E. coli NfsA: an alternative nitroreductase for prodrug activation gene therapy in combination with CB1954

Prodrug activation gene therapy is a developing approach to cancer treatment, whereby prodrug-activating enzymes are expressed in tumour cells. After administration of a non-toxic prodrug, its conversion to cytotoxic metabolites directly kills tumour cells expressing the activating enzyme, whereas the local spread of activated metabolites can kill nearby cells lacking the enzyme (bystander cell killing). One promising combination that has entered clinical trials uses the nitroreductase NfsB from Escherichia coli to activate the prodrug, CB1954, to a potent bifunctional alkylating agent. NfsA, the major E. coli nitroreductase, has greater activity with nitrofuran antibiotics, but it has not been compared in the past with NfsB for the activation of CB1954. We show superior in vitro kinetics of CB1954 activation by NfsA using the NADPH cofactor, and show that the expression of NfsA in bacterial or human cells results in a 3.5- to 8-fold greater sensitivity to CB1954, relative to NfsB. Although NfsB reduces either the 2-NO2 or 4-NO2 positions of CB1954 in an equimolar ratio, we show that NfsA preferentially reduces the 2-NO2 group, which leads to a greater bystander effect with cells expressing NfsA than with NfsB. NfsA is also more effective than NfsB for cell sensitisation to nitrofurans and to a selection of alternative, dinitrobenzamide mustard (DNBM) prodrugs

Validating TDP1 as an Inhibition Target for the Development of Chemosensitizers for Camptothecin-Based Chemotherapy Drugs.

Cancer chemotherapy sensitizers hold the key to maximizing the potential of standard anticancer treatments. We have a long-standing interest in developing and validating inhibitors of the DNA repair enzyme tyrosyl-DNA phosphodiesterase 1 (TDP1) as chemosensitizers for topoisomerase I poisons such as topotecan. Herein, by using thieno[2,3-b]pyridines, a class of TDP1 inhibitors, we showed that the inhibition of TDP1 can restore sensitivity to topotecan, results that are supported by TDP1 knockout cell experiments using CRISPR/Cas9. However, we also found that the restored sensitivity towards topoisomerase I inhibitors is likely regulated by multiple complementary DNA repair pathways. Our results showed that one of these pathways is likely modulated by PARP1, although it is also possible that other redundant and partially overlapping pathways may be involved in the DNA repair process. Our work thus raises the prospect of targeting multiple DNA repair pathways to increase the sensitivity to topoisomerase I inhibitors

THE CONCISE GUIDE TO PHARMACOLOGY 2021/22: Enzymes.

The Concise Guide to PHARMACOLOGY 2021/22 is the fifth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of nearly 1900 human drug targets with an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes over 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/bph.15542. Enzymes are one of the six major pharmacological targets into which the Guide is divided, with the others being: G protein-coupled receptors, ion channels, nuclear hormone receptors, catalytic receptors and transporters. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2021, and supersedes data presented in the 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate