Evaluation of drug mechanism and efficacy of a novel anti-angiogenic agent, TTAC-0001, using multi-modality bioimaging in a mouse breast cancer orthotopic model
Evaluation of drug mechanism and efficacy of a novel anti-angiogenic agent, TTAC-0001, using multi-modality bioimaging in a mouse breast cancer orthotopic model
Jinil Kim 0 1
Sang Hyun Choi 0 1
Su Jung Ham 1
Young Chul Cho 1
Seul-I Lee 1
Jeeheon Kang 1
Dong-Cheol Woo 1
Weon Sub Lee 1
Jin-San Yoo 1
Kyung Won Kim 0 1
Yoonseok Choi 1
0 Department of Radiology and the Research Institute of Radiology, University of Ulsan College of Medicine, Asan Medical Center , Seoul , Korea , 2 Bioimaging Center, Asan Institute for Life Sciences, Asan Medical Center , Seoul , Korea , 3 PharmAbcine; Inc., Daejeon Bioventure Town, Daejeon Korea, 4 Medical Research Institute, Gangneung Asan Hospital, University of Ulsan College of Medicine , Gangwon-do , Korea
1 Editor: Aamir Ahmad, University of South Alabama Mitchell Cancer Institute , UNITED STATES
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: This study was supported by the Ministry
of Health & Welfare, Republic of Korea; contract
grant number (HI14C1090), a grant from the
National Research Foundation of Korea (NRF)
funded by the Ministry of Education
(2016R1D1A1A02937258). The funding
organization did not play a role in the study design,
Targeting of vascular endothelial growth factor receptors (VEGFRs) has potential
antiangiogenic effects because VEGFR-2 is the major signaling regulator of VEGF/VEGFR
pathways. We aimed to elucidate the drug mechanism and anti-tumor efficacy of
TTAC0001, a novel, fully human anti-VEGFR-2/KDR monoclonal antibody, in mouse orthotopic
breast cancer model using multi-modal bioimaging.
Materials and methods
We used orthotopic xenograft tumor model in which human breast cancer cells
(MDA-MB231) were injected into the right mammary fat pad of Balb/c nude mice. We investigated its
biodistribution using serial fluorescence imaging after injecting fluorescent-labelled-drug
and mode of action using Matrigel plug angiogenesis assays. The anti-tumor efficacy of
drug was assessed using ultrasonography and bioluminescence imaging. Histopathologic
analyses, including hematoxylin and eosin staining and immunohistochemistry with
antiCD31 and anti-Ki-67 antibodies, were performed. Each experiment had four groups: control,
bevacizumab 10 mg/kg (BVZ-10 group), TTAC-0001 2 mg/kg (TTAC-2 group), and
TTAC0001 10 mg/kg (TTAC-10 group).
The TTAC-10 group showed good tumor targeting that lasted for at least 6 days and had a
good anti-angiogenic effect with decreased hemoglobin content and fewer CD31-positive
cells in the Matrigel plug. Compared with BVZ-10 and TTAC-2 groups, the TTAC-10 group
data collection and analysis, decision to publish, or
preparation of the manuscript. The funding
organization provided financial support in the form
of authors' salaries [J. Kim, S. J. Ham, J Kang, Y.
Choi], and research materials. The PharmAbcine
employees (W. S. Lee, J-S Yoo) provided the
antiangiogenic agent, TTAC-0001, and participated
in the study design and critical revision of the
manuscript. They did not have access to the data
collection and analysis.
Competing interests: I have read the journal's
policy and the authors of this manuscript have the
following competing interests. Two authors (W. S.
Lee, J-S Yoo) are employees of PharmAbcine inc.,
own stocks, and are inventors of patents of
TTAC0001 (US 9150650 B2). Four authors' salaries (J.
Kim, S. J. Ham, J Kang, Y. Choi) were supported
by the funding organizations including the Ministry
of Health & Welfare of Korea and the National
Research Foundation of Korea (NRF). This
experiment is conducted as a part of National
scientific program supported by these two grants
(Grant Nos. HI14C1090,
2016R1D1A1A02937258). The other authors have
no competing interests. These do not alter our
adherence to PLOS ONE policies on sharing data
showed the strongest anti-tumor efficacy, inhibiting tumor growth as detected by
ultrasonography and bioluminescence imaging. The TTAC-10 group also showed the lowest viable
tumor and micro-vessel areas and the lowest Ki-67 index in histopathologic analyses.
We firstly demonstrated that TTAC-0001 effectively inhibited tumor growth and
neovascularization in mouse orthotopic breast cancer model. It may provide a future treatment option
for breast cancer.
