# BIOCHEMISTRY OF 5-FLUOROURACIL EFFECTS

> **NIH NIH R01** · UNIVERSITY OF SOUTHERN CALIFORNIA · 1988 · $105,314

## Abstract

High-dose leucovorin addition to fluorouracil (FUra) therapy has
recently been shown to markedly increase response rates in
patients with metastic colorectal adenocarcinoma.  The rationale
for leucovorin addition is increased percentage and duration of
thymidylate synthase (TS) inhibition in tumors by 5-
fluorodeoxyuridylate (FdUMP), by enhanced stabilities in TS
FdUMP-folate ternary complexes.  For greatest effect, leucovorin
must be metabolized to 5,10-methylenetetrahydrofolate
(CH2FH4) and its polyglumates, which are the only folates that
form covalently-bonded ternary complexes.

We have developed and shown the clinical applicability of assays
of parameters related to TS inhibition performed on small biopsies
from over 80 patients receiving FUra.  These assays include free
and total TS levels by (3H) FdUMP ligand-binding and (3H)dUMP
tritium release; levels of FdUMP, total FdUMP-binding folates,
and CH2FH4 levels by use of (3H) FdUMP binding to L. Casei TS;
dUMP by (14C)dTMP synthesis; and levels of FUra incorporated
into RNA by isolation and isotopic derivatization of fluorouridine.
Recently, the clinical feasibility and usefulness of serial biopsies
of tumor after FUra or leucovorin has been demonstrated.

Two groups of patients receiving FUra plus high-dose leucovorin
are proposed for study of correlations between clinical outcome
and these biochemical parameters in biopsies of tumors.  Patients
with locally progressive, surgically incurable breast
adenocarinoma will be treated with weekly FUra plus leucovorin
give i.v. by a bolus schedule.  Patients with metastatic colorectal
adenocarcinoma will receive FUra and leucovorin by prolonged
infusion.  Biopsies of tumor will be obtained on days 1, 15 and 29
of therapy, and at relapse or progression.  Superficial breast
tumors will be sampled by serial biopsy over the period of drug
administration.  Intrahepatic colon tumor will be sampled by
skinny needle aspirate (single time point).  Results of CH2FH4
assays of tumor biopsies will be used as a basis for dose escalation
of leucovorin in all cases, to achieve a proposed effective
concentration of 5 muM.  Additional observations in selected
patients will include plasma pharmacokinetic studies of
leucovorin, 5-methyltetrahydrofolate, FUra, and dihydroFUra;
polyglutamate chain-length determination of folate pools in
tumors; levels of thymidine in large tumor biopsy specimens; and
TS and dihydrofolate reductase gene copy and mRNA levels.
Statistical evaluations will include analysis of variance with
repeated measures, to determine time trends in the biochemical
data and differences between responders and non-responders,
bolus vs infusion schedule, and between groups based on
parameters of TS inhibition.

## Key facts

- **NIH application ID:** 3178848
- **Project number:** 2R01CA039629-04
- **Recipient organization:** UNIVERSITY OF SOUTHERN CALIFORNIA
- **SAM.gov UEI:** G88KLJR3KYT5
- **Principal Investigator:** COLIN PAUL SPEARS
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 1988
- **Award amount:** $105,314
- **Award type:** 2
- **Project period:** 1985-05-01 → 1991-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/3178848

## Citation

> US National Institutes of Health, RePORTER application 3178848, BIOCHEMISTRY OF 5-FLUOROURACIL EFFECTS (2R01CA039629-04). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/3178848. Licensed CC0.

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