Combinatorial treatment with PARP and MAPK inhibitors overcomes phenotype switch-driven drug resistance in advanced melanoma.

Metastatic melanoma is either intrinsically resistant or rapidly acquires resistance to targeted therapy treatments, such as MAPK inhibitors. A leading cause of resistance to targeted therapy is a dynamic transition of melanoma cells from a proliferative to a highly invasive state, a phenomenon called phenotype switching. Mechanisms regulating phenotype switching represent potential targets for improving treatment of melanoma patients. Using a drug screen targeting chromatin regulators in patient-derived 3D MAPK inhibitor-resistant melanoma cell cultures, we discovered that PARP inhibitors restore sensitivity to MAPK inhibitors, independent of DNA damage repair pathways. Integrated transcriptomic, proteomic, and epigenomic analyses demonstrated that PARP inhibitors induce lysosomal autophagic cell death, accompanied by enhanced mitochondrial lipid metabolism that ultimately increases antigen presentation and sensitivity to T-cell cytotoxicity. Moreover, transcriptomic and epigenetic rearrangements induced by PARP inhibition reversed EMT-like phenotype switching, which redirected melanoma cells toward a proliferative and MAPK inhibitor-sensitive state. The combination of PARP and MAPK inhibitors synergistically induced cancer cell death both in vitro and in vivo in patient-derived xenograft models. Therefore, this study provides a scientific rationale for treating melanoma patients with PARP inhibitors in combination with MAPK inhibitors to abrogate acquired therapy resistance.