Download Achieving precision death with cell cycle inhibitors that target DNA

Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
Achieving precision death with cell cycle inhibitors that target DNA replication
and repair
Aimee Bence Lin1, Samuel C. McNeely2, and Richard P. Beckmann3
Early Phase Medical-Oncology1, Oncology Business Unit-Patient Tailoring2, and Oncology Translational
Research3, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN USA 46285
Corresponding Author: Richard P. Beckmann, Eli Lilly and Company, Lilly Corporate Center, Drop Code
0438, Indianapolis, IN, USA 46285. Phone: 1-317-276-4285, FAX: 1-317-276-6346. Email:
[email protected]
Running Title: Selective Targeting of Checkpoint Kinase Inhibitors
Disclosure of Potential Conflicts of interest: All authors are employees and shareholders of Eli Lilly and
Company
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 cell cycle
inhibitors. This review in particular focuses on the newer strategies which 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.
Introduction:
Tissue growth and homeostasis in multicellular organisms necessitates 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
1
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
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). Since 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 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).
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 DSBs), respectively, which activate CHK1 and CHK2, by phosphorylation
(Figure 1). CHK1 and CHK2 suppress cell cycle progression through down-regulation of the CDC25A and
CDC25C phosphatases, which promote progression by removing inhibitory phosphates on CDK2 and
CDK1, 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 single-strand DNA generated by
replication fork stalling (12,13).
Strategies for Clinical Development: Past and Present
2
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
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 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 1 trials demonstrated
proof-of-concept that CHK1 inhibitors could be safely combined with chemotherapy (17-25), Phase 2
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 2 studies have been published with checkpoint inhibitors
as monotherapy, evidence of efficacy has been observed in Phase 1. A Phase 1 evaluation of AZD1775
as a monotherapy enrolled 24 patients, 9 of which had a BRCA1/2 mutation. Two patients with a BRCA1
mutation [squamous cell cancer (SCC) of the base of the 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 1 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 tumor-specific vulnerabilities are leveraged to achieve selective cytotoxicity in cancer
cells. TP53 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 (Figure 1) (7). For this reason,
cancer cells that have lost either TP53 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 been tested in a Phase 2 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) (36). Similarly, in a randomized Phase 2 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 to the combination of paclitaxel and carboplatin (37). In a Phase 1 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=7),
melanoma (n=3), breast cancer (n=2), head and neck cancer (n=3), colorectal cancer (n=1), and SCC of
the skin (n=1). Patients with TP53 mutations (4/19, 23%) had a partial response compared to 4/33 (12%)
of patients with TP53 wild-type tumors. (38)
3
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
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 BRCA2deficient 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 since all of these kinases
contribute to sensing and reducing RS (Figure 2). In particular, WEE1 and CHK1 play complimentary
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. Since both CHK1 and WEE1 are important 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 since 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, a 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 MYC-driven 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
4
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
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
(p16) or RB1 genes and/or amplification of CCNE1, MYC, MYCL, or MYCN genes, all of which presumably
contribute to heightened RS (Figure 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, while 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
TP53 were particularly vulnerable to the ATR inhibitor AZD6738. Treatment with AZD6738 increased
replication initiation and fork stalling, resulting in RS and DNA damage which likely contributed to
selective cytotoxicity in cells with TP53 and/or ATM defects (64). In parallel, in a Phase 1 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’s sarcoma (ES) wherein the oncogenic drivers were fusion proteins unique to this
tumor (EWS/FLI1 or EWS/ERG) (59). In these studies, ES cell lines were more sensitive to inhibition of
ATR compared to sarcoma cell lines which 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 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). Additionally, WEE1 was
identified as a target in medulloblastoma, the most common pediatric malignant brain tumor (68).
AZD1175 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
improves the efficacy of radiation in mouse models of pediatric high-grade glioma (71). A Phase 1 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) Trial. 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). Additionally, synergistic growth inhibition was observed
with PF-00477736 and AZD1775 in cell lines and in a xenograft model for ovarian cancer (72). Synergy
5
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
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 to the monotherapy treatments (74).
