DNMT1 mutant ants develop normally but have disrupted oogenesis

Although DNA methylation is an important gene regulatory mechanism in mammals, its function in arthropods remains poorly understood. Studies in eusocial insects have argued for its role in caste development by regulating gene expression and splicing. However, such findings are not always consistent across studies, and have therefore remained controversial. Here we use CRISPR/Cas9 to mutate the maintenance DNA methyltransferase DNMT1 in the clonal raider ant, Ooceraea biroi. Mutants have greatly reduced DNA methylation, but no obvious developmental phenotypes, demonstrating that, unlike mammals, ants can undergo normal development without DNMT1 or DNA methylation. Additionally, we find no evidence of DNA methylation regulating caste development. However, mutants are sterile, whereas in wild-type ants, DNMT1 is localized to the ovaries and maternally provisioned into nascent oocytes. This supports the idea that DNMT1 plays a crucial but unknown role in the insect germline.

Effect of CCR2 Knockout on Tendon Biomechanical Properties in a Mouse Model of Delayed Rotator Cuff Repair

BACKGROUND

The high incidence of incomplete or failed healing after rotator cuff repair (RCR) has led to an increased focus on the biologic factors that affect tendon-to-bone healing. Inflammation plays a critical role in the initial tendon-healing response. C-C chemokine receptor type 2 (CCR2) is a chemokine receptor linked to the recruitment of monocytes in early inflammatory stages and is associated with an increase in pro-inflammatory macrophages. The purpose of this study was to evaluate the role of CCR2 in tendon healing following RCR in C57BL/6J wildtype (WT) and CCR2-/- knockout (CCR2KO) mice in a delayed RCR model.

METHODS

Fifty-two 12-week-old, male mice were allocated to 2 groups (WT and CCR2KO). All mice underwent unilateral supraspinatus tendon (SST) detachment at the initial surgical procedure, followed by a delayed repair 2 weeks later. The primary outcome measure was biomechanical testing. Secondary measures included histology, gene expression analysis, flow cytometry, and gait analysis.

RESULTS

The mean load-to-failure was 1.64 ± 0.41 N in the WT group and 2.50 ± 0.42 N in the CCR2KO group (p = 0.030). The mean stiffness was 1.43 ± 0.66 N/mm in the WT group and 3.00 ± 0.95 N/mm in the CCR2KO group (p = 0.008). Transcriptional profiling demonstrated 7 differentially expressed genes (DEGs) when comparing the CCR2KO and WT groups (p < 0.05) and significant differences in Type-I and Type-II interferon pathway scores (p < 0.01). Flow cytometry demonstrated significant differences between groups for the percentage of macrophages present (8.1% for the WT group compared with 5.8% for the CCR2KO group; p = 0.035). Gait analysis demonstrated no significant differences between groups.

CONCLUSIONS

CCR2KO may potentially improve tendon biomechanical properties by decreasing macrophage infiltration and/or by suppressing inflammatory mediator pathways in the setting of delayed RCR.

CLINICAL RELEVANCE

CCR2 may be a promising target for novel therapeutics that aim to decrease failure rates following RCR.

Poster 130: Tendon-to-bone Healing in a CCR2 Knockout Mouse Model of Delayed Rotator Cuff Repair

Objectives:

Rotator cuff tears are one of the most prevalent musculoskeletal injuries with over 250,000 rotator cuff repairs performed annually in the Unites States. While surgical techniques have advanced, incomplete/failed healing after rotator cuff repair is still relatively common with rates ranging from 11-95%. Extrinsic factors such as excessive early activity and patient comorbidities such as smoking and diabetes have been previously identified as factors which may contribute to decreased rates of rotator cuff repair healing. However, there has been a recent focus on the intrinsic biologic factors which affect repair healing at the tendon-bone interface. CCR2 is a chemokine receptor that has been linked to the recruitment of monocytes into wound sites in early inflammatory stages and is associated with an increase in “pro-inflammatory” macrophages. The purpose of this study was to evaluate the role of CCR2 on rotator cuff tendon healing by evaluating relative gene expression and biomechanics following rotator cuff repair in wildtype (WT) and CCR2-/- knockout (KO) mice in a chronic rotator cuff injury model. We hypothesized that CCR2 KO would lead to decreased inflammatory cell recruitment and increased biomechanical properties after rotator cuff repair compared to WT mice.

