Sebastian Kreil

Bio: Sebastian Kreil is an academic researcher from Heidelberg University. The author has contributed to research in topics: Transplantation & Imatinib mesylate. The author has an hindex of 19, co-authored 50 publications receiving 3357 citations. Previous affiliations of Sebastian Kreil include University of Mannheim & Salisbury District Hospital.

Molecular and chromosomal mechanisms of resistance to imatinib (STI571) therapy.

Abstract: Selective inhibition of the BCR-ABL tyrosine kinase by imatinib (STI571, Glivec/Gleevec) is a promising new therapeutic strategy in patients with chronic myelogenous leukemia (CML). Despite significant hematologic and cytogenetic responses, resistance occurs, particularly in patients with advanced disease. We sought to determine the underlying mechanisms. Sixty-six patients with CML in myeloid blast crisis (n = 33), lymphoid blast crisis (n = 2), accelerated phase (n = 16), chronic phase (n = 13), and BCR-ABL-positive acute lymphoblastic leukemia (n = 2) resistant to imatinib were investigated. Median duration of imatinib therapy was 148 days (range 6-882). Patients were evaluated for genomic amplification of BCR-ABL, overexpression of BCR-ABL transcripts, clonal karyotypic evolution, and mutations of the imatinib binding site in the BCR-ABL tyrosine kinase domain. Results were as follows: (1) Median levels of BCR-ABL transcripts, were not significantly changed at the time of resistance but 7/55 patients showed a >10-fold increase in BCR-ABL levels; (2) genomic amplification of BCR-ABL was found in 2/32 patients evaluated by fluorescence in situ hybridization; (3) additional chromosomal aberrations were observed in 19/36 patients; (4) point mutations of the ABL tyrosine kinase domain resulting in reactivation of the BCR-ABL tyrosine kinase were detected in 23/66 patients. In conclusion, although the heterogeneous development of imatinib resistance is challenging, the fact that BCR-ABL is active in many resistant patients suggests that the chimeric oncoprotein remains a good therapeutic target. However, patients with clonal evolution are more likely to have BCR-ABL-independent mechanisms of resistance. The observations warrant trials combining imatinib with other agents.

Early reduction of BCR-ABL mRNA transcript levels predicts cytogenetic response in chronic phase CML patients treated with imatinib after failure of interferon alpha.

Abstract: The degree of tumor load reduction as measured by cytogenetic response is an important prognostic factor for chronic myelogenous leukemia (CML) patients on therapy. We sought to determine whether BCR-ABL transcript levels can predict chromosomal response. Residual disease was evaluated in 120 CML patients in chronic phase (CP) treated with the selective tyrosine kinase inhibitor imatinib after resistance or intolerance to interferon alpha (IFN). Median time of therapy was 401 days (range 111-704). BCR-ABL and total ABL transcripts were measured in 486 peripheral blood (PB) specimens with a real time RT-PCR approach using fluorescent-labeled hybridization probes (LightCycler technology) and results were expressed as the ratio BCR-ABL/ABL. Cytogenetic response was determined in 3-monthly intervals: From 101 evaluable patients, 42 achieved a complete (CR, 0% Philadelphia chromosome (Ph)- positive metaphases), 18 a partial (PR, 1-34% Ph+), 13 a minor (MR, 35-94% Ph+), and 26 no response (NR, >94% Ph+). All PB samples were RT-PCR positive. The proportion of Ph+ metaphases and simultaneous BCR-ABL/ABL ratios correlated with r = 0.74, P < 0.0001. In order to investigate whether early molecular analysis may predict cytogenetic response, quantitative RT-PCR data obtained after 1 and 2 months of therapy were compared with cytogenetic response at 6 months. BCR-ABL/ABL ratios after 1 month were not predictive, but results after 2 months correlated with the consecutive cytogenetic response (P = 0.0008). The probability for a major cytogenetic response was significantly higher in patients with a BCR-ABL/ABL ratio <20% after 2 months of imatinib therapy. We conclude that: (1) quantitative determination of residual disease with real time RT-PCR is a reliable and sensitive method to monitor CML patients on imatinib therapy; (2) BCR-ABL/ABL ratios correlate well with cytogenetic response; (3) in IFN-pretreated patients all complete responders to imatinib have evidence of residual disease with the limited follow-up available; and (4) cytogenetic response at 6 months of therapy in CP patients is predictable with real time RT-PCR at 2 months.

Hematopoietic Stem-Cell Transplantation for Advanced Systemic Mastocytosis

Abstract: Purpose Advanced systemic mastocytosis (SM), a fatal hematopoietic malignancy characterized by drug resistance, has no standard therapy. The effectiveness of allogeneic hematopoietic stem-cell transplantation (alloHCT) in SM remains unknown.

