Interferon-gamma pharmacokinetics and pharmacodynamics in patients with colorectal cancer

The study objectives were to define subcutaneous (s.c.) interferon gamma (IFN-gamma) disposition in patients with gastrointestinal malignancies receiving 5-fluorouracil (5-FU) and leucovorin (LV) and to examine the relationship between IFN-gamma exposures and Fas upregulation in vivo and in vitro.

Patients received IFN-gamma (10, 25, 50, 75, and 100 microg/m(2)) with LV and 5-FU, and serial samples were collected after the first dose. IFN-gamma concentrations were measured by ELISA. A linear one-compartment model with a lag was fitted to the IFN-gamma plasma concentration-time data. To examine the relationship between IFN-gamma systemic exposure and biological activity in vivo, cell surface Fas upregulation was assessed in peripheral blood mononuclear cell (PBMC) subcompartments.

The median (range) apparent IFN-gamma clearance was 46 l/m(2) per hour (2.6-92 l/m(2) per hour). With increasing IFN-gamma dosages, the area under the concentration-time curve (AUC(0--> infinity )) and C(max) increased; however, significant interpatient variability was observed. IFN-gamma AUC(0--> infinity ) and time above 33.3 pg/ml significantly correlated with Fas upregulation in several PBMC compartments, but dosage was significantly correlated with this pharmacodynamic marker only in CD4(+) and CD56(+) cells. In vitro studies in HT29 cells demonstrated that clinically relevant IFN-gamma concentrations (1 to 10 U/ml for 6.5 h) with 5-FU/LV upregulated Fas expression 3.5-fold, similar to that in PBMC in vivo.

We characterized IFN-gamma disposition and developed a limited sampling model for use in future pharmacokinetic studies. Our results showed that IFN-gamma upregulates Fas in PBMC in vivo and in HT29 cells in vitro at tolerable, clinically relevant exposures and that monitoring IFN-gamma pharmacokinetics/pharmacodynamics may be warranted in IFN-gamma clinical use.