A nonpromoting phorbol from the samoan medicinal plant Homalanthus nutans inhibits cell killing by HIV-1

Extracts of Homalanthus nutans, a plant used in Samoan herbal medicine, exhibited potent activity in an in vitro, tetrazolium-based assay which detects the inhibition of the cytopathic effects of human immunodeficiency virus (HIV-1). The active constituent was identified as prostratin, a relatively polar 12-deoxyphorbol ester. Noncytotoxic concentrations of prostratin from greater than or equal to 0.1 to greater than 25 microM protected T-lymphoblastoid CEM-SS and C-8166 cells from the killing effects of HIV-1. Cytoprotective concentrations of prostratin greater than or equal to 1 microM essentially stopped virus reproduction in these cell lines, as well as in the human monocytic cell line U937 and in freshly isolated human monocyte/macrophage cultures. Prostratin bound to and activated protein kinase C in vitro in CEM-SS cells and elicited other biochemical effects typical of phorbol esters in C3H10T1/2 cells; however, the compound does not appear to be a tumor promoter. In skin of CD-1 mice, high doses of prostratin induced ornithine decarboxylase only to 25-30% of the levels induced by typical phorbol esters at doses 1/30 or less than that used for prostratin, produced kinetics of edema formation characteristic of the nonpromoting 12-deoxyphorbol 13-phenylacetate, and failed to induce the acute or chronic hyperplasias typically caused by tumor-promoting phorbols at doses of 1/100 or less than that used for prostratin.

Residues in the second cysteine-rich region of protein kinase C delta relevant to phorbol ester binding as revealed by site-directed mutagenesis

Phorbol esters bind with high affinity to protein kinase C (PKC) isozymes as well as to two novel receptors, n-chimaerin and Unc-13. The cysteine-rich regions present in these proteins were identified as the binding sites for the phorbol ester tumor promoters and the lipophilic second messenger sn-diacylglycerol. A 50-amino-acid peptide comprising the second cysteine-rich region of PKC delta, expressed in Escherichia coli as a glutathione S-transferase (GST)-fusion protein, bound [3H]phorbol 12,13-dibutyrate (PDBu) with high affinity (Kd = 0.8 nM). Using the cDNA of that cysteine-rich region as a template, a series of 37 point mutations was generated by site-directed mutagenesis, and the mutated proteins were analyzed quantitatively for binding of [3H]PDBu and, as appropriate, for binding of the ultrapotent analog [3H]bryostatin 1. Mutants displayed one of three patterns of behavior: phorbol ester binding was completely abolished, binding affinity was reduced, or binding was not significantly modified. As expected, five of the six cysteines as well as the two histidines involved in Zn2+ coordination are critical for the interaction of the protein with the phorbol esters. In addition, mutations in several positions, including phenylalanine 3, tyrosine 8, proline 11, leucines 20, 21 and 24, tryptophan 21, glutamine 27, and valine 38 drastically reduced the interaction with the ligands. The effect of these mutations can be rationalized from the three-dimensional (NMR) structure of the cysteine-rich region. In particular, the C-terminal portion of the protein does not appear to be essential, and the loop comprising amino acids 20 to 28 is implicated in the binding activity.

Bcl-2, Bax and p53 expression in B-CLL in relation to in vitro survival and clinical progression

Our previous data have shown that isolated leukemic cells from progressive chronic lymphocytic leukemia (B-CLL) patients respond to growth stimulation in vitro and express high levels of p53, immunoreactive with the configuration-specific antibody PAb 240. We have now analyzed the in vitro survival of B-CLL cells in relation to Bcl-2, Bax alpha and p53 expression and compared this with the clinical progression of the disease. Leukemic cells from patients with progressive disease demonstrated higher in vitro survival, compared with non-progressive B-CLL and normal B cells. All cells were sensitive to treatment with a combination of glucocorticoid and cAMP. Bcl-2 protein levels were not related to clinical progression, as measured by flow cytometry. Competitive PCR showed that Bcl-2 mRNA was over-expressed in most of the B-CLL samples and that p53 mRNA expression was similar between B-CLL groups and normal values and thus not related to clinical progression. However, since Bax alpha expression was lower in progressive than in non-progressive patients, the Bcl-2/Bax alpha ratio at the mRNA level was significantly higher in the progressive group. Our data suggest that the Bcl-2/Bax alpha ratio is important for the regulation of B-CLL cell survival, that p53 over-expression in progressive B-CLL is the result of post-transcriptional modifications and that a directed PKA activation may potentiate the cytolytic effect of glucocorticoids in vivo.

