Disulfiram treatment targeting cancer stem cells in breast cancer cell lines

Background:

Systemic adjuvant treatment of breast cancer by chemotherapy is limited due to cytotoxicity and drug resistance. Cancer stem cells (CSCs) are contributing to drug resistance and cancer recurrence. Conventional chemotherapy targets proliferating cells, while undifferentiated and quiescent CSC are unaffected retaining self-renewal properties. It is necessary to develop alternative adjuvant treatments that target CSCs.

Methods:

Monolayer-derived cells (MDCs) and spheroid-derived cells (SDCs) were collected and treated with DSF at different concentrations. The inhibitory effect of DSF on breast cancer CSCs was investigated by exploring aldehyde dehydrogenase (ALDH) activity with ALDEFLUOR assay by flow cytometry, expression of stemness-related transcription factors Sox2, Oct3/4, and Nanog by real-time PCR, and stemness by clonogenicity assay. Combination effect and synergism of DSF with cisplatin was quantitatively analyzed (CompuSyn software).

Results:

Levels of ALDH activity and Sox2, Oct3/4, and Nanog expression were significantly higher in SDCs than MDCs, suggesting their usefulness for evaluating stem cell activities in breast cancers. ALDH activity was inhibited by DSF in both SDCs and MDCs. The mRNA level of Sox2, Oct3/4, and Nanog was significantly decreased in SDCs after DSF treatment (2.04-fold, 7.24-fold, 16.95-fold in MCF7, 32.2-fold, 5.71-fold, 2.21-fold in MDA-MB-435S, 30.5-fold, 3.54-fold, 3.94-fold in SKB-R3, p < 0.05). DSF inhibited colony formation. Combination of DSF with cisplatin yielded synergistic effects in breast cancer cell lines (MCF7, MDA-MB-435S, SKB-R3) at broad concentration ranges (IC₅₀-IC₉₀).

Conclusions:

The inhibitory effect of DSF and synergistic effect with cisplatin proposes DSF as a treatment targeting breast cancer CSC.