Enhanced cytotoxicity in triple-negative and estrogen receptor-positive breast adenocarcinoma cells due to inhibition of the transient receptor potential melastatin-2 channel

We previously demonstrated a unique protective role for the transient receptor potential, melastatin-2 (TRPM2) cation channel in breast cancer cells. In the present study, we investigated the chemotherapeutic effects elicited by inhibiting this protective role in metastatic breast adenocarcinoma cells. TRPM2 inhibition led to dose-dependent increases in MDA-MB-231 breast adenocarcinoma cell death after treatment with doxorubicin or the DNA-methylating agent, N-methyl-N'-nitro-N-nitrosoguanidine. Similar results were observed after RNAi silencing of TRPM2 in these cells after doxorubicin treatment. However, TRPM2 RNAi silencing also led to increased MCF-7 breast adenocarcinoma cell death after tamoxifen treatment, yet not in non-cancerous human mammary epithelial cells. These results thus revealed that TRPM2 inhibition selectively increased cytotoxicity in a triple-negative and an estrogen receptor-positive breast cancer cell line, with minimal deleterious effects in non-cancerous breast cells. Analysis of DNA damage revealed enhanced DNA damage levels in MCF-7 cells treated with doxorubicin due to TRPM2 inhibition. Analysis of cell death demonstrated that inhibition of apoptosis, caspase-independent cell death or autophagy failed to significantly reduce cell death induced by TRPM2 inhibition and chemotherapy. These results indicate that TRPM2 inhibition activates alternative pathways of cell death in breast cancer cells. Taken together, our results provide significant evidence that TRPM2 inhibition is a potential strategy to induce triple-negative and estrogen receptor-positive breast adenocarcinoma cell death via alternative cell death pathways. This is expected to provide a basis for inhibiting TRPM2 for the improved treatment of breast cancer, which potentially includes treating breast tumors that are resistant to chemotherapy due to their evasion of apoptosis.