CC-1065 is a potent antitumor antibiotic which is cytotoxic to P388 and L1210 leukemia cells in vitro and in vivo. CC-1065 covalently binds to calf thymus DNA preferentially to adenine-thymine regions at N3 of adenine. Here, we compare CC-1065 interaction with P388-derived chromatin, DNA, and histones as measured by electronic absorption and circular dichroism. Two CC-1065 analogues (U-71,184 and its enantiomer, U-71,185) which show different biological activities from CC-1065 were also studied.

The shape and temporal behavior of the induced circular dichroism curves generated by CC-1065 or its analogues bound to chromatin were similar to CC-1065 plus DNA. This suggested that CC-1065 and its analogues bind to the minor groove of chromatin DNA in a manner similar to calf thymus DNA. However, the binding of CC-1065 and its analogues to DNA induced a more intense circular dichroism band than binding to chromatin. The order of interaction for both chromatin and DNA was CC-1065>U-71,184>U-71,185. In contrast to the essentially irreversible binding to DNA after 24-h incubation, binding to chromatin was primarily a reversible interaction, the degree of reversibility being U-71,185>U-71,184 = CC-1065. CC-1065 binds weakly and nonspecifically to histones.

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