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Background: Metastatic TNBC (mTNBC) has a poor prognosis. Preclinical data suggests benefit for combination therapy of immune checkpoint inhibitor and anti-angiogenesis. Olinvacimab (O) is a fully humanised monoclonal antibody (MAB) which binds to Vascular Endothelial Growth Factor Receptor 2 (VEGFR2) and antiangiogenic and antitumor effects have been demonstrated. Pembrolizumab (P) is an anti-PD1 MAB. This study aimed to identify the safety and tolerability of O and P to establish a phase 2 recommended dose of O. Methods: From December 2018 to September 2020, we conducted a two-site, single arm, open-label study of O and P in pts with mTNBC. Eligible patients (pts) were >18 years, had ER, PR & HER2-negative MBC with at least one measurable lesion and adequate organ function. Pts with history of serious thromboembolism, gastrointestinal haemorrhage and prior anti-VEGF therapy were excluded. A modified Toxicity Probability Interval design was used. Pts received O 12 mg/kg q7d (dose level 1) or 16mg/kg day q7d (dose level 2) in combination with P 200mg flat dose day 1 q21d. Treatment continued until dose limiting toxicity (DLT), disease progression (PD) or treatment intolerance. Results: 11 pts, median age 62 (range 39-67) were recruited and received at least one dose of treatment. 8 (73%) had ECOG PS 1 and 3 (27%) had ECOG PS 2. 5 pts had previous chemotherapy for mTNBC (with 3 pts also having received immunotherapy), 6 pts were treated in the first-line metastatic setting (with all pts having received anthracycline and taxane in the adjuvant setting). 5 pts received O at 12mg/kg with P, completing a median of 6 cycles (range 1-18). As no DLTs were seen, 6 pts were treated with O at 16mg/kg with median of 8 cycles (range 2-21), with no DLTs being observed. Treatment was ceased due to PD in 6 pts, 3 pts are receiving treatment at data cut-off. Haemangiomas were seen in 8 pts accounting for 47 events of CTCAE grade 1 and 21 events of grade 2. Treatment emergent adverse events (TEAEs) of ≥grade 3 was seen in 6 pts (27 events), with 8 events being related to treatment. 4 pts (36%) had partial response (PR) as best overall response 5 pts (45%) had clinical benefit (PR+SD≥24weeks). Conclusions: Combination therapy of O and P was well tolerated with evidence of efficacy in mTNBC pts who had all previously received anthracycline and taxanes, with 3 pts having previously received immunotherapy. These results support the combination entering into a phase 2 study. Citation Format: Arlene Chan, Eugene Moylan, Sally Jackson, Jeannette Devoto, Nicola Jones, Silvie Radmil, Kate Wilkinson, Aflah Roohullah, Tamiem Adam, Seon Young Lee, Weon Sup Lee, Jin-San Yoo. Phase Ib trial of olinvacimab and pembrolizumab in patients with metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-18.

TME (tumor microenvironment) consists of blood & lymphatic vessels, stromal cells, and immune cells such as lymphocytes, macrophages, and antigen-presenting cells (APC). Cellular interactions among various immune cell types within TME regulate tumor growth, metastasis, and resistance to cancer therapy. V-domain Ig suppressor of T cell activation (VISTA) is a negative checkpoint regulator highly expressed on tumor-infiltrating myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAMs) and VISTA blockade could enhance antitumor immunity in TME. PMC-309 binding to VISTA expressing cells is highly selective and the selectivity is maintained even in the low pH conditions that mimic TME. Binding of PMC-309 on MDSC cells enhances the secretion of IFN-γ, TNF-α, and IL-2 in Mixed Lymphocyte Reaction (MLR) settings. In in vivo study, PMC-309 suppressed tumor growth, which was further attenuated with an anti-PD1 antibody. The anti-tumor activity was associated with enhanced T cell activation, increased secretion of pro-inflammatory cytokines, and increased penetration of tumor-infiltrating leukocytes (TIL) into TME. Patients who became resistant to anti-CTLA-4 and anti-PD(L)1 antibody showed increased expression of VISTA, suggesting that anti-VISTA therapeutics can help to treat the patients who do not respond well to other immuno-oncology drugs. We are developing PMC-309 as a next generation immuno-oncology (IO) agent, which can convert immunologically cold into hot tumors as a mono- or combo- therapy with other IO agent. Citation Format: Cheon Ho Park, Sang Soon Byun, Jin Yong An, Sun Hyung Ha, Hye Rim Han, Nu Ri Kang, Beom Yong Park, Eun Ah Lee, Hyun Sun Park, Jin-San Yoo, Weon Sup Lee. PMC309, a highly selective anti-VISTA antibody enhances T cell activation through blocking the interaction of T cells and myeloid derived suppressor cells (MDSC) [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 1626.

