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Purpose:The influence of the transcriptional and immunologic context of mutations on therapeutic outcomes with targeted therapy in cancer has not been well defined. BRAF V600E–mutant (BM) colorectal cancer comprises two main transcriptional subtypes, BM1 and BM2. We sought to determine the impact of BM subtype, as well as distinct biological features of those subtypes, on response to BRAF/MEK/EGFR inhibition in patients with colorectal cancer.Patients and Methods:Paired fresh tumor biopsies were acquired at baseline and on day 15 of treatment from all consenting patients with BM colorectal cancer enrolled in a phase II clinical trial of dabrafenib, trametinib, and panitumumab. For each sample, BM subtype, cell cycle, and immune gene signature expression were determined using RNA-sequencing (RNA-seq), and a Cox proportional hazards model was applied to determine association with progression-free survival (PFS).Results:Confirmed response rates, median PFS, and median overall survival (OS) were higher in BM1 subtype patients compared with BM2 subtype patients. Evaluation of immune contexture identified greater immune reactivity in BM1, whereas cell-cycle signatures were more highly expressed in BM2. A multivariate model of PFS incorporating BM subtype plus immune and cell-cycle signatures revealed that BM subtype encompasses the majority of the effect.Conclusions:BM subtype is significantly associated with the outcome of combination dabrafenib, trametinib, and panitumumab therapy and may serve as a standalone predictive biomarker beyond mutational status. Our findings support a more nuanced approach to targeted therapeutic decisions that incorporates assessment of transcriptional context.

Supplementary Data

Supplementary Tables S1 & S2 from Large-Scale Molecular Comparison of Human Schwann Cells to Malignant Peripheral Nerve Sheath Tumor Cell Lines and Tissues

Malignant peripheral nerve sheath tumors (MPNST) are highly invasive soft tissue sarcomas that arise within the peripheral nerve and frequently metastasize. To identify molecular events contributing to malignant transformation in peripheral nerve, we compared eight cell lines derived from MPNSTs and seven normal human Schwann cell samples. We found that MPNST lines are heterogeneous in their in vitro growth rates and exhibit diverse alterations in expression of pRb, p53, p14Arf, and p16INK4a proteins. All MPNST cell lines express the epidermal growth factor receptor and lack S100β protein. Global gene expression profiling using Affymetrix oligonucleotide microarrays identified a 159-gene molecular signature distinguishing MPNST cell lines from normal Schwann cells, which was validated in Affymetrix microarray data generated from 45 primary MPNSTs. Expression of Schwann cell differentiation markers (SOX10, CNP, PMP22, and NGFR) was down-regulated in MPNSTs whereas neural crest stem cell markers, SOX9 and TWIST1, were overexpressed in MPNSTs. Previous studies have implicated TWIST1 in apoptosis inhibition, resistance to chemotherapy, and metastasis. Reducing TWIST1 expression in MPNST cells using small interfering RNA did not affect apoptosis or chemoresistance but inhibited cell chemotaxis. Our results highlight the use of gene expression profiling in identifying genes and molecular pathways that are potential biomarkers and/or therapeutic targets for treatment of MPNST and support the use of the MPNST cell lines as a primary analytic tool. (Cancer Res 2006; 66(5): 2584-91)

Purpose: The influence of the transcriptional and immunologic context of mutations on therapeutic outcomes with targeted therapy in cancer has not been well defined. BRAF V600E–mutant (BM) colorectal cancer comprises two main transcriptional subtypes, BM1 and BM2. We sought to determine the impact of BM subtype, as well as distinct biological features of those subtypes, on response to BRAF/MEK/EGFR inhibition in patients with colorectal cancer. Patients and Methods: Paired fresh tumor biopsies were acquired at baseline and on day 15 of treatment from all consenting patients with BM colorectal cancer enrolled in a phase II clinical trial of dabrafenib, trametinib, and panitumumab. For each sample, BM subtype, cell cycle, and immune gene signature expression were determined using RNA-sequencing (RNA-seq), and a Cox proportional hazards model was applied to determine association with progression-free survival (PFS). Results: Confirmed response rates, median PFS, and median overall survival (OS) were higher in BM1 subtype patients compared with BM2 subtype patients. Evaluation of immune contexture identified greater immune reactivity in BM1, whereas cell-cycle signatures were more highly expressed in BM2. A multivariate model of PFS incorporating BM subtype plus immune and cell-cycle signatures revealed that BM subtype encompasses the majority of the effect. Conclusions: BM subtype is significantly associated with the outcome of combination dabrafenib, trametinib, and panitumumab therapy and may serve as a standalone predictive biomarker beyond mutational status. Our findings support a more nuanced approach to targeted therapeutic decisions that incorporates assessment of transcriptional context.

