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Dvorit Samid - One of the best experts on this subject based on the ideXlab platform.

  • Phenylacetate and phenylbutyrate as novel, nontoxic differentiation inducers.
    Advances in experimental medicine and biology, 1997
    Co-Authors: Dvorit Samid, Sonsoles Shack, Lei Liu, W. R. Hudgins, P. Prasanna, Charles E. Myers
    Abstract:

    Phenylacetate, a common metabolite of phenylalanine, is a natural component of the human plasma and an endogenous growth regulator in plants (1,2). In humans, Phenylacetate conjugates glutamine to yield phenylacetylglutamine (PAG), which is subsequently excreted in the urine. The latter, leading to waste nitrogen excretion, has been the basis for using sodium Phenylacetate (NaPA) in treatment of hyperammonemia associated with inborn errors of urea synthesis or liver failure (3,4). Clinical experience obtained with these patients indicated that long-term treatment with high doses of NaPA (250–550 mg/kg/day) is well tolerated by both infants and adults, and effective in reducing plasma glutamine levels. These characteristics should be of value in cancer intervention considering the unique dependence of tumor cells on circulating glutamine. Preclinical studies exploring the antitumor efficacy of NaPA revealed that this simple aromatic fatty acid can selectively suppress the growth of various tumors in tissue culture and in animal models (5–7; Samid et al, unpublished). In addition to glutamine depletion in humans, Phenylacetate was found to induce tumor cytostasis and differentiation through several other mechanisms (see below). Most importantly, the antitumor activity was observed with pharmacological, non-toxic drug concentrations. The demonstrated antitumor activity, easy administration (oral or IV), and lack of significant adverse effects, made Phenylacetate an attractive candidate for clinical use in prevention and treatment of human neoplasms, including those which do not respond to conventional therapies. In the present report we provide a brief summary of the preclinical antitumor activity of NaPA and its derivatives.

  • Activation of a human peroxisome proliferator-activated receptor by the antitumor agent Phenylacetate and its analogs.
    Biochemical pharmacology, 1996
    Co-Authors: Thierry Pineau, W.robert Hudgins, Lei Liu, Li-chuan Chen, Talia Sher, Frank J. Gonzalez, Dvorit Samid
    Abstract:

    Abstract The aromatic fatty acid Phenylacetate and its analogs induce tumor cytostasis and differentiation in experimental models. Although the underlying mechanisms of action are not clear, effects on lipid metabolism are evident. We have now examined whether these compounds, structurally similar to the peroxisome proliferator clofibrate, affect the human peroxisome proliferator-activated receptor (hPPAR), a homolog of the rodent PPARα, a transcriptional factor regulating lipid metabolism and cell growth. Gene transfer experiments showed activation of hPPAR, evident by the increased expression of the reporter gene chloramphenicol acetyltransferase linked to PPAR-response element from either the rat acyl-CoA oxidase or rabbit CYP4A6 genes. The relative potency of tested drugs in the co-transfection assay was: 4-iodophenylbutyrate > 4-chlorophenylbutyrate > clofibrate > phenylbutyrate > naphthylacetate > 2,4-D > 4-chloroPhenylacetate > Phenylacetate ⪢> indoleacetate. Phenylacetylglutamine, in which the carboxylic acid is blocked, was inactive. The ability of the aromatic fatty acids to activate PPAR was confirmed in vivo, as CYP4A mRNA levels increased in hepatocytes of treated rats. Further studies using human prostate carcinoma, melanoma, and glioblastoma cell lines showed a tight correlation between drug-induced cytostasis, increased expression of the endogenous hPPAR, and receptor activation documented in the gene-transfer model. These results identify Phenylacetate and its analogs as a new class of aromatic fatty acids capable of activating hPPAR, and suggest that this nuclear receptor may mediate tumor cytostasis induced by these drugs.

  • The differentiating agent Phenylacetate increases prostate-specific antigen production by prostate cancer cells
    The Prostate, 1996
    Co-Authors: Ron M. Walls, Alain Thibault, William D. Figg, Lei Liu, Christopher G Wood, James M. Kozlowski, Maureen Sampson, Ronald J. Elin, Dvorit Samid
    Abstract:

