RESUMEN
The Na+/taurocholate cotransporting polypeptide (NTCP) is located in the basolateral membrane of hepatocytes, where it transports bile acids from the portal blood back into hepatocytes. Furthermore, NTCP has a role for the hepatic transport of some drugs. Extrapolation of drug transport data from rodents to humans is not always possible, because species differences in the expression level, localization, affinity, and substrate selectivity of relevant transport proteins must be considered. In the present study, a functional comparison of human NTCP (hNTCP) and mouse Ntcp (mNtcp) showed similar Km values of 67 ± 10 µM and 104 ± 9 µM for the probe substrate estrone-3-sulfate as well as of 258 ± 42 µM and 199 ± 13 µM for the drug rosuvastatin, respectively. IC50 values for the probe inhibitor cyclosporine A were 3.1 ± 0.3 µM for hNTCP and 1.6 ± 0.4 µM for mNtcp. In a drug and pesticide inhibitory screening on both transporters, 4 of the 15 tested drugs (cyclosporine A, benzbromarone, MK571, and fluvastatin) showed high inhibitory potency, but only slight inhibition was observed for the 13 tested pesticides. Among these compounds, only four drugs and three pesticides showed significant differences in their inhibition pattern on hNTCP and mNtcp. Most pronounced was the difference for benzbromarone with a fivefold higher IC50 for mNtcp (27 ± 10 µM) than for hNTCP (5.5 ± 0.6 µM).In conclusion, we found a strong correlation between the transport kinetics and inhibition pattern among hNTCP and mNtcp. However, specific compounds, such as benzbromarone, showed clear species differences. Such species differences have to be considered when pharmacokinetic data are transferred from rodent to humans.
Asunto(s)
Transporte Biológico/efectos de los fármacos , Activación del Canal Iónico/efectos de los fármacos , Transportadores de Anión Orgánico Sodio-Dependiente/metabolismo , Simportadores/metabolismo , Animales , Benzbromarona/farmacología , Ácidos y Sales Biliares/metabolismo , Células Cultivadas , Relación Dosis-Respuesta a Droga , Hepatocitos/metabolismo , Humanos , Cinética , RatonesRESUMEN
OBJECTIVES: The efficacy of temozolomide (TMZ) or dacarbazine (DTIC) in melanoma treatment depends on low O-6-methylguanine-DNA-methyltransferase (MGMT) repair and on high mismatch repair. The aim of this study was to identify individual host markers for hematologic side effects and the treatment efficacy of TMZ or DTIC in melanoma treatment. METHODS: Fifty-one Caucasian patients with metastasized melanoma were recruited. In each patient, the mRNA expression of MGMT and two essential mismatch repair genes, MLH1 and MSH2, was measured in peripheral blood. The coding gene regions, including splice sites, were sequenced to identify genetic variants, and the promoter methylation status of the genes was determined. RESULTS: Both constitutively low and high mRNA expression of MGMT, MLH1, and MSH2 were significantly associated with reduced hematologic side effects (P = 0.008-0.020), but did not correlate with treatment efficacy. We identified five variants in the MGMT gene, 13 variants in MLH1, and seven variants in MSH2, including five novel genetic variants in MLH1. Variations of the hosts' gene expression of MGMT, MLH1, and MSH2 did not result from promoter methylation. Of note, one variant in MSH2 (rs2303428) was associated with increased hematologic side effects and showed a tendency for better treatment response. CONCLUSION: Our results indicate that either low or high host expression of MGMT, MLH1, and MSH2 may serve as a marker for reduced hematologic side effects of TMZ or DTIC, but not for treatment efficacy in melanoma. The genetic variant rs2303428 (MSH2) might serve as a predictive marker for hematologic side effects and treatment response.