Large-scale Pan-cancer Cell Line Screening Identifies Actionable and Effective Drug Combinations

Oncology drug combinations can improve therapeutic responses and increase treatment options for patients. The number of possible combinations is vast and responses can be context-specific. Systematic screens can identify clinically relevant, actionable combinations in defined patient subtypes. We present data for 109 anticancer drug combinations from AstraZeneca's oncology small molecule portfolio screened in 755 pan-cancer cell lines. Combinations were screened in a 7 × 7 concentration matrix, with more than 4 million measurements of sensitivity, producing an exceptionally data-rich resource. We implement a new approach using combination Emax (viability effect) and highest single agent (HSA) to assess combination benefit. We designed a clinical translatability workflow to identify combinations with clearly defined patient populations, rationale for tolerability based on tumor type and combination-specific "emergent" biomarkers, and exposures relevant to clinical doses. We describe three actionable combinations in defined cancer types, confirmed in vitro and in vivo, with a focus on hematologic cancers and apoptotic targets.

SIGNIFICANCE

We present the largest cancer drug combination screen published to date with 7 × 7 concentration response matrices for 109 combinations in more than 750 cell lines, complemented by multi-omics predictors of response and identification of "emergent" combination biomarkers. We prioritize hits to optimize clinical translatability, and experimentally validate novel combination hypotheses. This article is featured in Selected Articles from This Issue, p. 695.

Preclinical Characterization of AZD9574, a Blood-Brain Barrier Penetrant Inhibitor of PARP1

PURPOSE

We evaluated the properties and activity of AZD9574, a blood-brain barrier (BBB) penetrant selective inhibitor of PARP1, and assessed its efficacy and safety alone and in combination with temozolomide (TMZ) in preclinical models.

EXPERIMENTAL DESIGN

AZD9574 was interrogated in vitro for selectivity, PARylation inhibition, PARP-DNA trapping, the ability to cross the BBB, and the potential to inhibit cancer cell proliferation. In vivo efficacy was determined using subcutaneous as well as intracranial mouse xenograft models. Mouse, rat, and monkey were used to assess AZD9574 BBB penetration and rat models were used to evaluate potential hematotoxicity for AZD9574 monotherapy and the TMZ combination.

RESULTS

AZD9574 demonstrated PARP1-selectivity in fluorescence anisotropy, PARylation, and PARP-DNA trapping assays and in vivo experiments demonstrated BBB penetration. AZD9574 showed potent single agent efficacy in preclinical models with homologous recombination repair deficiency in vitro and in vivo. In an O6-methylguanine-DNA methyltransferase (MGMT)-methylated orthotopic glioma model, AZD9574 in combination with TMZ was superior in extending the survival of tumor-bearing mice compared with TMZ alone.

CONCLUSIONS

The combination of three key features-PARP1 selectivity, PARP1 trapping profile, and high central nervous system penetration in a single molecule-supports the development of AZD9574 as the best-in-class PARP inhibitor for the treatment of primary and secondary brain tumors. As documented by in vitro and in vivo studies, AZD9574 shows robust anticancer efficacy as a single agent as well as in combination with TMZ. AZD9574 is currently in a phase I trial (NCT05417594). See related commentary by Lynce and Lin, p. 1217.

A Pilot Trial of Continuous Glucose Monitoring Upon Emergency Department Discharge Among People With Diabetes Mellitus

OBJECTIVE

People with diabetes mellitus, particularly those with limited access to longitudinal care, frequently present to the emergency department (ED). Continuous glucose monitoring (CGM) has been shown to improve outcomes in ambulatory settings, so we hypothesized that it would be beneficial if initiated upon ED discharge.

METHODS

We randomized adults with diabetes who were seen in the ED for hypo- or hyperglycemia to either 14 days of flash CGM or care coordination alone. All participants were scheduled to follow up in our diabetes specialty clinic. Outcomes included clinic attendance, the 3-month change in hemoglobin A1c, and repeat ED utilization.

RESULTS

We recruited 30 participants, including 13 with newly diagnosed diabetes. All but one (97%) had type 2 diabetes. We found no significant difference between the CGM (n = 16) and control (n = 14) groups in terms of clinic attendance (75 vs 64%, P = .61) or repeat ED utilization (31 vs 50%, P = .35), although our power was low. The absolute reduction in A1c was greater in the CGM group (5.2 vs 2.4%, P = .08). Among newly diagnosed participants for whom we had data, 7 out of 7 in the CGM group had a follow-up A1c under 7% compared to 1 out of 3 in the control group (P = .03). Over 90% of patients and providers found the CGM useful.

CONCLUSIONS

Our data demonstrate the feasibility of starting CGM in the ED, a valuable setting for engaging difficult-to-reach patients. Our pilot study was limited by its small sample size, however, as recruitment in the ED can be challenging.

Combined PARP and WEE1 inhibition triggers anti-tumor immune response in BRCA1/2 wildtype triple-negative breast cancer

Novel therapeutic strategies that can effectively combine with immunotherapies are needed in the treatment of triple-negative breast cancer (TNBC). We demonstrate that combined PARP and WEE1 inhibition are synergistic in controlling tumour growth in BRCA1/2 wild-type TNBC preclinical models. The PARP inhibitor (PARPi) olaparib combined with the WEE1 inhibitor (WEE1i) adavosertib triggered increases in anti-tumour immune responses, including STING pathway activation. Combinations with a STING agonist resulted in further improved durable tumour regression and significant improvements in survival outcomes in murine tumour models of BRCA1/2 wild-type TNBC. In addition, we have identified baseline tumour-infiltrating lymphocyte (TIL) levels as a potential predictive biomarker of response to PARPi, WEE1i and immunotherapies in BRCA1/2 wild-type TNBC.

MND1 and PSMC3IP control PARP inhibitor sensitivity in mitotic cells

The PSMC3IP-MND1 heterodimer promotes meiotic D loop formation before DNA strand exchange. In genome-scale CRISPR-Cas9 mutagenesis and interference screens in mitotic cells, depletion of PSMC3IP or MND1 causes sensitivity to poly (ADP-Ribose) polymerase inhibitors (PARPi) used in cancer treatment. PSMC3IP or MND1 depletion also causes ionizing radiation sensitivity. These effects are independent of PSMC3IP/MND1's role in mitotic alternative lengthening of telomeres. PSMC3IP- or MND1-depleted cells accumulate toxic RAD51 foci in response to DNA damage, show impaired homology-directed DNA repair, and become PARPi sensitive, even in cells lacking both BRCA1 and TP53BP1. Epistasis between PSMC3IP-MND1 and BRCA1/BRCA2 defects suggest that abrogated D loop formation is the cause of PARPi sensitivity. Wild-type PSMC3IP reverses PARPi sensitivity, whereas a PSMC3IP p.Glu201del mutant associated with D loop defects and ovarian dysgenesis does not. These observations suggest that meiotic proteins such as MND1 and PSMC3IP have a greater role in mitotic DNA repair.

Mechanisms of PARP Inhibitor Resistance

Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) represent the first medicines based on the targeting of the DNA damage response (DDR). PARPi have become standard of care for first-line maintenance treatment in ovarian cancer and have also been approved in other cancer indications including breast, pancreatic and prostate. Despite their efficacy, resistance to PARPi has been reported clinically and represents a growing patient population with unmet clinical need. Here, we describe the various mechanisms of PARPi resistance that have been identified in pre-clinical models and in the clinic.

Preclinical Characterization of AZD5305, A Next-Generation, Highly Selective PARP1 Inhibitor and Trapper

PURPOSE

We hypothesized that inhibition and trapping of PARP1 alone would be sufficient to achieve antitumor activity. In particular, we aimed to achieve selectivity over PARP2, which has been shown to play a role in the survival of hematopoietic/stem progenitor cells in animal models. We developed AZD5305 with the aim of achieving improved clinical efficacy and wider therapeutic window. This next-generation PARP inhibitor (PARPi) could provide a paradigm shift in clinical outcomes achieved by first-generation PARPi, particularly in combination.

EXPERIMENTAL DESIGN

AZD5305 was tested in vitro for PARylation inhibition, PARP-DNA trapping, and antiproliferative abilities. In vivo efficacy was determined in mouse xenograft and PDX models. The potential for hematologic toxicity was evaluated in rat models, as monotherapy and combination.

RESULTS

AZD5305 is a highly potent and selective inhibitor of PARP1 with 500-fold selectivity for PARP1 over PARP2. AZD5305 inhibits growth in cells with deficiencies in DNA repair, with minimal/no effects in other cells. Unlike first-generation PARPi, AZD5305 has minimal effects on hematologic parameters in a rat pre-clinical model at predicted clinically efficacious exposures. Animal models treated with AZD5305 at doses ≥0.1 mg/kg once daily achieved greater depth of tumor regression compared to olaparib 100 mg/kg once daily, and longer duration of response.

CONCLUSIONS

AZD5305 potently and selectively inhibits PARP1 resulting in excellent antiproliferative activity and unprecedented selectivity for DNA repair deficient versus proficient cells. These data confirm the hypothesis that targeting only PARP1 can retain the therapeutic benefit of nonselective PARPi, while reducing potential for hematotoxicity. AZD5305 is currently in phase I trials (NCT04644068).

Identification of a Molecularly-Defined Subset of Breast and Ovarian Cancer Models that Respond to WEE1 or ATR Inhibition, Overcoming PARP Inhibitor Resistance

PURPOSE

PARP inhibitors (PARPi) induce synthetic lethality in homologous recombination repair (HRR)-deficient tumors and are used to treat breast, ovarian, pancreatic, and prostate cancers. Multiple PARPi resistance mechanisms exist, most resulting in restoration of HRR and protection of stalled replication forks. ATR inhibition was highlighted as a unique approach to reverse both aspects of resistance. Recently, however, a PARPi/WEE1 inhibitor (WEE1i) combination demonstrated enhanced antitumor activity associated with the induction of replication stress, suggesting another approach to tackling PARPi resistance.

EXPERIMENTAL DESIGN

We analyzed breast and ovarian patient-derived xenoimplant models resistant to PARPi to quantify WEE1i and ATR inhibitor (ATRi) responses as single agents and in combination with PARPi. Biomarker analysis was conducted at the genetic and protein level. Metabolite analysis by mass spectrometry and nucleoside rescue experiments ex vivo were also conducted in patient-derived models.

RESULTS

Although WEE1i response was linked to markers of replication stress, including STK11/RB1 and phospho-RPA, ATRi response associated with ATM mutation. When combined with olaparib, WEE1i could be differentiated from the ATRi/olaparib combination, providing distinct therapeutic strategies to overcome PARPi resistance by targeting the replication stress response. Mechanistically, WEE1i sensitivity was associated with shortage of the dNTP pool and a concomitant increase in replication stress.