beta2-chimaerin is a novel target for diacylglycerol: binding properties and changes in subcellular localization mediated by ligand binding to its C1 domain

The members of the chimaerin family of Rac-GTPase-activating proteins possess a single C1 domain with high homology to those present in protein kinase C (PKC) isozymes. This domain in PKCs is involved in phorbol ester and diacylglycerol (DAG) binding. We previously have demonstrated that one of the chimaerin isoforms, beta2-chimaerin, binds phorbol esters with high affinity. In this study we analyzed the properties of beta2-chimaerin as a DAG receptor by using a series of conformationally constrained cyclic DAG analogues (DAG lactones) as probes. We identified analogs that bind to beta2-chimaerin with more than 100-fold higher affinity than 1-oleoyl-2-acetylglycerol. The potencies of these analogs approach those of the potent phorbol ester tumor promoters. The different DAG lactones show some selectivity for this novel receptor compared with PKCalpha. Cellular studies revealed that these DAG analogs induce translocation of beta2-chimaerin from cytosolic (soluble) to particulate fractions. Using green fluorescent protein-fusion proteins for beta2-chimaerin we determined that this novel receptor translocates to the perinuclear region after treatment with DAG lactones. Binding and translocation were prevented by mutation of the conserved Cys-246 in the C1 domain. The structural homology between the C1 domain of beta2-chimaerin and the C1b domain of PKCdelta also was confirmed by modeling analysis. Our results demonstrate that beta2-chimaerin is a high affinity receptor for DAG through binding to its C1 domain and supports the emerging concept that multiple pathways transduce signaling through DAG and the phorbol esters.

Convergent assembly of highly potent analogues of bryostatin 1 via pyran annulation: bryostatin look-alikes that mimic phorbol ester function

Highly potent bryostatin analogues which contain the complete bryostatin core structure have been synthesized using a pyran annulation approach as a key strategic element. The A ring pyran was assembled using a pyran annulation reaction between a C1-C8 hydroxy allylsilane and an aldehyde comprising C9-C13. This pyran was transformed to a new hydroxy allylsilane and then coupled with a preformed C ring aldehyde subunit in a second pyran annulation, with concomitant formation of the B ring. This tricyclic intermediate was elaborated to bryostatin analogues which displayed nanomolar to subnanomolar affinity for PKC, but displayed properties indistinguishable from a phorbol ester in a proliferation/attachment assay.

Beta2-chimaerin is a high affinity receptor for the phorbol ester tumor promoters

Beta2-chimaerin, a member of the GTPase-activating proteins for the small GTP-binding protein p21Rac, possesses a single cysteine-rich domain with high homology to those implicated in phorbol ester and diacylglycerol binding in protein kinase C (PKC) isozymes. We have expressed beta2-chimaerin in Sf9 insect cells using the baculovirus expression system and determined that, like PKCs, beta2-chimaerin binds phorbol esters with high affinity in the presence of phosphatidylserine as a cofactor. Scatchard plot analysis using the radioligand [3H]phorbol 12,13-dibutyrate revealed a dissociation constant of 1.9 +/- 0.2 nM for beta2-chimaerin. Likewise, beta2-chimaerin is a high affinity receptor for the bryostatins, a class of atypical PKC activators. A detailed comparison of structure-activity relations using several phorbol ester analogs revealed striking differences in binding recognition between beta2-chimaerin and PKCalpha. Although the diacylglycerol 1-oleoyl-2-acetylglycerol binds with similar potency to both beta2-chimaerin and PKCalpha, the mezerein analog thymeleatoxin has 56-fold less affinity for binding to beta2-chimaerin. To establish whether beta2-chimaerin responds to phorbol esters in cellular systems, we overexpressed beta2-chimaerin in COS-7 cells and monitored its subcellular distribution after phorbol ester treatment. Interestingly, as described previously for PKC isozymes, beta2-chimaerin translocates from cytosolic to particulate fractions as a consequence of phorbol ester treatment. Our results demonstrate that beta2-chimaerin is a novel target for the phorbol ester tumor promoters. The expansion of the family of phorbol ester receptors strongly suggests a potential for the "non-kinase" receptors as cellular mediators of the phorbol ester responses.

