Apatinib Combined With Radiotherapy Enhances Antitumor Effects in an In Vivo Nasopharyngeal Carcinoma Model

Abstract

Vascular endothelial growth factor (VEGF) and its receptor (VEGFR) are highly expressed in nasopharyngeal carcinoma; therefore, blocking the binding of VEGF and VEGFR may be a potential way to treat nasopharyngeal carcinoma. Apatinib inhibits tumor angiogenesis. Previous studies have suggested that treatment with apatinib has an antitumor effect on nasopharyngeal carcinoma. This study will investigate the effect of apatinib combined with radiotherapy. In this study, nude mice injected with CNE-2 nasopharyngeal carcinoma cells were randomly divided into 6 groups. Therapeutic effects were assessed by evaluating tumor inhibition rate, phosphorylation of VEGFR-2, CD31, partial oxygen pressure, and tumor metabolism. We found that the tumor inhibition of mice in the treated groups was better compared to that of the control group. In mice treated with apatinib alone, angiogenesis was prevented, and the tumor tissue partial oxygen pressure was reduced, thereby achieving an antitumor effect. Moreover, the tumor inhibitory effect of combined treatment was stronger than treatment with either apatinib or radiotherapy alone. Compared with monotherapy treatment, combined treatment better resisted angiogenesis. Apatinib combined with radiotherapy to treat nasopharyngeal carcinoma has synergistic effects, which may be related to enhanced antiangiogenesis.

Full text

Research Article
Apatinib Combined With Radiotherapy
Enhances Antitumor Effects in an In Vivo
Nasopharyngeal Carcinoma Model
Shanshan Liu, MD
1
, Fei Wu, MD
2
, Yanling Zhang, MD
3
, Rongsheng Qin, MD
4
,
Nengping Zhu, MD
4
, Yuan Li, MD
4
, Mingting Wang, MD
4
, Qin Zeng, MD
4
,
Danna Xie, MD
4
, Yinghua Li, MD
4
, Juan Fan, MD
4
, and Yunwei Han, PhD
4
Abstract
Vascular endothelial growth factor (VEGF) and its receptor (VEGFR) are highly expressed in nasopharyngeal carcinoma;
therefore, blocking the binding of VEGF and VEGFR may be a potential way to treat nasopharyngeal carcinoma. Apatinib inhibits
tumor angiogenesis. Previous studies have suggested that treatment with apatinib has an antitumor effect on nasopharyngeal
carcinoma. This study will investigate the effect of apatinib combined with radiotherapy. In this study, nude mice injected with
CNE-2 nasopharyngeal carcinoma cells were randomly divided into 6 groups. Therapeutic effects were assessed by evaluating
tumor inhibition rate, phosphorylation of VEGFR-2, CD31, partial oxygen pressure, and tumor metabolism. We found that the
tumor inhibition of mice in the treated groups was better compared to that of the control group. In mice treated with apatinib
alone, angiogenesis was prevented, and the tumor tissue partial oxygen pressure was reduced, thereby achieving an antitumor
effect. Moreover, the tumor inhibitory effect of combined treatment was stronger than treatment with either apatinib or
radiotherapy alone. Compared with monotherapy treatment, combined treatment better resisted angiogenesis. Apatinib com-
bined with radiotherapy to treat nasopharyngeal carcinoma has synergistic effects, which may be related to enhanced
antiangiogenesis.
Keywords
apatinib, nasopharyngeal carcinoma, radiotherapy, angiogenesis, partial oxygen pressure
Received August 04, 2019. Received revised February 03, 2020. Accepted for publication March 31, 2020.
Introduction
Nasopharyngeal carcinoma (NPC) originated from of naso-
pharyngeal epithelium cells, and abnormal differences were
found in race and geographical distribution. The highest inci-
dence rate was found in southern China, southeast Asia, north
Africa, and the Pacific islands.
1-4
Due to the anatomical posi-
tion and radiosensitivity of NPC, radiotherapy remains the
treatment of choice for NPC.
