Download Achieving Precision Death with Cell

Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Clinical
Cancer
Research
Review
Achieving Precision Death with Cell-Cycle
Inhibitors that Target DNA Replication and
Repair
Aimee Bence Lin1, Samuel C. McNeely2, and Richard P. Beckmann3
Abstract
All cancers are characterized by defects in the systems that
ensure strict control of the cell cycle in normal tissues. The
consequent excess tissue growth can be countered by drugs that
halt cell division, and, indeed, the majority of chemotherapeutics developed during the last century work by disrupting
processes essential for the cell cycle, particularly DNA synthesis,
DNA replication, and chromatid segregation. In certain contexts, the efficacy of these classes of drugs can be impressive, but
because they indiscriminately block the cell cycle of all actively
dividing cells, their side effects severely constrain the dose and
duration with which they can be administered, allowing both
normal and malignant cells to escape complete growth arrest.
Recent progress in understanding how cancers lose control of
the cell cycle, coupled with comprehensive genomic profiling of
human tumor biopsies, has shown that many cancers have
mutations affecting various regulators and checkpoints that
impinge on the core cell-cycle machinery. These defects introduce unique vulnerabilities that can be exploited by a next
generation of drugs that promise improved therapeutic windows in patients whose tumors bear particular genomic aberrations, permitting increased dose intensity and efficacy. These
developments, coupled with the success of new drugs targeting
cell-cycle regulators, have led to a resurgence of interest in cellcycle inhibitors. This review in particular focuses on the newer
strategies that may facilitate better therapeutic targeting of
drugs that inhibit the various components that safeguard the
fidelity of the fundamental processes of DNA replication and
repair. Clin Cancer Res; 23(13); 1–9. 2017 AACR.
Introduction
defective. This shift in focus was vindicated by success of
oncogene-targeting drugs such as trastuzumab, imatinib, erlotinib, vemurafenib, and crizotinib (1).
During this same period, next-generation sequencing ushered
in efforts to comprehensively catalog all genomic aberrations that
can drive cancer growth (2). Interestingly, these studies identified
key cell-cycle checkpoint genes that are commonly mutated in
cancer. In particular, checkpoints at three stages are targeted by
mutations in established cancer genes: (i) G1 phase checkpoints,
including the restriction point; (ii) S-phase checkpoints, including
DNA damage and origin firing checkpoints; and (iii) M-phase,
particularly the spindle assembly checkpoint.
Recent years have seen the introduction of inhibitors that
specifically target kinases that facilitate DNA replication and
repair such as inhibitors of ataxia telangiectasia mutated kinase
(ATM), ataxia telangiectasia and Rad3-related kinase (ATR),
WEE1, checkpoint kinase 1 (CHK1), and checkpoint kinase 2
(CHK2), collectively referred to herein as checkpoint kinase
inhibitors. Because their mechanisms of action inhibit crucial
components of DNA damage checkpoints, the initial interest in
this class of inhibitors was their use in combination with standard
cytotoxic (genotoxic) therapies as chemopotentiators. However,
preclinical investigations led to a next-generation strategy that
relies on the identification of underlying genetic or expression
alterations that can potentially enhance the susceptibly of cancer
cells to checkpoint kinase inhibitor monotherapy or to combination therapy with targeted drugs that do not induce generalized
DNA damage. Consequently, this article reviews the underlying
genetic drivers in tumors that facilitate better selective targeting of
these agents, with a focus on checkpoint kinase inhibitors that are
currently in development (Table 1).
Tissue growth and homeostasis in multicellular organisms
necessitate a variety of systems to regulate and coordinate cell
division. When these systems fail, unabated and uncoordinated
growth can lead to cancer. The core cell-cycle machinery
required for chromosome duplication, chromosome segregation, and cytokinesis can be distinguished from cell-cycle regulators that restrain the core engine via cell-cycle checkpoints.
Many traditional cancer therapies act on the core machinery,
either at S-phase, preventing nucleotide synthesis and DNA
replication (antimetabolites, DNA-damaging agents, and radiotherapy) or at mitosis (microtubule inhibitors). As they act on
processes essential for all dividing cells, these classical therapies
also affect normal proliferating tissues, and toxicities seemed
inevitable for cell-cycle inhibitors. Hence, in the 1990s, cancer
drug discovery shifted focus from cell-cycle targets to mitogenic
and oncogenic signaling pathways. Targeting somatic mutations
in genes encoding members of these signaling pathways offered
a better therapeutic window in the cancers where they were
1
Early Phase Medical-Oncology, Eli Lilly and Company, Lilly Corporate Center,
Indianapolis, Indiana. 2Oncology Business Unit-Patient Tailoring, Eli Lilly and
Company, Lilly Corporate Center, Indianapolis, Indiana. 3Oncology Translational
Research, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, Indiana.
Corresponding Author: Richard P. Beckmann, Eli Lilly and Company, Lilly
Corporate Center, Drop Code 0438, Indianapolis, IN 46285. Phone: 317-2764285; Fax: 317-651-6346; E-mail: [email protected]
doi: 10.1158/1078-0432.CCR-16-0083
2017 American Association for Cancer Research.
www.aacrjournals.org
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.
OF1
Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Lin et al.
Table 1. Cell-cycle kinase inhibitors currently in development
Target
Agent
Phase
Context
WEE1
AZD1775, MK1775
II
Monotherapy
Chemotherapy combinations: cisplatin, carboplatin,
docetaxel, gemcitabine, irinotecan, nab-paclitaxel,
paclitaxel, peglyated liposomal doxorubicin,
pemetrexed
Targeted therapy combinations: olaparib, belinostat
Radiation/chemoradiation combinations:
monotherapy, cisplatin, gemcitabine, temozolomide
Immunotherapy combinations: durvalumab
CHK1
Prexasertib,
LY2606368
II
Monotherapy
Chemotherapy combinations: cisplatin, 5-FU,
pemetrexed
Targeted therapy combinations: cetuximab,
LY3023414 (PI3K/mTOR inhibitor), ralimetinib
(p38 MAPK inhibitor), olaparib
Chemoradiation combinations: cetuximab, cisplatin
LY2880070, ESP-01
I
CCT245737, PNT-737
I
Monotherapy
Chemotherapy combinations: gemcitabine
Monotherapy
Chemotherapy combinations: gemcitabine, cisplatin
Monotherapy
Chemotherapy combinations: gemcitabine
Monotherapy
Chemotherapy combinations: cisplatin, carboplatin,
gemcitabine, etoposide, irinotecan, topotecan
Targeted combinations: veliparib
Chemoradiation combinations: monotherapy, cisplatin
Monotherapy
Chemotherapy combinations: carboplatin, paclitaxel
Targeted combinations: olaparib
Radiation
Immunotherapy combinations: durvalumab
GDC-0575, ARRY-575 I
ATR
ATM
VX970
II
AZD6738
I
VX803
I
AZD0156
I
Monotherapy
Chemotherapy combinations: gemcitabine, carboplatin,
cisplatin
Monotherapy
Chemotherapy combinations: irinotecan, olaparib
Populations being evaluated in all clinical contexts
Cervical, CRC, gastric/GEJ, glioblastoma, gliomas, HNSCC,
NSCLC, myeloid malignancies, ovarian, pancreatic,
pediatric tumors, SCLC, squamous NSCLC, TNBC
Biomarker focused:
Basket trial: molecular profiling–based assignment
Bladder: mutations in genes associated with cell-cycle
regulation (RB1, CDKN2A, CCNE1 or MYC amp)
CRC: KRAS/NRAS/BRAF mutations
Gastric/GEJ: TP53 mutations
NSCLC: biomarker-directed basket trial
Ovarian: BRCA1 mutations, BRCA2 mutations, TP53 mutations, window trial
Pediatric: basket trial stratifying based on molecular
anomalies
AML/high-risk MDS, CRC, HSNCC, NSCLC, ovarian,
pediatric, prostate, SCC of anus, squamous NSCLC,
SCLC, TNBC
Biomarker focused:
Basket trial: replication stress or homologous repair
deficiency (e.g., MYC or CCNE1 amp, Rb loss, FBXW7
mutation, BRCA1, BRCA2, PALB2, RAD51C, RAD51D,
ATR, ATM, CHK2, the Fanconi anemia pathway genes)
Breast: BRCA1 mutations, BRCA2 mutations
CRC: KRAS/BRAF mutations
NSCLC: KRAS/BRAF mutations
Ovarian: BRCA1 mutations, BRCA2 mutations
CRC, ovarian, TNBC
NSCLC, pancreatic
HNSCC (HPV negative), NSCLC, ovarian, SCLC, urothelial,
squamous NSCLC, TNBC
B-cell malignancies, gastric/GEJ, HNSCC, NSCLC
Biomarker focused:
CLL: loss of chromosome 11q or ATM deficient
Gastric/GEJ: low ATM expression
HNSCC: window trial
NSCLC: low ATM expression
Ovarian
NOTE: Source: www.clinicaltrials.gov.
