Primary/intrinsic and treatment-induced acquired resistance limit the initial response rate to and long-term efficacy of direct inhibitors of the KRASG12C mutant in cancer. To identify potential mechanisms of resistance, we applied a CRISPR/Cas9 loss-of-function screen and observed loss of multiple components of the Hippo tumor suppressor pathway, which acts to suppress YAP1/TAZ-regulated gene transcription. YAP1/TAZ activation impaired the antiproliferative and proapoptotic effects of KRASG12C inhibitor (G12Ci) treatment in KRASG12C-mutant cancer cell lines. Conversely, genetic suppression of YAP1/WWTR1 (TAZ) enhanced G12Ci sensitivity. YAP1/TAZ activity overcame KRAS dependency through two distinct TEAD transcription factor–dependent mechanisms, which phenocopy KRAS effector signaling. First, TEAD stimulated ERK-independent transcription of genes normally regulated by ERK (BIRC5, CDC20, ECT2, FOSL1, and MYC) to promote progression through the cell cycle. Second, TEAD caused activation of PI3K–AKT–mTOR signaling to overcome apoptosis. G12Ci treatment-induced acquired resistance was also caused by YAP1/TAZ-TEAD activation. Accordingly, concurrent treatment with pharmacologic inhibitors of TEAD synergistically enhanced KRASG12C inhibitor antitumor activity in vitro and prolonged tumor suppression in vivo. In summary, these observations reveal YAP1/TAZ-TEAD signaling as a crucial driver of primary and acquired resistance to KRAS inhibition and support the use of TEAD inhibitors to enhance the antitumor efficacy of KRAS-targeted therapies. Significance: YAP1/TAZ-TEAD activation compensates for loss of KRAS effector signaling, establishing a mechanistic basis for concurrent inhibition of TEAD to enhance the efficacy of KRASG12C-selective inhibitor treatment of KRASG12C-mutant cancers. See related commentary by Johnson and Haigis, p. 4005

The aggressive nature of pancreatic ductal adenocarcinoma (PDAC) mandates the development of improved therapies. As KRAS mutations are found in 95% of PDAC and are critical for tumor maintenance, one promising strategy involves exploiting KRAS-dependent metabolic perturbations. The macrometabolic process of autophagy is upregulated in KRAS-mutant PDAC, and PDAC growth is reliant on autophagy. However, inhibition of autophagy as monotherapy using the lysosomal inhibitor hydroxychloroquine (HCQ) has shown limited clinical efficacy. To identify strategies that can improve PDAC sensitivity to HCQ, we applied a CRISPR-Cas9 loss-of-function screen and found that a top sensitizer was the receptor tyrosine kinase (RTK) insulin-like growth factor 1 receptor (IGF1R). Additionally, reverse phase protein array pathway activation mapping profiled the signaling pathways altered by chloroquine (CQ) treatment. Activating phosphorylation of RTKs, including IGF1R, was a common compensatory increase in response to CQ. Inhibition of IGF1R increased autophagic flux and sensitivity to CQ-mediated growth suppression both in vitro and in vivo. Cotargeting both IGF1R and pathways that antagonize autophagy, such as ERK–MAPK axis, was strongly synergistic. IGF1R and ERK inhibition converged on suppression of glycolysis, leading to enhanced dependence on autophagy. Accordingly, concurrent inhibition of IGF1R, ERK, and autophagy induced cytotoxicity in PDAC cell lines and decreased viability in human PDAC organoids. In conclusion, targeting IGF1R together with ERK enhances the effectiveness of autophagy inhibitors in PDAC. Significance: Compensatory upregulation of IGF1R and ERK–MAPK signaling limits the efficacy of autophagy inhibitors chloroquine and hydroxychloroquine, and their concurrent inhibition synergistically increases autophagy dependence and chloroquine sensitivity in pancreatic ductal adenocarcinoma.

Of the thousands of genes and substrates identified in KRAS-mutant signaling networks in pancreatic ductal adenocarcinoma (PDAC), more than 200 are transcription factors, implying extensive and complex transcriptional regulation. However, we observed that genetic suppression of the transcription factor MYC alone was sufficient to phenocopy the effect of KRAS suppression in signaling, growth, and metabolic processes in PDAC cells. We determined the gene transcription changes caused by acute suppression of MYC function in KRAS -mutant PDAC cell lines and performed dependency map and pathway analyses on the affected gene sets. The expression of 1685 genes was increased upon suppression of MYC, and this gene set may comprise the bulk of the MYC-regulated genes essential for PDAC growth. In contrast, the 1325 genes whose expression was inhibited may comprise a compensatory response to oncogenic stress, mediated in part by the GTPase RHO. MYC-dependent transcriptional activity was largely ERK dependent, and almost one-third of ERK-regulated genes were also regulated by MYC in PDAC cells. Furthermore, chemical proteomic profiling revealed MYC-regulated protein kinases that can be targeted therapeutically. Together, these data provide a molecular portrait of MYC-dependent signaling that encompasses potentially exploitable mechanisms for treating PDAC.

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.

Primary/intrinsic and treatment-induced acquired resistance limit the initial response rate to and long-term efficacy of direct inhibitors of the KRASG12C mutant in cancer. To identify potential mechanisms of resistance, we applied a CRISPR/Cas9 loss-of-function screen and observed loss of multiple components of the Hippo tumor suppressor pathway, which acts to suppress YAP1/TAZ-regulated gene transcription. YAP1/TAZ activation impaired the antiproliferative and proapoptotic effects of KRASG12C inhibitor (G12Ci) treatment in KRASG12C-mutant cancer cell lines. Conversely, genetic suppression of YAP1/WWTR1 (TAZ) enhanced G12Ci sensitivity. YAP1/TAZ activity overcame KRAS dependency through two distinct TEAD transcription factor–dependent mechanisms, which phenocopy KRAS effector signaling. First, TEAD stimulated ERK-independent transcription of genes normally regulated by ERK (BIRC5, CDC20, ECT2, FOSL1, and MYC) to promote progression through the cell cycle. Second, TEAD caused activation of PI3K–AKT–mTOR signaling to overcome apoptosis. G12Ci treatment-induced acquired resistance was also caused by YAP1/TAZ-TEAD activation. Accordingly, concurrent treatment with pharmacologic inhibitors of TEAD synergistically enhanced KRASG12C inhibitor antitumor activity in vitro and prolonged tumor suppression in vivo. In summary, these observations reveal YAP1/TAZ-TEAD signaling as a crucial driver of primary and acquired resistance to KRAS inhibition and support the use of TEAD inhibitors to enhance the antitumor efficacy of KRAS-targeted therapies.Significance:YAP1/TAZ-TEAD activation compensates for loss of KRAS effector signaling, establishing a mechanistic basis for concurrent inhibition of TEAD to enhance the efficacy of KRASG12C-selective inhibitor treatment of KRASG12C-mutant cancers.See related commentary by Johnson and Haigis, p. 4005

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.