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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5615_Библиотеки_им_академика_М_И_Перельмана.pdf
10 PEGylated Nanocarriers forProtein andPeptide Delivery
297
in different nanocarriers along with a brief overview of methods of PEGylation. The
limitations of PEGylated nanocarriers and the subsequent challenges to overcome
those limitations have also been illustrated in this chapter.
10.2 Role ofPEGylation inNanocarriers
Drug delivery using nanocarriers, with or without ligand coating or coupling, is
very common. Because of their unique targeting mechanism and controlled drug
release prole, these carriers have gained immense popularity. However, the main
disadvantage of nanocarriers is that the reticuloendothelial system (RES) removes
them from the bloodstream. RES uptake, immune response, stability, drug loss, and
hydrophobicity are the main reasons why nanocarriers use is restricted in the biomedical eld, despite the fact that they have demonstrated a wide range of applications. PEGylation of nanocarriers can be used to get around the aforementioned
restrictions. PEGylation is the process of coating or conjugating polyethylene glycol (PEG) with nanocarrier systems (Gajbhiye etal. 2020) (Fig. 10.1). PEG coatings on nanoparticles (NPs) protect the surface from aggregation, opsonization, and
phagocytosis, thereby increasing the circulation time. For instance, Doxil®, the rst
PEGylated liposomal product approved by the FDA, was introduced in 1995. With
a drug half-life of 72h and a circulation half-life of 36h, Doxil “Stealth®” liposomes enhanced doxorubicin bioavailability about 90 times at 1week after injection
compared to the free drug (Ahmed etal. 2005; Gabizon etal. 2003; Laginha etal.
2005). Due to the increased permeability and retention (EPR) effect, long- circulating
PEGylated NPs provide an excellent opportunity to target tumors following intravenous administration (Agnihotri et al. 2023; Matsumura and Maeda 1986). The
chance of interactions between the ligands presented on the NP surface and the corresponding receptors on cell surfaces rises with enhanced circulation time. However,
the inclusion of ligands increases formulation complexity and may compromise the
Fig. 10.1 Schematic representation of PEGylation of various nanocarriers
298
T. G. Agnihotri et al.
“stealth” characteristics offered by surface PEG coatings (Moghimi etal. 2001).
PEGylation has been employed to decrease the immune response and increase the
circulation time of synthetic NPs as well as viral gene vectors like adenovirus and
adeno-associated viruses (Kim etal. 2012; Lee etal. 2005). Table10.1 represents
the overview of few research ndings regarding PEGylated nanocarriers-based protein/peptide delivery.
10.2.1 PEGylated Nanocarriers
PEGylated nanocarriers have gained widespread acceptance due to their distinct
targeting mechanism as well as their controlled drug release prole. PEGylated
NPs, liposomes, dendrimers, and polymeric micelles have been discussed in detail
in the following section.
10.2.1.1 Polymeric NPs
NPs are solid particles or particulate dispersions with sizes between 10–1000nm.
These NPs offer a number of benets, including biocompatibility and the ability to
control the rate and time of degradation with drug release. However, the use of bare
polymeric NPs is limited by RES uptake, drug loss, hemolysis, immune response,
and cytotoxicity. These restrictions are typically overcome by the PEGylation of
NPs (Janrao etal. 2022; Nag etal. 2016). Rheumatoid arthritis (RA) is an autoimmune disorder that causes joint inammation as well as immune system impairment. Inammation-ghting responses from the patient would be triggered by
pro-resolving mediators that target the inammation-resolving pathway. Ac2–26, a
25-amino acid peptide obtained from Annexin A (a pro-resolving mediator), has
demonstrated its effectiveness in treating inammatory disorders. The low bioavailability of Ac2–26 peptides, on the other hand, limits their efcacy in vivo. To
address this limitation, Qin etal. formulated PEGylated lipid nanoparticles (LDNPs)
by co-assembling L-ascorbyl palmitate (L-AP) and N-(carbonyl methoxypolyethylene glycol-2000)-1,2-distearoyl-snglycero-3 phosphoethanolamine (DSPE-PEG2k)
to encapsulate and deliver Ac2–26 peptides to arthritis rats. They exhibited excellent stability and biocompatibility. Ac2–26 peptide-loaded PEGylated lipid nanoparticles (ADNPs) showed longer invivo circulation time and improved accumulation
in inamed regions after intravenous administration (Qin etal. 2021a). New techniques or technologies that may prevent the development of primary tumors and
metastatic spread are particularly important since metastasis is the main cause of
mortality in cancer patients. There is strong evidence that inammation and tumor
growth are closely related. Inammation is frequently present in the tumor vasculature, which may enhance angiogenesis. The lining of endothelial cells of the tumor
vasculature has an overexpression of adhesion molecules, such as E-selectin. To
target E-selectin, Hao etal. chose a peptide and designed a PEGylated peptide-drug
conjugate (PEGylated PDC). This prodrug consists of E-selectin as a tumor vascular endothelial target, E-selectin binding peptide as a targeting ligand, and the drug
SN38 was combined with a spacer that could break and release SN38in the tumor
10 PEGylated Nanocarriers forProtein andPeptide Delivery
Table 10.1 Overview of research ndings concerning PEGylated peptide/protein-based
nanocarriers
Type of
PEGylated
Sr.
nanocarriers
No.
1 PEGylated
dendrimers of
polyglutamic
acid
2 Deoxycholic
acid
conjugated
PEGylated
polyhydroxy
butyrate
nanoparticles
3 PEGylated
albumin-based
poly-ionic
micelles
4 PEGylated
Nanoniosomes
5 PEGylated
liposomes
6 Peptide-
conjugated
PEGylated
liposomes
7 Octreotide-
conjugated
PEGylated
liposomes
8 PEGylated
Ferrisilicate
nanoparticles
Enclosed
protein/
peptide
Nattokinase Thrombolytic
Insulin Antihyperglycemic
Sprouty-1
protein
CDC-20
siRNA
Insulin Hypoglycemic
Parathyroid
hormone
(PTH)
analogous
(Teriparatide)
Lipocalin-2
siRNA
Insulin Hypoglycemic
Functions of
protein/peptide
activity
activity
Control cancer
development,
proliferation, and
metastasis
Inhibit the
overexpression of
CDC-20 protein and
thereby
Inhibit the
proliferation of
cancer cells
activity
Used for the
treatment of
osteoporosis
Lessen the
overexpression of
lipocalin-2 protein
in breast cancer
effect
Benets of
PEGylation
PEGylation
protects the
enzyme activity of
nattokinase and
increases its
systemic
circulation time.
Improved
hydrophilic
characteristic of
polyhydroxy
butyrate and
cellular uptake of
nanocarriers.
Improved
anticancer efcacy
and cytotoxicity of
Sprouty-1 protein.
Increased siRNA
protection against
nuclease enzyme
Increased insulin
stability in GIT
with prolonged
hypoglycemic
effect.
Increased blood
circulation time
and stability of the
formulation
Improved
circulation time,
biocompatibility,
and liposomal
stability.
Enhanced insulin
release from
nanoparticles.
299
Ref.
Zhang
etal.
(2017)
Chaturvedi
etal.
(2015)
Jiang etal.
(2016)
Hemati
etal.
(2019)
Iwanaga
etal.
(1997)
Salave
etal.
(2023)
Gote and
Pal (2021)
Jermy
etal.
(2023)
(continued)
300
T. G. Agnihotri et al.
Table 10.1
Sr.
No.
