Ciprofloxacin Derivatives Affect Parasite Cell Division and Increase the Survival of Mice Infected with <i>Toxoplasma gondii</i>

<div><p>Toxoplasmosis, caused by the protozoan <i>Toxoplasma gondii</i>, is a worldwide disease whose clinical manifestations include encephalitis and congenital malformations in newborns. Previously, we described the synthesis of new ethyl-ester derivatives of the antibiotic ciprofloxacin with ~40-fold increased activity against <i>T</i>. <i>gondii in vitro</i>, compared with the original compound. Cipro derivatives are expected to target the parasite’s DNA gyrase complex in the apicoplast. The activity of these compounds <i>in vivo</i>, as well as their mode of action, remained thus far uncharacterized. Here, we examined the activity of the Cipro derivatives <i>in vivo</i>, in a model of acute murine toxoplasmosis. In addition, we investigated the cellular effects <i>T</i>. <i>gondii</i> tachyzoites <i>in vitro</i>, by immunofluorescence and transmission electron microscopy (TEM). When compared with Cipro treatment, 7-day treatments with Cipro derivatives increased mouse survival significantly, with 13–25% of mice surviving for up to 60 days post-infection (vs. complete lethality 10 days post-infection, with Cipro treatment). Light microscopy examination early (6 and 24h) post-infection revealed that 6-h treatments with Cipro derivatives inhibited the initial event of parasite cell division inside host cells, in an irreversible manner. By TEM and immunofluorescence, the main cellular effects observed after treatment with Cipro derivatives and Cipro were cell scission inhibition - with the appearance of ‘tethered’ parasites – malformation of the inner membrane complex, and apicoplast enlargement and missegregation. Interestingly, tethered daughter cells resulting from Cipro derivatives, and also Cipro, treatment did not show MORN1 cap or centrocone localization. The biological activity of Cipro derivatives against <i>C</i>. <i>parvum</i>, an apicomplexan species that lacks the apicoplast, is, approximately, 50 fold lower than that in <i>T</i>. <i>gondii</i> tachyzoites, supporting that these compounds targets the apicoplast. Our results show that Cipro derivatives improved the survival of mice acutely infected with <i>T</i>. <i>gondii</i> and inhibited parasite replication early in the first cycle of infection <i>in vitro</i>, highlighting their therapeutic potential for the treatment of toxoplasmosis.</p>