Contemporary cancer treatment strategies are shifting toward targeted therapies to improve efficacy and minimize toxicity. Here, we report the design and preclinical evaluation of MBRC-101, a first-in-class antibody-drug conjugate (ADC) targeting EphA5, a receptor tyrosine kinase with an established role in embryonic development but not extensively studied in cancer. We show that EphA5 is expressed in multiple solid tumors, including cancers of the aerodigestive (non-small cell lung, head and neck, gastric, colon, and pancreatic) and genitourinary (bladder and ovary) tracts, as well as most breast cancer subsets (including triple-negative tumors), with limited expression in normal tissues. MBRC-101 is a humanized anti-EphA5 antibody conjugated to monomethyl auristatin E (MMAE) through a ThioBridge, thereby ensuring stable drug-to-antibody ratio and reducing off-target effects. MBRC-101 showed potent antitumor activity, achieving complete tumor regression in several patient-derived xenograft models. Preclinical Good Laboratory Practice-compliant toxicology studies in rats and nonhuman primates demonstrated that MBRC-101 is well tolerated, with observed toxicities limited to known MMAE off-target effects. These findings establish EphA5 as a therapeutic target in cancer and support the translational development of MBRC-101 as a promising ADC candidate for clinical evaluation, currently in a first-in-human multicenter investigational trial for patients with advanced solid tumors (ClinicalTrials.gov, NCT06014658).

TPS3161 Background: EphA5 receptor is a member of the Ephrin receptor tyrosine kinase family. Several lines of compelling nonclinical evidence indicate EphA5 is a novel and selective target for solid tumor-directed therapy. Expressed only minimally in normal tissues, it is highly expressed in non-small cell lung carcinoma (NSCLC), head and neck squamous cell carcinoma (HNSCC), and breast, colorectal, pancreatic, gastric, and hepatic malignancies. MBRC-101 is a novel antibody drug conjugate (ADC) composed of an anti-EphA5 antibody conjugated to an MMAE payload (drug-to-antibody ratio of 4) through a valine citrulline cleavable linker. In pre-clinical toxicology studies and testing against a variety of cell-derived (CDX) and patient-derived (PDX) xenograft solid tumor models expressing EphA5--including NSCLC, triple negative breast cancer (TNBC), and HNSCC--MBRC-101 demonstrated favorable safety profiles and robust anti-tumor activity. Methods: This first-in-human, Phase 1/1b, multicenter, open-label study is examining the safety and efficacy of MBRC-101 in patients with advanced metastatic solid tumors refractory to standard treatment. Phase 1 will identify potential optimal biologically relevant doses (OBRD) and the maximum tolerated dose (MTD) of MBRC-101 at one or more dosing regimens. Phase 1b will evaluate the safety and preliminary clinical activity of MBRC-101 at potential OBRDs. Phase 1 will enroll patients (n ≈ 30) with advanced or metastatic solid tumors. EphA5 expression will not be required for enrollment into Phase 1 but will be assessed retrospectively. A modified toxicity probability interval (mTPI-2) method will guide dose escalation using a pre-specified decision matrix. The primary endpoints are MTD, dose limiting toxicities (DLTs), treatment emergent adverse events (TEAEs), and clinical laboratory tests. Phase 1b (n ≈ 60 patients) will include 3 expansion cohorts (n ≈ 20 patients per cohort): Cohort A, NSCLC; Cohort B, triple negative or HR+/HER2- breast cancer; and Cohort C, solid tumors irrespective of histologic tissue type (i.e., tumor agnostic) excluding NSCLC and breast cancer. Expression of EphA5 in primary or metastatic tumor tissue will not be required for enrollment into cohorts A and B but will be required for Cohort C. The primary endpoints are TEAEs, clinical laboratory tests, and investigator-assessed objective response rate (ORR) by RECIST v1.1 and clinical evaluation. Secondary endpoints for Ph1 and 1b include PK analytes and EphA5 expression as determined by immunohistochemistry (IHC). A Safety Review Committee will monitor safety at each dose escalation in Phase 1 and at regular intervals throughout Phase 1b. Clinical trial information: NCT06014658 .

