Polo-like kinase1 (PLK1) is a new therapeutic target for osteosarcoma with good application prospects. Whether PLK1 is highly expressed in chondrosarcoma and whether PLK1 can be a potential therapeutic target for chondrosarcoma are worth exploring. However, PLK1 expression in chondrosarcoma is scarcely investigated. Therefore, we collected 11 cases of chondrosarcoma and 26 cases of osteochondroma with complete clinical pathological data and used immunohistochemical staining to detect the expression of PLK1 in chondrosarcoma and osteochondroma and then studied its significance and relationship with clinical pathological parameters. Our results showed that the positive expression rate of PLK1 in chondrosarcoma tissue (90.91%, 10/11) was significantly higher than the rate of osteochondroma tissues (53.85%, 14/26) (

Chen, Jiahan

Gu, Wenyi

Hu, Yali

Jiang, Jinfang

Li, Feng

Li, Kelu

Ma, Hongmei

Pang, Lijuan

Qi, Yan

Tao, Lin

Wang, Yue

Zhang, Kunpeng

Zheng, Xiuyan

Zou, Hong

University of Queensland eSpace

Int J Clin Exp Pathol 2018;11(3):1707-1711
www.ijcep.com /ISSN:1936-2625/IJCEP0055985
Original Article
Overexpression of Polo-like kinase1 (PLK1) in  
chondrosarcoma and its implications  
for cancer progression
Kelu Li1,2*, Hongmei Ma2*, Xiuyan Zheng2, Yali Hu2, Yue Wang2, Kunpeng Zhang2, Jiahan Chen3, Yan Qi1,2, 
Jinfang Jiang1,2, Lijuan Pang1,2, Lin Tao1,2, Wenyi Gu4, Feng Li5, Hong Zou1,2 
1Department of Pathology, First Affiliated Hospital, Shihezi University, Shihezi, China; 2Key Laboratory of Xinji-
ang Endemic and Ethnic Diseases, Department of Pathology, School of Medicine, Shihezi University, Ministry of 
Education of China, Shihezi, China; 3School of Medicine, Shihezi University, Shihezi, China; 4Australian Institute for 
Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Australia; 5Department of Pathol-
ogy, Beijing Chaoyang Hospital, Capital Medical University, Beijing, China. *Equal contributors.
Received April 22, 2017; Accepted July 5, 2017; Epub March 1, 2018; Published March 15, 2018
Abstract: Polo-like kinase1 (PLK1) is a new therapeutic target for osteosarcoma with good application prospects. 
Whether PLK1 is highly expressed in chondrosarcoma and whether PLK1 can be a potential therapeutic target 
for chondrosarcoma are worth exploring. However, PLK1 expression in chondrosarcoma is scarcely investigated. 
Therefore, we collected 11 cases of chondrosarcoma and 26 cases of osteochondroma with complete clinical path-
ological data and used immunohistochemical staining to detect the expression of PLK1 in chondrosarcoma and 
osteochondroma and then studied its significance and relationship with clinical pathological parameters. Our re-
sults showed that the positive expression rate of PLK1 in chondrosarcoma tissue (90.91%, 10/11) was significantly 
higher than the rate of osteochondroma tissues (53.85%, 14/26) (P<0.05). The expression of PLK1 enhanced 
gradually with the increase in histological grade (P<0.05). PLK1 was highly expressed in chondrosarcoma, and the 
high expression of PLK1 might be involved in cartilage tumor malignant progression.
Keywords: PLK1, chondrosarcoma, osteochondroma, immunohistochemistry
Introduction
Chondrosarcoma is a highly malignant tumor 
and accounts for 10%-20% [1] of primary malig-
nant bone tumors. The tumor has the capability 
of local infiltration and metastasis and is insen-
sitive to radiation or chemotherapy. Complete 
surgical resection is still the main therapy for 
chondrosarcoma. Most patients’ prognosis is 
poor because of the lack of effective auxiliary 
treatment [2]. Thus, new therapeutic targets 
must be discovered. Polo-like kinase1 (PLK1) is 
a member of the family of PLKs and widely 
exists in eukaryotic of silk/threonine protein 
kinase. Given that PLK1 plays an important role 
in cell cycle, this gene has attracted much 
attention in recent years. PLK1 is highly 
expressed in most tumors, such as osteosar-
coma [3], non-small-cell lung cancer (NSCLC) 
