by Dawn Brazell
Public Relations

Talk about a protein shake.

Researcher Philip H. Howe, Ph.D., points to a blender full of a protein-rich shrimp mix that he feeds his zebrafish. These rock stars of research are upstaging more traditional animal models that have been used. He keeps them healthy and well, given how they can advance cancer treatment, particularly in discovering how metastatic cancer progresses in humans.

Howe, who holds the Hans and Helen Koebig Chair for Clinical Oncology, said they are ideal for researchers studying the process of metastasis, especially since zebrafish embryos are completely transparent, making them ideally suited for studying developmental processes as they occur.

Dr. Philip H. Howe conducts zebrafish research in his laboratory in the Hollings Cancer Center.

The highly fertile fish, which even have their own website called the Zebrafish Information Network or ZFIN for short (http://zfin.org/), live about two years, with a pair of fish producing about 300 embryos in one week. The fish become full-grown in two days. A mouse, in comparison, would take 21 days.

Certain cancer cells are more aggressive in proliferating, similar to what happens in the embryonic development process when cells differentiate to form the tissue and organs of the body, he said. "Ninety percent of all cancer deaths are caused by the metastatic phase of the disease, where cells escape from the primary tumor and establish secondary tumors at multiple sites and organs. Our research is focused on the process of metastasis."
Most anti-cancer drugs take advantage of how cancer cells grow faster than normal cells, targeting the mechanism behind these proliferating cells. The modern view of cancer in the past 10 to 15 years is that it's an inappropriate reactivation of the normal, developmental processes, he said.

"Sometimes the cell forgets it's old and is supposed to be specialized, and it reverts back to this embryonic stage. Tumors can be viewed as corrupt forms of normal developmental processes. Most of the time the culprit genes and proteins that are implicated in these cancers also are found to be important during development."

Beyond the rapid embryonic growth and transparent eggs that make them popular research subjects, there also are economic benefits.

"It's much cheaper. This is a tenth of the cost of a mouse model. If you find something here, the next phase would be to go to a mouse model where you would validate your target."

As with the mouse model, the zebrafish genome has been sequenced. The vertebrate species has been found to develop almost any tumor type found in humans. It's another reason he got involved with zebrafish research about five years ago.

"It allows you to look at the pathways more specifically than the mouse model because of the transparency and because you can directly manipulate the fertilized egg. If you manipulate a fertilized egg with a mouse, then you have to re-implant it into the female. With zebrafish, it's all done externally."

Researchers can take eggs at the one-cell stage right after fertilization, and inject genes, knockout genes or over-expressed genes, and look at the effect of that on the development of the fish. "It's a really good model to study developmental processes and take what we learn and go back to cancer lines to analyze if those have become reactivated in certain cancers or not."

Another advantage to zebrafish research is that the eggs are permeable, allowing for large-scale drug screens. "You can breed animals so that they develop melanomas, for example. Then you can screen small molecule compounds or plant extracts or drug extracts to try to find out which ones might be beneficial. It allows for rapid, large-scale screening for a permeable drug or small-molecule compounds."

Given that researchers with the National Institutes of Health and chemical companies are going worldwide to isolate compounds from everything from exotic tree bark to sea bacteria, zebrafish offer a way to rapidly screen the libraries of chemical compounds being collected, which is exciting, he said.

Researchers inject embryos at the single cell stage, right after they are fertilized. Howe said timing is critical. They have to collect the eggs and microinject them within 15 minutes given the rate of embryonic growth of zebrafish.

An area of success in Howe's lab is in the study of a signaling pathway called the Wnt pathway, which is found to be abnormal in breast cancer, colon and a variety of hematological tumors. They have found the Wnt pathway regulates the growth of the last portion of the tail in the zebrafish, with researchers isolating a protein that blocks the pathway. "If we knock out the receptor that is responsible for this development, we can get a phenotype where we get no tail. We can rescue that phenotype with a human version of the protein that's not targeted by our protein."

Other exciting research, although it didn't involve zebrafish, is that his lab was the first to show results in 2010-2011 about TGF beta and how it can induce metastasis through a translational mechanism, RNA to protein, and not transcriptional from DNA to RNA. "This is a paradigm-shifting model," he said about one of his accomplishments. Other laboratories worldwide now also are working on this research area.

Howe, who is associate director of basic science for the Hollings Cancer Center, holds a number of prestigious grants from the National Cancer Institute and has been continually funded for 20 years. His hope is that research in his lab will help lead to promising cancer treatments.

Thinking back to when his interest in basic science began, Howe said his father isn't surprised about the work he's doing.

"They would give me toys, and I'd break them apart to see how they would work. We're breaking down cells using zebrafish to see how they work. There's a beauty in seeing how this stuff works. This can lead to all kinds of discoveries."