Role of crown-like side chains in the biological activity of substituted-phenoxazone drugs.

The antitumour activity of a number of synthetic crown-ether analogues of actinomycin D (AMD) was investigated in order to test the role of side chains that can complex metal cations. The AMD analogues consisted of two series of phenoxazone derivatives substituted with either benzo-15-crown-5 or benzo-18-crown-6 and with different lengths of spacers between the crown groups and the phenoxazone chromophore. The biological activities of the synthetic compounds were investigated by examination of drug-induced apoptosis and cell cycle perturbations in a human leukemia MOLT-3 cell line by flow cytometry. A compound with dimethylaminopropyl side chains on the phenoxazone chromophore was used as a control; this molecule was shown to intercalate into DNA by UV-visible spectroscopy and was found to have considerable cytotoxic activity in the 1-9 microM concentration range. Compounds with five-membered crown-ether side chains showed biological activity comparable with the control drug, whereas increasing the length of the spacers between the crown groups and the phenoxazone chromophore reduced the cytotoxic effect of the drugs. Compounds with six-membered crown-ether side chains reduced stabilization of the DNA double helical structure and abolished biological activity. Cell cycle alterations were observed only in drug systems which demonstrated cytotoxic activity. Cell cycle regulation was found to be sensitive to minor modifications (elongation of the spacer by one methylene group) in the side chains of the benzo-15-crown-5 derivatives, indicating that such series of synthetic drugs may serve as useful probes for investigation of cell cycle regulation processes.