New imaging Modality for Early Detection of Breast Cancer

Institution: University of California, Los Angeles
Investigator(s): William Pardridge, M.D. -
Award Cycle: 1997 (Cycle III) Grant #: 3IB-0006 Award: $149,500
Award Type: IDEA
Research Priorities
Detection, Prognosis and Treatment>Imaging, Biomarkers, and Molecular Pathology: improving detection and diagnosis

Initial Award Abstract (1997)
This work is aimed at developing a non-invasive diagnostic test that would allow for the early detection of breast cancer. This new approach will merge three methodologies in the biological sciences: tumor-specific proteins called monoclonal antibodies; x-ray imaging of these antibodies, which are tagged with radioactivity; and a chemical modification of the antibody, called "cationization", which gives the antibody electric charge. The novel feature of the proposed work is the use of "charged" antibodies as imaging probes for human breast cancer. The original promise of monoclonal antibodies as "magic bullets" has not been realized for a variety of reasons. However, a significant factor is the lack of access of the monoclonal antibody in the blood to the tumor antigen buried within the breast tumor. This lack of access is due to the fact that antibody proteins are too large in size to escape the blood circulation and do not effectively enter into the cancerous tissue from the blood.

The present application will use a new antibody delivery technology that allows circulating antibodies to rapidly escape from blood to enter the tumor issue. A specific antibody will be used in these studies, and this antibody targets a specific protein that is produced by many breast cancers. After the "cationization" modification of the antibody, it will be tagged with radioactivity. The tumor uptake of the antibody can then be detected by technologies available in standard x-ray clinics, such as single photon emission computed tomography (SPECT).

The present studies will use human breast cancer cells and these cells will be transplanted into experimental animals. The experimental tumors will then be imaged with the new antibody delivery technology. The ability of this technology to detect human breast cancer at the very early stage will be examined and it is hoped that the use of this antibody delivery technology will create a significant advance in the detection of human breast cancer. If these studies give positive results, then an entirely new approach to early detection of breast cancer will have been developed.

Final Report (2000)
Monoclonal antibodies (MAb) are potential new therapeutics that could be used as "antibody radiopharmaceuticals" to target tumor-specific proteins (monoclonal antibodies) expressed selectively on breast cancer cells. However the simple merger of monoclonal antibody technology and radiographic imaging technology may not be sufficient to enable imaging of human breast cancer with antibody radiopharmaceuticals. This is because the delivery of the circulating antibody radiopharmaceuticals to the breast cancer cell expressing the tumor-specific protein is greatly impeded by the capillary wall of the vessels within the tumor and these capillary walls form a blood-tumor barrier (BTB) in the body.

In order to get around the BTB problem, it is necessary to merge monoclonal antibody technology, nuclear medicine technology, and drug targeting technology. The latter technology enables enhanced delivery of the antibody radiopharmaceutical across the BTB. The targeting technology used in the present studies is the "cationization" technology, whereby the surface of the monoclonal antibody is altered to give the protein an excessive positive charge. This positive charge triggers transport of the antibody radiopharmaceutical across the BTB. Human breast cancer cells overexpress the HER2 protein, and originally a monoclonal antibody to HER2 was to be used in these studies. However, the commercial supplier refused to provide the MAb. Accordingly, a HER2-receptor related receptor, the epidermal factor receptor (EGFR) was selected as a new breast cancer selective target. The 528-MAb hybridoma was obtained and the 528-MAb was produced in large quantities in tissue culture laboratory. The 528-MAb was then modified using the cationization technology, and the neutral or the charged 528-MAb were both tagged with a special kind of radioactivity, called 111-indium. A human cancer line, the U87 line that overexpresses the EGFR, was obtained and grown in the tissue culture laboratory. The U87 cells were grown as experimental tumors in the sides of nude mice, and after the tumors reached a certain volume, the tumor bearing mice were injected with either neutral or the charged 528-MAb that was radiolabeled with 111-Indium. The uptake by the experimental human cancer of the native or cationized 528-MAb was determined with an external detection gamma counter, which is commonly used in clinical nuclear medicine laboratories. These studies show that the experimental cancer could be imaged with either the neutral or the charged 528-MAb. The charged form of the MAb did not give an enhanced tumor image. The reason for this was subsequently traced to a problem related to binding of the charged MAb by components in the blood. The blood inhibition problem has been reported previously and is a problem that varies from MAb to MAb. The 528 MAb is adversely affected by the blood inhibition phenomenon.

In conclusion, these studies demonstrate it is highly feasible to prepare charged antibody radiopharmaceuticals, and these molecules have much higher rates of transport across the BTB than do the neutral antibody radiopharmaceuticals. In future studies of the ‘cationized’ or charged antibody technology, early detection of blood inhibition phenomenon must be performed as this can limit the efficacy of charged antibody radiopharmaceuticals. Different antibodies must be screened to find a breast cancer specific antibody that is not inhibited by binding to blood proteins. Such an antibody, in its charged state, would be a promising new approach to imaging and early detection of breast cancer.

Enhanced endocytosis in cultured human breast carcinoma cells and in vivo biodistribution in rats of a humanized monoclonal antibody after cationization of the protein.
Periodical:Journal of Pharmacology and Experimental Therapeutics
Index Medicus: J Pharmacol Exp Ther
Authors: Pardridge WM, Buciak J, Yang J, Wu D
Yr: 1998 Vol: 286 Nbr: 1 Abs: Pg:548-54