Dr. Michael Rosenblum, Professor of Medicine at M. D. Anderson Cancer Center and senior author of the study, said tests of Vascular Endothelial Growth Factor121/rGelonin (or VEGF121/rGelonin) in mice demonstrated it could selectively destroy blood vessels supplying human solid tumors without harming the vasculature of normal tissue.

"This is like a 'Trojan horse' approach to kill the blood vessels that supply solid tumors. We're using the vascular endothelial growth factor as a carrier to deliver a toxic agent selectively to the tumor's blood supply -- in effect, starving the tumor," said Dr. Rosenblum.

In the current research, mice were injected with human melanoma and human prostate cancer cells. Tumor growth in mice that received the toxin linked to growth factor was reduced to 16 percent of that observed in untreated mice, said Dr. Philip Thorpe, who directed the tests.

"The anti-tumor effects of the VEGF/rGelonin fusion construct against both melanoma and human prostate cancer in mouse models was impressive in magnitude and prolonged," Dr. Thorpe said. "These studies suggest that VEGF/rGelonin has potential as an anti-tumor agent for treating cancer patients."

A clinical trial to test the new technique in patients is expected to begin within the year at M. D. Anderson, Dr. Rosenblum said.

"The significance of this fusion toxin is that it's not specific to one kind of tumor -- it has impressive anti-tumor effects in various kinds of tumors -- including melanoma and prostate cancers," Dr. Rosenblum said. "We need additional research to determine if it is equally effective in other cancers."

In the mouse study, destruction of the tumor blood vessels was observed as early as 48 hours after administration of the agent. There was no visible damage in any normal organs, including the kidneys, of the treated mice, Dr. Rosenblum said.

"The receptors for vascular endothelial growth factor are overexpressed on the endothelium of tumor vasculature but are almost undetectable in the adjacent normal tissue, so they make excellent targets for the development of therapeutic agents that inhibit tumor growth and metastatic spread by inhibiting the new blood vessel formation," Dr. Rosenblum said.

The researchers chose the genetically engineered toxin gelonin to link to the growth factor carrier because it does not appear to be antigenic in human clinical trials conducted thus far at M. D. Anderson, and it does not cause damage to normal blood vessels as do other toxins that have been explored for use in anti-tumor therapies, Dr. Rosenblum said.