Related Experiment Videos
Pharmacology of a new triazine antifolate in mice, rats, dogs, and monkeys
Abstract:
Triazinate (TZT), a potent inhibitor of dihydrofolate reductase, was selected for detailed investigation to determine its mechanism of selective action as well as its metabolic fate in mice, rats, dogs, and monkeys. The serum disappearance of TZT in normal and tumor-bearing mice was similar, with a rapid tissue equilibration phase and a slower elimination phase. Serum disappearance in normal and tumor-bearing rats was 1.5 to 2.2 hr. Serum disappearance in dogs and monkeys was similar, with half-lives of 3 to 4 and 2 to 4 hr, respectively. Urinary excretion of TZT at 24 hr was only 5 to 6% of the injected dose in mice and rats; in contrast, the dogs excreted 60% of the injected dose in 8 hr. TZT accumulated to comparable degrees in the organs of rats and mice, with progressively lesser concentrations in liver, kidney, spleen, and brain. Dihydrofolate reductase activity became almost undectectable in all tissues studied within 15 min after drug adminsitration. An important difference in drug accumulation was in the ascites cells of tumor-bearing animals: in mice, the drug level was consistently lower in the L1210 cells than in the ascites fluid; in contrast, by 30 min after treatment with TZT the drug level in Walker 256 cells was 10-fold higher than the level in the ascites fluid. No evidence for drug metabolism was found in extracts of urine, feces, or organ tissues from either mice or rats. TZT and two related triazines were studied for their ability to accumulate in the cerbrospinal fluid of dogs after i.v. administration. TZT achieved a cerebrospinal fluid level of approximately 15% of the serum concentration at 1 hr; in contrast, the other two triazines reached maximum cerebrospinal fluid values of 1% at 1 hr.
Insights
Triazinate (TZT), a dihydrofolate reductase inhibitor, shows rapid tissue distribution and varying elimination across species. It effectively inhibits dihydrofolate reductase in tissues but has limited metabolism and excretion in mice and rats.
Area of Science:
- Pharmacology
- Drug Metabolism and Pharmacokinetics
- Oncology
Background:
- Dihydrofolate reductase (DHFR) is a critical enzyme in folate metabolism, essential for DNA synthesis.
- DHFR inhibitors are established chemotherapeutic agents, but their selective action and metabolic fate require detailed investigation.
- Triazinate (TZT) is a potent DHFR inhibitor selected for comprehensive pharmacokinetic and pharmacodynamic studies.
Purpose of the Study:
- To elucidate the mechanism of selective action of Triazinate (TZT).
- To determine the metabolic fate and pharmacokinetic profile of TZT in various animal models.
- To compare TZT accumulation in different tissues and tumor cells.
Main Methods:
- Administered TZT intravenously to mice, rats, dogs, and monkeys.
- Monitored serum disappearance and tissue distribution of TZT.
- Assessed dihydrofolate reductase activity in various tissues post-administration.
- Analyzed urinary and fecal excretion of TZT.
- Investigated TZT accumulation in cerebrospinal fluid (CSF) and ascites cells.
Main Results:
- TZT exhibited rapid tissue equilibration and slower elimination, with half-lives varying by species (rats: 1.5-2.2 hr; dogs: 3-4 hr; monkeys: 2-4 hr).
- Urinary excretion was low in rodents (5-6%) but high in dogs (60%).
- DHFR activity was nearly undetectable in all tissues within 15 minutes.
- Differential accumulation of TZT was observed in tumor cells (higher in Walker 256 cells than ascites fluid; lower in L1210 cells than ascites fluid).
- TZT achieved approximately 15% of serum concentration in CSF, significantly higher than related triazines.
Conclusions:
- TZT demonstrates rapid and widespread tissue distribution and potent DHFR inhibition across species.
- Species-specific differences in excretion patterns were observed, with dogs showing significantly higher urinary excretion than rodents.
- Tumor cell-specific accumulation varied, suggesting potential for differential efficacy.
- TZT shows promising penetration into the cerebrospinal fluid compared to related compounds.