Research
The
MacMillan Lab is interested in the discovery of novel, biologically active
natural products from marine organisms, with an emphasis on culturable
marine bacteria.
Beginning with the discovery of penicillin by Alexander Fleming in the late 1920’s, microbial natural products chemistry has been an integral component of the modern drug discovery process. Over the course of the past twenty years the field of marine microbial natural products has become a new frontier for the discovery of biologically active novel secondary metabolites. By combining this novel resource with cutting edge analytical technology (LC-SPE-NMR, cryoprobes, LC-MS) and access to a world renown high-throughput biological screening facility we have a unique environment for natural products drug discovery.
Our Approach to the Natural Product Drug Discovery Process:
The process of drug discovery that we follow in the MacMillan lab is a traditional approach with the added advantage of analytical instrumentation capabilities to chemically analyze hundreds of strains per year in an efficient and comprehensive fashion. The overall goal is to generate libraries of pure natural products or enriched fractions that can be tested in not just a single assay, rather hundreds of assays over the course of a few years.
Sample Collection, Strain Isolation and Fermentation:
We collect samples from a variety of locations and habitats and ocean depths, but we are currently focused on sediment collections in the Gulf of Mexico and the Bahamas. Strain isolation, identification and fermentation are critically important factors in a successful microbial natural products lab. We have a well-equipped fermentation lab with multiple environmentally controlled shakers as well as two bioreactor units.
Analytical Capabilities:
We are highly reliant on modern analytical tools including the hyphenated techniques of LC-ELSD-MS and LC-SPE-NMR to provide quantitative results andhighly detailed spectroscopic data on all crude extracts. We are currently in the process of installing a Varian 600 MHz NMR with a HPLC, SPE liquid handling device and a 60µL flow probe for automated analysis of extracts. The instrument should be fully operational by late 2007.
High-Throughput Screening Facility:
UT-Southwestern has one of the few academic high-throughput screening facilities along with a chemical library of more than 200,000 compounds. The facility screens the library against assays pertaining to cancer, neurogenesis, bacterial virulence factors and many more. Our pure compounds, crude extracts and enriched fractions will all be added to a smaller chemical library (8K library) that is part of the pre-screening process for the HTS facility and will be exposed to the maximum number of screens.
Structural Determination, Stereochemistry
and Structure Activity Relationships:
Our work just begins after the identification of a biologically active pure compound. We use the standard NMR, X-Ray and MS techniques with a heavy reliance on 2-D NMR for structural determination. The “chemistry” NMR facility consists of four modern NMRs (300, 400, 500 and 600 MHz) and we have access to additional 600 MHz instruments equipped with cryoprobes for particularly sample-limited situations.
We also focus on solving difficult stereochemical problems in our lab. As difficult challenges arise we will develop new techniques for determination of stereochemistry using CD, NMR and synthetic techniques. We are currently focusing on developing techniques to determine the absolute configuration of diols such as those below.
Additional Projects:
Through collaborations with Wade Winkler (Department of Biochemistry, UTSW) and Vanessa Sperandio (Department of Microbiology, UTSW) we are looking at inhibition of biofilm formation in pathogenic bacteria such as Pseudomonas aeruginosa and Staphylococcus aureus.
We are also looking at the secondary metabolites responsible for the chemical defense of Caribbean sponges against predatory reef fish through a collaboration with Joe Pawlik (University of North Carolina-Wilmington).