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Stem cell in cancer: Do they matter?
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Invited Speakers/Experimental Hematology 43 (2015) S25–S43
1019 - STEM CELL IN CANCER: DO THEY MATTER? John E. Dick Princess Margaret Cancer Centre, Toronto, Ontario, Canada The cellular and molecular basis for intra-tumoral heterogeneity is poorly understood. Tumor cells can be genetically diverse due to mutations and clonal evolution resulting in intra-tumoral functional heterogeneity. Often proposed as mutually exclusive, cancer stem cell (CSC) models postulate that tumors are cellular hierarchies created due to epigenetic programs that are sustained by CSC. I will focus on three lines of evidence showing these models are highly integrated. Gene signatures specific to either AML LSC or normal HSC are highly similar and define a common stemness program. Compared to non-stem cell transcriptional programs, only stem cell signatures were significant independent predictors of patient survival in 4 large clinical databases of O1000 samples. Thus, determinants of stemness influence clinical outcome of AML across a spectrum of mutations indicating that many genetic abnormalities coalesce around stem cell properties. Secondly, we have carried out a series of combined genetic and functional studies of the LSC from either BALL or AML that point to commonalities between clonal evolution and CSC models of cancer. LSC from diagnostic patient samples were genetically diverse and reconstruction of their genetic ancestry showed that multiple LSC subclones were related through a complex branching evolutionary process and specific genetic events influence L-IC frequency. Also study of paired diagnostic (Dx) and relapse (Rel) samples are revealing that individual subclones possess distinct functional growth properties and that rare Dx subclones are chemotherapy resistant and become enriched at Rel. Thus the clonal evolution models are highly relevant in cancer but need to be extended to adopt the concept that CSC are subject to clonal evolutionary forces. Finally, the combined genetic and functional analysis of AML is revealing fundamental insights into the cell of origin, nature and biological consequences of initiating lesions and order of subsequent mutations; concepts that demonstrate how highly integrated the CSC and genetic evolution models must be. Highly purified hematopoietic stem cells (HSC), progenitor and mature cell fractions from the blood of AML patients were found to contain recurrent DNMT3a mutations (DNMT3amut) at high allele frequency, but without other mutations present in AML blasts. DNMT3amut-bearing HSC exhibited multilineage repopulation advantage over non-mutated HSC in xenografts, establishing their identity as pre-leukemic-HSC (preL-HSC). preL-HSC were found in remission samples indicating that they survive chemotherapy. Thus DNMT3amut arises early in AML evolution, likely in HSC, leading to a clonally expanded pool of preL-HSC from which AML evolves. Detailed studies based on identification of clone specific variants from WGS of 11 paired Dx/Rel followed by detailed tracking in sorted blasts and progenitor subpopulations as well as in xenografts derived from the paired samples to examine the LSC diversity allowed us to conclusively trace the origins of Rel. In all cases, the Rel clone was pre-existing in the Dx blood sample. Moreover in 2 cases Rel was directly related to Dx blasts/LSC that survived therapy, while in most samples Rel was composed of multiple subclones derived from minor LSC and/or pre-L HSC subclones. Our findings indicate therapeutic strategies must account for genetic subclones, LSC as well as ancestral preL-HSC.
1020 - ANGIOGENESIS REVISITED: ENDOTHELIAL CELL METABOLISM AS A TARGET? Peter Carmeliet VIB - KU Leuven, Leuven, Belgium Angiogenesis, the growth of new blood vessels, plays a crucial role in numerous diseases, including cancer. Anti-angiogenesis therapies have been developed to starve cancer cells from nutrients. Clinically approved anti-angiogenic drugs prolong the survival of cancer patients, but their success is limited by intrinsic refractoriness and acquired resistance. New strategies are thus needed to block tumor angiogenesis via alternative mechanisms. We recently reported that PFKFB3-driven glycolysis regulates the endothelial tip cell function during vessel sprouting, even capable of overruling the potent pro-stalk activity of Notch, and that its loss in endothelial cells causes vascular hypobranching defects. Moreover, partial and transient reduction of glycolysis by blocking PFKFB3 reduced pathological angiogenesis in several disease models. Ongoing studies explore the role of lipid and amino acid metabolism in vessel sprouting, and assess the therapeutic potential of targeting these metabolic pathways for anti-angiogenic therapy.