    The prostatic-specific antigen (PSA) is the tumor marker most widely relied upon for the monitoring of patients with prostate cancer. Recently, declines in the serum concentrations of PSA have been advocated as a surrogate marker of tumor response in clinical trials of investigational antitumor agents. We examined the hypothesis that this postulate may not apply to the evaluation of drugs such as Phenylacetate, a differentiating agent endowed with mechanisms of action different from those of classic cytotoxic chemotherapy. Using human prostatic carcinoma LNCaP cells as a model, we show that Phenylacetate induces PSA production despite inhibition of tumor cell proliferation. Incubation of LNCaP cultures with cytostatic doses of Phenylacetate (3-10 mM) resulted in a three- to fourfold increase in PSA secretion per cell. This appears to result from upregulation of PSA gene expression, as indicated by elevated PSA mRNA steady-state levels in treated cells. The increase in PSA production per cell was confirmed in rats bearing subcutaneous LNCaP tumor implants that were treated systemically with Phenylacetate. Further comparative studies indicate that upregulation of PSA is common to various differentiation inducers, including all-trans-retinoic acid, 1,25-dihydroxyvitamin D3, and butyrate but is not induced by other antitumor agents of clinical interest such as suramin. We conclude that declines in PSA may be treatment specific and that the exclusive use of this criterion as a marker of disease response may mislead the proper evaluation of differentiating agents in prostate cancer patients.

  • Cytostatic activity of Phenylacetate and derivatives against tumor cells: Correlation with lipophilicity and inhibition of protein prenylation
    Biochemical pharmacology, 1995
    Co-Authors: W.robert Hudgins, Sonsoles Shack, Charles E. Myers, Dvorit Samid
    Abstract:

    The aromatic fatty acid Phenylacetate, a common metabolite of phenylalanine, shows promise as a relatively non-toxic drug for cancer treatment. This slowly metabolized fatty acid alters tumor cell lipid metabolism causing, among other effects, inhibition of protein prenylation critical to malignant growth. In pursuit of more potent analogues, we have examined the activity of related compounds against tumor cell lines established from patients with advanced prostatic carcinoma, glioblastomas, and malignant melanoma. Like Phenylacetate, derivatives containing α-carbon or ring substitutions induced cytostasis and phenotypic reversion at non-toxic concentrations. Potency was correlated with the degree of calculated lipophilicity of the aromatic fatty acid, and the extent of inhibition of protein prenylation. Remarkably, a parallel cytostatic activity was reported in embryonic plant cells, which respond to Phenylacetate and its analogues in the same concentration range and the same rank order of lipophilicity. These data suggest that Phenylacetate and its analogues may act through common mechanisms to inhibit the growth of vastly divergent, undifferentiated cell types, and provide a basis for the development of new agents for the treatment of human malignancies.

  • Phase I study of Phenylacetate administered twice daily to patients with cancer
    Cancer, 1995
    Co-Authors: Alain Thibault, Dvorit Samid, William D. Figg, Anne Tompkins, Donna Headlee, Michael R. Cooper, David Venzon, Nicholas J. Patronas, David R. Kohler, Charles E. Myers
    Abstract:

    Background. The growth-inhibiting and differentiating effects of sodium Phenylacetate against hematopoietic and solid tumor cell lines has aroused clinical interest in its use as an anticancer drug. In an earlier Phase I trial of Phenylacetate aimed at maintaining serum drug concentrations in the range that proved active in vitro (>250 μg/ml) for 2 consecutive weeks, infusion rates approached the maximum velocity of drug elimination and commonly resulted in drug accumulation and reversible dose-limiting neurologic toxicity. In this study, the authors described the nonlinear pharmacokinetics, metabolism, toxicity, and clinical activity of Phenylacetate. Methods. The treatment regimen of this Phase I study was designed to expose patients intermittently to drug concentrations exceeding 250 μg/ml and to allow time for drug elimination to occur between doses to minimize accumulation. Sodium Phenylacetate was administered as a 1-hour infusion twice daily (8 a.m., 5 p.m.) at two dose levels of 125 and 150 mg/kg for a 2-week period. Therapy was repeated at 4-week intervals for patients who did not experience dose-limiting toxicity or disease progression. Results. Eighteen patients (4 of whom previously were treated with Phenylacetate by continuous intravenous infusion) received 27 cycles of therapy. Detailed pharmacokinetic studies for eight patients indicated that Phenylacetate induced its own clearance by a factor of 27% in a 2-week period. Dose-limiting toxicity, consisting of reversible central nervous system depression, was observed for three patients at the second dose level. One patient with refractory malignant glioma had a partial response, and one with hormone-independent prostate cancer achieved a 50% decline in prostate specific antigen level, which was maintained for 1 month. Conclusions. Phenylacetate administered at a dose of 125 mg/kg twice daily for 2 consecutive weeks is well tolerated. High grade gliomas and advanced prostate cancer are reasonable targets for Phase II clinical trials. Cancer 1995;75:2932–8.

Charles E. Myers - One of the best experts on this subject based on the ideXlab platform.

