A novel multi-stage acting antimalarial drug-candidate – plasmodrug

Malaria is still a major public health problem in 2018, since this infection due to the Plasmodium parasite, present in 91 countries, kills more than 440,000 people every year, with a majority of African children. As observed in most of infectious diseases, the emergence of resistant strains of P. falciparum toward antimalarials is nowadays responsible for a major concern, especially regarding the increasing resistant rate observed toward artemisinin derivatives (ref. treatments for P. falciparum malaria) in Asia, and the subsequent development of multi-resistant strains that could spread worldwide without any therapeutic option.

Then, to bypass parasitic resistance, new antimalarials are expected to be active on artemisinin-resistant strains and to possess a novel mechanism of action. It is also crucial to develop new molecules targeting both the asexual (hepatic and erythrocytic) and sexual (gametocytes) stages of the parasite, in a view to block malaria transmission. We previously identified a multi-stage acting lead compound in the thienopyrimidinone series, called Gamhepathiopine (or M1), which fulfills these criteria by acting on erythrocytic, hepatic and sexual stages of P. falciparum. This original molecule displays excellent in vitro activities even on the artemisinin-resistant parasites. In addition, our lead molecule does not exert its antiplasmodial activity by a mechanism of action already described for marketed antimalarials. Such promising results are however tempered by a rapid hepatic metabolization and a poor aqueous solubility, which limit gamhepathiopine activity in vivo.

In this context, we thus propose to pharmacomodulate gamhepathiopine to optimize its physico-chemical and pharmacokinetic properties and to potentiate its in vivo activity. To this aim, the metabolic stability issue will be addressed by modifying the two identified sites of metabolization of gamhepathiopine. In addition, the aqueous solubility will be improved by introduction of polar groups and/or synthesis of hydrophilic prodrugs. Additional pharmacomodulation work is also proposed in order to identify new antiplasmodial leads and to modulate the purine-analog character of the scaffold, in the hypothesis of a mode of action related to plasmodial kinase inhibition. The new molecules will be evaluated in vitro on the erythrocytic stages (sensible and resistant strains) and for their cytotoxicity. The most active compounds will be studied 1) for their mutagenicity 2) in vitro against hepatic stages ( (P. yoelii, P. falciparum and P. vivax and for their action on gametocytes and their capacity to block parasite transmission to Anopheles (vector of malaria)) then 3) in vivo, after potential preparation of lipidic nanoemulsions, on a murine model either infected by P. yoelii or humanized and infected by P. falciparum or P. vivax to validate the benefit of the chemical modifications toward PK properties and guarantee the preservation of the multi-stage acting properties. The last part of the project concerns the identification of the gamhepathiopine plasmodial target, in a view to elucidate its novel mechanism of action. A first hypothesis based on M1 chemical structure (purine analogue) and on recent literature data consists in postulating the possible involvement of a plasmodial kinase to explain its antiplasmodial activity. A phospho-proteomic study will thus be conducted to answer this question. In parallel and to extent the study of the mechanism of action of the lead molecule to potential non-kinase targets, an affinity chromatography procedure will be applied to Gamhepathiopine (immobilized on a solid support via a spacer) to try to isolate its target from a plasmodial lysate and to proceed to its identification by MALDI-TOF.