Characterization of EBV-carrying B-cell populations in healthy seropositive individuals with regard to density, release of transforming virus and spontaneous outgrowth

Peripheral or tonsil lymphocyte populations of EBV-seropositive donors give rise to EBV-carrying LCLs upon in vitro explantation. Such lines can arise either by a 2-step mechanism, namely release of virus from some of the explanted cells followed by infection of previously uninfected B cells, or by direct outgrowth of virus-harboring B cells (Rickinson et al., 1974; Dalens et al., 1975; Hinuma and Katsuki 1978; Katsuki et al., 1979). We observed that cells responsible for both the 2-step mechanism and for direct outgrowth are found in the purified B-cell compartment. Virus release was more frequent than direct outgrowth. The majority of virus-releasing cells were found in the low-density fraction that contains large, activated B blasts. Cells that were capable of spontaneous outgrowth in the presence of the viral inhibitor PFA and of virus-neutralizing antibody gave rise to cell lines that carried the sex chromosome marker of the original donor, rather than that of admixed cord blood lymphocyte of the opposite sex. Such cells were found in both the low- and the high-density fractions. The majority of the EBV-carrying B cells in vivo are thus low-density blasts. Rare small B cells of high density harboring EBV were capable of spontaneous outgrowth. This may be indicative of a host control mechanism that is removed upon cultivation in vitro.

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.

Characterization of the cysteine-rich region of the Caenorhabditis elegans protein Unc-13 as a high affinity phorbol ester receptor. Analysis of ligand-binding interactions, lipid cofactor requirements, and inhibitor sensitivity

The Caenorhabditis elegans Unc-13 protein is a novel member of the phorbol ester receptor family having a single cysteine-rich region with high homology to those present in protein kinase C (PKC) isozymes and the chimaerins. We expressed the cysteine-rich region of Unc-13 in Escherichia coli and quantitatively analyzed its interactions with phorbol esters and related analogs, its phospholipid requirements, and its inhibitor sensitivity. [3H]Phorbol 12,13-dibutyrate [3H]PDBu bound with high affinity to the cysteine-rich region of Unc-13 (Kd = 1.3 +/- 0.2 nM). This affinity is similar to that of other single cysteine-rich regions from PKC isozymes as well as n-chimaerin. As also described for PKC isozymes and n-chimaerin, Unc-13 bound diacylglycerol with an affinity about 2 orders of magnitude weaker than [3H]PDBu. Structure-activity analysis revealed significant but modest differences between recombinant cysteine-rich regions of Unc-13 and PKC delta. In addition, Unc-13 required slightly higher concentrations of phospholipid for reconstitution of [3H]PDBu binding. Calphostin C, a compound described as a selective inhibitor of PKC, was also able to inhibit [3H]PDBu binding to Unc-13, suggesting that this inhibitor is not able to distinguish between different classes of phorbol ester receptors. In conclusion, although our results revealed some differences in ligand and lipid cofactor sensitivities, Unc-13 represents a high affinity cellular target for the phorbol esters as well as for the lipid second messenger diacylglycerol, at least in C. elegans. The use of phorbol esters or some "specific" antagonists of PKC does not distinguish between cellular pathways involving different PKC isozymes or novel phorbol ester receptors such as n-chimaerin or Unc-13.

Conformationally constrained analogues of diacylglycerol (DAG). 16. How much structural complexity is necessary for recognition and high binding affinity to protein kinase C?

