Keywords
colon cancer - KRAS - gene expression - immunohistochemistry - type 2 diabetes
Introduction
Colon cancer and type 2 diabetes mellitus (T2DM) is an emerging health problem worldwide.[1]
[2] Both conditions share relatively similar risk factors, including, age, obesity,
reduced physical activity, diet, smoking, and alcohol.[3]
[4] T2DM is often considered an independent risk factor for the progression of colorectal
cancer.[5] The risk of colon cancer increases by 40 to 60% in patients with diabetes.[6] Although most of the risk factors for T2DM and colon cancers are similar, the potential
epidemiological evidence linking the two is still lacking or not fully understood.
One possible mechanism of cancer risk in diabetics is the elevated mitogenic activity
due to hyperinsulinemia. This is attributed to high-insulin and IGF-1 that mediate
the transformation and proliferation of colon cells, resulting in colon cancer.[7]
One of the most common events in colorectal cancers is a mutation of the KRAS gene. KRAS, a member of the RAS gene family, is one of the most studied oncogenes present in the short arm of chromosome
12. Among the three human RAS genes, namely, KRAS, NRAS, and HRAS, KRAS is reported to be the most frequently mutated gene.[8]
[9] The KRAS gene encodes a 21kD KRAS protein involved in intracellular signal transduction processes. KRAS protein is activated upon binding with GTP, which is mediated by intracellular signals.
Point mutation of KRAS at codon 12, 13, 59 or 61 impairs GTPase activity, thereby upregulating cellular
proliferation and carcinoma progression.[10] About 20 to 50% of colorectal cancers are reported to be mutated KRAS gene, and the mutation frequency depends on the grade of the tumor.[11] This study aimed to evaluate the KRAS gene in colon cancer tissues obtained from
patients with T2DM.
Materials and Methods
In this study, 315 tissue samples of previously resected colon cancer tissues were
retrieved from storage, including (a) fresh tissue specimens snap-freezing using liquid
nitrogen, and stored at -80°C. (b) Formalin-fixed and paraffin-embedded (FFPE) tissue
specimens. Fresh frozen tissues were used for molecular assessment. FFPE was used
for conventional histopathology as well as immunohistochemistry (IHC) assessment.
Of the 315 patients with colon cancer, 156 were diabetic patients (ascertained as
cases) and the remaining 159 were nondiabetic patients.
Variables such as gender, age, size of the tumor, histological types, and other clinicopathological
data were collected from their medical records.
Analyses of KRAS Gene Expression
The first-strand cDNA was formed from the 2 µg of total RNA after utilizing random
primers using the QuantiTect Reverse Transcription kit (Qiagen; Limburg, Netherlands)
and 100 units/mL of reverse transcriptase, based on the protocol from the manufacturer.
The utilization of primers for the cDNA amplification was developed after utilizing
a web application (Primer3) founded on the sequences acquired from the National Center
for Biotechnology Information (NCBI) database. The experiment was then normalized
to GAPDH. qPCR or quantitative polymerase chain reaction was undertaken by using the
SYBR Green PCR Core Reagent kit (Roche Diagnostics, Basel, Switzerland). At 95 °C
for 10 minutes, the samples were denatured and amplified by 40 cycles (95 °C for 15 seconds),
after which extension and annealing at 60 °C for 60 seconds was performed. The target
gene amount relative to the reference gene GAPDH was quantified utilizing the cycle
threshold (Cq). Amplification was then undertaken in duplicates with a real-time PCR
system after utilizing the TaqMan reaction Master Mix (7500, Applied Biosystems, Grand
Island, USA). The primer sequences included: GADPH, 5′-AACAGCCTCAAGATCATCAGCAA-3′ and 5′-CAGTCTGGGTGGCAGTGAT-3′; KRAS, 5′-CCTGCTGTGTCGAGAATATCCA-3′ and 5′-TTGACGATACAGCTAATTCAGAATCA-3′.
