Niraparib tosylate (MK-4827, ZEJULA) is a selective inhibitor ofPARP1/PARP2withIC50of 3.8 nM/2.1 nM. Niraparib increases formation of PARP-DNA complexes resulting in DNA damage,apoptosis, and cell death.
Micromolar concentrations of niraparib radiosensitizes tumor cell lines derived from lung, breast, and prostate cancers independently of their p53 status but not cell lines derived from normal tissues. Niraparib also sensitizes tumor cells to H2O2 and converts H2O2-induced single strand breaks (SSBs) into DSBs during DNA replication.
In vivo
MK-4827 strongly enhances the effect of radiation on a variety of human tumor xenografts, both p53 wild type and p53 mutant. MK-4827 reduces PAR levels in tumors by 1 h after administration which persisted for up to 24 h. In vivo treatment with MK-4827 and radiation prolonged survival (p<0.01) compared to single modalities. In vivo superiority of MK-4827 plus radiation is further documented by significant elevations of cleaved caspase-3 and γ-H2AX in tumors from the combination group compared to single modality cohorts.