Scientists study zebrafish in search of melanoma-fighting drugs

Melanoma is the most lethal type of skin cancer and unusually common in Arizona, where residents are exposed to higher-than-average amounts of ultraviolet radiation. However, Northern Arizona University scientists believe the formula for a combination of melanoma-fighting drugs is within reach.

Matthew Salanga, an assistant professor in NAU’s Department of Biological Sciences, is leading an 18-month project funded through a Flinn Foundation grant of $100,000. His team, which includes experts in experimental biology, computational systems biology and translational medicine, will study melanoma tumors on zebrafish, a small minnow-sized fish that has 70 percent of the same genes that are found in humans. Physiologically, zebrafish also have pigment cells in their skin, called melanocytes, which give them their stripes and their name. In humans, these cells are responsible for creating a tan when exposed to the sun, and if dysregulated can give rise to melanoma.

The majority of melanoma skin cancers are the result of a specific mutation in the BRAF gene (BRAF V600E). BRAF is a type of enzyme known as a protein kinase that adds a phosphate group to other proteins in cell signaling pathways. For this project, zebrafish that express the human form of mutated BRAF are employed to test strategies for treating melanoma.

“Fish don’t often get cancer,” said Salanga, an expert in cell and developmental biology, “but in the lab, we can engineer fish to contain human genes that we know are associated with cancer. Essentially, it’s a way to use non-human vertebrates as though they were human. We call this humanization.”

Currently there are around 30 zebrafish carrying the BRAF V600E human oncogene in Salanga’s lab that have visible melanoma tumors, and that number will grow as the study progresses. Activated BRAF acts to promote cell growth and proliferation. Salanga explains that the V600E mutation of BRAF leaves it stuck in the “on” position. This can result in unrestricted cell growth and proliferation. Drugs have been developed that specifically target and suppress tumor cells that have aberrant BRAF kinase activity. These drugs are in a class of drug called protein kinase inhibitors (PKIs), and are currently used clinically. However, not all patients respond and many relapse after a few months of therapy.

Researchers try to predict best drug combinations for inhibiting kinase activity

Salanga believes that there is a combination and dosage of PKIs recognizing distinct conformations of the BRAF kinase that can shut down the misfiring proteins and kill tumor cells dependent on oncogenic BRAF activity.

“The crux of the project is trying to predict which set of currently available drugs will work the best at inhibiting BRAF’s ability to turn things on inappropriately,” he said. “Molecular profiling of tumor cells might be used to guide the drug selection for individual patients.”

Critical to the NAU-based pilot project team is Richard Posner, a professor in NAU’s Department of Biological Sciences and William Hlavacek, a scientist at Los Alamos National Laboratory. Posner and Hlavacek are computational systems biologists who have developed mathematical models for predicting optimal strategies to target mutations in BRAF. In recent work, they and their collaborators predicted that two-drug combinations will be able to effectively suppress mutant BRAF (V600E) signaling. These predictions were validated in melanoma cell lines. The researchers are leveraging this computation pipeline to predict therapeutic responses to novel combinations of U.S. Food and Drug Administration-approved drugs in humanized zebrafish harboring melanoma skin cancer.

Also involved in the project is Haiyong Han, a scientist in the Molecular Medicine Division at the Translational Genomics Research Institute (TGen). His specialty is pancreatic cancer, which could potentially be treated using similar therapeutic strategies that are being proposed for melanoma.

The researchers, including undergraduate and graduate students, will be adding various combinations of inhibitors to see if they can find combinations that are most effective in targeting mutated RAF proteins.

Salanga says taking the melanoma-fighting research from the lab to medical facilities could happen quickly, as 150 PKIs are already in various stages of safety testing, and many are approved by the FDA.

“TGen and its partners can carry out these PKI clinical trials fairly routinely through its patient network and its scientists, who assist in these human studies. We could see humans receiving treatments like this within the next year or two,” he said.

Although early detection of melanoma contributes to an 89 percent, five-year survival rate, metastatic melanoma is often lethal, with less than a 20 percent survival rate.

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NAU’s grant for the project was awarded by the Flinn Foundation under its Seed Grants to Promote Translational Research initiative.