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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5373_Библиотеки_им_академика_М_И_Перельмана.pdf
16 Beyond PEGylation “PEGylation andits Alternatives”
457
to customized treatments, reduce side effects, and improve patient outcomes.
PEGylation has undeniably played a crucial role in enhancing drug delivery in the
dynamic world of pharmaceuticals and biotechnology. However, it is no longer
enough to rely on the achievements of this pioneering technology. Precision medicine, personalized therapy, and improved therapeutic efcacy necessitate a new
paradigm that takes us “Beyond PEGylation”. As we embark on this path, we should
expect to see a shift in how pharmaceuticals are developed, administered, and
adjusted to meet the changing requirements of patients. This conversation is a vital
step in the process, providing insight, analysis, and exploration of the potential
beyond PEGylation in the modern era of drug delivery (Yadav and Dewangan 2021).
In this in-depth review, we will dissect the concepts and applications of PEGylation
and critically explore the novel alternatives that can potentially reinvent drug delivery in the modern day. The key goal is to comprehend how these alternatives are
transforming the landscape of drug research by providing improved solutions and
addressing the limitations of PEGylation.
16.2 PEGylation andDrug Delivery Systems
Drug delivery systems (DDSs) are rationally designed to administer medications in
a controlled manner to achieve superior efcacy. Even though DDS has been extensively studied over the last couple of decades, they frequently suffer from rapid
clearance from the blood and kidneys, undesired nonspecic interactions, enzymatic degradation, poor aqueous solubility, and a proclivity to create neutralizing
antibodies (Allen and Cullis 2004; Tiwari et al. 2012). Over the years, various
approaches have been tried to bypass these concerns by making the DDS stealthy
and less susceptible to the aforementioned challenges. The surface of DDS has been
successfully decorated with neutral and hydrophilic molecules since foreign materials and opsonins primarily interact via hydrophobic, ionic, van der Waals, and electrostatic forces (Leucuta 2012). PEGylation is the process of covalently or
noncovalently attaching PEG (polyethylene glycol) molecules to different classes
of drugs or macromolecular structures such as proteins, oligonucleotides, or vesicles. This modication results in improved pharmacokinetic and pharmacodynamic
properties of the DDS (Allen and Cullis 2004; Nakamura etal. 2012; Jevševar etal.
2010) (Fig.16.1).
Fig. 16.1 PEGylation of compound of interest
458
S. Mohanta et al.
Frank Davis and colleagues pioneered the PEGylation technique in the 1970s to
achieve enhanced efcacy of polypeptide-based medications (Hoffman 2016). Due
to their neutral charge, exibility, and hydrophilicity, PEG chains can form a steric
barrier that reduces contact between the reticuloendothelial system and the DDS,
reducing immunogenicity and masking them from phagocytes. This is referred to as
PEG-chain-imparted stealthiness (Hamidi etal. 2006).
Furthermore, the strong hydration shield that envelopes the PEG molecules
improves the serum solubility of PEGylated DDS and protects the drug and formulation from enzyme-mediated degradation and quick elimination from kidneys
(Liechty etal. 2010).
The notion of PEGylation has since been generalized to several disciplines and
various chemical, enzymatic, and physical entrapment methods for functionalizing
the surface of DDS.PEGylation can play a critical role in biomolecules as it can
affect protein function invitro and lacks site specicity. However, these disadvantages are often outweighed in biological systems by other essential benets (Francis
etal. 1998; Dozier and Distefano 2015; Padín-González etal. 2022).
On the other hand, PEGylation has been shown in several studies over the last
decade to produce signicant reductions in drug delivery, including improved serum
protein binding, lower uptake by target cells, and elicitation of an immune response
that promotes clearance invivo. Some of the literature indicates the adverse effects
of PEGylation, calling into question the wisdom of using this technique in drug
development.
16.3 PEGylated Products
PEG stands for polyethylene glycol, a synthetic polymer composed of repeating
ethylene glycol units. PEGylated products refer to drugs, therapeutic agents, or
other biologically active molecules that have been modied through a process called
PEGylation. PEGylation involves the covalent attachment of PEG chains to the target molecule (lipid, protein, drug), typically through chemical reactions with functional groups on the molecule’s surface. This chapter discusses PEGylated proteins,
PEGylated liposomes, PEGylated G-CSF, and PEGylated nanoparticles.
