Accessibility statement

Professor Jo Milner

Emeritus

Gene expression and disease
Cancer, inflammatory disease, and macular degeneration are all examples of disease states linked with the expression of disease-related genes. One approach for treatment is via selectively silencing the expression of those genes concerned.

RNA interference and siRNA and therapeutics
RNA interference (RNAi) offers an exciting approach for silencing disease-related genes. RNAi is a natural process and is triggered by small interfering dsRNAs (siRNAs). Sequence-specific targeting by siRNA initiates selective destruction of a given mRNA, thereby silencing expression of the gene concerned. siRNAs can readily be designed as therapeutic agents to target given mRNAs, individual mRNA splice variants, or mutant over wild type mRNA.

siRNA is rapidly degraded in the body
One of the major hurdles for the development of RNAi-based therapeutics is the susceptibility of siRNA to degradation by nucleases in the blood stream and in other tissues. In order to counter this problem chemical modification of individual nucleotides within the synthetic siRNA molecule is employed.  However, when introduced into mammalian cells, the unnatural nature of the chemically modified siRNA backbone risks activating cellular stress responses.  This can result in unwanted side effects of treatment.

Stabilisation of siRNA via single-stranded DNA extension
At York we have explored the possibility of stabilizing siRNA by extension into a single stranded DNA structure known to be resistant to nuclease digestion (Jiang et al., Nucleic Acids Research; 2005). Specifically, one of the siRNA strands (unmodified) was extended with single-stranded DNA (also unmodified). The 3’ terminus of the DNA is composed of the sequence GCGAAGC which forms a compact mini-hairpin structure.  In isolation this DNA mini-hairpin is very stable and resistant to nuclease digestion. Remarkably we discovered that the 3’ GCGAAGC (i) does not affect the efficacy of RNA interference, and (ii) confers nuclease resistance to the siRNA. No evidence of cytotoxicity or stress was observed [Allison and Milner, Molecular Therapy Nucleic Acids; 2014].

Images of (i) the patent relating to a hybrid interfering RNA molecule comprising siRNA stabilized by a ssDNA extension with 3’GCGAAGC and (ii) Dr. Ming Jiang who was largely responsible for developing this novel technology whilst a member of the YCR P53 Research Unit, Department of Biology, University of York.

Taking siRNA/GCGAAGC towards the clinic
Synthetic siRNA/GCGAAGC remains (to my knowledge) the only nuclease-resistant siRNA without chemical modification of the RNA backbone. It would appear that the remarkable structural properties of the seven nucleotide sequence GCGAAGC may help unlock the huge potential of RNAi-based therapeutics.

Future development of this novel siRNA/GCGAAGC construct is being taken forward by Argonaute RNA Limited, a UK biotech company in the field of therapeutics.

Professor Jo Milner

Contact details

Professor Jo Milner
Professor
Department of Biology (Area 2)
University of York
PO Box 373
York
YO10 5YW

Tel: 01904 328620