title: Aziridinyldinitrobenzamides: synthesis and structure-activity relationships for activation by E. coli nitroreductase.
abstract: The 5-aziridinyl-2,4-dinitrobenzamide CB 1954 is a substrate for the oxygen-insensitive nitroreductase (NTR) from E. coli and is in clinical trial in combination with NTR-armed adenoviral vectors in a GDEPT protocol; CB 1954 is also of interest for selective deletion of NTR-marked cells in normal tissues. Since little further drug development has been carried out around this lead, we report here the synthesis of more soluble variants and regioisomers and structure-activity relationship (SAR) studies. The compounds were primarily prepared from the corresponding chloro(di)nitroacids through amide side chain elaboration and subsequent aziridine formation. One-electron reduction potentials [E(1)], determined by pulse radiolysis, were around -400 mV, varying little for aziridinyldinitrobenzamide regioisomers. Cytotoxicity in a panel of NTR-transfected cell lines showed that in the CB 1954 series there was considerable tolerance of substituted CONHR side chains. The isomeric 2-aziridinyl-3,5-dinitrobenzamide was also selective toward NTR+ve lines but was approximately 10-fold less potent than CB 1954. Other regioisomers were too insoluble to evaluate. While CB 1954 gave both 2- and 4-hydroxylamine metabolites in NTR+ve cells, related analogues with substituted carboxamides gave only a single hydroxylamine metabolite possibly because the steric bulk in the side chain constrains binding within the active site. CB 1954 is also a substrate for the two-electron reductase DT-diaphorase, but all of the other aziridines (regioisomers and close analogues) were poorer substrates with resulting improved specificity for NTR. Bystander effects were determined in multicellular layer cocultures and showed that the more hydrophilic side chains resulted in a modest reduction in bystander killing efficiency. A limited number of analogues were tested for in vivo activity, using a single ip dose to CD-1 nude mice bearing WiDr-NTR(neo) tumors. The most active of the CB 1954 analogues was a diol derivative, which showed a substantial median tumor growth delay (59 days compared with >85 days for CB 1954) in WiDr xenografts comprising 50% NTR+ve cells. The diol is much more soluble and can be formulated in saline for administration. The results suggest there may be advantages with carefully selected analogues of CB 1954; the weaker bystander effect of its diol derivative may be an advantage in the selective cell ablation of NTR-tagged cells in normal tissues.
authors.affiliation: Auckland Cancer Society Research Centre, School of Medical Sciences, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand. n.helsby@auckland.ac.nz
authors.forename: Nuala A
authors.initials: NA
authors.lastname: Helsby
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Atwell
authors.forename: Shangjin
authors.initials: S
authors.lastname: Yang
authors.forename: Brian D
authors.initials: BD
authors.lastname: Palmer
authors.forename: Robert F
authors.initials: RF
authors.lastname: Anderson
authors.forename: Susan M
authors.initials: SM
authors.lastname: Pullen
authors.forename: Dianne M
authors.initials: DM
authors.lastname: Ferry
authors.forename: Alison
authors.initials: A
authors.lastname: Hogg
authors.forename: William R
authors.initials: WR
authors.lastname: Wilson
authors.forename: William A
authors.initials: WA
authors.lastname: Denny
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D001388:Aziridines / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D001549:Benzamides / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D045744:Cell Line, Tumor; D006224:Cricetinae; D004354:Drug Screening Assays, Antitumor; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism; D009368:Neoplasm Transplantation; D009601:Nitroreductases / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D011355:Prodrugs / Q000138:chemical synthesis* / Q000378:metabolism / Q000494:pharmacology; D012995:Solubility; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014162:Transfection; D014183:Transplantation, Heterologous
chemical_list: D000970:Antineoplastic Agents; D001388:Aziridines; D001549:Benzamides; D029968:Escherichia coli Proteins; D011355:Prodrugs; D016660:NAD(P)H Dehydrogenase (Quinone); C116054:NfsB protein, E coli; D009601:Nitroreductases