mTOR: a new pathway
to target in oncology
Madlaina Breuleux, PhD
Novartis Phrma AG
The mTOR pathway and cancer
• 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
mTOR (mammalian “Target Of Rapamycin”):
mTOR: A central controller of tumor cell growth
mTOR inhibition decreases angiogenesis
• mTOR regulates HIF-1α
and HIF-2α expression
• HIF-1α/2α are normally
degraded by VHL protein
• HIF-1 and HIF-2 condition
the tumor to adapt to
growth under hypoxic
conditions and promote
HIF = hypoxia-inducible factor; VHL = von Hippel-Lindau protein.
Evidence of antiangiogenic activity
• Tumor xenograft–bearing 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
RAD001 reduces microvessel density
Vehicle Controls RAD001
Significant reduction in microvessel density following RAD001 treatment
in primary tumor and cranial lymphnode metastases (shown)
RAD001: Combination potential
– 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)
Although RAD001 has antiproliferative activity as a monotherapy, its potential
may be better realized in combination with other therapeutic agents
Combinations with cisplatin
(in RAD001-sensitive H596 NSCLC xenografts)
* P < 0.05 versus controls by the Dunnett test.
Combinations of RAD001 and low-dose cisplatin elicit a more potent antitumor
effect than either agent alone (also in model derived from resistant line)
Tumor Volumes Body Weights
Cisplatin combinations: Potentiate cell death
(A549 cells: cell death with sub-optimal cisplatin concentrations)
* Significant fold induction with P < 0.05, t-tests; two-way ANOVA indicates highly
significant interaction between RAD001 and cisplatin P < 0.001.
Cell death is dependent on p53 status
* Significant fold induction with P < 0.05, t-tests.
The p53/p21 response
Beuvink et al. Cell. 2005;120:747-759.
• DNA damage (i.e cisplatin
treatment) activates p53.
• In the presence of extensive DNA
damage, p53 initiates a cell death
• In the presence of sub-optimal
DNA damage, p53 induces p21
expression, a cell cycle inhibitor,
allows DNA repair (and cell
• RAD001 inhibits p21 expression
forcing tumor cell death even at
suboptimal cisplatin concentrations
(non-lethal DNA damage)
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.
Inhibition of estrogen-induced proliferation
(aromatase-expressing MCF7 cells)
Highly significant interactions ( p < 0.001; two-way ANOVA)
Synergistic effects (isobologram analysis)
Also in aromatase-expressing T47D cells
Potential RADIANT Trials
Decreased cell viability as compared to single agents
(YOPRO: p < 0.01; two-way ANOVA).
Defined as apoptosis (TUNEL: p < 0.05; Friedman Test).
Also in aromatase-expressing T47D cells
• 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.