Mutant-selective KRAS G12C inhibitors, such as MRTX849 (adagrasib) and AMG 510 (sotorasib), have demonstrated efficacy in KRAS G12C -mutant cancers including non-small cell lung cancer (NSCLC). However, mechanisms underlying clinical acquired resistance to KRAS G12C inhibitors remain undetermined. To begin to define the mechanistic spectrum of acquired resistance, we describe a KRAS G12C NSCLC patient who developed polyclonal acquired resistance to MRTX849 with the emergence of 10 heterogeneous resistance alterations in serial cell-free DNA spanning four genes (KRAS, NRAS, BRAF, MAP2K1), all of which converge to reactivate RAS-MAPK signaling. Notably, a novel KRAS Y96D mutation affecting the switch-II pocket, to which MRTX849 and other inactive-state inhibitors bind, was identified that interferes with key protein-drug interactions and confers resistance to these inhibitors in engineered and patientderived KRAS G12C cancer models. Interestingly, a novel, functionally distinct tri-complex KRAS G12C active-state inhibitor RM-018 retained the ability to bind and inhibit KRAS G12C/Y96D and could overcome resistance. STATEMENT OF SIGNIFICANCEIn one of the first reports of clinical acquired resistance to KRAS G12C inhibitors, our data suggest polyclonal RAS-MAPK reactivation as a central resistance mechanism. We also identify a novel KRAS switch-II pocket mutation that impairs binding and drives resistance to inactive-state inhibitors but is surmountable by a functionally-distinct KRAS G12C inhibitor.Research.

ATP-competitive fi broblast growth factor receptor (FGFR) kinase inhibitors, including BGJ398 and Debio 1347, show antitumor activity in patients with intrahepatic cholangiocarcinoma (ICC) harboring activating FGFR2 gene fusions. Unfortunately, acquired resistance develops and is often associated with the emergence of secondary FGFR2 kinase domain mutations. Here, we report that the irreversible pan-FGFR inhibitor TAS-120 demonstrated effi cacy in 4 patients with FGFR 2 fusion-positive ICC who developed resistance to BGJ398 or Debio 1347. Examination of serial biopsies, circulating tumor DNA (ctDNA), and patient-derived ICC cells revealed that TAS-120 was active against multiple FGFR2 mutations conferring resistance to BGJ398 or Debio 1347. Functional assessment and modeling the clonal outgrowth of individual resistance mutations from polyclonal cell pools mirrored the resistance profi les observed clinically for each inhibitor. Our fi ndings suggest that strategic sequencing of FGFR inhibitors, guided by serial biopsy and ctDNA analysis, may prolong the duration of benefi t from FGFR inhibition in patients with FGFR2 fusion-positive ICC. SIGNIFICANCE: ATP-competitive FGFR inhibitors (BGJ398, Debio 1347) show effi cacy in FGFR2-altered ICC; however, acquired FGFR2 kinase domain mutations cause drug resistance and tumor progression. We demonstrate that the irreversible FGFR inhibitor TAS-120 provides clinical benefi t in patients with resistance to BGJ398 or Debio 1347 and overcomes several FGFR2 mutations in ICC models.

Statement of Translational RelevanceDetection of persistent circulating tumor DNA (ctDNA) after curative-intent surgery to identify patients with minimal residual disease (MRD) who will ultimately recur has emerged as a potentially transformative approach in oncology. Early identification of patients with MRD through ctDNA detection could identify patients in whom additional therapy might salvage the chance of cure. To date, ctDNA MRD assays have employed a tumor-informed approach, requiring initial sequencing of tumor tissue to guide ctDNA detection, and thus cannot be used when a patient has insufficient tumor tissue for analysis. Here, we evaluate the first tumoruninformed, plasma-only ctDNA assay integrating genomic and epigenomic signatures to detect MRD in post-operative colorectal cancer (CRC) patients, without requiring parallel tumor sequencing, which produced favorable sensitivity and specificity, comparable to tumor-informed approaches. These data highlight the feasibility and potential clinical utility of plasma-only ctDNA-guided MRD detection.