The chondramides: cytostatic agents from myxobacteria acting on the actin cytoskeleton

Chondramides are cyclodepsipeptides produced by strains of the myxobacterium, Chondromyces crocatus. These peptides, which have been reported to inhibit yeast and mammalian cell proliferation, are related to jasplakinolide, which has been isolated from marine sponges of the genus Jaspis and has been shown to interfere with the actin cytoskeleton (a structural component of cells that helps maintain their shape and is involved in processes, such as cell division and cell locomotion). We studied the effects of the chondramides (A, B, C, and D) on tumor cell growth, on cytoskeletal structure, and on actin polymerization in vitro and compared these effects with those of cytochalasin D and jasplakinolide.

Cell proliferation was measured by means of tetrazolium salt reduction assays. Effects on the cytoskeleton were studied by use of fluorescence techniques, and actin polymerization in vitro was measured by means of viscosimetry.

Proliferation of tested tumor cell lines was inhibited by the chondramides. Concentrations that inhibited proliferation by 50% (IC50 values) ranged from 3 to 85 nM and were of the same order of magnitude as those found for cytochalasin D and jasplakinolide. Fluorescence staining of potoroo cells incubated with chondramides A and B showed that organization of the actin cytoskeleton was disrupted; however, the microtubule system was not affected. Viscosimetric measurement showed that, depending on the experimental conditions, chondramide A induced or accelerated actin polymerization in vitro.

The chondramides--unlike jasplakinolide--can be produced in large amounts by fermentation, and, similar to jasplakinolide, they appear to have antiproliferative activity against carcinoma cell lines by targeting the actin cytoskeleton.