The use of Tris-lipidation to modify drug cytotoxicity in multidrug resistant cells expressing P-glycoprotein or MRP1.

1. Increasing the lipophilicity is a strategy often used to improve a compound's cellular uptake and retention but this may also convert it into a substrate for an ATP-dependent transporter such as P-glycoprotein or the multidrug resistance-associated protein (MRP1), which are involved in cellular efflux of drugs. Tris-Lipidation of compounds is a convenient way of modifying drug lipophilicity and generating an array of derivatives with diverse properties. 2. To determine the effect of Tris-Lipidation on a drug's cytoxicity in multidrug resistant cells, various glycyl-Tris-mono- (GTP1), di- (GTP2) and tri-palmitate (GTP3) derivatives were prepared of the cancer chemotherapeutic drugs chlorambucil and methotrexate, and of the anti-HIV drug AZT. The cytotoxicity of these derivatives and their parent compounds was determined in the CEM/VLB(100) cells with increased P-glycoprotein expression, the CEM/E1000 cells that overexpress MRP1 and the parent, drug-sensitive CCRF-CEM cells. 3. Increasing the lipophilicity of AZT increased its cytotoxicity in the sensitive CCRF-CEM parental cell line while decreased cytotoxicity was observed for the methotrexate derivatives. For the chlorambucil derivatives, both increased (GTP1) and decreased (GTP2) cytotoxicity occurred in the CCRF-CEM cells. With the exception of AZT-GTP1, all GTP1 and GTP2 derivatives of chlorambucil, methotrexate and AZT had decreased cytotoxicity in the P-glycoprotein-expressing CEM/VLB(100) cells while chlorambucil-GTP1, methotrexate-GTP2 and methotrexate-GTP3 were the only compounds with decreased cytotoxicity in the MRP1-overexpressing CEM/E1000 cells. 4. The number of palmitate residues, the position of derivatisation and the type of linkage all may affect the P-glycoprotein and MRP1 substrate properties. 5. Tris-Lipidation may therefore provide a useful way of manipulating the pharmacokinetic properties of drugs.