Immunohistochemical Studies Using KRAS Antibody
KRAS protein expression of 79 metastatic tissue samples (49 from T2DM patients and 30
from nondiabetic patients) were evaluated by IHC.[12] Non-neoplastic colon mucosa adjacent to cancerous tissues served as an internal
negative control. A 3-µm thick tissue sections were treated with 1:1000 dilution of
KRAS antibody (F234 and SC-30) and automated stained using BenchMark ULTRA, based on the
instructions of the manufacturer. The expression of the protein in at least 10% of
tissue samples was scored as positive. Sections were visualized using Zeiss Axio Imager
2 research upright microscope. IHC scores were measured following standard procedure.[25]
The KRAS was considered negative when it had scores of 0 and + 1and positive with
scores of + 2 and + 3. To be considered as + 2 and + 3, the cell cytoplasm should
be completely stained in more than 10% of the tumor cells. Cells without staining,
with weak staining in part of the cell membrane, and in less than 10% of the tumor
cells were considered negative.
Statistical Analysis
The obtained data were analyzed via SPSS version 25. Pearson's correlation (r) was made to regulate the association of various clinicopathological variables and
KRAS mRNA expression. Data were further validated using Akaike's information criterion,
Hurvic, and Tsai's criterion. Variations in mRNA expressions between patients with
and without T2DM and between primary and metastatic tumors were analyzed using one-way
ANOVA. IHC scores (0–8) for each patient samples were summarized and analyzed using
Pearson's correlation between non-neoplastic and metastatic tumor tissues; p values < 0.05 were considered as significant. Means were detached employing the Duncan
Multiple Range Test (DMRT).
Results
Men represent the majority of patients with colon cancer 250/315 (79.4%), leading
to a male female ratio of 1:00 to 3.85. Diabetic was common among females 40/65 (61.5%),
hence most of the males' patients were nondiabetic 134/250 (53.6%). The majority of
the patients were found in the age range 46–55 years, followed by 56–65 years, and > 65
years, representing 163/315 (51.7%), 47/315 (15%), and 46/3015 (14.6%), respectively.
There was a relatively similar age distribution between diabetic and nondiabetic patients,
as indicated in [Table 1] and [Fig. 1].
Table 1
Distribution of colon cancer patients by sex and age
|
Variable
|
Diabetic
|
Nondiabetic
|
Total
|
|
Sex
|
|
|
|
|
Males
|
116
|
134
|
250
|
|
Females
|
40
|
25
|
65
|
|
Total
|
156
|
159
|
315
|
|
Age (years)
|
|
|
|
|
< 35
|
11
|
8
|
19
|
|
35–45
|
30
|
10
|
40
|
|
46–55
|
93
|
70
|
163
|
|
56–66
|
13
|
34
|
47
|
|
> 65
|
9
|
37
|
46
|
Fig. 1 Description of colon cancer patients by sex and age.
[Table 2] and [Fig. 2], summarized the distribution of colon cancer patients by clinicopathological features.
Concerning the lesion site, most lesions were in the distal colon, representing 197/315
(62.5%). The majority of the proximal site lesions were found among diabetic patients
32/53 (60.4%), whereas most distal site lesions were identified among nondiabetic
patients 113/197 (57.4%). For tumor size, most patients were observed with a size
range of 10 to 20 mm, representing 111/252 (44%). No immense difference in distribution
between the diabetic and diabetic groups was observed in the tumor size, as indicated
in [Table 2] and [Fig. 2]. About 79/315 (25%) of the tumors were metastasized (liver and rectal) as M1. A
round 43/250 (17.2%) and 9/250 (3.6%) of the patients were found with N1 and N2 nodal
involvement, in this order. Concerning the Union for International Cancer Control
(UICC) staging, Stage II, Stage III, and Stage VI, were identified in 79/250 (31.6%),
37/250 (14.8%), and 27/250 (10.8%), as indicated in [Table 2] and [Fig. 2].
Table 2
Distribution of colon cancer patients by clinicopathological features
|
Variable
|
Diabetic
|
Non-diabetic
|
Total
|
|
Lesion site
|
|
|
|
|
Proximal colon
|
32
|
21
|
53
|
|
Distal colon
|
84
|
113
|
197
|
|
Total
|
116
|
134
|
250
|
|
Tumor size (thickness in mm)
|
|
|
|
0–10 mm
|
17
|
38
|
55
|
|
11–20 mm
|
53
|
56
|
111
|
|
>20 mm
|
46
|
40
|
86
|
|
Metastasis
|
|
|
|
|
M0
|
97
|
104
|
201
|
|
M1
|
49
|
30
|
79
|
|
Nondefined
|
10
|
28
|
38
|
|
Nodal status
|
|
|
|
|
N0
|
75
|
123
|
198
|
|
N1
|
33
|
10
|
43
|
|
N2
|
8
|
1
|
9
|
|
UICC stage
|
|
|
|
|
Stage 0
|
9
|
29
|
38
|
|
Stage I
|
13
|
56
|
69
|
|
Stage II
|
48
|
31
|
79
|
|
Stage III
|
22
|
15
|
37
|
|
Stage IV
|
24
|
3
|
27
|
Abbreviation: UICC, Union for International Cancer Control.