The design of potent protein kinase C (PK-C) ligands with low nanomolar binding affinities was accomplished by the combined use of pharmacophore- and receptor-guided approaches based on the structure of the physiological enzyme activator, diacylglycerol (DAG). Earlier use of the former approach, which was based on the structural equivalence of DAG and phorbol ester pharmacophores, identified a fixed template for the construction of a semirigid "recognition domain" that contained the three principal pharmacophores of DAG constrained into a lactone ring (DAG-lactones). In the present work, the pharmacophore-guided approach was refined to a higher level based on the X-ray structure of the C1b domain of PK-Cdelta complexed with phorbol-13-O-acetate. A systematic search that involved modifying the DAG-lactone template with a combination of linear or branched acyl and alpha-alkylidene chains, which functioned as variable hydrophobic "affinity domains", helped identify compounds that optimized hydrophobic contacts with a group of conserved hydrophobic amino acids located on the top half of the C1 domain where the phorbol binds. The hydrophilic/hydrophobic balance of the molecules was estimated by the octanol/water partition coefficients (log P) calculated according to a fragment-based approach. The presence of branched alpha-alkylidene or acyl chains was of critical importance to reach low nanomolar binding affinities for PK-C. These branched chains appear to facilitate important van der Waals contacts with hydrophobic segments of the protein and help promote the activation of PK-C through critical membrane interactions. Molecular modeling of these DAG-lactones into an empty C1b domain using the program AutoDock 2.4 suggests the existence of competing binding modes (sn-1 and sn-2) depending on which carbonyl is directly involved in binding to the protein. Inhibition of epidermal growth factor (EGF) binding, an indirect PK-C mediated response, was realized with some DAG-lactones at a dose 10-fold higher than with the standard phorbol-12, 13-dibutyrate (PDBU). Through the National Cancer Institute (NCI) 60-cell line in vitro screen, DAG-lactone 31 was identified as a very selective and potent antitumor agent. The NCI's computerized, pattern-recognition program COMPARE, which analyzes the degree of similarity of mean-graph profiles produced by the screen, corroborated our principles of drug design by matching the profile of compound 31 with that of the non-tumor-promoting antitumor phorbol ester, prostratin. The structural simplicity and the degree of potency achieved with some of the DAG-lactones described here should dispel the myth that chemical complexity and pharmacological activity go hand in hand. Even as a racemate, DAG-lactone 31 showed low namomolar binding affinity for PK-C and displayed selective antitumor activity at equivalent nanomolar levels. Our present approach should facilitate the generation of multiple libraries of structurally similar DAG-lactones to help exploit molecular diversity for PK-C and other high-affinity receptors for DAG and the phorbol esters. The success of this work suggests that substantially simpler, high-affinity structures could be identified to function as surrogates of other complex natural products.

Modeling, chemistry, and biology of the benzolactam analogues of indolactam V (ILV). 2. Identification of the binding site of the benzolactams in the CRD2 activator-binding domain of PKCdelta and discovery of an ILV analogue of improved isozyme selectivity

Protein kinase C (PKC) is a complex enzyme system comprised of at least 11 isozymes that serves to mediate numerous extracellular signals which generate lipid second messengers. The discovery of isozyme-selective activators and inhibitors (modulators) of PKC is crucial to ascertaining the role of the individual isozymes in physiological and pathophysiological processes and to manipulating their function. The discovery of such small molecule modulators of PKC is at present a largely unmet pharmacological need. Herein we detail our modeling studies which reveal how the natural product indolactam V (ILV) and its 8-membered ring analogue, the benzolactam 15, bind to the CRD2 activator domain of PKC. These modeling studies reveal that not all PKC ligands possess a common pharmacophore, and further suggest an important role of specific hydrophobic contacts in the PKC-ligand interaction. The modeling studies find strong experimental support from mutagenesis studies on PKC alpha that reveal the crucial role played by the residues proline 11, leucine 20, leucine 24, and glycine 27. Next, we describe the synthesis of two 8-substituted benzolactams starting from L-phenylalanine and characterize their isozyme selectivity; one of the two benzolactams exhibits improved isozyme selectivity relative to the n-octyl-ILV. Lastly, we report inhibition of cellular proliferation of two different breast carcinoma cell lines by the benzolactam 5 and show that the compound preferentially down-regulates PKCbeta in both cell lines.

Psychiatric diagnoses in minority female adolescent suicide attempters

Psychiatric diagnoses were examined using the Schedule for Affective Disorders and Schizophrenia for School-Aged Children semistructured interview among three groups of minority adolescent females aged 12 to 17:61 suicide attempters, 31 psychiatrically disturbed nonattempters, and 23 nonattempting, nondisturbed girls. Major or minor depressive disorder was found in 42% of the suicide attempters; conduct disorder in 46%; multiple diagnoses in 38%, no diagnosis in 13%. These rates were very similar to those found in disturbed nonattempters. Only one symptom, suicidal ideation, distinguished attempters from disturbed nonattempters, while many symptoms distinguished these two groups from nondisturbed nonattempters.

The bryostatin 1 A-ring acetate is not the critical determinant for antagonism of phorbol ester-induced biological responses

The contribution of the A-ring C(7) acetate to the function of bryostatin 1 has been investigated through synthesis and biological evaluation of an analogue incorporating this feature into the bryopyran core structure. No enhanced binding affinity for protein kinase C (PKC) was observed, relative to previously characterized analogues lacking the C(7) acetate. Functional assays showed biological responses characteristic of those induced by the phorbol ester PMA and distinctly different from those observed with bryostatin 1.

