IN VITRO AND IN VIVO EFFECT OF SYK INHIBITORS AS A NEW ANTIMALARIAL DRUGS

The Artemisinin-based combination therapies remain the most effective treatment for uncomplicated P.falciparum malaria; however, resistance to artemisinin has been detected in some areas of the Southeast Asia. In the light of this topic, the development of new antimalarial represents one of the main target. During the intra-erythrocyte cycle of P.falciparum the band 3 is tyrosine phosphorylated by Syk kinase, inducing membrane vesiculation with a consequent membrane weakening. Syk inhibition suppresses both band 3 phosphorylation and vesiculation, consequently the parasite egress and their capability to infect new erythrocytes. The purpose of the present work is to investigate in vitro and in vivo activity of Syk inhibitors on parasite growth, and to evaluate the efficacy of the current antimalarial therapy in Vietnam, Dihidroartemisinin-Piperaquine, in order to obtain more information and to set a panel of tests required to evaluate the usefulness of a new Artemisinin Combination Therapy, containing Syk inhibitors, as malaria treatment. Different Syk inhibitors, Gleevec and the Syk inhibitor II, have been tested in P. falciparum infected RBCs. The in vitro and ex vivo experiments confirmed the activity of these Syk inhibitors to suppress the parasite growth, markedly affecting the egress phase, with an average of IC50 below 2 µM. The presence of delayed parasite clearance, DPC, was examined in Vietnam. In the provinces of Quang Tri, Gia Lai and Ninh Thuan, it was observed a high prevalence of DPC by qPCR and by light microscopy. In addition, in the Gia Lai province was observed a high prevalence (80 %) of the mutation C580Y on K13 gene, in the patients with DPC. According with WHO these results are indicative of artemisinin resistance; however, in the following months, the patients, which presented DPC, have not shown the recurrence of malaria symptoms. Successively factors that could influence the insurgence of DPC were investigate. The sex does not seem to interfere. Regarding the age in Quang Tri, the large majority of the malaria patients with a strongly reduced clearance has been observed in younger patients, indicating an important role of the immune response; nevertheless the poor number of young patients in the other provinces ,we cannot draw any assumptions. The analysis of some human mutations affecting the RBCs (HB E, Hb Constant Spring and G6PD deficiency Viangchan) in Quang Tri, revealed a significative prevalence of G6PD deficiency Viangchan, in the group of patients with delayed parasite clearance, indicating its potential interference. Conversely, in Gia Lai and Ninh Thuan, within the different groups of malaria patients, it has been observed no significant interference of any mutations with the DPC (p-value > 0.05). In the light of the prominent results obtained using Syk inhibitors, and considering that the artemisinin appears to be still efficacy, the future plan is to perform a new clinical trial in South Vietnam, to test the efficacy of Gleevec in combination with Dihidroartemisin.