PPM1D mutations are oncogenic drivers of de novo diffuse midline glioma formation

The role of PPM1D mutations in de novo gliomagenesis has not been systematically explored. Here we analyze whole genome sequences of 170 pediatric high-grade gliomas and find that truncating mutations in PPM1D that increase the stability of its phosphatase are clonal driver events in 11% of Diffuse Midline Gliomas (DMGs) and are enriched in primary pontine tumors. Through the development of DMG mouse models, we show that PPM1D mutations potentiate gliomagenesis and that PPM1D phosphatase activity is required for in vivo oncogenesis. Finally, we apply integrative phosphoproteomic and functional genomics assays and find that oncogenic effects of PPM1D truncation converge on regulators of cell cycle, DNA damage response, and p53 pathways, revealing therapeutic vulnerabilities including MDM2 inhibition.

Toward pharmacogenetic SLCO1B1-guided dosing of methotrexate in arthritis using a murine Slco1b2 knockout model

Low‐dose methotrexate (MTX) is a first‐line therapy for the treatment of arthritis. However, there is considerable interindividual variability in MTX exposure following standard dosing. Polymorphisms in SLCO1B1 significantly effect MTX clearance, altering therapeutic response. One decreased function variant, rs4149056 (c.521T>C, Val174Ala), slows MTX clearance and in vitro uptake of MTX. This phenotype was recapitulated in a mouse model using a knockout (KO) of the murine orthologue, Slco1b2. Our objective was to investigate the impact of this phenotype on the pharmacokinetics and therapeutic outcomes of low‐dose MTX in a murine model of collagen‐induced arthritis (CIA). We evaluated response to MTX in mice with CIA using wildtype (WT), heterozygous, and KO Slco1b2 mice on a DBA1/J background. Arthritis was macroscopically evaluated daily to quantify disease progression. Mice received 2 mg/kg or a pharmacogenetically guided MTX dose subcutaneously 3 times a week for 2 weeks. MTX concentrations were collected at the end of the study and exposure (day*µM) was estimated using a two‐compartment model. Mice displayed a seven‐fold range in MTX exposure and revealed a significant exposure‐response relationship (p = 0.0027). KO mice receiving the 2 mg/kg dosing regimen had 2.3‐fold greater exposure to MTX (p < 0.0001) and a 66% reduction in overall disease progression (p = 0.011) compared to WT mice. However, exposure and response were equivalent when pharmacogenetically guided dosing was used. These studies demonstrate that an exposure‐response relationship exists for MTX and that Slco1b2 genotype affects MTX exposure and therapeutic response. Such evidence supports the use of SLCO1B1‐pharmacogenetic dosing of low‐dose MTX for patients with arthritis.

Generation of diffuse intrinsic pontine glioma mouse models by brainstem-targeted in utero electroporation

BACKGROUND

Diffuse intrinsic pontine gliomas (DIPGs) are highly lethal childhood brain tumors. Their unique genetic makeup, pathological heterogeneity, and brainstem location all present challenges to treatment. Developing mouse models that accurately reflect each of these distinct features will be critical to advance our understanding of DIPG development, progression, and therapeutic resistance. The aims of this study were to generate new mouse models of DIPG and characterize the role of specific oncogenic combinations in DIPG pathogenesis.

METHODS

We used in utero electroporation (IUE) to transfect neural stem cells in the developing brainstem with PiggyBac DNA transposon plasmids. Combinations of platelet-derived growth factor B (PDGFB), PdgfraD842V, or PdgfraWT, combined with dominant negative Trp53 (DNp53) and H3.3K27M expression, induced fully penetrant brainstem gliomas.

RESULTS

IUE enabled the targeted transfection of brainstem neural stem cells. PDGFB + DNp53 + H3.3K27M induced the rapid development of grade IV gliomas. PdgfraD842V + DNp53 + H3.3K27M produced slower forming grade III gliomas. PdgfraWT + DNp53 + H3.3K27M produced high- and low-grade gliomas with extended latencies. PDGFB, PdgfraD842V, and PdgfraWT DIPG models display unique histopathological and molecular features found in human DIPGs. H3.3K27M induced both overlapping and unique gene expression changes in PDGFB and PdgfraD842V tumors. Paracrine effects of PDGFB promote disruption of pericyte-endothelial interactions and angiogenesis in PDGFB DIPG mouse models.

