Keynotes
The G4thering 2025 conference is pleased to showcase the following Keynote Speakers from June 2 – 6, 2025.

Cynthia Burrows
Thatcher Presidential Chair and Distinguished Professor
Department of Chemistry, University of Utah, USA
Oxidative Stress and Gene Expression Meet at G-Quadruplexes
After the great oxygenation event 2 billion years ago, life evolved to deal with the conundrum of O2 and Fe(II), a potentially toxic combination. Cells solved the toxicity problem of the Fenton reaction in a clever way using the free radical chemistry of bicarbonate as a redox buffer. Evidence for this hypothesis is gleaned from metabolomics, nanopore sequencing of RNA, and qPCR-based lesion detection in telomeric DNA. As a result, we show that oxidative DNA damage is focused on G-rich sequences, such as those that fold to G-quadruplexes (G4s). Many cancer-associated genes are regulated by G4s, and these same sequences are sensitive to oxidative damage that is repaired by the base excision repair glycosylases OGG1 and NEIL1-3. We describe studies indicating that oxidation of a guanosine base in a gene promoter G4 can lead to up- and downregulation of gene expression that is location dependent and involves the base excision repair pathway in which the first intermediate, an apurinic (AP) site plays a key role mediated by AP-endonuclease I (APE1/Ref-1). Surprisingly, Fe(II)-mediated DNA damage and strand breaks can turn on genes by assisting G4 folding!

Brad Chaires
Brown Chair in Cancer Biophysics
Professor, Department of Medicine & Department of Biochemistry & Molecular Biology, University of Louisville, USA
Senior Scientist, Brown Cancer Centre, USA
The G4 Folding Problem
A fundamental challenge in molecular biology is to understand how biological macromolecules fold. How do the linear chains in the primary structures of macromolecules transform into their specific three-dimensional structures that determine their function? What is the folding code – how do the primary structures of macromolecules dictate their 3D structure? What is their folding mechanism? Can native structures be predicted from primary sequences? Considerable progress toward understanding these issues has been made for proteins and RNA, but the folding of G-quadruplexes is distinctly different and remains poorly understood. I will review the status of mechanistic thermodynamic and kinetic studies of G4 folding here. The results of recent time-resolved small-angle X-ray scattering experiments that characterize early events in the folding process will be presented. A unifying model for the G4 folding process will be offered to stimulate future work.

Laurence Hurley
Professor Emeritus
College of Pharmacy and Arizona Cancer Center, University of Arizona, USA
Redefining the Molecular Target for Trabectedin (Yondelis®) as Irreversible Covalent Bonding to N2 of Guanine in Duplex Stem Loops of G-Quadruplexes
Trabectedin (Yondelis®) is a marine-derived antitumor agent from the Ecteinascidin family that is FDA-approved for treatment of soft tissue sarcomas. It features a carbinolamine that forms reversible covalent bonds with N2 of guanine, distinguishing it from typical DNA alkylating agents. Structurally, the Ecteinascidins are also distinct from other carbinolamine alkylating drugs by inclusion of a C-subunit that widens the DNA minor groove and induces transcriptional replication stress and genome instability. Taking into account the sensitivity of Ewing Sarcoma to Trabectedin and the role of EWS in binding to G-quadruplexes (G4s), especially those with longer stem loops, this presentation redefines Trabectedin’s molecular target by exploring its potential interaction with G4s. Building on these insights, we designed experiments using Trabectedin in combination with wild-type and mutant MYCN G4s to assess whether Trabectedin could irreversibly bond covalently to a consensus sequence within a duplex stem loop associated with a G4. Circular dichroism (CD) analysis confirmed that Trabectedin stabilized a G4 containing a consensus covalent bonding site within the associated hairpin loop. Mass spectrometry (MS) analysis demonstrated that a guanine in the Trabectedin consensus binding site is essential for this irreversible covalent bonding. Additionally, CD and MS showed that when Trabectedin was covalently bound to the duplex stem loop, it displaced a molecule (GSA0932) that binds noncovalently to both the core G4 structure and the stem loop. Significantly using antibody to G4s, it was observed that Trabectedin treatment significantly increased G4 frequency within cells. In conclusion, Trabectedin irreversibly bonds to N2 of guanine within a duplex stem loop of a G4 and belongs to the first clinically approved class of G4-targeted drugs.