A coral reef is a place of opulent wonder, with schools of iridescent, psychedelic fish as well as colourful sponges, sea urchins, anemones and coral polyps, awash in currents teeming with microorganisms. But the beauty is deceiving, for this watery nirvana is host to fierce battles of survival — many in the form of chemical warfare.
Lacking the ability to swim, crawl, bite or scratch, organisms like sponges have devised their own little chemical weapons laboratories. Woe to the hapless creature that chomps on a sponge, or the invertebrate muscling in on sponge territory. The toxins released will cause the invader to either flee — or die.
Such chemicals are elixir to natural products researchers, who gathered this past August for the annual two-day Maritime Natural Products Conference, hosted by Saint Francis Xavier University in Antigonish, N.S. The conference drew representatives from the biotechnology and food supplement industries, while students from the undergrad to postdoc level presented papers, says organizer and StFX assistant professor of chemistry Darren Derksen. Potential applications of natural products embraced health, nutraceuticals (health foods) and personal care products. The sources of the natural products spanned the planet, from fungi in plants to weeds, and all manner of sea creatures.
Mother Nature’s most noxious substances — as well as the more benign ones — have long been co-opted by chemists for use in natural product pharmaceuticals. The aim of such research is simple: find novel molecules with drug potential. A natural product chemist teases health-nurturing molecules out of a living organism using a simple bioassay, which assesses the potency of a compound by studying the effect on living cells. It has been a remarkably successful recipe: 50 per cent of drugs currently in clinical use are derived from natural products that originated from sea to shore. And two-thirds of today’s anti-cancer drugs today are rooted in nature, such as paclitaxel, derived from the Pacific Yew tree.
Despite the stellar track record, natural products research fell out of favour among chemists in the late 1990s with the rise of synthetic drug production and combinatorial chemistry, which allows for the testing of hundreds of thousands and even millions of compounds at a time. With natural products chemistry, the general rule of thumb has been: screen 10,000 compounds and you’ll likely get a drug candidate. With combinatorial chemistry, theoretically, the dramatic increase in potential compounds was expected to boost the likelihood of discovering useful drugs. Unfortunately, microbes are proving mightier than the pipette and scientists are losing ground to increasingly drug-resistant organisms. This spectre has helped reinvigorate natural products research, with laboratories across Canada undertaking some remarkably innovative science in the search for new compounds for pain and inflammation, infectious diseases like tuberculosis (TB), HIV-AIDS and malaria as well as scourges like cancer and Alzheimer’s.
Russell Kerr of the University of Prince Edward Island is the founder of the Maritime conference and hosted it for the first two years, starting in 2008. A Canada Research Chair in Marine Natural Products, Kerr says that this research creates libraries of compounds that potentially can be used in collaborative drug discovery projects with other scientists and pharmaceutical laboratories. This year, Kerr co-authored a conference paper with student Beth Pearce, who presented research into the natural product gorgonene, which is a byproduct of the purification of pseudopterosins, well-known commercial anti-inflammatories and anti-irritant compounds derived from the Caribbean soft octocoral, Pseudopterogorgia elisabethae. Using organic synthesis, Pearce took gorgonene, a biologically inactive molecule, and turned it into a series of molecules with “interesting biological activity,” says Kerr. The next step was to test the new synthetic compounds in an enzyme-based assay using protein tyrosine phosphatases, or PTPs, which are being studied as a potential target for treatment of Type 1 and Type 2 diabetes. Some of Pearce’s compounds exhibited selective inhibition of PTPs and thus will serve as drug leads. This makes Pearce’s research the first step in trying to make a useful drug from the waste product gorgonene. By isolating the biologically active molecules, a second-generation library containing dozens of derivatives of gorgonene can be created that may “progress towards animal trials,” Kerr says.
Surrounded by octocorals in the warm waters off San Salvador in the Bahamas, Russell Kerr of the University of Prince Edward Island places a piece of a sponge (Verongula gigantea) into a bag for testing in a diversity of biomedical assays. Photo credit: Stacey Kerr
The study of natural products has unique challenges and the possibility of isolating a novel active constituent from a crude plant or microorganism that can be turned into a marketable drug is small, time-consuming and expensive. “It’s a numbers’ game; very few molecules make it through to clinical trials,” says Kerr, who is also CEO of natural products firm Nautilus Biosciences Canada.
It isn’t just humans who benefit from Kerr’s research. Kerr, who has a cross-appointment with UPEI’s chemistry department and the Atlantic Veterinary College, is developing an anti-inflammatory agent derived from marine corals to treat puppy dermatitis, or belly rash. Such products are derived from the huge library of marine bacteria and fungi amassed over years of research. “We have a collection of several thousand purified marine-derived microbes,” Kerr says.
Kerr has extended his search for natural product-based drugs in such areas as the Caribbean and Colombia’s equatorial Amazon. Recently he began searching for microbes in Canada’s Arctic. Kerr has launched a “really exciting project” in Iqaluit, Nunavut, recruiting local Inuit who collect sediment and invertebrates to be used as a source of microbes for natural products study in his UPEI lab.
Even Kerr’s back yard is a potential source of compounds. Locally, the mussel and oyster industry is plagued by tunicates, or sea squirts, which are large invertebrates that envelop the aquaculture cages housing the tasty mollusks. Kerr and his research team were able to isolate and purify a compound from local seaweed that the tunicates avoided. Kerr is discussing the development of this compound with the Dutch paint company AkzoNobel for incorporation into marine paints.
