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N E Lewin

Publications and source records attributed to N E Lewin.

At least 37 records · Page 2Linked to original sources
PubMed1996

Conformationally constrained analogues of diacylglycerol. 13. Protein kinase C ligands based on templates derived from 2,3-dideoxy-L-erythro(threo)-hexono-1,4-lactone and 2-deoxyapiolactone.

In the present investigation, the last two possible modes of generating conformationally semirigid diacylglycerol (DAG) analogues embedded into five-membered ring lactones as templates III and IV are investigated. The first two templates studied in previous investigations corresponded to 2-deoxyribonolactone (template I) and 4,4-disubstituted gamma-butyrolactone (template II), with the latter producing potent protein kinase C (PK-C) ligands with low nanomolar binding affinities. The templates reported in this work correspond to 2,3-dideoxy-L-erythro- or -threo-hexono-1,4-lactone (template III) and 2-deoxyapiolactone (template IV). Compounds constructed with the dideoxy-L-erythro- or -threo-hexono-1,4-lactone template were synthesized stereospecifically from tri-O-acetyl-L-glucal and L-galactono-1,4-lactone, respectively. Compounds constructed with the 2-deoxyapiolactone template were synthesized stereoselectively from di-O-isopropylidene-alpha-D-apiose. Inhibition of the binding of [3H]phorbol-12,13-dibutyrate to PK-C alpha showed that only the threo-isomer, 5-O-tetradecanoyl-2,3-dideoxy-L-threo-hexono-1,4-lactone (2) was a good PK-C ligand (Ki = 1 microM). The rest of the ligands had poorer affinities with Ki values between 10 and 28 microM. With these results, the order of importance of five-membered ring lactones as competent templates for the construction of semirigid DAG surrogates with effective PK-C binding affinity can be established as II >> I approximately III > IV.

Diglycerides↗
PubMed1996

The bryostatins inhibit growth of B16/F10 melanoma cells in vitro through a protein kinase C-independent mechanism: dissociation of activities using 26-epi-bryostatin 1.

Bryostatin 1 is a potential cancer chemotherapeutic agent in Phase II clinical trials, with positive responses observed for malignant melanoma, among other tumors. The bryostatins are known to be potent ligands for protein kinase C (PKC), functioning as partial antagonists. In the present study, we explore the mechanism by which the bryostatins inhibit growth to B16/F10 mouse melanoma cells in vitro. Three experimental approaches suggest that the growth inhibition is independent of PKC. First, we characterized in detail the translocation and down-regulation of the PKC isozymes alpha, delta, and epsilon in response to phorbol ester and bryostatin 1 in these cells. Although the dose-response curves obtained for the translocation-activation of PKC isozymes showed good correlation with the growth-enhancing activity of phorbol 12-myristate 13-acetate, for no PKC isozyme was there a good correlation with the growth-inhibitory activity of bryostatin 1. Second, inhibition PKC, inhibited the growth of the B16/F10 melanoma cell lines with potency similar to that of bryostatin 1. We confirmed here that 26-epi-bryostatin 1 showed 60-fold reduced affinity for PKC and 30-60-fold reduced potency to translocate and downregulate PKC isozymes compared with bryostatin 1. We presumed that the principal toxicity of bryostatin 1 reflects its interaction with PKC, and we would thus predict that epi-bryostatin 1 would be less toxic. Indeed, we found at least 10-fold reduced toxicity of 26-epi-bryostatin 1 in C57BL/6 mice compared with bryostatin 1. We conclude that the growth inhibition of the bryostatins, at least in this system, does not result from interaction with PKC. As exemplified by 26-epi-bryostatin 1, this insight permits the design of analogues with comparable growth inhibition to bryostatin 1 but with reduced toxicity.

Animals↗
PubMed1996

Conformationally constrained analogues of diacylglycerol. 10. Ultrapotent protein kinase C ligands based on a racemic 5-disubstituted tetrahydro-2-furanone template.