  • Phenylacetate and phenylbutyrate as novel, nontoxic differentiation inducers.
    Advances in experimental medicine and biology, 1997
    Co-Authors: Dvorit Samid, Sonsoles Shack, Lei Liu, W. R. Hudgins, P. Prasanna, Charles E. Myers
    Abstract:

    Phenylacetate, a common metabolite of phenylalanine, is a natural component of the human plasma and an endogenous growth regulator in plants (1,2). In humans, Phenylacetate conjugates glutamine to yield phenylacetylglutamine (PAG), which is subsequently excreted in the urine. The latter, leading to waste nitrogen excretion, has been the basis for using sodium Phenylacetate (NaPA) in treatment of hyperammonemia associated with inborn errors of urea synthesis or liver failure (3,4). Clinical experience obtained with these patients indicated that long-term treatment with high doses of NaPA (250–550 mg/kg/day) is well tolerated by both infants and adults, and effective in reducing plasma glutamine levels. These characteristics should be of value in cancer intervention considering the unique dependence of tumor cells on circulating glutamine. Preclinical studies exploring the antitumor efficacy of NaPA revealed that this simple aromatic fatty acid can selectively suppress the growth of various tumors in tissue culture and in animal models (5–7; Samid et al, unpublished). In addition to glutamine depletion in humans, Phenylacetate was found to induce tumor cytostasis and differentiation through several other mechanisms (see below). Most importantly, the antitumor activity was observed with pharmacological, non-toxic drug concentrations. The demonstrated antitumor activity, easy administration (oral or IV), and lack of significant adverse effects, made Phenylacetate an attractive candidate for clinical use in prevention and treatment of human neoplasms, including those which do not respond to conventional therapies. In the present report we provide a brief summary of the preclinical antitumor activity of NaPA and its derivatives.

  • Cytostatic activity of Phenylacetate and derivatives against tumor cells: Correlation with lipophilicity and inhibition of protein prenylation
    Biochemical pharmacology, 1995
    Co-Authors: W.robert Hudgins, Sonsoles Shack, Charles E. Myers, Dvorit Samid
    Abstract:

    The aromatic fatty acid Phenylacetate, a common metabolite of phenylalanine, shows promise as a relatively non-toxic drug for cancer treatment. This slowly metabolized fatty acid alters tumor cell lipid metabolism causing, among other effects, inhibition of protein prenylation critical to malignant growth. In pursuit of more potent analogues, we have examined the activity of related compounds against tumor cell lines established from patients with advanced prostatic carcinoma, glioblastomas, and malignant melanoma. Like Phenylacetate, derivatives containing α-carbon or ring substitutions induced cytostasis and phenotypic reversion at non-toxic concentrations. Potency was correlated with the degree of calculated lipophilicity of the aromatic fatty acid, and the extent of inhibition of protein prenylation. Remarkably, a parallel cytostatic activity was reported in embryonic plant cells, which respond to Phenylacetate and its analogues in the same concentration range and the same rank order of lipophilicity. These data suggest that Phenylacetate and its analogues may act through common mechanisms to inhibit the growth of vastly divergent, undifferentiated cell types, and provide a basis for the development of new agents for the treatment of human malignancies.

  • Phase I study of Phenylacetate administered twice daily to patients with cancer
    Cancer, 1995
    Co-Authors: Alain Thibault, Dvorit Samid, William D. Figg, Anne Tompkins, Donna Headlee, Michael R. Cooper, David Venzon, Nicholas J. Patronas, David R. Kohler, Charles E. Myers
    Abstract:

    Background. The growth-inhibiting and differentiating effects of sodium Phenylacetate against hematopoietic and solid tumor cell lines has aroused clinical interest in its use as an anticancer drug. In an earlier Phase I trial of Phenylacetate aimed at maintaining serum drug concentrations in the range that proved active in vitro (>250 μg/ml) for 2 consecutive weeks, infusion rates approached the maximum velocity of drug elimination and commonly resulted in drug accumulation and reversible dose-limiting neurologic toxicity. In this study, the authors described the nonlinear pharmacokinetics, metabolism, toxicity, and clinical activity of Phenylacetate. Methods. The treatment regimen of this Phase I study was designed to expose patients intermittently to drug concentrations exceeding 250 μg/ml and to allow time for drug elimination to occur between doses to minimize accumulation. Sodium Phenylacetate was administered as a 1-hour infusion twice daily (8 a.m., 5 p.m.) at two dose levels of 125 and 150 mg/kg for a 2-week period. Therapy was repeated at 4-week intervals for patients who did not experience dose-limiting toxicity or disease progression. Results. Eighteen patients (4 of whom previously were treated with Phenylacetate by continuous intravenous infusion) received 27 cycles of therapy. Detailed pharmacokinetic studies for eight patients indicated that Phenylacetate induced its own clearance by a factor of 27% in a 2-week period. Dose-limiting toxicity, consisting of reversible central nervous system depression, was observed for three patients at the second dose level. One patient with refractory malignant glioma had a partial response, and one with hormone-independent prostate cancer achieved a 50% decline in prostate specific antigen level, which was maintained for 1 month. Conclusions. Phenylacetate administered at a dose of 125 mg/kg twice daily for 2 consecutive weeks is well tolerated. High grade gliomas and advanced prostate cancer are reasonable targets for Phase II clinical trials. Cancer 1995;75:2932–8.

