Professor Rozners has delivered invited lectures at various national and international conferences, major research universities as well as small colleges. If you are interested in hosting a lecture at your school please contact Professor Rozners directly.
Amide-Modified RNA: Synthesis, Structure and RNA Interference Activity
Discovery of RNA interference (RNAi) has reinvigorated interest in chemical modifications of RNA for in vivo applications. Our current work is focused on the development of novel nonionic analogues of RNA that have the phosphodiesters replaced by amide linkages (AM1). We hypothesize that reduced negative charge and hydrophobic nature of such modifications will not only increase the enzymatic stability but also have the potential to optimize potency, cellular uptake, and pharmacokinetics of small interfering RNAs (siRNAs). A further advantage of amide modifications is that they can be prepared using relatively straightforward peptide type couplings. This presentation will discuss synthesis, structure and RNAi activity of amide-modified RNA. NMR spectroscopy (1,2) and x-ray crystallography (3) show that amides are excellent mimics of the phosphodiester inter-nucleoside linkages in RNA and suggest interesting insights into how the formally hydrophobic modification interacts with hydration of RNA. RNAi assays show that multiple amides are tolerated at internal positions in both strands of siRNAs (2,3). Surprisingly, amide modifications at the 5´-end of the passenger strand increased the RNAi activity compared to unmodified siRNA (3). The implication of these studies for improving the properties of siRNAs for potential therapeutic applications will be discussed.
- Selvam, C.; Thomas, S.; Abbott, J.; Kennedy, S. D.; Rozners, E. Amides Are Excellent Mimics of Phosphate Linkages in RNA Angew. Chem. Int. Ed. 2011, 50, 2068-2070.
- Mutisya, D.; Hardcastle, T.; Cheruiyot, S. K.; Pallan, P. S.; Kennedy, S. D.; Egli, M.; Kelley, M. L.; van Brabant Smith, A.; Rozners, E. Amide linkages mimic phosphates in RNA interactions with proteins and are well tolerated in the guide strand of short interfering RNAs. Nucleic Acid Res. 2017, 45, 8142–8155.
- Hardcastle, T., Novosjolova, I., Kotikam, V., Cheruiyot, S. K., Mutisya, D., Kennedy, S. D., Egli, M., Kelley, M. L., Smith, Anja van B., and Rozners, E. A Single Amide Linkage in the Passenger Strand Suppresses Its Activity and Enhances Guide Strand Targeting of siRNAs. ACS Chem. Biol. 2018, 13, 533–536.
Sequence Selective Recognition of Double-Stranded RNA Using Modified Peptide Nucleic Acids
The important role that non-coding double-stranded RNAs (dsRNA) play in biology and development of disease makes them attractive targets for molecular recognition. However, designing of small molecules that selectively recognize RNA has been a challenging and involved process because RNA helix presents little opportunity for shape-selective recognition. We discovered (1) that cationic nucleobase- and backbone-modified peptide nucleic acids (PNA), as short as six nucleobases, bind with low nanomolar affinity and high sequence selectivity to dsRNA via major groove triple helix formation under physiological conditions. Most interestingly, the modified PNAs exhibited unique RNA selectivity and had at least two orders of magnitude higher affinity for the dsRNAs than for the same DNA sequences. It is conceivable that the deep and narrow major groove of RNA presented a better steric fit for the PNA ligands than the wider major groove of DNA. Conjugation of PNA with short lysine peptides further enhances binding affinity, RNA over DNA selectivity, and cellular uptake of PNA. PNAs carrying M and Lys modifications were efficiently taken up by HEK-293 cells, while the unmodified PNA showed little uptake (2). Finally, we found that the modified PNAs recognized dsRNA sequences present in biologically relevant RNAs, such as microRNAs and the A-site of ribosomal RNA, with high affinity under physiological conditions. Taken together the results suggest that the modified PNAs may have unique and previously underappreciated potential for molecular recognition of dsRNA and may be promising compounds for functional modulation of biologically relevant RNA in live cells. This presentation will discuss our most recent results on sequence selective recognition of such RNAs using chemically modified PNA analogues under physiological conditions.
- Zengeya, T.; Gupta, P.; Rozners, E. Triple Helical Recognition of RNA Using 2-Aminopyridine-Modified PNA at Physiologically Relevant Conditions. Angew. Chem., Int. Ed. 2012, 51, 12593-12596.
- Hnedzko, D.; McGee, D. W.; Karamitas, Y. A.; Rozners, E. Sequence-Selective Recognition of Double-Stranded RNA and Enhanced Cellular Uptake of Cationic Nucleobase and Backbone-Modified Peptide Nucleic Acids. RNA 2017, 23, 58-69.