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Background: Targeting constitutively active mutant kinases with selective small molecule inhibitors is a key therapeutic pillar of precision oncology. Phosphatidylinositol-4,5bisphosphate-3 kinase, catalytic subunit alpha (PIK3CA) mutations leading to oncogenic activation of PI3Kα represent the largest opportunity for this approach in solid tumors. However, there is no selective inhibitor that targets mutant PI3Kα in the clinic. Toxicity related to non-selective inhibition of WT PI3Kα (hyperglycemia) and other PI3K isoforms limits the tolerability, dosing and efficacy of the orthosteric inhibitor, alpelisib, the only approved solid tumor PI3K inhibitor. RLY-2608, a novel oral allosteric PI3Kα inhibitor, is uniquely designed to overcome these limitations via mutant- and isoform-selective PI3Kα inhibition for greater target coverage, improved tolerability and antitumor activity. We initiated a first-in-human (FIH), study to evaluate the clinical activity of RLY-2608 as a single agent in advanced solid tumor patients (pts) with PI3KCA mutations and in combination with fulvestrant in pts with PIK3CA mutant, HR+, HER2- metastatic breast cancer (MBC). Methods: This is a global, multi-center, dose escalation/expansion study (NCT05216432) of RLY2608 as a single agent in adults who have advanced solid tumors and are refractory, intolerant, or declined standard therapy and RLY-2608 in combination with fulvestrant in previously treated pts with HR+/HER2- MBC. Eligibility criteria include presence of PI3KCA mutation (blood or tumor) per local assessment, ECOG performance status 0-1, measurable or evaluable disease per RECIST 1.1 and no prior PI3K inhibitor (except combination group 2). RLY-2608 is administered on a continuous schedule with 4-week cycles. Adverse events (AEs) per CTCAE v5, PK, biomarkers (mutant ctDNAs and insulin pathway markers) and anti-tumor activity are assessed serially. Dose escalation employs a Bayesian Optimal Interval design to identify MTD and RP2D. Following dose escalation, pts will be treated with RLY-2608 at the MTD/RP2D in a monotherapy dose expansion with 5 groups (N=75, 15 each): 1. Clear cell ovarian carcinoma 2. Head and neck squamous cell carcinoma 3. Cervical cancer 4. Other solid tumors 5. PI3KCA double mutations. In addition, two expansion cohorts will enroll patients with HR+/HER2- MBC treated with RLY-2608 and fulvestrant combination (N = 30, 15 each): 1. No prior PI3K therapy 2. Intolerant to PI3K inhibitors. The primary endpoints are MTD/RP2D and AE profile for single agent and combination; key secondary endpoints are PI3KCA genotype in blood and tumor, PK, biomarkers, and overall response rate. US enrollment began December 2021 and ex-USA startup is under way. Citation Format: Andreas Varkaris, Erika Hamilton, Jason Henry, Alexander I. Spira, Alison M. Schram, Julia E. McGuinness, Gege Tan, Xiaoyan Li, Tamieka Hunter, Ramin Samadani, Alison Timm, Djuro Karanovic, Vivek Subbiah, Cesar A. Perez. First-in-human global multi-center study of RLY-2608, a pan mutant and isoform selective PI3Kα inhibitor, as a single agent in advanced solid tumor patients and in combination with fulvestrant in patients with advanced breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT3-22-01.

Supplementary Methods, Figures S1-S11, and Table Legends. Supplementary Methods: description of methods used in the Supplementary figures, expanded description of ELISA assays, and description of the computational model of multiple EGFR ligand antagonists. Supplementary Figure S1: Monoclonal EGFR antibodies poorly block signal amplification by high-affinity EGFR ligands. Supplementary Figure S2: Hierarchical clustering of EGFR ligand expression in primary colon, head and neck, and lung tumors. Supplementary Figure S3: Trends observed in EGFR ligand expression in TCGA data set are similarly apparent in primary colorectal samples analyzed by RT-qPCR. Supplementary Figure S4: Relative expression of EGFR ligands varies across cancer indications. Supplementary Figure S5: Simulated activity of a combination of two ligand antagonists versus single antagonists as a function of ligand affinity. Supplementary Figure S6: MM-151 antibodies have non-overlapping epitopes and can simultaneously engage the same EGF receptor molecule. Supplementary Figure S7: MM-151 elicits superior ligand antagonism. Supplementary Figure S8: MM-151 promotes potent down-regulation of EGFR that is dependent upon the oligoclonal combination of bivalent antibodies. Supplementary Figure S9: MM-151 promotes both antibody-dependent cell-mediated (ADCC) and complement-dependent (CDC) cytotoxicity. Supplementary Figure S10: Cell proliferation stimulated by high-affinity ligands is partially or completely resistant to cetuximab treatment but still sensitive to MM-151 treatment. Supplementary Figure S11: MM-151 overcomes signal amplification driven by high-affinity ligand. Legends for Supplementary Tables S1-S8.

Supplementary Tables S2, S3, S4. Structure of the computational model of multiple ligand antagonists: species (Table S2), parameters (Table S3), and Reactions (Table S4).

Supplementary Table S1. Cell lines and cell culture conditions

Supplementary Tables S5, S6, S7, S8. mRNA expression data for EGFR ligands as measured by RNAseq from The Cancer Genome Atlas (TCGA) across 14 cancer indications or by RT-qPCR of colorectal cancer FFPE samples. Table S5: Summary of TCGA datasets included in the analysis. Table S6: Raw and normalized expression data from TCGA. Table S7: EGFR ligand expression measured by RT-qPCR on commercially-obtained colorectal cancer FFPE samples. Table S8: Pairwise correlations of EGFR ligands across four TCGA indications.