  • Disposition of Phenylbutyrate and Its Metabolites, Phenylacetate and Phenylacetylglutamine
    Journal of clinical pharmacology, 1995
    Co-Authors: Stephen C. Piscitelli, Dvorit Samid, Alain Thibault, William D. Figg, Anne Tompkins, Donna Headlee, Ronald Lieberman, Charles E. Myers
    Abstract:

    Phenylacetate, an inducer of tumor cytostasis and differentiation, shows promise as a relatively nontoxic antineoplastic agent. Phenylacetate, however, has an unpleasant odor that might limit patient acceptability. Phenylbutyrate, an odorless compound that also has activity in tumor models, is known to undergo rapid conversion to Phenylacetate by beta-oxidation in vivo. This phase I study examined the pharmacokinetics of phenylbutyrate and characterized the disposition of the two metabolites, Phenylacetate and phenylacetylglutamine. Fourteen patients with cancer (aged 51.8 +/- 13.8 years) received a 30-minute infusion of phenylbutyrate at 3 dose levels (600, 1200, and 2000 mg/m2). Serial blood samples and 24-hour urine collections were obtained. Samples were assayed by high-performance liquid chromatography. A model to simultaneously describe the pharmacokinetics of all three compounds was developed using ADAPT II. Data were modeled as molar equivalents. The model fit the data well as shown by mean (+/- SD) coefficients of determination (r2) for phenylbutyrate, Phenylacetate, and phenylacetylglutamine, which were 0.96 +/- 0.07, 0.88 +/- 0.10, and 0.92 +/- 0.06, respectively. The intrapatient coefficient of variation percentage (CV%) around the parameter estimates were small (range 7.2-33.5%). Phenylbutyrate achieved peak concentrations in the range of in vitro tumor activity (500-2000 mumol/L) and exhibited saturable elimination (Km = 34.1 +/- 18.1 micrograms/mL and Vmax = 18.1 +/- 18 mg/h/kg). Metabolism was rapid; the times to maximum concentration for Phenylacetate and phenylacetylglutamine were 1 and 2 hours, respectively. The conversion of phenylbutyrate to Phenylacetate was extensive (80 +/- 12.6%), but serum concentrations of Phenylacetate were low owing to rapid, subsequent conversion to phenylacetylglutamine.(ABSTRACT TRUNCATED AT 250 WORDS)

  • growth inhibition tumor maturation and extended survival in experimental brain tumors in rats treated with Phenylacetate
    Cancer Research, 1994
    Co-Authors: Zvi Ram, Dvorit Samid, Alain Thibault, Charles E. Myers, Stuart Walbridge, Eric M Oshiro, John J Viola, Junghwa Taocheng, Sonsoles Shack, Edward H Oldfield
    Abstract:

    Phenylacetate is a naturally occurring plasma component that suppresses the growth of tumor cells and induces differentiation in vitro . To evaluate the in vivo potential and preventive and therapeutic antitumor efficacy of sodium Phenylacetate against malignant brain tumors, Fischer 344 rats ( n = 50) bearing cerebral 9L gliosarcomas received Phenylacetate by continuous s.c. release starting on the day of tumor inoculation ( n = 10) using s.c. osmotic minipumps (550 mg/kg/day for 28 days). Rats with established brain tumors ( n = 12) received continuous s.c. Phenylacetate supplemented with additional daily i.p. dose (300 mg/kg). Control rats ( n = 25) were treated in a similar way with saline. Rats were sacrificed during treatment for electron microscopic studies of their tumors, in vivo proliferation assays, and measurement of Phenylacetate levels in the serum and cerebrospinal fluid. Treatment with Phenylacetate extended survival when started on the day of tumor inoculation ( P < 0.01) or 7 days after inoculation ( P < 0.03) without any associated adverse effects. In the latter group, Phenylacetate levels in pooled serum and cerebrospinal fluid samples after 7 days of treatment were in the therapeutic range as determined in vitro (2.45 mm in serum and 3.1 mm in cerebrospinal fluid). Electron microscopy of treated tumors demonstrated marked hypertrophy and organization of the rough endoplasmic reticulum, indicating cell differentiation, in contrast to the scant and randomly distributed endoplasmic reticulum in tumors from untreated animals. In addition, in vitro studies demonstrated dose-dependent inhibition of the rate of tumor proliferation and restoration of anchorage dependency, a marker of phenotypic reversion. Phenylacetate, used at clinically achievable concentrations, prolongs survival of rats with malignant brain tumors through induction of tumor differentiation. Its role in the treatment of brain tumors and other cancers should be explored further.