Substitution on the A-ring confers to bryopyran analogues the unique biological activity characteristic of bryostatins and distinct from that of the phorbol esters

A close structural analogue of bryostatin 1, which differs from bryostatin 1 only by the absence of the C(30) carbomethoxy group (on the C(13) enoate of the B-ring), has been prepared by total synthesis. Biological assays reveal a crucial role for substitution in the bryostatin 1 A-ring in conferring those responses which are characteristic of bryostatin 1 and distinct from those observed with PMA.

Specific vanilloid responses in C6 rat glioma cells

Capsaicin and its ultrapotent analog resiniferatoxin (RTX) act through specific vanilloid receptors on sensory neurons. Here, we describe specific vanilloid responses in rat C6 glioma cells. Capsaicin and RTX stimulated 45Ca uptake in a similar fashion to that found for cultured rat dorsal root ganglion neurons (DRGs); this response was antagonized by the antagonists capsazepine and ruthenium red. As in DRGs, pretreatment of C6 cells with capsaicin or RTX produced desensitization to subsequent stimulation of 45Ca uptake. The potency for desensitization by RTX in the C6 cells corresponded to that for 45Ca uptake, whereas in DRGs it occurred at significantly lower concentrations corresponding to that for the high affinity [3H]RTX binding site. Consistent with this difference, in C6 cells we were unable to detect [3H]RTX binding. These characteristics suggest the presence of C-type but not R-type vanilloid receptors on C6 cells. After 2 day treatment, capsaicin but not RTX inhibited the proliferation and altered the differentiation of the cells and produced apoptosis. In the long term experiments, capsazepine, instead of antagonizing the effect of capsaicin, acted as an agonist. Moreover, capsazepine displayed these effects with higher potency than that of capsaicin. The different potencies and structure activity relations suggest a distinct mechanism for these long-term vanilloid effects. Our finding that C6 cells can respond directly to capsaicin necessitates a reevaluation of the in vivo pathway of response to vanilloids, and highlights the importance of the neuron-glial network.

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.

The discovery of novel, structurally diverse protein kinase C agonists through computer 3D-database pharmacophore search. Molecular modeling studies

A computer protein kinase C (PK-C) pharmacophore search on 206,876 nonproprietary structures in the NCI 3D-database led to the discovery of five compounds which were found to possess PK-C binding affinities in the low micromolar range and six others having detectable, but marginal, binding affinities. Molecular modeling studies showed that in addition to the presence of the defined pharmacophore, hydrophobicity and conformational energy are the two other important factors determining the PK-C binding affinity of a compound. The modeling results were confirmed by synthetic modification of two inactive compounds, producing two active derivatives. These newly discovered, structurally diverse lead compounds are being used as the basis for further synthetic modifications aimed at more potent PK-C ligands that will compete with the phorbol esters.

Antineoplastic agents. 340. Isolation and structural elucidation of bryostatins 16-18

Separation of two trace cancer cell growth inhibitory (P388 leukemia) fractions from about 1000 kg of wet Gulf of Mexico Bugula neritina (Bryozoa) has led to the isolation of bryostatins 16-18 (2-4). A combination of HRFABMS and high-field (400 MHz) 1H- and 13C-NMR spectral analyses were employed to assign the structures. The three new 20-desoxybryostatins 16 (2), 17 (3), and 18 (4) showed significant growth inhibitory activity (P388 ED50, 2, 9.3 x 10(-3) micrograms/mL, 3, 1.9 x 10(-2) micrograms/mL, and 4, 3.3 x 10(-3) micrograms/mL) against murine P388 lymphocytic leukemia.

Expanded T cell populations in patients with Wegener's granulomatosis: characteristics and correlates with disease activity

Patients with Wegener's granulomatosis have a high prevalence of expanded populations of CD4+ and CD8+ T cells bearing different alpha/beta T cell receptors. To elucidate the role of these populations, we studied the phenotypic and functional characteristics of 13 expanded T cell populations in four patients for a period of 35-51 months. The expanded populations generally showed a persistently high expression of the activation markers HLA-DR and CD25. This expression was independent of the activity of the disease. The expanded populations also expressed CD45RO and/or CD45RA and most of them expressed CD57 but not CD28. Analysis of intracellular presence and secretion of IFN-gamma, IL-2, and IL-4 showed that most of the expanded cell populations contained and/or secreted more of these cytokines than the nonexpanded populations, with an especially high expression/secretion of IFN-gamma and IL-2. The expanded populations showed little proliferative response to Con A and OKT3. The proliferative response of the cells was partly restored after preincubation in medium alone. Some of the expanded populations were associated with disease activity, thus suggesting a link between expanded T cells and the disease. The activated status of the expanded populations and the tendency for certain populations to correlate in magnitude with disease activity suggest their involvement in the disease process. The relative stability of these cell populations indicates that the stimulus driving them is persistent, in agreement with the chronicity of the disease.

