Panacea Laboratories
207 Perry Parkway
Suite #2
Gaithersburg, MD 20877
T: 240-404-9045
F: 240-465-0450
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TK Sensesm Background
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mRNA expression of the HAAH gene is increased in chronic myelogenous leukemia (CML) by greater than 4-fold and can be detected by qRT-PCR. |
Increased HAAH Expression in
Leukocytes from Patients with CML
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Expression of the HAAH gene significantly decreases when the leukocytes of CML patients are cultured in the presence of imatinib. A decrease in HAAH gene expression of greater than 30% correlates with drug response.
Patient non-responders to imatinib treatment do NOT show a significant decrease (<30%) in HAAH gene expression in the assay.
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Determining Imatinib Response Prior to Treatment
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Assay Procedures
Assay procedures are straight forward and require only a 10 ml blood draw. Leukocytes are isolated and cultured for 24 hours in the presence of imatinib. RNA is isolated, converted to cDNA and HAAH expression is determined by qRT-PCR. Patient response is compared directly to his/her own control untreated leukocytes to determine response.
Expression Levels of the BCR-ABL Gene do not Change in Response to Imatinib
The molecular hallmark of CML is the Philadelphia (Ph) chromosome, a shortened version of chromosome 22 that is the result of a translocation between chromosomes 9 and 22, and is found in 95% of CML patients. The Ph translocation results in the recombination of segments from the BCR and ABL genes creating a hybrid BCR-ABL gene. This hybrid gene is transcribed and translated to produce the BCR-ABL protein, an unregulated tyrosine kinase (TK) that alters cellular growth and function and serves as the molecular target for imatinib. Interestingly, overnight incubation of patient leukocytes with imatinib does not result in a down regulation of the BCR-ABL expression and thus, its expression level cannot be used to predict patient response to the drug.
Some other groups have explored further mutations in the BCR-ABL gene that correlate with the development of resistance to imatinib during the course of treatment. These mutations can be identified via sequencing of a mutation prone region of the BCR-ABL gene and, indeed, one such test has been made commercially available to identify these mutations. However, recent evidence suggests that "a mutant clone does not necessarily have a proliferative advantage and its presence does not always account for resistance to imatinib. Other mechanisms underlie resistance in at least some patients." (Khorashad JS, et al., "The presence of a BCR-ABL mutant allele in CML does not always explain clinical resistance to imatinib" Leukemia [2006] Apr;20[4]:658-63.) TK Sensesm does not predict imatinib resistance on the basis of mutational analysis, but detects resistance to drug empirically by directly treating patient leukocytes with the drug. Furthermore, since TK Sensesm detects gene expression events controlled by the BCR-ABL protein, it may potentially be used to detect resistance to newer tyrosine kinase inhibitors that are being developed to enhance or replace imatinib therapy.
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