PARP inhibition – basic science and clinical challenge
Thomas Helleday, PhD
Poly (ADP-ribose) Polymerase 1 (PARP1)
Reprinted by permission from Macmillan Publishers Ltd: Rouleau M et al. Nat Rev Cancer 2010;10:293-301 copyright (2010)
PARP family of proteins
DNA repair
Reprinted by permission from Macmillan Publishers Ltd: Schreiber J et al. Nat Rev Mol Cell Biol 2006;7:517-528 copyright (2006)
DNA damage/NAD+ levels dictate responses
Ström CE and Helleday T. Biomolecules 2012;2:635-649 by permission of CCPL (2012)
PARP1 is critical for efficient SSB repair
XRCC1
PCNA
FEN1Polβ
PNKP
PARP1
XRCC1 – Ligase3PNKP, APTX
Lig3
XRCC1
APTX
Lig3
XRCC1
PolβLig3
XRCC1Lig1
Polδ/εPCNA
Lig1Lig3
PCNA , Polδ/ε , Polβ,
Ligase1, FEN1Polβ
DNA single-strand break
short patch long patch
Ström CE et al. Nucleic Acids Res 2011;39:3166-3175 by permission of Oxford University Press
BRCA2 deficient cells are killed by PARP inhibitors
HR
V-C8+B2 V-C8
ggH
2A
xg
H2
Ax
+ D
NA
BRCA2 defective
Reprinted by permission from Macmillan Publishers Ltd: Bryant HE et al. Nature 2005;434(7035):913-917 copyright (2005);Farmer H et al. Nature 2005;434(7035):917-920
Specific killing of BRCA2 deficient tumours with PARP inhibitors
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
Re
lativ
e thig
h c
ircum
fere
nce
Days post implant
V-C8+B2 control
V-C8+B2 AG14361
V-C8 control
V-C8 AG14361
AG14361 25 mg/kg
Reprinted by permission from Macmillan Publishers Ltd: Bryant HE et al. Nature 2005;434(7035):913-917 copyright (2005)
Homologous Recombination
Synthetic lethality as an approach for anti-cancer treatments
Cancer cells
Survival
PARP Inhibition
Cell death
SSB repairHomologous
Recombination
Normal cells
SurvivalSurvival
PARPInhibition
BRCA2+/-BRCA2-/-
SSB repair
Helleday T.
PARP inhibitors in monotherapy
PARP inhibitors in treatment for BRCA1/2 cancer
>80 clinical trials with PARP inhibitors in phase I-II
0
40
60
80
Tre
atm
ent dura
tion
(week)
20
Progressive disease Stable disease Partial response Complete response
Ovarian cancer Prostate cancer Breast cancer
From Fong PC et al. New Engl J Med 2009;361(2):123-134. Copyright © (2009) Massachusetts Medical Society.Reprinted with permission from Massachusetts Medical Society
PARP inhibitors in treatment for BRCA1/2 ovarian cancer
Olaparib 400 mg twice daily Olaparib 100 mg twice daily
Reprinted from Audeh MW et al. Lancet 2010;376(9737):245-251. Copyright (2010), with permission from Elsevier
Response to PARP inhibitors in triple negative breast cancer is dictated by BRCA mutation
Olaparib 400 mg twice daily
Reprinted from Gelmon KA et al. Lancet Oncol 2011;12(9):852-861. Copyright (2011), with permission from Elsevier
Platinum resistant ovarian cancers and non-BRCA respond to PARP inhibitor
Reprinted from Gelmon KA et al. Lancet Oncol 2011;12(9):852-861. Copyright (2011), with permission from Elsevier
Olaparib maintenance treatment improve progression-free survival in relapsed high-grade serous ovarian cancer
3 6 9 120 150.0
0.2
0.4
0.6
0.8
1.0
Pro
babili
ty o
f pro
gre
ssio
n-f
ree s
urv
ival
Months since randomization
Hazard ratio, 0.35 (95% CI, 0.25-0.49)P<0.001
Olaparib
Placebo
Adapted from Ledermann J et al. N Engl J Med 2012;366(15):1382-1392
Ovarian cancers often have silenced Fanconi anemia (FA) pathway, rendering in homologous recombination defect
PARP-sensitive tumour PARP-resistant tumour?
