Genotype-Directed Synthetic Cytotoxicity of ATR Inhibition with Radiotherapy.

Area of Science:

• Oncology
• Radiation Oncology
• Molecular Biology

Background:

• Radiotherapy (RT) effectiveness is influenced by the DNA damage response.
• Previous attempts to enhance RT with radiosensitizers in unselected populations yielded limited success.
• Targeting DNA repair pathways presents a potential strategy for improving cancer treatment outcomes.

Purpose of the Study:

• To investigate the genotype-specific synergy between radiotherapy (RT) and an ataxia-telangiectasia and Rad3-related (ATR) kinase inhibitor (ATRi).
• To test the hypothesis that ATM-null tumors would exhibit radiosensitization when combined with an ATR inhibitor.
• To validate preclinical findings in a phase I/II clinical trial for patients with advanced cancer and ATM alterations.

Main Methods:

• Evaluated the synergistic potential of ATR inhibitor RP-3500 and RT in ATM-null and BRCA1-null murine models, both in vitro and in vivo.
• Assessed DNA double-strand breaks using γ-H2AX foci staining and analyzed immune responses via flow cytometry.
• Conducted tumor rechallenge experiments and enrolled patients with ATM alterations in a clinical trial.

Main Results:

• Synergy between RP-3500 and RT was confirmed in ATM-null cell lines, leading to increased DNA double-strand breaks.
• ATM-null tumor models showed durable control with the combination therapy, unlike BRCA1-null models where no synergy was observed.
• Early clinical trial results indicated complete responses in patients with ATM alterations.

Conclusions:

• Genotype-directed radiosensitization using ATR inhibitors and RT offers significant therapeutic benefits.
• This approach represents a novel strategy for developing effective combinatorial cytotoxic treatments.
• Targeting specific DNA damage response pathways based on tumor genotype can enhance RT efficacy.