Imidazoacridinones arrest cell-cycle progression in the G2 phase of L1210 cells

Imidazoacridinones are a new class of highly potent antineoplastic agents synthesised at the Technical University of Gdansk. The pharmacophoric alkyldiamine group, which is also present in anthracenediones (e.g. ametantrone, mitoxantrone), has been shown to be responsible for their antineoplastic activity. In view of their chemical similarity to anthracenediones, we anticipated that the imidazoacridinones would have a mechanism of action similar to that of these agents and that this would be reflected by a similar influence on cell-cycle progression. Flow cytometry was used to monitor the effect of three derivatives of imidazoacridinone (C-1263, C-1310 and C-1311) on L1210 cell cycle traverse at concentrations ranging from 0.01 to 0.9 microgram/ml, corresponding to their 50% and 90% effective concentrations (EC50 and EC90 values), over times of drug treatment ranging from 1 to 48 h. The results demonstrate that all of the compounds produced a similar effect, inducing preferential and complete arrest (accumulation) of cells in the G2 phase of the cell cycle (i.e. G2 block). The kinetics of the induction of G2 arrest were dependent on both the dose and the duration of treatment. Cell-cycle arrest was reversible for up to about 3 h of treatment, being quite irreversible at longer incubation times. Microscopic inspection of cells performed in parallel with flow cytometry confirmed that imidazoacridinones induced a G2, not a G2/M, block.