CONCLUSIONS

Targeting the replication stress response is a valid therapeutic option to overcome PARPi resistance including tumors without an underlying HRR deficiency. These preclinical insights are now being tested in several clinical trials where the PARPi is administered with either the WEE1i or the ATRi.

Drug-gene interaction screens coupled to tumour data analyses identify the most clinically-relevant cancer vulnerabilities driving sensitivity to PARP inhibition

Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) are currently indicated for the treatment of ovarian, breast, pancreatic and prostate cancers harbouring mutations in the tumour suppressor genes BRCA1 or BRCA2. In the case of ovarian and prostate cancers, their classification as homologous recombination repair (HRR) deficient (HRD) or mutated (HRRm) also makes PARPi an available treatment option beyond BRCA1 or BRCA2 mutational status. However, identification of the most relevant genetic alterations driving the HRD phenotype has proven difficult and recent data have shown that other genetic alterations not affecting HRR are also capable of driving PARPi responses. To gain insight into the genetics driving PARPi sensitivity, we performed CRISPR-Cas9 loss-of-function screens in 6 PARPi-insensitive cell lines and combined the output with published PARPi datasets from 8 additional cell lines. Ensuing exploration of the data identified 110 genes whose inactivation is strongly linked to sensitivity to PARPi. Parallel cell line generation of isogenic gene knockouts in ovarian and prostate cancer cell lines identified that inactivation of core HRR factors is required for driving in vitro PARPi responses comparable to the ones observed for BRCA1 or BRCA2 mutations. Moreover, pan-cancer genetic, transcriptomic and epigenetic data analyses of these 110 genes highlight the ones most frequently inactivated in tumours, making this study a valuable resource for prospective identification of potential PARPi-responsive patient populations. Importantly, our investigations uncover XRCC3 gene silencing as a potential new prognostic biomarker of PARPi sensitivity in prostate cancer.

Development and validation of a trans-ancestry polygenic risk score for type 2 diabetes in diverse populations

BACKGROUND

Type 2 diabetes (T2D) is a worldwide scourge caused by both genetic and environmental risk factors that disproportionately afflicts communities of color. Leveraging existing large-scale genome-wide association studies (GWAS), polygenic risk scores (PRS) have shown promise to complement established clinical risk factors and intervention paradigms, and improve early diagnosis and prevention of T2D. However, to date, T2D PRS have been most widely developed and validated in individuals of European descent. Comprehensive assessment of T2D PRS in non-European populations is critical for equitable deployment of PRS to clinical practice that benefits global populations.

METHODS

We integrated T2D GWAS in European, African, and East Asian populations to construct a trans-ancestry T2D PRS using a newly developed Bayesian polygenic modeling method, and assessed the prediction accuracy of the PRS in the multi-ethnic Electronic Medical Records and Genomics (eMERGE) study (11,945 cases; 57,694 controls), four Black cohorts (5137 cases; 9657 controls), and the Taiwan Biobank (4570 cases; 84,996 controls). We additionally evaluated a post hoc ancestry adjustment method that can express the polygenic risk on the same scale across ancestrally diverse individuals and facilitate the clinical implementation of the PRS in prospective cohorts.

RESULTS

The trans-ancestry PRS was significantly associated with T2D status across the ancestral groups examined. The top 2% of the PRS distribution can identify individuals with an approximately 2.5-4.5-fold of increase in T2D risk, which corresponds to the increased risk of T2D for first-degree relatives. The post hoc ancestry adjustment method eliminated major distributional differences in the PRS across ancestries without compromising its predictive performance.

CONCLUSIONS

By integrating T2D GWAS from multiple populations, we developed and validated a trans-ancestry PRS, and demonstrated its potential as a meaningful index of risk among diverse patients in clinical settings. Our efforts represent the first step towards the implementation of the T2D PRS into routine healthcare.

PARP inhibition is a modulator of anti-tumor immune response in BRCA-deficient tumors

PARP inhibitors are synthetically lethal with BRCA1/2 mutations, and in this setting, accumulation of DNA damage leads to cell death. Because increased DNA damage and subsequent immune activation can prime an anti-tumor immune response, we studied the impact of olaparib ± immune checkpoint blockade (ICB) on anti-tumor activity and the immune microenvironment. Concurrent combination of olaparib, at clinically relevant exposures, with ICB gave durable and deeper anti-tumor activity in the Brca1m BR5 model vs. monotherapies. Olaparib and combination treatment modulated the immune microenvironment, including increases in CD8+ T cells and NK cells, and upregulation of immune pathways, including type I IFN and STING signaling. Olaparib also induced a dose-dependent upregulation of immune pathways, including JAK/STAT, STING and type I IFN, in the tumor cell compartment of a BRCA1m (HBCx-10) but not a BRCA WT (HBCx-9) breast PDX model. In vitro, olaparib induced BRCAm tumor cell–specific dendritic cell transactivation. Relevance to human disease was assessed using patient samples from the MEDIOLA (NCT02734004) trial, which showed increased type I IFN, STING, and JAK/STAT pathway expression following olaparib treatment, in line with preclinical findings. These data together provide evidence for a mechanism and schedule underpinning potential benefit of ICB combination with olaparib.

ATR Inhibitor AZD6738 (Ceralasertib) Exerts Antitumor Activity as a Monotherapy and in Combination with Chemotherapy and the PARP Inhibitor Olaparib

AZD6738 (ceralasertib) is a potent and selective orally bioavailable inhibitor of ataxia telangiectasia and Rad3-related (ATR) kinase. ATR is activated in response to stalled DNA replication forks to promote G2-M cell-cycle checkpoints and fork restart. Here, we found AZD6738 modulated CHK1 phosphorylation and induced ATM-dependent signaling (pRAD50) and the DNA damage marker γH2AX. AZD6738 inhibited break-induced replication and homologous recombination repair. In vitro sensitivity to AZD6738 was elevated in, but not exclusive to, cells with defects in the ATM pathway or that harbor putative drivers of replication stress such as CCNE1 amplification. This translated to in vivo antitumor activity, with tumor control requiring continuous dosing and free plasma exposures, which correlated with induction of pCHK1, pRAD50, and γH2AX. AZD6738 showed combinatorial efficacy with agents associated with replication fork stalling and collapse such as carboplatin and irinotecan and the PARP inhibitor olaparib. These combinations required optimization of dose and schedules in vivo and showed superior antitumor activity at lower doses compared with that required for monotherapy. Tumor regressions required at least 2 days of daily dosing of AZD6738 concurrent with carboplatin, while twice daily dosing was required following irinotecan. In a BRCA2-mutant patient-derived triple-negative breast cancer (TNBC) xenograft model, complete tumor regression was achieved with 3 to5 days of daily AZD6738 per week concurrent with olaparib. Increasing olaparib dosage or AZD6738 dosing to twice daily allowed complete tumor regression even in a BRCA wild-type TNBC xenograft model. These preclinical data provide rationale for clinical evaluation of AZD6738 as a monotherapy or combinatorial agent.

SIGNIFICANCE

This detailed preclinical investigation, including pharmacokinetics/pharmacodynamics and dose-schedule optimizations, of AZD6738/ceralasertib alone and in combination with chemotherapy or PARP inhibitors can inform ongoing clinical efforts to treat cancer with ATR inhibitors.

Discovery of 5-{4-[(7-Ethyl-6-oxo-5,6-dihydro-1,5-naphthyridin-3-yl)methyl]piperazin-1-yl}-N-methylpyridine-2-carboxamide (AZD5305): A PARP1-DNA Trapper with High Selectivity for PARP1 over PARP2 and Other PARPs

Poly-ADP-ribose-polymerase (PARP) inhibitors have achieved regulatory approval in oncology for homologous recombination repair deficient tumors including BRCA mutation. However, some have failed in combination with first-line chemotherapies, usually due to overlapping hematological toxicities. Currently approved PARP inhibitors lack selectivity for PARP1 over PARP2 and some other 16 PARP family members, and we hypothesized that this could contribute to toxicity. Recent literature has demonstrated that PARP1 inhibition and PARP1-DNA trapping are key for driving efficacy in a BRCA mutant background. Herein, we describe the structure- and property-based design of 25 (AZD5305), a potent and selective PARP1 inhibitor and PARP1-DNA trapper with excellent in vivo efficacy in a BRCA mutant HBCx-17 PDX model. Compound 25 is highly selective for PARP1 over other PARP family members, with good secondary pharmacology and physicochemical properties and excellent pharmacokinetics in preclinical species, with reduced effects on human bone marrow progenitor cells in vitro.

Abstract 296: Structure-based and property-based drug design of AZD5305, a highly selective PARP1 inhibitor and trapper

Since the approval of olaparib in 2014 for BRCA mutated (BRCAm) ovarian cancer, many PARP inhibitors have been developed and have seen widespread success. However, as a class, these drugs are not without adverse events which have limited their ability to be combined with chemotherapy. Most first generation PARP inhibitors were developed and optimized before the concept of PARP1-DNA trapping was discovered as the mechanism by which PARP inhibitors exert their synthetic lethal effects on BRCAm cells. Moreover, the first generation PARP inhibitors were not optimized for selectivity across the PARP family potentially driving undesirable side effects, including intestinal toxicity from tankyrase inhibition or hematological toxicity from PARP2 inhibition. With this in mind, we set out to discover a best-in-class, second generation PARP inhibitor that was highly selective for PARP1 over the other 16 members of the PARP family, as well as a highly potent PARP1-DNA trapper.

PARP1 and PARP2 have a highly similar amino acid sequence, and most of the residues around the nicotinamide binding site are identical. However, there are some key residue differences in the helical domain which serves a regulator of the nicotinamide binding pocket. The publication of NMS-P118 in 2015 by Nerviano Medical Sciences showed that a highly selective PARP1 inhibitor could be found. This work inspired us to screen an extensive list of previously reported PARP inhibitors for selectivity against PARP2 and we found that FR257516 met the selectivity criteria as previously reported, but lacked the ability to trap PARP1 to DNA and hence lacked any activity in a cell colony formation assay in DLD-1 BRCA2-/- cells. Using parallel chemistry to generate diverse analogs, X-ray crystallography to enable structure-based design, and exploration of multiple nicotinamide mimetic cores, we were able to generate lead compound AZ4554, which was a PARP1 selective PARP1-DNA trapper with potent activity in BRCAm cells. Using concepts of property-based drug design, we were able to optimize lead compound AZ4554 into candidate drug AZD5305, making key improvements in secondary pharmacology, including reducing hERG activity, and intrinsic clearance in human microsomes through the introduction of polar atoms to lower logD without compromising permeability or oral bioavailability.