Coinhibition of TIGIT (T cell immunoreceptor with Ig and ITIM domains) and PD-1/PD-L1 (PD-1/L1) may improve response rates compared with monotherapy PD-1/L1 blockade in checkpoint naive non–small cell lung cancer with PD-L1 expression >50%. TIGIT mAbs with an effector-competent Fc can induce myeloid cell activation, and some have demonstrated effector T cell depletion, which carries a clinical liability of unknown significance. TIGIT Ab blockade translates to antitumor activity by enabling PVR signaling through CD226 (DNAM-1), which can be directly inhibited by PD-1. Furthermore, DNAM-1 is downregulated on tumor-infiltrating lymphocytes (TILs) in advanced and checkpoint inhibition–resistant cancers. Therefore, broadening clinical responses from TIGIT blockade into PD-L1low or checkpoint inhibition–resistant tumors, may be induced by immune costimulation that operates independently from PD-1/L1 inhibition. TNFSF14 (LIGHT) was identified through genomic screens, in vitro functional analysis, and immune profiling of TILs as a TNF ligand that could provide broad immune activation. Accordingly, murine and human bifunctional fusion proteins were engineered linking the extracellular domain of TIGIT to the extracellular domain of LIGHT, yielding TIGIT-Fc-LIGHT. TIGIT competitively inhibited binding to all PVR ligands. LIGHT directly activated myeloid cells through interactions with LTβR (lymphotoxin β receptor), without the requirement for a competent Fc domain to engage Fcγ receptors. LIGHT costimulated CD8+ T and NK cells through HVEM (herpes virus entry mediator A). Importantly, HVEM was more widely expressed than DNAM-1 on T memory stem cells and TILs across a range of tumor types. Taken together, the mechanisms of TIGIT-Fc-LIGHT promoted strong antitumor activity in preclinical tumor models of primary and acquired resistance to PD-1 blockade, suggesting that immune costimulation mediated by LIGHT may broaden the clinical utility of TIGIT blockade.

BackgroundOne of the pharmacodynamic measures of biologic compounds is an assessment of target receptor/ligand occupancy (RO). If the primary mechanism for drug clearance is through target binding, drug exposure may increase once RO is saturated. SL-172154 (SIRPα-Fc-CD40L) and SL-279252 (PD1-Fc-OX40L) are two bi-functional fusion proteins in phase I clinical trials (NCT04406623 and NCT03894618). The binding interaction between a biologic compound and its targets (CD47 or PD-L1) typically does not stimulate migration from the blood, allowing direct measurement of drug and target. Evaluation of RO for immune agonists (CD40 and OX40) is challenging because agonists can stimulate lymphocytes to rapidly extravasate from the peripheral blood following infusion, thus precluding direct RO measurement as target cells are no longer present in the blood (figure 1a).MethodsTo assess full receptor engagement of CD40 or OX40, the formula shown in figure 1b was derived. The formula captures cells that rapidly migrated from the blood, combined with those that remained in the blood within 2 hours post infusion using multiparameter FACS analysis. SAS JMP was used to calculate and visualize all parameters.ResultsWithin 2 hours of SL-172154 infusion at 1 mg/kg (n=3), CD40+ B cell counts decreased from a pre-dose average by 87%. Of the CD40+ B cells remaining in the blood, ~95% were bound with SL-172154. CD40+ B cell counts recovered in the blood by the next dose, and as counts increased so did the proportion of cells that were bound with SL-172154. Similarly, within 2 hours of SL-279252 infusion at 1 mg/kg (n=10), CD4+OX40+ T cell counts decreased from a pre-dose average by 41.5% (range 0 – 70%). Of the CD4+OX40+ cells remaining in the blood, ~32% were bound with SL-279252. CD4+OX40+ cells returned to pre-treatment numbers over a 7-day interval and nearly all cells remained bound with SL-279252. Taken together, these data demonstrate that a large proportion of CD40+ (SL-172154) or OX40+ (SL-279252) cells bind drug immediately post infusion, migrate from the blood, and slowly return to the blood with drug still bound to the cell surface.Abstract 3 Figure 1CD4+ OX40+ T cells and SL-279252ConclusionsAdministration of SL-172154 (CD40) and SL-279252 (OX40) stimulated rapid egress of target cells from the blood. An integrated assessment, termed ‘receptor engagement’, was developed to derive RO both on circulating cells and those that rapidly marginated. When CD40+ or OX40+ cells returned to the blood, they remained drug-bound, indicating that the compounds may piggy-back on target cells into tissues.AcknowledgementsThanks are extended to study participants; Takeda Pharmaceutical Company, Boston, MA, United States; Cathrine Leonowens, PhD, Nuventra Pharma Sciences, Durham, NC, United States and Cadence Communications and Research, Thousand Oaks, CA, United States. This study is funded by Shattuck Labs, Inc. Austin, TX and Durham, NC, USAEthics ApprovalThis study is being conducted in full conformity with the Declaration of Helsinki and was approved by all IRBs/ethics committees from each clinical site participating in the study. Specific approval numbers can be provided upon request.

