Human estrogen receptor alpha (ERα) targeted cyclic peptides inhibit cell growth and induce apoptosis in MCF-7 cells

Objectives Human estrogen receptor alpha (ER alpha) is considered an important target, especially in the treatment of breast cancer, as it has a vital role in cancer development. ER alpha-targeted therapies generally target the ligand binding domain (LBD) of ER alpha. However, over time, cells develop resistance to this mechanism alternative approaches to inhibit ER alpha activity target ER alpha-DNA or ER alpha-cofactor interactions. Inhibitors of ER alpha-cofactor interactions are designed by targeting the hydrophobic hollow region of the receptor box LXXLL motif.Methods In this context, helix-stabilized cyclic peptides (SPs) designed with in silico approaches were obtained by solid phase peptide synthesis. The effects of SPs on MCF-7 cells were examined with MTT and ATP, and qPCR and flow cytometry were used for further analysis.Results Our results demonstrated that the SPs were effective only in MCF-7 cells expressing ER alpha. In addition, cyclic peptide combinations (SPCs) showed anti-proliferative and toxic effects on MCF-7 cells. The impact of SPCs with the highest inhibitory effect in MCF-7 cells on ER alpha-related genes and markers of apoptosis was revealed. Moreover, the flow cytometry analysis result used to examine apoptotic cells proved the apoptosis of SPCs in MCF-7 cells.Conclusions These findings suggest that our novel SPs, which inhibit coactivator interactions of ER alpha, induce apoptosis of MCF-7 cells. Thus, considering this strong effect of SPs in the inhibition of receptors, it is pointed out that they can be further developed as an alternative to current clinical treatments or as an auxiliary approach in the generating of new targeted peptide-based therapies.