Host cell and malarial targets for docetaxel (Taxotere) during the erythrocytic development of Plasmodium falciparum.

The microtubular stabilizing agent docetaxel (Taxotere) is known to inhibit the intraerythrocytic development of Plasmodium falciparum. To investigate the mechanism(s) of inhibition, we analyzed the structural organization of the mitotic spindle by immunofluorescence and electron microscopy. When 30 microM docetaxel was applied for five hours on ring forms, alterations in the mitotic spindles leading to abnormal nuclear divisions were observed. At the trophozoite- and schizont-stage, docetaxel pulses prevent mitosis by stabilizing microtubular structures associated with the mitotic apparatus, giving abnormal spindles. However, this inhibition did not interfere with parasite DNA synthesis indicating the absence of a checkpoint that couples exit from mitosis with proper spindle assembly as observed in higher eukaryotic cells. In parallel, intraerythrocytic concentration of docetaxel was measured in parasitized erythrocytes, after incubation of cells with 3H-docetaxel for five hours. It was found to be 14-fold increased at the ring-stage of infected erythrocytes compared to normal ones, 170-fold increased at the trophozoite-stage and 1,500-fold increased at the schizont-stage. Our data show that, even though the overall intracellular concentration of docetaxel is low in docetaxel-pulsed rings, the agent might be sufficient to disturb the spindle organization. However, the existence of targets for docetaxel other than mitotic spindle microtubules, i.e. erythrocyte membrane components could interfere with mitotic spindle formation.