Background: Mitotane,(o,p-DDD)is a compound with potent adrenotoxic effect and is able to block cortisol synthesis by inhibiting 11β-hydroxylation and cholesterol chain cleavage. For these reasons, mitotane was widely used in the treatment of adrenocortical cancer. Nevertheless the biological mechanism induced by these treatments in this cancer cells remain unknown.
Aim: To study whether the o,p-DDD could increase the susceptibility to the radiation exposure in adrenocortical cancer cells, we investigated the cell growth inhibition, cell cycle perturbation and cell cycle related molecules at 24, 48, 72, 96 and 120 hours of post-irradiation (post-IR).
Results: The analysis of cell growth inhibition showed that o,p-DDD/6Gy/min combined treatment enhanced the inhibitory effect induced by 6Gy alone (83% and 50%, respectively). The cell cycle analysis performed at 24 hours post-IR showed that 6 Gy/min alone and o,p-DDD/6Gy/min combination induced the same accumulation of cells in the G2 phase, with a concomitant depletion from the G1 phase, as compared to untreated cells. However, a significant difference between the two treatments is observed during the cell cycle progression. In fact, at 120 hours post-IR, the H295-R cells are able to recover the 6 Gy/min induced G2 block (27%) while the cells treated with o,p-DDD/6Gy/min are still arrested in the G2 phase (43%). The inability of the cells to recover the G2 block could be related to cyclin B1, A and cdk2 modulation. Cortisol levels in pharmacological treatments were undetectable, while in irradiated cells its values are included in normal range. We found an increase both the irradiated and treated with adrenolytic therapy in a time dependent manner. Proteomic study are in progress for determination the proteic pattern induced by o,p-DDD in the same cell line.
Conclusions: The adrenolytic compound o,p-DDD renders adrenocortical cell line more susceptibility to radiotherapy determining a G2 irreversible block.