Abstract
With the advent of very rapid and cheap genome analyses and the linkage of these plus microbial metabolomics to potential compound structures came the realization that there was an immense sea of novel agents to be mined and tested. In addition, it is now recognized that there is significant microbial involvement in many natural products isolated from “nominally non-microbial sources”. This short review covers the current screening methods that have evolved and one might even be tempted to say “devolved” in light of the realization that target-based screens had problems when the products entered clinical testing, with off-target effects being the major ones. Modern systems include, but are not limited to, screening in cell lines utilizing very modern techniques (a high content screen) that are designed to show interactions within cells when treated with an “agent”. The underlying principle(s) used in such systems dated back to unpublished attempts in the very early 1980s by the pharmaceutical industry to show toxic interactions within animal cells by using automated light microscopy. Though somewhat successful, the technology was not adequate for any significant commercialization. Somewhat later, mammalian cell lines that were “genetically modified” to alter signal transduction cascades, either up or down, and frequently linked to luciferase readouts, were then employed in a 96-well format. In the case of microbes, specific resistance parameters were induced in isogenic cell lines from approximately the mid-1970s. In the latter two cases, comparisons against parent and sibling cell lines were used in order that a rapid determination of potential natural product “hits” could be made. Obviously, all of these assay systems could also be, and were, used for synthetic molecules. These methods and their results have led to a change in what the term “screening for bioactivity” means. In practice, versions of phenotypic screening are returning, but in a dramatically different scientific environment from the 1970s, as I hope to demonstrate in the short article that follows.
Highlights
In the days when the author was active in an industrial laboratory as a bench scientist, mainly in antibiotic discovery, the methods always involved the screening of compounds or extracts against microbial cells, usually a relatively safe surrogate, such as the standard FDA strain of Staphylococcus aureus known as “209P”, a common Escherichia coli strain, and a suitable Candida albicans strain, all designed to show activity that could be followed in a bioactivity-driven isolation format
Screening methods and perceived current practice Anyone who reads the literature related to the discovery of bioactive materials, irrespective of whether the sources are natural products, modified natural products, or synthetic compounds, has realized that, over the last 25–30 years, the paradigm changed from phenotypic screening to the use of isolated “targets”
The “collision” of the invention of the 96well plate, the rise of recombinant DNA technologies, and access to cheap and simple computing platforms permitted the rapid production of targets, their “interrogation” by semi-automated to automated systems, and the analyses of results in a short time period. This led to the realization that the numbers of available chemical compounds were much too low, and since the screens were run in campaign-mode, the time frame, usually less than 3 months for a given screen, was totally unsuitable for the screening of other than pure natural products in the late 1980s to mid-1990s
Summary
Over the last 40 or so years, bioactive natural product discovery and development has moved from what was known colloquially in the trade as “grind and find techniques”, termed “determining the phytochemistry of the plant”, to the use of very advanced analytical, genomic, metabolomic, and informatic techniques together with high throughput and/or “high content screening”. There is no one answer to this question, but what has been occurring over the last 7-plus years, because of the significant advances mentioned in the opening paragraph of the preamble, is that a very up-to-date version of “grind and find” has effectively taken over the initial screening systems, at least in the case of microbial secondary metabolites Discussions centered around such organisms will be the major focus of the rest of this review for the relatively simple reasons that a large percentage of all marine invertebrate-sourced natural products are the result of the interplay between microbes and their hosts. Except for an occasional patent or publication well after the programs had been shut down, only the memories of the scientists involved are left, as publication was not encouraged and, frequently at that time, the methodologies were proprietary
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