Kerr’s reflections on the challenges of natural product drug development are echoed by University of British Columbia chemist and entrepreneur Raymond Andersen, who was plenary lecturer at the Maritime conference. Andersen says that the key to success in natural products research is figuring out how to address a medical need and developing a new hypothesis for how to treat a particular disease. This usually means identifying a new molecular target that no one has previously developed a drug for. Andersen calls the discovery of novel structures the “holy grail” of chemistry, believing such breakthroughs are more likely with natural products chemistry than synthetic or combinatorial chemistry. “That’s the nice thing about natural products — nature doesn’t make things just randomly,” says Andersen. “With natural products these molecules have evolved for a purpose: they bind to a target.”
Andersen, who is last year’s winner of the Chemical Institute of Canada’s annual CIC Medal for outstanding contributions to the science of chemistry, is currently working on the development of a natural products process to fight tuberculosis (TB), a deadly disease that has infected one-third of the world’s population and is becoming more drug-resistant. Andersen’s research illustrates how looking at a disease in a whole new way paves the road for successful drug development. Andersen chose to analyze the process of autophagy, a process by which a cell breaks down its own enzymes for food. Normally a cell utilizes autophagy when undergoing stress that increases the need for nutrients. By scavenging for proteins that it can live without and breaking them down for recycling (autophagy), the cell is able to survive on amino acids. The process is also used by a cell in response to a foreign invader like a bacterium. When invaded, a cell’s lysosomes — an enclosed organelle containing enzymes that break down other enzymes or waste molecules — degrade the bacteria.
Raymond Andersen of the University of British Columbia has isolated the molecule clionamine B from a South African sea sponge. It is proving effective in the fight against tuberculosis.
Unfortunately, a clever invader like Mycobacterium tuberculosis (MTB) is able to ‘turn off’ cellular autophagy, using a complex of enzymes. This allows MTB to colonize and multiply, emerging as a full-blown TB infection. Andersen has isolated a compound called clionamine B from a South African sea sponge that stimulates autophagy “very effectively.” Theorizing that if autophagy could be ‘turned back on’ in the cell, an organism could then utilize its own innate defenses to fight MTB. And that’s exactly what happened in the laboratory. Andersen isolated clionamine while his colleague, Michele Roberge, a professor in the Department of Biochemistry and Molecular Biology at UBC, tested the compound to assess its ability to prompt autophagy. It proved to be “one of the best stimulators of autophagy ever known,” says Andersen. Another colleague, Yossef Av-Gay of UBC’s Division of Infectious Diseases in the Faculty of Medicine, tested clionamine’s ability to eliminate the MTB bacteria from white blood cells. “It completely clears it,” Andersen says.
The advantage of this mechanical approach to disease control over a new antibiotic is that the TB bacteria have nothing to develop resistance to. This is because the clionamine simply switches on a natural process that already exists in the cell, similar to flicking a light switch in a dark room. Andersen is in the process of patenting clionamine and synthesizing it into an extensive library of analogs based upon the molecule. His team is poised to embark upon the next step: studying clionamine’s toxicity on living creatures, such as mice. Andersen says that this discovery process followed a precise research pathway: find and isolate compounds with good science, identify a new target and come at disease treatment in a new, innovative way.
Christopher Gray of the University of New Brunswick’s Natural Products Research Group looks to First Nations medicinal plants, such as this balsam fir (Abies balsamea), to isolate endoyphytes for drug development. The aboriginal peoples of North America used the balsam fir as an antiseptic, applying it to wounds and bites. It was also taken internally to treat colds and headaches. Photo credit: Kathryn Melvin
Andersen has had even better success with a compound isolated from another sponge from Papua New Guinea. Working with researchers from the BC Cancer Agency, the group, under the umbrella of the biotech firm Aquinox Pharmaceuticals that was co-founded by Andersen, isolated a compound that activated a protein called SH2-containing Inositol 5’-Phosphatase, or SHIP, as a new way to treat blood cancers. Because the market for such a drug is potentially lucrative, several heavy hitters, including Johnson & Johnson Development Corp, Pfizer and Ventures West Capital in Vancouver, contributed $70 million towards the research. The investors’ faith is being rewarded. The compound was synthesized, found to be non-toxic in animal studies, and has gone — in six short years —to Phase II clinical trials in humans.
On the opposite side of Canada, at the University of New Brunswick, is Christopher Gray’s Natural Products Research Group, which draws inspiration from First Nations traditional medicine plants. One of the many plants native to New Brunswick is wild sarsaparilla, or Aralia nudicaulis. Sarsaparilla is showing promise as a source of compounds that inhibit the growth of TB. The plants themselves don’t necessarily spell death for bacteria, however, their endophytes do. Endophytes are organisms like fungi or bacteria that live symbiotically within a plant without causing it harm. So far, says Gray, his research team has isolated 81 endophytes from local traditional medicinal plants. (The study of ancient medical traditions is called ethnopharmacology.) Evidence indicates that TB was in North America long before Europeans arrived, so researchers look to traditional treatments for coughs and respiratory ailments — indicators of TB infection.
Gray’s investigative oeuvre includes finding ways to make old antibiotics effective again. Drug-resistant bacteria and cancer cells have developed a form of defence called efflux, which involves pumping medication out before it takes effect. So Gray is searching for compounds that stop this process. Another area of research is the nutraceutical market. The public’s ever-growing demand for alternative and complementary medicine and nutrition is spurring the markets for new natural products, Gray says.
As hopeful as the study into natural products is, a chill for its future hangs on the horizon. Ocean acidification is increasing due to rising carbon dioxide (CO2) in the environment. Scientists have discovered that coral reefs and its colourful residents in places like the Caribbean are being affected — even killed off — by high acid levels. “If those bacteria and fungi are lost through acidification of the ocean and other forms of pollution, then the implications for human health are phenomenal,” says Kerr.
Gray echoes Kerr’s concerns: “Nature is the inspiration for all of this. There’s no way we can synthetically match the diversity of chemicals that nature has produced over millennia.”