ABCC2-Mediated Biliary Transport of 4-Glutathionylcyclophosphamide and Its Contribution to Elimination of 4-Hydroxycyclophosphamide in Rat

Abstract

Hematopoietic stem cell transplantation patients conditioned with cyclophosphamide (CY) and total body irradiation have substantially greater risk of nonrelapse mortality when plasma area under the concentration-time curve (AUC) of O-carboxyethylcyclophosphoramide mustard (CEPM) is high. The discovery was paradoxical because CEPM is a nontoxic elimination route of the protoxic CY metabolite hydroxycyclophosphamide (HCY). CY was administered to Wistar and TRϪ rats (a Wistar strain lacking functional ABCC2) at doses of 100 and 200 mg/kg CY, respectively. After either dose, Wistar rats excreted 4-glutathionylcyclophosphamide (GSCY) abundantly in bile; GSCY was absent from bile of TRϪ rats. Liver AUC GSCY was 2-to 2.5-fold greater in TRϪ than Wistar rats after 100 and 200 mg/kg CY, respectively. Liver AUC HCY was 24 -46% greater in TRϪ rats than in Wistar rats after the respective CY doses. Plasma AUC CEPM of TRϪ rats was approximately twice that of Wistar rats after 100 mg/kg, but did not differ between the two strains after 200 mg/kg. Conversely, plasma AUC HCY was not different after 100 mg/kg CY, but was 40% greater in TRϪ rats after 200 mg/kg. The dose dependence of plasma AUC CEPM and AUC HCY was explained by the concentrations of HCY attained and the in vitro K m of aldehyde dehydrogenase and inhibition of aldehyde dehydrogense in TRϪ rats. We conclude that GSCY is a substrate of ABCC2, and plasma AUC CEPM functions as a reporter of liver exposure to HCY and toxins formed from it when HCY concentration is below the K m of aldehyde dehydrogenase and the activity is not compromised.

Expression of xenobiotic transporters in the human renal proximal tubule cell line RPTEC/TERT1

“…The development of resistances to anti-cancer compounds is also often due to increased expressions of these transporters. Several nephrotoxins are extruded via ABC transporters including, CsA, adefovir, cidofovir, ifosfamide and cisplatin (Foxwell et al, 1989;Imaoka et al, 2007;Miller et al, 2001;Qiu et al, 2004;Reid et al, 2003;Schramm et al, 1995;Schuetz et al, 1999;Takenaka et al, 2007;Tamai and Safa, 1990;Tian et al, 2005;Wijnholds et al, 2000). RPTEC/TERT1 cells exhibited similar transcript levels of P-glycoprotein, MRP2, MRP5 and BCRP as compared to primary hPTs.…”

Resistance to Chemotherapy in Cancer: A Complex and Integrated Cellular Response

“…There have been reports that isoforms of the drug efflux pumps ABC C1 , ABC C2 , ABC C4 and ABC G2 may mediate the efflux of some of these compounds, particularly the GSH conjugates [110,111] . Although the GSH conjugates are inactive, their transport out of tumour cells may alter the dynamic equilibrium between metabolic intermediates of CPA and IFO.…”

Potential Contribution of Cytochrome P450 2B6 to Hepatic 4-Hydroxycyclophosphamide Formation In Vitro and In Vivo

“…The current method of dosing CY based on body surface area or weight leads to considerable interpatient variability in systemic exposure to CY and its metabolites, including 4-hydroxycyclophosphamide (4HCY), the precursor to CY's primary cytotoxic metabolite phosphoramide mustard (de Jonge et al, 2005a;McCune et al, 2009). The precise mechanism of 4HCY intracellular transport has not been evaluated; however, ABCC2 and ABCC4 are involved in the transport of CY and other metabolites (Qiu et al, 2004;Tian et al, 2005). Variability in 4HCY exposure, quantitated as area under the plasma concentration-time curve (AUC), may account for interpatient differences in the efficacy of CY.…”