The structure-activity relations of a series of synthetic phenoxazone drugs with aminoalkyl side chains of variable length and different terminal groups were investigated by examining their biological activity and DNA complexation affinity. Biological activity was determined from their ability to induce apoptosis and cell cycle perturbations (activation of cell cycle checkpoints) using the human malignant MOLT-3 cell line. The thermodynamic parameters of drug-DNA complexation were determined by differential scanning calorimetry. By comparing the activities of compounds with different terminal groups (amino, dimethylamino and diethylamino), we found that the existence of a terminal dimethylamino group in the alkylamino side chain is an important factor for anti-tumour activity. Minor modifications in the dimethylaminoalkyl side chain (e.g. elongation by one methylene group) led to notable changes in both the anti-tumour activity and DNA-binding properties of the drug, providing unambiguous evidence of a marked structure-activity relation.

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