DNA repair pathway as novel therapeutic target for toxoplasmosis

ANGEL SO; VANAGAS L; RUIZ DM

Mar del Plata

Congreso; Reunión Anual de Sociedades de Biociencia; 2019

SAIC

Toxoplasma gondii is an apicomplexanparasite of medical importance which causes toxoplasmosis in humans. Greateffort is currently being devoted towards the identification of novel drugscapable of targeting such infection. The homologous recombination repair (HRR)pathway may be of particular interest in this regard. T. gondii presentsa complex life cycle composed of two stages in human (tachyzoite andbradyzoite). Tachyzoites rapidly replicate within host cells to produce acuteinfection during which the parasite disseminates to tissues and organs. Highlyreplicative cells are subject to Double Strand Breaks (DSBs) by replicationfork collapse which leads to HRR. We could observe that the parasite HRRpathway is mostly conserved in T. gondii, but some key molecules to modulatethe HRR would be missing.  Among the conserved proteins we identified aputative ATM kinase, a member of the PI3K family, which is a central factorthat initiates DSB repair and activates cell cycle checkpoints. The treatmentof intracellular tachyzoites with ATM kinase-inhibitor KU-55933 affectsparasite replication and intracellular growth rates in a dose-dependent manner.This treatment also induces G1-phase arrest. Addition of KU-55933 toextracellular tachyzoites also leads to a significant reduction of tachyzoitereplication upon infection of host cells. We observed that ATM kinasephosphorylates H2A.X (γH2AX), a marker of DSB. The level of γH2AX increases intachyzoites treated with camptothecin (CPT), a drug that generates forkcollapse. The combination of KU-55933 and other DNA damaging agents such asmethyl methane sulfonate (MMS) and CPT produce a synergic effect, suggestingthat TgATM kinase inhibition sensitizes the parasite to damaged DNA. Bycontrast, hydroxyurea (HU) did not further inhibit tachyzoite replication whencombined with KU-55933. In conclusion, we have observed that the HRR pathway ofT. gondii emerges as a new therapeutic target for toxoplasmosis.