Assessing transferrin modification of liposomes by atomic force microscopy and transmission electron microscopy

Site-specific delivery of drugs and therapeutics can significantly reduce drug toxicity and increase the therapeutic effect. Transferrin (Tf) is one suitable ligand to be conjugated to drug delivery systems to achieve site-specific targeting, due to its specific binding to transferrin receptors (TfR), expressed on several cell types of therapeutic interest. TfRs have been reported to be highly expressed on the surfaces of tumour cells and the well-characterised and efficient mechanism of internalisation of Tf has been exploited for the delivery of anticancer drugs, proteins, and therapeutic genes into primarily proliferating malignant cells. Liposomes are effective vehicles for drugs, genes and vaccines and can be easily modified with proteins, antibodies, and other appropriate ligands, resulting in attractive formulations for targeted drug delivery. In this study, we used atomic force microscopy (AFM) and transmission electron microscopy (TEM) to confirm the conjugation of Tf to liposomes by three different coupling methods. In addition, the conventional assays for quantification of protein amount (BCA) and phospholipid content (according to Steward) were performed. AFM and TEM were able to display Tf-molecules on the liposomal surfaces and can be routinely used to obtain additional visual information on the protein-drug carrier conjugation in a fast and reliable manner.