Marine pharmacology

The marine environment has proven to be an extremely rich source of novel natural products with activities in a variety of biological assays. The field of marine natural products chemistry has enjoyed an explosion of growth over the past 40 years and currently there are marine-derived metabolites in clinical trials for cancer, analgesia, allergy and cognitive diseases. Even with this tremendous development, it is clear that chemists and pharmacologists are only beginning to scratch the surface of the biomedical potential of marine organisms. One problem with this source of new pharmaceuticals is that the supply of such compounds can be problematic. The thesis describes projects directed at fundamental biosynthetic questions regarding terpenes from marine corals. In a general sense, these projects are directed as addressing the supply issue identified above. One project examined the origin of terpene building blocks in the coral Pseudopterogorgia elisabethae. A second project focused on the characterization of terpenes from Leptogorgia minimata. Here, a new cembranoid diterpene was isolated. Experiments were also conducted to identify a microbial source of terpene biosynthesis in this system. Data strongly supported a bacterial origin of these compounds.

Erythropodium caribaeorum is an octocoral known for its production of novel anticancer agents, such as eleutherobin and its analogs as well as for its complex association with symbiotic dinoflagellates (Zooxanthellae; genus Symbiodimum). With this in mind, two sets of experiments were conducted using the extracts of the symbiotic algal cells from Erythropodium caribaeorum: an isolation and characterization of a novel tri-hydroxy sterol and a bioassay-guided isolation of three additional compounds. All compounds exhibit significant bioactivity against the following three cell lines: the human melanoma cell line M14P, the colon cancer cell line RKO and the breast cancer cell line MDA-MB-231. Importantly, this study reports the first isolation of a bioactive polyhydroxy sterol from a gorgonian's symbiont and further suggests that these algae represent a promising sustainable resource for drug discovery.

The pseudopterosins are a class of diterpene glycosides isolated from the Caribbean sea whip, Pseudopterogorgia elisabethae. Pseudopterosins A-D possess potent anti-inflammatory and analgesic properties (ED50 ca. 3.0 mg/kg). There is a large demand in the pharmaceutical and cosmetic industries for pseudopterosin derivatives and presently, the only source of these chemicals is from wild-collected gorgonians. Preliminary experiments were performed to develop a reliable, cost-effective production method of the pseudopterosins in order to avoid large-scale harvesting. We exposed the gorgonians to various forms of "stress" in an attempt to increase the amount of pseudopterosins produced. We have also evaluated the feasibility of raising Pseudopterogorgia elisabethae in an aquaculture setting by studying their growth rates in different environments. Our studies indicate that aquaculture used with some simple induction methods can allow for the commercialization of this important biochemical resource.

The goal of this work was to investigate the biosynthetic origins of diterpene natural products (pseudopterosins, kallolides, bipinnatins, and cembrenes) from corals of the genus Pseudopterogorgia as well as the biosynthetic pathways by which they are produced. These studies have shown that the pseudopterosins from Pseudopterogorgia elisabethae are biosynthesized within the algal symbiont (or possibly a bacterium or fungus associated with the symbiont), are not inducible by manipulation of light levels, and do not change as a result of transplantation to new locations. Studies on Pseudopterogorgia bipinnata revealed that only one chemotype is capable of biosynthesizing the kallolide family of diterpenes. The biosynthetic pathway which gives rise to the kallolides has been shown to involve members of another family of diterpenes, the bipinnatins, which coexist within the coral holobiont. Two diterpene cyclase products have been discovered within P. bipinnata chemotype A, cembrene and neocembrene, and it has been shown that neocembrene gives rise to the kallolides. Finally, the enzymatic conversion of bipinnatin J to kallolide A has shown for the first time that these compounds are in fact biogenetically related.

The pseudopterosins and seco-pseudopterosins are diterpene glycosides isolated from the marine octocoral Pseudopterogorgia elisabethae . These compounds exhibit potent anti-inflammatory and analgesic properties superior to the industrial standard indomethacin. The overall goal of this work was to complete biosynthetic studies for the development of a biotechnological production method of the pseudopterosins and seco-pseudopterosins. The aim of this project was to identify all intermediates involved in pseudopterosin biosynthesis. Previously, the Kerr lab has shown that elisabetatriene and erogorgiaene are the first two committed steps in pseudopterosin biosynthesis. In a continuation of those metabolic studies, the isolation and utilization of 7-hydroxyerogorgiaene, 7,8-dihydroxyerogorgiaene, seco-pseudopterosin J, amphilectosins A and B in pseudopterosin biosynthesis is reported. The utilization of these compounds in pseudopterosin biosynthesis was assessed by incubating these compounds in radiolabeled form with viable cell-free extracts of P. elisabethae and monitoring for the incorporation of a radiolabel in the pseudopterosins. We also report the isolation of the pseudopterosin aglycone from extracts of P. elisabethae and identified the aglycone as the end product of this metabolic pathway.

Sponges are an important source of bioactive marine natural products, or secondary metabolites. The common Caribbean reef sponge, Axinella corrugata, produces an antitumor and antibacterial chemical, stevensine. This study determined whether environmental stressors, such as elevated temperature and exposure to Amphibalanus amphitrite larvae, affect the production of stevensine by A.corrugata and if the stressors caused A.corrugata to exhibit differential gene expression. Temperature stress resulted in no significant change in the production of stevensine; only two genes were significantly differentially expressed, including hsp70. Larval stressed resulted in increased production of stevensine and significant differential gene expression (more than seventy genes). This study suggests that A.corrugata may be resilient to elevations in temperature and that one of stevensine's roles in nature is as an antifoulant.