The immune system recognizes and attacks foreign cells, such as bacteria, that might harm our body. In order for cancer to develop and grow, tumor cells must hide from killer immune system cells.
A particular protein on the surface of healthy cells, CD47, tells the immune system not to eat the healthy cells. Recently, a preliminary laboratory study found that CD47 was also present in seven types of solid tumors and at higher levels than on normal cells. The researchers hypothesized that CD47 made it possible for tumor cells to evade the immune system, and tested an experimental drug called anti-CD47.
Anti-CD47 is an antibody, which is a protein that is part of the immune system and helps destroy harmful invaders. In test tube studies and experiments with mice, anti-CD47 shrank tumors and helped to prevent them from spreading.
This is not the first study of CD47. In 2004, researchers looked at whether a CD47 agonist (a chemical that binds to a receptor of a cell and triggers a response) might render breast cancer cells susceptible to death. They found that it induced death of four different types of breast tumor cells.
In 2009, scientists tested CD47 in cancers that had metastasized to patients' bones. These metastasized tumors are extremely painful and a significant cause of illness and death in cancer patients. In a study with mice, researchers found that manipulating the CD47 communication process (which controls cell activity) might help treat bone metastases without causing severe complications to the skeleton as traditional treatments for bone cancers do.
Anti-CD47 drugs may also someday provide the basis of treatment for human acute myeloid leukemia (AML). In patients with AML, CD47 seems to provide a survival advantage to leukemia stem cells, which give rise to new cancer cells.
These are not the first or the only studies on proteins and their role in cancer treatment. In 1967, for example, Stanislaw R. Burzynski, M.D., PhD identified naturally occurring peptides that control cancer growth. Proteins and peptides are formed by joining amino acids. Proteins have more than 50 molecules and peptides have fewer than 50. Unlike CD47, which cancer patients tend to have more of, Dr. Burzynski found that cancer patients are typically deficient in these peptides.
The studies of CD47 and cancer are still very preliminary and potential new drugs are not yet in clinical trials with humans. Before clinical trials begin, researchers must determine that a CD47 treatment would be not be toxic in humans.
Sources:
PubMed Health. "New 'multi-cancer drug' still some way off." Web. 27 Mar 2012. http://www.ncbi.nlm.nih.gov/pubmedhealth/behindtheheadlines/news/2012-03-27-new-multi-cancer-drug-still-some-way-off/
Majeti, Ravindra, Chao, Mark P., Alizadeh, Ash A., Pang, Wendy W., Jaiswal, Siddhartha, Gibbs, Kenneth D., Jr., van Rooijen, Nico, and Weissman, Irving L. "CD47 Is an Adverse Prognostic Factor and Therapeutic Antibody Target on Human Acute Myeloid Leukemia Stem Cells." Cell 138 (2009): 286-299. Web. 24 July 2009.
http://www.cell.com/abstract/S0092-8674(09)00650-3
Manna, Partha Pratim, and Frazier, William A. "CD47 Mediates Killing of Breast Tumor Cells via Gi-Dependent Inhibition of Protein Kinase A." Cancer Research 64 (2004): 1026. Web. 1 February 2004.
http://cancerres.aacrjournals.org/content/64/3/1026.full
Uluçkan, Özge Becker, Stephanie N., Deng, Hongju, Zou, Wei, Prior, Julie L., Piwnica-Worms, David, Frazier, William A., and Weilbaecher, Katherine N. "CD47 Regulates Bone Mass and Tumor Metastasis to Bone." Cancer Research 69 (2009): 3196. Web. 10 March 10, 2009. http://cancerres.aacrjournals.org/content/69/7/3196.full
Loza Coll, Mariano Loza. "Please do not eat the stem cells." Nature Reports Stem Cells. Web. 27 August 2009.
http://www.nature.com/stemcells/2009/0908/090827/full/stemcells.2009.116.html
Burzynski Clinic. "What are Antineoplastons?" Web.
http://www.burzynskiclinic.com/what-are-antineoplastons.html
