Abstract 559: Targeting MCL1 or SOS1 can overcome lenvatinib resistance in HCC

Lenvatinib (LEN), a front-line treatment for advanced liver cancer, has a short benefit of 13.6 months median overall survival. Understanding how resistance emerges may provide insight into LEN-combined therapies that might boost its clinical efficacy. LEN-sensitive liver cell lines were conditioned with LEN in culture to establish this study's three LEN-resistant (LR) models. All LR models exhibited a stable right shift in the LEN dose-response curve. The LR models were cross-resistant to other FGFR inhibitors and expressed markers linked to cancer aggressiveness. Pro-apoptosis signals, induced by LEN treatment in Hep3B parental cells, were no longer induced in Hep3B LR cells. Compared to parental cells, Hep3B LR and JHH4 LR cells were no longer Annexin-V positive with LEN treatment, supporting their ability to evade apoptosis. A validated HTS method, using Cell-Titer Glo to measure the cell viability of Hep3B and JHH4 models tested across 440 small molecule inhibitors and LEN at a single concentration, identified nine synergistic combinations. Vetting these leads using a multidose titration assay showed synergy with LEN across all three LR models for two drugs: MRTX0902 targeting SOS1, an intracellular RTK signaling protein, and S63845 targeting MCL1, an anti-apoptosis protein. Multiple RTKs were upregulated in the LR models, thus making SOS1 an attractive target for blocking convergent signals. LEN treatment of parental models increased the expression of pAKT, pERK, and MCL1. LEN with S63845 in Hep3B parental cells reduced pAKT, pERK, and MCL1 and increased γ-H2AX. LEN with S63845 induced more apoptosis than either single agents in parental models or Hep3B LR cells. Enhanced apoptosis was not observed using MRTX0902 alone or with LEN. MRTX0902 alone reduced pAKT and pERK in Hep3B parental cells and was able to offset LEN's accumulation of these proteins in combination. We performed RNA-seq analysis of our model systems at baseline and with LEN treatment. LEN-treated parental cells exhibited a statistically significant increase in MCL1 and SOS1 transcripts. GSEA analysis of LEN-treated parental cells revealed positive MAPK pathway enrichment consistent with SOS1 function. It also identified negative enrichment of genes involved in DNA replication and G2M checkpoint, a p53-regulated process. This novel finding suggested that LEN induces genotoxic stress. Indeed, immunofluorescent foci staining of γ-H2AX increased with LEN treatment of parental Hep3B cells and remained elevated in Hep3B LR cells. Therefore, SOS1 and MCL1 may have a role in overcoming genotoxic stress induced by LEN. Overall, our research has generated multiple LR models and used them to identify resistance components. We also showed that targeting these components (SOS1 and MCL1) synergizes with LEN and inhibits cancer growth. These findings may become relevant patient treatments to extend patient survival against liver cancer. Citation Format: Kevin Chau, Martina S. McDermott, Dennis J. Slamon. Targeting MCL1 or SOS1 can overcome lenvatinib resistance in HCC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 559.