Required information SiRNAs are fragments of double-stranded RNA (dsRNA) between 20 and 25 nucleotides long that are generated when an endonuclease calied Dicer cleaves long RNA into short pieces. These siRNA molecules join a multiprotein unit called an RNA-induced silencing complex (RISC) and that complex then binds to complementary mRNA and cleaves it. The cut mRNA is rapidly degraded, preventing translation. The sIRNA-RISC-mRNA binding occurs with 100% complementarity, so is highly specific. siRNAs are being used as candidate drugs to fight diseases such as cancer, an approach that involves silencing genes coding for proteins involved in that cancer development. Although siRNA drugs show promise in cancer treatment, one of the problems with them is actually getting the drug to its target, partly because siRNAs are degraded very quickly in the body, and even If siRNAs get to their target, they sometimes do not enter the cells efficiently. One of the ways researchers have developed to dellver siRNA drugs more efficiently is to combine them with biomaterials such as hydrogels. A hydrogel is a network of hydrophilic polymer chains that can form a three-dimensional structure by crosslinking. The hydrogel is infused with the required drug and is placed precisely at the site that it is needed, for example at the tumor. However, it has been shown that once the hydrogel is placed at the target, the drug diffuses out of it very quickly out into surrounding tissues, which means that although there is an initial delivery of high levels of the drug at the required site, it does not persist. Different methods have been tested in trying to slow the release of the siRNAs from the hydrogel, including reducing the pore size of the gel so it is difficult for the RNA to diffuse out of it, and chemically modifying the gel to trap the RNA in the gel for longer. Now collaborators from the University of Illinois (Chicago) and the Albert Einstein College of Medicine (New York) have developed a new way to couple the siRNA to the hydrogel so that its release can be controlled. They covalently tether (tie) the siRNA to the hydrogel with a linker that undergoes hydrolytic degradation in a water-based environment, such as in the body. Release of the siRNA is slowed because of the time it takes for the hydrolysis reaction to occur. The group tested their system using siRNA that prevents expression of a protein called green fluorescent protein (GFP). They found that while untethered siRNA diffused out of the hydrogel within three days, the tethered siRNA took 14 days to be completely released. This approach provides a promising way to control delivery of therapeutic nucleic acids in disease treatment. Source: Nguyen, M. N. et. Al. 2019. Covalently tethering siRNA to hydrogels for localized, controlled release and gene silencing Sci. Adv. 5 : eaax0801 Select the INCORRECT statement regarding sIRNA. Multiple Choice siRNAs are highly specilic in their action. sIPNAs are RNA.

1. Required information SiRNAs are fragments of double-stranded RNA (dsRNA) between 20 and
25 nucleotides long that are generated when an endonuclease calied Dicer cleaves long RNA into
short pieces. These siRNA molecules join a multiprotein unit called an RNA-induced silencing
complex (RISC) and that complex then binds to complementary mRNA and cleaves it. The cut
mRNA is rapidly degraded, preventing translation. The sIRNA-RISC-mRNA binding occurs
with 100% complementarity, so is highly specific. siRNAs are being used as candidate drugs to
fight diseases such as cancer, an approach that involves silencing genes coding for proteins
involved in that cancer development. Although siRNA drugs show promise in cancer treatment,
one of the problems with them is actually getting the drug to its target, partly because siRNAs
are degraded very quickly in the body, and even If siRNAs get to their target, they sometimes do
not enter the cells efficiently. One of the ways researchers have developed to dellver siRNA
drugs more efficiently is to combine them with biomaterials such as hydrogels. A hydrogel is a
network of hydrophilic polymer chains that can form a three-dimensional structure by
crosslinking. The hydrogel is infused with the required drug and is placed precisely at the site
that it is needed, for example at the tumor. However, it has been shown that once the hydrogel is
placed at the target, the drug diffuses out of it very quickly out into surrounding tissues, which
means that although there is an initial delivery of high levels of the drug at the required site, it
does not persist. Different methods have been tested in trying to slow the release of the siRNAs
from the hydrogel, including reducing the pore size of the gel so it is difficult for the RNA to
diffuse out of it, and chemically modifying the gel to trap the RNA in the gel for longer. Now
collaborators from the University of Illinois (Chicago) and the Albert Einstein College of
Medicine (New York) have developed a new way to couple the siRNA to the hydrogel so that its
release can be controlled. They covalently tether (tie) the siRNA to the hydrogel with a linker
that undergoes hydrolytic degradation in a water-based environment, such as in the body.
Release of the siRNA is slowed because of the time it takes for the hydrolysis reaction to occur.
The group tested their system using siRNA that prevents expression of a protein called green
fluorescent protein (GFP). They found that while untethered siRNA diffused out of the hydrogel
within three days, the tethered siRNA took 14 days to be completely released. This approach
provides a promising way to control delivery of therapeutic nucleic acids in disease treatment.
Source: Nguyen, M. N. et. Al. 2019. Covalently tethering siRNA to hydrogels for localized,
controlled release and gene silencing Sci. Adv. 5 : eaax0801 Select the INCORRECT statement
regarding sIRNA. Multiple Choice siRNAs are highly specilic in their action. sIPNAs are RNA
fragments 20-25 nucleotides in length. SIRINA combines with RiSC and binds to
complementary mRNA. siRNAs are created when Dicer cleaves double stranded RNA. sIRNA
prevents gene expression by blocking RNA polymerase. What are the problems with using
siRNAs to target tumors? Check All That Apply It is difficult to get the siRNA drug to the target
tissue. siRNAs are very non-specific so may damage healthy cells. siRNAs degrade target cell
DNA very quickly. SIRNAs undergo chemical modification in the body and become toxic.
SIRNA drugs may not enter the target cells efficiently. Delvering siRNA to the exact tissue site
it is needed by means of hydrogels has been somewhot successful. What is the main probiem
with this approach? Multiple Chioice sipNA infused into hydregels is tropped within the
crossiliked polymet, so does not enter the target tissue. Hydrogeis are polymers that can only be
infused wath concentrations of siaNA that are too low to be effective. The siPNA diffuses
quickly out of the gel, so does not remain at the site for long enough to work wet. Hydrogels are
polymens and pose a risk to the potient. Hydrogets rapioly difuse away from the initial tissue
site, so are not completely effective at delivering the siRnA What two approbches have

2. previously been taken to reduce the rapid diffusion of siRNA out of the hydrogel? Check All
That Apply Reducing the pore size of the gel. Crosslinking the hydrogel polymer chains.
Chemically modifying the gel to trap the siRNA. Crosslinking to sIRNA to the tissue. Using
increased amounts of siRNA. Check All That Apply Reducing the pore size of the gel.
Crosslinking the hydrogel polymer chains. Chemically modifying the gel to trap the siRNA.
Crosslinking to siRNA to the tissue. Using increased amounts of siRNA. Leaving the hydrogel in
place for longer. What did the researchers do in this report that solved the problem of siRNA
diffusing out of hydrogel too fast? Multiple Cholce They tethered the siRNA to the hydroget
with a link that is gradually degraded in the presence of water, slowing the RNA release from the
ge. They tethered the siRNA to the hydrogel with a link that is gradually strengthened in the
presence of water, slowing the RNA release from the gel. They tethered the siRNA to the tissue
directly with a link that is gradually degraded in the presence of water, as is found in the body.
They used a different type of siRNA that they were able to crossink to the hydrogel with a
hydrolytic enzyme. They decreased the pore size of the gel, added retainers to it, and tethered the
siRNA to the retainers with o biodegradable link.