The PARP1 Inhibitor Niraparib Represses DNA Damage Repair and Synergizes with Temozolomide for Antimyeloma Effects.

Purpose: Poly(ADP-ribose) polymerase 1 (PARP1) is necessary for single-strand break (SSB) repair by sensing DNA breaks and facilitating DNA repair through poly ADP-ribosylation of several DNA-binding and repair proteins. Inhibition of PARP1 results in collapsed DNA replication fork and double-strand breaks (DSBs). Accumulation of DSBs goes beyond the capacity of DNA repair response, ultimately resulting in cell death. This work is aimed at assessing the synergistic effects of the DNA-damaging agent temozolomide (TMZ) and the PARP inhibitor niraparib (Nira) in human multiple myeloma (MM) cells. Materials and Methods: MM RPMI8226 and NCI-H929 cells were administered TMZ and/or Nira for 48 hours. CCK-8 was utilized for cell viability assessment. Cell proliferation and apoptosis were detected flow-cytometrically. Immunofluorescence was performed for detecting Results: The results demonstrated that cotreatment with TMZ and Nira promoted DNA damage, cell cycle arrest, and apoptotic death in cultured cells but also reduced MM xenograft growth in nude mice, yielding highly synergistic effects. Immunoblot revealed that TMZ and Nira cotreatment markedly increased the expression of p-ATM, p-CHK2, RAD51, and Conclusion: Inhibition of PARP1 sensitizes genotoxic agents and represents an important therapeutic approach for MM. These findings provide preliminary evidence for combining PARP1 inhibitors with TMZ for MM treatment.