Abstract 4549: Combinations of ciclopirox olamine and metformin exert synergistic antitumor activity in triple-negative breast cancer
Authors: Wu Yakun , Lyu Hui , Tan Congcong , Larsen Margaret E. , Huang Shile , Liu Bolin 
Published: March 2024

Introduction: Triple-negative breast cancer (TNBC) represents a challenging subtype of breast cancer because of its limited treatment options. Recent research has highlighted the potential benefits of combining pharmacological agents to enhance therapeutic outcomes. Studies show that Ciclopirox olamine (CPX), an off-patent anti-fungal drug, induces cell cycle G1-phase arrest and activates the intrinsic apoptosis pathway by downregulating the anti-apoptotic proteins. Meanwhile, metformin, a safe and first-line drug for the treatment of type II diabetes, has been shown to induce cell cycle S-phase arrest and activates the extrinsic apoptosis pathway via induction of endogenous TRAIL in TNBC cells. However, whether the combinations of CPX and metformin would exert potent antitumor activity against TNBC remains unclear.

Methods: Cell proliferation (MTS) assays and LIVE/DEAD cell imaging were used to determine the combined inhibitory effects on TNBC cells. IC50s and the combination index (CI) were calculated. Flow cytometry assays were carried out to analyze if the combinations are more potent to block cell cycle progression. Apoptotic-specific ELISA and flow cytometry analysis of Annexin V-PI staining were performed to assess if the combinations are significantly more effective to induce apoptosis. Western blot assays were used to examine if the combinations markedly induced the expression of TRAIL and cleavages of PARP and caspases. Tumor xenograft models will be established to test the in vivo antitumor activity of CPX and metformin either alone or in combinations.

Results: Data indicated that both CPX and metformin independently inhibited the proliferation of TNBC cells. A synergistic effect was observed when CPX and metformin were used in combination, resulting in a more potent inhibition of TNBC cell proliferation. The combinatorial treatment effectively suppressed colony formation of TNBC cells. Synergy between CPX and metformin was partially linked to the enhanced activation of the AMPK-mTOR pathway, as the combination significantly enhanced the phosphorylation of AMPKα. The combinations also induced enhanced apoptosis in TNBC cells through both the intrinsic and extrinsic pathways. The combinatorial effects of CPX and metformin on in vivo tumor growth are under investigation.

Conclusions: Combinations of CPX and metformin show synergistic effects on inhibiting TNBC cell proliferation. Our studies suggest a potential therapeutic strategy for TNBC, with the combinations of these agents exhibiting an enhanced antitumor activity. Further investigation is warranted to validate the results and explore their clinical applications.

Key words: Triple-negative breast cancer, Ciclopirox olamine, Metformin, Combination, Apoptosis

Citation Format: Yakun Wu, Hui Lyu, Congcong Tan, Margaret E. Larsen, Shile Huang, Bolin Liu. Combinations of ciclopirox olamine and metformin exert synergistic antitumor activity in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4549.