16.3.1 PEGylated Liposomes
Liposomes are spherical nanoparticles composed of amphiphilic lipids with charged
or neutral headgroups. They can entrap small molecule drugs or diagnostic agents,
oligonucleotides, and other biomacromolecules such as proteins, vaccines, or
enzymes (Nakamura etal. 2012). While liposomes improve the therapeutic index of
drugs, they are susceptible to opsonization and subsequent destruction. Their biophysical properties and invivo efcacy can be adjusted by varying variables such as
size, surface charge, lipid composition, hydrophobic chain length, and degree of
unsaturation (Allen and Cullis 2013; Dzieciuch et al. 2015). In comparison to
16 Beyond PEGylation “PEGylation andits Alternatives”
Fig. 16.2 Surface modication of liposomes through PEGylation
459
unfunctionalized liposomes, PEGylated liposomes (Fig. 16.2) demonstrate prolonged blood circulation, enhanced drug bioavailability by bypassing the digestive
tract, improved safety prole, and passive targeting owing to the enhanced permeability and retention effect (Dzieciuch etal. 2015; Moghimi and Szebeni 2003;
Immordino etal. 2006). Several liposomal products like AmBisome® and Doxil®are
available in market and currently many others are being investigated in clinical trials.
The eld of PEGylated liposomes is still evolving. Ongoing research focuses on
improving liposome characteristics, discovering novel ligands for targeted delivery,
and expanding the technology’s versatility and safety. PEGylated liposomes are
projected to play an increasingly important role in tailoring medicines to specic
patients, maximizing therapeutic outcomes, and minimizing side effects as precision medicine gets a grip. With ongoing research and innovation, PEGylated liposomes are poised to revolutionize medication delivery and tailored therapy in the
coming years.
16.3.2 PEGylated G-CSF
PEGylated Granulocyte Colony-Stimulating Factor (PEG-G-CSF), a modied and
prolonged-release version of human granulocyte colony-stimulating factor, has
emerged as a transformational agent in hematology and oncology. This pharmacological breakthrough has been critical in the treatment of neutropenia, a disorder
that is characterized by unusually low neutrophil count, a type of white blood cell
essential for immunological function (De Volder etal. 2020). PEGylated G-CSF is
a big step forward in the treatment of neutropenia, particularly in patients undergoing chemotherapy or stem cell transplantation.
G-CSF is a cytokine that mimics the proliferation and differentiation of neutrophil precursors. They are also known to improve the function of mature neutrophils
(Marsh etal. 2007). Filgrastim, the rst approved G-CSF, has been indicated for use
in cancer patients receiving chemotherapy (Welte etal. 1996). G-CSF-type drugs
have been extensively used in the clinic to minimize chemotherapy-induced
460
S. Mohanta et al.
neutropenia (CIN) and are recommended for patients undergoing high febrile
neutropenia(FN) chemotherapy regimens (Aapro etal. 2011; Crawford etal. 2010).
Human G-CSF, on the other hand, has a short half-life due to its primary elimination
through the kidney, necessitating daily administration intravenously or subcutaneously, resulting in frequent injection site infection and decreased tolerance
(Fernandes et al. 2017; Tan et al. 2011). PEG was conjugated with G-CSF
(PEGylated G-CSF) to extend the half-life by altering the clearance site, resulting in
lowered systemic clearance. A single dose of PEGylated G-CSF showed efcacy
comparable to daily injections of normal G-CSF (Bond et al. 2018; Kuan etal.
2017). Fewer injections have improved patient compliance and reduced the burden
on the healthcare system in the case of various tumors and non-Hodgkin’s lymphoma (NHL) (Botteri etal. 2018). Hendler etal. (2011) discovered that both types
of G-CSF reduced the incidence of FN, enhanced safety, and lowered the cost of
chemotherapy in breast cancer patients. Many studies have compared data between
PEGylated and non-PEGylated G-CSF in breast cancer patients, and the superiority
of the former has not been established in terms of safety or effectiveness (Bond
etal. 2018; Botteri etal. 2018; Kuan etal. 2017; Cornes etal. 2018; Schwartzberg
etal. 2018).
