Pages 12-15 - eCM journal

European Cells and Materials Vol. 3. Suppl. 2, 2002 (pages 12-15)
ISSN 1473-2262
THE MTC TECHNOLOGY: A PLATFORM TECHNOLOGY FOR THE
SITE-SPECIFIC DELIVERY OF PHARMACEUTICAL AGENTS
Jacqueline Johnson, Thomas Kent, Joy Koda, Caryn Peterson, Scott Rudge, Gilles Tapolsky
FeRx Inc., 12635 E. Montview Blvd. - Suite 300, Aurora, CO 80010, USA
Magnetic Targeted Carriers (MTCs) are
microparticles composed of metallic iron and
activated carbon and are prepared by a high-energy
milling process. Very pure elemental iron comprises
approximately 75% of the microparticle mass while
high surface area activated carbon comprises the
remaining. The synergy between these two
components creates a magnetically susceptible
particle capable of carrying therapeutic quantities
of a wide range of pharmaceutical agents which
may be targeted and localized at the desired site.
MTCs range in size from 0.5 µm to 5 µm with an
average diameter of approximately 1 µm [1-3].
Using a small, externally positioned magnet to
create a localized magnetic field within the body,
MTCs can be targeted to specific sites following
intra-arterial administration as illustrated in Fig. 1
[4]. Having a higher magnetic susceptibility and
saturation than particles made of iron oxides
(including magnetite, Fe3O4, and hematite, Fe2O3),
the iron containing MTCs are captured by the
external magnetic field more efficiently and at
depths up to 14 cm, a clinically relevant depth for
most solid tumors. In response to the magnetic field,
the MTCs are pulled out of the circulation through
the vasculature by a physical process of
extravasation leading to the localization of the
particles in the surrounding tissue.
incubate for 30 minutes at room temperature to
ensure complete absorption. The MTC-DOX
complex is then diluted with a vehicle that provides
a homogeneous suspension for administration. The
MTC-DOX suspension is administered intraarterially by placing a catheter proximal to the
selected tumor site and a magnet positioned on the
surface of the body over the desired site. The MTCDOX is then slowly infused with the magnet in
place for an additional 15 minutes following
administration [4]. MTCs are localized within the
interstitial space, thus providing a retention
mechanism that does not allow for redistribution.
In vivo characteristics of the MTCs have been
investigated in preclinical animal studies as well as
in ongoing human clinical trials. These studies
defined the preliminary safety profile of MTC-DOX
and the efficiency of magnetic targeting and
retention of the MTCs.
Fig. 2: Administration of the microparticles.
Preclinical Studies
MTCs can be selectively targeted in a large animal
model to specific sites. Targeting was assessed
through the use of gamma camera images following
adsorption of 99mTc to MTCs. 99mTc is a gamma
emitting radionuclide widely used for imaging
purposes. Results showed that the MTCs can be
targeted to the desired site (4). Targeting has been
shown in lung, liver, pancreas, kidney, brain, and
breast [5].
Fig. 1: Schematic Representation of the targeting of the
MTCs
The pharmaceutical agent to be delivered to solid
tumors is simply adsorbed onto the microparticles
(activated carbon component) at the hospital
pharmacy just prior to administration. As illustrated
in Fig. 2, a commercial formulation of the
chemotherapeutic agent doxorubicin, is combined
with the MTCs and the mixture is allowed to
Clinical Investigation
The lead product developed by FeRx, MTCDoxorubicin (MTC-DOX), is under investigation in
the U.S. in a phase I/II clinical trial in patients with
hepatocellular carcinoma. In humans, the efficiency
12
of the targeting and the fate of the MTCs over time
are assessed by MRI. To date, 32 patients have
been enrolled and clinical results confirm the
preclinical findings, highlighting the efficiency of
tumor targeting and the retention of MTCs at the
targeted site. An angiogram taken immediately after
administration of MTC-DOX to a tumor lesion in
the liver of a patient with hepatocellular carcinoma
is shown in Figure 3. It demonstrates that the
mechanism for retention is extravasation of the
MTCs and not embolization.
Chemotherapeutic drugs
The use of systemic chemotherapeutic agents, alone
or in combination is a common treatment against
many cancers. However, the efficacy of the
systemic administration of current chemotherapies
has been limited by the low effective concentration
at the tumor site and from the systemic toxicity of
these drugs. FeRx’s lead product is based on
doxorubicin, a widely used chemotherapeutic agent.
