Role of the human GTPase Rac1 in Plasmodium falciparum infection of erythrocytes

Malaria is the deadliest parasitosis worldwide, causing 216 million cases and 445.000 casualties in 2016. The disease is caused by Plasmodium parasites that develop and grow inside human erythrocytes. Among them, Plasmodium falciparum is the deadliest one. The human protein Rac1 is a GTPase involved in the development of several cancers and essential in the invasion of the host cell by many intracellular pathogens, including Toxoplasma gondii, which belongs to the same phylum as P. falciparum. Rac1 has been extensively studied and several cell permeable inhibitors of the GTPase have already been developed. In order to investigate a possible role of Rac1 in malaria infection, we analysed Rac1 subcellular localization in P. falciparum infected erythrocytes by immuno-fluorescence assays. We showed that during invasion of the host cell, Rac1 is recruited to the site of parasite entrance and is activated by the parasite. During the intraerythrocytic growth of the parasite, Rac1 is further recruited from the cell membrane to the parasitophorous vacuole membrane . These data suggest that Rac1 may play a role in P. falciparum infection of human erythrocytes.To confirm these data, we performed invasion assays on wt erythrocytes from donor, in the presence of two different Rac1-specific inhibitors, further confirming the role of the GTPase in parasite invasion of the host cell. Both the Rac1 inhibitors show an effect also on parasite growth. Finally, 9 different chemical inhibitors of Rac1 were tested on synchronous P. falciparum cultures. These reduced parasite growth with a half minimal inhibitory concentration (IC50) below 40 µM, indicating that Rac1 is a druggable target . Two among the inhibitors showed nanomolar IC50. Rac1 may be thus considered an interesting target for the development of novel anti-malarial drugs. with the advantage of being a well studied protein, with a known x-ray crystal structure and several specific inhibitors on commerce. Moreover, therapies targeting the host instead of the parasite reduce the probability of resistance insurgence, a critical issue for currently available drugs.