Abstract 2494: ATR inhibitor AZD6738 as monotherapy and in combination with olaparib or chemotherapy: defining pre-clinical dose-schedules and efficacy modelling

Introduction: AZD6738 is a potent and selective oral inhibitor of the ataxia telangiectasia and rad3 related (ATR) protein kinase. ATR has a key role in the DNA replication stress response (RSR) pathway of DNA repairby facilitating the recovery and repair of potentially cytotoxic persistent, stalled DNA replication forks. Inhibition of ATR leads to the inability to resolve replication associated damage and the accumulation of DNA strand breaks, which if remains unrepaired leads to cell death. AZD6738 is currently in Phase I/II clinical trials being evaluated as a monotherapy and in combination with novel agents olaparib / Lynparza (PARP DNA damage response inhibitor), durvalumab (PD-L1 immune checkpoint inhibitor) and DNA-damaging agents such as carboplatin and ionising radiation. Critical in helping to guide the clinical usage of AZD6738 and maximise patient benefit, pre-clinical studies were performed to determine optimal doses and schedules as monotherapy and in combination with olaparib and carboplatin.

Experimental procedures: Human cancer cell lines, xenograft and patient-derived explant (PDX) models of non-small cell lung cancer (NSCLC), head & neck squamous cell carcinoma (HNSCC), and triple-negative breast cancer (TNBC) were tested comparing once daily versus twice daily dosing, the number of consecutive days dosing (3 days/week, 5 days/week, continuous) and co-dosing versus sequential or intermittent dosing with AZD6738 alone or in combination with olaparib or carboplatin. The magnitude and duration of anti-tumour responses were then compared with AZD6738 mouse pharmacokinetic (PK), pharmacodynamic (PD) and in vitro target (IC) / growth inhibition (GI) profiles.

Results: A mathematical model was derived which adequately described the AZD6738 PK/PD-efficacy relationship. This modelling confirms that duration of cover (time) above cellular ATR target inhibition thresholds (IC90 pCHK1 / GI90) per day, rather than Cmax or exposures per se, is the major determinant of anti-tumour responses. As monotherapy, in sensitive ATM-deficient models, it is necessary to inhibit ATR continuously to give tumour stabilisation, which can be achieved through repeat daily of AZD6738 over several weeks. Co-dosing AZD6738 in combination with olaparib or carboplatin gives best efficacy compared to sequential dosing and PK cover over the first 48-72 hours is necessary to give tumour regressions. The models predict that extending the duration of ATR cover, achieved through repeat daily dosing, further increases efficacy. These pre-clinical dose-schedules were compared to human free plasma AZD6738 PK data and predicted efficacious exposures found to be clinically achievable.

Conclusions: Together these data further support the clinical evaluation of AZD6738 and suggest optimal dosing schedules for ATR inhibitors.

Citation Format: Alan Y. Lau, James Yates, Zena Wilson, Lucy A. Young, Adina M. Hughes, Alienor Berges, Amy Cheung, Rajesh Odedra, Elaine Brown, Mark J. O'Connor, Simon Hollingsworth. ATR inhibitor AZD6738 as monotherapy and in combination with olaparib or chemotherapy: defining pre-clinical dose-schedules and efficacy modelling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2494. doi:10.1158/1538-7445.AM2017-2494

Resolution of cannabis hyperemesis syndrome with topical capsaicin in the emergency department: a case series

BACKGROUND

Cannabinoid hyperemesis syndrome (CHS) is characterized by symptoms of cyclic abdominal pain, nausea, and vomiting in the setting of prolonged cannabis use. The transient receptor potential vanilloid 1 (TRPV1) receptor may be involved in this syndrome. Topical capsaicin is a proposed treatment for CHS; it binds TRPV1 with high specificity, impairing substance P signaling in the area postrema and nucleus tractus solitarius via overstimulation of TRPV1. This may explain its apparent antiemetic effect in this syndrome.

PURPOSE

We describe a series of thirteen cases of suspected cannabis hyperemesis syndrome treated with capsaicin in the emergency departments of two academic medical centers.

METHODS

A query of the electronic health record at both centers identified thirteen patients with documented daily cannabis use and symptoms consistent with CHS who were administered topical capsaicin cream for symptom management.

RESULTS

All 13 patients experienced symptom relief after administration of capsaicin cream.

CONCLUSION

Topical capsaicin was associated with improvement in symptoms of CHS after other treatments failed.

