Novel Isoxazole-Based Antifungal Drug Candidates

Abstract

Microbiological communities have a significant impact on health and disease. Candida are ubiquitous fungal pathogens that colonize the mucosal surfaces of the genital, urinary, respiratory, and gastrointestinal tracts, as well as the oral cavity. If the immune system is inadequate, then Candida infections may pose a significant threat. Due to the limited number of clinically approved drugs for the treatment of Candida albicans-based infections and the rapid emergence of resistance to the existing antifungals, a novel series of isoxazole-based derivatives was synthesized and evaluated in vitro for their anti-Candida potential. Two compounds, PUB14 and PUB17, displayed selective antifungal activity without negatively affecting beneficial microbiota, such as Lactobacillus sp., at the same time. Moreover, these compounds exhibited significantly lower cytotoxicity in comparison to conventionally applied local antimicrobial (octenidine dihydrochloride), indicating their potential for safe and effective clinical application in conditions such as vulvovaginal candidiasis. The selective antifungal activity of PUB14 and PUB17 against C. albicans, coupled with its absence of antibacterial effects and minimal cytotoxicity towards HeLa cells, suggests a targeted mechanism of action that warrants further investigation. Consideration of the need to search for new antifungal agents and the discovery of an antifungal potential drug that does not inhibit lactobacilli growth could be a potential strategy to prevent and combat vulvovaginal candidiasis. This striking capacity to eradicate biofilm formed by Candida reveals a new approach to eradicating biofilms and sheds light on isoxazole-based derivatives as promising anti-biofilm drugs.

Keywords: anti-Candida; biofilm; isoxazoles.

Figure 1

Isoxazole-based derivatives with antimicrobial activity obtained by our team.

Figure 2

The series of isoxazole-based derivatives PUB11–18.

Figure 2

The series of isoxazole-based derivatives PUB11–18.

Figure 3

Visualization of C. albicans biofilm exposed to PUB17 and PUB14 compounds. C+ is a biofilm exposed to saline; “Oct” is a C. albicans biofilm exposed to octenidine dihydrochloride, a compound of known anti-biofilm activity. Performed in 3 repeats (1–3). Red shapes are dead C. albicans biofilm-forming cells; green shapes are live C. albicans biofilm-forming cells. Black shapes are areas devoid of live and dead cells. Live/dead Biofilm visualization kit; objective × 20; LumaScope 620 magnification × 20 (EtaLuma, San Diego, CA, USA).

Figure 4

% cytotoxicity of PUB14, PUB17 and 0.1% octenidine dihydrochloride towards HeLa cells. Asterisks indicate statistically significant differences between levels of cytotoxicity in analyzed compounds, ns—lack of statistical differences (p < 0.0001, ANOVA/Brown–Forsythe test for multiple comparisons).