Targeted therapy of CML with imatinib mesylate Gleevec

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Targeted therapy ofCML with imatinib mesylate
(Gleevec)

• March 26, 2003

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Chronic Myelogenous Leukemia

• Myeloproliferative disorder
• Leukocytosis
• Splenomegaly
• Median age at presentation is 53
• Nonspecific symptoms (fatigue, weight loss, early
  satiety, often asymptomatic)
• Incidence of 1 per 100,000 persons
• Represents 7-15 of all leukemia in adults

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Normal Blood smear
CML Blood smear
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Natural History of CML

• Chronic Phase
• Leukocytosis usually easily controlled with
  treatment. Minimal symptoms
• Accelerated Phase
• Increasing of blasts in the bone marrow
• Progressive splenomegaly
• Blast Crisis (evolution to acute myeloid or
  lymphoid leukemia)
• Median survival is less than 6 months
• In the first two years after diagnosis 5-15 of
  patients will enter blast crisis. Thereafter,
  20-25 progression per year

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Chronic Phase
Blast Crisis
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Treatment of CML

• Standard chemotherapy (Hydroxyurea)
• Control leukocytosis and splenomegaly in chronic
  phase
• No effect on progression to blast crisis
• Alpha Interferon
• Many side effect (fatigue, depression)
• Modest prolongation of survival
• Allogeneic bone marrow transplantation
• Only potentially curative therapy
• Acute mortality of 20-30
• Gleevac (STI571)

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1960 (Nowell and Hungerford) Philadelphia
chromosome identified as the first recurrent
chromosomal abnormality associated with cancer
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1973 (Rowley) Studies showed that the Ph1
chromosome is the result of a reciprocal
translocation between chromosomes 9 and 22 (t
922)(q34.1 q11.21)
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Ch 9
Ch 22

• 1983-86 Identification of the BCR/ABL fusion
  product
• Present in nearly 100 of cases of CML

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• Non-receptor tyrosine kinase
• Cycles between cytoplasm and nucleus?
• Regulate cell cycle progression
• Overexpression leads to cell cycle arrest
• Knock-out mice Runted, lymphopenia, perinatal
  death

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• Coiled-coil oligomerization domain.
• Serine/threonine kinase activity in vitro
• Guanine-nucleotide exchange factor (GEF) domain
• RacGAP domain (activity towards Rac/CDC42)
• Bcr (-/-) mice Viable, normal hematopoiesis.
• Increased neutrophil superoxide production.

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Potential mechanisms of leukemogenesis for the
BCR-ABL translocation

• Gain of function
• Bcr-abl fusion protein.
• Abl-bcr fusion protein. The reciprocal
  translocation results in the production of a
  novel abl-bcr fusion protein that is expressed in
  the majority of cases of CML.
• Loss of function
• Potential contribution of ABL of BCR
  haploinsufficiency in leukemogenesis

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Questions

• Is BCR/ABL sufficient to induce CML?
• What are the mechanisms of BCR/ABL-induced
  leukemogenesis?

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Early Studies of bcr-abl p210
Assay
p210
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Primary murine bone marrow transduction/transplant
ation
IL-3, SCF, TPO, FLT-3
5-FU
Total BM
Transduce with virus
Harvest transduced cells
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Vector alone
Bcr-abl
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Tec Transgenic Mice
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Detection of Bcr-Abl mRNA in Healthy Individuals

• Nested RT-PCR sensitive to 1 copy of bcr-abl mRNA
  
• in 108 cells
• Analyzed blood leukocyte RNA from 117 normal
  subjects
• Extensive controls to exclude contamination

Beirnaux et al,. Blood 863118, 1995
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Questions

• Is BCR/ABL sufficient to induce CML?

• What are the mechanisms of BCR/ABL-induced
  leukemogenesis?

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Mechanisms of Leukemogenesis

• Mutagenesis of p210 bcr-abl
• Constitutive activation of p210 is dependent upon
  the coiled-coiled motif of bcr
• Kinase inactive mutants are dead
• Characterization of Signaling Pathways
• Many pathways altered

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Pathways activated by BCR/ABL an
oversimplification
Deininger et al., Blood 2000
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Inhibiting the kinase activity of BCR/ABL wont
work because

• ATP binding pocket of ABL is well conserved among
  many TKs
• e.g. tyrphostins are notoriously nonspecific
• Besides, inhibition of BCR/ABL will also inhibit
  c-ABL, giving unknown toxicity
• What we need is drug to block cancer-specific
  pathways!

