Proteasomal degradation of Mcl-1 by maritoclax induces apoptosis and enhances the efficacy of ABT-737 in melanoma cells.
OBJECTIVE
Metastatic melanoma remains one of the most invasive and highly drug resistant cancers. The over expression of anti-apoptotic protein Mcl-1 has been associated with inferior survival, poor prognosis and chemoresistance of malignant melanoma. A BH3 mimetic, ABT-737, has demonstrated efficacy in several forms of cancers. However, the efficacy of ABT-737 depends on Mcl-1. Because the over expression of Mcl-1 is frequently observed in melanoma, specifically targeting of Mcl-1 may overcome the resistance of ABT-737. In this study, we investigated the effects of Maritoclax, a novel Mcl-1-selective inhibitor, alone and in combination with ABT-737, on the survival of human melanoma cells.


METHODS
For cell viability assessment we performed MTT assay. Apoptosis was determined using western blot and flow cytometric analysis.


RESULTS
The treatment of Maritoclax reduced the cell viability of melanoma cells with an IC50 of between 2.2-5.0 µM. Further, treatment of melanoma cells with Maritoclax showed significant decrease in Mcl-1 expression. We found that Maritoclax was able to induce apoptosis in melanoma cells in a caspase-dependent manner. Moreover, Maritoclax induced Mcl-1 degradation via the proteasome system, which was associated with its pro-apoptotic activity. We also found that Maritoclax treatment increased mitochondrial translocation of Bim and Bmf. Importantly, Maritoclax markedly enhanced the efficacy of ABT-737 against melanoma cells in both two- and three-dimensional spheroids.


CONCLUSIONS
Taken together, these results suggest that targeting of Mcl-1 by Maritoclax may represent a new therapeutic strategy for melanoma treatment that warrants further investigation as a single therapy or in combination with other agents such as Bcl-2 inhibitors.
Department of Pharmacology, Penn State College of Medicine, Hershey, Pennsylvania, United States of America.
Manoj K
MK
Pandey
Krishne
K
Gowda
Kenichiro
K
Doi
Arun K
AK
Sharma
Hong-Gang
HG
Wang
Shantu
S
Amin
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D001713:Biphenyl Compounds / Q000494:pharmacology*; D020169:Caspases / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D006131:Growth Inhibitors / Q000494:pharmacology*; D006801:Humans; D020128:Inhibitory Concentration 50; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000235:genetics* / Q000378:metabolism; D009596:Nitrophenols / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects* / Q000378:metabolism; D059748:Proteolysis; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology*; D015398:Signal Transduction; D012867:Skin / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D013449:Sulfonamides / Q000494:pharmacology*
C501332:ABT-737; D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; C486655:BMF protein, human; D000072224:Bcl-2-Like Protein 11; D001713:Biphenyl Compounds; D006131:Growth Inhibitors; C579095:MCL1 protein, human; D008565:Membrane Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009596:Nitrophenols; D010879:Piperazines; D011518:Proto-Oncogene Proteins; D011758:Pyrroles; D013449:Sulfonamides; C528298:marinopyrrole A; D020169:Caspases; D046988:Proteasome Endopeptidase Complex