Experimental conditions for testing the inhibitory activity of chloroquineon the formation of beta-hematin

Some antimalarial drugs act by inhibiting the process of ferriprotoporphyri n IX polymerization which protects the parasite against the noxious effect of this product of host cell hemoglobin digestion. As the quest for new dru gs with a similar mode of action continues, high-throughput screening metho ds are needed. We demonstrate herein that such a recently described screeni ng technique (Basilico et al., J. Antimicrob. Chemoter. 42, 55-60, 1998) is considerably disturbed by certain ions. Thus, at the assay's pH 2.6, the p hosphate ions are responsible for the inhibitory activity of chloroquine ph osphate, rather than chloroquine itself. Using a combination of solubility tests and Fourier transform infrared spectrometry we also show that two alt ernative methods using higher pH's are also prone to salt effects and demon strate that these can be minimized by extensive washing of the product with DMSO. (C) 2000 Academic Press.