Loss of Response to Imatinib: Mechanisms and Management

Hematology ◽  
2005 ◽  
Vol 2005 (1) ◽  
pp. 183-187 ◽  
Author(s):  
Neil P. Shah
Keyword(s):  
Kinase Inhibitor ◽  
Kinase Domain ◽  
Imatinib Resistance ◽  
Early Clinical Trial ◽  
Abl Kinase ◽  
Imatinib Resistant ◽  
Trial Experience ◽  
Highly Effective ◽  
Mutant Forms

AbstractThe treatment of chronic myeloid leukemia (CML) has been revolutionized by the small molecule BCR-ABL-selective kinase inhibitor imatinib. Although imatinib is highly effective initially and generally well-tolerated, relapse is increasingly encountered clinically. Until recently, for the majority of CML patients with disease no longer responsive to imatinib, as well as for patients with imatinib intolerance, few effective therapeutic options existed. Our understanding of the major mechanisms of imatinib resistance has led to the clinical development of two novel BCR-ABL inhibitors that harbor significant therapeutic promise in early clinical trial experience. These agents, dasatinib (BMS-354825) and AMN107, are more potent inhibitors of BCR-ABL than imatinib, and moreover, harbor activity against nearly all imatinib-resistant BCR-ABL kinase domain mutant forms tested in vitro. Notably, neither of these compounds is effective against the imatinib-resistant BCR-ABL/T315I mutation. The potential availability of highly effective medications for the treatment of imatinib-resistant and intolerant cases of CML is expected to further complicate the timing of other effective therapies, such as allogeneic stem cell transplantation. Additionally, periodic genotyping of the BCR-ABL kinase domain to screen for drug-resistant mutations may play an increasingly important role in the future management of CML cases.

Correlation of Clinical Response to Nilotinib with BCR-ABL Mutation Status in Advanced Phase Chronic Myelogenous Leukemia (CML-AP) Patients with Imatinib-Resistance or Intolerance.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 1940-1940 ◽  
Author(s):  
Giuseppe Saglio ◽  
Dong-Wook Kim ◽  
Andreas Hochhaus ◽  
Simona Soverini ◽  
P. Erben ◽  
...  
Keyword(s):  
Disease Progression ◽  
Cytogenetic Response ◽  
Kinase Domain ◽  
Mutant Clone ◽  
Imatinib Resistance ◽  
Mutation Status ◽  
Abl Kinase ◽  
Imatinib Resistant ◽  
Kinase Domain Mutations

Abstract The 2nd-generation bcr-abl inhibitor nilotinib is more potent than imatinib (IC50 <30 nM) against unmutated bcr-abl and active against 32/33 imatinib-resistant BCR-ABL mutants in vitro. We investigated the in vivo activity of nilotinib stratified by the baseline BCR-ABL mutation status in 127 imatinib-resistant or -intolerant CML-AP patients (pts) enrolled in an open-label phase II trial of nilotinib. Eighty-five pts (85/127, 67%) were screened prior to nilotinib therapy for BCR-ABL kinase domain mutations by direct sequencing. Of the 85 pts, 75 (88%) were resistant to imatinib and 10 (12%) were intolerant using standard published criteria. Twenty-two different baseline mutations involving 19 amino acids were identified in 50 (59%) pts analyzed. Other 35 (41%) pts did not have a baseline mutation. The most frequent mutation types identified included M351T (8 pts), G250E (7 pts), Y253H (6 pts), M244V (5 pts), F359V (5 pts) and T315I (5 pts). Twenty-two percent of pts with baseline mutations (11/50) showed more than one mutation (9 with two, 1 with three, and 1 with four mutations). All baseline mutations occurred in imatinib-resistant pts but none in intolerant pts. After 12 months of therapy, confirmed (confirmed in two consecutive analyses 4 week apart) hematologic response (HR) was achieved in 48% (21/50), major cytogenetic response (MCR) in 20% (10/50), and complete cytogenetic response (CCR) in 16% (8/50) of imatinib-resistant pts with baseline mutation versus 44% (12/25), 40% (10/25), and 20% (2/25) of imatinib-resistant pts without baseline mutation, respectively. Responses appeared to be affected by the in vitro sensitivity of the mutant clone against nilotinib. Pts with less sensitive mutation (cellular IC50 of >200nM: Y253H, E255K, E255V, F359C) representing 13% (11/85) of all patients assessed for baseline mutation, showed 13% (1/11) HR and 13% (1/11) MCyR compared to 74% (17/28) and 18% (5/28) respectively in the mutant group with IC50 of ≤200 nM. The nilotinib resistant T315I mutation occurred in 5 pts. Only one of these 5 pts who had T315I and G250E dual mutation achieved HR conceivably reflecting the sensitivity of G250E or non-mutant clone to nilotinib. At the time of data analyses, 50% of pts with baseline mutation were free of disease progression versus 62% of pts without baseline mutation. Rate of progression was 64% (7/11) in the group with less sensitive mutations and 60% (3/5) in pts. with T315I. However, the mutants most frequently associated with progression were F359V and M244V both having 4/5 pts (80%) progressed. In summary, BCR-ABL kinase domain mutations were identified at baseline in 59% of all pts in this cohort and in 67% of pts with imatinib resistance. Responses were observed across a broad spectrum of mutant genotypes. The rate of responses and disease progression may be affected by the baseline mutation types, although a larger data set with longer follow up is needed to further establish the correlation.

