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Published on: September 20, 2016
Persistent detection of alternatively spliced BCR-ABL variant results in a failure to achieve deep molecular response
Junichiro Yuda1, Toshihiro Miyamoto1, Jun Odawara1,2
1Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Science, Fukuoka, Japan.
Abstract:
Treatment with tyrosine kinase inhibitors (TKI) may sequentially induce TKI-resistant BCR-ABL mutants in chronic myeloid leukemia (CML). Conventional PCR monitoring of BCR-ABL is an important indicator to determine therapeutic intervention for preventing disease progression. However, PCR cannot separately quantify amounts of BCR-ABL and its mutants, including alternatively spliced BCR-ABL with an insertion of 35 intronic nucleotides (BCR-ABLIns35bp ) between ABL exons 8 and 9, which introduces the premature termination and loss of kinase activity. To assess the clinical impact of BCR-ABL mutants, we performed deep sequencing analysis of BCR-ABL transcripts of 409 samples from 37 patients with suboptimal response to frontline imatinib who were switched to nilotinib. At baseline, TKI-resistant mutations were documented in 3 patients, whereas BCR-ABLIns35bp was detected in all patients. After switching to nilotinib, both BCR-ABL and BCR-ABLIns35bp became undetectable in 3 patients who attained complete molecular response (CMR), whereas in the remaining all 34 patients, BCR-ABLIns35bp was persistently detected, and minimal residual disease (MRD) fluctuated at low but detectable levels. PCR monitoring underestimated molecular response in 5 patients whose BCR-ABLIns35bp was persisted, although BCR-ABLIns35bp does not definitively mark TKI resistance. Therefore, quantification of BCR-ABLIns35bp is useful for evaluating "functional" MRD and determining the effectiveness of TKI with accuracy.
Insights
Quantifying BCR-ABL inserts (BCR-ABLIns35bp) improves monitoring of chronic myeloid leukemia (CML) treatment response. This method offers a more accurate assessment of tyrosine kinase inhibitor (TKI) effectiveness than standard PCR.
Area of Science:
- Hematology
- Molecular Biology
- Oncology
Background:
- Tyrosine kinase inhibitors (TKIs) are standard treatment for chronic myeloid leukemia (CML).
- TKI treatment can induce resistant BCR-ABL mutants, complicating disease management.
- Conventional PCR monitoring of BCR-ABL may not accurately reflect treatment response due to BCR-ABL mutants.
Purpose of the Study:
- To assess the clinical impact of BCR-ABL mutants, specifically BCR-ABLIns35bp, in CML patients.
- To evaluate the utility of quantifying BCR-ABLIns35bp for monitoring TKI effectiveness and minimal residual disease (MRD).
- To compare deep sequencing with conventional PCR for assessing molecular response in CML.
Main Methods:
- Deep sequencing analysis of BCR-ABL transcripts was performed on 409 samples from 37 CML patients with suboptimal response to imatinib, switched to nilotinib.
- Baseline and post-treatment samples were analyzed for BCR-ABL and BCR-ABLIns35bp.
- Comparison of molecular response assessment between deep sequencing and conventional PCR.
Main Results:
- BCR-ABLIns35bp was detected in all patients at baseline.
- Persistent detection of BCR-ABLIns35bp was observed in 34 out of 37 patients after switching to nilotinib, with fluctuating minimal residual disease (MRD).
- Conventional PCR underestimated molecular response in 5 patients due to persistent BCR-ABLIns35bp.
Conclusions:
- Quantification of BCR-ABLIns35bp provides a more accurate evaluation of 'functional' MRD in CML patients.
- Measuring BCR-ABLIns35bp is crucial for accurately determining TKI effectiveness, especially in cases of suboptimal response.
- Deep sequencing offers superior sensitivity for detecting and quantifying BCR-ABL mutants compared to conventional PCR.