Supplemental Figure S2: Istiratumab inhibits growth factor-induced AKT phosphorylation across a pancreatic cancer cell line panel.

Table S3

Purpose: Insulin-like growth factor receptor 1 (IGF-1R) is critically involved in pancreatic cancer pathophysiology, promoting cancer cell survival and therapeutic resistance. Assessment of IGF-1R inhibitors in combination with standard-of-care chemotherapy, however, failed to demonstrate significant clinical benefit. The aim of this work is to unravel mechanisms of resistance to IGF-1R inhibition in pancreatic cancer and develop novel strategies to improve the activity of standard-of-care therapies.Experimental Design: Growth factor screening in pancreatic cancer cell lines was performed to identify activators of prosurvival PI3K/AKT signaling. The prevalence of activating growth factors and their receptors was assessed in pancreatic cancer patient samples. Effects of a bispecific IGF-1R and ErbB3 targeting antibody on receptor expression, signaling, cancer cell viability and apoptosis, spheroid growth, and in vivo chemotherapy activity in pancreatic cancer xenograft models were determined.Results: Growth factor screening in pancreatic cancer cells revealed insulin-like growth factor 1 (IGF-1) and heregulin (HRG) as the most potent AKT activators. Both growth factors reduced pancreatic cancer cell sensitivity to gemcitabine or paclitaxel in spheroid growth assays. Istiratumab (MM-141), a novel bispecific antibody that blocks IGF-1R and ErbB3, restored the activity of paclitaxel and gemcitabine in the presence of IGF-1 and HRG in vitro. Dual IGF-1R/ErbB3 blocking enhanced chemosensitivity through inhibition of AKT phosphorylation and promotion of IGF-1R and ErbB3 degradation. Addition of istiratumab to gemcitabine and nab-paclitaxel improved chemotherapy activity in vivo.Conclusions: Our findings suggest a critical role for the HRG/ErbB3 axis and support the clinical exploration of dual IGF-1R/ErbB3 blocking in pancreatic cancer. Clin Cancer Res; 24(12); 2873–85. ©2018 AACR.

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Macrophages can be co-opted to contribute to neoplastic, neurologic, and inflammatory diseases. Colony-stimulating factor 1 receptor (CSF1R)-dependent macrophages and other inflammatory cells can suppress the adaptive immune system in cancer and contribute to angiogenesis, tumor growth, and metastasis. CSF1R-expressing osteoclasts mediate bone degradation in osteolytic cancers and cancers that metastasize to bone. In the rare disease tenosynovial giant cell tumor (TGCT), aberrant CSF1 expression and production driven by a gene translocation leads to the recruitment and growth of tumors formed by CSF1R-dependent inflammatory cells. Small molecules and antibodies targeting the CSF1/CSF1R axis have shown promise in the treatment of TGCT and cancer, with pexidartinib recently receiving FDA approval for treatment of TGCT. Many small-molecule kinase inhibitors of CSF1R also inhibit the closely related kinases KIT, PDGFRA, PDGFRB, and FLT3, thus CSF1R suppression may be limited by off-target activity and associated adverse events. Vimseltinib (DCC-3014) is an oral, switch control tyrosine kinase inhibitor specifically designed to selectively and potently inhibit CSF1R by exploiting unique features of the switch control region that regulates kinase conformational activation. In preclinical studies, vimseltinib durably suppressed CSF1R activity in vitro and in vivo, depleted macrophages and other CSF1R-dependent cells, and resulted in inhibition of tumor growth and bone degradation in mouse cancer models. Translationally, in a phase I clinical study, vimseltinib treatment led to modulation of biomarkers of CSF1R inhibition and reduction in tumor burden in TGCT patients.

Background IL-27 is a heterodimeric cytokine consisting of IL 27p28 and Epstein-Barr virus-induced gene 3 (EBI3) that binds the IL-27 receptor subunit alpha and glycoprotein 130. IL-27 is produced by activated macrophages and dendritic cells and limits the intensity and duration of immune responses in the tumor microenvironment by inducing the expression of immunoregulatory receptors (PD-L1, TIM3, LAG-3, TIGIT) and inhibiting production of proinflammatory cytokines (IFNγ, IL-17, TNFα). The IL-27 subunit EBI3 is elevated in plasma from patients with certain cancers including renal cell carcinoma, where it correlates with poor outcome. Based on high expression of IL-27 transcript in tumors from patients with hepatocellular carcinoma (HCC), the role of IL-27 was further explored in patient samples and a mouse model of HCC. Methods Gene expression profiles from the Cancer Genome Atlas (TCGA) were analyzed to identify tumors with elevated IL-27 transcripts. Serum from patients with HCC was analyzed for levels of the IL-27 subunit EBI3. The ability of SRF388, a first-in-class IL-27-blocking antibody that binds to IL-27p28, to reverse IL-27-induced inhibition of cytokine production in human immune cell cultures from patients with HCC was assessed in vitro. Finally, the anti-tumor activity of SRF388 was assessed in an orthotopic murine model of HCC. Results TCGA expression data revealed that IL-27p28 transcripts were elevated in tumors from patients with HCC relative to other indications. Serum levels of EBI3 were: 1) elevated in a subset of HCC patients; 2) inversely correlated with survival; 3) independent of serum alpha-fetoprotein levels; and 4) elevated in both hepatitis B/C virus positive and negative patients. Treatment with SRF388 stimulated increased cytokine production in activated peripheral blood mononuclear cells from patients with HCC that was further enhanced when combined with PD-1 blockade. Furthermore, SRF388 inhibited the growth of orthotopic Hepa1-6 liver tumors. mRNA transcriptional profiling of treated tumors revealed that SRF388 profoundly altered the transcriptional landscape in this model. In particular, treatment with SRF388 inhibited expression of immunoregulatory receptors PD-L1 and TIGIT, repressed transcripts associated with TGF-β signaling, and altered myeloid and natural killer cell transcripts. Conclusions These data indicate that elevated IL-27 subunit EBI3 is a hallmark of HCC and is associated with poor outcomes in these patients. Blockade of IL-27 with SRF388, currently being evaluated in a Phase 1 clinical trial in patients with advanced solid tumors (NCT04374877), may represent a promising therapy for patients with HCC where it can potentiate anti-tumor immune responses.

