Comparative analysis of in vitro antifungal activity and in vivo acute toxicity of the nystatin analogue S44HP produced via genetic manipulation

New polyene macrolide S44HP was purified from the culture of recombinant Streptomyces noursei strain with engineered nystatin polyketide synthase. S44HP, nystatin (NYS), and amphotericin B (Amph-B) were tested against 19 clinical fungal isolates in agar diffusion assay, which demonstrated clear differences in antifungal activities of these antibiotics. Sodium deoxycholate suspensions of all three antibiotics were subjected to acute toxicity studies in vivo upon intravenous administration in mice. NYS exhibited the lowest acute toxicity in mice in these experiments, while both Amph-B and S44HP were shown to be 4 times more toxic as judged from the LD₅₀ values. While the acute toxicity of S44HP was higher than that of Amph-B, the data analysis revealed a significantly increased LD₁₀ to LD₅₀ dose interval for S44HP compared to Amph-B. The data revealed structural features of polyene macrolides, which might have an impact on both the activity and toxicity profiles of these antibiotics. These results represent the first example of preclinical evaluation of an «engineered» polyene macrolide, and can be valuable for rational design of novel antifungal drugs with improved pharmacological properties.