Washington: Scientists have revealed that a single antibody shrank a variety of human tumours transplanted into laboratory mice, a pioneering research which may someday
pave the way for effective treatments for a number of cancers.
A team at Stanford University School of Medicine says that the antibody works by masking a protein flag on cancer cells that protects them from macrophages and other cells in the immune system.
The scientists achieved the breakthrough with human breast, ovarian, colon, bladder, brain, liver and prostate cancer samples.
"Blocking this `don`t-eat-me` signal inhibits the growth in mice of nearly every human cancer we tested, with minimal toxicity. This shows conclusively that this protein, CD47, is a legitimate and promising target for human cancer therapy," said Prof Irving Weissman, who led the team.
The antibody treatment also significantly inhibited the ability of the tumours to metastasise throughout the animals` bodies, say the scientists.
In their research, the scientists collected surgical samples of a variety of human tumours, including ovarian, breast, colon, bladder, brain, liver and prostate.
They showed that nearly every human cancer cell they examined expressed CD47 -- usually at higher levels than did non-cancerous cells. Furthermore, people whose cancer cells express a lot of CD47 tend to have shorter life spans than people with similar cancers that express less CD47.
This suggests that an analysis of the levels of CD47 expression in some types of tumours could be a valuable prognostic tool for patients and their doctors, according to the scientists.
The scientists then implanted the different human tumour cells into matching locations in the bodies of mice -- breast cancer tumours into the mammary fat pads, and ovarian cancer tumours into the abdomen, for example. Once the tumours were well-established after two weeks or more, they treated the animals with the anti-CD47 antibody.
They found that most of the established tumours begin to shrink and even, in some cases, disappear within weeks of treatment with the antibody. In one case, antibody treatment cured five mice injected with the human breast cancer cells.
When the tumour was gone, the treatment was discontinued; the mice were monitored for four months with no signs of recurrence, the scientists said in a release.
"These results indicate that anti-CD47 antibodies can dramatically inhibit the growth of human solid tumours by blocking the ability of CD47 to transmit the `don`t-eat-me` signal to macrophages," the scientists said.
The findings have been published in the `Proceedings of the National Academy of Sciences` journal.