Effects of Akt inhibitors on radiation sensitivity, oxidative stress, EMT reversal, and immune microenvironment reprogramming in pancreatic cancer.

Abstract

e16462 Background: Locally advanced and borderline resectable pancreatic tumors are treated with multi-agent cytotoxic chemotherapy or chemoradiation therapy. Beyond the current use of capecitabine as a radiosensitizer in chemoradiation regimens, integration of newer targeted agents offers the promise of further improving treatment responses. Recognizing that most pancreatic cancers are Kras mutant, we evaluated the efficacy of combining agents that selectively inhibit Akt downstream of constitutively active Kras. Methods: Human and murine pancreatic cancer cell lines (Panc1, KPC, Panc02) and a murine macrophage cell line (RAW264.7) were studied. Akt inhibitors (capivasertib or ipatasertib), singly or in combination with capecitabine, were evaluated for their radiation sensitization potential, using capecitabine-radiation as the standard-of-care reference for comparisons. Studies included apoptosis assays, clonogenic survival assays, westerns blot analyses, qPCR, and flow cytometry. Results: Compared to capecitabine-radiation, the addition of either Akt inhibitor significantly reduced clonogenic survival in the panel of pancreatic cell lines tested. This was associated with an increase in apoptotic cell death, reduction in phospho-PRAS40 and GSK3B downstream of phospho-Akt, augmentation of radiation-induced oxidative stress with reduced expression of the free radical scavenger NQO1, and reversal of epithelial-to-mesenchymal transition (EMT) with increased E-cadherin expression. Furthermore, addition of Akt inhibitors significantly increased PDL1 and ICOSL mRNA levels, suggesting that combination with immune checkpoint blockade or immune co-stimulatory molecules could enhance immune-mediated cytotoxicity. In keeping with this, Akt inhibition also repolarized pro-tumorigenic M2 macrophages to anti-tumor M1 macrophages. Conclusions: Collectively, our results suggest that inhibition of Akt signaling sensitizes pancreatic cancers to radiation therapy by amplifying radiation-induced oxidative stress and abrogating the pro-survival signaling drive downstream of constitutively active mutant Kras. This also reverses EMT and reprograms the immunosuppressive tumor microenvironment to a more immunogenic phenotype that may be primed for further enhancement by targeted immunotherapies. Taken together, these results suggest that Akt inhibition may be a promising strategy for sensitization of pancreatic cancer to radiation therapy via multiple orthogonal mechanisms that include EMT reversal and immune reprogramming.