Georg Fuchs - One of the best experts on this subject based on the ideXlab platform.

  • bacterial phenylalanine and Phenylacetate catabolic pathway revealed
    Proceedings of the National Academy of Sciences of the United States of America, 2010
    Co-Authors: Robin Teufel, Wael Ismail, Wolfgang Eisenreich, V Mascaraque, M Voss, J Perera, Wolfgang Haehnel, Georg Fuchs
    Abstract:

    Aromatic compounds constitute the second most abundant class of organic substrates and environmental pollutants, a substantial part of which (e.g., phenylalanine or styrene) is metabolized by bacteria via Phenylacetate. Surprisingly, the bacterial catabolism of phenylalanine and Phenylacetate remained an unsolved problem. Although a Phenylacetate metabolic gene cluster had been identified, the underlying biochemistry remained largely unknown. Here we elucidate the catabolic pathway functioning in 16% of all bacteria whose genome has been sequenced, including Escherichia coli and Pseudomonas putida. This strategy is exceptional in several aspects. Intermediates are processed as CoA thioesters, and the aromatic ring of phenylacetyl-CoA becomes activated to a ring 1,2-epoxide by a distinct multicomponent oxygenase. The reactive nonaromatic epoxide is isomerized to a seven-member O-heterocyclic enol ether, an oxepin. This isomerization is followed by hydrolytic ring cleavage and β-oxidation steps, leading to acetyl-CoA and succinyl-CoA. This widespread paradigm differs significantly from the established chemistry of aerobic aromatic catabolism, thus widening our view of how organisms exploit such inert substrates. It provides insight into the natural remediation of man-made environmental contaminants such as styrene. Furthermore, this pathway occurs in various pathogens, where its reactive early intermediates may contribute to virulence.

  • Phenylacetate metabolism in thermophiles characterization of Phenylacetate coa ligase the initial enzyme of the hybrid pathway in thermus thermophilus
    Current Microbiology, 2008
    Co-Authors: Wael Ismail, Georg Fuchs
    Abstract:

    Phenylacetate-CoA ligase (E.C. 6.2.1.30), the initial enzyme in the metabolism of Phenylacetate, was studied in Thermus thermophilus strain HB27. Enzymatic activity was upregulated during growth on Phenylacetate or phenylalanine. The Phenylacetate-CoA ligase gene (paaK) was cloned and heterologously expressed in Escherichia coli and the recombinant protein was purified. The enzyme cat- alyzed Phenylacetate + CoA + MgATP ? phenylacetyl- CoA + AMP + MgPPi with a Vmax of 24 lmol/min/mg protein at a temperature optimum of 75C. The apparent Km values for ATP, CoA, and Phenylacetate were 6, 30, and 50 lM, respectively. The protein was highly specific toward Phenylacetate and showed only low activity with 4-hy- droxyPhenylacetate. Despite an amino acid sequence identity of (50% with its mesophilic homologues, phenyl- acetate-CoA ligase was heat stable. The genome contained further homologues of genes, which are postulated to be involved in the CoA ester-dependent metabolic pathway of Phenylacetate (hybrid pathway). Enzymes of this thermo- phile are expected to be robust and might be useful for further studies of this yet unresolved pathway.

  • Functional genomics by NMR spectroscopy. Phenylacetate catabolism in Escherichia coli.
    European journal of biochemistry, 2003
    Co-Authors: Wael Ismail, Magdy El-said Mohamed, Barry L. Wanner, Kirill A. Datsenko, Wolfgang Eisenreich, Felix Rohdich, Adelbert Bacher, Georg Fuchs
    Abstract:

    Aerobic metabolism of phenylalanine in most bacteria proceeds via oxidation to Phenylacetate. Surprisingly, the further metabolism of Phenylacetate has not been elucidated, even in well studied bacteria such as Escherichia coli. The only committed step is the conversion of Phenylacetate into phenylacetyl-CoA. The paa operon of E. coli encodes 14 polypeptides involved in the catabolism of Phenylacetate. We have found that E. coli K12 mutants with a deletion of the paaF, paaG, paaH, paaJ or paaZ gene are unable to grow with Phenylacetate as carbon source. Incubation of a paaG mutant with [U-13C8]Phenylacetate yielded ring-1,2-dihydroxy-1,2-dihydrophenylacetyl lactone as shown by NMR spectroscopy. Incubation of the paaF and paaH mutants with Phenylacetate yielded Δ3-dehydroadipate and 3-hydroxyadipate, respectively. The origin of the carbon atoms of these C6 compounds from the aromatic ring was shown using [ring-13C6]Phenylacetate. The paaG and paaZ mutants also converted Phenylacetate into ortho-hydroxyPhenylacetate, which was previously identified as a dead end product of Phenylacetate catabolism. These data, in conjunction with protein sequence data, suggest a novel catabolic pathway via CoA thioesters. According to this, phenylacetyl-CoA is attacked by a ring-oxygenase/reductase (PaaABCDE proteins), generating a hydroxylated and reduced derivative of phenylacetyl-CoA, which is not re-oxidized to a dihydroxylated aromatic intermediate, as in other known aromatic pathways. Rather, it is proposed that this nonaromatic intermediate CoA ester is further metabolized in a complex reaction sequence comprising enoyl-CoA isomerization/hydration, nonoxygenolytic ring opening, and dehydrogenation catalyzed by the PaaG and PaaZ proteins. The subsequent β-oxidation-type degradation of the resulting CoA dicarboxylate via β-ketoadipyl-CoA to succinyl-CoA and acetyl-CoA appears to be catalyzed by the PaaJ, PaaF and PaaH proteins.