To Study Resistant Mechanisms and Reversal In An Imatinib Resistant Ph+ Positive Acute Lymphoblastic Leukemia Cell Line

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 2135-2135
Author(s):  
Hongyun Xing ◽  
Yuping Gong ◽  
Ting Liu
Keyword(s):  
Cell Signaling ◽  
Cell Line ◽  
Lymphoblastic Leukemia ◽  
Kinase Domain ◽  
Rt Pcr ◽  
Imatinib Resistance ◽  
Abl Kinase ◽  
Imatinib Resistant ◽  
Cell Signaling Pathways

Abstract Abstract 2135 Objective To establish an imatinib resistant Bcr-Abl positive acute lymphoblastic leukemia (ALL) cell line in vitro and to study imatibin resistance in Ph+ ALL. The reversal of the imatinib resistance by rapamycin, the second generation tyrosine kinase inhibitor and proteasome inhibitor was studied. Methods Ph(+) ALL SUP-B15 cell line was cultured in gradually increasing concentrations of imatinib to generate the imatinib resistant cell line at 6 μM imatinib. The cytotoxic effect of imatinib and other drugs was analyzed by MTT assay. RT-PCR, flow cytometry, Western blot analyses of proteins, DNA sequence analysis of ABL kinase domain were used to clarify the possible mechanisms of the imatinib resistance in the SUP-B15/RI cell line. Results We established the imatinib resistant Ph+ ALL cell line. The fusion bcr-abl gene was 6.1 times as high as that of the parental sensitive cell, and the mdr1 gene also increased 1.7 times in SUP-B15/RI cell line by the RT-PCR detection. However, the expression of hoct1 Abcl–2 and topoIIα gene were no difference between two cell lines by the RT-PCR detection. A K362S point mutation in the Abl kinase domain of SUP-B15/RI was found. The detection of cell signaling pathway of PI3K/AKT/mTOR, RAS/RAF, NF-κBA JNK and STAT showed the expression of PTEN and 4EBP-1 was down-regulated, AKT, mTOR and P70S6K was up-regulated and the expression of other cell signaling pathways in SUP-B15/RI was similar to its parental sensitive cell line. Dasatinib, nilotinib, and bortezomib could inhibit proliferation of SUP-B15/RI cells at nM concentration. SUP-B15/RI cell line also showed partial resistance to dasatinib and nilotinib, but not bortezomib. The combination of imatinib with rapamycin had synergistic effect to the resistance cell line. Conclusion In vitro, we establish imatinib resistant Ph + ALL cell line. Overexpression of bcr-abl and mdr1 gene, K362S point mutation in ABL kinase domain and up-regulation of the cell signaling pathways of PI3K/AKT/mTOR, RAS/RAF in SUP-B15/RI cell line were involved in the resistance mechanisms. The SUP-B15/RI cell line was also resistant to the second generation tyrosine kinaeses dasatinib and nilotinib,not bortezomib in vitro. However, the combination of imatinib with rapamycin can partially overcome the resistance. Blockade of the ubiquitin-proteasome could be a promising pathway to overcome resistance to imatinib. Disclosures: No relevant conflicts of interest to declare.

