Abstract 3552: Selective inhibition of copper metabolism as a novel approach to treat triple-negative breast cancer

Rationale: Treatment of patients with triple-negative breast cancer (TNBC) remains challenging due to unpredictable disease progression and acquired resistance to chemotherapy. Finding novel targets in TNBC is important for the development of anticancer therapy. Cancer cells frequently adapt to cytotoxicity of existing pharmacological agents by exploiting metabolic pathways. Elevated copper metabolism and adaptations to oxidative stress have been linked to cancer progression. Copper chelation with tetrathiomolybdate (TM) was reported to control disease progression, especially in patients with TNBC. However, long-term consequences of global copper depletion are still under investigation. An alternative strategy is provided by a recently developed small molecule DCAC50 that blocks the copper transfer interface of two major copper chaperons, ATOX-1 and CCS. Protein levels of ATOX-1 and CCS are elevated in TNBC cells compared to normal cells. Thus, we hypothesized that disrupting copper transport by targeting ATOX-1 and CCS with DCAC50 may suppress TNBC progression. Results: We investigated efficacy and potency of novel small molecule DCAC50 to induce cytotoxicity in a panel of TNBC cells lines. DCAC50 reduced cell proliferation in dose-dependent manner, measured by MTS assay. IC50 doses ranged from 3-10uM. Most importantly, DCAC50 induced apoptosis in TNBC cells, detected by Caspase 3/7 activity and Annexin V/PI staining. As expected, DCAC50 elevated intracellular copper levels. Moreover, TNBC cells treated with DCAC50 had significantly higher levels of oxidized glutathione (GSSG) and caused increased oxidation of DCF-DA reagent, demonstrating elevated oxidative stress. Surprisingly, activity of CCS downstream target, SOD1, was not affected by selective inhibition of copper transport with DCAC50; suggesting that intracellular copper accumulation and oxidative stress is mediated by ATOX-1 inhibition. Interestingly, copper depletion with TM inhibited SOD1 activity but failed to significantly impact oxidative stress in TNBC cells. Recognizing DCAC50 generates oxidative stress triggering apoptosis in TNBC cells we evaluated benefits of combining DCAC50 treatment with paclitaxel. Multi-drug combination dose-response analysis revealed that co-treatment induced synergistic cytotoxicity and resulted in favorable dose reduction of both drugs. Conclusions: Selective inhibition of copper metabolism with novel small molecule DCAC50 elevates oxidative stress triggering apoptosis in TNBC cells. This approach may be valuable in combination with chemotherapy especially when tumor cells acquire resistance to first line therapy in TNBC. Ongoing studies comparing selective inhibition of copper transport to global copper chelation, and investigating efficacy and biological activity of DCAC50 in vivo will help further estimate benefits and clinical relevance of this approach for treatment of TNBC patients. Citation Format: Olga Karginova, Claire Weekley, Akila Raoul, Alhareth Alsayed, Tong Wu, Chuan He, Olufunmilayo I. Olopade. Selective inhibition of copper metabolism as a novel approach to treat triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3552. doi:10.1158/1538-7445.AM2017-3552