Adam Burr

Adam Burr, MD, PhD

Assistant Professor (CHS)

Department of Human Oncology


Resident, University of Wisconsin–Madison, Radiation Oncology (2020)

Intern, University of Wisconsin–Madison, (2016)

MD, PhD, University of Cincinnati, (2015)

BS, University of Minnesota, Biomedical Engineering (2007)

Academic Appointments

Assistant Professor (CHS), Human Oncology (2020)

Selected Honors and Awards

Elected to AOA (2014)

FASEB First Place Poster Prize at New Directions in Skeletal Muscle Biology (2011)

Excellence in Physiology Award (2008)

IT Merit Scholarship, University of Minnesota (2006–2007)

  • Pulsed reduced-dose rate re-irradiation for patients with recurrent grade 2 gliomas Neuro-oncology advances
    Harari CM, Burr AR, Morris BA, Tomé WA, Bayliss A, Bhatia A, Grogan PT, Robins HI, Howard SP
    2024 May 10;6(1):vdae073. doi: 10.1093/noajnl/vdae073. eCollection 2024 Jan-Dec.
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      BACKGROUND: Patients with grade 2 glioma exhibit highly variable survival. Re-irradiation for recurrent disease has limited mature clinical data. We report treatment results of pulsed reduced-dose rate (PRDR) radiation for patients with recurrent grade 2 glioma.

      METHODS: A retrospective analysis of 58 patients treated with PRDR from 2000 to 2021 was performed. Radiation was delivered in 0.2 Gy pulses every 3 minutes encompassing tumor plus margin. Survival outcomes and prognostic factors on outcome were Kaplan-Meier and Cox regression analyses.

      RESULTS: The median survival from the date of initial surgery was 8.6 years (95% CI: 5.5-11.8 years). 69% of patients showed malignant transformation to grade 3 (38%) or grade 4 (31%) glioma. Overall survival following PRDR was 12.6 months (95% CI: 8.3-17.0 months) and progression-free survival was 6.2 months (95% CI: 3.8-8.6 months). Overall response rate based on post-PRDR MRI was 36%. In patients who maintained grade 2 histology at recurrence, overall survival from PRDR was 22.0 months with 5 patients remaining disease-free, the longest at 8.2 and 11.4 years. PRDR was generally well tolerated.

      CONCLUSIONS: To the best of our knowledge, this is the largest reported series of patients with recurrent grade 2 gliomas treated with PRDR radiation for disease recurrence. We demonstrate promising survival and acceptable toxicity profiles following re-irradiation. In the cohort of patients who maintain grade 2 disease, prolonged survival (>5 years) is observed in selected patients. For the entire cohort, 1p19q codeletion, KPS, and longer time from initial diagnosis to PRDR were associated with improved survival.

      PMID:38845694 | PMC:PMC11154132 | DOI:10.1093/noajnl/vdae073

      View details for PubMedID 38845694
  • Combining Obinutuzumab With Radiation for Refractory DLBCL: Retrospective Safety and Efficacy Analysis Advances in radiation oncology
    Morris BA, Merfeld EC, Burr AR, Bradley KA, Fletcher CD
    2024 Apr 27;9(7):101524. doi: 10.1016/j.adro.2024.101524. eCollection 2024 Jul.
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      PURPOSE: Approximately 30% of patients with diffuse large B cell lymphoma (DLBCL) will develop relapsed or treatment-refractory disease after primary chemotherapy. Patients unable to undergo aggressive chemotherapy and stem cell transplant or chimeric antigen receptor T-cell (CAR T-cell) therapy have limited treatment options. Here, we investigated the safety and efficacy of combining obinutuzumab with cytoreductive radiation to all areas of disease in patients with relapsed DLBCL.

      METHODS AND MATERIALS: A retrospective review of patients with treatment refractory DLBCL was performed. All patients were treated with external beam radiation to all sites of refractory disease with concurrent and adjuvant obinutuzumab. Toxicities were evaluated based on Common Terminology Criteria for Adverse Events v5.0 criteria. Kaplan-Meier analysis was used to calculate progression-free survival and overall survival.

      RESULTS: Between 2016 and 2022, 7 patients with refractory DLBCL were treated with concurrent radiation and obinutuzumab. No grade 3 or greater treatment-related toxicity was observed. Four of the 7 patients had a complete response at the radiated site on first postradiation imaging. The median progression-free survival and overall survival were 30 months.

      CONCLUSIONS: In this small cohort of treatment-refractory patients with DLBCL, the combination of radiation and obinutuzumab was well tolerated without excessive treatment-related toxicity. The combination resulted in durable disease control with a prolonged overall survival without additional treatment in a subset of patients.

      PMID:38799107 | PMC:PMC11127189 | DOI:10.1016/j.adro.2024.101524

      View details for PubMedID 38799107
  • Review of recent advances in managing periocular skin malignancies Frontiers in oncology
    Trotier DC, Huang L, van Landingham W, Burr AR, Ma VT
    2024 Mar 4;14:1275930. doi: 10.3389/fonc.2024.1275930. eCollection 2024.
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      Management of cutaneous malignancies can be particularly challenging when they are located in the periocular region. The standard of care for localized disease is complete surgical excision, but this may not be possible without significant disruption to visual structures and facial appearance. Definitive radiation may be an option for some patients who cannot or do not wish to undergo surgery. Advances in systemic treatment options for locally advanced and metastatic skin cancers in the past 10 years have prompted investigation into neoadjuvant treatment of periocular cancers. The use of chemotherapy, immune checkpoint inhibitors, and targeted therapies have all been reported with varying degrees of success. For many patients, targeted therapies or immune checkpoint inhibitors should be considered depending on the cancer type, symptoms, and goals with the input of a multidisciplinary cancer care team. In this article, we systematically review the latest updates in surgical, radiotherapeutic, and medical management of periocular malignancies.

      PMID:38500654 | PMC:PMC10944901 | DOI:10.3389/fonc.2024.1275930

      View details for PubMedID 38500654
  • Voxel-Level Dosimetry for Combined Iodine 131 Radiopharmaceutical Therapy and External Beam Radiation Therapy Treatment Paradigms for Head and Neck Cancer International journal of radiation oncology, biology, physics
    Adam DP, Grudzinski JJ, Marsh IR, Hill PM, Cho SY, Bradshaw TJ, Longcor J, Burr A, Bruce JY, Harari PM, Bednarz BP
    2024 Jul 15;119(4):1275-1284. doi: 10.1016/j.ijrobp.2024.02.005. Epub 2024 Feb 16.
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      PURPOSE: Targeted radiopharmaceutical therapy (RPT) in combination with external beam radiation therapy (EBRT) shows promise as a method to increase tumor control and mitigate potential high-grade toxicities associated with re-treatment for patients with recurrent head and neck cancer. This work establishes a patient-specific dosimetry framework that combines Monte Carlo-based dosimetry from the 2 radiation modalities at the voxel level using deformable image registration (DIR) and radiobiological constructs for patients enrolled in a phase 1 clinical trial combining EBRT and RPT.

