Gene regulation with polyvalent siRNA-nanoparticle conjugates
Authors: David A Giljohann
Andrew E Prigodich
Pinal C Patel
Chad A Mirkin
Dwight S Seferos
Journal: Journal of the American Chemical Society (2009)
Discipline: CHEMISTRY
Keywords: polyvalent RNA-gold nanoparticle conjugates; RNAi pathway; synthetic RNA oligonucleotides; siRNA duplexes; auxiliary passivating agent
Affiliations: Department of Chemistry and International Institute for Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.

Abstract:  We report the synthesis and characterization of polyvalent RNA-gold nanoparticle conjugates (RNA-Au NPs), nanoparticles that are densely functionalized with synthetic RNA oligonucleotides and designed to function in the RNAi pathway. The particles were rationally designed and synthesized to be free of degrading enzymes, have a high surface loading of siRNA duplexes, and contain an auxiliary passivating agent for increased stability in biological media. The resultant conjugates have a half-life six times longer than that of free dsRNA, readily enter cells without the use of transfection agents, and demonstrate a high gene knockdown capability in a cell model. 

Retracted: No

PubPeer comments:
 In this article, the Mirkin group reports results similar to their 2006 Science paper . These  polyvalent siRNA-Nanoparticle Conjugates are supposed to magically access the inside of the cells and do their siRNA job. There is no discussion whatsoever of the mechanism of entry. The word endocytosis does not figure in the article. Endocytosis is the likely mechanism of entry. This would result in the particles being in compartment where they cannot do their siRNA jobs and where they would be likely to be degraded. Fig 1 shows that the particle enter. That is unsurprising. Their localisation is perinuclear which is suggestive of endocytosis. The fact that we can see the particles by fluorescence in Fig 1 is also suggesting degradation of the particles since otherwise there should be significant quenching (no data on quenching so this is a guess). It turns out that if the particles are prepared with the  normal protocol, they aggregate in the cell medium. You can find this information in the Supporting Information, figure S3 (the legend is clear although the figure itself is mindboggling). For this reason, they add an OEG ligand... and they say that the number of oligo strands is not changed, which does not seem very plausible given that the particles physical properties are very significantly altered: they are now stable in cell medium. A good way to show encouraging results is to compare oneself to a very poor positive control. That is what happens in Fig 2. Their positive control is lipofectamine 2000 and they achieve between 50 and 60% of reduced luciferase signal at 2, 3 and 4 days (not sure why one day is not shown). They show that their siRNA particles do worse than lipofectamine at day 2 and 3, and slightly better at day 4... BUT, the lipofectamine should not achieve 50-60%: it should do much much better; more in the 5-10% range, especially for easy to transfect HeLa cells; see for example this 2004 (i.e. 5 years before the Giljohann paper) review, fig 7b . So this is at best a very poor transfection agent compared to already available reagents at that time, however the conclusion is  Given their straightforward synthesis, these RNAu2212Au NPs, in addition to useful intracellular gene regulation materials, may be promising candidates for therapeutic and diagnostic applications. ,