In vitro sensitivity to imatinib-induced inhibition of ABL kinase activity is predictive of molecular response in patients with de novo CML

Abstract

Most patients with de novo chronic myeloid leukemia (CML) achieve good responses to imatinib, but the rate and degree of molecular response is variable. We assessed the inhibitory concentration 50% for imatinib (IC50 imatinib ) in 62 patients with de novo chronic-phase CML as a predictor of molecular response. IC50 imatinib was determined in pretherapy blood samples by measuring the in vitro imatinib-induced reduction of the phosphorylated form of the adaptor protein Crkl (CT10 regulator of kinase like). There was marked variability between patients, with IC50 imatinib ranging from 0.375 to 1.8 M (median, 0.6 M). Patients with low IC50 imatinib (IC50 < 0.6 M; n ‫؍‬ 36) had a 36% probability of achieving 2-log reduction in BCR-ABL (breakpoint cluster region-abelson) by 3 months compared with 8% in patients with high IC50 imatinib (n ‫؍‬ 26) (P ‫؍‬ .01). The IC50 imatinib was also predictive of molecular response at 12 months, with 47% of patients in the low IC50 imatinib group achieving 3-log reduction and 23% in the high IC50 imatinib group (P ‫؍‬ .03). The predictive power of IC50 imatinib was particularly strong in patients with low Sokal scores. These data provide strong evidence that intrinsic sensitivity to imatinib is variable in previously untreated patients with CML, and the actual level of BCR-ABL kinase inhibition achieved is critical to imatinib response. The IntroductionChronic myeloid leukemia (CML) is a clonal hematologic malignancy characterized by the presence of the Philadelphia chromosome (Ph) which arises from a balanced translocation between chromosomes 9 and 22. This translocation results in the fusion of the ABL gene on chromosome 9 with the BCR gene on chromosome 22. [1][2][3] The resulting BCR-ABL (breakpoint cluster regionabelson) fusion protein is a constitutively active tyrosine kinase, conferring enhanced proliferative activity and decreased sensitivity to apoptotic cell death in the cells in which it is expressed. As such, BCR-ABL is critical to the pathogenesis of the disease. [4][5][6] Imatinib (Glivec, formerly STI571; Novartis Pharmaceuticals) is a 2-phenylaminopyramidine compound that is a potent inhibitor of all ABL tyrosine kinases (c-ABL, BCR-ABL, and Tel/ABL). In addition, imatinib is an inhibitor of the tyrosine kinases of the platelet-derived growth factor (PDGF) receptor, 7,8 ARG 9 and c-Kit, 7,10 and the macrophage colony-stimulating receptor, c-fms. 11 Clinical trials have demonstrated the efficacy of imatinib in chronic-phase CML. 12,13 Approximately 95% of patients with de novo chronic-phase CML achieve complete hematologic response, with 90% achieving major, and 80% complete, cytogenetic remissions. 14 At the molecular level, significant reductions in the level of BCR-ABL transcript as measured by quantitative real-time PCR (RQ-PCR) have been observed. 15 Although these outcomes demonstrate a significant role for imatinib in the treatment of CML, the response of some patients remains suboptimal.In the International Randomized Study of Interferon versus STI571 (IRIS)...

Short-term intense Bcr–Abl kinase inhibition with nilotinib is adequate to trigger cell death in BCR-ABL+ cells

“…6 Within 30 min of exposure, 1 mM nilotinib reduced p-Crkl by 85-90% of control. Next, K562 and KU812 cells were cultured with nilotinib (0-2 mM) either for short term (cells were cultured with nilotinib for 30 min, followed by thorough drug washout and reculture in drug-free medium for the remainder of 72 h) or for long term (cells were cultured with nilotinib for 30 min, followed by washout and reculture with nilotinib for a total of 72 h).…”

Activity of tyrosine kinase inhibitors against human NUP214-ABL1-positive T cell malignancies

“…[22][23][24] CrKL couples nonreceptor tyrosine kinases to downstream signaling cascades that regulate gene expression 25 and is regarded as a surrogate of ABL1 kinase activation. 26 Exposure of PEER cells to increasing concentrations of imatinib and nilotinib for 3 h resulted in inhibition of CrKL phosphorylation, but this was more pronounced upon nilotinib exposure (Figure 5a). Exposure to escalating concentrations of either TKI did not affect significantly the expression of the NUP214 protein.…”

Chronic myeloid leukemia patients with the e13a2 BCR-ABL fusion transcript have inferior responses to imatinib compared to patients with the e14a2 transcript

“…Briefly RNA was isolated from total white blood cells, cDNA was prepared and BCR-ABL transcripts were measured by real-time quantitative polymerase chain reaction (PCR), using a LightCycler as previously decribed. 15 All 78 patients aged 16 2007 and with a minimum of 12 months follow-up were included in this study. The 71 patients who presented with either e13a2 or e14a2 BCR-ABL transcripts are the subject of the main investigation; patients presenting with both e13a2 and e14a2 transcripts are discussed separately (n=3).…”

“…16 Cells ( ~5×10 5 ) were resuspended in 500 µL of 2% paraformaldehyde (VWR, Lutterworth, UK) and fixed for 10 min at 37°C. Cells were then chilled on ice for 1 min and centrifuged at 770 g for 3 min.…”