Selective small molecule PARG inhibitor causes replication fork stalling and cancer cell death

Area of Science:

• Molecular Biology
• Cancer Research
• Drug Discovery

Background:

• Poly(ADP-ribose)ylation (PARylation) is crucial for DNA damage response, regulated by PARP1 and PARG.
• Conflicting data on PARG function complicates its role in cancer cell resistance to PARP1 inhibitors.
• PARG expression is frequently upregulated in various cancers.

Purpose of the Study:

• To identify and optimize selective, bioavailable inhibitors of PARG.
• To investigate the mechanism of PARG inhibition and its effects on cancer cells.
• To evaluate the therapeutic potential of PARG inhibition in cancer, including PARP inhibitor-resistant models.

Main Methods:

• Chemical library screening to identify methylxanthine derivatives as PARG inhibitors.
• Structure-based drug design and crystal structure analysis to understand inhibitor binding.
• Cell-based assays to assess PARG inhibition, PARP1 hyperPARylation, DNA damage response, and cancer cell survival.

Main Results:

• Identification and optimization of selective methylxanthine-based PARG inhibitors.
• Demonstration of competitive inhibition mechanism via structural and biochemical data.
• Selective PARG inhibition leads to PARP1 hyperPARylation, increased sensitivity to radiation-induced DNA damage, and impaired cancer cell survival.
• PARG inhibition shows efficacy comparable to Nedaplatin in PARP inhibitor-resistant glioblastoma cells.

Conclusions:

• Selective PARG inhibition represents a viable strategy to impair cancer cell survival.
• PARG inhibitors can overcome resistance to PARP1 inhibitors and enhance efficacy of DNA-damaging agents.
• Optimized methylxanthine derivatives provide a proof-of-concept for targeting PARG in cancer therapy.