ABSTRACT The present study describes the impact of chrysosplenetin, in the absence and presence of artemisinin, on in vitro breast cancer resistance protein-mediated transport activity in Caco-2 cell monolayers using aristolochic acid I as a specific probe substrate. We observed that novobiocin, a known breast cancer resistance protein active inhibitor, increased Papp (AP-BL) of aristolochic acid I 3.13 fold (p < 0.05) but had no effect on Papp (BL-AP). Efflux ratio (PBA/PAB) declined 4.44 fold (p < 0.05). Novobiocin, consequently, showed a direct facilitation on the uptake of AAI instead of its excretion. Oppositely, both artemisinin and chrysosplenetin alone at dose of 10 µM significantly decreased Papp (BL-AP) instead of Papp (AP-BL). Chrysosplenetin alone attenuated the efflux ratio, which was suggestive of being as a potential breast cancer resistance protein suppressant. Oddly, Papp (BL-AP) as well as efflux ratio were respectively enhanced 2.52 and 2.58 fold (p < 0.05), when co-used with artemisinin and chrysosplenetin in ratio of 1:2. The potential reason remains unclear; it might be relative to binding sites competition between artemisinin and chrysosplenetin or the homodimer/oligomer formation of breast cancer resistance protein bridged by disulfide bonds, leading to an altered in vitro breast cancer resistance protein-mediated efflux transport function.

ABSTRACT Our previous work revealed that chrysosplenetin in combination with artemisinin inhibited in vivo P-glycoprotein (P-gp, one of classic multi-drug resistance proteins) mediated digoxin transportation activity by reversing the upregulated P-gp/Mdr1 mRNA expression levels by artemisinin. Therefore, chrysosplenetin might be a potential artemisinin-resistance reversal agent as a P-gp inhibitor. But it still remains unknown if chrysosplenetin has an impact on another pivotal multi-drug resistance protein, breast cancer resistance protein (Bcrp), which is co-expressed with P-gp in apical membrane of intestinal epithelial cell and overlaps some of the substrates and inhibitors. This study, therefore, further addressed the impact of chrysosplenetin, per se or in combination with artemisin, on Bcrp/ABCG2 mRNA expression levels in mice small intestine determined by western blot and real time-quantitative polymerase chain reaction (RT-qPCR) assay. The drugs were intragastrically administrated once per day for 7 days. Novobiocin, a known Bcrp inhibitor, was observed to have no impact on Bcrp/ABCG2 levels with or without artemisinin versus vehicle. Interestingly, artemisinin alone attenuated Bcrp level while chrysosplenetin alone increased it (p < 0.05). Relative mRNA level was significantly decreased when co-used with artemisinin and chrysosplenetin in ratio of 1:2 (p < 0.05). The discrepant results for chrysosplenetin on Bcrp/ABCG2 mRNA expressions might be closely related to the transcriptional or posttranscriptional regulation.