High-Throughput Screening to Identify Inhibitors of Plasmodium falciparum Importin alpha

The global burden of malaria and toxoplasmosis has been limited by the use of efficacious anti-parasitic agents, however, emerging resistance in Plasmodium species and Toxoplasma gondii threatens disease control worldwide, implying that new agents/therapeutic targets are urgently needed. Nuclear localization signal (NLS)-dependent transport into the nucleus, mediated by members of the importin (IMP) superfamily of nuclear transporters, has shown potential as a target for intervention to limit viral infection. Here, we show for the first time that IMP alpha from P. falciparum and T. gondii have promise as targets for small molecule inhibitors. We use high-throughput screening to identify agents able to inhibit P. falciparum IMP alpha binding to a P. falciparum NLS, identifying a number of compounds that inhibit binding in the mu M-nM range, through direct binding to P. falciparum IMP alpha, as shown in thermostability assays. Of these, BAY 11-7085 is shown to be a specific inhibitor of P. falciparum IMP alpha-NLS recognition. Importantly, a number of the inhibitors limited growth by both P. falciparum and T. gondii. The results strengthen the hypothesis that apicomplexan IMP alpha proteins have potential as therapeutic targets to aid in identifying novel agents for two important, yet neglected, parasitic diseases.