AZD5305 is a highly selective binder of PARP1 over PARP2 and other PARP enzymes by fluorescence polarization, surface plasmon resonance, and single molecule spectroscopy. It is highly potent against DLD-1 BRCA2-/- cells, while sparing isogenic BRCA WT cells. The secondary pharmacology of AZD5305 is remarkably clean, with hERG activity >40 µM. AZD5305 has a very favorable pre-clinical PK profile, low predicted human dose, and has shown efficacy in an MDA-MB-436 mouse xenograft model.

Citation Format: Sudhir Hande, Amber Balazs, Sébastien L. Degorce, Kevin Embrey, Avipsa Ghosh, Sonja J. Gill, Anders Gunnarsson, Giuditta Illuzzi, Jordan Lane, Carrie Larner, Elisabetta Leo, Andrew Madin, Lisa McWilliams, Mark J. O'Connor, Jonathan Orme, Fiona Pachl, Martin Packer, Andy Pike, Philip Rawlins, Marianne Schimpl, Anna D. Staniszewska, Andrew Zhang, Xiaolan Zheng, Jeffrey W. Johannes. Structure-based and property-based drug design of AZD5305, a highly selective PARP1 inhibitor and trapper [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 296.

Radiopotentiation Profiling of Multiple Inhibitors of the DNA Damage Response for Early Clinical Development

Radiotherapy is an effective anticancer treatment, but combinations with targeted agents that maximize efficacy while sparing normal tissue are needed. Here, we assess the radiopotentiation profiles of DNA damage response inhibitors (DDRi) olaparib (PARP1/2), ceralasertib (ATR), adavosertib (WEE1), AZD0156 (ATM), and KU-60648 (DNA-PK). We performed a radiotherapy combination screen and assessed how drug concentration and cellular DDR deficiencies influence the radiopotentiation ability of DDRi. We pre-selected six lung cancer cell lines with different genetic/signaling aberrations (including mutations in TP53 and ATM) and assessed multiple concentrations of DDRi in combination with a fixed radiotherapy dose by clonogenic assay. The effective concentration of DDRi in radiotherapy combinations is lower than that required for single-agent efficacy. This has the potential to be exploited further in the context of DDR deficiencies to increase therapeutic index and we demonstrate that low concentrations of AZD0156 preferentially sensitized p53-deficient cells. Moreover, testing multiple concentrations of DDRi in radiotherapy combinations indicated that olaparib, ceralasertib, and adavosertib have a desirable safety profile showing moderate increases in radiotherapy dose enhancement with increasing inhibitor concentration. Small increases in concentration of AZD0156 and particularly KU-60648, however, result in steep increases in dose enhancement. Radiopotentiation profiling can inform on effective drug doses required for radiosensitization in relation to biomarkers, providing an opportunity to increase therapeutic index. Moreover, multiple concentration testing demonstrates a relationship between drug concentration and radiotherapy effect that provides valuable insights that, with future in vivo validation, can guide dose-escalation strategies in clinical trials.

The influence of mechanical Circulatory support on post-transplant outcomes in pediatric patients: A multicenter study from the International Society for Heart and Lung Transplantation (ISHLT) Registry

BACKGROUND

Mechanical circulatory support (MCS) is increasingly being used as a bridge to transplant in pediatric patients. We compare outcomes in pediatric patients bridged to transplant with MCS from an international cohort.

METHODS

This retrospective cohort study of heart-transplant patients reported to the International Society for Heart and Lung Transplantation (ISHLT) registry from 2005-2017 includes 5,095 patients <18 years. Pretransplant MCS exposure and anatomic diagnosis were derived. Outcomes included mortality, renal failure, and stroke.

RESULTS

26% of patients received MCS prior to transplant: 240 (4.7%) on extracorporeal membrane oxygenation (ECMO), 1,030 (20.2%) on ventricular assist device (VAD), and 54 (1%) both. 29% of patients were <1 year, and 43.8% had congenital heart disease (CHD). After adjusting for clinical characteristics, compared to no-MCS and VAD, ECMO had higher mortality during their transplant hospitalization [OR 3.97 & 2.55; 95% CI 2.43-6.49 & 1.42-4.60] while VAD mortality was similar [OR 1.55; CI 0.99-2.45]. Outcomes of ECMO+VAD were similar to ECMO alone, including increased mortality during transplant hospitalization compared to no-MCS [OR 4.74; CI 1.81-12.36]. Patients with CHD on ECMO had increased 1 year, and 10 year mortality [HR 2.36; CI 1.65-3.39], [HR 1.82; CI 1.33-2.49]; there was no difference in survival in dilated cardiomyopathy (DCM) patients based on pretransplant MCS status.

CONCLUSION

Survival in CHD and DCM is similar in patients with no MCS or VAD prior to transplant, while pretransplant ECMO use is strongly associated with mortality after transplant particularly in children with CHD. In children with DCM, long term survival was equivalent regardless of MCS status.

Olaparib increases the therapeutic index of hemithoracic irradiation compared with hemithoracic irradiation alone in a mouse lung cancer model

Background

The radiosensitising effect of the poly(ADP-ribose) polymerase inhibitor olaparib on tumours has been reported. However, its effect on normal tissues in combination with radiation has not been well studied. Herein, we investigated the therapeutic index of olaparib combined with hemithoracic radiation in a urethane-induced mouse lung cancer model.

Methods

To assess tolerability, A/J mice were treated with olaparib plus whole thorax radiation (13 Gy), body weight changes were monitored and normal tissue effects were assessed by histology. In anti-tumour (intervention) studies, A/J mice were injected with urethane to induce lung tumours, and were then treated with olaparib alone, left thorax radiation alone or the combination of olaparib plus left thorax radiation at 8 weeks (early intervention) or 18 weeks (late intervention) after urethane injection. Anti-tumour efficacy and normal tissue effects were assessed by visual inspection, magnetic resonance imaging and histology.

Results

Enhanced body weight loss and oesophageal toxicity were observed when olaparib was combined with whole thorax but not hemithorax radiation. In both the early and late intervention studies, olaparib increased the anti-tumour effects of hemithoracic irradiation without increasing lung toxicity.

Conclusions

The addition of olaparib increased the therapeutic index of hemithoracic radiation in a mouse model of lung cancer.

SLFN11 informs on standard of care and novel treatments in a wide range of cancer models

BACKGROUND

Schlafen 11 (SLFN11) has been linked with response to DNA-damaging agents (DDA) and PARP inhibitors. An in-depth understanding of several aspects of its role as a biomarker in cancer is missing, as is a comprehensive analysis of the clinical significance of SLFN11 as a predictive biomarker to DDA and/or DNA damage-response inhibitor (DDRi) therapies.

METHODS

We used a multidisciplinary effort combining specific immunohistochemistry, pharmacology tests, anticancer combination therapies and mechanistic studies to assess SLFN11 as a potential biomarker for stratification of patients treated with several DDA and/or DDRi in the preclinical and clinical setting.

RESULTS

SLFN11 protein associated with both preclinical and patient treatment response to DDA, but not to non-DDA or DDRi therapies, such as WEE1 inhibitor or olaparib in breast cancer. SLFN11-low/absent cancers were identified across different tumour types tested. Combinations of DDA with DDRi targeting the replication-stress response (ATR, CHK1 and WEE1) could re-sensitise SLFN11-absent/low cancer models to the DDA treatment and were effective in upper gastrointestinal and genitourinary malignancies.

CONCLUSION

SLFN11 informs on the standard of care chemotherapy based on DDA and the effect of selected combinations with ATR, WEE1 or CHK1 inhibitor in a wide range of cancer types and models.

A meta-analysis of reversion mutations in BRCA genes identifies signatures of DNA end-joining repair mechanisms driving therapy resistance

BACKGROUND

Germline mutations in the BRCA1 or BRCA2 (BRCA) genes predispose to hereditary breast and ovarian cancer and, mostly in the case of BRCA2, are also prevalent in cases of pancreatic and prostate malignancies. Tumours from these patients tend to lose both copies of the wild-type BRCA gene, which makes them exquisitely sensitive to platinum drugs and poly(ADP-ribose) polymerase inhibitors (PARPi), treatments of choice in these disease settings. Reversion secondary mutations with the capacity of restoring BRCA protein expression have been documented in the literature as bona fide mechanisms of resistance to these treatments.

PATIENTS AND METHODS

We analysed published sequencing data of BRCA genes (from tumour or circulating tumour DNA) in 327 patients with tumours harbouring mutations in BRCA1 or BRCA2 (234 patients with ovarian cancer, 27 with breast cancer, 13 with pancreatic cancer, 11 with prostate cancer and 42 with a cancer of unknown origin) that progressed on platinum or PARPi treatment.

RESULTS

We describe 269 cases of reversion mutations in 86 patients in this cohort (26.0%). Detailed analyses of the reversion events highlight that most amino acid sequences encoded by exon 11 in BRCA1 and BRCA2 are dispensable to generate resistance to platinum or PARPi, whereas other regions are more refractory to sizeable amino acid losses. They also underline the key role of mutagenic end-joining DNA repair pathways in generating reversions, especially in those affecting BRCA2, as indicated by the significant accumulation of DNA sequence microhomologies surrounding deletions leading to reversion events.

CONCLUSIONS

Our analyses suggest that pharmacological inhibition of DNA end-joining repair pathways could improve durability of drug treatments by preventing the acquisition of reversion mutations in BRCA genes. They also highlight potential new therapeutic opportunities when reversions result in expression of hypomorphic versions of BRCA proteins, especially with agents targeting the response to DNA replication stress.

Abstract 626: Mechanistic differentiation of targeted DDR agent combinations

The DNA damage response (DDR) safeguards genome stability and promotes cellular survival by counteracting deleterious consequences of DNA damage. Deficiencies in DDR pathways contribute to genome instability, a hallmark of cancer development, and targeting the DDR is a promising anti-cancer therapy strategy. We describe here in vitro and in vivo studies allowing mechanistic understanding of the benefit of combining our DDR kinase inhibitors (DDRi) targeting ATM (AZD0156), ATR (AZD6738) and DNA-PK (AZD7648) with the PARP inhibitor, olaparib, in homologous recombination-deficient backgrounds. Using the break-induced replication (BIR) assay, which measures homologous-recombination repair (HRR) of DNA double-strand breaks resembling broken replication forks, we observed that ATRi decreases this type of homologous recombination repair by up to 50%, while inhibiting DNA-PK or ATM showed no effect. This provides a mechanistic rationale for combining ATRi with compounds that cause replication-fork collapse, such as PARPi. Indeed, combination of olaparib with the ATRi in BRCA1 mutant UWB1.289 cells enhanced olaparib sensitivity a thousand-fold (GI50 from 590 nM to 0.6 nM). This correlates with the complete tumour growth inhibitions (TGI) observed for the ATRi + olaparib combination in the BRCA2 mutant HBCx-10 triple negative breast cancer PDX model and is consistent with a synergistic increase of genome instability measured by metaphase spread analysis (total aberrations: olaparib; 11, ATRi; 8, combination; 35). DNA-PKi, however, did not synergise with olaparib, showing little enhancement of olaparib single-agent treatment (GI50 from 0.59 μM to 0.33 μM) and no significant impact on the total amount of chromosomal aberrations (total aberrations: olaparib; 11, DNA-PKi ; 3, combination; 14), suggesting that DNA-PKi alone or in combination with olaparib have little impact on BRCA1 mutated tumours. In ATM KO FaDu xenografts, ATRi or DNA-PKi single-agent treatment resulted in TGI, with complete tumour regressions when combined. Focusing on the olaparib combination, metaphase spread analysis of ATRi-treated FaDu ATM KO cells showed an enhancement of DNA replication-dependent chromatid breaks (1.3 vs 0.2 breaks/spread in ATM WT), while DNA-PKi treatment predominantly caused chromosome breaks (1.7 vs 0.2 breaks/spread in ATM WT) that are not dependent on replication. When combined with olaparib, ATRi acted synergistically and in a manner similar to that observed in the BRCA1 mutant cells, while the DNA-PKi + olaparib combination was additive. These data suggest that enhanced olaparib sensitisation of ATM KO cells by ATRi or DNA-PKi combinations occurs through different mechanisms. Together, these findings provide mechanistic differentiation of our DDRi in specific genetic backgrounds. This work informs how to clinically position these agents to benefit the right patients not only as single-agent treatments, but also in combination.

Citation Format: Josep V. Forment, Paul Wijnhoven, Antonio Ramos-Montoya, Jacqueline Fok, Valeria Follia, Mercedes Vazquez-Chantada, Rajesh Oderda, Zena Wilson, Alan Lau, Elisabetta Leo, Stephen Durant, Elaine Cadogan, Mark J. O'Connor. Mechanistic differentiation of targeted DDR agent combinations [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 626.

Differential therapeutic effects of PARP and ATR inhibition combined with radiotherapy in the treatment of subcutaneous versus orthotopic lung tumour models

Background

Subcutaneous mouse tumour models are widely used for the screening of novel antitumour treatments, although these models are poor surrogate models of human cancers.

Methods

We compared the antitumour efficacy of the combination of ionising radiation (IR) with two DNA damage response inhibitors, the PARP inhibitor olaparib and the ATR inhibitor AZD6738 (ceralasertib), in subcutaneous versus orthotopic cancer models.

Results

Olaparib delayed the growth of irradiated Lewis lung carcinoma (LL2) subcutaneous tumours, in agreement with previous reports in human cell lines. However, the olaparib plus IR combination showed a very narrow therapeutic window against LL2 lung orthotopic tumours, with nearly no additional antitumour effect compared with that of IR alone, and tolerability issues emerged at high doses. The addition of AZD6738 greatly enhanced the efficacy of the olaparib plus IR combination treatment against subcutaneous but not orthotopic LL2 tumours. Moreover, olaparib plus AZD6738 administration concomitant with IR even worsened the response to radiation of head and neck orthotopic tumours and induced mucositis.

Conclusions

These major differences in the responses to treatments between subcutaneous and orthotopic models highlight the importance of using more pathologically relevant models, such as syngeneic orthotopic models, to determine the most appropriate therapeutic approaches for translation to the clinic.

Characteristics of Patients with Recurrent Emergency Medical Services Utilization for Symptomatic Hypoglycemia in an Urban Setting

Background: Symptomatic hypoglycemia frequently results in utilization of emergency medical services (EMS). Understanding the characteristics of hypoglycemic patients with high EMS utilization may help providers optimize resource allocation. Objective: To describe characteristics of patients utilizing EMS for hypoglycemia and to determine if any factors identifiable in the prehospital setting are associated with recurrent EMS utilization. Methods: A retrospective chart review of prehospital care records from an urban EMS system was performed. Patients who received oral glucose, parenteral glucose, or intramuscular glucagon for hypoglycemia over a one-year period were identified. Extracted information included demographics, prehospital treatment, disposition, zip code median income, and the number of subsequent EMS utilizations within 365 days. Results: We identified 549 subjects, mean age 55 years (range 5 to 104, 65% male). The mean glucose level for all patients was 44 mg/dl with standard deviation (SD) of 15. In total, 69% of patients received oral glucose, 26% received parenteral glucose, 3% received glucagon, and 2% received more than one medication. At the index visit, 81% of patients accepted hospital transportation. The rate of recurrent EMS utilization for hypoglycemia was 10%, and 3% of patients had 3 or more repeat utilizations within 365 days. The mean finger-stick glucose at index visit was 39 mg/dL (SD 15) for patients with multiple EMS utilizations and 44 mg/dL (SD 14) for those with one EMS visit (P = 0.006). Repeat utilizers were more likely to have received medications other than oral glucose at index visit, 51% vs. 28% (P < 0.001). Age, gender, median zip code income, and disposition were not associated with recurrent EMS utilization. The overall annual rate of hypoglycemia requiring EMS treatment per estimated diabetic population was 0.84%. Conclusion: A low proportion of patients utilizing EMS for hypoglycemia had subsequent EMS visits within 365 days. Those who did had lower initial blood glucose at the index visit and were more likely to have received prehospital treatment with medications other than oral glucose. Demographic characteristics did not yield any patterns predictive of repeat utilization. Refusing transport to the hospital after EMS treatment for hypoglycemia did not increase the risk of recurrent utilization.

Pharmacology of the ATM Inhibitor AZD0156: Potentiation of Irradiation and Olaparib Responses Preclinically

AZD0156 is a potent and selective, bioavailable inhibitor of ataxia-telangiectasia mutated (ATM) protein, a signaling kinase involved in the DNA damage response. We present preclinical data demonstrating abrogation of irradiation-induced ATM signaling by low doses of AZD0156, as measured by phosphorylation of ATM substrates. AZD0156 is a strong radiosensitizer in vitro, and using a lung xenograft model, we show that systemic delivery of AZD0156 enhances the tumor growth inhibitory effects of radiation treatment in vivo Because ATM deficiency contributes to PARP inhibitor sensitivity, preclinically, we evaluated the effect of combining AZD0156 with the PARP inhibitor olaparib. Using ATM isogenic FaDu cells, we demonstrate that AZD0156 impedes the repair of olaparib-induced DNA damage, resulting in elevated DNA double-strand break signaling, cell-cycle arrest, and apoptosis. Preclinically, AZD0156 potentiated the effects of olaparib across a panel of lung, gastric, and breast cancer cell lines in vitro, and improved the efficacy of olaparib in two patient-derived triple-negative breast cancer xenograft models. AZD0156 is currently being evaluated in phase I studies (NCT02588105).

Klinefelter Syndrome and Diabetes

PURPOSE OF REVIEW

Klinefelter syndrome (KS) is associated with increased insulin resistance and high rates of type 2 diabetes (T2DM). Our aim was to review what is known about the prevalence of diabetes in men with KS, potential mechanisms underlying the observed metabolic phenotype, and the data that are available to guide treatment decisions.

RECENT FINDINGS

The increased prevalence of T2DM seen in men with KS appears to be the result of multiple mechanisms including increased truncal adiposity and socioeconomic disadvantages, but it is likely not a direct consequence of hypogonadism alone. No randomized trials have been conducted to evaluate the impact of testosterone replacement therapy on T2DM in men with KS, but observational data suggest that testosterone replacement is not associated with lower rates of diabetes or improved glycemic control. Metabolic derangements are common in KS, but treatment strategies specific to this population are lacking. Early lifestyle and dietary interventions are likely important. Additional research is needed to dissect the complex interaction between genotype and metabolic phenotype. Collaboration between academic centers caring for men with KS is needed to facilitate the development of evidence-based clinical practice guidelines, which would inform optimal screening and treatment strategies for this patient population.

Abstract 932: Reversing PARP inhibitor resistance by targeting the replication stress response

PARP1/2 inhibitors (PARPi) are the first approved targeted DNA damage response (DDR) inhibitors and have been shown to have clinical benefit, particularly in tumors harboring mutations in BRCA1/BRCA2 and other genes of homologous recombination repair (HRR). However, resistance to PARPi monotherapy will impact on both the breadth and depth of response. We showed that HRR-mutant TNBC and ovarian cancer patient-derived tumor xenograft (PDX) models frequently exhibit innate or acquired PARP inhibitor resistance and that this resistance is linked to a proficient or reactivated HRR, indicated by the ability to form RAD51 foci. A key component of PARPi mechanism of action results from trapping PARP onto DNA, which has the potential to generate replication stress. Moreover, recent data demonstrate that PARP1, along with components of the HRR, are associated with the re-start and protection of stalled replication forks. Here, we assessed whether combinations of the PARPi olaparib together with inhibitors of the replication stress response (RSR) could reverse PARPi resistance in our PDX cohort and we analyzed the effects on RSR by immunofluorescence and immunoblotting. Our data demonstrate that 7/27 models exhibit WEE1i (AZD1775) single agent activity measured as tumor regressions (≤ -30% change in tumor volume), all of which were PARPi resistant. Of the PARPi and WEE1i resistant models, 5 responded to combination treatment and demonstrated a significant increase in the RSR markers pRPA32 and pan-γH2AX compared to either single agent treatment alone. For monotherapy ATRi treatment, there were three models showing tumor regression with AZD6738, all harbored ATM mutations, two also responding to WEE1i monotherapy and one responded to olaparib monotherapy. There were an additional two models that responded to the combination of PARPi plus ATRi, and one of these also responded to the WEE1i/PARPi combination. Together, our analysis demonstrates that by targeting the replication stress response we could cause tumor regression in 13/20 PARPi resistant PDX models and in 6 of these cases the response required PARP inhibition, with DDR signalling indicating that the PARPi was impacting on the RSR. Further insights will be presented into which genetic backgrounds and acquired PARPi resistant mechanisms are reversed by targeting either WEE1 or ATR, thus highlighting the potential for how PARPi resistance can be reversed by targeting alternative DDR dependencies.