      METHODS AND MATERIALS: Serial single-photon emission computed tomography (SPECT)/computed tomography (CT) patient scans were performed at approximately 24, 48, 72, and 168 hours postinjection of 577.2 MBq/m2 (15.6 mCi/m2) CLR 131, an iodine 131-containing RPT agent. Using RayStation, clinical EBRT treatment plans were created with a treatment planning CT (TPCT). SPECT/CT images were deformably registered to the TPCT using the Elastix DIR module in 3D Slicer software and assessed by measuring mean activity concentrations and absorbed doses. Monte Carlo EBRT dosimetry was computed using EGSnrc. RPT dosimetry was conducted using RAPID, a GEANT4-based RPT dosimetry platform. Radiobiological metrics (biologically effective dose and equivalent dose in 2-Gy fractions) were used to combine the 2 radiation modalities.

      RESULTS: The DIR method provided good agreement for the activity concentrations and calculated absorbed dose in the tumor volumes for the SPECT/CT and TPCT images, with a maximum mean absorbed dose difference of -11.2%. Based on the RPT absorbed dose calculations, 2 to 4 EBRT fractions were removed from patient EBRT treatments. For the combined treatment, the absorbed dose to target volumes ranged from 57.14 to 75.02 Gy. When partial volume corrections were included, the mean equivalent dose in 2-Gy fractions to the planning target volume from EBRT + RPT differed -3.11% to 1.40% compared with EBRT alone.

      CONCLUSIONS: This work demonstrates the clinical feasibility of performing combined EBRT + RPT dosimetry on TPCT scans. Dosimetry guides treatment decisions for EBRT, and this work provides a bridge for the same paradigm to be implemented within the rapidly emerging clinical RPT space.

      PMID:38367914 | DOI:10.1016/j.ijrobp.2024.02.005

      View details for PubMedID 38367914
  • Marrow-Derived Autologous Stromal Cells for the Restoration of Salivary Hypofunction (MARSH): A pilot, first-in-human study of interferon gamma-stimulated marrow mesenchymal stromal cells for treatment of radiation-induced xerostomia Cytotherapy
    Blitzer GC, Glazer T, Burr A, Gustafson S, Ganz O, Meyers R, McDowell KA, Nickel KP, Mattison RJ, Weiss M, Chappell R, Rogus-Pulia NM, Galipeau J, Kimple RJ
    2023 Nov;25(11):1139-1144. doi: 10.1016/j.jcyt.2023.07.009. Epub 2023 Aug 15.
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      BACKGROUND AIMS: Xerostomia, or the feeling of dry mouth, is a significant side effect of radiation therapy for patients with head and neck cancer (HNC). Preliminary data suggest that mesenchymal stromal/stem cells (MSCs) can improve salivary function. We performed a first-in-human pilot study of interferon gamma (IFNγ)-stimulated autologous bone marrow-derived MSCs, or MSC(M), for the treatment of radiation-induced xerostomia (RIX). Here we present the primary safety and secondary efficacy endpoints.

      METHODS: A single-center pilot clinical trial was conducted investigating the safety and tolerability of autologous IFNγ-stimulated MSC(M). The study was conducted under an approved Food and Drug Administration Investigational New Drug application using an institutional review board-approved protocol (NCT04489732). Patients underwent iliac crest bone marrow aspirate and MSC(M) were isolated, cultured, stimulated with IFNγ and cryopreserved for later use. Banked cells were thawed and allowed to recover in culture before patients received a single injection of 10 × 106 MSC(M) into the right submandibular gland under ultrasound guidance. The primary objective was determination of safety and tolerability by evaluating dose-limiting toxicity (DLT). A DLT was defined as submandibular pain >5 on a standard 10-point pain scale or any serious adverse event (SAE) within 1 month after injection. Secondary objectives included analysis of efficacy as measured by salivary quantification and using three validated quality of life instruments. Quantitative results are reported as mean and standard deviation.

      RESULTS: Six patients with radiation-induced xerostomia who had completed radiation at least 2 years previously (average 7.8 years previously) were enrolled in the pilot study. The median age was 71 (61-74) years. Five (83%) patients were male. Five patients (83%) were treated with chemoradiation and one patient (17%) with radiation alone. Grade 1 pain was seen in 50% of patients after submandibular gland injection; all pain resolved within 4 days. No patients reported pain 1 month after injection, with no SAE or other DLTs reported 1 month after injection. The analysis of secondary endpoints demonstrated a trend of increased salivary production. Three patients (50%) had an increase in unstimulated saliva at 1 and 3 months after MSC(M) injection. Quality of life surveys also showed a trend toward improvement.

      CONCLUSIONS: Injection of autologous IFNγ-stimulated MSC(M) into a singular submandibular gland of patients with RIX is safe and well tolerated in this pilot study. A trend toward an improvement in secondary endpoints of salivary quantity and quality of life was observed. This first-in-human study provides support for further investigation into IFNγ-stimulated MSC(M) injected in both submandibular glands as an innovative approach to treat RIX and improve quality of life for patients with HNC.

      PMID:37589639 | PMC:PMC10615723 | DOI:10.1016/j.jcyt.2023.07.009

      View details for PubMedID 37589639
  • Management of Subglottic Cancer Otolaryngologic clinics of North America
    Mann H, Seligman K, Colwell N, Burr A, Glazer TA
    2023 Apr;56(2):305-312. doi: 10.1016/j.otc.2022.11.001.
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      Primary subglottic carcinoma is a rare subgroup of laryngeal malignancy with exact incidence unknown due to the lack of a standard definition of its anatomic boundaries. Early-stage subglottic carcinoma can be treated with either primary radiation or surgery with similar overall survival rates. Most patients present at an advanced stage due to a paucity of symptoms, and these patients are treated in a multidisciplinary fashion. Particular attention should be paid to the prelaryngeal and pretracheal nodal basins, as well as the stoma region, when managing these patients.