BackgroundSIRPα-Fc-CD40L is a hexameric, bi-functional fusion protein consisting of SIRPα (binding affinity to CD47 is 0.628 nM) linked to CD40L (binding affinity to CD40 is 4.74 nM) through an Fc linker protein.1 By augmenting antigen processing and promoting antigen presenting cell (APC) maturation, this molecule is designed to bridge innate and adaptive immunity, enhancing tumor cell phagocytosis and antigen cross-presentation to CD8 T cells.MethodsThe first-in-human, Phase 1 dose escalation study is evaluating SL-172154 as monotherapy in patients (pts) with platinum resistant ovarian, fallopian tube and primary peritoneal cancers. Objectives include evaluation of safety, dose-limiting toxicity (DLT) and recommended phase 2 dose (RP2D), pharmacokinetic (PK) parameters, pharmacodynamic (PD) effects and antitumor activity based on RECIST.ResultsAs of 6 July 2021, 14 heavily pretreated pts (median age, 67 years) were enrolled and treated with intravenous (IV) administration of SL-172154 across 4 dose levels on 2 schedules: schedule 1 (day 1, 8, 15, 29, Q2 weeks) at 0.1, 0.3 mg/kg and schedule 2 (weekly) at 0.3, 1.0, 3.0 mg/kg. The most common treatment-related (>20%) adverse events (AEs) of any grade (G) were fatigue (n=7, 50%), infusion-related reactions (IRR) (n=6, 43%), nausea (n=4, 29%), and decreased appetite (n=3, 21%). Treatment-related IRRs (G1/G2) generally occurred near the end of infusion or immediately post-infusion; the full dose was able to be delivered in each IRR event, and subsequent infusions in patients having IRRs were managed with pre-medications. No treatment related ≥G3 AEs or DLTs have occurred. CD47 receptor occupancy (RO) on leukocytes approached 90% at 1.0 and 3.0 mg/kg. Minimal binding to CD47+ red blood cells was observed at all dose levels. CD40 RO on B cells was >60% at doses ≥0.1 mg/kg and 75%–100% at 1.0 and 3.0 mg/kg. Rapid, transient B cell and monocyte margination was observed following infusion of SL-172154 and was consistent with dose-dependent increases in IL-12, MCP-1, MIP-1β, MIP-1α, and MDC. No appreciable increases in IL-6 or TNFα were noted and there was no correlation between IRRs and cytokine increases. Among 12 evaluable pts, the best response was stable disease in 3 pts.ConclusionsSL-172154 has been well tolerated with no evidence of anemia, thrombocytopenia, liver dysfunction or cytokine release syndrome. A unique serum cytokine signature consistent with CD40 RO and activation has been observed and this signature is maintained following repeat dosing. Dose escalation is ongoing.AcknowledgementsThanks are extended to study participants; Cathrine Leonowens, PhD, Nuventra Pharma Sciences, Durham, NC, United States and Cadence Communications and Research, Thousand Oaks, CA, United States. This study is funded by Shattuck Labs, Inc. Austin, TX and Durham, NC, United States.Trial RegistrationNCT04406623Referencesde Silva S, Fromm G, Shuptrine CW, Johannes K, Patel A, Yoo KJ, et al. CD40 enhances type I interferon responses downstream of CD47 blockade, bridging innate and adaptive immunity. Cancer Immunol Res 2020; 8: 230–245.Ethics ApprovalThis study is being conducted in full conformity with the Declaration of Helsinki and was approved by all IRBs/ethics committees from each clinical site participating in the study. Specific approval numbers can be provided upon request.

Approximately 20-40% of cancer patients who initially benefit from PD-1/L1 checkpoint blockade later develop progressive disease, which is associated with genetic and/or phenotypic changes in tumor cells that enable acquired resistance. Tumors from patients who have developed acquired resistance to checkpoint blockade (CPI-AR) typically demonstrate downregulation of specific antigens or proteins involved in antigen presentation on MHC class I, and dysregulation of interferon response pathways. With increasing CPI use across a large number of tumor types, the proportion of cancer patients with CPI-AR is increasing. Pre-clinical tumor models which mimic CPI-AR in humans are needed. We generated in vivo CPI-AR tumor models by serially passaging common CPI responsive murine syngeneic tumor cell lines (i.e. CT26) in vivo, followed by the excision and ex vivo expansion of the tumors that failed to respond to anti-PD1. This was repeated until passaged tumors no longer responded to anti-PD1 therapy. Transcriptomes of CT26 parental, CT26/CPI-AR, and B16.F10 melanoma (considered CPI primary resistant, CPI-PR) tumors were sequenced either under normal culture conditions or following 24 hour exposure to IFNg to assess interferon responsiveness. Here we present the genomic characterization of the CPI -PR and -AR models. Paradoxically, CPI-AR tumors maintain a state of type I/II IFN gene hyperactivation and increased expression of genes involved in MHC class I mediated antigen presentation/processing. Despite this transcriptional hyperactivity, CPI-AR tumor cells have a decreased capacity to translate and traffic these associated proteins to the cell membrane. Interestingly, upon challenge with IFNg, CPI-AR tumors down-regulate gene expression for PD-L1, TAP1, TAP2, β2M and other key pathways typically up-regulated by IFN stimulation. Collectively, the CPI-AR and -PR tumor models reflect many of the genomic and phenotypic changes reported in CPI-AR cancer patients. The CT26/CPI-AR tumors reproduce a state of IFN hypo-responsiveness and genetic/protein dysregulation. These clinically relevant models can be used to screen therapeutics that may translate to meaningful benefit for CPI-AR cancer patients. Citation Format: George J. Fromm, Danish Memon, Suresh de Silva, Kyung Jin Yoo, Kellsey Johannes, Casey Shuptrine, Jaya Miriyala, Arpita Patel, Fatima Rangwala, Zachary Opheim, Thuy-Ai Nguyen, Louis Gonzalez, Fatima Rangwala, Taylor H. Schreiber, Matthew D. Hellmann, Martin L. Miller, Taylor H. Schreiber. The development of an in vivo model of checkpoint acquired resistance, reveals a program of interferon hyperstimulation, resulting in dysregulation of MHC class I, protein translation/trafficking, and other unique pathways, that may be useful for guiding clinical strategy in patients with phenotypic similarities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1697.

