A Combination of an Antimitotic and a Bromodomain 4 Inhibitor Synergistically Inhibits the Metastatic MDA-MB-231 Breast Cancer Cell Line

Abstract

Current chemotherapeutic agents have many side effects and are toxic to normal cells, providing impetus to identify agents that can effectively eliminate tumorigenic cells without damaging healthy cells. The aim of this study was to examine whether combining a novel BRD4 inhibitor, ITH-47, with the antimitotic estradiol analogue, ESE-15-ol, would have a synergistic effect on inhibiting the growth of two different breast cancer cell lines in vitro. Our docking and molecular dynamics studies showed that compared to JQ1, ITH-47 showed a similar binding mode with hydrogen bonds forming between the ligand nitrogens of the pyrazole, ASN99, and water of the BRD4 protein. Data from cell growth studies revealed that the GI50 of ITH-47 and ESE-15-ol after 48 hours of exposure was determined to be 15 μM and 70 nM, respectively, in metastatic MDA-MB-231 breast cancer cells. In tumorigenic MCF-7 breast cancer cells, the GI50 of ITH-47 and ESE-15-ol was 75 μM and 60 nM, respectively, after 48 hours of exposure. Furthermore, the combination of 7.5 μM and 14 nM of ITH-47 and ESE-15-ol, respectively, resulted in 50% growth inhibition of MDA-MB-231 cells resulting in a synergistic combination index (CI) of 0.7. Flow cytometry studies revealed that, compared to the control, combination-treated MDA-MB-231 cells had significantly more cells present in the sub-G1 phase and the combination treatment induced apoptosis in the MDA-MB-231 cells. Compared to vehicle-treated cells, the combination-treated cells showed decreased levels of the BRD4, as well as c-Myc protein after 48 hours of exposure. In combination, the selective BRD4 inhibitor, ITH-47, and ESE-15-ol synergistically inhibited the growth of MDA-MB-231 breast cancer cells, but not of the MCF-7 cell line. This study provides evidence that resistance to BRD4 inhibitors may be overcome by combining inhibitors with other compounds, which may have treatment potential for hormone-independent breast cancers.

The emerging role of BET inhibitors in breast cancer

“…ESE-15-ol is a microtubule-targeting agent, which interferes with normal formation of mitotic spindle and thus leads to mitotic arrest [76]. ITH-47 BRD4-selective inhibitor showed synergistic activity with ESE-15-ol in TNBC cells [77].…”

Integration of Molecular Docking and In Vitro Studies: A Powerful Approach for Drug Discovery in Breast Cancer

“…The table reports the drug, its target with PDB ID, in silico/in vitro/in vivo methods used to test the drug, clinical trials, mechanism of action and reference. In another study [68], the authors investigated the combination of two novel compounds, namely, ITH-47 (a BRD4 inhibitor) and ESE-15-ol (an antimitotic agent). The in vitro study revealed that the combination of these two compounds inhibits the growth of MDA-MB-231.…”

“…To compare the binding energy of the two molecules, they performed molecular docking with a known drug-i.e., JQ1-which revealed that, compared to JQ1, the molecules can achieve similar binding energies and sites as bromodomain-containing protein 4 (BRD4). BRD4 plays a role in regulating c-Myc, a key regulator of cell growth and apoptosis [68].…”