Phase II study investigating the efficacy and safety of glesatinib (MGCD265) in patients with advanced NSCLC containing MET activating alterations.

OBJECTIVES: Dysregulated signaling by mesenchymal epithelial transition factor (MET) and heightened AXL activation are implicated in the pathogenesis of non-small cell lung cancer (NSCLC). Glesatinib (MGCD265) is an investigational, oral inhibitor of MET and AXL. MATERIALS AND METHODS: This open-label, Phase II study investigated glesatinib (free-base suspension [FBS] capsule 1050 mg BID or spray-dried dispersion [SDD] tablet 750 mg BID) in patients with advanced, previously treated NSCLC across four cohorts grouped according to presence of MET activating mutations or amplification in tumor or ctDNA. The primary endpoint was objective response rate (ORR). RESULTS: Sixty-eight patients were enrolled: n = 28 and n = 8 with MET exon 14 skipping mutations in tumor tissue and ctDNA, respectively, and n = 20 and n = 12 with MET gene amplification in tumor tissue and ctDNA, respectively. Overall, ORR was 11.8 %, median progression-free survival was 4.0 months, and median overall survival was 7.0 months. Among patients with MET activating mutations, ORR was 10.7 % with tumor testing and 25.0 % with ctDNA testing. For MET amplification, responses were observed only in patients enrolled by tumor testing (ORR 15.0 %). Diarrhea (82.4 %), nausea (50.0 %), increased alanine aminotransferase (41.2 %), fatigue (38.2 %), and increased aspartate aminotransferase (36.8 %) were the most frequent adverse events assessed as related to study medication. Glesatinib exposure was similar with the SDD tablet and FBS capsule formulations. The study was terminated early by the sponsor due to modest clinical activity. CONCLUSIONS: Glesatinib had an acceptable safety profile in patients with advanced, pre-treated NSCLC with MET activating alterations. Modest clinical activity was observed, which likely reflects suboptimal drug bioavailability suggested by previously reported Phase I data, and pharmacodynamic findings of lower than anticipated increases in circulating soluble shed MET ectodomain (s-MET).

Discovery of Five SOS2 Fragment Hits with Binding Modes Determined by SOS2 X-Ray Cocrystallography.

SOS1 and SOS2 are guanine nucleotide exchange factors that mediate RTK-stimulated RAS activation. Selective SOS1:KRAS PPI inhibitors are currently under clinical investigation, whereas there are no reports to date of SOS2:KRAS PPI inhibitors. SOS2 activity is implicated in MAPK rebound when divergent SOS1 mutant cell lines are treated with the SOS1 inhibitor BI-3406; therefore, SOS2:KRAS inhibitors are of therapeutic interest. In this report, we detail a fragment-based screening strategy to identify X-ray cocrystal structures of five diverse fragment hits bound to SOS2.

A classical epithelial state drives acute resistance to KRAS inhibition in pancreas cancer.

Intra-tumoral heterogeneity in pancreatic ductal adenocarcinoma (PDAC) is characterized by a balance between basal and classical epithelial cancer cell states, with basal dominance associating with chemoresistance and a dismal prognosis. Targeting oncogenic KRAS, the primary driver of pancreatic cancer, shows early promise in clinical trials but efficacy is limited by acquired resistance. Using genetically engineered mouse models and patient-derived xenografts, we find that basal PDAC cells are highly sensitive to KRAS inhibitors. Employing fluorescent and bioluminescent reporter systems, we longitudinally track cell-state dynamics in vivo and reveal a rapid, KRAS inhibitor-induced enrichment of the classical state. Lineage-tracing identifies these enriched classical PDAC cells to be a reservoir for disease relapse. Genetic ablation of the classical cell-state is synergistic with KRAS inhibition, providing a pre-clinical proof-of-concept for this therapeutic strategy. Our findings motivate combining classical-state directed therapies with KRAS inhibitors to deepen responses and counteract resistance in pancreatic cancer.

Adeno-to-squamous transition drives resistance to KRAS inhibition in LKB1 mutant lung cancer.

KRASG12C inhibitors (adagrasib and sotorasib) have shown clinical promise in targeting KRASG12C-mutated lung cancers; however, most patients eventually develop resistance. In lung patients with adenocarcinoma with KRASG12C and STK11/LKB1 co-mutations, we find an enrichment of the squamous cell carcinoma gene signature in pre-treatment biopsies correlates with a poor response to adagrasib. Studies of Lkb1-deficient KRASG12C and KrasG12D lung cancer mouse models and organoids treated with KRAS inhibitors reveal tumors invoke a lineage plasticity program, adeno-to-squamous transition (AST), that enables resistance to KRAS inhibition. Transcriptomic and epigenomic analyses reveal ΔNp63 drives AST and modulates response to KRAS inhibition. We identify an intermediate high-plastic cell state marked by expression of an AST plasticity signature and Krt6a. Notably, expression of the AST plasticity signature and KRT6A at baseline correlates with poor adagrasib responses. These data indicate the role of AST in KRAS inhibitor resistance and provide predictive biomarkers for KRAS-targeted therapies in lung cancer.

Discovery of Pyridopyrimidinones that Selectively Inhibit the H1047R PI3Kα Mutant Protein.

