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At least 19 recordsLinked to original sources
PubMed1993

Purification and characterization of phenylacetate-coenzyme A ligase from a denitrifying Pseudomonas sp., an enzyme involved in the anaerobic degradation of phenylacetate.

The enzyme catalysing the first step in the anaerobic degradation pathway of phenylacetate was purified from a denitrifying Pseudomonas strain KB 740. It catalyses the reaction phenylacetate + CoA + ATP-->phenylacetyl-CoA + AMP + PPi and requires Mg2+. Phenylacetate-CoA ligase (AMP forming) was found in cells grown anaerobically with phenylacetate and nitrate. Maximal specific enzyme activity was 0.048 mumol min-1 x mg-1 protein in the mid-exponential growth phase. After 640-fold purification with 18% yield, a specific activity of 24.4 mumol min-1 mg-1 protein was achieved. The enzyme is a single polypeptide with Mr of 52 +/- 2 kDa. The purified enzyme shows high specificity towards the aromatic inducer substrate phenylacetate and uses ATP preferentially; Mn2+ can substitute for Mg2+. The apparent Km values for phenylacetate, CoA, and ATP are 60, 150, and 290 microM, respectively. The soluble enzyme has an optimum pH of 8.5, is insensitive to oxygen, but is rather labile and requires the presence of glycerol and/or phenylacetate for stabilization. The N-terminal amino acid sequence showed no homology to other reported CoA-ligases. The expression of the enzyme was studied by immunodetection. It is present in cells grown anaerobically with phenylacetate, but not with mandelate, phenylglyoxylate, benzoate; small amounts were detected in cells grown aerobically with phenylacetate.

Adenosine Monophosphate↗
PubMed1993

Phenylacetate-coenzyme A ligase is induced during growth on phenylacetic acid in different bacteria of several genera.

Nine different bacterial strains that utilise phenylacetic acid as the only carbon and energy source were isolated from samples of different geographical origin. The isolates were characterised taxonomically and physiologically. Evidence is presented that in all the isolates as well as in four previously isolated control strains with the ability to utilize phenylacetic acid, the enzyme phenylacetate-CoA ligase is specifically induced during growth on phenylacetic acid. The Michaelis constant (Km) in one Pseudomonas strain was sufficiently low (-1 mM) to suggest that the enzyme may have a role in phenylacetic acid metabolism.

Acinetobacter↗
PubMed2001

Isolation and in vivo and in vitro antifungal activity of phenylacetic acid and sodium phenylacetate from Streptomyces humidus.

The antifungal substances SH-1 and SH-2 were isolated from Streptomyces humidus strain S5-55 cultures by various purification procedures and identified as phenylacetic acid and sodium phenylacetate, respectively, based on the nuclear magnetic resonance, electron ionization mass spectral, and inductively coupled plasma mass spectral data. SH-1 and SH-2 completely inhibited the growth of Pythium ultimum, Phytophthora capsici, Rhizoctonia solani, Saccharomyces cerevisiae, and Pseudomonas syringae pv. syringae at concentrations from 10 to 50 microg/ml. The two compounds were as effective as the commercial fungicide metalaxyl in inhibiting spore germination and hyphal growth of P. capsici. However, the in vivo control efficacies of the two antifungal compounds against P. capsici infection on pepper plants were similar to those of H(3)PO(3) and fosetyl-AI but less than that of metalaxyl.

Antifungal Agents↗
PubMed1994

Aerobic catabolism of phenylacetic acid in Pseudomonas putida U: biochemical characterization of a specific phenylacetic acid transport system and formal demonstration that phenylacetyl-coenzyme A is a catabolic intermediate.