In addition to RS, deficiencies in homologous recombination repair (HRR) may also contribute to greater
sensitivity to checkpoint kinase inhibition since homologous recombination deficiencies (HRDs) reduce
the efficiency of repair of DSBs that result from RS generated by these inhibitors (Figure 2). Deficiencies
in the Fanconi anemia (FA) genes (FANC), like defects in BRCA1/2, also disrupt HRR (75), and studies
with the CHK1 inhibitor Gö6976 showed that FA-deficient cell lines were highly sensitive to Gö6976 and
to interfering-RNA (RNAi) silencing of CHK1 mRNA expression when compared to isogenic lines that
were FA-proficient (76). An RNAi based screen which targeted 230 DNA repair genes identified many
FANC genes as SL with Gö6976 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. Since 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 crosslinks (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 also 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). Additionally, 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 to the single-agent treatments (80). More recent studies have shown in
BRCA1/2 mutated high-grade serous ovarian cancer (HGSOC) models that combination therapy with
olaparib and either MK8776 (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
6
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
(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, since approximately half
harbor mutations in genes that modulate HRR, including mutations that impact BRCA1 and BRCA2
(39,82). Additionally, 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 BRCA1/2, CCNE1 is amplified in 15-20% of HGSOCs (82,84). RB1
loss is also observed in about 15% of these cancers (83). Since cyclin E is required for activation of CDK2,
its overexpression induces RS and DNA damage that activates HRR and may increase sensitivity to singleagent 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 which 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 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 since 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
7
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
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.
Figure Legends:
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 (CDKs) 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 cyclins 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 single-strand breaks (SSBs) and
double-strand breaks (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 (TP53) 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.
Figure 2: The ATR-CHK1 pathway reduces replication stress (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 which may enhance cyclin E expression or CDK2 activity possibly include 1) losses in
FBXW7, which facilities proteasomal degradation of cyclin E or 2) alterations which disrupt regulation of
the primary restriction point controlling progression from G1 into S including activation of CDK4, CDK6,
D-type cyclins, or loss of RB1 which serve to activate E2F thereby promoting the transcription of the
8
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
genes that encode cyclin E and CDK2 as well as other gene products which promote DNA replication.
Notably as indicated by the red X’s, 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 double-stranded breaks leading to the activation of DNA
damage and repair responses such as homologous recombination repair.
9
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Table 1: Cell Cycle Kinase Inhibitors Currently in Development
Agent
Phase
Context
Populations
AZD1775
(MK1775)
II
Monotherapy
Cervical, CRC, gastric/GEJ, glioblastoma, gliomas, HNSCC,
NSCLC, myeloid malignancies, ovarian, pancreas,
pediatric tumors, SCLC, squamous NSCLC, TNBC
Chemotherapy combinations: cisplatin, carboplatin,
docetaxel, gemcitabine, Irinotecan, nab-palitaxel,
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
I
Monotherapy, gemcitabine
I
Monotherapy, gemcitabine, cisplatin
NSCLC, pancreatic
I
Monotherapy, Gemcitabine
II
Monotherapy
Chemoradiation combinations: cetuximab, cisplatin
ATR
AML/high risk MDS, CRC
HSNCC , NSCLC, ovarian, pediatric, prostate, SCC of
anus, sqNSCLC , 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: BRCA1/2m
CRC: KRAS/BRAF mutations
NSCLC: KRAS/BRAF mutations
Ovarian: BRCA1/2m
CRC, ovarian, TNBC
Targeted therapy combinations: cetuximab,
LY3023414 (PI3K/mTOR inhibitor), ralimetinib (p38
inhibitor), olaparib
LY2880070,
ESP-01
CCT245737
PNT-737
GDC-0575
ARRY-575
VX970
Biomarker Focused:
Basket trial: Molecular profiling based assignment
Bladder: mutations in genes associated with cell cycle
regulation (RB1, CDKN2A, CCNE1 or MYC amp)
CRC: RAS/NRAS/BRAF mutations
Gastric/GEJ: TP53 mut
NSCLC: Biomarker directed basket trial
Ovarian: BRCA1/2m, TP53 mutated, window trial
Pediatric: basket trial stratifying based on molecular
anomalies
HNSCC (HPV-), NSCLC, ovarian, SCLC, urothelial,
10
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Target
WEE-1
sqNSCLC, TNBC
Targeted combinations: veliparib
AZD6738
I
Chemoradiation combinations: monotherapy,
cisplatin
Monotherapy
Chemotherapy combinations: carboplatin,
Paclitaxel
Targeted combinations: olaparib
Radiation
ATM
VX803
AZD0156
I
I
Immunotherapy combinations: durvalumab
Monotherapy, gemcitabine, carboplatin, cisplatin
Monotherapy, irinotecan, olaparib
B-cell malignancies, gastric/GEJ, HNSCC, NSCLC
Biomarker Focused:
CLL: 11q or ATM-deficient
Gastric/GEJ: Low ATM expression
HNSCC: window trial
NSCLC: Low ATM expression
Ovarian
Source: www.clinicaltrials.gov
Abbreviations: AML= acute myeloid leukemia, amp = amplification, CRC = colorectal cancer, GEJ = gastro esophageal junction, HPV = human papilloma virus, HNSCC: squamous cell
head and neck cancer, m= mutation, MDS = myelodysplastic syndrome, NSCLC: non-small cell lung cancer, SCC = squamous cell cancer SCLC: small-cell lung cancer, TNBC: triple
negative breast cancer,
11
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Chemotherapy combinations: cisplatin, carboplatin,
gemcitabine, etoposide, irinotecan, topotecan
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
References:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
Chin L, Andersen JN, Futreal PA. Cancer genomics: from discovery science to personalized
medicine. Nat Med 2011;17(3):297-303 doi 10.1038/nm.2323.