9 PEGylated
10 PEGylated
11 PEGylated
12 Acid-sensitive
(continued)
Type of
PEGylated
nanocarriers
silicon
nanoparticles
lipid
nanoparticles
lipid
nanoparticles
PEGylated
solid lipid
nanoparticles
Enclosed
protein/
peptide
Insulin Hypoglycemic
KRAS
targeting
siRNA
Ac2–26
(Annexin A
protein
equivalent)
Tumor
necrosis
factor-α
(TNF-α)
siRNA
Functions of
protein/peptide
effect
Knocking down
proto-oncogene
(KRAS) expression
Anti-inammatory
effect
Decreased the
formation of
TNF-α-associated
inammatory
cytokines
Benets of
PEGylation
Increased GIT
stability and
mucoadhesive
property of silicon
nanoparticles
Increased
circulation time of
lipid nanoparticles
Extended in
Vivo circulation
time and enhanced
accumulation of
nanocarrier at
inamed site
Increased delivery
of siRNA at the
targeted site
Ref.
Andreani
etal.
(2014)
Sasayama
etal.
(2019)
Qin etal.
(2021b))
Aldayel
etal.
(2018)
microenvironment’s high glutathione (GSH) concentration. Due to the amphiphilic
properties of this prodrug, known as PEG-Pep-SN38, NPs could form in aqueous
conditions. These self-assembled NPs enabled the simultaneous death of activated
endothelium cells and the surrounding tumor cells by enhancing drug concentration
and retention at the tumor site. It was found that the formation of PEG-Pep-SN38
signicantly improved the solubility in water and in vivo toxicity of SN38.
PEGylated PDCs have several advantages over antibody-drug conjugates (ADCs),
(1) high structural diversity because peptides may be chemically altered more often
than antibodies; (2) low cost because PEGylated PDCs can be produced on a large
scale using chemical methods; and (3) low immune response (Ahmad etal. 2021).
Targeted administration of an anti-inammatory drug in osteoarthritis (OA)
treatment has the ability to signicantly reduce unwanted systemic adverse reactions and lower the required therapeutic dosage. A targeted, non-invasive drug
delivery system was developed by McMasters etal. to lessen the inammation in an
exvivo osteoarthritis model. For the making of the osteoarthritis model, cartilage
plugs from 3-month-old bovine knee joints that were procured from a slaughterhouse within 24h after the animal’s death were collected. They were then washed
three times in a medium which is serum-free and equilibrated in 5% FBSsupplemented media for 3 days. The removal of native aggrecan simulated OA conditions. To remove aggrecan, plugs were treated at 37°C for about 3h with 0.5%
(w/v) trypsin in HBSS. To inactivate residual trypsin activity, plugs were rinsed
three times in HBSS and incubated for 20min in 20% FBS after trypsin treatment.
In the plugs, inammation was induced by administering 20ng/mL IL-1β. Hollow
10 PEGylated Nanocarriers forProtein andPeptide Delivery
301
thermoresponsive poly (N-isopropyl acrylamide) (pNIPAM) NPs were produced by
degrading a cross-linked N,N′-bis(acryloyl)cystamine (BAC) core out of a nondegradable pNIPAM shell. In the shell, sulfated 2-acrylamido-2-methyl-1- propanesulfonic acid (AMPSA) was copolymerized to improve the passive loading
of an anti-inammatory cell-penetrating peptide (KAFAK) that inhibits mitogenactivated protein kinase (MK2). The hollow PEGylated NPs exhibited a decrease in
hydrodynamic radius, increased hydrophilicity, increased uptake, and a higher loading of KAFAK compared to their solid NPs. The hollow NPs loaded more KAFAK
and released a larger proportion of their cargo for an extended period of time than
the solid NPs. The drug-loaded hollow PEGylated NPs were successful in decreasing pro-inammatory interleukin-6 (IL-6) expression after interleukin-1 beta (IL-1
β) activation in bovine cartilage explants by releasing a therapeutically effective
dose of KAFAK.These thermosensitive hollow PEGylated NPs offer an excellent
platform for the delivery of peptide drugs into highly proteolytic settings, such as
osteoarthritis (Mcmasters et al. 2017). Movileanu et al. developed magnetite
nanoparticles (Fe3O4) stabilized with PEG and the surface was modied with folic
acid (FA) to enable targeted internalization in cells expressing the folic acid receptors (FR). These NPs, which are functionalized with FA, may be used to deliver
various therapeutics such as biologically active proteins, peptides, vaccines, etc.
(Movileanu etal. 2022).
10.2.1.2 Liposomes
Liposomes resemble cell membranes in that they have an aqueous core surrounded
by a lipid bilayer. This distinction facilitates the fusion of liposomes with cell membranes and subsequent cellular uptake. Because liposomes are amphipathic, they
can be used to encapsulate drugs that are both hydrophilic and hydrophobic. RES
uptake results in the rapid clearance of liposomes from the circulation, which then
builds up in the liver and spleen. Biocompatible PEG polymers have been used to
sterically stabilize conventional liposomes. Conventional liposomes are PEGylated
to signicantly extend their half-life in circulation (Marzban etal. 2015; Tang etal.
2018). Orally given insulin must overcome the harsh gastrointestinal tract environ-
ment, cross the enteric epithelial barrier, and avoid the rst pass effect before reaching the systemic circulation. To address this issue, Sarhadi et al. developed
PEGylated liposomal insulin and modied it with B12 to increase the stability and
absorption of insulin in the gastrointestinal environment. As compared to nontargeted liposomes, B12-targeted PEGylated liposomes signicantly increased cellular uptake in Caco-2 cells, according to in vitro results (Sarhadi et al. 2022).
Yamazoe etal. investigated the viability of using liposomes modied with dense
PEG2000 as mucus-penetrating particles (MPPs) for oral administration of systemically absorbed peptides. The densely PEGylated liposomes showed mucus permeability in an in vitro articial mucus model. Fluorescein isothiocyanate dextran
(FD) was used as a model peptide drug to assess the in vivo oral absorption of
liposomes in rats. PEGylated liposomes had a greater oral absorption than unmodied liposomes (Yamazoe etal. 2020). By taking advantage of PEGylation, Yazdi
etal. prepared liposomal preparation by using phospholipids, which are having a
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T. G. Agnihotri et al.
high transition temperature (Tm) combined with folic acid. The prepared liposomal
formulation showed improved stability and high penetrating ability. The cell uptake
results showed that FA conjugation increased insulin uptake. The results of biodistribution also revealed that FA-targeted PEGylated liposomes had greater concentrations in the blood and liver and longer residence times in the stomach and
intestine. The PEGylated liposomes conjugated with FA had effective benets in
increasing insulin levels and decreasing blood glucose, as shown by the anti- diabetic
effects of the formulation invivo. The results of this study suggested that employing
phospholipids with high Tm, PEGylation, and targeting ligands could increase the
effectiveness of liposome oral delivery (Yazdi etal. 2020). An effective PEGylated
liposomal delivery system having two ligands with target selectivity and characteristics that would improve cellular uptake was developed by Golam Kibria etal. The
lipid lm hydration process was used to produce PEGylated liposomes (PEG-LP).
On the PEG-LP, the cyclic RGD (Arg-Gly-Asp) peptide, a specic ligand with an
afnity for integrin αvβ3, was attached. Octa arginine that has been stearylated
(STR-R8) was added, which acts as a second ligand (R8/RGD-PEG-LP) that serves
as a Cell Penetrating Peptide (CPP) to the surface of the RGD-PEG-LP.In cells
expressing Integrin αvβ3, R8/RGD-PEG-LP indicated improved cellular uptake in
addition to greater transfection efciency. From this, they concluded that PEG-LP
attached with dual ligands has a high capacity for internalizing PEG-LP effectively,
and as a result, it would be a useful tool for the targeted delivery of peptides and
anti-cancer drugs (Kibria etal. 2011). On a similar note, Kato etal. created a new
adapter-lipid compound that permits several click-reaction-based cyclic peptide
modications. The cyclic RGDfK (cRGD) peptide was used as the cyclic peptide
ligand, which targeted integrin αvβ3.They developed a new alkyne tagged lipid having distinct peptide spacer and it was combined with cRGD peptide with the help of
click reaction, which resulted in cRGD complexed lipid with excellent water dispersibility for formulating cRGD-modied PEGylated liposomes utilizing the postinsertion method. The prepared PEGylated liposomes showed excellent cytotoxicity
when they were loaded with anticancer drug doxorubicin (Kato et al. 2022)
(Fig.10.2).