CONCLUSION

Brainstem-targeted IUE provides a rapid and flexible system to generate diverse DIPG mouse models. Using IUE to investigate mutation and pathohistological heterogeneity of DIPG will provide a valuable tool for future genetic and preclinical studies.

MODL-29. EVALUATING TUMOR-IMMUNE INTERACTIONS IN MOUSE MODELS OF DIFFUSE INTRINSIC PONTINE GLIOMA

BACKGROUND

While adult gliomas show some level of immune cell infiltration, diffuse intrinsic pontine glioma (DIPG) is characterized as having an “immune cold” state. We have developed new immunocompetent mouse models of DIPG. These models faithfully recapitulate the pathological hallmarks of DIPG and provides a unique platform to investigate immune modulatory therapies and potential therapeutic benefits of check point inhibitor combination therapies.

METHODS

To evaluate the effects of CDK4/6 inhibition (CDK4/6i) on cell proliferation and immune interactions we performed a series of in vitro and in vivo studies using DIPG mouse models. In vitro assays included dose response curves, transcriptional profiling, and MHC1 expression. In vivo preclinical studies treated mouse models with CDK4/6i with or without immune check-point inhibitors (ICI). We also examined other candidate immune modulatory therapies in vitro.

RESULTS

CDK4/6i (Abemeciclib) reduced proliferation of DIPG cells derived from mouse models, and displayed a modest increase in immune activation by MHC1 expression and transcriptome. Pilot in vivo preclinical studies did not show any significant changes in DIPG proliferation or immune changes with CDK4/6i treatment, ICI treatment, or the combination of CDK4/6i + ICI. In vitro testing of other immune-modulatory drugs identified additional candidates that can be tested in vivo.

CONCLUSION

CDK4/6i displayed in vitro action, but lacked efficacy in DIPG mouse models in vivo. Further use of spontaneous DIPG mouse models will provide a rapid preclinical platform to evaluate in vivo tumor-immune interactions, drug efficacy, and mechanisms of resistance.

DIPG-53. CHARACTERIZING THE ROLE OF PPM1D MUTATIONS IN THE PATHOGENESIS OF DIFFUSE INTRINSIC PONTINE GLIOMAS (DIPGS)

INTRODUCTION

We have previously found that up to 15% of all DIPGs harbor mutations in PPM1D, resulting in the expression of an activated and truncated PPM1D (PPM1Dtr). Here we evaluate the mechanisms through which PPM1Dtr enhances glioma formation and identify its associated therapeutic vulnerabilities.

METHODS

We have developed multiple in vitro and in vivo models of PPM1D-mutant DIPGs and applied quantitative proteomic and functional genomic approaches to identify pathways altered by PPM1Dtr and associated dependencies.

RESULTS

PPM1D mutations are clonal events that are anti-correlated to TP53 mutations. We find ectopic expression of PPM1Dtr to be sufficient to enhance glioma formation and to be necessary in PPM1D-mutant DIPG cells. In addition, endogenous truncation of PPM1D is sufficient to enhance glioma formation in the presence of mutant H3F3A and PDGFRA. PPM1Dtr overexpression attenuates g-H2AX formation and suppresses apoptosis and cell-cycle arrest in response to radiation treatment. Deep scale phosphoproteomics analyses reveal DNA-damage and cell cycle pathways to be most significantly associated with PPM1Dtr. Furthermore, preliminary analysis of genome-wide loss-of-function CRISPR/Cas9 screens in isogenic GFP and PPM1Dtr overexpressing mouse neural stem cells reveal differential dependency on DNA-damage response genes in the PPM1Dtr overexpressing cells. Consistent with PPM1D’s role in stabilizing MDM2, PPM1D-mutant DIPG models are sensitive to a panel of MDM2 inhibitors (Nutlin-3a, RG7388, and AMG232).