The phenylacetic acid transport system (PATS) of Pseudomonas putida U was studied after this bacterium was cultured in a chemically defined medium containing phenylacetic acid (PA) as the sole carbon source. Kinetic measurement was carried out, in vivo, at 30 degrees C in 50 mM phosphate buffer (pH 7.0). Under these conditions, the uptake rate was linear for at least 3 min and the value of Km was 13 microM. The PATS is an active transport system that is strongly inhibited by 2,4-dinitrophenol, 4-nitrophenol (100%), KCN (97%), 2-nitrophenol (90%), or NaN3 (80%) added at a 1 mM final concentration (each). Glucose or D-lactate (10 mM each) increases the PATS in starved cells (140%), whereas arsenate (20 mM), NaF, or N,N'-dicyclohexylcarbodiimide (1 mM) did not cause any effect. Furthermore, the PATS is insensitive to osmotic shock. These data strongly suggest that the energy for the PATS is derived only from an electron transport system which causes an energy-rich membrane state. The thiol-containing compounds mercaptoethanol, glutathione, and dithiothreitol have no significant effect on the PATS, whereas thiol-modifying reagents such as N-ethylmaleimide and iodoacetate strongly inhibit uptake (100 and 93%, respectively). Molecular analogs of PA with a substitution (i) on the ring or (ii) on the acetyl moiety or those containing (iii) a different ring but keeping the acetyl moiety constant inhibit uptake to different extents. None of the compounds tested significantly increase the PA uptake rate except adipic acid, which greatly stimulates it (163%). The PATS is induced by PA and also, gratuitously, by some phenyl derivatives containing an even number of carbon atoms on the aliphatic moiety (4-phenyl-butyric, 6-phenylhexanoic, and 8-phenyloctanoic acids). However, similar compounds with an odd number of carbon atoms (benzoic, 3-phenylpropionic, 5-phenylvaleric, 7-phenylheptanoic, and 9-phenylnonanoic acids) as well as many other PA derivatives do not induce the system, suggesting that the true inducer molecule is phenylacetyl-coenzyme A (PA-CoA). Furthermore, after P. putida U is cultured in the same medium containing other carbon sources (glucose or octanoic, benzoic, or 4-hydroxyphenylacetic acid) in the place of PA, the PATS and PA-CoA are not detected; neither the PATS nor PA-CoA is found in cases in which mutants (PA- and PCL-) lacking the enzyme which catalyzed the initial step of the PA degradation (phenylacetyl-CoA ligase) are used. PA-CoA has been extracted from bacteria and identified as a true PA catabolite by high-performance liquid chromatography and also enzymatically with pure acyl-CoA:6-aminopenicillanic acid acyltransferase from Penicillium chrysogenum.

Acetyl Coenzyme A↗
PubMed2000

Biochemical and molecular characterization of phenylacetate-coenzyme A ligase, an enzyme catalyzing the first step in aerobic metabolism of phenylacetic acid in Azoarcus evansii.

Phenylacetate-coenzyme A ligase (PA-CoA ligase; AMP forming, EC 6.2. 1.30), the enzyme catalyzing the first step in the aerobic degradation of phenylacetate (PA) in Azoarcus evansii, has been purified and characterized. The gene (paaK) coding for this enzyme was cloned and sequenced. The enzyme catalyzes the reaction of PA with CoA and MgATP to yield phenylacetyl-CoA (PACoA) plus AMP plus PPi. The enzyme was specifically induced after aerobic growth in a chemically defined medium containing PA or phenylalanine (Phe) as the sole carbon source. Growth with 4-hydroxyphenylacetate, benzoate, adipate, or acetate did not induce the synthesis of this enzyme. This enzymatic activity was detected very early in the exponential phase of growth, and a maximal specific activity of 76 nmol min(-1) mg of cell protein(-1) was measured. After 117-fold purification to homogeneity, a specific activity of 48 micromol min(-1) mg of protein(-1) was achieved with a turnover number (catalytic constant) of 40 s(-1). The protein is a monomer of 52 kDa and shows high specificity towards PA; other aromatic or aliphatic acids were not used as substrates. The apparent K(m) values for PA, ATP, and CoA were 14, 60, and 45 microM, respectively. The PA-CoA ligase has an optimum pH of 8 to 8.5 and a pI of 6.3. The enzyme is labile and requires the presence of glycerol for stabilization. The N-terminal amino acid sequence of the purified protein showed no homology with other reported PA-CoA ligases. The gene encoding this enzyme is 1, 320 bp long and codes for a protein of 48.75 kDa (440 amino acids) which shows high similarity with other reported PA-CoA ligases. An amino acid consensus for an AMP binding motif (VX2SSGTTGXP) was identified. The biochemical and molecular characteristics of this enzyme are quite different from those of the isoenzyme catalyzing the same reaction under anaerobic conditions in the same bacterium.