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Specificity of STI571

• INHIBITION (0.3uM)
• ABL
• PDGFR
• c-Kit

• NO INHIBITION (gt100uM)
• EGF-R
• HER2/neu
• Insulin receptor
• Insulin-like growth factor receptor 1
• c-FGR
• c-Lck, c-Lyn, c-Src
• Serine/threonine kinases
• FLT3
• c-Fms

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Druker et al., Nature Medicine 2561, 1996
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Drug Development

• 2001 - 70 approved drugs
• FDA approval of a drug - 10-12 years
• Average cost per drug - 100,000,000

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Clinical Trials

• Clinical evaluation in patients
• 3 Phases
• Specific goals
• Eligible patients
• Good performance status
• Normal kidney, liver, and bone marrow function

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Phase I Clinical Trial

• Goal To assess toxicity and characterize drug
  pharmacokinetics
• Maximum tolerated dose determined
• Design
• Nonrandomized, non-blinded, usually single
  institution.
• Cohorts of 3-6 subjects are given escalating
  doses of drug until the maximum tolerated dose
  achieved.
• Response rates generally lt10 (efficacy not a
  stated goal)!

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STI571 (imatinib) Phase I Data

• Highly bioavailable as oral formulation
• Dose escalation 25 500 mg
• 54 patients at 10 dose levels 4 wks Rx
• All patients at greater than 140 mg had response
  (PRCR)
• At 300 mg or greater, 96 had CR
• Two cytogenetic remissions
• Negligible toxicity

Blood Abstract 1639, 1999
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Phase II Clinical Trial

• Goal To demonstrate drug efficacy in a
  particular disease
• Design
• Nonrandomized, non-blinded, single or multiple
  institution.
• Small number of patients required (range 50-500)
• Usually sponsored by drug companies

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Imatinib Phase II Results for Chronic Phase

• 532 patients with late-chronic phase CML in whom
  IFN had failed
• 400 mg imatinib po qd
• Complete hematologic response 95
• Major cytogenetic response 60
• Major side effects 2

Kantarjian, et al., NEJM, 2002
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Phase III Clinical Trial

• Goal To compare efficacy of a new drug with
  standard therapy.
• Design
• Randomized, double-blinded, usually
  multi-institutional.
• Generally, large number of patients required
  (hundreds to thousands).
• Costs. Generally, sponsored by drug
  companies.

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Progression-free Survival in Chronic Phase CML
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Drug Approval Process

• Approval based on classic endpoints
• Cure
• Prolongation of survival
• Improvement in in quality of life
• Approval based on surrogate endpoints
• Reduced toxicity
• Delay in clinical deterioration
• Improvement in markers of biologic activity
• Further studies must be done by sponsor to verify
  benefit

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Imatinib Phase II Results for Myeloid Blast Crisis

• 229 patients with confirmed blast crisis (with
  30 blasts in peripheral blood or marrow)
• 400 or 600 mg imatinib po qd
• Complete hematologic response 8
• Sustained heme response 31
• Median response duration 10 months
• Major cytogenetic responses 16

Talpaz, et al., Blood, 2002
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Overall survival of myeloid blast crisis pts
treated with imatinib
Sawyers, Blood, 2002
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What is the mechanism of resistance to imatinib?

• Increased drug efflux (MDR transporters)?
• Sequestration or inactivation of drug?
• Additional mutations making BCR-ABL kinase
  activity no longer necessary?
• Mutations of BCR-ABL rendering them resistant to
  imatinib

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Phospho-CrkL in patient samples
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BCR-ABL mutants are resistant to imatinib in
vitro
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Evidence for amplification of BCR-ABL in leukemic
cells
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BCR-ABL mutations impair imatinib binding but not
kinase
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Imatinib-resistant BCR-ABL kinase domain
mutations
Shah, Cancer Cell, 2002
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Mechanisms of imatinib-resistant mutations
Shah, Cancer Cell, 2002
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Time to progression in chronic phase pts with
hematologic, but not cytogenetic response
Shah, Cancer Cell, 2002
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Take home messages

• The successful development of imatinib (Gleevec)
  represents the first successful molecular
  targeted therapy in cancer (40 years in the
  making)
• Resistance to imatinib occurs due at least in
  part to the selection of clones with mutant
  BCR-ABL, and is mostly a problem in advanced
  disease
• Understanding the signals downstream of BCR-ABL
  may help with the development of novel therapies
  for pts in blast phase
• Role of TK inhibitors in other cancers is an area
  of active investigation

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• Hypothesis Activating mutations in one or more
  cytokine signaling genes occur in every patient
  with AML

PTPN11 (SHP-2)
Rasgrp1 (RAS-GAP)