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The FLT3 Tyrosine Kinase in Leukemia: Deciphering the Downstream Signaling Events and Drug-Escape Mechanisms
Linköping University, Department of Clinical and Experimental Medicine, Experimental Hematology. Linköping University, Faculty of Health Sciences.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Acute myeloid leukemia (AML) is a severe disease, which originates in blood-forming cells. Although major advances in understanding the biology of AML, the majority of patients eventually succumb to the disease. The tyrosine kinase receptor FLT3 has become an attractive therapeutic target AML for two major reasons; 1) It is one of the most frequently mutated genes in AML (about 30%). 2) Most of these mutations (FLT3-ITDs) correlate with an increased risk of relapse and poor overall survival. Small targeting inhibitors towards FLT3 have been designed and evaluated in clinical trials. However, the experiences from clinical trials are that drug resistance develops in a substantial number of patients. To overcome these resistance-associated problems it its important to improve the understanding of how FLT3 mutations function and how they respond to targeting drugs. This was addressed in this thesis by elucidating FLT3-ITD cell transformation mechanisms, identifying key downstream target molecules of mutated FLT3 and exploring the effect of various targeting inhibitors. The major finding of my thesis is that FLT3-targeting drugs elicit apoptosis through a FOXO3a-dependent upregulation of proapoptotic BH3-only protein Bim via inactivation of the PI3K/AKT signaling pathway. Furthermore, we have identified an interesting apoptotic mechanism, linked to increased ROS levels caused by expressing hyperactivated AKT in hematopoietic stem cells and bone marrow progenitor cells from FLT3-ITD transgenic mice. These findings are interesting from a therapeutic point of view. We have also shown that canertinib, an inhibitor of the ERBB receptor family, targets mutated FLT3 in vitro and in vivo. The irreversible binding mechanism of canertinib, as well as its multikinase activity, is attractive features. Overall, the results presented herein could provide basis for future directions in treatment of FLT3 mutant positive AML patients. Finally, we studied nine different FLT3-ITD mutations ranging in length from 6-33 amino acids. Data from this study suggest that different FLT3-ITDs may induce distinct degrees of transformation and that they respond differentially to FLT3-targeting drugs. These differences were not associated with size of the duplication but rather the mutational composition. In conclusion, this thesis explores the biologic features of FLT3 mutations and therapeutic targeting opportunities.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 69 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1355
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-88202ISBN: 978-91-7519-685-5 (print)OAI: oai:DiVA.org:liu-88202DiVA: diva2:602086
Public defence
2013-02-26, Nils Holgersalen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:15 (Swedish)
Opponent
Supervisors
Available from: 2013-01-31 Created: 2013-01-31 Last updated: 2017-07-07Bibliographically approved
List of papers
1. BH3-only protein Bim more critical than Puma in tyrosine kinase inhibitor-induced apoptosis of human leukemic cells and transduced hematopoietic progenitors carrying oncogenic FLT3.
Open this publication in new window or tab >>BH3-only protein Bim more critical than Puma in tyrosine kinase inhibitor-induced apoptosis of human leukemic cells and transduced hematopoietic progenitors carrying oncogenic FLT3.
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2009 (English)In: Blood, ISSN 0006-4971, E-ISSN 1528-0020, Vol. 113, no 10, 2302-2311 p.Article in journal (Refereed) Published
Abstract [en]