Adenosine Triphosphate↗
PubMed1998

Uptake of phenylacetic acid by two strains of Penicillium chrysogenum.

Uptake of phenylacetic acid, the side-chain precursor of benzylpenicillin, was studied in Penicillium chrysogenum Wisconsin 54-1255 and in a strain yielding high levels of penicillin. In penicillin fermentations with the high-yielding strain, 100% recovery of phenylacetic acid in benzylpenicillin was found, whereas in the Wisconsin strain only 17% of the supplied phenylacetic acid was incorporated into benzylpenicillin while the rest was metabolized. Accumulation of total phenylacetic acid-derived carbon in the cells was nonsaturable in both strains at high external concentrations of phenylacetic acid (250-3500 microM), and in the high-yielding strain at low phenylacetic acid concentrations (2. 8-100 microM), indicating that phenylacetic acid enters the cells by simple diffusion, as concluded earlier for P. chrysogenum by other authors. However, at low external concentrations of phenylacetic acid saturable accumulation appeared in the Wisconsin strain. HPLC-analyses of cell extracts from the Wisconsin strain showed that phenylacetic acid was metabolized immediately after entry into the cells and different [14C]-labeled metabolites were detected in the cells. Up to approximately 50% of the accumulated phenylacetic acid was metabolized during the transport-assay period, the conversion having an impact on the uptake experiments. Nevertheless, accumulation of free unchanged phenylacetic acid in the cells showed saturation kinetics, suggesting the possible involvement of a high-affinity carrier in uptake of phenylacetic acid in P. chrysogenum Wisconsin 54-1255. At high concentrations of phenylacetic acid, contribution to uptake by this carrier is minor in comparison to simple diffusion and therefore, of no importance in the industrial production of penicillin.

Bacteriological Techniques↗
PubMed2006

Evaluation of [14C]phenylacetate as a prototype tracer for the measurement of glial metabolism in the rat brain.

[(14)C]Phenylacetate was designed as a prototype tracer for the measurement of glial metabolism, and its potency in comparison with that of [(14)C]acetate was evaluated in this study. Normal rats were intravenously injected with [(14)C]phenylacetate or [(14)C]acetate, and radioactivity concentrations were measured in the plasma, cerebral cortex, cerebellum and peripheral tissues by dissection method. In addition, [(14)C]phenylacetate uptake in the rat brain was compared by autoradiography with that of [(14)C]acetate following the injection of fluorocitrate, a selective glial toxin, into the brain. [(14)C]Phenylacetate was rapidly taken up into the brain and was retained at high levels up to 20 min postadministration. The levels of [(14)C]phenylacetate in the cerebral cortex were about threefold higher than those of [(14)C]acetate at 1 min postinjection. Microinjection of fluorocitrate into the right striatum resulted in a significant decrease of the uptake of both [(14)C]phenylacetate and [(14)C]acetate into the right striatum. Radiochemical analysis confirmed the rapid hydrolysis of [(14)C]phenylacetate in the rat brain, with less than 20% of radioactivity representing unmetabolized [(14)C]phenylacetate at 1 min postinjection. These results suggest that [(14)C]phenylacetate is rapidly taken up into the brain and is hydrolyzed and converted to [(14)C]acetate. [(14)C]Phenylacetate may have the potential to serve as a tracer for the measurement of glial metabolism in an intact brain.

