Undergraduate Honors Thesis


Azacitidine and MCL1 inhibitors in combination may provide novel treatment for patients with melanoma Public Deposited

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  • Treatment options for melanoma have progressed in recent years, with the rise of targeted therapy and immunotherapy. However, options are still limited for BRAF wildtype patients, which account for 50-60% of all patients, and for those who do not respond to immunotherapy. The BCL2 family of proteins regulates apoptosis, and the anti-apoptotic members are implicated in the development of treatment resistance in a variety of cancers. Drugs mimicking the pro-apoptotic BH3 only proteins, termed BH3 mimetics, are a promising therapeutic option for patients who are resistant to or ineligible for other therapies. The BH3 mimetic ABT-199 (venetoclax) is approved for use as a single agent in chronic lymphocytic leukemia (CLL), and was recently approved for use in combination with the hypomethylating agent azacitidine in selected patients with acute myelogenous leukemia (AML). This combination was found to selectively target leukemia stem cells (LSCs), and greatly improved the treatment options for leukemia patients not eligible for more toxic chemotherapy. A hallmark of melanoma is resistance to chemotherapy and increased expression of anti-apoptotic proteins. We therefore examined similar combinations on fourteen patient-derived and commercially available melanoma cell lines. The BH3 mimetics tested include MCL1 inhibitors (S63845, S64315), an inhibitor of BCL2, BCLXL, and BCLW (navitoclax/ABT-263), a BCL2 inhibitor (venetoclax/ABT-199), and a BCLXL inhibitor (A1331852). Our data showed that treatments with MCL1 inhibitors plus azacitidine were effective in reducing melanoma cell viability in vitro. The MCL1 inhibitor, S63845, was the most potent compound when combined with azacitidine, with ~85% of melanoma cell lines achieving less than 50% viability at the highest dose. Treatment with azacitidine in combination with ABT-263 or A1331852, had appreciably less effect with only 64% and 50% of cell lines responding at the highest dose, respectively. Response to ABT-199 with azacitidine was considerably lower with only 21% of cell lines demonstrating a decrease in viability at the highest concentration. The S63845 plus azacitidine combination increased the level of MCL1 protein, a result that has been shown by other groups to be due to increased protein stability. Additionally, treatment with S63845 plus azacitidine disrupted sphere formation in melanoma initiating cell (MICs), a subset of melanoma cells thought to be responsible for relapse. Finally, knockdown of BIM and MCL1 was shown to sensitize cells to treatment with S63845 plus azacitidine, an effect that may be due to the metabolic roles of these proteins. Our data demonstrate that treatment with the MCL1 inhibitor S63845 in combination with azacitidine was highly effective in suppressing growth of melanoma cells in vitro including rare uveal, acral and mucosal subtypes. Mechanistic experiments exploring the potential role of disruption in energy metabolism to explain these results are planned. A better understanding of how this novel combination works may provide an alternative therapeutic approach for patients with melanoma.

Date Awarded
  • 2020-11-04
Academic Affiliation
Granting Institution
Last Modified
  • 2020-11-06
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