[4], and breast cancer [5], and is closely related 
to the tumor cell proliferation and prognosis of 
patients. In 2013, Wenyi Gu [6] found that PLK1 
is highly expressed in osteosarcoma cell lines 
(KHOS), and the growth of osteosarcoma can 
be significantly inhibited using nanometer 
material carrier SiRNA technology to silence 
PLK1 gene. Thereafter, Chou YS [7] found 
that PLK1 inhibitor gsk461364 can terminate 
osteosarcoma cell mitosis, inhibit tumorous 
cellular growths, and accelerate cell apoptosis. 
Therefore, PLK1 is considered a good applica-
tion prospect of new therapeutic target for 
osteosarcoma. No related studies on PLK1 
expression in chondrosarcoma are available, 
and whether PLK1 can be potential therapeutic 
targets of chondrosarcoma is still unknown. As 
a result, these issues must be explored. Hence, 
we used the immunohistochemical method to 
detect the expression of PLK1 in chondrosar-
coma, contrasted the said expression to the 
Overexpression of PLK1 in chondrosarcoma
1708 Int J Clin Exp Pathol 2018;11(3):1707-1711
PLK1 expression of osteochondroma to explore 
its relationship with clinicopathological param-
eters and meaning, and laid the foundation for 
further discussion of the possible clinical 
application.
Materials and methods
Reagents
Rabbit anti-human PLK1 monoclonal antibody 
(ab15529, clone number #2602) was purch- 
ased from Abcam of England. Envision staining 
kits, PBS buffer powder, and two resistance 
and DAB chromogenic reagents used for im- 
munohistochemistry were purchased from 
Zhongshan Jinqiao Biological Technology Co., 
Ltd. (Beijing, China).
Patients and tissue specimens
A total of 11 cases of chondrosarcoma and 26 
cases of osteochondroma were collected from 
the first affiliated hospital of Shihezi University 
School of Medicine from 2009 to 2016. All the 
patients had complete medical historical and 
clinical pathological data. All the cases were 
confirmed by operation and pathology. Paraffin 
block and corresponding HE sections were 
collected, and HE sections were read by two 
senior pathologists. Chondrosarcomas were 
grouped and classified according to the WHO 
standards.
Immunohistochemical staining
The two-step immunohistochemical envision 
method was applied. The cases of chondrosar-
coma and osteochondroma organization were 
used as samples of 5 μm- thick serial section. 
Samples were dried, followed by conventional 
xylene dewaxing, hydration, gradient alcohol at 
20% EDTA antigen repairing buffer (PH 9.0) in 
high temperature and high pressure antigen for 
8 min. Then, samples underwent natural cool-
ing to room temperature, 3% H2O2 incubation 
for 10 min at room temperature, and removal of 
endogenous hydrogen peroxide enzyme. The 
rabbit anti-monoclonal antibody was added 
(1:200 dilution), followed by 4°C incubation 
overnight. The rabbit mouse universal biotin 
Figure 1. A and B: Show the low- and high-power microscopic images of a chondrosarcoma; C: Shows the strongly 
positive expression of PLK1 in the tissue of chondrosarcoma (3+) and its detected location in the cell nucleus. D and 
E: Show the low- and high-power microscopic images of osteochondroma; F: Shows the negative or weakly positive 
expression of PLK1 in the tissue of osteochondroma (0-1+) and its detected location in the cell nucleus.
Overexpression of PLK1 in chondrosarcoma
1709 Int J Clin Exp Pathol 2018;11(3):1707-1711
HuaEr resistance and hydrogen peroxide con-
tent were used to label the antibodies. Then, 
DAB chromogenic, hematoxylin redyeing was 
conducted for 2 min, followed by dehydration of 
transparent seal. With known positive colon tis-
sue slices as positive control, PBS solution was 
used instead of a resistance as a blank 
control.
Result processing
The positive expression of PLK1 was located in 
the cell nucleus and presented a dark-brown 
granulation. Each slice was then selected using 
five high-power microscopes (400×) for image 
acquisition. The results were determined on 
the basis of the percentage of positive cells 
and the depth of positive staining. The scoring 
criteria were as follows: IHC staining slides 
were scored as positive or negative by percent-
age and intensity of positive cells. The scoring 
percentages of positively stained cells were as 
follows: 0≤5%, 1 = 6%-25%, 2 = 26%-50%, 3 = 
51%-75%, and 4 = 76%-100%. The scoring of 
staining intensity was as follows: 0 = absent, 1 
= weak, 2 = moderate, and 3 = strong. The final 
score was based on multiplying both scores 
from individual slides, where 0-1 was negative 
(-), 2-3 was weakly positive (1+), 4-6 was moder-
ately positive (2+), and 8-12 was strongly posi-
tive (3+).
Statistical analysis
The positive expression of PLK1 between chon-
drosarcoma and osteochondroma tissues were 
compared by X2 test. Kruskal-Wallis rank test 
Results
PLK1 was highly expressed in chondrosar-
coma but lowly expressed in osteochondroma 
(Figure 1; Table 1)
The immunohistochemical staining results 
showed that PLK1 protein was located in the 
nucleus. The positive expression rate of chon-
drosarcoma was 90.91% (9/11), and the major-
ity showed moderately to strong positively 
(2-3+). The positive expression rate of osteo-
chondroma was 53.85% (14/26), and all the 14 
cases were weakly positive (1+). A significant 
difference in PLK1 expression between chon-
drosarcoma and osteochondroma was found (P 
= 0.014, Table 1). Among the 14 cases of posi-
tively expressed osteochondroma, 57.14% 
(8/14) were multiple osteochondroma. PLK1 
was negatively expressed in normal bone and 
cartilage tissue (4/4).
The expression of PLK1 in chondrosarcoma 
was positively correlated with clinical category 
(Figure 1; Table 1)
For this group of chondrosarcoma, 6 cases 
were in grade 1, 2 cases were in grade 2, 3 
cases were in grade 3. Among them, PLK1 
expression was different between the hierarchi-
cal groups: the positive expression rates in lev-
els 1, 2, and 3 were 66.67% (4/6), 100% (2/2), 
and 100% (3/3) respectively. PLK1 protein was 
associated with the clinical classification of 
chondrosarcoma, and PLK1 was negatively 
expressed in normal cartilage tissue adjacent 
to tumor tissue of chondrosarcoma. The expres-
sion rate of PLK1 in high-grade chondrosarco-
ma was higher than that in low-grade chondro-
sarcoma, and the difference was statistically 
significant (P = 0.017, Table 2).
Discussion
In 1994, Golsteyn [8] was the first to report that 
PLK1 is located in 16p12. PLK1 is highly 
expressed in cells with active proliferative abil-
Table 1. Expression of PLK1 in chondrosarcoma and osteo-
chondroma tissues
Groups Cases (N)
Positive 
(N)
Positive  
combination (%) OR
P
Chondrosarcoma 11 10 90.91% 11.667 0.014
Osteochondroma 26 14 53.85%
Table 2. Correlation between expression of 
PLK1 and clinicopathological parameters in 
chondrosarcoma
Stage
Cases (N)
OR P
-/+ 2+ 3+
Clinical stage 1 2 3 1 0.699 0.017
2 0 1 1
3 0 0 3
was applied to analyze correlation 
between expression of PLK1 and 
clinicopathological parameters in 
chondrosarcoma. All analysis was 
performed by SPSS version 17.0, 
and p-values <0.05 were consid-
ered to be significant.
Overexpression of PLK1 in chondrosarcoma
1710 Int J Clin Exp Pathol 2018;11(3):1707-1711
ity, such as those in the placenta, ovary, testis, 
and spleen; however, PLK1 does not express or 
is lowly expressed in most adult organizations 
(such as the liver, brain, thymus, and heart). 
PLK1 can regulate the cell cycle, inhibit tumor 
cell apoptosis, and promote tumor formation. 
The activity of its kinase is closely related to the 
development of cell cycle and progress of vari-
ous types of cancers. Therefore, PLK1 is con-
sidered a good application prospect of new 
therapeutic target for malignant tumor. Pre- 
clinical research showed that the interference 
of PLK1 expression can significantly inhibit the 
growth of a series of tumor cells, including gas-
trosarcoma [6], nasopharyngeal carcinoma [9], 
NSCLC [10], lymphoma [11, 12], and colorectal 
