Strepoxazine A, a new cytotoxic phenoxazin from the marine sponge-derived bacterium Streptomyces sp. SBT345

One new phenoxazin analogue, strepoxazine A (1), along with two known antibiotic phenazines phencomycin (2) and tubermycin B (3) were isolated from the solid culture of Streptomyces sp. SBT345 which had previously been recovered from the Mediterranean sponge Agelas oroides. The structures of compounds 1, 2 and 3 were determined by spectroscopic analyses including 1D and 2D NMR, and HR-ESI-MS experiments as well as comparison to the literature. We further investigated the apoptotic effect of the three compounds on the human promyelocytic leukaemia cells HL-60 and human breast adenocarcinoma cells MCF-7. Only strepoxazine A (1) showed cytotoxicity against leukaemia cells HL-60 cells. These results demonstrate that sponge-associated actinomycetes are rich sources for natural products with new pharmacological activities and relevance to drug discovery.