BACKGROUND: Current treatment outcomes for patients with recurrent HGG are poor, with median progression-free survival (PFS) and overall survival (OS) of 2.5 and 7.5 months, respectively. Dabrafenib (BRAF inhibitor) + trametinib (MEK inhibitor) resulted in an intracranial overall response rate (ORR) of 58% in BRAF V600–mutated melanoma brain metastases. Dabrafenib + trametinib was evaluated as treatment for patients with BRAF V600E–mutated HGG. METHODS: In this phase 2, open-label trial (NCT02034110), patients with BRAF V600E mutations in 9 rare tumor types, including HGG, received continuous dabrafenib (150 mg BID) + trametinib (2 mg QD) until unacceptable toxicity, disease progression, or death. For the HGG cohort, eligible patients had histologically confirmed recurrent or progressive WHO grade 3 or 4 glioma and had prior treatment with radiotherapy and first-line chemotherapy or concurrent chemoradiation therapy. The primary endpoint was investigator-assessed ORR by RANO criteria. Secondary endpoints included duration of response (DOR), PFS, OS, and safety. RESULTS: Thirty-seven patients with HGG had enrolled at data cutoff (3 January 2018). Median age was 42 years, 31 of 37 patients were evaluable for response. Investigator-assessed confirmed ORR was 26% (8/31; 95% CI, 12%-45%), including 1 complete response (CR). Six of 8 responses were ongoing at data cutoff. Five of 8 responding patients had a DOR of ≥ 12 months. Median PFS was 1.9 months (95% CI, 1.7–18.5). Median OS was 11.7 months (95% CI, 6.4-not reached). Adverse events (AEs) in patients with HGG included fatigue (35%), headache (30%), and rash (24%). Grade 3/4 AEs included neutropenia (8%) and fatigue (5%). Biomarker analyses are ongoing and will be presented. CONCLUSIONS: Dabrafenib + trametinib demonstrated promising efficacy in patients with BRAF V600E-mutated recurrent/refractory HGG, as 1 patient had a CR, and most responders had a prolonged DOR.

Although BRAF inhibitor monotherapy yields response rates >50% in BRAFV600-mutant melanoma, only approximately 5% of patients with BRAFV600E colorectal cancer respond. Preclinical studies suggest that the lack of efficacy in BRAFV600E colorectal cancer is due to adaptive feedback reactivation of MAPK signaling, often mediated by EGFR. This clinical trial evaluated BRAF and EGFR inhibition with dabrafenib (D) + panitumumab (P) ± MEK inhibition with trametinib (T) to achieve greater MAPK suppression and improved efficacy in 142 patients with BRAFV600E colorectal cancer. Confirmed response rates for D+P, D+T+P, and T+P were 10%, 21%, and 0%, respectively. Pharmacodynamic analysis of paired pretreatment and on-treatment biopsies found that efficacy of D+T+P correlated with increased MAPK suppression. Serial cell-free DNA analysis revealed additional correlates of response and emergence of KRAS and NRAS mutations on disease progression. Thus, targeting adaptive feedback pathways in BRAFV600E colorectal cancer can improve efficacy, but MAPK reactivation remains an important primary and acquired resistance mechanism. Significance: This trial demonstrates that combined BRAF + EGFR + MEK inhibition is tolerable, with promising activity in patients with BRAFV600E colorectal cancer. Our findings highlight the MAPK pathway as a critical target in BRAFV600E colorectal cancer and the need to optimize strategies inhibiting this pathway to overcome both primary and acquired resistance. Cancer Discov; 8(4); 428–43. ©2018 AACR. See related commentary by Janku, p. 389. See related article by Hazar-Rethinam et al., p. 417. This article is highlighted in the In This Issue feature, p. 371