Abstract IA03: Targeting the DNA damage response to generate new medicines for cancer treatment

Cancers are characterized by high levels of genomic instability and endogenous DNA damage. Traditional cancer therapies include radiotherapy and DNA-damaging chemotherapy, but these treatments are associated with significant damage to normal tissue. These unwanted side effects may be reduced by using targeted treatment approaches that preferentially affect tumor cells with specific mutations. The DNA damage response (DDR) in cancer cells differs in at least three aspects to those of normal cells, namely the loss of one or more DDR pathway or capability, increased levels of replication stress and higher levels of endogenous DNA damage. In addition, an analysis of DDR associated genes suggests that there are more than 450 gene products involved in various aspects of DDR, many of which are performing enzymatic activities that could be targeted by small molecule inhibitors. DDR therefore represents both a hallmark of cancer and a weakness that can be exploited for new cancer therapies. Both the opportunities and challenges associated with translating inhibitors of DDR into new medicines for cancer patients will be presented.

Citation Format: Mark J. O'Connor. Targeting the DNA damage response to generate new medicines for cancer treatment [abstract]. In: Proceedings of the AACR Special Conference on DNA Repair: Tumor Development and Therapeutic Response; 2016 Nov 2-5; Montreal, QC, Canada. Philadelphia (PA): AACR; Mol Cancer Res 2017;15(4_Suppl):Abstract nr IA03.

AZD6738, A Novel Oral Inhibitor of ATR, Induces Synthetic Lethality with ATM Deficiency in Gastric Cancer Cells

Ataxia telangiectasia and Rad3-related (ATR) can be considered an attractive target for cancer treatment due to its deleterious effect on cancer cells harboring a homologous recombination defect. The aim of this study was to investigate the potential use of the ATR inhibitor, AZD6738, to treat gastric cancer.In SNU-601 cells with dysfunctional ATM, AZD6738 treatment led to an accumulation of DNA damage due to dysfunctional RAD51 foci formation, S phase arrest, and caspase 3-dependent apoptosis. In contrast, SNU-484 cells with functional ATM were not sensitive to AZD6738. Inhibition of ATM in SNU-484 cells enhanced AZD6738 sensitivity to a level comparable with that observed in SNU-601 cells, showing that activation of the ATM-Chk2 signaling pathway attenuates AZD6738 sensitivity. In addition, decreased HDAC1 expression was found to be associated with ATM inactivation in SNU-601 cells, demonstrating the interaction between HDAC1 and ATM can affect sensitivity to AZD6738. Furthermore, in an in vivo tumor xenograft mouse model, AZD6738 significantly suppressed tumor growth and increased apoptosis.These findings suggest synthetic lethality between ATR inhibition and ATM deficiency in gastric cancer cells. Further clinical studies on the interaction between AZD 6738 and ATM deficiency are warranted to develop novel treatment strategies for gastric cancer. Mol Cancer Ther; 16(4); 566-77. ©2017 AACR.

Webinar | Deciphering cancer: Genomic instability in cancer

While it is well established that DNA damage can increase the risk of cancer, changes to the epigenome or the chromatin architecture are equally important. DNA damage triggers a redistribution of DNA-binding proteins around the site of damage, resulting in localized and temporary alteration of chromatin structure. However, repeated cycles of DNA damage and repair may lead to permanent changes in the epigenome, thereby promoting the onset of pathological diseases such as cancer. This webinar will examine how we may be able to develop effective new therapeutic options for cancer treatment by targeting proteins responsible for chromatin modifications.

The orally active and bioavailable ATR kinase inhibitor AZD6738 potentiates the anti-tumor effects of cisplatin to resolve ATM-deficient non-small cell lung cancer in vivo