Tumor angiogenesis is the process that leads to the formation of blood vessels in a tumor and a prognostic indicator in various cancers. Vascular endothelial growth factor (VEGF) and its receptors are considered to be primary regulators of tumor-induced angiogenesis and activation of VEGFR2/KDR is the major signaling pathway for tumor growth. In addition, VEGFR2/KDR is also expressed in many cancer cells, and regulates cell growth and survival through autocrine pathway. In this study, we evaluated the therapeutic potential of TTAC-0001, fully human antibody against VEGFR2/KDR, for the inhibition of tumor growth. In the tube formation assay using HUVEC, TTAC-0001 exhibited a potent anti-angiogenic activity in vitro. In U-87 MG glioblastoma cells, TTAC-0001 significantly inhibited the phosphorylation of VEGFR2/KDR mediated by VEGF. To reveal in vivo efficacy, we have tested TTAC-0001 in glioblastoma and colorectal xenograft models. We demonstrated that antitumor activity of TTAC-0001 in preclinical models correlated with induction of growth arrest and apoptosis as well as the inhibition of angiogenesis. Currently, we are evaluating the combination of TTAC-0001 with chemotherapeutic agents in xenograft models. A single dose study performed in mouse allowed us to establish the relationship between the pharmacokinetics (PK) and efficacy of TTAC-0001. Taken together, our data suggest that targeting VEGFR2 pathway by TTAC-0001 would be a promising candidate for the treatment of cancer. (This study was supported by grants of the Korea Healthcare technology R&D Project, Ministry for Health & Welfare Affairs (A092255 and A040016) and Advanced Medi-cluster R&D Project, DaejeonTechnoPark, Republic of Korea. Seol HJ and Nam DH are co-corresponding authors for this manuscript.) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 647. doi:10.1158/1538-7445.AM2011-647

Angiogenesis, the recruitment of new blood vessels is a crucial mechanism required for both tumor growth and metastasis. Vascular endothelial growth factor (VEGF) and its receptors, particularly VEGF receptor 2 (VEGFR2, or kinase insert domain-containing receptor, KDR), play a critical role in tumor-associated angiogenesis. Monoclonal antibodies (mAb), due to their high specificity towards a given target, represent a unique class of novel therapeutics as angiogenesis inhibitors. We developed TTAC-0001, anti-KDR antibody from a fully human naïve single chain variable fragment (ScFv) phage library. Interestingly, TTAC-0001 displayed cross reactivity against murine homologue, Flk-1, which allows us to evaluate the anti-tumor efficacy in various in vivo models. TTAC-0001 inhibits VEGF-mediated proliferation and migration. In HUVEC, TTAC-0001 inhibited the phosphorylation of VEGFR2/KDR and ERK mediated by VEGF. TTAC-0001 inhibited VEGF-mediated sprouting endothelial cells from rat aortic rings and showed a potent anti-angiogenic activity in VEGF-mediated matrigel model in nude mice. Further in vivo anti-tumor efficacy of TTAC-0001 was seen in the xenografts of A549 (lung) and HCT116 (colorectal) human cancer. These changes were accompanied by the inhibition of microvessel density and induction of apoptosis in the tumors. In summary, our data indicates that TTAC-0001 blocks the binding of VEGF to VEGFR2/KDR and inhibits VEGFR-induced angiogenesis. Therefore, this data strongly supports for the further development of TTAC-0001 as an anti-cancer agent (This study was supported by grants of the Korea Healthcare technology R&D Project, Ministry for Health & Welfare Affairs (A092255 and A040016) and Advanced Medi-cluster R&D Project, Daejeon TechnoPark, Republic of Korea). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4244. doi:10.1158/1538-7445.AM2011-4244