NEW YORK, Jan 18 (Reuters Health) -- Metastatic tumors -- tumors that
arise secondary to an original tumor -- form new blood vessels at a very early
stage in mice and rats, when the tumor consists of only 60 to 80 cells,
researchers report.
The finding may lead to new therapies aimed at preventing cancers from
growing or spreading.
New blood vessel formation is known as angiogenesis. "Contrary to previous
reports, we found out that tumor cells can initiate angiogenesis very early,
instead of when they grew to 1 or 2 millimeters, which would contain millions of
cells," Dr. Chuan-Yuan Li told Reuters Health.
"So this means that chemotherapeutic agents, for example, may be able to
access these tumor cells very early on," he added. "Using angiogenesis
inhibitors, you may be able to block tumor growth at very early times."
Li and colleagues at Duke University Medical Center in Durham, North
Carolina, injected 20 to 50 rat or mouse breast cancer cells under the skin of
rats or mice, respectively. The tumor cells had been modified with a gene that
caused the cells to glow green, allowing the researchers to follow the growth of
the tumor at high resolution.
By day 4, cells could be seen proliferating and migrating towards existing
blood vessels. Further signs of angiogenesis were observed by day 6, when the
tumor consisted of only 60 to 80 cells. By day 8, when the tumor consisted of
300 to 400 cells, functional blood vessels containing red blood cells were
observed. The researchers estimated that blood vessels must have started to form
by day 6 or 7, when approximately 100 to 300 cells were present.
In particular, tumor cells divided and migrated towards target blood
vessels and seemed to align themselves along the new vessels, suggesting "active
'cross-talk' during the early stages of tumor growth," according to the authors.
The report is published in the January 19th issue of the Journal of the National
Cancer Institute.
Next, Li's group injected mice with a shortened form of the receptor for
vascular endothelial growth factor. "It basically soaks up a very potent
angiogenesis factor called vascular endothelial growth factor. It binds to the
growth factor, but cannot translate its signal," Li explained.
When injected along with 40 to 50 tumor cells, the protein completely
inhibited tumor growth in 4 of 6 cases, with all tumor cells disappearing within
5 days. In the other 2 cases, tumor growth was either slowed down substantially
or reversed.
Although this research mainly applies to metastatic tumors, Li points out
that metastasis is a major problem in cancer therapy. His group plans to try
other angiogenesis inhibitors, since they think that multiple proteins are
probably involved in angiogenesis.
