Acta Polytechnica


doi:10.14311/AP.2015.55.0242
Acta Polytechnica 55(4):242–246, 2015 © Czech Technical University in Prague, 2015

available online at http://ojs.cvut.cz/ojs/index.php/ap

A SYSTEM AND A DEVICE FOR ISOLATING CIRCULATING
TUMOR CELLS FROM THE PERIPHERAL BLOOD IN VIVO

Michal Megoa, Miroslav Kocifajb, c, ∗, František Kundracikc

a Department of Oncology, Comenius University, Medical Faculty and National Cancer Institute, Klenová 11,
833 10 Bratislava, Slovak Republic

b ICA, Slovak Academy of Sciences, Dúbravská Cesta 9, 845 03 Bratislava, Slovak Republic
c Faculty of Mathematics, Physics, and Informatics, Comenius University, Mlynská dolina, 842 48 Bratislava,

Slovak Republic
∗ corresponding author: kocifaj@savba.sk

Abstract. Circulating tumor cells (CTC) play a crucial role in disseminating tumors and in the
metastatic cascade. CTCs are found only in small numbers, and the limited amount of isolated
CTCs makes it impossible to characterize them closely. This paper presents a proposal for a new
system for isolating CTCs from the peripheral blood in vivo. The system enables CTCs to be isolated
from the whole blood volume for further research and applications. The proposed system consists of
magnetic nanoparticles covered by monoclonal antibodies against a common epithelial antigen, large
supermagnets, which are used to control the position of the nanoparticles within the human body, and
a special wire made of a magnetic core wrapped in a non-magnetic shell. The system could be used
not only for isolating CTCs, but also for in vivo isolation of other rare cells from the peripheral blood,
including hematopoietic and/or mesenchymal stem cells, with applications in regenerative medicine
and/or in stem cell transplantation.

Keywords: circulating tumor cells, in vivo isolation, magnetic nanoparticles.

1. Introduction
Circulating tumor cells (CTCs) play a crucial role in
tumor dissemination and in the metastatic cascade.
CTCs are very rarely-occurring cells, surrounded by
billions of hematopoietic cells in the bloodstream. Re-
cent advances in detection methods have enabled them
to be identified reproducibly and further character-
ized [1]. CTCs consistently showed a prognostic value
for several types of cancer, including breast, prostate
and colon cancer [2–4]. However, CTCs represent a
heterogeneous population of cells with various phe-
notypes and biological values [1]. Different methods
detect different CTC subpopulations with different
clinical and biological values. All data on CTCs should
therefore be interpreted within the context of the
detection method that is used [1]. Despite recent
technological advances, we are still only beginning to
understand CTC-related processes in tumor dissemi-
nation and progression.

Various strategies are used for detecting and charac-
terizing CTCs, including morphological and physical
characteristics, such as size and weight, and detect-
ing the expression of specific markers. In carcinomas,
CTCs are usually identified on the basis of the expres-
sion of epithelial-lineage markers, such as EpCaMs
(epithelial cell adhesion molecules) or cytokeratins (cy-
toskeletal proteins present in epithelial cells) and the
absence of a common leukocyte marker (CD45) and/or
by the presence of putative tumor-specific antigens
(for example MUC1 and HER2) [1].

Due to the small numbers of CTCs, almost all de-
tection methods include enrichment steps (negative
selection, including depletion of hematopoietic cells,
or positive selection, typically using an anti EpCAM
antibody) to increase the detection success rate. De-
spite this enrichment, there is only a very limited
amount of isolated CTCs, and CTCs cannot be char-
acterized more closely. Almost all current detection
methods detect CTCs from a limited amount of pe-
ripheral blood that is drawn from the venous system,
while all CTC isolation steps are performed in vitro.
In this paper, we propose a new system and device
for isolating CTCs from the peripheral blood in vivo.
The system enables more cells to be isolated for fur-
ther research and applications. A major advantage
of the proposed system is that it could isolate CTCs
(or other cells of interest) from the whole volume of
the blood, whereas existing detection methods isolate
CTC from a limited volume of blood.

2. Material and methods
2.1. Magnetic nanoparticles
The system with magnetic nanoparticles covered by
monoclonal antibodies against a common epithelial
antigen (EpCAM) is used to isolate circulating tumor
cells from the peripheral blood. Magnetic nanoparti-
cles are used because they can be manipulated easily
(held and transported) by means of a magnetic field.
Magnetic particles can thus be fixed in a vein for a
long time, using permanent supermagnets attached to

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vol. 55 no. 4/2015 System for in vivo Isolation of CTC

Figure 2. Magnetic induction, B, determined along the line perpendicular the wire and crossing the wire between
the pellets. Inset: Magnetic field lines in the vicinity of the wire.