Methods:

All procedures were approved by our Institutional Animal Care and Use Committee (Protocol# 2019-0021). A total of 28 12-week-old male mice were utilized for this study and divided into 2 groups (wildtype C57BL/6J and CCR2 KO). All mice underwent unilateral supraspinatus tendon detachment at the initial surgery, followed by delayed supraspinatus repair 2 weeks following the initial procedure. They were sacrificed at the 4-week time point following the second procedure (Fig 1). The primary outcome measures included biomechanical testing and gene expression analysis. Biomechanical testing was performed on the repaired rotator cuff tendons on a custom-designed materials testing system. Contralateral intact tendons were also tested as controls. Specimens were prepared and loaded to failure at a rate of 1mm/min. Load-to-failure data were recorded and stiffness was calculated from the load-deformation curves. Following total RNA isolation from both the control and repaired tendons (50ng) and muscles (100ng), gene expression was measured using the NanoString nCounter® Fibrosis Panel. Genes were assessed based on fold change and significance level, determined by adjusted p-values using the Benjamini-Yekutieli procedure. The significance level was set at p=0.05 for all statistical analyses.

Results:

All repaired tendons remained intact at the time of sacrifice 4 weeks following repair. The CCR2 KO group had thicker, more robust tendons on gross inspection than the WT controls. Biomechanical analysis demonstrated a significantly increased load-to-failure and stiffness of the supraspinatus tendon repair in the CCR2 KO group compared to the WT group. Mean load-to-failure in the WT group was 1.64 N ± 0.41 N versus 2.50 N ± 0.42 N in the CCR2 KO group (p<0.001) (Fig 2A). Mean stiffness in the WT group was 1.43 ± 0.66 N/mm versus 3.00 ± 0.95 N/mm in the CCR2 KO group (p=0.001) (Fig 2B). There were significant differences in both load-to-failure and stiffness between the repaired tendons and the intact contralateral tendons in both the WT and CCR2 KO groups (p<0.001). There were no significant differences in load-to-failure or stiffness between the WT and CCR2 KO controls. The site of failure was in the tendon midsubstance for all of the rotator cuff repair samples in both groups. NanoString analysis comparing WT repaired tendons with WT controls revealed 42 differentially expressed genes (see Fig 3 for relative pathway scores). There was significantly increased expression of Ccr2 in the WT repair group compared to the WT control group (log2 fold ratio: 3.28, 95% CI 2.63 to 3.94, p=0.003). NanoString analysis of the repaired tendon samples confirmed lower expression of Ccr2 in the repaired tendons of the CCR2 KO mice compared to WT tendons. There were no significant differences in expression ratios of the supraspinatus muscle samples between the CCR2 KO repair group and the WT repair group. There were also no significant differences in gene expression between the CCR2 KO repair group and the CCR2 KO control group muscles.

Conclusions:

In this study, we utilized a delayed rotator cuff repair model, which is more clinically relevant than previously established models of acute tendon transection and repair. Utilizing CCR2 KO mice, we found that there were significant differences in biomechanical properties – both load-to-failure and stiffness – between the WT mice and the CCR2 KO mice. Given the role of CCR2 in recruitment and accumulation of pro-inflammatory macrophages, these data suggest that excessive or unresolved inflammation may hinder tendon healing. Our results suggest that CCR2 KO leads to improved biomechanical properties in a mouse model of delayed rotator cuff repair. Additional studies are necessary to further elucidate the role of CCR2 in inflammation in the setting of chronic rotator cuff disease; however, CCR2 may be a promising target for novel therapeutics which aim to improve tendon healing and decrease re-tear rates following rotator cuff repair.

Evaluation of the safety of tranexamic acid use in pediatric patients undergoing spinal fusion surgery: a retrospective comparative cohort study

Background

Pediatric spinal fusion may be associated with significant intraoperative blood loss, leading to complications from transfusion, hypoperfusion and coagulopathy. One emerging strategy to mediate these risks is by utilization of the anti-fibrinolytic agent tranexamic acid (TXA). However, concerns regarding potential adverse reactions, specifically postoperative seizures and thrombotic events, still exist. To assess these risks, we examined the perioperative morbidity of TXA use in a large national database.