Purpose: Insulin-like growth factor receptor 1 (IGF-1R) is critically involved in pancreatic cancer pathophysiology, promoting cancer cell survival and therapeutic resistance. Assessment of IGF-1R inhibitors in combination with standard-of-care chemotherapy, however, failed to demonstrate significant clinical benefit. The aim of this work is to unravel mechanisms of resistance to IGF-1R inhibition in pancreatic cancer and develop novel strategies to improve the activity of standard-of-care therapies. Experimental Design: Growth factor screening in pancreatic cancer cell lines was performed to identify activators of prosurvival PI3K/AKT signaling. The prevalence of activating growth factors and their receptors was assessed in pancreatic cancer patient samples. Effects of a bispecific IGF-1R and ErbB3 targeting antibody on receptor expression, signaling, cancer cell viability and apoptosis, spheroid growth, and in vivo chemotherapy activity in pancreatic cancer xenograft models were determined. Results: Growth factor screening in pancreatic cancer cells revealed insulin-like growth factor 1 (IGF-1) and heregulin (HRG) as the most potent AKT activators. Both growth factors reduced pancreatic cancer cell sensitivity to gemcitabine or paclitaxel in spheroid growth assays. Istiratumab (MM-141), a novel bispecific antibody that blocks IGF-1R and ErbB3, restored the activity of paclitaxel and gemcitabine in the presence of IGF-1 and HRG in vitro. Dual IGF-1R/ErbB3 blocking enhanced chemosensitivity through inhibition of AKT phosphorylation and promotion of IGF-1R and ErbB3 degradation. Addition of istiratumab to gemcitabine and nab-paclitaxel improved chemotherapy activity in vivo. Conclusions: Our findings suggest a critical role for the HRG/ErbB3 axis and support the clinical exploration of dual IGF-1R/ErbB3 blocking in pancreatic cancer. Clin Cancer Res; 24(12); 2873–85. ©2018 AACR.

Therapeutically targeting receptor tyrosine kinases has proven to be paramount to overcoming chemotherapy resistance in several cancer indications, improving patient outcomes. Insulin-Like Growth Factor Receptor 1 (IGF-1R) and Epidermal Growth Factor Receptor 3 (ErbB3) have been implicated as two such drivers of resistance, however their simultaneous role in ovarian cancer chemotherapy resistance remains poorly elucidated. The aim of this work is to determine the effects of dual IGF-1R/ErbB3 inhibition on ovarian cancer cell signaling, growth, and in vivo efficacy. Assessment of in vitro chemotherapy response across a panel of ovarian cancer cell lines revealed that increased IGF-1R cell surface expression correlates with decreased sensitivity to chemotherapy, and that growth induced by IGF-1R and ErbB3 ligands is blocked by the tetravalent bispecific antibody targeting IGF-1R and ErbB3, istiratumab. In vitro chemotherapy treatment increased ovarian cancer cell line capacity to activate prosurvival PI3K signaling in response to ligand, which could be prevented with istiratumab treatment. Furthermore, in vivo efficacy of standard of care chemotherapies using a xenograft model of ovarian cancer was potentiated with istiratumab. Our results suggest a role for IGF-1R and ErbB3 in driving chemotherapy resistance of ovarian cancer.

CD39 (ENTPD1) is a key enzyme responsible for the degradation of extracellular adenosine triphosphate (ATP) and is upregulated in the tumor microenvironment (TME). High levels of extracellular ATP, often generated in the TME as a result of tissue damage and immunogenic cell death, can initiate proinflammatory responses that are blocked by the enzymatic activity of CD39. In addition, extracellular adenosine accumulates in cancerous tissues through the degradation of ATP by CD39 and other ectonucleotidases (eg, CD73), and constitutes an important mechanism of tumor immune escape, induction of angiogenesis, and metastasis. Thus, inhibition of CD39 can convert a suppressive TME to a proinflammatory environment. SRF617 is an investigational fully human anti-CD39 antibody that binds to human CD39 with nanomolar affinity and potently inhibits its enzymatic function. Results of the current studies show that CD39 is predominantly expressed in tumor stroma and on tumor-infiltrating immune cells in samples from patients with cancer. Similar expression patterns are observed in various murine tumor models. In vivo, SRF617 has significant single-agent anti-tumor activity in a variety of cell line-derived xenograft models that express CD39. Cancer therapies, such as immunogenic cell death agents, can increase inflammation and ATP levels in the TME; combination studies of SRF617 with these agents showed improved preclinical efficacy and led to significant improvement in survival. In addition, a mouse-specific anti-CD39 surrogate antibody demonstrated potent binding and enzymatic inhibition of murine CD39 in vitro and significantly decreased tumor growth in a syngeneic murine tumor model. Pharmacodynamic studies demonstrated mechanistic changes in the tumor-infiltrating leukocytes and plasma chemokine levels. Combination treatment of a murine anti-CD39 surrogate and an anti-mouse PD-1 displayed improved activity and an increase in overall survival in the CT-26 mouse model. In addition, administration of SRF617 in combination with other immunotherapies also demonstrated a similar improvement in activity and survival. In summary, these studies demonstrate that SRF617 is a potent inhibitor of CD39 enzymatic activity both in vitro and in vivo. Inhibition of CD39 potentiates the activity of chemotherapy and immunotherapy agents to improve tumor growth inhibition and survival in mice. These findings support future clinical studies of SRF617 as monotherapy and in combination with other therapeutic agents in treating patients with cancer. Citation Format: Sonia G. Das, Austin Dulak, Gege Tan, Marc Johnson, Tauqeer H. Zaidi, Michael C. Warren, Secil Koseoglu, Erik Devereaux, Marisa O. Peluso, Alison M. Paterson, Benjamin H. Lee, Vito J. Palombella, Pamela M. Holland, Andrew C. Lake. SRF617, a potent enzymatic inhibitor of CD39, demonstrates single-agent activity and cooperates with various cancer therapies in both solid tumor and hematologic malignancies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6639.