Abbreviations: AML, acute myeloid leukemia; amp, amplification; CLL, chronic lymphocytic leukemia; CRC, colorectal cancer; GEJ, gastroesophageal junction; HPV,
human papillomavirus; HNSCC, squamous cell head and neck cancer; MDS, myelodysplastic syndrome; NSCLC, non–small cell lung cancer; SCC, squamous cell cancer;
SCLC, small-cell lung cancer; TNBC, triple-negative breast cancer.
ATM, ATR, WEE1, CHK1, and CHK2 are crucial components of
DNA damage response (DDR) signaling networks responsible for
contributing either to the detection and repair of damage or for
coordinating DNA replication (3–6). These DDR checkpoint
kinases function collectively to maintain genomic integrity by
providing cells time to repair any DNA damage prior to replication or mitosis, and to initiate an apoptotic response if the damage
is beyond repair. ATR and ATM act as sensors of single-strand and
double-strand breaks (SSB and DSB), respectively, which activate
CHK1 and CHK2 by phosphorylation (Fig. 1). CHK1 and CHK2
suppress cell-cycle progression through downregulation of the
CDC25A and CDC25C phosphatases, which promote progression by removing inhibitory phosphates on CDK2 and CDK1,
OF2 Clin Cancer Res; 23(13) July 1, 2017
respectively (7). WEE1 also prevents cell-cycle progression via
inhibitory phosphorylation of CDK1 and CDK2 (8–11). The
ATR–CHK1 response is also initiated in response to ssDNA
generated by replication fork stalling (12, 13).
Strategies for Clinical Development: Past
and Present
The initial preclinical studies evaluating these inhibitors clearly
demonstrated that the chemical inhibition of checkpoint kinases
enhances the activity of cytotoxic therapies that damage DNA
through diverse mechanisms. Good reviews have been published
recently describing this biology, and, therefore, it will not be
Clinical Cancer Research
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.
Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Selective Targeting of Checkpoint Kinase Inhibitors
Endogenous or exogenous events
DSB
SSB
ATM
ATR
CHK2
CHK1
P
P
P
P
(Sequestration)
(Proteolysis)
WEE1
P
WEE1
P
CDC25A
CDC25C
P
P
P
P
CDK2
CDK2
CDK1
CDK1
Cyclin E
Cyclin E
Cyclin A/B
Cyclin A/B
P
p53
p21
G1
S
G2
M
© 2017 American Association for Cancer Research
Figure 1.
ATR, ATM, CHK1, CHK2, and WEE1 inhibit cell-cycle progression into S-phase and mitosis following DNA damage. This regulation occurs ultimately through the
control of the cyclin-dependent kinases (CDK) that facilitate entry into the S- and M-phases of the cell cycle, namely CDK2 and CDK1, respectively. The
activity of CDK1 and CDK2 are controlled by phosphorylation as well as by the partnership of these kinases with their regulatory cyclin subunits,
whereby activation of CDK2 requires association with cyclin E and CDK1 activation requires association with either cyclin A or B. Phosphorylation of either
CDK1 or CDK2 is regulated in part by the opposing actions of the WEE1 kinase and the CDC25A/CDC25C phosphatases. ATR and ATM are sensors of
SSBs and DSBs, respectively, which activate CHK1 and CHK2, respectively, by phosphorylation. The inhibition of cell-cycle progression by activated
(phosphorylated) CHK1 and CHK2 results from the inhibition of CDK1 and CDK2, which is mediated by preventing the removal of inhibitory phosphates placed
on CDK1 and CDK2, by WEE1. CHK1 and CHK2 prevent the removal of these phosphates by suppressing the CDC25A and CDC25C phosphatases
through phosphorylation, whereby this phosphorylation facilitates proteolytic degradation of CDC25A and the sequestration of CDC25C by 14-3-3. p53 is
activated upon DNA damage by phosphorylation by ATM and CHK2 and serves as an additional pathway to inhibit cell-cycle progression by
promoting transcription of p21, which in turn inhibits the kinase activity of the cyclinE–CDK2 complex.
summarized here (7, 10, 12–16). As a result of these data, clinical
trials with early CHK1 inhibitors focused on the chemopotentiation of cytotoxic drugs. Although phase I trials demonstrated
proof of concept that CHK1 inhibitors could be safely combined
with chemotherapy (17–25), phase II studies failed to meet their
primary endpoints (26, 27). Early CHK1 inhibitors were not
successful for a variety of reasons, including pharmacokinetic
properties, unacceptable toxicities, and business considerations.
However, newer inhibitors, which are more diverse and include
not only CHK1 inhibitors but also WEE1, ATR, and ATM inhibitors, continue to test this hypothesis with a variety of genotoxic
agents and as monotherapies (Table 1). Although no phase II
studies have been published with checkpoint inhibitors as monotherapy, evidence of efficacy has been observed in phase I. A phase
I evaluation of AZD1775 as a monotherapy enrolled 24 patients,
nine of whom had BRCA1 or BRCA2 mutations. Two patients with
a BRCA1 mutation [squamous cell cancer (SCC) of the base of the
www.aacrjournals.org
tongue and papillary serous ovarian cancer] had partial responses
(28). Prexasertib, a CHK1 inhibitor, demonstrated objective
responses in patients with SCC of the anus and head and neck
cancer in a phase I study with multiple expansion cohorts (29).
These preliminary results suggest that the newer inhibitors may be
more successful than initial CHK1 inhibitors, which were only
developed as chemopotentiators.