5
By continuously updating and
advancing radiotherapy equipment and technology, the sur-
vival rate of NPC has been greatly improved. However, several
patients are resistant to radiotherapy, which results in a reduc-
tion of the cure rate of NPC.
6
Therefore, reducing radiotherapy
resistance may be the key target for improving the therapeutic
effect of NPC.
1
Department of General Medicine, The Affiliated Hospital of Southwest
Medical University, Luzhou, China
2
Department of Thyroid Surgery, The Affiliated Hospital of Southwest Medical
University, Luzhou, China
3
Department of Health Management, The Affiliated Hospital of Southwest
Medical University, Luzhou, China
4
Department of Oncology, The Affiliated Hospital of Southwest Medical
University, Luzhou, China
Corresponding Authors:
Juan Fan and Yunwei Han, The Affiliated Hospital of Southwest Medical
University, 25 Taiping Street, Luzhou, China.
Emails: fj-joan@163.com; 530018842@qq.com
Cancer Control
Volume 27: 1-8
ªThe Author(s) 2020
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The main function of radiotherapy is the disruption of
double-stranded DNA, causing proteins to be blocked or initi-
ate apoptosis to cause cell death.
7
Oxygen is an effective radio-
active sensitizer, which can be released during the irradiation
process to promote the production of reactive oxygen species/
free radicals, resulting in major DNA damage.
8,9
As the tumor
grows, the tumor microenvironment lacks sufficient blood sup-
ply, leading to low perfusion and hypoxia.
10
Clinical data have
shown that hypoxia in tumor tissue associated with a poor
treatment efficacy of many tumors including head and neck
tumors.
11-13
Therefore, improving the blood supply and oxygen
input of NPC tumor tissues may significantly improve the ben-
eficial effect of radiotherapy in NPC.
Angiogenesis is a multistep process of new blood vessel
formation involved in tumor development.
14,15
Angiogenic
factors include vascular endothelial growth factor (VEGF),
basic fibroblast growth factor, and insulin-like growth factor.
Among them, vascular endothelial growth factor receptor-2
(VEGFR-2) is the main signal sensor of angiogenesis. During
the stimulation of VEGF, VEGFR-2 is phosphorylated in the
carboxyl terminal and kinase insertion area, thereby promoting
angiogenesis.
16-19
In most patients with NPC, the VEGF/
VEGFR complex was found to be overexpressed, which asso-
ciated with an increased risk of metastasis of NPC and a reduc-
tion in survival time.
20-23
Apatinib is a small molecule VEGFR-2 tyrosine kinase inhi-
bitor that competes highly selectively for the Adenosine Tri-
phosphate (ATP)-binding site of VEGFR-2, inhibits
phosphorylation of VEGFR-2 (p-VEGFR2), and blocks VEGF
and its receptor binding signaling transduction pathway. It
strongly inhibits tumor angiogenesis and plays an antitumor
role. Jain demonstrated that antiangiogenic drugs have a
reshaped vascular system, which can result in blood vessel
“normalization” of “time window.”
24
In the “time window,”
antiangiogenic drugs briefly improve the function of the tumor
vascular system, thereby increasing the interaction with oxy-
gen, and reducing the pressure of the interstitial fluid. This has
formed the theoretical basis for the combination of antiangio-
genic drugs and radiotherapy. Teicher et al were the first to
show that inhibiting angiogenesis enhances the therapeutic
efficacy of radiotherapy treatment.
25
In addition, Peng et al
demonstrated that apatinib decreased tumor microvascular den-
sity and increased cell apoptosis by inhibiting VEGFR-2,
which had an antitumor effect on CNE-2 NPC.
26
Studies that
report on the use of apatinib in combination with radiotherapy
and its synergistic antitumor effects on NPC are limiting. The
goal of this study was to explore the effect of apatinib com-
bined with radiotherapy for the treatment of NPC and to pro-
vide guidance for future research and clinical practice.
Materials and Methods
Cell Lines and Mice
CNE-2 NPC cells were provided by the Experimental Center of
the Affiliated Hospital of the Southwest Medical University
(Luzhou, China), which were maintained in Roswell Park
Memorial Institute (RPMI) medium at 37Cand5%CO
2
.