CONCLUSION

Our study shows that PPM1Dtr is both an oncogene and a dependency in PPM1D- mutant DIPG, and there are novel therapeutic vulnerabilities associated with PPM1D that may be exploited.

DIPG-22. DISSECTING THE ONCOGENIC ROLE OF FOXR2 IN DIFFUSE INTRINSIC PONTINE GLIOMA

BACKGROUND

Diffuse intrinsic pontine gliomas (DIPGs) pose particular challenges for treatment. We recently completed a genomic analysis of close to 200 DIPGs and high-grade gliomas. We identified that nearly 10% of all DIPGs have increased expression of the fork head domain transcription factor FOXR2. We hypothesize that FOXR2 accelerates gliomagenesis in histone mutant DIPGs and represents a previously unexplored therapeutic target.

METHODS

To determine whether FOXR2 is sufficient to mediate gliomagenesis, we applied an integrative genomics approach using both in vitro and in vivo DIPG models: mouse neural stem cell models expressing FOXR2, in vivo mouse models using in utero brainstem electroporation, patient-derived DIPG cell lines, and RNA sequencing analysis of human and mouse tumors expressing FOXR2.

RESULTS

Our data shows that FOXR2 indeed is an oncogene that rapidly accelerates gliomagenesis using an in vivo brainstem in utero electroporation model of DIPG. In human tumors, increased FOXR2 expression is mutually exclusive with MYC amplification suggesting functional redundancy. In vivo, FOXR2 results in large brainstem gliomas and rapid neurologic decline of animals. Transcriptional profiling of these tumors demonstrates activation of MYC signaling pathways. In vitro, we have further identified patient-derived cell lines with increased expression of FOXR2.

CONCLUSION

FOXR2 is sufficient to enhance gliomagenesis and represents a previously understudied therapeutic target for patients with the devastating disease DIPG.

Morbidity and mortality meetings at Australian major trauma centres: A proof of concept study

Background

Morbidity and mortality meetings are held at all Australian major trauma centres and provide a forum to identify problems and improve practices. Meetings should focus on addressing factors in the system to prevent similar errors occurring, rather than individual culpability. This paper describes current meeting practices and assesses the use of a systems approach.

Methods

This proof of concept study used a convenience sample of four Australian major trauma centres. Trauma leaders at each centre were surveyed regarding morbidity and mortality meeting practices. The use of a systems approach was measured by assessing practices against the London Protocol for Systems Analysis of Clinical Incidents. Meeting participants were also surveyed regarding perceptions of the objectives and effectiveness of meetings.

Results

This study found variable utilisation of a systems approach. Cases are not routinely analysed for contributing system factors and effective processes are not always used to correct problems that are identified. Meeting practices also vary between centres in terms of frequency, case selection criteria and use of audit filters. Participants generally view quality improvement as the most important objective of meetings.

Conclusion

Morbidity and mortality meeting practices vary between Australian major trauma centres and a systems approach has not been fully adopted.

Predictive Factors for Positive Non-Sentinel Nodes Following a Positive Sentinel Node Biopsy: NSABP B-32

