The cell biology of microtubule inhibition in Plasmodium falciparum

Abstract

Malaria is among the most prevalent human infections worldwide and both the lack of a viable vaccine and the spread of resistance to commonly used drugs have limited the options for control of the parasite, especially Plasmodium falciparum, the cause of the most severe form of the disease. The cell division cycle o f the blood-borne stages of P. falciparum, also known as schizogony, is crucial to malarial disease but is poorly characterised and has features that seem to contradict the accepted model of cell-cycle regulation in eukaryotes. Various techniques for (apparent) cell-cycle synchronisation have been used to shed light on the mechanisms involved in cell division and its control in other eukaryotes. There is no technique for cell-cycle synchronisation (as opposed to selection of parasites of a limited age-range) in Plasmodium. An attempt was made to do this by applying a number of inhibitors of cell cycle progression, namely inhibitors of DNA synthesis, the mitotic spindle, or cell-cycle control elements (such as cyclin-dependent kinases) to cultures of the parasite. Surprisingly, most of these compounds did not cause a block at a specific phase. Three compounds, Hoechst 33342, roscovitine and L-mimosine, did block development at the trophozoite-schizont transition (S or G2 phase). The block caused by the latter two inhibitors was reversible, suggesting that they might be used as synchronising agents. However, a consideration of the perturbing effects of inhibitors and problems with 'batch' synchronisation techniques in general lead us to believe that any results obtained using roscovitine- or L-mimosine-treated parasites may not be reflective of the normal cell cycle.