Acetates↗
PubMed2003

Functional genomics by NMR spectroscopy. Phenylacetate catabolism in Escherichia coli.

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 delta3-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 beta-oxidation-type degradation of the resulting CoA dicarboxylate via beta-ketoadipyl-CoA to succinyl-CoA and acetyl-CoA appears to be catalyzed by the PaaJ, PaaF and PaaH proteins.

Acetyl Coenzyme A↗
PubMed1999

Phenylacetate inhibits growth and vascular endothelial growth factor secretion in human thyroid carcinoma cells and modulates their differentiated function.

There is increasing evidence that phenylacetate inhibits growth and modulates differentiation in a variety of tumors with effects on gene expression, and protein prenylation and glycosylation at concentrations that have been safely used in humans. We evaluated the antineoplastic effects of phenylacetate in five thyroid cancer cell lines of follicular cell origin in vitro. We found early growth inhibition occurred with phenylacetate treatment at a dose of 2.5-10 mmol/L. The growth inhibition was cytostatic with the thyroid carcinoma cells arrested in the G0-1 cell phase. When evaluating the effect of phenylacetate on the differentiated functions of thyroid carcinoma cells, phenylacetate exposure: 1) decreased the TSH (10 mU/mL) growth response; 2) increased radioactive iodine (125I) uptake in two out of five cell lines; and 3) inhibited thyroglobulin secretion. Phenylacetate also inhibited the secretion of vascular endothelial growth factor (a glycoprotein dependent on glycosylation for efficient cellular excretion) from the thyroid cancer cell lines. Our results support that phenylacetate has an antiproliferative effect in many cell types, but the differentiating effects were not uniform. Importantly, we have identified that phenylacetate inhibits the secretion of vascular endothelial growth factor, which possibly mediates the antiangiogenic effects observed in vivo. Because of the minimal toxicity associated with phenylacetate treatment in humans, at concentrations we show to have a significant antineoplastic effect in thyroid carcinoma cells, phenylacetate could be useful in patients with differentiated thyroid cancer who fail conventional therapy or as an adjuvant to radioactive iodine therapy in patients with aggressive tumors.

Antineoplastic Agents↗
PubMed1999

Disruption of phacA, an Aspergillus nidulans gene encoding a novel cytochrome P450 monooxygenase catalyzing phenylacetate 2-hydroxylation, results in penicillin overproduction.

Aspergillus nidulans utilizes phenylacetate as a carbon source via homogentisate, which is degraded to fumarate and acetoacetate. Mutational evidence strongly suggested that phenylacetate is converted to homogentisate through two sequential hydroxylating reactions in positions 2 and 5 of the aromatic ring. Using cDNA substraction techniques, we have characterized a gene, denoted phacA, whose transcription is strongly induced by phenylacetate and which putatively encodes a cytochrome P450 protein. A disrupted phacA strain does not grow on phenylacetate but grows on 2-hydroxy- or 2, 5-dihydroxyphenylacetate. Microsomal extracts of the disrupted strain are deficient in the NADPH-dependent conversion of phenylacetate to 2-hydroxyphenylacetate. We conclude that PhacA catalyzes the ortho-hydroxylation of phenylacetate, the first step of A. nidulans phenylacetate catabolism. The involvement of a P450 enzyme in the ortho-hydroxylation of a monoaromatic compound has no precedent. In addition, PhacA shows substantial sequence divergence with known cytochromes P450 and defines a new family of these enzymes, suggesting that saprophytic fungi may represent a source of novel cytochromes P450. Phenylacetate is a precursor for benzylpenicillin production. phacA disruption increases penicillin production 3-5-fold, indicating that catabolism competes with antibiotic biosynthesis for phenylacetate and strongly suggesting strategies for Penicillium chrysogenum strain improvement by reverse genetics.

Aspergillus nidulans↗
PubMed1996

Plasma protein binding of phenylacetate and phenylbutyrate, two novel antineoplastic agents.