Reprinted by permission from Macmillan Publishers Ltd: Taniguchi T et al. Nat Med 2003;9(5):568-574 copyright (2003)
Biomarkers for PARP inhibitor sensitivity in monotherapy?
� BRCA1/2 mutation
� Silenced or mutated BRCA related genes
� PARP1 protein levels or PARP activity
� Functional homologous recombination assay (RAD51 foci, FA
status)
� RNA/DNA signatures correlating with BRCA status
� BRCA mutational signature
Resistance to PARP inhibitors
Resis
tant
clo
ne
Cancer cells
SurvivalCell Death
PARP inhibitor BRCA2 mutation
Rottenberg S et al. Proc Natl Acad Sci U S A 2008;105(44):17079-17084;
Reprinted by permission from Macmillan Publishers Ltd: Sakai W et al. Nature 2008;451:1116-1120 copyright (2003)
Complicity of genetic networks – 53BP1 loss as resistance mechanism
PARPiBRCA
53BP1
Ancestrial suppressed network
Reprinted from Bunting SF et al. Cell 2010;141:243-254. Copyright (2010), with permission from Elsevier
PARP inhibitors in combination therapy
Iniparib plus chemotherapy in metastatic triple-negative breast cancer
2 6 10 120 140
20
40
60
80
100
Overa
ll surv
ival (%
)
Months
Hazard ratio for death with iniparib, 0.57 (95% CI, 0.36-0.90)P=0.01
4 8 16 18 20 22 24
Gemcitabine-carboplatinplus iniparib
Gemcitabine-carboplatinalone
Adapted from O'Shaughnessy J et al. N Engl J Med 2011;364(3):205-214
Iniparib plus chemotherapy in metastatic triple-negative breast cancer
� Reasons for phase III to fail?
� Phase II design (open label)
� Combination with gem-carbo?
� No selection for BRCA mutated
patients?
� Iniparib is not a PARP inhibitor
O'Shaughnessy J et al. N Engl J Med 2011;364(3):205-214;
Reprinted from Patel AG et al. Clin Cancer Res 2012;18:1655-1662, with permission from AACR
Rucaparib (PF-01367338, AG014699), with temozolomide in patients with metastatic melanoma
� Conclusion: This study show that temozolomide
(150–200 mg/m2/day) can safely be given with a PARP inhibitory
dose of rucaparib, increasing progression-free survival over
historical controls in metastatic melanoma patients
Redrawn from Plummer R et al. Cancer Chemother Pharmacol 2013;71(5):1191-1199
0.4
0.6
0.2
0.0
0.8
1.0
Surv
ival pro
babili
ty
Overall survival (months)
+ Censored 95% Confidence limits
0 2
46 39
4
34
6
30
8
25
10
23
12
18
14
13
16
7
18
7
Kaplan Meier Plot with number of subjects at risk
-40.00
0.00
-60.00
-100.00
20.00
60.00
Best
% tum
our
shrinkage f
rom
baselin
e
Patient
-80.00
-20.00
40.00
replicationstress
+chemoPARPactive
+chemonot PARPactivate
d replicationstress
e replicationstress
f DNA damagestress
+CDK1inhibitor
c normal
PARP inhibitorsselectively toxic toBRCAmut cancer
PARP inhibitors withsome toxicity to DNA damaged cancer cells
PARP inhibitorssensitise all cells tochemotherapy no clinical benefit
PARP inhibitors + chemotherapy workwith additive effect, potential clinicalbenefit
Targeted inhibitors activate PARP in cancer, PARP inhibitors have clinicalbenefit
g DNA damagestress
hypoxia hypoxia activatesPARP in cancer, PARP inhibitors mayhave clinical benefit
a normal no DNA damage
BRCAmutb normal
PARP inhibitorshave no clinicalbenefit
Strategies using PARP inhibitors as anti-cancer agents - overview
� Potentiating
chemotherapy
� Synthetic lethality
� Combined with
targeted therapies
� Enhance cancer-
specific DNA damage