Tumor angiogenesis is a potential target for anti-cancer therapy, as it plays an essential role in
oxygen and nutrient supply [
]. Antibodies against either vascular endothelial growth
factors (VEGFs) or their receptors have been developed to target tumor angiogenesis [
Bevacizumab, the first approved anti-angiogenic agent to target VEGF itself, achieved notable
success as a novel targeted drug to treat several cancers, including colon, renal, and non-small
cell lung cancer. Although its therapeutic efficacy is limited, it is generally used as part of a
combination treatment regimen.
Targeting VEGF receptors (VEGFRs) is an alternative approach to inhibit angiogenesis in
tumors. In particular, inhibition of the VEGFR-2/kinase insert domain receptor (KDR) has
potential anti-angiogenic effects because VEGFR-2 is the major signaling regulator of VEGF/
VEGFR pathways [
]. From this perspective, TTAC-0001, a human anti-VEGFR-2/KDR
monoclonal antibody, was developed. TTAC-0001 binds to the VEGF-binding domain of
VEGFR-2 and neutralizes the biological activity of VEGFR-2 by blocking the binding of VEGF
]. Preclinical research revealed potential anti-tumor activity of TTAC-0001 in colorectal,
non-small-cell lung cancer and glioblastoma tumor models [6±10]. Recently, a phase I clinical
trial of TTAC-0001 was completed, and a phase IIa trial is ongoing. However, there have been
no previous studies of TTAC-0001 for breast cancer.
In terms of chemotherapy for breast cancer, the major challenge is to develop an effective
regimen for triple-negative breast cancer [
]. Bevacizumab had been incorporated as a
second-line chemotherapy regimen for metastatic triple-negative breast cancer, but was
revoked by the FDA due to inadequate therapeutic effect, suggesting that targeting the
VEGF ligand itself may not be the best strategy [
]. Therefore, an alternative approach,
inhibition of VEGFR-2/KDR, is worthy of investigation for treatment of triple-negative
Bioimaging plays important roles in anti-cancer drug research [14, 15]. Multiple modalities
such as magnetic resonance imaging, positron emission tomography have been applied for the
oncologic drug development and each modality showed its own values to facilitate the
development steps. Particularly, size measurement with ultrasonography (US) provides more
accurate values of regressed tumor volumes [
] when the drugs are treated and the utilization
of optical imaging (fluorescence and bioluminescence) enables the studies of mode of action
mechanisms and biodistribution of the drugs .
The validation of TTAC-0001 in triple-negative breast cancer has not been performed yet.
Therefore, we aimed to investigate the drug mechanism and anti-tumor efficacy of
TTAC0001, a novel anti-angiogenic agent, in a mouse orthotopic breast cancer model using
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Materials and methods
Cells and drugs
Human breast cancer cells (MDA-MB-231) were purchased from the Korean Cell Line Bank
(KCLB, Seoul, Korea) and were used in cell culture and animal experiments. For the
establishment of MDA-MB-231+luc cells, MDA-MB-231 cells were transfected with a lentiviral vector
containing the firefly luciferase reporter gene. Both MDA-MB-231 and MDA-MB-231+luc
cells were cultured in Dulbecco's modified Eagle's medium (Welgene, Seoul, Korea)
supplemented with 10% (v/v) heat-inactivated fetal bovine serum (GIBCO, Seoul, Korea).
TTAC-0001 (PharmAbcine, Daejeon, Korea; Table 1) was kindly provided by the
manufacturer. Bevacizumab (Avastin1, Genentech, San Francisco, CA, USA) from clinically packaged
vials was used for comparison of anti-angiogenic and anti-tumor efficacy.
All animal experiments were performed according to our Institutional Animal Care and Use
Committee approved protocol. The protocol was approved by the Committee on the Ethics of
Animal Experiments of the Asan Medical Center (IACUC Number 2015-12-066). Female
Balb/c nude mice (n = 91), 6 weeks old and weighing 20±25 g, were used. In our experiment,
we used an orthotopic xenograft tumor model in which suspended cells were injected into the
right mammary fat pad of the animals. The mice were treated with therapeutic agents
approximately 2 weeks after tumor implantation, when the tumor diameter had reached
approximately 5±6 mm in diameter (70±130 mm3 in volume). All therapeutic agents were dissolved in
saline (0.1 mL) and injected intraperitoneally. Detailed information regarding the number of
animals and experimental groups is presented in Fig 1.