Mycoplasma testing has been done for the cells used and no
mycoplasma infection was found. Medium was replaced every
3 days.
BALB/c female nude mice (4-5 weeks of age, 18.85 +2.15
g) were purchased from Tengxin Biotechnology Co Ltd
(Chongqing, China). Mice were housed in the animal research
center of the Affiliated Hospital of Southwest Medical Univer-
sity. During the week prior to the experiment, animals were
strictly kept in an air-clean laminar rack at a constant tempera-
ture (24C+2C), constant humidity (50%+10%relative
humidity), and specific pathogen-free environment. The mouse
cage, air filter cover, bedding, food, and drinking water were
sterilized and replaced in a sterile environment. Their care was
in accordance with institution guidelines.
Drugs and Major Reagents
Apatinib was provided by Jiang Su Heng Rui Medicine Co Ltd
(Jiangsu, China). Anti-CD31 monoclonal antibody was pur-
chased from BioWorld Technology Co Ltd (Nanjing, China),
and anti phosphorylation of VEGFR-2 (p-VEGFR-2) monoclo-
nal antibody (Tyr951) was purchased from Cell Signaling
Technology, Inc, Shanghai, China, and antibodies were affinity
purified from rabbit antiserum and used at dilutions of 1:50 to
1:200.
Establishing and Experimental Design of the Tumor
Model
Exponential phase CNE-2 cells were adjusted to 1 10
7
cells
per 0.1 mL and injected into the right thigh of BALB/c nude
mice. When the average volume of tumor reached 150 to 200
mm
3
, mice were randomly divided into 6 groups (n ¼8 per
group) and received treatment as follows: (1) the control group
was administered 0.1 mL normal saline (NS) per day on days 1
to 7, (2) the apatinib group received 200 mg/kg/d on days 1 to
7, (3) single radiotherapy 6 Gy group: 0.1 mL NS per day on
days 1 to 7 and single radiotherapy (6 Gy) on day 8, (4) single
radiotherapy 12 Gy group: 0.1 mL NS per day on days 1 to
7 and single radiotherapy (12 Gy) on day 8, (5) apatinib þ6
Gy: apatinib 200 mg/kg on days 1 to 7 and single radiotherapy
(6 Gy) on day 8, (6) apatinib þ12 Gy: apatinib 200 mg/kg on
days 1 to 7 and single radiotherapy (12 Gy) on day 8. The
solvent for apatinib was NS, and both NS and apatinib were
administered by gastric irrigation.
The tumor diameter (mm) along the major (a) and minor
axes (b) were measured every 3 days using a Vernier caliper,
and the volume (V; mm
3
) of the tumor was calculated accord-
ing to the Steel formula, V ¼0.5 ab
2
. At 18 days after the
start of treatment, mice were euthanized by cervical disloca-
tion, and the tumor growth inhibition rate was calculated as
follows: (1 average volume of experimental group/average
volume of control group) 100%. The combined effects of 2
types of treatments were determined by Q: Q ¼E(A þB) / [EA
2Cancer Control

þ(1 EA) EB], in which E (A þB) represented the
inhibition rate of the combined group, whereas EA and EB
represented the inhibitory rate of apatinib or radiotherapy,
respectively. Q < 0.85 indicated that the 2 therapeutic effects
were antagonistic to each other, 0.85 < Q < 1.15 indicated an
additive effect of these 2 therapeutic effects, while Q > 1.15
indicated a synergistic effect of the 2 therapeutic treatments.
Radiation Approach
Nude mice were installed in a homemade Plexiglas box, and the
hind limbs containing the tumor were pulled out and fixed with a
string. The tumor site was exposed to the center of the field and
was located more than 1 cm from the edge of the field. The upper
and lower parts of the irradiation were filled with 2-cm oil yarn,
the remainder of the mouse’s body was outside the field.