Stratton MR, Campbell PJ, Futreal PA. The cancer genome. Nature 2009;458(7239):719-24 doi
10.1038/nature07943.
Ciccia A, Elledge SJ. The DNA damage response: making it safe to play with knives. Mol Cell
2010;40(2):179-204 doi 10.1016/j.molcel.2010.09.019.
Harper JW, Elledge SJ. The DNA damage response: ten years after. Mol Cell 2007;28(5):739-45
doi 10.1016/j.molcel.2007.11.015.
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(2):477-86 doi 10.1093/nar/gkr697.
Jones RM, Petermann E. Replication fork dynamics and the DNA damage response. Biochem J
2012;443(1):13-26 doi 10.1042/BJ20112100.
McNeely S, Beckmann R, Bence Lin AK. CHEK again: revisiting the development of CHK1
inhibitors for cancer therapy. Pharmacol Ther 2014;142(1):1-10 doi
10.1016/j.pharmthera.2013.10.005.
Parker LL, Piwnica-Worms H. Inactivation of the p34cdc2-cyclin B complex by the human WEE1
tyrosine kinase. Science 1992;257(5078):1955-7.
Watanabe N, Broome M, Hunter T. Regulation of the human WEE1Hu CDK tyrosine 15-kinase
during the cell cycle. EMBO J 1995;14(9):1878-91.
Do K, Doroshow JH, Kummar S. Wee1 kinase as a target for cancer therapy. Cell Cycle
2013;12(19):3159-64 doi 10.4161/cc.26062.
Matheson CJ, Backos DS, Reigan P. Targeting WEE1 Kinase in Cancer. Trends Pharmacol Sci
2016;37(10):872-81 doi 10.1016/j.tips.2016.06.006.
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(1):109-17 doi
10.1016/j.ctrv.2013.03.002.
Weber AM, Ryan AJ. ATM and ATR as therapeutic targets in cancer. Pharmacol Ther
2015;149:124-38 doi 10.1016/j.pharmthera.2014.12.001.
Ma CX, Janetka JW, Piwnica-Worms H. Death by releasing the breaks: CHK1 inhibitors as cancer
therapeutics. Trends Mol Med 2011;17(2):88-96 doi 10.1016/j.molmed.2010.10.009.
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(4):368-73 doi
10.1016/j.molonc.2011.07.002.
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(3):358-69 doi
10.1111/bcp.12139.
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(5):251-60 doi 10.1159/000448621.
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(5):955-68 doi 10.1007/s10637-0140114-5.
Daud AI, Ashworth MT, Strosberg J, Goldman JW, Mendelson D, Springett G, et al. Phase I doseescalation trial of checkpoint kinase 1 inhibitor MK-8776 as monotherapy and in combination
12
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
with gemcitabine in patients with advanced solid tumors. J Clin Oncol 2015;33(9):1060-6 doi
10.1200/JCO.2014.57.5027.
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(10):1043-53 doi 10.1097/CAD.0000000000000278.
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. Clin Cancer Res 2016 doi 10.1158/1078-0432.CCR-16-1782.
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(24):6723-31 doi 10.1158/1078-0432.CCR-12-2442.
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(3):539-49 doi
10.1007/s00280-014-2380-5.
Seto T, Esaki T, Hirai F, Arita S, Nosaki K, Makiyama A, et al. Phase I, dose-escalation study of
AZD7762 alone and in combination with gemcitabine in Japanese patients with advanced solid
tumours. Cancer Chemother Pharmacol 2013;72(3):619-27 doi 10.1007/s00280-013-2234-6.
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(1):136-44 doi 10.1007/s10637-012-9815-9.
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(5):625-35 doi
10.1007/s10637-016-0368-1.
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(23):2563-.
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(30):3409-15 doi 10.1200/JCO.2014.60.4009.
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(15):176471 doi 10.1200/JCO.2015.64.5788.
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(9):2955-66 doi 10.1158/1535-7163.MCT-08-0492.
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(11):2992-3000 doi 10.1158/1535-7163.MCT-09-0463.
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(2):213-26 doi 10.1007/s10637-013-0036-7.
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(9):2799-806 doi
10.1158/1078-0432.CCR-10-2580.
13
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
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(7):428-30
doi 10.1038/nchembio.573.
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(6):721-7 doi 10.1038/nsmb.2076.
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(36):4354-61.
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
2015;33(suppl; abstr 5506).
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(36):4371-80 doi
10.1200/JCO.2016.67.5991.
Lord CJ, Ashworth A. BRCAness revisited. Nat Rev Cancer 2016;16(2):110-20 doi
10.1038/nrc.2015.21.
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(16):8109-15 doi 10.1158/0008-5472.CAN-06-0140.
Bryant HE, Schultz N, Thomas HD, Parker KM, Flower D, Lopez E, et al. Specific killing of BRCA2deficient tumours with inhibitors of poly(ADP-ribose) polymerase. Nature 2005;434(7035):913-7
doi 10.1038/nature03443.
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(7035):917-21 doi
10.1038/nature03445.
Dobbelstein M, Sorensen CS. Exploiting replicative stress to treat cancer. Nat Rev Drug Discov
2015;14(6):405-23 doi 10.1038/nrd4553.
Lecona E, Fernandez-Capetillo O. Replication stress and cancer: it takes two to tango. Exp Cell
Res 2014;329(1):26-34 doi 10.1016/j.yexcr.2014.09.019.
Hills SA, Diffley JF. DNA replication and oncogene-induced replicative stress. Curr Biol
2014;24(10):R435-44 doi 10.1016/j.cub.2014.04.012.
Gaillard H, Garcia-Muse T, Aguilera A. Replication stress and cancer. Nat Rev Cancer
2015;15(5):276-89 doi 10.1038/nrc3916.
Zeman MK, Cimprich KA. Causes and consequences of replication stress. Nat Cell Biol
2014;16(1):2-9 doi 10.1038/ncb2897.
Mazouzi A, Velimezi G, Loizou JI. DNA replication stress: causes, resolution and disease. Exp Cell
Res 2014;329(1):85-93 doi 10.1016/j.yexcr.2014.09.030.
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(12):1331-5 doi 10.1038/nsmb.2189.
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(11):2719-31
doi 10.1038/sj.emboj.7601714.
14
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
Petermann E, Woodcock M, Helleday T. Chk1 promotes replication fork progression by
controlling replication initiation. Proc Natl Acad Sci U S A 2010;107(37):16090-5 doi
10.1073/pnas.1005031107.
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(8):3336-41 doi 10.1073/pnas.1012351108.
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(445):ra90 doi
10.1126/scisignal.aac9704.
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 Bcell lymphoma. Oncotarget 2015;6(9):6553-69 doi 10.18632/oncotarget.2720.
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-/Tcell progenitor acute lymphoblastic leukemia. Oncotarget 2016;7(33):53377-91 doi
10.18632/oncotarget.10535.
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 yields significant antitumor effects Cancer Res 2016;76(14
Supplement):2458- doi 10.1158/1538-7445.AM2016-2458
Mohni KN, Kavanaugh GM, Cortez D. ATR pathway inhibition is synthetically lethal in cancer cells
with ERCC1 deficiency. Cancer Res 2014;74(10):2835-45 doi 10.1158/0008-5472.CAN-13-3229.
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(445):ra91 doi 10.1126/scisignal.aad8243.
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 doi 10.18632/oncotarget.11643.
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(5):557-68 doi 10.1016/j.ccell.2015.09.015.
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(35):3722940 doi 10.18632/oncotarget.5954.
Saini P, Li Y, Dobbelstein M. Wee1 is required to sustain ATR/Chk1 signaling upon replicative
stress. Oncotarget 2015;6(15):13072-87 doi 10.18632/oncotarget.3865.
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(23):2978-90 doi 10.1038/onc.2014.248.
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(5):582-95 doi 10.1182/blood-2015-05-644872.
Yap TA, Luken MJdM, O'Carrigan B, Roda D, Papadatos-Pastos D, Lorente D, et al. Abstract PR14:
Phase I trial of first-in-class ataxia telangiectasia-mutated and Rad3-related (ATR) inhibitor VX970 as monotherapy (mono) or in combination with carboplatin (CP) in advanced cancer
patients (pts) with preliminary evidence of target modulation and antitumor activity. Molecular
Cancer Therapeutics 2015;14(12 Supplement 2):PR14-PR doi 10.1158/1535-7163.targ-15-pr14.
