Co-targeting the CDK4/6 pathway
in hormone receptor positive
breast cancer
Valerie Malyvanh Jansen, MD, PhD
Vanderbilt-Ingram Cancer Center
Vanderbilt University
May 1, 2015
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Disclosure Information
TOPS Annual Meeting 2015
• I have no financial relationships to disclose.
- and –
• I will not discuss off label use and/or investigational
use in my presentation.
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Resistance to endocrine therapy results in ER+
breast cancer deaths
• More than 70% of breast cancers express the
estrogen receptor (ER+).
• Endocrine therapies aimed at targeting ERsignaling is the mainstay of treatment in ER+
breast cancer.
– SERM (tamoxifen)
– SERD (fulvestrant)
– Aromatase inhibitors (letrozole, anastrozole, exemestane)
• Up to 50% of ER+ breast cancers acquire
resistance to therapy.
– Gene amplification (HER2, FGFR1)
– Gene mutations (PIK3CA, ESR1)
American Cancer Society,
Cancer Facts & Figures 2014
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Targeting CDK4/6 in breast cancer
• CDK4 is required for estrogenindependent ER+ breast cancer cell
growth (Miller TW et al. Cancer Discov. 2011; 1 (4): 338-51.)
• CDK4/6 inhibitors prevent the
phosphorylation of pRb, thereby halting
cell cycle progression in the G1 phase.
• Palbociclib is FDA-approved for use in
combination with letrozole for advanced
ER+ breast cancer.
• We utilized a kinome wide RNA
interference screen to investigate
genes:
Ribociclib (LEE011)
Palbociclib (PD-0332991)
Abemaciclib (LY2835219)
X
1. whose inhibition will increase sensitivity to
CDK4/6 inhibition;
2. that are candidates for rational combination
therapy.
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Approach: RNA interference screen to identify
sensitizers to CDK4/6 inhibition
siNT
siDEATH
5
Kinase screen identifies PDK1 as a determinant of
sensitivity to CDK4/6 inhibition
Ribociclib (LEE011)
Palbociclib (PD-0332991)
Abemaciclib (LY2835219)
PDK1 = 3-phosphoinositide dependent protein kinase-1
[1] Rader J et al. Clin Cancer Res. 2013; 19(22): 6173-82.
[2] Fry DW et al. Mol Cancer Ther. 2004; 3(11): 1427-1438.
[3] Sanchez-Martinez et al. Mol Cancer Ther. 2011.
Fry MJ. Breast Cancer Res. 2001; 3(5): 304-12.
Lin HJ et al. Brit J Cancer. 2005; 93(12): 1372-81.
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RNAi-mediated knockdown of PDK1 sensitizes ER+
breast cancer cells to CDK4/6 inhibition
P  0.05
7
GSK2334470 is a highly specific inhibitor of PDK1
Medina J et al. J. Med. Chem. 2011:54 (6):1871–1895.
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MCF-7
600
400
200
0
D
G
SK MS
23 O
34
4
LE 70
E0
G
SK 1 1
Pa + L
lb EE
oc
G
SK icli
+P b
al
bo
Average Colony Number
PDK1 inhibitor cooperates with CDK4/6 inhibitors
in reducing ER+ BC cell proliferation
LEE011 = CDK4/6i; GSK2334470 = PDK1i; Palbociclib = CDK4/6i
1500
1000
500
P  0.05
0
D
G
SK MS
23 O
34
4
LE 70
E0
G
SK 11
Pa +L
lb EE
oc
G
SK icli
+P b
al
bo
Average Colony Number
T47D
9
PDK1 is upregulated upon acute and long-term
treatment with CDK4/6 inhibitor
Long-term Treatment
Acute treatment
DMSO
MCF-7
LEE011 [1µM]
MCF-7
Hrs 0 0.5 1 2 6 12 24 48 72
P-Rb
MCF-7/LR
P-Rb
EC50
0.05 µM PDK1
MCF-7
1.35 µM
MCF-7/LR
P-PDK1
P-S6
P-RSK2
P-p70S6K
P-SGK3
Actin
LEE011 [1µM]
Cell viability (Fraction of CTL)
PDK1
1.5
P-S6
1.0
ACTIN
0.5
0.0
-2
-1
0
1
log [M LEE011]
10
PDK1 inhibitor re-sensitizes LEE011-resistant cells
to CDK4/6 inhibition
0.2
log [M inhibitors]
•
50
2.
25
1.
64
50
2.
25
1.
0.
64
CIm = 0.62±0.02
0.0
32
50
2.
25
1.
64
0.
32
0.
16
0.
01
0.0
0.2
0.
CIm = 0.58±0.12
0.4
16
0.2
0.6
0.
0.4
0.8
01
0.6
T47D/LR
1.0
0.
0.8
Cell viability (Fraction of CTL)
T47D
1.0
0.
GSK+LEE
Cell viability (Fraction of CTL)
LEE011 GSK2334470
0.
log [M inhibitors]
log [M inhibitors]
DMSO
32
CIm = 0.46±0.04
0.0
16
2.
50
1.
25
0.
64
0.
32
0.0
CIm = 0.34±0.10
0.
16
0.2
0.4
0.
0.4
0.6
0.
0.6
0.8
01
0.8
MCF-7/LR
1.0
0.
MCF-7
Cell viability (Fraction of CTL)
Resistant
1.0
0.
01
Cell viability (Fraction of CTL)
Parental
log [M inhibitors]
Mean combination index (CIm) <1 indicates
synergy for the combination.
LEE011 = CDK4/6i; GSK2334470 = PDK1i
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PDK1 mediates resistance to CDK4/6 inhibitor
independent of AKT
GSK2334470
MCF-7 Xenografts
BYL719
MCF-7/LR
1024
LEE011
Tumor Volume (mm3)
MK2206
Vehicle (n=7)
LEE011 (n=7)
GSK2334470 (n=7)
GSK+LEE (n=7)
512
256
128
P = 0.03
64
0
10
20
30
Days on treatment
40
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Conclusions
• Inhibition of PDK1 sensitizes ER+ breast cancer cells to CDK4/6
inhibition.
• PDK1 is upregulated upon acute and long-term treatment
with CDK4/6 inhibitor, LEE011, suggesting it is a mechanism of
adaptation and/or resistance to inhibition of CDK4/6.
• Combined inhibition of CDK4/6 and PDK1 synergistically
inhibits proliferation of ER+ breast cancer cells.
• This effect appears to be independent of AKT but temporally
correlated with activation of other direct targets of PDK1.
• Clinical trials of combination of CDK4/6 and PDK1 inhibitors
are worthy of investigation in ER+ breast cancer.
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Acknowledgements
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