Abstract Introduction: The receptor tyrosine kinase EphA5 has the classical receptor kinase topology with an extracellular-binding domain, a single-pass transmembrane domain, and a cytoplasmic kinase domain. Previously, EphA5 has been shown to contribute to DNA-damage repair and radiation therapy resistance in lung cancer. We investigated EphA5 expression in lung cancer as well as breast, pancreatic, gastric, and colorectal cancer and assessed its potential as a therapeutic target using a novel ADC, MBRC-101. Methods: MBRC-101 is composed of a humanized anti-EphA5 IgG1 monoclonal antibody conjugated to monomethyl auristatin E (MMAE) via a cleavable valine-citrulline linker using site-specific ThioBridge™ technology. The specificity profile of the anti-EphA5 antibody was characterized using a membrane proteome array. Receptor-mediated antibody internalization was determined by real-time live-cell analysis, and cell killing assays were performed using analysis of cell confluence and luminescent-based viability. Expression of EphA5 in archival human tissue sections was evaluated by immunohistochemistry (IHC) using a commercial antibody. Efficacy studies used patient-derived xenograft (PDX) models of lung adenocarcinoma, squamous cell carcinoma of both lung and head and neck, and breast cancer. Results: IHC demonstrated selective EphA5 membrane expression in 78% (18/23) of triple negative and 88% (23/26) of hormone receptor-positive breast cancer tumors tested. EphA5 membrane expression was also detected in 85% (29/34), 73% (16/22), 70% (7/10), 70% (15/22), and 50% (6/12) of lung squamous cell carcinoma, lung adenocarcinoma, gastric, colorectal, and pancreatic patient tumors tested, respectively. EphA5 expression was not detected in adjacent, non-malignant tissue in any of the tumors examined. The anti-EphA5 antibody bound exclusively to EphA5 and did not cross-react with other members of the Eph receptor/ephrin ligand family. Binding of the anti-EphA5 antibody on the cell surface triggered rapid internalization and processing through the endosomal-lysosomal system. MBRC-101 was cytotoxic to EphA5-expressing cells and its activity was concentration-dependent and commensurate to levels of EphA5 on the cell surface. In PDX models, once weekly administrations of intravenous MBRC-101 showed dose-dependent, robust, and reproducible anti-tumor activity. Partial tumor responses were observed at doses of 2.5 mg/Kg and complete tumor responses starting at 5 mg/Kg. Toxicologic findings in Sprague-Dawley rats and cynomolgus monkeys were attributed to the MMAE payload and not target-related. Based on an HNSTD of 10 mg/kg in monkeys, the starting human dose was 0.5 mg/kg with ~15-fold safety margin. Conclusions: EphA5 is a new and promising molecular target for the development of ADC-based therapies against many human cancers. A Phase 1/1b study of MBRC-101 is currently recruiting (NCT06014658). Citation Format: Fernanda I. Staquicini, Fenny H. Tang, Vanessa de Oliveira, Daniela I. Staquicini, Yongjian Wu, Kirstin F. Barnhart, J Kellogg Parsons, Wadih Arap, Isan Chen, Renata Pasqualini. MBRC-101: a novel antibody-drug conjugate (ADC) targeting the tyrosine kinase receptor EphA5 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 738.

Objectives: ADCs have emerged as a major advance in contemporary medical oncology. The receptor tyrosine kinase (RTK) EphA5 possesses the classical receptor kinase topology with an extracellular-binding domain, a single-pass transmembrane domain, and a cytoplasmic kinase domain. We have previously shown that EphA5 is highly expressed in non-small cell lung cancer and contributes to DNA-damage repair and radiation therapy resistance. Others have reported EphA5 expression in gastric, ovarian, and pancreatic cancers. Here, we investigated the expression of EphA5 in breast cancer (BC) and assessed EphA5 as a potential cancer-specific target using a novel ADC designated MBRC-101. Methods: MBRC-101 is composed of a humanized anti-EphA5 IgG1 kappa monoclonal antibody conjugated to the small molecule microtubule-disrupting agent monomethyl auristatin E (MMAE) via a protease cleavable valine-citrulline (vc) ThioBridge linker (ThioBridge™-Glu-[Val-Cit-PAB-MMAE] PEG [24u]). MBRC-101 averages a drug-to-antibody ratio (DAR)=4. The specificity profile of the anti-EphA5 monoclonal antibody was characterized using a Membrane Proteome Array (MPA). Receptor-mediated antibody internalization was determined by real-time live-cell analysis; cell killing assays used both live-cell analysis of cell confluence and the CellTiter-Glo® luminescent cell viability assay. Expression of EphA5 in archival human breast tumor tissue sections was evaluated by immunohistochemistry (IHC) using a commercial polyclonal antibody against human EphA5. In vivo efficacy studies used patient-derived xenograft (PDX) models of BC. Results: IHC demonstrated robust and selective EphA5 expression in 87% (20 of 23) of triple negative breast cancer (TNBC) and 88% (23 of 26) of hormone receptor-positive (HR+) patient tumors tested. EphA5 expression was not detected in adjacent, non-malignant breast tissue. Antibody-specificity profile testing showed that the anti-EphA5 antibody bound exclusively to EphA5 and did not cross-react with other members of the Eph receptor/ephrin ligand family. Binding of the anti-EphA5 antibody to EphA5 on the cell surface triggered rapid internalization and processing of the EphA5/antibody complex through the endosomal-lysosomal system. Consistently, MBRC-101 was cytotoxic to EphA5-expressing cells and its activity was concentration-dependent and commensurate to the levels of EphA5 on the cell surface. In PDX murine models of TNBC, once weekly administrations of intravenous (IV) MBRC-101 showed dose-dependent, robust, and reproducible anti-tumor activity in vivo. Partial tumor responses were observed at doses of 2.5 mg/Kg IV and complete and nearly complete tumor responses starting at 5 mg/Kg IV. Doses up to 10 mg/Kg IV were well-tolerated in tumor-bearing mice with no observable weight loss. Pre-clinical safety confirmed MBRC-101 is also well tolerated in rats and in cynomolgus monkeys. Conclusions: These results support EphA5 as a new and promising membrane-associated molecular target for the design and development of ADC-based therapies against hormone-positive breast cancer and TNBC and support the conduct of a Phase 1/1b study of MBRC-101 in patients with breast cancer. Citation Format: Fernanda Staquicini, Fenny Tang, Vanessa de Oliveira, Daniela Staquicini, Yongjian Wu, Kirstin Barnhart, J Kellogg Parsons, Wadih Arap, Isan Chen, Renata Pasqualini. MBRC-101: a novel antibody-drug conjugate (ADC) targeting the membrane-associated tyrosine kinase receptor EphA5 in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-18-04.