Constitutively activating internal tandem duplications (ITD) of FLT3 (FMS-like tyrosine kinase 3) are the most common mutations in acute myeloid leukemia (AML) and correlate with poor prognosis. Receptor tyrosine kinase inhibitors targeting FLT3 have developed as attractive treatment options. Because relapses occur after initial responses, identification of FLT3-ITD–mediated signaling events are important to facilitate novel therapeutic interventions. Here, we have determined the growth-inhibitory and proapototic mechanisms of 2 small molecule inhibitors of FLT3, AG1295 or PKC412, in hematopoietic progenitor cells, human leukemic cell lines, and primary AML cells expressing FLT3-ITD. Inactivation of the PI3-kinase pathway, but not of Ras–mitogen-activated protein (MAP) kinase signaling, was essential to elicit cytotoxic responses. Both compounds induced up-regulation of proapoptotic BH3-only proteins Bim and Puma, and subsequent cell death. However, only silencing of Bim, or its direct transcriptional activator FOXO3a, abrogated apoptosis efficiently. Similar findings were made in bone marrow cells from gene-targeted mice lacking Bim and/or Puma infected with FLT3-ITD and treated with inhibitor, where loss of Puma only provided transient protection from apoptosis, but loss of Bim preserved clonal survival upon FLT3-ITD inhibition.

 

Place, publisher, year, edition, pages
Washington, D.C: The American Society of Hematology, 2009
National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:liu:diva-52728 (URN)10.1182/blood-2008-07-167023 (DOI)
Available from: 2010-01-11 Created: 2010-01-11 Last updated: 2017-12-12
2. Irreversible pan-ERBB inhibitor canertinib elicits anti-leukaemic effects and induces the regression of FLT3-ITD transformed cells in mice
Open this publication in new window or tab >>Irreversible pan-ERBB inhibitor canertinib elicits anti-leukaemic effects and induces the regression of FLT3-ITD transformed cells in mice
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2011 (English)In: British Journal of Haematology, ISSN 0007-1048, E-ISSN 1365-2141, Vol. 155, no 2, 198-208 p.Article in journal (Refereed) Published
Abstract [en]

Recent findings have indicated that tyrosine kinase inhibitors (TKIs) targeting the ERBB receptor family display anti-leukaemic effects, despite the lack of receptor expression on human leukaemic cells. The occurrence of activating mutations in the gene encoding FMS-like tyrosine kinase 3 (FLT3) in patients with acute myeloid leukaemia (AML) has rendered inhibition of this receptor a promising therapeutic target. Due to possibility of cross-reactivity, we investigated the effect of the irreversible pan-ERBB inhibitor canertinib (CI-1033) on leukaemic cells expressing FLT3. The drug had anti-proliferative and apoptotic effects on primary AML cells and human leukaemic cell lines expressing mutated FLT3. In several AML patient samples, a blast cell population expressing FLT3-internal tandem duplication (ITD) was eradicated by canertinib. Canertinib inhibited receptor autophosphorylation and kinase activity of both mutated and FLT3 ligand stimulated wildtype FLT3, leading to inhibition of the PI3-kinase and MAP kinase pathways. Apoptotic induction was dependent on pro-apoptotic BH3-only protein BCL2L11/BIM because siRNA silencing attenuated apoptosis. Moreover, the drug induced regression of cells expressing FLT3-ITD in a murine in vivo-transplantation model at previously described tolerated doses. These results indicate that canertinib, as an irreversible TKI, could constitute a novel treatment regimen in patients with mutated or overexpressed FLT3.