Micro 18F-FDG Positron Emission Tomography/
Computed Tomography Imaging
One day after treatment, mice were anesthetized by 1%pento-
barbital sodium. After the tail vein injection with contrast agent
(18F-FDG)150 to 200 uCi, the positron emission tomography/
computed tomography (PET/CT) (Siemens, Inveon, Berlin,
Germany) was performed using a 20-minute scan. After apply-
ingcorrectionfactors,animage representing the 18F-FDG
distribution was obtained. The region of interest (ROI) cover-
ing the entire tumor was drawn manually. In addition, ROIs
were drawn on the contralateral paraspinal muscles. The stan-
dard uptake value (SUV) in the tumor site and in contralateral
paraspinal muscles was determined. The ratio of the maximum
SUV of the tumor and the maximum SUV to the contralateral
paraspinal muscles represented the T/M (the ratio of the max-
imum SUV of the tumor and the maximum SUV to the con-
tralateral paraspinal muscles) value.
Unisense-Dissolved Oxygen Microelectrode to Detect
Tumor Tissue Partial Oxygen Pressure
A Unisense-dissolved oxygen microelectrode is a miniaturized
Clark-type dissolved oxygen microelectrode with a protective
cathode. In this study, after the mice were euthanized, the
tumor tissue was immediately removed and the tumor long axis
and short axis were measured. Each tumor was measured in 4
parts, including 1/16 short axis, 1/8 short axis, 1/4 short axis,
and 1/2 short axis. After the average value of each part was
measured, the average of the partial oxygen pressure of the 4
parts was considered the partial oxygen pressure of the tumor
tissue. The total time for each mouse from death to test was less
than 5 minutes.
Phosphorylation of VEGFR-2 and CD31
Immunohistochemical Detection in Tumor Specimens
Prior to embedding in paraffin, tumor tissue was fixed in
10%formalin solution. All experiments were strictly carried
out according to the manufacturer’s guidelines. Microscopic
evaluation was performed at 400 magnification and
showed that the cell membrane or cytoplasm appeared as a
brownish-yellow or brown color, indicating p-VEGFR-2
expression in the membrane or cytoplasm. From each section,
a total of 5 views were randomly selected, and the percentage
of positive cells per field cells was counted. The average of
the 5 percentages was considered the percentage of
p-VEGFR-2-positive cells in the section.
The microvessel density (MVD) was quantified according
to the method described by Weidner et al.
27
First, screening
was performed at a low magnification (100) to scan the
tumor area and to identify the most intensive areas of vascu-
larization, designated as “hot spots.” In these hot spots, the
microvessels were counted using a high-power magnification
field (400). The MVD was expressed as the number of
microvessels per field. Endothelial cells, identified by CD31
staining, that were clearly separated from adjacent microves-
sels, tumor cells or connective tissue were considered micro-
vessels. In each section, 5 hot spots were selected for
microvascular counts, the average represented the MVD of
the section.
Statistical Analyses
Data analyses were performed using SPSS software version
17.0 (SPSS, Inc, Chicago, Illinois). Data were expressed as the
mean +standard deviation. Comparisons between multiple
groups were made using the 1-way analysis of variance test.
P< .05 was considered statistically significant.
Results
Antitumor Effect of Apatinib Combined
With Radiotherapy
When the average volume of tumor reached 150 to 200
mm3 and treated with various treatments. Figure 1 presents
the average volume of tumor xenografts per group from 1 to
18 days posttreatment, and the statistical analysis was per-
formed including all groups. In the control group, the tumor
growth was increased compared to the other groups (P<
.05). The inhibition effect of 12 Gy group better than that of
6Gygroup(P< .05). In addition, there was no difference
between the 6 Gy group and the apatinib group (P>.05).
Moreover, the inhibition of tumor growth in mice in the
apatinib þradiotherapy combination group was stronger
compared to apatinib treatment or radiotherapy treatment
alone (P< .05).
Table 1 presents the tumor volume and inhibition rate per
treatment group. The tumor inhibition rate of apatinib, 6 Gy
alone, 12 Gy alone, apatinib þ6 Gy, and apatinib þ12 Gy
were 33.3%, 38.8%, 61.5%, 63.8%, and 85.9%, respectively.