Methods

Retrospective data from pediatric patients (age 18 years or younger), discharged between January 2013 to December 2015, who underwent primary or revision posterior spinal fusions, was collected from the Premier Perspective database (Premier, Charlotte, NC). Patients were stratified by TXA use and records were assessed for complications of new onset seizures, strokes, pulmonary embolisms (PE) or deep vein thromboses (DVT) occurring during the perioperative period.

Results

In this cohort of 2,633 pediatric patients undergoing posterior spinal fusions, most often to treat adolescent idiopathic scoliosis, 15% received TXA. Overall, adverse events were rare in this patient population. The incidence of seizure, stoke, PE, or DVT in the control group was 0.54% (95% CI, 0.31% to 0.94%) and not significantly different from the TXA group. There was no significant difference in the incidence of DVTs, and no incidences of stroke in either group. There were no new-onset seizures or PEs in patients who received TXA.

Conclusions

The use of TXA was not associated with an increased risk of adverse events including seizure, stroke, PE, and DVT. Our findings support the safety of TXA use in pediatric patients undergoing spinal fusion surgery.

Utility of Multimodality Molecular Profiling for Pediatric Patients with Central Nervous System Tumors

Background

As our molecular understanding of pediatric central nervous system (CNS) tumors evolves, so too do diagnostic criteria, prognostic biomarkers, and clinical management decision-making algorithms. Here, we explore the clinical utility of wide-breadth assays including whole-exome sequencing (WES), RNA sequencing (RNAseq), and methylation array profiling as an addition to more conventional diagnostic tools for pediatric CNS tumors.

Methods

This study comprises an observational, prospective cohort followed at a single academic medical center over three years. Paired tumor and normal control specimens from 53 enrolled pediatric patients with CNS tumors underwent WES. A subset of cases also underwent RNAseq (n=28) and/or methylation array analysis (n=27).

Results

RNAseq identified driver and/or targetable fusions in 7/28 cases, including potentially targetable NTRK fusions, and uncovered possible rationalized treatment options based on outlier gene expression in 23/28 cases. Methylation profiling added diagnostic confidence (8/27 cases) or diagnostic subclassification endorsed by the WHO (10/27 cases). WES detected clinically pertinent Tier 1 or Tier 2 variants in 36/53 patients. Of these, 16/17 SNVs/indels and 10/19 copy number alterations would have been detected by current in-house conventional tests including targeted sequencing panels.

Conclusions

Over a heterogeneous set of pediatric tumors, RNAseq and methylation profiling frequently yielded clinically relevant information orthogonal to conventional methods while WES demonstrated clinically-relevant added-value primarily via copy number assessment. Longitudinal cohorts comparing targeted molecular pathology workup versus broader genomic approaches including therapeutic selection based on RNA-expression data will be necessary to further evaluate the clinical benefits of these modalities in practice.

SURG-24. REPEAT CONVECTION-ENHANCED DELIVERY FOR DIFFUSE INTRINSIC PONTINE GLIOMA

INTRODUCTION

While the safety and efficacy of convection-enhanced delivery (CED) have been studied in patients receiving single dose drug infusions, agents for oncologic therapy require repeated or chronic infusions to maintain therapeutic concentrations. Repeat/chronic CED infusions have rarely been described for oncologic purposes. We report on the safety and experience in a group of pediatric patients who received sequential CED into the brainstem for the treatment of diffuse intrinsic pontine glioma (DIPG).

METHODS

Patients were enrolled in a phase I single center clinical trial using 124I-8H9 monoclonal antibody (124I-Omburtamab, Y-mAbs Therapeutics) administered by CED (NCT01502917). Retrospective chart review was used to assess demographic data, CED infusion data, and post-operative neurologic and surgical outcomes. MRI scans were analyzed using iPlan® Flow software (Brainlab AG, Munich, Germany) for volumetric measurements. Target and catheter coordinates as well as radial, depth, and absolute error in MRI space were calculated with the Clearpoint imaging software (Clearpoint®, MRI Interventions Inc. Irvine, USA).

RESULTS

Seven patients underwent two or more sequential CED infusions. No patients experienced deficits Clinical Terminology Criteria for Adverse Events (CTCAE) grade 3 or greater. One patient had persistent grade 2 cranial nerve deficit after a second infusion. No patients experienced hemorrhage or stroke post-operatively. There was a statistically significant decrease in radial error (p= 0.005) and absolute tip error (p=0.008) for infusion two compared to the initial infusion. Sequential infusions did not result in significantly different distribution capacity between the first and second infusion (Vd:Vi ratio: 2.66 ± 0.35 versus 2.42 ± 0.75; p=0.45).

