Association of The Common CYP1A1*2C Variant
(Ile462Val Polymorphism) with Chronic Myeloid
Leukemia (CML) in Patients Undergoing
Cytochrome P450 is one of the major drug metabolizing enzyme families and
its role in metabolism of cancer drugs cannot be less emphasized. The association be-
tween single nucleotide polymorphisms (SNPs) in CYP1A1 and pathogenesis of chronic
myeloid leukemia (CML) has been investigated in several studies, but the results observed
vary based on varied risk factors. The objective of this study was to investigate the risk
factors associated with the
Materials and Methods
In this case-control study,
We observed a significant difference in the frequency distribution of
The higher frequency of AG in controls indicates that AG may play a protec- tive role against developing CML. We also found that patients with the AG genotype showed favorable treatment response towards imatinib therapy, indicating that this polymorphism could serve as a good therapeutic marker in predicting response to such therapy.
Chronic myeloid leukemia (CML) is an acquired
hematopoietic stem cell disease, characterized by
an increased production of immature granulocytes
(blasts) which accumulate in the bone marrow and
interfere with the normal blood cell production, accounting
for 30% of adult leukemias (1). The symptoms
of CML include bone marrow hypercellularity,
anaemia, splenomegaly and leucocytosis (1). CML
progresses slowly in three phases of chronic phase
(CP), accelerated phase (AP) and blast phase (BP)
which are differentiated by the number of blast cells
in the blood and the bone marrow, and the severity
of the symptoms. In 95% of CML cases, chromosomal
translocation resulting in the formation of the
Philadelphia (Ph) chromosome is observed (2, 3),
which in turn leads to the formation of the
The genetic variability single nucleotide polymorphisms (SNPs) in genes encoding phase I and phase II drug metabolizing enzymes which detoxify the xenobiotics [xenobiotic metabolizing enzymes (XMEs)], have been linked with the variation in susceptibility of different individuals toward leukemia (11, 12) as well as with therapeutic response of individuals toward drugs (13). Our previous work on SNPs in genes encoding drug metabolizing enzymes and drug transporters showed that these polymorphisms affect drug response in breast cancer (14-16), and head and neck cancer (17).
Cytochrome P450, family 1, Subfamily A, polypeptide
Three single nucleotide polymorphisms of
Materials and Methods
In this case-control study, the association of
Study population and their stratification
132 patients diagnosed with CML and 140 healthy age and sex matched controls formed our study group. The cohort of patients consisted of 76 (58%) male and 56 (42%) female patients with a mean age of 37.5 years. In addition, 102 (77%) patients were in the chronic phase, 20 (15%) patients were in the accelerated phase and 10 (8%) patients were in the blast crisis phase. CML patients were diagnosed at the Department of Medical Oncology, Nizam’s Institute of Medical Sciences (NIMS), Hyderabad, India. The control group consisted of individuals without the history of cancer and other diseases like genetic disorders, allergy, asthma, etc.
Inclusion and exclusion criteria
In this study, fully diagnosed CML patients receiving
Imatinib treatment (n=129) and few CML
patients prior to Imatinib treatment (n=3) were included
as cases. Age range of the CML patients
was 14-60 years in females and 15-64 years in
males. The diagnosis of CML was based on the
standard clinico-hematological criteria by detecting
the Ph chromosome (karyotyping) and/or the
Patient’s data including occupational history, complete clinical examination and routine laboratory tests such as complete blood picture [white blood cell (WBC) count and platelet count], liver and kidney functions were obtained. In addition, clinical data including phase of the disease and response to imatinib therapy were collected from the medical records with the permission of the attending medical oncologist. Patients were stratified based on response according to the European LeukemiaNet (ELN) criteria. Response status of patients to imatinib therapy (hematological, cytogenetic) was classified on the basis of WBC count, percentage of Ph+ cells and the duration of response to imatinib therapy (29, 30). We stratified the patients in our study based on these parameters to examine the efficacy of their treatment regimen. The effect of imatinib treatment was assessed after 3, 6 and 12 months. An ideal treatment regimen leads to a major/complete hematological response (MHR) and at least a minor cytogenetic response (mCyR) within 3 months, a partial CyR (PCyR) within 6 months and a complete CyR (CCyR) within 12 months
New method of stratification of chronic myeloid leukemia patients
We established one more criterion of stratification
of the CML patients, with reference to imatinib therapy,
based on the genotypes of the drug metabolizing
Venous blood samples (5 ml) from patients diagnosed with CML and treated with imatinib therapy, and from control individuals were collected in ethylenediamine tetraacetic acid (EDTA, BD, India) coated vacutainers. Genomic DNA was isolated by a standard salting out method (31) and then stored at -20˚C until use for mutational analysis.
