Introduction in Clinical Nanomedicine

348 Pages·2013·31.09 MB·English

Chapter 1
Introduction in Clinical Nanomedicine
S. Logothetidis
Aristotle University of Thessaloniki, Physics Department,
Lab of “Thin Films–Nanosystems & Nanometrology (LTFN)”,
54124 Thessaloniki, Greece
[email protected]
Nanotechnology represents the possibility of revolutionising many
aspects of our lives. Nanomedicine, the application of nanotechnology
to health, is one of the most promising fields of biomedical research,
building up a novel research culture by encompassing the principles
of traditional disciplinary boundaries (i.e., physics, chemistry,
biology and engineering). Nanomedicine has the potential to give
intelligent solutions to many of the current medical problems, by
opening the door to a new generation of advanced drug delivery
systems, improved diagnostic systems (in vitro and in vivo) and
novel methods and materials for regenerative medicine. There are
currently two families of therapeutic nanocarriers (i.e., liposomes
and albumin nanoparticles) that have been approved and used
in clinical settings, providing clinical benefit. Moreover, several
nanocarriers are in clinical trials and even more are in pre-clinical
Horizons in Clinical Nanomedicine
Edited by Varvara Karagkiozaki and Stergios Logothetidis
Copyright © 2014 Pan Stanford Publishing Pte. Ltd.
ISBN 978-981-4411-56-1 (Hardcover), 978-981-4411-57-8 (eBook)
www.panstanford.com
2 Introduction in Clinical Nanomedicine
phases. Despite the cutting-edge developments in nanomedicine, the
process of converting basic research to viable products is expected
to be long and ambitious. A crucial factor that should also be taken
into consideration is the toxic effects of the novel therapeutical
products in human health. Thus, a massive effort is required to
translate laboratory innovation to the clinic and begin to change the
landscape of medicine,.
1.1 Introduction
1
Richard Feynman in 1959 was the first one to claim that ‘there is
plenty of room at the bottom’, and since then, a booming interest in
studying the nanoscale has emerged. The nano prefix comes from
the Greek word meaning ‘dwarf’ 1 nanometre (nm) being equal to
–9
one billionth of a metre (10 m), or 10 water molecules, or about
the width of six carbon atoms. Atoms are smaller than 1 nm, whereas
many molecules, including proteins, can differ in size between 1
2
nm and larger, as shown in Fig. 1.1. Studying at such scales is of
great importance, as the properties of matter differ significantly,
especially due to quantum effects and the large surface-to-volume
atom ratio. As a result of this, new findings arise, contributing to a
better understanding of science.
Figure 1.1
3
Nanoworld and Macroworld: the scale of natural objects.
Introduction 3
Nanoscience and Nanotechnology is a multidisciplinary field,
derived from material science, physics, chemistry, biology, medicine
and engineering, covering a vast and diverse array of devices, with at
least one dimension sized about 1–100 nm.

The primary aim of nanotechnology is the manipulation,
synthesis, characterisation and production of novel materials,
with nanoscale features, targeting better material properties and
challenging applications. Two basic production approaches exist,
according to the processes involved in creating nanoscale structures.
The top down process is a technique that uses nanofabrication tools,
starting from larger dimensions, to create nanoscaled structures
or devices of a desired shape and order. On the other hand, the
bottom up approach involves the use of molecular self–assembly/
self-organisation to derive functional systems from the controlled
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deposition of atoms or molecules. Biological systems especially
utilise the bottom up approach, as it is crucial to the function of cells
that exist in the organism. This is exhibited in the self-assembly
of lipids to form the cellular membrane, the formation of the double
helical DNA through hydrogen bonds of the individual strands, and
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the assembly of proteins.
The use of molecular knowledge of the human body as well
molecular tools, such as engineered nanodevices and nanostructures,
is of great significance. Key expectations of present and future
applications of nanomedicine are nanodiagnostics, regenerative
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medicine and targeted drug delivery (Fig. 1.2).
Drug Delivery
Regenerative
Diagnostics
medicine
Figure 1.2

The three main pillars of nanomedicine.
