- Thiopurine metabolism and identification of the thiopurine metabolites transported by MRP4 and MRP5 overexpressed in human embryonic kidney cells. Wielinga, P.R., Reid, G., Challa, E.E., van der Heijden, I., van Deemter, L., de Haas, M., Mol, C., Kuil, A.J., Groeneveld, E., Schuetz, J.D., Brouwer, C., De Abreu, R.A., Wijnholds, J., Beijnen, J.H., Borst, P. Mol. Pharmacol. (2002)