By Dean A. Haycock

Special To BioWorld Today

Cut the enemy's supply lines.

It is a basic strategy in war, whether the enemy is a soldier in an invading army or a cancer cell in a growing tumor.

If, however, the enemy receives its essential supplies from an intricate network of blood vessels, as malignant tumors do, the task of severing the supply lines is much trickier than bombing rail lines or capturing bridges. It requires significantly more finesse.

A report in today's issue of Nature Medicine by Yiping Wang, a postdoctoral fellow, and Dorothea Becker, associate professor of pathology at the University of Pittsburgh School of Medicine, Cancer Institute, in Pittsburgh, Pa., suggests that antisense technology may provide that finesse.

The strategy behind antisense-based therapy can be traced directly to the old central dogma of molecular biology: DNA leads to RNA leads to protein. Antisense technology cuts this flow of information. One antisense approach targets information transfer from DNA to RNA. It does it by using a short stretch of nucleic acid (an oligonucleotide) that is complementary to the DNA molecule. This antisense molecule probe binds to DNA. The result: whatever protein blueprint the DNA encodes is not passed on to messenger RNA (mRNA), a single-stranded nucleic acid intermediate that carries genetic information from DNA to ribosomes, where it is translated into a protein.

In a successful antisense experiment, mRNA and protein levels are down-regulated. (An alternative antisense approach cuts the pathway between mRNA and protein.) This strategy could be applicable to many diseases, including heart disease and cancer. In their article, "Antisense targeting of basic fibroblast growth factor and fibroblast growth factor-1 in human melanoma blocks intratumoral angiogenesis and tumor growth," Wang and Becker describe the promising results they obtained using an antisense strategy against melanoma cells.

Like other cancer cells, melanoma cells depend on proteins called growth factors. Melanoma cells overexpress basic fibroblast growth factor (bFGF). While their normal counterparts, melanocytes, can only grow in cell cultures if bFGF is added to the culture media, melanoma cells can thrive without similar help; they make enough bFGF on their own.

This growth factor promotes the growth of new blood vessels, angiogenesis, which tumors need to thrive. Melanoma cells also overexpress mRNA for one of the receptors for bFGF (FGFR-1). It is here that antisense weapons make the supply lines vulnerable to attack.

Both Methods Worked In Liposomal Delivery

To target this potential weak spot, the authors prepared two varieties of antisense molecules. One blocked DNA carrying the code for bFGF and the other did the same for the receptor, FGFR-1.

"The key molecule is the receptor. It is sort of the gatekeeper. There are other ligands that can bind and signal transduce via the receptor. Initially we thought it may be more effective than just going after the ligand [bFGF]. As it turns out, targeting bFGF and FGFR-1 individually is as effective as targeting them simultaneously," Becker told BioWorld Today.

They delivered the antisense-oriented vectors using liposomes, packages made of fat that can deliver products through cell membranes. The same technique is used to transfer genes into cells.

Leaf Huang, professor of pharmacology at the University of Pittsburgh, developed the liposome delivery system used by Wang and Becker. He is impressed with what they did with them.

"It is a very significant study. It is the first time someone has shown that by down-regulating the FGF receptor, one can actually arrest the angiogenesis of the tumor and cause the tumor to regress," Huang said.

The liposomes filled with antisense vector construct were injected into human melanoma tumors growing under the skin of mice. The researchers demonstrated that this treatment halted growth of melanoma tumors and even caused some to shrink.

This strategy eventually may provide a new way to treat patients with advanced-stage melanoma. This would be a welcome development, since melanoma is predicted to occur in one of every 75 persons by the year 2000. Early diagnosis and surgical removal of the primary tumor cures many cases. If the cancer spreads, however, the cure rate drops dramatically. Because metastatic melanoma does not respond to conventional cancer treatments, chemotherapy and radiation, the search for effective treatments has largely concentrated on immunotherapy. The antisense approach described by Wang and Becker offers a promising new angle of attack.

Becker's next priority is to see if the treatment works systemically.

"The danger with this disease is the metastatic growth phase. It kills patients very rapidly. What we need to see is if this will be applicable to metastatic disease. Obviously, there you can only take a systemic approach," Becker said.

The authors suggest that perhaps, in combination with other inhibitors of angiogenesis, this antisense approach might be developed into a useful therapy for patients who are at risk of either a recurrence of a melanoma that has been surgically removed or of metastatic cancer. *