Tiancimycins (TNMs) are a group of 10-membered anthraquinone-fused enediynes, newly discovered from Streptomyces sp. CB03234. Among them, TNM-A and TNM-D have exhibited excellent antitumor performances and could be exploited as very promising warheads for the development of anticancer antibody-drug conjugates (ADCs).However, their low titers, especially TNM-D, have severely limited following progress.Therefore, the streptomycin-induced ribosome engineering was adopted in this work for strain improvement of CB03234, and a TNMs high producer S. sp. CB03234-S with the K43N mutation at 30S ribosomal protein S12 was successfully screened out. Subsequent media optimization revealed the essential effects of iodide and copper ion on the production of TNMs, while the substitution of nitrogen source could evidently promote the accumulation of TNM-D, and the ratio of produced TNM-A and TNM-D was responsive to the change of carbon and nitrogen ratio in the medium. Further amelioration of the pH control in scaled up 25 L fermentation increased the average titers of TNM-A and TNM-D up to 13.7 ± 0.3 and 19.2 ± 0.4 mg/L, respectively. The achieved over 45-fold titer improvement of TNM-A, and 109-fold total titer improvement of TNM-A and TNM-D enabled the efficient purification of over 200 mg of each target molecule from 25 L fermentation. Our efforts have demonstrated a practical strategy for titer improvement of anthraquinone-fused enediynes and set up a solid base for the pilot scale production and preclinical studies of TNMs to expedite the future development of anticancer ADC drugs.

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The complex life cycle of streptomycetes is closely related to their secondary metabolisms, all controlled by cascade regulations. Tiancimycins (TNMs) are ten-membered enediynes possessing great potential for antitumor drug development. However, their low yields in Streptomyces sp. CB03234 have greatly limited subsequent studies. Through transcriptome analysis and genetic characterization, we proved that WblA is one pivotal global regulator to repress the biosynthesis of TNMs. The deletion of wblA could significantly enhance the production of TNMs, but also abolish the sporulation in CB03234. By constructing the NitRε-caprolactam inducible genetic switch, the expression of wblA was governed in CB03234-NRW, thereby sustaining the overproduction of TNMs and recovering the normal sporulation upon induction, which were practical for the scaled-up production of TNMs. Considering the prevalence and conserved regulatory roles of WblA in streptomycetes, our developed strategy shall provide an effective and practical approach to facilitate titer improvement and discovery of natural products.

Background: Tuberculosis (TB) and its evolving drug resistance have exerted severe threats on the global health, hence it is still essential to develop novel anti-TB antibiotics. Ilamycin-E1/E2 is a pair of cycloheptapeptide enantiomers obtained from a marine Streptomyces atratus SCSIO ZH16-ΔilaR mutant, and has presented significant anti-TB activities as promising drug lead compounds, but their clinical development has been hampered by low fermentation titers. Main methods and major results:By applying the statistical Plackett-Burman design (PBD) model, bacterial peptone was first screened out as the only significant but negative factor to affect the ilamycin-E1/E2 production. Subsequent single factor optimization in shaking flasks revealed that the replacement of bacterial peptone with malt extract could not only eliminate the accumulation of porphyrin-type competitive byproducts but also improve the titer of ilamycin-E1/E2 from original 13.6 ± 0.8 to 142.7 ± 5.7 mg L −1 , about 10.5-fold increase. Next, a pH coordinated feeding strategy was adopted in 30 L fermentor and obtained 169.8 ± 2.5 mg L −1 ilamycin-E1/E2, but further scaled-up production in 300 L fermentor only gave a titer of 131.5 ± 7.5 mg L −1 due to the unsynchronization of feeding response and pH change. Consequently, a continuous pulse feeding strategy was utilized in 300 L fermentor to solve the above problem and finally achieved 415.7 ± 29.2 mg L −1 ilamycin-E1/E2, representing a 30.5-fold improvement.Implication: Our work has provided a solid basis to acquire sufficient ilamycin-E1/E2 lead compounds and then support their potential anti-TB drug development.

The identification and characterization of enediyne polyketide synthases (PKSE) revealed that PKSE-bound polyene is a common intermediate, while its subsequent tailoring steps to enediyne cores remains obscure. Herein, we report...