      PMID:37030943 | DOI:10.1016/j.otc.2022.11.001

      View details for PubMedID 37030943
  • Functional Outcomes After Transoral Plus Lateral Pharyngotomy Approach for Advanced Oral and Oropharyngeal Tumors OTO open
    Colevas SM, Merfeld EC, Pflum ZE, Gessert TG, Wieland AM, Glazer TA, Burr AR, Harari PM, Hartig GK
    2023 Feb 23;7(1):e35. doi: 10.1002/oto2.35. eCollection 2023 Jan-Mar.
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      OBJECTIVE: The aim of this study was to evaluate our institutional experience with the combined transoral plus lateral pharyngotomy (TO+LP) approach in a subset of patients with advanced or recurrent oral and oropharyngeal malignancy.

      STUDY DESIGN: A retrospective study of procedures utilizing TO+LP for cancer resection between January 2007 and July 2019.

      SETTING: Tertiary academic medical center.

      METHODS: Thirty-one patients underwent a TO+LP approach for the resection of oral and oropharyngeal tumors. Functional and oncologic outcomes were analyzed.

      RESULTS: Eighteen (58.1%) patients were treated with TO+LP for recurrent disease. Twenty-nine required free tissue transfer and 2 (6.5%) had positive margins. The median time to decannulation was 22 days (range 6-100 days). Thirteen (41.9%) patients still required enteral feeding at their most recent follow-up. Patients without a history of prior radiation were decannulated sooner (p = .009) and were less likely to require enteral feeding at the first postoperative follow-up (p = .034) than those who had prior head and neck radiotherapy.

      CONCLUSION: A TO+LP approach can be used to achieve good functional and oncologic results for selected patients with advanced or recurrent oral and oropharyngeal cancer when minimally invasive options such as transoral robotic surgery, transoral laser microsurgery, or radiotherapy are not possible.

      PMID:36998565 | PMC:PMC10046711 | DOI:10.1002/oto2.35

      View details for PubMedID 36998565
  • Metrics of dose to highly ventilated lung are predictive of radiation-induced pneumonitis in lung cancer patients Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology
    Flakus MJ, Kent SP, Wallat EM, Wuschner AE, Tennant E, Yadav P, Burr A, Yu M, Christensen GE, Reinhardt JM, Bayouth JE, Baschnagel AM
    2023 May;182:109553. doi: 10.1016/j.radonc.2023.109553. Epub 2023 Feb 20.
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      PURPOSE: To identify metrics of radiation dose delivered to highly ventilated lung that are predictive of radiation-induced pneumonitis.

      METHODS AND MATERIALS: A cohort of 90 patients with locally advanced non-small cell lung cancer treated with standard fractionated radiation therapy (RT) (60-66 Gy in 30-33 fractions) were evaluated. Regional lung ventilation was determined from pre-RT 4-dimensional computed tomography (4DCT) using the Jacobian determinant of a B-spline deformable image registration to estimate lung tissue expansion during respiration. Multiple voxel-wise population- and individual-based thresholds for defining high functioning lung were considered. Mean dose and volumes receiving dose ≥ 5-60 Gy were analyzed for both total lung-ITV (MLD,V5-V60) and highly ventilated functional lung-ITV (fMLD,fV5-fV60). The primary endpoint was symptomatic grade 2+ (G2+) pneumonitis. Receiver operator curve (ROC) analyses were used to identify predictors of pneumonitis.

      RESULTS: G2+ pneumonitis occurred in 22.2% of patients, with no differences between stage, smoking status, COPD, or chemo/immunotherapy use between G<2 and G2+ patients (P≥ 0.18). Highly ventilated lung was defined as voxels exceeding the population-wide median of 18% voxel-level expansion. All total and functional metrics were significantly different between patients with and without pneumonitis (P≤ 0.039). Optimal ROC points predicting pneumonitis from functional lung dose were fMLD ≤ 12.3 Gy, fV5 ≤ 54% and fV20 ≤ 19 %. Patients with fMLD ≤ 12.3 Gy had a 14% risk of developing G2+ pneumonitis whereas risk significantly increased to 35% for those with fMLD > 12.3 Gy (P = 0.035).

      CONCLUSIONS: Dose to highly ventilated lung is associated with symptomatic pneumonitis and treatment planning strategies should focus on limiting dose to functional regions. These findings provide important metrics to be used in functional lung avoidance RT planning and designing clinical trials.

      PMID:36813178 | PMC:PMC10283046 | DOI:10.1016/j.radonc.2023.109553

      View details for PubMedID 36813178
  • Interstitial Brachytherapy for Lip Cancer: Technical Aspects to Individualize Treatment Approach and Optimize Outcomes Practical radiation oncology
    Merfeld EC, Witek ME, Francis DM, Burr AR, Wallace CR, Kuczmarska-Haas A, Lamichhane N, Kimple RJ, Glazer TA, Wieland AM, McCulloch TM, Hartig GK, Harari PM
    2023 Jul-Aug;13(4):340-345. doi: 10.1016/j.prro.2023.01.004. Epub 2023 Jan 25.
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      Primary radiation therapy using interstitial brachytherapy (IBT) provides excellent local tumor control for early-stage squamous cell carcinoma of the lip. Technical aspects of treatment are important to optimize outcomes. In this report, we discuss patient selection criteria, procedural details, and dosimetric considerations for performing IBT for cancers of the lip. Catheters are inserted across the length of tumor entering and exiting approximately 5 mm beyond the palpable tumor extent. A custom mouthpiece is fabricated to facilitate normal tissue sparing. Patients undergo computed tomography imaging, the gross tumor volume is contoured based on physical examination and computed tomography findings, and an individualized brachytherapy plan is generated with the goals of achieving gross tumor volume D90% ≥ 90% and minimizing V150%. Ten patients with primary (n = 8) or recurrent (n = 2) cancers of the lip who received high-dose-rate lip IBT using 2.0- to 2.5-week treatment regimens are described (median prescription: 47.6 Gy in 14 fractions of 3.4 Gy). Local tumor control was 100%. There were no cases of acute grade ≥4 or late grade ≥2 toxicity, and cosmesis scores were graded as good to excellent in all patients. IBT represents an excellent treatment option for patients with lip squamous cell carcinoma. With careful attention to technical considerations furthered described in the present report, high rates of tumor control, low rates of toxicity, and favorable esthetic and functional outcomes can be achieved with IBT for lip cancer.

      PMID:36709044 | PMC:PMC10330101 | DOI:10.1016/j.prro.2023.01.004

      View details for PubMedID 36709044
  • Patterns of failure for hypopharynx cancer patients treated with limited high-dose radiotherapy treatment volumes Radiation oncology journal
    Burr A, Harari P, Wieland A, Kimple R, Hartig G, Witek M
    2022 Dec;40(4):225-231. doi: 10.3857/roj.2022.00311. Epub 2022 Dec 2.
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      PURPOSE: Optimal radiotherapy treatment volumes for patients with locally advanced hypopharynx squamous cell carcinoma should ensure maximal tumor coverage with minimal inclusion of normal surrounding structures. Here we evaluated the effectiveness of a direct 3-mm high-dose gross tumor volume to planning target volume expansion on clinical outcomes for hypopharynx cancers.

      MATERIALS AND METHODS: We performed a retrospective analysis of patients with hypopharynx carcinoma treated between 2004 and 2018 with primary radiotherapy using a direct high-dose gross tumor volume to planning target volume expansion and with or without concurrent systemic therapy. Diagnostic imaging of recurrences was co-registered with the planning CT. Spatial and volumetric analyses of contoured recurrences were compared with planned isodose lines. Failures were initially defined as in field, marginal, elective nodal, and out of field. Each failure was further classified as central high-dose, peripheral high-dose, central intermediate/low-dose, peripheral intermediate/low-dose, and extraneous. Clinical outcomes were analyzed by Kaplan-Meier estimation.

      RESULTS: Thirty-six patients were identified. At a median follow-up at 52.4 months, estimated 5-year overall survival was 59.3% (95% confidence interval [CI], 36.3%-74.1%), 5-year local and nodal control was 71.7% (95% CI, 47.1%-86.3%) and 69.9% (95% CI, 57.0%-82.6%), respectively. The most common failure was in the high-dose primary target volume. The gastrostomy tube retention rate at 1 year among patients without recurrence was 13.0% (95% CI, 3.2%-29.7%).

      CONCLUSION: Minimal high-dose target volume expansions for hypopharynx cancers were associated with favorable locoregional control. This approach may enable therapy intensification to improve clinical outcomes.

      PMID:36456541 | PMC:PMC9830040 | DOI:10.3857/roj.2022.00311

      View details for PubMedID 36456541
  • Targeting the GTV in medically inoperable endometrial cancer using brachytherapy Brachytherapy
    Merfeld EC, Kuczmarska-Haas A, Burr AR, Witt JS, Francis DM, Ntambi J, Desai VK, Huang JY, Miller JR, Lawless MJ, Wallace CR, Anderson BM, Bradley KA
    2022 Nov-Dec;21(6):792-798. doi: 10.1016/j.brachy.2022.07.006. Epub 2022 Aug 24.
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      PURPOSE: We aimed to determine the relationship between gross tumor volume (GTV) dose and tumor control in women with medically inoperable endometrial cancer, and to demonstrate the feasibility of targeting a GTV-focused volume using imaged-guided brachytherapy.

      METHODS AND MATERIALS: An endometrial cancer database was used to identify patients. Treatment plans were reviewed to determine doses to GTV, clinical target volume (CTV), and OARs. Uterine recurrence-free survival was evaluated as a function of CTV and GTV doses. Brachytherapy was replanned with a goal of GTV D98 EQD2 ≥ 80 Gy, without regard for coverage of the uninvolved uterus and while respecting OAR dose constraints.

      RESULTS: Fifty-four patients were identified. In the delivered plans, GTV D90 EQD2 ≥ 80 Gy was achieved in 36 (81.8%) patients. Uterine recurrence-free survival was 100% in patients with GTV D90 EQD2 ≥ 80 Gy and 66.7% in patients with EQD2 < 80 Gy (p = 0.001). On GTV-only replans, GTV D98 EQD2 ≥ 80 Gy was achieved in 39 (88.6%) patients. Mean D2cc was lower for bladder (47.1 Gy vs. 73.0 Gy, p < 0.001), and sigmoid (47.0 Gy vs. 58.0 Gy, p = 0.007) on GTV-only replans compared to delivered plans. Bladder D2cc was ≥ 80 Gy in 11 (25.0%) delivered plans and four (9.1%) GTV-only replans (p = 0.043). Sigmoid D2cc was ≥ 65 Gy in 20 (45.4%) delivered plans and 10 (22.7%) GTV-only replans (p = 0.021).

      CONCLUSIONS: OAR dose constraints should be prioritized over CTV coverage if GTV coverage is sufficient. Prospective evaluation of image-guided brachytherapy to a reduced, GTV-focused volume is warranted.

      PMID:36030167 | DOI:10.1016/j.brachy.2022.07.006

      View details for PubMedID 36030167
  • Prospective Study of PET/MRI Tumor Response During Chemoradiotherapy for Patients With Low-risk and Intermediate-risk p16-positive Oropharynx Cancer American journal of clinical oncology
    Witek ME, Kimple RJ, Avey GD, Burr AR, Chandereng T, Yu M, Hu R, Wieland AM, Labby ZE, Bruce JY, Brower JV, Hartig GK, Harari PM
    2022 May 1;45(5):202-207. doi: 10.1097/COC.0000000000000910. Epub 2022 Apr 12.
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      OBJECTIVE: The objective of this study was to examine tumor response with positron emission tomography (PET)/magnetic resonance imaging (MRI) during chemoradiotherapy as a predictor of outcome in patients with p16-positive oropharynx cancer.

      MATERIALS AND METHODS: Patients with p16-positive oropharynx cancer were treated with chemoradiotherapy. Low-risk (LR) disease was defined as T1-T3 and N0-2b and ≤10 pack-years and intermediate-risk (IR) disease as T4 or N2c-3 or >10 pack-years. Patients underwent a PET/MRI scan pretreatment and at fraction 10. Change in value of imaging means were analyzed by analysis of variance. K-means clustering with Euclidean distance functions were used for patient clustering. Silhouette width was used to determine the optimal number of clusters. Linear regression was performed on all radiographic metrics using patient and disease characteristics.

      RESULTS: Twenty-four patients were enrolled with 7 LR and 11 IR patients available for analysis. Pretreatment imaging characteristics between LR and IR patients were similar. Patients with LR disease exhibited a larger reduction in maximum standardized uptake value (SUV) compared with IR patients (P<0.05). Cluster analysis defined 2 cohorts that exhibited a similar intratreatment response. Cluster 1 contained 7 of 7 LR patients and 8 of 11 IR patients. Cluster 2 contained 3 of 11 IR patients. Cluster 2 exhibited significant differences compared with cluster 1 in the change in primary tumor peak SUV and largest lymph node median SUV.

