Sulfatase 2 inhibition sensitizes triple-negative breast cancer cells to paclitaxel through augmentation of extracellular ATP

The highest incidence and cancer-related mortality rate among women worldwide is due to breast cancer. Triple-negative breast cancers (TNBC) are associated with more inferior outcomes than other breast cancers because of their progressive nature and the deficit in available therapies. Therefore, there is a need for new therapeutic approaches. Our lab determined that chemotherapy induces the release of extracellular adenosine triphosphate (eATP), and, hence, augments TNBC cells' response to chemotherapy. Despite this, eATP concentrations are restricted by a variety of extracellular ATPases. We propose that, as an ATPase inhibitor, heparan sulfate (HS) would augment eATP concentrations and TNBC vulnerability induced by chemotherapy. Sulfatase 2 (SULF2) removes sulfate from HS, the functional group essential for ATPase inhibition. Consequently, we propose that TNBC cell death and eATP release induced by chemotherapy would be intensified by SULF2 inhibitors. We examined eATP and cell viability in paclitaxel-treated TNBC and nontumorigenic immortal mammary epithelial MCF-10A cells in the presence of OKN-007, a selective SULF2 inhibitor, and/or heparan sodium sulfate. Furthermore, sulfatase 1 (SULF1) and SULF2 protein expressions were ascertained. We found that the expression of SULF2 was greater in TNBC cell lines when compared to MCF-10A cells. The release of eATP and loss of TNBC cell viability induced by chemotherapy was enhanced by OKN-007. The co-treatment of chemotherapy and OKN-007 also attenuated cancer-initiating cells. This data implies that the combination of SULF2 inhibitors with chemotherapy augments eATP and decreases cell viability of TNBC greater than chemotherapy alone.