Now, researchers at the University of Illinois at Chicago have isolated a protein secreted by bacteria that kills cancer cells but appears to have no harmful side effects. Tested in mice injected with human melanomas, the protein shrank the malignancies, but, in contrast with other studies using whole bacteria, caused no deaths or adverse reactions in the laboratory animals.
"Bacterial proteins could well be a new weapon in the war against cancer," said Ananda Chakrabarty, distinguished professor of microbiology and immunology and one of the study's investigators.
Results of the three-year-long study are published in the October 29 issue of the Proceedings of the National Academy of Sciences.
Oddly, the protein the researchers isolated is a well-studied molecule called azurin that is involved in the everyday process cells use to generate energy. This is the first report, however, that azurin is an effective anticancer agent.
The protein was isolated from the growth medium of Pseudomonas aeruginosa, a bacterium that is often resistant to antibiotics and causes serious respiratory infections in people who are particularly susceptible, such as patients with cystic fibrosis or severe burns. The bacterium protects itself from destruction by killing macrophages, the immune system's first line of attack against a foreign body.
In the UIC study, specially-bred immunodeficient mice implanted with human melanoma were treated with half a milligram of azurin daily for 22 days. At the conclusion of the trial, the average size of the tumors in these mice was 60 percent smaller than those in untreated mice. None of the mice showed signs of illness or loss of weight.