IL-27 is a heterodimeric member of the IL-12/IL-23 cytokine family that consists of two subunits, IL-27p28 and Epstein-Barr virus-induced gene 3 (EBI3), and binds to a heterodimeric receptor composed of the IL-27 receptor subunit alpha (IL-27RA) and glycoprotein 130 (gp130). IL-27 signals through the JAK-STAT pathway to limit the duration and intensity of T cell-mediated immunity by altering immunoregulatory receptor expression and proinflammatory cytokine secretion during infection and cancer. Analysis of data from The Cancer Genome Atlas (TCGA) revealed that IL-27p28, EBI3, and IL-27RA transcript levels are often elevated in tumors from patients with renal cell carcinoma (RCC) and that high levels of these genes are associated with poor clinical outcome. Using an IL-27 gene signature derived from activated CD4+T cells, several genes downstream of IL-27 signaling were found to be coordinately regulated in a subset of RCC patients and associated with poor prognosis. Moreover, plasma levels of the EBI3 subunit of IL-27 were found to be elevated in a subset of RCC patients and inversely correlated with both disease-free and overall survival. The ability of IL-27 to dampen immune responses and the association of elevated levels of this cytokine with poor clinical outcome in RCC suggest that IL-27 blockade may represent a promising strategy to treat cancer in patients with high circulating EBI3. SRF388 is a first-in-class IL-27p28 antibody that blocks the interaction of IL-27 with IL-27RA and inhibits IL-27 signaling in primary human immune cells. This mechanism results in diminished inhibitory receptor expression and increased cytokine production. Exogenous IL-27 inhibited the activity of PD-1 blockade in vitro by counteracting the increased cytokine production observed after treatment of activated human PBMCs from healthy donors and RCC patients. Furthermore, treatment with SRF388 stimulated increased cytokine production in activated PBMCs from patients with RCC in the absence of exogenous IL-27; this proinflammatory response was further enhanced when combined with PD-1 blockade. Finally, SRF388 demonstrated single-agent anti-tumor activity in a murine orthotopic model of RCC. These data indicate that blockade of IL-27 can potentiate anti-tumor responses by counteracting IL-27-mediated immune escape and may represent a promising strategy for treating cancer patients. Citation Format: Matthew Rausch, Jing Hua, Devapregasan Moodley, Kerry F. White, Katherine H. Walsh, Christine E. Miller, Gege Tan, Benjamin H. Lee, Isabelle Cousineau, Jean-Baptiste Lattouf, John Stagg, Vito J. Palombella, Pamela M. Holland, Jonathan A. Hill. Increased IL-27 is associated with poor prognosis in renal cell carcinoma and supports use of SRF388, a first-in-class IL-27p28 blocking antibody, to counteract IL-27-mediated immunosuppression in this setting [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4550.

Although EGFR is a validated therapeutic target across multiple cancer indications, the often modest clinical responses to current anti-EGFR agents suggest the need for improved therapeutics. Here, we demonstrate that signal amplification driven by high-affinity EGFR ligands limits the capacity of monoclonal anti-EGFR antibodies to block pathway signaling and cell proliferation and that these ligands are commonly coexpressed with low-affinity EGFR ligands in epithelial tumors. To develop an improved antibody therapeutic capable of overcoming high-affinity ligand-mediated signal amplification, we used a network biology approach comprised of signaling studies and computational modeling of receptor–antagonist interactions. Model simulations suggested that an oligoclonal antibody combination may overcome signal amplification within the EGFR:ERK pathway driven by all EGFR ligands. Based on this, we designed MM-151, a combination of three fully human IgG1 monoclonal antibodies that can simultaneously engage distinct, nonoverlapping epitopes on EGFR with subnanomolar affinities. In signaling studies, MM-151 antagonized high-affinity EGFR ligands more effectively than cetuximab, leading to an approximately 65-fold greater decrease in signal amplification to ERK. In cell viability studies, MM-151 demonstrated antiproliferative activity against high-affinity EGFR ligands, either singly or in combination, while cetuximab activity was largely abrogated under these conditions. We confirmed this finding both in vitro and in vivo in a cell line model of autocrine high-affinity ligand expression. Together, these preclinical studies provide rationale for the clinical study of MM-151 and suggest that high-affinity EGFR ligand expression may be a predictive response marker that distinguishes MM-151 from other anti-EGFR therapeutics. Mol Cancer Ther; 14(7); 1625–36. ©2015 AACR.