Abstract Objectives: ADCs have emerged as a major advance in contemporary medical oncology. The receptor tyrosine kinase (RTK) EphA5 possesses the classical receptor kinase topology with an extracellular-binding domain, a single-pass transmembrane domain, and a cytoplasmic kinase domain. We have previously shown that EphA5 is highly expressed in non-small cell lung cancer and contributes to DNA-damage repair and radiation therapy resistance. Others have reported EphA5 expression in gastric, ovarian, and pancreatic cancers. Here, we investigated the expression of EphA5 in breast cancer (BC) and assessed EphA5 as a potential cancer-specific target using a novel ADC designated MBRC-101. Methods: MBRC-101 is composed of a humanized anti-EphA5 IgG1 kappa monoclonal antibody conjugated to the small molecule microtubule-disrupting agent monomethyl auristatin E (MMAE) via a protease cleavable valine-citrulline (vc) ThioBridge linker (ThioBridge™-Glu-[Val-Cit-PAB-MMAE] PEG [24u]). MBRC-101 averages a drug-to-antibody ratio (DAR)=4. The specificity profile of the anti-EphA5 monoclonal antibody was characterized using a Membrane Proteome Array (MPA). Receptor-mediated antibody internalization was determined by real-time live-cell analysis; cell killing assays used both live-cell analysis of cell confluence and the CellTiter-Glo® luminescent cell viability assay. Expression of EphA5 in archival human breast tumor tissue sections was evaluated by immunohistochemistry (IHC) using a commercial polyclonal antibody against human EphA5. In vivo efficacy studies used patient-derived xenograft (PDX) models of BC. Results: IHC demonstrated robust and selective EphA5 expression in 87% (20 of 23) of triple negative breast cancer (TNBC) and 88% (23 of 26) of hormone receptor-positive (HR+) patient tumors tested. EphA5 expression was not detected in adjacent, non-malignant breast tissue. Antibody-specificity profile testing showed that the anti-EphA5 antibody bound exclusively to EphA5 and did not cross-react with other members of the Eph receptor/ephrin ligand family. Binding of the anti-EphA5 antibody to EphA5 on the cell surface triggered rapid internalization and processing of the EphA5/antibody complex through the endosomal-lysosomal system. Consistently, MBRC-101 was cytotoxic to EphA5-expressing cells and its activity was concentration-dependent and commensurate to the levels of EphA5 on the cell surface. In PDX murine models of TNBC, once weekly administrations of intravenous (IV) MBRC-101 showed dose-dependent, robust, and reproducible anti-tumor activity in vivo. Partial tumor responses were observed at doses of 2.5 mg/Kg IV and complete and nearly complete tumor responses starting at 5 mg/Kg IV. Doses up to 10 mg/Kg IV were well-tolerated in tumor-bearing mice with no observable weight loss. Pre-clinical safety confirmed MBRC-101 is also well tolerated in rats and in cynomolgus monkeys. Conclusions: These results support EphA5 as a new and promising membrane-associated molecular target for the design and development of ADC-based therapies against hormone-positive breast cancer and TNBC and support the conduct of a Phase 1/1b study of MBRC-101 in patients with breast cancer. Citation Format: Fernanda Staquicini, Fenny Tang, Vanessa de Oliveira, Daniela Staquicini, Yongjian Wu, Kirstin Barnhart, J Kellogg Parsons, Wadih Arap, Isan Chen, Renata Pasqualini. MBRC-101: a novel antibody-drug conjugate (ADC) targeting the membrane-associated tyrosine kinase receptor EphA5 in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-18-04.

PDF file - 401K, Supplementary Figure S1. Parental and 2nd generation anti-androgen resistant cell line proliferation. Supplementary Figure S2. AR levels in parental and 2nd generation anti-androgen resistant cell lines. Supplementary Figure S3. AR levels in transfection assays. Supplementary Figure S4. Transcriptional reporter assay of AR mutants. Supplementary Figure S5. Ligand binding domain of the AR bound to DHT (1T7T;(1)). Supplementary Figure S6. Competitive binding assay of wild-type AR vs. F876L AR. Supplementary Figure S7. AR levels in AR overexpressing cell lines. Supplementary Figure S8. LNCaP/AR(cs), LNCaP/SRF876L and LNCaP/pCDNAF876L cell proliferation. Supplementary Figure S9. Transcriptional activity of ARN-509 and enzalutamide in LNCaP/pCDNAF876L cells. Supplementary Figure S10. AR ChIP analysis of AR target genes. Supplementary Figure S11. PSA response for 3 patients with detectable AR F876L mutation.

