A Novel Allosteric Inhibitor Targets PLK1 in Triple Negative Breast Cancer Cells

Abstract

While Polo-like kinase 1 (PLK1) inhibitors have shown promise in clinical settings for treating triple-negative breast cancer tumors and other solid tumors, they are limited by their ability to bind non-selectively to the ATP kinase domain. Therefore, we sought to develop a PLK1 allosteric inhibitor targeting the PLK1 T-loop (a switch responsible for activation) and evaluate its effects in triple-negative breast cancer cells. A novel compound, RK-10, was developed based on an in silico model, and its effects on specificity, viability, migration, and cell cycle regulation in MCF-10A and MDA-MB 231 cells were evaluated. When MDA-MB 231 cells were treated with 0–50 µg/mL RK-10, phospho-PLK1 (Thr-210) was decreased in cells cultured adherently and cells cultured as mammospheres. RK-10 significantly inhibited viability after 24 h; however, by 48 h, 25–50 µM RK-10 caused >50% reduction. RK-10 attenuated wound healing by up to 99.7% and caused S and G2/M cell cycle arrest, which was associated with increased p21 expression. We developed a novel allosteric inhibitor which mediates anti-proliferative and anti-migratory properties through targeting phospho-PLK1 (Thr-210) in mammospheres and causing S phase and G2/M cell cycle arrest. Further development of PLK1 allosteric inhibitors may be a promising approach for TNBC treatment.

Characteristics and prognostic significance of polo‐like kinase‐1 (PLK1) expression in breast cancer

“…In addition, a PLK1 Inhibitor (Onvansertib), is currently used for the treatment of relapsed small cell lung cancer patients, who have either not responded to or are unable to tolerate chemotherapy. Recently, a novel PLK1 inhibitor (RK‐10) was developed in TNBC cells and has been shown to have antiproliferative and antimigratory properties causing S phase and G2/M cell cycle arrest 51 …”

“…5,49,50 In addition, a strong association was observed between high PLK1 expression and TNBC subtype at both the proteomic and transcriptomic levels, confirming previous studies. 10,48,51 With dichotomisation of the whole cohort into molecular classes, high PLK1 expression had a significant association with longer BCSS and DMFS in luminal BC. These findings are in line with recent studies that showed that PLK1 has tumour suppressor functions in ER-positive tumours.…”

“…Recently, a novel PLK1 inhibitor (RK-10) was developed in TNBC cells and has been shown to have antiproliferative and antimigratory properties causing S phase and G2/M cell cycle arrest. 51 It is known that PLK1 is downregulated by P53 as part of the G2/M cell cycle checkpoint, [65][66][67] and in the meantime, PLK1 has a pivotal role both in the p53-mediated regulation of DNA damage repair and mitosis. 20 In this study, we found a significant association between low PLK1 expression and poor outcome in P53 mutated tumours.…”