6(5H)-Phenanthridinone

6(5H)-Phenanthridinone is a small molecule poly(ADP-ribose) polymerase (PARP) inhibitor with immunosupperessive effects. 6(5H)-Phenanthridinone has been shown to inhibit concanavilin A-induced lymphocyte proliferation, producing the observed immunosuppressant activity of this compound. It has also been shown to potentiate the effect of ionizing radiation on developing cells, strongly increasing the radiation-induced inhibition of cell proliferation, which suggests use of 6(5H)-Phenanthridinone as a probe into the role of PARP in cellular response to irradiation. Treatment of cells with 6(5H)-Phenanthridinone and various DNA-damaging agents showed a resistance to apoptosis versus treatment with DNA-damaging agents alone, indicating that PARP activity is involved in the apoptotic process.