Abstract 3968: OT-101/Chemotherapy - A novel mechanism of action (MOA) in pancreatic cancer immunization therapy

Abstract

Abstract Background: OT-101 is a phosphorothioate antisense oligodeoxynucleotide targeting the human TGF-β2 mRNA. OT-101 breaks down immune tolerance and activates immunity against the tumor. The Subsequent Chemotherapy (SC) releases tumor antigens and boosts the immunity response along with further epitope expansion. The phase 1/2 clinical data for OT-101/SC is presented here along with supporting preclinical MOA studies. Methods: Total of 37 pts, 2nd line and beyond received OT-101 with option to go on SC (OT-101/SC) or Best Supportive Care (BSC) (OT-101/BSC). Overall survival (OS) was compared using log-rank statistics. Stratification by treatment line, schedule, metastasis location, disease control (DC), and baseline CA19-9, was performed. For cytokine analysis, plasma levels of 31 cyto-/chemokine were measured over 8 time points during 3 cycles of intravenous OT-101 therapy and a subset of 12 patients. Results: In vitro cell kill assay and in vivo xenograft study were performed with human PBMC and OT-101. OT-101 reduced TGF-β2 secretion and increased LAK cell-activity against all tumor lines by 400% and 364% in comparison to the untreated control and the Lipofectin control, respectively. Addition of active rh-TGF-β2 protein suppressed the cytotoxic activity of the immune cells in a dose dependent manner. Preclinical- LS174T xenograft was treated with PBMC or PBMC + OT-101. OT-101 significantly enhanced the activity of PBMC against the xenograft. Median OS (mOS) of the 18 pts receiving OT-101/SC was 9.4mos vs. the 19 pts on OT-101/BSC (2.8mos, p=0.0004). Pts with only liver mets had a mOS of 9.5mos while those with liver mets and others only had a mOS of 4.7mos (p=0.0077). Among the former, one patient had complete response beyond 77.3mos and another had stable disease with OS of 40.3mos. OS was higher for liver mets. only group with OT-101/SC - 12.4mos versus 1.9mos, p=0.0006. There were 16 of 37 pts with DC, with mOS of 9.7mos vs. 3.0mos (p<0.0001). OS was higher for DC group with OT-101/SC - 11.8mos vs. 5.0mos, p=0.0021. Patients exhibited spike in IL-8 level which returned to basal level at treatment stop. R2 relating the IL-8 spike and OS were 0.8522 and 0.9895 and p values were 0.0011 and 0.0053 for pts treated subsequently with SC and BSC, respectively. The two lines intersect at the origin with higher response for those with OT-101/SC, suggesting exaggerated response expected for antigen boost during the SC phase. Conclusions: Escalating Intratumoral heterogeneity (IH) resulting in xenogenization, which is countered by overexpression of TGF-β. Here we report on the use of OT-101/SC to break immune tolerance to pancreatic cancer (PC) for the cure. The MOA for OT-101/SC is consistent with the reactivation of immunity during TGF-β suppression and subsequent boosting/expansion of immunity during SC. Contrary to traditional tumor vaccine- this is universally applicable to all patients. Citation Format: David Nam, Larn Hwang, Vuong Trieu. OT-101/Chemotherapy - A novel mechanism of action (MOA) in pancreatic cancer immunization therapy [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 3968.