Fluorouracil combined with the pure (6S)-stereoisomer of folinic acid in high doses for treatment of patients with advanced colorectal carcinoma: a phase I-II study.
BACKGROUND
Potentiation of the antitumor activity of fluorouracil (5-FU) by folinic acid has been demonstrated in patients with colorectal adenocarcinoma. Modulation is due to the interaction of thymidylate synthase, fluorodeoxyuridine monophosphate, and methylene tetrahydrofolate, which leads to the formation of a stable ternary complex with concomitant enzyme inactivation. Folinic acid consists of a mixture of equal parts of two stereoisomers differing in chirality at the C-6 carbon of the pteridine ring. Only the levorotatory (6S)-stereoisomer of folinic acid is transformed into active folate cofactors. However, the (6R)-stereoisomer of folinic acid is not inert; it was shown to interfere with the (6S) form at the cellular level.


OBJECTIVE
The possibility of a deleterious effect of the unnatural stereoisomer on the modulation of 5-FU led us to carry out a phase I-II study of 5-FU combined with the (6S)-stereoisomer of folinic acid given in high doses for treatment of patients with advanced colorectal carcinoma. We also determined the plasma pharmacokinetics of folates after intravenous (IV) injection of (6S)-folinic acid at the dose used in this study.


METHODS
Treatment consisted of 5-FU (350-550 mg/m2 per day by IV infusion for 2 hours) and (6S)-folinic acid (100 mg/m2 per day by IV bolus injection) given for 5 consecutive days; the treatment was repeated every 21 days. Twenty-five patients with advanced colorectal carcinoma, who had had no prior chemotherapy, were evaluated for antitumor activity. The quantity of folates in plasma was measured using a microbiological assay.


RESULTS
The median follow-up time was 9 months (range, 3.5-15.2 months). The response rate was 52% (complete response, 12%; partial response, 40%). The median time to disease progression for responding patients was 9.2 months (range, 5.9-15+ months). The estimated probability of survival at 12 months was 73%. Palliative improvement in quality of life was achieved in most patients who had symptoms due to the tumor before the start of treatment. The dose-limiting toxic effects were grade 3 diarrhea, dermatitis, and oral mucositis. Grade 4 toxicity did not occur. Myeloid toxicity was minor. After IV injection, (6S)-folinic acid was rapidly cleared from plasma (mean half-lives: alpha = 7.2 minutes and beta = 126 minutes). The mean concentration of the unchanged compound 2 hours after injection was 5.8 mumol/L.


CONCLUSIONS
The (6S)-form of folinic acid potentiates the antitumor effect of 5-FU given concomitantly.


CONCLUSIONS
Our results justify a more complete exploration of the pure active stereoisomer as a modulator of the fluoropyrimidines.
Machover
D
D
Grison
X
X
Goldschmidt
E
E
Zittoun
J
J
Lotz
J P
JP
Metzger
G
G
Richaud
J
J
Hannoun
L
L
Marquet
J
J
Guillot
T
T
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000009:adverse effects / Q000627:therapeutic use*; D015179:Colorectal Neoplasms / Q000188:drug therapy*; D004334:Drug Administration Schedule; D004341:Drug Evaluation; D004357:Drug Synergism; D005260:Female; D005472:Fluorouracil / Q000008:administration & dosage; D006801:Humans; D002955:Leucovorin / Q000008:administration & dosage / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D013237:Stereoisomerism; D016019:Survival Analysis; D016896:Treatment Outcome
D002955:Leucovorin; D005472:Fluorouracil