Background: Emerging evidence supports combining immune checkpoint inhibitors (ICIs) with conventional or targeted therapies to enhance ICI antitumour activity and broaden the spectrum of patients who respond to ICIs. Here, we present the safety and preliminary efficacy of ramucirumab, an anti-VEGFR2 IgG1, plus durvalumab, an antiePD-

Vascular endothelial growth factor (VEGF), a potent and specific activator of endothelial cells, is expressed as multiple homodimeric forms resulting from alternative RNA splicing. VEGF121 does not bind heparin while the other three isoforms do, and it has been documented that the binding of VEGF165 to its receptor is dependent upon cell surface heparin sulfate proteoglycans. Little is known about the biochemical mechanism that allows for heparin regulation of growth factor binding. For example, it is not clear whether heparin interactions with growth factor or with cell surface receptors or both are essential for VEGF binding to its receptor. In this manuscript we provide results which are consistent with the hypothesis that an interaction between heparin and a site on the KDR receptor subtype is essential for VEGF165 binding. First, we demonstrate that expression of KDR into a CHO cell line deficient in heparan sulfate biosynthesis does not allow VEGF165 binding unless heparin is exogenously added during the binding assay. Secondly, we show that a ten amino acid synthetic peptide, corresponding to a sequence from the extracellular domain of the KDR, both inhibits VEGF165 binding to the receptor and also binds heparin with high avidity. Third, affinity purification of heparin molecules on a KDR-derived peptide affinity column, together with capillary electrophoresis and polyacrylamide electrophoresis analysis, was used to show that the KDR-derived peptide interacts with a specific subset of polysaccharide chains contained in the unfractionated heparin. Taken together, these results are consistent with the hypothesis that interactions between cell surface heparan sulfate proteoglycans and the VEGF receptor contribute to allowing maximal VEGF binding.

2528 Background: A Phase 1b study (NCT02572687) was conducted to examine the combined effects of Ram (anti VEGFR2) and Durva (anti PD-L1). Methods: Patients (pts) with previously-treated, advanced NSCLC (Cohort [CH] A), G/GEJ adenocarcinoma (CH B), HCC (CH C), ECOG PS 0-1, and no prior Ram or IO therapy, received Ram (10 mg/kg) + Durva (1125 mg) Q3W (CH A) or Ram (8 mg/kg) + Durva (750 mg) Q2W (CH B, C). Primary objective was to assess safety; efficacy was also examined. PD-L1 expression of tumor cells (TC) +/- immune cells (IC) in pretreatment tumor biopsies were assessed using SP263 immunohistochemistry. “High” PD-L1 is ≥25% TC for NSCLC and ≥25% TC or IC for G/GEJ, HCC. Results: CH A, B and C enrolled pts with ECOG PS 1 (%) of 43, 66, 68; and average of 2, 2, 1 prior regimens, respectively. The most common grade 3/4 treatment-emergent adverse events (AE) are hypertension (HTN) (14.3, 17.2, 17.9%), anemia (3.6, 24.1, 21.4%), and fatigue (10.7, 10.3, 10.7%). Grade 3/4 AEs of special interest ( > 5% total pts) for Ram: HTN, bleeding events (3.6, 10.3, 10.7%), Venous thromboembolic events (0, 10.3, 7.1%); for Durva: increase in lipase (10.7, 3.4, 10.6%) and AST (3.6, 3.4, 17.9 %). Data from CH B,C suggest a trend toward increased efficacy in pts with high PD-L1 expressing tumors. Conclusions: Ram + Durva generated no unexpected toxicities and demonstrated antitumor activity. Results in pts with high PD-L1 HCC and G/GEJ cancer warrant further evaluation. Clinical trial information: NCT02572687. [Table: see text]

92 Background: Angiogenesis and immunosuppression are hallmarks of tumor growth. This global phase 1 trial evaluates the combination of R (anti-VEGFR2) and D (anti-PD-L1) in pts with G/GEJ by simultaneously targeting these two processes. Methods: This ongoing, multi-cohort, phase 1a/b trial (NCT02572687) enrolled pts with confirmed G/GEJ adenocarcinoma with prior progression on 1 or 2 lines of systemic therapy, measurable disease, ECOG PS 0-1, and baseline tumor tissue. PD-L1 expression was assessed using the SP-263 IHC; MSI status was determined using PCR. Enrolled pts received R (8 mg/kg IV) and D (750 mg IV) every two weeks on a 28-day cycle. Primary objective was to assess safety and tolerability of R+D; preliminary efficacy was also examined. Results: As of 26-May-2017, 29 G/GEJ adenocarcinoma pts were treated. The median age was 55 y; 69% were male; 66% had ECOG PS of 1; 48% had PD-L1 ≥25% expression in tumor or immune cells, 3.5% were MSI-high; and 72% received study treatment as second line for advanced disease. Median duration of treatment was 2.5 mo for R and 3.0 mo for D. Treatment-emergent adverse events (TEAEs) occurred in 29 (100%) pts and 21 (72%) pts experienced grade 3/4 TEAEs, while treatment-related AEs (TRAE) occurred in 24 (83%) pts; none resulted in treatment discontinuation. Ten (35%) pts had grade 3 TRAEs, and no grade 4 or 5. All grade TRAEs occurring in ≥10% of pts were hypertension (34%), fatigue (31%), headache (24%), diarrhea (21%), pyrexia (10%) and decreased appetite (10%). Five pts (17%) reported a serious adverse event related to study treatment. Preliminary efficacy data (RECIST v1.1) showed 5 of 29 pts (17%) achieved a confirmed PR. Only 1 responding pt was MSI high. The overall response rate for pts with PD-L1 ≥25% was 36%. Median PFS was 2.6 mo (95% CI, 1.45 to 6.28). As of data cut-off, 6 pts (21%) remain on treatment. Conclusions: R+D generated no unexpected toxicity, and demonstrated antitumor activity in pts with previously treated advanced G/GEJ adenocarcinoma. Clinical trial information: NCT02572687.

Vascular endothelial growth factor receptor 2 (VEGFR2) is an attractive therapeutic target in solid malignancies due to its central role in tumor angiogenesis. Ramucirumab (Cyramza®, LY3009806) is a human monoclonal antibody specific for VEGFR2 approved for several adult indications and currently in a phase 1 clinical trial for pediatric patients with solid tumors (NCT02564198). Here, we evaluated ramucirumab in vitro and the anti-murine VEGFR2 antibody DC101 in vivo with or without chemotherapy across a range of pediatric cancer models. Ramucirumab abrogated in vitro endothelial cord formation driven by cancer cell lines representing multiple pediatric histologies; this response was independent of the origin of the tumor cell-line. Several pediatric cancer mouse models responded to single agent DC101-mediated VEGFR2 inhibition with tumor growth delay. Preclinical stable disease and partial xenograft regressions were observed in mouse models of Ewing’s sarcoma, synovial sarcoma, neuroblastoma, and desmoplastic small round cell tumor treated with DC101 and cytotoxic chemotherapy. In contrast, DC101 treatment in osteosarcoma models had limited efficacy alone or in combination with chemotherapeutics. Our data indicate differential efficacy of targeting the VEGFR2 pathway in pediatric models and support the continued evaluation of VEGFR2 inhibition in combination with cytotoxic chemotherapy in multiple pediatric indications.