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Abstract
Background
Imatinib mesylate, the tyrosine kinase activity of the BCR-ABL fusion gene, induces a remarkable remission in chronic myeloid leukemia (CML) patients. However, resistance to imatinib has been observed in a significant proportion of subjects, with the point mutations of the BCR-ABL kinase domain clinically identified as a possible mechanism. The aim of this study was to investigate clinical resistance to imatinib in Korean CML patients, and search for the point mutation of the BCR-ABL gene.
Methods
The clinical data and cytogenetic results of thirty two CML patients, who were treated with imatinib, between Jan. 2002 and Aug. 2003, were evaluated. Mutational analyses for the point mutations of the BCR-ABL kinase domain in clinically resistant patients were tested using RT-PCR and direct sequencing methods.
Background
Imatinib mesylate, the tyrosine kinase activity of the BCR-ABL fusion gene, induces a remarkable remission in chronic myeloid leukemia (CML) patients. However, resistance to imatinib has been observed in a significant proportion of subjects, with the point mutations of the BCR-ABL kinase domain clinically identified as a possible mechanism. The aim of this study was to investigate clinical resistance to imatinib in Korean CML patients, and search for the point mutation of the BCR-ABL gene.
Methods
The clinical data and cytogenetic results of thirty two CML patients, who were treated with imatinib, between Jan. 2002 and Aug. 2003, were evaluated. Mutational analyses for the point mutations of the BCR-ABL kinase domain in clinically resistant patients were tested using RT-PCR and direct sequencing methods.
Results
Complete hematological remission was obtained in all CML patients with a chronic phase and in 4 of 6 CML with accelerated or blast crisis. However, 4 patients (2 in the chronic phase and 2 with blast crisis) relapsed to blast crisis following continued treatment. A major cytogenetic response was observed in 67% of the chronic phase patients, but in 2, the Philadelphia chromosomes reemerged in a follow-up chromosome study. Mutational analyses showed point mutations in the 351st amino acid of the BCR-ABL kinase domain in 2 patients: M351T, which has previously been reported in many studies, and a novel substitution, M351L.
Conclusion
The frequency of imatinib resistance in Koreans was similar to that found in well-controlled western studies. Point mutations of the BCR-ABL kinase domain were detected in two patients. Further studies, with more sensitive methods and a greater number of patients will help reveal other mechanisms of imatinib resistance and establish more effective treatment plans.
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Fig. 1.
Amino acid sequences and characteristic domains of BC R-ABL tyrosine kinase and summary of previously reported mutations of BCR-ABL kinase domain in CML patients with imatinib-resistance.9-16) The number between parenthesis following each mutation site means total number of patients with the mutation.
Fig. 3.
Sequence analysis of BC R-ABL kinase domain. Normal ABL gene (NM_005157) has ATG sequence coding for methionine (M) at codon 351 (A). A substitution at codon 351 changed ATG to AC G coding for threonine completely (M351T) in a patient, BC 2 (B) and to TTG coding for leucine partially (M351 and M351L) in another patient, CP9 (C).
Fig. 4.
3D structure of ABL kinase domain acquired from PDB Number 1IEP using C n3D program ver 4.1. M351 is not in contact with imatinib and is not within the sequence of P-loop or activation-loop.
Table 1.