Our study was composed of three experimental parts as follows:
1. Biodistribution of the drug, focusing on tumor targeting, by serial fluorescence imaging
after injecting fluorescently labeled drug.
2. Use of Matrigel plug angiogenesis assays to evaluate the mode of action of the
3. Monitoring of anti-tumor efficacy of the drugs by ultrasonography and bioluminescence
Biodistribution for tumor targeting
Experimental groups. For the biodistribution assay, the animals were divided into three
groups: a control group administered immunoglobulin G (n = 5), a TTAC -2 group treated
TTAC-0001 is a fully human monoclonal antibody derived from a fully human single
chain variable fragment phargelibrary. The TTAC-0001 neutralizes the vascular
endothelial growth factor receptor2/vascular endothelial growth factor axis, which
is a major mediator of tumor-angiogenesis, and therefore blocks angiogenesis and inhibits
tumor growth and metastasis.
Fully human IgG1 monoclonal antibody
Solid tumor (including glioblastoma, triple negative breast cancer)
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Fig 1. Flow chart of the experimental protocol of the animal study.
with fluorescently labeled TTAC-0001 2 mg/kg (n = 5), and a TTAC -10 group treated with
labeled TTAC-0001 10 mg/kg (n = 5).
Labeling of TTAC-0001. To perform fluorescent labeling of TTAC-0001, we used a
commercial kit (Alexa Fluor1 647 Antibody Labelling Kit, Thermo Fisher Scientific, Waltham,
MA, USA), according to the manufacturer's protocol. Briefly, we induced a conjugation
reaction between the Alexa Fluor1 647 reactive dye and TTAC-0001, and the purified labeled
TTAC-0001 was collected. To determine the degree of labeling, the concentration of the dye
was calculated based on absorbance at 280 and 650 nm. The collected labeled drug was
stabilized at room temperature for 1 h and then intravenously injected into the mice.
Serial fluorescence imaging. Biodistribution of Alexa Fluor1 647-labeled TTAC-0001
was performed using the IVIS Lumina II machine (PerkinElmer, Waltham, MA, USA). Mice
were anesthetized with 1% isoflurane (Forane1, Choongwae, Korea), and Alexa Fluor1
647-labeled TTAC-0001 was intravenously injected at doses of 2 and 10 mg/kg. Serial
fluorescence images were then acquired at baseline and at 1, 2, 4, and 8 h and 1, 2, 4, and 6 days after
drug injection. Imaging was performed with an exposure time of 1 s and an f/stop of 1. Using
Living Image1 4.2 software (Caliper Life Sciences, Hopkinton, MA, USA), the peak total
signal was measured by placing regions of interest (ROIs) at the tumors, which reflected the
accumulated amount of Alexa Fluor1 647-labeled drug.
Mode of action for the anti-angiogenic effect
Experimental groups. For evaluating the mode of action, the animals were divided into
four groups that were treated with vehicle (control group, n = 5), bevacizumab 10 mg/kg
(BVZ-10 group, n = 5), low-dose (2 mg/kg) TTAC-0001 (TTAC-2 group, n = 5), or high-dose
(10 mg/kg) TTAC-0001 (TTAC-10 group, n = 5).
Matrigel plug angiogenesis assay. We used Matrigel plug angiogenesis assay (Corning,
NY, USA) to evaluate the in vivo anti-angiogenic effect of TTAC-0001. It is based on the fact
that VEGF secreted from Matrigel tumor cells exerts pro-angiogenic effects on the
surrounding tissue, thus promoting neovascular development that is visualized in the Matrigel. If a drug
inhibits the effect of VEGF by inhibiting either VEGF or VEGFR, then the decreased levels of
neovascular development in the Matrigel can be evaluated.
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Matrigel (0.5 mL) was premixed with 5 × 106 MDA-MB-231 cells and then engrafted into
the right mammary fat pad of Balb/c nude mice (n = 5). A single 2 or 10 mg/kg treatment of
TTAC-0001 or saline was administered to the respective groups by intravenous injection after
implantation. After 10 days, Matrigel plugs were removed and frozen for immunofluorescence
analysis. To measure the hemoglobin (Hb) content, excised plugs (n = 5 plugs/group) were cut
into small pieces and placed in 500 uL of cold, distilled water at 4ÊC overnight to liquefy the
Matrigel. Specimens were centrifuged at 1500 rpm for 20 mins, and the supernatant was
collected. Hb content was quantified using a Hb assay kit (Sigma-Aldrich) and
Immunofluoroscence staining. Cryosections (30 um) of the removed plugs were
obtained. Plugs were then immunostained with an anti-mouse CD31 monoclonal antibody
(1:300, Abcam, Cambridge, MA, UK) and a secondary goat anti-rabbit Alexa 594 antibody
(1:5000, Life Technologies, Carlsbad, CA, USA), according to the manufacturer's protocol.