ATR and ATM are DNA damage signaling kinases that phosphorylate several thousand substrates. ATR kinase activity is increased at damaged replication forks and resected DNA double-strand breaks (DSBs). ATM kinase activity is increased at DSBs. ATM has been widely studied since ataxia telangiectasia individuals who express no ATM protein are the most radiosensitive patients identified. Since ATM is not an essential protein, it is widely believed that ATM kinase inhibitors will be well-tolerated in the clinic. ATR has been widely studied, but advances have been complicated by the finding that ATR is an essential protein and it is widely believed that ATR kinase inhibitors will be toxic in the clinic. We describe AZD6738, an orally active and bioavailable ATR kinase inhibitor. AZD6738 induces cell death and senescence in non-small cell lung cancer (NSCLC) cell lines. AZD6738 potentiates the cytotoxicity of cisplatin and gemcitabine in NSCLC cell lines with intact ATM kinase signaling, and potently synergizes with cisplatin in ATM-deficient NSCLC cells. In contrast to expectations, daily administration of AZD6738 and ATR kinase inhibition for 14 consecutive days is tolerated in mice and enhances the therapeutic efficacy of cisplatin in xenograft models. Remarkably, the combination of cisplatin and AZD6738 resolves ATM-deficient lung cancer xenografts.

The PARP Inhibitor AZD2461 Provides Insights into the Role of PARP3 Inhibition for Both Synthetic Lethality and Tolerability with Chemotherapy in Preclinical Models

The PARP inhibitor AZD2461 was developed as a next-generation agent following olaparib, the first PARP inhibitor approved for cancer therapy. In BRCA1-deficient mouse models, olaparib resistance predominantly involves overexpression of P-glycoprotein, so AZD2461 was developed as a poor substrate for drug transporters. Here we demonstrate the efficacy of this compound against olaparib-resistant tumors that overexpress P-glycoprotein. In addition, AZD2461 was better tolerated in combination with chemotherapy than olaparib in mice, which suggests that AZD2461 could have significant advantages over olaparib in the clinic. However, this superior toxicity profile did not extend to rats. Investigations of this difference revealed a differential PARP3 inhibitory activity for each compound and a higher level of PARP3 expression in bone marrow cells from mice as compared with rats and humans. Our findings have implications for the use of mouse models to assess bone marrow toxicity for DNA-damaging agents and inhibitors of the DNA damage response. Finally, structural modeling of the PARP3-active site with different PARP inhibitors also highlights the potential to develop compounds with different PARP family member specificity profiles for optimal antitumor activity and tolerability. Cancer Res; 76(20); 6084-94. ©2016 AACR.

A Biobank of Breast Cancer Explants with Preserved Intra-tumor Heterogeneity to Screen Anticancer Compounds

The inter- and intra-tumor heterogeneity of breast cancer needs to be adequately captured in pre-clinical models. We have created a large collection of breast cancer patient-derived tumor xenografts (PDTXs), in which the morphological and molecular characteristics of the originating tumor are preserved through passaging in the mouse. An integrated platform combining in vivo maintenance of these PDTXs along with short-term cultures of PDTX-derived tumor cells (PDTCs) was optimized. Remarkably, the intra-tumor genomic clonal architecture present in the originating breast cancers was mostly preserved upon serial passaging in xenografts and in short-term cultured PDTCs. We assessed drug responses in PDTCs on a high-throughput platform and validated several ex vivo responses in vivo. The biobank represents a powerful resource for pre-clinical breast cancer pharmacogenomic studies (http://caldaslab.cruk.cam.ac.uk/bcape), including identification of biomarkers of response or resistance.

Abstract P4-07-04: PARP1/2 inhibition in a subset of triple negative breast cancer (TNBC) patient-derived tumor xenografts (PDX) identifies predictive biomarkers of response

Background: BRCA1/2 mutation carriers (gBRCA) have a higher risk of breast or ovarian cancer, since BRCA1/2 mutation results in impaired high-fidelity DNA repair by homologous recombination (HR) and subsequently genetic instability. In non-gBRCA TNBC, HR deficiency occurs at the somatic level, by means of BRCA1 mutation, BRCA1 epigenetic loss or mutation in other HR-associated genes. Because PARP1/2 inhibitors (PARPi) are well-tolerated and active anti-cancer agents in the advanced setting of gBRCA tumors, we sought to expand their applicability by identifying response biomarkers in TNBC.

Methods: We have assessed the antitumor response of the PARP1/2 inhibitor olaparib as single agent in a panel of 12 primary and advanced TNBC PDX models. On PDXs exhibiting primary sensitivity to olaparib, we have developed models of acquired resistance by continuous exposure to the drug and identifying progression on treatment. We have characterized the models through targeted sequencing and the analysis of the hypermethylation and expression levels of BRCA1 transcript to find potential correlates of drug-sensitivity.

