Manipulating the biosynthesis of capuramycin-type antibiotics for new anti-TB drugs

Tuberculosis (TB), a disease primarily caused by the bacterial pathogen Mycobacterium tuberculosis, was estimated to be the source more than 1.3 million deaths in 2008 (1). Around 9.3 million new cases of TB were also reported during 2008, and, alarmingly, 5 % of these new cases—or 465,000—were associated with M. tuberculosis that was resistant to minimally one of the first-line anti-TB drugs (2, 3). Furthermore, extensively drug-resistant M. tuberculosis is rapidly emerging as a serious global health concern (4). Several additional problems associated with treating TB using current antibiotic regimens are also evident, including the long administration periods ranging from 6 to 24 months, patient noncompliance and/or lack of medical oversight during this lengthy treatment, and the relatively low efficacy (60% cure rate) and adverse affects of second-line anti-TB drugs. Capuramycin-type antibiotics are excellent candidates as new anti-TB drugs because they: (i) have a novel structure relative to currently used antibiotics including anti-TB drugs (5). This novel structure not only expands the chemical space of clinically utilized antibiotics but is expected to make capuramycin-type antibiotics less susceptible to known mechanisms of drug resistance. (ii) inhibit bacterial translocase I, a novel target involved in peptidoglycan cell wall biosynthesis that is essential for the survival of all bacteria (6). Several revolutionary and indispensable drugs such as amoxicillin and vancomycin function by inhibiting distinct enzyme-catalyzed reactions in peptidoglycan biosynthesis, yet no inhibitor of bacterial translocase I is currently available on the market. (iii) kill M. tuberculosis—including drug-resistant strains—much faster than first-line anti-TB drugs (7). (iv) have no toxicity in mice in contrast to the well-known bacterial translocase I inhibitor tunicamyin (8, 9). Our long-term goal is to develop a therapeutically useful capuramcyin-type antibiotic that is a first-line drug against extensively drug-resistant M. tuberculosis. We recently identified a novel mechanism of amide bond formation that occurs during the biosynthesis of A-503083, a capuramycin-type antibiotic (10), and it is our objective in this request for an administrative supplement to exploit this mechanism of amide bond formation to generate A-503083 analogues for structure-activity relationship studies and identify the analogous mechanism involved in the assembly of the capuramycin-type antibiotic A-102395. We hypothesize that, by understanding the inherent specificity of the enzymes from two independent pathways, strains can be readily engineered and optimized to produce therapeutically important capuramycin-type antibiotics.