RESUMO
INTRODUCTION: We have previously shown that human colorectal cancer tissue is able to inactivate the anticancer drug paclitaxel through cytochrome P450 (CYP)2C8 and CYP3A4 metabolisms. The aim of this study was to evaluate whether changes in the expression levels of genes coding for such enzymes are related to anticancer drug resistance after long-term exposure to the drug. METHODS: Human colorectal cancer cells (Caco-2) that are sensitive to paclitaxel were exposed to increasing concentrations of the drug from 0-250 nM during one year, in order to select paclitaxel-resistant cells. Subsequently, we compared the sensitivity to paclitaxel and the extent of expression of the CYP2C8, CYP3A4 and CYP3A5 genes in original and resistant cells. RESULTS: Resistant cancer cells displayed a 246-fold increased lethal dose (LD)50 to paclitaxel (p < 0.004) as compared with original cancer cells. A 4.4-fold (p = 0.005) enhancement of CYP2C8 expression and a 5.6-fold (p = 0.001) increase of multidrug resistance (MDR)1 expression was observed in resistant cells exposed to paclitaxel. When paclitaxel was removed from the culture medium, CYP2C8, but not MDR1 expression, reverted to basal levels and the resistance to paclitaxel decreased 3.2-fold (p = 0.005). No major changes in the expression levels of CYP3A4 and CYP3A5 were observed. CONCLUSIONS: Caco-2 cells are capable of increasing the expression levels of CYP2C8 as a response to long-term exposure to paclitaxel. This study provides evidence for a mechanism of acquired resistance to anticancer therapy based on the induction of anticancer-metabolizing enzymes.
Assuntos
Antineoplásicos Fitogênicos/farmacologia , Hidrocarboneto de Aril Hidroxilases/biossíntese , Hidrocarboneto de Aril Hidroxilases/genética , Paclitaxel/farmacologia , Sequência de Bases , Células CACO-2 , Sobrevivência Celular/efeitos dos fármacos , Neoplasias Colorretais/tratamento farmacológico , Neoplasias Colorretais/enzimologia , Neoplasias Colorretais/genética , Citocromo P-450 CYP2C8 , Citocromo P-450 CYP3A , Sistema Enzimático do Citocromo P-450/genética , DNA Complementar/genética , Resistencia a Medicamentos Antineoplásicos/genética , Indução Enzimática/efeitos dos fármacos , Indução Enzimática/genética , Fluoruracila/farmacologia , Expressão Gênica/efeitos dos fármacos , Genes MDR , Humanos , Dose Letal Mediana , FarmacogenéticaRESUMO
OBJECTIVE: Our objective was to evaluate the presence of CYP3A4 gene variants in white individuals with low CYP3A4 enzyme activity. METHODS: Persons with extremely low enzyme activity, either in vitro or in vivo, were selected in a panel of 97 healthy subjects. Genetic analyses for CYP3A4 variant alleles present in white subjects, including CYP3A4*1B, CYP3A4*2, CYP3A4*4, CYP3A4*5, CYP3A4*6, CYP3A4*8, CYP3A4*11, CYP3A4*12, and CYP3A4*13, were performed on genomic deoxyribonucleic acid from these subjects by amplification-restriction and sequencing. RESULTS: With the exception of CYP3A4*1B, none of the variant alleles analyzed were present in 30 genes from persons with extremely low enzyme activity. CYP3A4*1B was present in the population studied with an allele frequency of 5.5%. Nevertheless, the presence of CYP3A4*1B does not correlate with low enzyme activity, either in vivo or in vitro, in either heterozygosity or homozygosity. CYP3A4*2 was not identified in 290 genes from Spanish persons or in 70 genes from Finnish persons. CONCLUSIONS: Although the genetic component of the interindividual variability of CYP3A4 enzyme activity seems to be high, our findings do not support a key role for the variant alleles analyzed on the majority of white persons with low CYP3A4 activity. This suggests the occurrence of as yet unknown mutations that affect CYP3A4 or other functionally related genes.