Androgen exposure stimulates the growth of beard hair follicles. The follicle dermal papilla appears to be the site of androgen action; however, the molecular mechanisms that regulate this process are not well understood. In an attempt to identify genes that contribute to the androgen-responsive phenotype, we compared gene expression patterns in unstimulated and androgen-treated cultured human dermal papilla cells isolated from beard (androgen-sensitive) and occipital scalp (androgen-insensitive) hair follicles. Through this analysis, we identified three genes that are expressed at significantly higher levels in beard dermal papilla cells. One of these genes, sfrp-2 has been identified as a dermal papilla signature gene in mouse pelage follicles. Two of these genes, mn1 and atp1beta1, have not been studied in the hair follicle. A fourth, fibulin-1d, was slightly upregulated in beard dermal papilla cells. The differences in the expression of these genes in cultured beard and scalp dermal papilla cells reflected similar differences in microdissected dermal papilla isolated from intact beard and scalp follicles. Our findings introduce potentially novel signaling pathways in dermal papilla cells. In addition, this study supports that cultured dermal papilla cells provide a cell-based model system that is reflective of the biology of in vivo hair follicle cells.

Ewing’s sarcoma family tumors (ES) are aggressive tumors that often present as metastatic in bone and soft tissue and predominantly affect adolescents and younger adults. Current treatment for ES includes surgical resection followed by loco-regional radiotherapy and chemotherapy. Survival rates for patients with metastatic disease continue to offer a particularly difficult clinical challenge, with a five-year survival rate of 20-30% for these patients. ES is primarily a genetic disease caused by fusion between the 5’ segment of the Ewing sarcoma breakpoint region 1 gene (EWSR1) on chromosome 22 and the 3’ portion of Friend leukemia virus integration site 1 (FLI1) on chromosome 11. Fusions of EWSR1 and other ETS transcription factors result in dis-regulated transcription factors which promote malignant progression of ES tumors. Recent studies have shown that most ES cell lines and clinical samples express IGF-1R. Importantly, an activated IGF-1R pathway appears to be a prerequisite for malignant transformation by the EWS-FLI1 translocation, presumably via activation of the PI3K-AKT and MAPK pathways. These findings have led to the preclinical and clinical evaluation of multiple IGF-1R-targeted therapeutics with varying results. Clinical experience with anti-IGF1R targeting therapies has demonstrated striking anticancer activity in minor subsets of patients with ES. Importantly, the paucity of a clinically useful biomarker to select patients continues to hinder IGF-1R drug development in ES. Istiratumab is an investigational, bi-specific, monoclonal antibody that acts as a tetravalent inhibitor of PI3K/AKT/mTOR, a major pro-survival pathway tumor cells use as a resistance mechanism to anticancer therapies. Istiratumab is designed to interfere with this pathway by blocking ligand-induced signaling through the IGF-1R and ErbB3 receptors, based on findings that ErbB3 activation mediates resistance to the IGF-1R blockade. We will present data in multiple ES models demonstrating the importance of both IGF-1R and ErbB3 in this disease as a mechanism of growth and resistance. Furthermore, preclinical xenograft studies demonstrate that the combination of istiratumab with an irinotecan-based chemotherapy regimen offers significant benefit over chemotherapy alone. These studies suggest that clinical evaluation of istiratumab in ES is warranted. Citation Format: Isabel Yannatos, Adam Camblin, Zhenhua Li, Michael Curley, Gege Tan, Chrystal U. Louis, Vasileios Askoxylakis, Greg Finn, Birgit Schoeberl, Rachel Nering. Dual-targeting of IGF-1R and ErbB3 pathways in Ewing’s Sarcoma cellular models with istiratumab (MM-141), a bispecific, tetravalent monoclonal antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 521. doi:10.1158/1538-7445.AM2017-521

Insulin-like growth factor receptor 1 (IGF-1R) signaling has been implicated in the pathogenesis of ovarian cancer. However, clinical trials evaluating monospecific IGF-1R inhibitors have demonstrated limited clinical efficacy. Our data indicate that ErbB3, a member of the ErbB receptor tyrosine kinase family, can activate pro-survival AKT signaling in response to IGF-1R blockade and may represent a potential escape route in the development of resistance to therapy. Istiratumab (MM-141), an IGF-1R and ErbB3 directed bispecific antibody, inhibits ligand activation of these signaling pathways and degrades IGF-1R and ErbB3 receptor-containing complexes, leading to inhibition of downstream pro-survival signaling. Here we tested the activity of istiratumab, alone and in combination with chemotherapy, in in vitro and in vivo models of ovarian cancer. Anti-proliferative activity of istiratumab monotherapy was evaluated in a panel of ovarian cancer cell lines in vitro. The effects of istiratumab and the ligands IGF-1 and heregulin on IGF-1R- and ErbB3-mediated survival signaling were tested by ELISA and immunoblotting. Co-treatment assays with istiratumab and chemotherapy investigated mechanisms of synergy and additivity. Anti-tumor activity of istiratumab, alone and in combination with chemotherapy, was tested in in vivo ovarian xenograft tumor models. Our results indicated that istiratumab monotherapy inhibits ovarian cancer cell line proliferation in vitro. In addition, istiratumab blocked ligand-mediated resistance to chemotherapy. Co-treatment of istiratumab, ligands or chemotherapy indicated a strong correlation between drug activity and IGF-1R expression. Furthermore, co-treatment of chemotherapies and ligands potentiated AKT activation, which was inhibited by istiratumab. In vivo studies showed that istiratumab potentiates the activity of chemotherapy in ovarian xenograft tumor models. Our findings demonstrate that co-inhibition of IGF-1R and ErbB3 signaling with istiratumab can potentiate standard of care chemotherapies in ovarian tumor models and warrant further investigation of istiratumab as a potential therapy for ovarian cancer patients. Citation Format: Michael D. Curley, Gege Tan, Isabel Yannatos, Adam Camblin, Sergio Iadevaia, Chrystal Louis, Alexey Lugovskoy. Istiratumab (MM-141), a bispecific antibody targeting IGF-1R and ErbB3, inhibits pro-survival signaling in vitro and potentiates the activity of standard of care chemotherapy in vivo in ovarian cancer models. [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 1209.