Results: Three out of 12 PDXs (25%) treated with single agent olaparib, exhibit tumor regression or disease stabilization. BRCA1 is hypermethylated in two of these PARPi-sensitive TNBC PDX models and is associated with loss of BRCA1 mRNA expression. The third PARPi-sensitive TNBC PDX harbors a frameshift, heterozygous PALB2 mutation, which is no longer detected in the acquired resistance PDX model. Acquired resistance in the hypermethylated PDXs is under study as well as the duration of response compared to gBRCA PDX models.

Conclusions: Our study highlights that somatic HR-deficiency is frequent in TNBC and provides the basis of sensitivity to PARPi.

Citation Format: Serra V, Cruz C, Bruna A, Ibrahim YH, Vivancos A, Vivancos A, Nuciforo P, Bellet M, Gómez P, Pérez JM, Saura C, Vidal M, Serres X, Rueda OM, Peg V, Caldas C, O'Connor MJ, Baselga J, Cortés J. PARP1/2 inhibition in a subset of triple negative breast cancer (TNBC) patient-derived tumor xenografts (PDX) identifies predictive biomarkers of response. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-07-04.

Abstract PL05-03: Exploiting cancer replication stress using pharmacological inhibitors of ATR and WEE1

Replication stress is a hallmark of cancer (Macheret and Halazonetis, 2015) and as well as representing an important aspect of cancer aetiology (Bartkova et al., 2005; Gorgoulis et al., 2005) has the potential to be exploited by targeted cancer therapies (Lecona and Fernandez-Capetillo, 2014). A molecular definition of replication stress is the uncoupling of the DNA polymerase from the replisome helicase activity (Byun et al., 2005; Zeman and Cimprich, 2014). Factors that can induce replication stress include insufficiency in nucleotide pools or other replication factors, for example resulting from the abrogation of cell cycle control and premature entry into S-phase and DNA replication before the necessary resources for replication have been generated (Buisson et al., 2015). Cyclin E amplification and oncogenic drivers such KRAS mutations or MYC amplification can also increase replication stress through increased replication origin firing and the promotion of clashes between the replication and transcription processes and, in the case of MYC amplification through the generation of increased levels of reactive oxygen species and DNA damage (Jones et al., 2013; Rohban et al., 2014; Vafa et al., 2002).

Consistent with these causes, it can be seen why replication stress generated by DNA damaging chemotherapy will be greater in cancers than in normal cells, since cancers but not normal cells will also be associated with cell cycle checkpoint deregulation, oncogenic drivers, and higher levels of intrinsic DNA damage. However, there is still collateral damage in rapidly dividing normal cells such as gut epithelia, haematopoietic cells, and hair follicles. The goal for targeting cancer DNA damage response (DDR) dependencies associated with the replication stress response, is therefore to understand which DDR targets provide a potentially better therapeutic index than current standard of care chemotherapies and how best to select cancers that will demonstrate the greatest susceptibility to those DDR targeted agents.

The replication stress response initiated by RPA bound to ssDNA is regulated primarily by the Ataxia Telangiectasia and Rad3 Related serine/threonine kinase (ATR) and its effector kinase CHK1 that together control the firing of replication origins, the repair of damaged replication forks and the prevention of DNA double strand break formation (Cimprich and Cortez, 2008; Petermann et al., 2010; Buisson et al., 2015). The tyrosine kinase WEE1 also represents an important regulator of the replication stress response through the control of CDK1 and CDK2 activity and when WEE1 is inhibited, CDK1 and CDK2 de-regulation leads to increased replication origin firing, a decrease in nucleotide availability and an increase in DNA DSBs mediated through endonuclease activity (Beck et al, 2012). In addition, ATR, CHK1 and WEE1 inhibitors also have the potential to promote premature entry into mitosis, even in the presence of under-replicated DNA or DNA damage, thus promoting mitotic catastrophe and cancer cell death (Aarts et al., 2012; Do et al., 2013).

