Durable responses to ATR inhibition with ceralasertib in tumors with genomic defects and high inflammation

BACKGROUNDPhase 1 study of ATRinhibition alone or with radiation therapy (PATRIOT) was a first-in-human phase I study of the oral ATR (ataxia telangiectasia and Rad3-related) inhibitor ceralasertib (AZD6738) in advanced solid tumors.METHODSThe primary objective was safety. Secondary objectives included assessment of antitumor responses and pharmacokinetic (PK) and pharmacodynamic (PD) studies. Sixty-seven patients received 20-240 mg ceralasertib BD continuously or intermittently (14 of a 28-day cycle).RESULTSIntermittent dosing was better tolerated than continuous, which was associated with dose-limiting hematological toxicity. The recommended phase 2 dose of ceralasertib was 160 mg twice daily for 2 weeks in a 4-weekly cycle. Modulation of target and increased DNA damage were identified in tumor and surrogate PD. There were 5 (8%) confirmed partial responses (PRs) (40-240 mg BD), 34 (52%) stable disease (SD), including 1 unconfirmed PR, and 27 (41%) progressive disease. Durable responses were seen in tumors with loss of AT-rich interactive domain-containing protein 1A (ARID1A) and DNA damage-response defects. Treatment-modulated tumor and systemic immune markers and responding tumors were more immune inflamed than nonresponding.CONCLUSIONCeralasertib monotherapy was tolerated at 160 mg BD intermittently and associated with antitumor activity.TRIAL REGISTRATIONClinicaltrials.gov: NCT02223923, EudraCT: 2013-003994-84.FUNDINGCancer Research UK, AstraZeneca, UK Department of Health (National Institute for Health Research), Rosetrees Trust, Experimental Cancer Medicine Centre.

Predicting progression-free survival after systemic therapy in advanced head and neck cancer: Bayesian regression and model development

Background

Advanced head and neck squamous cell carcinoma (HNSCC) is associated with a poor prognosis, and biomarkers that predict response to treatment are highly desirable. The primary aim was to predict progression-free survival (PFS) with a multivariate risk prediction model.

Methods

Experimental covariates were derived from blood samples of 56 HNSCC patients which were prospectively obtained within a Phase 2 clinical trial (NCT02633800) at baseline and after the first treatment cycle of combined platinum-based chemotherapy with cetuximab treatment. Clinical and experimental covariates were selected by Bayesian multivariate regression to form risk scores to predict PFS.

Results

A 'baseline' and a 'combined' risk prediction model were generated, each of which featuring clinical and experimental covariates. The baseline risk signature has three covariates and was strongly driven by baseline percentage of CD33+CD14+HLADRhigh monocytes. The combined signature has six covariates, also featuring baseline CD33+CD14+HLADRhigh monocytes but is strongly driven by on-treatment relative change of CD8+ central memory T cells percentages. The combined model has a higher predictive power than the baseline model and was successfully validated to predict therapeutic response in an independent cohort of nine patients from an additional Phase 2 trial (NCT03494322) assessing the addition of avelumab to cetuximab treatment in HNSCC. We identified tissue counterparts for the immune cells driving the models, using imaging mass cytometry, that specifically colocalized at the tissue level and correlated with outcome.

Conclusions

This immune-based combined multimodality signature, obtained through longitudinal peripheral blood monitoring and validated in an independent cohort, presents a novel means of predicting response early on during the treatment course.

Funding

Daiichi Sankyo Inc, Cancer Research UK, EU IMI2 IMMUCAN, UK Medical Research Council, European Research Council (335326), Merck Serono. Cancer Research Institute, National Institute for Health Research, Guy's and St Thomas' NHS Foundation Trust and The Institute of Cancer Research.

Clinical trial number

NCT02633800.

