A bioassay for evaluating antimalarial activity and for measuring concentration in plasma

Area of Science:

• Pharmacology
• Parasitology
• Biotechnology

Background:

• Malaria remains a significant global health challenge.
• Accurate measurement of antimalarial drug concentrations and activity in patients is crucial for effective treatment.
• Chloroquine (CQ) is a widely used antimalarial, but its efficacy can be affected by metabolism and resistance.

Purpose of the Study:

• To develop and validate a bioassay method for quantifying chloroquine (CQ) and its metabolite, monodesethylchloroquine (DCQ), in human serum.
• To compare the bioassay results with high-performance liquid chromatography (HPLC) for validation.
• To assess the relative antimalarial activity of CQ and DCQ.

Main Methods:

• Development of a bioassay based on the Desjardins isotopic microtest using a continuous culture of Plasmodium falciparum.
• Analysis of 32 human serum samples from Filipino malaria patients treated with CQ.
• Blind comparison of bioassay results with HPLC measurements of CQ and DCQ concentrations.

Main Results:

• A strong correlation (r² = 0.90) was observed between HPLC-determined CQ + DCQ concentrations and bioassay-equivalent CQ levels.
• The antimalarial activity of DCQ was found to be nearly identical to CQ, with DCQ activity being 0.9 times that of CQ.
• The bioassay demonstrated reliability, semi-automation, and reproducibility.

Conclusions:

• The developed bioassay is a reliable and reproducible method for measuring the biological activity of chloroquine and its metabolites in serum.
• This bioassay can serve as a complementary technique to HPLC for pharmacokinetic studies and the detection of new metabolites.
• The method has potential applications for other protozoan infections with available in vitro models.