Landscape of Clinical Resistance Mechanisms to FGFR Inhibitors in FGFR2-Altered Cholangiocarcinoma.

PURPOSE: FGFR inhibitors are effective in FGFR2-altered cholangiocarcinoma, leading to approval of reversible FGFR inhibitors, pemigatinib and infigratinib, and an irreversible inhibitor, futibatinib. However, acquired resistance develops, limiting clinical benefit. Some mechanisms of resistance have been reported, including secondary FGFR2 kinase domain mutations. Here, we sought to establish the landscape of acquired resistance to FGFR inhibition and to validate findings in model systems. EXPERIMENTAL DESIGN: We examined the spectrum of acquired resistance mechanisms detected in circulating tumor DNA or tumor tissue upon disease progression following FGFR inhibitor therapy in 82 FGFR2-altered cholangiocarcinoma patients from 12 published reports. Functional studies of candidate resistance alterations were performed. RESULTS: Overall, 49 of 82 patients (60%) had one or more detectable secondary FGFR2 kinase domain mutations upon acquired resistance. N550 molecular brake and V565 gatekeeper mutations were most common, representing 63% and 47% of all FGFR2 kinase domain mutations, respectively. Functional studies showed different inhibitors displayed unique activity profiles against FGFR2 mutations. Interestingly, disruption of the cysteine residue covalently bound by futibatinib (FGFR2 C492) was rare, observed in 1 of 42 patients treated with this drug. FGFR2 C492 mutations were insensitive to inhibition by futibatinib but showed reduced signaling activity, potentially explaining their low frequency. CONCLUSIONS: These data support secondary FGFR2 kinase domain mutations as the primary mode of acquired resistance to FGFR inhibitors, most commonly N550 and V565 mutations. Thus, development of combination strategies and next-generation FGFR inhibitors targeting the full spectrum of FGFR2 resistance mutations will be critical.

Phase I/II Study of Combined BCL-xL and MEK Inhibition with Navitoclax and Trametinib in KRAS or NRAS Mutant Advanced Solid Tumors.

PURPOSE: MEK inhibitors (MEKi) lack monotherapy efficacy in most RAS-mutant cancers. BCL-xL is an anti-apoptotic protein identified by a synthetic lethal shRNA screen as a key suppressor of apoptotic response to MEKi. PATIENTS AND METHODS: We conducted a dose escalation study (NCT02079740) of the BCL-xL inhibitor navitoclax and MEKi trametinib in patients with RAS-mutant tumors with expansion cohorts for: pancreatic, gynecologic (GYN), non-small cell lung cancer (NSCLC), and other cancers harboring KRAS/NRAS mutations. Paired pretreatment and day 15 tumor biopsies and serial cell-free (cf)DNA were analyzed. RESULTS: A total of 91 patients initiated treatment, with 38 in dose escalation. Fifty-eight percent had ≥3 prior therapies. A total of 15 patients (17%) had colorectal cancer, 19 (11%) pancreatic, 15 (17%) NSCLC, and 32 (35%) GYN cancers. The recommended phase II dose (RP2D) was established as trametinib 2 mg daily days 1 to 14 and navitoclax 250 mg daily days 1 to 28 of each cycle. Most common adverse events included diarrhea, thrombocytopenia, increased AST/ALT, and acneiform rash. At RP2D, 8 of 49 (16%) evaluable patients achieved partial response (PR). Disease-specific differences in efficacy were noted. In patients with GYN at the RP2D, 7 of 21 (33%) achieved a PR and median duration of response 8.2 months. No PRs occurred in patients with colorectal cancer, NSCLC, or pancreatic cancer. MAPK pathway inhibition was observed in on-treatment tumor biopsies. Reductions in KRAS/NRAS mutation levels in cfDNA correlated with clinical benefit. CONCLUSIONS: Navitoclax in combination with trametinib was tolerable. Durable clinical responses were observed in patients with RAS-mutant GYN cancers, warranting further evaluation in this population.

Combined PD-1, BRAF and MEK inhibition in BRAFV600E colorectal cancer: a phase 2 trial.

While BRAF inhibitor combinations with EGFR and/or MEK inhibitors have improved clinical efficacy in BRAFV600E colorectal cancer (CRC), response rates remain low and lack durability. Preclinical data suggest that BRAF/MAPK pathway inhibition may augment the tumor immune response. We performed a proof-of-concept single-arm phase 2 clinical trial of combined PD-1, BRAF and MEK inhibition with sparatlizumab (PDR001), dabrafenib and trametinib in 37 patients with BRAFV600E CRC. The primary end point was overall response rate, and the secondary end points were progression-free survival, disease control rate, duration of response and overall survival. The study met its primary end point with a confirmed response rate (24.3% in all patients; 25% in microsatellite stable patients) and durability that were favorable relative to historical controls of BRAF-targeted combinations alone. Single-cell RNA sequencing of 23 paired pretreatment and day 15 on-treatment tumor biopsies revealed greater induction of tumor cell-intrinsic immune programs and more complete MAPK inhibition in patients with better clinical outcome. Immune program induction in matched patient-derived organoids correlated with the degree of MAPK inhibition. These data suggest a potential tumor cell-intrinsic mechanism of cooperativity between MAPK inhibition and immune response, warranting further clinical evaluation of optimized targeted and immune combinations in CRC. ClinicalTrials.gov registration: NCT03668431.

Clinical Acquired Resistance to KRASG12C Inhibition through a Novel KRAS Switch-II Pocket Mutation and Polyclonal Alterations Converging on RAS-MAPK Reactivation.

Mutant-selective KRASG12C 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 KRASG12C inhibitors remain undetermined. To begin to define the mechanistic spectrum of acquired resistance, we describe a patient with KRAS G12C NSCLC 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 patient-derived KRAS G12C cancer models. Interestingly, a novel, functionally distinct tricomplex KRASG12C active-state inhibitor RM-018 retained the ability to bind and inhibit KRASG12C/Y96D and could overcome resistance. SIGNIFICANCE: In one of the first reports of clinical acquired resistance to KRASG12C 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 KRASG12C inhibitor.See related commentary by Pinnelli and Trusolino, p. 1874.This article is highlighted in the In This Issue feature, p. 1861.