Targeting cancer with cys-diabody conjugated polymerized liposomal nanoparticles (PLNs)

Abstract

Abstract Background: Polymerized liposomal nanoparticles (PLNs) are a promising new technology for delivery of chemotherapeutic drugs to cancer cells. They are easy to prepare, biocompatible, and can carry a wide variety of therapeutics. Additionally, PLNs have the potential to be conjugated to a tumor targeting agent in hopes of delivering a cytotoxic payload directly to the cancer cells, thus minimizing systemic toxicity. Cys-diabodies are the smallest tumor antibody fragment (55 Kd) that retain the bivalency of an intact antibody. The goal of this study was to determine our ability to conjugate various engineered cys-diabody fragments to PLNs and to evaluate the ability to specifically target tumor cells based on the specificity of the diabody-tumor antigen interaction. Methods: Cys-diabody constructs against tumor antigens (ALCAM, HER2/neu, Ca19.9) were engineered, expressed in NSO myeloma cells and purified using HPLC. A cysteine residue was inserted at the C-terminus to provide the free sulhydryl group necessary for the conjugation reaction. Using malemide chemistry, cys-diabodies were conjugated to PLNs. Immunofluorescence and flow cytometry were performed to evaluate targeting of conjugated PLNs to human pancreatic and breast cancer cell lines. Unconjugated PLNs and tumor antigen negative cell lines were used as controls. Results: Anti-HER2/neu, ALCAM, and CA19.9 cys-diabodies were characterized by flow cytometry showing specific binding to MCF7 (HER2/neu positive), HPAF (ALCAM positive), and BxPC3 (CA19.9 positive) cell lines, respectively. No binding was observed to antigen-negative cell lines nor with the unconjugated PLNs. Conjugation of cys-diabodies to PLNs was indicated by immunofluorescence showing specific binding of PLN-cys-diabody conjugates to breast and pancreatic cancer cells in vitro (Figure 1). These data were also confirmed by flow cytometry. Conclusions: We have demonstrated the ability to conjugate our PLN with engineered anti-tumor cys-diabodies. Furthermore, we have demonstrated that after conjugation, the PLNs demonstrate specific tumor-cell targeting based on the specificity of the diabody-tumor antigen affinity. These studies represent an important first step in the development of targeted PLNs with the ultimate goal of delivering high doses of a chemotherapeutic directly to the cancer cells.