Thus, the inhibition rate of apatinib þradiotherapy was higher
compared to that of apatinib or radiotherapy group alone (P<
.05). The Q value of apatinib þ6 Gy was 1.079 (Q value was
Liu et al 3

0.85-1.15), indicating that the therapeutic effect of apatinib þ
6 Gy included the addition of the 2 individual treatments. The
Q value of apatinib þ12 Gy was 1.156 (Q value >1.15), indi-
cating that the therapeutic effect of apatinib þ12 Gy had a
synergistic effect when compared with the treatment effect of
individual treatment. Because the 2 combined treatment groups
showed a Q value of >0.85, it was suggested that apatinib
treatment combined with radiotherapy had a synergistic effect
on the treatment of NPC.
Micro 18F-FDG PET/CT Imaging
Positron emission tomography/CT examination was performed
the day after the treatment regimen was completed, and the
results of PET/CT imaging on the transplantation of NPC in
nude mice are shown in Figure 2. The tumor metabolism of
control mice was significantly higher compared to that
of treated mice (P< .05). Moreover, the tumor metabolism
of 12 Gy–treated mice was lower compared to that of the 6
Gy–treated mice (P< .05). Mice treated with a combination of
apatinib and radiotherapy showed a lower tumor metabolism
compared to mice treated with apatinib or radiotherapy alone
(P< .05). Therefore, we concluded that apatinib combined with
radiotherapy had a synergistic inhibitory effect on the tumor
metabolism in NPC.
Tumor Tissue Partial Oxygen Pressure Condition
After different treatment regimens and completion of PET/CT
examination, the partial oxygen pressure of tumor tissues was
determined. Figure 3 shows the results of the partial oxygen
pressure of tumor tissues per treatment group. The tumor par-
tial oxygen pressure in the control group was significantly
higher compared to that of the other groups (P< .05). More-
over, the partial oxygen pressure of tumor tissue in 12 Gy–
treated mice was lower compared to that of 6 Gy–treated mice
(P< .05). The tumor partial oxygen pressure in the combined
group was lower compared to that in mice that were treated
with apatinib or radiotherapy alone (P< .05).
Immunohistochemistry Using Antibodies Directed Against
p-VEGFR-2 and CD31
Immunohistochemical staining of xenografts using an antibody
directed against p-VEGFR-2 revealed the effects of different
treatment regimens and showed that the proportion of p-
VEGFR-2 positive cells in each treatment group was different
(Figure 4). The highest proportion of positive cells was
observed in the control group (P< .05). The proportion of
p-VEGFR-2 positive cells in 12 Gy–treated mice was lower
compared to that in 6 Gy–treated mice (P< .05). Moreover,
the proportion of p-VEGFR-2 positive cells in mice in the
combined treatment group was lower compared to that in
mice that were treated with either apatinib or radiotherapy
alone (P<.05).
CD31-positive cells had a brownish appearance and showed
a heterogeneous distribution in tumor tissues (Figure 5) and
was used for the determination of MVD, which was used as a
marker of angiogenesis. The MVD of mice in the control group
was higher compared to that of mice in other groups (P< .05).
The MVD in 12 Gy–treated mice was lower compared to that of
6 Gy–treated mice (P< .05). Moreover, the MVD of mice that
were treated with a combination of apatinib þradiotherapy
was lower compared to mice that were treated with apatinib
or radiotherapy alone (P< .05).
Figure 1. Tumor growth curve. Average volume of tumors xenograft into nude mice from 1 to 18 days’ post treatment, and the statistical
analysis was performed including all groups; *P< .05 versus the control group, **P< .05 versus the individual treatment group.
Table 1. Tumor Inhibition Rate.
a
Groups N
Tumor
Volume(mm
3
)
Tumor Inhibition
Rate (%)
Control group 8 2042 +143.12233
Apatinib 8 1360 +166.28289
b
33.3
6 Gy 8 1248 +118.09530
b
38.8
12 Gy 8 785 +125.19984
b
61.5
Apatinib þ6 Gy 8 738 +92.44458
b,c
63.8
Apatinib þ12 Gy 8 286 +52.28767
b,d
85.9
a
The tumor volume and inhibition rate determined on the 18th day.
b
P< .05 versus the control group.
c
P< .05 versus the apatinib group, 6 Gy.
d
P< .05 versus the apatinib group, 12 Gy.