In addition, these data suggest the optimal use of these inhibitors may require the identification of contexts where tumorspecific vulnerabilities are leveraged to achieve selective cytotoxicity in cancer cells. p53 is a critical mediator of the DDR, which is
activated through phosphorylation by CHK2 and ATM, and
participates in a parallel pathway to ATR, CHK1, and WEE1 (Fig. 1;
ref. 7). For this reason, cancer cells that have lost either p53
function or ATM may show greater reliance on ATR, CHK1, and
WEE1 for efficient repair and, hence, greater sensitivity to treatments that inhibit these kinases (30–35). This hypothesis has
Clin Cancer Res; 23(13) July 1, 2017
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.
OF3
Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Lin et al.
been tested in a phase II trial where patients with TP53-mutated
ovarian cancer who were refractory or resistant (<3 months) to
first-line therapy received AZD1775 in combination with carboplatin. The combination demonstrated manageable toxicity, and
in 21 evaluable patients, the objective response rate was 43%.
Median progression-free and overall survival times were 5.3
months and 12.6 months, respectively. In addition to TP53
mutations, patients with an objective response had alterations
in BRCA1, KRAS, MYC, or CCNE (cyclin E; ref. 36). Similarly, in a
randomized, phase II trial in platinum-sensitive, TP53-mutant
ovarian cancer, the WEE1 inhibitor AZD1775 combined with
paclitaxel and carboplatin met the primary and secondary endpoints and significantly prolonged progression-free survival compared with the combination of paclitaxel and carboplatin (37). In
a phase I, multi-arm combination study assessing AZD1775 with
either gemcitabine, cisplatin, or carboplatin, 176 patients were
evaluable for response. Responses were observed in patients with
ovarian cancer (n ¼ 7), melanoma (n ¼ 3), breast cancer (n ¼ 2),
head and neck cancer (n ¼ 3), colorectal cancer (n ¼ 1), and SCC
of the skin (n ¼ 1). Patients with TP53 mutations (4/19, 23%) had
a partial response compared with 4/33 (12%) of patients with
TP53 wild-type tumors (38).
Ongoing studies with AZD1775 continue to evaluate this
hypothesis in TP53-mutated gastric cancer (with paclitaxel,
NCT02448329), TP53- or KRAS-mutated solid tumors (with
olaparib, NCT02576444), and TP53-mutated (with either MYC
amplification or CDKN2A mutation) relapsed small-cell lung
cancer (SCLC; monotherapy, NCT02688907). Similarly, the
ATR inhibitor AZD6738 has an ongoing clinical study
(NCT02264678) in ATM-low/deficient NSCLC (with carboplatin) or gastric cancer (with olaparib). These studies will further
characterize the impact of TP53 mutations and ATM deficiency
not only in the context of cytotoxic chemotherapy but also with
targeted agents and monotherapy.
The emerging clinical data with TP53 mutations are one example of potential synthetic lethality (SL), where functional alterations in one pathway lead to enhanced sensitivity to inhibition of
another pathway. This is the strategy guiding the use of PARP
inhibitors as therapies for BRCA1- or BRCA2-deficient breast or
ovarian cancers (39–42). Leveraging SL for checkpoint kinase
inhibitors requires knowledge about functional alterations in
cancer cells that make them more vulnerable to the inhibition
of these kinases than normal cells. Although TP53 mutations are
the most well-characterized example of SL with the checkpoint
inhibitors, the concept of replication stress (RS) is emerging as a
potential SL mechanism (43, 44). RS can arise in any situation
that leads to inappropriate replication origin licensing or firing
(45). This results in stalled replication forks and DNA breaks if
the stalled forks are not adequately resolved (46–48). In cancer
cells, oncogene-driven events can contribute to higher degrees of
RS by promoting growth to a point that strains the replicative
capacity of the cell (45, 49). As a result, inhibitors of checkpoint
kinases may induce SL with tumors that have high RS, as all of
these kinases contribute to sensing and reducing RS (Fig. 2). In
particular, WEE1 and CHK1 play complementary roles in restricting the initiation of replication origins by inhibiting CDK2, which
when activated, promotes replication (6, 50, 51). Thus, treatment
with an inhibitor of CHK1 or WEE1 augments ongoing RS by
effectively neutralizing one of the mechanisms available for
suppressing replication origin firing, resulting in more stalling
and DNA breaks. As both CHK1 and WEE1 are important
OF4 Clin Cancer Res; 23(13) July 1, 2017
signaling components in the response to DNA damage, damage
that results from the additional RS is potentially exacerbated
because it cannot be repaired effectively. Likewise, ATR plays an
important role as a sensor for RS as it is recruited to regions of
ssDNA that become exposed by replication fork stalling. Subsequently, ATR is responsible for activating CHK1, which in turn
suppresses replication, as indicated above (15). An ongoing
challenge is to identify tumors that have reached near-critical
levels of RS and are likely the most susceptible to treatment with
checkpoint kinase inhibitors.
Validation of therapeutic strategies to exploit RS has recently
emerged from several studies (52–63). For example, an SL relationship was described between oncogene-induced RS by MYC
activation and ATR loss in lymphomas (49). Specifically in the
context of ATR-deficient cells, MYC expression induced higher RS
and apoptosis and contributed to greater sensitivity to ATR and
CHK1 inhibitors. Analogous observations were derived from
studies in neuroblastoma models wherein sensitivity to CHK1
inhibition was correlated with MYCN expression (52). Studies in
other model systems for hematologic malignancies such as MYCdriven diffuse large B-cell lymphoma, cyclin D1–driven mantle
cell lymphomas, T-cell acute lymphoblastic leukemia, and acute
myeloid leukemia suggest that oncogene-induced RS in these
cancers may make them particularly vulnerable to treatment with
checkpoint kinase inhibitors (53–55, 58, 61, 63). The hypothesis
that MYC may drive RS and increase sensitivity to checkpoint
kinase inhibitors is being tested in several ongoing clinical trials,
including a biomarker-directed study with AZD1775 and durvalumab in muscle-invasive bladder cancer. To be eligible, patients
must have mutations in CDKN2A or RB1 genes and/or amplification of CCNE1, MYC, MYCL, or MYCN genes, all of which
presumably contribute to heightened RS (Fig. 2). Other agents
are focusing on SCLC, a tumor associated with RS and MYC
amplifications: AZD1775 (NCT02593019) and prexasertib
(NCT02735980) are being assessed as monotherapy, whereas
VX970 is being evaluated with topotecan (NCT02487095).
Another opportunity for SL may be inhibition of ATR in the
context of ATM deficiency. In preclinical models of hematologic
malignancies, cells that lack ATM (e.g., due to 11q deletions) or
have defects in p53 signaling were particularly vulnerable to the
ATR inhibitor AZD6738. Treatment with AZD6738 increased
replication initiation and fork stalling, resulting in RS and DNA
damage that likely contributed to selective cytotoxicity in cells
with p53 and/or ATM defects (64). In parallel, in a phase I trial
with the ATR inhibitor VX970 and carboplatin, a patient with
colorectal cancer and ATM loss achieved a complete response
(65). This hypothesis is being further tested in a trial of AZD6738
in patients with relapsed/refractory B-cell malignancies with
prospectively identified 11q-deleted or ATM-deficient relapsed/
refractory CLL (NCT01955668).