5,5-Bis(hydroxymethyl)tetrahydro-2-furanone and its isomer 4,4-bis(hydroxymethyl)tetrahydro-2-furanone were investigated as possible templates for the construction of conformationally constrained analogues of the biologically important second messenger, diacylglycerol (DAG). The former lactone contains embedded within its structure an exact glycerol moiety, while in the latter the ring oxygen has been transposed to the other side of the carbonyl group. All target compounds were synthesized as racemates from 1,3-dihydroxy-2-propanone. The 5,5-bis(hydroxymethyl)tetrahydro-2-furanone proved to be the better template for the construction of DAG surrogates that were demonstrated to have high binding affinities for the biological target, protein kinase C (PK-C). The simplest target compounds derived from this template (3e and 3f) have one of the hydroxyl moieties functionalized either as a myristate or as an oleate ester. The simplest target compound (9c) derived from the ineffective 4,4-bis-(hydroxymethyl)tetrahydro-2-furanone template was investigated only with a myristoyl acyl chain. Reducing the long acyl chain to an acetyl moiety and attaching a compensating lipophilic chain to the lactone ring as an alpha-alkylidene moiety produced compounds 10e and 10f (Z-isomers) and 11e and 11f (E-isomers), which were constructed on the more effective 5,5-bis(hydroxymethyl)tetrahydro-2-furanone template. Targets 14c (Z-isomer) and 15c (E-isomer) were derived, in turn, from 4,4-bis(hydroxymethyl)tetrahydro-2-furanone. The affinities of these ligands for PK-C were assessed in terms of their ability to displace bound [3H-20]phorbol 12,13-dibutyrate (PDBU) from the single isozyme PK-C alpha. The biological data support the hypothesis that the increase in binding affinity for PK-C shown by some of these constrained DAG mimetics appears to be entropic in nature. Two of the designed ligands (10e and 10f) showed the highest affinities (34 and 24 nM, respectively) reported so far for a DAG analogue. Assuming that the interaction between these racemic compounds and PK-C is stereospecific, the potency of the active enantiomer is anticipated to double.

4-Butyrolactone↗
PubMed1996

Conformationally constrained analogues of diacylglycerol. 11. Ultrapotent protein kinase C ligands based on a chiral 5-disubstituted tetrahydro-2-furanone template.

Conformationally constrained analogues of diacylglycerol (DAG) built on a racemic 5(-)[(acyloxy)-methyl]-5-(hydroxymethyl)tetrahydro-2-furanone template were shown previously to have excellent binding affinities for protein kinase C (PK-C). Since the interaction of PK-C with DAG is stereospecific, it was anticipated that PK-C would bind tightly to only one enantiomeric form of the compounds constructed with this new lactone template. Separation of enantiomers by chiral HPLC was discarded due to the ease with which acyl migration occurs in these class of compounds, and a total chiral synthesis was undertaken. Prior to chemical synthesis, the selection of the "correct" enantiomeric template was predicted by a molecular conformational analysis that compared the two enantiomers of DAG in their presumed "active" conformation with the two enantiomeric lactone templates. This presumed "active" conformation for DAG was derived from a previously developed pharmacophore model that uses the molecule of a potent phorbol diester as the ideal rigid template. The results from this analysis indicated that the "correct" lactone template corresponded to the inactive (R)-isomer of DAG. This analysis also predicted that the lactone template corresponding to the active (S)-DAG enantiomer would not fit adequately into the pharmacophore. The chiral syntheses of target compounds 2, 4, and 6, constructed on the selected, and presumably "correct" lactone template, were achieved from a common bicyclic intermediate (5R,8R,9R)-8,9-O-isopropylidene-2-keto-1,7-dioxaspiro[4.4]nonane (10) that was synthesized from commercially available 1,2:3,5-di-O-isopropylidene-alpha-D-threo-apiofuranose (7) by a very effective spirolactonization approach. On the basis of their ability to inhibit the binding of [3H-20]phorbol 12,13-dibutyrate (PDBU) to PK-C alpha, the enantiomeric ligands 2, 4, and 6 were twice as potent as the corresponding racemates. These results confirm that binding of these lactones is stereospecific and consistent with a binding mechanism similar to that of DAG.