Fig. 2 Description of colon cancer patients by clinicopathological features.
The KRAS expression was significantly complex in patients with T2DM than nondiabetics. Correlation
between clinicopathological parameters showed a significant increase in expression,
with an increase in the thickness (r = 0.73, p = 0.02) and diameter (r = 0.65, p = 0.03) of tumors in patients with T2DM. Similarly, increment in gene expression
was noted with increase in tumor differentiation (r = 0.54, p = 0.006) and depth of invasion (r = 0.66, p = 0.001) among T2DM patients ([Table 3]). Differential expression was observed between proximal and distal colon tumor sites
in both the patient types. T2DM patients exhibited more mucinous tumors than nondiabetics.
Expression was significantly upregulated in the metastatic tumor of both the patient
types. The least information criterion of KRAS expression in a patient with T2DM was 713.721 (R
2 = 0.53) based on the Akaike's information criterion, Hurvic, and Tsai's criterion.
Table 3
Correlations between KRAS gene expression and clinicopathological characteristics of patients with and without
T2DM
|
Variables
|
With T2DM
|
Without T2DM
|
|
Tumor thickness
|
0.022[*]
|
0.423
|
|
Tumor diameter
|
0.031[*]
|
0.212
|
|
Tumor location
|
0.034[*]
|
0.054
|
|
Tumor differentiation
|
0.006[*]
|
0.065
|
|
Invasion depth
|
0.001[*]
|
0.224
|
|
Mucin secretion
|
0.040[*]
|
0.435
|
|
Metastasis
|
0.015[*]
|
0.007[*]
|
|
Lymph node status
|
0.320
|
0.765
|
|
Tumor stage
|
0.006[*]
|
0.046[*]
|
Abbreviation: T2DM, type 2 diabetes mellitus.
* Significant at p < 0.05.
Expression of KRAS mRNA in 156 cases with T2DM and 159 without T2DM is summarized in [Fig. 3A]. Elevated mRNA expression was significantly associated with the patient with T2DM
and tumor stage. A two to six-fold increase in expression level was noticed in T2DM
subjects than nondiabetics. Expression levels were normalized to GADPH mRNA. Expression of KRAS mRNA in 201 cases with primary tumors and 79 with metastatic lesions are summarized
in [Fig. 3B]. The KRAS mRNA levels were significantly amplified from primary to metastatic lesions (p < 0.001). The proportionate increase being 9.2% in primary tumors to 26.7% in metastatic
lesions.
Fig. 3 Box plots showing KRAS mRNA expression levels in patients (A) with or without type 2 diabetes mellitus (T2DM) and (B) between primary tumors and metastatic lesions. **p <0.05.
KRAS protein expression was overexpressed in cancerous samples of T2DM patients. Two KRAS antibodies, F234 and SC-30, perform well in IHC on paraffin-embedded tissues. The
results were more satisfactory for antibody F234, showing more positive scores compared
with SC-30. IHC analyses showed positive cytoplasmic and nuclear staining. Immunohistochemical
analyses indicated 56 to 83% KRAS protein expression in metastatic tumors from T2DM patients compared with 9 to 22%
in nondiabetic patients. The upregulation of expression was associated with tumor
invasion and advanced stage. The expression level exhibited different outcomes relative
to tumor location. Expressions in metastatic tissues (r = 0.79) were significant (p < 0.05) compared with non-neoplastic tissues (r = 0.48) collected adjacent to cancerous tissues. Average IHC scores for non-neoplastic
colon tissues and metastatic tumor tissues ranged from 3.7 to 4.3 and 5.9 to 6.7,
respectively for KRAS proteins ([Fig. 4]).
