Synthesis of folate-conjugated amphiphiles for tumor-targeted drug delivery

Folic acid was derivatized specifically at its γ-carboxyl group to retain its ligand-binding activity to the folate receptor α (FRα) present on HeLa cells. Amphiphilic molecules labeled with folic acid were prepared by conjugation of long-chain primary amines directly or via diamine linkers to the γ-carboxyl group of folic acid. Folic acid amphiphiles labeled with fluorescent 7-amino-4-carbamoylmethylcoumarin (ACC) were also prepared to visualize the uptake of amphiphiles in folate receptor positive cells. The structures of the new compounds were verified by proton NMR and MALDI-TOF mass spectrometry. The amphiphiles form micelles in water. Critical micelle concentrations (CMCs) were determined by the pyrene fluorescence method for folic acid amphiphiles and the rise in capillary height method for the fluorescently labeled amphiphile. The CMCs of the amphiphiles were studied in buffer solution at pH 8 and ranged from 2 to 64 μM. The formation of micelle increased the solubility of paclitaxel, a model lipophilic anticancer compound, by more than 80%. A significant amount of the fluorescently tagged amphiphile was internalized into HeLa cells known to express FRsα when compared with Caco-2 cells that do not express FRα. Therefore, folate-labeled amphiphiles show promise in targeting antitumor agents to FRα-expressing cancer cells.