mTOR: a new pathway to target in oncology

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mTOR a new pathwayto target in oncology

• Madlaina Breuleux, PhD
• Novartis Phrma AG
• Basel, Switzerland

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The mTOR pathway and cancer
mTOR (mammalian Target Of Rapamycin)

• A high molecular weight serine-threonine kinase
• Senses and responds to cellular nutrient and
  energy levels
• Influences protein translation regulating G1
  progression, S-phase entry, and ultimately cell
  growth and proliferation
• Functions downstream of the PI3 kinase / AKT
  pathway, which is often deregulated in human
  cancer
• mTOR pathway deregulation causes loss of growth
  control in cancer

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mTOR A central controller of tumor cell growth
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mTOR A controller of angiogenic processes
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RAD001 (Everolimus) An oral mTOR pathway
inhibitor

• Broad antiproliferative and antitumor properties

• Inhibits the mTOR pathway
• Sensor of physiological signals
• Downstream of PI3K / AKT pathway
• RAD001 activity associated with overactivation of
  the PTEN / PI3K / AKT pathway

• Inhibits tumor cell growth
• Delays G1/S phase progression
• Sensitises tumor cells to targeted and
  chemotherapeutic agents

• Anti-angiogenic properties
• Direct and indirect activity
• Phase IB/II clinical trials in oncology

Model of RAD001 binding to intracellular receptor
(FKBP-12) to form complex inhibiting mTOR pathway
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p-AKT levels correlate with RAD001 sensitivity
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RAD001 Broad in vivo antitumor activity
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mTOR inhibition decreases angiogenesis

• mTOR regulates HIF-1a and HIF-2a expression
  (transcription factors mediating hypoxia-induced
  gene expression)
• HIF-1a/2a are normally degraded by VHL protein
• HIF-1 and HIF-2 condition the tumor to adapt to
  growth under hypoxic conditions and promote
  angiogenesis and metastasis

HIF hypoxia-inducible factor VHL von
Hippel-Lindau protein.
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Evidence of antiangiogenic activity

• Tumor xenograftbearing mice single 5 mg/kg oral
  dose
• RAD001 plasma levels never exceed the in vitro
  IC50 for HCT116 (colon) or KB-31 (epidermoid)
  tumor cells
• However, both HCT116 and KB-31 xenografts are
  sensitive to RAD001 in vivo at this dose
• RAD001 levels exceed the in vitro IC50 for VEGF-
  or FGF-stimulated human umbilical vein
  endothelial cultures (HUVECs)
• RAD001 inhibits tumor cell VEGF production in
  vitro and decreases tumor and plasma VEGF levels
  in animal models
• RAD001 selectively inhibits VEGF-dependent
  angiogenic response in vivo, and reduces
  microvessel density in tumors derived from
  sensitive or resistant cell lines
• These data suggest an antiangiogenic effect
  against tumors

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RAD001 reduces microvessel density (B16/BL6)
Vehicle Controls
RAD001
Significant reduction in microvessel density
following RAD001 treatment in primary tumor and
cranial lymphnode metastases (shown)
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RAD001 Combination potential
Although RAD001 has antiproliferative activity as
a monotherapy, its potential may be better
realized in combination with other therapeutic
agents

• Chemotherapeutics
• DNA-damaging agents (i.e. cisplatin,
  temozolomide)
• Topoisomerase inhibitors (i.e. doxorubicin)
• MT active agents (i.e. Taxol)
• Targeted therapeutics
• ErbB inhibitors (i.e. AEE788 trastuzumab)
• Estrogen antagonists - aromatase inhibitors (i.e.
  letrozole)
• BCR-ABL, Kit inhibitors (i.e. imatinib)
• VEGFR inhibitors (i.e. PTK787)
• IGF-1R inhibitors (i.e. AEW541)
• Radiotherapy

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Combinations with cisplatin(in RAD001-sensitive
H596 NSCLC xenografts)
Tumor Volumes
Body Weights
Combinations of RAD001 and low-dose cisplatin
elicit a more potent antitumor effect than either
agent alone (also in model derived from resistant
line)
P lt 0.05 versus controls by the Dunnett test.
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Cisplatin combinations Potentiate cell
death(A549 cells cell death with sub-optimal
cisplatin concentrations)
Significant fold induction with P lt 0.05,
t-tests two-way ANOVA indicates
highlysignificant interaction between RAD001 and
cisplatin P lt 0.001.
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Cell death is dependent on p53 status
Significant fold induction with P lt 0.05,
t-tests.
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The p53/p21 response

• DNA damage (i.e cisplatin treatment) activates
  p53.
• In the presence of extensive DNA damage, p53
  initiates a cell death program.
• In the presence of sub-optimal DNA damage, p53
  induces p21 expression, a cell cycle inhibitor,
  allows DNA repair (and cell survival).
• RAD001 inhibits p21 expression forcing tumor cell
  death even at suboptimal cisplatin concentrations
  (non-lethal DNA damage)

Beuvink et al. Cell. 2005120747-759.
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Rationale for combination with letrozole

• Akt activation predicts a worse outcome for
  breast cancer patients treated with endocrine
  therapy.
• Activated Akt mediates resistance to antiestrogen
  therapy (related to HER2 overexpression).
• mTOR inhibition restores responses to tamoxifen
  in breast cancer models with high levels of Akt
  activity.
• Synergistic in vitro and in vivo effects have
  been seen with combined antiestrogen therapy and
  mTOR inhibition.

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Inhibition of estrogen-induced proliferation(arom
atase-expressing MCF7 cells)
Highly significant interactions (??? p lt 0.001
two-way ANOVA) Synergistic effects (isobologram
analysis) Also in aromatase-expressing T47D cells
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Potential RADIANT Trials
TUNEL
YOPRO
Decreased cell viability as compared to single
agents (YOPRO ?? p lt 0.01 two-way
ANOVA). Defined as apoptosis (TUNEL ? p lt 0.05
Friedman Test). Also in aromatase-expressing T47D
cells
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Summary

• mTOR acts as a central regulator of tumor cell
  growth and survival, and activation of the
  PI3K/AKT pathway may predict tumor response to
  mTOR inhibition.
• RAD001 exhibits a broad antitumor activity, and
  inhibits elements of the angiogenic process.
• Combination therapy targeting mTOR and other
  targets/processes deregulated in human cancer may
  provide enhanced anticancer activity.

Targeting deregulated pathways has been a
successful clinical strategy in cancer.