| Summary: | 碩士 === 國防醫學院 === 藥學研究所 === 95 === Physiologically, breast cancer resistance protein（BCRP）is widely expressed in the epithelial cells of tissue . In the intestine especially, BCRP causes the mal-absorption of drugs which then result in clinical therapeutic failure. However, the effective inhibition of BCRP mediated drug efflux can help improving the drug absorption in the intestinal tract, increasing bioavailability, decreasing the individual variability of drug absorption and restoring drug cytotoxic effect in cancer cells. The purpose of this research is to study potent BCRP modulators from Chinese herbal enhancers (CHEs) in order to improve drug bioavailability, decrease individual variability of drug absorption and reduce multidrug resistance in cancer therapy.
Our goal to this experiment was to setup and characterize a screening method using H460/MX20 cell line to study the effect of CHEs on BCRP-mediated transport of a model substrate, mitoxantrone (MX). The functional activities of BCRP can be estimated by measuring the fluorescent intensity of MX under flow cytometer to see the retention of MX in the presence of BCRP modulators. The increased fluorescent intensity indicated that the intracellular accumulation of MX elevated.
83 pure constituents selected from CHEs had been completed. The results indicated that the efflux of BCRP was significantly inhibited by some CHEs in concentration dependent manner. At 0.5 uM, the intracellular retention of MX of HUCHE 79 and 63 were significantly increased 1.6 to 2.3 fold (p<0.001) as compared with the control. On the other hand, HUCHE 79, 63, 64, 10, 81 and 11 at 5 uM were significantly increased 1.8 to 3.3 fold (p<0.001), and HUCHE 14, 44, 10, 11, 79, 63, 26, 81, 64, 37, 77, 0.1 and 34 at 50 uM were increased 2.8 to 3.8 fold (p<0.001) as compared with the control. The results of in vitro screening studies suggested that coadministration of BCRP-reversing CHE and BCRP-transporting oral drugs may improve the bioavailability of some orally drugs in vivo transported by BCRP.
The potent CHEs on the modulation of BCRP function will be further evaluated in vivo. The in vivo experiment was done by using the specific substrate of BCRP, topotecan, as a model substrate. Sprague-Dawley (S.D.) rats were first given HUCHE 79 (25 mg/kg), and 30 minutes after topotecan was administered p.o. (gavagingly) with or without CHEs. The plasma of the S.D. rats was then drawn and the concentration of topotecan was quantified by a liquid chromatography/tandem mass spectrometer (LC/MS/MS). The plasma concentration of topotecan following oral administration was significantly increased by coadministration of topotecan and HUCHE 79 in S.D. rats. The area under the curve (AUC) of topotecan following oral administration was strikingly increased 2 fold as compared with control. These results showed that HUCHE 79 increased the absorption of topotecan in small intestine.
Therefore, HUCHE 79 may improve pharmacokinetics of orally administered topotecan and it may be the potential substance in the future development of BCRP modulator researches.
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