The immunofluorescence images were analyzed using NIH-Image J software (National
Institutes of Health, Bethesda, Maryland, USA). A free-hand ROI was drawn around the
tumor, and CD31-positive cells were selected using the global histogram-derived thresholding
]. The percentage area of CD31-positive cells was calculated by dividing the area of
the CD31-positive cells by the area of the tumor ROI.
To evaluate the anti-tumor efficacy of the drugs, we used two types of cells and imaging
methods as follows: (1) MDA-MB-231 cells for ultrasonography (US) evaluation and (2)
MDA-MB231+luc cells for bioluminescence imaging (BLI). The reason why we used imaging for tumor
monitoring is that the orthotopic tumors in the mammary fat pad may be barely visible, thus
making it very difficult to measure tumor size if the tumor decreases during treatment. In
addition, utilization of both US and BLI modalities allows a more accurate evaluation of the
tumor volume and viability, respectively.
Experimental groups. To evaluate the anti-tumor efficacy of the drugs, tumors were
engrafted into 80 mice. Of these, 56 mice (70%) that met the tumor volume criteria (70±130
mm3) were selected and randomly assigned to four groups, which were treated with saline
(control group), bevacizumab 10 mg/kg (BVZ-10 group), low-dose (2 mg/kg) TTAC-0001
(TTAC-2 group), and high-dose (10 mg/kg) TTAC-0001 (TTAC-10 group).
Mice were monitored daily for up to 30 days after treatment for tumor volume, body
weight, and general body condition, such as appearance, food/water intake, respiration, and
ambulation. Animals were euthanized when they showed signs of distress, when the tumors
were >2 cm in diameter, when the weight loss was >15% of body weight, or when the tumor
interfered with the ability to eat or drink.
Ultrasonography. All US examinations were performed by a board-certified radiologist
(K.W.K) using an iU22 unit (Philips Healthcare, Bothell, WA, USA) with a 20 MHz linear
transducer. To assess tumor volume, we measured the longest diameter of the tumor on the
axial and coronal axes and the height of the tumor every 3 days during the 1 month follow-up.
We calculated the tumor volume according to the following formula: 4.19 × axial longest
diameter × coronal longest diameter × height.
Bioluminescence imaging. BLI is an established in vivo imaging techniques assessing
assessing angiogenesis and evaluating the efficacy of angiogenesis-directed therapies [
BLI was performed using the IVIS Lumina II machine (PerkinElmer, Waltham, MA, USA).
Mice were anesthetized with 1% isoflurane (Forane1, Choongwae, Korea), then D-Luciferin
(Caliper Life Sciences, Hopkinton, MA, USA) dissolved in phosphate-buffered saline (PBS; 1.5
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mg luciferin/100 μL PBS) was injected intraperitoneally at a dose of 150 mg luciferin/kg, and
serial images were acquired with an exposure time of 10 s, an f/stop of 1, and pixel binning of
8, over 20 min. The BLI was performed at baseline (i.e., 2 h before injecting therapeutic agents)
and after treatment (every 5 days during the 1 month follow-up). Using Living Image1 4.2
software (Caliper Life Sciences, Hopkinton, MA, USA), we measured the total flux (photons/s)
of the tumor bioluminescence signal by placing an ROI at the tumor.
Histopathologic study. All animals were euthanized at day 30 after treatment. The
extracted tumors were perfused with PBS and fixed with 4% paraformaldehyde in PBS.
Tumors were then embedded in paraffin and sectioned at a thickness of 5 μm at the largest
To evaluate the tumor morphology and extent of viable tumor, hematoxylin and eosin
(H&E) staining was performed. In representative sections of the tumor, H&E images were
analyzed using NIH-Image J software. The viable tumor cells were regarded as cells stained with
H&E in both the nucleus and cytoplasm, whereas necrotic/apoptotic areas were regarded as
cells stained with eosin only or no stain. After drawing ROIs around the whole tumor, viable
cells were selected based on the hematoxylin staining of the nuclei using the global
histogramderived thresholding method [
]. The percentage of viable tumor area was calculated by
dividing the area of viable cells by the whole tumor area.