PDF file - 183K, Supplementary Table S1. 1st and 2nd generation AR antagonist activity on F876L-AR. Supplementary Table S2. LNCaP/SRF876L Xenograft Pharmacokinetics Supplementary Table S3. AR nucleotide changes monitored by BEAMing assay Supplementary Table S4. Primary F876L BEAMing of ARN-509-001 Patients Supplementary Table S5. Transcriptional Real-time PCR Oligonucleotide Sequence Supplementary Table S6. ChIP Real-time PCR Oligonucleotide Sequence

Purpose A randomized, phase III trial demonstrated superiority of sunitinib over interferon alfa (IFN-α) in progression-free survival (primary end point) as first-line treatment for metastatic renal cell carcinoma (RCC). Final survival analyses and updated results are reported. Patients and Methods Seven hundred fifty treatment-naïve patients with metastatic clear cell RCC were randomly assigned to sunitinib 50 mg orally once daily on a 4 weeks on, 2 weeks off dosing schedule or to IFN-α 9 MU subcutaneously thrice weekly. Overall survival was compared by two-sided log-rank and Wilcoxon tests. Progression-free survival, response, and safety end points were assessed with updated follow-up. Results Median overall survival was greater in the sunitinib group than in the IFN-α group (26.4 v 21.8 months, respectively; hazard ratio [HR] = 0.821; 95% CI, 0.673 to 1.001; P = .051) per the primary analysis of unstratified log-rank test (P = .013 per unstratified Wilcoxon test). By stratified log-rank test, the HR was 0.818 (95% CI, 0.669 to 0.999; P = .049). Within the IFN-α group, 33% of patients received sunitinib, and 32% received other vascular endothelial growth factor–signaling inhibitors after discontinuation from the trial. Median progression-free survival was 11 months for sunitinib compared with 5 months for IFN-α (P < .001). Objective response rate was 47% for sunitinib compared with 12% for IFN-α (P < .001). The most commonly reported sunitinib-related grade 3 adverse events included hypertension (12%), fatigue (11%), diarrhea (9%), and hand-foot syndrome (9%). Conclusion Sunitinib demonstrates longer overall survival compared with IFN-α plus improvement in response and progression-free survival in the first-line treatment of patients with metastatic RCC. The overall survival highlights an improved prognosis in patients with RCC in the era of targeted therapy.

Background:We have previously shown that the long non-coding (lnc)RNA prostate cancer associated 3 (PCA3; formerly prostate cancer antigen 3) functions as a trans-dominant negative oncogene by targeting the previously unrecognized prostate cancer suppressor gene PRUNE2 (a homolog of the Drosophila prune gene), thereby forming a functional unit within a unique allelic locus in human cells. Here, we investigated the PCA3/PRUNE2 regulatory axis from early (tumorigenic) to late (biochemical recurrence) genetic events during human prostate cancer progression. Methods:The reciprocal PCA3 and PRUNE2 gene expression relationship in paired prostate cancer and adjacent normal prostate was analyzed in two independent retrospective cohorts of clinically annotated cases post-radical prostatectomy: a single-institutional discovery cohort (n=107) and a multi-institutional validation cohort (n=497). We compared the tumor gene expression of PCA3 and PRUNE2 to their corresponding expression in the normal prostate. We also serially examined clinical/pathological variables including time to disease recurrence. Results:We consistently observed increased expression of PCA3 and decreased expression of PRUNE2 in prostate cancer compared with the adjacent normal prostate across all tumor grades and stages. However, there was no association between the relative gene expression levels of PCA3 or PRUNE2 and time to disease recurrence, independent of tumor grades and stages. Conclusions:We concluded that upregulation of the lncRNA PCA3 and targeted downregulation of the protein-coding PRUNE2 gene in prostate cancer could be early (rather than late) molecular events in the progression of human prostate tumorigenesis but are not associated with biochemical recurrence. Further studies of PCA3/PRUNE2 dysregulation are warranted. Funding:We received support from the Human Tissue Repository and Tissue Analysis Shared Resource from the Department of Pathology of the University of New Mexico School of Medicine and a pilot award from the University of New Mexico Comprehensive Cancer Center. RP and WA were supported by awards from the Levy-Longenbaugh Donor-Advised Fund and the Prostate Cancer Foundation. EDN reports research fellowship support from the Brazilian National Council for Scientific and Technological Development (CNPq), Brazil, and the Associação Beneficente Alzira Denise Hertzog Silva (ABADHS), Brazil. This work has been funded in part by the NCI Cancer Center Support Grants (CCSG; P30) to the University of New Mexico Comprehensive Cancer Center (CA118100) and the Rutgers Cancer Institute of New Jersey (CA072720).