As research continues to unveil its broader potential in other clinical contexts,
PEGylated G-CSF stands as a shining example of how biopharmaceutical innovation can profoundly impact patient care and outcomes in the elds of oncology and
hematology (Li etal. 2020).
16.3.3 PEGylated Proteins
Because of their great biological activity and selectivity, protein therapeutics have
become an essential modern pharmaceutical product. Due to its nontoxic and highly
hydrophilic properties, PEG can be combined with the protein’s inactive regions to
increase the protein drug’s molecular weight. Bound PEG can enhance protein stability, extend its circulation half-life, and lower undesired immune responses (Sun
etal. 2023). The use of PEGylation in protein therapeutics has, however, sparked
widespread criticism around the globe (Fig.16.3).
Since 1982, the US Food and Drug Administration (FDA) has licensed approximately 200 protein or peptide-based drugs for clinical use in the treatment of various human disorders (Cattani et al. 2015; Jevševar et al. 2010). Although these
modalities have been known for some time, some limitations still need to be
addressed. Proteins frequently suffer rapid degradation, aggregation, breakdown by
various proteases, solubility concerns, short circulation times, and immunogenicity
issues (Dozier and Distefano 2015). Davis and Abuchowski demonstrated for the
rst time in 1977 that PEGylated bovine serum albumin demonstrated an extended
serum half-life and reduced immunogenicity compared to native proteins (Alconcel
etal. 2011). Several studies have reported improved protein shell life and stability,
enhanced solubility, decreased aggregation, and proteolysis (Zuma etal. 2022).
16 Beyond PEGylation “PEGylation andits Alternatives”
Fig. 16.3 PEGylation of protein
461
As a result, PEGylation has been explored and has evolved into a diverse method
for improving the pharmacokinetics of proteins and peptide-based therapeutics. The
rst PEGylated protein was introduced to the market in 1990, and nine distinct
PEGylated protein therapeutics are now in the clinic for various indications. A few
additional PEGylated biotherapeutics are also in late-stage clinical studies (Carter
2011; Alconcel et al. 2011; Milla etal. 2012). This technology has expanded the
possibilities in drug development and enhanced the quality of life for patients needing protein-based therapies. As research advances and new applications emerge,
PEGylated proteins will continue to play a crucial role in modern medicine, offering
innovative solutions for various medical conditions.
16.3.4 PEGylated Nanoparticles
Nanotechnology has opened up a new frontier in drug delivery, diagnostics, and
various other sectors. PEGylated nanoparticles have emerged as a spectacular innovation in this eld, potentially revolutionizing several parts of medical research and
technology. PEGylated nanoparticles have become a exible tool with a wide range
of uses, particularly in the eld of drug administration, by combining the benets of
nanoparticles with the benets of polyethylene glycol (PEG) coatings. Nanoparticles
are microscopic structures of nanoscale dimensions (usually fewer than 100 nanometers). These nanoparticles can be programmed to deliver medicines, genetic
material, or other bioactive molecules. PEGylation, on the other hand, is the process
by which PEG chains are attached to the surface of these nanoparticles(Fig. 16.4).
PEG is a hydrophilic polymer known for its biocompatibility and stealth-like qualities (Otsuka etal. 2003).
PEGylated nanoparticles have diverse applications in the elds of medicine and
biotechnology. PEGylated nanoparticles are widely used to deliver chemotherapeutic agents, vaccines, and various drugs. Their targeted drug delivery capabilities
reduce systemic side effects while improving therapeutic efcacy. Nanoparticles
462
Fig. 16.4 PEGylation of gold nanoparticle (AuNP)
S. Mohanta et al.
can be loaded with contrast agents for diagnosis, such as computed tomography
(CT) or magnetic resonance imaging (MRI). PEGylation enhances their circulation
time and biocompatibility invivo (Park etal. 2017). PEGylated nanoparticles can
efciently deliver genetic material, such as plasmid DNA or RNA, to target cells.
This is a critical aspect of gene therapy and RNA-based treatments. PEGylated
nanoparticles have shown promise as vaccine carriers, enhancing the immune
response to antigens and improving the duration of protection (Vila etal. 2004).
