Metabolism of GS-7340, a novel phenyl monophosphoramidate intracellular prodrug of PMPA, in blood

PMPA, an acyclic nucleoside phosphonate analog, is a potent inhibitor of HIV. In the cells, PMPA is efficiently phosphorylated by intracellular kinases to produce PMPApp, the pharmacologically active metabolite. Despite its demonstrated antiviral potency, PMPA has limited cell permeability presumably resulting from the presence of two negative charges on the phosphonyl group. To enhance intracellular concentrations of PMPA, we developed a prodrug, selectively metabolized inside cells. GS-7340 (9-[(R)-2-[[[[(S)-1-(isopropoxycarbonyl)ethyl] amino] phenoxy-phosphinyl]-methoxy] propyl] adenine) is a prodrug which is orally bioavailable in dogs as the intact prodrug and has demonstrated anti-HIV activity in cell culture of over 1000-fold greater than that of PMPA. The metabolism of PMPA in peripheral blood mononuclear cells (PBMC), red blood cells (RBC) and plasma was examined following exposure of whole blood to PMPA or GS-7340 at concentrations similar to ones observed systemically following oral administration in dogs. Following 1 hour incubation with whole blood, GS-7340 was stable in plasma, produced high levels of PMPA and its phosphorylated metabolites in PBMC but not in RBC. No intact prodrug was present in PBMC. The only other species present in PBMC was monoalaninyl PMPA. The levels of PMPA and the phosphorylated metabolites were over 20 times greater than those after incubation with PMPA. The dog and human blood data were similar. The intracellular levels of PMPA and PMPApp were roughly proportional to GS-7340 over a 10-fold concentration range indicating a lack of saturability of uptake and phosphorylation. Since PMPApp is the species responsible for antiviral activity of PMPA, the high intracellular levels of PMPApp should be an important indicator of greater clinical efficacy of GS-7340.     

METABOLISM OF GS-7340, A NOVEL PHENYL MONOPHOSPHORAMIDATE INTRACELLULAR PRODRUG OF PMPA,IN BLOOD

PMPA, an acyclic nucleoside phosphonate analog, is a potent inhibitor of HIV. In the cells, PMPA is efficiently phosphorylated by intracellular kinases to produce PMPApp, the pharmacologically active metabolite. Despite its demonstrated antiviral potency, PMPA has limited cell permeability presumably resulting from the presence of two negative charges on the phosphonyl group. To enhance intracellular concentrations of PMPA, we developed a prodrug, selectively metabolized inside cells. GS-7340 (9-[R)-2-[[[[S)-1-(isopropoxycarbonyl)ethyl] amino] phenoxy-phosphinyl]-methoxy] propyl] adenine) is a prodrug which is orally bioavailable in dogs as the intact prodrug and has demonstrated anti-HIV activity in cell culture of over 1000-fold greater than that of PMPA. The metabolism of PMPA in peripheral blood mononuclear cells (PBMC), red blood cells (RBC) and plasma was examined following exposure of whole blood to PMPA or GS-7340 at concentrations similar to ones observed systemically following oral administration in dogs. Following 1 hour incubation with whole blood, GS-7340 was stable in plasma, produced high levels of PMPA and its phosphorylated metabolites in PBMC but not in RBC. No intact prodrug was present in PBMC. The only other species present in PBMC was monoalaninyl PMPA. The levels of PMPA and the phosphorylated metabolites were over 20 times greater than those after incubation with PMPA. The dog and human blood data were similar. The intracellular levels of PMPA and PMPApp were roughly proportional to GS-7340 over a 10-fold concentration range indicating a lack of saturability of uptake and phosphorylation. Since PMPApp is the species responsible for antiviral activity of PMPA, the high intracellular levels of PMPApp should be an important indicator of greater clinical efficacy of GS-7340.     