Many other chemotherapeutic drugs have been
shown to adsorb onto the MTCs, such as
mitomycin C, etoposide, paclitaxel, oxaliplatin. The
adsorption of the drug onto the MTCs is done at
room temperature. The release characteristics are
studied in human plasma and the cytotoxicity
profile is investigated by combining with an
appropriate cell line either the MTCs drug complex
or the solution of the drug after release from the
MTCs. A complete study of MTC-DOX and MTCTaxol are described in Rudge et al. [1] and Allen et
al. [2].
Fig. 3: Angiogram taken immediately after administration
of MTC-DOX.
Radioisotopes
External beam radiation is a widely used treatment
in solid tumors with good efficacy. However,
radiation exposure to normal tissue surrounding the
tumor or in the path to a tumor is the limiting step
of this therapy [7]. The MTC technology could
overcome these limitations by direct localization of
MTCs labeled with radionuclides inside the tumor.
In vitro labeling studies with various radionuclides
have shown that irreversible binding with simple
chemistry modifications. Efficiency and stability of
the labeling in human plasma at 37°C are shown in
Figure 5 for Rhenium 188 labeled MTCs [8,9].
Investigation of 90Y, 131I, and 111In is underway and
results will be reported soon [10]. These in vitro
results indicate that MTCs are well suited for local
radiation therapy and animal experiments are
underway to evaluate the feasibility of using MTCs
for the localized radiation therapy of solid tumors.
In addition, a MRI scan is done in order to verify
the targeting efficiency. As shown in Figure 4, the
MTCs are localized only in the tumor where they
are retained [6].
Fig. 4: MRI scan of an HCC lesion in a patient following
targeted delivery of MTC-DOX.
100
Finally, in this Phase I/II clinical trial designed to
determine the tolerability and safety profile of this
product, a Maximum Tolerated Dose of 60 mg
Doxorubicin and 600 mg MTCs was reached.
5 min
20 min
45 min
60 min
120 min
40
20
80
60
40
20
0
Wash1
Wash2
99_deg.opj 9/1/00 gtp
Platform Technology
The platform nature of the MTC technology has
been demonstrated by the wide range of
pharmaceutical agents that can be adsorbed onto
the MTCs, the control of the release rate, and the
targeting to many different organs [5].
100
60
Labeling Efficiency [%]
% Radioactivity Bound
80
5
20
45
60
120
Minutes of Incubation
99_deg.opj gtp 9/1/00
0
0
10
20
30
Time (hours)
13
40
50
Fig. 5: Labeling Efficiency and Stability of 188Re perrhenate
labeled MTCs.
dramatic regression in some patients. Therefore,
achieving adequate local concentrations of TNF-α
may reduce or eliminate the systemic toxicities
while increasing the efficacy through site specific
delivery of the therapeutic agent.
Peptides
We selected a peptide being developed for the
radioimmunotherapy of neuroendocrine tumors as a
model peptide. Octreotate is a synthetic eight amino
acid peptide that binds to somatostatin receptor
subtypes 2. This peptide has been further
functionalized and includes a chelator moiety,
DOTA. Octreotate can thus be radiolabeled with
radionuclides such 177Lu or 90Y for the therapy of
neuroendocrine tumors [11].
Adsorption of TNF-α was rapid and quantitative with more
than 95% being adsorbed after 1 hour. The desorption
from MTCs in human plasma was investigated: 10
µg of TNF-α in aqueous solution at neutral pH was
mixed with 1 mg of MTCs. After binding at room
temperature for 1 hour, the MTC/TNF-α complex
was washed once with phosphate buffer at pH 7.4.
Human plasma was then added to investigate the
desorption at different time points. Results shown in
Figure 7 indicated that TNF-α is desorbed from
MTCs slowly under the conditions studied.
The radiolabeled peptide binds quantitatively to MTCs
(99.5 + 0.1%) at room temperature. The desorption of
DOTAOC:Y90=20, MTC-KB
Amount desorbed ( µ g)
Octreotate from MTCs in human plasma at 37ºC is
shown in Fig. 6. Three types of MTCs that were
prepared with activated carbons having different
characteristics show different rates of release. The
MTC-HP particles prepared with the carbon HP
have the most desirable set of properties with the
preferred release profile in human plasma.
DOTAOC:Y90=20, MTC-HP
DOTAOC:Y90=20, MTC-Fe
% Radioactivity
Bound
100%
1
0.8
0.6
0.4
0.2
0
0
80%
60
120 180 240 300
Time (min)
60%
Fig. 7: Release profiles in human plasma at 37ºC.
40%
Furthermore, the cytotoxicity of TNF is unchanged
throughout this adsorption/desorption process. The
preliminary in vitro cytotoxicity of MTC/TNF-α
was investigated using the WEHI-13Var cell line
(Fig. 8). Results indicate that the biological activity
of TNF-α adsorbed onto and then desorbed from
MTCs is retained.
