Comparison of Imatinib, AMN107 and Dasatinib in an Accelerated Cell-Based Mutagenesis Screen.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 691-691 ◽  
Author(s):  
Michael W.N. Deininger ◽  
Heather Bradeen ◽  
Taiping Jia ◽  
Thomas O’Hare ◽  
Stephanie G. Willis ◽  
...  
Keyword(s):  
Structural Changes ◽  
Kinase Inhibitors ◽  
Kinase Domain ◽  
Abl Kinase ◽  
Drug Concentrations ◽  
A Cell ◽  
Vitro Model ◽  
Proliferation Assays ◽  
Abl Kinase Inhibitors

Abstract Background. Mutations in the Bcr-Abl kinase domain (KD) are the leading cause of acquired imatinib (IM) resistance. Dasatinib (BMS354825) and AMN107 are potent alternate Abl inhibitors with activity at nanomolar levels against wild type Bcr-Abl and most KD mutants, with the exception of T315I. In a cell-line based mutagenesis assay we compared incidence and type of Bcr-Abl mutants emerging in the presence of IM, AMN107 and dasatinib. Methods. BaF3-p210Bcr-Abl cells were mutagenized by 24 hours exposure to 0.42 μM N-ethyl-N-nitrosourea (ENU), a dose with minimal cytotoxicity. After ENU washout cells were seeded at 5 x 105/well in 96-well plates and observed for growth for up to 4 weeks. Cells from wells with growth were expanded and subjected to BCR-ABL KD sequencing. Results: The frequency of wells with growth decreased with higher doses of all 3 inhibitors (table 1) and growth tended to occur later. Only isolated wells had growth without ENU exposure. At ≥2 μM IM (2-fold the IC90 in cell proliferation assays) 18 different mutations were seen, with highly resistant mutants prevailing at higher concentrations (table 2). At 50 nM AMN107 (2-fold the IC90) Y253H, G250E, F359C, E255K, L384M, L387F, E292V and T315I were detected, at 500 nM Y253H, E255V and T315I were recovered and only T315I at 2000 nM. At 5 nM dasatinib (2-fold the IC90), E255K, L284V, F317V were detected in addition to T315I, at 10 nM T315I, F317V/I and V299L were found and at 25 nM only T315I. All resistant clones growing out at ≥4 μM IM, 500 nM AMN107 or 10 nM dasatinib were KD mutant, suggesting that KD mutations were the sole cause of the observed resistance. Conclusions: (i) At drug concentrations corresponding to 2-fold IC9018 different mutations were recovered with IM, 9 with AMN107 and 6 with dasatinib, suggesting that the conformational requirements for dasatinib binding to Abl may be least stringent. If free plasma trough levels ≥25 nM dasatinib or ≥2000 nM AMN107 are achievable, the only mutant predicted to emerge clinically is T315I. (ii) No additional mutations were observed with AMN107 compared to IM, suggesting the structural changes in AMN107 compared to IM did not generate novel vulnerable sites. (iii) At least in this in vitro model, resistance to Abl kinase inhibitors is entirely dependent on Bcr-Abl, despite the fact that ENU treatment is expected to induce multiple additional mutations. Thus a T315I inhibitor combined with AMN107 or dasatinib may be effective at preventing the emergence of resistance to Abl kinase inhibitors. Table 1 Recovery of resistant clones (representative experiment) Imatinib (microM) Wells with mutations/wells sequenced/wells with growth Dasatinib (nM) Wells with mutations/wells sequenced/wells with growth AMN107 (nM) Wells with mutations/wells sequenced/wells with growth 2 62/62/82 5 8/24/96 10 0/24/96 4 74/74/74 10 38/38/56 50 20/24/96 8 27/27/42 25 22/22/24 500 45/45/46 16 12/12/12 100 20/20/21 2000 23/23/24 Table 2 Percentage of resistant clones with T315I mutations Imatinib (μM) number of different mutations/% T315I Dasatinib (nM) number of different mutations/% T315I AMN107 (nM) number of different mutations/% T315I 2 16/27.8 5 4/16.7 10 0/0.0 4 7/43.2 10 3/63.2 50 8/20.8 8 4/37.4 25 1/100 500 3/62.0 16 4/50.0 100 1/100.0 2000 1/100.0

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<25 nM: M244V, T315I, F359V, V379I, L387M, H396P, and H396R), medium (IC50<300 nM: Q252H, Y253H, E255K, and F311L), and low (IC50>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.

