Bacterial symbionts and natural products

Natural products as sources of new drugs over the 30 years from 1981 to 2010

This review is an updated and expanded version of the three prior reviews that were published in this journal in 1997, 2003, and 2007. In the case of all approved therapeutic agents, the time frame has been extended to cover the 30 years from January 1, 1981, to December 31, 2010, for all diseases worldwide, and from 1950 (earliest so far identified) to December 2010 for all approved antitumor drugs worldwide. We have continued to utilize our secondary subdivision of a "natural product mimic" or "NM" to join the original primary divisions and have added a new designation, "natural product botanical" or "NB", to cover those botanical "defined mixtures" that have now been recognized as drug entities by the FDA and similar organizations. From the data presented, the utility of natural products as sources of novel structures, but not necessarily the final drug entity, is still alive and well. Thus, in the area of cancer, over the time frame from around the 1940s to date, of the 175 small molecules, 131, or 74.8%, are other than "S" (synthetic), with 85, or 48.6%, actually being either natural products or directly derived therefrom. In other areas, the influence of natural product structures is quite marked, with, as expected from prior information, the anti-infective area being dependent on natural products and their structures. Although combinatorial chemistry techniques have succeeded as methods of optimizing structures and have been used very successfully in the optimization of many recently approved agents, we are able to identify only one de novo combinatorial compound approved as a drug in this 30-year time frame. We wish to draw the attention of readers to the rapidly evolving recognition that a significant number of natural product drugs/leads are actually produced by microbes and/or microbial interactions with the "host from whence it was isolated", and therefore we consider that this area of natural product research should be expanded significantly.

Fungal biofilm inhibitors from a human oral microbiome-derived bacterium

The human mouth is home to a rich assortment of native and transient microorganisms. One of the commonly encountered bacterial species, Streptococcus mutans, was shown to generate the novel hybrid polyketide-nonribosomal peptide metabolite mutanobactin A (1). We have characterized three new analogues, mutanobactins B-D (2-4), and subjected these compounds to further biomedical evaluation. Metabolites 1, 2, and 4 were found to inhibit biofilm formation by the fungal oral-pathogen Candida albicans. Compound 4 was the most potent metabolite with an IC(50) value of 5.3 ± 0.9 μM. Using a combination of Marfey's analysis, proton spin-spin coupling, and (1)H-(1)H NOESY data, we proposed absolute configuration assignments in toto for 1-3 and a partial assignment for 4. In addition, feeding studies with isotopically labeled precursor metabolites (acetate and amino acids) have helped to determine the biosynthetic origins of this unique natural product family.