  • Anaerobic metabolism of L-phenylalanine via benzoyl-CoA in the denitrifying bacterium Thauera aromatica.
    Archives of Microbiology, 1997
    Co-Authors: Sabine Schneider, Magdy El-said Mohamed, Georg Fuchs
    Abstract:

    The anaerobic metabolism of phenylalanine was studied in the denitrifying bacterium Thauera aromatica, a member of the β-subclass of the Proteobacteria. Phenylalanine was completely oxidized and served as the sole source of cell carbon. Evidence is presented that degradation proceeds via benzoyl-CoA as the central aromatic intermediate; the aromatic ring-reducing enzyme benzoyl-CoA reductase was present in cells grown on phenylalanine. Intermediates in phenylalanine oxidation to benzoyl-CoA were phenylpyruvate, phenylacetaldehyde, Phenylacetate, phenylacetyl-CoA, and phenylglyoxylate. The required enzymes were detected in extracts of cells grown with phenylalanine and nitrate. Oxidation of phenylalanine to benzoyl-CoA was catalyzed by phenylalanine transaminase, phenylpyruvate decarboxylase, phenylacetaldehyde dehydrogenase (NAD+), Phenylacetate-CoA ligase (AMP-forming), enzyme(s) oxidizing phenylacetyl-CoA to phenylglyoxylate with nitrate, and phenylglyoxylate:acceptor oxidoreductase. The capacity for phenylalanine oxidation to Phenylacetate was induced during growth with phenylalanine. Evidence is provided that α-oxidation of phenylacetyl-CoA is catalyzed by a membrane-bound enzyme. This is the first report on the complete anaerobic degradation of an aromatic amino acid and the regulation of this process.

  • Anaerobic oxidation of Phenylacetate and 4-hydroxyPhenylacetate to benzoyl-coenzyme A and CO2 in denitrifying Pseudomonas sp.
    Archives of Microbiology, 1993
    Co-Authors: Magdy El-said Mohamed, Birgit Seyfried, Andreas Tschech, Georg Fuchs
    Abstract:

    Anaerobic degradation of (4-hydroxy)Phenylacetate in denitrifying Pseudomonas sp. was investigated. Evidence is presented for α-oxidation of the coenzyme A (CoA)-activated carboxymethyl side chain, a reaction which has not been described. The C6−C2 compounds are degraded to benzoyl-CoA and furtheron to CO2 via the following intermediates: Phenylacetyl-CoA, phenylglyoxylate, benzoyl-CoA plus CO2; 4-hydroxyphenylacetyl-CoA, 4-hydroxyphenylglyoxylate, 4-hydroxybenzoyl-CoA plus CO2, benzoyl-CoA. Trace amounts of mandelate possibly derived from mandelyl-CoA were detected during Phenylacetate degradation in vitro. The reactions are catalyzed by (i) Phenylacetate-CoA ligase which converts Phenylacetate to phenylacetyl-CoA and by a second enzyme for 4-hydroxyPhenylacetate; (ii) a (4-hydroxy)-phenylacetyl-CoA dehydrogenase system which oxidizes phenylacetyl-CoA to (4-hydroxy)phenylglyoxylate plus CoA; and (iii) (4-hydroxy)phenylglyoxylate: acceptor oxidoreductase (CoA acylating) which catalyzes the oxidative decarboxylation of (4-hydroxy)phenylglyoxylate to (4-hydroxy)benzoyl-CoA and CO2. (iv) The degradation of 4-hydroxyPhenylacetate in addition requires the reductive dehydroxylation of 4-hydroxybenzoyl-CoA to benzoyl-CoA, catalyzed by 4-hydroxybenzoyl-CoA reductase (dehydroxylating). The whole cell regulation of these enzyme activities supports the proposed pathway. An ionic mechanism for anaerobic α-oxidation of the CoA-activated carboxymethyl side chain is proposed. Phenylacetic acids are plant constituents and in addition are formed from a large variety of natural aromatic compounds by microorganisms; their degradation therefore plays a significant role in nature, as illustrated in the preceding paper (Mohamed and Fuchs 1993). We have investigated and purified an enzyme which catalyzes the first step in the anaerobic degradation of Phenylacetate in a denitrifying Pseudomonas sp. Phenylacetate is converted to phenylacetyl-CoA by Phenylacetate-CoA ligase (AMP forming). The postulated function of this enzyme is corroborated by the strict regulation of its expression. 4-HydroxyPhenylacetate appears to be similarly activated by an independent enzyme prior to further degradation.

