Slow Dissociation from the PARP1-HPF1 Complex Drives Inhibitor Potency

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Poly (ADP-ribose) polymerase 1 (PARP1) is crucial for DNA repair via poly ADP-ribosylation (PARylation).
• HPF1 acts as a cofactor, altering the PARP1 active site and directing PARylation towards histones.
• The mechanism of PARP1 inhibitor (PARPi) potency, especially with HPF1, remains unclear.

Purpose of the Study:

• To investigate the binding kinetics of various PARPi to the PARP1-HPF1 complex.
• To determine the key kinetic parameter correlating with PARPi cellular potency.
• To guide the rational design of next-generation PARPi.

Main Methods:

• Measured association rates (k_on) for eight PARPi binding to PARP1.
• Characterized dissociation rates (k_off) and binding constants (K_D) for specific PARPi with the PARP1-HPF1 complex.
• Correlated kinetic parameters with in-cell PARPi potency.

Main Results:

• PARPi association rates (k_on) to PARP1 showed minor differences with or without HPF1.
• Dissociation half-life for saruparib was 22.5 hours; fluzoparib exhibited higher affinity for PARP1 in the presence of HPF1.
• PARPi cellular potency strongly correlated with the dissociation rate (k_off) from the PARP1-HPF1 complex.

Conclusions:

• The dissociation rate from the PARP1-HPF1 complex is a critical determinant of PARPi efficacy.
• Slower drug dissociation from the PARP1-HPF1 complex is key for enhanced PARPi potency.
• Dissociation kinetics from the PARP1-HPF1 complex should guide future PARPi drug development.