C linical characteristics and hematologic /cytogenetic response to imatinib in chronic phase C ML patents
| No. | Age /Sex | Stage at start of imtinib§ | Treatment duration (month) | Hematologic response | C ytogenetic response | Comments | |||
|---|---|---|---|---|---|---|---|---|---|
| Initial | F /U | Resistance | Best response (month) | Resistance | |||||
| C P1 | 67/M | Late-C P | 5 | C HR | CHR | No | Complete (3) | No | |
| C P2 | 27/F | Early-C P | 7 | C HR | CHR | No | Complete (5) | No | |
| C P3 | 60/M | Early-C P | 27 | C HR | CHR | No | Complete (4) | No | |
| C P4 | 47/F | Early-C P | 17 | C HR | CHR | No | Complete (6) | No | |
| C P5 | 54/M | Early-C P | 13 | C HR | CHR | No | Complete (4) | No | |
| C P6 | 21/M | Early-C P | 19 | C HR | CHR | No | Complete (3) | No | |
| C P7 | 60/F | Early-C P | 6 | C HR | CHR | No | Complete (5) | No | |
| C P8 | 44/F | Early-C P | 5 | C HR | CHR | No | Complete (5) | No | Before BMT |
| C P9 | 58/F | Early-C P | 6 | C HR | CHR | No | Complete (4) | Yes (2nd)† | |
| C P10 | 11/M | Early-CP | 13 | C HR | CHR | No | Complete (3) | Yes (2nd)‡ | |
| C P11 | 35/F | Late-C P | 9 | C HR | CHR | No | Partial (5) | No | |
| C P12 | 67/M | Early-C P | 9/(7)∗/9 | C HR | CHR | No | Partial (4) | No | |
| C P13 | 12/M | Early-C P | 3 | C HR | CHR | No | Partial (3) | No | Before BMT |
| C P14 | 48/M | Early-C P | 3 | C HR | CHR | No | Partial (3) | No | Before BMT |
| C P15 | 27/F | Early-C P | 6 | C HR | CHR | No | Minor (3) | Yes (1st) | |
| C P16 | 64/M | Early-C P | 5 | C HR | CHR | No | Minor (4) | Yes (1st) | |
| C P17 | 37/F | Early-C P | 15 | C HR | BC | Yes | Minor (3) | Yes (1st) | |
| C P18 | 41/F | Late-C P | 16 | C HR | CHR | No | Minimal (6) | Yes (1st) | |
| C P19 | 53/M | Late-C P | 26 | C HR | CHR | No | Minimal (5) | Yes (1st) | C lonal evoluton |
| (+8) | |||||||||
| C P20 | 41/F | Early-C P | 14 | C HR | CHR | No | Minimal (5) | Yes (1st) | |
| C P21 | 33/M | Early-C P | 9 | C HR | BC | Yes | No (5) | Yes (1st) | |
| C P22 | 62/F | Late-C P | 6 | C HR | CHR | No | No (2) | ND | |
| C P23 | 68/M | Early-C P | 1/(7)∗/5 | C HR | CHR | No | No (2) | ND | |
| C P24 | 69/F | Late-C P | 13 | C HR | CHR | No | NT | ND | |
| C P25 | 24/M | Late-C P | 19 | C HR | CHR | No | NT | ND | |
| C P26 | 5/F | Early-C P | 3 | C HR | CHR | No | NT | ND | Before BMT |
† Patient's initial cytogenetic response (after 4 months) showed complete cytogenetic response, but follow-up after 6 months showed partial response (20%)
Table 2.
C linical characteristics and hematologic /cytogenetic response to imatinib in accelerated phase and blast crisis CML patents
| No. | Age /Sex | Stage at T start of imtinib§ | Treatment duration (month) | Hematologic response | C ytogenetic response | C omments | ||
|---|---|---|---|---|---|---|---|---|
| Initial F /U | Resistance | Best response (month) | Resistance | |||||
| AP1 | 32/M | AP | 27 | C HR | C HR | No | No (5) | Yes (1st) |
| BC 1 | 64/F | M-BC | 3.5 | C HR | C HR | No | ND† | ND |
| BC 2 | 15/F | B -BC | 12 | C HR | BC | Yes | No (11)‡ | Yes (1st) |
| BC 3 | 69/F | L-BC | 9 | C HR | BC | Yes | NT | ND |
| BC 4 | 24/F | M-BC | 2/(4)∗/1 | No | BC | Yes | No (2) | ND |
| BC 5 | 71/F | M-BC | 6 | No | BC | Yes | NT | ND |
Table 3.
Mutation analysis of BC R -ABL kinase domain in patients with hematologic and cytogenetic resistance
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