title: Iridals are a novel class of ligands for phorbol ester receptors with modest selectivity for the RasGRP receptor subfamily.
abstract: Since 1990, the National Cancer Institute has performed extensive in vitro screening of compounds for anticancer activity. To date, more than 70 000 compounds have been screened for their antiproliferation activities against a panel of 60 human cancer cell lines. We probed this database to identify novel structural classes with a pattern of biological activity on these cell lines similar to that of the phorbol esters. The iridals form such a structural class. Using the program Autodock, we show that the iridals dock to the same position on the C1b domain of protein kinase C delta as do the phorbol esters, with the primary hydroxyl group of the iridal at the C3 position forming two hydrogen bonds with the amide group of Thr12 and with the carbonyl group of Leu 21 and the aldehyde oxygen of the iridal forming a hydrogen bond with the amide group of Gly23. Biological analysis of two iridals, NSC 631939 and NSC 631941, revealed that they bound to protein kinase C alpha with K(i) values of 75.6 +/- 1.3 and 83.6 +/- 1.5 nM, respectively. Protein kinase C is now recognized to represent only one of five families of proteins with C1 domains capable of high-affinity binding of diacylglycerol and the phorbol esters. NSC 631939 and NSC 631941 bound to RasGRP3, a phorbol ester receptor that directly links diacylglycerol/phorbol ester signaling with Ras activation, with K(i) values of 15.5 +/- 2.3 and 41.7 +/- 6.5 nM, respectively. Relative to phorbol 12,13-dibutyrate, they showed 15- and 6-fold selectivity for RasGRP3. Both compounds caused translocation of green fluorescent protein tagged RasGRP3 expressed in HEK293 cells, and both compounds induced phosphorylation of ERK1/2, a downstream indicator of Ras activation, in a RasGRP3-dependent fashion. We conclude that the iridals represent a promising structural motif for design of ligands for phorbol ester receptor family members.
authors.affiliation: Drug Discovery Program, University of Michigan Cancer Center, Department of Internal Medicine, University of Michigan, 1500 E. Medical Center Drive, Ann Arbor, Michigan 48109-0934, USA.
authors.forename: L
authors.initials: L
authors.lastname: Shao
authors.forename: N E
authors.initials: NE
authors.lastname: Lewin
authors.forename: P S
authors.initials: PS
authors.lastname: Lorenzo
authors.forename: Z
authors.initials: Z
authors.lastname: Hu
authors.forename: I J
authors.initials: IJ
authors.lastname: Enyedy
authors.forename: S H
authors.initials: SH
authors.lastname: Garfield
authors.forename: J C
authors.initials: JC
authors.lastname: Stone
authors.forename: F J
authors.initials: FJ
authors.lastname: Marner
authors.forename: P M
authors.initials: PM
authors.lastname: Blumberg
authors.forename: S
authors.initials: S
authors.lastname: Wang
mesh_terms: D000171:Acrolein / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D001667:Binding, Competitive; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D002460:Cell Line; D018360:Crystallography, X-Ray; D003511:Cyclohexanols / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D016208:Databases, Factual; D004224:Diterpenes; D004354:Drug Screening Assays, Antitumor; D049452:Green Fluorescent Proteins; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D027621:Iridaceae / Q000737:chemistry*; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D008024:Ligands; D008164:Luminescent Proteins / Q000235:genetics; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008958:Models, Molecular; D010704:Phorbols / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000737:chemistry / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta; D011869:Radioligand Assay; D011955:Receptors, Drug / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013141:Spiro Compounds / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D013237:Stereoisomerism; D013729:Terpenes / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D020663:ras Guanine Nucleotide Exchange Factors
chemical_list: C439953:26-hydroxy-22-methylcycloirid-16-enal; C439954:29-acetoxy-26-hydroxy-15,28,16,17-tetradehydro-14,15-dihydrospiroiridal; D000972:Antineoplastic Agents, Phytogenic; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D003511:Cyclohexanols; D004224:Diterpenes; D020662:Guanine Nucleotide Exchange Factors; D007527:Isoenzymes; D008024:Ligands; D008164:Luminescent Proteins; D010704:Phorbols; C413212:RASGRP3 protein, human; D011955:Receptors, Drug; D011993:Recombinant Fusion Proteins; D013141:Spiro Compounds; D013729:Terpenes; C083141:phorbol ester binding protein; C027776:phorbol ester receptor; D020663:ras Guanine Nucleotide Exchange Factors; D049452:Green Fluorescent Proteins; C011309:mezerein; D000171:Acrolein; C496628:PRKCA protein, human; C497258:PRKCD protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051745:Protein Kinase C-delta; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases