KRAS promoter can form G-quadruplex structure and regulate gene transcription. The drugs which can bind with G-quadruplex of KRAS promoter may be potential remedy for treatment of cancers associated with KRAS mutation. The interaction mechanism between the G-quadruplex of KRAS promoter and three isoquinoline alkaloids (jatrorrhizine, berberine and sanguinarine) has been investigated by UV-visible, fluorescence and circular dichroism spectroscopic methods. The results showed that the three alkaloids can form complexes with G-quadruplex KRAS promoter with the molecular ratio of 1:1, and the binding constants were (0.90 ± 0.16) × 10 6 L mol − 1 , (0.93 ± 0.21) × 10 6 L mol − 1 and (1.16 ± 0.45) × 10 6 L mol − 1 for jatrorrhizine , berberine and sanguinarine . The absorption spectra, KI quenching and fluorescence anisotropy and polarization studies suggested jatrorrhizine and berberine interacted with G-quadruplex by not only end-stacking binding mode but also grooves or loops binding mode, while sanguinarine by end-stacking binding mode. Sanguinarine was more beneficial to maintain the stability and parallel conformation of KRAS promoter G-quadruplex. MTT assay was performed to evaluate antiproliferation effects of the three isoquinoline alkaloids on SW620 cells, and the antiproliferation effects of the three alkaloids were sanguinarine > berberine > jatrorrhizine. All the three alkaloids can bind with KRAS promoter G-quadruplex, and sanguinarine had the better binding property and antiproliferation effects on SW620 cells. The results obtained are meaningful to explore potential reagents targeting the parallel G-quadruplex structure of KRAS promoter for gene theraphy of colorectal carcinomas.
Folding of nucleic acids is strongly dependent on metal ions. For example, G-quadruplex (G4) structures are usually determined by the specific K+/Na+ coordination. However, G4 constructs highly selective to high-valent metal ions (for instance, trivalent metal ions) have not been found due to their strong and nonspecific phosphate backbone interactions. Herein, a higher-order G4 structure having a heptad junction formed by GGA repeats (for example, GGA8 with eight repeats) of the human c-myb promoter region was found to stoichiometrically recruit three Tb3+ ions. The junction binding of Tb3+ did not affect the global G4 structure of GGA8 because of its high stability in K+. The three context A/A contacts with a proper stacking orientation and an appropriate interbase distance were proved to be the specific binding sites of Tb3+ (A/Tb3+/A). Other high-valent metal ions were unable to interfere with this specific Tb3+ binding, suggestive of the potential of GGA8 serving as an aptamer-like DNA for Tb3+. This A/Tb3+/A binding was also found in another KRAS promoter G4 structure with the same A/A contact, indicating the potential of Tb3+ in selectively probing G4 structures. This work will also inspire more interest in searching higher-order G4 structures for selectively coordinating high-valent metal ions with the purpose of their detection, enrichment, and recovery.
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