Tallysomycin S10b: experimental antitumor activity and toxicity

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.

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.

Phase II study of tallysomycin S10b in patients with advanced colorectal cancer

A total of 16 patients with histologically confirmed colorectal cancer were entered into this phase II trial, designed to evaluate the efficacy and safety of tallysomycin S10b. The compound was given i.v. weekly at a dose of 2.5 mg/m2 by push injection. Pulmonary toxicity was the most significant side effect; it was observed in three patients and required treatment discontinuation in one. Skin lesions occurred in three patients. Other side effects were mild and their relationship to drug administration was ill-defined. No responses were observed in this group of patients, most of whom had received prior therapy.

Exacerbation of tallysomycin toxicity in rats by concurrent exposure to sublethal hyperoxia

Rats were given daily subcutaneous injections of tallysomycin S10b (TLM) or bleomycin (BLM) for 6 days (1.25 or 2.50 mg/day). One half of each group was exposed to 80% oxygen for the last 4 days of drug treatment and then returned to room air. TLM produced marked mortality in contrast to equal doses of BLM. Exposure to 80% oxygen increased the lethality of either TLM and BLM treatments. The cause of death appeared to be related to pulmonary changes. Two weeks following the end of treatment in the low dose experiment, the lungs of surviving BLM-hyperoxia, TLM, and TLM-hyperoxia rats demonstrated severe vascular damage consistent with both endothelial cell and smooth muscle proliferation in pulmonary blood vessels. BLM-hyperoxia rats also demonstrated a more typical diffuse interstitial disease. All treatments produced an increase in lung-to-body weight ratio and a decrease in vital capacity and total lung compliance, as compared to age-matched controls. TLM toxicity was exacerbated by short-term exposure to 80% oxygen. Morbidity and mortality appeared to be related to severe lung changes similar to the hyperoxic potentiation of BLM lung disease.

A radioimmunoassay procedure for tallysomycin S10b in human plasma and urine

A simple and sensitive radioimmunoassay (RIA) procedure was developed and validated for the analysis of tallysomycin S10b in human plasma and urine. The assay utilized antisera developed in rabbits, 125I-tallysomycin as the radioligand, and dextran-coated charcoal to separate free and bound antigen. The antibody was specific in that it did not cross-react with either tallysomycin A or bleomycin. The lower limit of quantification was 5 ng per ml plasma or urine, and the linear range of the assay was 5-320 ng tallysomycin S10b base per ml plasma or urine. The within-day assay variability (%RSD) for plasma and urine was 11% at a concentration of 50 ng per ml, and 3% and 7% for plasma and urine, respectively at 200 ng per ml. Within-day accuracy ranged from 100% to 108% of the theoretical value. Tallysomycin S10b was stable in human plasma and urine at concentrations of 20 and 160 ng per ml for at least 7 months when stored at -20 degrees C. The method was applied to the analysis of plasma and urine samples from a patient given tallysomycin S10b as part of a phase I study.