抄録
Cyanobacteria have drawn attention for their ability to produce a large number and variety of bioactive compounds. In our ongoing efforts to explore cytotoxic cyanobacterial metabolites, we isolated novel macrolides leptolyngbyalides A-D (1-4) from marine cyanobacterium Leptolyngbya sp. We report here the isolation, structure determination, and bioactivities of leptolyngbyalides and related compounds. Leptolyngbya sp. collected in Okinawa, Japan, was extracted with Me0H. After partition of the extract, the organic layer was subjected to fractionation using column chromatography. Finally, bioassay-guided fractionation afforded leptolyngbyalide A (1) and its analogs (2-4) as colorless amorphous solids. The molecular formula of 1 was determined to be C_<46>H_<76>O_<15> on the basis of ESIMS and NMR data. The planer structures of 1 and its analogs were established by spectral analysis, including 2D NMR techniques. Sugar moiety was determined to be xylose based on the coupling constants of acylated derivative. We are now trying to prepare for co-crystal of actin-leptolyngbyalide A for the purpose of X-ray crystal structure determination. Leptolyngbyalides showed remarkable growth inhibition against HeLa S_3 cells with IC_<50> values of 0.099-0.64 μM. They were revealed to depolymerize F-acin, by monitoring the fluorescent intensity of pyrene-labeled actin. Trypan blue dye exclusion assay and DNA ladder analysis showed that 1-4 induced apoptosis in HeLa cells. In addition, 1 selectively inhibited the phosphorylation of ERK in PDGF-stimulated NRK cells. Based on the above result, we expected that other actin depolymerizing compounds also exhibit apoptosis inducing activity. Aplyronine A (5) and mycalolide B (6), known as actin depolymerizing compounds, were revealed to induce apoptosis against HeLa S_3 cells and HL60 cells. These results made us focus on the potential correlation between depolymerization of actin and apoptosis. Then, we employed synthetic analogs of aplyronine A 7-10 to evaluate the correlation. Growth inhibitory activities of 7-10 were positively correlated with their actin depolymerizing activities, and analog 10 induced apoptosis against HL60 cells. These results suggested the possibility that apoptosis induced by 1-6 were caused by depolymerization of actin, and it is the subject of further study.
