Dynemicin A Derivatives as Potential Cancer Chemotherapeutics by Mutasynthesis.

The enediyne antitumor antibiotics have remarkable structures and exhibit potent DNA cleavage properties that have inspired continued interest as cancer therapeutics. Their complex structures and high reactivity, however, pose formidable challenges to their production and development in the clinic. We report here proof-of-concept studies using a mutasynthesis strategy to combine chemical synthesis of select modifications to a key iodoanthracene-γ-thiolactone intermediate in the biosynthesis of dynemicin A and all other known anthraquinone-fused enediynes (AFEs). By chemical complementation of a mutant bacterial producer that is incapable of synthesizing this essential building block, we show that derivatives of dynemicin can be prepared substituted in the A-ring of the anthraquinone motif. In the absence of competition from native production of this intermediate, the most efficient utilization of these externally-supplied structural analogues for precursor-directed biosynthesis becomes possible. To achieve this goal, we describe the required Δorf15 blocked mutant and a general synthetic route to a library of iodoanthracene structural variants. Their successful incorporation opens the door to enhancing DNA binding and tuning the bioreductive activation of the modified enediynes for DNA cleavage.

Internal abstraction of dynemicin A: An MD approach.

Dynemicin A has the ability to undergo the Bergman cyclization, forming a para-benzyne moiety with the ability to induce DNA strand scission. This property of dynemicin A makes it a promising anti-tumor agent. Past research has shown conclusively that dynemicin A binds to and abstracts a hydrogen atom (H5') from the DNA backbone, but the molecular mechanism of the binding event is not fully understood. We have used AMBER Molecular Dynamics simulations to investigate the dynamics associated with the reaction mechanisms. Previously, two binding mechanisms have been proposed, of which the second is more supported: (1) dynemicin A intercalates between two base pairs and directly abstracts a hydrogen atom from DNA and (2) dynemicin A inserts into the minor groove and directly abstracts a hydrogen atom from DNA. We propose a third mechanism, where dynemicin A intercalates, then undergoes a proximate, intramolecular hydrogen atom abstraction (internal abstraction). While not studied here, the resulting radical would then subsequently abstract a hydrogen atom from DNA.