In addition to neuroblastomas, as mentioned above, other
pediatric cancers, particularly sarcomas, may represent another
opportunity for exploiting oncogenic drivers of RS, as demonstrated by recent studies in models for Ewing sarcoma (ES)
wherein the oncogenic drivers were fusion proteins unique to
this tumor (EWS/FLI1 or EWS/ERG; ref. 59). In these studies, ES
cell lines were more sensitive to inhibition of ATR compared with
sarcoma cell lines that lacked the EWS fusions, and ATR inhibitor
monotherapy resulted in near-complete to complete growth
inhibition of human ES xenografts. Related studies with the CHK1
inhibitor prexasertib (56) showed that monotherapy resulted in
Clinical Cancer Research
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.
Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Selective Targeting of Checkpoint Kinase Inhibitors
Cyclin E
P
P
P
CDK2
CDC25A
CHK1
WEE1
Cyclin E
CDK2
RPA
RPA
TopBP1
ATRIP
DNA lesion
ATR
RPA
“Activation”
P
RPA
Replication stress
• Oncogenes
• Enhanced cyclin E or CDK2 expression/activity
• Loss of regulation of G1 → S progression
• Loss of function of ATR, CHK1, or WEE1
Fork collapse → DSBs
Homologous
recombination repair
© 2017 American Association for Cancer Research
Figure 2.
The ATR–CHK1 pathway reduces RS. The kinase function of CDK2 requires activation by association with cyclin E. When activated by cyclin E, CDK2 facilitates
the progression of cells from G1 into S-phase and subsequently promotes replication origin firing. ATR and CHK1 suppress replication origin firing in part by
suppressing the activity of CDK2 through regulation of downstream effectors that coordinate the phosphorylation of CDK2. Specifically, the presence of long
stretches of single-stranded DNA, which can occur in situations where the DNA polymerases lag behind the unwinding activity of the helicases, trigger ATR, which is
recruited by a complex of proteins including replication protein A (RPA), topoisomerase-binding protein 1 (TopBP1), and ATR-interacting protein (ATRIP).
ATR then activates CHK1 (through phosphorylation), which subsequently through phosphorylation of the CDC25A phosphatase, negatively regulates CDK2 by
preventing the removal of inhibitory phosphates by this phosphatase. The actions of CDC25A are also opposed by WEE1, which contributes to the inhibition
of CDK2 by catalyzing the inhibitory phosphates that are removed by CDC25A. As shown at the bottom half of the figure, RS can result from endogenous or
exogenous DNA damage as well as through the action of growth-promoting oncogenes, such as MYC, which serve to drive progression into S-phase. In
addition, RS can also arise through other alterations that disrupt control at the G1–S interface, such as changes that lead to enhanced expression of cyclin
E or loss of inhibition of CDK2. Alterations that may enhance cyclin E expression or CDK2 activity possibly include (i) losses in FBXW7, which facilitates
proteasomal degradation of cyclin E or (ii) alterations that disrupt regulation of the primary restriction point controlling progression from G1 into S including
activation of CDK4, CDK6, and D-type cyclins or loss of RB1 that serves to activate E2F, thereby promoting the transcription of the genes that encode cyclin E
and CDK2 as well as other gene products that promote DNA replication. Notably, as indicated by the red Xs, the inhibition or loss of function of ATR, CHK1,
or WEE1 can elevate ongoing RS by effectively removing the control over CDK2. The result of this inhibition or loss is replication fork collapse, with eventual
DNA DSBs leading to the activation of DNA damage and repair responses such as homologous recombination repair.
complete regressions in xenograft models for desmoplastic small
round cell tumor, which also expresses an oncogenic EWS fusion
protein known as EWS–WT1, or alveolar rhabdomyosarcoma, a
malignancy driven by another unique oncogenic fusion protein
(66, 67). These nonclinical studies with prexasertib have led to an
interest in exploring prexasertib in pediatric solid tumors
(NCT02808650). In addition, WEE1 was identified as a target in
medulloblastoma, the most common pediatric malignant brain
tumor (68). AZD1775 induced DNA damage and suppressed the
growth of medulloblastoma cells both in vitro and in vivo (68),
potentially by exploiting MYC-induced RS (69). AZD1775 has
also demonstrated in vitro activity in rhabdomyosarcoma as
monotherapy and in combination with conventional therapies
(70) and improved the efficacy of radiation in mouse models of
www.aacrjournals.org
pediatric high-grade glioma (71). A phase I study of AZD1775 and
radiation in children with diffuse intrinsic pontine gliomas is
ongoing (NCT01922076). AZD1775 is also being assessed in the
European Proof-of-Concept Therapeutic Stratification Trial of
Molecular Anomalies in Relapsed or Refractory Tumors
(ESMART). In this basket study, molecular profiling of pediatric
tumors is used to direct patients to individual treatment
arms, including a combination of AZD1775 and carboplatin
(NCT02813135).
Strategies exploiting RS also include combining inhibitors
targeting different checkpoint kinases. Accordingly, RNA interference (RNAi) studies exploring SL with the CHK1 inhibitor
PF-00477736 identified WEE1 as the most significant hit (72).
In addition, synergistic growth inhibition was observed with
Clin Cancer Res; 23(13) July 1, 2017
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.
OF5
Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Lin et al.
PF-00477736 and AZD1775 in cell lines and in a xenograft
model for ovarian cancer (72). Synergy was also observed with
AZD1775 and the CHK1 inhibitor MK-8776 (73). Analogous
studies showed that treatment of cancer cells in culture with the
CHK1 inhibitor AZD7762 and the ATR inhibitor VE-821 elevated RS, leading to replication catastrophe and death by
apoptosis. The combination was associated with a significant
inhibition of tumor growth and an increase in overall survival
in mice bearing human NCI-H460 NSCLC xenografts when
compared with the monotherapy treatments (74).
In addition to RS, deficiencies in homologous recombination
repair (HRR) may also contribute to greater sensitivity to checkpoint kinase inhibition, as homologous recombination deficiencies (HRD) reduce the efficiency of repair of DSBs that result from
RS generated by these inhibitors (Fig. 2). Deficiencies in the
Fanconi anemia (FA) genes (FANC), such as defects in BRCA1
or BRCA2, also disrupt HRR (75), and studies with the CHK1
inhibitor G€
o6976 showed that FA-deficient cell lines were highly
sensitive to G€
o6976 and to RNAi silencing of CHK1 mRNA
expression when compared with isogenic lines that were FA
proficient (76). An RNAi-based screen that targeted 230 DNA
repair genes identified many FANC genes as SL with G€
o6976
treatment, including FANCA, FANCC, FANCD1, FANCD2,
FANCE, FANCF, and FANCG.
A similar approach using siRNA to target 240 DNA replication
and repair genes explored SL with ATR inhibitors (57). These
studies uncovered that loss of expression of ATR pathway genes
had the strongest association for SL including losses of ATR itself,
ATRIP, RPA, and CHK1. As the ATR pathway is crucial for
responding to RS, the observations from this study as well as
others provide support regarding the therapeutic benefits that
may be derived from the combined inhibition of targets within
this pathway to elevate RS further (62, 72–74). In addition, the
results confirm the benefit that may be attained through monotherapy by selective targeting of tumors with preexisting mutations in this pathway. Of note, these studies demonstrated that
loss of excision repair cross-complementation group 1 protein
(ERCC1), which functions in the repair of bulky DNA adducts,
DSBs, and interstrand cross-links (77), was a significant SL interaction with ATR and CHK1 inhibition. Similar SL interactions
were observed between ATR inhibition and loss of another repair
gene known as XRCC1, which plays a role base excision repair
(78) and with ATM deficiency (34).