Gerald WL, Haber DA. The EWS-WT1 gene fusion in desmoplastic small round cell tumor. Semin
Cancer Biol 2005;15(3):197-205 doi 10.1016/j.semcancer.2005.01.005.
15
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
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(2):216-31 doi
10.1158/2159-8290.CD-13-0639.
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 doi 10.1186/1476-4598-13-72.
Moreira D, Venkataraman S, Balakrishnan I, Prince E, Foreman N, Vibhakar R. MB-71THE ROLE
OF WEE1 IN Myc-DRIVEN MEDULLOBLASTOMA. Neuro-Oncology 2016;18(suppl_3):iii113-iii doi
10.1093/neuonc/now076.67.
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(2):313-23 doi 10.1007/s00280-016-3077-8.
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(3):352-60 doi
10.1093/neuonc/not220.
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 in vivo. Cell Cycle
2012;11(13):2507-17 doi 10.4161/cc.20899.
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(1):45 doi 10.1186/1475-2867-12-45.
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(2):298-309 doi 10.1016/j.celrep.2015.12.032.
Kennedy RD, D'Andrea AD. The Fanconi Anemia/BRCA pathway: new faces in the crowd. Genes
Dev 2005;19(24):2925-40 doi 10.1101/gad.1370505.
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 doi
10.1186/1476-4598-8-24.
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(10):983-91 doi 10.1056/NEJMoa060570.
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(2):e57098 doi 10.1371/journal.pone.0057098.
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(2):195-201 doi 10.1038/ncb1212.
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(5):458-65 doi 10.4161/cbt.24424.
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. Clinical
Cancer Research 2016 doi 10.1158/1078-0432.ccr-16-2273.
Konstantinopoulos PA, Ceccaldi R, Shapiro GI, D'Andrea AD. Homologous Recombination
Deficiency: Exploiting the Fundamental Vulnerability of Ovarian Cancer. Cancer Discov
2015;5(11):1137-54 doi 10.1158/2159-8290.CD-15-0714.
16
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
83.
84.
85.
86.
Bowtell DD, Bohm S, Ahmed AA, Aspuria PJ, Bast RC, Jr., Beral V, et al. Rethinking ovarian cancer
II: reducing mortality from high-grade serous ovarian cancer. Nat Rev Cancer 2015;15(11):66879 doi 10.1038/nrc4019.
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(48):19489-94 doi 10.1073/pnas.1314302110.
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(32):3744-53 doi 10.1038/onc.2012.387.
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 high-grade serous ovarian cancer (HGSOC) and germline BRCA
mutation-associated ovarian cancer (gBRCAm+ OvCa). Annals of Oncology
2016;27(Supplemental 6; Abstract # 8550):305 doi 10.1093/annonc/mdw362.
17
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
Figure 1:
Endogenous or exogenous events
Double-strand break
Single-strand break
P
P
ATM
ATR
CHK2
CHK1
P
P
(Proteolysis)
WEE1
(Sequestration)
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
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
Figure 2:
Cyclin E
P
P
P
CDK2
CDC25A
CHK1
WEE1
Cyclin E
CDK2
RPA
RPA
TopBP1
ATRIP
DNA lesion
RPA
“Activation”
RPA
ATR
P
Replication stress
đƫ*+#!*!/
đƫ*$*! ƫ5(%*ƫƫ+.ƫĂƫ!4,.!//%+*ĥ0%2%05
đƫ+//ƫ+"ƫ.!#1(0%+*ƫ+"ƫāƫlƫƫ,.+#.!//%+*
đƫ+//ƫ+"ƫ"1*0%+*ƫ+"ƫČƫāČƫ+.ƫā
+.'ƫ+((,/!ƫl/
+)+(+#+1/
.!+)%*0%+*ƫ.!,%.
© 2017 American Association for Cancer Research
Downloaded from clincancerres.aacrjournals.org on June 17, 2017. © 2017 American Association for Cancer
Research.
Author Manuscript Published OnlineFirst on March 22, 2017; DOI: 10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.
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
Author
Manuscript
E-mail alerts
Reprints and
Subscriptions
Permissions
Access the most recent version of this article at:
doi:10.1158/1078-0432.CCR-16-0083
Author manuscripts have been peer reviewed and accepted for publication but have not yet been
edited.
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 June 17, 2017. © 2017 American Association for Cancer
Research.