Citation Format: Mark J. O'Connor, Cristina Cruz, Marta Castroviejo-Bermejo, Urszula M. Polanska, Gemma N. Jones, Anderson Wang, Zhongwu Lai, Josep Forment, Krishna Bulusu, Alba Llop-Guevara, Brian Dougherty, Cristina Saura, Rachel Brough, Chris J. Lord, Alejandra Bruna, Carlos Caldas, Stephen Fawell, J Carl Barrett, Susan E. Critchlow, Judith Balmaña, Elaine Cadogan, Violeta Serra. Reversing PARP inhibitor resistance by targeting the replication stress response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 932.

Abstract 2077: A novel assay for PARP-DNA trapping provides insights into the mechanism of action (MoA) of clinical PARP inhibitors (PARPi)

Treatments with PARPi in cancers with impaired DNA repair mechanisms (i.e. with Homologous Recombination Repair Deficiency, HRD) causes unsupportable genomic instability resulting in tumor cell death. PARPi act via a dual mechanism: 1) they block PARylation activity that normally occurs in response to DNA damage; 2) they trap PARP onto DNA lesions creating potentially cytotoxic PARP-DNA complexes. The longer PARP is inhibited and trapped onto the DNA, the greater the cytotoxic effect of PARPi in preclinical models. However, differences in preclinical PARP trapping potency have not translated into increased clinical efficacy with standard clinical doses used. Therefore, the ability to assess PARP-chromatin trapping in cancer models is critical for understanding the MoA of existing clinical PARPi. To date, this has been achieved by low throughput assays in non-HRD models using high PARPi concentrations and the addition of exogenous DNA damage.

Here, we describe the development of a novel assay, a high throughput in situ cell extraction platform, where PARP-chromatin trapping is monitored by immunofluorescence and can be multiplexed with the analysis of other relevant biomarkers. Our novel assay has several advantages compared to conventional methods: the overall experimental process is simpler and less time consuming with results being quantitative and less error prone. Most importantly, the higher throughput allows a thorough evaluation of PARP1-chromatin trapping kinetics and their effects with dose-response in a time-dependent manner for clinical PARPi following both continuous treatment or after a wash out of drug.

Using this new assay, we tested the kinetics in isogenic cell line pairs (BRCA2-/- and WT) and followed in parallel the appearance of biomarkers of DNA damage (e.g. γ-H2AX). The data have revealed important elements of differentiation between the MoA of clinical PARPi including the important insight that the strongest PARP trapper (talazoparib) has clearly reduced cytotoxic specificity for HRD cells, which likely explains the significantly reduced dose used in the clinic compared to other PARPi. These along with other data presented highlight how this next generation PARP trapping assays can provide important insights into PARPi MoA.

Citation Format: Giuditta Illuzzi, Mark J O'Connor, Elisabetta Leo. A novel assay for PARP-DNA trapping provides insights into the mechanism of action (MoA) of clinical PARP inhibitors (PARPi) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2077.

PARP Inhibitors: Extending Benefit Beyond BRCA-Mutant Cancers

A mounting body of evidence now indicates that PARP inhibitors have the potential to be used as a foundation for both monotherapy and combination strategies across a wide spectrum of molecular backgrounds and tumor types. Although PARP inhibitors as a class display many similarities, critical differences in structure can translate into differences in tolerability and antitumor activity that have important implications for the clinic. Furthermore, while PARP inhibitors have demonstrated a clear role in treating tumors with underlying homologous recombination deficiencies, there is now biological and early clinical evidence to support their use in other molecular subsets of cancer, including tumors associated with high levels of replication stress such as small-cell lung cancer. In this article, we highlight the key similarities and differences between individual PARP inhibitors and their implications for the clinic. We discuss data that currently support clinical strategies for extending the benefit of PARP inhibitors beyond BRCA-mutant cancers, toward broader populations of patients through the use of novel biomarkers of homologous recombination repair deficiency (HRD), as well as predictive biomarkers rooted in mechanisms of sensitivity outside of HRD. We also explore the potential application of PARP inhibitors in earlier treatment settings, including neoadjuvant, adjuvant, and even chemoprevention approaches. Finally, we focus on promising combination therapeutic strategies, such as those with other DNA damage response (DDR) inhibitors such as ATR inhibitors, immune checkpoint inhibitors, and non-DDR-targeted agents that induce "chemical BRCAness."

Sequential Therapy with PARP and WEE1 Inhibitors Minimizes Toxicity while Maintaining Efficacy

We demonstrate that concurrent administration of poly(ADP-ribose) polymerase (PARP) and WEE1 inhibitors is effective in inhibiting tumor growth but poorly tolerated. Concurrent treatment with PARP and WEE1 inhibitors induces replication stress, DNA damage, and abrogates the G₂ DNA damage checkpoint in both normal and malignant cells. Following cessation of monotherapy with PARP or WEE1 inhibitors, effects of these inhibitors persist suggesting that sequential administration of PARP and WEE1 inhibitors could maintain efficacy while ameliorating toxicity. Strikingly, while sequential administration mirrored concurrent therapy in cancer cells that have high basal replication stress, low basal replication stress in normal cells protected them from DNA damage and toxicity, thus improving tolerability while preserving efficacy in ovarian cancer xenograft and patient-derived xenograft models.

A RAD51 assay feasible in routine tumor samples calls PARP inhibitor response beyond BRCA mutation

Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) are effective in cancers with defective homologous recombination DNA repair (HRR), including BRCA1/2-related cancers. A test to identify additional HRR-deficient tumors will help to extend their use in new indications. We evaluated the activity of the PARPi olaparib in patient-derived tumor xenografts (PDXs) from breast cancer (BC) patients and investigated mechanisms of sensitivity through exome sequencing, BRCA1 promoter methylation analysis, and immunostaining of HRR proteins, including RAD51 nuclear foci. In an independent BC PDX panel, the predictive capacity of the RAD51 score and the homologous recombination deficiency (HRD) score were compared. To examine the clinical feasibility of the RAD51 assay, we scored archival breast tumor samples, including PALB2-related hereditary cancers. The RAD51 score was highly discriminative of PARPi sensitivity versus PARPi resistance in BC PDXs and outperformed the genomic test. In clinical samples, all PALB2-related tumors were classified as HRR-deficient by the RAD51 score. The functional biomarker RAD51 enables the identification of PARPi-sensitive BC and broadens the population who may benefit from this therapy beyond BRCA1/2-related cancers.

The Combination of the PARP Inhibitor Olaparib and the WEE1 Inhibitor AZD1775 as a New Therapeutic Option for Small Cell Lung Cancer

Purpose: Introduced in 1987, platinum-based chemotherapy remains standard of care for small cell lung cancer (SCLC), a most aggressive, recalcitrant tumor. Prominent barriers to progress are paucity of tumor tissue to identify drug targets and patient-relevant models to interrogate novel therapies. Following our development of circulating tumor cell patient-derived explants (CDX) as models that faithfully mirror patient disease, here we exploit CDX to examine new therapeutic options for SCLC.Experimental Design: We investigated the efficacy of the PARP inhibitor olaparib alone or in combination with the WEE1 kinase inhibitor AZD1775 in 10 phenotypically distinct SCLC CDX in vivo and/or ex vivo These CDX represent chemosensitive and chemorefractory disease including the first reported paired CDX generated longitudinally before treatment and upon disease progression.Results: There was a heterogeneous depth and duration of response to olaparib/AZD1775 that diminished when tested at disease progression. However, efficacy of this combination consistently exceeded that of cisplatin/etoposide, with cures in one CDX model. Genomic and protein analyses revealed defects in homologous recombination repair genes and oncogenes that induce replication stress (such as MYC family members), predisposed CDX to combined olaparib/AZD1775 sensitivity, although universal predictors of response were not noted.Conclusions: These preclinical data provide a strong rationale to trial this combination in the clinic informed by prevalent, readily accessed circulating tumor cell-based biomarkers. New therapies will be evaluated in SCLC patients after first-line chemotherapy, and our data suggest that the combination of olaparib/AZD1775 should be used as early as possible and before disease relapse. Clin Cancer Res; 24(20); 5153-64. ©2018 AACR.

Androgen Receptor Inhibitor Enhances the Antitumor Effect of PARP Inhibitor in Breast Cancer Cells by Modulating DNA Damage Response

The androgen receptor (AR) is expressed in 60%-70% of breast cancers regardless of estrogen receptor status, and has been proposed as a therapeutic target in breast cancers that retain AR. In this study, the authors aimed to investigate a new treatment strategy using a novel AR inhibitor AZD3514 in breast cancer. AZD3514 alone had a minimal antiproliferative effect on most breast cancer cell lines irrespective of AR expression level, but it downregulated the expressions of DNA damage response (DDR) molecules, including ATM and chk2, which resulted in the accumulation of damaged DNA in some breast cancer cells. Furthermore, AZD3514 enhanced cellular sensitivity to a PARP inhibitor olaparib by blocking the DDR pathway in breast cancer cells. Furthermore, the downregulation of NKX3.1 expression in MDA-MB-468 cells by AZD3514 occurred in parallel with the suppression of ATM-chk2 axis activation, and the suppression of NKX3.1 by AZD3514 was found to result from AZD3514-induced TOPORS upregulation and a resultant increase in NKX3.1 degradation. The study shows posttranslational regulation of NKX3.1 via TOPORS upregulation by AZD3514-induced ATM inactivation-increased olaparib sensitivity in AR-positive and TOPORS-expressing breast cancer cells, and suggests the antitumor effect of AZD3514/olaparib cotreatment is caused by compromised DDR activity in breast cancer cell lines and in a xenograft model. These results provide a rationale for future clinical trials of olaparib/AR inhibitor combination treatment in breast cancer.

Outcomes of Prehospital Chemical Sedation With Ketamine Versus Haloperidol and Benzodiazepine or Physical Restraint Only

OBJECTIVE

The goal of this study is to describe complications and outcomes of prehospital ketamine use for agitation as compared to other methods of physical or chemical restraint such as haloperidol plus benzodiazepine or physical restraint only.

METHODS

We conducted a single-center retrospective review of patient encounters in which restraint was administered in the prehospital setting. At the beginning of our study window, only physical restraint was available to paramedics managing agitated patients but subsequently, haloperidol and benzodiazepines were introduced, followed by ketamine 2 years later. By comparing patients before and after each transition, we divided subjects into 3 cohorts based on restraint type: physical restraint, haloperidol plus benzodiazepine, and ketamine. Demographic data were collected, and outcome measures included intubation rate, need for additional physical or chemical restraint, emergency department (ED) length of stay, need for hospital admission, and employee injury.