4-Butyrolactone↗
PubMed1996

Conformationally constrained analogues of diacylglycerol. 12. Ultrapotent protein kinase C ligands based on a chiral 4,4-disubstituted heptono-1,4-lactone template.

Conformationally constrained analogues of diacylglycerol (DAG) built on a 5(-)[(acyloxy)methyl]-5-(hydroxymethyl)tetrahydro-2-furanone template (1, Chart 1) were shown previously to bind tightly to protein kinase C alpha (PK-C alpha) in a stereospecific manner. These compounds, however, racemized readily through rapid acyl migration and lost biological potency. In order to circumvent this problem, the "reversed ester" analogues were designed as a new set of PK-C ligands. This reversal of the ester function produced some new DAG mimetics that are embedded in a C-4 doubly-branched heptono-1,4-lactone template. The reversed ester analogues were impervious to racemization, and their chemically distinct branches facilitated the enantiospecific syntheses of all targets. Compound 2, the simplest reversed ester analogue of 1 (Chart 1), exhibited a 3.5-fold reduction in binding affinity toward PK-C alpha which we attributed to the loss of a stabilizing gauche interaction that caused the ester branch in 2 to be more disordered than in the normal ester 1. However, conversion of the propanoyl branch of 2 into a propenoyl branch restored binding affinity (3 versus 5). As expected, the compounds bound to the enzyme with strict enantioselectivity (3 and 5 versus 4 and 6). Functionalization of the propenoyl-branched compounds as alpha-alkylidene lactones, in a manner which proved successful with the 5(-)[(acyloxy)methyl]-5-(hydroxymethyl)tetrahydro-2-furanone template (9 and 10), produced stable compounds with equivalent ultrapotent binding affinities for PK-C alpha (7 and 8). The additional incorporation of the propenoyl-branched carbonyl into a gamma-lactone ring was performed (11-14) not only to derive a possible additional entropic advantage but also to confirm the spatial disposition of this carbonyl function in the ligand-enzyme complex. Although no additional entropic advantage was derived, the high binding affinities displayed by compounds 11 and 12 helped to establish the correct orientation of the equivalent carbonyl group in PK-C-bound DAG. As expected, these DAG analogues activated PK-C alpha. The most potent agonist, compound 8, stimulated phosphorylation of the alpha-pseudosubstrate peptide, and in primary mouse keratinocytes it caused inhibition of binding of epidermal growth factor with an ED50 of approximately 1 microM. In contrast to the phorbol esters, compound 8 did not induce acute edema or hyperplasia in skin of CD-1 mice, and its pattern of downregulation with several PK-C isozymes was different from that of phorbol 12-myristate 13-acetate (PMA).

4-Butyrolactone↗
PubMed1996

Synthesis of bis-gamma-butyrolactones containing conformationally constrained (S)- and (R)-diacylglycerol structures.

The synthesis of two sets of rigid diacylglycerol (DAG) analogues with either the (S)-DAG or (R)-DAG enantiomer embedded into a bis-gamma-butyrolactone template was accomplished stereoselectively from di-O-isopropylidene-alpha-D-apiose. The key step in both syntheses was the assemblage of the bicyclic perhydrofuro[3,4-b]furan ring system via a radical exo-dig intramolecular cyclization. A lipophilic undecanyl alkyl chain attached at C-3 of the fully assembled perhydrofuro[3,4-b]furan-2,4-dione (bis-gamma-butyrolactone) template can adopt two orientations with the one directed away from the concave face of the bicyclic system favored by a 4 to 1 ratio in each case. Evaluation of the final target pairs of enantiomers as PK-C alpha ligands revealed that the template containing an embedded (R)-DAG structure was more effective. The difference in binding affinity was also modulated by the direction of the alkyl chain.

