chemically modified short interfering sirna for targeted ... · gene silencing 4 any technique or...
TRANSCRIPT
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http://www.cancer.gov/cancertopics/types/pancreatic
Pancreatic cancer is the fourth most common cause of cancer-related deaths in the United States.
Estimated new cases and deaths from pancreatic cancer in the United States in 2013:
New cases: 45,220 Deaths: 38,460
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Genes and Disorders
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Gene Silencing
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Any technique or mechanism in which the expression of a gene is prevented.
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•Protein Inhibition
•Inhibition of translation
•Degradation of the mRNA
•Regulation of
transcription
•siRNA •AONs
Strategies for Gene Silencing
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Milhavet, O.; Gary, D.S.; Mattson, M.P. Pharmacol. Rev. 2003, 55, 629.
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Gene Silencing
Food and agriculture
Gene therapy
Cancer
Cardiovascular and Cerebrovascular
Diseases
Neurodegenerative Disorders
(Huntington's disease)
Viral infections
Gene Silencing
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Robinson, R. RNAi therapeutics: PLoS Biol. 2, E28 (2004).
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Antisense Oligonucleotides (AONs)
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2012 Pearson education, Inc 8
Short Interfering RNA (siRNA)
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siRNA
Deleavey, G.F.; Damha, M.J. Chem. Biol. 2012, 19, 937.
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si-RNA
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Fire, A.; Xu, S.; Montgomery, M.K.; Kostas, S.A.; Driver, S.E. Mello, C.C. Nature 1998, 391, 806.
Elbashir, S.M.; Harborth, J.; Lendeckel, W.; Yalcin, A.; Weber, K.; Tuschl, T. Nature 2001, 411, 494.
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Importance of siRNA
Andrew Fire (1998) “double-stranded RNA was substantially more effective at producing interference than was either strand individually.”
Thomas Tuschl (2001) First report of using synthetic siRNA in mammalian cell line
siRNA: More resistant to nuclease degradation
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Zhou, J.; Shum, K.T.; Burnett, J.C.; Rossi, J.J. Pharmaceuticals 2013, 6, 85.
Liver cancer
Hypercholesterolemia
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siRNAs in Clinical Pipeline
Asthma
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Outline
Nucleotides
Double stranded structures
siRNA Synthesis Techniques
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Nucleotides Structure
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Natural Nucleotides
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Molecular Cell Biology, Sixth edition 2008 W.H. Freeman and Company 15
Double Stranded Structures
Characteristic A-DNA B-DNA Z-DNA
Helix Direction Right-handed Right-handed Left-handed
Average base pairs per turn 11 10 12
Rotation per base pair 32.7 36 -30
Distance between adjacent bases
0.26 nm 0.34 nm 0.37nm
Diameter 2.3 nm 1.9 nm 1.8 nm
Overall shape Short and wide Long and narrow Elongated and narrow
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Synthesis of siRNA
Synthesis of siRNA
Enzymatically Generated siRNAs
Chemically Synthesized siRNAs
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T7 RiboMAX™ Express RNAi System protocol
Advantages: Quick
Cost effective
Disadvantage: Limited to natural nucleotides
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Enzymatically generated siRNA
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Somoza, A. Chem. Soc. Rev. 2008, 37, 2668.
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Chemically Synthesized siRNAs
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Stability Targeting Side effect
Endonuclease Target delivery Off target effects
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General Problems for siRNA as a Drug Candidate
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Modification of siRNA
• A/U at the 5'end antisense strand (guide strand)
• Avoiding immunostimulators (GU rich sequences, blunt structure at 3´ end etc.)
• siRNA conjugation and delivery systems
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Frequently Utilized Modifications
Chen, Y.; Wang , X.; Huang, Y.; Zhang, L. H.; Yang, Z. JCPS 2012, 21, 5
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Frequently Utilized Modifications
Internucleotide linkage Modifications
Sugar Modifications
Nucleobase Modifications
Chemical Modification of Nucleotides
Chen, Y.; Wang , X.; Huang, Y.; Zhang, L. H.; Yang, Z. JCPS 2012, 21, 5
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Internucleotide Linkage Modifications
Decreasing Charge Density
Increasing Lipophilicity
Increasing Stability
Hall, A.H.; Wan, J.; Shaughnessy, E.E.; Ramsay Shaw, B.; Alexander, K.A. Nucleic Acids Res. 2004, 32, 5991.
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Sugar Modification
Deleavey, G.F.; Damha, M.J. Chem. Biol. 2012, 19, 937.
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Sugar Conformations
0.34 nm 0.26 nm
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2´-O-Me modification
• Pegaptanib(FDA approved 2004)
2´-O-MOE modification
• Mipomersen(FDA approved 2013)
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Commercial Available Products
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Peacock, H.; Kannan, A.; Beal, P.A.; Burrows, C.J. J. Org. Chem. 2011, 76, 7295.
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Nucleobases Modification
Affecting Hydrogen bonding in order to control:
Duplex Stability OTEs
Nucleobases modification is less common than sugar and backbone modifications
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Wang, Y.; Juranek, S.; Li, H.; Sheng, G.; Tuschl, T.; Patel, D. J. Nature, 2008, 456, 921. 27
Crystal Structure of Thermus thermophilus Argonaute
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Puthenveetil, S.; Whitby, L.; Ren, J.; Kelnar, K.; Krebs, J. F.; Beal, P. A. Nucleic Acids Res., 2006 34, 4900.
Peacock, H.; Maydanovych, O.; Beal, P. A. Org. Lett. 2010, 12, 1044.
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siRNA instability
•RNA-dependent Protein Kinase (PKR) •Adenosine Deaminases (ADAR-1)
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Molecular Biology of the Gene, Watson et al, 5th Edition Chapter 6 Page 98 29
Minor Groove & Major Groove
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Minor Groove Modification: a New Strategy for Increasing the Stability of siRNA
Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
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Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
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Development of a Method for Switching Steric Groups away from the Minor Groove when the Guide Strand Enters RISC
siRNA Guide Strand of siRNA +
Target mRNA
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Nikolova, E. N.; Kim, E.; Wise, A. A.; O’Brien, P. J.; Andricioaei,I.; Al-Hashimi, H. M. Nature, 2011, 470, 498.
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Hoogsteen Base Pairing
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Bruner, S. D.; Norman, D. P. G.; Verdine, G. L. Nature 2000, 403, 859.
Cheng,X.;Kelso,C.;Hornak,V.; de los Santos,C.;Grollman,A. P.;Simmerling, C. J. Am. Chem. Soc. 2005, 127, 13906.
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8-Oxopurines as a potential frameworks
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Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
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N²-alkyl-8-oxo-7,8-dihydroguanosine
Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
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Kannan, A.; Burrows, C. J. J. Org. Chem. 2011, 76, 720–723 36
Preparation of N²-Alkyl-8-oxo-7,8-dihydro-2´- deoxyguanosine Phosphoramidites
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Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
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Design of siRNAs
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38 http://www.atdbio.com/content/53/DNA-duplex-stability
The temperature at which under specific condition double stranded structure is changed(50%) to single stranded nucleic acid.
Thermal Stability of siRNA
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Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
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Thermal Stability Tm
R = H (O) > R = propyl (P) > R = benzyl
55 °C
60 °C
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the presence of a single OG:A Hoogsteen pair in the RISC does not diminish the activity
The location of addition of single alkyl group (propyl or benzyl) is important for siRNA function.
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Knockdown Studies with Single Modification
Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
Propyl Benzyl
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Multiple substitutions with the benzyl substituent compromise the activity of siRNA more severely!
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Knockdown Studies with 2 or 3 Modification
Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
Substitution of a U in two or three positions of the guide strand with an OG was detrimental to knockdown activity.
Propyl Benzyl
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PKR Quantification
MW
siRNA1 siRNA2 siRNA3 siRNA4
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Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
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PKR Binding Assay
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Kannan, A.; Fostvedt, E.; Beal, P.A.; Burrows, C.J. J. Am. Chem. Soc. 2011, 133, 6343.
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PKR binding assay
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So far ….
Hoogsteen base pair formed by 8-oxoguanine in the syn conformation pairing with a target adenosine is tolerated in the seed region.
