PHI-501, a dual inhibitor of RAF and DDR1/2, overcomes MAPK drug resistance in Melanoma

Melanoma, an aggressive skin cancer caused by BRAF or NRAS mutations, is characterized by the hyperactivation of the MAPK pathway. Despite the initial clinical success of RAF and MEK inhibitors in BRAF V600E-mutant melanoma, resistance mechanisms, including MAPK pathway reactivation, compromise their efficacy. This study investigated PHI-501, a next-generation pan-RAF/DDR dual inhibitor, as a potential strategy for overcoming this resistance. The anti-proliferative activity of PHI-501 was evaluated in parental and acquired drug-resistant melanoma cell lines and compared with clinically relevant RAF inhibitors. Mechanistic studies included analyses of ERK, AKT, and DDR1/2 phosphorylation, as well as transcriptomic profiling of resistance-associated pathways. In vivo efficacy was assessed using xenograft models of SK-MEL-3 melanoma cells with acquired resistance to dabrafenib alone or to combined dabrafenib plus trametinib treatment. PHI-501 exhibited greater cytotoxic activity than conventional RAF inhibitors in acquired drug-resistant melanoma cells. PHI-501 suppressed MAPK and PI3K/AKT signaling, as evidenced by reduced phosphorylation of ERK, AKT, and DDR1/2. Transcriptomic profiling revealed coordinated downregulation of key resistance-associated signaling pathways. In xenograft models derived from melanoma cells resistant to RAF inhibitor monotherapy or combined RAF/MEK inhibition, PHI-501 significantly inhibited tumor growth. PHI-501 exhibited potent anti-tumor activity in models of drug-resistant melanoma through dual targeting of RAF and DDR1/2. These findings support further preclinical evaluation of PHI-501 for MAPK inhibitor–resistant melanoma.