4Cancer Control

Discussion
Apatinib is a small molecular VEGFR-2 tyrosine kinase inhi-
bitor, which can inhibit tumor angiogenesis and thereby
achieve an antitumor effect. Many studies have shown that
VEGF/VEGFR overexpression is observed in patients with
NPC. Peng et al showed that apatinib has an antitumor effect
on CNE-2 NPC and has a synergistic effect with cisplatin by
inhibiting VEGFR-2.
26
In this study, we explored the effects of
apatinib combined with radiotherapy for treating NPC in a
mouse xenograft model.
Our study showed that apatinib had antitumor effects. By
gradually increasing the radiation dose, the tumor growth of
mice that underwent radiation alone gradually increased. In
mice treated with a combination of apatinib and radiotherapy,
tumor growth was significantly inhibited, and the inhibitory
effect was higher compared to the effect of treatment with
apatinib or radiotherapy alone. The combined effect Q showed
that apatinib was synergistic with the combination of radio-
therapy in the treatment of NPC.
The VEGF/VEGFR-2 signaling pathway is the main path-
way involved in angiogenesis. Apatinib inhibits angiogenesis
through inhibiting p-VEGFR-2 and reduces nutrition and oxy-
gen supply of tumor tissue. Compared with mice in the indi-
vidual treatment groups, mice in the combined treatment
groups showed better inhibition of the expression of
p-VEGFR-2 in the tumor, inhibition of angiogenesis, and
reduction in the nutrition and oxygen supply of tumor tissue.
We hypothesized that apatinib may be able to briefly improve
the hypoxia state of the tumor, however due to the strong
inhibition of angiogenesis and the reduction in oxygen supply,
the measured partial oxygen pressure decreased. The antiangio-
genic effect of the combination treatment was stronger com-
pared to the effect of apatinib treatment alone, resulting in a
lower partial oxygen pressure in the tumor. Antibodies directed
against VEGFR-2 (DC101) combined with radiotherapy inhib-
ited tumor angiogenesis and thereby showed a synergistic anti-
tumor effect. The degree of hypoxia in mice that received
combination treatment was significantly higher compared to
mice that received monotherapy treatment.
28
Treatment with
cediranib (AZD2171) combined with radiotherapy increased the
Figure 2. Micro 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) imaging. A, Representative
18F-FDG PET scans of mice one day posttreatment with various regimens. B, T/M (the ratio of the maximum SUV of the tumor and the
maximum SUV to the contralateral paraspinal muscles) associated with various treatment regimens. *P< .05 versus the control group. **P<.05
versus the apatinib group, 6 Gy. ***P< .05 versus the apatinib group, 12 Gy.
Figure 3. Tumor tissue partial oxygen pressure. Partial oxygen
pressure was determined after the mice were euthanized. *P<.05
versus the control group. **P< .05 versus the apatinib group, 6 Gy.
***P< .05 versus the apatinib group, 12 Gy.
Liu et al 5

degree of hypoxia in tumor tissue.
29
These findings were con-
sistent with the results of our study. We found that, compared
with the apatinib þ6Gy–treatedmice(Q¼1.079), apatinib þ
12 Gy–treated mice (Q ¼1.156) showed a better antitumor
effect. Moreover, the results indicated that the main mechanism
of synergistic inhibition of apatinib and radiotherapy in NPC
treatment may involve the inhibition of angiogenesis.
The metabolism of tumor cells is vigorous. As the most
widely used metabolic imaging agent, 18F-FDG can
quantitatively analyze the glucose metabolism of tumor. The
PET-CT examination is widely used for the evaluation of
tumor metabolism. Tumors with poor fluorodeoxyglucose
(FDG) uptake tend to respond more favorably to treatment,
whereas tumors that rapidly uptake FDG tend to respond poorly
to treatment and have a worse prognosis.