Background: Following a positive sentinel node biopsy (SNB), current guidelines recommend an axillary dissection (AD) regardless of SN metastatic tumor size. In the majority of clinically node negative patients the risk for positive non-sentinel axillary nodes (NSN) is low. Predictive factors for positive NSNs following a positive SNB are analyzed in NSABP B-32 with inclusion of SN metastatic tumor size.Materials and Methods: After stratification, women with operable invasive breast cancer and clinically negative nodes were randomized to Sentinel Node Resection (SNR) with immediate conventional Axillary Dissection (AD) [Group 1] or to SNR without AD [Group 2]. Group 2 patients with positive SNs underwent AD. A multivariate analysis of SN positive patients from both groups for whom both a SNR and an AD had been performed was used to assess the need for AD following SNB. Nodes were classified as either SNs or NSNs, defined as all axillary dissection nodes plus any intramammary or other nodes that were not resected as SNs.Results: Between May 1999 and February 2004, 5,611 patients were entered into NSABP Protocol B-32. There were a total of 1,361 SN positive patients with AD from both groups. Data from 1,166 patients were available for multivariate analysis which included SN metastatic tumor size in 735 patients: 424 patients with macrometastaes (&gt;2 mm) and 311 with micrometastases (&lt;2 mm). In 626 patients SN metastatic size was unknown.In patients with positive SNB, results from the final multivariate model based on 653 patients with known covariate values indicated clinical tumor size was a significant predictor for positive NSN (p=0.044, OR: 1.17). Lymphovascular invasion was a significant predictor for positive NSN (p=0.0004, OR: 1.85). SN metastatic tumor size (Macro vs Micro) was a highly significant predictor for positive NSN (p&lt;0.0001, OR: 3.42). Age at study entry, treatment type, proposed type of surgery, HER-2 status, and location of tumor were not significant multivariate predictors for positive NSN. Predictive modeling for positive NSN probability will be presented.Conclusion: Completion AD following a positive SNB, although helpful in prognosis and treatment planning, may not be required in patients with small tumors, absence of lymphovascular invasion, and micrometastases.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 301.

Variation in the use of breast-conserving therapy for Medicare beneficiaries in Virginia: clinical, geographic, and hospital characteristics

BACKGROUND

Treatment for early-stage breast cancer has evolved significantly in recent years. Breast-conserving therapy (BCT) has been shown to offer equivalent survival compared to traditional mastectomy. However, there is marked variation in the performance of BCT which may not reflect clinical appropriateness or patient preference. Little is known about the factors related to variation in BCT performance in older women with early-stage breast cancer.

METHODS

Retrospective claims analysis of 1,512 Medicare patients using part-A data for the years 1992 to 1993, with additional explicit chart review. A clinical algorithm was developed to categorize patients according to their candidacy for BCT and compare this to their treatment. Demographic, clinical, and geographic variables were included in the model.

RESULTS

The overall BCT rate in Virginia was 20%, with marked variation among providers of all types. BCT rates ranged from 0% to 44% among hospitals caring for more than 12 cases per year. Twenty-six percent of patients considered good candidates for BCT by current guidelines received this option. Large urban hospitals had significantly higher rates of BCT than smaller hospitals, regardless of the presence of radiation oncology capability. Distance from radiation oncology facilities was a factor in low BCT rates of rural populations, but low BCT rates also were present even in facilities with access to radiation oncology services.

CONCLUSIONS

These data present a detailed analysis of the patterns of BCT for Virginia Medicare beneficiaries with early-stage breast cancer. Clinical contraindications to BCT for confirmed early-stage disease were uncommon. Despite similar patient profiles and hospital-reported range of cancer services, marked variation in BCT rates exists. A large number of patients chose traditional mastectomy over BCT due to fears of radiation, but few received radiation oncology consultation. BCT rates were highest in hospitals with radiation oncology facilities on grounds; hospitals with facilities nearby had rates similar to those without access to radiation facilities. Patient preferences are documented poorly. This study provides further evidence that many women are receiving BCT in patterns that may not reflect clinical appropriateness for BCT nor access to necessary facilities.

Colorectal cancer in young adults

This retrospective study reviews our experience of the management of colorectal cancer in 481 consecutive patients. Details of presentation, surgery, Dukes staging, histological grading, recurrence and survival were analysed. We have compared patients 50 years of age and over with their younger counterparts. Thirty-six (7.5%) were less than 50 years of age. Half of the older group presented to hospital within 3 months of the onset of symptoms. Only 17.5% of the younger group presented so promptly (p less than 0.01). There was a higher proportion of younger patients with metastatic disease at the time of presentation. While there was no evidence to suggest a more aggressive surgical approach in the younger patients, 27.8% had adjuvant therapy compared with only 14.2% of the over 50s (p less than 0.05). The median survival was significantly better in the younger group (p less than 0.02).