In Vitro PLK1 Inhibition by BI 2536 Decreases Proliferation and Induces Cell-Cycle Arrest in Melanoma Cells

May 2012 | Volume 11 | Issue 5 | Original Article | 587 | Copyright © 2012

Abstract

Melanoma is one of the most treatment-resistant malignancies and regardless of new therapeutic tactics the outcome remains dismal. Polo-like kinase 1 (PLK1) has been shown to be over-expressed in a variety of tumors, becoming an attractive target for cancer management. In the present study we tested the in vitro antitumor activities of BI 2536, a selective inhibitor of PLK1, against two melanoma cell lines. Our results showed that nanomolar concentrations (10-150 nmol/L) of the drug significantly decreased cell proliferation and clonogenicity, promoting cell cycle arrest in G2/M. Targeting the cell cycle offers an attractive potential cancer-treatment option. Herein we show that PLK1 inhibition may be a feasible approach for the impairment of tumor progression and dissemination. This in vitro profile of melanoma cell growth inhibition by PLK1 modulation may be an interesting model to be tested in association with first-line antineoplasic agents in melanomas.

J Drugs Dermatol. 2012;11(5):587-592.

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INTRODUCTION

Human cutaneous malignant melanoma is one of the most resistant tumors to treat, being responsible for 75% of skin cancer-related deaths.1Despite improvements in the management of this tumor, its treatment by surgery or systemic therapy is largely unsuccessful. Advanced melanoma patients have an exceedingly poor outcome with an estimated survival of less than one year.2 Thus, development of new novel agents with more effective antitumor activity is a high priority in the treatment of this tumor.

Polo-like kinase 1 (PLK1) is a conserved Ser/Thr protein kinase that mediates various mitotic events, such as mitotic entry, spindle formation, and chromosome segregation.3 A compelling body of evidence suggests that altered PLK1 expression in different neoplasia correlates to the prognosis of cancer patients.4 Regarding melanoma, Strebhardt et al5 demonstrated that while PLK1 protein is not detectable in melanocytes of normal skin, elevated expression of this protein is a shared parameter for the prognosis of patients suffering from different subtypes of this tumor (including superficial spreading melanoma, nodular melanoma, lentigo maligna melanoma, and acrolentiginous melanoma).

The inhibition of PLK1 by different methods has been shown to cause cell cycle arrest and to increase apoptosis in several models.6 Specifically, short hairpin RNA (shRNA)-mediated knockdown of PLK1 as well as its chemical inhibition by GW843682X has previously resulted in decreased cell viability and proliferation in human melanoma cell lines.7In the current study, we present more evidence of the antiproliferative response to PLK1 inhibition in melanoma cells treated with BI 2536, reinforcing the likelihood of using pharmacological PLK1 inhibitors as a therapeutic approach to combat this disease.

METHODS

Cell Culture

The established melanoma cell line LB-373-MEL (provided by Dr. D. T. Covas, Faculty of Medicine of Ribeirão Preto, Brazil) was cultured in HAM F10 (Gibco BRL, Life Technologies®,Carlsbad, CA) supplemented with 10% foetal bovine serum, penicillin (100U/mL), and streptomycin (100ug/mL) at 37°C in a humidified 5% CO2 incubator. The 1389-MEL primary culture was derived from an invasive acral lentiginous melanoma (Clark level IV) obtained from an amputated finger from a 73-year-old woman diagnosed at the University Hospital. Cultures were obtained according to Brassesco et al8 and maintained at low passage numbers (p2-p4) under standard culture conditions (Research Ethics Committee HC-FMRP, Proc: 1387/2004).

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