Selective Inhibition of SIN3 Corepressor with Avermectins as a Novel Therapeutic Strategy in Triple-Negative Breast Cancer

Abstract

Triple negative breast cancers (TNBC) lacking estrogen, progesterone and HER2 receptors account for 10–20% of breast cancer and are indicative of poor prognosis. The development of effective treatment strategies therefore represents a pressing unmet clinical need. We previously identified a molecularly-targeted approach to target aberrant epigenetics of TNBC using a peptide corresponding to the SIN3 interaction domain (SID) of MAD. SID peptide selectively blocked binding of SID-containing proteins to the paired α-helix (PAH2) domain of SIN3, resulting in epigenetic and transcriptional modulation of genes associated with epithelial-mesenchymal transition (EMT). To find small molecule inhibitor (SMI) mimetics of SID peptide we performed an in silico screen for PAH2 domain-binding compounds. This led to the identification of the avermectin macrocyclic lactone derivatives selamectin and ivermectin (Mectizan) as candidate compounds. Both selamectin and ivermectin phenocopied the effects of SID peptide to block SIN3-PAH2 interaction with MAD, induce expression of CDH1 and ESR1 and restore tamoxifen sensitivity in MDA-MB-231 human and MMTV-Myc mouse TNBC cells in vitro. Treatment with selamectin or ivermectin led to transcriptional modulation of genes associated with EMT and maintenance of a cancer stem cell phenotype in TNBC cells. This resulted in impairment of clonogenic self-renewal in vitro and inhibition of tumor growth and metastasis in vivo. Underlining the potential of avermectins in TNBC, pathway analysis revealed that selamectin also modulated the expression of therapeutically-targetable genes. Consistent with this, an unbiased drug screen in TNBC cells identified selamectin-induced sensitization to a number of drugs, including those targeting modulated genes.

PTK6 Inhibition Suppresses Metastases of Triple-Negative Breast Cancer via SNAIL-Dependent E-Cadherin Regulation

“…Hs578t cells (ATCC) were cultured in DMEM supplemented with 10% FBS. MMTVmyc cells obtained from Dr. Eduardo Farias (Icahn School of Medicine at Mount Sinai, New York, NY) and were cultured in DMEM/F12 supplemented with 5% FBS and 4 mg/mL insulin (31). MMTV-myc cells were validated as a triple-negative cell line by Western blot and qRT-PCR analyses.…”

Emerging Roles of Epigenetic Regulator Sin3 in Cancer

“…To address this, one of the most recent advancements is the prospect of targeting metastatic progression of TNBC in adjuvant settings by using small molecule inhibitors that block PAH2 domain-mediated protein interactions of Sin3A (Kwon et al, 2015). As discussed in Section 8, SID decoys were shown to be very effective in reprogramming TNBC cells toward a more differentiated phenotype with significantly decreased metastatic potential (Fig.…”

“…3) Farias et al, 2010). To evaluate the relevance of translating this strategy from bench to bedside, an in silico screen for PAH2 domain-binding compounds led to identification several candidate compounds, one of them being avermectin macrocyclic lactone derivatives selamectin and ivermectin (Mectizan, an FDA approved drug for the treatment of River Night Blindness) (Kwon et al, 2015). Both selamectin and ivermectin phenocopied SID decoys and modulated the expression of therapeutically targetable genes.…”

“…Selamectin also inhibited invasion and downregulated expression of genes like MMP9 and MT1-MMP/MMP14 that are associated with invasion and metastasis. Although avermectins had a very modest effect on primary tumor growth, in postsurgical adjuvant settings severalfold decrease in metastatic dissemination to the lungs was reported (Kwon et al, 2015). These are clinically significant results since 90% of morbidity and mortality in cancer patients is due to metastasis of the primary tumor cells (Mehlen & Puisieux, 2006;Nguyen, Bos, & Massague, 2009).…”

Ivermectin: enigmatic multifaceted ‘wonder’ drug continues to surprise and exceed expectations

“…Ivermectin addition led to transcriptional modulation of genes associated with epithelial-mesenchymal transition and maintenance of a cancer stem cell phenotype in triple-negative breast cancers cells, resulting in impairment of clonogenic self-renewal in vitro and inhibition of tumor growth and metastasis in vivo. 112 It has been reported that ivermectin induces chloride-dependent membrane hyperpolarization and cell death in leukemia cells and it has also been suggested that ivermectin synergizes with the chemotherapy agents cytarabine and daunorubicin to induce cell death in leukemia cells, with researchers claiming that ivermectin could be rapidly advanced into clinical trials. 113 This potential has been supported by reports that ivermectin displays bioactivity against chronic lymphocytic leukemia cells and against ME-180 cervical cancer cells.…”