Semi‐Synthetic Mithramycin SA Derivatives with Improved AntiCancer Activity

Abstract

Mithramycin (MTM) is a potent anti‐cancer agent that has recently garnered renewed attention. This manuscript describes the design and development of mithramycin derivatives through a combinational approach of biosynthetic analogue generation followed by synthetic manipulation for further derivatization. Mithramycin SA is a previously discovered analogue produced by the M7W1 mutant strain alongside the improved mithramycin analogues mithramycin SK and mithramycin SDK. Mithramycin SA shows decreased anti‐cancer activity compared to mithramycin and has a shorter, two carbon aglycon side chain that is terminated in a carboxylic acid. The aglycon side chain is responsible for an interaction with the DNA‐phosphate backbone as mithramycin interacts with its target DNA. It was therefore decided to further functionalize this side chain through reactions with the terminal carboxylic acid in an effort to enhance the interaction with the DNA phosphate backbone and improve the anti‐cancer activity. This side chain was modified with a variety of molecules increasing the anti‐cancer activity to a comparable level to mithramycin SK. This work shows the ability to transform the previously useless mithramycin SA into a valuable molecule and opens the door to further functionalization and semi‐synthetic modification for the development of molecules with increased specificity and/or drug formulation.

Dimerization and DNA recognition rules of mithramycin and its analogues

“…Microtiter plates were purchased from Thermo Fisher (Waltham, MA). MTM, MTM SDK, PreMTM B, and MTM SA Ala, were produced by previously reported procedures [17,19,31]. …”

“… a The solvent used for NMR experiments was methanol- d4 . b 13 C NMR data was inferred from gHSQC and gHMBC spectra. c The numbers in the parentheses are based on previously published mithramycin data [19]. …”

“…Combinatorial biosynthetic and semisynthetic approaches yielded several MTM analogues including MTM SDK (for Short side chain, DiKeto) [17], MTM SK (for Short side chain, Keto), MTM SA (for Short side chain, Acid) [18], and MTM SA-amino acid residue derivatives (Fig. 1) [19]. Genetic engineering of the MTM-producing bacterium Streptomyces argillaceus to inactivate the gene mtmW encoding the enzyme catalyzing the final step of the MTM biosynthetic pathway, the ketoreductase MtmW, yielded derivatives MTM SA, MTM SK [18], and MTM SDK [17].…”

“…MTM SA had a decreased cytotoxicity [18] but the carboxylic moiety provided a chemical handle that could be readily and selectively modified to further diversify this analogue towards derivatives with increased activity. The amino acid residue derivatives of MTM SA contained glycine, valine, cysteine, and alanine residues, of which MTM SA-Ala was the most promising, although still not as potent as MTM SK or MTM SDK against a human non-small cell lung cancer cell line A549 [19]. Consequently, additional MTM SA amino acid derivatives have been generated including the most promising MTM SA-Trp, which we present here for the first time.…”

One-step high-efficiency CRISPR/Cas9-mediated genome editing in <italic>Streptomyces</italic>

“…They produce many compounds with various structures and biological activities, including antibacterial, antifungal, immunosuppressive, anticancer, and antivirus activities, which are major sources of clinically important medicines and are lead candidates for new drug development [1][2][3][4][5][6][7][8][9][10]. More than two-thirds of natural antibiotics [11,12] and large numbers of intermediates for semi-synthetic drug development [13][14][15] originate from Streptomyces. Whole genome sequencing of Streptomyces has uncovered a large group of cryptic secondary metabolite biosynthetic gene clusters, most of which are structurally and functionally unknown and represent an important asset for the discovery of pharmaceutically valuable compounds [16][17][18][19][20].…”