ( Table ). Among EPO-alfa studies, those using higher EPO doses had higher ER rates vs. studies using standard EPO doses (p [Table: see text] [Table: see text]

19564 Background: Emerging data suggest that initiating EPO therapy earlier (at a higher hemoglobin [Hb] trigger) in the setting of active CT may provide better maintenance of Hb within a target range with no adverse safety consequence. Reported here are the final results of the first study to explore the efficacy and safety of early vs standard intervention with EPO initiated Q3W at 120,000 U. Methods: This 16-wk open-label randomized study enrolled pts with non-myeloid malignancy, baseline (BL) Hb =11.0 and =12.0 g/dL, and CT planned for =9 wks. Pts were randomized (1:1) to receive EPO 120,000 U subcutaneously Q3W immediately (early intervention group, EIG) or when their Hb fell to 13.0 g/dL at any dosing visit; dose was reduced for Hb >12.0 g/dL or Hb increase >1.5 g/dL in a 3-wk period (current prescribing information recommends target Hb not to exceed 12 g/dL). Hb response was defined as Percent Values in Range (PVR; the mean proportion of weekly Hb levels that were =11.0 and =13.0 g/dL) and by mean Hb change from BL. Hb data following switch to 40,000 U QW were censored. Results: A total of 136 pts were randomized (68 per group). Demographics were similar; BL Hb was 11.5 g/dL in both groups. PVR was 60% in the EIG and SIG. Mean Hb change from BL to final value on Q3W dosing was -0.1 g/dL in both groups. Among the 51 pts whose Hb fell below 11 g/dL in the SIG, their Hb decreased to a mean of 10.4 g/dL before initiation of EPO. Their subsequent mean Hb increase was 0.7 g/dL at the final visit on Q3W therapy. PRBC transfusion rates after the first 4 wks of EPO treatment were 8.8% (6/68) and 7.8% (4/51) for the EIG and SIG, respectively. In the EIG vs SIG, EPO was withheld in 38% vs 22% of pts and reduced in 43% vs 26% of pts. Two deaths and 6 clinically relevant TVEs while on EPO treatment were reported in each group. Conclusions: This is the first study to show EPO may be initiated at 120,000 U every 3 wks. Hb outcomes in the EIG and SIG were similar. These data provide further evidence that half-life of erythropoietins may not correlate with their effectiveness when used at extended dosing intervals. Future research is warranted. No significant financial relationships to disclose.

6572 Background: Refractory anemia is a clinical hallmark of MDS. The most consistently used therapy for this anemia is EPO. Prior to the introduction of IWGc in 1997, ER rates varied substantially between studies. The present meta-analysis was undertaken to compare ER rates in studies of EPO-treated patients in MDS when defined by either IWGc or non-IWGc. Methods: A systematic review and data extraction of studies published from 1990–2005 in MDS patients treated with EPO was performed and yielded 21 studies evaluating a total of 895 patients. Pooled estimates of ER rates, stratified by IWGc, were calculated using random-effects meta-analysis methods, which incorporated both between- and within-study variations. Univariate meta-regression analyses were conducted to identify study characteristics that were significant determinants of ER rate. Results: Ten studies (604 patients) used the IWGc to define ER (overall, major, minor), while 11 studies (291 patients) used other definitions. Mean age for all patients was 70.6 years; 45% women. Mean baseline (BL) serum erythropoietin level and proportion of patients with refractory anemia or refractory anemia with ringed sideroblasts were comparable between studies; however, the proportion of transfusion-dependent patients at BL was lower in the IWG studies vs the non-IWG studies (36% vs. 84%, respectively, p [Table: see text]