CRISPR-Cas9 Screening Identifies Resistance Mechanisms to KRAS Inhibition in Pancreatic Cancer.

[UNLABELLED] KRAS inhibitors (KRASi) targeting various KRAS mutations have entered clinical trials for pancreatic cancer. Despite promising preliminary clinical responses, most patients relapse due to intrinsic or acquired resistance. Thus, combination treatments are essential to extend the efficacy of KRAS-targeted therapies. To further determine the genetic mechanisms of KRASi resistance, we performed KRASi-anchored CRISPR-Cas9 loss-of-function screens in KRASG12D-, KRASG12C-, KRASG12R-, and KRASQ61H-mutant pancreatic ductal adenocarcinoma (PDAC) cell lines, using six KRASi, to identify genes that modulate sensitivity to KRAS inhibition. Several hits from the screens, including EGFR, CK2, p110α, p110γ, and YAP, were validated by combining targeted inhibitors with KRASi. KRASQ61H-mutant PDAC cell lines were intrinsically less dependent on KRAS for survival than other KRAS mutational subtypes. Furthermore, the EGFR inhibitor erlotinib synergized with the RAS(ON) multiselective inhibitor RMC-7977 in KRASQ61H-mutant PDAC cell lines and in cell lines with highly active EGFR by mitigating ERK rebound activity. KRASi-resistant cell lines featured sustained ERK/MAPK dependence despite decreased ERK activity. Together, these findings enhance the understanding of intrinsic and acquired resistance to KRASi and identify therapeutic vulnerabilities that can potentially be exploited for KRASi combination therapies in patients with pancreatic cancer.

[SIGNIFICANCE] A comprehensive assessment of genetic modulators of KRAS inhibitor sensitivity identifies combination approaches to increase the efficacy of KRAS inhibitors and demonstrates the limited response of KRASQ61H-mutant cancer cells to KRAS inhibition.