Fig. 4 Immunohistochemical (IHC) scores for KRAS in non-neoplastic and metastatic tumor tissues among 79 patients. **p < 0.05 versus normal.
Discussion
Recent researches revealed an increasing trend of colorectal cancers in Saudi Arabia,
most of which have been implicated in KRAS mutations.[13] Although KRAS mutations are highly restricted to colon cancer, it can be expressed in other cancers.[9]
[14]
The present study found that patients with T2DM had higher colon cancer risk as revealed
by elevated KRAS mRNA expression. These findings support the previous reports suggesting that patients
with diabetes history have an increased risk for colorectal cancer.[15] A recent study reported a significant association between T2DM and the incidence
of colorectal adenomas. This indicates that diabetic patients are at a higher risk
of developing colorectal cancer, thus are in higher need for controlled colonoscopy.[16]
[17] However, these facts may suggest further considerations when assessing diabetic
patients with colon cancer in terms of clinical features, treatment, and prognosis.
The current findings revealing a strong association between diabetic-related colon
cancer and male sex. However, there is a lack of data in this context, but it might
be attributed to an elevated number of colon cancer patients. The findings further
indicate that diabetic patients with KRAS mutated gene had a higher risk of colon cancer compared with nondiabetics. This has
an important clinical implication, as the management of T2DM might lower the risk
of colon cancer. However, the results contradict some earlier studies, suggesting
that diabetes does not play a role in the development of colon cancer.[18] Currently, epidemiological studies testified that diabetes intensifies the mortality
rate of patients with colorectal cancers.[5]
Further, the correlation between clinicopathological parameters showed a significant
increase in KRAS mRNA expression, with an increase in thickness and diameter of tumors, tumor differentiation
and depth of invasion in T2DM patients. Differential expression was observed between
proximal and distal tumor sites. Proximal colon tumors were found to be associated
with male, older age, advanced stage, and differentiated histology. Similar discrepancies
were reported in earlier studies.[19]
The findings of the present study might suggest that elevated KRAS mRNA expressions were associated with tumor-specific phenotypes. The weak expression
in the patients without T2DM may be attributed to a lack of differentiated tumors.
Such findings validate some of the earlier reports.[20] The KRAS mRNA expression was amplified significantly from primary to metastatic lesions. The
present results were in agreement with some of the earlier literature on KRAS gene expression.[21] Besides, the association of KRAS mutation and diabetes with the risk of colon cancer, there might be other factors
predisposing the development of colon cancer. Several explanations have been proposed
for the increased risk of colon cancers in diabetic patients. These include prolonged
bowel transit time, altered bile acid metabolism, hyperinsulinemia, and decreasing
gut mucosa.[15]
[22] Immunohistochemical analyses indicated the upregulation of KRAS protein expression in metastatic tumors from T2DM patients with advanced-stage and
tumor invasion. This may be attributed to the expression of the adhesion molecule
promoting tumor invasiveness.[20] Expression in metastatic tissues was significant compared with adjacent non-neoplastic
tissues. Furthermore, there is a lack of literature linking KRAS gene mutation to T2DM; thus, further studies to explore the association between KRAS gene mutation and T2DM would strengthen the genetic credibility of a cause-and-effect
association via categorization of the molecular pathways incriminated. In other words,
look for specific KRAS gene molecular signature associated with T2DM, and ultimately
discover T2DM-specific approaches to prevent cancer-associated molecular evolution.
It was well-known that KRAS mutations in codons 12 and 13 are established predictive
biomarkers for treatment of advanced colorectal cancer, with the antiepidermal growth
factor receptor (EGFR) antibodies cetuximab and panitumumab.[23]
[24] KRAS involves mutations in several codons, some of which may show resistance to
anti-EGFR treatment. However, this may further indicate the diversity in clinicopathological
features, progression, and pattern of invasion and metastasis.
Although the present study provided valuable information regarding the association
between T2DM and colon cancer or KRAS gene mutation in the Saudi population, it has some limitations including the absence of
some variables such as the duration of T2DM and history of other comorbid conditions.
Conclusion
The association between T2DM and colon cancer was well-established in the present
study. Although KRAS gene mutation was related to colon cancer, the findings of this study suggest some intermolecular
relationships with T2DM. Further search is needed to explore the interrelation between
T2DM and KRAS gene mutation.
