The Combination of a BCL-xL PROTAC and an mTOR Inhibitor Sensitizes Pancreatic Ductal Adenocarcinoma to KRASG12D Inhibitor Treatment

TL;DR

Combining a BCL-xL degrader and an mTOR inhibitor with a KRASG12D inhibitor improves treatment of pancreatic cancer in preclinical models.

Contribution

A novel triple therapy combination that enhances the efficacy of KRASG12D inhibitors in pancreatic cancer.

Findings

The triple combination significantly increased cell death and reduced tumor growth in KRASG12D-mutant PDAC models.

The treatment overcame resistance to the KRASG12D inhibitor in both in vitro and in vivo models.

The combination enhanced apoptosis while blocking survival signals in cancer cells.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with poor survival and lacks effective treatments. MRTX1133, a new investigational drug targeting the KRAS G12D mutation, which is common in PDAC, shows promise in preclinical studies but is unlikely to be effective as a single agent. In this study, we combined MRTX1133 with a BCL-xL-targeting degrader (DT2216) and the mTOR inhibitor everolimus for enhanced therapeutic efficacy. The triple combination more effectively killed KRAS G12D-mutant PDAC cells in culture and slowed tumor growth in mice than MRTX1133 alone, which was associated with simultaneously strengthening pro-death signals and blocking survival mechanisms in cancer cells. Notably, the triple combination also showed efficacy against mouse tumors that developed resistance to MRTX1133. These findings suggest that combining MRTX1133 with DT2216 and everolimus could be a more effective treatment strategy for patients with KRAS G12D-mutant PDAC.

Background/Objectives: Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive cancer with a five-year survival rate of approximately 13%, partly because of limited treatment options and resistance to therapies. Although the recently discovered KRAS G12D inhibitor MRTX1133 has shown promising efficacy in preclinical models, its clinical efficacy as a single agent is expected to be limited, as is the case with KRAS G12C inhibitors. Therefore, in this study, we evaluated potential combination strategies to enhance the therapeutic effect of MRTX1133. We combined MRTX1133 with the BCL-xL proteolysis-targeting chimera (PROTAC) DT2216 and the mTOR inhibitor everolimus. Methods: The sensitization of MRTX1133 by the combination of DT2216 + everolimus was tested in KRAS G12D-mutant PDAC cell lines using colony formation and apoptosis assays. The effects of MRTX1133 and/or DT2216 + everolimus on KRAS signaling and BCL-2 family proteins were assessed by immunoblotting and/or RT-PCR. The functional roles of BIM/NOXA were elucidated via immunoprecipitation (IP) and siRNA knockdown. Triple combination efficacy was evaluated in AsPC1 parental and MRTX1133-resistant xenografts, with pharmacodynamic effects confirmed by immunoblotting and immunohistochemistry. Results: The triple combination leads to significantly greater colony growth inhibition and apoptosis induction as compared with single agents or two-drug combinations in multiple KRAS G12D-mutant PDAC cell lines. Mechanistically, MRTX1133 treatment increased BIM and decreased NOXA levels, and the combination of DT2216/everolimus simultaneously enhanced BIM release and stabilized NOXA. In vivo, DT2216/everolimus combination significantly potentiated the anti-tumor activity of MRTX1133 in the AsPC1 PDAC xenograft model. Furthermore, the triple combination effectively overcame acquired MRTX1133 resistance in vitro and in the AsPC1 xenograft model. Conclusions: Collectively, our findings suggest that the combination of DT2216/everolimus potentiates the anti-tumor efficacy of MRTX1133 associated with enhanced apoptosis induction and inhibition of compensatory survival signaling.

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