20%
0%
0
20
40
Time (hours)
60
80
Fig. 6: Release profiles in human plasma at 37ºC.
These results indicate that therapeutic peptides can
be adsorbed and desorbed from MTCs. Peptides
with molecular targeting function could also benefit
from the physical targeting of MTCs by increasing
their local concentration and eventually improving
the percentage of peptide being efficiently targeted
by pre-localizing them at the desired site.
Proteins
Tumor Necrosis Factor alpha (TNF-α) is a 17 kDa
macrophage derived cytokine that has been shown
to have anti-tumor activity against a variety of
malignancies in murine models [12]. However, its
clinical development has been hampered because of
its systemic side effects such as hypotension, which
severely limits the systemic use of this drug. High
doses of TNF-α administered by intra-tumoral
injections or isolated limb perfusion have shown
14
magnetic targetable drug carrier for paclitaxel”
100
Scientific and Clinical applications of magnetic carriers.
New York, Plenum, 481 (1997). 3Volkonsky, V. A.,
S. D. Dvukhsherstnov, S. V. Chernyakov, US
4
5,705,195. Goodwin, S., C. Peterson, C. Hoh, and
C. Bittner, “Targeting and retention of magnetic
targeted carriers (MTCs) enhancing intra-arterial
chemotherapy”, J. MMM, 194, 132 (1999). 5Hill, J.,
Bittner, C., Bonilla, S., Bonneville, A., Melinek, J.,
Goodwin, S. Proceedings American Association of
6
Cancer Research 41, #1646, March 2000. Goodwin,
S., Hill J., Gordon, R., Kerlan, R., Walser, E.,
Suhocki, P., 25th Annual Meeting of the Society of
Cardiovascular and Interventional Radiology, April
2000. 7Gaze, Mark N., “The current Status of
Radiotherapy in Clinical Practice”, Phys. Med. Biol.
41, 1895 (1996). 8Knapp, F.F. “A generator for
cancer therapy”. Cancer Biother. Radiopharm. 13, 337
(1998). 9Häfeli, U., Pauer, G., Failing, S.,
Tapolsky, G. “ Radiolabeling of Magnetic Particles
with Rhenium188 for Cancer Therapy”, Journal of
Magnetism and Magnetic Materials, 225: 73-8 (2001).
10
Yu, Y., Häfeli, U., Li, Y., Tapolsky, G.
“Radiolabeling of Magnetic Targeted Carriers with
Indium 111” manuscript in preparation. 11deJong
M., Breeman W., Kooij P., Valekame E., and
Krenning E., “Therapy of neuroendocrine tumors
with radiloabeled somatostatin analogs”, Q. J. Nucl.
12
Med. , 43, 356 (1999). Corti, A. and Marcucci, F.,
“Review: Tumor Necrosis Factor: Strategies for
Improving the Therapeutic Index”, J. Drug Targeting,
5, 403 (1998).
%Growth inhibition
80
60
40
TNF in water
20
TNF in Plasma
TNF 15 min desorb
0
TNF 4 hr desorb
-20
0.000000001
0.0000001
0.00001
0.001
0.1
10
Concentration [µg/mL]
Fig. 8: Cytotoxicity of TNF, shown as growth inhibition,
before and after adsorption to MTC.
Conclusions
The MTC technology is an innovative technology
with well-characterized in vitro and in vivo
properties. Because of their unique properties, these
microparticles are targeted to the desired sites,
extravasated into the tissue, and do not redistribute
over
time.
They
can
reversibly
bind
chemotherapeutic drugs, peptides, and proteins or
irreversibly bind radionuclides. Thus, MTCs could
be used for the site-specific delivery of
chemotherapeutic agents or localized radiation
therapy. On-going human clinical trials with MTCDOX show that these microparticles are efficiently
targeted to liver tumors. Expansion to other clinical
indications and intra-tumoral radiation therapy are
planned for the near future.
ACKNOWLEDGMENTS
Results presented in this paper are the work of
FeRx’s personnel and especially Jacqueline
Johnson, Caryn Peterson, Joy Koda, Scott Rudge,
Tom Kent, Yuhua Li, Sarah Failing, and
collaborators including Scott Goodwin (PHS Grant
# 5M01 R00865-25), Jennifer Hill, Urs Häfeli, and
Marion de Jong.
BIBLIOGRAPHY
1
Rudge, S., T. Kurt, and C. Vessely, “Preparation,
characterization and performance of magnetic
iron/carbon microparticles for chemotherapy”,
2
Biomaterials 21, 1411, (2000). Allen, L.R., Kent,
T., Wolfe, C., Ficco, C., and Johnson, J. “A
15