BackgroundSitravatinib, a tyrosine kinase inhibitor that targets TYRO3, AXL, MERTK and the VEGF receptor family, is predicted to increase the M1 to M2-polarized tumor-associated macrophages ratio in the tumor microenvironment and have synergistic antitumor activity in combination with anti-programmed death-1/ligand-1 agents. SNOW is a window-of-opportunity study designed to evaluate the immune and molecular effects of preoperative sitravatinib and nivolumab in patients with oral cavity squamous cell carcinoma.MethodsPatients with newly-diagnosed untreated T2-4a, N0-2 or T1 >1 cm-N2 oral cavity carcinomas were eligible. All patients received sitravatinib 120 mg daily from day 1 up to 48 hours pre-surgery and one dose of nivolumab 240 mg on day 15. Surgery was planned between day 23 and 30. Standard of care adjuvant radiotherapy was given based on clinical stage. Tumor photographs, fresh tumor biopsies and blood samples were collected at baseline, at day 15 after sitravatinib alone, and at surgery after sitravatinib–nivolumab combination. Tumor flow cytometry, multiplex immunofluorescence staining and single-cell RNA sequencing (scRNAseq) were performed on tumor biopsies to study changes in immune-cell populations. Tumor whole-exome sequencing and circulating tumor DNA and cell-free DNA were evaluated at each time point.ResultsTen patients were included. Grade 3 toxicity occurred in one patient (hypertension); one patient required sitravatinib dose reduction, and one patient required discontinuation and surgery delay due to G2 thrombocytopenia. Nine patients had clinical-to-pathological downstaging, with one complete response. Independent pathological treatment response (PTR) assessment confirmed a complete PTR and two major PTRs. With a median follow-up of 21 months, all patients are alive with no recurrence. Circulating tumor DNA and cell-free DNA dynamics correlated with clinical and pathological response and distinguished two patient groups with different tumor biological behavior after sitravatinib alone (1A) versus sitravatinib–nivolumab (1B). Tumor immunophenotyping and scRNAseq analyses revealed differential changes in the expression of immune cell populations and sitravatinib-targeted and hypoxia-related genes in group 1A vs 1B patients.ConclusionsThe SNOW study shows sitravatinib plus nivolumab is safe and leads to deep clinical and pathological responses in oral cavity carcinomas. Multi-omic biomarker analyses dissect the differential molecular effects of sitravatinib versus the sitravatinib–nivolumab and revealed patients with distinct tumor biology behavior.Trial registration numberNCT03575598.

Aim: This first-in-human, dose-finding study evaluated safety, pharmacokinetics and pharmacodynamics of crizotinib and established a recommended Phase II dose (RP2D) among patients with advanced solid malignancies. Patients & methods: Patients received oral crizotinib in a 3 + 3 dose escalation design. Results: Thirty-six patients received crizotinib (50 mg once daily-300 mg twice daily); maximum tolerated dose (and RP2D) was 250 mg twice daily. Most patients (89%) experienced ≥1 treatment-related adverse event. Three patients had grade 3 dose-limiting toxicities: alanine aminotransferase increased (n = 1) and fatigue (n = 2). Generally, an increase in soluble MET was found with increasing crizotinib concentrations. Conclusion: Crizotinib demonstrated a favorable safety profile. The observed pharmacodynamic effect on soluble MET provide evidence for targeted MET inhibition by crizotinib. Clinicaltrials. gov identifier: NCT00585195.

10052 Background: Mocetinostat is a class I/IV HDAC inhibitor with HDAC1/2/3/11 activity. Preclinical murine data suggest that HDAC inhibition has immune activity and may augment the clinical benefit of checkpoint inhibition. Several trials are assessing the effects of adding HDAC inhibition to PD-1 blockade. Methods: Patients with therapy-naive metastatic melanoma were treated in a pilot phase Ib trial with nivolumab at 3 mg/kg/ipilimumab at 1 mg/kg every three weeks four times and a starting dose of mocetinostat at 70 mg orally three times a week in a 12-week induction cycle followed by 12-week maintenance cycles of nivolumab 240 mg every 2 weeks and mocetinostat at the same dose and schedule as induction. Endpoints were toxicity, definition of a recommended phase 2 dose and preliminary assessment of response as well as correlative marker determination. Peripheral blood mononuclear blood cells from patients were tested in vitro at varying concentrations of mocetinostat, and its impact on T, regulatory T and myeloid-derived suppressor cell phenotypes were assessed by flow cytometry, as well as cytokine production by Luminex. Results: In the mocetinostat, nivolumab and ipilimumab phase I trial, 10 patients were treated, including 5 males and 5 females with a median age of 59. There were 2 complete and 5 partial responses confirmed; 6 of 7 are maintained at a median of 16 months of follow up. Three patients had progressive disease. Seven patients had grade 3-4 immune related adverse events; in 3 they were multiple. No patients died. In vitro, mocetinostat at doses from 125 to 500 nM increased relative percentage of CD4/CD8 central memory T cells, and decreased IL-6 levels while increasing interferon-gamma production (p = 0.005). Percentages of regulatory T and monocytic myeloid-derived suppressor cells were decreased by mocetinostat (p = 0.005), which also down-modulated regulatory T cell function by reducing FOXP3, HELIOS and GARP (p = 0.001). Conclusions: In vitro, mocetinostat promoted accumulation of central memory CD8 and CD4 T cells from melanoma patients, and decreased percentages and suppressive activity of T regulatory cells and myeloid-derived suppressor cells. In a pilot clinical trial, mocetinostat combined with nivolumab and ipilimumab in treatment-naïve metastatic melanoma patients exhibited a response rate of 70% with long duration of response but all ten patients treated had at least one grade 3 or 4 immune-related toxicity. De-escalation of the mocetinostat dose to 50 mg three times a week was felt to be indicated due to the toxicity of the triple regimen. Clinical trial information: NCT03565406.

