RESUMO
Flavopiridol is the first cyclin-dependent kinase inhibitor to enter clinical trials. Flavopiridol has been shown to mimic, in part, the effect of the cell cycle control gene p16, which is frequently lost or mutated in malignant melanoma, making it an ideal candidate for targeted therapy in this disease. In these studies we investigated the effect of flavopiridol, at various concentrations, on the growth and gene expression of nine human melanoma cell lines with intact, absent or mutated p16. A cytostatic effect of flavopiridol on the growth of six melanoma cell lines with a mutated or non-expressed p16 (p16-) was seen at low concentrations of flavopiridol (mean 50% inhibitory concentration [IC(50)] = 12.5 nM), while the three melanoma cell lines with intact p16 (p16+) required higher concentrations (mean IC(50) = 25 nM) to produce this effect. Apoptotic cell death increased with increasing concentrations of flavopiridol in both p16- and p16+ cells. Exposure of cells to high flavopiridol concentrations (>100 nM) resulted in decreased expression of genes downstream in the normal p16 cell cycle control pathway (Rb and E2F) and the anti-apoptotic gene BCL2. No change in BCL2 expression was found after exposure to IC(50) concentrations of flavopiridol. These data indicate that flavopiridol in low, clinically achievable concentrations may have significant cytostatic effects, particularly in p16- melanoma cells, and may provide new molecular-based therapies for melanoma, particularly when combined with agents that target anti-apoptotic mechanisms.
Assuntos
Inibidor p16 de Quinase Dependente de Ciclina/efeitos dos fármacos , Flavonoides/farmacologia , Genes p16 , Melanoma/genética , Melanoma/patologia , Piperidinas/farmacologia , Neoplasias Cutâneas/genética , Neoplasias Cutâneas/patologia , Antineoplásicos/farmacologia , Ciclo Celular/efeitos dos fármacos , Ciclo Celular/genética , Inibidor p16 de Quinase Dependente de Ciclina/genética , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/farmacologia , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Humanos , Concentração Inibidora 50 , Melanoma/metabolismo , Neoplasias Cutâneas/metabolismo , Células Tumorais Cultivadas/citologiaRESUMO
BACKGROUND: Population-based studies have identified several clinical variables associated with an increased risk of developing cutaneous melanoma that include phenotype, amount of and response to sun exposure, and family history. However, these observations are of limited relevance to clinical practice as the risk associated with each factor is individually modest and the characteristics of these variables lack precision when applied to a particular individual. OBJECTIVE: To review the literature regarding recent advances made in the understanding of the genes and genetics of clinical variables associated with an increased risk of melanoma. CONCLUSION: Variants of the MC1R (melanocortin-1 receptor) have been identified as major determinants of high-risk phenotypes, such as red hair and pale skin, and the ability to tan in response to UV exposure. Several studies also suggest that such variants may increase melanoma risk independent of their contribution to phenotype. A strong genetic basis for both nevus density and size has been demonstrated and the link between nevi and the development of MM has become better defined. Finally, germline defects in several genes involved in cell cycle regulation, namely, p16 and CDK4, have been demonstrated in many familial melanoma kindreds. This progress has introduced the prospect of genetic testing as a means of identifying a limited number of high-risk individuals who can be targeted with regular screening and education regarding UV exposure and skin self-examination. Ultimately, through rational genetic therapy targeted to correcting the underlying molecular defect, altering the natural history of melanoma development may be possible.
