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

Metastatic melanoma is either intrinsically resistant or rapidly acquires resistance to targeted drugs such as MAPK inhibitors (MAPKi). Here, using a drug screen targeting chromatin regulators in patient-derived 3D melanoma cell cultures, we discovered that PARP inhibitors are capable of restoring MAPKi sensitivity. This synergy was found to be independent of DNA damage repair pathways and was effective both in vitro and in vivo in patients-derived xenografts. Strikingly, through integrated transcriptomic, proteomic and epigenomic analysis, we discovered that PARPi induces lysosomal autophagy which was accompanied by enhanced mitochondrial lipid metabolism that, ultimately, increased antigen presentation and sensitivity to T-cell cytotoxicity. Moreover, we also found that PARP inhibitors regulated EMT-like phenotype switching by dampening the mesenchymal phenotype via transcriptomic and epigenetic rearrangements. This, in turn, redirected melanoma cells towards a proliferative and, thus, MAPKi-sensitive state. Our study provides a scientific rational for treating patients with PARPi in combination with MAPKi to annihilate acquired therapy resistance.