4 Introduction in Clinical Nanomedicine
In this direction, the application of nanotechnology to medicine
and biology holds promise in the effective treatment of diseases
that currently lack therapy. Nanomedicine can be defined as the
science and technology of monitoring, repairing, constructing and
controlling human biological systems at the molecular level, in order
7,8
to preserve and improve human health. Cancer, for instance, is a
fatal disease that lacks therapy in many cases.. A further analysis of
this issue is presented in Chapter 3. Indeed, today extensive studies
to understand the mechanism behind the tumour and cellular
biology indicate that targeting therapy is very promising compared
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to conventional chemotherapy.
In addition to this, dramatic changes are taking place in diagnostics
and imaging, which promise great benefits to nanomedicine.
Nanoparticles and quantum dots (QDs) can be applied for early in
vitro and in vivo diagnosis, as they are used as tracers or contrast
agents. Unique nanodevices with nanomaterial features contribute
to this aim. Also, several benefits of nano-imaging emerge, such as the
early detection, and the monitoring of disease stages. Bio-electronics
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and biosensors, too, are headed in that direction. The optimistic
goal of nanotechnology is the repair, replacement or regeneration of
cells, tissues and organs, giving new horizons to medicine that can
definitely result in immense health benefits, providing a better and
sufficient life to patients.
Although nanomedicine has become a very active and vital area
of research, enabling evolutionary changes in several medical topics,
great concern persists on the possible risks that can attributed
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to nanomaterials, especially to nanoparticles and nanotubes.
Due to their small dimensions, it is easy to penetrate cells and
accumulate into vital organs. Haemocompatibility and activation
of the human defence system are parameters that should also be
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taken into consideration, in order to evaluate the cytotoxicity and
the biocompatibility of such materials before they appear in the
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market.
The importance of the nanoscale and how nanotechnology
influences medicine, raising expectations of further applications in
crucial medical issues, is presented in Section 1.1, in this chapter.
Section 1.2 describes nanocarrier-based systems—a very promising
and challenging field, especially in the domain of targeted drug
delivery, referred to in Section 1.5. Regenerative medicine, is
discussed in Section 1.3 as an idea of implementing nanosciences and
Nanomedicine and Diversity of Nanocarriers 5
nanotechnology in order to construct tissue substitutes. The third
very promising tool of nanomedicine refers to in vitro and in vivo
diagnostics for the early detection and prevention of diseases; this
is analysed in Section 1.4. Finally, the potential risk of nanomaterial
toxicity is discussed in Section 1.6.
1.2 Nanomedicine and Diversity of Nanocarriers
This chapter focuses on the development of nanomaterials for
enabling and improving the targeted delivery of therapeutic and
diagnostic agents.
Nanotechnology - based carrier systems can specifically target
the site of disease, either by targeted drug delivery, imaging,
or by simultaneous strategic drug and gene delivery, reducing
the drug dose and its harmful results to healthy tissues and
14,15,16
organs. Imaging contributes to a better outcome by the usage
of multifunctionalized pharmaceutical nanocarrier systems that
enhance the image contrast, by real-time bio-distribution. Several
molecules or polymeric structures can be used (Fig. 1.3). Protein
based nanocarriers are very interesting, too, as their contribution
to gene and drug delivery is very promising because of their low
cytotoxicity, the abundant renewable sources, as well as their high
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drug binding capacity.
Figure 1.3
The schematic structure of the assembly of the multifunctional
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pharmaceutical nanocarrier.
6 Introduction in Clinical Nanomedicine
organic-based
Nanocarriers can be divided into three basic categories: (a)
, such as polymeric naninoocragrarnieircs-b a(is.eed., dendrimers,
micelles), liposomes and carbon-based nanocarriers hy(bir.eid.,
cfuolmlebriennaetsio annd carbon nanotubes); (b) (i.e., metallic
nanoparticles, silica nanoparticles, quantum dots); and (c) a
of the above to develop a multi-functional carrier
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system. Because of their size, nanocarrier systems represent a
good perspective, as they can migrate through cell membranes and
20,21
penetrate across physiological drug barriers. Figure 1.4 depicts
the relevant size of several types of nanocarriers with a virus, the
platelet, the blood cells and the capillaries in the human body.
