Selectivity of major isoquinoline alkaloids from Chelidonium majus towards telomeric G-quadruplex: A study using a transition-FRET (t-FRET) assay

Abstract

BackgroundNatural bioproducts are invaluable resources in drug discovery. Isoquinoline alkaloids of Chelidonium majus constitute a structurally diverse family of natural products that are of great interest, one of them being their selectivity for human telomeric G-quadruplex structure and telomerase inhibition. MethodsThe study focuses on the mechanism of telomerase inhibition by stabilization of telomeric Gquadruplex structures by berberine, chelerythrine, chelidonine, sanguinarine and papaverine. Telomerase activity and mRNA levels of hTERT were estimated using quantitative telomere repeat amplification protocol and qPCR, in MCF-7 cells treated with different groups of alkaloids. The selectivity of the main isoquinoline alkaloids of Chelidonium majus towards telomeric Gquadruplex forming sequences were explored using a sensitive modified thermal FRET-melting measurement in the presence of the complementary oligonucleotide CT22. We assessed and monitored G-quadruplex topologies using circular dichroism (CD) methods, and compared spectra to previously well-characterized motifs, either alone or in the presence of the alkaloids, Molecular modeling was performed to rationalize ligand binding to the G-quadruplex structure. ResultsThe results highlight strong inhibitory effects of chelerythrine, sanguinarine and berberine on telomerase activity, most likely through substrate sequestration. These isoquinoline alkaloids interacted strongly with telomeric sequence G-quadruplex. In comparison, chelidonine and papaverine had no significant interaction with the telomeric quadruplex, while they strongly inhibited telomerase at transcription level of hTERT. Altogether, all of the studied alkaloids showed various levels and mechanisms of telomerase inhibition. ConclusionsWe report on a comparative study of anti-telomerase activity of the isoquinoline alkaloids of Chelidonium majus. Chelerythrine was most effective in inhibiting telomerase activity by substrate sequesteration through G-quadruplex stabilization. General SignificanceUnderstanding structural and molecular mechanisms of anti-cancer agents can help in developing new and more potent drugs with fewer side effects. Isoquinolines are the most biologically active agents from Chelidonium majus, which have shown to be telomeric G-quadruplex stabilizers and potent telomerase inhibitors.

Molecular Recognition of the Hybrid‐2 Human Telomeric G‐Quadruplex by Epiberberine: Insights into Conversion of Telomeric G‐Quadruplex Structures

“…[13] Berberine (Figure S2) and its derivatives have been shown to stabilize telomeric G4s and inhibit telomerase. [14] We recently found that EPI (Figure 1c) exhibits great fluorescence enhancement upon binding to human telomeric G4 in K + solution, up to 45 times stronger than other G4s and double-stranded and single-stranded DNA. [15] Here, we report that EPI specifically recognizes the hybrid-2 telomeric G4 and we elucidate the molecular mechanism for this specific recognition by NMR structure determination of the 1:1 EPI-wtTel26 complex in K + solution.…”

Telomere shortening in breast cancer cells (MCF7) under treatment with low doses of the benzylisoquinoline alkaloid chelidonine

“…Relative average telomere length can be measured by MMQPCR using primers that hybridize with the telomere hexamer repeats because the number of binding sites for the primers increases as average telomere length increases [ 37 , 38 ]. However, MMQPCR simultaneously counts the copy number of albumin as a single copy gene in each reaction tube using a specific primer pair, so the relative amount of telomere copies (T) to albumin (S) of the untreated control is measured.…”

Terpenes from essential oils and hydrolate ofTeucrium alopecurustriggered apoptotic events dependent on caspases activation and PARP cleavage in human colon cancer cells through decreased protein expressions

“…Natural bioproducts are invaluable resources in drug discovery [28]. Many reports have documented the antitumor effects of essential oils and their bioactive compounds.…”