TGF-β inhibition enhances chemotherapy action against triple-negative breast cancer

After an initial response to chemotherapy, many patients with triple-negative breast cancer (TNBC) have recurrence of drug-resistant metastatic disease. Studies with TNBC cells suggest that chemotherapy-resistant populations of cancer stem-like cells (CSCs) with self-renewing and tumor-initiating capacities are responsible for these relapses. TGF-βhas been shown to increase stem-like properties in human breast cancer cells. We analyzed RNA expression in matched pairs of primary breast cancer biopsies before and after chemotherapy. Biopsies after chemotherapy displayed increased RNA transcripts of genes associated with CSCs and TGF-βsignaling. In TNBC cell lines and mouse xenografts, the chemotherapeutic drug paclitaxel increased autocrine TGF-βsignaling and IL-8 expression and enriched for CSCs, as indicated by mammosphere formation and CSC markers. The TGF-βtype I receptor kinase inhibitor LY2157299, a neutralizing TGF-βtype II receptor antibody, and SMAD4 siRNA all blocked paclitaxel-induced IL8 transcription and CSC expansion. Moreover, treatment of TNBC xenografts with LY2157299 prevented reestablishment of tumors after paclitaxel treatment. These data suggest that chemotherapy-induced TGF-βsignaling enhances tumor recurrence through IL-8-dependent expansion of CSCs and that TGF-βpathway inhibitors prevent the development of drug-resistant CSCs. These findings support testing a combination of TGF-βinhibitors and anticancer chemotherapy in patients with TNBC.