10.2.1.3 Dendrimers
Dendrimers are well-dened, highly branching, nanoscale macromolecules with
numerous active groups that may bind to other functional moieties for active targeting. Despite many advantages dendrimers have for drug delivery, their toxic properties due to amine groups make their clinical translation difcult. PEG conjugation
has been employed in order to decrease the toxicity of amine groups on the surface
of dendrimers due to their nonimmunogenic characteristics and hydrophilic nature
(Alibolandi etal. 2021). PEGylation and acetylation of polyamidoamine (PAMAM)
dendrimers can improve biocompatibility, reduce cytotoxicity, and delay their clearance from the bloodstream. Molecular dynamics simulations have been carried out
by Khamseh etal. to study the interaction of eptibatide (EPT) with native acetylterminated G4-PAMAM dendrimers and its partially (25, 50, and 75%) PEGylated
analogs. Chains with molecular weights of 500 and 1000Da were used to examine
10 PEGylated Nanocarriers forProtein andPeptide Delivery
Fig. 10.2 Schematic illustration of cRGD-modied PEGylated liposomes utilizing click reaction
approach and doxorubicin as a model drug
303
the effect of PEG length. The G4-16PEG1000 system (1:7) was able to achieve its
maximum loading capacity largely owing to the conjugation of 3 EPT molecules on
the surface and the encapsulation of 4 EPT molecules in the internal cavities.
G4-16PEG1000 is the most potential carrier for EPT in terms of loading capacity,
preferred drug molecule binding sites, and release patterns (Badalkhani-Khamseh
et al. 2023). Due to its less solubility in pharmaceutical solvents, 7-Ethyl-10hydroxy-camptothecin (SN38) belongs to the camptothecin family with the highest
biological activity, and cannot be used widely. PAMAM dendrimers can be used as
an effective drug delivery system for molecules with low aqueous solubility.
Mahmoudi etal. designed two CPPs (BR2 and CyLoP1) conjugated formulations of
PEGylated PAMAM dendrimers having SN38 as a drug. Studies on cellular uptake
proved that CPP-conjugated dendrimers showed higher values in a time-dependent
manner. The majority of CPP-conjugated formulations signicantly outperformed
irinotecan in inhibiting tumor growth, according to invivo studies, and all the formulations which were prepared showed increased survival rates. The majority of
formulations had higher tumor accumulation than the commercial irinotecan formulation (positive control), according to bio-distribution studies by collecting whole
tumors, various organs like kidneys, spleen, heart, and a part of the liver and lung.
In summary, prepared dendrimeric formulations of SN38 that are combined with
CPP showed effective tumor-inhibitory properties (Mahmoudi et al. 2019).
Nattokinase (NK) has been used as a new-generation thrombolytic drug because of
its high degree of safety, low cost, and few adverse effects. It is, however, easily
affected by external environmental changes and may lose its enzymatic activity. The
characteristics of peptide dendrimers, such as their surface functional groups, biodegradability, minimal toxicity, and biocompatibility make them an ideal vehicle for
