Inhibition of Chk1 by the G2 DNA damage checkpoint inhibitor isogranulatimide.

Abstract

Inhibitors of the G(2) DNA damage checkpoint can selectively sensitize cancer cells with mutated p53 to killing by DNA-damaging agents. Isogranulatimide is a G(2) checkpoint inhibitor containing a unique indole/maleimide/imidazole skeleton identified in a phenotypic cell-based screen; however, the mechanism of action of isogranulatimide is unknown. Using natural and synthetic isogranulatimide analogues, we show that the imide nitrogen and a basic nitrogen at position 14 or 15 in the imidazole ring are important for checkpoint inhibition. Isogranulatimide shows structural resemblance to the aglycon of UCN-01, a potent bisindolemaleimide inhibitor of protein kinase C beta (IC(50), 0.001 micromol/L) and of the checkpoint kinase Chk1 (IC(50), 0.007 micromol/L). In vitro kinase assays show that isogranulatimide inhibits Chk1 (IC(50), 0.1 micromol/L) but not protein kinase C beta. Of 13 additional protein kinases tested, isogranulatimide significantly inhibits only glycogen synthase kinase-3beta (IC(50), 0.5 micromol/L). We determined the crystal structure of the Chk1 catalytic domain complexed with isogranulatimide. Like UCN-01, isogranulatimide binds in the ATP-binding pocket of Chk1 and hydrogen bonds with the backbone carbonyl oxygen of Glu(85) and the amide nitrogen of Cys(87). Unlike UCN-01, the basic N15 of isogranulatimide interacts with Glu(17), causing a conformation change in the kinase glycine-rich loop that may contribute importantly to inhibition. The mechanism by which isogranulatimide inhibits Chk1 and its favorable kinase selectivity profile make it a promising candidate for modulating checkpoint responses in tumors for therapeutic benefit.

• Authors: Xiuxian Jiang, Baoguang Zhao, Robert Britton, Lynette Y Lim, Dan Leong, Jasbinder S Sanghera, Bin-Bing S Zhou, Edward Piers, Raymond J Andersen, Michel Roberge
• Journal: Molecular cancer therapeutics (Mol Cancer Ther) Vol. 3 Issue 10 Pg. 1221-7 (Oct 2004) ISSN: 1535-7163 [Print] United States
• PMID: 15486189 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antineoplastic Agents
• Imidazoles
• Indoles
• Maleimides
• isogranulatimide
• Glutamine
• Protein Kinases
• CHEK1 protein, human
• Checkpoint Kinase 1
• GSK3B protein, human
• Glycogen Synthase Kinase 3 beta
• Protein Kinase C
• Protein Kinase C beta
• Glycogen Synthase Kinase 3
• Cysteine
• bisindolylmaleimide
• Nitrogen

Topics

• Antineoplastic Agents (pharmacology)
• Catalytic Domain
• Cell Line, Tumor
• Checkpoint Kinase 1
• Crystallography, X-Ray
• Cysteine (chemistry)
• DNA Damage
• Dose-Response Relationship, Drug
• G2 Phase
• Glutamine (chemistry)
• Glycogen Synthase Kinase 3 (metabolism)
• Glycogen Synthase Kinase 3 beta
• Humans
• Imidazoles (pharmacology)
• Indoles (antagonists & inhibitors, pharmacology)
• Inhibitory Concentration 50
• Maleimides (antagonists & inhibitors)
• Models, Chemical
• Models, Molecular
• Nitrogen (chemistry)
• Phenotype
• Protein Binding
• Protein Kinase C (metabolism)
• Protein Kinase C beta
• Protein Kinases (metabolism, physiology)
• Protein Structure, Tertiary
• Time Factors