Saumya Roy

Selective Targeting of G-Quadruplex Using Furan-Based Cyclic Homooligopeptides: Effect on c-MYC Expression

Quadruplex-specific molecules can serve as suitable drugs in cancer therapy. We have synthesized a pair of furan-based cyclic homooligopeptides, ligand 1 and ligand 2, to specifically target G-quadruplexes. We have shown by CD spectroscopy and UV melting that these ligands can effectively induce G-quadruplex structures in the G-rich 22-mer c-MYC DNA sequence and further stabilize the structure. Equilibrium binding constants measured by isothermal titration calorimeter methods indicate a high affinity of the ligands for the quadruplex structures (K ∼ 10(7) M(-1)) and no affinity for the duplex DNA, demonstrating that these ligands are selective for G-quadruplex structures. Surface plasmon resonance was also used to compute the binding while fluorescence resonance energy transfer-based assay was additionally used to confirm the selectivity. Moreover, using real time PCR we observed up to 90% downregulation of c-MYC transcripts after 24 h of ligand treatment in HeLa cells. Using a luciferase assay we show the downregulation of the protein levels. Fluorescent-assisted cell sorter-based cell cycle analysis showed a prominent arrest of cells in the sub-G1 stage upon treatment of ligands that leads toward apoptosis. Altogether, these experiments support the hypothesis that the present molecules are effective in specifically binding and stabilizing quadruplexes and provide a suitable scaffold to develop into a quadruplex-targeting therapeutic agent.

Formal Total Synthesis of (+)-Neopeltolide

This paper describes the formal total synthesis of (+)-neopeltolide, a cytotoxic macrolide isolated from the marine sponge Neopeltidae. The key features of the synthesis include an asymmetric Evans alkylation to fix the C9-methyl center, Jacobsen hydrolytic kinetic resolution of terminal epoxides followed by their regioselective opening to fix the stereocenters at the C11 and C13 positions, respectively, a Pd-catalyzed oxa-Michael reaction to construct the tetrahydropyran ring, and Yamaguchi macrolactonization to form the macrocyclic core of the molecule.

In the Sense of Transcription Regulation by G-Quadruplexes: Asymmetric Effects in Sense and Antisense Strands

G-Quadruplexes occupy important regulatory regions in the genome. DNA G-quadruplexes in the promoter regions and RNA quadruplexes in the UTRs (untranslated regions) have been individually studied and variously implicated at different regulatory levels of gene expression. However, the formation of G-quadruplexes in the sense and antisense strands and their corresponding roles in gene regulation have not been studied in much detail. In the present study, we have elucidated the effect of strand asymmetry in this context. Using biophysical methods, we have demonstrated the formation of stable G-quadruplex structure in vitro using CD and UV melting. Additionally, ITC was employed to demonstrate that a previously reported selective G-quadruplex ligand was able to bind and stabilize the G-quadruplex in the present sequence. Further, we have shown using reporter constructs that although the DNA G-quadruplex in either strand can reduce translation efficiency, transcriptional regulation differs when G-quadruplex is present in the sense or antisense strand. We demonstrate that the G-quadruplex motif in the antisense strand substantially inhibits transcription, while when in the sense strand, it does not affect transcription, although it does ultimately reduce translation. Further, it is also shown that the G-quadruplex stabilizing ligand can enhance this asymmetric transcription regulation as a result of the increased stabilization of the G-quadruplex.

Furan based cyclic homo-oligopeptides bind G-quadruplex selectively and repress c-MYC transcription

We demonstrate the synthesis and selective binding of two novel furan based tricyclic homo-oligopeptides to G-quadruplex and using Real Time PCR show its repressive effect on c-MYC transcription. CD spectroscopy and FRET melting studies show that these ligands can induce G-quadruplex structures in the G rich 22 mer c-MYC DNA sequence and further stabilize the structure. Using real time polymerase chain reaction we observed that up to 70% downregulation of c-MYC transcripts upon ligand treatment in HeLa cells.

Morphological effects of G-quadruplex stabilization using a small molecule in zebrafish.

Zebrafish (Danio rerio) embryos are transparent and advantageous for studying early developmental changes due to ex utero development, making them an appropriate model for studying gene expression changes as a result of molecular targeting. Zebrafish embryos were injected with a previously reported G-quadruplex selective ligand, and the phenotypic changes were recorded. We report marked discrepancies in the development of intersegmental vessels. In silico analysis determined that the putative G-quadruplex motif occur in the upstream promoter region of the Cdh5 (N-cadherin) gene. A real-time polymerase chain reaction-based investigation indicated that in zebrafish, CDH-2 (ZN-cad) was significantly downregulated in the ligand-treated embryos. Biophysical characterization of the interaction of the ligand with the G-quadruplex motif found in this promoter yielded strong binding and stabilization of the G-quadruplex with this ligand. Hence, we report for the first time the phenotypic impact of G-quadruplex targeting with a ligand in a vertebrate organism. This study has unveiled not only G-quadruplex targeting in non-human animal species but also the potential that G-quadruplexes can provide a ready tool for understanding the phenotypic effects of targeting certain important genes involved in differentiation and developmental processes in a living eukaryotic organism.