304
T. G. Agnihotri et al.
the delivery and protection of drugs. A PEGylated dendrimer (Gn-PEG-Gn),
n=2,3,4 made of polyglutamic acid was developed by Zhang etal. as a delivery
system for NK for the treatment of thrombus. A panel of PEGylated dendrimers
with three distinct generations of G2, G3, and G4 was developed in order to study
the effects of dendrimer architecture on the shape, size, and therapeutic effectiveness of the resultant NK-loaded delivery systems. The results showed that, of all the
formulations, the NK-loaded G3-PEG-G3 (G3-PEG-G3/NK ratio of 6:1) displayed
better enzyme activity for dissolving thrombus invitro and which showed considerable potential for the therapy of thrombus (Zhang etal. 2017). Bortezomib (BTZ),
an anticancer drug, has poor water solubility, which continues to be a major challenge in developing an effective formulation. Delivering BTZ with increased solubility may be possible with the dendrimeric drug delivery system. PEGylated
PAMAM dendrimers encapsulated with BTZ were prepared by Sahoo etal. In comparison to the pure drug, the aqueous solubility of BTZ in PAMAM-PEG conjugate
was increased about 68 times. It was found that the invitro drug release lasted for
up to 72h. BTZ-PEG-PAMAM’s bioavailability was 8.63 times higher than that of
the pure drug in an invivo pharmacokinetic study on Sprague Dawley rats. BTZPEG-PAMAM’s pharmacokinetic characteristics were superior to those of BTZ and
other prepared formulations. In conclusion, the developed BTZ-PEG- PAMAM formulation produced meaningful results, and this approach may be explored further
for improved delivery of BTZ (Sahoo etal. 2020).
10.2.1.4 Polymeric Micelles
Polymeric micelles are composed of amphiphilic block or graft copolymers with
hydrophilic and hydrophobic segments. These polymeric micelles have a hydrophobic inner core and a hydrophilic outer shell. Although there are many different types
of amphiphilic copolymers, block copolymers create stable polymeric micelles with
a characteristic core-shell structure. PEGylated polymeric micelles increase the
aqueous solubility, stability, and circulation time of the drugs (Kamimura and
Nagasaki 2014). A new ligand for colorectal neoplasia, LTTHYKL peptide, was
added to PEGylated octadecyl lithocholate micelles by Khondee etal. to develop a
targeted nanomedicine. Free rapamycin, rapamycin not labeled with micelles, and
rapamycin micelles labeled with peptide were given intraperitoneally for 35days to
Apc mice that developed colonic adenomas. Adenoma regression in vivo was
assessed using endoscopy. When compared to normal rapamycin micelles, the mean
regression rate was considerably greater for peptide-labeled rapamycin micelles
with P˂0.01. Results showed no other toxicities and peptide-labeled rapamycin
micelles had less renal toxicity than the free drug. Together, these distinct targeted
micelles offer a potential treatment for colorectal neoplasia that has systemic toxicity that is signicantly lower and therapeutic efcacy that is comparable to the
rapamycin-free drug (Khondee etal. 2015). Siyu Guan etal. developed two strategies for developing a multi-targeted delivery system by utilizing tumor characteristics. The rst was the production of pH-dependent micelles, which enabled increased
drug release by taking advantage of the tumor’s acidic environment. The second
10 PEGylated Nanocarriers forProtein andPeptide Delivery
Fig. 10.3 text
305
method involved using the tumors’ surface-exposed phosphatidylserine (PS), which
is usually found in the inner leaet of healthy cells. Using PS as the target site, PS
binding peptide (PSBP-6) was combined to pH-dependent mixed micelles consisting of poly (ethylene glycol)-b-poly (L-histidine) (PEG-PHIS) and poly (ethylene
glycol)-b-poly (D, L-lactide) (PEG-PDLLA). After the micelles were successfully
prepared, the anti-cancer drug paclitaxel was used to assess for drug loading capacity and encapsulation effectiveness. The results showed 7.9% and 83.5%, drug loading capacity and encapsulation efciency, respectively. At pH5.0, 6.5, and 7.4, the
invitro release of PTX from mixed micelles was 78.1, 56.8, and 51.4%, respectively, showing acid-triggered drug release. In comparison to unmodied mixed
micelles, the micelles modied with PSBP-6 signicantly increased invitro cytotoxicity and showed increased cellular uptake in the HeLa cell lines. Additionally,
studies on the pharmacokinetics, invivo biodistribution, and uorescence imaging
of PSBP-6-PEG-PDLLA/PEG-PHIS mixed micelles demonstrated that they
increased blood circulation time and promote tumor accumulation (Guan et al.