Genotyping and the detection of
To detect the
The relationship between the
The mean age of CML patients was 36.7 years in females and 38.3 years in males. The CML patients were divided into 4 groups according to their age at diagnosis (i.e., <20, 20-30, 31-40 and 41-60 years). Incidence of CML was found to be highest in the age group 21-30 (39%), followed by 41-60 years (34%). In contrast, the incidence was found to be low in the age group 31-40 years (22%) and lowest in those less than 20 years (5%). This indicates that the onset of CML is generally after 20 years of age.
CYP1A1*2C genotyping analysis
The distribution of
Demographic characteristics of the study population
The mean age at the onset of CML was found to be 37.5 years and ranged between 14 and 60 years. Male predominance has been observed in the present study with a sex ratio of 1.3:1 indicating that the male population are at higher risk for CML development. The results of our analysis of clinical characteristics in CML patients are presented in table 3.
|Genotype||Patients (n=132) n (%)||Controls (n=140) n (%)||OR||95% CI||P value|
|Ile/Ile (AA)- Wild||50 (38)||22 (16)||3.2705||1.84 - 5.81||0.0001|
|Ile/Val (AG)- Hetero||76 (57)||110 (78)||0.3701||0.218-0.63||0.0002|
|Val/Val (GG)- Homo mutant||6 (5)||8 (6)||0.7857||0.265-2.33||0.6635|
CML; Chronic myeloid leukemia, n; Number of subjects, OR; Odds ratio and CI; Confidence interval.
|Allele||Patients allele frequency||Controls allele frequency|
CML; Chronic myeloid leukemia.
|Characteristics||Total CML cases n=132 (%)||Wild type AA (Ile/Ile) n=51 (38%)||Heterozygous AG (Ile/Val) n=75 (58%)||Homo mutant GG (Val/Val) n=6 (4%)||P value|
|Males||76 (58)||32 (42)||39 (51)||5 (6.6)||0.23|
|Females||56 (42)||19 (34)||36 (64)||1 (1.8)||0.23|
|Age of diagnosis (Y)|
|<20||7 (5)||3 (43)||3 (43)||1 (14)||0.62|
|20-30||51 (39)||19 (37)||32 (63)||-||0.54|
|31-40||29 (22)||12 (41)||16 (55)||1 (3.4)||0.77|
|>40 (up to 60)||45 (34)||17 (38)||24 (53)||4 (8.8)||0.87|
|Chronic||114 (86)||46 (40)||62 (54)||6 (5)||0.24|
|Accelerated||13 (10)||3 (23)||10 (77)||-||0.18|
|Blast crisis||5 (4)||2 (40)||3 (60)||-||0.98|
|WBC count (cells/ cubic.mm of blood)|
|<20 000||15 (11)||10 (67)||5 (33)||-||0.03*|
|>20 000||117 (89)||41 (35)||70 (60)||6 (5)||0.03*|
|Normal count (1.5-4.0 lakhs cells/cubic.mm of blood)||71 (54)||28 (40)||38 (54)||5 (7)||0.64|
|Thrombocytopenia (<1.5 lakhs/cubic.mm)||3 (2.3)||2 (67)||1 (33)||-||0.37|
|Thrombocytosis (>4 lakhs/cubic.mm)||58 (44)||21 (36)||36 (62)||1 (1.7)||0.45|
|Splenomegaly present||104 (79)||36 (35)||64 (62)||4 (3.8)||0.04*|
|Splenomegaly absent||28 (21)||15 (53.5)||11 (39)||2 (7)||0.04*|
WBC; White blood corpuscles, CML; Chronic myeloid leukemia and *; Indicates statistically significant (P<0.05).