      CONCLUSIONS: We identified that IR p16-positive oropharynx cancers exhibit heterogeneity in their PET/MRI response to chemoradiotherapy. These data support further study of intratreatment imaging response as a potential mechanism to identify patients with IR oropharynx cancer suitable for treatment deintensification.

      PMID:35446279 | PMC:PMC9623610 | DOI:10.1097/COC.0000000000000910

      View details for PubMedID 35446279
  • De-escalating Locoregional Therapy for Axillary Micrometastases in Breast Cancer: How Much is Too Much? Clinical breast cancer
    Merfeld EC, Burr AR, Brickson C, Neuman HB, Anderson BM
    2022 Jun;22(4):336-342. doi: 10.1016/j.clbc.2022.01.001. Epub 2022 Jan 12.
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      BACKGROUND: The applicability of modern prospective data on adjuvant radiotherapy (RT) fields in patients with micrometastases is limited because many trials occurred prior to routine measurement of nodal metastasis size and modern sentinel lymph node evaluation techniques. We aimed to determine prognostic factors for patients with micrometastases and evaluate the impact of adjuvant RT on disease outcomes.

      PATIENTS AND METHODS: Patients diagnosed with pathologic T1-T3 N1mi breast cancers between 2004-2015 were identified. Cox proportional hazards methods were used to determine characteristics predictive of locoregional recurrence (LRR). Tumor and treatment-specific factors were further evaluated using log-rank statistics to compare rates of LRR-free survival.

      RESULTS: This analysis included 156 patients. On multivariable analysis, grade 3 histology (HR 10.84, 95% CI 2.72-43.21) and adjuvant RT (HR 0.22, 95% CI 0.06-0.81) were independent predictors of LRR. Among patients with grade 1-2 histology, 5-year LRR-free survival was 98.8% in patients who received adjuvant RT versus 100% in patients who did not receive adjuvant RT (P = .82). Among patients with grade 3 histology, 5-year LRR-free survival was 90.1% in patients who received adjuvant RT versus 53.0% in patients who did not receive adjuvant RT (P = .025), and 100% in patients receiving comprehensive nodal irradiation versus 76.7% in patients receiving whole breast irradiation or no RT (P = .045).

      CONCLUSION: Patients with grade 3 micrometastases are at substantial risk for LRR. Adjuvant RT, including comprehensive nodal irradiation, should be strongly considered in these women.

      PMID:35105500 | DOI:10.1016/j.clbc.2022.01.001

      View details for PubMedID 35105500
  • Stereotactic Radiation Therapy for an Arteriovenous Malformation of the Oral Tongue: A Teaching Case Advances in radiation oncology
    Merfeld EC, Labby ZE, Miller JR, Burr AR, Wong F, Diamond C, Wieland AR, Aagaard-Kienitz B, Howard SP
    2021 Dec 16;7(3):100870. doi: 10.1016/j.adro.2021.100870. eCollection 2022 May-Jun.
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      PMID:35079666 | PMC:PMC8777148 | DOI:10.1016/j.adro.2021.100870

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  • Defining high-risk elective contralateral neck radiation volumes for oropharynx cancer Head & neck
    Witek ME, Woody NM, Musunuru HB, Hill PM, Yadav P, Burr AR, Ko HC, Ross RB, Kimple RJ, Harari PM
    2022 Feb;44(2):317-324. doi: 10.1002/hed.26924. Epub 2021 Nov 11.
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      BACKGROUND: To define the location of the initial contralateral lymph node (LN) metastasis in patients with oropharynx cancer.

      METHODS: The location of the LN centroids from patients with oropharynx cancer and a single radiographically positive contralateral LN was defined. A clinical target volume (CTV) inclusive of all LN centroids was created, and its impact on dose to organs at risk was assessed.

      RESULTS: We identified 55 patients of which 49/55 had a single contralateral LN in level IIA, 4/55 in level III, 1/55 in level IIB, and 1/55 in the retropharynx. Mean radiation dose to the contralateral parotid gland was 15.1 and 21.0 Gy, (p <0.001) using the modeled high-risk elective CTV and a consensus CTV, respectively.

      CONCLUSIONS: We present a systematic approach for identifying the contralateral nodal regions at highest risk of harboring subclinical disease in patients with oropharynx cancer that warrants prospective clinical study.

      PMID:34761832 | PMC:PMC9723806 | DOI:10.1002/hed.26924

      View details for PubMedID 34761832
  • Opioid use in patients undergoing treatment for oral cavity cancer Journal of pain management
    Ko HC, Mehra MN, Burr AR, Wieland AM, Kimple RJ, Hartig GK, Harari PM, Witek ME
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      OBJECTIVE: In the context of the opioid epidemic, there is value in examining the use of opioids in specific cancer patient cohorts. We analyzed opioid use in patients undergoing adjuvant therapy for oral cavity cancer to define the incidence of new persistent use beyond 3 months.

      STUDY DESIGN: Retrospective.

      SETTING: Comprehensive academic cancer center.

      SUBJECTS AND METHODS: We performed a retrospective IRB-approved analysis of opioid use in patients who received adjuvant radiotherapy with or with concurrent systemic therapy for surgically resected oral cavity cancer between 2003 and 2016. Factors associated with opioid use were evaluated by Chi-square test and one-way ANOVA. The Kaplan-Meier method was used to estimate overall survival.

      RESULTS: Of 77 identified patients, 10 (13%) patients received opioid prescriptions at 3 months or greater following completion of radiotherapy. Patients who were opioid naive prior to surgery required significantly fewer opioid prescriptions than intermittent or chronic opioid users. No specific factors were associated with new persistent opioid use.

      CONCLUSIONS: Patients undergoing surgery and adjuvant radiotherapy for oral cavity cancer who required opioids for cancer treatment related pain are at minimal risk for new dependency. Judicious pain management should be applied for patients with a history of prior opioid use. Larger patient cohorts will be needed to identify patient, disease, and treatment characteristics associated with new persistent use given its limited incidence.

