Binding of these diarylureas to non-telomeric quadruplexes,
for example the two found in the c-kit promoter,9–11 is very
dependent on the nature of the substituents and the particular
quadruplex, suggesting that the compounds may be tuneable
for a given target quadruplex (to be published).
This work was supported by CRUK and the EU (FP6
Project on Molecular Cancer Medicine). We are grateful to
Dr Mekala Gunaratnam for help with cell biology and Dr JE
Moses for much useful advice on click chemistry.
Notes and references
Fig. 2 The FRET-based competition assay where G4 stabilisation is
shown as the percentage of DTm1mM retained upon addition of
CT-DNA.
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G4 vs. duplex DNA selectivity was also assessed by FRET-
based methods, initially screening each of the ligands against a
duplex-forming oligonucleotide containing a range of interca-
lative binding sites [50FAM-(TA)2GC(TA)2T6(TA)2GC-
(TA)2-TAMRA30] (ds DNA). This showed that these ligands
have significantly enhanced G4 over duplex stabilisation
relative to BRACO-19 (Table 1; ESIw). The G4 selectivity of
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ligand to retain G4 stabilising affinity was challenged by excess
ratios of calf thymus DNA (CT-DNA). This shows (Fig. 2) that
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basic group of a side chain had little influence on G4 selectivity
other than for the morpholino analogue (9; B80% selective).
The combined results of these assays demonstrate the impor-
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pattern for G4 selectivity over duplex DNA, with the ortho-urea
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compounds show no toxic cellular effects up to the limits of
aqueous solubility (425 mM), across all three cell lines. Some
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ꢀc
This journal is The Royal Society of Chemistry 2008
Chem. Commun., 2008, 5295–5297 | 5297