PLK1 and NOTCH Positively Correlate in Melanoma and their Combined Inhibition Results in Synergistic Modulations of Key Melanoma Pathways

Melanoma is one of the most serious forms of skin cancer, and its increasing incidence coupled with non-lasting therapeutic options for metastatic disease highlight the need for additional novel approaches for its management. In this study, we determined the potential interactions between 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) in melanoma. Employing an in-house human melanoma tissue microarray (TMA) containing multiple cases of melanomas and benign nevi, coupled with high-throughput, multispectral quantitative fluorescence imaging analysis, we found a positive correlation between PLK1 and NOTCH1 in melanoma. Further, TCGA database analysis of melanoma patients showed an association of higher mRNA levels of PLK1 and NOTCH1 with poor overall as well as disease-free survival. Next, utilizing small-molecule inhibitors of PLK1 and NOTCH (BI 6727 and MK-0752, respectively), we found a synergistic anti-proliferative response of combined treatment in multiple human melanoma cells. To determine the molecular targets of the overall and synergistic responses of combined PLK1-NOTCH inhibition, we conducted RNA-sequencing analysis employing a unique regression model with interaction terms. We identified the modulations of several key genes relevant to melanoma progression/metastasis, including MAPK, PI3K, and RAS, as well as some new genes such as Apobec3G, BTK and FCER1G which have not been well-studied in melanoma. In conclusion, our study demonstrated a synergistic anti-proliferative response of a concomitant targeting of PLK1 and NOTCH in melanoma, unravelling a potential novel therapeutic approach for detailed preclinical/clinical evaluation. For RNA-seq analysis, total RNA was isolated from cells in 4 replicates in each group. There are total 4 treatment groups: DMSO as control, BI6727 treatment, MK-0752 treatment, and BI6727+MK-0752 combined treatment. A total of 16 samples were submitted to the University of Wisconsin Biotechnology Center Gene Expression Center for quality control, library construction and further analysis.