Development of the alternative method for renal drug excretion using Xenopus oocyte expression system combined with a high throughput method, OOCYTEXPRESS

Organic anion transporters (OATs) play an important role in the renal elimination of drugs. To date, we succeeded in the development of in vitro pharmacokinetics prediction system by establishing the cell lines stably-expressing several OATs. Although this system is suitable to evaluate the uptake of drugs, it seems not completely appropriate to examine their efflux. Here, we tried to develop a novel high-throughput method to evaluate the efflux function of drug transporters by using Xenopus oocytes expression system combined with a high throughput method, OOCYTEXPRESS. In this study, we examined the efflux function of renal apical organic anion transporter NPT1 whose efflux function is still unknown. To evaluate the drug efflux, in vitro transcribed human NPT1 (hNPT1) cRNA was injected into oocytes. After three days incubation, we again injected the [C]p-aminohippuric acid (PAH) directly into the oocytes and measured the radioactivities of the outside buffer. hNPT1 cRNA-injected oocytes showed significantly higher count than control, indicating that hNPT1 can function as a drug efflux transporter. These results indicated that our method for renal drug excretion combined with the OOCYTEXPRESS seems suitable for the evaluation of the drug efflux and is an alternative method for mammalian kidney slices.