Ligand-Mediated Coating of Liposomes with Human Serum Albumin

Coating liposome surfaces with human serum albumin (HSA) can improve the colloidal stability and prevent opsonization. HSA coating via specific binding with alkyl ligands is promising because although the ligand-mediated coating is relatively stable it can spontaneously exchange with fresh HSA. However, to achieve surface coating with HSA, multiple hydrophobic ligands must be exposed to an aqueous medium prior to binding with HSA. This presents a challenge, as hydrophobic ligands tend to be buried in the liposomal membrane. Here we present the first HSA modification of liposome surfaces via alkyl ligands. We found that a relatively short alkyl ligand, or a long alkyl ligand with a terminal carboxylate, could be exposed on the liposome surface without causing aggregation of the liposomes and these ligands could subsequently bind HSA. The resulting HSA-coated liposomes were as inert as conventional PEGylated liposomes in terms of macrophage recognition.

Design of a ligand for cancer imaging with long blood circulation and an enhanced accumulation ability in tumors

The use of imaging agents to visualize tumor cells is an advantageous technique to achieve a more efficient intraoperative diagnosis and effective debulking operations. Targeting of these agents to certain receptors that are overexpressed in cancer cells, such as the folate receptor, aids in tumor targeting. Several imaging probes have been developed using this strategy. However, these ligand-targeting cancer imaging probes are rapidly cleared during systemic delivery due to their small size, which compromises their biodistribution and circulation. Improving the detection of cancer requires higher accumulation and effective retention activities of imaging probes. Here we developed a new design for a folate-fluorophore conjugate that is modified with palmitoyl. Palmitic acid has a strong binding affinity with human serum albumin (HSA), which has the ability to form non-covalent host-guest complexes and has a blood half-life of 19 days. In this strategy, HSA is expected to serve as an endogenous nanocarrier for the designed probe in blood circulation. We hypothesized that via a reversible interaction with HSA, this simple palmitoyl modification on a folate-fluorophore conjugate can induce long blood circulation of the probe. Our folate-targeted probe could show longer blood circulation compared to the probe which lacks palmitoyl.