RESULTS

Of 214 subjects included in the study, 95 patients were administered ketamine, 68 received haloperidol and benzodiazepine, and 51 were physically restrained. Eleven of the patients (11.6%) who received ketamine were intubated. Compared to patients who received haloperidol plus benzodiazepine, patients who received ketamine were more likely to be intubated (odds ratio [OR] = 8.77, 95% confidence interval [CI], 1.10-69.68) and were more likely to require additional chemical restraint when compared to haloperidol/benzodiazepine or physical restraint only (OR =2.94, 95% CI, 1.49-5.80, and OR =2.15, 95% CI, 1.07-4.31, respectively). There were no differences between the 2 chemical sedation groups in terms of ED length of stay or hospital admission rate.

CONCLUSIONS

This study demonstrates a lower intubation rate in patients administered ketamine than prior literature in association with a lower weight-based dosing regimen. Ketamine use was correlated with a higher frequency of intubation and a greater need for additional chemical restraint when compared with other restraint modalities, though exogenous factors such as provider preference may have impacted this result. There was no difference in ED length of stay or admission rate between the ketamine and haloperidol plus benzodiazepine groups. Further prospective study is needed to determine whether there is a subset of patients for whom ketamine would be beneficial compared to other therapies.

ATR kinase inhibitor AZD6738 potentiates CD8+ T cell-dependent antitumor activity following radiation

DNA-damaging chemotherapy and radiation therapy are integrated into the treatment paradigm of the majority of cancer patients. Recently, immunotherapy that targets the immunosuppressive interaction between programmed death 1 (PD-1) and its ligand PD-L1 has been approved for malignancies including non-small cell lung cancer, melanoma, and head and neck squamous cell carcinoma. ATR is a DNA damage-signaling kinase activated at damaged replication forks, and ATR kinase inhibitors potentiate the cytotoxicity of DNA-damaging chemotherapies. We show here that the ATR kinase inhibitor AZD6738 combines with conformal radiation therapy to attenuate radiation-induced CD8+ T cell exhaustion and potentiate CD8+ T cell activity in mouse models of Kras-mutant cancer. Mechanistically, AZD6738 blocks radiation-induced PD-L1 upregulation on tumor cells and dramatically decreases the number of tumor-infiltrating Tregs. Remarkably, AZD6738 combines with conformal radiation therapy to generate immunologic memory in complete responder mice. Our work raises the possibility that a single pharmacologic agent may enhance the cytotoxic effects of radiation while concurrently potentiating radiation-induced antitumor immune responses.

Shieldin complex promotes DNA end-joining and counters homologous recombination in BRCA1-null cells

BRCA1 deficiencies cause breast, ovarian, prostate and other cancers, and render tumours hypersensitive to poly(ADP-ribose) polymerase (PARP) inhibitors. To understand the resistance mechanisms, we conducted whole-genome CRISPR-Cas9 synthetic-viability/resistance screens in BRCA1-deficient breast cancer cells treated with PARP inhibitors. We identified two previously uncharacterized proteins, C20orf196 and FAM35A, whose inactivation confers strong PARP-inhibitor resistance. Mechanistically, we show that C20orf196 and FAM35A form a complex, 'Shieldin' (SHLD1/2), with FAM35A interacting with single-stranded DNA through its C-terminal oligonucleotide/oligosaccharide-binding fold region. We establish that Shieldin acts as the downstream effector of 53BP1/RIF1/MAD2L2 to promote DNA double-strand break (DSB) end-joining by restricting DSB resection and to counteract homologous recombination by antagonizing BRCA2/RAD51 loading in BRCA1-deficient cells. Notably, Shieldin inactivation further sensitizes BRCA1-deficient cells to cisplatin, suggesting how defining the SHLD1/2 status of BRCA1-deficient tumours might aid patient stratification and yield new treatment opportunities. Highlighting this potential, we document reduced SHLD1/2 expression in human breast cancers displaying intrinsic or acquired PARP-inhibitor resistance.

Abstract 4302: Analysis of the dose and schedule dependence of tumor kill in nonclinical tumour models after treatment with the WEE1 inhibitor AZD1775

AZD1775 is a highly selective, small-molecule inhibitor of WEE1 being developed to treat patients with advanced solid tumors, as monotherapy and in combination with olaparib (Lynparza). Previously a mathematical model was developed using data from patient-derived explant (PDX) and xenografted models with a range of sensitivities to AZD1775. This mathematical model could describe the dose and schedule dependency of pharmacokinetics, pCDK1 reduction in tumor and anti-tumor activity. This was for a dose range of 30mg/kg-120mg/kg dosed p.o. on a range of schedules from 3 days on 4 days off to 5 days on 9 days off. The model was then used to rank the potential effectiveness of each dosing regimen by calculating the fraction of tumor killed per week at doses resulting in drug exposure comparable to that observed in the clinic. This calculation was performed by integrating over time the rate of tumor kill predicted by the model. This analysis was complimented with a log cell kill (LCK) analysis using post treatment regrowth data to estimate in a more empirical manner the fraction of tumor killed over the treatment period. Specifically, if TC and TT are the times it takes the controls and treated tumors to grow to a prescribed volume and DT is the doubling time of control tumors then LCK=(TT-TC)/(2.3xDT). The analysis demonstrated that across the data set there was a consistent trend of increased LCK with dose level and number of days dosing in a week. The LCK values for each regimen were normalized by the total number of doses administered, to give an LCK per dose. There appeared to be a consistent LCK per dose level across the dose range considered. Interestingly, there was a greater than linear increase of LCK with increasing dose level. This was consistent with the observation that higher doses with shorter durations of dosing, were at least as active as more chronically administered lower doses. In the TNBC HBCx17 (Xentech) model, over a four-week period 60mg/kg dosed 5 days per week results in an LCK of 0.5 (70% killed) whereas 90mg/kg dosed 3 days per week has an LCK of 0.75 (83% killed). The same relationship was derived from the model simulated fraction tumor kill: higher doses generated significantly larger proportions of tumor kill, thus requiring shorter periods of dosing for the same net effect. The analysis drew greater differentiation between regimen than could be achieved by a tumor growth inhibition (TGI) analysis: where regressions were observed there were a few percentage point differences in TGI between regimen, but up to an order of magnitude difference in LCK. By concentrating on predicting potential cell kill, regimens were identified that are more likely to lead to responses in the clinic. The insights from this analysis have informed recommended dose and schedule for subsequent efficacy expansions.

Citation Format: James William Thomas Yates, Elaine Cadogan, Jennifer I. Hare, Adina M. Hughes, Urszula M. Polanska, Mark J. O'Connor, Susan E. Critchlow. Analysis of the dose and schedule dependence of tumor kill in nonclinical tumour models after treatment with the WEE1 inhibitor AZD1775 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4302.

Abstract 5451: Testing a combination of AKT inhibitor (AZD5363) with PARP inhibitor olaparib plus carboplatin in TNBC

Background: AKT, a hallmark of cancer in a wide range of solid tumors, is a serine/threonine protein kinase. Inhibition of AKT is known to cause the perturbation of cell proliferation signals and induction of apoptosis in several preclinical in vitro and in vivo models. AKT inhibitor AZD5363 shows promise in different solid tumors in patients with activating mutations of AKT (E17K) (Hyman D. M. et al., JCO 2017), the efficacy is not substantial in patients with PIK3CA mutations (Banerji. U, CCR 2017). PI3K-PTEN-AKT pathway alterations are very common in TNBC. Alterations of AKT1/2/3 (15%), PTEN (29%) and PIK3CA (25%) mediated upregulation of the PI3K pathway are common in TNBC (De et al., 2016; cBioPortal). In our Avera cohort (January 2014-June 2017) of TNBC patients (n=93), we have recorded a total of 16.5 % alteration in AKT1/2/3. We have also identified an integral role of the PI3K-AKT pathway in the DDR-mediated antitumor action of PARP inhibitor in TNBC (De et al., 2014).

Aim: Here we tested the role of genetic background in determining the effectiveness of a combination of AZD5363 with PARP inhibitor Olaparib (O, Lynparza) plus carboplatin (C) in TNBC.

Methods: Using cell line based models of TNBC with defined genetic backgrounds, we studied proliferation (Incucyte) and cell cycle by PI (Accuri). Mechanistic induction of apoptosis was evaluated by live-cell triple immuno-fluorescence (IF) (MitoView Blue+NucView488 Casp3 substrate + CF 594 AnnexinV) with a simultaneous quantification of Annexin (Accuri). Long-term clonogenic response to triple combination was tested using 3D On-Top Matrigel assay.

Result: AZD5363 treatment in PTEN-null SUM149 cells with BRCA1 mutation [2288delT (fs&gt;735X)] responded synergistically to O and C with a dose-dependent increase apoptosis but with limited G1 increase. AZD5363 treatment in PTEN-null MDA-MB468 cells with wt BRCA1 led to an additive effect in slowing proliferation when combined with O and C and a very strong G1 increase but limited induction of apoptosis. AZD5363 as a single agent slowed proliferation and increased G1 in PIK3CA (P539R/H1074R) mutated BT20 cells with a concomitant increase in apoptosis. Mechanistically AZD5363 inhibited pophoyrlation of AKT substrates PRAS40 and GSKβ in TNBC cell lines. As expected KRAS/BRAF mutated (G13D/G464V), BRCA1 wt MDA-MB231 cells showed no effect on either proliferation or apoptosis. Best effect on the inhibition of clonogenic growth (reducing 3D colony formation and size as compared to control over single or double treatment) was recorded in SUM149 compared to MDA468 &gt; BT20, &gt; HCC1937.

Summary: Here we present the effect of the combination of AZD5363 and O plus C in several TNBC cell line based models. Our data demonstrate that maximum effect of the triple combination is seen in PTEN-null cell line harboring BRCA1 mutations followed by PTEN-null cell BRCA1wt. Mechanistic work utlizing AKT1-E17K transfected cells is ongoing.

Citation Format: Jennifer H. Carlson, Mark J. O'Connor, Casey Williams, Pradip De, Nandini Dey, Brian Leyland-Jones. Testing a combination of AKT inhibitor (AZD5363) with PARP inhibitor olaparib plus carboplatin in TNBC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5451.

