Inhibitors of Rho kinases (ROCK) induce multiple mitotic defects and synthetic lethality in BRCA2-deficient cells

Area of Science:

• Cell Biology
• Cancer Biology
• Genetics

Background:

• Poly-ADP-ribose polymerase inhibitors (PARPi) induce synthetic lethality (SL) in BRCA2-deficient cells via DNA replication stress.
• DNA damage is considered essential for SL in BRCA2-deficient contexts.
• A novel mechanism for SL in BRCA2-deficient cells, independent of DNA damage, is explored.

Purpose of the Study:

• To investigate if ROCK inhibition triggers SL in BRCA2-deficient cells independently of replication stress.
• To elucidate the cellular events preceding SL upon ROCK inhibition.
• To identify novel therapeutic strategies targeting BRCA2-deficient cancers.

Main Methods:

• Inhibition of Rho-associated coiled-coil kinase (ROCK) in BRCA2-deficient cell lines.
• Analysis of cell cycle progression, cytokinesis, and mitosis.
• Assessment of cell viability and synthetic lethality (SL).
• Depletion of Early mitotic inhibitor 1 (EMI1) to modulate mitotic entry.

Main Results:

• ROCK inhibition induces SL in BRCA2-deficient cells without acute replication stress.
• Cytokinesis failure, leading to polyploidy and binucleation, precedes SL.
• Mitotic abnormalities, including anaphase bridges and multipolar spindles, are observed.
• Inhibition of Citron Rho-interacting kinase also triggers SL, supporting the role of cytokinesis defects.
• Preventing mitotic entry enhances survival in cells treated with ROCK inhibitors.

Conclusions:

• Cytokinesis failure is a key trigger for mitotic abnormalities and SL in BRCA2-deficient cells.
• Mitosis, rather than DNA damage, represents a critical vulnerability in BRCA2-deficient cells.
• Targeting cytokinesis or M phase offers a novel therapeutic avenue for BRCA2-deficient cancers.