Decreasing cancer stem cell population and dedifferentiation in breast cancer cells by selective inhibition of canonical and non- canonical pathways of WNT signaling

Breast cancer is the most common cancer in women. Although success rate of treatments is high in early diagnosed cases, treatment success rate decreases in locally advanced and metastatic cases. Surgery, radiotherapy, chemotherapy or different combinations of those are being used fort he treatment of breast cancer. Despite the treatment modalities that seem to be successful in the beginning, breast cancer may come out with local recurrence or distant metastasis months or years after the treatment. For this late recurrence process, many mechanisms including dedifferentiation of tumor cells, accumulation of new mutations, development of resistant cancer stem cells (CSC), CSCs getting into dormancy and escaping from therapeutic modalities are all being discussed in the literature. In order to increase treatment effectiveness for breast cancer, different treatment modalities including inhibitors for pathways related to CSC formation (Wnt, Notch, Hedgehog etc), immunotherapy methods for CSC surface markers, inhibitors or monoclonal antibodies for signal pathways which stimulate CSC proliferation such as VEGF/VEGFR2, CXCR4; therapies targeting histone deacetylase enzyme (HDAC) to prevent CSC proliferation or stimulate apoptosis and differentiation, are all under clinical investigation. Today, several therapeutic molecules especially acting on Notch1, Hedgehog and Wnt signalling pathways, are shown to be effective in clearing CSCs in some preclinical studies. In our study with ER+ and triple-negative breast cancer cell lines, the more aggressive structure of triple-negative breast cancer cells, the presence of higher rates of CSC and their molecular markers were shown in accordance with the literature. Clear findings were obtained in favor of reducing the CSC populations, especially in the 24th hour findings in the MDA-MB-231 cell line by suppression of canonical and other non-canonical Wnt pathways in combination. In our study, for the first time in the literature, combined blockade of the Wnt-calcium pathway combination with the canonical Wnt pathway was performed in breast cancer cell lines using thapsigargine. Our study confirmed the existence of the synergy of the Wnt classical pathway and the Wnt-calcium pathway, which was previously proposed in a single study, by testing it on cancer cells. Wnt classical pathway suppression via the LRP5/6 receptor with niclosamide has been shown to be very effective and its use with Wnt-calcium or other combinations has been shown to be effective in reducing CSCs in triple-negative breast cancers. The results of our study supports the need for targeted treatment, especially in triple-negative breast cancers, which account for 12-15% of breast cancers in the world. We believe that the results of our study will lead to the elucidation of the mechanisms that determine CSC activity in patients with breast cancer, which is an important cause of mortality, and to develop new targeted treatment options.