Mithramycin analogues generated by combinatorial biosynthesis show improved bioactivity

Area of Science:

• Microbiology
• Biochemistry
• Pharmacology

Background:

• Mithramycin (MTM) is an antitumor drug with limitations in its therapeutic application.
• Modifying the glycosylation pattern of MTM can potentially enhance its efficacy and overcome resistance.
• Streptomyces argillaceus is a known producer of mithramycin.

Purpose of the Study:

• To engineer Streptomyces argillaceus to produce novel mithramycin derivatives with altered saccharide patterns.
• To investigate the impact of overexpressing the nucleoside-diphosphate (NDP)-activated l-digitoxose biosynthetic pathway on MTM production.
• To evaluate the anticancer activity of the novel MTM derivatives against breast cancer cell lines.

Main Methods:

• Overexpression of the l-digitoxose biosynthetic pathway using plasmid pLNBIV in Streptomyces argillaceus.
• Fermentation and isolation of novel mithramycin derivatives.
• Structural elucidation of the new compounds.
• Apoptosis induction assay using TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) on MCF-7 (ER-positive) and MDA-231 (ER-negative) breast cancer cell lines.

Main Results:

• Production of four new mithramycin derivatives (1-4) with unique sugar decoration patterns.
• The novel sugars influenced glycosyl transfer at positions B, D, and E of the MTM structure.
• Compounds 1 and 3 demonstrated improved apoptosis induction in MCF-7 cells compared to MTM.
• Compounds 1 and 4 showed significant apoptosis induction in MDA-231 cells, where MTM was ineffective.

Conclusions:

• Overexpression of the l-digitoxose pathway successfully generated novel MTM derivatives with altered glycosylation.
• The new derivatives exhibit enhanced or novel anticancer activity against specific breast cancer subtypes.
• These findings provide a basis for developing improved mithramycin-based chemotherapeutics.