      PMID:34457108 | PMC:PMC8388255

      View details for PubMedID 34457108
  • Late Radiation Related Brachial Plexopathy After Pulsed Reduced Dose Rate Reirradiation of an Axillary Breast Cancer Recurrence Practical radiation oncology
    Morris BA, Burr AR, Anderson BM, Howard SP
    2021 Sep-Oct;11(5):319-322. doi: 10.1016/j.prro.2021.06.003. Epub 2021 Jun 24.
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      Radiation induced brachial plexopathy (RIBP) is an unfortunate complication of radiation involving the axilla and supraclavicular fossa. This case report highlights development of RIBP in a patient 15 years after initial radiation and 11 years after pulsed low dose rate (PRDR) re-irradiation for recurrent disease. PRDR is a radiation technique believed to lower normal tissue toxicity due to improved sublethal intrafraction damage repair of these tissues at low radiation dose rates with good reported long term locoregional control in the re-irradiation setting. However, RIBP, as seen in this patient, is a devastating side effect of high dose radiation to this region, with no effective treatment options outside of symptom management and control. In this case, the patient has remained disease free following her recurrence but has had continued RIBP with minimal improvement using pentoxyfilline for management.

      PMID:34171539 | DOI:10.1016/j.prro.2021.06.003

      View details for PubMedID 34171539
  • Combined Immunotherapy and Stereotactic Radiotherapy Improves Neurologic Outcomes in Patients with Non-small-cell Lung Cancer Brain Metastases Clinical lung cancer
    Enright TL, Witt JS, Burr AR, Yadav P, Leal T, Baschnagel AM
    2021 Mar;22(2):110-119. doi: 10.1016/j.cllc.2020.10.014. Epub 2020 Nov 10.
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      BACKGROUND: The purpose of this study was to compare the outcomes of patients with non-small cell lung cancer (NSCLC) brain metastases treated with stereotactic radiotherapy (SRT) alone versus SRT and immune checkpoint inhibitors (ICIs).

      PATIENTS AND METHODS: Patients treated for their first diagnosis of intracranial metastases with SRT or SRT plus ICI were retrospectively identified. Overall survival (OS), local control (LC), distant brain failure (DBF), neurologic death, and rates of radiation necrosis were calculated. Univariate (UVA) and multivariable (MVA) analyses with competing risk analysis were performed.

      RESULTS: Seventy-seven patients with 132 lesions were analyzed, including 44 patients with 68 lesions in the SRT group and 33 patients with 64 lesions in the SRT plus ICI group. There were no differences in baseline factors between groups. Use of ICI predicted for decreased DBF (hazard ratio [HR], 0.45; 95% confidence interval [CI], 0.24-0.84; P = .01), decreased rates of neurologic death (HR, 0.29; 95% CI, 0.10-0.85; P = .02), and better OS (HR, 0.46; 95% CI, 0.23-0.91; P = .03). Two-year LC was 97% for the SRT + ICI group, and 86% for the SRT-alone group (P = .046). Actuarial 2-year DBF was 39% for the SRT + ICI group and 66% for the SRT alone group (P = .016). On MVA, ICI use persisted in predicting lower incidence of neurologic death (HR, 0.25; 95% CI, 0.09-0.72; P = .01) and DBF (HR, 0.47; 95% CI, 0.25-0.85; P = .01) when adjusted for competing risk of death.

      CONCLUSION: In this cohort of patients with NSCLC brain metastases, ICI use combined with SRT predicted for improved LC and OS and decreased DBF and risk of neurologic death.

      PMID:33281062 | DOI:10.1016/j.cllc.2020.10.014

      View details for PubMedID 33281062
  • Outcomes From Whole-Brain Reirradiation Using Pulsed Reduced Dose Rate Radiation Therapy Advances in radiation oncology
    Burr AR, Robins HI, Bayliss RA, Baschnagel AM, Welsh JS, Tomé WA, Howard SP
    2020 Jul 8;5(5):834-839. doi: 10.1016/j.adro.2020.06.021. eCollection 2020 Sep-Oct.
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      PURPOSE: Recurrent intracranial metastases after whole-brain irradiation pose a clinical challenge owing to the escalating morbidity associated with their treatment. Although stereotactic radiosurgery is increasingly being used, there are still situations in which whole-brain reirradiation (ReRT) continues to be appropriate. Here, we report our experience using whole-brain pulsed reduced dose rate radiation therapy (PRDR), a method that delivers radiation at a slower rate of 0.067 Gy/min to potentially increase sublethal damage repair and decrease toxicity.

      METHODS AND MATERIALS: Patients undergoing whole-brain ReRT with PRDR from January 1, 2001 to March 2019 were analyzed. The median PRDR ReRT dose was 26 Gy in 2 Gy fractions, resulting in a median total whole-brain dose of 59.5 Gy. Cox regression analysis was used for multivariate analysis. The Kaplan-Meier method was used for overall survival, progression free survival, and to evaluate the ReRT score. Binary logistic regression was employed to evaluate variables associated with rapid death.

      RESULTS: Seventy-five patients were treated with whole-brain PRDR radiation therapy. The median age was 54 (range, 26-72), the median Karnofsky performance status (KPS) was 80, and 86.7% had recursive partitioning analysis scores of 2. Thirty-two patients had over 10 metastases and 11 had leptomeningeal disease. The median overall survival was 4.1 months (range, 0.29-59.5 months) with a 1 year overall survival of 10.4%. Age, KPS, dexamethasone usage, and intracranial disease volume were significantly correlated with overall survival on multivariate analysis. A KPS ≤70 was associated with rapid death after radiation. The prognostic value of the ReRT score was validated. The most common acute toxicities were fatigue (23.1%) and headache (16.9%).

      CONCLUSIONS: In this large cohort of patients with advanced intracranial metastases, PRDR achieves acceptable survival and may decrease toxicity associated with ReRT. PRDR is an easily implemented technique and is a viable treatment option for ReRT of brain metastases.

      PMID:33083645 | PMC:PMC7557211 | DOI:10.1016/j.adro.2020.06.021

      View details for PubMedID 33083645
  • Dramatic Improvement of Antitranscription Intermediary Factor-1-γ/α Antibody-Positive Dermatomyositis After Stereotactic Body Radiation Therapy to Presumed Lung Primary: A Case Report Practical radiation oncology
    Kuczmarska-Haas A, Burr AR, Witt JS, Francis DM, Ali H, Sonneborn H, Mahadevan A, Brower JV
    2020 Nov-Dec;10(6):e551-e556. doi: 10.1016/j.prro.2020.06.008. Epub 2020 Jul 2.
  • Clinical outcomes for larynx patients with cancer treated with refinement of high-dose radiation treatment volumes Head & neck
    Burr AR, Harari PM, Haasl AM, Wieland AM, Bruce JY, Kimple RJ, Hartig GK, McCulloch TM, Witek ME
    2020 Aug;42(8):1874-1881. doi: 10.1002/hed.26098. Epub 2020 Feb 14.
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      BACKGROUND: To evaluate disease control, toxicities, and dose to dysphagia/aspiration risk structures (DARS) using a direct gross tumor volume (GTV70Gy ) to planning target volume expansion (dPTV70Gy ) for patients with squamous cell carcinoma of the larynx (LSCC).