Figure 1.4
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Size and shape diversity of nanocarrier-based systems.
It is essential to highlight the fact that nanoparticles are about
100 to 10.000 times smaller than human cells and similar in size to
large biological molecules (e.g., enzymes and cell receptors). For that
reason, size plays a key role in lending optimism to the treatment
of uncured diseases. Due to their small size, they can readily
interact with biomolecules on the surface and inside the cells. More
specifically, there are two possible mechanisms, which depend to a
large extend on the nanocarrier’s size. Nanocarriers smaller than 50
nm can easily enter most cells, either via passive diffusion or through
active processes such as endocytocis and exocytosis, whereas those
Nanomedicine and Diversity of Nanocarriers 7
smaller than 20 nm follow the paracellular mechanism, as they can
move out of blood vessels sourr pfaacses thcrhoaurgghe epithelial cells to circulate
through the body.
The nanoparticle’s is also considered in
determining its behavior. For example, nanoparticles interact with
oppositely charged cells, as well as clustering in the blood flow, or
adhering to it. For targeted drug delivery, a prolonged circulation of
nanNocaanrorpiearrst iicnle tsh e body is needed so as to achieve drug efficacy and
specificity compared to conventional drug approaches.
are spherical structures, with sizes ranging about
100 nm, with the ability to encapsulate the drug. Nanoparticles also
include nanospheres and nanocapsules. One obvious difference
between these two is that in nanospheres the drug is distributed
throughout the particles, whereas in nanocapsules, there is a
23,24
polymeric membrane cavity where the drug is included.
Nanoparticles and other nanocarriers used in nanomedicine are
sustained by proper surface treatment in order to be protected of
reticuloendothelial system. This treatment involves the proper
surface coating, usually with polyethylene glycol (PEG), a procedure
called PEGylation. The outcome of this procedure is the increase
of time they stay in the blood circulation, as carriers are not easily
taken up by the macrophages. The significance of this is found in the
fact that the longer the nanoparticles stay in the organism, the better
the accumulation of the drug in a specific site, providing satisfactory
results to drug delivery medicine. Also, nanocarriers through
PEGylation exhibit a good solubility in aqueous solutions, flexibility
o f itLsi ppoo2s5loymmeesr chain, low toxicity, immunogenicity, and antigenicity
as well.
consist of one or more phospholipid bilayers, which
are chemically active in order to enhance its efficient accumulation
in the target site. A liposome encapsulates a region of aqueous
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solution, making it appear like a spherical vesicle. In addition to
this, electrostatic interaction plays a great role as the cell surface
glycoproteines are negatively charged. The method of PEGylation,
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referred to above, is especially used for liposome - carriers.
Viruses display a diversity of shape and sizes, varying between
20 and 300 nm. Virus particles form a hollow scaffold via self-
assembly, in which their viral nucleic acid is encapsulated. They can
be easily tailored at the genetic level, and appear to be biocompatible
and easy to functionalise for several applications. So, many viruses
8 Introduction in Clinical Nanomedicine
(e.g., cowpea chlorotic mottle virus, cowpea mosaic virus, red clover
necrotic mosaic virus, MS2 RNA-containing bacteriophage, the
bacteriophage Qβ, M13 bacteriophage, etc.) have been studied for
the potential to use them as nanocarrier systems for drug delivery
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applications. Packing drug molecules into virus-like particles is
based on supramolecular chemistry. The idea relies on the principle
that the viral RNA or DNA packages into the virus, and this way,
f uncDteionndarli mcearrsgoes can also be packed through self-assembly and
disassembly processes.
have tree-like structures with very small dimensions
(1–10 nm). Their shape is globular and present unique features,
20
compared to traditional polymers. The core of these molecules
consists of amino acids or sugars, whereas the branches are
polymeric chains, developed by a series of polymerisation reactions,
around the dendrimer’s core. Thanks to their size, dendrimers can
slip through openings in cell membrane in order to act as delivery
p artMicilceesll. esDrugs are attached to surface groups, which exist in
internal cavities, via chemical modifications.