OX40 and 4-1BB delineate distinct immune profiles in sarcoma

Systemic relapse after radiotherapy and surgery is the major cause of disease-related mortality in sarcoma patients. Combining radiotherapy and immunotherapy is under investigation as a means to improve response rates. However, the immune contexture of sarcoma is understudied. Here, we use a retrospective cohort of sarcoma patients, treated with neoadjuvant radiotherapy, and TCGA data. We explore therapeutic targets of relevance to sarcoma, using genomics and multispectral immunohistochemistry to provide insights into the tumor immune microenvironment across sarcoma subtypes. Differential gene expression between radioresponsive myxoid liposarcoma (MLPS) and more radioresistant undifferentiated pleomorphic sarcoma (UPS) indicated UPS contained higher transcript levels of a number of immunotherapy targets (CD73/NT5E, CD39/ENTPD1, CD25/IL2RA, and 4-1BB/TNFRSF9). We focused on 4-1BB/TNFRSF9 and other costimulatory molecules. In TCGA data, 4-1BB correlated to an inflamed and exhausted phenotype. OX40/TNFRSF4 and 4-1BB/TNFRSF9 were highly expressed in sarcoma subtypes versus other cancers. Despite OX40 and 4-1BB being described as Treg markers, we identified that they delineate distinct tumor immune profiles. This was true for sarcoma and other cancers. While only a limited number of samples could be analyzed, spatial analysis of OX40 expression identified two diverse phenotypes of OX40+ Tregs, one associated with and one independent of tertiary lymphoid structures (TLSs). Patient stratification is of intense interest for immunotherapies. We provide data supporting the viewpoint that a cohort of sarcoma patients, appropriately selected, are promising candidates for immunotherapies. Spatial profiling of OX40+ Tregs, in relation to TLSs, could be an additional metric to improve future patient stratification.

Harnessing radiotherapy-induced NK-cell activity by combining DNA damage-response inhibition and immune checkpoint blockade

BACKGROUND

Despite therapeutic gains from immune checkpoint inhibitors (ICI) in many tumor types, new strategies are needed to extend treatment benefits, especially in patients failing to mount effective antitumor T-cell responses. Radiation and drug therapies can profoundly affect the tumor immune microenvironment. Here, we aimed to identify immunotherapies to increase the antitumor response conferred by combined ataxia telangiectasia and Rad3-related kinase inhibition and radiotherapy.

METHODS

Using the human papillomavirus (HPV)-negative murine oral squamous cell carcinoma model, MOC2, we assessed the nature of the antitumor response following ataxia telangiectasia and Rad3-related inhibitor (ATRi)/radiotherapy (RT) by performing RNA sequencing and detailed flow cytometry analyses in tumors. The benefit of immunotherapies based on T cell immunoreceptor with Ig and ITIM domains (TIGIT) and Programmed cell death protein 1 (PD-1) immune checkpoint blockade following ATRi/RT treatment was assessed in the MOC2 model and confirmed in another HPV-negative murine oral squamous cell carcinoma model called SCC7. Finally, immune profiling was performed by flow cytometry on blood samples in patients with head and neck squamous cell carcinoma enrolled in the PATRIOT clinical trial of combined ATRi/RT.

RESULTS

ATRi enhances radiotherapy-induced inflammation in the tumor microenvironment, with natural killer (NK) cells playing a central role in maximizing treatment efficacy. We demonstrated that antitumor activity of NK cells can be further boosted with ICI targeting TIGIT and PD-1. Analyses of clinical samples from patients receiving ATRi (ceralasertib) confirm the translational potential of our preclinical studies.

CONCLUSION

This work delineates a previously unrecognized role for NK cells in the antitumor immune response to radiotherapy that can be augmented by small-molecule DNA damage-response inhibitors and immune checkpoint blockade.

Inflammatory microenvironment remodelling by tumour cells after radiotherapy

The development of immune checkpoint inhibitors (ICIs) is revolutionizing the way we think about cancer treatment. Even so, for most types of cancer, only a minority of patients currently benefit from ICI therapies. Intrinsic and acquired resistance to ICIs has focused research towards new combination therapy approaches that seek to increase response rates, the depth of remission and the durability of benefit. In this Review, we describe how radiotherapy, through its immunomodulating effects, represents a promising combination partner with ICIs. We describe how recent research on DNA damage response (DDR) inhibitors in combination with radiotherapy may be used to augment this approach. Radiotherapy can kill cancer cells while simultaneously triggering the release of pro-inflammatory mediators and increasing tumour-infiltrating immune cells - phenomena often described colloquially as turning immunologically 'cold' tumours 'hot'. Here, we focus on new developments illustrating the key role of tumour cell-autonomous signalling after radiotherapy. Radiotherapy-induced tumour cell micronuclei activate cytosolic nucleic acid sensor pathways, such as cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING), and propagation of the resulting inflammatory signals remodels the immune contexture of the tumour microenvironment. In parallel, radiation can impact immunosurveillance by modulating neoantigen expression. Finally, we highlight how tumour cell-autonomous mechanisms might be exploited by combining DDR inhibitors, ICIs and radiotherapy.