FGF2 Mediates Resistance In CML Patients In The Absence Of Kinase Domain Mutations, and Resistance Is Overcome By Ponatinib

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 3983-3983
Author(s):  
Elie Traer ◽  
Nathalie Javidi-Sharifi ◽  
Anupriya Agarwal ◽  
Jennifer B Dunlap ◽  
Isabel English ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Stromal Cells ◽  
Kinase Inhibitors ◽  
K562 Cells ◽  
Kinase Domain ◽  
Bone Marrow Microenvironment ◽  
Abl Kinase ◽  
Mechanism Of Resistance ◽  
Kinase Domain Mutations

Abstract Background Development of resistance to kinase inhibitors remains a challenge in chronic myeloid leukemia (CML). Kinase domain mutations are a common mechanism of resistance, yet the mechanism of resistance in the absence of mutations remains less clear. Recent evidence suggests that the bone marrow microenvironment provides a sanctuary for leukemia cells, and may be involved in mediating resistance to imatinib – particularly in the absence of BCR-ABL kinase domain mutations. We tested selected cytokines, growth factors, and extracellular matrix proteins expressed by cells in the bone marrow microenvironment for their ability to protect CML cells from imatinib. Results We found that fibroblast growth factor 2 (FGF2) was the most protective protein for the K562 CML cell line when exposed to imatinib. FGF2 was not only capable of promoting growth in short-term culture, but uniquely able to promote long-term resistance in vitro (p<0.0001 by 2-way ANOVA analysis). To analyze the mechanism of resistance, we used siRNA to target the FGF receptors 1-4 and found that only siRNA targeting FGFR3 was able to abrogate the protective effect of FGF2. Phospho-chip and Western blot analysis revealed that FGF2 binds FGFR3, which then signals the downstream kinases Ras, c-RAF, MEK1, and ERK1/2 to promote survival in the presence of imatinib. Inhibition of FGFR3 with the specific FGFR inhibitor PD173074 led to dephosphorylation of this signaling cascade, and restored sensitivity to imatinib of FGF2-mediated resistant K562 cells. Resistance could also be overcome with ponatinib, a multi-kinase inhibitor that targets both BCR-ABL and FGFR, whereas imatinib, nilotinib and dasatinib were all ineffective against FGF2-mediated resistant K562 cells. Although ponatinib was rationally designed to circumvent the BCR-ABL T315I gatekeeper mutation, it was also able to achieve major cytogenetic responses in 62% of patients without detectable kinase domain mutations in the recent PACE trial. We theorized that increased FGF2 may drive resistance in the subset of patients without kinase domain mutations who respond to ponatinib, similar to our in vitro findings. To evaluate this possibility, we identified patients without kinase domain mutations who were responsive to ponatinib and quantified bone marrow FGF2 by immunohistochemistry. In comparison to ponatinib-responsive patients with kinase domain mutations, patients without kinase domain mutations had increased FGF2 in their bone marrow (50.5% versus 36.6%, p=0.033). Moreover, FGF2 in the marrow decreased concurrently with response to ponatinib, further suggesting that FGF2-mediated resistance is interrupted by FGFR inhibition (-15.9% versus 0.8%, when compared to the change in FGF2 of patients with kinase domain mutations, p=0.012). Qualitatively, FGF2 was predominantly localized in supportive stromal cells (consistent with previous reports), supporting a paracrine mechanism of resistance. Furthermore, we also evaluated a single patient without kinase domain mutations who was resistant to ponatinib. In this patient’s marrow, there was no elevation in FGF2 or change in FGF2 with ponatinib treatment. Taken together, inhibition of FGFR appears to be critical for the clinical activity of ponatinib in patients without kinase domain mutations. Conclusions In summary, our data supports a model of resistance in which FGF2 production by the marrow stromal cells promotes resistance to multiple ABL kinase inhibitors without the need for mutation of the ABL kinase domain. Resistance occurs via FGF2 ligand-induced activation of the FGFR3/Ras/MAPK pathway, and can be overcome by concomitant inhibition of ABL and FGFR. In combination with recent clinical data with ponatinib, our data suggest that FGF2-mediated resistance is a major mechanism of resistance in CML patients without kinase domain mutations. These results illustrate the clinical importance of ligand-induced resistance to kinase inhibitors and support an approach of developing rational inhibitor combinations to circumvent resistance, particularly in other kinase-driven malignancies that routinely develop resistance to kinase inhibitors. Disclosures: Tyner: InCyte Corporation: Research Funding. Druker:Novartis, Bristol-Myers Squibb, & ARIAD: Novartis, BMS & ARIAD clin trial funding. OHSU holds contracts; no salary/lab research funds. OHSU & Druker have financial interest in MolecularMD; technology used in some studies licensed to MolecularMD. This conflict reviewed and managed by OHSU. Other.

Rac GTPases Are Potential Therapeutic Targets in p210-BCR-ABL-Induced Myeloproliferative Disease (MPD).

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 465-465
Author(s):  
Emily K. Thomas ◽  
Jose A. Cancelas ◽  
Heedon Chae ◽  
Adrienne D. Cox ◽  
Patricia J. Keller ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Median Survival ◽  
Peripheral Blood ◽  
Kinase Inhibitors ◽  
Abl Kinase ◽  
Rac Gtpases ◽  
Imatinib Resistant ◽  
Abl Kinase Inhibitors

Abstract The p210-BCR-ABL fusion protein is a constitutively active tyrosine kinase that is necessary and sufficient for the development of chronic myelogenous leukemia (CML). ABL-kinase inhibitors such as imatinib mesylate (Gleevec, STI571) potently block BCR-ABL activation, but the continued presence of leukemic stem cells and the emergence of imatinib-resistant BCR-ABL mutants suggest that ABL kinase inhibitors alone cannot completely eradicate disease. Rac GTPases have been implicated in BCR-ABL-mediated proliferation in cell lines and regulate many of the same signaling pathways as BCR-ABL, suggesting that these proteins could be additional therapeutic targets in CML. We have found that Rac1, Rac2, and, to a lesser extent, Rac3 were hyperactivated in CD34+ cells purified from the peripheral blood of two CML patients. To better study the role of Rac in BCR-ABL disease development, murine hematopoietic stem cells (HSC) genetically deficient in Rac1 and/or Rac2 were transduced with a retroviral vector expressing p210-BCR-ABL. Wild type (WT) and Rac1−/− mice experienced similar disease progression [median survival 23 ± 6 days (n=30) and 22 ± 4 days (n=8), respectively], Rac2−/− mice exhibited significantly attenuated development of BCR-ABL-mediated MPD [median survival 43 ± 27 days (n=18); p<0.001], and Rac1−/−;Rac2−/− animals showed markedly prolonged survival [median survival 92 ± 34 days (n=19); p<0.001]. p210-BCR-ABL WT, Rac1−/−, and Rac2−/− mice had elevated circulating myeloblasts 30 days post-transplant, while Rac1−/−;Rac2−/− mice had normal peripheral blood morphology. Attenuation of disease in Rac2- and Rac1/Rac2-deficient animals correlated with severely diminished activation of BCR-ABL-induced signaling pathways, including p44/42 and p38 ERK, JNK, CrkL, and Akt. The leukemogenesis impairment induced by Rac deficiency did not appear to be due to loss of p210-BCR-ABL vector integration, as clonal analysis of leukemic bone marrow from mice in each genotype by LAM-PCR showed similar, oligoclonal reconstitution of p210-BCR-ABL expressing cells. Interestingly, bone marrow cells obtained from Rac1/Rac2-deficient animals that developed late leukemia showed marked hyperactivation of Rac3 and initiated disease in recipients with a latency of three weeks, suggesting that leukemia-initiating cells were able to engraft, in spite of Rac1/Rac2 deficiency. Treatment of BCR-ABL-expressing murine HSC with NSC23766, a rationally-designed Rac-specific small molecule antagonist, potently inhibited cell proliferation in vitro and increased the survival of leukemic animals treated in vivo, compared to PBS control-treated animals (p<0.05). NSC23766 also inhibited the growth of an imatinib-resistant p210-BCR-ABL-T315I-expressing Ba/F3 leukemic cell line by 90%, compared to <5% by imatinib alone, blocked the growth of primary human chronic phase Rac-hyperactivated CML blast colonies by 80% in vitro, and inhibited survival of these cells in NOD-SCID mice. These results suggest that individual Rac proteins play both unique and combinatorial roles in stem cell transformation and may represent unique targets for therapy of BCR-ABL-persistent and imatinib-resistant CML.

Dynamics of BCR-ABL kinase domain mutations in chronic myeloid leukemia after sequential treatment with multiple tyrosine kinase inhibitors

Blood ◽  
2007 ◽  
Vol 110 (12) ◽  
pp. 4005-4011 ◽  
Author(s):  
Jorge Cortes ◽  
Elias Jabbour ◽  
Hagop Kantarjian ◽  
C. Cameron Yin ◽  
Jianqin Shan ◽  
...  
Keyword(s):  
Chronic Myeloid Leukemia ◽  
Tyrosine Kinase ◽  
Tyrosine Kinase Inhibitors ◽  
Myeloid Leukemia ◽  
Kinase Inhibitors ◽  
Kinase Domain ◽  
Differential Sensitivity ◽  
Mutation Site ◽  
Abl Kinase

AbstractDasatinib and nilotinib are potent tyrosine kinase inhibitors (TKIs) with activity against many imatinib-resistant chronic myeloid leukemia (CML) clones with BCR-ABL kinase domain (KD) mutations, except T315I. We assessed for changes in the BCR-ABL KD mutation status in 112 patients with persistent CML who received a second-generation TKI after imatinib failure. Sixty-seven different KD mutations were detected before the start of therapy with a second TKI, with T315I seen in 15%. Equal numbers of patients received nilotinib or dasatinib following imatinib, and 18 received 3 TKIs. Response rates were similar for patients with and without mutations, regardless of mutation site except for T315I. Overall, 29 patients (26%) developed new KD mutations after therapy with a second (n = 24) or third (n = 5) TKI, but only 4 (4%) developed T315I. In 73% of cases, the KD mutations that persisted or developed following switch to new TKI were at sites also found in prior in vitro TKI mutagenesis assays. Although there is only a mild increase in mutation frequency with sequential TKI treatment, novel mutations do occur and mutation regression/acquisition/persistence generally reflects the in vitro differential sensitivity predicted for each TKI. In this study, there was no marked increase in development of T315I.

Synthesis and in vitro examination of [124I]-, [125I]- and [131I]-2-(4-iodophenylamino) pyrido[2,3-d]pyrimidin-7-one radiolabeled Abl kinase inhibitors

2005 ◽  
Vol 32 (4) ◽  
pp. 313-321 ◽  
Author(s):  
Darren R. Veach ◽  
Mohammad Namavari ◽  
Tatiana Beresten ◽  
Julius Balatoni ◽  
Maria Minchenko ◽  
...  
Keyword(s):  
Kinase Inhibitors ◽  
Abl Kinase ◽  
Abl Kinase Inhibitors ◽  
In Vitro Examination

A Cell-Based Screening Method for Resistance of Bcr-Abl Positive Leukemia Identifies the Mutation Pattern for an Alternative Abl Kinase Inhibitor.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 558-558
Author(s):  
Nikolas von Bubnoff ◽  
Darren R. Veach ◽  
Heiko van der Kuip ◽  
Walter E. Aulitzky ◽  
Jana Saenger ◽  
...  
Keyword(s):  
Kinase Inhibitors ◽  
Screening Method ◽  
Point Mutations ◽  
Kinase Domain ◽  
Screening Strategy ◽  
Culture Conditions ◽  
Cross Resistance ◽  
Imatinib Resistance ◽  
Abl Kinase ◽  
A Cell

