Metastatic Melanoma Patient-Derived Xenografts Respond to MDM2 Inhibition as a Single Agent or in Combination with BRAF/MEK Inhibition.

Purpose: Over 60% of patients with melanoma respond to immune checkpoint inhibitor (ICI) therapy, but many subsequently progress on these therapies. Second-line targeted therapy is based on mutation status, but no available agents are available for , and mutations. Over 70% of melanoma tumors have activation of the MAPK pathway due to or mutations, while loss or mutation of occurs in approximately 40% of melanomas, resulting in unregulated MDM2-mediated ubiquitination and degradation of p53. Here, we investigated the therapeutic efficacy of over-riding MDM2-mediated degradation of p53 in melanoma with an MDM2 inhibitor that interrupts MDM2 ubiquitination of p53, treating tumor-bearing mice with the MDM2 inhibitor alone or combined with MAPK-targeted therapy.

Experimental Design: To characterize the ability of the MDM2 antagonist, KRT-232, to inhibit tumor growth, we established patient-derived xenografts (PDX) from 15 patients with melanoma. Mice were treated with KRT-232 or a combination with BRAF and/or MEK inhibitors. Tumor growth, gene mutation status, as well as protein and protein-phosphoprotein changes, were analyzed.

Results: One-hundred percent of the 15 PDX tumors exhibited significant growth inhibition either in response to KRT-232 alone or in combination with BRAF and/or MEK inhibitors. Only tumors responded to KRT-232 treatment alone while PDXs exhibited a synergistic response to the combination of KRT-232 and BRAF/MEK inhibitors.

Conclusions: KRT-232 is an effective therapy for the treatment of either or PAN melanomas. In combination with BRAF and/or MEK inhibitors, KRT-232 may be an effective treatment strategy for BRAF-mutant tumors.