Abstract:
Malaria remains a big challenge the world-over especially in Sub-sahara Africa.
Since there is no malaria vaccine currently, chemotherapy is the only curative
intervention option available. At present, there are few known drug targets in the
parasite. Worse still, most of these targets have mutated leading to widespread
resistance to current drugs. There is therefore an urgent need for discovery and
development of new antimalarial chemotherapeutic interventions and targets. An
“Achilles' heel” in the parasite biology that could be exploited for
chemotherapeutic intervention is the parasite cell cycle mechanisms. Thus,
recent malaria drug discovery efforts have focused on targeting parasite-derived
cyclin-dependent kinase proteins as potential new drug targets. The aim of this
study was therefore to to establish the functional relationships between two of
these kinases, PfMRK and PfPK6, with a putative P. falciparum replication
licensing factor (PfRLF) with a view of establishing their potential as drug
targets.
A non-radiactive kinase assay was used to assess phosphorylation capacities of
PfMRK and PfPK6 on PfRLF. Bioinformatic tools were also used to
characterize PfRLF. Kinase inhibition assays using locally sourced natural
products as inhibitors to PfMRK and PfPK6 were carried out to unravel the drug
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target potential of these kinanses. Bioinformatic analyses revealed that the
putative PfRLF is actually the P.falciparum Minichromosome Maintenance 6
(PfMCM6) protein involved in replication. The kinase assays established that
both PfPK6 and PfMRK phosphorylate PfMCM6 in vitro and that PfMAT1
enhances PfMRK activity on PfMCM6. Enhancement of PfMRK activity by
PfMAT1 confirms previous observations that PfMRK is the plasmodial CDK7
equivalent. The Kinase inhibition assays showed that the Abyssinone class of
flavonoids actively inhibits the activity of PfMRK and PfPK6 on PfMCM6.
This study has confirmed the potential of PfMRK and PfPK6 as drug targets for
malaria treatment. Flavonoids, especially prenylated abyssinones are lead
compounds for antimalarials targeting these two kinases. Modification and
further characterization of these lead compounds may lead to therapeutic agents
with higher efficacy and specificity.
