A Novel Calcium-Dependent Protein Kinase 1 Inhibitor Potently Prevents Toxoplasma gondii Transmission to Foetuses in Mouse.

Treatments currently used to prevent congenital toxoplasmosis are non-specific of Toxoplasma gondii and have grievous side effects. To develop a more specific and less toxic drug, we have designed SP230, an imidazo[1,2-b]pyridazine salt targeting the Toxoplasma gondii calcium-dependent protein kinase 1 (TgCDPK1) and active against acute toxoplasmosis in mice. Efficiency of SP230 to inhibit foetal transmission of the parasite was evaluated in a mouse model of congenital toxoplasmosis. Swiss mice were infected at mid-pregnancy with tachyzoites or cysts of the ME49 strain of T. gondii by intraperitoneal and oral route, respectively, and treated with SP230 at 50 mg/kg for 5 days by the same routes. Parasite burden in organs of dams and in foetuses was measured by quantitative PCR. Intraperitoneal administration of SP230 drastically reduced the number of parasites (more than 97% of reduction) in the brain and lungs of dams, and led to a reduction of 66% of parasite burden in foetuses. Oral administration of SP230 was particularly efficient with 97% of reduction of parasite burdens in foetuses. SP230 did not impact number and weight of offspring in our conditions. This inhibitor of TgCDPK1 is a promising candidate for the development of alternative therapeutics to treat infected pregnant women.

Imidazo[1,2-b]pyridazines targeting Toxoplasma gondii calcium-dependent protein kinase 1 decrease the parasite burden in mice with acute toxoplasmosis.

The current therapeutic arsenal for toxoplasmosis is restricted to drugs non-specific to the parasite which cause important side effects. Development of more efficient and specific anti-Toxoplasma compounds is urgently needed. Imidazo[1,2-b]pyridazines designed to inhibit the calcium-dependent protein kinase 1 of Toxoplasma gondii (TgCDPK1) and effective against tachyzoite growth in vitro at submicromolar ranges were modified into hydrochloride salts to be administered in vivo in a mouse model of acute toxoplasmosis. All protonated imidazo[1,2-b]pyridazine salts (SP230, SP231 and SP232) maintained their activity on TgCDPK1 and T. gondii tachyzoites. Rat and mouse liver microsomes were used to predict half-life and intrinsic clearance, and the pharmacokinetic profile of the most rapidly degraded imidazo[1,2b]pyridazine salt (SP230) was determined in serum, brain and lungs of mice after a single administration of 50 mg/kg. Compounds were then tested in vivo in a murine model of acute toxoplasmosis. Mice infected with tachyzoites of the ME49 strain of T. gondii were treated for 4, 7 or 8 days with 25 or 50 mg/kg/day of SP230, SP231 or SP232. The parasite burdens were strongly diminished (>90% reduction under some conditions) in the spleen and the lungs of mice treated with imidazo[1,2-b]pyridazine salts compared with untreated mice, without the need for pre-treatment. Moreover, no increases in the levels of hepatic and renal toxicity markers were observed, demonstrating no significant signs of short-term toxicity. To conclude, imidazo[1,2-b]pyridazine salts have strong efficacy in vivo on acute toxoplasmosis and should be further tested in a model of mouse congenital toxoplasmosis.

Enhancement of the protective efficacy of a ROP18 vaccine against chronic toxoplasmosis by nasal route.

Infection with the parasite Toxoplasma gondii causes serious public health problems and is of great economic importance worldwide. No vaccine is currently available, so the design of efficient vaccine strategies is still a topical question. In this study, we evaluated the immunoprophylactic potential of a T. gondii virulence factor, the rhoptry kinase ROP18, in a mouse model of chronic toxoplasmosis: first using a recombinant protein produced in Schneider insect cells adjuvanted with poly I:C emulsified in Montanide SV71 by a parenteral route or adjuvanted with cholera toxin by the nasal route and second using a DNA plasmid encoding ROP18 adjuvanted with GM-CSF ± IL-12 DNA. If both intranasal and subcutaneous recombinant ROP18 immunizations induced predominantly anti-ROP18 IgG1 antibodies and generated a mixed systemic Th1-/Th2-type cellular immune response characterized by the production of IFN-γ, IL-2, Il-10 and IL-5, only intranasal vaccination induced a mucosal (IgA) humoral response in intestinal washes associated with a significant brain cyst reduction (50 %) after oral challenge with T. gondii cysts. DNA immunization induced antibodies and redirected the cellular immune response toward a Th1-type response (production of IFN-γ and IL-2) but did not confer protection. These results suggest that ROP18 could be a component of a subunit vaccine against toxoplasmosis and that strategies designed to enhance mucosal protective immune responses could lead to more encouraging results.

The antigen-specific response to Toxoplasma gondii profilin, a TLR11/12 ligand, depends on its intrinsic adjuvant properties.

Agonists that activate Toll-like receptors (TLR) are potential vaccine adjuvants. In particular, Toxoplasma gondii profilin (TgPRF) is recognized by TLR11/12 to generate an inflammatory response. Unlike most TLR ligands, TgPRF is also a protein and can therefore simultaneously induce innate and adaptive immune responses. We found that variations in the conformation of TgPRF can affect its ability to induce a TLR11/12-dependent inflammatory response. The secreted recombinant T. gondii (S2-profilin), produced by Schneider 2 cells, has lost its ability to generate an IL-12 response. Reduction of the intramolecular disulfide bonds in S2-profilin rescued the TLR11/12-dependent IL-12 response. Immunization of mice with reduced S2-profilin induced strong cellular and humoral responses compared to mice immunized with unreduced S2-profilin. A mixed Th1/Th2 response was induced with both S2-profilins. However, a more polarized Th1-type response, which was consistent with the IgG2a-polarized humoral response, was observed with reduced S2-profilin. In conclusion, the intrinsic adjuvant properties of TgPRF had significant consequences on the immune response against TgPRF.