Mechanisms of action and targets of new antimalarial redox molecules – MaTuRe

Indolone-N-oxides represent a new class of compounds with high antimalarial activity, but are insoluble in water. This is a limiting factor to study their mechanisms of action their efficacy and toxicity in vivo which are needed to assess their potential as drug candidate. To obtain this information, new molecules were designed and synthesized, technology formulations have been implemented to improve their solubility, cellular and mouse models expressing differentiated stages of the parasite, liver and red blood cell cycle were constructed to assess their in vitro and in vivo activity. The mechanisms of action have also been specified by combining several biological and physico-chemical methods. The relationships between redox molecules and these new properties malaria activities were specifically studied. This multidisciplinary approach supported by three university teams identified the potential of indolone-N-oxides and strongly encourages further steps of development.

With the aim to discover new antimalarials, we have identified several distinct chemo-type leading to the selection of indolone-N-oxide core (INOD) as a key structure with a redox pharmacophore (indolone-N-oxide core) and antimalarial activity . The project objectives were i) to study the biological activities in vitro and in vivo of the best hits on liver and erythrocyte stages, ii) improve their dissolution in water using formulation technologies, iii) understand their mechanisms of action in order to identify the development potential of these molecules. For this purpose, new molecules were designed and synthesized, technology formulations have been implemented, cellular and mouse models expressing differentiated stages of the parasite, liver and red blood cell cycle were constructed. The development of albumin-based nanoparticles, greatly increasing the aqueous dissolution of INODs, yielded inhibition of parasitemia of 99.1% and 97.5% in mouse model and humanized mice, respectively, with very significant increase in survival time (greater than 34 days compared with 17 days with conventional antimalarials) at a dose of 25 days mg/kg/sourisx4. The reversible oxidation-reducible nature of the nitrogen-carbon (C2) function of these molecules is essential for the activity; the radical intermediate formed by bioreduction in the erythrocyte initiates a redox signal fatal to the parasite. The demonstration of strong antimalarial activity in vivo on a murine model, thanks to the nano-formulation, and a better understanding of the mechanism of action have opened a partnership with a pharma industry.

The scientific impact of the results obtained during the project, thanks to the three partners, is very important: the originality of the series INOD has been demonstrated and has generated a collaboration with an industrial interested in drugs for neglected diseases of developing countries and open discussions with another organization for Phase 1 trials of the artemisinin formulation.

A multi-partner scientific publication was edited (Ibrahim N. Ibrahim H., J. Dormoi, Briolant S., B. Pradines, A. Moreno, Mazier D., Ph. Legrand, Nepveu F. Albumin-bound nanoparticles of practically water-insoluble antimalarial lead greatly enhance its efficacy. Int. J. Pharmaceutics efficacy., 2014, 464, 214-224). Two other joint publications are in preparation. Five monopartner publications were published. Oral papers were presented including 5 invited lectures. A French patent filed in May 2013 has been extended to the European level in May 2014.

To fight the burden of malaria strong efforts have to be joined on complementary scientific areas: malaria vaccine research, malaria drugs, and research on parasite biology and disease development. The human malaria parasites must go through a multiplication phase in the liver before the pathogenic infection of red blood cells is initiated. The liver stage parasites of all species can be targeted by various drugs, but only one drug, primaquine, is currently used against liver stage parasites. The challenge for the next generation of molecules is to discover new therapies which protect the world against the emergence of resistance to artemisinins and which prevent relapse from liver sleeping forms of the parasite. The MaTuRe project has been grounded to propose compounds which could be developed into drug candidates against malaria with a chemoprophylactic and curative profile. The project takes leads previously identified in a new series and active against the blood stage of the parasite life cycle to start a research program on their mechanisms of action and biological activities on the liver stages. Comprehension of their mode of action and biotransformation together with the use of drug delivery strategies to improve their biological activities in vivo are the main tasks of the project. The MaTuRe project in this way combines knowledge and technologies of pharmacochemistry and pharmacology, parasitology, biophysics and physical-chemistry, brought by three academic and one private partners.