ATR

Notes

original target text: ATR inhibitor

ATR (Ataxia Telangiectasia and Rad3-related protein) is a kinase that acts as a central sensor of DNA replication stress and single-strand DNA damage. When DNA replication forks stall or DNA is damaged, ATR is activated and triggers a signaling cascade that pauses the cell cycle, primarily at the G2/M checkpoint, giving the cell time to repair its genome before dividing. Cancer cells often rely heavily on this checkpoint because they already carry high levels of replication stress and genomic instability, or because they have lost other DNA repair pathways, such as those involving ATM. Inhibiting ATR removes this safety mechanism, forcing damaged cells to proceed through division with unrepaired DNA, which leads to catastrophic errors and cell death. This rationale is used broadly in oncology, particularly for tumors with defects in DNA repair genes or in combination with agents that themselves cause DNA damage, such as chemotherapy, radiation, or other DNA repair inhibitors, since disabling both damage-detection and damage-response simultaneously can be more lethal to cancer cells than either approach alone. ATR inhibition is a small-molecule-driven strategy, reflecting the kinase's accessible catalytic pocket, and is studied across a range of solid tumor types where replication stress is a defining feature of malignant growth.