To evaluate the microvessel areas, immunohistochemical staining for a vascular endothelial
antigen, CD31, was performed using a primary rabbit anti-mouse CD31 antibody (BD
Pharmingen, San Diego, CA, USA) and a secondary goat anti-rabbit antibody (1:1000, Molecular
Probes, Eugene, OR, USA). The images of immunohistochemical stains were analyzed using
NIH-Image J software to calculate microvessel area. In the tumor ROI, microvessels were
selected based on areas of CD31-positive cells [
]. The percentage microvessel area was
calculated by dividing the area of CD31-positive cells by the area of the tumor ROI.
To evaluate tumor cell proliferation (i.e., the Ki-67 index), immunohistochemical stating
for Ki-67 was performed using an anti-mouse Ki-67 antibody (1:100, Novus Biologicals, CO,
USA). Detection was performed by incubating with the Dako EnVision + System HRP-labeled
polyclonal anti-rabbit antibody (Agilent Inc., Palo Alto, CA, USA) for 30 min, followed by
DAB chromogen (Agilent Inc.). In the tumor ROI, the Ki-67-positive cells were selected based
on brownish nuclear staining using the global histogram-derived thresholding method [
We set the threshold to select the hematoxylin-stained nuclei and count the number of whole
tumor cells. Then we reset the color threshold to select the brownish nuclei and count the
number of Ki-67-stained tumor cells. The Ki-67 index was calculated by dividing the number
of Ki-67-positive cells by the number of whole tumor cells.
For the Matrigel plug angiogenesis assay, Hb content and percentage area of CD31-positive
cells in the four different treatment groups were compared using one-way ANOVA with a
post-hoc t-test with least significant difference significance (LSD).
For US and BLI analyses, the tumor volume on US and signal intensity on BLI over time
(every 3 days on USI and every 5 days on BLI) using a repeated measures analysis of variance
and post-hoc comparison tests with LSD were used. In addition, we compared the mean values
of the tumor volume on US and signal intensity on BLI at 30 days in the four different
treatment groups using one-way ANOVA with a post-hoc t-test with LSD.
For histopathologic analysis, we compared the percentage viable tumor area, percentage
microvessel area, and Ki-67 index at 30 days in the four different treatment groups using
oneway ANOVA with a post-hoc t-test with LSD.
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Statistical analysis was performed using a computer software package (SPSS, version 21.0;
SPSS; Chicago, IL, USA).
Biodistribution for tumor targeting
After injecting Alexa Fluor1 647-labeled TTAC-0001, a focal signal appeared in the right
flank area after 24 h and was detected in both TTAC-2 and TTAC-10 groups, but not in the
control group. These results are suggestive of tumor targeting of TTAC-0001 to the right
mammary fat pad of the mouse. The TTAC-10 group demonstrated higher fluorescence
accumulation at the tumor implantation site and a longer fluorescence accumulation of up to 6 days
than TTAC-2 group (Fig 2), indicating a higher and longer level of tumor targeting in the
high-dose TTAC-10 group.
Mode of action of the anti-angiogenic effect
Matrigel plugs from TTAC-0001-treated groups were pale white in appearance, but those from
the control group were bright red (Fig 3), indicating a reduction in new blood vessel formation
in the TTAC-0001-treated groups. The Hb content in the Matrigel plugs was the highest in the
control group, followed by BVZ-10, TTAC-2, and TTAC-10 groups. A significant difference
was noted between both TTAC-0001-treated groups (TTAC-2 and TTAC-10 groups) and the
BVZ-10 group (P = 0.004 and P = 0.004, Fig 3). However, there was no significant difference
between the TTAC-2 and TTAC-10 Matrigel plugs (P = 0.971, Fig 3).
The percentage area of CD31-positive cells showed a similar tendency in that the TTAC-2
and TTAC-10 groups had a significantly reduced area of CD31-positive cells compared with
the control group and the BVZ-10 group (P < 0.05, Fig 3). These results consistently indicated
that the mode of action of TTAC-0001 was an anti-angiogenetic effect, which was the strongest
in the TTAC-10 group, followed by the TTAC-2 and BVZ-10 groups.
Of the 56 mice involved in the anti-tumor efficacy evaluation, none were found dead during
the 30-day treatment period. No significant differences in weights were seen between the four
groups in the US and BLI experiments (S1 Fig and S2 Fig). Signs of drug toxicity, such as
Fig 2. Biodistribution of TTAC-0001 using Alexa Fluor1 647 reactive dye labeling. (A) Serial fluorescence images were acquired at baseline and at 1, 2, 4, and
8 h and 1, 2, 4, and 6 days after drug injection. (B) Plots of fluorescence accumulation at the tumor implantation site for each group show the serial changes over
time. TTAC-2, TTAC-0001 2 mg/kg; TTAC-10, TTAC-0001 10 mg/kg.