The PERK Inhibitor GSK2606414 Enhances Reovirus Infection in Head and Neck Squamous Cell Carcinoma via an ATF4-Dependent Mechanism

Reovirus type 3 Dearing (reovirus) is a tumor-selective oncolytic virus currently under evaluation in clinical trials. Here, we report that the therapeutic efficacy of reovirus in head and neck squamous cell cancer can be enhanced by targeting the unfolded protein response (UPR) kinase, protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK). PERK inhibition by GSK2606414 increased reovirus efficacy in both 2D and 3D models in vitro, while perturbing the normal host cell response to reovirus-induced endoplasmic reticulum (ER) stress. UPR reporter constructs were used for live-cell 3D spheroid imaging. Profiling of eIF2a-ATF4, IRE1a-XBP1, and ATF6 pathway activity revealed a context-dependent increase in eIF2a-ATF4 signaling due to GSK2606414. GSK2606414 blocked eIF2a-ATF4 signaling because of the canonical ER stress agent thapsigargin. In the context of reovirus infection, GSK2606414 induced eIF2a-ATF4 signaling. Knockdown of eIF2a kinases PERK, GCN2, and PKR revealed eIF2a-ATF4 reporter activity was dependent on either PERK or GCN2. Knockdown of ATF4 abrogated the GSK2606414-induced increase in reovirus protein levels, confirming eIF2a-ATF signaling as key to the observed phenotype. Our work identifies a novel approach to enhance the efficacy and replication of reovirus in a therapeutic setting.

Patritumab or placebo, with cetuximab plus platinum therapy in recurrent or metastatic squamous cell carcinoma of the head and neck: A randomised phase II study

BACKGROUND

The fully human monoclonal antibody patritumab blocks HER3 activation, a resistance mechanism to cetuximab, induced by heregulin (HRG). A phase Ib study in recurrent and/or metastatic (R/M) squamous cell carcinoma of the head and neck (SCCHN) demonstrated tolerability and tumour response of patritumab + cetuximab + platinum.

METHODS

This was a randomised, double-blind, phase II study of patritumab + cetuximab with platinum-based therapy for first-line treatment of R/M SCCHN (Clinicaltrials.gov identifier: NCT02633800). Patients aged ≥18 years received patritumab or placebo, both combined with cetuximab + cisplatin or carboplatin. Co-primary end-points were progression-free survival (PFS) in the intent-to-treat (ITT) and the high-expression HRG (HRG high) populations.

RESULTS

Eighty-seven patients (n = 43 in the patritumab group; n = 44 in placebo group) enrolled. A median (range) of 6.5 (1-24) patritumab cycles were completed. Median PFS was similar between the patritumab group and placebo group in the ITT population (5.6 versus 5.5 months; hazard ratio [HR] 0.99 [95% confidence interval [CI], 0.6-1.7]; P = 0.96) and HRG-high subgroup (n = 51; 5.6 versus 5.6 months; HR 0.93 [95% CI, 0.5-1.8]; P = 0.82). Median overall survival in the ITT population was also similar (10.0 versus 12.7 months; HR 1.3 [95% CI, 0.69-2.29]; P = 0.46). All patients experienced ≥1 treatment-emergent adverse event (TEAE). Grade ≥III TEAEs were more frequent in the patritumab than the placebo group (84.1% versus 60.5%). The most common grade ≥III patritumab-related TEAE in the patritumab group (20.5% overall) was rash (6.8%).

CONCLUSION

Patritumab + cetuximab + platinum was tolerable but not superior to cetuximab + platinum.

ATR Inhibition Potentiates the Radiation-induced Inflammatory Tumor Microenvironment

PURPOSE

ATR inhibitors (ATRi) are in early phase clinical trials and have been shown to sensitize to chemotherapy and radiotherapy preclinically. Limited data have been published about the effect of these drugs on the tumor microenvironment.Experimental Design: We used an immunocompetent mouse model of HPV-driven malignancies to investigate the ATR inhibitor AZD6738 in combination with fractionated radiation (RT). Gene expression analysis and flow cytometry were performed posttherapy.

RESULTS

Significant radiosensitization to RT by ATRi was observed alongside a marked increase in immune cell infiltration. We identified increased numbers of CD3+ and NK cells, but most of this infiltrate was composed of myeloid cells. ATRi plus radiation produced a gene expression signature matching a type I/II IFN response, with upregulation of genes playing a role in nucleic acid sensing. Increased MHC I levels were observed on tumor cells, with transcript-level data indicating increased antigen processing and presentation within the tumor. Significant modulation of cytokine gene expression (particularly CCL2, CCL5, and CXCL10) was found in vivo, with in vitro data indicating CCL3, CCL5, and CXCL10 are produced from tumor cells after ATRi + RT.