These studies suggest that therapeutic strategies aimed at disrupting HRR may facilitate SL with checkpoint kinase inhibitors.
In this regard, CHK1, in addition to its role in limiting RS, is
required for HRR by facilitating the essential recruitment of
RAD51 to sites of repair (79). Thus, CHK1 inhibition would be
expected to promote further deficiencies in HRR in addition to
exacerbating RS. In support of this concept, augmented growth
inhibition by the PARP inhibitor olaparib was observed upon the
RNAi silencing of genes encoding CHK1, CHK2, ATR, ATM, and
RPA1 as well as genes encoding proteins that contribute to HRR
such as RAD51, NBS1, FANCA, FANCD2, and FANCC (40). In
addition, studies in breast carcinoma cell lines showed that the
combination of PARP inhibitors (olaparib, veliparib, NU1025, or
rucaparib) with CHK1 inhibitors (UCN-01, AZD7762, or
LY2603618) increased DNA damage and cytotoxicity, as compared with the single-agent treatments (80). More recent studies
have shown in BRCA1- or BRCA2-mutated high-grade serous
ovarian cancer (HGSOC) models that combination therapy with
OF6 Clin Cancer Res; 23(13) July 1, 2017
olaparib and either MK-8776 (CHK1) or AZD6738 (ATR) acted
synergistically to decrease survival and colony formation in vitro
and inhibit tumor xenograft growth in vivo (81). Clinical trials
evaluating PARP inhibition with AZD1775 (NCT02511795),
AZD0156 (NCT02588105), VX970 (NCT02723864), or
AZD6738 (NCT02264678) are ongoing. In addition, a study with
AZD1775 and olaparib (OLAPCO) is a molecularly directed trial
that requires mutations in TP53 or KRAS (NCT02576444).
As outlined above, the optimal context for a checkpoint kinase
inhibitor might be tumors that have both high RS and HRD. Of
notable interest are ovarian cancers, particularly HGSOCs, as
approximately half harbor mutations in genes that modulate
HRR, including mutations that impact BRCA1 and BRCA2
(39, 82). In addition, nearly all HGSOCs have mutations in TP53
(83). Mutations in ATM and ATR have been observed in 2% of
HGSOCs, and 5% have mutations in genes of the FA DNA repair
pathway (39). Mutually exclusive with mutations in BRCA1 and
BRCA2, CCNE1 is amplified in 15% to 20% of HGSOCs (82, 84).
RB1 loss is also observed in about 15% of these cancers (83). As
cyclin E is required for activation of CDK2, its overexpression
induces RS and DNA damage that activates HRR and may increase
sensitivity to single-agent CHK1, ATR1, and/or WEE1 inhibition
(85). Likewise loss of RB1 can contribute to RS by promoting the
progression of cells into S-phase. Therefore, HGSOCs present a
provocative context for therapy with the checkpoint kinase inhibitors by providing an opportunity to leverage the dual presence
of higher RS and HRD (28, 86). Accordingly, AZD1775, prexasertib, LY2880070, VX970, VX803, and AZD0156 are being
assessed in a variety of subsets of ovarian cancer (Table 1), and
it may be notable that AZD1775 has demonstrated clinical
activity in both platinum-sensitive and platinum-resistant ovarian cancer (36, 37).
As our understanding of SL interactions and the underlying
mechanisms of the checkpoint kinase inhibitors grows, the
optimal context may shift from a focus on a particular histology
such as ovarian cancer, to the genetic attributes of the tumor
regardless of histology. This approach is already being implemented in multiple clinical trials. In a prexasertib basket trial
(NCT02873975), patients whose tumors show alterations consistent with RS (MYC amplification, CCNE1 amplification, Rb
loss, or FBXW7 mutation) or HRD (BRCA1, BRCA2, PALB2,
RAD51C, RAD51D, ATR, ATM, CHK2, or the FA pathway genes)
are eligible. Similarly, AZD1775 is being assessed in the Molecular Profiling–Based Targeted Therapy (MPACT) trial, which
assigns patients with solid tumors to a treatment regimen
based on their mutation/amplification category. One of these
arms assesses AZD1775 in combination with carboplatin
(NCT01827384). One obvious goal from these types of studies,
besides improved efficacy, is to identify tumor-specific biomarkers that can be used to predict response to monotherapy or
combination therapy with one or more checkpoint kinase
inhibitors. Preclinical studies indicate that alterations inducing
RS or HRD contribute to greater sensitivity to these inhibitors.
However, the crucial challenge from a clinical perspective is
going beyond just identifying which of these alterations indicate the presence of RS or HRD to identifying situations where
tumors are at near-unstainable levels of RS or HRD and,
therefore, are most susceptible to interventions that further
augment RS or compromise HRR.
The identification of expression or genetic alterations in a small
subset of stand-alone biomarkers for predicting response is
Clinical Cancer Research
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.
Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Selective Targeting of Checkpoint Kinase Inhibitors
certainly desirable and may be achievable in certain cancers, but
for other cancers, additional methodologies may be required to
adequately measure the extent to which RS and HRD are near
catastrophic. However, these challenges should not dampen our
enthusiasm for the ongoing clinical trials with the various checkpoint kinase inhibitors, as some of these trials may provide patient
data that will allow us to validate and refine our biomarker
hypotheses. The preclinical studies have provided a solid foundation leading to the concept of leveraging RS and HRD to achieve
SL in human tumors. The clinical data will allow us to return to the
bench to explore additional concepts that will further enhance
the therapeutic benefit of the checkpoint kinase inhibitors.
Disclosure of Potential Conflicts of Interest
A.B. Lin, S.C. McNeely, and R.P. Beckmann hold ownership interest in
Eli Lilly and Company. No other potential conflicts of interest were
disclosed.
The costs of publication of this article were defrayed in part by the
payment of page charges. This article must therefore be hereby marked
advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate
this fact.
Received October 17, 2016; revised November 29, 2016; accepted March 15,
2017; published OnlineFirst March 22, 2017.
References
1. Chin L, Andersen JN, Futreal PA. Cancer genomics: from discovery science
to personalized medicine. Nat Med 2011;17:297–303.
2. Stratton MR, Campbell PJ, Futreal PA. The cancer genome. Nature
2009;458:719–24.
3. Ciccia A, Elledge SJ. The DNA damage response: making it safe to play with
knives. Mol Cell 2010;40:179–204.
4. Harper JW, Elledge SJ. The DNA damage response: ten years after. Mol Cell
2007;28:739–45.
5. Sorensen CS, Syljuasen RG. Safeguarding genome integrity: the checkpoint
kinases ATR, CHK1 and WEE1 restrain CDK activity during normal DNA
replication. Nucleic Acids Res 2012;40:477–86.
6. Jones RM, Petermann E. Replication fork dynamics and the DNA damage
response. Biochem J 2012;443:13–26.