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Fig 3. Anti-angiogenic activity of TTAC-0001 in the Matrigel plug assay. (A) Gross overview of Matrigel plugs and (B) hemoglobin content (mean ± sd,
n = 5). (C) Immunohistochemical images showing CD31-positive blood vessels (red) in the Matrigel plug. Scale bars; 200 um. (D) Density of CD31-positve
blood vessels (mean ± sd) in the Matrigel plugs. , P < 0.001; , P < 0.01; , P < 0.05. BVZ-10, bevacizumab 10 mg/kg; TTAC-2, TTAC-0001 2 mg/kg;
TTAC-10, TTAC-0001 10 mg/kg.
ruffled fur, anorexia, cachexia, skin tenting, skin ulcerations, or toxic death [
], were not seen
in any of the mice.
Serial US monitoring. Serial changes in the mean tumor volume in mice transplanted
with MDA-MB-231 cells were measured every 3 days and are summarized in Table 2. The
control group showed a continuous increase in tumor volume over time. In contrast, all treated
groups (BVZ-10, TTAC-2, and TTAC-10) showed significantly smaller mean tumor volumes
(P < 0.001, Fig 4). The efficacy of tumor growth inhibition was the strongest in the TTAC-10
group, followed by the TTAC-2 and BVZ-10 groups (P = 0.018), but the TTAC-10 group did
not differ significantly from the TTAC-2 group (P = 0.182).
Serial BLI monitoring. The BLI signal intensities of MDA-MB-231+luc cell tumors
showed different characteristics between the groups, as summarized in Table 3. In the control
group, the signal intensity of tumors continuously increased until 30 days. In the BVZ-10
group, the signal intensity of the tumors fluctuated during the treatment period (Fig 5). In
both TTAC-2 and TTAC-10 groups, the signal intensity of tumors showed a tendency to
decrease. Notably, the TTAC-10 group showed a rapid drop in the signal intensity of tumors
after 20 days (Fig 5).
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At the end of the treatment period (30th day), the efficacy of tumor inhibition was the
strongest in the TTAC-10 group, followed by the TTAC-2 and BVZ-10 groups (P = 0.040), but the
TTAC-10 group did not differ from TTAC-2 group (P = 0.831).
Histopathologic findings. H&E staining demonstrated different characteristics of tumor
apoptosis/necrosis between the four groups (Fig 6). Tumor cells with active mitosis were
abundant in the control group, whereas they were sparse in the treatment groups. The percentage
of viable tumor areas significantly differed between groups (P < 0.001, one-way ANOVA) (Fig
6). The post-hoc test showed that the percentage of viable tumor area was the lowest in the
TTAC-10 group, followed by the TTAC-2 and BVZ-10 groups, with a significant difference in
each pair (P 0.016).
Fig 4. Serial ultrasonography images of mouse breast cancer before and after anti-angiogenic treatment. (A) The longest diameter of the tumor on
the axial and coronal axes and the height of the tumor were measured using ultrasonography. (B) Plots of tumor volumes for each group show the serial
changes over the treatment period. Data are presented as mean ± sd in the graphs. BVZ-10, bevacizumab 10 mg/kg; TTAC-2, TTAC-0001 2 mg/kg;
TTAC-10, TTAC-0001 10 mg/kg.
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Immunohistochemical staining for CD31 showed that tumor vessels were abundant in the
control group, but sparse in treated groups, with smaller microvessel areas (Fig 7). One-way
ANOVA revealed that the percentage of microvessel area significantly differed between the
four groups (P < 0.001). The post-hoc test revealed that the TTAC-10 group showed the lowest
percentage of microvessel area, followed by the TTAC-2 (P = 0.001) and BVZ-10 groups.
However, there was no significant difference between the TTAC-2 and TTAC-10 groups
(P = 0.084).
Fig 5. Serial bioluminescence imaging of mouse breast cancer before and after anti-angiogenic treatment. (A) The bioluminescence
imaging signal was measured at baseline and every 5 days after the administration of anti-angiogenic agents. (B) Plots of tumor volumes
for each group show the serial changes over the treatment period. Data are presented as mean ± sd in the graphs. BVZ-10, bevacizumab
10 mg/kg; TTAC-2, TTAC-0001 2 mg/kg; TTAC-10, TTAC-0001 10 mg/kg.
