Expanding the Chemical Diversity of the Antitumoral Compound Mithramycin by Combinatorial Biosynthesis and Biocatalysis: The Quest for Mithralogs with Improved Therapeutic Window

Abstract

Mithramycin is an antitumor compound of the aureolic acid family produced by Streptomyces argillaceus. It has been used to treat several types of cancer including testicular carcinoma, chronic and acute myeloid leukemia as well as hypercalcemias and Paget's disease. Although the use of mithramycin in humans has been limited because its side effects, in recent years a renewed interest has arisen since new uses and activities have been ascribed to it. Chemically, mithramycin is characterized by a tricyclic aglycone bearing two aliphatic side chains attached at C3 and C7, and disaccharide and trisaccharide units attached at positions 2 and 6, respectively. The mithramycin gene cluster has been characterized. This has allowed for the development of several mithramycin analogs ("mithralogs") by combinatorial biosynthesis and/or biocatalysis. The combinatorial biosynthesis strategies include gene inactivation and/or the use of sugar biosynthesis plasmids for sugar modification. In addition, lipase-based biocatalysis enabled selective modifications of the hydroxyl groups, providing further mithramycin analogs. As a result, new mithramycin analogs with higher antitumor activity and/or less toxicity have been generated. One, demycarosyl-3D-β-D-digitoxosyl-mithramycin SK (EC-8042), is being tested in regulatory preclinical assays, representing an opportunity to open the therapeutic window of this promising molecular scaffold.

Identification of Mithramycin Analogues with Improved Targeting of the EWS-FLI1 Transcription Factor

“…In order to accomplish this, we generated a panel of more than 20 mithramycin analogs for their ability to reverse EWS-FLI1 activity. Mithramycin chemical space was expanded by genetic engineering of the MMA biosynthesis pathway and enzymatic biocatalysis to generate mithralogs showing both lower toxicity and higher biological activity (19–21). We found several mithralogs that suppressed EWS-FLI1 to a comparable or greater extent than mithramycin.…”

Activation and Characterization of Cryptic Gene Cluster: Two Series of Aromatic Polyketides Biosynthesized by Divergent Pathways

“…50 kb, Figure B; see Table S1) which contains: i) genes encoding minimal PKS TjhA1, A2, and A3, the specific cyclases TjhC3‐C4, TjhC1, and TjhA5, and the oxygenases Tjh O2/O3, which are highly homologous to OxyA, B, C, and Oxy J‐K (first‐ring cyclase), OxyN (second‐ring cyclase), SsFL2/MtmL (the fourth‐ring cyclase), and oxygenase (OxyL and OxyE), respectively. These components are involved in the biosynthesis of either oxytetracycline or SF2575 and produce the key naphthecene intermediate (see Figure S2A), beyond which, TjhA1/A2, bearing the highest similarity with the minimal PKS, is involved in the biosynthesis of the anticancer agent mithramycin (see Figure S3); ii) tjhO4 encoding a FAD‐dependent oxidase exhibiting homology with either TcmG, for the triple hydroxylation of tetracenomycin A2 to tetracenomycin C, or the Baeyer–Villiger monooxygenase MtmOIV, the key skeleton‐modifying enzyme in mithramycin biosynthesis (see Figure S2B); iii) enzymes encoded by the tjhB9/B10 gene pair, with high homology to either KstD7/D8 or TxnB3/B4, participating in the biosynthesis of γ‐branched octose (see Figures S1 and S2C) . Additionally, the gene product of tjhO1 shows homology to the quinone‐forming monooxygenase AknX, usually involved in catalyzing the oxidization of the second ring of anthracyclines to form the anthraquinone portion of most anthracyclines .…”

Bioanalytical method for quantitative determination of mithramycin analogs in mouse plasma by HPLC–QTOF

“…Therefore, regardless of therapeutic potential, major concerns over toxicity and safety have prevented MTM from becoming a clinically useful treatment option. Recent efforts have sought to circumvent these toxicities by developing MTM analogs (Baig et al, ; Mendez, Gonzalez‐Sabin, Moris, & Salas, ; Nunez et al, ; Osgood et al, ; Remsing et al, ; Scott, Chen, Bae, & Rohr, ). This approach has merit as demonstrated by the discovery of less toxic cisplatin analogs, camptothecin analogs and taxane or vinca alkaloid analogs, among others (Barnett et al, ; Bissery, Guenard, Gueritte‐Voegelein, & Lavelle, ; Harrap, ; Johnson, Hargrove, Harris, Wright, & Boder, ; Kunimoto et al, ).…”