7. McNeely S, Beckmann R, Bence Lin AK. CHEK again: revisiting the development of CHK1 inhibitors for cancer therapy. Pharmacol Ther 2014;
142:1–10.
8. Parker LL, Piwnica-Worms H. Inactivation of the p34cdc2-cyclin B complex
by the human WEE1 tyrosine kinase. Science 1992;257:1955–7.
9. Watanabe N, Broome M, Hunter T. Regulation of the human WEE1Hu CDK
tyrosine 15-kinase during the cell cycle. EMBO J 1995;14:1878–91.
10. Do K, Doroshow JH, Kummar S. Wee1 kinase as a target for cancer therapy.
Cell Cycle 2013;12:3159–64.
11. Matheson CJ, Backos DS, Reigan P. Targeting WEE1 kinase in cancer. Trends
Pharmacol Sci 2016;37:872–81.
12. Fokas E, Prevo R, Hammond EM, Brunner TB, McKenna WG, Muschel RJ.
Targeting ATR in DNA damage response and cancer therapeutics. Cancer
Treat Rev 2014;40:109–17.
13. Weber AM, Ryan AJ. ATM and ATR as therapeutic targets in cancer.
Pharmacol Ther 2015;149:124–38.
14. Ma CX, Janetka JW, Piwnica-Worms H. Death by releasing the
breaks: CHK1 inhibitors as cancer therapeutics. Trends Mol Med
2011;17:88–96.
15. Toledo LI, Murga M, Fernandez-Capetillo O. Targeting ATR and Chk1
kinases for cancer treatment: a new model for new (and old) drugs. Mol
Oncol 2011;5:368–73.
16. Thompson R, Eastman A. The cancer therapeutic potential of Chk1 inhibitors: how mechanistic studies impact on clinical trial design. Br J Clin
Pharmacol 2013;76:358–69.
17. Calvo E, Braiteh F, Von Hoff D, McWilliams R, Becerra C, Galsky MD, et al.
Phase I study of CHK1 inhibitor LY2603618 in combination with gemcitabine in patients with solid tumors. Oncology 2016;91:251–60.
18. Calvo E, Chen VJ, Marshall M, Ohnmacht U, Hynes SM, Kumm E, et al.
Preclinical analyses and phase I evaluation of LY2603618 administered in
combination with pemetrexed and cisplatin in patients with advanced
cancer. Invest New Drugs 2014;32:955–68.
19. Daud AI, Ashworth MT, Strosberg J, Goldman JW, Mendelson D, Springett
G, et al. Phase I dose-escalation trial of checkpoint kinase 1 inhibitor MK8776 as monotherapy and in combination with gemcitabine in patients
with advanced solid tumors. J Clin Oncol 2015;33:1060–6.
20. Doi T, Yoshino T, Shitara K, Matsubara N, Fuse N, Naito Y, et al. Phase I
study of LY2603618, a CHK1 inhibitor, in combination with gemcitabine in Japanese patients with solid tumors. Anticancer Drugs 2015;26:
1043–53.
www.aacrjournals.org
21. Infante JR, Hollebecque A, Postel-Vinay S, Bauer TM, Blackwood E,
Evangelista M, et al. Phase I study of GDC-0425, a checkpoint kinase
1 inhibitor, in combination with gemcitabine in patients with refractory solid tumors [abstract]. In: Proceedings of the 106th Annual
Meeting of the American Association for Cancer Research; 2015
Apr 18–22; Philadelphia, PA. Philadelphia (PA): AACR; 2015.
Abstract nr CT139.
22. Karp JE, Thomas BM, Greer JM, Sorge C, Gore SD, Pratz KW, et al. Phase I
and pharmacologic trial of cytosine arabinoside with the selective checkpoint 1 inhibitor Sch 900776 in refractory acute leukemias. Clin Cancer Res
2012;18:6723–31.
23. Sausville E, Lorusso P, Carducci M, Carter J, Quinn MF, Malburg L, et al.
Phase I dose-escalation study of AZD7762, a checkpoint kinase inhibitor,
in combination with gemcitabine in US patients with advanced solid
tumors. Cancer Chemother Pharmacol 2014;73:539–49.
24. Seto T, Esaki T, Hirai F, Arita S, Nosaki K, Makiyama A, et al. Phase I, doseescalation study of AZD7762 alone and in combination with gemcitabine
in Japanese patients with advanced solid tumours. Cancer Chemother
Pharmacol 2013;72:619–27.
25. Weiss GJ, Donehower RC, Iyengar T, Ramanathan RK, Lewandowski K,
Westin E, et al. Phase I dose-escalation study to examine the safety and
tolerability of LY2603618, a checkpoint 1 kinase inhibitor, administered 1
day after pemetrexed 500 mg/m(2) every 21 days in patients with cancer.
Invest New Drugs 2013;31:136–44.
26. Scagliotti G, Kang JH, Smith D, Rosenberg R, Park K, Kim SW, et al. Phase II
evaluation of LY2603618, a first-generation CHK1 inhibitor, in combination with pemetrexed in patients with advanced or metastatic non-small
cell lung cancer. Invest New Drugs 2016;34:625–35.
27. Webster JA, Tibes R, Blackford A, Morris L, Patnaik MM, Wang L, et al.
Randomized phase II trial of timed sequential cytosine arabinoside with
and without the CHK1 inhibitor MK-8876 in adults with relapsed and
refractory acute myelogenous leukemia. Blood 2015;126:2563.
28. Do K, Wilsker D, Ji J, Zlott J, Freshwater T, Kinders RJ, et al. Phase I study of
single-agent AZD1775 (MK-1775), a Wee1 kinase inhibitor, in patients
with refractory solid tumors. J Clin Oncol 2015;33:3409–15.
29. Hong D, Infante J, Janku F, Jones S, Nguyen LM, Burris H, et al. Phase I study
of LY2606368, a checkpoint kinase 1 inhibitor, in patients with advanced
cancer. J Clin Oncol 2016;34:1764–71.
30. Zabludoff SD, Deng C, Grondine MR, Sheehy AM, Ashwell S, Caleb BL,
et al. AZD7762, a novel checkpoint kinase inhibitor, drives checkpoint
abrogation and potentiates DNA-targeted therapies. Mol Cancer Ther
2008;7:2955–66.
31. Hirai H, Iwasawa Y, Okada M, Arai T, Nishibata T, Kobayashi M, et al.
Small-molecule inhibition of Wee1 kinase by MK-1775 selectively sensitizes p53-deficient tumor cells to DNA-damaging agents. Mol Cancer Ther
2009;8:2992–3000.
32. King C, Diaz H, Barnard D, Barda D, Clawson D, Blosser W, et al.
Characterization and preclinical development of LY2603618: a selective
and potent Chk1 inhibitor. Invest New Drugs 2014;32:213–26.
33. Rajeshkumar NV, De Oliveira E, Ottenhof N, Watters J, Brooks D, Demuth
T, et al. MK-1775, a potent Wee1 inhibitor, synergizes with gemcitabine to
achieve tumor regressions, selectively in p53-deficient pancreatic cancer
xenografts. Clin Cancer Res 2011;17:2799–806.
Clin Cancer Res; 23(13) July 1, 2017
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.
OF7
Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Lin et al.
