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Targetting malarial cell cycle kinases

Final Activity Report Summary - MALKIN (Targetting malarial cell cycle kinases)

Plasmodium falciparum, the protozoan parasite responsible for the lethal form of human malaria, causes between 1 and 3 million deaths every year, mostly among children in sub-Saharan Africa. Within eukaryotes, protein kinases are involved in key processes of the life cycle of a cell. Such proteins have been identified in P. falciparum and thus are promising targets for novel anti-malarial drug design.

Firmly based in the post-genomic era, this work consisted of structure determination by X-ray crystallography of complexes between two P. falciparum protein kinases and small molecule ATP-competitive inhibitors: (i) PfPK5 which shows 56% sequence homology to human Cyclin Dependent Kinase 1 (CDK1), and (ii) PfPK7 which is an atypical kinase and cannot be ascribed to any protein kinase family. Fourteen inhibitors were tested on an active PfPK5/cyclin A complex. Nu6102 and Purvalanol B which show respectively IC50 values of 215 nM and 130 nM are the two most interesting compounds, but are more potent on human CDKs. This information will be of use in the design of more selectivePfPK5 inhibitors. The structure of PfPK7, determined in this project, is the first of an atypical kinase. It shows novel characteristics which it may be possible to exploit for the design of selective and specific inhibitors.

Using new technologies we have identified a putative substrate for PfPK7, PfRab11B. This substrate is the first plasmodial kinase substrate to be identified. We have also identified 5 compounds that bind tightly to PfPK7 in vitro and that have IC50 values in the range xxx-yyy. Co-crystallisation trials and biochemical assays to characterise these compound as PfPK7 inhibitors are in progress.