Natural killer cell cytotoxicity is not regulated by folic acid in vitro.

OBJECTIVES: Folate supplementation may be associated with an increased risk of developing several types of cancer and a derangement of immune function. Among the latter, Natural killer (NK) cells are involved in non-MHC-restricted natural immunity against malignant target cells. Abnormalities in NK cell number or function have been associated with a higher cancer risk. The aim of this study was to study in vitro the possible effect of different concentrations of 5-methyltetrahydrofolic acid (5-MTHF) or folic acid on NK cell cytotoxic function, and expression of the stimulatory and inhibitory receptors KIRDL4, KIRDL3, and NKG2D. METHODS: Volunteer-derived peripheral mononuclear cells (PBMC) and highly enriched NK cells (95% CD56+ CD16+) were grown in folic acid free-RPMI 1640, supplemented either with folic acid or 5-MTHF (15-100 nM) during 72 h to 96 h. RESULTS: No differences in the cytolytic activity of PBMC and enriched NK cells were observed. After 96 h of in vitro culture without folate or supplemented with FA or 5-MTHF (30 or 100 nM), there were no changes in the percentage of HPNK receptor-positive cells. CONCLUSIONS: Our data indicate that a high dose of 5-MTHF or folic acid does not influence NK cell function in vitro.

A sensitive and specific radioimmunoassay for LY309887, a potent inhibitor of glycinamide ribonucleotide formyltransferase.

LY309887, a reduced analogue of folic acid, is a potent inhibitor of glycinamide ribonucleotide formyltransferase and possesses a broad spectrum of antitumor activity. During preclinical studies using supplementation with oral folic acid, this second-generation inhibitor displayed both the desired safety profile and the pharmacology to warrant clinical investigation. A sensitive analytical method was needed to assess the pharmacokinetics of LY309887 due to the low doses planned for Phase I studies and the potential for low concentrations in plasma long after i.v. administration. We therefore undertook the development of a competitive RIA. A highly specific antiserum was raised in rabbits following immunization with LY309887 coupled to BSA. A RIA tracer was prepared by radioiodination of compound 389753, the adduct of LY309887 with p-tyramine. We developed a competitive-binding RIA procedure and used superparamagnetic particles coated with goat antirabbit IgG as a method for separating the bound and free forms of LY309887. The RIA is sensitive (0.5 ng/ml in serum and 25 ng/ml in urine), specific (negligible interference from endogenous folates), and reproducible (interassay coefficients of variation ranging from 8.1 to 15.4% and 7.6 to 8.3% for serum and urine controls, respectively). We used the RIA to assess the i.v. pharmacokinetics of LY309887 in both patients with metastatic cancer and dogs. The sensitivity of the RIA permitted the demonstration that serum concentrations of LY309887 decline in a multiexponential manner with a prolonged terminal elimination phase. We conclude that the RIA is a valid method for quantifying LY309887 in biological fluids.