Detection of phosphonoacetate degradation and phnA genes in soil bacteria from distinct geographical origins suggest its possible biogenic origin

Phosphonoacetate is regarded as an antiviral xenobiotic whose mineralization can be catalysed by an enzyme, phosphonoacetate hydrolase, encoded by the phnA gene. To date the enzyme's activity has been detected in only a limited number of bacteria. Its expression has been shown to occur in a manner independent of the phosphate status of the cell, in direct contrast to the general rule of organophosphonate metabolism being under the control of the pho regulon. In this study the environmental occurrence of the phnA gene was evaluated by polymerase chain reaction amplification of DNA extracts obtained directly from various soil environments. Sensitivity of this method was improved such that a positive result was routinely obtained with soil spiked with as few as 6 colony-forming units (cfu) per gram of soil of Pseudomonas fluorescens 23F (phnA(+)). When total DNA from a variety of Northern Irish, Greek and Bolivian soils was tested, all were positive for phnA. Bacteria capable of utilizing phosphonoacetate as sole carbon, energy and phosphorus source, with the release of essentially equimolar concentrations of phosphate to the culture supernatant, were isolated from all soil samples tested. Analysis of three such isolates revealed all to be species of Pseudomonas sensu stricto, possessing phosphonoacetate hydrolase activity in cell-free extracts. Sequence determination of the phnA gene revealed a similarity of the putative protein sequences at levels of 98.3-99.3% between the Pseudomonas strains. This is the first study to use molecular methods to investigate the distribution of a gene encoding organophosphonate metabolism, and indicates that the phnA gene is ubiquitous within soils from geographically distinct regions. Such an observation supports the proposition that phosphonoacetate is a compound that may also have a biogenic origin.

Mass spectrometric technique for the determination of N-phosphonoacetyl-L-aspartic acid in serum

N-Phosphonoacetyl-L-aspartic acid (PALA), a potent inhibitor of aspartic acid transcarbamylase, is now undergoing Phase I clinical trials. Initial experiments revealed that PALA is not metabolized to phosphonoacetic acid (PAA) in humans. Thus PALA may be quantified in serum after in vitro conversion to PAA. Serum is deproteinized with perchloric acid, lipid extracted with methylene chloride, hydrolyzed with 8 N hydrochloric acid at 100 degrees for 3 h, and evaporated to dryness with nitrogen. The residue is silylated, and PAA is quantified by monitoring the (M + 1)+ ions of the protonated molecular ions of trimethylsilyl derivatives of PAA and phosphonopropionic acid (internal standard) obtained in chemical ionization with methane. Limit of detection is 0.5 microM (150 ng/ml) PALA using 1 ml serum. PALA was given by continuous infusion to cancer patients at various doses. Maximum levels of PALA (50-500 microM range) were obtained at the end of infusion, followed in most cases by biexponential decay. Persistent residual PALA levels (5 microM for 48 h after infusion) correlated with increased toxicity.

Determination of N-(Phosphonacetyl)-L-aspartic acid (PALA) in dog serum and urine by gas chromatography and selected lon monitoring

Methods are described for quantitating N-(phosphonacetyl)L-aspartic acid (PALA), a new antitumor agent presently undergoing clinical evaluation. These methods were developed to measure this compound in serum by gas chromatography using the selectivity of a nitrogen-phosphorus detector and in serum and urine by the gas chromatographic/mass spectrometric technique of selected ion monitoring. PALA and the internal standard, N-(phosphonacetyl)-L-glutamic acid (HOMOPALA), were analyzed as their tetramethyl derivatives. Extraction from the biologic fluids was achieved by first precipitating the protein with acetone and then drying the serum with subsequent washes of acetone and diethyl ether. PALA and HOMOPALA were than extracted from the dried serum into an anhydrous HCL/methanol/tetrahydrofuran solution. After removing the solvent, the extract was reacted with diazomethane to form the tetramethyl derivatives. The feasibility of the method was demonstrated in the dog by comparing the total radioactivity with PALA equivalents determined in blood and urine samples following iv administration of PALA-14C. The range of the analysis was 20.0--200 microgram/ml for the urine samples and 0.5--15 microgram/ml for the serum samples.

Enzymatic assay for the antitumor agent-N-(phosphonacetyl)-L-aspartic acid (PALA)

A method is described for the assay of N-(phosphonacetyl)-L-aspartic acid in plasma or urine, based on inhibition of partially purified aspartate carbamoyltransferase from rat liver. Concentrations of N-(phosphonacetyl)-L-aspartic acid as low as 0.1 microgram/ml can be detected. Plasma disappearance and urinary excretion curves from one patient are shown as examples of the application of the method.

An enzymatic technique for measuring N-phosphonacetyl-L-aspartic acid in tissues

An enzymatic technique is presented for measuring N-phosphonacetyl-L-aspartic acid (PALA; NSC-224131) in biologic specimens. Tightly bound PALA is quantitatively detached from its target enzyme, L-aspartic acid transcarbamylase (ATCase), by heating at 95 degrees C for 5 minutes. Denatured proteins are removed by centrifugation. PALA in the supernatant fluid is quantitated by exposing intact splenic ATCase to representative aliquots or subdilutions of the resultant supernatant in the presence of L-[4-14C]aspartic acid and carbamyl phosphate. After 30 minutes' incubation at 37 degrees C, unreacted L-[4-14 C]aspartic acid is dissipated enzymatically and newly formed [4-14C]carbamyl-L-aspartic acid is quantitated by scintillation spectrometry. The percentage inhibition of ATCase responds in a linear way to the logarithm of the concentration of PALA between 0.10 and 1.00 micrometer. The PALA concentration of an unknown is determined indirectly by matching the percentage inhibition caused by the unknown to the inhibition caused by a known series of standard concentrations of PALA over the linear range. This assay is sensitive, adequately reproducible despite the use of an unpurified enzyme, and notably facile. It can be used to measure PALA in plasma, urine, tissues, and tumors of subjects treated with this new oncolytic drug.