Iridals are a novel class of ligands for phorbol ester receptors with modest selectivity for the RasGRP receptor subfamily

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.

New amide-bearing benzolactam-based protein kinase C modulators induce enhanced secretion of the amyloid precursor protein metabolite sAPPalpha

Protein kinase C (PKC) is known to participate in the processing of the amyloid precursor protein (APP). Abnormal processing of APP through the action of the beta- and gamma-secretases leads to the production of the 39-43 amino acid Abeta fragment, which is neurotoxic and which is believed to play an important role in the etiology of Alzheimer's disease. PKC activation enhances alpha-secretase activity, which results in a decrease of the amyloidogenic products of beta-secretase. In this article, we describe the synthesis of 10 new benzolactam V8 based PKC activators having side chains of varied saturation and lipophilicity linked to the aromatic ring through an amide group. The K(i) values measured for the inhibition of phorbol ester binding to PKCalpha are in the nanomolar range and show some correlation with their lipophilicity. Compounds 5g and 5h show the best binding affinity among the 10 benzolactams that were synthesized. By use of a cell line derived from an AD patient, significant enhancement of sAPPalpha secretion was achieved at 1 microM concentration for most of the compounds studied and at 0.1 microM for compounds 5e and 5f. At 1 microM the enhancement of sAPPalpha secretion for compounds 5c-h is higher than that observed for the control compound 8-(1-decynyl)benzolactam (BL). Of interest is the absence of activity found for the highly lipophilic ligand 5i, which has a K(i) of 11 nM. On the other hand, its saturated counterpart 5j, which possesses a comparable K(i) and ClogP, retains activity in the secretase assay. In the hyperplasia studies, 5f showed a modest response at 100 microg and 5e at 300 microg, suggesting that 5f was approximately 30-fold less potent than the PKC activator mezerein and 100-fold less potent than TPA. 5e was approximately 3-fold less active than 5f. On the basis of the effect of unsaturation for other potent PKC ligands, we would predict that 5e would retain biological activity in most assays but would show a marked loss of tumor-promoting activity. Compound 5e thus becomes a viable candidate compound in the search for Alzheimer's therapeutics capable of modulating amyloid processing.

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.

Searching for disease modifiers-PKC activation and HDAC inhibition - a dual drug approach to Alzheimer's disease that decreases Abeta production while blocking oxidative stress

A series of benzolactam compounds were synthesized, some of which caused a concentration-dependent increase in sAPPalpha and decrease in Abeta production in the concentration range of 0.1-10 microM. Moreover, some compounds showed neuroprotective effects in the 10-20 microM range in the HCA cortical neuron model of oxidative stress and no toxicity in measurements of neuron viability by MTT assay, even at the highest concentrations tested (20 microM). Alzheimer's disease (AD) is a well-studied neurodegenerative process characterized by the presence of amyloid plaques and neurofibrillary tangles. In this study, a series of protein kinase C (PKC) activators were investigated, some of which also exhibit histone deacetylase (HDAC) inhibitory activity, under the hypothesis that such compounds might provide a new path forward in the discovery of drugs for the treatment of AD. The PKC-activating properties of these drugs were expected to enhance the alpha-secretase pathway in the processing of amyloid precursor protein (APP), while their HDAC inhibition was anticipated to confer neuroprotective activity. We found that benzolactams 9 and 11-14 caused a concentration-dependent increase in sAPPalpha and decrease in beta-amyloid (Abeta) production in the concentration range of 0.1-10 microM, consistent with a shift of APP metabolism toward the alpha-secretase-processing pathway. Moreover, compounds 9-14 showed neuroprotective effects in the 10-20 microM range in the homocysteate (HCA) cortical neuron model of oxidative stress. In parallel, we found that the most neuroprotective compounds caused increased levels of histone acetylation (H4), thus indicating their likely ability to inhibit HDAC activity. As the majority of the compounds studied also show nanomolar binding affinities for PKC, we conclude that it is possible to design, de novo, agents that combine both PKC-activating properties along with HDAC inhibitory properties. Such agents would be capable of modulating amyloid processing while showing neuroprotection. These findings may offer a new approach to therapies that exhibit disease-modifying effects, as opposed to symptomatic relief, in the treatment of AD.