SBIR-STTR Award

Production of novel ketolide antibiotics with potent antibacterial activity against macrolide susceptible and resistant bacterial pathogens. PHASE I: We will develop a biological process for production of 15-methyl-6- deoxyerythronolide B, the precursor of 15-methylerythromycin A, through genetic engineering of the 6-deoxyerythronolide B polyketide synthase. This will be accomplished by optimizing the biosynthetic pathway of a substrate used to make the target compound in Streptomyces coelicor, a related actinomycete strain of Escherichia coli. That substrate will be used by an engineered 6-deoxyerythronolide B polyketide synthase to make 15-methyl-6-deoxyerythronolide B, which will be isolated and bioconverted to 15-methylerythromycins by a strain of Saccharopolyspora erythraea or directly to this compound by an engineered strain of Streptomyces fradiae that contains the genes for production of 15-methyl-deoxyerythronolide B and the 15- methylerythromycins. PHASE II: This process will be optimized for large scale production of 15- methyerythromycins that will be used to make ketolide antibiotics in sufficient amount for preclinical and clinical development. Kosan has discovered a lead ketolide in partnership with The R.W. Johnson Pharmaceutical Research Institute and expects that this compound or a close analog will be developed into a drug that is competitive with the two current front runners in this area. PROPOSED COMMERCIAL APPLICATIONS: There is a growing need to discover and develop noel antibiotics that can overcome resistance mechanisms. The proposed research will generate modified macrolide antibiotics which are effective against macrolide resistant organisms. Since world-wide sales of macrolide antibiotics exceed $3B per year, these new antibiotics should have significant commercial value.

Thesaurus Terms:
Escherichia coli, Streptomyces, antibacterial agent, drug design /synthesis /production, drug discovery /isolation, erythromycin, macrolide antibiotic bacteria infection mechanism, bacteriolysis, biotherapeutic agent, biotransformation, cholinesterase, coenzyme A, combinatorial chemistry, drug resistance, enzyme activity, enzyme biosynthesis, microorganism disease chemotherapy, microorganism immunology, molecular genetics, polyketide synthase biotechnology, polymerase chain reaction

The long-term goal of this Phase II proposal is the production of new ketolide antibiotics with potent antibacterial activity against macrolide-susceptible and macrolide-resistant bacterial pathogens of humans. In Phase I research, we successfully developed a biological process for production of 15-R-6-deoxyerythronolide B, the biochemical precursor of 15-R-erythromycins (R=various chemical groups), that involves expression of the 6-deoxyerythronolide B (DEBS) polyketide synthase (PKS) genes in an Escherichia coli strain carrying the requisite PKS substrate supply genes. In Phase II this process will be optimized for large-scale production of the desired 15-R-6-deoxyerythronolide B (15-R-6dEB) by feeding the 5R-3-hydroxy-2-methylpentanoic acid N-acetylcysteamine thioester ("diketide-SNAC") to an E. coli strain expressing the engineered DEBS1 module 2/DEBS2/DEBS3 genes. The resulting 15-R-6dEB will be used subsequently to produce a lead ketolide Kosan has discovered in partnership with another company. The specific aims for the Phase II research are: 1) to determine the relationship between the titer of polyketide produced and the level of DEBS PKS, substrate supply enzymes and substrates. These data will help us design and construct a recombinant E. coli strain that produces >100 mg/L of 15-R-6dEB in a diketide-fed, shake flask fermentation. 2) To isolate, by random mutagenesis of an E. coli strain bearing DEBS PKS and substrate supply genes, mutant strains with a >10-fold increase in 15-R-6dEB titer in a diketide-fed, shake flask fermentation. The improved genetic background of these mutants is expected to enhance the performance of the optimum arrangement of the DEBS PKS and substrate supply genes created in Specific Aim 1. 3) To introduce the optimal metabolically engineered DEBS PKS and substrate supply genes from Specific Aim 1 into the E. coli strain from Specific Aim 2 to create an E. coli recombinant strain that produces >250 mg/L of 15-R-6dEB in a diketide-fed, shake flask fermentation. 4) To optimize the physiological and process parameters for maximum production of 15-R-6dEB at >1 g/L by high cell density E. coli cultures in a 2 liter stirred fermentor. This will be done with a strain obtained through achievement of Specific Aim 3. Several of the ketolide series of analogs based on 15-R-erythromycin A have excellent in vitro and in vivo antibacterial activity, comparable to or better than the leading ketolides in current clinical trials or approved by the FDA for specific uses. We intend to move the best compound to pre-clinical testing in collaboration with our partner.

Thesaurus Terms:
Escherichia coli, Streptomyces, antibacterial agent, drug design /synthesis /production, drug discovery /isolation, erythromycin, macrolide antibiotic, polyketide synthase bacteria infection mechanism, bacteriolysis, biotherapeutic agent, biotransformation, cholinesterase, coenzyme A, combinatorial chemistry, drug resistance, enzyme activity, enzyme biosynthesis, microorganism disease chemotherapy, microorganism immunology, molecular genetics, recombinant protein biotechnology, polymerase chain reaction