Abstract 2826: Differential activity of ATR and WEE1 inhibitors in DLBCL subtypes is linked to replication stress and differences in mode of action

The checkpoint kinases ATR and WEE1 protect cells from replication stress (RS), a hallmark of cancer that has potential to be exploited for cancer treatment. ATR and WEE1 inhibitors are in early clinical trials. Here we report selective anti-tumour activity of inhibitors to ATR (AZD6738) and WEE1 (AZD1775) in a subset of diffuse large B-cell lymphoma (DLBCL) cell lines. Using the cell-of-origin (COO) gene expression scoring system, we found enhanced sensitivity to AZD6738 in the activated B-cell like (ABC, n=6) and unclassified cell lines (n=6) with a combined median GI50 of 0.372 µM, compared to germinal centre B-cell like (GCB, n=7) cell lines, with median GI50 of 1.554 µM. Grouping the cells into AZD6738 sensitive (GI50 ≤ 0.5 µM) or insensitive (≥ 1 µM), we show that the ABC/unclassified COO score, together with high c-MYC protein or CDKN2A/B deletion identified 7/8 sensitive cell lines and 0/7 insensitive cell lines. Furthermore, markers of RS correlated with cell line sensitivity. Treatment of cells with 0.5 µM AZD6738 increased the quantity of 53BP1 nuclear bodies by 3-6 fold across the sensitive cell lines compared to only 2 fold across the insensitive cell lines. DNA fibre analysis also showed that sensitive cells lines had slower rates of replication fork progression (0.80 - 1.12 kbmin-1) compared to insensitive cell lines (1.22 - 1.41 kbmin-1). Across the same DLBCL cell line panel sensitivity to the WEE1 inhibitor AZD1775 was positively correlated with AZD6738 sensitivity, although at lower concentrations. However, using OCI-LY19 and DB cells to reflect high and low replication stress respectively, we show that AZD6738 and AZD1775 differ mechanistically in the extent of DNA damage and apoptosis induced within cell cycle phases. Treatment with 1 µM AZD1775 induced S-phase arrest and increased γH2AX+ cells in S/G2 from 4% to 20% in both cell lines at 8 h, indicating replication-associated DNA damage. However, earlier onset of cell death was observed in the OCI-LY19 cells, with 30% γH2AX+ cells undergoing apoptosis at 24 h compared to 25% γH2AX+ DB cells at 72 h. In contrast, AZD6738 only caused G1 arrest in OCI-LY19 daughter cells, with 20% apoptosis at 72 h. These findings are reflected in the anti-tumour activity of the inhibitors in xenograft DLBCL models in vivo. Once-daily, oral dosing of 50 mg/kg/day AZD6738 or 120 mg/kg/day AZD1775 in OCI-LY19 xenograft model showed efficacy with mean % tumour growth inhibition (%TGI) at day 8 of 104.1% (n=10) and 114.3% (n=10) respectively. In addition, the combination of AZD1775 (60 mg/kg/day; monotherapy %TGI=88.7, n=10) and AZD6738 (25 mg/kg/day; monotherapy %TGI=89.8%, n=10) dosed using a 5 day on, 9 day off dosing schedule was tolerated in mice and resulted in tumour regressions (combination %TGI=108.4%, n=8). These data suggest potential for both single agent and combination opportunities for ATR and WEE1 inhibitors in the DLBCL ABC subtype.

Citation Format: Lucy A. Young, Lenka Oplustil O'Connor, Zena Wilson, Corinne Reimer, Alan Lau, Jiri Bartek, Mark J. O'Connor. Differential activity of ATR and WEE1 inhibitors in DLBCL subtypes is linked to replication stress and differences in mode of action [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2826.

Abstract 2816: Patient derived ovarian cancer xenograft (OC-PDX) to study the response of the PARP inhibitor olaparib

Up to 50% of High Grade Serous (HGS) ovarian cancer patients exhibit homologous recombination deficiency (HRD) through various mechanisms including germline and somatic mutations in BRCA-1 or 2. Olaparib, a poly(ADP-ribose)polymerase (PARP) inhibitor, was recently approved for the treatment of patients with germline BRCA-mutated-advanced ovarian cancer. We have analyzed our panel of patient derived ovarian cancer xenografts (OC-PDX)1 to investigate the association of the somatic BRCA1/2 mutational status with the response to olaparib.

Whole Exome Sequencing (Illumina HiSeq4000) was performed on a panel (n=26) of OC-PDX to identify mutations in BRCA1/2. Next Generation Sequencing (NGS) results were confirmed by Sanger sequencing on tumor DNA and RNA. Thirteen OC-PDX were selected and treated with 100mg/kg olaparib for 4 weeks or as a maintenance regimen until progression. Cisplatin was used as reference drug. Efficacy was evaluated as the best T/C% (best growth inhibition) for subcutaneous (s.c) tumors. To mimick patient disease, OC-PDX were also established as intra-peritoneal models (i.p.) and best ILS% (best increment of lifespan) calculated.

Response to olaparib varied among the models with distinct responsive and non-responsive groups associated with BRCA mutational status.

OC-PDX with a homozygous frameshift mutation in BRCA1/2 (n=5), loss of BRCA1 (n=1) or no expression of BRCA1/2 (n=1) showed a sustained response to olaparib after 4 week treatment (T/C values from 2% to 40%; ILS of one representative OC-PDX = 74%), with complete responses following a longer term maintenance treatment. One BRCA1 mutated OC-PDX model was resistant, progressing rapidly under treatment. In this orthotopic model ILS% and tumor dissemination score of treated mice were similar to vehicle. Models responsive to olaparib were in general also sensitive to cisplatin. BRCA1/2 wild type OC-PDX models (n=4 s.c and n=1 i.p) did not respond to olaparib, even following a longer term treatment (T/C from 41% to 86%; ILS = 5%). NGS revealed a heterozygous mutation in BRCA2 in one OC-PDX. Sanger sequencing of the RNA confirmed the presence of both the wild type and the mutated BRCA2 transcripts. This OC- PDX was poorly responsive to olaparib (T/C = 57%).

Our data showed that in general tumors with a homozygous mutation, loss or no expression of BRCA1/2 responded to olaparib; the drug was not active on those with mutation in heterozygosis (BRCA2+/-) or wild type. These findings indicate that tumor somatic mutations play a role in the response to olaparib. Models of OC-PDX moderately responsive to olaparib offer the opportunity to assess the potential of combination treatments.

1 Ricci, F. et al. Patient-derived ovarian tumor xenografts recapitulate human clinicopathology and genetic alterations. Cancer Res 74, 6980–90 (2014)

Citation Format: Francesca Bizzaro, Alessia C. Marchetti, Alessandra Decio, Francesca Ricci, Mark J. O'Connor, Molly A. Taylor, Zhongwu Lai, Simon T. Barry, Maria R. Bani, Raffaella Giavazzi. Patient derived ovarian cancer xenograft (OC-PDX) to study the response of the PARP inhibitor olaparib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2816.

RAD51 foci as a functional biomarker of homologous recombination repair and PARP inhibitor resistance in germline BRCA-mutated breast cancer

Background

BRCA1 and BRCA2 (BRCA1/2)-deficient tumors display impaired homologous recombination repair (HRR) and enhanced sensitivity to DNA damaging agents or to poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi). Their efficacy in germline BRCA1/2 (gBRCA1/2)-mutated metastatic breast cancers has been recently confirmed in clinical trials. Numerous mechanisms of PARPi resistance have been described, whose clinical relevance in gBRCA-mutated breast cancer is unknown. This highlights the need to identify functional biomarkers to better predict PARPi sensitivity.

Patients and methods

We investigated the in vivo mechanisms of PARPi resistance in gBRCA1 patient-derived tumor xenografts (PDXs) exhibiting differential response to PARPi. Analysis included exome sequencing and immunostaining of DNA damage response proteins to functionally evaluate HRR. Findings were validated in a retrospective sample set from gBRCA1/2-cancer patients treated with PARPi.

Results

RAD51 nuclear foci, a surrogate marker of HRR functionality, were the only common feature in PDX and patient samples with primary or acquired PARPi resistance. Consistently, low RAD51 was associated with objective response to PARPi. Evaluation of the RAD51 biomarker in untreated tumors was feasible due to endogenous DNA damage. In PARPi-resistant gBRCA1 PDXs, genetic analysis found no in-frame secondary mutations, but BRCA1 hypomorphic proteins in 60% of the models, TP53BP1-loss in 20% and RAD51-amplification in one sample, none mutually exclusive. Conversely, one of three PARPi-resistant gBRCA2 tumors displayed BRCA2 restoration by exome sequencing. In PDXs, PARPi resistance could be reverted upon combination of a PARPi with an ataxia-telangiectasia mutated (ATM) inhibitor.

Conclusion

Detection of RAD51 foci in gBRCA tumors correlates with PARPi resistance regardless of the underlying mechanism restoring HRR function. This is a promising biomarker to be used in the clinic to better select patients for PARPi therapy. Our study also supports the clinical development of PARPi combinations such as those with ATM inhibitors.

Fanconi anemia and homologous recombination gene variants are associated with functional DNA repair defects in vitro and poor outcome in patients with advanced head and neck squamous cell carcinoma

Mutations in Fanconi Anemia or Homologous Recombination (FA/HR) genes can cause DNA repair defects and could therefore impact cancer treatment response and patient outcome. Their functional impact and clinical relevance in head and neck squamous cell carcinoma (HNSCC) is unknown. We therefore questioned whether functional FA/HR defects occurred in HNSCC and whether they are associated with FA/HR variants. We assayed a panel of 29 patient-derived HNSCC cell lines and found that a considerable fraction is hypersensitive to the crosslinker Mitomycin C and PARP inhibitors, a functional measure of FA/HR defects. DNA sequencing showed that these hypersensitivities are associated with the presence of bi-allelic rare germline and somatic FA/HR gene variants. We next questioned whether such variants are associated with prognosis and treatment response in HNSCC patients. DNA sequencing of 77 advanced stage HNSCC tumors revealed a 19% incidence of such variants. Importantly, these variants were associated with a poor prognosis (p = 0.027; HR = 2.6, 1.1–6.0) but favorable response to high cumulative cisplatin dose. We show how an integrated in vitro functional repair and genomic analysis can improve the prognostic value of genetic biomarkers. We conclude that repair defects are marked and frequent in HNSCC and are associated with clinical outcome.

BRD4 Inhibition Is Synthetic Lethal with PARP Inhibitors through the Induction of Homologous Recombination Deficiency

Poly(ADP-ribose) polymerase inhibitors (PARPi) are selectively active in cells with homologous recombination (HR) deficiency (HRD) caused by mutations in BRCA1, BRCA2, and other pathway members. We sought small molecules that induce HRD in HR-competent cells to induce synthetic lethality with PARPi and extend the utility of PARPi. We demonstrated that inhibition of bromodomain containing 4 (BRD4) induced HRD and sensitized cells across multiple tumor lineages to PARPi regardless of BRCA1/2, TP53, RAS, or BRAF mutation status through depletion of the DNA double-stand break resection protein CtIP (C-terminal binding protein interacting protein). Importantly, BRD4 inhibitor (BRD4i) treatment reversed multiple mechanisms of resistance to PARPi. Furthermore, PARPi and BRD4i are synergistic in multiple in vivo models.