CONCLUSIONS

We show that DNA damage by ATRi and RT leads to an IFN response through activation of nucleic acid-sensing pathways. This triggers increased antigen presentation and innate immune cell infiltration. Further understanding of the effect of this combination on the immune response may allow modulation of these effects to maximize tumor control through antitumor immunity.

PD-1 Blockade Following Isolated Limb Perfusion with Vaccinia Virus Prevents Local and Distant Relapse of Soft-tissue Sarcoma

PURPOSE

The prevention and treatment of metastatic sarcoma are areas of significant unmet need. Immune checkpoint inhibitor monotherapy has shown little activity in sarcoma and there is great interest in identifying novel treatment combinations that may augment responses. In vitro and in vivo, we investigated the potential for an oncolytic vaccinia virus (GLV-1h68) delivered using isolated limb perfusion (ILP) to promote antitumor immune responses and augment response to PD-1 blockade in sarcoma.Experimental Design: In an established animal model of extremity sarcoma, we evaluated the potential of locoregional delivery of a vaccinia virus (GLV-1h68) alongside biochemotherapy (melphalan/TNFα) in ILP. Complementary in vitro assays for markers of immunogenic cell death were performed in sarcoma cell lines.

RESULTS

PD-1 monotherapy had minimal efficacy in vivo, mimicking the clinical scenario. Pretreatment with GLV-1h68 delivered by ILP (viral ILP) significantly improved responses. Furthermore, when performed prior to surgery and radiotherapy, viral ILP and PD-1 blockade prevented both local and distant relapse, curing a previously treatment-refractory model. Enhanced therapy was associated with marked modulation of the tumor microenvironment, with an increase in the number and penetrance of intratumoral CD8+ T cells and expansion and activation of dendritic cells. GLV-1h68 was capable of inducing markers of immunogenic cell death in human sarcoma cell lines.

CONCLUSIONS

Viral ILP augments the response to PD-1 blockade, transforming this locoregional therapy into a potentially effective systemic treatment for sarcoma and warrants translational evaluation.

Patritumab with Cetuximab plus Platinum-Containing Therapy in Recurrent or Metastatic Squamous Cell Carcinoma of the Head and Neck: An Open-Label, Phase Ib Study

PURPOSE

Patritumab plus cetuximab with platinum as first-line therapy for patients with recurrent and/or metastatic (R/M) squamous cell carcinoma of the head and neck (SCCHN) was evaluated for safety and to determine the recommended phase II combination dose.

PATIENTS AND METHODS

Patients aged ≥18 years with confirmed R/M SCCHN received intravenous patritumab (18 mg/kg loading dose; 9 mg/kg maintenance dose every 3 weeks) + cetuximab (400 mg/m² loading dose; 250 mg/m² maintenance dose weekly) + cisplatin (100 mg/m² every 3 weeks) or carboplatin (AUC of 5) for six cycles or until toxicity, disease progression, or withdrawal. Primary endpoints were dose-limiting toxicities [DLT; grade ≥3 (21-day observation period)] and treatment-emergent adverse events (TEAE). Pharmacokinetics, human antihuman antibodies (HAHA), tumor response, progression-free survival (PFS), and overall survival (OS) were assessed.

RESULTS

Fifteen patients completed a median (range) of 8.7 (2.0-20.7) patritumab cycles. No DLTs were reported. Serious adverse events were reported in 9 patients (patritumab-related n = 4). TEAEs (N = 15 patients) led to patritumab interruption in 7 patients. Patritumab-related dose reductions were reported in 1 patient. Patritumab (18 mg/kg) pharmacokinetics (N = 15) showed mean (SD) AUC_0-21d of 2,619 (560) μg/day/mL and maximum concentration of 499.9 (90.4) μg/mL. All patients were HAHA-negative at study end (single, transient low titer in 1 patient). Tumor response rate (complete plus partial response; N = 15) was 47%. Median (95% confidence interval) PFS and OS (N = 15) were 7.9 (3.7-9.7) and 13.5 (6.6-17.5) months, respectively.

CONCLUSIONS

Patritumab (18 mg/kg loading dose, 9 mg/kg maintenance dose) plus cetuximab/platinum was tolerable, active in SCCHN, and selected as the phase II dose regimen.