Phosphoramidates of 2′-β-d-arabinouridine (AraU) as phosphate prodrugs; design,synthesis, in vitro activity and metabolism

2′-β-d-Arabinouridine (AraU), the uridine analogue of the anticancer agent AraC, was synthesized and evaluated for antiviral activity and cytotoxicity. In addition, a series of AraU monophosphate prodrugs in the form of triester phosphoramidates (ProTides) were also synthesized and tested against a range of viruses, leukaemia and solid tumour cell lines. Unfortunately, neither the parent compound (AraU) nor any of its ProTides showed antiviral activity, nor potent inhibitory activity against any of the cancer cell lines. Therefore, the metabolism of AraU phosphoramidates to release AraU monophosphate was investigated. The results showed carboxypeptidase Y, hog liver esterase and crude CEM tumor cell extracts to hydrolyse the ester motif of phosphoramidates with subsequent loss of the aryl group, while molecular modelling studies suggested that the AraU l-alanine aminoacyl phosphate derivative might not be a good substrate for the phosphoramidase enzyme Hint-1. These findings are in agreement with the observed disappearance of intact prodrug and concomitant appearance of the corresponding phosphoramidate intermediate derivative in CEM cell extracts without measurable formation of araU monophosphate. These findings may explain the poor antiviral/cytostatic potential of the prodrugs.     

A plant plasma membrane ATP binding cassette-type transporter is involved in antifungal terpenoid secretion

ATP binding cassette (ABC) transporters, which are found in all species, are known mainly for their ability to confer drug resistance. To date, most of the ABC transporters characterized in plants have been localized in the vacuolar membrane and are considered to be involved in the intracellular sequestration of cytotoxins. Working on the assumption that certain ABC transporters might be involved in defense metabolite secretion and their expression might be regulated by the concentration of these metabolites, we treated a Nicotiana plumbaginifolia cell culture with sclareolide, a close analog of sclareol, an antifungal diterpene produced at the leaf surface of Nicotiana spp; this resulted in the appearance of a 160-kD plasma membrane protein, which was partially sequenced. The corresponding cDNA (NpABC1) was cloned and shown to encode an ABC transporter. In vitro and in situ immunodetection showed NpABC1 to be localized in the plasma membrane. Under normal conditions, expression was found in the leaf epidermis. In cell culture and in leaf tissues, NpABC1 expression was strongly enhanced by sclareolide and sclareol. In parallel with NpABC1 induction, cells acquired the ability to excrete a labeled synthetic sclareolide derivative. These data suggest that NpABC1 is involved in the secretion of a secondary metabolite that plays a role in plant defense.     

Synthesis of 9-(2-beta-C-methyl-beta-d-ribofuranosyl)-6-substituted purine derivatives as inhibitors of HCV RNA replication

A series of 9-(2'-beta-C-methyl-beta-d-ribofuranosyl)-6-substituted purine derivatives were synthesized as potential inhibitors of HCV RNA replication. Their inhibitory activities in a cell based HCV replicon assay were reported. A prodrug approach was used to further improve the potency of these compounds by increasing the intracellular levels of 5'-monophosphate metabolites. These nucleotide prodrugs showed much improved inhibitory activities of HCV RNA replication.     

Effect of virazole on the antiviral activity of poly(G) X poly(C) and other polyribonucleotide interferonogens

The effect of virazole on the antiviral activity of poly (G) X poly (C), poly (G, A) X X poly (C) and poly(G, I) X poly (C) was studied in cell cultures and on mice. It was shown that virazole in concentrations not sufficient for significant inhibition of the development of vesicular stomatitis virus or Sindbis virus in chick embryo cell cultures markedly increased the antiviral effect and allowed decreasing the minimum effective doses of the synthetic polyribonucleotide complexes with respect to the above viruses. Combined administration of poly (G) X poly (C) and virazole to mice 1-2 or 24 hours after infection with tick-borne encephalitis virus provided a much more pronounced decrease in the death rate of the animals than the use of the interferonogen alone. Virazole per se was little active and had no significant effect on the intensity of interferonogenesis promoted by the use of poly (G) X poly (C). A possibility of successful therapy of viral infections with polyribonucleotide interferonogens in combination with virazole or other chemotherapeutic drugs with broad antiviral spectrum is discussed.     

