Histone Parylation factor 1 contributes to the inhibition of PARP1 by cancer drugs

Poly-(ADP-ribose) polymerase 1 and 2 (PARP1 and PARP2) are key enzymes in the DNA damage response. Four different inhibitors (PARPi) are currently in the clinic for treatment of ovarian and breast cancer. Recently, histone PARylation Factor 1 (HPF1) has been shown to play an essential role in the PARP1- and PARP2-dependent poly-(ADP-ribosylation) (PARylation) of histones, by forming a complex with both enzymes and altering their catalytic properties. Given the proximity of HPF1 to the inhibitor binding site both PARPs, we hypothesized that HPF1 may modulate the affinity of inhibitors toward PARP1 and/or PARP2. Here we demonstrate that HPF1 significantly increases the affinity for a PARP1 - DNA complex of some PARPi (i.e., olaparib), but not others (i.e., veliparib). This effect of HPF1 on the binding affinity of Olaparib also holds true for the more physiologically relevant PARP1 - nucleosome complex but does not extend to PARP2. Our results have important implications for the interpretation of PARP inhibition by current PARPi as well as for the design and analysis of the next generation of clinically relevant PARP inhibitors. PARP1 is the target of clinically approved anti-cancer drugs whose in vivo efficacy has been hard to predict. Here the authors show how an altered active site formed between PARP1 and Histone PARylation Factor 1 (HPF1) changes the efficacy of some of these inhibitors.

Automated summary

PARP1 and PARP2 are key enzymes in the DNA damage response. HPF1 plays an essential role in modulating the PARylation of histones by forming a complex with both PARP1 and PARP2. Results show how HPF1 can affect the binding affinity of certain inhibitors to PARP1.