Abstract
In the search for selective antitumour dmgs. recent studies have centred on DNA-binding ligands with enhanced GC-recognition properties. Such agents are attractive, since the 5 '-flank of some oncogenes are GC-rich and many successful anticancer drugs are GC-selective.The interaction of covalent minor-groove binders, such as CC1065 and the pyrrolo[2,1-c][ 1,4]benzodiazepines (PBDs), with DNA is thought to comprise two discrete components, referred to as "bonding" and "binding". Both mechanisms govern sequence selectivity and binding affinity. however, in the case of the PBDs, it is not known which component exerts a controlling influence. Although covalent bonding to DNA through guanine-N2 is well established, sequence-selectivity appears to extend beyond that of simple guanine alkylation (PBDs exhibit a preference for PuGPu triplets).
In order to investigate the influence of the secondary ("binding") component of DNA-interaction, a series of fifteen pyITolof2. 1-c H 1,4 ]benzodiazepine-5, I 1-diones (dilactams; 50, 57-70) have been synthesised and evaluated for binding using thermal denaturation and fluorescence quenching techniques. These compounds lack the NIO-Cl I carbinolamine essential for covalent bonding. Two dilactams of the series, SO and 57, were found to exhibit non-covalent bonding, suggesting that secondary interactions contribute significantly to the overall DNA-interaction of naturally occurring PBDs.
Based on these observations, it was anticipated that modification of the PBD ring should produce changes in sequence selectivity and/or binding affinity. Molecular modelling of an anthramycin-bound 5'-CGA-3' sequence suggested that replacement of Cl with oxygen might improve binding and modify sequence-recognition in favour of GC-regions. This necessitated synthesis of the novel oxazolo[2,3-c][I,4]benzodiazepine (OBD) system.
Four OBDs (92a,b,d,e) were synthesised, with substitution patterns based on biologically active PBDs. For comparison, the equivalent PBDs (103a,b,d,e) were also prepared. Both sets of compounds were evaluated for cytotoxicity in three cell lines, and their DNA interaction studied by footprinting and molecular modelling. All compounds examined were found to bind to DNA and were cytotoxic. The OBDs thus represent a new class of DNA-interactive antitumour agents. Between the OBDs and PBDs, and also within each series, a general correlation was found between molecular modelling and footprinting, and in vitro cytotoxicity (8-hydroxy-7-methoxy ~ 8-bcnzyloxy-7-methoxy > 9-hydroxy-8-methyl > 9-methyl). However, some differences in sequence preference were noted in the OBD-series.
These results further highlight the influence of secondary interactions on the binding mechanism in this family of compounds, and prove that sequence selectivity is a function of structure. These findings should prove useful in future drug design.
| Date of Award | 1991 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | David E. Thurston (Supervisor) |