volasertib and Melanoma

The objective of this study was to determine the therapeutic potential of polo-like kinase 1 (Plk1) inhibition in melanoma, in vivo. Employing Vectra technology, we assessed the Plk1 expression profile in benign nevi, malignant (stages I-IV) and metastatic melanomas. We found a significant elevation of Plk1 immunostaining in melanoma tissues. Further, a second generation small molecule Plk1 inhibitor, BI 6727, resulted in reductions in growth, viability and clonogenic survival, as well as an increase in apoptosis of A375 and Hs 294T melanoma cells. BI 6727 treatment also resulted in a G2/M-as well as S-phase cell cycle arrest in melanoma cells. Importantly, BI 6727 (intravenous injection; 10 and 25 mg/kg body weight) treatment resulted in significant tumor growth delay and regression in vivo in A375-and Hs 294T-implanted xenografts in athymic nude mice. These anti-melanoma effects were accompanied with a decreased cellular proliferation (Ki-67 staining) and induction of apoptosis (caspase 3 activation). In addition, BI 6727 treatment caused a marked induction of p53 and p21 in vitro as well as in vivo. Overall, we suggest that Plk1 inhibition may be a useful approach as a monotherapy as well as in combination with other existing therapeutics, for melanoma management.

Topics: Animals; Antineoplastic Agents; Apoptosis; Caspase 3; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Cyclin-Dependent Kinase Inhibitor p21; Dose-Response Relationship, Drug; G2 Phase Cell Cycle Checkpoints; Humans; Ki-67 Antigen; Melanoma; Mice, Nude; Molecular Targeted Therapy; Mutation; Polo-Like Kinase 1; Protein Kinase Inhibitors; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins B-raf; Pteridines; S Phase Cell Cycle Checkpoints; Signal Transduction; Skin Neoplasms; Time Factors; Tumor Burden; Tumor Suppressor Protein p53; Xenograft Model Antitumor Assays

Polo-like kinase 1 (Plk1) is a serine/threonine kinase that plays a key role during the cell cycle by regulating mitotic entry, progression, and exit. Plk1 is overexpressed in a variety of human cancers and is essential to sustained oncogenic proliferation, thus making Plk1 an attractive therapeutic target. However, the clinical efficacy of Plk1 inhibition has not emulated the preclinical success, stressing an urgent need for a better understanding of Plk1 signaling. This study addresses that need by utilizing a quantitative proteomics strategy to compare the proteome of BRAF(V600E) mutant melanoma cells following treatment with the Plk1-specific inhibitor BI 6727. Employing label-free nano-LC-MS/MS technology on a Q-exactive followed by SIEVE processing, we identified more than 20 proteins of interest, many of which have not been previously associated with Plk1 signaling. Here we report the down-regulation of multiple metabolic proteins with an associated decrease in cellular metabolism, as assessed by lactate and NAD levels. Furthermore, we have also identified the down-regulation of multiple proteasomal subunits, resulting in a significant decrease in 20S proteasome activity. Additionally, we have identified a novel association between Plk1 and p53 through heterogeneous ribonucleoprotein C1/C2 (hnRNPC), thus providing valuable insight into Plk1's role in cancer cell survival.

Topics: Cell Cycle Proteins; Cell Line, Tumor; Heterogeneous-Nuclear Ribonucleoprotein Group C; Humans; Melanoma; Mutation; Polo-Like Kinase 1; Proteasome Endopeptidase Complex; Protein Kinase Inhibitors; Protein Serine-Threonine Kinases; Proteomics; Proto-Oncogene Proteins; Proto-Oncogene Proteins B-raf; Pteridines; Skin Neoplasms; Tandem Mass Spectrometry