Figure 1. Special wire containing supermagnetic
pellets in a non-magnetic mantle.

the arm. This approach is likely to be more comfort-
able for patients. The magnetic force, Fmag, acting on
the nanoparticles should be strong enough in relation
to the viscous force, Fvis, caused by the blood flow.
Nacev et al. [5] have analyzed the diffusion effects and
the velocity profiles of venous blood, and have shown
that the ratio Fmag/Fvis > 5 · 10−5 for typical viscous
forces in the central parts of the vein. Because there
is continuous lowering of the blood velocity from the
central parts of a vein to its walls, a fixed nanoparticle
layer will be formed at the edges — i.e., at the venous
walls. The magnetic force acting on a nanoparticle is
proportional to its volume, so large-sized nanoparti-
cles are usually preferred for this application. In cases
that are important for practically applications, com-
mercially available particles about 30 nm in diameters
would be a suitable choice.

2.2. Magnets
An external magnetic field is an advantageous concept,
since it prevents magnetically guidable nanoparticles
spreading over the blood vessels. Large supermagnets
are used to control the position of the nanoparticles,
and to prevent them moving beyond the area of the
arm. The nanoparticles are exposed to circulating tu-
mor cells, and CTCs are picked up by binding them to
an EpCAM antibody on the surface of each nanopar-

ticle. By manipulating them with large magnets, the
nanoparticles can easily be transported towards the
venous cannula after the in vivo incubation period.

2.3. A wire with a magnetic core
A special wire made of a magnetic core wrapped in
a non-magnetic shell (Figure 1) is inserted into the
cannula, and the large magnets are removed. The
nanoparticles with CTCs are attracted by the wire,
and are then transferred from the cannula to a tube
with an appropriate medium, where the particles scat-
ter within a short time. Before further analysis, the
magnetic core should be removed. To make this pro-
cedure possible, the wire has to produce a magnetic
force large enough to act on the nanoparticles, but low
enough to interact with the large magnets. Since the
magnetic force is proportional to the magnetic field
gradient, the magnetic core can be advantageously
made as a chain of supermagnetic pellets with oppo-
site orientations. In this type of configuration the
magnetic field of the pellets is pulled out of the wire
and large gradients are produced near the touching
pellets. Since the force-vector between the pellets and
the large magnets changes its direction, the resulting
net force between the whole wire and the large mag-
nets is relatively small. If the individual pellets are
well separated (e.g., equispaced), rather than glued
together, the wire becomes flexible enough for use in
in vivo manipulation.

We used a software implementation of the finite-
element method [6] to analyze the wire shown in Fig-
ure 1. Pellets 1 mm in diameter and 2 mm in length
made from standard neodymium magnets were con-
sidered. Figure 2 demonstrates the magnetic induc-

243



M. Mego, M. Kocifaj, F. Kundracik Acta Polytechnica

Figure 3. Proof of concept.

tion, B, computed along a line perpendicular to the
wire and crossing the wire between the pellets (the
length is measured from the axis of symmetry). A mag-
netic field gradient of 500 T/m was found at a distance
of 1 mm from the center of the wire (0.5 mm above the
surface of the pellets). Magnetic induction exceeding
0.2 T is large enough to saturate the magnetization of
the nanoparticles in this region [7].
The magnetic properties of Fe3O4 nanoparticles

30 nm in size [7] were taken into consideration when de-
termining the magnetic force: density of 5 g/cm3 and
magnetic saturation of 20 emu/g = 100 emu/cm3 =
105 A/m. The magnetic force acting on a nanoparticle
with radius r is

Fmag = MV grad B =
4πMr3 grad B

3
,

where M is the magnetization of the particle and V
is the volume of the particle. Using the parameters
mentioned above, we obtain Fmag = 5.7 · 10−15 N. The

viscous force in a non-turbulent flow can be expressed
as follows:

Fvis = 6πrηv,

where η is the dynamic viscosity of the blood plasma
and v is the velocity of the blood at the center of
the vein. Using typical values [8] η = 1.3 · 10−3 Pa s
and v = 10 cm/s, we obtained Fvis = 3.7 · 10−11 N. A
ratio of Fmag/Fvis = 1.5 · 10−4 is sufficient to hold the
nanoparticles near the wall of the magnetic wire.