34. Reaper PM, Griffiths MR, Long JM, Charrier JD, Maccormick S, Charlton PA,
et al. Selective killing of ATM- or p53-deficient cancer cells through
inhibition of ATR. Nat Chem Biol 2011;7:428–30.
35. Toledo LI, Murga M, Zur R, Soria R, Rodriguez A, Martinez S, et al. A
cell-based screen identifies ATR inhibitors with synthetic lethal properties for cancer-associated mutations. Nat Struct Mol Biol 2011;18:
721–7.
36. Leijen S, van Geel RM, Sonke GS, de Jong D, Rosenberg EH, Marchetti S,
et al. Phase II study of WEE1 inhibitor AZD1775 plus carboplatin in
patients with TP53-mutated ovarian cancer refractory or resistant to
first-line therapy within 3 months. J Clin Oncol 2016;34:4354–61.
37. Oza AM, Weberpals JI, Provencher DM, Grischke E-M, Hall M, Uyar D, et al.
An international, biomarker-directed, randomized, phase II trial of
AZD1775 plus paclitaxel and carboplatin (P/C) for the treatment of
women with platinum-sensitive, TP53-mutant ovarian cancer. J Clin Oncol
33, 2015 (suppl; abstr 5506).
38. Leijen S, van Geel RM, Pavlick AC, Tibes R, Rosen L, Razak AR, et al. Phase I
study evaluating WEE1 inhibitor AZD1775 as monotherapy and in combination with gemcitabine, cisplatin, or carboplatin in patients with
advanced solid tumors. J Clin Oncol 2016;34:4371–80.
39. Lord CJ, Ashworth A. BRCAness revisited. Nat Rev Cancer 2016;16:
110–20.
40. McCabe N, Turner NC, Lord CJ, Kluzek K, Bialkowska A, Swift S, et al.
Deficiency in the repair of DNA damage by homologous recombination
and sensitivity to poly(ADP-ribose) polymerase inhibition. Cancer Res
2006;66:8109–15.
41. Bryant HE, Schultz N, Thomas HD, Parker KM, Flower D, Lopez E, et al.
Specific killing of BRCA2-deficient tumours with inhibitors of poly(ADPribose) polymerase. Nature 2005;434:913–7.
42. Farmer H, McCabe N, Lord CJ, Tutt AN, Johnson DA, Richardson TB, et al.
Targeting the DNA repair defect in BRCA mutant cells as a therapeutic
strategy. Nature 2005;434:917–21.
43. Dobbelstein M, Sorensen CS. Exploiting replicative stress to treat cancer.
Nat Rev Drug Discov 2015;14:405–23.
44. Lecona E, Fernandez-Capetillo O. Replication stress and cancer: it takes two
to tango. Exp Cell Res 2014;329:26–34.
45. Hills SA, Diffley JF. DNA replication and oncogene-induced replicative
stress. Curr Biol 2014;24:R435–44.
46. Gaillard H, Garcia-Muse T, Aguilera A. Replication stress and cancer. Nat
Rev Cancer 2015;15:276–89.
47. Zeman MK, Cimprich KA. Causes and consequences of replication stress.
Nat Cell Biol 2014;16:2–9.
48. Mazouzi A, Velimezi G, Loizou JI. DNA replication stress: causes, resolution and disease. Exp Cell Res 2014;329:85–93.
49. Murga M, Campaner S, Lopez-Contreras AJ, Toledo LI, Soria R, Montana
MF, et al. Exploiting oncogene-induced replicative stress for the selective
killing of Myc-driven tumors. Nat Struct Mol Biol 2011;18:1331–5.
50. Maya-Mendoza A, Petermann E, Gillespie DA, Caldecott KW, Jackson DA.
Chk1 regulates the density of active replication origins during the vertebrate S phase. EMBO J 2007;26:2719–31.
51. Petermann E, Woodcock M, Helleday T. Chk1 promotes replication fork
progression by controlling replication initiation. Proc Natl Acad Sci U S A
2010;107:16090–5.
52. Cole KA, Huggins J, Laquaglia M, Hulderman CE, Russell MR, Bosse K, et al.
RNAi screen of the protein kinome identifies checkpoint kinase 1 (CHK1)
as a therapeutic target in neuroblastoma. Proc Natl Acad Sci U S A
2011;108:3336–41.
53. David L, Fernandez-Vidal A, Bertoli S, Grgurevic S, Lepage B, Deshaies D,
et al. CHK1 as a therapeutic target to bypass chemoresistance in AML. Sci
Signal 2016;9:ra90.
54. Derenzini E, Agostinelli C, Imbrogno E, Iacobucci I, Casadei B, Brighenti E,
et al. Constitutive activation of the DNA damage response pathway as a
novel therapeutic target in diffuse large B-cell lymphoma. Oncotarget
2015;6:6553–69.
55. Ghelli Luserna Di Rora A, Iacobucci I, Imbrogno E, Papayannidis C,
Derenzini E, Ferrari A, et al. Prexasertib, a Chk1/Chk2 inhibitor, increases
the effectiveness of conventional therapy in B-/T- cell progenitor acute
lymphoblastic leukemia. Oncotarget 2016;7:53377–91.
56. May C, Beckmann R, Blosser W, Dowless M, VanWye A, Burke T, et al.
Targeting checkpoint kinase 1 (CHK1) with the small molecule inhibitor
LY2606368 mesylate monohydrate in models of high-risk pediatric cancer
OF8 Clin Cancer Res; 23(13) July 1, 2017
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
yields significant antitumor effects [abstract]. In: Proceedings of the 107th
Annual Meeting of the American Association for Cancer Research; 2016 Apr
16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14
Suppl):Abstract nr 2458.
Mohni KN, Kavanaugh GM, Cortez D. ATR pathway inhibition is synthetically lethal in cancer cells with ERCC1 deficiency. Cancer Res 2014;74:
2835–45.
Morgado-Palacin I, Day A, Murga M, Lafarga V, Anton ME, Tubbs A, et al.
Targeting the kinase activities of ATR and ATM exhibits antitumoral activity
in mouse models of MLL-rearranged AML. Sci Signal 2016;9:ra91.
Nieto-Soler M, Morgado-Palacin I, Lafarga V, Lecona E, Murga M, Callen E,
et al. Efficacy of ATR inhibitors as single agents in Ewing sarcoma.
Oncotarget 2016;7:58759–67.
Pfister SX, Markkanen E, Jiang Y, Sarkar S, Woodcock M, Orlando G, et al.
Inhibiting WEE1 selectively kills histone H3K36me3-deficient cancers by
dNTP starvation. Cancer Cell 2015;28:557–68.
Restelli V, Chila R, Lupi M, Rinaldi A, Kwee I, Bertoni F, et al. Characterization of a mantle cell lymphoma cell line resistant to the Chk1 inhibitor
PF-00477736. Oncotarget 2015;6:37229–40.
Saini P, Li Y, Dobbelstein M. Wee1 is required to sustain ATR/Chk1
signaling upon replicative stress. Oncotarget 2015;6:13072–87.
Sarmento LM, Povoa V, Nascimento R, Real G, Antunes I, Martins LR, et al.
CHK1 overexpression in T-cell acute lymphoblastic leukemia is essential
for proliferation and survival by preventing excessive replication stress.
Oncogene 2015;34:2978–90.