BACKGROUND: Approximately 9%-18% of LGGs possess BRAF V600E mutations. Combined BRAF and MEK inhibition is efficacious in BRAF V600–mutated melanoma, lung cancer, and anaplastic thyroid cancer. Dabrafenib (BRAF inhibitor) + trametinib (MEK inhibitor) was evaluated as treatment for patients with recurrent/refractory BRAF V600E–mutated LGG. METHODS: In this phase 2, open-label trial (NCT02034110), patients with BRAF V600E mutations in 9 rare tumor types, including LGG, received continuous dabrafenib (150 mg BID) + trametinib (2 mg QD) until unacceptable toxicity, disease progression, or death. For the LGG cohort, eligible patients had histologically confirmed recurrent or progressive WHO grade 1 or 2 glioma that was refractory to standard-of-care therapies. The primary endpoint was investigator-assessed overall response rate (ORR) by RANO criteria. Secondary endpoints included duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. RESULTS: Nine patients with LGG had enrolled at data cutoff (3 January 2018). Eight of 9 patients were evaluable for response. Median age was 33 years. Eight of 9 patients had received prior surgery. Investigator-assessed confirmed ORR was 50% (4/8; 95% CI, 16%-84%), with 3 of 4 responses ongoing at data cutoff. Two of 4 patients had a DOR of ≥ 18 months. The PFS and OS Kaplan-Meier estimates at 18 months were 50% (95% CI, 15%-78%) and 86% (95% CI, 33%-98%), respectively. Adverse events (AEs) in patients with LGG included fatigue (67%), headache (67%), arthralgia, nausea, and pyrexia (56% each). Grade 3/4 AEs included fatigue (22%), arthralgia, headache, and diarrhea (11% each). Biomarker analyses are ongoing and will be presented. CONCLUSIONS: Dabrafenib + trametinib demonstrated promising efficacy in patients with recurrent/refractory BRAF V600E-mutated LGG, with manageable AEs and no new safety signals

BACKGROUND: Hairy cell leukemia is a rare, indolent, B-cell lymphoproliferative disease characterized by the BRAF V600E mutation in 90% to 100% of patients. Few treatment options are available for patients who progress on first-line therapy with a purine analogue and/or rituximab. The efficacy of combined BRAF and MEK inhibition is well established in BRAF V600-mutated melanoma, non-small cell lung cancer, and anaplastic thyroid cancer. Here we report interim results of treatment with the combination of dabrafenib (BRAF inhibitor) and trametinib (MEK inhibitor) in patients with recurrent/refractory BRAF V600E-mutated HCL. METHODS: In this phase 2, open-label trial (ROAR; NCT02034110), patients with BRAF V600E mutations in 9 rare tumor types, including HCL, received continuous dabrafenib (150 mg twice daily) and trametinib (2 mg once daily) until unacceptable toxicity, disease progression, or death. For the HCL cohort, eligible patients had histologically confirmed HCL (according to WHO classification) that was refractory to first-line treatment with a purine analogue or relapsed after ≥ 2 prior lines of treatment. The presence of a BRAF V600E mutation was assessed locally and confirmed by a central laboratory. The primary endpoint was investigator-assessed overall response rate (ORR) based on criteria adapted from NCCN guidelines. Secondary endpoints were duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Minimal residual disease (MRD) status was assessed by flow cytometry in both peripheral blood and bone marrow aspirates. For complete response (CR) without MRD, both peripheral blood and bone marrow aspirate samples had to be negative. RESULTS: At the data cutoff (January 3, 2018), 43 patients with HCL had enrolled. Median age was 67 years (range, 40-81) and 38 (88%) were male. Twenty-one patients (49%) had received ≥ 4 prior treatments. At the time of data cutoff, 35 patients (81%) remained on study treatment, 5 (12%) in follow-up; 2 (5%) had withdrawn from study (loss to follow-up and consent withdrawal [n = 1 each]), and 1 (2%) had died. Eight patients had discontinued therapy due to adverse events (AEs; 5 [12%]), study withdrawal (2 [5%]), or disease progression (1 [2%]). Median time on study treatment was 17 months (range, 1-39). Among 41 patients evaluable for response, the investigator-assessed confirmed ORR was 78% (32/41; 95% CI, 62%-89%) with 20 (49%) having CR, (6 [15%] CR without MRD and 14 [34%] CR with MRD), and 12 (29%) partial response. All responses were ongoing at the data cutoff; 16 (50%) responses were lasting ≥ 18 months. PFS and OS rates at 12 months were both 97.6% (95% CI, 83.9%-99.7%). The most common AEs in patients with HCL were pyrexia (67%), chills (51%), hyperglycemia (44%), nausea (44%), peripheral edema (42%), cough (40%), and fatigue (40%). Grade 3/4 AEs were reported in 49% of patients, with the most common (> 5%) being hyperglycemia (9%), anemia (7%), and neutropenia (7%). AEs led to dose reduction and treatment interruption in 42% and 56% of patients, respectively. AEs led to permanent discontinuation in 5 patients (12%; headache and malaise [n = 1]; pyrexia, chills and palmar-plantar erythrodysesthesia syndrome [n = 1]; fat necrosis [n = 1]; hyperglycemia and pancreatic adenocarcinoma [n = 1]; Hodgkin lymphoma [n = 1]). CONCLUSIONS: Dabrafenib + trametinib was well tolerated and demonstrated a high rate of durable responses in patients with heavily pretreated recurrent/refractory BRAF V600E-mutated HCL. Disclosures Kreitman: NIH: Patents & Royalties: Co-inventor on the NIH patent for Moxetumomab Pasudotox. Moreau:Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees. Blay:Roche: Honoraria, Other: Non-financial support, Research Funding; Novartis: Honoraria, Other: Non-financial support, Research Funding. Wainberg:Merck: Consultancy; EMD Serono: Consultancy; Lilly: Consultancy; Five Prime: Consultancy; Novartis: Consultancy. Stein:Novartis: Other: Patient documentation fees; GSK: Other: Patient documentation fees. Willenbacher:Merck: Honoraria; Celgene: Honoraria, Research Funding; Roche: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; BMS: Honoraria; Novartis: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; Amgen: Honoraria, Other: Steering board, Research Funding. Ravandi:Macrogenix: Honoraria, Research Funding; Abbvie: Research Funding; Xencor: Research Funding; Astellas Pharmaceuticals: Consultancy, Honoraria; Sunesis: Honoraria; Seattle Genetics: Research Funding; Bristol-Myers Squibb: Research Funding; Xencor: Research Funding; Abbvie: Research Funding; Amgen: Honoraria, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Research Funding; Orsenix: Honoraria; Seattle Genetics: Research Funding; Macrogenix: Honoraria, Research Funding; Orsenix: Honoraria; Jazz: Honoraria; Jazz: Honoraria; Sunesis: Honoraria; Astellas Pharmaceuticals: Consultancy, Honoraria; Amgen: Honoraria, Research Funding, Speakers Bureau. Burgess:Novartis: Employment. Mookerjee:Novartis: Employment. Subbiah:Roche/Genentech: Research Funding; LOXO: Research Funding; Blueprint Medicine: Research Funding; Novartis: Research Funding; Abbvie: Research Funding; Bayer: Research Funding.

