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Effect of quercetin on Hoechst 33342 transport by purified and reconstituted P-glycoprotein
1Division of Molecular and Structural Biology, Ontario Cancer Institute/Princess Margaret Hospital, Toronto, Canada.
Abstract:
Multidrug resistance due to P-glycoprotein is a serious impediment to successful chemotherapy of cancer. Numerous compounds are known that inhibit the drug-exporting function of P-glycoprotein. Understanding the mechanisms of action of these chemosensitizers is made difficult by the complexity of the in vivo cell systems usually employed. To examine the direct effects of chemosensitizers, we have developed a system in which purified and reconstituted P-glycoprotein transports. Hoechst 33342 from the lipid membrane to the aqueous interior of proteoliposomes, requiring ATP hydrolysis (Shapiro AB and Ling V, J Biol Chem 270: 16167-16175, 1995). Here, we use this system to understand the effect on P-glycoprotein of quercetin, one of three flavonoids that have been reported to have the unique property of stimulating drug transport by P-glycoprotein in vivo (Phang et al., Cancer Res 53: 5977-5981, 1993). Since flavonoids are abundant in food, it is important to understand their effects on the function of P-glycoprotein because of the implications for cancer chemotherapy. In our hands, quercetin inhibited P-glycoprotein-mediated Hoechst 33342 efflux and enhanced accumulation, as measured by flow cytometry, by multidrug-resistant CHRC5 cells. In the purified system, quercetin strongly inhibited Hoechst 33342 transport by P-glycoprotein, at least in part by inhibiting the ATPase activity of P-glycoprotein required for transport. We conclude that the previously reported stimulatory effect of quercetin on drug efflux from multidrug-resistant cells is not a direct effect on P-glycoprotein. The ATPase domain of P-glycoprotein may be an attractive target for new chemosensitizing agents.
Insights
Quercetin, a flavonoid, inhibits P-glycoprotein drug transport and ATPase activity in purified systems. This finding clarifies its role in multidrug resistance and cancer chemotherapy, suggesting new therapeutic targets.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- P-glycoprotein mediates multidrug resistance, hindering cancer chemotherapy.
- Existing chemosensitizers' mechanisms are complex to study in vivo.
- Flavonoids, like quercetin, are abundant in food and their effects on P-glycoprotein are significant for cancer treatment.
Purpose of the Study:
- To investigate the direct effects of quercetin on purified P-glycoprotein function.
- To elucidate the mechanism by which quercetin interacts with P-glycoprotein.
- To clarify the discrepancy between in vitro and in vivo effects of quercetin on drug transport.
Main Methods:
- Utilized a reconstituted proteoliposome system with purified P-glycoprotein to study Hoechst 33342 transport.
- Assessed quercetin's effect on P-glycoprotein-mediated drug efflux and accumulation in multidrug-resistant cells (CHRC5) using flow cytometry.
- Measured the impact of quercetin on P-glycoprotein's ATPase activity.
Main Results:
- Quercetin inhibited P-glycoprotein-mediated Hoechst 33342 efflux and increased drug accumulation in resistant cells.
- In the purified system, quercetin significantly inhibited Hoechst 33342 transport by P-glycoprotein.
- Quercetin's inhibition of transport was partly due to reduced P-glycoprotein ATPase activity.
Conclusions:
- The previously reported stimulatory effect of quercetin on drug efflux is not a direct action on P-glycoprotein.
- Quercetin directly inhibits P-glycoprotein's drug transport function and ATPase activity.
- The ATPase domain of P-glycoprotein represents a promising target for developing novel chemosensitizing agents.