Inhibition of BCR/ABL-T315I by Dismantling the Hydrophobic Spine.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 2129-2129
Author(s):  
Mohammad Azam ◽  
Markus Seeliger ◽  
John T Powers ◽  
Nathanael Gray ◽  
John Kuriyan ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Kinase Domain ◽  
Myelogenous Leukemia ◽  
Resistance Mutations ◽  
Imatinib Resistance ◽  
Principal Mechanism ◽  
Abl Kinase ◽  
Molecule Inhibitor ◽  
Mutant Forms

Abstract Mutation in the ABL kinase domain is the principal mechanism of imatinib resistance (IMR) in patients with chronic myelogenous leukemia (CML). The second generation BCR/ABL inhibitors, Nilotinib and Dasatinib, are effective in inhibiting essentially all IMR variants, but not the gatekeeper mutant T315I. Substitution of a bulky hydrophobic residue for the gatekeeper threonine not only causes steric blockade to the inhibitor but also stabilizes the active kinase conformation through a network of hydrophobic connections dubbed the hydrophobic-spine. In this study we describe the molecular mechanisms employed by the gatekeeper mutation to stabilize the active conformation, and demonstrate that these structural components can be targeted by the small molecule inhibitor compound #14, which efficiently inhibits native and gatekeeper mutant forms of the BCR/ABL kinase. Structural modeling and mutagenesis of residues constituting the spine suggests that compound #14 inhibits the kinase by disrupting the hydrophobic spine. Screening for drug resistance in vitro selected for clones having compound mutations involving both the P-loop and gatekeeper residues. Our studies provide structural guidance for the design of inhibitors against the gatekeeper mutant, and suggest that combination therapy may be required to prevent the emergence of compound resistance mutations.

Complete Suppression of in Vitro Resistance by AP24534, a Pan-BCR-ABL Inhibitor

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 726-726 ◽  
Author(s):  
Thomas O’Hare ◽  
Christopher A. Eide ◽  
Lauren T. Adrian ◽  
Victor M. Rivera ◽  
William C. Shakespeare ◽  
...  
Keyword(s):  
Kinase Inhibitor ◽  
Kinase Domain ◽  
Complete Suppression ◽  
In Vitro Mutagenesis ◽  
Mutagenesis Screen ◽  
Abl Kinase ◽  
Imatinib Resistant ◽  
Escape Mutants ◽  
Selection Of

Abstract The BCR-ABL inhibitor imatinib is front-line therapy for chronic myeloid leukemia (CML). The second-line inhibitors dasatinib and nilotinib provide treatment options for controlling imatinib-resistant CML associated with BCR-ABL kinase domain mutations. However, the T315I mutant of BCR-ABL is resistant to all 3 clinical inhibitors, and is a frequent cause of salvage therapy failure. AP24534 is an oral, multi-targeted kinase inhibitor with activity against native and kinase domain-mutant BCR-ABL, including T315I. We have previously utilized an in vitro mutagenesis-screening assay to successfully predict the profile of mutations that confer resistance to imatinib, dasatinib, and nilotinib in patients. Here we use the in vitro mutagenesis screen to test whether BCR-ABL mutants can emerge in the presence of AP24534. Methods: To determine a resistance profile for AP24534, Ba/F3 cells expressing native BCR-ABL were mutagenized with ENU, washed, and plated in the presence of graded concentrations of AP24534 (5–80 nM). For each condition, 4.8×107 mutagenized cells were distributed into 480 wells and observed for growth for 4 weeks. Resistant clones were expanded in the continued presence of AP24534 and sequenced for mutations in the BCR-ABL kinase domain. Results: We first established IC50 values for inhibition of proliferation of Ba/F3 cells expressing native BCR-ABL (IC50: 0.5 nM) and an extensive panel of imatinib-resistant BCR-ABL mutants (IC50 range: 0.5 nM to 35.7 nM) including T315I (IC50: 11.4 nM) and E255V (IC50: 35.7 nM). Parental Ba/F3 cells were not inhibited up to a concentration of 1713 nM AP24534. Corresponding immunoblot analyses confirmed the same rank order for effective inhibition of CrkL phosphorylation in cells expressing native BCR-ABL, the T315I mutant, or the E255V mutant. Inhibition of CrkL phosphorylation was also demonstrated with primary hematopoetic cells from CML patients harboring native BCR-ABL or the T315I mutant. In the mutagenesis screen starting with Ba/F3 cells expressing native BCR-ABL, resistant clones recovered in 10 nM AP24534 expressed native BCR-ABL or one of several imatinib-resistant BCR-ABL mutants (168/1440 wells in 3 independent experiments). By contrast, when the screen was conducted in the presence of 20 nM AP24534, the frequency of outgrowth of escape mutants was extremely low and limited to cells expressing the T315I mutant (2/1440 wells) or the E255V mutant (1/1440 wells). Remarkably, outgrowth was completely suppressed by 40 nM AP24534. Conclusions: AP24534 is a potent inhibitor of native BCR-ABL and all tested BCR-ABL mutants, including T315I. Mutagenesis screening reveals that single-agent AP24534 (40 nM) completely suppressed outgrowth of escape mutants. This is in marked contrast to any of the BCR-ABL inhibitors previously profiled in this assay, where outgrowth was evident at the highest tested drug concentrations and complete suppression was observed only when dasatinib or nilotinib was combined with an investigational T315I inhibitor (PNAS2008; 105: 5507). As sequential BCR-ABL kinase inhibitor therapy has been linked to selection of rare subclones in which 2 mutations occur in the same BCR-ABL molecule, compound mutations are potentially capable of thwarting any of the current clinical BCR-ABL inhibitors, even in combination. Front-line therapy with a pan-BCR-ABL inhibitor could improve the depth and durability of responses by preventing selection of drug-resistant kinase domain point mutants. Our pre-clinical profiling indicates that AP24534 is an important new option in controlling resistance in CML. A phase 1 clinical trial designed to evaluate AP24534 treatment in patients with refractory CML and other hematologic malignancies has recently commenced.

Hematologic and Cytogenetic Responses in Imatinib-Resistant Chronic Phase Chronic Myeloid Leukemia Patients Treated with the Dual SRC/ABL Kinase Inhibitor BMS-354825: Results from a Phase I Dose Escalation Study.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1-1 ◽  
Author(s):  
Charles L. Sawyers ◽  
Neil P. Shah ◽  
Hagop M. Kantarjian ◽  
Nicholas Donato ◽  
John Nicoll ◽  
...  
Keyword(s):  
Phase I ◽  
Dose Escalation ◽  
Clinical Benefit ◽  
Kinase Inhibitor ◽  
Chronic Phase ◽  
Pharmacokinetic Studies ◽  
Imatinib Resistance ◽  
Abl Kinase ◽  
Imatinib Resistant

Abstract Disease relapse in CML patients treated with imatinib is often associated with mutations in the BCR-ABL gene that interfere with the ability of imatinib to block BCR-ABL kinase activity. BMS-354825 is a novel, orally available, dual SRC/ABL kinase inhibitor with more than 100-fold greater potency than imatinib that has in vitro and in vivo preclinical activity against 14 of 15 imatinib resistant BCR-ABL mutants (Shah et al, Science, 305:399, 2004). Here we report the phase I clinical results of BMS-354825 in Philadelphia chromosome positive (Ph+) CML patients in chronic phase with hematologic progression or intolerance while being treated with imatinib. To date (Aug 6, 2004), 29 patients have been treated on 9 cohorts with doses ranging from 15 to 180 mg of BMS-354825 per day given in single or divided doses for 5–7 days per week, for up to 9 months. Similar to imatinib, BMS-354825 has been well tolerated in all patients, with a single episode of grade 4 thrombocytopenia as the only potential drug related adverse event. BMS-354825 is rapidly absorbed with peak concentrations achieved within 2 hours and a terminal phase half-life of about 5 hours. Serum levels well above the concentration required to block CML cell proliferation in vitro have been readily achieved without side effects. Pharmacodynamic studies demonstrate greater than 50 percent inhibition of phosphorylation of the BCR-ABL substrate CRKL and the SRC kinase Lyn, consistent with the serum concentrations observed in pharmacokinetic studies. Patients not receiving optimal clinical benefit were escalated to the next higher dose for which safety parameters were available, thereby allowing a preliminary assessment of clinical activity. To date, 26 patients (22 with imatinib resistance, 4 with imatinib intolerance; average CML duration 6.1 years) have been followed for greater than 4 weeks and are eligible for assessment of hematologic benefit. 22 patients had detectable BCR-ABL kinase domain mutations prior to starting BMS-354825. All 26 patients have been treated with doses of 35 mg per day or greater and have had clinical benefit, including 19 with complete hematologic responses (73%). Of the 7 partial responders, two subsequently had disease progression, one of whom had expansion of a CML subclone containing the imatinib-resistant T315I mutation in BCR-ABL, which also confers resistance to BMS-354825 in preclinical studies. The other 5 partial responders are now being treated with higher doses to attempt conversion to complete hematologic response. 11 of 21 patients (52%) treated for greater than 3 months have cytogenetic benefit, including 6 major (1–35% Ph+), 1 minor (36–65% Ph+) and 4 minimal (66–95% Ph+) cytogenetic responses. One patient has achieved complete cytogenetic response. Dose escalation continues, and phase II studies in chronic, accelerated and blast crisis CML are currently being initiated. These data provide compelling evidence supporting the safety and efficacy of BMS-354825 in imatinib-resistant chronic phase CML.

Comparative Analysis of Two BCR-ABL Small Molecule Inhibitors Reveals Overlapping but Distinct Mechanisms of Resistance.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 552-552 ◽  
Author(s):  
Michael R. Burgess ◽  
Neil P. Shah ◽  
Brian J. Skaggs ◽  
Francis Y. Lee ◽  
Charles L. Sawyers
Keyword(s):  
Small Molecule ◽  
Small Molecule Inhibitors ◽  
Point Mutations ◽  
Kinase Domain ◽  
Drug Binding ◽  
Saturation Mutagenesis ◽  
Imatinib Resistance ◽  
Abl Kinase ◽  
Imatinib Resistant