A Plant Plasma Membrane ATP Binding Cassette–Type Transporter Is Involved in Antifungal Terpenoid Secretion

ATP binding cassette (ABC) transporters, which are found in all species, are known mainly for their ability to confer drug resistance. To date, most of the ABC transporters characterized in plants have been localized in the vacuolar membrane and are considered to be involved in the intracellular sequestration of cytotoxins. Working on the assumption that certain ABC transporters might be involved in defense metabolite secretion and their expression might be regulated by the concentration of these metabolites, we treated a Nicotiana plumbaginifolia cell culture with sclareolide, a close analog of sclareol, an antifungal diterpene produced at the leaf surface of Nicotiana spp; this resulted in the appearance of a 160-kD plasma membrane protein, which was partially sequenced. The corresponding cDNA (NpABC1) was cloned and shown to encode an ABC transporter. In vitro and in situ immunodetection showed NpABC1 to be localized in the plasma membrane. Under normal conditions, expression was found in the leaf epidermis. In cell culture and in leaf tissues, NpABC1 expression was strongly enhanced by sclareolide and sclareol. In parallel with NpABC1 induction, cells acquired the ability to excrete a labeled synthetic sclareolide derivative. These data suggest that NpABC1 is involved in the secretion of a secondary metabolite that plays a role in plant defense.     

In vivo Antiretroviral Efficacy of Oral bis(POM)-PMEA,the bis(Pivaloyloxymethyl)prodrug of 9-(2-Phosphonylmethoxyethyl) adenine (PMEA)

Abstract

The bis-pivaloyloxymethyl(POM)- and diphenyl-ester prodrugs of the broad spectrum antiviral agent 9-(2-phosphonylmethoxyethyl)adenine (PMEA) have been evaluated in vivo for antiviral efficacy upon oral administration in severe combined immune deficiency (SCID) mice infected with Moloney murine sarcoma virus (MSV). Oral bis (POM)-PMEA proved highly efficient in delaying MSV-induced tumor formation and associated death, its effect being equal to that of subcutaneous PMEA at an equimolar dose. Compared to bis(POM)-PMEA, oral diphenyl-PMEA had lower antiviral efficacy, whereas PMEA as such was poorly effective when administered orally. Our studies indicate that bis(POM)-PMEA must have a favorable oral bioavailability and justify its clinical investigation as an oral prodrug of PMEA in the treatment of HIV infections.     

Differential regulation of extracellular matrix proteoglycan (PG) gene expression. Transforming growth factor-beta 1 up-regulates biglycan (PGI), and versican (large fibroblast PG) but down-regulates decorin (PGII) mRNA levels in human fibroblasts in culture

Proteoglycans (PGs) comprise a group of extracellular matrix macromolecules which play an important role in matrix biology. In this study, normal human skin and gingival fibroblast cultures were incubated with transforming growth factor-beta 1 (TGF-beta 1), and the expression of three PGs, viz. biglycan (PGI), decorin (PGII), and versican (a large fibroblast proteoglycan) was examined. The results indicate that TGF-beta 1 (5 ng/ml) markedly increased the expression of biglycan (up to 24-fold) and versican (up to 6-fold) mRNAs and the enhancement of biglycan expression was coordinate with elevated type I procollagen gene expression in the same cultures. In contrast, the expression of decorin mRNA was markedly (up to approximately 70%) inhibited by TGF-beta 1. The response to TGF-beta 1 was similar in both skin and gingival fibroblasts, although the gingival cells were clearly more responsive to stimulation by TGF-beta 1 with respect to biglycan gene expression. Analysis of 35S-labeled proteoglycans in the culture media of skin and gingival fibroblasts also revealed stimulation of biglycan and versican production, and reduction in decorin production. Quantitation of both [35S]sulfate and [3H]leucine-labeled decorin in cell culture media by immunoprecipitation revealed a 50% reduction in decorin production in cell cultures treated with TGF-beta 1. This TGF-beta 1-elicited reduction was accompanied by an apparent increase in the size of the decorin molecules, although the size of the core protein was not altered, as judged by Western immunoblotting following chondroitinase ABC digestion. Analysis of the proteoglycans in the matrix and membrane fractions also revealed increased amounts of versican in cultures treated with TGF-beta 1. These results indicate differential regulation of PG gene expression in fibroblasts by TGF-beta 1, and these observations emphasize the role of PGs in the extracellular matrix biology and pathology.     