cancer [13]. Interestingly, such interference 
exerts no obvious effect on normal cells [14]. At 
present, small molecular PLK1 inhibitors (such 
as BI2536 and BI6727) or siRNA has entered 
clinical trials. Duan Z [15] found that using 
shRNA to silence PLK1 gene of osteosarcoma 
cell lines KHOS and U-2OS can inhibit cell prolif-
eration and promote apoptosis; their research 
suggested that PLK1 can be a potential thera-
peutic target for osteosarcoma. Then, Chou YS 
[7] verified that PLK1 inhibitor gsk461364 may 
terminate osteosarcoma cell mitosis, inhibit 
tumor cell proliferation, and promote cell apop-
tosis. The findings are consistent with the view 
that inhibition of PLK1 protein may downregu-
late cell cycles of osteosarcoma by decreasing 
the activity of p53, thereby leading to the inhibi-
tion of tumor cell proliferation. Given that chon-
drosarcoma is derived from the bone, whether 
inhibition of PLK1 can contribute to treatment 
of tumor is worth exploring. However, PLK1 
expression in chondrosarcoma has not been 
reported to date.
Our study confirmed that PLK1 was highly 
expressed in chondrosarcoma and was posi-
tively related to the clinical classification. The 
results suggested that high expression of PLK1 
might be involved in the malignant progress of 
chondrosarcoma. This issue needs further 
study with large sample size. Our research also 
discovered that PLK1 was negatively expressed 
or weakly positively expressed in normal bone 
and cartilage; among these positive expression 
cases of osteochondroma, 57.14% (8/14) were 
multiple osteochondroma. Multiple osteochon-
droma may [16] progress to malignant chondro-
sarcoma. Whether PLK1 is involved in the 
malignant progress of cartilage tumor and 
whether PLK1 is the key event to the malignant 
transformation of cells deserve further study. 
Chondrosarcoma is a highly malignant tumor 
with the capability of local invasion and distant 
metastasis and is insensitive to radiation or 
chemotherapy; thus, most patients’ prognosis 
is poor. PLK1 expression is associated with 
poor prognosis of a series of tumors, and small-
molecule PLK1 inhibitors can increase the sen-
sitivity of chemotherapy drugs in many kinds of 
tumors, including osteosarcoma [17], pancre-
atic cancer [18], and liver cancer [19]. Accord- 
ingly, the curative effect and the prognosis of 
patients are enhanced. Whether existing PLK1 
inhibitors or other treatments can be effective 
in chondrosarcoma deserves further research 
and discussion.
In conclusion, PLK1 protein was highly ex- 
pressed in chondrosarcoma, and the expres-
sion of PLK1 was positively related to the histo-
logic grade of chondrosarcoma. PLK1 might 
participate in the occurrence and development 
of chondrosarcoma, and might be associated 
with malignant progress of cartilage tumor. 
With further research on PLK1 in cartilage 
tumor, the antineoplastic drug target for PLK1 
gene or protein in combination with commonly 
used surgery, radiation, and chemotherapy, 
might be promising cartilage tumor treatment 
strategies in the near future.
Acknowledgements
This study was supported by grants from the 
National Natural Science Foundation of China 
(Nos. 81460383 and 81660411).
Disclosure of conflict of interest
None.
Address correspondence to: Drs. Hong Zou and Lin 
Tao, Key Laboratory of Xinjiang Endemic and Ethnic 
Diseases, Department of Pathology, School of Me- 
dicine, First Affiliated Hospital, Shihezi University, 
Ministry of Education of China, Shihezi, China. Tel: 
+86-13899528366; E-mail: zouhong_patho@163.
com (HZ); Tel: +86-13999335086; E-mail: taolin- 
419315@163.com (LT)
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Overexpression of Polo-like kinase1 (PLK1) in chondrosarcoma and its implications for cancer progression

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Overexpression of Polo-like kinase1 (PLK1) in chondrosarcoma and its implications for cancer progression

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