Abstract A novel dual SRC/ABL kinase inhibitor, BMS-354825, is showing promise for the treatment of imatinib-resistant chronic myeloid leukemia not only in vitro (Shah NP, et al., Science 305:399), but also in a phase I clinical trial (ASH abstract: Sawyers CL, et al.) Resistance to imatinib is increasingly found in patients due to point mutations in the BCR-ABL kinase domain that do not impair kinase activity but prevent drug binding. BMS-354825 is more potent than imatinib and retains activity against 14 of 15 imatinib-resistant BCR-ABL mutants in vitro. The compound’s ability to inhibit imatinib-resistant forms of BCR-ABL is presumed to be due to its relaxed binding requirements, whereas imatinib requires the adoption of a closed conformation of the kinase to bind. We addressed the hypothesis that the relaxed binding requirements of BMS-354825 would limit the range of BCR-ABL mutations that confer drug resistance. To address this question, we employed a saturation mutagenesis experiment as described by others (Azam M, et al., Cell 112:831) and found that the spectrum of BMS-354825-resistant mutants was reduced compared to that of imatinib. In a series of such screens, mutations at only four amino acids have been isolated, two of which account for the vast majority of resistant clones. In contrast, Azam et al. isolated over 20 mutations in a screen for imatinib resistance, a finding which has been generally reproduced in our lab. All four BMS-354825-resistant mutations map to known BMS-354825 contact residues as shown by co-crystallographic studies (ASH abstract: Tokarski JS et al., Bristol-Myers Squibb). Mutations at L248, T315, and F317 show BMS-354825 resistance and have been previously reported to confer imatinib resistance. Mutation at V299 represents a novel mode of resistance. Interestingly, some point mutations conferring BMS-354825 resistance were at positions known to be mutated in cases of imatinib resistance, but the mutated residues differed. Furthermore, the identity of the mutated residue was crucial in conferring sensitivity or resistance to an individual drug as shown by comparison of cellular IC50’s (see table). For example, F317L was shown previously to confer imatinib resistance. F317V, on the other hand, demonstrates relative BMS-354825-resistance but is still exquisitely sensitive to imatinib. In a screen for mutants simultaneously resistant to both drugs, we consistently recover 30–50 fold fewer mutant clones compared to single drug treatment. All such clones isolated to date encode for T315I. Kinase domain point mutation is becoming an increasingly encountered clinical problem in diseases treated with small molecule inhibitors. Our findings suggest that combination therapy with imatinib and BMS-354825 may be of clinical utility in CML, particularly by delaying the development of resistance. IC50 for growth (nM) Baf3 Clone imatinib BMS-354825 p210 wt < 1,000 < 5 T315I > 10,000 > 500 T315A 1,000 100 F317L 2,000 10 F317V < 1,000 60 V299L 1,000 20 L248R > 10,000 20

BCR-ABL P-Loop Deletion Detected in Imatinib-Resistant CML Patients Corresponds to Splice Variant Associated with L248V Point Mutation, Retains BCR-ABL Kinase Activity, and Responds to Dasatinib Treatment.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2168-2168
Author(s):  
Nikolas von Bubnoff ◽  
Philipp Erben ◽  
Martin Müller ◽  
Tanja Lahaye ◽  
Susanne Schnittger ◽  
...  
Keyword(s):  
Splice Variant ◽  
Kinase Activity ◽  
Kinase Inhibitors ◽  
Point Mutations ◽  
Kinase Domain ◽  
Imatinib Resistance ◽  
Abl Kinase ◽  
Imatinib Resistant ◽  
Exon 4