Here, data will be presented on the activity of both an ATR inhibitor (AZD6738) and a WEE1 inhibitor (AZD1775) in a number of preclinical in vitro and in vivo models. Initially, we assessed ATR inhibitor sensitivity in diffuse-large B-cell lymphoma (DLBCL) cancer models and identified an association of ATR inhibitor sensitivity with high levels of c-MYC protein, CDKN2A/B deletion and low BCL-6 expression and also demonstrated a strong correlation with the level of replication stress in these models. A similar trend in sensitivity in DLBCL was observed for the WEE1 inhibitor AZD1775 and the CHK1/2 inhibitor AZD7762, but with what appeared to be a greater potency compared to ATR inhibition. Investigation of both the cell cycle and cell death effects resulting from treatment with the ATR and WEE1 inhibitors in DLBCL models highlighted differences consistent with the greater potency of the WEE1 inhibitor and an assessment of in vivo activity further supported these findings. AZD1775 treatment of a larger panel of in vivo patient-derived explant (PDX) models of multiple tumour types demonstrated both the significant breadth and depth of the WEE1 inhibitor single agent activity. Moreover, we observed the potential for this activity to be enhanced further through combination with olaparib, a PARP inhibitor that induces S-phase DNA damage. Together, these data have led to the recent initiation of AZD1775 monotherapy as well as AZD1775/ olaparib combination clinical trials.

Citation Format: Mark J. O'Connor. Exploiting cancer replication stress using pharmacological inhibitors of ATR and WEE1. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr PL05-03.

Randomized, Double-Blind Phase II Trial With Prospective Classification by ATM Protein Level to Evaluate the Efficacy and Tolerability of Olaparib Plus Paclitaxel in Patients With Recurrent or Metastatic Gastric Cancer

PURPOSE

Gastric cancer cell lines, particularly those with low levels of ataxia telangiectasia mutated (ATM), a key activator of DNA damage response, are sensitive to the poly (ADP-ribose) polymerase inhibitor olaparib. We compared the efficacy of olaparib plus paclitaxel (olaparib/paclitaxel) with paclitaxel alone in patients with recurrent or metastatic gastric cancer and assessed whether low ATM expression is predictive of improved clinical outcome for olaparib/paclitaxel.

PATIENTS AND METHODS

In this phase II, double-blind study (Study 39; NCT01063517), patients were randomly assigned to oral olaparib 100 mg twice per day (tablets) plus paclitaxel (80 mg/m(2) per day intravenously on days 1, 8, and 15 of every 28-day cycle) or placebo plus paclitaxel (placebo/paclitaxel), followed by maintenance monotherapy with olaparib (200 mg twice per day) or placebo. The study population was enriched to 50% for patients with low or undetectable ATM levels (ATMlow). Primary end point was progression-free survival (PFS).

RESULTS

One hundred twenty-three of 124 randomly assigned patients received treatment (olaparib/paclitaxel, n = 61; placebo/paclitaxel, n = 62). The screening prevalence of ATMlow patients was 14%. Olaparib/paclitaxel did not lead to a significant improvement in PFS versus placebo/paclitaxel (overall population: hazard ratio [HR], 0.80; median PFS, 3.91 v 3.55 months, respectively; ATMlow population: HR, 0.74; median PFS, 5.29 v 3.68 months, respectively). However, olaparib/paclitaxel significantly improved overall survival (OS) versus placebo/paclitaxel in both the overall population (HR, 0.56; 80% CI, 0.41 to 0.75; P = .005; median OS, 13.1 v 8.3 months, respectively) and the ATMlow population (HR, 0.35; 80% CI, 0.22 to 0.56; P = .002; median OS, not reached v 8.2 months, respectively). Olaparib/paclitaxel was generally well tolerated, with no unexpected safety findings.

CONCLUSION

Olaparib/paclitaxel is active in the treatment of patients with metastatic gastric cancer, with a greater OS benefit in ATMlow patients. A phase III trial in this setting is under way.

Histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA), enhances anti-tumor effects of the poly (ADP-ribose) polymerase (PARP) inhibitor olaparib in triple-negative breast cancer cells

Introduction

Olaparib, a poly (ADP-ribose) polymerase (PARP) inhibitor, has been found to have therapeutic potential for treating cancers associated with impaired DNA repair capabilities, particularly those with deficiencies in the homologous recombination repair (HRR) pathway. Histone deacetylases (HDACs) are important for enabling functional HRR of DNA by regulating the expression of HRR-related genes and promoting the accurate assembly of HRR-directed sub-nuclear foci. Thus, HDAC inhibitors have recently emerged as a therapeutic agent for treating cancer by inhibiting DNA repair. Based on this, HDAC inhibition could be predicted to enhance the anti-tumor effect of PARP inhibitors in cancer cells by blocking the HRR pathway.

