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Tyrosyl-DNA phosphodiesterase 2 (TDP2) is a DNA repair enzyme that removes 5'-phosphotyrosyl blockages resulting from topoisomerase II (TOP2)-DNA cleavage complexes trapped by TOP2 inhibitors. TDP2 is a logical target for the development of therapeutics to complement existing treatments based on inhibition of TOP2. There is, however, no TDP2 inhibitor in clinical development at present. Of the reported TDP2 inhibitors, the deazaflavins are the most promising chemical class centered around the lead compound SV-5-153. Recently we reported new subtypes derived within the deazaflavin family with improved membrane permeability properties. In this work we characterize two representative analogues from two new deazaflavin subtypes based on their biochemical TDP2 inhibitory potency and drug-likeness. We demonstrate that the ZW-1288 derivative represents a promising direction for the development of deazaflavins as therapeutic agents. ZW-1288 exhibits potent inhibitory activity at low nanomolar concentrations against recombinant and cellular human TDP2 with profile similar to that of the parent analog SV-5-153 based on high resistance against murine TDP2 and human TDP2 mutated at residue L313H. While expressing weak cytotoxicity on its own, ZW-1288 potentiates the clinical TOP2 inhibitors etoposide (ETP) and mitoxantrone in human prostate DU145 and CCRF-CEM leukemia and chicken lymphoma DT40 cells while not impacting the activity of the topoisomerase I (TOP1) inhibitor camptothecin or the PARP inhibitor olaparib. ZW-1288 increases the uptake of ETP to a lesser extent than SV-5-153 and remained active in TDP2 knockout cells indicating that the deazaflavin TDP2 inhibitors have additional cellular effects that will have to be taken into account for their further development as TDP2 inhibitors., (Published by Elsevier B.V.)

Dibenzothiophene monooxygenase is the initiating enzyme in the Rhodococcus 4S biodesulfurization pathway. A member of the Class D flavin monooxygenases, it uses FMN to activate molecular oxygen for oxygenation of the substrate, dibenzothiophene. Here, we have used stopped-flow spectrophotometry to show that DszC forms a peroxyflavin intermediate in the absence of substrate. Mutagenesis of Ser163 and His391 to Ala appears to decrease the binding affinity for reduced FMN and eliminates the enzyme's ability to stabilize the peroxyflavin intermediate., (Copyright © 2016 Elsevier Inc. All rights reserved.)