Spectroscopic investigation of the interaction between G-quadruplex of KRAS promoter sequence and three isoquinoline alkaloids

• Binding modes of three alkaloids with KRAS G-quadruplex were comparatively probed by different spectroscopic methods.
• Sanguinarine was more beneficial to maintain the parallel G-quadruplex structure.
• Sanguinarine had a better binding capacity and a more effective antiproliferation activity on SW620 cells.
• Binding property with KRAS G-quadruplex and antiproliferation effects of alkaloids were related to molecular structures.

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) × 106 L mol− 1, (0.93 ± 0.21) × 106 L mol− 1 and (1.16 ± 0.45) × 106 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.

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