Acute Leukemia and the FLT3 Receptor

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Acute Leukemia and the FLT3 Receptor

• By Betty Sa
• Mentor Dr. Govind Bhagat
• Site Columbia University
• Vanderbilt Clinic

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BACKGROUND

• Leukemia is a cancer of the blood in which
  immature hematopoietic cells proliferate in an
  uncontrolled manner. Leukemia originates in the
  bone marrow and quickly spreads elsewhere. There
  are four major types of Leukemia, Acute Myeloid
  Leukemia (AML), Acute Lymphoblastic Leukemia
  (ALL), Chronic Myeloid Leukemia, and Chronic
  Lymphocytic Leukemia. But we are only focusing
  on AML and ALL. Acute means that the disease
  appears quickly and advances rapidly, so patients
  with ALL and AML usually require immediate
  treatment.

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INTRODUCTION

• Acute Lymphocytic Leukemia (ALL) is a rapidly
  progressing disease marked by the overabundance
  of immature lymphoid cells (lymphoblasts) in the
  blood or bone marrow most commonly found in
  children. Healthy lymphocytes fight bacterial
  and viral infections. But in patients with ALL
  the lymphocytes do not develop into mature cells,
  and remain immature cells called lymphoblasts. In
  this type of Leukemia blood cells differentiation
  and gets stuck at the lymphoblast stage and
  continues proliferation. So the abnormal cells
  crowd the normal cells in the bone marrow and
  prevent the production of red blood cells, other
  white blood cells, and platelets. This causes
  most ALL patients to become anemic, susceptible
  to infection, and bruise or bleed easily.
• Acute Myeloid Leukemia (AML) is a cancer in which
  there is uncontrollable growth of immature
  myeloid cells (myeloblasts, promyelocytes,
  monoblasts, erythroblasts, megakaryoblasts) in
  the bone marrow that leads to a deficiency of red
  blood cells, platelets, and white blood cells. In
  these types of Leukemia blood cell differention
  gets stuck at various stages of myeloid,
  monocytic, erythroid, or megakaryocytic
  differentiation and these cells continue to
  proliferate.

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INTRO CONTINUES...

• There are different sub-types of AML, depending
  upon exactly which type of cell has become
  leukemic the stage of maturation the cells are at
  and whether the cells are differentiated, these
  sub-types include Acute Myeloid Leukemia without
  maturation, Acute Myeloid Leukemia with
  maturation, Acute Promyelocytic Leukemia (APL),
  Acute Myelomonocytic Leukemia, Acute
  Monocytic/Monoblastic Leukemia, Acute
  Erythroleukemia, and Acute Megakaryoblastic
  Leukemia.
• In AML where the granulocytic (neutrophilic)
  series is affected, there is a block in the
  production of mature neutrophils. Neutrophilis
  fight infections caused by bacteria. The
  production of mature neutrophilis is usually
  tightly regulated. Mature neutrophilis develop
  from less mature white cells in a process called
  differentiation. In AML, acquired mutations in
  the blood-forming cells disrupt the normal
  process of differentiation, resulting in the
  accumulation of large members of immature cells
  called myeloblasts. If the erythroid lineage is
  affected, blasts cannot function like fully
  developed, healthy red blood cells. The large
  number of blasts also reduces the production of
  healthy red blood cells and platelets. So,
  patients are usually anemic.

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ALL
AML
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FLT3

• FLT3 stands for FMS-like tyrosine kinase 3 gene,
  which encodes a membrane-bound receptor tyrosine
  kinase (RTK) that has a crucial role in normal
  haematopoiesis.
• Normally, FLT3 expression is restricted to CD34
  hematopoietic stem/progenitor cells, brain,
  placenta, and gonads. Activation of FLT3 by
  FLT3-Ligand promotes the normal, in vitro growth
  of early progenitor cells.
• In Acute Leukemia, mutations of the FLT3 gene
  have been found to be one of the most common
  acquired genetic lesions. FLT3 mutations can be
  detected in 30 of AML patients. There are two
  frequent types of somatic FLT3 genetic mutations
  internal tandem duplications (ITDs) in the
  juxtamembrane (JM) domain and point mutations in
  the activation loop of the tyrosine kinase domain
  (TKD).
• Studies have shown that ITD mutations are
  triggered by any elongation or shortening of the
  JM domain of FLT3 due to additions or deletions
  of amino acids that result in the constitutive
  activation of FLT3. The presence of FLT3/ITD
  mutations is associated with a poor clinical
  outcome in both pediatric and adult patients
  with AML.

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FLT3 Continues...

• Point mutations in the activation loop of the
  kinase domain (FLT3/TKD) involves the aspartic
  acid, D835 residue, which leads to an activated
  configuration and transformation of myeloid
  cells. D835 mutations are missense mutations that
  results in substitution of tyrosine, histidine,
  valine, glutamic acid or asparagine for
  aspartatic acid at amino acid 835 of FLT3.
• This mutation has been reported in 7 of patients
  with AML. TKD mutations, unlike ITD mutations,
  have not been shown to have any prognostic
  significance in AML patients.
• Both types of FLT3 mutation cause
  ligand-independent activation of the receptor and
  activation of downstream signaling pathways.

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Statistics

• In 2006 an estimated 3,930 adults (2,150 men and
  1,780 women) in the US will be diagnosed with ALL
  and an estimated 1,490 (900 men, 590 women)
  deaths will occur. ALL is more common in adults
  older than 50. 20 to 30 of adults with ALL
  experience long-term disease remission or are
  cured of the disease.
• ALL is more common in children than in adults
  74 of all new cases are diagnosed in children
  ages 0 to 19.
• In 2006, an estimated 11,930 people (6,350 men
  and 5,580 women) in the US will be diagnosed with
  AML and an estimated 9,040 deaths will occur
  (5,090 men and 3,950 women). AML is most common
  in older adults around 60-65 years old.
• The percentage of patients who survived at least
  five years after being diagnosed, for adults
  under the age 65 with AML is 33.

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PURPOSE

• To get a better understanding of the molecular
  abnormalities underlying Acute Leukemia's.
• I will study the different types of FLT 3
  tyrosine kinase mutations in subsets of acute
  leukemias to determine their relative frequency
  and impact on the biologic course of disease .
• I will also correlate the presence of FLT3
  mutations with other cytogenetic abnormalities in
  different types of acute leukemias to better
  understand the multi-step pathways of
  leukemogenesis.

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Material and Methods

• Case selection Acute leukemias diagnosed at
  Columbia University Medical Center over the past
  5 years for which cytogenetic information is
  available (at least 100 cases)
• DNA extraction from peripheral blood or bone
  marrow aspirate samples
• PCR using primers specific for certain portions
  of the FLT3 gene
• Capillary gel electrophoresis
• Analysis of spectrophoretograms for FLT3 TKD and
  FLT3-ITD mutations

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REFERENCES

• http//www.dsrct.demon.co.uk/cells.jpg
• www.nature.com/reviews/cancer
• www.vghtpe.gov
• www.health.sa.gov.au/cancare
• www.elsevier.com/locate/biocel
• www.sciencedirect.com
• health.on-topic.net/health/AcuteLymphocytic...

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Acknownledgements

• Dr. Govind Bhagat
• Dr. Mahesh Mansukhani
• Columbia University
• Dr. Sat
• MSKCC
• Harlem Children Society