Marine natural products

Genomics has been revolutionized by improved sequencing technologies, allowing for the detailed exploration of microbial dark matter and complex microscopic ecosystems. The bottleneck in genomic workflows has shifted from high-throughput sequencing to data analysis. This dissertation developed the Florida Center for Coastal and Human Health Shotgun Metagenomics Workflow (FCHsm) that is easy to use and tailor to unique datasets. This work acts as the beta-testing for the workflow, as it analyzes disparate biomes (environmental and host microbiomes) at varying sequencing depths (shallow and deep). FCHsm was used to resolve molecular dynamics and mine trans-kingdom metagenomes for secondary metabolic biosynthetic gene clusters (BGCs) in two marine environments— Indian River Lagoon toxic harmful algal blooms (IRL HABs) and the medicinal Leiodermatium sponge holobiont.
First, an in silico mock dataset was analyzed to benchmark the FCHsm workflow. Sourmash, coupled with the Genome Taxonomy Database, outcompeted the other taxonomic profilers by accurately predicting the size of the mock metagenome (450 genomes) and recalling the highest number of species (82 %) and strains (44 %). Nonpareil calculated the sequencing effort needed for 100 % coverage for all the datasets and correctly estimated the 75 Gbp of sequencing needed for almost 100 % coverage of the mock metagenomes (99.5 %). Next, the trans-kingdom metagenomes of the IRL were explored, and potential HAB biomarkers were identified.

Marine sponges are one of the most prolific sources of chemical compounds with pharmaceutical importance. To establish a supply of such compounds large enough for clinical development, in vitro production methodology was investigated. Since all sponge cells do not divide in culture, it was hypothesized that the fusion of rapidly dividing cells of a sponge that does not produce any compounds of interest with cells of a nondividing but compound-producing sponge would result in a hybridoma that produces the compound of interest. In this study, hybridomas have been produced with cells of two marine sponges, Axinella corrugata, which produces the antitumor compound stevensine, and Geodia neptuni, which divides rapidly in a nutrient medium optimized for sponge cell culture. Successful hybridization and subsequent cell division and in vitro stevensine production may unlock the potential for sustainable mass production of other sponge-derived compounds.

Cultivation of microbial populations is a necessity for the use of microbes within the biotechnological and pharmaceutical industries, however, approximately only 1% of bacteria have been successfully cultivated in the lab. Dilution to Extinction (DTE) is a technique which involves serially diluting a microbial suspension to single cell inoculum prior to inoculation in a liquid medium designed to replicate natural aquatic environments. This technique was used here for the cultivation of diverse, potentially novel microbes from the marine sponge, Mycale microsigmatosa. One hundred thirty-six samples were successfully sequenced and identified with the majority belonging to the classes Alphaproteobacteria and Gammaproteobacteria. Furthermore, when combined with miniaturized fermentation, DTE allowed for the isolation and identification of marine natural products (3-Heptyl-3-hydroxy-2,4 (1H, 3H)-quinolinedione and 2-Heptyl-4-hydroxyquinoline) active against Methicillin-resistant Staphylococcus aureus. These metabolites originated from Pseudomonas aeruginosa, an isolate obtained from Mycale microsigmatosa using this technique.

In 2020, the National Institute of Health reported that more than 1.8 million people in the U.S. were diagnosed with cancer and over half a million died from those diseases. There is an urgent need for innovative and effective new treatments which stem from novel cancer drug targets. Survivin, the smallest member of the inhibitor of apoptosis protein (IAP) family, is highly expressed during development and in cancer cells but not in differentiated tissues, making it a tumor-selective target for new drug therapies. At only 16.5 kDa, it consists of a single Baculovirus IAP Repeat (BIR) domain and an α-helical coiled coil. Survivin plays a multitude of roles in the growth and survival of cancer cells—which can be attributed to the variable cellular localizations and posttranslational modifications of the protein—including inhibition of apoptosis, mitosis and cell cycle progression, DNA damage repair, drug resistance, metastasis, angiogenesis, and cell senescence, among others. A drug that is able to target surviving transcription or posttranslational modification or disrupt one of these critical pathways may serve as an attractive new cancer therapy. Despite decades of research on surviving and its intracellular functions, researchers have yet to find an FDA approved drug.
Using a high throughput approach, Harbor Branch Oceanographic Institute’s chemical library of marine natural products was screened by the Guzmán lab to identify compounds capable of downregulating survivin expression in A549 non-small cell lung carcinoma and DLD-1 colorectal adenocarcinoma cell lines. From the screening assay, pure compounds were identified which reduce levels of survivin protein in cancer cells. Chapter 2 describes the isolation and structure elucidation of five polyhydroxylated sterol analogs from Ellisella paraplexauroides, four of them novel. Chapter 3 describes the isolation and structure elucidation of two compounds from Eudistoma olivaceum, eudistomin H and I. Chapter 4 describes the secondary biological testing employed to determine if the reduction of survivin expression was driven by reducing de novo production or increasing the degradation of existing protein by evaluating differential gene expression of survivin mRNA using reverse transcriptase quantitative polymerase chain reaction and measuring degradation rates of survivin protein, respectively.

Throughout history, natural products have produced a plethora of biologically active compounds that have established applications in medicine, biology, and pharmacy. The exploration for improved cytotoxic agents has continued to be a crucial path in natural products drug discovery. The focal point of this thesis sheds light on the biosynthetic relationship between the two distinct classes of briarane diterpenoids, the γ-lactone briarane and the briareolate esters. Additionally, this study elaborates on the discovery and elucidation of structurally unique secondary metabolites from the gorgonian coral Briareum asbestinum.
The first chapter of this thesis provides a review of the development and discovery of diverse
secondary metabolites. In addition, this chapter describes the role of natural products in drug discovery and summarizes the research progress in marine natural product chemistry in conjunction with a detailed overview of the current marine-derived pharmaceuticals.

Natural products play a historical role in the discovery of medicine but present unique challenges for chemical isolation, identification and production. In this work we describe the identification of twenty novel diterpenoids. These were isolated by use of chromatography, and the structures determined by spectroscopic methods, primarily 1D and 2D NMR. Six of these possess unprecedented diterpenoid skeletons and two of them show significant growth inhibitory effects on cancer cell lines in vitro (GI50 < 10 μM). The biomimetic semisynthesis of diterpendoids and analogues is also presented.
Access to the bielschowskyane carbon skeleton by dearomatization of a furanocembranoid precursor is described. Highlights include a stereoselective alkene epoxidation, a novel kinetic furan dearomatization method, and an efficient [2+2] photochemical cycloaddition. The role of conformational steering was studied spectroscopically using VT 1H-NMR and NOESY as well as quantum chemical calculations at the DFT level of theory. We also disclose a biomimetic synthesis of providencin using a photochemical Norrish-Yang cyclization. This provided the absolute configuration by chemical correlation with the precursor bipinnatin E, the latter determined by x-ray diffraction. An unexpected, regioisomeric byproduct was observed and a possible mechanism is proposed. A biomimetic synthesis of the diterpene alkaloid aceropterine is also described, using an epoxidation-rearrangement cascade. This work led to a revised structure of aceropterine, formulated by spectroscopic methods. Finally, the isolation and structure elucidation of a novel, cyclic lipopeptide from Pseudomonas sp. is described. The compound was obtained using a unique antibiotic crowd sourcing approach and the structure determined by spectroscopic methods and advanced Marfey’s analysis.