Abstract 4666: HC-7366, a potent GCN2 kinase activator, augments osimertinib therapy to delay resistance in EGFR mutant NSCLC models

Abstract Despite the efficacy seen with EGFR tyrosine kinase inhibitors (TKIs) in the treatment of EGFR mutant NSCLC, the long-term prognosis remains unfavorable due to resistance. Osimertinib is used as the first- and second-line treatment for EGFR exon 19 deletion, L858R mutation, and acquired T790M mutation. Resistance is driven by both EGFR-dependent and independent events, such as gene amplification and upregulation of HIF1α. Metabolic events also drive resistance by increasing oxidative phosphorylation (OXPHOS) caused by osimertinib-induced glycolysis inhibition. HiberCell has developed HC-7366, a GCN2 activator currently being investigated in a Ph1 clinical trial in patients with solid tumors (NCT05121948). GCN2 activation by HC-7366 drives the integrated stress response (ISR) by inducing the expression of ATF4. This results in translation inhibition, cell cycle arrest, HIF1α suppression, and apoptosis in cancer cells. Our preclinical data suggest HC-7366 can reduce glycolysis, TCA cycle metabolites, and OXPHOS, thereby causing mitochondrial dysregulation. We hypothesized that combination of HC-7366 with osimertinib could reduce resistance by evading the adaptive resistance mechanisms. We treated the NCI-H1975 xenograft model with HC-7366, a clinically relevant dose of osimertinib, and the combination for 21 days and then followed for tumor regrowth. At day 21, the HC-7366 group showed efficacy with tumor growth inhibition (TGI) of 55%, while osimertinib resulted in tumor regression of 97% with 8/10 CRs and 2/10 PRs. The combination had tumor regression of 99% with 10/10 CRs. After treatment cessation for 74 days, tumors in the osimertinib group quickly regrew with 6/10 tumors progressing and 4/10 mice tumor-free. In contrast, the combination group had only 2/10 tumors regrow with 8/10 mice tumor-free. In an EGFR-dependent resistance model NCI-H1975 (EGFR C797S), combination achieved 63% TGI versus 31% with osimertinib. In an EGFR-independent resistant PDX with EGFR exon 19 deletion, combination benefit was seen at 70% TGI compared to 40% for osimertinib, while a PDX with EGFR L858R showed a trend for combination benefit. To understand the mechanism of action, we examined osimertinib-resistance pathways to determine how GCN2 activation could affect them. Combination with HC-7366 reduced the expression of short-lived proteins involved in osimertinib resistance, including HIF1α, MET, cyclin D1, and CDK4. Combination decreased TIM17A and TIM23, proteins essential for mitochondrial protein translocation, potentially causing mitochondrial dysfunction. We found a proliferation reduction by Ki67 and an increase in apoptotic proteins CHOP, PUMA, and cleaved caspase 3. Taken together, these data reveal that combination of HC-7366 and osimertinib, and potentially other EGFR TKIs, may be an effective treatment strategy at targeting adaptive resistance mechanisms. Citation Format: Crissy Dudgeon, Sho Fujisawa, Olivia Funk, Feven Tameire, Takashi O. Kangas, Weiyu Zhang, Eric S. Lightcap, David Surguladze, Nandita Bose. HC-7366, a potent GCN2 kinase activator, augments osimertinib therapy to delay resistance in EGFR mutant NSCLC models abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 4666.