741 Background: Adjuvant chemotherapy (AC) following chemoradiation (CRT) and total mesorectal excision (TME) for locoregionally advanced rectal cancer (LARC) is a standard of care in the United States despite limited data. The purpose of this study was to examine the role, optimal regimen, and duration of AC in the mandatory, prospectively collected cancer registry of the largest integrated health system in the US. Methods: Using the VA Central Cancer Registry, stage II-III rectal cancer patients diagnosed between 1/2001-4/2011 were included if they received neoadjuvant CRT followed by TME with or without AC. Adequate chemotherapy was defined as at least 4 months of therapy. Kaplan-Meier and Log-Rank tests were used to assess survival. Propensity score (PS) adjustment was performed to compare survival outcomes while adjusting for baseline characteristics, including AJCC stage, age, gender, race, smoking status, and comorbidity. Results: 649 patients were identified; 323 received AC while 326 did not (OBS). Median follow-up was 66 months. Mean age was 63 years. 85.1% were white; 98.8% were male. 49.2% had stage II disease. Median overall survival (OS) for all patients was 92 months; 6-year OS was 56.8%. Median OS was 72 months for the OBS group and not reached (NR) for the AC group (p < 0.001). OS at 6 years was 49.5% for OBS and 64.1% for AC (p < 0.0001). On PS matched analysis, OS was improved favoring AC (p < 0.0001). Median disease-specific survival (DSS) was NR for the whole group and NR for the OBS and AC groups. 6-year DSS was 73.6% for the whole group and 67.9% for OBS vs. 79.2% for AC (p < 0.001). PS matched analysis for DSS favored AC (p = 0.0004). There was no significant difference in OS (p = 0.554) or DSS (p = 0.680) when comparing single versus multi-agent chemotherapy and no significant difference in OS (p = 0.766) or DSS (p = 0.271) when comparing adequate ( > / = 4 months) versus inadequate chemotherapy ( < 4 months). Conclusions: In this VA population of LARC patients treated with neoadjuvant CRT followed by TME, the addition of AC was found to improve both OS and DSS compared to OBS. There was no improvement in OS or DSS with the addition of a multi-agent over single-agent chemotherapy.

