Oligonucleotide drugs sit between small molecules and large protein drugs and have a polyanionic backbone of DNA. Jan Meffert, Early Stage Researcher at Ghent University, introduced some of his research on oligonucleotides in therapeutic applications.
Oligonucleotides’ specificity (via Watson-Crick base pairing) makes them promising; however, they face hurdles like poor cellular uptake. To overcome this, Meffert is aiming to combine oligonucleotides with antibodies. The method of choice in this research was cysteine modification since cysteines are naturally occurring in antibodies, and due to their nucleophilicity, they can easily react.
Maleimides can react with thiols containing proteins or peptides from the conjugate. Although Maleimide linkers are widely used for conjugation, they suffer from instability (retro-Michael reaction, premature hydrolysis), which makes them unreliable for stable therapeutic conjugates.
So, a new linker, 5HP2O, developed from modified furan chemistry, offers a stable alternative. It allows bioconjugation through thiol reactivity and enables dual modifications of two residues introduced in one step. The linker offers improved stability over maleimides as well as customisable side chains for enhanced solubility and targeting.
Comparative chemistry studies between maleimide and 5HP2O showed that 5HP2O-based conjugates remain stable under physiological conditions, while maleimide-based ones degrade significantly. For instance, under glutathione exchange conditions 5HP2O achieved 80% retention, whereas maleimide only retained 40%.  Additionally, 5HP2O achieved superior hydrolytic stability, which was particularly evident at pH 8.
Through systematic testing of various linker-PNA combinations, they identified a construct using arginine-modified PNA and ethylene glycol-containing 5HP2O that enabled successful conjugation without precipitation. Merhett concluded his presentation with a streamlined method for direct DNA modification using 5HP2O, offering a fast and efficient alternative to traditional multi-step processes. 
