In vitro and in vivo effects of the arylamine human immunodeficiency virus protease inhibitor 4R-(4alpha,5alpha,6beta, 7beta)-1-[(3-(1-imidazoylcarbamoyl)phenyl)methyl]-3-[(3-aminophenyl)m ethyl]hexahydro-5,6-dihydroxy-4,7-bis(phenylmethyl)-2H-1, 3-diazepin-2-one (SD894) on rat hepatic cytochrome P450 2B and 3A.

The human immunodeficiency virus-1 protease inhibitor SD894 was evaluated as an inhibitor and inducer of cytochromes P450 (CYPs) in rats. After addition of 10 microM SD894 and 2 mM NADPH to liver microsomes from dexamethasone-treated rats, a type II spectrum appeared. Within 2 min, it was replaced by a type III spectrum, with absorbance maxima at 426 and 456 nm, similar to those observed with alkylamines (SKF-525A) and arylamines (p-chloroaniline). Preincubation of microsomes from dexamethasone-treated rats with SD894 and NADPH resulted in a time-dependent inhibition of testosterone 6beta-hydroxylation (CYP 3A1/2 activity), which was decreased to 25% of controls after 30 min. Testosterone 16beta-hydroxylation (CYP 2B1/2 activity) was unaffected under these conditions. Testosterone 6beta-hydroxylation rates in liver microsomes from pregnenolone 16alpha-carbonitrile-treated rats incubated with 10 microM SD894 and NADPH, washed, and reisolated by ultracentrifugation were reduced by 71%, whereas 16beta-hydroxylation was unaffected by SD894. Immunoblots of liver microsomes from rats dosed iv with SD894 or ip with TAO displayed increased CYP 2B1 and CYP 3A1 levels, respectively. Testosterone 6beta-hydroxylase activity in microsomes from TAO-treated rats was greater than controls. Preincubation of these microsomes with potassium ferricyanide produced an additional 50% increase, consistent with disruption of a metabolite-CYP complex. Microsomes from SD894-treated rats displayed a 3-fold increase in testosterone 16beta-hydroxylation. Potassium ferricyanide preincubation did not increase activity. Thus, although SD894 appears to inhibit CYP in vitro in a manner typical of other amine-containing, mechanism-based inhibitors, in vivo induction by 10 mg/kg daily doses of SD894 affects a different isozyme than does inhibition. The mechanism of induction is unknown.

Determination of a HIV protease inhibitor (DMP 450) in animal and human plasma by solid-phase extraction and high-performance liquid chromatography.

Extraction of DMP 450 from plasma was performed with C2 solid-phase extraction columns, using 0.1 M ammonium acetate in 90% methanol to elute DMP 450. The extraction recovery over the range of 10 to 10 000 ng/ml averaged 81.0, 96.2, 77.4, 95.2 and 68.0% from rat, dog, monkey, chimpanzee (25-10 000 ng/ml) and human plasma, respectively. HPLC analysis was carried out with a C18 column and a mobile phase of acetonitrile, methanol and 30 mM potassium phosphate (pH 3), the composition dependent on the type of plasma being analyzed, and monitored at a wavelength of 229 nm. Intra-day and inter-day coefficients of variation were less than 9.9 and 12.9%, respectively. Absolute differences were less than 11.5%.

A pharmacokinetic evaluation of HIV protease inhibitors, cyclic ureas, in rats and dogs.

The pharmacokinetics of a series of novel cyclic, non-peptide inhibitors of HIV protease were studied in rats or dogs after intravenous and oral administration. Six symmetrically substituted cyclic urea compounds (XK234, XM311, XM320, XM321, XM323, and XM412), which effectively inhibited HIV virus replication, with IC90 values of 0.03-1.0 microM (0.017-0.76 microgram mL-1), were evaluated. Plasma concentrations were measured in rats and dogs using specific and sensitive HPLC methods. In rats, the maximum plasma concentrations of 0.21-1.88 micrograms mL-1 were detected within 1 h of oral administration of 10 mg kg-1 of the compounds. The elimination half-lives ranged from 1.25 to 3.3 h in rats and the absolute oral bioavailability ranged from 18 to 100%. In dogs, the maximum plasma concentration and absolute oral bioavailability were 4.37 micrograms mL-1 and 48%, 1.07 micrograms mL-1 and 16%, and 1.48 mg ML-1 and 38% for XK234, XM311, and XM323, respectively. The data demonstrated that the maximum plasma concentrations of these cyclic ureas were several times higher than the IC90 for inhibition of viral replication after single doses of 10 mg kg-1 in rats and dogs. With this combination of high potency against virus replication and good oral bioavailability, these cyclic ureas represent a new class of compounds that are suitable for development as therapeutic agents for the treatment of HIV-associated diseases.

Pharmacokinetics of HIV protease inhibitor DMP 323 in rats and dogs.

