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

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1.0

Surv

ival pro

babili

ty

Overall survival (months)

+ Censored 95% Confidence limits

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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

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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!