Drugs in Clinical Pipeline: KU-60019

KU-60019 [2-((2S,6R)-2,6-dimethylmorpholino)-N-(5-(6-morpholino-4-oxo-4H-pyran-2-yl)-9H-thioxanthen-2-yl)acetamide] is a novel, specific and very potent small molecule inhibitor of Ataxia-Telangiectasia Mutated (ATM) Kinase. The serine/threonine protein kinase ATM signals to cell cycle and DNA repair components by phosphorylating downstream targets such as p53, CHK2, NBS1, and BRCA1. Mutation of ATM occurs in the human autosomal recessive disorder ataxia-telangiectasia, which is characterized by hypersensitivity to ionizing radiation and a failure of cells to arrest the cell cycle after the induction of DNA double-strand breaks. It has thus been proposed that ATM inhibition would cause cellular radio- and chemosensitization [1].

The activity of KU-60019 is as follows:

IC₅₀ (ATM enzyme assay) = 6.3 nM

Common Name: KU-60019

Synonyms:  KU-60019; KU 60019; KU60019

IUPAC Name: 2-((2S,6R)-2,6-dimethylmorpholino)-N-(5-(6-morpholino-4-oxo-4H-pyran-2-yl)-9H-thioxanthen-2-yl)acetamide

CAS Number: 925701-49-1

Mechanism of Action: Kinase Inhibitor; ATM Inhibitor

Indication: Various Cancers

Development Stage: Phase I

Company: KuDOS Pharmaceuticals

The cellular response to DNA damage is one of coordinated repair and moderation of proliferation. ATM is a protein kinase member of the phosphatidylinositol 3'-kinase (PI3K)-related kinase (PIKK) family that plays a critical role in the maintenance of genome integrity . The Mr 345 000 phospho-protein plays key roles in coordinating cellular responses to IR-induced DNA double-strand breaks. Mutation of ATM occurs in the human autosomal recessive disorder ataxia-telangiectasia (A-T), which is characterized by several symptoms, including cerebellar degeneration, oculocutaneous telangiectasia, growth retardation, immune deficiencies, and characteristics of premature aging. At the cellular level, A-T is characterized by a hypersensitivity to ionizing radiation and radiomimetic drugs, radioresistant DNA synthesis, and chromosomal instability. In addition, there is a failure of A-T cells to arrest the cell cycle after DNA damage, thus reducing the opportunity for the repair of the genome before DNA replication or mitosis. Exposure of normal cells to ionizing radiation results in cell cycle arrest and ATM appears to be critical for the induction of these events, orchestrating the response by the downstream signaling to other response factors [1].

KU-60019 is an improved inhibitor of the ATM kinase with an IC50 of 6.3 nM, approximately half that of KU-55933. The IC₅₀ values for DNA-PKcs and ATR are 1.7 and >10 µM, respectively, almost 270-and 1600-fold higher than for ATM. KU-60019 has similar if not identical target specificity as KU-55933 with little to no non-specific target effects at 1 µM against a panel of 229 protein kinases with PI3K (p110ß/p85a), PI3K (p120g), and PI3K (p110d/p85a) inhibited 9, 3, and 27%, respectively (Millipore KinaseProfiler™ and PI3-Kinase HTRF™ assay). Notably, mTOR and mTOR/FKBP12 were not inhibited.

KU-60019 is a highly effective radiosensitizer of human glioma cells. A-T fibroblasts were not radiosensitized by KU-60019 strongly suggesting that the ATM kinase is specifically targeted. Furthermore, KU-60019 reduced basal S473 AKT phosphorylation, suggesting that the ATM kinase might regulate a protein phosphatase acting on AKT. The effect of KU-60019 on AKT phosphorylation was countered by low levels of okadaic acid, a phosphatase inhibitor, and A-T cells were impaired in S473 AKT phosphorylation in response to radiation and insulin, and unresponsive to KU-60019. KU-60019 inhibits glioma cell migration and invasion in vitro, suggesting that glioma growth and motility might be controlled by ATM via AKT. Inhibitors of MEK and AKT did not further radiosensitize cells treated with KU-60019 supporting the idea that KU-60019 interferes with prosurvival signaling separate from its radiosensitizing properties. Altogether, KU-60019 inhibits the DNA damage response, reduces AKT phosphorylation and prosurvival signaling, inhibits migration and invasion, and effectively radiosensitizes human glioma cells [2].