Combined ATR and DNA-PK Inhibition Radiosensitizes Tumor Cells Independently of Their p53 Status

Head and neck squamous cell carcinoma (HNSCC) is a significant cause of cancer deaths. Cisplatin-based chemoradiotherapy is a standard of care for locally advanced disease. ATR and DNA-PK inhibition (DNA-PKi) are actively being investigated in clinical trials with preclinical data supporting clinical translation as radiosensitizers. Here, we hypothesized that targeting both ATR and DNA-PK with small molecule inhibitors would increase radiosensitization of HNSCC cell lines. Radiosensitization was assessed by Bliss independence analysis of colony survival data. Strong cell cycle perturbing effects were observed with ATR inhibition reversing the G2/M arrest observed for radiation-DNA-PKi. Increased apoptosis in combination groups was measured by Sub-G1 DNA populations. DNA-PKi increased radiation-induced RAD51 and gamma-H2Ax foci, with the addition of ATR inhibition reducing levels of both. A sharp increase in nuclear fragmentation after aberrant mitotic transit appears to be the main driver of decreased survival due to irradiation and dual ATR/DNA-PKi. Dual inhibition of DNA-PK and ATR represents a novel approach in combination with radiation, with efficacy appearing to be independent of p53 status. Due to toxicity concerns, careful assessment is necessary in any future translation of single or dual radiosensitization approaches. Ongoing clinical trials into the ATR inhibitor AZD6738 plus radiation, and the phenotypically similar combination of AZD6738 and the PARP inhibitor olaparib, are likely to be key in ascertaining the toxicity profile of such combinations.

Abstract CT084: A Phase I dose-escalation study of ATR inhibitor monotherapy with AZD6738 in advanced solid tumors (PATRIOT Part A)

Many cancers have high levels of replication stress and a poorly functional G1/S DNA damage checkpoint. This may render them more susceptible than normal tissues to inhibition of ATR, an apical kinase in the DNA damage response and critical part of the response to DNA replication stress.

We report the early results of the monotherapy dose-escalation phase of the PATRIOT study of AZD6738, an orally active ATR inhibitor in patients (pts) with advanced solid tumors (NCT02223923), whose endpoints were MTD, safety, tolerability, pharmacokinetics (PK) and preliminary efficacy.

26 pts were enrolled between July 2014 and July 2016 in a 3+3 design. Pts received continuous BD dosing. PK analyses were performed.

Dose limiting toxicities (table 1) were thrombocytopenia (G3 with epistaxis, 1 participant; G4, 2 participants), pancytopenia (G4, 1 participant), increased amylase (G3, 1 participant).

Other treatment-related AEs (probably or definitely caused by AZD6738) affecting ≥2 participants were fatigue (9; 35% G1-4, 0% G3-4), anemia (7; 23% G1-4, 12% G3-4), nausea (4; 15% G1-4, 0% G3-4), thrombocytopenia (5; 19% G1-4, 15% G3-4), anorexia (3; 12% G1-4, 0% G3-4), dysgeusia (3; 12% G1-4, 0% G3-4), vomiting (2; 8% G1-4, 0% G3-4).

The MTD was 160 mg BD, given continuously.

Two RECIST partial responses were observed in pts with SCCHN and nasopharyngeal carcinoma, one confirmed.

Median duration taking AZD6738 was 97 days, range 30-279 days (evaluable patients only).

Two pts remain on treatment, three pts discontinued due to treatment-related toxicity.

Expansion cohorts have been initiated at 160mg BD, exploring a number of alternative treatment schedules designed to offset cumulative toxicity and test efficacy of AZD6738 monotherapy and the presence of high replication stress, DNA damage response deficiencies or ATM loss. Schedules include: AZD6738 given at 160mg BD for 21 of a 28 day cycle and 5 days on, 2 days off. A parallel study is investigating AZD6738 in combination with palliative radiotherapy.[Funded by CRUK CRUKD/14/007]

Dose Level (mg)Evaluable (total treated)Number DLTsG3-4 AEs203 (3)0elevation GGT (1, G3)403 (3)0nil806 (7)1Thrombocytopenia with epistaxis (1, G3)1606 (6)0Anaemia (1, G3)2406 (7)4Thrombocytopenia (2, G4), pancytopenia (1, G4), elevated amylase (1, G3), photosensitivity (1, G3), mucositis (1, G3), anemia (1, G3)Baseline DemographicsTumor TypesMedian (range) age59 (40-79)SCCHN6 (23%)Median (range) prior systemic therapy2 (1-4)Colorectal6 (23%)% Female31Nasopharyngeal2 (8%)Other12 (46%)

