CDK8 remodels the tumor microenvironment and promotes resistance to KRASG12D inhibitors and daraxonrasib in PDAC

Abstract

Mutations in KRAS are a dominant driver of pancreatic ductal adenocarcinoma (PDAC), with about 50% of patients presenting with KRASG12D mutations. Small molecule inhibitors targeting KRASG12D suppress PDAC; however, the contribution of the tumor microenvironment (TME) to the sustained efficacy of KRASG12D inhibition and mechanisms of resistance to KRASG12D suppression remain to be elucidated. Here, integrated spatial transcriptomics, single-cell RNA sequencing, and CODEX-based spatial proteomics analyses of PDAC mouse models uncover that while KRASG12D inhibition by MRTX1133 initially increases CD11c+ cells and T cell infiltration proximal to cancer cells, long-term treatment results in reversal of the immune responses leading to resistance promoted by multiprotein mediator complex associated kinase CDK8. CDK8 imparts this resistance via induction of CXCL2 chemokine secretion, inhibition of FAS expression, and remodeling of the TME to promote immune evasion. Targeting CDK8 by itself or in combination with αCTLA-4 immunotherapy overcomes resistance to KRASG12D inhibition. We also provide evidence of CDK8 upregulation in PDX tumors resistant to inhibitors selective for RAS(ON) and RASG12D(ON): daraxonrasib and zoldonrasib, respectively, highlighting a common KRAS vulnerability node for TME resistance. Targeting of oncogenic KRAS mutations suppresses cancer growth, however relapse arises by unclear mechanisms. This study identifies mediator complex kinase CDK8 as a driver of resistance towards KRASG12D inhibition in pancreatic ductal adenocarcinoma (PDAC), promoting stromal remodeling and immunosuppression. Priming with oncogenic KRAS inhibitors and subsequent combination treatment with checkpoint immunotherapy significantly delays or prevents resistance. Long-term inhibition of oncogenic KRAS alone induces eventual therapy resistance in PDAC mouse models. CDK8 is upregulated in PDX tumors resistant to inhibitors selective for RAS(ON) and RASG12D(ON) protein states, Daraxonrasib and Zoldonrasib, respectively. CDK8 mediates KRAS inhibition resistance via reprogramming the tumor microenvironment and deficiency in immunological memory response. CDK8 confers resistance by re-initiating suppression of FAS expression and inducing secretion of the chemokine CXCL2. Targeting CDK8 overcomes resistance to KRASG12D inhibition. While tumors resistant to oncogenic KRAS inhibition also lose the ability to respond to anti-CTLA-4 immunotherapy, CDK8 inhibition in resistant tumors re-primes PDAC to anti-CTLA-4 immunotherapy efficacy. Priming with oncogenic KRAS inhibitors and subsequent combination treatment with checkpoint immunotherapy significantly delays or prevents resistance. Long-term inhibition of oncogenic KRAS alone induces eventual therapy resistance in PDAC mouse models. CDK8 is upregulated in PDX tumors resistant to inhibitors selective for RAS(ON) and RASG12D(ON) protein states, Daraxonrasib and Zoldonrasib, respectively. CDK8 mediates KRAS inhibition resistance via reprogramming the tumor microenvironment and deficiency in immunological memory response. CDK8 confers resistance by re-initiating suppression of FAS expression and inducing secretion of the chemokine CXCL2. Targeting CDK8 overcomes resistance to KRASG12D inhibition. While tumors resistant to oncogenic KRAS inhibition also lose the ability to respond to anti-CTLA-4 immunotherapy, CDK8 inhibition in resistant tumors re-primes PDAC to anti-CTLA-4 immunotherapy efficacy. Mediator complex kinase CDK8 is a novel common vulnerability for stromal resistance towards oncogenic RAS inhibition in pancreatic cancer.