CONCLUSIONS

This series demonstrates the ability to safely perform sequential CED infusions into the pediatric brainstem. Past treatments did not negatively influence the procedural work flow, technical application of the targeting interface, or distribution capacity. This limited experience provides a foundation for using repeat CED for oncologic purposes.

Repeat convection-enhanced delivery for diffuse intrinsic pontine glioma

OBJECTIVE

While the safety and efficacy of convection-enhanced delivery (CED) have been studied in patients receiving single-dose drug infusions, agents for oncological therapy may require repeated or chronic infusions to maintain therapeutic drug concentrations. Repeat and chronic CED infusions have rarely been described for oncological purposes. Currently available CED devices are not approved for extended indwelling use, and the only potential at this time is for sequential treatments through multiple procedures. The authors report on the safety and experience in a group of pediatric patients who received sequential CED into the brainstem for the treatment of diffuse intrinsic pontine glioma.

METHODS

Patients in this study were enrolled in a phase I single-center clinical trial using 124I-8H9 monoclonal antibody (124I-omburtamab) administered by CED (clinicaltrials.gov identifier NCT01502917). A retrospective chart and imaging review were used to assess demographic data, CED infusion data, and postoperative neurological and surgical outcomes. MRI scans were analyzed using iPlan Flow software for volumetric measurements. Target and catheter coordinates as well as radial, depth, and absolute error in MRI space were calculated with the ClearPoint imaging software.

RESULTS

Seven patients underwent 2 or more sequential CED infusions. No patients experienced Clinical Terminology Criteria for Adverse Events grade 3 or greater deficits. One patient had a persistent grade 2 cranial nerve deficit after a second infusion. No patient experienced hemorrhage or stroke postoperatively. There was a statistically significant decrease in radial error (p = 0.005) and absolute tip error (p = 0.008) for the second infusion compared with the initial infusion. Sequential infusions did not result in significantly different distribution capacities between the first and second infusions (volume of distribution determined by the PET signal/volume of infusion ratio [mean ± SD]: 2.66 ± 0.35 vs 2.42 ± 0.75; p = 0.45).

CONCLUSIONS

This series demonstrates the ability to safely perform sequential CED infusions into the pediatric brainstem. Past treatments did not negatively influence the procedural workflow, technical application of the targeting interface, or distribution capacity. This limited experience provides a foundation for using repeat CED for oncological purposes.

Influence of an intratumoral cyst on drug distribution by convection-enhanced delivery: case report

Convection-enhanced delivery (CED) uses positive pressure to induce convective flow of molecules and maximize drug distribution. Concerns have been raised about the effect of cystic structures on uniform drug distribution with CED. The authors describe the case of a patient with a diffuse intrinsic pontine glioma (DIPG) with a large cyst and examine its effect on drug distribution after CED with a radiolabeled antibody. The patient was treated according to protocol with CED of ¹²⁴I-8H9 to the pons for nonprogressive DIPG after radiation therapy as part of a Phase I trial (clinical trial registration no. NCT01502917, clinicaltrials.gov). Care was taken to avoid the cystic cavity in the planned catheter track and target point. Co-infusion with Gd-DTPA was performed to assess drug distribution. Infusate distribution was examined by MRI immediately following infusion and analyzed using iPlan Flow software. Analysis of postinfusion MR images demonstrated convective distribution around the catheter tip and an elongated configuration of drug distribution, consistent with the superoinferior corticospinal fiber orientation in the brainstem. This indicates that the catheter was functioning and a pressure gradient was established. No infusate entry into the cystic region could be identified on T2-weighted FLAIR or T1-weighted images. The effects of ependymal and pial surfaces on drug delivery using CED in brainstem tumors remain controversial. Drug distribution is a critical component of effective application of CED to neurosurgical lesions. This case suggests that cyst cavities may not always behave as fluid "sinks" for drug distribution. The authors observed that infusate was not lost into the cyst cavity, suggesting that lesions with cystic components can be treated by CED without significant alterations to target and infusion planning.