Abstract 302: The combined inhibition of Plk1 and Notch1 results in a synergistic anti-proliferative response in human melanoma cells
Authors: Su Shengqin , Chhabra Gagan , Singh Chandra K. , Ndiaye Mary A. , Ahmad Nihal 
Published: August 2019

Abstract
Melanoma is the most aggressive form of skin cancer, and its incidence and mortality have been increasing over the past thirty years. Therefore, additional therapeutic strategies are needed for an effective management of this neoplasm. We previously demonstrated that polo-like kinase 1 (Plk1, a serine/threonine kinase involved in mitotic regulation) and Notch1 (a type I transmembrane protein deciding cell fate during development) are strongly correlated in melanoma (Cancer Res 2018; 78 (13 Suppl): Abstract nr 2530). In addition, a number of studies from our lab and elsewhere have suggested the important functions of Plk1- as well as Notch- signaling in melanoma progression. Based on these observations, in this study, we determined the potential efficacy of a combined inhibition of Plk1 and Notch1 against melanoma cells. Employing Plk1 inhibitor volasertib (BI6727) and Notch1 inhibitor MK-0752, we determined the effects of concomitant targeting of these pathways in A375 (wild type TP53) and SK-MEL-2 (mutant TP53) human melanoma cell lines. Employing RealTime-Glo and trypan blue exclusion assays, we found that volasertib (10 and 20 nM) and MK-0752 (50 and 100 μM) resulted in a significant decrease (60-80%) in viability and growth of human melanoma cells A375 and SK-MEL-2. The Combination Index (CI), as calculated using the Chou-Talalay theorem, was less than 1 when volasertib at 10 nM was given with MK-0752 at 50 and 100 μM, indicating a synergism between these two drugs. As a result of the synergism, the melanoma cells treated with combined drugs showed decreased colony formation ability compared to individual drugs. In addition, the combined treatment also resulted in enhanced apoptosis of melanoma cells. Interestingly, cell cycle analysis by flow cytometry showed that combined inhibition of Plk1 and Notch1 caused a G2-M phase arrest of melanoma cells. Furthermore, our data demonstrated that volasertib and MK-0752 combination caused a marked increase of cleaved PARP (poly ADP ribose polymerase) and cleaved caspase-3 in both melanoma cell lines, as well as increased expression of tumor suppressor protein TP53 and its target p21 (CDKN1A) in A375 melanoma cells. Taken together, our data demonstrated that a combined targeting of Plk1- and Notch1- signaling pathways imparts a synergistic anti-proliferative response against melanoma. However, additional experiments are needed i) to validate our in vitro data to in vivo situations in human relevant melanoma models, and ii) to define the interactive mechanism(s) of the observed synergistic response.
Citation Format: Shengqin Su, Gagan Chhabra, Chandra K. Singh, Mary A. Ndiaye, Nihal Ahmad. The combined inhibition of Plk1 and Notch1 results in a synergistic anti-proliferative response in human melanoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 302.