Abstract 1999: DIRAS3 induces autophagy and enhances sensitivity to anti-autophagic therapy in KRAS-driven pancreatic and ovarian carcinomas

Abstract

Abstract Mutant KRAS drives human cancers from several sites, including pancreatic ductal adenocarcinoma (PDAC) and low-grade serous ovarian cancer (LGSOC). Despite the prevalence of RAS mutations in many different cancers, effective RAS-targeted treatment remains a challenge. More than 90% of PDACs are driven by mutant KRAS. Genetic suppression of KRAS or pharmacological inhibition of its effectors, ERK/MAPK, enhances the reliance of PDAC on autophagy that can provide a target for treatment. DIRAS3 (ARHI) is an imprinted tumor suppressor gene that is downregulated in pancreatic and ovarian cancers. When re-expressed, DIRAS3 blocks cancer cell proliferation, inhibits motility, and induces autophagy by multiple mechanisms. DIRAS3 inhibits RAS signaling by heterodimerizing directly with KRAS, inhibiting homodimerization of KRAS and disrupting KRAS nanoclustering. In this study, we tested whether inhibiting RAS signaling by re-expressing DIRAS3 would sensitize RAS-driven cancers to autophagy inhibition. Re-expression of DIRAS3 decreased phosphorylation of Erk1/2 (pThr202/Tyr204), inhibiting the RAF-MEK-ERK signaling pathway. Re-expression of DIRAS3 induced autophagic flux indicated by an increased LC3-mCherry/eGFP ratio. DIRAS3 re-expression decreased LKB1 (pS428) and increased AMPK (pT172) and ULK1 (pS555), suggesting that induction of autophagic flux may be partly mediated by the activation of the energy-sensing LKB1-AMPK1-ULK1 axis following suppression of upstream RAF-MEK-ERK signaling. In addition, we confirmed that DIRAS3-induced autophagy enhanced the sensitivity of cancer cells to autophagy inhibition as evidenced by decreasing the IC50 of both chloroquine (CQ) and di-chloroquine (DC661) in human KRAS-driven PDAC and LGSOC. The greater potency of DC661, blocking autophagy with an IC50 in the low nanomolar range, should prove more effective for combinatorial therapies in vivo. Citation Format: Gamze Bildik, Joshua P. Gray, Weiqun Mao, Robert C. Bast, Zhen Lu. DIRAS3 induces autophagy and enhances sensitivity to anti-autophagic therapy in KRAS-driven pancreatic and ovarian carcinomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1999.