Methods

We determined whether suberoylanilide hydroxamic acid (SAHA), a HDAC inhibitor, could enhance the anti-tumor effects of olaparib on breast cancer cell lines using a cytotoxic assay, cell cycle analysis, and Western blotting. We evaluated how exposure to SAHA affects the expression of HRR-associated genes. The accumulation of DNA double strand breaks (DSBs) induced by combination treatment was assessed. Induction of autophagy was monitored by imaging green fluorescent protein-tagged microtubule-associated protein 1A/1B-light chain 3 (LC3) expression following co-treatment with olaparib and SAHA. These in vitro data were validated in vivo using a human breast cancer xenograft model.

Results

Triple-negative breast cancer cell (TNBC) lines showed heterogeneous responses to the PARP and HDAC inhibitors. Co-administration of olaparib and SAHA synergistically inhibited the growth of TNBC cells that expressed functional Phosphatase and tensin homolog (PTEN). This effect was associated with down-regulation of the proliferative signaling pathway, increased apoptotic and autophagic cell death, and accumulation of DNA damage. The combined anti-tumor effect of olaparib and SAHA was also observed in a xenograft model. These data suggest that PTEN expression in TNBC cells can sensitize the cell response to simultaneous inhibition of PARP and HDAC both in vitro and in vivo.

Conclusion

Our findings suggest that expression of functional PTEN may serve as a biomarker for selecting TNBC patients that would favorably respond to a combination of olaparib with SAHA. This provides a strong rationale for treating TNBC patients with PTEN expression with a combination therapy consisting of olaparib and SAHA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0534-y) contains supplementary material, which is available to authorized users.

Systolic and diastolic mechanics in stress cardiomyopathy

BACKGROUND

Stress cardiomyopathy (SCM) is a peculiar form of reversible left ventricular dysfunction seen predominantly in women and occurs in response to emotional or physical stress. Because dysfunction in SCM is reversible and that of acute myocardial infarction (MI) is not, we hypothesized that these fundamental mechanistic differences between SCM and MI would be associated with different systolic and diastolic properties.

METHODS AND RESULTS

We examined 3 groups, all women: patients with SCM (n=24; mean age, 63±12 years), those with left anterior (LAD) ST-segment-elevation MI (n=36; mean age, 63±10 years), and referent control subjects (n=30; mean age, 62±8 years). All underwent angiography, ventriculography, and pressure measurements within 48 hours of presentation. Left ventricular volumes, diastolic pressures, and diastolic stiffness were higher in SCM and LAD MI patients than in control subjects but no different from each other. Similarly, left ventricular diastolic pressures and diastolic stiffness were elevated in the SCM and LAD MI groups compared with the control group. Left ventricular ejection fraction in SCM and LAD MI were 40.8±12.3% and 49.6±5.6%, respectively, versus 70.4±9.4% in control subjects (P<0.001), and stroke work less than half the value of control subjects. Indexes of contractility and ventricular-arterial coupling were similarly abnormal in SCM and LAD MI.

CONCLUSIONS

SCM and LAD MI show severe diastolic dysfunction. At similar left ventricular volumes, their diastolic pressures are more than twice as high as in control subjects, and systolic dysfunction is equally reduced in SCM and LAD MI. Despite a completely different pathophysiology in terms of systolic and diastolic function, SCM is indistinguishable from acute LAD-territory MI.

ATM kinase inhibition preferentially sensitizes p53-mutant glioma to ionizing radiation

PURPOSE

Glioblastoma multiforme (GBM) is the most lethal form of brain cancer with a median survival of only 12 to 15 months. Current standard treatment consists of surgery followed by chemoradiation. The poor survival of patients with GBM is due to aggressive tumor invasiveness, an inability to remove all tumor tissue, and an innate tumor chemo- and radioresistance. Ataxia-telangiectasia mutated (ATM) is an excellent target for radiosensitizing GBM because of its critical role in regulating the DNA damage response and p53, among other cellular processes. As a first step toward this goal, we recently showed that the novel ATM kinase inhibitor KU-60019 reduced migration, invasion, and growth, and potently radiosensitized human glioma cells in vitro.

EXPERIMENTAL DESIGN

Using orthotopic xenograft models of GBM, we now show that KU-60019 is also an effective radiosensitizer in vivo. Human glioma cells expressing reporter genes for monitoring tumor growth and dispersal were grown intracranially, and KU-60019 was administered intratumorally by convection-enhanced delivery or osmotic pump.

