“The good news is it didn’t kill the mice,” said Bill Baker, a chemistry professor at the University of South Florida. “It did kill their cancer, so we know it has the physiological properties to act like a drug.”
The toxin in question comes from a bacterium living inside ascidians, the sea squirts that cling to the Antarctic seafloor. The animals use it to ward off predators. Baker says it can be “repurposed”, and his team’s earlier work shows it killed melanoma cells in mice. Melanoma is the deadliest form of skin cancer.
Six weeks on the ice
Researchers from USF, the Desert Research Institute and the Scripps Institution of Oceanography came back recently from a six-week expedition to collect more specimens. Divers went down as far as 130 feet, for about half an hour at a time. The National Science Foundation paid for the trip.
Ben Meister, a USF diving safety officer on the expedition, said the cold was only one of the problems. “In Antarctica, you’re dealing with ice, leopard seals, changing seas and sometimes very limited visibility,” he said. “Every dive must be carefully planned to balance getting the work done while keeping everyone safe.”
The team returned “exhausted”, Baker said, but eager to start laboratory work, some of which is already running through partnerships with the two partner institutions.
The supply problem
The hard part is quantity. A bigger mouse study, and eventually human trials, would need hundreds of milligrams to grams of the compound. “From a basketball-size collection of ascidians we might get one-thousandth of that,” Baker said.
Gathering 1,000 basketballs’ worth is out of the question. “That would destroy the ecology,” he said. The lab therefore has to find a way to make the toxin synthetically.
The trip did help in other ways. Baker said it taught the team more about how the melanoma-killing bacterium lives inside the sea squirt and about the relationship between the two. That knowledge should guide the animal and human work to come, he said.
He acknowledged that the route to an approved drug is long, with a series of tightly regulated and expanding trials even after a drug is formulated. Baker began his career in marine biology and chemistry in 1990, and he noted that more than half of Food and Drug Administration-approved drugs come from natural sources. He has found other promising compounds in sponges, corals and tunicates.
He called the melanoma finding “sort of a career pinnacle”. “Killing cancer cells in a petri dish is one thing, but going beyond that is much harder,” he said. “Now we’ve got to make the next hurdle.”
Sources
- Antarctica sea squirt toxin kills melanoma in mice, leaves the animals unharmed
- Tiny Antarctic sea creature could be key to treating melanoma, researchers say