Treatment response of chronic myeloid leukemia patients carrying the CYP1A*2C polymorphism
Association of the
Influence of the
on chronic myeloid leukemia with respect to
MHR was observed to be higher in patients carrying the AG genotype (67%) than non-carriers (P=0.03), whereas, patients without the polymorphism (AA) (62%) exhibited a poorer hematological response than the patients with genotype AG (31%) (P=0.04), indicating that the patients carrying the polymorphism (AG) showed positive therapeutic response compared with wild type (AA) patients. Patients with the homozygous genotype (GG) (8%) exhibited poor hematological response (Table 4,).
CYP1A1*2C polymorphism on
chronic myeloid leukemia with respect to cytogenetic
We observed that most of the major cytogenetic responders (65%) carried a high frequency of Ile/ Val variant genotype, whereas most poor cytogenetic responders (78%) carried a high frequency of wild genotype (AA) (P=0.02). This indicates that this polymorphism may be associated with positive cytogenetic response to imatinib therapy. Patients with homozygous variant genotype (GG) (1%) exhibited major cytogenetic response (Table 4,).
|Imatinib treatment response||Total n=95 n (%)||Total n=37 n (%) AA||Total n=57 n (%) AG||Total n=1 n (%) GG||P value|
|i. Hematological response|
|Major (MHR)||70 (74)||23 (33)||47 (67)||-||0.03*|
|Minor (mHR)||12 (13)||6 (50)||6 (50)||-||0.42|
|Poor (PHR)||13 (14)||8 (62)||4 (31)||1 (8)||0.04*|
|Major (MCyR)||71 (75)||24 (34)||46 (65)||1 (1)||0.08|
|Minor (mCyR)||15 (16)||6 (40)||9 (60)||-||0.90|
|Poor (pCyR)||9 (9)||7 (78)||2 (22)||-||0.02*|
AA; Wild genotype, AG; Heterozygous genoype, GG; Homozygous variant genotype, MHR; Major hematological response, mHR; Minor hematological response, PHR; Poor hematological response, MCyR; Major cytogenetic response, mCyR; Minor cytogenetic response, pCyR; Poor cytogenetic response and *; Indicates statistically significant (P<0.05).
Polymorphisms in genes encoding the drug metabolizing
Presence of the A4889G SNP in
We found that although CML occurs at any age,
a higher incidence was found in adults of age
above 20 with most diagnosed to be in the chronic
phase. CML patients are generally treated with the
drug imatinib mesylate (Gleevec®, Novartis) with
chronic phase CML patients responding well to
this therapy. Hence it may be possible that SNPs in
Our findings suggest that AG genotype may
play a protective role in reducing CML risk in
our cohort. We had also analysed the influence of
We also found that the AG genotype was associated with good therapeutic response towards IM, which was measured in terms of hematological and cytogenetic responses, hence a good predictor of imatinib therapy.
Consistent with our findings, AML patients carrying
Taspinar et al. (26) reported a higher distribution
Analysis of SNPs with respect to therapeutic response is expected to aid in designing novel, alternative therapeutic strategies to treat CML which may be efficient alone or may be useful in combination with existing therapies. With the advent of new techniques, obtaining the complete genomic sequence of every individual is becoming a possibility with which the SNPs in the genome could be identified and subsequently the risk of developing cancer may be predicted. In addition, the identified SNPs may not only serve as genetic markers in determining the susceptibility of an individual to a disease, it can also predict response to a therapy. Such advances are expected to pave the way for the development of personalized medicine.
We showed that the AG genotype of
We thank Dr. Sailaja Kagita and Mr. Kirmani Natukula for their technical support and JNIAS for the facilities provided. No financial support was received for this study. The authors declare no conflict of interest.