      METHODS: A retrospective review was performed on patients with LSCC treated between 2003 and 2018. Clinical outcomes, toxicities, and dosimetric data were analyzed.

      RESULTS: Seventy-three patients were identified. Overall survival at 5-years was 57.8%. Five-year local and regional control was 79.8% and 88.2%, respectively. Distant metastatic-only failure was 2.7%. Eighty percent of failures were 95% contained within the dPTV70Gy . Mean dose and the volume of DARS receiving 70 Gy was significantly lower for dPTV70Gy compared to a consensus-defined PTV70Gy .

      DISCUSSION: Judicious reduction in high-dose target volumes can preserve high tumor control rates while reducing dose to normal surrounding structures underscoring the potential benefit of this approach in enabling local therapy intensification to improve locoregional control.

      PMID:32057151 | PMC:PMC7369226 | DOI:10.1002/hed.26098

      View details for PubMedID 32057151
  • Pulsed Reduced Dose Rate for Reirradiation of Recurrent Breast Cancer Practical radiation oncology
    Burr AR, Robins HI, Bayliss RA, Howard SP
    2020 Mar-Apr;10(2):e61-e70. doi: 10.1016/j.prro.2019.09.004. Epub 2019 Sep 14.
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      PURPOSE: Locoregionally recurrent breast cancer within a previously irradiated field requires weighing the benefits of reirradiation against the increased rates of toxicity. Here we evaluate the outcomes of patients treated with pulsed reduced dose rate (PRDR) radiation therapy with concurrent low-dose capecitabine as a method to increase the therapeutic ratio of re-treatment.

      METHODS AND MATERIALS: Patients treated from November 2000 to June 1, 2018 with PRDR radiation therapy at University of Wisconsin were identified. Patients were re-treated to a median dose of 54 Gy (range, 37.5-66 Gy) using PRDR radiation therapy, delivering radiation at an apparent dose rate of 6.67 cGy/min to allow for increased sublethal damage repair of normal tissues. The median cumulative dose was 109.8 Gy. Twenty-two patients were treated with concurrent capecitabine, most frequently at 500 mg twice per day. The Kaplan-Meier method was used for survival analysis, and Cox regression analysis was used for univariate and multivariate analysis.

      RESULTS: Forty-three patients were identified who underwent reirradiation for locoregionally recurrent invasive breast cancer, with a median follow-up of 20.5 months. Twenty-four patients had gross disease. Nineteen patients had simultaneous metastatic disease. The complete response rate was 83.3% in treated patients with gross disease. Locoregional recurrence-free survival was 81.3% and 73.8% for all patients at 1 and 2 years, respectively. Overall survival for patients with localized disease was 95.7% at 1 year and 91.1% at 2 years. The rate of acute grade 3 radiation dermatitis was 25.6% with no other acute grade 3 toxicities. Grade 3 late toxicity occurred in 18.6% of patients.

      CONCLUSIONS: PRDR radiation therapy with capecitabine was a well-tolerated and effective method for treating patients with recurrent breast cancer. Prospective studies are necessary to compare side effects and efficacy with conventional dose rate reirradiation and to evaluate the potential role for capecitabine in the recurrent setting.

      PMID:31526900 | DOI:10.1016/j.prro.2019.09.004

      View details for PubMedID 31526900
  • Reducing radiotherapy target volume expansion for patients with HPV-associated oropharyngeal cancer Oral oncology
    Burr AR, Harari PM, Ko HC, Bruce JY, Kimple RJ, Witek ME
    2019 May;92:52-56. doi: 10.1016/j.oraloncology.2019.03.013. Epub 2019 Mar 22.
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      PURPOSE: To evaluate clinical outcomes and patterns of failure using a direct gross tumor volume to planning target volume expansion in patients with p16-positive oropharyngeal squamous cell carcinoma.

      METHODS AND MATERIALS: We performed a retrospective review of patients with p16-positive oropharyngeal squamous cell carcinomas treated between 2002 and 2017 with primary radiotherapy with or without concurrent systemic therapy. Patient and disease characteristics associated with disease control and clinical outcomes were analyzed by Cox proportional hazards regression and Kaplan-Meier analyses. Imaging at the time of first failure was used to categorize failure patterns.

      RESULTS: We identified 134 patients with a median follow-up of 56.2 months (range 8.2-160.2 months). Local and regional control at 5 years was 91.5% (95% CI: 86.8-96.4%), and 90.8% (95% CI: 85.6-96.2%), respectively. Of the 14 locoregional failures, there were 10 in-field (Type A), 3 marginal (Type B), and 1 geographic (Type E). Age >70 years (HR 5.42; 95% CI: 1.87-15.68) and T4 versus T1-3 (HR 4.09; 95% CI: 1.01-2.65) were associated with increased rates of locoregional failure on multivariate analysis. The rate of gastrostomy tube retention at one year was 6.0% (range 2.8-12.7%).

      CONCLUSIONS: Management of patients with p16-positive oropharyngeal squamous cell carcinoma using definitive radiotherapy and a high-dose planning target volume created without a gross tumor volume to clinical tumor volume expansion resulted in high locoregional control with the vast majority of failures occurring within the high-dose field. These data warrant prospective evaluation of this technique as a therapy de-intensification approach.

      PMID:31010623 | PMC:PMC7062456 | DOI:10.1016/j.oraloncology.2019.03.013

      View details for PubMedID 31010623
  • HPV impacts survival of stage IVC non-oropharyngeal HNSCC cancer patients Otorhinolaryngology-head and neck surgery
    Burr AR, Harari PM, Ko HC, Chen S, Yu M, Baschnagel AM, Kimple RJ, Witek ME
    2018;3(1):10.15761/OHNS.1000160. doi: 10.15761/OHNS.1000160. Epub 2018 Feb 24.
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      OBJECTIVES: Human papillomavirus (HPV) status is a favorable prognostic marker for patients with oropharyngeal squamous cell carcinoma (OPSCC) and non-metastatic head and neck non-OPSCC. We evaluated the impact of HPV status on overall survival (OS) for patients with Stage IVC non-OPSCC.