26
The ratio of the
maximum SUV of the tumor and the maximum SUV to the
contralateral paraspinal muscles represented the T/M value.
The higher the FDG uptake in tumor tissues, the higher the
Figure 4. Expression of phosphorylation of VEGFR-2 (p-VEGFR-2) in CNE-2 nasopharyngeal carcinoma (NPC) tumor tissue. A, Immunohis-
tochemical staining of xenograft CNE-2 NPC mice treated with various treatment regimens with a p-VEGFR-2 antibody. B, p-VEGFR-2 positivity
(%) within treatment groups. *P< .05 versus the control group. **P< .05 versus the apatinib group, 6 Gy. ***P< .05 versus the apatinib group,
12 Gy.
Figure 5. Expression of CD31 in CNE-2 nasopharyngeal carcinoma (NPC) tumor tissue. A, Immunohistochemical staining of xenograft mice
treated with various treatment regimens using a CD31 antibody revealed the differences in microvessel density. B, Histograms showing the
number of vessels in each group. *P< .05 versus the control group. **P< .05 versus the apatinib group, 6 Gy. ***P< .05 versus the apatinib group,
12 Gy.
6Cancer Control

T/M value, and vice versa. Groves et al showed that 18F-FDG
uptake was highly significantly associated with angiogenesis in
early breast cancer, and 18F-FDG PET might have a role in the
management of patients with primary breast cancer even in
early stage disease.
30
Kaira et al showed that the amount of
18F-FDG uptake in metastatic pulmonary tumors was deter-
mined by the presence of glucose metabolism (Glut1), phos-
phorylation of glucose (hexokinase I), hypoxia (HIF-1a), and
angiogenesis (VEGF and MVD).
31
Guoetalshowedthat
angiogenesis correlated positively with 18F-FDG uptake in
lung adenocarcinomas.
32
Kaira et al showed that the metabolic
activity of primary tumors as evaluated by PET study with 18F-
FMT and 18F-FDG was related to tumor angiogenesis and the
proliferative activity in non-small cell lung cancer.
33
Studies
had also shown that 18F-FDG kinetics were modulated by
angiogenesis-related gene.
34
The above studies found a posi-
tive correlation between tumor FDG uptake and angiogenesis.
In this study, we hypothesized that reduced FDG uptake in the
treatment group may also be associated with reduced angiogen-
esis, and the combined treatment group reduced tumor meta-
bolism by inhibiting angiogenesis, thus achieving synergistic
antitumor effect.
In summary, apatinib has antitumor effects on NPC, and
there was a synergistic effect of apatinib combined with radio-
therapy for NPC. Compared with the apatinib þ6 Gy–treated
mice, apatinib þ12 Gy–treated mice showed a better antitu-
mor effect. According to the data presented above, the fol-
lowing hypotheses were proposed: (1) Apatinib inhibited
tumor angiogenesis by inhibiting p-VEGFR-2, reduced MVD,
and reduced tissue partial oxygen pressure to achieve antitu-
mor effects; (2) Apatinib combined with radiotherapy
enhanced antiangiogenesis, thereby enhancing antitumor
effects; (3) The main mechanism of the synergistic antitumor
effects of apatinib and radiotherapy involves enhancing
antiangiogenesis.
Authors’ Note
S.L. and F.W. contributed equally to this work. Animal studies were
approved by the Institutional Animal Care and Use Committee in the
Methods of the Affiliated Hospital of Southwest Medical University
(Luzhou, China), and the approval number is 201603005.
Acknowledgments
The authors thank the members of the Department of Pathology of the
Southwest Medical University for their assistance with immunohisto-
chemical staining experiments and analysis of results. The authors
also thank the members of the Department of Nuclear Medicine of
Southwest Medical University for their assistance in the micro PET/
CT studies and support of the oncology radiotherapy room for the
radiation of nude mice.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to
the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, author-
ship, and/or publication of this article.
ORCID iD
Yunwei Han https://orcid.org/0000-0002-6694-5846
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8Cancer Control