Overcoming adaptive resistance to KRASG12D blockade in pancreatic cancer through vertical pathway inhibition.

[PURPOSE] Oncogenic KRAS mutations are present in >90% of pancreatic ductal adenocarcinoma (PDAC) with KRASG12D being the most common. Mutant-selective KRASG12D inhibitors (KRASiG12D) have demonstrated promising initial clinical activity in KRASG12D-mutant PDAC. However, adaptive resistance to KRASi constrains efficacy in some tumor types, such as colorectal cancer, where EGFR-mediated RAS-MAPK pathway reactivation can be targeted toimprove response. Some studies have suggested a similar role for EGFR in PDAC, but the mechanisms of adaptive resistance to KRAS inhibition are unclear.

[EXPERIMENTAL DESIGN] Mechanisms of adaptive resistance to KRASiG12D were investigated in a panel of KRASG12D-mutant PDAC models.

[RESULTS] We observed RTK-driven adaptive reactivation of RAS pathway signaling following KRASiG12D in PDAC models. EGFR was a primary driver of adaptive RAS-MAPK reactivation in some models, but limited to those with epithelial differentiation. Conversely, adaptive RAS MAPK reactivation in models with mesenchymal differentiation was primarily driven by FGFR signaling. In clinical PDAC specimens from TCGA, EGFR and ERBB3 expression was highly correlated with expression of epithelial markers, while expression of FGFR1 and mesenchymal markers were correlated. Notably, a RAS(ON) multi-selective inhibitor, which inhibits both wild-type and mutant RAS, abrogated RAS-MAPK reactivation in combination with KRASi in both epithelial and mesenchymal models and led to more consistent antitumor activity compared to combinations of KRASi and EGFR blockade.

[CONCLUSIONS] In PDAC, adaptive RAS-MAPK reactivation following KRASG12D inhibition can be mediated by different RTKs and influenced by cell state. Combinations of mutant-selective KRASi and RAS(ON) multi-selective inhibitors may represent a promising universal strategy to surmount adaptive resistance in PDAC patients.