RESULTS

Our results show that the combined effect of KU-60019 and radiation significantly increased survival of mice 2- to 3-fold over controls. Importantly, we show that glioma with mutant p53 is much more sensitive to KU-60019 radiosensitization than genetically matched wild-type glioma.

CONCLUSIONS

Taken together, our results suggest that an ATM kinase inhibitor may be an effective radiosensitizer and adjuvant therapy for patients with mutant p53 brain cancers.

Abstract 3442: Olaparib increases antitumor effects on epigenetically RAD51C-deficient human cancer cells

Background: The poly (ADP-ribose) polymerase (PARP) inhibitor, olaparib, has been found to have a therapeutic potential for treating cancers that have an impaired DNA repair ability. RAD51C has been reported to play an essential role in DNA repair mediated by homologous recombination. In addition, RAD51C is a gene that affects human cancer susceptibility, similar to BRCA1 and BRCA2. RAD51C-defective cancers can therefore be potentially treated with olaparib because DNA damage induced by olaparib cannot be effectively repaired by HR since RAD51C deficiency interferes with RAD51-mediated HR.

Materials and Methods: We studied the growth inhibitory effects of olaparib on human cancer cell lines using clonogenic survival assays. Cell cycle analysis and molecular changed induced by olaparib were also performed. DNA methylation status in cancer cells and tumor tissue samples was also determined by using bisulfate sequencing.

Results: Olaparib is effective to RAD51C-defective cells. Olaparib leads to the accumulation of unrepaired DSBs due to dysfunctional RAD51 foci formation along with increased caspase 3-dependent cell death and G2/M arrest in RAD51C-defective cells. Moreover, the growth of RAD51C-deficient SNU601 tumor cells in a xenograft model decreased significantly following treatment with olaparib. Furthermore, RAD51C expression was significantly decreased in cancer and the lack of RAD51C was attributed to DNA methylation and histone modification. Our findings showed that the loss of RAD51C expression due to epigenetic silencing leads to olaparib sensitivity in cancer cells.

Conclusion: The loss of RAD51C expression was frequently associated with human cancers. We used a novel synthetic lethal approach using PARP inhibitors and observed that RAD51C was a participant in the DNA repair pathway. Our findings have potential clinical application for treating cancers with RAD51C deficiencies. Furthermore, we determined that RAD51C may serve as a novel biomarker for identifying olaparib-sensitive patients, thereby allowing physicians to select the most effective modalities for treating these individuals.

Citation Format: Ahrum Min, Seongyeong Kim, Seock-Ah Im, Young-Kwang Yoon, Sang-Hyun Song, Hyun-Jin Nam, Hyung-Seok Hur, Kyung-Hun Lee, Sae-Won Han, Do-Youn Oh, Tae-You Kim, Mark J. O`Connor, Woo-Ho Kim, Yung-Jue Bang. Olaparib increases antitumor effects on epigenetically RAD51C-deficient human cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3442. doi:10.1158/1538-7445.AM2013-3442

RAD51C-deficient cancer cells are highly sensitive to the PARP inhibitor olaparib

A PARP inhibitor is a rationally designed targeted therapy for cancers with impaired DNA repair abilities. RAD51C is a paralog of RAD51 that has an important role in the DNA damage response. We found that cell lines sensitive to a novel oral PARP inhibitor, olaparib, had low levels of RAD51C expression using microarray analysis, and we therefore hypothesized that low expression of RAD51C may hamper the DNA repair process, resulting in increased sensitivity to olaparib. Compared with the cells with normal RAD51C expression levels, RAD51C-deficient cancer cells were more sensitive to olaparib, and a higher proportion underwent cell death by inducing G2-M cell-cycle arrest and apoptosis. The restoration of RAD51C in a sensitive cell line caused attenuation of olaparib sensitivity. In contrast, silencing of RAD51C in a resistant cell line enhanced the sensitivity to olaparib, and the number of RAD51 foci decreased with ablated RAD51C expression. We also found the expression of RAD51C was downregulated in cancer cells due to epigenetic changes and RAD51C expression was low in some gastric cancer tissues. Furthermore, olaparib significantly suppressed RAD51C-deficient tumor growth in a xenograft model. In summary, RAD51C-deficient cancer cells are highly sensitive to olaparib and offer preclinical proof-of-principle that RAD51C deficiency may be considered a biomarker for predicting the antitumor effects of olaparib.