KU-55933: Potent and Selective ATM Kinase Inhibitor for DNA Damage Response Research

Executive Summary: KU-55933 is a highly selective inhibitor of the ataxia-telangiectasia mutated (ATM) kinase, exhibiting an IC₅₀ of 13 nM and a Ki of 2.2 nM under biochemical assay conditions (APExBIO). ATM kinase is central to the DNA damage response (DDR), phosphorylating substrates such as Akt at Ser473, which is crucial for cell survival signaling (Zhen et al., 2023). KU-55933 blocks ATM-mediated phosphorylation events, induces G1 cell cycle arrest by downregulating cyclin D1, and inhibits proliferation in cancer cell lines at micromolar concentrations. The compound alters cellular metabolism by increasing lactate and glucose uptake and decreasing ATP levels. APExBIO supplies KU-55933 as a solid, soluble at ≥41.67 mg/mL in DMSO, making it suitable for diverse research workflows.

Biological Rationale

ATM kinase is a serine/threonine protein kinase in the phosphatidylinositol 3-kinase-related kinase (PIKK) family. ATM is activated by DNA double-strand breaks (DSBs) and orchestrates the DNA damage response by phosphorylating numerous substrates, including p53, H2AX, and Akt (Zhen et al., 2023). ATM activity preserves genomic stability and regulates cell cycle checkpoints. Dysfunction in ATM signaling is implicated in ataxia-telangiectasia, cancer predisposition, and radiosensitivity. Pharmacological inhibition of ATM enables precise interrogation of DDR pathways, checkpoint activation, and the interplay with innate immunity via cGAS-STING signaling (Zhen et al., 2023).

Mechanism of Action of KU-55933 (ATM Kinase Inhibitor)

KU-55933 (SKU: A4605) competitively inhibits the ATP-binding site of ATM kinase, with >100-fold selectivity over related kinases such as DNA-PK, PI3K, PI4K, ATR, and mTOR (APExBIO). Inhibition of ATM by KU-55933 suppresses phosphorylation of downstream effectors, most notably the inactivation of Akt at Ser473, which is essential for cell survival and proliferation pathways. KU-55933 induces G1 phase arrest by reducing cyclin D1 levels and blocks cell cycle progression. In cancer cell lines like MDA-MB-453 and PC-3, treatment with 10 μM KU-55933 results in approximately 50% inhibition of cell proliferation. In MCF-7 cells, ATM inhibition by KU-55933 increases lactate production and glucose uptake while decreasing intracellular ATP, reflecting altered metabolic flux (APExBIO).

Evidence & Benchmarks

• KU-55933 inhibits ATM kinase with an IC₅₀ of 13 nM and a Ki of 2.2 nM in biochemical assays (APExBIO).
• Selective inhibition: >100-fold selectivity for ATM over DNA-PK, PI3K, PI4K, ATR, and mTOR under identical in vitro conditions (APExBIO).
• Reduces Akt phosphorylation at Ser473, a critical step in survival signaling after DNA damage (Zhen et al., 2023).
• Induces G1 cell cycle arrest and downregulation of cyclin D1 in multiple cancer cell lines at 10 μM concentration (APExBIO).
• Inhibits proliferation by ~50% in MDA-MB-453 and PC-3 cells at 10 μM in vitro (APExBIO).
• Alters metabolism: increases lactate production, glucose consumption, and decreases ATP levels in MCF-7 cells (APExBIO).
• ATM inhibition impairs DSB repair, modulating cGAS activation and the innate immune response (Zhen et al., 2023).

This article extends the mechanistic depth of KU-55933: Advanced Insights into ATM Kinase Inhibition and DNA Damage Response by providing updated quantitative benchmarks and clarifying the compound’s impact on Akt phosphorylation. It builds on the metabolic insights summarized at KU-55933: ATM Kinase Inhibitor Redefining iPSC-Based DNA Damage Response Research by specifying the metabolic alterations observed in MCF-7 cells. For further troubleshooting and advanced application guidance, see KU-55933: Potent ATM Kinase Inhibitor for DNA Damage Response Research.

Applications, Limits & Misconceptions

KU-55933 is used in studies of DNA damage checkpoint signaling, cancer cell proliferation, metabolic regulation, and apoptosis. It is a reference tool for dissecting ATM-mediated signaling and is widely applied in iPSC platforms for disease modeling. DNA damage-induced nuclear translocation of cGAS and its involvement in genome stability are also investigated with ATM inhibition (Zhen et al., 2023).

Common Pitfalls or Misconceptions

• KU-55933 is not effective against non-PIKK family kinases; off-target effects are minimal at recommended concentrations.
• It does not inhibit DNA-PK or ATR at concentrations used for ATM inhibition (selectivity >100-fold).
• The compound is insoluble in water and ethanol; use DMSO (≥41.67 mg/mL) with gentle warming for stock solutions (APExBIO).
• Long-term storage of solutions at room temperature leads to rapid degradation; prepare fresh aliquots and store at <-20°C.
• Not suitable for in vivo use in animals due to poor pharmacokinetic properties unless specifically formulated.

Workflow Integration & Parameters

KU-55933 is supplied as a solid by APExBIO and should be dissolved in DMSO to a concentration of ≥41.67 mg/mL with gentle warming. Working solutions are typically prepared at 10 μM for in vitro cell-based assays. For storage, keep the compound desiccated at -20°C; stock solutions in DMSO are stable for several months below -20°C. Use solutions promptly after thawing to avoid loss of potency. Negative controls should include DMSO-only treatments. For DDR studies, ATM inhibition should be validated by reduced Ser473 phosphorylation of Akt or loss of H2AX phosphorylation. Integration into iPSC, cancer cell, and metabolic profiling platforms is well documented (KU-55933: ATM Kinase Inhibitor Empowering Personalized DNA Damage Research).

Conclusion & Outlook

KU-55933 is a benchmark ATM kinase inhibitor enabling quantitative, reproducible interrogation of DNA damage response, cell cycle arrest, and related metabolic changes in cancer biology and iPSC-based models. Its selectivity profile and well-characterized action make it suitable for dissecting ATM-dependent signaling in DDR research. For ordering and further specifications, refer to the KU-55933 (ATM Kinase Inhibitor) product page from APExBIO. Ongoing research into nuclear cGAS and ATM axis regulation continues to expand the compound’s utility in genome stability and cancer research (Zhen et al., 2023).