Free and encapsulated tunicamycin significantly enhances the suppression of PD-L1 by gemcitabine through blocking K-Ras G12D expression in pancreatic ductal adenocarcinoma cells

Pancreatic ductal adenocarcinoma (PDAC) remains one of the leading causes of cancer mortality worldwide, including among U.S. Veterans, and it is expected to become the second leading cause by 2040. The standard treatment options include surgical resection (when possible), chemotherapy, targeted therapy, immunotherapy, and radiation therapy. These treatments can be administered individually or in combination. Unfortunately, these treatment options have not significantly improved overall survival rates for patients with PDAC. Thus, currently, the first-line treatments for PDAC are still FOLFIRINOX (a combination of fluorouracil, leucovorin, oxaliplatin, and irinotecan) and Gemcitabine (GEM), either alone or in combination with nab-paclitaxel. While initial responses to chemotherapy, such as Gemcitabine alone or with other agents, can occur, these are often followed by the development of resistance. This resistance leads to increased programmed death-ligand 1 (PD-L1) expression in PDAC cells via the JAK-STAT pathway, posing a significant challenge for immunotherapy. Consequently, there is an urgent need for targeted therapies to overcome these limitations. Our research has identified Tunicamycin (TM), a glycosylation inhibitor antibiotic, as a potent agent that effectively targets PDAC cells and significantly reduces GEM-induced PD-L1 production. We found that treating Panc-1 and KPC cells with free or nanoencapsulated Tunicamycin ( NP TM) at a dose of 0.25 μM for 48 hours can overcome the limitations associated with Gemcitabine. Specifically, we observed that Gemcitabine treatment at 0.5 μM did not suppress PD-L1 expression; however, when combined with TM, Gemcitabine significantly reduced PD-L1 levels in these cells in vitro and in vivo . Although the mechanism by which TM regulates PD-L1 is not fully understood, previous studies have shown that K-RAS mutations can directly influence PD-L1 expression by activating the MAPK/ERK pathway, which Tunicamycin inhibits. Therefore, we hypothesize that TM reduces PD-L1 expression in PDAC cells by suppressing K-RAS G12D . (These studies are supported by the VA Merit grants)