DMP 323 is a symmetrically substituted cyclic urea compound with demonstrated activity against human immunodeficiency virus (HIV) in vitro. DMP 323 has been measured in rat and dog plasma via liquid-liquid extraction and HPLC. The limit of quantitation is 10 ng/ml using 0.5 ml plasma. Following an intravenous dose of 5 mg/kg to rats, DMP 323 exhibited an apparent volume of distribution at steady-state of 6.36 liters/kg and clearance of 7.12 liters/hr/kg. The same dose administered intravenously to dogs resulted in apparent volume of distribution at steady-state and clearance values of 2.28 liters/kg and 1.48 liters/hr/kg, respectively. Elimination half-lives were 0.95 hr in rats and 1.80 hr in dogs. DMP 323 was rapidly absorbed from oral solution doses in rats (3, 5, and 10 mg/kg) and dogs (5 and 10 mg/kg), achieving maximum plasma concentrations in 1 hr or less in both species. Absolute bioavailability of DMP 323 from oral doses ranged from 15 to 27% in rats and from 37 to 38% in dogs. Pharmacokinetics were unchanged in rats and dogs over 8-day t.i.d. and 5-day b.i.d. multiple oral dose regimens, respectively. Oral doses administered to fed animals resulted in lower plasma concentrations of DMP 323 than the same doses administered to fasted animals. Because of its in vitro high potency and acceptable pharmacokinetics, DMP 323 seems to be a worthy candidate for further study in the effort to develop an inhibitor of HIV protease for use in the therapy of AIDS.

Serum stimulation of UDP-glucose dehydrogenase activity in Swiss 3T3 fibroblasts.

A new HPLC assay was developed to measure UDP-glucose dehydrogenase (UDP-GDH) activity in crude homogenates of 3T3 fibroblasts. UDP-GDH activity is directly related to the proliferative activity of the cell culture: enzyme activity is highest in log phase cells and decreases as the culture approaches quiescence. Serum stimulation of quiescent 3T3 fibroblasts results in an increase in UDP-GDH activity that has two components that are differentially affected by inhibitors of protein synthesis. Following serum stimulation, changes in cellular UDP-glucuronic acid concentrations mirror changes in UDP-GDH activity. UDP-xylose is a potent inhibitor of UDP-GDH but inhibitory concentrations of UDP-xylose could not be detected in cell extracts.

Effect of high-protein diet on pyrimidine synthesis and response to PALA in mouse tissues.

BACKGROUND: High-protein diets have been found to protect mice from the lethal effects of cytotoxic pyrimidine analogues and to reduce the toxicity of the antipyrimidine fluorouracil (5-FU), but the biochemical explanation for these effects is not known. PALA potentiates the chemotherapeutic efficacy of 5-FU, and each of the two agents can produce dose-limiting intestinal toxic effects. We have shown that intraperitoneal infusion of ammonium chloride stimulates intestinal de novo pyrimidine synthesis. This stimulation with excess ammonia, which can also result from high-protein intake, is dependent on the presence of carbamoyl phosphate synthetase I, an enzyme in the liver and intestine but not in most tumors. These findings suggest that a high-protein diet can stimulate pyrimidine synthesis in the liver and intestine but leave it unchanged in tumor tissue. PURPOSE: The purpose of this study was to determine whether varying dietary protein causes pharmacologically relevant and preferential changes in de novo pyrimidine synthesis. METHODS: Mice were fed diets containing 18%, 35%, or 50% casein. Dietary effects on de novo pyrimidine synthesis were measured in the intestine, liver, and B16 mouse melanoma in mice treated with PALA and in untreated mice. De novo synthesis was measured by infusion of [15N]alanine into intact animals, determination of 15N incorporation into uracil by use of gas chromatography-mass spectrometry, and calculation of the fraction of the uracil nucleotide pool formed by de novo synthesis. RESULTS: In mice on a 50% casein diet (high protein), de novo pyrimidine synthesis increased substantially in the liver and intestine, compared with synthesis in mice receiving 18% casein. Increase in pyrimidine synthesis in B16 tumor tissue was negligible. The high-protein diet protected the intestine and liver from depletion of uracil nucleotide pools by PALA, and toxicity in tumor-free animals was reduced, as determined by mortality after PALA treatment. Sensitivity of the B16 tumor to the biochemical and cytotoxic effects of PALA was not diminished. CONCLUSIONS: We propose that the basis for these effects of a high-protein diet is the generation of excess carbamoyl phosphate in tissues containing carbamoyl phosphate synthetase I. This carbamoyl phosphate can stimulate de novo pyrimidine synthesis and compete with drugs that interact with enzymes of the de novo pathway, thereby selectively protecting the liver and intestine. IMPLICATIONS: These data provide a biochemical explanation for reported effects of high-protein diet on toxicity of antipyrimidines like 5-FU. Studies are underway to determine if stimulation of pyrimidine synthesis by excess ammonia improves therapy with 5-FU alone or combined with PALA.

Derivatization of N-methyl and cyclic amino acids with dimethylformamide dimethyl acetal.

Six amino acids containing either an N-methyl or a cyclic secondary amine were converted to volatile derivatives by reaction with dimethylformamide dimethyl acetal. The amine functionalities were formylated by way of an amide acetal intermediate while the carboxylic acid groups were esterified directly. The resulting N-formyl esters were stable to solvent extraction and exhibited gas chromatography-mass spectrometry properties suitable for assay development.