� Context specific
synthetic lethality
PA
RP
activity
stain
ed
by P
AR
poly
mers
High PAR
Low PAR
Helleday T. Curr Opin Oncol 2013;25:609-614
What combination will work in the clinic depends on tumour characteristics and drug mechanism of action
PR
IMA
RY
TU
MO
UR
Re
ce
pto
r n
eg
ati
ve
ca
nc
er,
p5
3 m
uta
ted
an
d
Fa
nc
on
i’s
an
em
ia(F
A)
sile
nc
ed
Radiotherapy
Therapy Value Comment
+ATR/Chk1 inhibitors sensitises to radiotherapy and are especially active in p53 mutated cancer. Furthermore, FA silenced cells exhibit replication lesions requiring ATR/Chk1 for survival
Platinum-basedchemo
-
Temozolomide
Platinum-basedchemo
Platinum-basedchemo
+
++
- -
- - -
-
Platinum-basedchemo
+++
FA silenced cells exhibit decreased homologous recombination and sensitivity to PARP inhibitors
FA silenced cells are sensitive to both platinum-based chemo and PARP inhibitors, which cause different DNA lesions, additive effect with both treatments, some normal tissue toxicity.
Proteasome inhibitors inhibit FA-mediated crosslink repair. Preferential induction of normal tissue toxicity.
Sensitivity to crosslinking agents in FA-silenced cells depend on active DNA-PK activity. Cancer cells become selectively resistant to platinum-based chemo.
FA silenced cells rely on non-FA mediated repair for survival, which normal cells do not. This pathway not yet identified.
Temozolomide not standard in ovarian cancer, PARP activity required for normal cell survival. Risk of potentiating side effects.
RE
SID
UA
L T
UM
OU
R
Pla
tin
um
re
sis
tan
t b
y D
NA
-PK
lo
ss Doxorubicin
Paclitaxel
Paclitaxel
DNA repair inhibitor
ATR/Chk1 inhibtor
PARP inhibitor
PARP inhibitor
PARP inhibitor
Proteasome inhibitor
DNA-PK inhibitor
Non-FA crosslink inhibitor
PARP inhibitor
Chk1 inhibitor
-
++
+++
+
DNA-PK lost cells rely on PARP-mediated backup-end joining repair of doxorubicin-induced double-strand breaks. Normal cells have DNA-PK and are not sensitised by PARP inhibitors
Mitosis inhibitor causing uncapping at telomers and DNA damage signalling-mediated cell death.
Docetaxel triggers Chk1-mediated mitotic checkpoint required for survival in p53 mutated cells
PARP inhibitor mechanism of action
PARP is involved in SSBR, replication repair, alt-NHEJ, fork protection, NER and BER
Ström CE and Helleday T. Biomolecules 2012;2:635-649
PARP1 trapping is required for PARP inhibitor toxicity
Reprinted from Murai J et al. Cancer Res 2012;72(21):5588-5599, with permission from AACR
PARP1 + BRCA2 protects replication forks from Mre11 degradation
Reprinted from Ying S et al. Cancer Res 2012;72(11):2814-2821, with permission from AACR
PARP1 + BRCA2 protects replication forks from Mre11 degradation
HR BER RR
PARP inhibitors
Prot Trap
PARP inhibitors inhibits several PARP family member
alt
NHEJ
Reprinted from Ying S et al. Cancer Res 2012;72(11):2814-2821, with permission from AACR
SUMMARY
� Efficacy of PARP inhibitors in monotherapy coupled with HR defect
� Combination strategy complex and in depth mechanistic
understanding needed
� PARP inhibitors trap PARP on DNA and has different effect from
protein loss
� PARP1 is involved in SSB repair, replication restart, fork protection,
B-NHEJ
� Resistance can develop to PARP inhibitors
Thank you!
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