2020). Khan etal. described the recent accomplishments in the design and formula-
tion of nanoscale pH-responsive micelles conjugated with CPPs to provide con-
trolled drug release in the tumor cells. They have also explained about the drawbacks
and future prospects of stimuli-sensitive drug delivery systems complexed with
CPPs (Fig.10.3). The summary of their study is the use of pH-sensitive polymeric
micelles- based DDSs combined with peptides for controlled administration might
be thought as a viable strategy to increase the therapeutic index of anticancer medications (Khan etal. 2021).
10.3 PEGylated Nanocarriers forMiscellaneous Applications
Under the realm of gene therapy, major advancements are expected in the use of
siRNA as a therapeutic agent in the treatment of chronic illnesses and genetic
abnormalities. However, delivering it, particularly via systemic ways, remains a
difculty. Since cells do not easily absorb siRNA, practical applications of siRNA
rely heavily on the development of delivery mechanisms capable of delivering
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T. G. Agnihotri et al.
intact siRNA into the cytoplasm of the target cells. Gene delivery systems should
be developed to preserve genetic materials from a premature breakdown in the
systemic circulation while still transferring therapeutic genes to target cells effectively. While the PEGylation of these delivery methods preserves the siRNA,
additional issues may arise, such as a reduction in gene transfection owing to
decreased cellular absorption or restricted endosomal release (Ryan etal. 2008).
To overcome this, pH- cleavable PEGylation of monomolecular siRNA complexes
was proposed by DeRouchey and his team who found that PEG coating of siRNAPEG complexes elicited biodegradability with hydrazone moiety or pH-sensitive
disulde linker between K14 (14-lysine) and PEG (DeRouchey etal. 2008). As
naked siRNA suffers from rapid degradation and siRNA complex tends to accumulate within blood or get captured by macrophages, PEGylation of siRNA is
often exercised. However, PEGylation of siRNA does not correlate well with gene
silencing efciency, thus creating a great need for effectively delivering
siRNA.Ultrasound coupled with microbubbles has been a popular choice, in the
recent past for delivering siRNA.However, gene silencing efciency is often low
requiring a greater load of siRNA to be delivered when it is associated with ultrasound-microbubbles technique. Vandenbroucke et al. combined these two
approaches of PEGylated siPlex (siRNA-liposome complex)-loaded microbubbles, which can be induced on exposure to ultrasound which exhibited greater
gene silencing expressions both in terms of space and time-controlled settings
(Vandenbroucke etal. 2008).
PEGylation also has a special place in pulmonary delivery. For instance, Qiu
etal. PEGylated synthetic cationic peptide KL4 to deliver mRNA through the pulmonary route, which eventually formed a complex with mRNA at 10:1 ratio (w/w).
The PEGylation of the peptide was done to serve two purposes. One is being able to
overcome poor solubility issues owing to the presence of leucine residues present in
peptide structure and the other is to impart steric hindrance, which further facilitates
the stability against degrading enzymes. This complex was then formulated into dry
powder formulation and evaluated on human lung epithelial cells and in animals.
The results were promising enough to establish PEGylated peptide as an effective
non-viral vector for the delivery of mRNA via a pulmonary route of administration
(Qiu etal. 2019).
The therapeutic potential of PEGylated salmon calcitonin derivatives (PEG-sCT)
was investigated by Youn etal. On administration of PEG-sCT intratracheally, it
was subjected to a bioactivity study, proteolytic resistance determination, and pulmonary pharmacokinetic study. The results showed improved invivo efcacy and
prolonged half-life owing to their proteolytic stability and also showed an enhanced
area under the curve when sCT was attached to 5kDa molecular weight PEG as
compared to the 1 and 2kDa variants (Lee etal. 2009; Qin etal. 2022; Youn etal.
2008). However, the molecular weight of PEG (20 and 40kDa) had a negligible
effect on the therapeutic retention of anti-interleukin-17A and anti-interleukin-13
fragments of antibody in the lungs when administered through the intratracheal
route. Instead, the location of delivery had a major role to play in the retention of
antibody fragments in the lungs of mice (Patil etal. 2018).