Effect of verapamil on daunorubicin accumulation in lymphocytes isolated from patients undergoing chemotherapy

Efflux of Rhodamine From CD56+ Cells as a Surrogate Marker for Reversal of P-Glycoprotein–Mediated Drug Efflux by PSC 833

The expression of high levels of P-glycoprotein (Pgp) in circulating mononuclear cells allowed us to use an ex vivo assay as a surrogate measure of Pgp antagonism. Efflux of rhodamine from CD56+cells was measured before the start of PSC 833 and at varying times thereafter. Patients receiving PSC 833 had decreased rhodamine efflux from their circulating CD56+ cells. Time course studies showed that following a single oral dose of PSC 833, decreased rhodamine efflux was found in some patients within 15 minutes of treatment. Maximal inhibition was observed at times ranging from 45 minutes to 60 minutes. A dose-response relationship was shown between the concentration of PSC 833 in the blood and the inhibition of rhodamine efflux, with an apparent plateau of the inhibition of rhodamine efflux at approximately 1,000 ng/mL. The Ki, defined as the concentration required for half-maximal inhibition of Pgp-mediated rhodamine efflux, was determined to be in the range of 29 to 181 ng/mL; although results in two patients were distinctly different, with Ki values of 914 and 916 ng/mL. MRK-16 staining was similar among all patients. We conclude that measurement of rhodamine efflux from CD56+ cells provides a surrogate assay with the potential for monitoring Pgp antagonism in clinical trials.

Efflux of Rhodamine From CD56+ Cells as a Surrogate Marker for Reversal of P-Glycoprotein–Mediated Drug Efflux by PSC 833

The expression of high levels of P-glycoprotein (Pgp) in circulating mononuclear cells allowed us to use an ex vivo assay as a surrogate measure of Pgp antagonism. Efflux of rhodamine from CD56+cells was measured before the start of PSC 833 and at varying times thereafter. Patients receiving PSC 833 had decreased rhodamine efflux from their circulating CD56+ cells. Time course studies showed that following a single oral dose of PSC 833, decreased rhodamine efflux was found in some patients within 15 minutes of treatment. Maximal inhibition was observed at times ranging from 45 minutes to 60 minutes. A dose-response relationship was shown between the concentration of PSC 833 in the blood and the inhibition of rhodamine efflux, with an apparent plateau of the inhibition of rhodamine efflux at approximately 1,000 ng/mL. The Ki, defined as the concentration required for half-maximal inhibition of Pgp-mediated rhodamine efflux, was determined to be in the range of 29 to 181 ng/mL; although results in two patients were distinctly different, with Ki values of 914 and 916 ng/mL. MRK-16 staining was similar among all patients. We conclude that measurement of rhodamine efflux from CD56+ cells provides a surrogate assay with the potential for monitoring Pgp antagonism in clinical trials.

Doxorubicin induced expression of P-glycoprotein in a canine osteosarcoma cell line

Canine and human osteosarcoma are very similar with respect to clinical presentation, radiological and histopathological features, metastatic rate and pattern and response to therapy. For these reasons, canine osteosarcoma is a useful intermediate model for the disease in humans. Overexpression of P-glycoprotein, the product of the MDR1 gene, is the most important predictor of an adverse clinical course in human patients with osteosarcoma. Exposure of canine osteosarcoma cells to doxorubicin resulted in overexpression of MDR1 mRNA and P-glycoprotein. Furthermore, these cells failed to accumulate doxorubicin intracellularly and were less sensitive to vincristine-induced cytotoxicity as compared to parental cells.

[Colchicine: recent data on pharmacokinetics and clinical pharmacology]

Colchicine is widely used in the treatment of acute goutty arthritis. Recently, colchicine was shown to be effective in inflammatory diseases such as familial Mediterranean fever. Two proteins can modulate its pharmacokinetics: tubulin, the specific intracellular receptor for colchicine which determines the plasma half-life, and P-glycoprotein, an active efflux pump towards some anticancer drugs which regulates colchicine absorption, distribution, and elimination. Therapeutic dosage is monitored empirically, by the control of the balance between the occurrence of side effects and the clinical efficacy. Recently, using a specific and sensitive radioimmunoassay, the investigation of plasma concentrations during single and multiple dose studies has allowed to define the colchicine pharmacokinetic parameters. Following oral route, colchicine bioavailability is extremely variable (from 24 to 88% of the administered dose), the distribution volume is elevated (7 l/kg) but the binding to albumin is moderate. Colchicine elimination occurred mainly via hepatic pathways and the elimination half-life ranged from 20 to 40 hours. In multiple dose study (1 mg/d), the steady-state is reached 8 days after the first oral administration and plasma concentrations ranged from 0.3 to 2.5 ng/ml. Pharmacokinetic/pharmacodynamic studies show that the biological effects of colchicine were not related to plasma concentrations but with intraleukocyte concentrations. Drug interactions may occur when colchicine is associated to drugs which interact with cytochrome P450 and/or P-glycoprotein and modify renal and/or hepatic clearances. The therapeutic drug monitoring of colchicine during these circumstances could allow to prevent the observation of side effects.