Cytotoxicity of pivoxil esters of antiviral acyclic nucleoside phosphonates: adefovir dipivoxil versus adefovir

Biological effectiveness of antiviral acyclic nucleoside phosphonate adefo vir, 9-[2-(phosphonomethoxy)ethy]ade nine (PMEA) and its more lipophilic (bis)pivaloyloxymethyl ester prodrug adefovir dipivoxil (bis-POM-PMEA) were compared under in vitro conditions in mammalian cell systems. Proliferation of murine splenocytes was inhibited in a concentration-dependent manner, the bis-POM-PMEA being more effective than PMEA. In contrast to PMEA, bis-POM-PMEA inhibited production of nitric oxide (NO) in macrophages activated with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS). Viability of both splenocytes and macrophages remained uninfluenced by PMEA, whereas pronounced cytocidal effects were exhibited by bis-POM-PMEA. The IC(50)s reached the values of 15 microM and 30 microM in cultures of macrophages and splenocytes, respectively (assayed at the interval of 24 hrs). The effects could partly be mimicked by formaldehyde, a decomposition product of the pivoxil moiety of bis-POM-PMEA. The other possible product, pivalic acid, was ineffective in this respect. The present data are consistent with the view that pivoxil prodrug of PMEA, bis-POM-PMEA possesses enhanced but also broader spectrum of biological effects than the parent compound.     

Obligatory involvement of CD26/dipeptidyl peptidase IV in the activation of the antiretroviral tripeptide glycylprolylglycinamide (GPG-NH(2))

GPG-NH2 and G-NH2 are highly selective antiretroviral agents in cell culture, and both compounds inhibit HIV replication in CEM cell cultures to an equal extent (50% effective concentration: approximately 30 microM). The lymphocyte surface glycoprotein marker CD26, which is identical to dipeptidyl peptidase IV, efficiently converted GPG-NH2 to G-NH2 releasing the dipeptide GP-OH. The closely related QPG-NH2 derivative was also inhibitory to HIV, presumably by the dipeptidyl peptidase IV (DPP IV)-catalyzed release of G-NH2. In contrast, the cyclic pQPG-NH2 derivative in which the glutamine at the amino terminal position of QPG-NH2 was replaced by pyroglutamine and which is resistant to cleavage by purified CD26, was devoid of antiviral activity. CD26 is abundantly expressed on a variety of HIV target cells and is also present in serum of bovine, murine and human origin. The CD26/DPP IV enzymatic activity in serum and in cell suspensions could be efficiently inhibited by the CD26/DPP IV inhibitor L-isoleucinepyrrolidine (IlePyr) with 50% inhibitory concentrations ranging between 20 and 100 microM. When combined in HIV-1-infected cell cultures, IlePyr and Diprotin A (DP-A), another CD26/DPP IV inhibitor, abrogated the antiviral activity of GPG-NH2 but not of G-NH2. Therefore, it was concluded that the anti-HIV drug GPG-NH2 is not active as such, but rather behaves as a prodrug that must be obligatorily cleaved by CD26/DPP IV to G-NH2 to exert its antiretroviral activity. This is the first demonstration of a lymphocyte activation/differentiation marker (i.e. CD26) that plays a direct regulatory and indispensable role in the eventual antiretroviral activity of small synthetic molecules such as the antiretroviral (pro)drug GPG-NH2.     

Antiviral activity in L1210 cells of liposome-encapsulated (2'-5')oligo(adenylate) analogues

Evidence is available for a role of a (2'-5')(A)n-activated endoribonuclease (RNase L) in the antiviral activity of interferon for several RNA viruses. (2'-5')(A)n and their analogues might thus provide an interesting alternative to exogenous interferons or their inducers in antiviral chemotherapy. In addition, the evaluation of the activity of (2'-5)(A)n as mediators of interferon's biological activities or as cell growth regulators requires biochemical studies using agonists or antagonists of the system. Non-disruptive techniques for the introduction of (2'-5')(A)n and their analogues into cell lines or tissues are required for these studies since these highly charged compounds are cell impermeable. (2'-5')(A)n oligomers and analogues of increased stability towards phosphodiesterases were derived by chemical modification of their 2' end and encapsulated in protein-A-bearing liposomes. The specific delivery of liposome contents into L1210 mouse leukemic cells was achieved with the help of monoclonal antibodies directed against the appropriate class I major histocompatibility complex-encoded proteins expressed by these cells. This intracellular delivery led to transient inhibition of protein synthesis and an antiviral activity, both compatible with activation of RNase L. This activity was enhanced for the analogues designed to resist degradation, with respect to the natural product.     

