Folate-targeted liposomes for drug delivery

The folate receptor has been identified as a marker for ovarian carcinomas and is also up-regulated in many other types of cancer. Folate- conjugation has been successfully applied in the tumor cell-selective targeting of liposomes. A long polyethyleneglycol (PEG) spacer between the targeting ligand (i.e. folio acid) and the liposome surface is required for receptor recognition. Ligand binding is compatible with the PEG-coating of the liposomes needed for prolonged systemic circulation. Folate-targeted liposomes have been shown to enhance the in vitro cytotoxicity of liposome- entrapped doxorubicin and antisense oligodeoxynucleotides to receptor- bearing tumor cells. Folate, as a targeting ligand, offers unique advantages over immunoliposomes, i.e., easy liposomal incorporation, low cost, high receptor affinity and tumor specificity, extended stability, and potential lack of immunogenicity.