CHK1 inhibition exacerbates replication stress induced by IGF blockade

Area of Science:

• Oncology
• Molecular Biology
• Cancer Therapeutics

Background:

• Insulin-like growth factor receptor (IGF-1R) inhibition slows DNA replication and induces stress by downregulating RRM2, affecting deoxynucleotide triphosphate (dNTP) supply.
• This mechanism presents a potential therapeutic vulnerability in cancer treatment.

Purpose of the Study:

• To identify therapeutic strategies by screening compounds in combination with IGF inhibition.
• To investigate the synergistic effects and underlying mechanisms of co-inhibiting IGF-1R with other agents in breast cancer.

Main Methods:

• Compound screening in five breast cancer cell lines using IGF-neutralizing antibody xentuzumab.
• Co-inhibition experiments with IGF-1R and checkpoint kinase CHK1 (or WEE1) in 2D and 3D cell cultures, and in vivo tumor models.
• Analysis of DNA replication, dNTP supply, RRM2 expression, and cell death markers.

Main Results:

• Checkpoint kinase CHK1 was identified as a potent synergistic hit when combined with IGF inhibition.
• Co-inhibition of IGF-1R and CHK1 resulted in synergistic suppression of cell viability, survival, and tumor growth.
• The combination therapy led to further RRM2 downregulation, reduced dNTPs, delayed replication forks, and replication catastrophe, with RRM2 re-expression rescuing these effects.

Conclusions:

• Co-inhibition of IGF-1R with CHK1 or WEE1 represents a novel synthetic lethality strategy in breast cancer.
• RRM2 is a critical target in the functional interaction between IGF signaling and DNA replication checkpoints.
• These findings identify new therapeutic vulnerabilities and may guide future clinical trials for IGF inhibitory drugs.