Interaction of thiazolidinediones (glitazones) with the ATP-binding cassette transporters P-glycoprotein and breast cancer resistance protein.

AIMS: Thiazolidinediones (glitazones) are frequently prescribed antidiabetic drugs commonly used in combination drug regimens. To evaluate the risk of drug-drug interactions, we therefore aimed to systematically investigate the inhibitory and inductive effects of all glitazones on 2 of the most relevant drug transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), in vitro.
METHODS: The inhibition of P-gp and BCRP was assessed by fluorometric assays quantifying the increase in the intracellular concentration of fluorescent P-gp or BCRP substrates caused by their combination with the glitazones. The induction of mRNA expression was quantified by real-time RT-PCR after the treatment of HuH-7 cells with the respective compounds for 4 days.
RESULTS: Rosiglitazone and troglitazone significantly inhibited P-gp and BCRP function and induced mRNA expression of BCRP but not of P-gp. Pioglitazone, which exhibited very low solubility, could only be tested up to 0.5 micromol/l and did not provoke an effect in any of the assays.
CONCLUSIONS: After comparison of the in vitro data and published clinical studies, it seems unlikely that the inhibition of BCRP and P-gp by rosiglitazone plays a role in the clinical situation. In contrast, BCRP induction by rosiglitazone might be of relevance in vivo, but has to be verified in dedicated clinical studies. Copyright 2009 S. Karger AG, Basel.