Nitroreductase-activated nitric oxide (NO) prodrugs

Due to the involvement of nitric oxide (NO) in numerous and diverse physiological processes, site-directed delivery of therapeutic NO in order to minimize unwanted side-effects is necessary. O²-(4-Nitrobenzyl) diazeniumdiolates are designed as substrates for Escherichia coli nitroreductase (NTR), an enzyme that is frequently used to facilitate directed delivery of cytotoxic species to cancers. O²-(4-Nitrobenzyl) diazeniumdiolates are found to be stable in aqueous buffer but are metabolized by NTR to produce NO. A cell viability assay revealed that cytotoxic effects of O²-(4-nitrobenzyl)1-(2-methylpiperidin-1-yl)diazen-1-ium-1,2-diolate (4b) towards two cancer cell lines is significantly enhanced in the presence of NTR suggesting the potential for use of this compound in nitric oxide-based directed prodrug therapy.     

Synthesis of poly(ethylene glycol)-based saquinavir prodrug conjugates and assessment of release and anti-HIV-1 bioactivity using a novel protease inhibition assay

Various poly(ethylene glycol)(PEG)-based prodrug conjugates of the HIV-1 protease inhibitor (PI) saquinavir (SQV) were prepared using several types of chemical groups potentially capable of modifying its pharmacokinetic properties. These prodrug conjugates included SQV-cysteine-PEG3400, SQV-cysteine-PEG3400-biotin, SQV-cysteine(R.I.CK-Tat9) [a cationic retro-inverso-cysteine-lysine-Tat nonapeptide]-PEG3400, and SQV-cysteine(R.I.CK(stearate)-Tat9)-PEG3400. SQV was linked to cysteine to form a releasable SQV-cysteine ester bond in all of the conjugates. The amino group of the cysteine moiety provided an attachment site for a slower-degrading amide bond with N-hydroxysuccinimide-activated forms of PEG- and PEG-biotin. Disulfide bonds were used to attach the cationic peptides, R.I.CK-Tat9 and R.I.CK(stearate)-Tat9 to the cysteine moiety in order to provide cell-specific release. An assay was established and validated for measuring the activity of SQV and other protease inhibitors in biological samples. In this assay, cleavage of an internally quenched fluorescent substrate, Arg-Glu(EDANS)-Ser-Gln-Asn-Tyr-Pro-Ile-Val-Gly-Lys(DABCYL)-Arg by HIV-1 protease was inhibited by SQV in a dose-dependent manner at concentrations of 0.05-0.5 microM. All prodrug conjugates were shown to be inactive in this assay until the ester bond was cleaved and active SQV was released. The prodrug reconversion half-lives in 0.1 N HCl, phosphate-buffered saline (PBS) at pH 7.4 and in spiked plasma at 37 degrees C were 9, 14, and 0.9 h, respectively. The anti-HIV-1 activity (ED(50)) of the PEG-based SQV prodrug conjugates was evaluated in MT-2 cells using an MTT assay. The activity of conjugated SQV was reduced (ED(50) = 900 nM) for the PEG only conjugate, but restored with the addition of biotin (ED(50) = 125 nM), R.I.CK-Tat9 (ED(50) = 15 nM), and R.I.CK(stearate)-Tat9 (ED(50) = 62 nM) as compared to maximum achievable anti-HIV-1 activity (unconjugated SQV, control, ED(50) = 15 nM), suggesting enhanced cellular uptake of conjugates. Cytotoxicity (LD(50)) was assessed for all prodrug conjugates using non-HIV-1 infected cells and was found to be in the micromolar range. The difference between the LD(50) and ED(50) suggests a favorable therapeutic index for the prodrug conjugates. In conclusion, these promising initial results demonstrate that the reconversion of the conjugate prodrugs was complete and that active SQV was released. Since the major delivery advantages of PEG prodrug conjugates can only be observed in vivo, issues of reconversion and elimination half-lives in plasma will have to be further studied in an in vivo model. The current results also demonstrate that the protease inhibition assay is a simple yet effective bioanalytical tool that can be used to assess the release and anti-HIV-1 activity of HIV-1 PIs from their prodrug forms.     