Phenylacetate and phenylbutyrate, two novel inducers of tumor cytostasis and differentiation, are currently in clinical trials for the treatment of cancer in adults. The purpose of our study was to evaluate the plasma protein-binding characteristics of phenylacetate and phenylbutyrate in the plasma of normal volunteers and that of patients with cancer. Drug plasma protein-binding analysis was examined using three separate devices: a micropartition system and two equilibrium dialysis systems, all of which exhibited similar results. Phenylacetate and phenylbutyrate concentrations were determined by high-performance liquid chromatography. Both drugs exhibited concentration-dependent binding. Our results showed sodium phenylacetate to have a higher free fraction than sodium phenylbutyrate at corresponding concentrations (> 0.442 +/- 0.008 and > 0.188 +/- 0.001, respectively). Plasma pH did not greatly affect protein binding of either drug. As albumin concentration decreased, an increase in free fraction of both drugs was observed, however alpha 1-acid glyco-protein showed no change in free fraction as its concentration increased. Patients with cancer with lower levels of albumin showed an increase in free fraction with both phenylacetate and phenylbutyrate. When phenylacetate and phenylbutyrate were added together in plasma, the free fraction of phenylacetate increased, whereas the phenylbutyrate free fraction slightly decreased. We conclude that phenylacetate and phenylbutyrate have high free fractions that change with varying albumin levels and when both phenylacetate and phenylbutyrate are present together in plasma.

Adult↗
PubMed1995

Penicillium chrysogenum Takes up the Penicillin G Precursor Phenylacetic Acid by Passive Diffusion.

Penicillium chrysogenum utilizes phenylacetic acid as a side chain precursor in penicillin G biosynthesis. During industrial production of penicillin G, phenylacetic acid is fed in small amounts to the medium to avoid toxic side effects. Phenylacetic acid is taken up from the medium and intracellularly coupled to 6-aminopenicillanic acid. To enter the fungal cell, phenylacetic acid has to pass the plasma membrane. The process via which phenylacetic acid crosses the plasma membrane was studied in mycelia and liposomes. Uptake of phenylacetic acid by mycelium was nonsaturable, and the initial velocity increased logarithmically with decreasing external pH. Studies with liposomes demonstrated a rapid passive flux of the protonated species through liposomal membranes. These results indicate that phenylacetic acid passes the plasma membrane via passive diffusion of the protonated species. The rate of phenylacetic acid uptake at an external concentration of 3 mM is at least 200-fold higher than the penicillin production rate in the Panlabs P2 strain. In this strain, uptake of phenylacetic acid is not the rate-limiting step in penicillin G biosynthesis.

Journal Article↗
PubMed1995

Disposition of phenylbutyrate and its metabolites, phenylacetate and phenylacetylglutamine.

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)

Adult↗
PubMed1986

Waste nitrogen excretion via amino acid acylation: benzoate and phenylacetate in lysinuric protein intolerance.

Benzoate and phenylacetate improve prognosis in inherited urea cycle enzyme deficiencies by increasing waste nitrogen excretion as amino acid acylation products. We studied metabolic changes caused by these substances and their pharmacokinetics in a biochemically different urea cycle disorder, lysinuric protein intolerance (LPI), under strictly standardized induction of hyperammonemia. Five patients with LPI received an intravenous infusion of 6.6 mmol/kg L-alanine alone and separately with 2.0 mmol/kg of benzoate or phenylacetate in 90 min. Blood for ammonia, serum urea and creatinine, plasma benzoate, hippurate, phenylacetate, phenylacetylglutamine, and amino acids was obtained at 0, 120, 180, and 270 min. Urine was collected in four consecutive 6-h periods. Alanine caused hyperammonemia: maximum increase 107, 28-411 microM (geometric mean, 95% confidence interval); ammonia increments were nearly identical after alanine + benzoate (60, 17-213 microM) and alanine + phenylacetate (79, 13-467 microM) (NS). Mean plasma benzoate was 6.0 mM when extrapolated to the end of alanine + benzoate infusions; phenylacetate was 4.9 mM at the end of alanine + phenylacetate. Transient toxicity (dizziness, nausea, vomiting) occurred in four patients at the end of combined infusions, and we suggest upper therapeutic plasma concentrations of 4.5 mM for benzoate and 3.5 mM for phenylacetate. Benzoate and phenylacetate then decreased following first-order kinetics with t1/2S of 273 and 254 min, respectively. Maximal plasma hippurate (0.24, 0.14-0.40 mM) was lower than maximal phenylacetylglutamine (0.48, 0.22-1.06 mM, p = 0.008).(ABSTRACT TRUNCATED AT 250 WORDS)