4-Butyrolactone↗
PubMed1996

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.

Animals↗
PubMed1995

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.

Amino Acid Sequence↗
PubMed1995

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.

Amino Acid Sequence↗
PubMed1995

Protein kinase C in cell signaling: strategies for the development of selective inhibitors.

Protein kinase C plays a central role in the cellular signaling pathway for the lipophilic second messenger sn-1,2-diacylglycerol, which is involved in many biological responses, including tumor promotion and inflammation. A major effort has been directed at understanding diversity within this system in order to develop strategies for selective inhibition. Two classes of ligands for the regulatory domain of protein kinase C have been identified which, although they function in vitro as activators of the enzyme, paradoxically behave in vivo as partial antagonists. Identification of targets for the phorbol esters distinct from protein kinase C argues that antagonists acting on the regulatory and catalytic domains of protein kinase C will have different spectra of action.

Animals↗
PubMed1995

Resiniferatoxin-amide and analogues as ligands for protein kinase C and vanilloid receptors and determination of their biological activities as vanilloids.

The naturally occurring diterpene resiniferatoxin (RTX) is an ultrapotent analogue of capsaicin. Acting on polymodal afferent neurons, RTX induces a generally similar pattern of responses as does capsaicin. However, the two compounds, as well as other vanilloid derivatives, display different relative potencies for different responses. In the present study, we examined the vanilloid-like activities of two new derivatives, the amide analogue of RTX and phorbol 12,13-dibenzoate 20-homovanillylamide. Structurally, RTX-amide resembles capsaicin more closely than does RTX, and after cleavage of the amide bond the resulting amine would be predicted to not bind to protein kinase C in contrast to resiniferonol 9,13,14-orthophenylacetate, the parent diterpene of RTX. In contrast to our expectations the binding potency of the RTX-amide for the vanilloid receptor present in rat spinal cord was 450-fold lower than that of RTX (Ki values for the RTX-amide and RTX were 10.4 +/- 0.7 nM and 23.1 +/- 3.2 pM, respectively). In the case of phorbol 12,13-dibenzoate 20-homovanillylamide, there was a further loss of affinity for the vanilloid receptor compared with RTX; nonetheless, the Ki (8.56 +/- 0.61 microM) was comparable with that of capsaicin (5.31 +/- 0.37 microM). Computer fitting of the binding data yielded Hill coefficient values of 2.25 +/- 0.03, 2.33 +/- 0.03, and 1.84 +/- 0.05 for RTX, RTX-amide, and phorbol 12,13-dibenzoate 20-homovanillylamide, respectively, indicating that both new compounds induced apparent positive cooperativity among vanilloid binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Effect of alteration of the heterocyclic nucleus of ILV on its isoform selectivity for PKC. Palladium catalyzed route to benzofuran analogues of ILV.

A palladium catalyzed route for the preparation of several benzofuran analogues of the PKC activator indolactam V (ILV) is described together with the ability of these compounds to activate the isoforms of PKC. The benzofuran analogues of ILV are shown to activate PKC with a slightly different pattern of isotype selectivity than ILV or 7-n-octyl-ILV. Moreover, in an examination of the effect of stereochemistry at the C-14 center of the teleocidins on PKC binding activity, a clear preference for R-stereochemistry at the C-14 center was found, thus providing additional verification of previously published structural correlations between the families of PKC activators.

Benzofurans↗
PubMed1994

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.

Information Systems↗
PubMed1994

Binding of [26-3H]bryostatin 1 and analogs to calcium-dependent and calcium-independent protein kinase C isozymes.