The H1047R mutation of PIK3CA is highly prevalent in breast cancers and other solid tumors. Selectively targeting PI3KαH1047R over PI3KαWT is crucial due to the role that PI3KαWT plays in normal cellular processes, including glucose homeostasis. Currently, only one PI3KαH1047R-selective inhibitor has progressed into clinical trials, while three pan mutant (H1047R, H1047L, H1047Y, E542K, and E545K) selective PI3Kα inhibitors have also reached the clinical stage. Herein, we report the design and discovery of a series of pyridopyrimidinones that inhibit PI3KαH1047R with high selectivity over PI3KαWT, resulting in the discovery of compound 17. When dosed in the HCC1954 tumor model in mice, 17 provided tumor regressions and a clear pharmacodynamic response. X-ray cocrystal structures from several PI3Kα inhibitors were obtained, revealing three distinct binding modes within PI3KαH1047R including a previously reported cryptic pocket in the C-terminus of the kinase domain wherein we observe a ligand-induced interaction with Arg1047.

The SOS1 Inhibitor MRTX0902 Blocks KRAS Activation and Demonstrates Antitumor Activity in Cancers Dependent on KRAS Nucleotide Loading.

KRAS is the most frequently mutated oncogene in human cancer and facilitates uncontrolled growth through hyperactivation of the receptor tyrosine kinase (RTK)/mitogen-activated protein kinase (MAPK) pathway. The Son of Sevenless homolog 1 (SOS1) protein functions as a guanine nucleotide exchange factor (GEF) for the RAS subfamily of small GTPases and represents a druggable target in the pathway. Using a structure-based drug discovery approach, MRTX0902 was identified as a selective and potent SOS1 inhibitor that disrupts the KRAS:SOS1 protein-protein interaction to prevent SOS1-mediated nucleotide exchange on KRAS and translates into an anti-proliferative effect in cancer cell lines with genetic alterations of the KRAS-MAPK pathway. MRTX0902 augmented the antitumor activity of the KRAS G12C inhibitor adagrasib when dosed in combination in eight out of 12 KRAS G12C-mutant human non-small cell lung cancer and colorectal cancer xenograft models. Pharmacogenomic profiling in preclinical models identified cell cycle genes and the SOS2 homolog as genetic co-dependencies and implicated tumor suppressor genes (NF1 and PTEN) in resistance following combination treatment. Lastly, combined vertical inhibition of RTK/MAPK pathway signaling by MRTX0902 with inhibitors of EGFR or RAF/MEK led to greater downregulation of pathway signaling and improved antitumor responses in KRAS-MAPK pathway-mutant models. These studies demonstrate the potential clinical application of dual inhibition of SOS1 and KRAS G12C and additional SOS1 combination strategies that will aide in the understanding of SOS1 and RTK/MAPK biology in targeted cancer therapy.

Defining the KRAS- and ERK-dependent transcriptome in KRAS-mutant cancers.

How the KRAS oncogene drives cancer growth remains poorly understood. Therefore, we established a systemwide portrait of KRAS- and extracellular signal-regulated kinase (ERK)-dependent gene transcription in KRAS-mutant cancer to delineate the molecular mechanisms of growth and of inhibitor resistance. Unexpectedly, our KRAS-dependent gene signature diverges substantially from the frequently cited Hallmark KRAS signaling gene signature, is driven predominantly through the ERK mitogen-activated protein kinase (MAPK) cascade, and accurately reflects KRAS- and ERK-regulated gene transcription in KRAS-mutant cancer patients. Integration with our ERK-regulated phospho- and total proteome highlights ERK deregulation of the anaphase promoting complex/cyclosome (APC/C) and other components of the cell cycle machinery as key processes that drive pancreatic ductal adenocarcinoma (PDAC) growth. Our findings elucidate mechanistically the critical role of ERK in driving KRAS-mutant tumor growth and in resistance to KRAS-ERK MAPK targeted therapies.

Mechanisms of resistance to oncogenic KRAS inhibition in pancreatic cancer.

KRAS inhibitors demonstrate clinical efficacy in pancreatic ductal adenocarcinoma (PDAC); however, resistance is common. Among patients with KRASG12C-mutant PDAC treated with adagrasib or sotorasib, mutations in PIK3CA and KRAS, and amplifications of KRASG12C, MYC, MET, EGFR, and CDK6 emerged at acquired resistance. In PDAC cell lines and organoid models treated with the KRASG12D inhibitor MRTX1133, epithelial-to-mesenchymal transition and PI3K-AKT-mTOR signaling associate with resistance to therapy. MRTX1133 treatment of the KrasLSL-G12D/+;Trp53LSL-R172H/+;p48-Cre (KPC) mouse model yielded deep tumor regressions, but drug resistance ultimately emerged, accompanied by amplifications of Kras, Yap1, Myc, and Cdk6/Abcb1a/b, and co-evolution of drug-resistant transcriptional programs. Moreover, in KPC and PDX models, mesenchymal and basal-like cell states displayed increased response to KRAS inhibition compared to the classical state. Combination treatment with KRASG12D inhibition and chemotherapy significantly improved tumor control in PDAC mouse models. Collectively, these data elucidate co-evolving resistance mechanisms to KRAS inhibition and support multiple combination therapy strategies.