Selective USP7 Inhibition Synergizes with MEK1/2 Inhibitor to Enhance Immune Responses and Potentiate Anti-PD-1 Therapy in NRAS-Mutant Melanoma

Targeted therapy for NRAS-mutant melanoma remains an unmet clinical need. We found that inhibiting USP7 with the selective ubiquitin-specific protease 7 inhibitor (USP7i) FT671 inhibited cell proliferation in NRAS-mutant melanoma cell lines. In addition, we identified and validated that knockout of TP53BP1, TP53, or CDKN1A conferred resistance to FT671, suggesting that the activation of a functional p53 signaling pathway is essential for the efficacy of USP7i. In Nras-mutant melanoma isograft models, FT671 treatment delayed tumor growth. Moreover, the combinatorial treatment with FT671 and MAPK/(extracellular signal-regulated kinase) kinase 1/2 inhibitor was synergistic and induced pyroptosis in vitro. In immunocompetent mice, the combined treatment profoundly suppressed tumor growth, prolonged survival, and enhanced intratumoral immune cell infiltration, particularly increasing the ratios of CD8(+) T cells and mature dendritic cells, indicative of activated antitumor immunity. Notably, the triple combination of USP7i, MAPK/(extracellular signal-regulated kinase) kinase 1/2 inhibitor, and anti-PD-1 antibody resulted in durable tumor regression, with effects persisting beyond 80 days after treatment cessation. These findings establish USP7i + MAPK (extracellular signal-regulated kinase) kinase 1/2 inhibitor as a promising strategy for targeting NRAS, an 'undruggable' mutation in melanoma, and provide a strong rationale for the clinical development of USP7i plus MAPK (extracellular signal-regulated kinase) kinase 1/2 inhibitor as an adjuvant therapy to enhance anti-PD-1 immunotherapy in patients with NRAS-mutant melanoma.