Graceful and solitary, the sea turtle has been gliding through blue-green waters since the time of the dinosaurs, but its existence is threatened by an agent that also kills people: cancer. Now, scientists are one step closer to saving the species, thanks to a drug that’s also used on humans.
Green sea turtles are plagued by a specific, cancer-causing virus called fibropapillomatosis, a tumor-causing illness that is undermining efforts to save the species. To date, the cause of fibropapillomatosis is not fully understood, although scientists theorize that it’s driven by a combination of viral and environmental factors, the latter of which is caused by the depletion of the ozone layer.
On Thursday, researchers announced in a study published in Communications Biology that they discovered tumors in sea turtles share similar genetic vulnerabilities with human cancers.
This realization led them to successfully treat sea turtles with human cancer treatments: After surgical removal of tumors and application of the anticancer drug fluorouracil, they were able to reduce the reoccurrence of fibropapilloma tumors from 60 to 18 percent. This is good news for turtles and for humans, too: Sixty percent of emerging infectious disease events in humans are caused by diseases transmitted from animals, and 70 percent of these diseases originate in wildlife.
“Therefore, a more concerted effort to improve our understanding of pathogen-induced cancers in wildlife, including potential exacerbating effects of human coastal land use, is crucial for enhancing both human and wildlife health,” writes the team of University of Florida scientists.
While fibropapillomatosis was first spotted in turtles in the early 1900s and studied since, scientists still don’t have a great understanding of the molecular events and genes that drive the formation of tumors. The rapidly growing tumors are benign yet can ultimately cause turtles to die because of their interference with eating, swimming, and sight. Surgical removal is currently the primary treatment for fibropapillomatosis, but there’s a 60 percent chance that the tumors will regrow post surgery.
In this study, the scientists worked to rectify this by taking and comparing biopsies of tumor tissue and non-tumor tissue from two diseases juvenile green turtles found off the coast of northern Florida. They applied precision medicine approaches from human oncology to the samples, including, they write, “next-generation Illumina RNA sequencing transcriptomic profiling and a computationally-based systems-level analysis.” They discovered that the tumors were driven by altered expression of host genes, and not by the genes from the virus.
Further analysis revealed that the fibropapilloma tumors shared a striking similarity to a number of human cancers — especially human basal cell carcinoma, which causes skin cancer. Human skin cancer is linked to a network of proteins that promote its spread, and fibropapilloma is ignited by a similar network. This was an important realization for two main reasons, the first being that because it clued them into treating the turtles with the anticancer drug fluorouracil.
But it also signaled to the scientists that ultraviolet radiation might be a risk factor driving fibropapillomatosis, just as it drives human skin cancer. This adds to the hypothesis that environmental factors, driven by human actions, influence the rate of cancer development in animals: The depletion of the ozone layer has driven the intensity of UV radiation at the Earth’s surface, and humans have contributed to that depletion.
“Wildlife populations are under intense anthropogenic pressures, with the geographic range of many species shrinking, dramatic reductions in population numbers, and undisturbed habitats, and biodiversity loss,” the scientists write. “It is postulated that we are in the midst of a sixth mass extinction event, the first to be induced by human activity.”
How to stop causing animals to develop cancer largely comes down to our ability to curb pollution and climate change. Innovative approaches are needed to keep animals healthy, say the scientists, and innovative here means helping turtles fight cancer with how we fight it ourselves.