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Phospholipid metabolism, a novel target for antimalarial drugs - development of the pharmacological model


The main objective of the project is the development of new antimalarial drugs that interact with the malarial parasite phospholipid metabolism and could provide a solution to P. falciparum polychemoresistant malaria.

Although there is no indication of potential resistance to date, we believe that we must actively initiate studies concerning mechanisms that could be involved in potential acquisition of resistance to the effectors. This molecular approach is worth immediate investigation since precise mechanisms can be expected from the suspected drug site. Results could lead to the knowledge of a whole set of metabolic pathways vital for parasite growth.

The main objectives will be to synthesize new series of original and potentially alternative compounds aimed at improving tolerance and oral absorption. Identification, isolation and characterization of the pharmacological target.

To carry out thorough antimalarial activity studies including chemosensitivity, therapeutic index after in vivo oral formulations in P. falciparum-infected monkeys, and against others stages (non erythrocytic) or species (e.g. P. vivax).

To describe the pharmacokinetic properties and toxic evaluation of lead compounds will also be studied.

Experimental induction of resistances, characterisation of effector-resistant P. falciparum malaria and alternative to resistance. In case of resistance, combinations with other current approaches would be studied.
Expected Outcome

The work content is totally devoted to the establishment of a new pharmacological model. Although the outcome of fundamental and experimental research can never be known in advance, the numerous complementary experimental approaches that are planned within the different partner laboratories, should allow to reach the proposed objectives. It is anticipated that some of our research effort will lead to potential industrial or pharmacological outcomes.
Concerning malaria, by now, the most urgent need concerns a first-line oral substitute to chloroquine. That is one of the reasons we want to achieve an oral formulation of our compounds, rather than risking the development of a non-oral administerable compound.
The target could be a common one between different parasites. However, until now, significant inhibition at concentrations lower that 1 mg/l has not been observed for any other parasites except Babesia. On the other hand, the susceptibility of the protozoan parasite Babesia, that also invades erythrocytes but is not sensitive to haemoglobin degradation-related lysomotropic agents, is interesting as it confirms the absence of cross-resistance of the PL metabolism pharmacological effectors with the current lysomotropic antimalarial agents.
* Chemical synthesis of compounds aimed at improving tolerance and oral absorption. This includes compounds with new cationic heads that could be used if the current lead compounds may prove to have unacceptable drawbacks, and also the synthesis of prodrugs with the aim of improving oral absorption and, eventually to promote the development a new generation of effectors.

* Identification and characterisation of the pharmacological target. Affinity chromatography using a column of immobilized effectors is proposed. If necessary, chemists will also synthesise photoreactive lead compound derivatives. Pharmacological target cloning should allow its complete characterisation, determination of the active site and help in the design of new effectors.

* It is of utmost interest to study the mechanisms of regulation of PL biosynthesis pathways in Plasmodium. More than just a problem of metabolic regulation, this program concerns mechanisms which could be involved in resistance that the parasite could develop when the supply of choline is blocked due to pharmacological interference. Biochemical and genetical approaches will be used as a powerful tool for the elucidation of metabolic regulations as well as the biological significance of the different metabolic pathways in Plasmodium. We will be particularly concerned by the metabolites and activities of CDP-choline pathway which synthesizes de novo PC. Additionally, we will focus on PS Decarboxylase activity which also provides Plasmodium for an important part of PC.

* Antimalarial activity, pharmacokinetics and toxic evaluation of lead compounds. The first priority tasks will be (1) in vitro and in vivo evaluation of antimalarial activity against P. falciparum blood stages. (2) 4 to 5 lead compounds will be tested in the P. falciparum / SCID mouse model , (3) therapeutic index of various formulations (intramuscular and oral modes) of 2-3 compounds in Aotus monkeys infected with P. falciparum. Blood samples will also be collected to perform bio-assays of the seric compounds.

* Activity of 2-3 lead compounds against P. falciparum isolates with various degrees of resistance will be determined.

* To evaluate antimalarial activity against P. vivax/P. cynomolgi blood stages. (2-4 lead compounds). According to results, to evaluate against P. cynomolgi in rhesus monkey and against P. vivax in Saimiri monkey for comparison with P. falciparum/Aotus.

To test the activity of the lead compounds against the non-erythrocytic stages of Plasmodium.

* To determine pharmacokinetics properties of lead compounds (ex vivo tests), and to determine toxicity of lead compounds.

* Resistance mechanism and alternative to resistance. This includes the in vitro induction of resistance against choline analogs, the characterisation of effector-resistant P. falciparum malaria (pharmacological target and lipid metabolism), and examination of genes associated with resistance to standard antimalarial drugs Alternatives to resistance would include combined action of PL metabolism inhibitors with known antimalarial drugs

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Place Eugène Bataillon

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Participants (5)