Abstract 2512: TMEM doorways are an actionable target in pancreatic adenocarcinoma

Abstract Introduction: Pancreatic adenocarcinoma (PDAC) is highly lethal due to overwhelming metastatic burden [1]. The mechanisms underpinning metastasis in PDAC have not been identified. The TMEM doorway is the sole portal of intravasation in breast cancer [2, 3]. Importantly, intravasation and dissemination via TMEM doorways is inhibited by Tie2 blockade in breast cancer [4]. We evaluated whether TMEM Doorways are a common targetable mechanism of dissemination in PDAC. Methods: Tumor samples from treatment-naïve patients who underwent curative-intent resection of PDAC were stained for TMEM doorways using a triple immunohistochemistry (IHC) stain (tumor cells expressing the actin regulatory protein Mena, macrophages expressing CD68, and endothelial cells expressing CD31). TMEM doorways were manually counted in the highest TMEM doorway-bearing 400x field (hotspot) identified at 100x scanning magnification for each case. TMEM doorway function was assessed in a murine model of PDAC treated with or without rebastinib (an investigational oral Tie2 inhibitor [4]) by analyzing; (1) TMEM doorway mediated opening using high-molecular weight dextran (155kD-TMR dextran); (2) circulating tumor cells and (3) disseminated tumor cells in murine livers. The Wilcoxon Test was used for the human TMEM doorway scoring comparisons. A student t-test was used for the murine analyses. Results: TMEM doorways were observed in all PDAC tumors from 50 unique treatment-naïve patients. The TMEM doorway score was ≈6x higher than observed in published breast cancer patient samples. Mean TMEM doorway score in “hotspots” from resected human PDAC was 19 and 34 in low- and high-grade tumors, respectively (p-value < 0.01). TMEM doorway mediated opening was decreased by rebastinib treatment (159.8 µm2 ± sd26.5 vs 22.6 µm2 ± sd3.5, p<0.01). PDAC tumor bearing mice treated with rebastinib had a 6.5-fold decrease in the number of circulating tumor cells compared to control (5554 ± sd1017 vs 852 ± sd412 cells/mL blood, p<0.01). PDAC tumor bearing mice treated with rebastinib had fewer disseminated tumor cells compared to untreated mice (11.6 vs 7.0 DTCs/mm2). Conclusions: TMEM doorways appear to be a common mechanism of dissemination in PDAC and breast cancer. TMEM doorway concentration is significantly associated with PDAC tumor grade. Inhibition of Tie2 with the selective inhibitor, rebastinib, preclinically leads to decreased TMEM doorway function and dissemination in PDAC. Tie2 is a promising therapeutic target for decreasing dissemination and potential metastasis in PDAC that warrants further clinical development in the PDAC space. 1.Siegel, R.L., et al. CA: A Cancer Journal for Clinicians, 2022. 72(1): p. 7-33.2.Harney, A.S., et al. Cancer Discovery, 2015. 5(9): p. 932-943.3.Karagiannis, G.S., et al., Science Translational Medicine, 2017. 9(397): p. eaan0026.4.Harney, A.S., et al. Molecular Cancer Therapeutics, 2017. 16(11): p. 2486-2501. Citation Format: Jakeb Petersen, Robert Eddy, Xianjun Ye, Christian Adkisson, David Entenberg, Maja Oktay, John Condeelis, Nicole Panarelli, John Christopher McAuliffe. TMEM doorways are an actionable target in pancreatic adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2512.