Purpose: Regulatory T cells (Tregs) help maintain immunological tolerance to cancer cells by suppressing T cell effector function. The depletion of Tregs with the CTLA-4 inhibitor antibody ipilimumab has been proven to be a productive therapeutic strategy in melanoma. Additionally, levels of insulin-like growth factor 1 (IGF-1) are often elevated following chemotherapy treatment and have been associated with poor prognosis in multiple malignances. We demonstrate that IGF-1 can stimulate Treg proliferation. Istiratumab, a tetravalent bispecific antibody that targets both the IGF-1 receptor (IGF-1R) and ErbB3, inhibits IGF-1 signaling by blocking ligand binding and inducing rapid receptor internalization. Based on its mechanism of action, we evaluated the activity of istiratumab on Treg proliferation and in combination with immune checkpoint targeting antibodies in murine models of cancer. Experimental Procedures: Mouse-derived splenocytes were harvested to evaluate the effect of IGF-1 and/or istiratumab treatment on Treg expansion and proliferation in vitro. Flow cytometry studies assessed surface receptor expression of T cell populations isolated from murine splenocytes. Efficacy studies using immunocompetent mice bearing syngeneic murine tumors determined the activity of istiratumab and immune checkpoint targeting antibodies, alone and in combination, on tumor growth alongside isotype-matched controls. Mice whose tumors were eradicated by treatment were maintained and subsequently used in tumor re-challenge studies to assess the development of tumor-specific, immunological, long-term memory. In addition, pharmacodynamic studies analyzed the expression of tumor cell signaling pathway markers, effects on relevant T cell sub-populations and effects on post-treatment cytokine profiles. Data Summary: Our in vitro T cell analyses indicated that sub-populations of murine CD4+ CD25+ FoxP3+ Tregs express IGF-1R, and that istiratumab can reverse IGF-1 driven Treg proliferation in vitro. In addition, istiratumab monotherapy treatment had significant anti-tumor activity in vivo in immunogenic, syngeneic murine tumor models. Moreover, istiratumab potentiated the activity of immune checkpoint targeting antibodies in efficacy studies leading to curative outcomes in a subset of treated animals. These animals developed long-term immunological memory directed against the original tumor cell line. A pharmacodynamic analysis of tumor cell signaling- and immunology-related markers demonstrated that istiratumab impacts tumor cell survival signaling and contributes to overall immunological changes that favor breaking immunological tolerance in relevant syngeneic tumor models, thus enabling the development of an effective and durable anti-tumor immune response. Conclusions: Our in vitro and in vivo pre-clinical studies demonstrate that istiratumab (MM-141) inhibits both tumor cell survival and Treg proliferation in host mice, thereby potentiating the anti-tumor activity of clinically-relevant immune checkpoint inhibitor antibodies. Citation Format: Sharlene Adams, Michael D. Curley, Adam J. Camblin, Sergio Iadevaia, Lin Nie, Gege Tan, Chrystal U. Louis, Alexey A. Lugovskoy. Istiratumab (MM-141), a bispecific antibody co-targeting IGF-1R and ErbB3, potentiates the activity of immune checkpoint inhibitors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A89.

Background: MM-141 is a tetravalent bi-specific monoclonal antibody that binds IGF-1R and ErbB3, oncogenic receptors commonly co-expressed in solid tumors. In preclinical models, MM-141 blocks both ligand-dependent and -independent PI3K/AKT/mTOR signaling initiated through IGF-1R and ErbB3 complexes and potentiates the activity of gemcitabine, paclitaxel, nab-paclitaxel, docetaxel, irinotecan, tamoxifen, and everolimus. A multi-arm phase I study is ongoing, with continuing patient enrollment in Arm B (MM-141 in combination with everolimus). Monotherapy Arm A and combination Arm C (MM-141 with nab-paclitaxel and gemcitabine) are completed. Methods: Tumor expression of IGF-1R and ErbB3 was measured by immunohistochemistry. In vitro expression and degradation of IGF-1R and ErbB3 in pancreatic cell line models post-treatment were measured by immunoblotting and ubiquitination, respectively. The phase I dose-escalation study evaluated safety, tolerability, pharmacokinetic (PK), and pharmacodynamic (PD) properties of MM-141 as monotherapy (Arm A, n = 15) and in combination with everolimus (Arm B) or with nab-paclitaxel and gemcitabine (Arm C, n = 11). Pre- and post-treatment biopsies were acquired where mandated. Patients in the monotherapy Arm A received MM-141 at 6, 12, 20 mg/kg weekly or 40 mg/kg biweekly. Patients in the dose-escalation portion of Arm C received MM-141 at a weekly dose of 12 or 20 mg/kg in combination with weekly nab-paclitaxel (125 mg/m2) and gemcitabine (1000 mg/m2) on a schedule of 3 weeks on, 1 week off. Enrollment in Arm B (MM-141 in combination with everolimus) is ongoing. Patient serum free IGF-1 levels were detected using an in-house developed CLIA validated ELISA-based assay. Results: Here we report common co-expression of IGF-1R and ErbB3 in solid tumors. In stage IV metastatic pancreatic cancer, co-expression of IGF-1R and ErbB3 was associated with decreased patient survival. In preclinical models, increased expression of IGF-1R and ErbB3 desensitized tumors to gemcitabine and paclitaxel. However, co-treatment with MM-141 reversed this acquired resistance through blockade of growth factor binding and induction of IGF-1R and ErbB3 degradation. In the monotherapy arm of a phase I study, no dose-limiting toxicities were observed at any of the studied dose levels. The safety, tolerability, PK and PD profile of MM-141 support 2.8g bi-weekly MM-141 phase II recommended dose. The analysis of pre- and post-treatment biopsies confirmed that levels of IGF-1R and ErbB3 were decreased following MM-141 administration. In Arm C, the observed safety profile of MM-141 in combination with nab-paclitaxel and gemcitabine was comparable to expected toxicities reported with the chemotherapy combination when used alone. Retrospective analysis of serum free IGF-1 levels in breast cancer patients (Arm B) demonstrated that patients with elevated levels of this potential biomarker remained on study longer and received a greater number of doses of MM-141. Conclusion: These data support continued development of MM-141 in biomarker-selected patient populations and the upcoming phase II study of MM-141 in combination with nab-paclitaxel and gemcitabine in front-line metastatic pancreatic cancer patients with detectable free IGF-1 serum levels. Citation Format: Alexey A. Lugovskoy, Michel Curley, Jason Baum, Sharlene Adams, Sergio Iadevaia, Victoria Rimkunas, Adam Camblin, Lin Nie, Gege Tan, Bryan Johnson, Sara Mathews, Kerry Horgan, Chrystal U. Louis, Akos G. Czibere, Monica Arnedos, Jean-Charles Soria, Rastilav Bahleda, Anthony Shields, Patricia M. LoRusso, Mansoor Saleh, Steven J. Isakoff. Preclinical characterization and first-in-human study of MM-141, a dual antibody inhibitor of IGF-1R and ErbB3. [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 CT237. doi:10.1158/1538-7445.AM2015-CT237

