BIOMEDICAL APPLICATIONS OF MBT - INTRODUCTION

The Primary Importance of 'Secondary Metabolites'

Marine organisms, like their terrestrial counterparts, are amazing living chemical factories, producing a collection of metabolic compounds ranging from the mundane to the miraculous.

Some of these compounds (e.g., sugars, fats, and proteins) are organic building blocks and storage molecules. Others are used as cellular energy currency or transport molecules (ATP and hemoglobin, respectively). And still others are employed to preserve, duplicate, and perpetuate life's blueprints (e.g., nucleic acids). Biochemical compounds such as these are called 'primary metabolites.' They are essential for basic, life-sustaining physiological functions like growth, metabolism and respiration, energy storage and transfer, and genetic information management.

But, living organisms produce a separate broad category of compounds known as 'secondary metabolites.' Also referred to as 'natural products,' secondary metabolites are not known to be directly involved in central physiological functions, yet they are nonetheless essential contributors to the fitness and survival of individual organisms.

Marine chemical ecologists are scientists who are interested in the manner in which organisms use the secondary metabolites they produce. Such scientists have demonstrated, for example, that certain seaweeds and invertebrates containing specific natural products in their tissues are less readily attacked by grazers and predators than similar organisms without the compounds. In some cases it has been further demonstrated that an initial grazer attack can actually promote increased production of these defensive chemical compounds, resulting in decreased attacks over time. In other cases, grazers have been able to overcome a prey species' built-in defenses, sometimes even sequestering the defensive metabolite in their own tissues for their own protection. An example of this strategy of stolen defenses is seen in the Caribbean tiger flatworm, Maritigrella crozierae, an animal that sequesters the secondary metabolites produced by its food source, the ascidian (tunicate) Ectinascidia turbinata for its own defenses.

Can these bioactive compounds be of some value to us if we remove them from the natural milieu in which they are produced? As the tiger flatworm shows in the present example, an organism does not have to be able produce a chemical product in order to benefit from it. And in fact, one of the natural products produced by E. turbinata and pilfered by the predatory flatworm, the alkaloid ecteinascidin- 743 (Yondelis®), is currently in human clinical trials as a potential drug therapy for treating a variety of cancers.

A chemical produced by a sea squirt growing on mangrove roots, now being evaluated as a cutting edge anti-cancer agent? It's true. Better still, it's just the tip of the iceberg as far as the biomedical potential of the world's living marine resources.