1193 DRP1 Inhibition as an adjuvant for BH3 mimetics in melanoma

Abstract

Current melanoma treatment have limitations of relapse. BH3 mimetics against BCL-2 family members have gained excitement with recent success in hematological cancers. However, single drug BH3 therapy not effective in melanoma due to escape by the anti-apoptotic protein MCL-1 and/or survival of Melanoma Initiating Cells (MICs). Melanoma progression correlates with increase in Dynamin-related protein 1 (DRP1). DRP1 interacts with BCL-2 family members, but its potential effects on BH3 mimetic treatment is not defined in melanoma. This study targeted the above components to develop treatment options for melanoma. We tested the efficacy of the BH3 mimetics combination of A-1210477 (MCL-1 inhibitor) and ABT-263 (BCL-2/BCL-XL/BCL-W inhibitor), and examined how inhibiting DRP1 may influence this effect. We used multiple assays (cell viability, bright field, immunoblot, and sphere formation), as well as the CRISPR/Cas9 genome-editing technique. To make the study clinically relevant, we utilized patient samples of different mutation status, including some relapsed from current treatments such as anti-PD-1 immunotherapy. We found that the BH3 mimetic combination de-bulks and kills MICs in all samples irrespective of the mutation status or relapsed state (p<0.05). Unexpectedly, cell death occurs independent of major pro-apoptotic proteins such as NOXA,BIM or BID. Moreover, the combination treatment impedes the activation of DRP1 and inhibition of DRP1 further enhances the combination-induced apoptosis (p<0.05). This finding is different from those seen in other cancers. We are currently studying how manipulation of DRP1 affects BCL-2 family members in melanoma. These results suggest that inhibiting the major anti-apoptotic proteins are sufficient to induce cell death in melanoma even without involvement from major pro-apoptotic proteins, and provide new insights into BCL-2 familys regulation of the apoptotic pathway. Importantly, our study also indicate that DRP1 Inhibition is a promising adjuvant for BH3 mimetics in melanoma treatment.