Abstract Clonal selection of cells harboring point mutations of the BCR-ABL kinase domain are considered a major cause of resistance to imatinib. More than 40 different point mutations have been described that cause a variable degree of imatinib resistance, and display a differential response to alternative kinase inhibitors, like dasatinib or nilotinib. Here, we describe three cases (2 m, 1 f) with imatinib resistant chronic myelogenous leukemia (CML) associated with a specific deletion of 81 bp of ABL exon 4. Patients were diagnosed with chronic phase (CP) CML at the age of 52, 54, and 68 years. After initial interferon alpha based therapies for 32, 60, and 71 mo, imatinib therapy was initiated at dosages between 400–800 mg per day. After 18, 24, and 29 mo patients lost hematologic response in CP CML (n=2) or progressed to lymphoid blast crisis (BC, n=1). Molecular analysis of the ABL kinase domain revealed a deletion of a 81 bp fragment associated with a loss of amino acids 248–274 in all cases. In one patient, an additional M351T mutation was found. In the two cases with CP CML, dasatinib was commenced for imatinib resistance, resulting in a partial hematologic and minor cytogenetic response (60 and 70% Ph+ metaphases, respectively) after 14 mo of therapy. The patient with lymphoid BC was treated with vincristine and prednisone and died 24 mo after appearance of imatinib resistance. In two cases, sequencing of genomic DNA revealed an underlying CTG/GTG mutation associated with a L248V amino acid switch. The point mutation activated a cryptic splice site within ABL exon 4 leading to an in-frame splice variant characterized by the loss of a 81 bp 3′ portion of exon 4. We sought to evaluate the BCR-ABL kinase activity of the splice variant and the response to tyrosine kinase inhibitors in vitro. The 81 bp deletion of p210 BCR-ABL was cloned using cDNA from one of the patients. Using this construct, retrovirally transduced Ba/F3 cells were transformed upon growth factor withdrawal. These cells expressed BCR-ABL at the transcript and protein levels. Presence of the 81 bp deletion was confirmed by sequencing. Despite the presence of the corresponding 27 amino acid P-loop deletion (Δ248–274), Western blot indicated strong autophosphorylation of BCR-ABL, which decreased in the presence of imatinib to non-detectable levels at concentrations of 1.25μM and above. In the presence of imatinib/nilotinib/dasatinib, the growth of BCR-ABL expressing Ba/F3 cells was shifted from an IC50 of 125/30/0.5nM for wild-type BCR-ABL to 470/185/1.9nM for Δ248–274 cells. Thus, in vitro data demonstrate that deletion of almost the entire P-loop does not abrogate BCR-ABL kinase activity and results in only marginal resistance towards ABL kinase inhibitors. We conclude that deletions of BCR-ABL may be the result of alternative splicing generated by point mutations associated with resistance to imatinib. The Δ248–274 splice variant retains BCR-ABL kinase activity and sensitivity to imatinib, nilotinib, and dasatinib.

Inhibition of T315I Bcr-Abl and Other Imatinib-Resistant Bcr-Abl Mutants by the Selective Abl Kinase Inhibitor SGX70393.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1373-1373 ◽  
Author(s):  
Thomas O’Hare ◽  
Christopher A. Eide ◽  
Jeffrey W. Tyner ◽  
Matthew J. Wong ◽  
Caitlyn A. Smith ◽  
...  
Keyword(s):  
Kinase Inhibitors ◽  
Kinase Inhibitor ◽  
Kinase Domain ◽  
Imatinib Resistance ◽  
Abl Kinase ◽  
Imatinib Resistant ◽  
Escape Mutants ◽  
A Cell ◽  
Almost All ◽  
Proliferation Assays

Abstract Imatinib effectively inhibits the tyrosine kinase activity of Bcr-Abl, the molecular driver of CML. Emergence of imatinib resistance due to mutations within the Bcr-Abl kinase domain (KD) has prompted the development of new Abl kinase inhibitors. A particularly important target is Bcr-Abl(T315I), which accounts for 15–20% of patients with resistance. To address this unresolved need, we profiled the novel Abl kinase inhibitor SGX70393 against native and mutant Bcr-Abl. Methods: We assessed the efficacy of SGX70393 in cellular and biochemical assays against a panel of KD mutants. Cell proliferation assays and Bcr-Abl tyrosine phosphorylation immunoblot analyses were performed for parental Ba/F3 cells, Ba/F3 cells expressing unmutated Bcr-Abl, or Ba/F3 cells expressing a single Bcr-Abl KD mutation (M244V, G250E, Q252H, Y253F, Y253H, E255K, E255V, F311L, T315I, F317L, M351T, F359V, V379I, L387M, H396P, or H396R). The resistance profile of SGX70393 was also evaluated using a recently developed accelerated, cell-based mutagenesis assay (Bradeen, et al. Blood, June 2006; doi:10.1182). Results: SGX70393 inhibited growth of cells expressing Bcr-Abl(T315I) (IC50: 7.3 nM) or unmutated Bcr-Abl (IC50: 12 nM). Sensitivity of Bcr-Abl mutants to SGX70393 partitioned into three categories: high (IC50&lt;25 nM: M244V, T315I, F359V, V379I, L387M, H396P, and H396R), medium (IC50&lt;300 nM: Q252H, Y253H, E255K, and F311L), and low (IC50&gt;500 nM: G250E, Y253F, E255V, and F317L). A cell-based mutagenesis screen for Bcr-Abl kinase domain escape mutants emerging in the presence of SGX70393 revealed a concentration-dependent reduction in surviving clones, with five previously reported Bcr-Abl mutations (L248M; G250E; Y253F; E255V; F317V) accounting for almost all resistance. Conclusions: (a) SGX70393 is a potent inhibitor of native and T315I mutant Bcr-Abl. (b) SGX70393 coverage extends to most clinically relevant mutants except mutations of the p-loop and F317.