289 Background: Gemcitabine, the first-line treatment for pancreatic cancer, has been improved by addition of nab-paclitaxel. However, patient response to this regimen is limited. Oncogenic insulin-like growth factor 1 (IGF-1) and heregulin (HRG) signaling are associated with increased cancer risk and decreased response to anti-metabolites and taxanes. Therefore, we explored MM-141, a novel bispecific antibody that blocks ErbB3 and IGF-1 receptor (IGF-1R) signaling, in combination with nab-paclitaxel and gemcitabine in preclinical models of pancreatic cancer. Methods: Combinations with MM-141, gemcitabine, and nab-paclitaxel were investigated in pancreatic cancer cell lines, in vitro and in vivo. The effects of MM-141, gemcitabine, and nab-paclitaxel on tumor growth and signaling were measured by 3D spheroid growth, ELISA, Western, and mouse xenograft experiments. Results: In vitro studies show that IGF-1 and HRG are potent activators of AKT signaling, leading to increased pancreatic tumor cell proliferation and decreased sensitivity to gemcitabine and nab-paclitaxel. MM-141 inhibits ligand-induced AKT activation, induces IGF-1R and ErbB3 degradation better than a mixture of IGF-1R and ErbB3 antibodies, and sensitizes cells to gemcitabine and nab-paclitaxel, in vitro. In vivo, MM-141 combines favorably with a nab-paclitaxel/gemcitabine regimen, leading to curative outcomes in a subset of treated mice. Conclusions: ErbB3 and IGF-1R co-inhibition is required to inhibit AKT signaling in pancreatic adenocarcinoma cell lines. These receptors are associated with chemoresistance to gemcitabine and nab-paclitaxel, which is abrogated by co-administration with MM-141. MM-141-induced degradation of oncogenic receptor complexes is likely essential to reverse chemoresistance and enhance effects of the nab-paclitaxel/gemcitabine regimen. These data, taken together with wide-spread expression of IGF-1R and ErbB3 in Stage IV pancreatic adenocarcinoma tissue, support clinical exploration of a MM-141/nab-paclitaxel/gemcitabine regimen in frontline metastatic pancreatic cancer. Preparations for a randomized Phase 2 study are underway.

Cancer, the second most common cause of death in the United States, is a collection of diseases caused by uncontrolled cell growth and metastasis. The main treatment for cancer is chemotherapy, which generally kills fast growing cells nonspecifically and has many side effects. A different type of cancer treatment, called targeted therapy, aims to avoid general toxicity by using drugs that block the activity of specific gene products, usually encoded by oncogenes, which have been shown to drive tumor growth. To date, targeted therapies, alone or in combination with chemotherapies, have mainly been successful in rare subsets of patients with tumors addicted to single oncogenes. This has created a rationale to mainly treat patients with an oncogene-addiction (such as those carrying mutated or overexpressed kinases) with targeted therapies like erlotinib and trastuzumab, which inhibit human epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2/ErbB2), respectively. Here, evidence is provided that targeted therapies are also effective in tumors that are dependent on multiple growth factors – a phenomenon that is called combinatorial ligand addiction. Specifically, it is shown that ligands that bind the EGFR family and the hepatocyte growth factor receptor (HGFR/MET) can activate protein kinase B (PKB/AKT) across a broad set of cancer cell lines, suggesting that ligand signaling is redundant and widespread. It is also shown that ErbB ligands have distinct signaling dynamics and strengths, which provides a rationale for investigating each component of the ErbB signaling network. Using a systematic approach, we found that ErbB3 is an important therapeutic target even though it is not overexpressed and lacks kinase activity. Furthermore, it is shown that cell lines with and without known oncogene-addiction express autocrine ligands and have improved growth inhibition with drug combinations that include autocrine ligand-blocking antibodies. This research demonstrates that combinatorial ligand addiction creates a new rationale for therapeutic combinations to improve efficacy and prevent resistance in cancer cells that are treated with current targeted drugs. This proffered talk is also presented as Poster A22. Citation Format: Emily A. Pace, Ulrik B. Nielsen, Birgit Schoeberl, Diana H. Chai, Anand Parikh, Ashish Kalra, Shinji Oyama, Bryan Johnson, Gege Tan, Aaron Fulgham, Raghida Bukhalid. Investigating combinatorial ligand addiction provides insights into rational drug combinations in cancer therapy [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 PR9.

