Bafilomycin C1

Bafilomycin C1, which was isolated from Streptomyces albolongus in our previous work, exhibited strong cytotoxicity against several cancer cell lines. This study aimed to evaluate its antitumor effect on human hepatocellular cancer SMMC7721 cells and the underlying mechanism in vitro and in vivo. MTT assay revealed that bafilomycin C1 retarded SMMC7721 cell growth and proliferation. Western blot and real-time qPCR analysis revealed that bafilomycin C1 caused partial G0/G1 phase cell-cycle arrest, downregulated the expression of cyclin D3, cyclin E1, CDK2, CDK4, and CDK6 and upregulated the expression of p21. Moreover, bafilomycin C1 caused mitochondrial membrane dysfunction through oxidative stress. Furthermore, bafilomycin C1 decreased the expression of Bcl-2; increased the expression of Bax, p53, and P-p53; and increased cleavage of caspase-9 and caspase-3, thereby inducing the intrinsic caspase-dependent apoptotic pathway. In vivo experiments in mice suggested that bafilomycin C1 suppressed tumor growth with few side effects. Cell-cycle arrest and induced apoptosis in tumor tissues in a mouse model treated with bafilomycin C1 were demonstrated by histological analyses, western blot and TUNEL. These findings indicate that bafilomycin C1 may be a promising candidate for hepatic cellular cancer therapy.

Streptomyces halstedii K122 was previously found to produce antifungal compounds on solid substrates that inhibit radial growth of fungi among Ascomycetes, Basidiomycetes, Deuteromycetes, Oomycetes, and Zygomycetes, and strongly affected hyphal branching and morphology. During growth of S. halstedii K122 in submerged culture, no antifungal activity could be detected. However, cultivation of S. halstedii in thin (1 mm) liquid substrate layers in large surface-area tissue culture flasks caused intense growth and sporulation of S. halstedii K122, and the biologically active compounds could be extracted from the mycelium with methanol. Antifungal compounds were purified using C18 solid phase extraction and silica gel column chromatography, and identified as bafilomycins B1 and C1, using 2D NMR and FAB MS. Production of bafilomycins, which are specific inhibitors of vacuolar ATPases, has not been reported from S. halstedii previously. Minimum inhibitory concentrations (MIC) of bafilomycins B1 and C1, amphotericin B, and nikkomycin Z were determined at pH 5.5 and 7.0 for the target fungi Aspergillus fumigatus, Mucor hiemalis, Penicillium roqueforti, and Paecilomyces variotii. Penicillium roqueforti was the most sensitive species to all the compounds investigated. The MIC values for amphotericin B were 0.5-4 micrograms.mL-1 for the fungi tested, and pH did not affect the toxicity. The MIC values for nikkomycin Z ranged from < 0.5 microgram.mL-1 for Mucor hiemalis to > 500 micrograms.mL-1 for Aspergillus fumigatus, and pH had no influence on toxicity. Bafilomycins B1 and C1 were equally active against the fungal species tested, with MIC values in the range of < 0.5-64 micrograms.mL-1. All fungi were more sensitive to both bafilomycin B1 and C1 at pH 7.0 than at pH 5.5.

Microbes sense and respond to their environment with small molecules, and discovering these molecules and identifying their functions informs chemistry, biology, and medicine. As part of a study of molecular exchanges between termite-associated actinobacteria and pathogenic fungi, we uncovered a remarkable fungal metabolite, homodimericin A, which is strongly upregulated by the bacterial metabolite bafilomycin C1. Homodimericin A is a hexacyclic polyketide with a carbon backbone containing eight contiguous stereogenic carbons in a C20 hexacyclic core. Only half of its carbon atoms have an attached hydrogen, which presented a significant challenge for NMR-based structural analysis. In spite of its microbial production and rich stereochemistry, homodimericin A occurs naturally as a racemic mixture. A plausible nonenzymatic reaction cascade leading from two identical achiral monomers to homodimericin A is presented, and homodimericin A's formation by this path, a six-electron oxidation, could be a response to oxidative stress triggered by bafilomycin C1.