Kwok M, Davies N, Agathanggelou A, Smith E, Oldreive C, Petermann E,
et al. ATR inhibition induces synthetic lethality and overcomes chemoresistance in TP53- or ATM-defective chronic lymphocytic leukemia cells.
Blood 2016;127:582–95.
Yap TA, Luken MJdM, O'Carrigan B, Roda D, Papadatos-Pastos D, Lorente
D, et al. Phase I trial of first-in-class ataxia telangiectasia-mutated and Rad3related (ATR) inhibitor VX-970 as monotherapy (mono) or in combination with carboplatin (CP) in advanced cancer patients (pts) with preliminary evidence of target modulation and antitumor activity. Mol Cancer
Ther 2015;14(12 Suppl 2):PR14.
Gerald WL, Haber DA. The EWS-WT1 gene fusion in desmoplastic small
round cell tumor. Semin Cancer Biol 2005;15:197–205.
Shern JF, Chen L, Chmielecki J, Wei JS, Patidar R, Rosenberg M, et al.
Comprehensive genomic analysis of rhabdomyosarcoma reveals a landscape of alterations affecting a common genetic axis in fusion-positive and
fusion-negative tumors. Cancer Discov 2014;4:216–31.
Harris PS, Venkataraman S, Alimova I, Birks DK, Balakrishnan I, Cristiano
B, et al. Integrated genomic analysis identifies the mitotic checkpoint
kinase WEE1 as a novel therapeutic target in medulloblastoma. Mol Cancer
2014;13:72.
Moreira D, Venkataraman S, Balakrishnan I, Prince E, Foreman N, Vibhakar
R. MB-71 The role of wee1 in Myc-driven medulloblastoma. Neuro Oncol
2016;18(suppl_3):iii113.
Kahen E, Yu D, Harrison DJ, Clark J, Hingorani P, Cubitt CL, et al.
Identification of clinically achievable combination therapies in childhood
rhabdomyosarcoma. Cancer Chemother Pharmacol 2016;78:313–23.
Mueller S, Hashizume R, Yang X, Kolkowitz I, Olow AK, Phillips J, et al.
Targeting Wee1 for the treatment of pediatric high-grade gliomas. Neuro
Oncol 2014;16:352–60.
Carrassa L, Chila R, Lupi M, Ricci F, Celenza C, Mazzoletti M, et al.
Combined inhibition of Chk1 and Wee1: in vitro synergistic effect translates to tumor growth inhibition invivo. Cell Cycle 2012;11:2507–17.
Guertin AD, Martin MM, Roberts B, Hurd M, Qu X, Miselis NR, et al.
Unique functions of CHK1 and WEE1 underlie synergistic anti-tumor
activity upon pharmacologic inhibition. Cancer Cell Int 2012;12:45.
Sanjiv K, Hagenkort A, Calderon-Montano JM, Koolmeister T, Reaper PM,
Mortusewicz O, et al. Cancer-specific synthetic lethality between ATR and
CHK1 kinase activities. Cell Rep 2016;14:298–309.
Kennedy RD, D'Andrea AD. The Fanconi Anemia/BRCA pathway: new
faces in the crowd. Genes Dev 2005;19:2925–40.
Chen CC, Kennedy RD, Sidi S, Look AT, D'Andrea A. CHK1 inhibition as a
strategy for targeting Fanconi Anemia (FA) DNA repair pathway deficient
tumors. Mol Cancer 2009;8:24.
Olaussen KA, Dunant A, Fouret P, Brambilla E, Andre F, Haddad V, et al.
DNA repair by ERCC1 in non-small-cell lung cancer and cisplatin-based
adjuvant chemotherapy. N Engl J Med 2006;355:983–91.
Clinical Cancer Research
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.
Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Selective Targeting of Checkpoint Kinase Inhibitors
78. Sultana R, Abdel-Fatah T, Perry C, Moseley P, Albarakti N, Mohan V, et al.
Ataxia telangiectasia mutated and Rad3 related (ATR) protein kinase
inhibition is synthetically lethal in XRCC1 deficient ovarian cancer cells.
PLoS One 2013;8:e57098.
79. Sorensen CS, Hansen LT, Dziegielewski J, Syljuasen RG, Lundin C, Bartek J,
et al. The cell-cycle checkpoint kinase Chk1 is required for mammalian
homologous recombination repair. Nat Cell Biol 2005;7:195–201.
80. Booth L, Cruickshanks N, Ridder T, Dai Y, Grant S, Dent P. PARP and CHK
inhibitors interact to cause DNA damage and cell death in mammary
carcinoma cells. Cancer Biol Ther 2013;14:458–65.
81. Kim H, George E, Ragland RL, Rafail S, Zhang R, Krepler C, et al. Targeting
the ATR/CHK1 axis with PARP inhibition results in tumor regression in
BRCA mutant ovarian cancer models. Clin Cancer Res 2016 Dec 19. [Epub
ahead of print].
82. Konstantinopoulos PA, Ceccaldi R, Shapiro GI, D'Andrea AD. Homologous recombination deficiency: exploiting the fundamental vulnerability
of ovarian cancer. Cancer Discov 2015;5:1137–54.
www.aacrjournals.org
83. Bowtell DD, Bohm S, Ahmed AA, Aspuria PJ, Bast RCJr, Beral V,
et al. Rethinking ovarian cancer II: reducing mortality from
high-grade serous ovarian cancer. Nat Rev Cancer 2015;15:
668–79.
84. Etemadmoghadam D, Weir BA, Au-Yeung G, Alsop K, Mitchell G, George J,
et al. Synthetic lethality between CCNE1 amplification and loss of BRCA1.
Proc Natl Acad Sci U S A 2013;110:19489–94.
85. Jones RM, Mortusewicz O, Afzal I, Lorvellec M, Garcia P, Helleday
T, et al. Increased replication initiation and conflicts with transcription underlie Cyclin E-induced replication stress. Oncogene
2013;32:3744–53.
86. Lee J-M, Karzai FH, Zimmer A, Annunziata CM, Lipkowitz S, Parker B, et al.
A phase II study of the cell cycle checkpoint kinases 1 and 2 inhibitor
(LY2606368; Prexasertib monomesylate monohydrate) in sporadic highgrade serous ovarian cancer (HGSOC) and germline BRCA mutationassociated ovarian cancer (gBRCAmþ OvCa). Ann Oncol 2016;27Suppl
6:855O.
Clin Cancer Res; 23(13) July 1, 2017
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.
OF9
Published OnlineFirst March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Achieving Precision Death with Cell-Cycle Inhibitors that
Target DNA Replication and Repair
Aimee Bence Lin, Samuel C. McNeely and Richard P. Beckmann
Clin Cancer Res Published OnlineFirst March 22, 2017.
Updated version
E-mail alerts
Reprints and
Subscriptions
Permissions
Access the most recent version of this article at:
doi:10.1158/1078-0432.CCR-16-0083
Sign up to receive free email-alerts related to this article or journal.
To order reprints of this article or to subscribe to the journal, contact the AACR Publications
Department at [email protected].
To request permission to re-use all or part of this article, contact the AACR Publications
Department at [email protected].
Downloaded from clincancerres.aacrjournals.org on August 3, 2017. © 2017 American Association for Cancer
Research.