A simple ex vivo bioassay for 5-FU transport into healthy buccal mucosal cells

A simple ex vivo bioassay for 5-FU transport into healthy buccal mucosal cells:

Abstract

Purpose

Fluorouracil (5-FU), a chemotherapeutic agent widely used in the treatment of numerous common malignancies, causes oral mucositis in a proportion of patients. The contribution of drug transport processes to the development of this toxicity is currently unknown. This work aimed to establish and optimise a simple phenotyping assay for 5-FU uptake into primary buccal mucosal cells (BMC).

Methods

The uptake kinetics of radiolabelled 5-FU were determined in pooled BMC freshly collected from healthy volunteers. The inter- and intra-individual variability in 5-FU uptake was then assessed across a cohort that included both healthy volunteers and cancer patients.

Results

5-FU uptake into pooled primary BMC was both time and concentration dependent. An Eadie–Hofstee analysis suggested two components; a high-affinity (K_M = 3.3 µM) low-capacity (

\(V_{\text{MAX}}\)

 = 57.8 pmol min⁻¹ 10⁵ viable cells⁻¹) transporter, and a high-capacity (

\(V_{\text{MAX}}\)

 = 1230 pmol min⁻¹ 10⁵ viable cells⁻¹) low-affinity (K_M = 3932 µM) transporter. There was 180-fold variation in the rate of 5-FU uptake into BMC (0.10–17.86 pmol min⁻¹ 10⁵ viable cells⁻¹) across the 34 subjects (healthy participants N = 24, cancer patients N = 10). Notably, retesting of a subset of these participants (N = 16) multiple times over a period of up to 140 days demonstrated poor stability of the uptake phenotype within individuals.

Conclusion

The uptake of 5-FU into healthy oral mucosal cells is a highly variable process facilitated by membrane transporters at pharmacologically relevant concentrations. This bioassay is simple, minimally invasive, and suitable for phenotypic analysis of drug transport in healthy primary cells.