Phase II study of tallysomycin S10b in patients with advanced head and neck cancer

Engineered production and evaluation of 6'-deoxy-tallysomycin H-1 revealing new insights into the structure-activity relationship of the anticancer drug bleomycin

The bleomycins (BLMs), a family of glycopeptide antibiotics, are currently used clinically in combination with a number of other agents for the treatment of malignant tumors. Other members of the BLM family include tallysomycins (TLMs), phleomycins and zorbamycin (ZBM). We previously cloned and characterized the biosynthetic gene clusters for BLMs, TLMs and ZBM. Applications of combinatorial biosynthesis strategies to the three biosynthetic machineries enabled the engineered production of several BLM analogs with unique structural characteristics and varying DNA cleavage activities, thereby providing an outstanding opportunity to study the structure-activity relationship (SAR) for the BLM family of anticancer drugs. We now report the engineered production of a new BLM-TLM-ZBM hybrid metabolite, named 6'-deoxy-TLM H-1, which consists of the 22-desmethyl-BLM aglycone, the TLM A C-terminal amine and the ZBM disaccharide, by heterologous expression of the zbmGL genes from the ZBM biosynthetic gene cluster in the Streptoalloteichus hindustanus ΔtlmH mutant strain SB8005. Evaluation of the DNA cleavage activities of 6'-deoxy-TLM H-1 as a measurement for its potential anticancer activity, in comparison with TLM H-1 and BLM A2, reveals new insight into the SAR of BLM family of anticancer drugs.The Journal of Antibiotics advance online publication, 23 August 2017; doi:10.1038/ja.2017.93.

Functional characterization of tlmH in Streptoalloteichus hindustanus E465-94 ATCC 31158 unveiling new insight into tallysomycin biosynthesis and affording a novel bleomycin analog

Tallysomycins (TLMs) belong to the bleomycin (BLM) family of anticancer antibiotics and differ from the BLMs principally by the presence of a 4-amino-4,6-dideoxy-L-talose attached to C-41 of the TLM backbone as part of a glycosylcarbinolamide. To facilitate an understanding of the differences in anticancer activities observed between TLMs and BLMs, we thought to generate des-talose TLM analogs by engineering TLM biosynthesis in Streptoalloteichus hindustanus E465-94 ATCC 31158. Here we report (i) the engineering of the DeltatlmH mutant SB8005 strain that produces the two TLM analogs, TLM H-1 and TLM H-2, (ii) production, isolation, and structural elucidation of TLM H-1 and TLM H-2 by NMR and mass spectroscopic analyses as the desired des-talose TLM analogs, and (iii) comparison of the DNA cleavage activities of TLM H-1 with selected TLMs and BLMs. These findings support the previous functional assignment of tlmH to encode an alpha-ketoglutarate-dependent hydroxylase and unveil the TlmH-catalyzed hydroxylation at both C-41 and C-42 and the TlmK-catalyzed glycosylation of a labile carbinolamide intermediate as the final two steps for TLM biosynthesis. TlmH is apparently distinct from other enzymes known to catalyze carbinolamide formation. The availability of TLM H-1 now sets the stage to study the TlmH enzymology in vitro and to elucidate the exact contribution of the l-talose to the anticancer activities of TLMs in vivo.

Functional characterization of tlmK unveiling unstable carbinolamide intermediates in the tallysomycin biosynthetic pathway

Tallysomycins (TLMs) belong to the bleomycin family of anticancer antibiotics. TLMs differ from bleomycins primarily by the presence of a 4-amino-4,6-dideoxy-l-talose sugar attached to C-41 as part of a glycosylcarbinolamide. We previously proposed, on the basis of bioinformatics analysis of the tlm biosynthetic gene cluster from Streptoalloteichus hindustanus E465-94 ATCC 31158, that the tlmK gene is responsible for the attachment of this sugar moiety. We now report that inactivation of tlmK in S. hindustanus abolished TLM A and TLM B production, the resultant DeltatlmK mutant instead accumulated five new metabolites, and introduction of a functional copy of tlmK to the DeltatlmK mutant restored TLM A and TLM B production. Two major metabolites, TLM K-1 and TLM K-2, together with three minor metabolites, TLM K-3, TLM K-4, and TLM K-5, were isolated from the DeltatlmK mutant, and their structures were elucidated. These findings provide experimental evidence supporting the previous functional assignment of tlmK to encode a glycosyltransferase and unveil two carbinolamide pseudoaglycones as key intermediates in the TLM biosynthetic pathway. TlmK stabilizes the carbinolamide intermediates by glycosylating their hemiaminal hydroxyl groups, thereby protecting them from hydrolysis during TLM biosynthesis. In the absence of TlmK, the carbinolamide intermediates fragment to produce an amide TLM K-1 and aldehyde intermediates, which undergo further oxidative fragmentation to afford carboxylic acids TLM K-2, TLM K-3, TLM K-4, and TLM K-5.

The tallysomycin biosynthetic gene cluster from Streptoalloteichus hindustanus E465-94 ATCC 31158 unveiling new insights into the biosynthesis of the bleomycin family of antitumor antibiotics

The tallysomycins (TLMs) belong to the bleomycin (BLM) family of antitumor antibiotics. The BLM biosynthetic gene cluster has been cloned and characterized previously from Streptomyces verticillus ATCC 15003, but engineering BLM biosynthesis for novel analogs has been hampered by the lack of a genetic system for S. verticillus. We now report the cloning and sequencing of the TLM biosynthetic gene cluster from Streptoalloteichus hindustanus E465-94 ATCC 31158 and the development of a genetic system for S. hindustanus, demonstrating the feasibility to manipulate TLM biosynthesis in S. hindustanus by gene inactivation and mutant complementation. Sequence analysis of the cloned 80.2 kb region revealed 40 open reading frames (ORFs), 30 of which were assigned to the TLM biosynthetic gene cluster. The TLM gene cluster consists of nonribosomal peptide synthetase (NRPS) genes encoding nine NRPS modules, a polyketide synthase (PKS) gene encoding one PKS module, genes encoding seven enzymes for deoxysugar biosynthesis and attachment, as well as genes encoding other biosynthesis, resistance, and regulatory proteins. The involvement of the cloned gene cluster in TLM biosynthesis was confirmed by inactivating the tlmE glycosyltransferase gene to generate a TLM non-producing mutant and by restoring TLM production to the DeltatlmE::ermE mutant strain upon expressing a functional copy of tlmE. The TLM gene cluster is highly homologous to the BLM cluster, with 25 of the 30 ORFs identified within the two clusters exhibiting striking similarities. The structural similarities and differences between TLM and BLM were reflected remarkably well by the genes and their organization in their respective biosynthetic gene clusters.

Monoclonal antibody mediated intracellular targeting of tallysomycin S10b

The potency of tallysomycin S(10b) (TLM S(10b)) an analogue bleomycin was enhanced by up to 875-fold when it was conjugated to the internalizing antibody BR96. Attachment to the antibody is achieved via a Cathepsin B cleavable linker. The enhancement in potency is believed to be a result of cellular uptake of the conjugate upon antigen binding followed by rapid release of the drug inside the lysosome. This method provides a novel approach for increasing the potency and therapeutic index of nominally moderately-active cytotoxic agents.