Revisiting Poly(ADP-ribose) Polymerase as an Emerging Therapeutic Target for Various Cancer Treatments

Poly(adenosine diphosphate [ADP]-ribose) polymerases (PARPs) synthesize poly(ADP-robose) chains with linear or branched forms. PARPs play an essential role in the addition of ADP-ribose monomers to specific residues of proteins and are involved in repairing damaged DNA. In cancer therapy, particularly radiotherapy, PARP1 has emerged as a promising drug target. Moreover, PARP1 inhibition has been shown to sensitize cancer cells to mechanisms involving synthetic lethality. Consequently, the structure of PARP1 has been studied, and several PARP1 inhibitors have been developed and launched. Although the structure of the catalytic domain of PARP1 is known, the whole structure of PARP1 has not yet been elucidated. In addition, the precise mechanism underlying the function of PARP1 remains unclear. To develop novel anticancer agents targeting PARP1, current and comprehensive information on PARP1 is necessary. In this review, we describe the structure of PARP1 in complex with its inhibitors, as well as its native structure, which provides structural information on PARP1 inhibitor-binding modes. The pharmaceutical profiles of the launched PARP1 inhibitors are also summarized. In addition, we discuss possible strategies for the development of novel inhibitors targeting PARP1 based on the structural features of PARP1 and its inhibitor-binding modes.