Marie Claude Rouxschmitt - One of the best experts on this subject based on the ideXlab platform.

Sonsoles Shack - One of the best experts on this subject based on the ideXlab platform.

  • Phenylacetate and phenylbutyrate as novel, nontoxic differentiation inducers.
    Advances in experimental medicine and biology, 1997
    Co-Authors: Dvorit Samid, Sonsoles Shack, Lei Liu, W. R. Hudgins, P. Prasanna, Charles E. Myers
    Abstract:

    Phenylacetate, a common metabolite of phenylalanine, is a natural component of the human plasma and an endogenous growth regulator in plants (1,2). In humans, Phenylacetate conjugates glutamine to yield phenylacetylglutamine (PAG), which is subsequently excreted in the urine. The latter, leading to waste nitrogen excretion, has been the basis for using sodium Phenylacetate (NaPA) in treatment of hyperammonemia associated with inborn errors of urea synthesis or liver failure (3,4). Clinical experience obtained with these patients indicated that long-term treatment with high doses of NaPA (250–550 mg/kg/day) is well tolerated by both infants and adults, and effective in reducing plasma glutamine levels. These characteristics should be of value in cancer intervention considering the unique dependence of tumor cells on circulating glutamine. Preclinical studies exploring the antitumor efficacy of NaPA revealed that this simple aromatic fatty acid can selectively suppress the growth of various tumors in tissue culture and in animal models (5–7; Samid et al, unpublished). In addition to glutamine depletion in humans, Phenylacetate was found to induce tumor cytostasis and differentiation through several other mechanisms (see below). Most importantly, the antitumor activity was observed with pharmacological, non-toxic drug concentrations. The demonstrated antitumor activity, easy administration (oral or IV), and lack of significant adverse effects, made Phenylacetate an attractive candidate for clinical use in prevention and treatment of human neoplasms, including those which do not respond to conventional therapies. In the present report we provide a brief summary of the preclinical antitumor activity of NaPA and its derivatives.

  • Cytostatic activity of Phenylacetate and derivatives against tumor cells: Correlation with lipophilicity and inhibition of protein prenylation
    Biochemical pharmacology, 1995
    Co-Authors: W.robert Hudgins, Sonsoles Shack, Charles E. Myers, Dvorit Samid
    Abstract:

    The aromatic fatty acid Phenylacetate, a common metabolite of phenylalanine, shows promise as a relatively non-toxic drug for cancer treatment. This slowly metabolized fatty acid alters tumor cell lipid metabolism causing, among other effects, inhibition of protein prenylation critical to malignant growth. In pursuit of more potent analogues, we have examined the activity of related compounds against tumor cell lines established from patients with advanced prostatic carcinoma, glioblastomas, and malignant melanoma. Like Phenylacetate, derivatives containing α-carbon or ring substitutions induced cytostasis and phenotypic reversion at non-toxic concentrations. Potency was correlated with the degree of calculated lipophilicity of the aromatic fatty acid, and the extent of inhibition of protein prenylation. Remarkably, a parallel cytostatic activity was reported in embryonic plant cells, which respond to Phenylacetate and its analogues in the same concentration range and the same rank order of lipophilicity. These data suggest that Phenylacetate and its analogues may act through common mechanisms to inhibit the growth of vastly divergent, undifferentiated cell types, and provide a basis for the development of new agents for the treatment of human malignancies.

  • Phenylacetate in chemoprevention: in vitro and in vivo suppression of 5-aza-2'-deoxycytidine-induced carcinogenesis.
    Clinical cancer research : an official journal of the American Association for Cancer Research, 1995
    Co-Authors: Premakala Prasanna, Sonsoles Shack, Vincent L. Wilson, Dvorit Samid
    Abstract:

    Differentiation inducers selected for their low cytotoxic and genotoxic potential could be of major value in chemoprevention and maintenance therapy. We focus here on Phenylacetate, a naturally occurring plasma component recently shown to affect the growth and differentiation of established neoplasms in experimental models. The ability of Phenylacetate to prevent carcinogenesis by the chemotherapeutic hypomethylating drug 5-aza-2'-deoxycytidine (5AzadC) was tested in vitro and in mice. Transient exposure of immortalized, but poorly tumorigenic ras-transformed 4C8 fibroblasts to 5AzadC resulted in neoplastic transformation manifested by loss of contact inhibition of growth, acquired invasiveness, and increased tumorigenicity in athymic mice. The latter was associated with elevation in ras expression and a decline in collagen biosynthesis. These profound phenotypic and molecular changes were prevented by a simultaneous treatment with Phenylacetate. Protection from 5AzadC carcinogenesis by Phenylacetate was: (a) highly efficient despite DNA hypomethylation by both drugs, (b) free of cytotoxic and genotoxic effects, (c) stable after treatment was discontinued, and (d) reproducible in vivo. Whereas athymic mice bearing 4C8 cells developed fibrosarcomas following a single i.p. injection with 5AzadC, tumor development was significantly inhibited by systemic treatment with nontoxic doses of Phenylacetate. Phenylacetate and its precursor suitable for oral administration, phenylbutyrate, may thus represent a new class of chemopreventive agents, the efficacy and safety of which should be further evaluated.

  • growth inhibition tumor maturation and extended survival in experimental brain tumors in rats treated with Phenylacetate
    Cancer Research, 1994
    Co-Authors: Zvi Ram, Dvorit Samid, Alain Thibault, Charles E. Myers, Stuart Walbridge, Eric M Oshiro, John J Viola, Junghwa Taocheng, Sonsoles Shack, Edward H Oldfield
    Abstract:

    Phenylacetate is a naturally occurring plasma component that suppresses the growth of tumor cells and induces differentiation in vitro . To evaluate the in vivo potential and preventive and therapeutic antitumor efficacy of sodium Phenylacetate against malignant brain tumors, Fischer 344 rats ( n = 50) bearing cerebral 9L gliosarcomas received Phenylacetate by continuous s.c. release starting on the day of tumor inoculation ( n = 10) using s.c. osmotic minipumps (550 mg/kg/day for 28 days). Rats with established brain tumors ( n = 12) received continuous s.c. Phenylacetate supplemented with additional daily i.p. dose (300 mg/kg). Control rats ( n = 25) were treated in a similar way with saline. Rats were sacrificed during treatment for electron microscopic studies of their tumors, in vivo proliferation assays, and measurement of Phenylacetate levels in the serum and cerebrospinal fluid. Treatment with Phenylacetate extended survival when started on the day of tumor inoculation ( P < 0.01) or 7 days after inoculation ( P < 0.03) without any associated adverse effects. In the latter group, Phenylacetate levels in pooled serum and cerebrospinal fluid samples after 7 days of treatment were in the therapeutic range as determined in vitro (2.45 mm in serum and 3.1 mm in cerebrospinal fluid). Electron microscopy of treated tumors demonstrated marked hypertrophy and organization of the rough endoplasmic reticulum, indicating cell differentiation, in contrast to the scant and randomly distributed endoplasmic reticulum in tumors from untreated animals. In addition, in vitro studies demonstrated dose-dependent inhibition of the rate of tumor proliferation and restoration of anchorage dependency, a marker of phenotypic reversion. Phenylacetate, used at clinically achievable concentrations, prolongs survival of rats with malignant brain tumors through induction of tumor differentiation. Its role in the treatment of brain tumors and other cancers should be explored further.

  • Selective activity of Phenylacetate against malignant gliomas: resemblance to fetal brain damage in phenylketonuria.
    Cancer research, 1994
    Co-Authors: Dvorit Samid, Zvi Ram, Stuart Walbridge, Sonsoles Shack, Edward H Oldfield, Lei Liu, W. R. Hudgins, Charles E. Myers
    Abstract:

    Abstract Phenylacetate, a deaminated metabolite of phenylalanine, has been implicated in damage to immature brain in phenylketonuria. Because primary brain tumors are highly reminiscent of the immature central nervous system, these neoplasms should be equally vulnerable. We show here that sodium Phenylacetate can induce cytostasis and reversal of malignant properties of cultured human glioblastoma cells, when used at pharmacological concentrations that are well tolerated by children and adults. Treated tumor cells exhibited biochemical alterations similar to those observed in phenylketonuria-like conditions, including selective decline in de novo cholesterol synthesis from mevalonate. Because gliomas, but not mature normal brain cells, are highly dependent on mevalonate for production of sterols and isoprenoids vital for cell growth, sodium Phenylacetate would be expected to affect tumor growth in vivo while sparing normal tissues. Systemic treatment of rats bearing intracranial gliomas resulted in significant tumor suppression with no apparent toxicity to the host. The data indicate that Phenylacetate, acting through inhibition of protein prenylation and other mechanisms, may offer a safe and effective novel approach to treatment of malignant gliomas and perhaps other neoplasms as well. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.