THE LASONOLIDE MYSTERIES: Where are they, and how do they kill cancer cells?

In 1987, scientists from Harbor Branch Oceanographic were using one of the institution's submersibles in the Bahamas to collect sponge samples for biomedical research when they gathered a small, nondescript reddish sponge. Chemical and biological analysis of the sponge revealed nothing unusual, so it was logged into the institution's collection of more than 30,000 samples, stored in an ultra-cold freezer in a hurricane-proof bunker, and all but forgotten.

Nearly five years later, a group from Harbor Branch was collecting samples in the British Virgin Islands when they came upon another reddish sponge. By this time they had begun using a new test of pharmaceutical potential, and to the team's excitement, chemicals from the sponge showed an outstanding ability to kill lung, breast, and other cancer cells. But if work on the promising compounds was to continue, the group simply had to have more of the sponge to study.

Back to the Bunker

So, the Harbor Branch team began digging through records and samples in the bunker in search of more of the red sponge, no simple task considering that an estimated 10,000 species of sponge exist and many have overlapping physical characteristics. But in time, they realized that beginning with the 1987 Bahamas collection, a few other specimens of the sponge, mostly small ones, had been collected.

Using the material available, analysis of the sponge (which had been identified as a species of Forcepia) continued. A group of compounds the sponge produced, dubbed the lasonolides, continued to show great promise. Though the team was able to decipher their chemical structure, confirm their novelty, and receive patents, but they desperately needed still more natural material to continue the research.

Of the Forcepia pieces already collected, the largest had come from trawl work off southwest Florida. So, the team used trawls again to work the area on various trips during the 1990s, but to little avail. They could find only a few bits of the sponge, and not enough to support their research goals. Finally, the group was forced to give up in frustration, at least temporarily, unsure whether their work with the lasonolides could continue.

An Accidental Sponge Farm

But by 1999, the potential importance of the lasonolides was clear enough that the Harbor Branch team returned to explore the Gulf site by submersible. They had low expectations for the day's dives in the relatively barren area, but they knew of no other way to continue the Forcepia quest. Ultimately, their fears of unproductive dives proved unfounded and they extended their stay from one to five days, because they discovered an almost unimaginable wealth of Forcepia, so much in fact that to this day they refer to the region fondly as Forcepia Land. As it turns out, the species of Forcepia in question is especially prone to break up in trawl nets, but working with the submersible on the seafloor they were there intact for the plucking. Because the team found so much of the sponge they suspect they "seeded" the area by breaking sponges up while trawling with each fragment growing into a new sponge colony.

Mysterious Killer

With sufficient material in hand, the group, currently led by Amy Wright , was able to perform more advanced experiments with the lasonolides, most notably working in cooperation with the National Cancer Institute to run the compounds through a series of tests to identify specific known cancer-killing mechanisms. To everyone's astonishment, all the tests came out negative, suggesting the lasonolides anti-cancer bioactivity stems from a mechanism never before seen.

The result was as intriguing as it was troublesome. A new mechanism for killing cancer cells could mean a new level of efficacy against dread forms of cancer or perhaps an ability to attack cancers resistant to existing treatments. But understanding the actual mechanism a drug uses to kill cancer cells is a critical step in the development process required to predict a potential treatment's effects on humans.

On the Killer's Trail

To understand the lasonolides' activity, the Harbor Branch group has explored, and continues to explore, a number of possible routes. For one approach, the team has Florida Sea Grant funding to apply a technique called affinity chromatography to the problem. Affinity chromatography involves attaching molecules of the lasonolides to small beads, and adding mixtures of protein extracts from broken up cancer cells. Then researchers can determine which of the proteins in cancer cells attach to the lasonolides, indicating which proteins are affected by the compounds. Identifying such proteins could help lead the group to the cancer cell mechanisms targeted by the lasonolides.

The team is also using DNA microarrays to compare cancer cells treated with lasonolides to untreated cancer cells to determine differences in gene expression between them to zero in on the critical mechanisms. Microarrays are one of the most powerful tools in the field of genomics. They are small plates containing thousands of DNA segments, or probes, from various organisms that code for genes. Because the sequence and function of the genes that makeup the microarray probes are typically already known, if an expressed sponge gene matches, researchers can infer that that gene serves roughly the same purpose in the sponge. So, each match, or hybridization, can allow identification of a sponge gene and its function.

A final route the Harbor Branch group is taking to solving the lasonlide activity mystery is to collaborate with a commercial partner to apply additional modern genomics techniques to the problem. To date, however, the lasonolides have not yet been licensed.

Although Harbor Branch has made substantial progress toward the goal of understanding how lasonolides work, the story of the lasonolides is far from over as the group and its collaborators work toward the goal of getting the drugs into clinical trials and hopefully on to market.