Leukemia stem cells in AML: implications for therapy and potential targeting strategies'

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Leukemia stem cells in AML implications for
therapy and potential targeting strategies.

• Brian Huntly
• University of Cambridge
• Educational sessions
• 11th congress of the European Hematology
  Association
• Amsterdam, Friday 16th June, 2006.

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Overview

• Background and evidence for the existence of
  leukemia stem cells (LSC) in AML.

• Current implications of LSC for therapy of
  AML

• Targeting LSC Surface phenotype
• - self-renewal
• - apoptosis.

• Conclusions

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Background to the cancer stem cell hypothesis

• Cellular heterogeneity is an intrinsic feature of
  many cancers, despite the fact that tumors are
  clonal in origin, arising from a single cell.

• Tumour cells are inefficient at generating
  clonal
• growth in both in vitro and in vivo assays

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Cancer stem cell model
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Cancer stem cell model
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Leukaemia stem cells exist in human acute myeloid
leukaemia (AML)
CD34/ CD38-
LEUKAEMIA
Leukaemic blasts from AML patients
CD34/ CD38
NO LEUKAEMIA
John Dick and Dominique Bonnett
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Leukaemia is arranged as a hierarchy similar to
normal haematopoiesis
LEUKAEMIA
NORMAL
CD34/ CD38-
HSC
Leukaemogenic events
lymphoid progenitor
myeloid progenitor
Bulk leukaemia cells
Block terminal differentiation
John Dick and Dominique Bonnett
B-cell
T-cell
Erythrocyte
Platelet Monocyte Granulocyte
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Therapeutic implications current therapies may
spare Leukemia stem cells
Targeted elimination of Leukemia stem cells
Huntly and Gilliland, Nature Reviews Cancer, 2005
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Leukemia stem cells may subvert normal stem cell
functions to evade cancer therapies

• Quiescent phenotype - protection cell cycle
• specific agents

• ? ABC and other transporters prevent build
• up of therapeutic drug dosage

• Niche may be a haven

• Lack of oncogene addiction differential
• requirement for oncogene between stem cells
• and less primitive tumour types

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Quiescent CML stem cells are resistant to Imatinib

• Primary CML CD34 cells
• Cultured in the presence and absence
• of growth factors and Imatinib.
• Dividing cells exquisitely sensitive to
• Imatinib.
• Quiescent cells not sensitive to Imatinib
• Oncogene addiction in CML LSC?
• BCR-ABL CD34 cells are present
• in patients in CCR.

Tessa Holyoake Ravi Bhatia
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Considerations in targeting LSC

• Effectively target leukemia stem cells whilst
  selectively sparing normal HSC function.

• Target potential biological differences between
  LSC and
• normal HSC
• - Surface phenotype
• - Self-renewal mechanisms.
• - Apoptotic mechanisms.

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Targeting leukemia stem cells

• Surface phenotype.
• Mechanisms of self-renewal.
• Mechanisms of apoptosis.

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Antigen expression on LSC in AML
CD34 CD38- CD123- HLADR- CD33 CLL-1- CD90 CD117

• Normal HSC phenotype

CD34 CD38- CD123 HLADR- CD33 CLL-1 CD90- CD117
- ?CD44

• AML HSC phenotype

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Immunotherapy of AML LSC
Y
LSC
HSC
Leukeamic progeny
Normal progeny
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Immunotherapy of AML LSC
Y
LSC
HSC
Y
Y
Leukeamic progeny
Normal progeny
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Immunotherapy of AML LSC
LSC
HSC
Leukeamic progeny
Normal progeny
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Immunotherapy of AML LSC
HSC
Eradication of disease
Normal progeny
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Immunotherapy directed to the IL-3 Receptor (CD
123) present on AML stem cells.
DT388-IL3 fusion protein Trauncated diptheria
toxin fused to IL-3

• Difference between expression of IL-3R on LSC
  and HSC
• NOD/SCID model prior Rx with DT388-IL3 no
  significant effect on
• normal human CRU.
• NOD/SCID model AML- IP Rx /- Ara-C
• 5 mice (each /-) transplanted with AML
• FU 16 weeks - No evidence of disease.
• Well tolerated in Cynomoglus monkeys No
  haematological phenotype.
• Phase I trial- North Carolina and Vancouver,
  relapsed/refractory disease.