3. Results
This is a new system and device for isolating circu-
lating tumor cells from the peripheral blood in vivo.
The system is based on isolating CTCs in vivo, us-
ing magnetic nanoparticles covered by a monoclonal
antibody (Figure 3A.) Magnetic nanoparticles (A)
covered by monoclonal antibodies against a common
epithelial antigen are slowly injected into the cubital
vein (or into another appropriate vein) through the

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vol. 55 no. 4/2015 System for in vivo Isolation of CTC

venous cannula. The position of these nanoparticles
is controlled by large magnets, and their movement
is limited to the area of the arm (or to another area
of interest) (Figure 3B). Nanoparticles are exposed to
the circulating tumor cells, and CTCs are picked up by
binding them to an EpCAM antibody on the surface
of a nanoparticle. The special wire (B) consists of a
magnetic core covered by a non-magnetic mantle. The
wire is used for removing nanoparticles with the CTCs
attached to them from the bloodstream (Figure 3C).
After in vivo incubation, the nanoparticles are moved
closer to the venous cannula by moving the large mag-
nets. Then a special wire (B) is inserted through the
cannula (Figure 3D). Subsequently, the large magnets
are removed and the nanoparticles are attracted by a
magnetic wire. Then the magnetic wire covered with
nanoparticles with CTCs attached to them is removed
from the cannula (Figure 3E). The wire is placed into
the tube with an appropriate medium. The magnetic
core is removed, and the nanoparticles with CTCs
attached to them are released into the medium for
further analysis (Figure 3F).

4. Discussion
Numerous methods are used for isolating CTCs from
the peripheral blood, with various levels of success, in
detecting CTCs, ranging from 1 cell/7.5 mL of blood
to several thousand, but with most of the methods the
number of CTCs that are detected is very small (1,
9, 10). Almost all of these methods isolate CTCs from
a limited volume (5–30 mL) of peripheral blood. CTCs
occur in small numbers in the blood, and a limited
number of CTCs could be used for further biological
characterization. Our system and device overcome
this limitation by utilizing in vivo isolation of CTCs.
In comparison with a similar system [11], the main ad-
vantage of our system is that the nanoparticles float in
the bloodstream, and are therefore exposed to CTCs
from the whole volume of the blood. These nanoparti-
cles are exposed to the blood not just at the site where
the venous cannula is inserted (as is the case in [11]),
but they can be moved to large veins with a bigger
blood flow, so they can be exposed to more CTCs
from the whole blood. Moreover, the nanoparticles
can be exposed to the blood flow for several hours,
so they can be washed with the whole volume of the
blood several times before they are extracted from
the bloodstream. Their positions are controlled by
external magnets, and the nanoparticles can be placed
in any vein of the human body. Another advantage is
that the blood does not leave the blood vasculature,
so our method is not associated with any blood losses,
even when there is repeated isolation of CTCs. Unlike
apheresis methods for CTC isolation, the system that
we propose here does not need blood anti-coagulation,
and the blood is not discharged outside the blood
vasculature into any artificial equipment. The method
is therefore safer and more comfortable for patients.
In addition, the patient is not bed bound. The system

can be moved while the patient is exercising, and nor-
mal activities can be performed during the procedure.
One of the limitations of the proposed method is

that it utilizes positive selection using an anti-EpCAM
antibody. CTCs without EpCAM expression, includ-
ing those undergoing the epithelial-to-mesenchymal
transition, are therefore not detected by this method.
However, depending on the antibody that is utilized
on the surface of the nanoparticles, this system could
be used for detecting other rare cells present in the
peripheral blood, including hematopoietic stem cells.

This system has several potential applications. For
example, it can be used in CTC research to better
characterize CTCs, to identify therapeutic targets
on CTCs, to perform molecular profiling of tumors
that are seeded by CTCs, to study the mechanism
of drug resistance, and/or to develop cancer vaccines
from the predominant CTC clones. Other potential
applications include in vivo isolation of dendritic cells
for developing tumor vaccines, or mesenchymal stem
cells with applications in regenerative medicine and/or
in stem cell transplantation. In addition, the system
can be utilized for detecting and isolating any cell of
interest present in the blood and/or in another body
fluid, with potential uses in translational research,
personalized medicine and treatment.
In conclusion, our new system for isolating CTCs

from the peripheral blood in vivo enables CTCs to
be isolated from the whole volume of the blood for
further research and applications. In addition to its
use for isolating CTCs, the system could be used for
isolating other rare cells from the peripheral blood
in vivo, including hematopoietic and/or mesenchymal
stem cells, with applications in regenerative medicine
and/or in stem cell transplantation.

Acknowledgements
The methods described in this paper present a patent
application submitted by Miroslav Kocifaj and Michal
Mego. This publication is an outcome of project 1/0724/11,
funded by the Slovak Grant Agency VEGA, and project
APVV-0016-11, supported by the Slovak Research and
Development Agency. This work also received support
from the Slovak National Grant Agency VEGA (grant
2/0002/12). The work presented here has also been
supported by Research & Development Operational Pro-
gramme project 26240120026, funded by the ERDF.

There are no competing interests.
The study involves no human subjects.

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	Acta Polytechnica 55(4):242–246, 2015
	1 Introduction
	2 Material and methods
	2.1 Magnetic nanoparticles
	2.2 Magnets
	2.3 A wire with a magnetic core

	3 Results
	4 Discussion
	Acknowledgements
	References