Citation Format: Magnus T. Dillon, Aude Espinasse, Sally Ellis, Kabir Mohammed, Lorna G. Grove, Lyndall McLellan, Simon A. Smith, Graham Ross, Sola Adeleke, Kin Woo, Eleni Josephides, James F. Spicer, Martin D. Forster, Kevin J. Harrington. A Phase I dose-escalation study of ATR inhibitor monotherapy with AZD6738 in advanced solid tumors (PATRIOT Part A) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT084. doi:10.1158/1538-7445.AM2017-CT084

Radiosensitization by the ATR Inhibitor AZD6738 through Generation of Acentric Micronuclei

AZD6738 is an orally active ATR inhibitor (ATRi) currently in phase I clinical trials. We found in vitro growth inhibitory activity of this ATRi in a panel of human cancer cell lines. We demonstrated radiosensitization by AZD6738 to single radiation fractions in multiple cancer cell lines independent of both p53 and BRCA2 status by the clonogenic assay. Radiosensitization by AZD6738 to clinically relevant doses of fractionated radiation was demonstrated in vitro using a 3D tumor spheroid model and, in vivo, AZD6738 radiosensitized by abrogating the radiation-induced G2 cell-cycle checkpoint and inhibiting homologous recombination. Mitosis with damaged DNA resulted in mitotic catastrophe as measured by micronucleus formation by live-cell fluorescent-ubiquitination cell-cycle imaging of cell-cycle progression and nuclear morphology. Induction of micronuclei was significantly more prominent for AZD6738 compared with inhibition of the downstream kinase CHK1 alone at isoeffective doses. Micronuclei were characterized as acentric chromosomal fragments, which displayed characteristics of increased DNA damage and cell-cycle dyssynchrony when compared with the primary nucleus. Mol Cancer Ther; 16(1); 25-34. ©2016 AACR.

Human Papillomavirus-Negative Pharyngeal Cancer

Human papillomavirus-negative head and neck squamous cell carcinoma (HNSCC) carries a poor prognosis, and despite optimal treatment with chemoradiotherapy to the limit of tolerance, many patients will relapse. A number of methods for intensifying treatment of HNSCC have been investigated, leading to the current standards of care. Novel agents targeting tumor cell and stromal signaling, DNA damage response, and immune system are now reaching clinical trials in combination with chemoradiotherapy. In this review, we discuss the evidence for the current treatment of locally advanced human papillomavirus-negative HNSCC, as well as investigational therapies, such as hypoxia modification, molecular targeting of epidermal growth factor receptor family, vascular endothelial growth factor receptor or DNA damage response proteins in combination with radiation therapy.

Selective targeting of the G2/M cell cycle checkpoint to improve the therapeutic index of radiotherapy

Despite tremendous advances in radiotherapy techniques, allowing dose escalation to tumour tissues and sparing of organs at risk, cure rates from radiotherapy or chemoradiotherapy remain suboptimal for most cancers. In tandem with our growing understanding of tumour biology, we are beginning to appreciate that targeting the molecular response to radiation-induced DNA damage holds great promise for selective tumour radiosensitisation. In particular, approaches that inhibit cell cycle checkpoint controls offer a means of exploiting molecular differences between tumour and normal cells, thereby inducing so-called cancer-specific synthetic lethality. In this overview, we discuss cellular responses to radiation-induced damage and discuss the potential of using G2/M cell cycle checkpoint inhibitors as a means of enhancing tumour control rates.

Mouse model for thoracic congenital scoliosis

SUMMARY

This study sought to produce a dose-response curve for acute and chronic maternal carbon monoxide (CO) exposure versus vertebral anomalies in mouse offspring and to determine the critical day of exposure. In Part I, pregnant CD-1 mice were exposed to an acute dose of CO at 9 days of gestation. A positive dose-response relationship of acute maternal CO exposure and vertebral anomalies in the offspring was produced. In Part II, pregnant females were exposed to chronic CO for the first 11 days of gestation. Chronic exposure to CO did not produce significant vertebral anomalies. In Part III, pregnant females were exposed to an acute dose of 600 ppm of CO at gestation day 8, 9, or 10. Day 9 in this mouse breed is the critical day for maternal exposure to CO. The detected anomalies were predominately in the thoracic spine.