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Fig 6. Histopathologic specimens with hematoxylin and eosin staining. (A) Microscope images (magnification × 200) of the four groups (control,
BVZ-10, TTAC-2, TTAC-10). (B) The viable areas in tumors are shown for each group. Data are presented as mean ± sd in the graphs. , P < 0.001; ,
P < 0.01; , P < 0.05. BVZ-10, bevacizumab 10 mg/kg; TTAC-2, TTAC-0001 2 mg/kg; TTAC-10, TTAC-0001 10 mg/kg.
Immunohistochemical staining with Ki-67 demonstrated that cell proliferation markedly
decreased in both TTAC-2 and TTAC-10 groups (Fig 8). One-way ANOVA revealed that the
Ki-67 indexes significantly differed between the four groups (P < 0.001). The post-hoc test
revealed that the TTAC-10 group showed the lowest Ki-67 index, followed by TTAC-2 and
BVZ-10 groups, with a significant difference between each pair (P 0.041).
Fig 7. Immunohistochemistry with the anti-CD31 antibody for blood vessel detection. (A) Microscope images (magnification × 200) of the four
groups (control, BVZ-10, TTAC-2, TTAC-10). (B) The vessel density in the tumors is shown for each group. Data are presented as mean ± sd in the
graphs. , P < 0.001; , P < 0.01; , P < 0.05. BVZ-10, bevacizumab 10 mg/kg; TTAC-2, TTAC-0001 2 mg/kg; TTAC-10, TTAC-0001 10 mg/kg.
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Fig 8. Immunohistochemistry with the anti-Ki-67 antibody to detect proliferation. (A) Microscope images (magnification × 400) of the four
groups (control, BVZ-10, TTAC-2, TTAC-10). (B) The Ki-67-positive cells in tumors are shown for each group. Data are presented as mean ± sd in
the graphs. , P < 0.001; , P < 0.01; , P < 0.05. BVZ-10, bevacizumab 10 mg/kg; TTAC-2, TTAC-0001 2 mg/kg; TTAC-10, TTAC-0001 10 mg/kg.
In our study, TTAC-0001, a novel fully human anti-VEGFR-2/KDR monoclonal antibody that
blocks VEGF/VEGFR-2 signaling, showed selective tumor targeting that lasted at least 6 days,
an anti-angiogenic effect to inhibit neovascularization, and anti-tumor efficacy. Among the
three treatment groups, TTAC-10 showed the highest level of tumor targeting, anti-angiogenic
effects, and anti-tumor efficacy, compared with the TTAC-2 and the BVZ-10 groups. The
antitumor efficacy for inhibition of tumor growth was similar between the TTAC-2 and BVZ-10
groups. In histopathologic examination, the TTAC-10 group showed the lowest viable tumor
area, microvessel area, and cellular proliferation among the treatment groups. In addition, no
significant toxicity or death was noted for all treated mice. Consistent with a previous report
], our results indicate the validity of TTAC-0001 10 mg/kg as a potent anti-angiogenic agent.
Targeting VEGFR-2/KDR may be more effective than targeting the VEGF ligand itself.
Considering the fact that other VEGF-like heparin-binding growth factors can prevent specific
inhibition of the anti-VEGF antibody in hypoxic tumor microenvironments, targeting
VEGFR-2/KDR is more effective for anti-angiogenesis [
8, 23, 24
]. VEGFR-2/KDR is more
easily targetable than VEGF because VEGFR-2/KDR is highly expressed on the surface of the
activated endothelium in tumor tissues, in contrast to VEGF, which is mainly located in the
interstitial space between cells. Therefore, the VEGFR-2 antibody can more effectively inhibit
]. Moreover, different acting mechanisms of anti-VEGFR-2 antibody
which inhibits the binding of VEGFR2 and all of VEGF-A, VEGF-C, and VEGF-D compared
to VEGF antagonist, which only inhibits VEGF-A activity may contribute the increased
antiangiogenic efficacy of TTAC-0001 . These findings support our results showing that
TTAC-0001 10 mg/kg has a more potent anti-angiogenic effect and anti-tumor efficacy than
bevacizumab 10 mg/kg.
