Cellular uptake of chloroquine is dependent on binding to ferriprotoporphyrin IX and is independent of NHE activity in Plasmodium falciparum

Here we provide definitive evidence that chloroquine (CQ) uptake in Plasmod ium falciparum is determined by binding to ferriprotoporphyrin IX (FPIX), S pecific proteinase inhibitors that block the degradation of hemoglobin and stop the generation of FPIX also inhibit CQ uptake. Food vacuole enzymes ca n generate cell-free binding, using human hemoglobin as a substrate. This b inding accounts for CQ uptake into intact cells and is subject to identical inhibitor specificity. Inhibition of CQ uptake by amiloride derivatives oc curs because of inhibition of CQ-FPIX binding rather than inhibition of the Na+/H+ exchanger (NHE), Inhibition of parasite NHE using a sodium-free med ium does not inhibit CQ uptake nor does it alter the ability of amilorides to inhibit uptake. CQ resistance is characterized by a reduced affinity of CQ-FPIX binding that is reversible by verapamil. Diverse compounds that are known to disrupt lysosomal pH can mimic the verapamil effect. These effect s are seen in sodium-free medium and are not due to stimulation of the NHE. We propose that these compounds increase CQ accumulation and overcome CQ r esistance by increasing the pH of lysosomes and endosomes, thereby causing an increased affinity of binding of CQ to FPIX.