Single Site Modifications of this type led to knockdown of protein expression that was more efficient than the unmodified siRNA. (only in specific locations)
PKR binding assay supported the model.
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Collins, L. V.; Hajizadeh, S.; Holme, E.; Jonsson, I.M.; Tarkowski, A. J. Leukocyte Biol. 2004, 75, 995.
Pope, B. L.; MacIntyre, J. P.; Kimball, E.; Lee, S.; Zhou, L.;Taylor, G. R.; Goodman, M. G. Cell. Immunol. 1995, 162, 333.
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Improvement of Model
Loxoribine 8-oxo-2´-deoxyguanosine
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Ghanty, U.; Fostvedt, E.; Valenzuela, R.; Beal P.A.; Burrows, C.J. J. Am. Chem. Soc. 2012, 134, 17643.
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Alternative Purine Modifications
8-alkoxyadenosine phosphoramidites
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Ghanty U, Fostvedt E, Valenzuela R, Beal PA, Burrows CJ: J Am Chem Soc 2012, 134: 17643–17652. 48
Base Switch
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Ghanty, U.; Fostvedt, E.; Valenzuela, R.; Beal P.A.; Burrows, C.J. J. Am. Chem. Soc. 2012, 134, 17643.
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8-AlkoxyA
Delivery as Hoogsteen pair Watson-Crick pairing in the RISC
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Synthesis of 8-AlkoxyA
Ghanty, U.; Fostvedt, E.; Valenzuela, R.; Beal P.A.; Burrows, C.J. J. Am. Chem. Soc. 2012, 134, 17643.
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Synthesis of 8-AlkoxyA
Ghanty, U.; Fostvedt, E.; Valenzuela, R.; Beal P.A.; Burrows, C.J. J. Am. Chem. Soc. 2012, 134, 17643.
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Ghanty, U.; Fostvedt, E.; Valenzuela, R.; Beal P.A.; Burrows, C.J. J. Am. Chem. Soc. 2012, 134, 17643.
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siRNA design
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Alkoxy group appears to introduce instability in the RNA
duplexes.
In Watson−Crick Model hydrogen bonding is
still preferred.
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Thermal analysis
Ghanty U, Fostvedt E, Valenzuela R, Beal PA, Burrows CJ: J Am Chem Soc 2012, 134: 17643–17652.
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Ghanty U, Fostvedt E, Valenzuela R, Beal PA, Burrows CJ: J Am Chem Soc 2012, 134: 17643–17652. 54
Thermal analysis
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Ghanty, U.; Fostvedt, E.; Valenzuela, R.; Beal P.A.; Burrows, C.J. J. Am. Chem. Soc. 2012, 134, 17643.
Knockdown Ability of the modified nucleotides is sensitive to position.
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Knockdown Studies with Modified Adenosine-Containing siRNAs
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Ghanty, U.; Fostvedt, E.; Valenzuela, R.; Beal P.A.; Burrows, C.J. J. Am. Chem. Soc. 2012, 134, 17643.
Multiple 8-ROA substitutions at the guide strands showed significantly reduced silencing efficacy.
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Knockdown Studies (2 sites modification)
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Importance of Switching the Steric Blockade from the Minor to the Major Groove in the RISC
Ghanty, U.; Fostvedt, E.; Valenzuela, R.; Beal P.A.; Burrows, C.J. J. Am. Chem. Soc. 2012, 134, 17643.
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Ghanty, U.; Fostvedt, E.; Valenzuela, R.; Beal P.A.; Burrows, C.J. J. Am. Chem. Soc. 2012, 134, 17643.
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PKR binding assay
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Summary
Chemical modification is a promising strategy to increase the potency and specificity of siRNAs .
A purine ribonucleoside can exist in both syn and anti conformations around the glycosidic bond depending on the base-pairing partner.
Singly modified siRNAs were capable of inhibiting PKR−siRNA interactions.
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Acknowledgement
• Dr Huang
• Group members: Hovig, Herbert, Isaac, Steven
Qian, Berm, Peng, Jicheng, Zeren, Weizhun,
Zhao-Jun, Claire, Joe
• My Friends
• And you for your attention
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