Preclinical results do not guarantee the success of clinical trials. However, the more
information obtained in the preclinical drug development stage, the greater the probability of
success in clinical trials [
]. As the researchers recognized the values of information from the
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imaging experiments, utilization of various imaging modalities has become increased. In our
study, we showed the anti-tumor efficacy by using an orthotopic tumor model and US/BLI
imaging methods, through which we expect to increase the translatability of our results to
clinical trials [
]. Moreover, validation of targeting capacity of TTAC-0001 confirmed by the
biodistribution exams can be used as a reference for predicting the mode of action and
therapeutic efficacy of TTAC-0001 in humans as the TTAC-0001 has cross-reactivity between
human and murine species [
]. It is expected that TTAC-0001 can binds to the N-terminus of
these domains in the extracellular region of either human or mice KDR [
bevacizumab has no cross-reactivity between human and murine species, previous studies
demonstrated anti-angiogenic effect in human cancer cell line xenografts [
Although the anti-tumor activity of TTAC-0001 has been shown in colorectal,
non-smallcell lung cancer [8±10], our study is the first study to demonstrate anti-tumor activity of
TTAC-0001 in triple-negative breast cancer. In contrast to previous studies, as we used
orthotopic xenograft tumor model, the assessment of anti-tumor activity is more reliable than other
tumor models, as the orthotopic xenograft models have similar tumor microenvironment as
the original tumor [
]. In addition, we first showed the drug mechanism and the
antitumor efficacy of the TTAC-0001 using bioimaging methods.
In patients with triple-negative breast cancer, anti-angiogenic agents, such as bevacizumab
and ramucirumab, have not been successful [
]. In particular, bevacizumab, the first
approved anti-angiogenic agent to bind all isoforms of VEGF-A, was approved for metastatic,
HER2-negative breast cancer in 2008, based on the E2100 trial in which the progression-free
survival was significantly improved [
]. However, subsequent trials did not show that
improvement of progression-free survival leads to an overall survival gain in patients with
metastatic breast cancer [
]. Although data from basic and translational science and the
clinical success in improving progression-free survival may imply the effectiveness of
antiangiogenic therapy for inhibition of tumor growth, anti-angiogenic agents might be effective
only in a proportion of breast cancer patients as the breast cancer is regarded as a heterogenous
group of tumors [
]. The next step may include the development of a more potent
anti-angiogenic agent covering more targets, and the selective use of anti-angiogenic agents in a selected
population of breast cancer patients [
11, 32, 36
In summary, TTAC-0001, a novel fully human monoclonal antibody against VEGFR-2/KDR,
was shown to have anti-angiogenic effects and good anti-tumor efficacy for inhibition of
tumor growth and neovascularization in a mouse orthotopic triple-negative breast cancer
model. These preclinical results may assist translation into clinical investigation of
TTAC0001 for breast cancer patients.
S1 Fig. Monitoring of mice body weight during the 30-day treatment period in the
ultrasonography experiment. Body weight of the four groups (control, bevacizumab 10 mg/kg;
TTAC-0001 2 mg/kg; TTAC-0001 10 mg/kg) was monitored prior to any treatment (0 day)
and then every 3 days.
S2 Fig. Monitoring of mice body weight during the 30-day treatment period in the
bioluminescence imaging experiment. Body weight of the four groups (control, bevacizumab 10
mg/kg; TTAC-0001 2 mg/kg; TTAC-0001 10 mg/kg) was monitored prior to any treatment (0
13 / 16
day) and then every 5 days.
This study was supported by Korean Health Technology R&D Project through the Korean
Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare,
Republic of Korea; contract grant number (HI14C1090) and a grant from Basic Science
Research Program through the National Research Foundation of Korea(NRF) funded by the
Ministry of Education(2016R1D1A1A02937258).
Conceptualization: Sang Hyun Choi, Kyung Won Kim, Yoonseok Choi.
Data curation: Jinil Kim, Su Jung Ham, Young Chul Cho, Seul-I Lee, Jeeheon Kang.
Formal analysis: Jinil Kim, Sang Hyun Choi, Su Jung Ham, Seul-I Lee, Jeeheon Kang,
Cheol Woo, Kyung Won Kim, Yoonseok Choi.
Funding acquisition: Yoonseok Choi.
Investigation: Jinil Kim, Sang Hyun Choi, Su Jung Ham, Young Chul Cho, Seul-I Lee, Jeeheon
Kang, Dong-Cheol Woo.
Methodology: Kyung Won Kim.
Resources: Jin-San Yoo.
Supervision: Weon Sub Lee, Jin-San Yoo.
Validation: Dong-Cheol Woo, Weon Sub Lee, Jin-San Yoo.
Writing ± original draft: Sang Hyun Choi, Kyung Won Kim.
Writing ± review & editing: Sang Hyun Choi, Dong-Cheol Woo, Weon Sub Lee, Jin-San Yoo,
Kyung Won Kim, Yoonseok Choi.
14 / 16
15 / 16
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