Donna Hogge, Arthur Frankel, David Rizzieri
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Cell fates available to a stem cell
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Targeting leukemia stem cells

• Surface phenotype.
• Mechanisms of self-renewal.
• Mechanisms of apoptosis.

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Mechanisms of self-renewal in LSC

• Proposed mechanisms of self-renewal in leukemia
  stem cells.
• Wnt/?-Catenin.
• Notch.
• BMI-1.
• Shh.
• HOX genes.

• ALL ALSO IMPLICATED IN NORMAL STEM CELL
  SELF-RENEWAL

• Identification of self-renewal pathways
  preferentially utilised by LSC

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Both stem and progenitor cells may generate LSC
in AML
LSC
Brian Huntly Gary Gilliland Irv Weissman
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Identification of candidate self-renewal
genes/programs in AML
Brian Huntly Gary Gilliland
Candidate genes involved in self-renewal
Resort GFP positive cells
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Differential requirements for self-renewal in HSC
vs LSC

• PTEN-/- Mouse HSC loss of self-renewal and a
  transplantable acute leukaemia.

• PTEN inactivation leads to PI3-K/Akt
• activation Pathway constitutively active
• in AML.

• mTOR activation major downstream
• events inhibited by Rapamycin.

Rapamycin

• Rapamycin Rx of mice both prevented and
• treated leukaemias.

• Restored normal HSC function.

• Rapamycin in vitro and in vivo efficacy in
• AML currently in Phase II/III trials.

Sean Morrison, Linheng Li, Andreas Trumpp
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Targeting leukemia stem cells

• Surface phenotype.
• Mechanisms of self-renewal.
• Mechanisms of apoptosis.

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NF-?B is constituitively activated in AML

• Active NF-?B has been shown to have antiapoptotic
  activity.
• Suggested to be a key survival factor for many
  types of cancer.
• Inhibition of NF-?B has been shown to induce
  apoptosis in many
• tumour cell types.
• NF-?B is active in primItive AML progenitors.

NF-kB
Craig Jordan
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ParthenolideAn LSC-specific toxin?
Parthenolide (PTL)

• Sesquiterpene lactone
• Mexican-Indian medicinal plants (Feverfew)
• Commonly used for headache and inflammation
• Potent inhibitor of NF-kB (via IKK)
• Anti-tumor activity

Craig Jordan
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Parthenolide selectively ablates primitive AML
cells in vitro
5µM
Craig Jordan
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Parthenolide selectively inhibits LSC activity in
NOD/SCID mice
Craig Jordan
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NF-kB inhibition correlates with AML-specific
apoptosis

• Proapoptotic activation of p53
• Increase in reactive oxygen species (ROS).
• PTL other IKK inhibitors Phase I/II trials

Craig Jordan
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Conclusions

• The leukemia stem cell (LSC) is the critical
  target in AML therapy.

• A further understanding of the biology of
  both the LSC and the
• normal HSC is required.

• Target pathways preferentially utilised by
  LSC.

• Growing body of evidence that differences in
  biology between LSC
• and HSC may be exploited for therapeutic
  benefit.

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Acknowledgements
John Dick Dominique Bonnet Tessa Holyoake Ravi
Bhatia Donna Hogge Arthur Frankel David
Rizzieri Irving Weissman Sean Morrison Linheng
Li Craig Jordan
CAMBRIDGE Inusha De Silva Brynn
Kvinlaug Shubha Anand Tony Green Alan
Warren Bertie Gottgens BOSTON Gary
Gilliland Scott Armstrong