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Endothelin receptor-A is required for the recruitment of antitumor T cells and modulates chemotherapy induction of cancer stem cells

Background: The endothelin receptor-A (ETRA) plays an important role in tumor cell migration, metastasis, and proliferation. The endothelin receptor B (ETRB) plays a critical role in angiogenesis and the inhibition of anti-tumor immune cell recruitment. Thus dual blockade of ETRA and ETRB could have significant anti-tumor effects. Results: Dual ETRA/ETRB blockade with macitentan (or the combination of the ETRA and ETRB antagonists BQ123 and BQ788) did not enhance antitumor immune cell recruitment. In vitro studies demonstrate that ETRA inhibition prevents the induction of ICAM1 necessary for immune cell recruitment. When used as a single agent against human tumor xenografts, macitentan demonstrated non-significant anti-tumor activity. However, when used in combination with chemotherapy, macitentan specifically reduced tumor growth in cell lines with CD133+ cancer stem cells. We found that ETRA is primarily expressed on CD133+ CSC in both cell lines and primary human tumor cells. ETRA inhibition of CSC prevented chemotherapy induced increases in tumor stem cells. Furthermore, ETRA inhibition in combination with chemotherapy reduced the formation of tumor spheres. Methods: We tested the dual ETRA/ETRB antagonist macitentan in conjunction with (1) an anti-tumor vaccine and (2) chemotherapy, in order to assess the impact of dual ETRA/ETRB blockade on anti-tumor immune cell infiltration and ovarian tumor growth. In vitro murine and human cell line, tumor sphere assays and tumor xenograft models were utilized to evaluate the effect of ETRA/ETRB blockade on cell proliferation, immune cell infiltration and cancer stem cell populations. Conclusions: These studies indicate a critical role for ETRA in the regulation of immune cell recruitment and in the CSC resistance to chemotherapy.