Malignant peripheral nerve sheath tumors (MPNST) are highly invasive soft tissue sarcomas that arise within the peripheral nerve and frequently metastasize. To identify molecular events contributing to malignant transformation in peripheral nerve, we compared eight cell lines derived from MPNSTs and seven normal human Schwann cell samples. We found that MPNST lines are heterogeneous in their in vitro growth rates and exhibit diverse alterations in expression of pRb, p53, p14Arf, and p16INK4a proteins. All MPNST cell lines express the epidermal growth factor receptor and lack S100β protein. Global gene expression profiling using Affymetrix oligonucleotide microarrays identified a 159-gene molecular signature distinguishing MPNST cell lines from normal Schwann cells, which was validated in Affymetrix microarray data generated from 45 primary MPNSTs. Expression of Schwann cell differentiation markers (SOX10, CNP, PMP22, and NGFR) was down-regulated in MPNSTs whereas neural crest stem cell markers, SOX9 and TWIST1, were overexpressed in MPNSTs. Previous studies have implicated TWIST1 in apoptosis inhibition, resistance to chemotherapy, and metastasis. Reducing TWIST1 expression in MPNST cells using small interfering RNA did not affect apoptosis or chemoresistance but inhibited cell chemotaxis. Our results highlight the use of gene expression profiling in identifying genes and molecular pathways that are potential biomarkers and/or therapeutic targets for treatment of MPNST and support the use of the MPNST cell lines as a primary analytic tool. (Cancer Res 2006; 66(5): 2584-91)

Background Malignant peripheral nerve sheath tumors (MPNSTs) occur most frequently in patients with neurofibromatosis type 1 and are often fatal. Current therapy relies upon radical surgical resection, which often fails to completely remove the tumor. To address the need for novel treatment approaches for this disease, we sought to determine if human MPNST-derived cell lines are sensitive to oncolytic Herpes simplex virus (oHSV) infection. Activation of the Ras pathway and its inhibitory effects on protein kinase R (PKR) activation have been shown to dictate cellular permissivity to oHSV mutants. Because NF-1-associated MPNSTs possess inherent hyperactive Ras, we hypothesized these tumors would be ideal therapeutic targets for oHSVs. Procedure Human MPNST-derived cell lines were examined for sensitivity to oHSV-mediated gene transduction, virus replication, cytotoxicity, and apoptosis. These parameters were correlated with PKR activation following oHSV infection and compared with normal human Schwann cells (NHSCs) without hyperactive Ras. Results MPNST-derived cell lines were efficiently transduced, supported virus replication and were killed by the oncolytic HSV mutants, including sporadic MPNSTs without hyperactive Ras. In contrast to the highly sensitive MPNST cell lines, NHSCs did not support mutant virus replication. Conclusions MPNSTs are susceptible to lysis by oncolytic HSV mutants, regardless of Ras status. Tumor-selective virus replication in MPNST cells appears to be mediated by both cellular expression of ribonucleotide reductase and prevention of eIF2α phosphorylation. Virus-induced cytotoxicity of MPNST cell lines was caused by both direct lysis and apoptosis. Our data suggest the use of oncolytic HSV mutants may represent a novel treatment approach for patients with MPNSTs. © 2005 Wiley-Liss, Inc.

The neurofibromatosis type 1 tumor suppressor protein neurofibromin, is a GTPase activating protein for H-, N-, K-, R-Ras and TC21/R-Ras2 proteins. We demonstrate that Schwann cells derived from Nf1-null mice have enhanced chemokinetic and chemotactic migration in comparison to wild-type controls. Surprisingly, this migratory phenotype is not inhibited by a farnesyltransferase inhibitor or dominant-negative (dn) (N17)H-Ras (which inhibits H-, N-, and K-Ras activation). We postulated that increased activity of R-Ras and/or TC21/R-Ras2, due to loss of Nf1, contributes to increased migration. Mouse Schwann cells (MSCs) express R-Ras and TC21/R-Ras2 and their specific guanine exchange factors, C3G and AND-34. Infection of Nf1-null MSCs with a dn(43N)R-Ras adenovirus (to inhibit both R-Ras and TC21/R-Ras2 activation) decreases migration by approximately 50%. Conversely, expression of activated (72L)TC21/R-Ras2, but not activated (38V)R-Ras, increases migration, suggesting a role of TC21/R-Ras2 activation in the migration of neurofibromin-deficient Schwann cells. TC21/R-Ras2 preferentially couples to the phosphatidylinositol 3-kinase (PI3-kinase) and MAP kinase pathways. Treatment with a PI3-kinase or MAP kinase inhibitor reduces Nf1-null Schwann cell migration, implicating these TC21 effectors in Schwann cell migration. These data reveal a key role for neurofibromin regulation of TC21/R-Ras2 in Schwann cells, a cell type critical to NF1 tumor pathogenesis.

