A novel assay for monitoring internalization of nanocarrier coupled antibodies

The specificity of the assay was demonstrated with different antibodies to the ErbB-2 and EGF receptors. Antibody-uptake correlated with receptor expression levels in tumor cell lines with a range of receptor expression. Furthermore, Ni-NTA liposomes containing doxorubicin were used to screen for the ability of antibodies to confer target-specific cytotoxicity. Using an anti-ErbB2 single chain Fv (scFv) (F5) antibody, cytotoxicity could be conferred to ErbB2-overexpressing cells; however, a poly(ethylene glycol)-linked lipid (DSPE-PEG-NTA-Ni) was necessary to allow for efficient loading of the drug and to reduce nonspecific drug leakage during the course of the assay.The CLIA method we describe here represents a rapid, sensitive and robust assay for the identification and characterization of tumor-specific antibodies capable of high drug-delivery efficiency when conjugated to liposomal nanocarriers.Antibodies and antibody fragments can deliver a variety of agents, including drugs, genes, toxins or radioisotopes to target cells expressing the appropriate receptor-antigen. Internalization of the antibody fragment to the interior of the cell can in many cases increase the therapeutic effect of the therapeutic agent [1,2]. A major advantage of receptor mediated internalization as a drug delivery route is that therapeutic agents can be delivered to target cells that specifically overexpress the receptor-antigen and thereby increase efficacy while reducing systemic toxicity. For example, anti-ErbB2 antibodies have been used to target doxorubicin containing liposomes [3,4] or Pseudomonas exotoxin (immunotoxin) into the interior of ErbB2 overexpressing tumor cells [5,6]. A considerable fraction of antibodies generated by immunization do not bind receptors in a manner that triggers internalization [7,8]. Thus, it is desirable to screen for antibodies that can elicit the desired internalization response.The most common method for monitoring internalization of ligands and anti