Place, publisher, year, edition, pages
Blackwell Publishing, 2011
Keyword
acute myeloid leukaemia, apoptosis, signalling, drugs, murine model, leukaemia therapy
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-72031 (URN)10.1111/j.1365-2141.2011.08819.x (DOI)000296063400006 ()
Note
Funding Agencies|Swedish Cancer Foundation||Swedish Childrens Cancer Foundation||Swedish Research Council||County Council of Ostergotland||Cancer Foundation of Ostergotland||Ollie and Elof Ericssons Foundation||Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2017-12-08
3. A comparative study of various FLT3-ITDs in relation to function and signaling
Open this publication in new window or tab >>A comparative study of various FLT3-ITDs in relation to function and signaling
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Internal tandem duplications (ITD) in the FMS like tyrosine kinase (FLT3) receptor are one of the most common classes of mutations in acute myeloid leukemia (AML), which presence indicates a poor prognosis. Lengths of FLT3-ITD mutations found in patients can vary from 3 up to hundreds of nucleotides and may be located either in the juxtamembrane domain or the tyrosine kinase-1 domain (TKD1). There are contradicting opinions whether the length of the ITD has an impact on the clinical situation and whether tyrosines duplicated are of any significance for oncogenic signaling. Considering the substantial differences in lengths as well as the variability of start and end points of ITDs, we have performed a study of various FLT3-ITD mutations isolated from AML-patients. The ITD region from leukemic blasts of nine AML patients were sequenced and cloned by PCR into the human wildtype FLT3 cDNA, inserted to a retroviral GFP-containing vector. The hematopoietic progenitor cell line FDC-P1 was used to elucidate the impact of the different ITDs on growth, survival, signal transduction, and resistance to the FLT3-targeting inhibitor PKC412. Interestingly, the shortest and the longest ITDs were two of the three mutations that lead to the poorest survival of cells upon cytokine-deprivation, indicating that ITD size may not influence the transforming potential of cells. Furthermore one ITD that starts and ends relatively 3´ positioned, and comprises the 5´-part of the TKD1 showed both a survival advantage in starvation experiments and a significantly higher proliferation potential in comparison to several other mutations. Two other ITDs spanning this region, but with more 5´localized starting points, displayed less sensitivity to PKC412 treatment. However, this was not associated to STAT5 activity and MCL-1 upregulation as suggested by previous report. Taken together, this study suggests that different FLT3-ITD mutations may induce distinct signaling and response towards FLT3 targeting drugs, dependent of FLT3-ITD composition and not length.

Keyword
FLT3-ITD, proliferation, apoptosis, tyrosine kinase inhibitor, resistance
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-88200 (URN)
Available from: 2013-01-31 Created: 2013-01-31 Last updated: 2013-01-31Bibliographically approved
4. Hyperactivated AKT is incompatible with survival when coexpressed with additional oncogenes and drives hematopoietic stem and progenitor cells to cell cycle inhibition and apoptosis
Open this publication in new window or tab >>Hyperactivated AKT is incompatible with survival when coexpressed with additional oncogenes and drives hematopoietic stem and progenitor cells to cell cycle inhibition and apoptosis
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The PI3K-AKT signaling pathway plays an important role in cell growth and metabolism. Increased AKT activity is frequently seen in patients with acute myeloid leukemia (AML), providing leukemic cells with both growth-promoting and survival signals involved in the transformation process. In AML up to 30% of all patients carry activating mutations in the tyrosine kinase receptor FLT3, leading to activation of the PI3K/AKT pathway as well as STAT5. Here, we investigated the effect of hyperactivated AKT (myristylated AKT) by retroviral transfer to hematopoietic progenitor cells coexpressing STAT5, FLT3-ITD, or antiapoptotic Bcl-2. AKT was unable to relieve cytokine-dependence. Surprisingly, uncontrolled AKT activity was linked to accumulation of cells in the G0 stage of the cell cycle and increased cell numbers became apoptotic. Hyperactivated AKT was incompatible with STAT5-driven proliferation and triggered apoptosis. The same was true also in FLT3-ITDexpressing progenitor cells of transgenic mice. Transplantable hematopoietic stem cells of wildtype and Bcl-2 transgenic mice were impaired in their engraftment ability to recipient mice when expressing hyperactivated AKT. This was linked to AKT-mediated pro-apoptotic functions and not due to effects on homing or migration. Cells expressing hyperactivated AKT displayed higher levels of reactive oxygen species. However, the addition of the antioxidant N-acetyl-L-lysine significantly reduced apoptosis. Taken together, the results indicate that constitutive AKT activity is incompatible with the growth- and survivalpromoting ability of FLT3-ITD and its downstream targets. These findings may provide a novel tool to intervene with AKT activity in leukemia.

Keyword
Hematopoiesis, transplantation, oncogenes, AKT, STAT5, FLT3-ITD, Bcl-2, apoptosis
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-88201 (URN)
Available from: 2013-01-31 Created: 2013-01-31 Last updated: 2013-01-31

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