Acylation↗
PubMed1994

Growth inhibition, tumor maturation, and extended survival in experimental brain tumors in rats treated with phenylacetate.

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.

Animals↗
PubMed1998

A non-pungent resiniferatoxin analogue, phorbol 12-phenylacetate 13 acetate 20-homovanillate, reveals vanilloid receptor subtypes on rat trigeminal ganglion neurons.

Capsaicin, the vanilloid responsible for the pungent taste of hot peppers, binds to receptors found primarily in polymodal nociceptors. Capsaicin initially stimulates polymodal nociceptors and subsequently inhibits them from responding to a variety of stimuli. This property makes it useful clinically as an analgesic and anti-inflammatory compound. There is mounting, albeit indirect, evidence for the existence of several subtypes of vanilloid receptors. One such piece of evidence comes from studying analogues of capsaicin, such as phorbol 12-phenylacetate 13 acetate 20-homovanillate. This compound binds to (capsaicin) vanilloid receptors on sensory neurons, but unlike capsaicin it is non-pungent and does not produce hypothermia. To determine how sensory neurons respond to phorbol 12-phenylacetate 13 acetate 20-homovanillate, and to compare these responses with those evoked by capsaicin, whole-cell patch-clamp measurements were performed on cultured rat trigeminal ganglion neurons. It was found that 63% of the neurons held at -60 mV were activated by 3 microM, phorbol 12-phenylacetate 13 acetate 20-homovanillate, and 87% of these were also activated by 1 microM capsaicin. In a given neuron, phorbol 12-phenylacetate 13 acetate 20-homovanillate, like capsaicin, could activate kinetically distinct inward currents. The current-voltage curves characterizing phorbol 12-phenylacetate 13 acetate 20-homovanillate responses were asymmetric and had reversal potentials at -5.8 +/- 6.0 mV and 10.4 +/- 4 mV. The averaged dose-response curves for phorbol 12-phenylacetate 13 acetate 20-homovanillate were fit to the Hill equation and had binding constants (K(1/2)s) of 2.73 microM and 0.96 microM and Hill coefficients (ns) of approximately 1 for a rapidly- and slowly-activating current, respectively. These parameters are consistent with those obtained from binding experiments and calcium-influx experiments on sensory nerves. Repeated applications of phorbol 12-phenylacetate 13 acetate 20-homovanillate every 3 min caused a complete reduction in the rapidly-activating currents leaving only a reduced slowly-activating current. This provides strong evidence for the independence of these currents and the existence of subtypes of vanilloid receptors. Additional evidence for the existence of receptor subtypes is that 10 microM capsazepine, a specific and competitive inhibitor of capsaicin-evoked responses, did not inhibit the phorbol 12-phenylacetate 13 acetate 20-homovanillate-induced currents in some neurons and partially inhibited them in other neurons. Thus, there are capsazepine-sensitive and capsazepine-insensitive subtypes of vanilloid receptors. In summary, we have obtained electrophysiological and pharmacological evidence for distinct subtypes of vanilloid receptors.

Animals↗
PubMed1995

Phase I study of phenylacetate administered twice daily to patients with cancer.

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 micrograms/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 micrograms/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.

Adult↗