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

Abstract

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-β has 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-β signaling. In TNBC cell lines and mouse xenografts, the chemotherapeutic drug paclitaxel increased autocrine TGF-β signaling and IL-8 expression and enriched for CSCs, as indicated by mammosphere formation and CSC markers. The TGF-β type I receptor kinase inhibitor LY2157299, a neutralizing TGF-β type 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-β signaling enhances tumor recurrence through IL-8-dependent expansion of CSCs and that TGF-β pathway inhibitors prevent the development of drug-resistant CSCs. These findings support testing a combination of TGF-β inhibitors and anticancer chemotherapy in patients with TNBC.

Targeting TGF-β Signaling for Therapeutic Gain

“…Importantly, the small molecule TbRI inhibitor, LY2157299 (galunisertib), resensitizes drug-tolerant cells to anticancer drugs (Huang et al 2012). Proof of this concept was shown in clinical material from paclitaxel-treated primary breast cancer patients wherein paclitaxel treatment in the neoadjuvent setting increased a TGF-b gene expression signature in the primary tumor (Bhola et al 2013). TGFBR2, TGFBR3, and SMAD4 mRNA levels were increased approximately twofold, TGFBR1, TGFB1, TGFB3, SMAD2, and SMAD7 to a lesser degree, and the CSC-related CD44 and ALDHA1 mRNAs were also elevated after chemotherapy.…”

“…TGFBR2, TGFBR3, and SMAD4 mRNA levels were increased approximately twofold, TGFBR1, TGFB1, TGFB3, SMAD2, and SMAD7 to a lesser degree, and the CSC-related CD44 and ALDHA1 mRNAs were also elevated after chemotherapy. Moreover, coadministration of paclitaxel with TGF-b signaling inhibitors (galunisertib, antiTbRII antibody or siSMAD4) in a nude mouse xenograft model reduces primary tumor growth compared with tumors receiving paclitaxel alone (Bhola et al 2013). Most important, the number of tumor initiating cells within the primary tumor, assayed by their ability to generate mammospheres in cell culture, was decreased in mice treated with the TGF-b inhibitor compared with paclitaxel alone (Bhola et al 2013).…”

“…Moreover, coadministration of paclitaxel with TGF-b signaling inhibitors (galunisertib, antiTbRII antibody or siSMAD4) in a nude mouse xenograft model reduces primary tumor growth compared with tumors receiving paclitaxel alone (Bhola et al 2013). Most important, the number of tumor initiating cells within the primary tumor, assayed by their ability to generate mammospheres in cell culture, was decreased in mice treated with the TGF-b inhibitor compared with paclitaxel alone (Bhola et al 2013). Because the tumor initiating cells are essential for tumor growth and metastasis, these studies show the essential need for TGF-b signaling for tumor growth and metastatic spread.…”

Implications of Different Cancer Stem Cell Phenotypes in Breast Cancer

“…Furthermore, increased expression of homeobox A1 and mucin 4 were associated with high ALDH1 activity, also contributing to tumor relapse and metastasis. Activation of transforming grow factor-beta 2 signaling pathway was also shown to be involved in the pathological regulation of ALDH1 in breast cancer (49)(50)(51).…”

Chemotherapy triggers HIF-1–dependent glutathione synthesis and copper chelation that induces the breast cancer stem cell phenotype

“…In addition, BCSCs have increased resistance to chemotherapy through expression of drug transporter proteins, expression of survival factors, and other mechanisms (7). BCSCs are enriched in response to chemotherapy, further potentiating the risk of tumor recurrence and metastasis (8)(9)(10). The enrichment of BCSCs can be measured by the Aldefluor assay, which is based on the high aldehyde dehydrogenase activity (ALDH) in BCSCs (11), or by the mammosphere assay, which is based on the ability of BCSCs to generate multicellular spheroids in suspension culture (12).…”