In this study we explored the pattern of protein kinase C (PKC) isozyme selectivity of the bryostatins, a unique class of PKC activators that induce only a subset of the typical phorbol ester responses and antagonize those phorbol ester-mediated responses that they themselves fail to induce. The binding properties of individual recombinant PKC isozymes that had been expressed in insect cells, isolated, and reconstituted in Triton X-100/phosphatidylserine mixed micelles were determined. [3H]Bryostatin 1 showed lower affinity for PKC-beta 1 and -gamma, compared with PKC-alpha, -delta, -epsilon, and -eta. This pattern contrasts with that observed for other PKC ligands. These latter assays were conducted with isozymes reconstituted in phosphatidylserine, conditions that unfortunately do not permit quantitation of bryostatin 1 binding under equilibrium conditions. Using delta 19,20-bryostatin 10 and delta 19,20-isobryostatin 10, we could distinguish the respective roles of ligand and lipid in the pattern of selectivity. When isozymes were reconstituted in phosphatidylserine vesicles, delta 19,20-bryostatin 10 and delta 19,20-isobryostatin 10 showed similar affinities for PKC-alpha and -gamma, similarly to the phorbol esters. However, in the mixed micellar system, PKC-gamma showed a significantly lower binding affinity, as had been observed for bryostatin 1. These results suggest that the unique pattern of biological responses to the bryostatins does not represent a unique pattern of isotype recognition. Furthermore, the lipid environment of PKC plays an important role in determining the binding selectivity for individual isozymes.

Animals↗
PubMed1992

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.

Animals↗
PubMed1992

Binding of [3H]bryostatin 4 to protein kinase C.

The bryostatins represent a unique class of activators of protein kinase C (PKC) which induce only a subset of the responses typical of the phorbol esters and block those responses to the phorbol esters which they themselves do not induce. To better understand the interaction of the bryostatins with PKC, we have synthesized [26-3H]bryostatin 4 and characterized its binding to PKC. [3H]Bryostatin 4 and [3H]phorbol 12,13-dibutyrate ([3H]PDBu) differed markedly in their binding to PKC reconstituted with phosphatidylserine (PS). The binding affinity of [3H]bryostatin 4 under these conditions was too high to measure and the rate of release of bound bryostatin was much slower than that of the phorbol esters, with a half-time of several hours. These properties caused bryostatin 1 to appear to inhibit [3H]PDBu binding under these conditions in a non-competitive fashion. Both the high potency and the slow rate of release of the bryostatins may contribute to their unique pattern of biological activity. By reconstituting PKC in a mixture of 1.5% Triton X-100:0.3% PS, we were able to establish reversible conditions for [3H]bryostatin 4 binding. Under these latter conditions, binding of [3H]bryostatin 4 was competitively inhibited by PDBu, consistent with both the bryostatin and phorbol esters binding to PKC in a qualitatively similar fashion. Binding affinities to PKC isozymes alpha, beta, and gamma were compared and little difference was found, suggesting that differential recognition by these isozymes does not account for the unique biological activity of the bryostatins.

Animals↗
PubMed1992

Identification of alpha-1-acid glycoprotein (orosomucoid) as a major vanilloid binding protein in serum.

We have used the vanilloid (capsaicin) receptor assay to search for modulators of binding activity. We report here that both capsaicin and its ultrapotent analog, resiniferatoxin (RTX), bind to the plasma protein alpha-1-acid glycoprotein (AGP) with high affinity (10.5 and 0.3 microM, respectively). AGP seems to be the dominant vanilloid (capsaicin/RTX) binding protein in serum. [3H] RTX binding to AGP is inhibited by chlorpromazine and by Trisbutoxyethylphosphate, indicating that vanilloids compete for a well-characterized drug binding domain on the AGP molecule. The 35-fold difference in the affinity of AGP for RTX and capsaicin may result in differences in the pharmacodynamics and pharmacokinetics of these two compounds; the contribution of AGP binding to the unique spectra of action of RTX or to the marked species differences in vanilloid actions, however, remains to be determined. An important practical application of AGP is its inclusion in the [3H]RTX binding assay utilizing sensory ganglion membranes to reduce nonspecific binding by up to 5-fold.

Animals↗