Avaliação da atividade de produtos naturais otimizados em células planctônicas e biofilmes de Candida spp., Cryptococcus neoformans e Sporothrix spp

Abstract

In recent decades, cases of severe fungal infections have increased, driven by the growing number of immunocompromised individuals, with reports of resistance and relapse becoming increasingly common. With only five existing classes of antifungals, the search for new drugs becomes urgent. In this sense, natural products have shown great potential. However, their low solubility, instability, and potential toxicity restrict their use. Optimization strategies, such as semisynthesis and microencapsulation, can be used in this regard. Considering this, this study aimed to evaluate the effects on planktonic cells and biofilms of natural products optimized by semisynthesis against Candida spp., Cryptococcus neoformans, and Sporothrix brasiliensis, and by microencapsulation of essential oils against Sporothrix spp. The study was conducted in two phases. The first evaluated the semisynthetic histone deacetylase inhibitors (iHDACs) N-hydroxy-8-(3-methoxyphenyl)octanamide (LDT536) and 8-(2-carbomethoxy)-N-hydroxy- 8-(3-methoxyphenyl)octanamide (LDT537) against Candida albicans, Candida tropicalis, C. neoformans, and S. brasiliensis through molecular docking, planktonic susceptibility, checkerboard assays with azoles, biofilm inhibition, cytotoxicity, and in vivo toxicity in Galleria mellonella. In the second phase, the in vitro planktonic susceptibility, drug interaction, and biofilm susceptibility of Sporothrix spp. to lemongrass and geranium essential oils encapsulated in chitosan microparticles were evaluated. In the in silico analyses, LDT536 and LDT537 demonstrated affinity for the catalytic sites of Class I fungal HDACs. In vitro, they inhibited the planktonic growth of the fungi, with MICs ranging from 32 to >64 µg/mL for LDT536 and from 8 to >64 µg/mL for LDT537, reducing the metabolic activity of C. albicans biofilms by more than 50% at a concentration of 4 µg/mL. In association with azole antifungals, they exhibited strong synergism against resistant strains of C. tropicalis, reducing the MIC of fluconazole by up to 256-fold. LDT536 demonstrated cytotoxicity at a concentration of 53.07 μg/mL, while LDT537 showed IC50 values of 9.42 μg/mL, with no deaths observed in G. mellonella larvae at a dose of 600 µg/mL. Meanwhile, the microparticles were able to inhibit in vitro planktonic cells and biofilms of Sporothrix spp. In the filamentous form of the fungus, empty microparticles (MQ) obtained the lowest MICs, between 0.25 and 2 µg/mL. In the yeast phase, MQGEO stood out with an MIC of 1 µg/mL for all evaluated strains. In combination with amphotericin B (AMB), MQCL and MQ demonstrated strong synergism against yeasts, reducing the MIC of AMB by up to 32 and 16 times, respectively. Against mature yeast biofilms, MQGEO reduced fungal metabolic activity starting at 32 µg/mL, presenting anSMIC50 of 161.27 µg/mL. Thus, it is concluded that both chemical-pharmaceutical semisynthesis and microencapsulation proved to be promising strategies in optimizing the antimicrobial activity of natural products, mainly in association with classical drugs, offering new perspectives for the management of invasive and refractory fungal infections.