Background: Squamous cell carcinoma of the oral cavity (SCCOC) often presents at early stages but its prognosis remains guarded, with a 5-year survival rate of 60% despite curative-intent therapies. Preoperative window-of-opportunity (WOO) studies in resectable SCCOC enable pharmacodynamic evaluation of molecular endpoints without compromising curative-intent treatment. Preoperative nivolumab in SCCOC was safe and showed promising tumor responses in CheckMate-358 WOO study (Ferris et al. ESMO 2017, LBA46). Sitravatinib, a receptor tyrosine kinase inhibitor which potently inhibits Tyro, AXL, Mer, and VEGF family of receptors, has shown encouraging results when combined with nivolumab in non-small cell lung cancer patients who have progressed on anti-PD-1 agents (Leal et al. ESMO 2018, 1129O). We hypothesize that sitravatinib and nivolumab have synergistic antitumor and immunogenic effects by increasing tumor immune infiltration and by blocking oncogenic pathways implicated in disease progression and immune-checkpoint resistance. Methods: Trial design: SNOW is a single-center, non-randomized WOO study of preoperative sitravatinib and nivolumab in patients with resectable SCCOC. Sitravatinib 120 mg is given orally once daily from day 1 until 48h before surgery or for a maximum period of 28 days. Nivolumab 240mg is given intravenously on day 15 for one dose only. Surgery is planned between days 23-30 following study treatment initiation. Fresh tumor biopsies and serial blood samples for extensive immunophenotyping and evaluation of other pharmacodynamic biomarkers, as well as clinical photographs of the tumor, are collected at baseline, on day 15 prior to nivolumab and at the time of surgery. 18FAZA-PET scans are performed at baseline and before surgery. Key eligibility criteria: previously untreated and resectable SCCOC; T2-4a, N0-2 or T1 (greater than 1 cm)-N2; no history of tumor bleeding or invasion of major vessels; adequate organ function; no autoimmune disorders; no immunosuppressive therapy. Study objectives: primary objective is to evaluate the immune and pharmacodynamic effects of sitravatinib plus nivolumab. Secondary objectives are: safety and tolerability including toxicity, rate of surgery completion within the planned window and rate of postoperative complications; antitumor activity including rate of complete pathological response; pharmacokinetics of sitravatinib alone and in combination with nivolumab. Correlative studies: tumor and blood immunophenotyping, tumor genome and transcriptome analysis, changes in intratumoral hypoxia based on 18FAZA-PET testing. Sample size: SNOW is a proof-of-concept study with no specific statistical assumptions at trial onset. We plan to enroll 12-15 patients evaluable for correlative studies. Study activation: Aug 30th, 2018. Two patients enrolled as of Jan 10th2019. Clinical trial identification: NCT03575598. Citation Format: Marc Oliva Bernal, Douglas Chepeha, Amy Prawira, Douglass Vines, Anna Spreafico, Scott Bratman, John De Almeida, Aaron Hansen, David Goldstein, Ralph Gilbert, Patrick Gullane, Dale H. Brown, Ilan Weinreb, Bayardo Perez-Ordoñez, Pamela S. Ohashi, Tracy McGaha, Ben X. Wang, Jonathan Irish, Isan Chen, Lillian L. Siu. Sitravatinib and nivolumab in oral cavity cancer window of opportunity study (SNOW) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT124.

