Potencial antifúngico de heterocíclicos tiazólicos contra Cryptococcus spp

Abstract

Cryptococcosis is a fungal infection caused by yeasts of the genus Cryptococcus, being the species Cryptococcus neoformans the most frequently isolated and of great clinical importance. The thiazoline nucleus is a chemical structure found in different synthetic substances with wide biological activity. The objective of this work was, in the first part, to evaluate, through in vitro and in vivo tests, the antifungal potential of thiazole heterocyclic substances against Cryptococcus spp and the effects on virulence factors of C. neoformans. In the second part of this work, the objective was to evaluate the in vivo antifungal activity of the substance RN-104 in its complexed form with cyclodextrin in the treatment of an experimental model of murine cryptococcosis. The antifungal activity of 23 synthetic substances against isolates of C. neoformans H99 and C. neoformans L27/01 were evaluated using the Minimum Inhibitory Concentration (MIC) test. It was observed that 12 substances showed efficacy against the evaluated isolates, with MIC values ranging from 0.05 – 7.80 μg/mL. Furthermore, it was observed that substance PD76, a thiazole degradation product, presented a MIC value of 0.05 μg/mL, lower than that presented by its precursor. The substances HTI-12, HTI-13 and HTI-14 were evaluated against yeasts of medical importance of the genus Candida and the lowest MIC value was found for the substance HTI-14, with Candida albicans SC5314 being susceptible to the 3 substances evaluated. The toxicity of substances HTI-7, HTI-12, HTI-13 and HTI-14 was evaluated in the invertebrate model Tenebrio molitor and found LD50 >10 mg/kg. The substance HTI-14 was selected and evaluated in vitro against 12 isolates of C. neoformans and presented MIC values between 0.12 – 0.48 μg/mL, and CFM50 value equal to 0.17. The substance HTI-14 showed an indifferent interaction with the antifungals fluconazole and amphotericin B in the fractional inhibitory concentration test. When evaluating the effect of the substance HTI-14 on some virulence factors of C. neoformans, a reduction in metabolic activity was observed in sessile biofilm cells formed by the isolate C. neoformans H99 after treatment for 24 hours. In the evaluation of the antifungal activity in the invertebrate model Tenebrio molitor, the substances HTI-7 and HTI-14 were evaluated and showed to be able to increase the survival of the larvae with a performance compared to fluconazole. In the in vivo murine model, it was found that the substance HTI-7 at a concentration of 10mg/kg/day was efficient, being able to maintain 50% of survival of the treated animals after 72 days. In the evaluation of the antifungal activity of the substance RN-104 free and complexed with cyclodextrin in the experimental model of cryptococcosis, it was verified in the group of animals treated with the RN-104/cyclodextrin complex a reduction in the fungal load recovered from the brain tissue. The results presented in this work demonstrate the potential antifungal activity of heterocyclic thiazole substances against Cryptococcus spp. in vitro and in vivo, as well as a broad spectrum of activity in other yeasts of medical importance. The results found in this present work may represent potential prototypes for the study and development of new antifungal drugs, in order to expand the arsenal of drugs for the treatment of cryptococcosis.