Abstract 5879: Role of the inner mitochondrial membrane protein (Mic60) in MAPKi-resistant melanoma

Abstract Introduction: Metastatic melanoma is one of the most aggressive cancers, despite recent improvements in therapy. The rising melanoma incidence and mortality, along with its high propensity for metastasis highlights the urgency to find more effective therapeutic targets. The efficacy of targeted MAPK signaling pathway inhibitors (MAPKi) in metastatic melanoma therapy is limited by the development of resistance mechanisms that result in disease relapse. This situation necessitates alternative treatments for melanoma patients who develop resistance to targeted therapy. We have recently found out that there exists a group of human tumors that express lower levels of Mic60, a mitochondrial structural protein also known as mitofilin or inner membrane mitochondrial protein (IMMT). In a model of prostate cancer, we showed that Mic60-low tumors have lower mitochondrial fitness, but increased cell motility, invasion, and propensity to metastasize. However, a potential differential expression of Mic60 in melanoma has not been investigated and whether reduced mitochondrial fitness in Mic60-low tumors can expose new therapeutic vulnerabilities in combination with targeted therapies has not been determined. Experimental Procedures: We analyzed melanoma-specific TMA for differential expression of Mic60 in tumor vs. adjacent normal tissue by IHC. Differential mRNA expression levels were examined by single-cell RNA-Seq and quantified by bioinformatics analysis. Differential therapeutic vulnerabilities of Mic60-low melanoma cell lines to mitochondrial-targeted small molecule Hsp90 inhibitor, Gamitrinib, were assessed for cell death induction and mitochondrial dysfunction. Results: We identified subsets of melanoma patients with constitutively reduced or outright undetectable expression of Mic60, in vivo. By single-cell RNA-Seq, Mic60-low melanomas were characterized by reduced oxidative phosphorylation and decreased ATP production, slower cell cycle progression but paradoxically increased cell motility and invasion. Loss of Mic60 exposed new, actionable therapeutic vulnerabilities, and the combination of Gamitrinib plus MAPKi potently induced mitochondrial cell death in MAPKi-resistant melanoma cell lines. Conclusion: Mic60 is heterogeneously expressed and often reduced in melanoma. Although this is associated with increased cell invasion and metastatic propensity, the combination of Gamitrinib plus MAPKi restored mitochondrial cell death in therapy-resistant, Mic60-low melanoma cells. Citation Format: Jagadish C. Ghosh, Segundo Del Aguila, Haiyin Li, Jessie Villanueva, Dario C. Altieri. Role of the inner mitochondrial membrane protein (Mic60) in MAPKi-resistant melanoma [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(6_Suppl):Abstract nr 5879.