PEGylated lipid nanoparticles (LNPs) were used to formulate mRNA-based
COVID-19 vaccines like Comirnaty™ (McCrudden etal. 2023).
16.4 Limitations ofPEGylation
Over the past 20years, PEGylated products have become an important element in
medication, surfactants, and dispersion agents, for both clinical and industrial applications. While the notion of PEGylation is straightforward and effective in most
circumstances, numerous possible safety issues have lately been suggested due to
the long-term use of PEG-related products. Several studies have shown PEGylated
products to cause immunological responses (with both oral and intravenous administration), cytoplasmic vacuolation, hypersensitivity, and antibody induction under
certain conditions. Furthermore, PEG is nonbiodegradable, and larger molecular
weight PEG tends to accumulate in tissues (Engler etal. 2015; Hatakeyama etal.
2013; Knop etal. 2010; Zhang etal. 2014; Han etal. 1997; Pisal etal. 2010).
While PEGs of lower molecular weight are preferred for use in several biomedical applications, they are known to generate toxic oxidative side products. PEG is
also known to degrade under thermal and mechanical stresses (Han etal. 1997).
This could have an impact on PEG medication formulation and storage. A few
reports have claimed that protein PEGylation decreases biologic activity and binding afnity as concentrated solutions tend to be highly waxy. Product analysis
becomes more complicated due to the inherent polydispersity of commercialized
activated PEG and its derivatives (Hatakeyama etal. 2013; Zhang etal. 2014; Han
et al. 1997). Although PEG conjugation with biologics is conceptually
16 Beyond PEGylation “PEGylation andits Alternatives”
463
straightforward, it frequently necessitates extensive optimization; specically, the
paucity of site-specic conjugation techniques results in poorly dened structures,
producing unsatisfactory outcomes. Synthetic contaminants, such as formaldehyde,
1,4- dioxane, and cyclic dimers of ethylene oxide, highlight the need for highly puried PEG for biomedical applications. It’s important to note that the drawbacks of
PEGylation vary depending on the specic drug or nanoparticle, the PEGylation
method employed, and individual patient factors. Ongoing research aims to address
these limitations and develop innovative strategies to optimize PEGylation and mitigate its potential downsides while harnessing its advantages in various biomedical
applications.
16.5 Potential Alternatives ofPEG
As PEG-mediated immune response limits its utility, many alternative polymers
that mirror the physicochemical features of PEG without affecting its pharmacokinetic behavior have been developed. The primary requirements for developing
PEG-alternative materials are outstanding stealth qualities, facile synthesis, degradability, biocompatibility, and a delicate balance of hydrophilicity and hydrophobicity. Recent advances in material chemistry and polymer science have played a
critical role in developing PEG alternatives (Fig.16.5) and exploring their potential
biological applications (Hoang Thi etal. 2020).
16.5.1 Poly(Zwitterions)
Poly(zwitterions) are amphiphilic polymers that have found use as a potential alternative to nonionic PEG polymers in recent years (Wang etal. 2016). Poly(zwitterions),
particularly poly(sulfobetaine), poly(phosphobetaine), and poly(carboxybetaine)
(Fig.16.6) or other materials coated with these polymers, demonstrated enhanced
protein immobilization and non-fouling characteristics, as well as high resistance to
biolm formation and bacterial adhesion (Wu etal. 2016; Keefe and Jiang 2012).
Due to their unique chemical structure and characteristics, poly(zwitterions)
have a PEG-like effect. As zwitterions are molecules with both positive and negative
charges in the same structure, resulting in no net charge, this feature, together with
zwitterions’ hydrophilic nature, contributes to their PEG-like actions via numerous
mechanisms: poly(zwitterions), like PEG, can provide a hydrophilic surface that
repels protein adsorption. This avoids opsonization, a process in which proteins in
the blood bind to the surface of nanoparticles or other drug delivery systems, potentially identifying them for elimination by the immune system. Poly(zwitterions)
assist nanoparticles in evading rapid clearance from circulation by avoiding protein
adsorption. Opsonization resistance and decreased absorption by macrophages and
the reticuloendothelial system (RES) result in longer circulation times for drug
delivery systems, including poly(zwitterions). This increased circulation time
increases the possibility that the drug will reach its intended place within the body.
