Received for publication April 29, 2008.
Revised September 12, 2008.
Accepted for publication September 16, 2008.

GF120918 as a chemical Abcg2 knockout model to study nitrofurantoin transfer into milk

Abstract

Genetic knockout mice studies suggested ABCG2/Abcg2 translocates nitrofurantoin at the mammary – blood barrier resulting in drug accumulation in milk. The purpose of this study was to establish the role of Abcg2 in nitrofurantoin accumulation in rat milk using GF120918 as a "chemical knockout" equivalent. The inhibitory effect of GF120918 was verified in MDCKII cells stably expressing rat Abcg2 with Hoechst 33342 and nitrofurantoin flux in transwells. Nitrofurantoin was infused (0.5mg/h) in the absence and presence GF120918 (10mg/kg in DMSO) to Sprague Dawley lactating female rats using a balanced crossover design. Administration of GF120918 increased nitrofurantoin concentration in serum (from 443±51 to 650±120ng/ml) and decreased concentration in milk (from 18.1±0.9 to 1.9±1.2ìg/ml), resulting in corresponding mean values for M/S of 41.4±19.1 vs. 3.04±2.27 in the absence and presence of GF120918 (p<0.05), respectively. There was a decrease in systemic clearance with GF120918 (2.8±0.5 L/h/kg) compared to vehicle controls (4.1±0.5L/h/kg; p<0.05). Western blot analysis revealed good expression of Abcg2 and no P-gp expression in mammary gland while immunohistochemistry confirmed the apical expression of Abcg2 in lactating mammary gland epithelia. Nitrofurantoin active transport into rat milk can be inhibited by GF120918 resulting in a 10-fold lower M/S. Although GF120918 inhibits both Abcg2 and P-gp, the high expression of Abcg2 and the absence of detectable P-gp expression in lactating mammary gland validates an important role for Abcg2 in nitrofurantoin accumulation in rat milk. GF120918 is particularly useful as a rat "chemical knockout" model to establish ABCG2’s role in drug transfer into milk during breastfeeding.

Key words: ABC transporters, active transport, drug distribution, pharmacokinetics, toxicokinetics, transporters