In comparion to KU-55933, KU-60019 has following features:

1. KU-60019 is an improved ATM kinase-specific inhibitor

2. KU-60019 is a more potent inhibitor of the ATM kinase than KU-55933

3. KU-60019 is a more potent radiosensitizer than KU-55933

4. KU-60019 specifically targets the ATM kinase to radiosensitize cells

5. KU-60019 modulates phosphorylation of AKT at S473

6. Radiation- and insulin-induced AKT phosphorylation is impaired in human A-T fibroblasts

7. KU-60019 inhibits migration and invasion of human glioma cells in vitro

8. Inhibition of AKT or MEK/ERK signaling does not enhance KU-60019 radiosensitization

KU-60019 is a specific and much improved ATM kinase inhibitor able to radiosensitize human glioma cells in the low micromolar range. Radiosensitization is likely caused by the ability of KU-60019 to inhibit the plethora of ATM phosphorylation targets and upset cell cycle checkpoints, reduce DNA repair, and increase cell death. Furthermore, our results suggest that KU-60019 alone (without radiation) inhibits glioma motility and invasion perhaps acting on the AKT and MEK/ERK pro-survival signaling pathways [2].

Glioblastoma (GB)-initiating cells (GIC) with low expression and/or mutation of TP53 and high expression of PI3K ("responder" genetic profile) can be effectively and safely radiosensitized by the ATM inhibitor KU60019. It’s diffusion and elimination from the animal body and brain, effects on orthotopic GB and efficacy toward pediatric GIC are reported. Healthy mice were infused by convection enhanced delivery (CED) with KU60019 and the drug kinetics followed by high performance liquid chromatography-mass spectrometry. Already at the end of CED, KU60019 had diffused from the injection site to the ipsilateral and, to a lower extent, controlateral hemisphere. After 24 hr, no drug could be detected all over the brain or in other organs, indicating rapid draining and excretion. After intraperitoneal injection, traces only of KU60019 could be detected in the brain, indicating inability to cross the brain-blood barrier. glioblastoma (GB)-initiating cells (GIC) with low expression and/or mutation of TP53 and high expression of PI3K ("responder" genetic profile) can be effectively and safely radiosensitized by the ATM inhibitor KU60019. We report here on drug's diffusion and elimination from the animal body and brain, its effects on orthotopic GB and efficacy toward pediatric GIC. Healthy mice were infused by convection enhanced delivery (CED) with KU60019 and the drug kinetics followed by high performance liquid chromatography-mass spectrometry. Already at the end of CED, KU60019 had diffused from the injection site to the ipsilateral and, to a lower extent, controlateral hemisphere. After 24 hr, no drug could be detected all over the brain or in other organs, indicating rapid draining and excretion. After intraperitoneal injection, traces only of KU60019 could be detected in the brain, indicating inability to cross the brain-blood barrier [4].

References:

1. Hickson, I.; et. al. Identification and Characterization of a Novel and Specific Inhibitor of the Ataxia-Telangiectasia Mutated Kinase ATM. Cancer Res 2004, 64(24), 9152-9159.

2. Golding, S. E.; et. al. Improved ATM kinase inhibitor KU-60019 radiosensitizes glioma cells, compromises insulin, AKT and ERK prosurvival signaling, and inhibits migration and invasion. Mol Cancer Ther 2009, 8(10), 2894-2902.

3. Li Smith, G. C. M.; et. al. Atm inhibitor. WO2007026157A1
4. Vecchio, D.; et. al. Pharmacokinetics, pharmacodynamics and efficacy on pediatric tumors of the glioma radiosensitizer KU60019. Int J Cancer 2015, 136(6), 1445-1457.