Studies on cell-cycle synchronization in the asexual erythrocytic stages of Plasmodium falciparum.

Multiplication of Plasmodium parasites within human erythrocytes is essential to malarial disease. The cell-division cycle of this organism, however, is still poorly understood. In other eukaryotes, various techniques for (apparent) cell-cycle synchronization have been used to shed light on the mechanisms involved in cell division and its control. Thus far there is no technique for cell-cycle synchronization (as opposed to selection of parasites of a limited age-range) in Plasmodium. We therefore investigated the possibility that inhibitors of DNA synthesis, the mitotic spindle, or cell-cycle control elements (such as cyclin-dependent kinases) could be used to synchronize P. falciparum cultures to a particular cell-cycle phase. 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 2 inhibitors was reversible, suggesting that they might be used as synchronizing agents. However, a consideration of the perturbing effects of inhibitors and problems with 'batch' synchronization 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.