Background: Sitravatinib is a spectrum-selective TKI which targets TAM receptors (Axl, MER), split family receptors (VEGFR2 and KIT), and MET. Inhibition of these receptor tyrosine kinases may enhance antitumor activity by reducing Type 2 tumor-associated macrophages, regulatory T cells and myeloid-derived suppressor cells and enhancing a T cell-mediated anti-tumor immune response. Thus, this combination is a rational approach to enhancing or restoring the clinical activity of checkpoint inhibitor therapy (CIT) in pts with immunotherapy resistant NSCLC. Methods: Study objectives include evaluation of safety and efficacy in pts with non-squamous NSCLC who have progression of disease (PD) on or after treatment with CIT. Sitravatinib is administered orally in continuous 28-Day cycles; nivolumab is administered via IV, 240 mg every 2 weeks. Treatment arms are stratified by prior clinical benefit (PCB) vs no prior clinical benefit (NPCB [PD in ≤ 12 weeks]). A predictive probability design is used for assessment of enrollment expansion in each stage. Other objectives include PK and correlative biomarkers. Results: Enrollment in Stage 2 of the CIT-experienced cohorts is complete and enrollment is ongoing. As of April 13, 2018, the CIT-experienced cohorts enrolled 46 pts and 25/46 have had at least one on-study tumor assessment. Twenty-one out of 25 pts have demonstrated tumor reductions. Seven pts out of the 25 have achieved a partial response (PR); 4 confirmed and 3 unconfirmed (1 PR/3 uPR in PCB; 3 PRs in NPCB cohorts, respectively); with the longest treatment duration exceeding 50 weeks. Sitravatinib-related AEs (>10% of pts; all grades) included diarrhea, nausea, vomiting, decreased appetite, fatigue, mucosal inflammation, dysphonia, AST/ALT increase, weight decrease, hypertension, and palmar-plantar erythrodysaesthesia syndrome. Updated safety and efficacy data will be presented. Conclusions: The combination of sitravatinib with nivolumab is clinically active with manageable side effects. Correlation of clinical activity with molecular analyses, including specific gene alterations and tumor mutation burden, is underway and will be presented. Clinical trial identification: NCT02954991. Legal entity responsible for the study: Mirati Therapeutics, Inc. Funding: Mirati Therapeutics, Inc. Disclosure: T.A. Leal: Advisory board (consulting): Takeda, AstraZeneca, Novartis, AbbVie, BMS. A.I. Spira: Consulting and research support (to institution): Mirati Therapeutics. C. Blakely: Research funding: Mirati, Novartis, Ignyta, Medimmune, Clovis; Consulting: Jazz Pharmaceuticals. E. Massarelli: Speakers bureau: AstraZeneca, Merck; Consultant: Genetech; Grants and research support: BMS, Genetech, I. Chen: Employment: Mirati Therapeutics. J. Christensen, P. Olson: Employment and stock ownership: Mirati Therapeutics. V. Tassell: Employment and stock ownership: Mirati Therapeutics; Stock ownership: Pfizer. L. Horn: Consulting: Abbvie, AstraZeneca, BMS, Genentech, Merck, Incyte, Xcovery. All other authors have declared no conflicts of interest.

Background: Sitravatinib (MGCD516) is a small molecule inhibitor of TAM (AXL, MER) and split (VEGFR2, PDGFR, KIT) family RTKs, RET, and MET. CBL encodes an E3-ubiquitin ligase that regulates the degradation of activated RTKs that are inhibited by sitravatinib. Thus, CBL loss-of-function mutations may increase signaling of a subset of sitravatinib target RTKs in tumors and predict sensitivity to treatment with sitravatinib. Methods: Study 516-001 is a Phase 1/1b study of sitravatinib in patients (pts) with advanced solid tumors. After determination of the MTD, pts with tumors harboring inactivating genetic alteration in CBL were enrolled into a preplanned Phase1b expansion cohort using a 2-stage Simon optimal design. Pts received sitravatinib once daily at 150mg or 120mg and were evaluated for safety, PK and clinical activity. Here we report the completion of Stage 1 for the Phase1b cohort of pts with CBL-inactivated tumors. Results: 105 pts (57 men/48 women; median age 67 years; range 36-84) with advanced solid tumors were enrolled in Phase1b cohorts, including 12 pts with malignancies harboring inactivating genetic alterations in CBL, comprising single nucleotide variants in the RING domain and indels compromising the coding region. Two partial responses (PR) were observed among the first 8 evaluable pts (melanoma 2; NSCLC 2; sarcoma 2; other 2) in Stage 1, which met criteria for enrollment of 16 additional evaluable pts for Stage 2. Confirmed PRs were observed in NSCLC (1/2) and melanoma (1/2) with response durations over 4 months for both. Prolonged stable disease for ≥17 weeks was observed in 2 additional pts (pancreatic neuroendocrine tumor and esophageal cancer). Treatment-related AEs (>20% of Phase1b pts; Grades 1-3) included diarrhea, fatigue, hypertension, nausea, vomiting and decreased appetite. Conclusions: Stage 1 enrollment of the Study 516-001 Phase1b cohort of pts with CBL-inactivated tumors was completed. Sitravatinib treatment resulted in 2 confirmed PRs in a heavily pre-treated patient population with a manageable safety profile. CBL mutations may be a novel target. Further evaluation of sitravatinib in NSCLC, melanoma, and other tumors is ongoing, and testing for CBL mutations may be warranted. Clinical trial identification: NCT02219711. Legal entity responsible for the study: Mirati Therapeutics, Inc. Funding: Mirati Therapeutics, Inc. Disclosure: R.D. Carvajal: Consulting: BMS, Castle Biosciences, Foundation Medicine, Immunocore, Incyte, Merck, Roche/Genentech; Advisory board: Aura Biosciences, Chimeron, Rgenix. R.S. Heist: Consulting: Boehringer Ingelheim; Research funding (to institution): Mirati, Celgene, Genentech Roche, Novartis, Peregrine, Debiopharm, Corvus, Abbvie, Millenium, Incyte. T. Werner: Research support to institution as the PI for industry sponsored trials Tesaro, Abbvie, Novartis, BMS. S. Neuteboom, J. Christensen: Employee and shareholder: Mirati Therapeutics. D. Potvin: Consultant: Mirati Therapeutics, Inc. I. Chen: Employee: Mirati Therapeutics; Stock ownership: Mirati Therapeutics. R. Chao: Employee: Mirati Therapeutics; Stock ownership: Mirati, Pfizer, and Merck. A. Alva: Advisor: Merck, Genetech, Astra Zeneca; Corporate sponsored research via institution: BMS, Merck, AstraZeneca, Calithera, Celgene, Bayer. All other authors have declared no conflicts of interest.