MET Amplification Leads to Gefitinib Resistance in Lung Cancer by Activating ERBB3 Signaling

Abstract: The epidermal growth factor receptor (EGFR) kinase inhibitors gefitinib and erlotinib are effective treatments for lung cancers with EGFR activating mutations, but these tumors invariably develop drug resistance. Here, we describe a gefitinib-sensitive lung cancer cell line that developed resistance to gefitinib as a result of focal amplification of the MET proto-oncogene. inhibition of MET signaling in these cells restored their sensitivity to gefitinib. MET amplification was detected in 4 of 18 (22%) lung cancer specimens that had developed resistance to gefitinib or erlotinib. We find that amplification of MET causes gefitinib resistance by driving ERBB3 (HER3)–dependent activation of PI3K, a pathway thought to be specific to EGFR/ERBB family receptors. Thus, we propose that MET amplification may promote drug resistance in other ERBB-driven cancers as well.

Kinase Mutations and Imatinib Response in Patients With Metastatic Gastrointestinal Stromal Tumor

Abstract: Purpose: Most gastrointestinal stromal tumors (GISTs) express constitutively activated mutant isoforms of KIT or kinase platelet-derived growth factor receptor alpha (PDGFRA) that are potential therapeutic targets for imatinib mesylate. The relationship between mutations in these kinases and clinical response to imatinib was examined in a group of patients with advanced GIST. Patients and Methods: GISTs from 127 patients enrolled onto a phase II clinical study of imatinib were examined for mutations of KIT or PDGFRA. Mutation types were correlated with clinical outcome. Results: Activating mutations of KIT or PDGFRA were found in 112 (88.2%) and six (4.7%) GISTs, respectively. Most KIT mutations involved exon 9 (n = 23) or exon 11 (n = 85). All KIT mutant isoforms, but only a subset of PDGFRA mutant isoforms, were sensitive to imatinib, in vitro. In patients with GISTs harboring exon 11 KIT mutations, the partial response rate (PR) was 83.5%, whereas patients with tumors containing an exon 9 KIT mutation ...

Overriding Imatinib Resistance with a Novel ABL Kinase Inhibitor

Abstract: Resistance to the ABL kinase inhibitor imatinib (STI571 or Gleevec) in chronic myeloid leukemia (CML) occurs through selection for tumor cells harboring BCR-ABL kinase domain point mutations that interfere with drug binding. Crystallographic studies predict that most imatinib-resistant mutants should remain sensitive to inhibitors that bind ABL with less stringent conformational requirements. BMS-354825 is an orally bioavailable ABL kinase inhibitor with two-log increased potency relative to imatinib that retains activity against 14 of 15 imatinib-resistant BCR-ABL mutants. BMS-354825 prolongs survival of mice with BCR-ABL-driven disease and inhibits proliferation of BCR-ABL-positive bone marrow progenitor cells from patients with imatinib-sensitive and imatinib-resistant CML. These data illustrate how molecular insight into kinase inhibitor resistance can guide the design of second-generation targeted therapies.

Somatic Mutations of Calreticulin in Myeloproliferative Neoplasms

Abstract: BACKGROUND Approximately 50 to 60% of patients with essential thrombocythemia or primary myelofibrosis carry a mutation in the Janus kinase 2 gene (JAK2), and an additional 5 to 10% have activating mutations in the thrombopoietin receptor gene (MPL). So far, no specific molecular marker has been identified in the remaining 30 to 45% of patients. METHODS We performed whole-exome sequencing to identify somatically acquired mutations in six patients who had primary myelofibrosis without mutations in JAK2 or MPL. Resequencing of CALR, encoding calreticulin, was then performed in cohorts of patients with myeloid neoplasms. RESULTS Somatic insertions or deletions in exon 9 of CALR were detected in all patients who underwent whole-exome sequencing. Resequencing in 1107 samples from patients with myeloproliferative neoplasms showed that CALR mutations were absent in polycythemia vera. In essential thrombocythemia and primary myelofibrosis, CALR mutations and JAK2 and MPL mutations were mutually exclusive. Among patients with essential thrombocythemia or primary myelofibrosis with nonmutated JAK2 or MPL, CALR mutations were detected in 67% of those with essential thrombocythemia and 88% of those with primary myelofibrosis. A total of 36 types of insertions or deletions were identified that all cause a frameshift to the same alternative reading frame and generate a novel C-terminal peptide in the mutant calreticulin. Overexpression of the most frequent CALR deletion caused cytokine-independent growth in vitro owing to the activation of signal transducer and activator of transcription 5 (STAT5) by means of an unknown mechanism. Patients with mutated CALR had a lower risk of thrombosis and longer overall survival than patients with mutated JAK2. CONCLUSIONS Most patients with essential thrombocythemia or primary myelofibrosis that was not associated with a JAK2 or MPL alteration carried a somatic mutation in CALR. The clinical course in these patients was more indolent than that in patients with the JAK2 V617F mutation. (Funded by the MPN Research Foundation and Associazione Italiana per la Ricerca sul Cancro.)