KU-0063794 - THE NEW mTOR INHIBITOR

by Selleckchem | Mar 19 2012

Introduction: The mTOR pathway

Since many of the protein kinases are structurally similar their effects in the signaling sequence sometimes overlap. One of the central points of a several different pathways is the mTOR protein. Located mostly in the cytosole this protein can receive signals directly from the extracellular system as well as regulation by cell membrane induced signals. Discovered in relation to the then unknown target for a molecule called rapamycin this protein was name mTOR (“mammalian Target For Rapamycin”), not an original name but serves the purpose [1;2]. Downstream signaling of the mTOR protein can lead to direct effects on gene transcription, RNA formation, cellular growth and apoptotic death. Structurally this protein resembled the lipid kinases far more than the typical protein kinases but its functions revealed significant activity in the tyrosine kinase phosphorylation processes [3]. Different ligands binding to the mTOR induce conformational changes that can lead to the building of scaffolding around damaged DNA, adaption of repair mechanisms, growth stimulation or inhibition and regulation of its own function [4]. Inhibition of the mTOR protein has serious consequences on such pathways as EGFR [5;6]or AKT [7] as well as in the organization of actin or in gene transcription in relation to the start codon (AUG) [8]

KU-0063794: Properties and availability

KU-0063794 was originally developed as part of the Kudos Biochemical experimental program, Pfizer in 2009 bought Kudos Biochemicals for its pipeline portfolio, KU has not been clinically developed since then. The KU-0063794 structure is based on an pyrido-pyrimidine core containing a three substitution methoxyphenol based groups. KU-0063794 is a highly specific inhibitor against mTOR 1&2 with KU-0063794 IC50 of approximately 3-100 nM for mTOR1 and 2 depending on which cell line is tested. KU-0063794 solubility in water and ethanol is poor, although KU-0063794 is soluble in DMSO but only to a maximal concentration of 15 mg/ml. KU-0063794 stability is listed for its powdered form and this can be stored for upwards of 2 years if kept at -20^oC or below. In solution it has been established that KU-0063794 is light sensitivity but can be stored for one month at 4-8°C for research purposes. Researchers can buy KU-0063794 from a variety of KU-0063794 suppliers although KU-0063794 cost is dependent on the supplier. KU-0063794 price of a 10 mg vial can range from $59 up to $234 for the free base; researchers are advised to shop very carefully for this product.

KU-0063794: Research Applications

KU-0063794 was discovered during the screening a series of purine derivatives but despite its mTOR activity it was never developed commercially and no KU-0063794 clinical trials are recorded. KU-0063794 was used as a skeletal basis for the design of a new molecular series. From this investigation AZD8055 was discovered, this is another mTOR inhibitor but with far more clinical success. Currently AZD8055 is in phase I to phase II status awaiting results of several clinical trials. KU-0063794 has been determined to be activated against mTOR1 (IC⁵⁰ – 0.003 µM) \, mTOR2 (IC⁵⁰ – 0.15 µM), PI3K (IC⁵⁰ – 5.3 µM), ATR (IC⁵⁰ – 10µM) and DNA-PK (IC-⁵⁰ – 10µM). The mechanism of action for KU-0063794 has been determined to be the direct inhibition of both mTOR1 and mTOR2, the effect of this is to disrupt the cell cycle process[9]. KU-0063794 was determined to be cell permeable and was observed to halt cell proliferation at the G1 stage. Research use of KU-0063794 in the inhibition of mTOR has revealed similarities in the mutations of mTOR to those found in PI3K protein of cancerous tumors. Research established that a unique domain bound the inhibitor ligands blocking action. Structural information concerning this domain and its conformational changes during inhibition has revealed substantial information about binding properties necessary in inhibitor design [10]. Recently KU-0063794 was investigated in cell lines of Gliomblasts which demonstrate mutations in PI3K and activation of mTOR, results were promising hinting at a possible clinical role for KU-0063794 [11].

References

1. Gangloff YG, Mueller M et al. Disruption of the mouse mTOR gene leads to early postimplantation lethality and prohibits embryonic stem cell development. Mol Cell Biol 2004; 24(21):9508-9516.

2. Murakami M, Ichisaka T et al. mTOR is essential for growth and proliferation in early mouse embryos and embryonic stem cells. Mol Cell Biol 2004; 24(15):6710-6718.

3. Harris TE, Lawrence JC, Jr. TOR signaling. Sci STKE 2003; 2003(212):re15.

4. Caron E, Ghosh S et al. A comprehensive map of the mTOR signaling network. Mol Syst Biol 2010; 6:453.

5. Steelman LS, Chappell WH et al. Roles of the Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR pathways in controlling growth and sensitivity to therapy-implications for cancer and aging. Aging (Albany NY) 2011; 3(3):192-222.

6. Chappell WH, Steelman LS et al. Ras/Raf/MEK/ERK and PI3K/PTEN/Akt/mTOR inhibitors: rationale and importance to inhibiting these pathways in human health. Oncotarget 2011; 2(3):135-164.

7. Karar J, Maity A. PI3K/AKT/mTOR Pathway in Angiogenesis. Front Mol Neurosci 2011; 4:51.

8. Liu L, Parent CA. Review series: TOR kinase complexes and cell migration. J Cell Biol 2011; 194(6):815-824.

9. Garcia-Martinez JM, Moran J et al. Ku-0063794 is a specific inhibitor of the mammalian target of rapamycin (mTOR). Biochem J 2009; 421(1):29-42.

10. Sturgill TW, Hall MN. Activating mutations in TOR are in similar structures as oncogenic mutations in PI3KCalpha. ACS Chem Biol 2009; 4(12):999-1015.

11. Fan QW, Weiss WA. Inhibition of PI3K-Akt-mTOR signaling in glioblastoma by mTORC1/2 inhibitors. Methods Mol Biol 2012; 821:349-359.

Cat.No.	Product Name	Information
S1226	KU-0063794	KU-0063794 is a potent and highly specific dual-mTOR inhibitor of mTORC1 and mTORC2 with IC50 of ~10 nM in cell-free assays; no effect on PI3Ks.
S1555	AZD8055	AZD8055 is a novel ATP-competitive mTOR inhibitor with IC50 of 0.8 nM in MDA-MB-468 cells with excellent selectivity (∼1,000-fold) against PI3K isoforms and ATM/DNA-PK. AZD8055 induces caspase-dependent apoptosis and also induces autophagy. Phase 1.