Functional Characterization of Cytochrome P450 Hydroxylase YpmL in Yangpumicin A Biosynthesis and Its Application for Anthraquinone-Fused Enediyne Structural Diversification

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.

Normal and Aberrant Methyltransferase Activities Give Insights into the Final Steps of Dynemicin A Biosynthesis

The naturally occurring enediynes are notable for their complex structures, potent DNA cleaving ability, and emerging usefulness in cancer chemotherapy. They can be classified into three distinct structural families, but all are thought to originate from a common linear C15-heptaene. Dynemicin A (DYN) is the paradigm member of anthraquinone-fused enediynes, one of the three main classes and exceptional among them for derivation of both its enediyne and anthraquinone portions from this same early biosynthetic building block. Evidence is growing about how two structurally dissimilar, but biosynthetically related, intermediates combine in two heterodimerization reactions to create a nitrogen-containing C30-coupled product. We report here deletions of two genes that encode biosynthetic proteins that are annotated as S-adenosylmethionine (SAM)-dependent methyltransferases. While one, DynO6, is indeed the required O-methyltransferase implicated long ago in the first studies of DYN biosynthesis, the other, DynA5, functions in an unanticipated manner in the post-heterodimerization events that complete the biosynthesis of DYN. Despite its removal from the genome of Micromonospora chersina, the ΔdynA5 strain retains the ability to synthesize DYN, albeit in reduced titers, accompanied by two unusual co-metabolites. We link the appearance of these unexpected structures to a substantial and contradictory body of other recent experimental data to advance a biogenetic rationale for the downstream steps that lead to the final formation of DYN. A sequence of product-forming transformations that is in line with new and existing experimental results is proposed and supported by a model reaction that also encompasses the formation of the crucial epoxide essential for the activation of DYN for DNA cleavage.

Application of a Biocatalytic Strategy for the Preparation of Tiancimycin-Based Antibody-Drug Conjugates Revealing Key Insights into Structure-Activity Relationships

Antibody-drug conjugates (ADCs) are cancer chemotherapeutics that utilize a monoclonal antibody (mAb)-based delivery system, a cytotoxic payload, and a chemical linker. ADC payloads must be strategically functionalized to allow linker attachment without perturbing the potency required for ADC efficacy. We previously developed a biocatalytic system for the precise functionalization of tiancimycin (TNM)-based payloads. The TNMs are anthraquinone-fused enediynes (AFEs) and have yet to be translated into the clinic. Herein, we report the translation of biocatalytically functionalized TNMs into ADCs in combination with the dual-variable domain (DVD)-mAb platform. The DVD enables both site-specific conjugation and a plug-and-play modularity for antigen-targeting specificity. We evaluated three linker chemistries in terms of TNM-based ADC potency and antigen selectivity, demonstrating a trade-off between potency and selectivity. This represents the first application of AFE-based payloads to DVDs for ADC development, a workflow that is generalizable to further advance AFE-based ADCs for multiple cancer types.