In vivo toxicological evaluation of 3-benzylideneindolin-2-one: antifungal activity against clinical isolates of dermatophytes

Dermatophytes, the primary causative agents of superficial cutaneous fungal infections in humans, present a significant therapeutic challenge owing to the increasing prevalence of recurrent infections and the emergence of antifungal resistance. To address this critical gap, this study was designed to investigate the antifungal potential of 3-benzylideneindolin-2-one against dermatophytes and assess its in vivo toxicological profile using brine shrimp and zebrafish embryo models. The antifungal activity of 3-benzylideneindolin-2-one was evaluated against 30 clinical isolates of dermatophyte species, including Trichophyton mentagrophytes, Trichophyton rubrum, Microsporum gypseum, Microsporum canis, and Epidermophyton floccosum, by determining the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) using the broth microdilution method. The fungicidal activity was evaluated using time-kill assays. Toxicological effects were investigated using the brine shrimp lethality assay to determine Artemia salina nauplii mortality after 48 h of exposure, and the fish embryo acute toxicity test, which assessed lethality and developmental abnormalities in zebrafish (Danio rerio) embryos over a 96 h post-fertilization period. 3-Benzylideneindolin-2-one exhibited consistent fungicidal activity across all dermatophyte species, with MICs ranging from 0.25 to 8 mg/L and MFCs ranging from 1 to 32 mg/L. Time-kill assays revealed a concentration-dependent fungicidal effect on the microconidia. The compound exhibited moderate toxicity to A. salina nauplii, with LC50 values of 69.94 mg/L and 52.70 mg/L at 24 and 48 h, respectively, while showing no significant lethality within the MIC range. In zebrafish embryos, concentrations below 7.5 mg/L did not significantly affect lethality, hatchability, or induce morphological abnormalities. However, at a concentration of 10 mg/L, the compound induced mild toxicity in embryos, evidenced by a significant increase in mortality and the presence of morphological anomalies such as yolk-sac and pericardial edema compared to the control group. The consistent antifungal activity of 3-benzylideneindolin-2-one against clinically significant dermatophyte species, combined with its low toxicity within the therapeutic window, underscores its potential as a promising lead compound for the development of effective therapeutics for dermatophytosis.