are polymeric structures, below 50 nm, dispersed in a
liquid colloid. Micelles have a hydrophilic head, surrounded by solvent
and a hydrophobic tail in their core. The drug is encapsulated into
the core cavity formed by the hydrophobic tail. Polymeric micelles
might have several advantages; some of them would be their size,
the loading capacity, as well the reduced toxicity. The hydrophilic
head provides a long circulation time in the bloodstream and their
penetration ability through tissues and cells makes them candidates
for targeted drug and gene delivery therapies. Until now, micelles
have been studied for several antitumour drugs, both in pre-clinical
a ndN calninoitcuabl etsr aian1l4ds. f uRlelesruelntse sthat derive from these endeavours are
very promising.
exhibit good electric, electronic, thermal
and optical properties. Carbon nanotubes, cylindrical in shape, are
useful carrier ‘vehicles’, which can be functionalised to act as a drug
delivery system. As the drug is encapsulated into the nanotube, a
drug-CNT complex develops, whose structural properties as well as
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the dynamic of the system drug-CNT. Some recent surveys report
that nanotubes can be loaded to the tumour site and then excited
with radio waves, resulting in the heating up of the abnormal cells
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that would kill them. Fullerenes form a sphere or an ellipsoid,
inside which drug molecules can be incorporated. Compared to
Nanomedicine in Regenerative Medicine 9
nanotubes, fullerenes also have some good properties. However,
the real advantage of therapies based on fullerenes as compared to
o theQru taanrtguemte ddo tthserapeutic3 0agents is that fullerenes are expected to
carry multiple drug loads.
(QDs) are semiconductor nanocrystals, about 2–10
nm. QDs implications derive from the diagnostics segment, as they
are vital for in vivo imaging, that provides real-time biodistribution
and target accumulation of drug. They can also be easily attached
to a variety of surface ligands and finally inserted into the body,
enhancing the in vivo drug efficiency. By the illumination effect of
ultraviolet light, QDs are used to localise cells or their activities.
The physical principle behind the phenomenon relies on the fact
that different sizes of the QDs give corresponding wavelengths.
Specifically, smaller QDs result in larger energy jumps between
the highest valence band and the lowest conduction band, and
consequently more energy is needed in order to excite the dot. There
are several reports demonstrating the advantages of QDs compared
to fluorescent molecules, indicating that the intensity of the signal is
brighter and present better photostability as well. Due to the better
photostability, the acquisition of many consecutive focal-plane
images is feasible, providing a three-dimensional image with high
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resolution.
1.3 Nanomedicine in Regenerative Medicine
A very challenging and promising domain of implementing
nanotechnology is regenerative medicine. Regenerative medicine,
or tissue engineering, can be defined as the application of physical
theories and principles in the design, construction, modification,
development and maintenance of living tissues. It is considered to
be a multi-disciplinary field, as many different scientists contribute
to it with knowledge that derives from material science, molecular
biology, engineering, medicine, etc. (Fig. 1.5 ).
The ultimate goal of regenerative medicine is to solve the
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problem of donor shortage of tissues and organs. Patients with
osteoarthritis (OA), for example, resulting from trauma or age-
related disease, present a significant clinical challenge because of
the limited repair of articular cartilage. Another implementation of
tissue engineering can be on cardiovascular issues, finding solutions
10 Introduction in Clinical Nanomedicine
to clinical problems of heart valves, arteries and myocardium by
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developing tissue replacements in vitro or inside the human body.
Also, tissue engineering is supposed to work with the patient’s
repair mechanisms in order to prevent and treat chronic diseases
and their consequences, such as diabetes and disorders of the central
5
nervous system. The concept of tissue engineering is based on three
segments—cells, scaffold, bioactive factors—as shown in Fig. 1.5.
Figure 1.5
(A) Basic principle for tissue engineering: A scaffold or matrix,
living cells and/or biologically active (mBo)lecules are used in
variable strategies to form a “tissue-engineered construct
promoting the construction of tissue. Multidisciplinarity
and complexity of combining tissue engineering and genetic
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engineering within the context of regenerative medicine.
The first part of tissue engineering is the proper polymeric
scaffold, either biodegradable or not, that will support the formation
of tissue. Most mammalian cells have to adhere onto a proper
substrate in order to proliferate and function properly. The ideal