Abstract 1909: Stromal cell driven proteolysis of versican is limited by epithelial cells in pancreatic ductal adenocarcinoma

Abstract

Background: Clinical responses to checkpoint inhibitors in gastrointestinal cancers have largely been limited to MSI-high disease. Proteolysis of an immunosuppressive proteoglycan versican (VCAN) by ADAMTS proteases correlates with enhanced CD8+ T cell infiltration in colorectal cancer independent of mismatch repair status. Here we investigate the potential of this biomarker in pancreatic ductal adenocarcinoma (PDAC) as VCAN is abundant VCAN in this disease. Methods: KPC mice were used to generate mouse PDAC tissue and organotypic spheroids. A human PDAC tissue microarray (TMA) was developed representing normal and neoplastic pancreatic tissues across 131 patients. IHC was used to determine levels of VCAN, an immunostimulatory fragment versikine (Vkine), and CD8+ T cells. Bone marrow-derived macrophages (BMDMs) were derived from BALB/c mice. VCAN-specific ADAMTS protease expression profiles were compared between antitumor (M1) and protumor (M2) mouse macrophages, human pancreatic stellate cells (PSCs) and patient-derived PDAC-organotypic spheroids. Results: IHC analysis of normal murine pancreas demonstrated low VCAN and Vkine staining. VCAN is abundant in metaplastic/neoplastic KPC mouse pancreatic tissues. Rare VCAN proteolytic predominant areas (samples with both low VCAN and high Vkine) in KPC tumors had increased tumor-infiltrating CD8+ T cells/ high-powered field compared to weak areas (17 vs 4, p<0.001). Human PDACs had abundant VCAN expression compared to normal pancreatic tissues (p<0.001, n=118). Vkine was absent from normal tissues and present only at low levels in tumor cores (p<0.001, n=117). No human PDAC VCAN proteolytic-predominant samples were identified. M1 BMDMs demonstrated high relative expression (RE) of VCAN-specific ADAMTS proteases relative to unpolarized M0 BMDMs; however, these levels decreased under KPC-conditioned media (ADAMTS4, 101 vs 5, p=0.003; ADAMTS9, 80 vs 1, p=0.02; ADAMTS15, 103 versus 1.6, p<0.001; ADAMTS20, 881 vs 3.2, p<0.001). Similarly, M2 BMDMs had elevated ADAMTS-levels that were reduced under KPC-conditioned media, (ADAMTS4, 42 vs 0.4, p=0.0029; ADAMTS9, 40 vs 1, p=0.002; ADAMTS15, 23 vs 3, p=0.027; ADAMTS20, 310 vs 0.8, p<0.001; n=3). RE levels of ADAMTS proteases in KPC spheroids was consistently lower than reported above in macrophages. RE of ADAMTS proteases in human PSCs were between 18 and 304. No differences in ADAMTS expression were identified under PDAC-conditioned media in the human PSCs (p=0.3). Conclusions: The VCAN proteolysis predominant phenotype correlates with increased CD8+ T cell infiltration in PDAC though is rarely present in the human disease. PDAC epithelial cells influence the stromal cells to reduce VCAN proteolysis through decreased ADAMTS expression by macrophages. Future studies examining measures to enhance VCAN proteolysis could result in a more immune permissive microenvironment. Citation Format: Philip B. Emmerich, Chelsie Sievers, Hanna Rainiero, Rosabella Pitera, Connor Maloney, Susan Payne, Mitchell Depke, Cheri Pasch, Linda Clipson, Jillian K. Johnson, Kristina Matkowskyj, Fotis Asimakopoulos, Dustin A. Deming. Stromal cell driven proteolysis of versican is limited by epithelial cells in pancreatic ductal adenocarcinoma [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 1909.