Conformationally Constrained Analogues of Diacylglycerol. 21. A Solid-Phase Method of Synthesis of Diacylglycerol Lactones as a Prelude to a Combinatorial Approach for the Synthesis of Protein Kinase C Isozyme-Specific Ligands

α-Arylidene Diacylglycerol-Lactones (DAG-Lactones) as Selective Ras Guanine-Releasing Protein 3 (RasGRP3) Ligands

Diacylglycerol-lactones have proven to be a powerful template for the design of potent ligands targeting C1 domains, the recognition motif for the cellular second messenger diacylglycerol. A major objective has been to better understand the structure activity relations distinguishing the seven families of signaling proteins that contain such domains, of which the protein kinase C (PKC) and RasGRP families are of particular interest. Here, we synthesize a series of aryl- and alkyl-substituted diacylglycerol-lactones and probe their relative selectivities for RasGRP3 versus PKC. Compound 96 showed 73-fold selectivity relative to PKCα and 45-fold selectivity relative to PKCε for in vitro binding activity. Likewise, in intact cells, compound 96 induced Ras activation, a downstream response to RasGRP stimulation, with 8-29 fold selectivity relative to PKCδ S299 phosphorylation, a measure of PKCδ stimulation.

Conformationally constrained analogues of diacylglycerol. 29. Cells sort diacylglycerol-lactone chemical zip codes to produce diverse and selective biological activities

Diacylglycerol-lactone (DAG-lactone) libraries generated by a solid-phase approach using IRORI technology produced a variety of unique biological activities. Subtle differences in chemical diversity in two areas of the molecule, the combination of which generates what we have termed "chemical zip codes", are able to transform a relatively small chemical space into a larger universe of biological activities, as membrane-containing organelles within the cell appear to be able to decode these "chemical zip codes". It is postulated that after binding to protein kinase C (PKC) isozymes or other nonkinase target proteins that contain diacylglycerol responsive, membrane interacting domains (C1 domains), the resulting complexes are directed to diverse intracellular sites where different sets of substrates are accessed. Multiple cellular bioassays show that DAG-lactones, which bind in vitro to PKCalpha to varying degrees, expand their biological repertoire into a larger domain, eliciting distinct cellular responses.

Wealth of opportunity - the C1 domain as a target for drug development

The diacylglycerol-responsive C1 domains of protein kinase C and of the related classes of signaling proteins represent highly attractive targets for drug development. The signaling functions that are regulated by C1 domains are central to cellular control, thereby impacting many pathological conditions. Our understanding of the diacylglycerol signaling pathways provides great confidence in the utility of intervention in these pathways for treatment of cancer and other conditions. Multiple compounds directed at these signaling proteins, including compounds directed at the C1 domains, are currently in clinical trials, providing strong validation for these targets. Extensive understanding of the structure and function of C1 domains, coupled with detailed insights into the molecular details of ligand - C1 domain interactions, provides a solid basis for rational and semi-rational drug design. Finally, the complexity of the factors contributing to ligand - C1 domain interactions affords abundant opportunities for manipulation of selectivity; indeed, substantially selective compounds have already been identified.

Protein kinase C regulatory domains: the art of decoding many different signals in membranes

Protein kinase C (PKC) is a member of a family of Ser/Thr phosphotransferases that are involved in many cellular signaling pathways. These enzymes possess two regulatory domains, C1 and C2, that are the targets of different second messengers. The purpose of this review is to describe in molecular terms the diverse mechanisms of activation of PKCs in the light of very significant advances made in this field over recent years. The role of some critical amino acid residues concerning activation of the enzymes and their location within known structures of isolated domains will be presented. For example, the recently deduced 3D structures of the C2 domains show that these domains can additionally act as PtdIns(4,5)P(2)-binding or phosphotyrosine-binding modules depending on the isoenzyme. All these capacities to play different roles in the cell wide web of signals underline the notion that we are dealing with a multifunctional family of enzymes which, after 30 years of investigation, we are just beginning to understand.

A Novel Diacylglycerol-lactone Shows Marked Selectivity in Vitro among C1 Domains of Protein Kinase C (PKC) Isoforms α and δ as Well as Selectivity for RasGRP Compared with PKCα

Although multiple natural products are potent ligands for the diacylglycerol binding C1 domain of protein kinase C (PKC), RasGRP, and related targets, the high conservation of C1 domains has impeded the development of selective ligands. We characterized here a diacylglycerol-lactone, 130C037, emerging from a combinatorial chemical synthetic strategy, which showed substantial selectivity. 130C037 gave shallow binding curves for PKC isoforms alpha, beta, gamma, delta, and epsilon, with apparent Ki values ranging from 340 nm for PKCalpha to 29 nm for PKCepsilon. When binding to isolated C1 domains of PKCalpha and -delta, 130C037 showed good affinity (Ki= 1.78 nm) only for deltaC1b, whereas phorbol 12,13-dibutyrate showed affinities within 10-fold for all. In LNCaP cells, 130C037 likewise selectively induced membrane translocation of deltaC1b. 130C037 bound intact RasGRP1 and RasGRP3 with Ki values of 3.5 and 3.8 nm, respectively, reflecting 8- and 90-fold selectivity relative to PKCepsilon and PKCalpha. By Western blot of Chinese hamster ovary cells, 130C037 selectively induced loss from the cytosol of RasGRP3 (ED50 = 286 nm), partial reduction of PKCepsilon (ED50 > 10 microm), and no effect on PKCalpha. As determined by confocal microscopy in LNCaP cells, 130C037 caused rapid translocation of RasGRP3, limited slow translocation of PKCepsilon, and no translocation of PKCalpha. Finally, 130C037 induced Erk phosphorylation in HEK-293 cells ectopically expressing RasGRP3 but not in control cells, whereas phorbol ester induced phosphorylation in both. The properties of 130C037 provide strong proof of principle for the feasibility of developing ligands with selectivity among C1 domain-containing therapeutic targets.