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Folinic acid modulation of fluorouracil: tissue kinetics of bolus administration
C P Spears1, B G Gustavsson, R Frösing
1University of Southern California Comprehensive Cancer Center, Los Angeles 90033.
Abstract:
Thymidylate synthase (TS) is the enzyme target of 5-fluorouracil (FUra) that recent laboratory and clinical studies with folinic acid (calcium leucovorin) suggest may mediate important antitumor cytotoxicity. Measurement in carcinoma tissue of parameters related to TS inhibition by 5-fluorodeoxyuridylate (FdUMP), by analogy to hormone receptor analysis, should be useful to determine which patients should receive fluoropyrimidine drug therapy and to evaluate folinic acid requirements. Folinic acid is metabolized to 5,10-methylenetetrahydropteroylglutamine (CH2FH4), which must be present in large excess to effect desired levels of maximal inhibition of TS, by promoting formation and stabilization of TS-FdUMP-CH2FH4 ternary complexes. In patients with metastatic disease, serial biopsies of tumor and normal tissues for studies of pharmacodynamic responses to test-dose FUra or folinic acid are shown to be easily added to routine intraoperative management. A suitable methodologic approach is described and examples given of assays of free TS, FdUMP, dUMP, and CH2FH4 levels after FUra or folinic acid, that may be useful in future studies aimed at improving the cost-effectiveness of FUra-folinic acid combinations.
Insights
Measuring thymidylate synthase (TS) inhibition by 5-fluorouracil (FUra) and folinic acid in tumors can guide patient treatment. This approach helps determine optimal drug therapy and folinic acid needs for better cancer treatment outcomes.
Area of Science:
- Oncology
- Pharmacology
- Biochemistry
Background:
- Thymidylate synthase (TS) is the primary enzyme target for the chemotherapeutic agent 5-fluorouracil (FUra).
- Folinic acid (calcium leucovorin) enhances FUra's antitumor activity by stabilizing the inhibitory complex.
- Measuring TS inhibition parameters could personalize fluoropyrimidine therapy.
Purpose of the Study:
- To evaluate the utility of measuring TS inhibition parameters in carcinoma tissue.
- To determine patient suitability for fluoropyrimidine therapy and assess folinic acid requirements.
- To explore pharmacodynamic monitoring of FUra and folinic acid response.
Main Methods:
- Assays were developed to measure levels of free TS, 5-fluorodeoxyuridylate (FdUMP), dUMP, and 5,10-methylenetetrahydropteroylglutamine (CH2FH4).
- Serial tumor and normal tissue biopsies were analyzed for pharmacodynamic responses to test doses of FUra or folinic acid.
- Methodology was adapted for integration into routine intraoperative management.
Main Results:
- The study describes a methodologic approach for assessing TS inhibition markers.
- Examples of assays for key molecular components are provided.
- Pharmacodynamic monitoring via serial biopsies is feasible in patients with metastatic disease.
Conclusions:
- Measurement of TS inhibition parameters in tumor tissue can guide fluoropyrimidine drug selection.
- Assessing these markers may optimize folinic acid dosage for enhanced efficacy.
- This approach could improve the cost-effectiveness of FUra-folinic acid combination therapies.