Invited Speakers/Experimental Hematology 43 (2015) S25–S43
1019 - STEM CELL IN CANCER: DO THEY MATTER? John E. Dick Princess Margaret Cancer Centre, Toronto, Ontario, Canada The cellular and molecular basis for intra-tumoral heterogeneity is poorly understood. Tumor cells can be genetically diverse due to mutations and clonal evolution resulting in intra-tumoral functional heterogeneity. Often proposed as mutually exclusive, cancer stem cell (CSC) models postulate that tumors are cellular hierarchies created due to epigenetic programs that are sustained by CSC. I will focus on three lines of evidence showing these models are highly integrated. Gene signatures specific to either AML LSC or normal HSC are highly similar and define a common stemness program. Compared to non-stem cell transcriptional programs, only stem cell signatures were significant independent predictors of patient survival in 4 large clinical databases of O1000 samples. Thus, determinants of stemness influence clinical outcome of AML across a spectrum of mutations indicating that many genetic abnormalities coalesce around stem cell properties. Secondly, we have carried out a series of combined genetic and functional studies of the LSC from either BALL or AML that point to commonalities between clonal evolution and CSC models of cancer. LSC from diagnostic patient samples were genetically diverse and reconstruction of their genetic ancestry showed that multiple LSC subclones were related through a complex branching evolutionary process and specific genetic events influence L-IC frequency. Also study of paired diagnostic (Dx) and relapse (Rel) samples are revealing that individual subclones possess distinct functional growth properties and that rare Dx subclones are chemotherapy resistant and become enriched at Rel. Thus the clonal evolution models are highly relevant in cancer but need to be extended to adopt the concept that CSC are subject to clonal evolutionary forces. Finally, the combined genetic and functional analysis of AML is revealing fundamental insights into the cell of origin, nature and biological consequences of initiating lesions and order of subsequent mutations; concepts that demonstrate how highly integrated the CSC and genetic evolution models must be. Highly purified hematopoietic stem cells (HSC), progenitor and mature cell fractions from the blood of AML patients were found to contain recurrent DNMT3a mutations (DNMT3amut) at high allele frequency, but without other mutations present in AML blasts. DNMT3amut-bearing HSC exhibited multilineage repopulation advantage over non-mutated HSC in xenografts, establishing their identity as pre-leukemic-HSC (preL-HSC). preL-HSC were found in remission samples indicating that they survive chemotherapy. Thus DNMT3amut arises early in AML evolution, likely in HSC, leading to a clonally expanded pool of preL-HSC from which AML evolves. Detailed studies based on identification of clone specific variants from WGS of 11 paired Dx/Rel followed by detailed tracking in sorted blasts and progenitor subpopulations as well as in xenografts derived from the paired samples to examine the LSC diversity allowed us to conclusively trace the origins of Rel. In all cases, the Rel clone was pre-existing in the Dx blood sample. Moreover in 2 cases Rel was directly related to Dx blasts/LSC that survived therapy, while in most samples Rel was composed of multiple subclones derived from minor LSC and/or pre-L HSC subclones. Our findings indicate therapeutic strategies must account for genetic subclones, LSC as well as ancestral preL-HSC.
1020 - ANGIOGENESIS REVISITED: ENDOTHELIAL CELL METABOLISM AS A TARGET? Peter Carmeliet VIB - KU Leuven, Leuven, Belgium Angiogenesis, the growth of new blood vessels, plays a crucial role in numerous diseases, including cancer. Anti-angiogenesis therapies have been developed to starve cancer cells from nutrients. Clinically approved anti-angiogenic drugs prolong the survival of cancer patients, but their success is limited by intrinsic refractoriness and acquired resistance. New strategies are thus needed to block tumor angiogenesis via alternative mechanisms. We recently reported that PFKFB3-driven glycolysis regulates the endothelial tip cell function during vessel sprouting, even capable of overruling the potent pro-stalk activity of Notch, and that its loss in endothelial cells causes vascular hypobranching defects. Moreover, partial and transient reduction of glycolysis by blocking PFKFB3 reduced pathological angiogenesis in several disease models. Ongoing studies explore the role of lipid and amino acid metabolism in vessel sprouting, and assess the therapeutic potential of targeting these metabolic pathways for anti-angiogenic therapy.