The Epidermal Growth Factor Receptor (EGFR/ErbB1) is a receptor tyrosine kinase whose activation has been shown to play a key role in tumor growth and development. The EGFR ligand family is comprised of seven transmembrane precursor proteins whose expression and processing is highly regulated. These ligands can be classified based upon their affinity to EGFR; epidermal growth factor (EGF), betacellulin (BTC), heparin-binding epidermal growth factor (HB-EGF), and transforming growth factor alpha (TGFα) are considered high-affinity ligands, whereas amphiregulin (AREG), epiregulin (EREG), and epigen (EPI) are considered low-affinity ligands. EGFR overexpression in tumors is associated with higher risk of recurrence, metastasis, poorer survival and resistance to chemotherapy. Therefore, this pathway is a compelling target for the development of anti-EGFR therapeutics. Using Merrimack's Network Biology approach, we performed a computational systems analysis to identify an optimal strategy to inhibit the EGFR-ERK signaling network, which is characterized by robust signal amplification from the receptor to downstream effectors. As a result, we developed MM-151, an oligoclonal therapeutic composed of three fully human monoclonal antibodies targeted to distinct EGFR epitopes. MM-151 inhibits EGFR pathway activation by the dual mechanism of EGFR ligand-blocking and enhancement of receptor downregulation. Our preclinical in vitro studies revealed greater potency for MM-151 versus existing monoclonal antibodies (e.g. cetuximab, panitumumab and nimotuzumab). Importantly, MM-151 was shown to inhibit in vitro ERK signaling and cell proliferation induced by both high- and low-affinity EGFR ligands, unlike existing monoclonal therapeutics, which only block low-affinity ligand-induced signaling and cell proliferation. In in vitro cell proliferation assays, several cell line models that were responsive to anti-EGFR monoclonals in the presence of the low-affinity ligand AREG became increasingly unresponsive to treatment upon titrating in increasing amounts of the high-affinity ligand EGF. Conversely, cells remained responsive to MM-151 even in the presence of high-affinity EGF ligand burden. In preclinical non-small cell lung cancer (NSCLC) and head and neck squamous cell carcinoma (HNSCC) EGFR-wildtype cell line models, overexpression of autocrine AREG is positively correlated with increased sensitivity to the anti-EGFR monoclonal cetuximab or tyrosine kinase inhibitor gefitinib (K. Yonesaka et al., Clin. Cancer Res., 2008, 14: 6963–6973). In the clinic, metastatic colon cancer patients with wild type K-ras tumors highly expressing the low-affinity ligands AREG and EREG are more likely to exhibit disease control on cetuximab treatment (J. B. Baker et al., Br. J. Cancer, 2011, 104: 488–495). Our preclinical data suggest that elevated high-affinity ligand expression would likely correlate with decreased patient response to anti-EGFR monoclonals, and that patients whose tumors are driven by high-affinity EGFR ligands might instead benefit from MM-151 treatment. Together, these data suggest that MM-151, capable of blocking both high and low affinity ligand-driven EGFR signaling, may have the potential to more broadly benefit lung and colon cancer patients as compared to existing EGFR-directed therapies. 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 A144.

Epidermal growth factor receptor (EGFR) is a key regulator of cancer cell proliferation, apoptosis, invasion, and metastasis. However, the clinical benefits of EGFR targeted agents such as erlotinib and cetuximab have been modest. Using Merrimack's Network Biology platform, a computational systems analysis was performed to identify how best to inhibit signaling through the EGFR-ERK network. These simulations predicted that enhanced inhibition is required to overcome the robust signal amplification inherent to this network and is best achieved through treatment with a combination of at least two noncompetitive ligand antagonists. The MM-151 therapeutic was developed to achieve the simulated design criteria and consists of a mixture of three fully human monoclonal antibodies directed against distinct non-overlapping epitopes in EGFR. Detailed in vitro and on-cell binding experiments, supported by computational simulations, with single component antibodies and their monovalent Fab variants, display a rich complexity of antibody affinity and avidity. All three antibodies are shown to have subnanomolar monovalent affinity to EGFR but to vary in the degree to which they functionally crosslink receptor (two antibodies display high avidity while the third has weak avidity). Ligand competition experiments with saturating antibody concentrations (EC90 of on-cell binding) demonstrate that two of the antibodies are each complete ligand antagonists while the third antibody is a partial (approx. 25%) antagonist. When combined into the MM-151 mixture, these antibodies simultaneously engage and robustly crosslink receptor to form a highly antagonistic therapeutic. Treatment of human tumor-derived cell lines with MM-151 elicits complete inhibition of ligand-mediated ERK signaling over a wide range of both EGF receptor density (as high as 2×10∘6 receptors per cell in the A431 cell line) and ligand burden (8 and 80nM EGF). In contrast, monoclonal EGFR targeted therapeutics, such as cetuximab and panitumumab, as well as oligoclonal inhibitors similar to MM-151, show weaker or even no effect on ERK signaling under similar conditions. Furthermore, the potency of monovalent MM-151 (Fab variants) is diminished in EGF mediated EGFR and ERK signaling, highlighting the importance of receptor crosslinking through antibody avidity as a determinant of efficacy. Together, these data demonstrate that MM-151 is a potent inhibitor of the EGFR-ERK signaling axis with the potential of improved efficacy over current EGFR targeted therapies. 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 A210.