NS-187, a potent and selective dual Bcr-Abl/Lyn tyrosine kinase inhibitor, is a novel agent for imatinib-resistant leukemia

Blood ◽  
2005 ◽  
Vol 106 (12) ◽  
pp. 3948-3954 ◽  
Author(s):  
Shinya Kimura ◽  
Haruna Naito ◽  
Hidekazu Segawa ◽  
Junya Kuroda ◽  
Takeshi Yuasa ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Tyrosine Kinase Inhibitor ◽  
Kinase Inhibitor ◽  
Inhibitory Effect ◽  
Kinase Domain ◽  
Imatinib Resistance ◽  
Abl Tyrosine Kinase ◽  
Imatinib Resistant ◽  
Novel Agent

Although the Abelson (Abl) tyrosine kinase inhibitor imatinib mesylate has improved the treatment of breakpoint cluster region–Abl (Bcr-Abl)–positive leukemia, resistance is often reported in patients with advanced-stage disease. Although several Src inhibitors are more effective than imatinib and simultaneously inhibit Lyn, whose overexpression is associated with imatinib resistance, these inhibitors are less specific than imatinib. We have identified a specific dual Abl-Lyn inhibitor, NS-187 (elsewhere described as CNS-9), which is 25 to 55 times more potent than imatinib in vitro. NS-187 is also at least 10 times as effective as imatinib in suppressing the growth of Bcr-Abl–bearing tumors and markedly extends the survival of mice bearing such tumors. The inhibitory effect of NS-187 extends to 12 of 13 Bcr-Abl proteins with mutations in their kinase domain but not to T315I. NS-187 also inhibits Lyn without affecting the phosphorylation of Src, Blk, or Yes. These results suggest that NS-187 may be a potentially valuable novel agent to combat imatinib-resistant Philadelphia-positive (Ph+) leukemia.

Bcr-Abl kinase domain mutations, drug resistance, and the road to a cure for chronic myeloid leukemia

Blood ◽  
2007 ◽  
Vol 110 (7) ◽  
pp. 2242-2249 ◽  
Author(s):  
Thomas O'Hare ◽  
Christopher A. Eide ◽  
Michael W. N. Deininger
Keyword(s):  
Chronic Myeloid Leukemia ◽  
Myeloid Leukemia ◽  
Kinase Inhibitor ◽  
Therapeutic Potential ◽  
Kinase Domain ◽  
Imatinib Resistance ◽  
The Road ◽  
Abl Kinase ◽  
Imatinib Resistant ◽  
Kinase Domain Mutations

Mutations in the kinase domain (KD) of BCR-ABL are the most prevalent mechanism of acquired imatinib resistance in patients with chronic myeloid leukemia (CML). Here we examine predisposing factors underlying acquisition of KD mutations, evidence for acquisition of mutations before and during therapy, and whether the detection of a KD mutation universally implies resistance. We also provide a perspective on how the second-line Abl inhibitors dasatinib and nilotinib are faring in the treatment of imatinib-resistant CML, especially in relation to specific KD mutations. We discuss the growing importance of the multi-inhibitor–resistant 315T>I mutant and the therapeutic potential that a 315T>I inhibitor would have. Last, we assess the potential of Abl kinase inhibitor combinations to induce stable responses even in advanced CML and interpret the emerging data in the context of CML pathogenesis.

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