TPS708 Background: Sitravatinib is a potent oral tyrosine kinase inhibitor that targets multiple receptor tyrosine kinase pathways including the vascular endothelial growth factor (VEGF), c-MET, and the Tyro3, Axl, and MER family. These pathways can allow tumor cells to escape immune surveillance despite immune checkpoint therapy. We therefore hypothesized that combining sitravatinib with the anti-PD1 antibody nivolumab will enhance antitumor immune responses in pts with ccRCC. The present study is designed to determine the optimal dose for this combination using efficacy and toxicity as co-primary outcomes. Methods: This phase I/II trial uses the sequentially adaptive late-onset EffTox design (Jin et al. J Am Stat Assoc 2014), which accounts for potential late-onset toxicities induced by immunotherapy, and allows dose-finding based on both the efficacy and toxicity of each successive dose. Eligible pts have metastatic ccRCC that progressed on prior VEGF-targeted therapy. Each pt receives initially a pre-specified daily oral dose, among 4 dose levels (60mg, 80 mg, 120 mg, 150 mg), of sitravatinib monotherapy for 2 weeks to allow the drug to reach a pharmacokinetic steady state. Nivolumab is then added at the dose of 240 mg intravenously every 2 weeks. A maximum of 60 pts will be treated in up to 20 cohorts of 3 pts each. Tumor biopsies and peripheral blood are collected to assess changes in tumor microenvironment and immune markers at 4 different time points: 1) at baseline, up to 14 days prior to initiation of sitravatinib, 2) following 2 weeks of sitravatinib monotherapy, 3) after 2 infusions of nivolumab in combination with sitravatinib, and 4) at disease progression. The primary endpoint is optimal dose of sitravatinib based on toxicity (by week 12) and disease control rate (at week 6). Secondary endpoints include objective response rate, progression-free survival, and overall survival. At deadline for abstract submission, 4 pts have been treated on this study. Clinical trial information: NCT03015740.

Immune checkpoint inhibitors produce durable clinical responses in a subset of patients, however strategies are needed to improve clinical efficacy of these agents and overcome innate or acquired resistance to therapy. Growing evidence suggests that tumors evade immune detection through modulation of intrinsic immunogenicity and inhibition of both innate and adaptive anti-tumor immune responses. Mocetinostat, a class I histone deacetylase inhibitor, has multiple potential immunomodulatory features including: 1) induction of tumor associated antigens and major histocompatibility complex Class I and Class II expression on tumor cells, 2) induction of immunogenic cell death via activation and cross-presentation of tumor antigens by antigen presenting cells, 3) enhanced function of T effector cells, and 4) decreased function of immunosuppressive cell subsets including regulatory T cells and myeloid derived suppressor cells. Given these pleiotropic immune activating effects, combination therapy of mocetinostat and PD-L1 blocking mAb, durvalumab, is a rational approach to restoring or enhancing the clinical activity of immune checkpoint blockade in patients with NSCLC. This open-label Phase 1/2 study is evaluating the tolerability and clinical activity of mocetinostat in combination with durvalumab. Secondary objectives include pharmacokinetics, incidence of anti-drug antibodies, and changes in tumor PD-L1 expression. Exploratory objectives evaluate changes in circulating and tumor cell PD-L1, circulating and tumor infiltrating immune cell populations and cytokines. Phase 1 explores increasing doses of mocetinostat administered orally (50, 70, 90 mg three times weekly [TIW]) in combination with durvalumab in patients with advanced solid tumors. The regimen begins with a 7-Day Lead-in Period of mocetinostat single agent TIW followed by the combination regimen with durvalumab (1500 mg intravenously every 28 days). Phase 2 evaluates the clinical activity of mocetinostat and durvalumab, as assessed by Objective Response Rate (ORR) by RECIST 1.1., in patients with NSCLC who have previously received at least one platinum containing doublet chemotherapy regimen for advanced disease. Four population cohorts are included: 1) immunotherapy naïve, no/low PD-L1 expression, 2) immunotherapy naïve, high PD-L1 expression, 3) prior clinical benefit with PD-L1 or PD-1 inhibitor treatment followed by progression, 4) prior treatment with PD-L1 or PD-1 inhibitor with progression within 16 weeks of initiation of treatment. Tumor PD-L1 expression will be determined by the SP263 assay. The sample sizes for the populations are based on two-stage Simon Optimal Designs. Status: Enrollment into the study opened in June 2016. Clinical Trial Information: NCT02805660 Section not applicable. Section not applicable.