Absorptive and secretory transport of selected artemisinin derivatives across Caco-2 cell monolayers

BACKGROUND: Malaria continues to be a major health concern and affects more than 200 million people a year. Drugs currently used for treatment of malaria are increasingly rendered ineffectual by the ongoing emergence of parasite resistance. For any new drugs, however, knowledge of their membrane permeability is an essential pre-requisite for eventual use. Treatment failure and emergence of resistance can occur as a result of reduced availability of the drug at the desired site of action. Cellbased permeability assays such as Caco-2 cell monolayers serve as a model for predicting drug absorption and efflux, and provide an estimate of drug bioavailability. OBJECTIVE: Here we have studied the bi-directional transport of new anti-malarial compounds, artemisone and artemiside, as well as reference compounds, namely the known anti-malarial drug artemether, and caffeine and atenolol. METHODS: The Caco-2 cell monolayer model was used to assess the membrane permeation properties of these compounds, and to identify if they are subject to P-gp associated efflux, in the presence and absence of verapamil. The effect of piperine on the transport of the compounds that were identified to be P-gp substrates was also assessed. Samples withdrawn from the acceptor chambers at pre-determined time intervals were analysed by means of high-performance liquid chromatography (HPLC). RESULTS: Transport results in terms of the absorptive direction revealed that artemisone and artemether had low absorption rates relative to the reference compounds. It was further demonstrated that artemisone is slightly effluxed, and although both artemether and artemiside were susceptible to P-gp mediated efflux, it appears that other efflux proteins may also be involved. CONCLUSION: The low permeability of anti-malarial drugs must be borne in mind during development of effective dosage regimens of new drugs.