Barbara A. Moreno Diaz

Abstract Pancreatic ductal adenocarcinoma (PDAC) is associated with mutations in Kras, a known oncogenic driver of PDAC; and the KRAS G12D mutation is present in nearly half of PDAC patients. Recently, a non-covalent small molecule inhibitor (MRTX1133) was identified with specificity to the Kras G12D mutant protein. Here we explore the impact of Kras G12D inhibition by MRTX1133 on advanced PDAC and its influence on the tumor microenvironment. Employing different orthotopic xenograft and syngeneic tumor models, eight different PDXs, and two different autochthonous genetic models, we demonstrate that MRTX1133 reverses early PDAC growth, increases intratumoral CD8 + effector T cells, decreases myeloid infiltration, and reprograms cancer associated fibroblasts. Autochthonous genetic mouse models treated with MRTX1133 leads to regression of both established PanINs and advanced PDAC. Regression of advanced PDAC requires CD8 + T cells and immune checkpoint blockade therapy (iCBT) synergizes with MRTX1133 to eradicate PDAC and prolong overall survival. Mechanistically, inhibition of mutant Kras in advanced PDAC and human patient derived organoids (PDOs) induces Fas expression in cancer cells and facilitates CD8 + T cell mediated death. These results demonstrate the efficacy of MRTX1133 in different mouse models of PDAC associated with reprogramming of stromal fibroblasts and a dependency on CD8 + T cell mediated tumor clearance. Collectively, this study provides a rationale for a synergistic combination of MRTX1133 with iCBT in clinical trials.

KRAS is among the most frequently mutated oncogenes in cancer, and for decades, efforts at pharmacological blockade of its function in solid cancers have been unsuccessful. A notable advance in this endeavor is the recent development of small-molecule KRAS inhibitors, which enable direct targeting of the mutant oncoprotein. Here, we comprehensively evaluated the preclinical efficacy of BI-2493, a first-in-class allele-agnostic mutant-KRAS inhibitor (panKRASi), in pancreatic ductal adenocarcinoma (PDAC). We report effective tumor growth suppression across a broad range of models, including cell lines, patient-derived xenografts (PDXs), and syngeneic orthotopic models, and prolonged survival in genetically engineered mouse models. Overall, transcriptomic, proteomic, and phosphoproteomic profiling of panKRASi-treated models confirmed RAS pathway inhibition along with up-regulation of LKB1/AMPK (liver kinase B1/AMP-activated protein kinase) targets. In panKRASi-treated immune-replete models, we observed increased intratumoral CD8 + effector T cells and decreased infiltration of myeloid cells, along with remodeling of the tumor microenvironment (TME), enabling responses to immune checkpoint blockade. In the long term, emergence of resistance to panKRASi monotherapy was associated with increased YAP signaling within tumor cells and enhanced expression of immune checkpoints in the TME that impede effective T cell function. Our multifaceted approach identified potential combinatorial approaches for generating sustained responses to panKRASi.

Abstract Mutations in KRAS are a dominant driver of pancreatic ductal adenocarcinoma (PDAC), with over 40% of PDAC patients presenting with KRAS G12D mutations. The recent development of small molecule inhibitors targeting KRAS G12D has enabled targeting of mutant KRAS signaling and suppression of PDAC; however, the contribution of the tumor microenvironment (TME) to the sustained therapeutic efficacy of KRAS G12D inhibition and mechanism/s of resistance to KRAS G12D suppression remain to be elucidated. Here, we employed spatial transcriptomics, single cell RNA sequencing, and CODEX-based spatial proteomics to evaluate cancer cell intrinsic and extrinsic responses to KRAS G12D inhibition with MRTX1133. While KRAS G12D inhibition initially increases CD11c + cells with impactful T cell infiltration within proximity to cancer cells, long-term treatment with MRTX1133 resulted in reversal of the immune responses leading to KRAS G12D therapy resistance promoted by CDK8, a multiprotein mediator complex associated kinase. CDK8 imparts resistance in part through induction of downstream CXCL2 chemokine secretion, inhibition of FAS expression, and remodeling of the TME to promote immune evasion. Targeting CDK8 by itself and in combination with αCTLA-4 immunotherapy overcomes resistance to KRAS G12D inhibition with prolonged survival with translational implications.

Abstract Mutations in KRAS are a dominant driver of pancreatic ductal adenocarcinoma (PDAC), with over 50% of PDAC patients presenting with KRASG12D mutations. The recent development of small molecule inhibitors targeting KRASG12D has enabled effective targeting of mutant KRAS signaling and suppression of tumor growth; however, the contribution of the tumor microenvironment to the therapeutic efficacy of KRASG12D inhibition and mechanisms of resistance to KRASG12D suppression remain to be fully elucidated. Here, we employed spatial transcriptomics and proteomics to evaluate cancer cell intrinsic and extrinsic responses to KRASG12D inhibition with MRTX1133. MRTX1133 treatment was associated with increased antigen presenting cells (APCs), T cells, and putative tumor-restraining fibroblasts within proximity to cancer cells, suggesting that antigen presentation and remodeling of the local microenvironment facilitates an effective response to KRASG12D inhibition. In the context of relapsed MRTX1133 treated tumors, single cell RNA sequencing and validation identified CDK8 as an intrinsic mediator of resistance and CXCL2 as an extrinsic mediator of resistance. Together, these studies identify APCs and CDK8 as therapeutic targets for enabling long term responses to small molecule KRASG12D inhibition with MRTX1133. Citation Format: Kathleen M. McAndrews, Krishnan K. Mahadevan, Bingrui Li, Amari M. Sockwell, Sami J. Morse, Patience J. Kelly, Michelle L. Kirtley, Meagan R. Conner, Sarah I. Patel, Shreyasee V. Khumbar, Kent A. Arian, Yasaman Barekatain, Barbara A. Moreno Diaz, Hengyu Lyu, Hikaru Sugimoto, Lakshmi Kavitha Sthanam, Navid Sobhani, Francesca Paradiso, Vincent Bernard, Paola Guerrero, Haoqiang Ying, Anirban Maitra, Timothy P. Heffernan, Raghu Kalluri. CDK8 and CXCL2 remodel the tumor microenvironment to contribute to KRASG12D small molecule inhibition resistance in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr B092.