6023 Background: ATC is a rare, aggressive malignancy with a dismal prognosis. Median overall survival (OS) is < 6 mo. Combined BRAF and MEK inhibition is efficacious in BRAF V600–mutated melanoma and lung cancer. One-fourth of ATCs harbor activating BRAF V600E mutations; thus, D (BRAF inhibitor) + T (MEK inhibitor) was evaluated as a treatment for pts with BRAF V600E–mutated ATC. Methods: In this phase 2, open-label trial (NCT02034110), pts with BRAF V600E mutations in 9 rare tumor types, including ATC, received continuous D (150 mg BID) + T (2 mg QD) until unacceptable toxicity, disease progression, or death. Eligible pts had advanced or metastatic cancer with no standard-of-care treatment options. The primary endpoint was investigator-assessed overall response rate (ORR). Secondary endpoints included duration of response (DOR), progression-free survival (PFS), OS, and safety. We report data from the ATC cohort. Results: 16 pts with BRAF V600E–mutated ATC had evaluable data with a median follow-up time of 47 wk (range 4-120 wk). BRAF V600E mutations were centrally confirmed in 15/16 pts. Median age was 72 y; all 16 pts had undergone prior tumor radiation and/or surgery and 6/16 pts (38%) had received ≥1 prior line of systemic therapy. Investigator-assessed confirmed ORR was 69% (11/16; 95% CI, 41%-89%), with 7/11 responses ongoing at the time of data cut. The Bayesian estimate of ORR was 69% (95% credible interval, 47%-87%) with a 100% probability that this ORR exceeded the 15% historical RR. Median DOR, PFS, and OS were not estimable due to insufficient progression and death events. Kaplan-Meier estimates of DOR, PFS, and OS at 12 mo were 90%, 79%, and 80%, respectively. The safety population comprised 100 pts enrolled in 7/9 histologies. Among all pts, 92% had an AE. Common AEs of any grade for all histologies were fatigue (38%), pyrexia (37%), and nausea (35%). In the ATC cohort, the most common grade 3/4 events were hyponatremia (19%), pneumonia (13%), and anemia (13%). Conclusions: D+T combination therapy significantly improved outcomes in ATC with a favorable safety profile. This regimen represents a clinically meaningful therapeutic advance for pts with advanced/metastatic BRAF V600–mutated ATC. Clinical trial information: NCT02034110.

We have characterized the α-bungarotoxin receptors (BgtRs) found on the cell surface of undifferentiated pheochromocytoma (PC12) cells. The PC12 cells express a homogeneous population of α7-containing receptors that bind α-Bgt with high affinity (Kd= 94 pm). The BgtRs mediate most of the response elicited by nicotine, because the BgtR-specific antagonists methyllycaconitine and α-Bgt block ∼90% of the whole-cell current. The binding of nicotinic agonists to cell-surface BgtRs was highly cooperative with four different agonists showing Hill coefficients in the range of 2.3–2.4. A similar agonist binding cooperativity was observed for BgtR homomers formed from chimeric α7/5HT3 subunits expressed in tsA 201 cells. Two classes of agonist binding sites, in the ratio of 4:1 for PC12 cell BgtRs and 3:1 for α7/5HT3 BgtRs, were revealed by bromoacetylcholine alkylation of the reduced sites on both PC12 BgtRs and α7/5HT3 BgtRs. We conclude from this data that PC12 BgtRs and α7/5HT3 homomers contain at least three distinguishable agonist binding sites and thus are different from other nicotinic receptors.

TPS2604Background: Combination D + T is approved for the treatment of BRAF V600E/K–mutant unresectable or metastatic melanoma. BRAF V600E mutations have also been identified in some rare cancers, including anaplastic thyroid cancer, biliary tract cancer, gastrointestinal stromal tumor, nonseminomatous germ cell tumor, hairy cell leukemia (HCL), World Health Organization (WHO) grade I/II glioma, WHO grade III/IV glioma, multiple myeloma, and adenocarcinoma of the small intestine. US incidence rates of these rare tumors range from 0.07 to 6.3 per 100,000, with BRAF V600E mutation frequency ranging from 3% in high-grade glioma to 90% in HCL. Therefore, the ROAR study is underway in pts with these 9 rare BRAF-mutant cancers to assess the safety and efficacy of D + T combination therapy. Methods: This international, multicenter, open-label phase 2 study (NCT02034110) uses a Bayesian hierarchical statistical design that increases study power by borrowing information across histology cohorts based on the emergin...

Histoplasmosis and penicilliosis are fungal infections with similar clinical presentation and laboratory findings that were reported mainly in the era prior to highly active antiretroviral therapy. We conducted a retrospective review at two hospitals in Central Thailand of the medical records of HIV-positive patients with microbiologic evidence of histoplasmosis or penicilliosis between January 2003 to September 2007 when antiretrovirals became widely available in Thailand. Fifty patients met inclusion criteria; 36 had histoplasmosis, and 14 had penicilliosis. Symptoms and laboratory findings on presentation were similar between the two infections except for a greater incidence of tachypnea and neutropenia among patients with histoplasmosis (both p0.05). For histoplasmosis, blood culture had a significantly lower yield for detecting infection compared to tissue microscopic examination highlighting the importance of obtaining tissue for diagnosis (p0.05).