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Posted: December 3, 2007
Antibody targeting boosts liposomal drug anticancer activity
(Nanowerk News) The first drug-loaded nanoparticle approved to treat cancer is in line for an upgrade. Researchers at Northeastern University have improved the tumor-killing activity of liposomal doxorubicin, known as Doxil™, by attaching a monoclonal antibody that recognizes a protein found on the surface of cancer cells. The resulting targeted liposome improves drug uptake by malignant cells and, more importantly, increases the potency of the original liposome by as much as eightfold. This work is reported in the European Journal of Pharmaceutical Sciences ("Enhanced cytotoxicity of monoclonal anticancer antibody 2C5-modified doxorubicin-loaded PEGylated liposomes against various tumor cell lines").
To target liposomal doxorubicin, Vladimir Torchilin, Ph.D., and former graduate student Tamer Elbayoumi, Ph.D., used a monoclonal antibody discovered a decade ago by Torchilin and his colleagues. This antibody binds to a protein found in nucleosomes, a protein-DNA construct that organizes the chromosomes of all multicellular organisms, including humans. In healthy cells, nucleosomes are found only in the cell nucleus, but a broad variety of cancer cells contain a receptor on the cell membrane that recognizes nucleosomes. This particular monoclonal antibody, named mAb 2C5, recognizes and binds to that same receptor, while showing no propensity to bind to healthy cells. Each modified liposome contains approximately 70 to 80 surface-attached monoclonal antibodies.
Tests using a wide range of cultured tumor cells showed that mAb 2C5-targeted liposomal doxorubicin bound avidly to the cells. More importantly, uptake by those cells was rapid, far faster than with untargeted Doxil™ or Doxil™ modified with a control antibody that does not recognize tumor cells. Similarly, the targeted formulation was far more toxic toward all seven tumor cell lines tested, as it was in one preliminary in vivo study using a mouse xenograft model of human cancer. In addition, the investigators found that the targeted formulation, but not plain Doxil™, was also effective at killing a colon cancer cell line that is normally resistant to both Doxil™ and free doxorubicin.