Elicitor-like effects of low-energy ultrasound on plant (Panax ginseng) cells: induction of plant defense responses and secondary metabolite production

In this work we examined the elicitor-like effects of low-energy ultrasound (US) on plant cells with respect to the induction of plant defense responses and secondary metabolite production. Panax ginseng cells in suspension culture were exposed to US (power 相似文献   

Synthesis, hydrolyses and dermal delivery of N-alkyl-N-alkyloxycarbonylaminomethyl (NANAOCAM) derivatives of phenol, imide and thiol containing drugs

Synthesis, characterization and hydrolysis in aqueous buffers of novel N-alkyl-N-alkyloxycarbonylaminomethyl (NANAOCAM) derivatives of substituted phenols, theophylline (Th) and 6-mercaptopurine (6MP) were carried out. The mechanism of hydrolysis was further investigated by synthesis, characterization and hydrolysis of N-aryl-N-alkyloxycarbonylaminomethyl (NArNAOCAM) derivatives of phenols. The hydrolysis follows pseudounimolecular first order kinetics and operates by way of an S(N)1-type mechanism. Topical delivery of selected derivatives of acetaminophen (APAP), Th and 6MP was examined in in vitro diffusion cell experiments from IPM across hairless mice skins. The prodrug of APAP and 6MP increased permeation across the skin by about 2- and 4-fold, respectively, compared to the parent drug. NANAOCAM promoieties can act as novel prodrug derivatives of phenol, imide and thiol containing drugs for enhancing topical absorption.     

IFN-beta 2, B cell differentiation factor 2, or hybridoma growth factor (IL-6) is expressed and released by human epidermal cells and epidermoid carcinoma cell lines

IL-6, which is also known as IFN-beta 2, hybridoma growth factor, hepatocyte-stimulating factor, and B cell differentiation factor, mediates acute phase responses including fever, has lymphocyte-stimulating capacities, and antiviral activity. IL-6 is produced by monocytes, fibroblasts, certain lymphocytes, and various tumor cells. The present study demonstrates that this multifunctional cytokine is released also by normal human epidermal cells (EC) and human epidermoid carcinoma cell lines (A431, KB). Accordingly, supernatants derived from freshly isolated EC, long term keratinocyte cultures, A431, or KB cells stimulated the proliferation of a hybridoma growth factor/IL-6-dependent plasmacytoma cell line (B9). IL-6 constitutively was produced in the presence of serum proteins. The addition of IL-1 alpha, IL-1 beta, or the tumor promoter PMA significantly enhanced the synthesis and release of EC-derived IL-6 (EC-IL 6). Like monocyte or fibroblast-derived IL-6, EC-IL-6 exhibited Mr microheterogeneity within 21 and 28 kDa. Similarly in Western blotting experiments an antiserum directed against human rIFN-beta 2/IL-6 detected the different Mr forms of EC-IL-6. Moreover, this antiserum was able to block the B9 cell growth-promoting capacity of EC-IL-6 strongly suggesting that this EC-derived mediator is closely related, if not identical with IL-6. This was further confirmed by Northern blot analysis detecting IL-6 specific mRNA both in long term cultured keratinocytes and A431 cells by hybridization with a cDNA fragment encoding for B cell differentiating factor 2/IL-6. Therefore, in addition to the production of other cytokines as previously reported, EC and in particular keratinocytes also synthesize and release IL-6. This further supports the important regulatory role of the epidermis during the pathogenesis of inflammatory, autoimmune, and neoplastic diseases.