ATM protein is deficient in over 40% of lung adenocarcinomas

Lung cancer is the leading cause of cancer-related mortality in the USA and worldwide, and of the estimated 1.2 million new cases of lung cancer diagnosed every year, over 30% are lung adenocarcinomas. The backbone of 1^st-line systemic therapy in the metastatic setting, in the absence of an actionable oncogenic driver, is platinum-based chemotherapy. ATM and ATR are DNA damage signaling kinases activated at DNA double-strand breaks (DSBs) and stalled and collapsed replication forks, respectively. ATM protein is lost in a number of cancer cell lines and ATR kinase inhibitors synergize with cisplatin to resolve xenograft models of ATM-deficient lung cancer. We therefore sought to determine the frequency of ATM loss in a tissue microarray (TMA) of lung adenocarcinoma. Here we report the validation of a commercial antibody (ab32420) for the identification of ATM by immunohistochemistry and estimate that 61 of 147 (41%, 95% CI 34%-50%) cases of lung adenocarcinoma are negative for ATM protein expression. As a positive control for ATM staining, nuclear ATM protein was identified in stroma and immune infiltrate in all evaluable cases. ATM loss in lung adenocarcinoma was not associated with overall survival. However, our preclinical findings in ATM-deficient cell lines suggest that ATM could be a predictive biomarker for synergy of an ATR kinase inhibitor with standard-of-care cisplatin. This could improve clinical outcome in 100,000's of patients with ATM-deficient lung adenocarcinoma every year.

Abstract P1-03-04: Role of PTEN and BRCA1 as determinants of synergy for the combination of vistusertib with carboplatin and olaparib in TNBC

Introduction: Platinum agents are being used in combination with targeted agents in advanced triple-negative breast cancer (TNBC) (See K. Gelmon et al., 2012). Additionally inhibition of PARP is also being considered as a “targeted” therapy for TNBC (Anders CK et al., 2010). PARP inhibitor (i), Lynparza (olaparib,AstraZeneca)met the primary endpoint of a Phase III trial in which Lynparza was compared to physician's choice of a standard of care chemotherapy in patients with HER2-negative metastatic BC harboring germline BRCA1/2 mutations (BRCAm). Based on cBioportal data analyses and experimental studies we and others have reported that more than 30% PTEN loss in TNBC leads to activation/upregulation of the PI3K pathway (Nature. 2012; Ellis and Perou, 2013; Dey et al., 2012; De et al., 2016; Reed and Shokat 2017;). In line with active kinase profiling, genetic and pharmacological data which defined mTOR as an important target in TNBC (Montero JC et al., 2012), we have demonstrated that mTORi has anti-tumor activity in TNBC (De et al., 2014). Aim: These studies focused on exploring the synergy of biology-based targeted drugs PARPi (olaparib, O), mTOR kinase (vistusertib, V), and platinum (C) in TNBC models. Method: TNBC cells of multiple genetic backgrounds were used to test the combination(s) on proliferation and apoptosis by monitoring growth and using real time Annexin V reagent in a microscopy-based assay (Essen IncuCyte Zoom). Flow cytometric analysis of cell cycle progression by PI staining was also used. Long term clonogenic 3D growth was monitored in matrigel. Results: In BRCAm/PTEN null Sum149 and HCC1937 cells and BRCA wild type (wt)/PTEN null MDA-MB-468 the addition of (V) to (O) and (C) enhanced apoptosis induction and further slowed growth. In Sum149 cells, single agent V treatment induced G1 arrest while O plus C or the triple combination increased S phase accumulation. In MDA-MB-468 cells G1 arrest was seen with V alone and in the triplet. In BRCA wt/PTEN null HCC70 cells V decreased cell proliferation and induced G1 arrest. In the HCC70 model, the addition of O plus C did not synergize with V. In BT20, a BRCA wt/PTEN wt but PI3KCA mutant cell line, no effect on proliferation or apoptosis was seen in the O plus C treated arms. V slowed cell proliferation and increased G1 arrest in a dose-dependent manner. As expected in a BRCA wt/PTEN wt, but RAS active mutant cell line MDA-MB-231 this treatment combination was not effective and was used as an internal negative control. Based on ratios of the normalized slopes of proliferation curves (for triplet), the cells were graded in terms of synergy as SUM149&gt;MDA-MB-468&gt;HCC1937 and HCC70&gt;BT20&gt;MDA-MB231. Treatment with the triplet had the largest effect on reducing 3D colony formation and size as compared to control over single or double treatment. Summary: Here, we present the effect of the combination of vistusertib with olaparib plus carboplatin in several TNBC models. Our data demonstrate that increased effectiveness of the triple combination is seen in cells harboring BRCA1 and PTEN-null mutations. The mechanistic role of these two targets on determining this synergy is being worked out and will be presented at the meeting.

Citation Format: Carlson JH, O'Connor MJ, De P, Dey N, Leyland-Jones B. Role of PTEN and BRCA1 as determinants of synergy for the combination of vistusertib with carboplatin and olaparib in TNBC [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-03-04.

Laying a trap to kill cancer cells: PARP inhibitors and their mechanisms of action

Poly(ADP-ribose) polymerase (PARP) inhibitors are the first DNA damage response targeted agents approved for cancer therapy. Here, we focus on their molecular mechanism of action by PARP "trapping" and what this means for both clinical monotherapy and combination with chemotherapeutic agents.

PARP1 Trapping and DNA Replication Stress Enhance Radiosensitization with Combined WEE1 and PARP Inhibitors

KRAS mutations in non-small cell lung cancer (NSCLC) cause increased levels of DNA damage and replication stress, suggesting that inhibition of the DNA damage response (DDR) is a promising strategy for radiosensitization of NSCLC. This study investigates the ability of a WEE1 inhibitor (AZD1775) and a PARP inhibitor (olaparib) to radiosensitize KRAS-mutant NSCLC cells and tumors. In addition to inhibiting the DDR, these small-molecule inhibitors of WEE1 and PARP induce DNA replication stress via nucleotide exhaustion and PARP trapping, respectively. As monotherapy, AZD1775 or olaparib alone modestly radiosensitized a panel of KRAS-mutant NSCLC lines. The combination of agents, however, significantly increased radiosensitization. Furthermore, AZD1775-mediated radiosensitization was rescued by nucleotide repletion, suggesting a mechanism involving AZD1775-mediated replication stress. In contrast, radiosensitization by the combination of AZD1775 and olaparib was not rescued by nucleosides. Whereas both veliparib, a PARP inhibitor that does not efficiently trap PARP1 to chromatin, and PARP1 depletion radiosensitized NSCLC cells as effectively as olaparib, which does efficiently trap PARP, only olaparib potentiated AZD1775-mediated radiosensitization. Taken together, these mechanistic data demonstrate that although nucleotide depletion is sufficient for radiosensitization by WEE1 inhibition alone, and inhibition of PARP catalytic activity is sufficient for radiosensitization by olaparib alone, PARP1 trapping is required for enhanced radiosensitization by the combination of WEE1 and PARP inhibitors.Implications: This study highlights DNA replication stress caused by nucleotide depletion and PARP1 trapping as an important mechanism of radiosensitization in KRAS-mutant tumors and supports further development of DNA replication as a therapeutic target. Mol Cancer Res; 16(2); 222-32. ©2017 AACR.

Neoadjuvant olaparib targets hypoxia to improve radioresponse in a homologous recombination-proficient breast cancer model

Clinical trials are studying the benefits of combining the PARP-1 inhibitor olaparib with chemotherapy and radiotherapy treatment in a variety of cancer increasing the therapeutic ratio for olaparib may come from its ability to modify the tumour microenvironment by targeting homologous recombination-deficient, hypoxic tumour clonogens, and/or increasing tumour-associated vasodilation to improve oxygenation. Herein, we investigated the effect of prolonged neoadjuvant exposure to olaparib on the tumor microenvironment using a genetically-engineered mouse p53−/− syngeneic breast cancer model, which is proficient in homology-directed DNA repair. We observed increased in vivo growth delay and decreased ex vivo clonogenic survival following pre-treatment with olaparib 50 mg/kg bid Olaparib for 7 days ending 48 hours prior to a radiation dose of 12Gy. This increased in vivo radioresponse was associated with a decreased hypoxic fraction. This study suggests that the radiation response in patients can be improved with limited toxicity if olaparib is given in a purely neoadjuvant setting to modify the tumor microenviroment prior to the start of the radiotherapy treatment. Consequently a significant gain can be achieved in therapeutic window and clinical studies are needed to confirm this preclinical data.

Long-Term Responders on Olaparib Maintenance in High-Grade Serous Ovarian Cancer: Clinical and Molecular Characterization

Purpose: Maintenance therapy with olaparib has improved progression-free survival in women with high-grade serous ovarian cancer (HGSOC), particularly those harboring BRCA1/2 mutations. The objective of this study was to characterize long-term (LT) versus short-term (ST) responders to olaparib.Experimental Design: A comparative molecular analysis of Study 19 (NCT00753545), a randomized phase II trial assessing olaparib maintenance after response to platinum-based chemotherapy in HGSOC, was conducted. LT response was defined as response to olaparib/placebo >2 years, ST as <3 months. Molecular analyses included germline BRCA1/2 status, three-biomarker homologous recombination deficiency (HRD) score, BRCA1 methylation, and mutational profiling. Another olaparib maintenance study (Study 41; NCT01081951) was used as an additional cohort.Results: Thirty-seven LT (32 olaparib) and 61 ST (21 olaparib) patients were identified. Treatment was significantly associated with outcome (P < 0.0001), with more LT patients on olaparib (60.4%) than placebo (11.1%). LT sensitivity to olaparib correlated with complete response to chemotherapy (P < 0.05). In the olaparib LT group, 244 genetic alterations were detected, with TP53, BRCA1, and BRCA2 mutations being most common (90%, 25%, and 35%, respectively). BRCA2 mutations were enriched among the LT responders. BRCA methylation was not associated with response duration. High myriad HRD score (>42) and/or BRCA1/2 mutation was associated with LT response to olaparib. Study 41 confirmed the correlation of LT response with olaparib and BRCA1/2 mutation.Conclusions: Findings show that LT response to olaparib may be multifactorial and related to homologous recombination repair deficiency, particularly BRCA1/2 defects. The type of BRCA1/2 mutation warrants further investigation. Clin Cancer Res; 23(15); 4086-94. ©2017 AACR.