Abstract The increasing impact of targeted cancer treatment demands strategies to identify and evaluate resistance mechanisms toward kinase inhibitors prior to their therapeutic application. Point mutations within the Bcr-Abl kinase domain constitute the major mechanism of resistance toward imatinib mesylate in Philadelphia-positive (Ph+) leukemia. Using Bcr-Abl-transformed Ba/F3 cells, we established a cell-based screening strategy for the prediction of specific kinase mutations that cause resistance toward kinase inhibitors. With imatinib at clinically relevant concentrations, we generated 368 resistant Ba/F3 sublines that were derived from resistant colonies. Thirty-two different single point mutations within the kinase domain of Bcr-Abl were identified in twenty-five per cent (liquid culture conditions) and seventy-two per cent (solid culture conditions) of these lines at known and novel positions. Using imatinib, the pattern and relative frequency of mutations reflected matters observed in patients with imatinib resistance. We then applied this screen to the pyrido-pyrimidine PD166326 (PD16), an investigational Abl kinase inihibitor. Compared to imatinib, we observed a five to seven times lower frequency of resistant colonies with equipotent concentrations of PD16. In addition, PD16 produced a distinct pattern of Bcr-Abl mutations. P-loop, A-loop and the known imatinib contact site T315 were affected with both inhibitors, whereas C-helix and SH2 contact sites were affected in imatinib resistant colonies exclusively. In contrast to imatinib, where kinase domain mutations were still widely distributed over the kinase domain even at at 4μM, mutations observed with PD16 at a concentration of 100nM narrowed to the exchange at position T315 to iseulicine. We did not detect mutations outside the kinase domain. Some resistant sublines displayed increased Bcr-Abl activity. Mutations that were derived from the screen were cloned and examined for the extent of cross-resistance to both inhibitors. The majority of mutations were effectively suppressed by PD16 at 50–500nM. In contrast, only few mutations were inhibited by imatinib at 5–10μM. However, exchanges at position F317 mediated resistance toward PD16, but were inhibited by standard concentrations of imatinib. Since this cell-based system produced results that are clinically significant, it may be used to predict resistance mutations in Bcr-Abl and other oncogenic kinases like cKit, EGFR, FIP1L1-PDGFRalpha or FLT3 towards clinically applicated and investigational drugs. Thus, this robust and simple screening strategy provides a rational basis for combinatorial and sequential treatment strategies.

Dynamics of BCR-ABL Kinase Domain Mutations in Patients with Chronic Myeloid Leukemia (CML) after Treatment with One, Two or Three Tyrosine Kinase Inhibitors (TKI).

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 750-750 ◽  
Author(s):  
Elias Jabbour ◽  
Dan Jones ◽  
Hagop Kantarjian ◽  
Susan O’Brien ◽  
Guillermo Garcia-Manero ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Tyrosine Kinase Inhibitors ◽  
Kinase Inhibitors ◽  
Kinase Domain ◽  
Imatinib Resistance ◽  
Mutation Status ◽  
Abl Kinase ◽  
Kinase Domain Mutations ◽  
New Mutations

Abstract Dasatinib (D) and nilotinib (N) are potent tyrosine kinase inhibitors (TKIs) with activity against many imatinib (IM) resistant BCR-ABL kinase domain mutants, except T315I. In vitro mutant models have selected specific mutations occurring after incubation with IM, D and N. Therapy with these new TKI may select for patients with T315I or other mutations relatively insensitive to them. We assessed the change in mutation status of the bcr-abl kinase domain (codons 220 to 500) in 113 patients (pts) with CML who received therapy with D and/or N after imatinib failure. Median age was 60 years (range, 21 to 82 years). Seventy-one (63%) pts received prior interferon (IFN). Median time on imatinib was 28 months (range, 2 to 78 months). At the time of imatinib failure, mutations were detected in 46 of 85 (54%) pts who had DNA sequencing. The evolution of mutations after a second TKI was as follows (Table 1). Twenty pts received a third TKI after failing IM and a second TKI. The evolution of mutations in this cohort was as follows (Table 2). Overall, 19 of 101 evaluable pts (19%), cases had new mutations emerge following TKI switch 17 after a 2nd TKI (12 nilotinib, 5 dasatinib), and 2 after a 3rd TKI (2 dasatinib). We analyzed whether these N- and D-associated new mutations were at sites that have been detected following D and N treatment in vitro (Burgess et al, PNAS 2005; Bradeen et al, Blood 2006; Von Bubnoff et al, Blood 2006). Only 14/46 (30%) kinase domain mutations that developed after D (7) or N (7) corresponded with an in vitro-identified site. Only 5 of 134 (4%) mutations identified were T315I (3 after dasatinib, 2 after nilotinib), but the mutation status of these patients was unknown after IM. We conclude that the spectrum of mutations that develops in vivo after TKI switch is broader and includes common imatinib-resistance sites as well. There appears to no marked increase in the incidence of T315I mutation after TKI switch. Table 1. Dynamics of mutations after 2nd TKI Post IM mutation No. Post-2nd TKI Mutation (New + Same + Lost) *1 pt acquired new mutation with persistence of pre-existing mutation, 1 lost 3 mutations and acquired 1, and 1 pt lost 2 mutations. Nilotinib Dasatinib Absent 39 8+NA+NA/21 3+NA+NA/18 Present 46 3+20+3/26 2+16+2*/20 Unknown 28 8/9 13/19 Table 2. Dynamics of mutations after 3rd TKI Post IM mutation No. Post-3nd TKI Mutation (compared to status after 2nd TKI) (New + Same + Lost) Nilotinib Dasatinib Absent 5 0/1 1+NA+NA/4 Present 12 0+1+0/1 2+6+3/11 Unknown 3 1/3 NA