464
S. Mohanta et al.
Fig. 16.5 Alternatives of PEG
Because, poly(zwitterions) lack a net charge and are hydrophilic, they are less likely
to elicit immunological responses (Leng etal. 2015; Xing etal. 2017) (Fig.16.7).
Several chemistries can be used to conjugate poly(zwitterions) to various drug
carriers or nanoparticles. The functional groups on the polymer and the surface of
the drug carrier or nanoparticle determine the chemistry utilized. The following is a
broad overview of how poly(zwitterions) can be conjugated; reactive groups must
be added to both the poly(zwitterion) and the drug carrier or nanoparticle. Amino
(-NH2), carboxyl (-COOH), and thiol (-SH) groups are common functional groups
that have been used for amido bond formation, click chemistry, and thiol-ene reactions. If both the poly(zwitterion) and the carrier contain amine groups, they can be
conjugated by rst activating one of them with a coupling reagent like
N-hydroxysuccinimide (NHS). This activated compound then can react with the
other, which contains carboxyl groups (Keefe and Jiang 2012). In some
16 Beyond PEGylation “PEGylation andits Alternatives”
Fig. 16.6 Chemical
structure of
poly(sulfobetaine), a
zwitterionic polymer
Fig. 16.7 Chemical
structure of poly(glycerol
sebacate), a poly(glycerol)
465
circumstances, poly(zwitterions) may be employed for surface modication rather
than direct conjugation. The polymer forms a protective layer around the drug carrier or nanoparticle; in this case, creating a stealthy, biocompatible surface. It is vital
to note that the individual application and the attributes of the intended drug delivery system will determine the poly(zwitterion) and conjugation chemistry used.
Poly(zwitterions) with different zwitterionic moieties and side chains may function
differently in a given application. The functional group compatibility determines
not only the specic chemistry utilized for conjugation, but also the stability of the
resultant bond (Liu etal. 2016b) (Fig.16.8).
To ensure the safe and efcient use of poly(zwitterions) in drug delivery systems
or biomaterial applications, many precautions should be taken. This primarily
includes biocompatibility testing to evaluate the substances’ immunogenicity, cytotoxicity, and possible allergic reactions. Testing the safety and effectiveness of
poly(zwitterion)-based systems can be done invitro and invivo, and the chemical
stability should be analyzed in the environment where it will be used. Some polymers may deteriorate or lose their useful properties under particular pH, temperature, or enzymatic conditions. To ensure the polymer’s performance for the necessary
466
Fig. 16.8 Conjugation of PEG alternatives
S. Mohanta et al.
amount of time, it is crucial to understand its stability prole. Proper dosage and
method of administration for the poly(zwitterion)-based system should be determined, and to avoid any potential negative responses or side effects, it is essential to
comprehend the ideal concentration and frequency of administration. It is recommended to investigate possible interactions between the poly(zwitterion) and other
elements of the drug delivery system or the biological setting in material interaction
studies (Jin etal. 2014). Knowing how the polymer interacts with other substances
might assist in avoiding unanticipated reactions or changes in the system’s intended
function. The effect of employing poly(zwitterions) in the intended application on
the long-term outcomes should also be examined. To guarantee the polymer’s safety
and efcacy in prolonged use, it is essential to understand the potential accumulation, degradation, or removal of the polymer over a protracted period.
As for the safety prole, one example involves using poly(zwitterions) to develop
stealth nanoparticles for targeted drug delivery. In this case, a specic poly(zwitterion)
is utilized to coat the surface of nanoparticles, preventing opsonization and improving their circulation time in the bloodstream. This leads to reduced recognition by
the immune system, enhancing their capacity to reach the intended target site.
Poly(carboxybetaine methacrylate) is a poly(zwitterion) polymer that has shown
promise in drug delivery applications. It is known for its PEG-like effect and biocompatibility. Here’s a simplied safety prole example for pCBMA:
(a) The biocompatibility of pCBMA has been thoroughly investigated.
(b) In vitro studies have revealed negligible cytotoxicity and low immunogenicity.