DCC-2036: A Novel Switch Pocket Inhibitor of ABL Tyrosine Kinase with Therapeutic Efficacy Against BCR-ABL T315I In Vitro and in a CML Mouse Model.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 463-463 ◽  
Author(s):  
Richard A. Van Etten ◽  
Wayne W. Chan ◽  
Virginia M. Zaleskas ◽  
Peter Evangelista ◽  
Katherine Lazarides ◽  
...  
Keyword(s):  
Kinase Inhibitors ◽  
De Novo ◽  
Acquired Resistance ◽  
Peripheral Blood Leukocyte ◽  
Kinase Domain ◽  
Leukemic Cells ◽  
Prolonged Survival ◽  
Structure Based Drug Design ◽  
Abl Kinase

Abstract Therapy with ATP-competitive ABL kinase inhibitors, including imatinib (Gleevec), dasatinib (Sprycel), and nilotinib (Tasigna), has revolutionized the treatment of chronic myeloid leukemia (CML), but a substantial proportion of patients develop resistance to these agents. A major mechanism of acquired resistance is mutations in the ABL kinase domain that render BCR-ABL insensitive to the drug; in particular, mutation of the ABL kinase “gatekeeper” Thr315 residue to Ile (T315I) confers pan-resistance to all ATP-competitive ABL inhibitors. To address this need, we developed and characterized a novel chemical class of compounds that bind to five structural pockets involved in the endogenous “switch” mechanism used by the ABL kinase to conformationally control its activity state. Using a structure-based drug design approach, diversity in these “switch pockets” between kinases can be exploited to develop inhibitors with high potency and specificity. The resulting ABL inhibitors have several attractive features, as they: act through a non-ATP-competitive mechanism; avoid steric clash with Ile315; inhibit purified ABL that is either unphosphorylated (switch-off) or phosphorylated (switch-on) at Tyr393 with IC50 of 0.8–4.0 nM; co-crystallize with phospho-Y393-ABL WT and T315I; and have very prolonged residency time on the kinase (off-rate ∼400 min vs. 3 min for imatinib). A lead compound, DCC-2036, is highly selective for ABL, FLT3, and SRC family kinases, and has favorable pharmacokinetic and toxicity profiles in animals. In vitro, DCC-2036 inhibited proliferation and induced apoptosis of Ba/F3 cells expressing BCR-ABL WT or several common imatinib-resistant mutants (Y253F, T315I, M351T) with IC50 from 5 to 25 nM, without appreciable inhibition of parental Ba/F3 cells in IL-3 (IC50 >1000 nM). In Balb/c mice injected with Ba/F3-BCR-ABL T315I cells, pharmacodynamic studies indicated >8 hour inhibition of phospho-Stat5 and phospho-ABL in the leukemic cells following a single oral 100 mg/kg dose of DCC-2036, whereas daily dosing of DCC-2036 significantly prolonged survival. In the mouse retroviral bone marrow transduction/transplantation model of CML, DCC-2036 at 100 mg/kg/d also reduced peripheral blood leukocyte counts and significantly prolonged survival vs. vehicle-treated control mice. These results demonstrate that ABL switch pocket inhibitors are a promising new pharmacologic weapon for the treatment of de novo and drug-resistant CML, including BCR-ABL T315I.

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.

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