      MATERIALS AND METHODS: Patients diagnosed with Stage IVC non-OPSCC and known HPV status between 2010-2013 were identified in the National Cancer Database. Univariate and multivariate analyses were performed to determine factors associated with OS. Propensity score-weighted Kaplan-Meier estimation was used to adjust for confounders in OS analyses. Multiple imputation method was used for sensitivity analysis.

      RESULTS: We identified 708 patients with Stage IVC non-OPSCC with 30% being HPV-positive. Unadjusted median survival was 10.3 months for HPV-negative patients and 21.4 months for HPV-positive patients (p<0.0001). Age ≥ 65 and tumor diameter were associated with worse OS (p<0.05) while treatment versus no treatment and HPV-positive status were associated with improved OS on multivariate analysis (p<0.001). Adjusted median survival for patients with HPV-negative and HPV-positive disease was 11.1 months and 23.8 months, respectively (p<0.001). On unadjusted subgroup analysis, patients with HPV-positive oral cavity disease exhibited improved outcomes (p<0.0001) while HPV-positive hypopharynx (p<0.06) and larynx (p<0.12) patients exhibited a trend for improved OS compared to HPV-negative patients. The survival advantage associated with HPV positivity was maintained on sensitivity analysis (p<0.01).

      CONCLUSION: These data demonstrate a clinically meaningful association between HPV status and OS in patients with non-OSPCC presenting with Stage IVC disease. In the absence of randomized data, these findings support active consideration of HPV status in clinical decision making, clinical trial design, and patient counseling regarding prognosis.

      PMID:30271885 | PMC:PMC6157736 | DOI:10.15761/OHNS.1000160

      View details for PubMedID 30271885
  • STIM1 elevation in the heart results in aberrant Ca²⁺ handling and cardiomyopathy Journal of molecular and cellular cardiology
    Correll RN, Goonasekera SA, van Berlo H, Burr AR, Accornero F, Zhang H, Makarewich CA, York AJ, Sargent MA, Chen X, Houser SR, Molkentin JD
    2015 Oct;87:38-47. doi: 10.1016/j.yjmcc.2015.07.032. Epub 2015 Aug 1.
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      Stromal interaction molecule 1 (STIM1) is a Ca(2+) sensor that partners with Orai1 to elicit Ca(2+) entry in response to endoplasmic reticulum (ER) Ca(2+) store depletion. While store-operated Ca(2+) entry (SOCE) is important for maintaining ER Ca(2+) homeostasis in non-excitable cells, it is unclear what role it plays in the heart, although STIM1 is expressed in the heart and upregulated during disease. Here we analyzed transgenic mice with STIM1 overexpression in the heart to model the known increase of this protein in response to disease. As expected, STIM1 transgenic myocytes showed enhanced Ca(2+) entry following store depletion and partial co-localization with the type 2 ryanodine receptor (RyR2) within the sarcoplasmic reticulum (SR), as well as enrichment around the sarcolemma. STIM1 transgenic mice exhibited sudden cardiac death as early as 6weeks of age, while mice surviving past 12weeks of age developed heart failure with hypertrophy, induction of the fetal gene program, histopathology and mitochondrial structural alterations, loss of ventricular functional performance and pulmonary edema. Younger, pre-symptomatic STIM1 transgenic mice exhibited enhanced pathology following pressure overload stimulation or neurohumoral agonist infusion, compared to controls. Mechanistically, cardiac myocytes isolated from STIM1 transgenic mice displayed spontaneous Ca(2+) transients that were prevented by the SOCE blocker SKF-96365, increased L-type Ca(2+) channel (LTCC) current, and enhanced Ca(2+) spark frequency. Moreover, adult cardiac myocytes from STIM1 transgenic mice showed both increased diastolic Ca(2+) and maximal transient amplitude but no increase in total SR Ca(2+) load. Associated with this enhanced Ca(2+) profile was an increase in cardiac nuclear factor of activated T-cells (NFAT) and Ca(2+)/calmodulin-dependent kinase II (CaMKII) activity. We conclude that STIM1 has an unexpected function in the heart where it alters communication between the sarcolemma and SR resulting in greater Ca(2+) flux and a leaky SR compartment.

      PMID:26241845 | PMC:PMC4637225 | DOI:10.1016/j.yjmcc.2015.07.032

      View details for PubMedID 26241845
  • Na+ dysregulation coupled with Ca2+ entry through NCX1 promotes muscular dystrophy in mice Molecular and cellular biology
    Burr AR, Millay DP, Goonasekera SA, Park KH, Sargent MA, Collins J, Altamirano F, Philipson KD, Allen PD, Ma J, López JR, Molkentin JD
    2014 Jun;34(11):1991-2002. doi: 10.1128/MCB.00339-14. Epub 2014 Mar 24.
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      Unregulated Ca(2+) entry is thought to underlie muscular dystrophy. Here, we generated skeletal-muscle-specific transgenic (TG) mice expressing the Na(+)-Ca(2+) exchanger 1 (NCX1) to model its identified augmentation during muscular dystrophy. The NCX1 transgene induced dystrophy-like disease in all hind-limb musculature, as well as exacerbated the muscle disease phenotypes in δ-sarcoglycan (Sgcd(-/-)), Dysf(-/-), and mdx mouse models of muscular dystrophy. Antithetically, muscle-specific deletion of the Slc8a1 (NCX1) gene diminished hind-limb pathology in Sgcd(-/-) mice. Measured increases in baseline Na(+) and Ca(2+) in dystrophic muscle fibers of the hind-limb musculature predicts a net Ca(2+) influx state due to reverse-mode operation of NCX1, which mediates disease. However, the opposite effect is observed in the diaphragm, where NCX1 overexpression mildly protects from dystrophic disease through a predicted enhancement in forward-mode NCX1 operation that reduces Ca(2+) levels. Indeed, Atp1a2(+/-) (encoding Na(+)-K(+) ATPase α2) mice, which have reduced Na(+) clearance rates that would favor NCX1 reverse-mode operation, showed exacerbated disease in the hind limbs of NCX1 TG mice, similar to treatment with the Na(+)-K(+) ATPase inhibitor digoxin. Treatment of Sgcd(-/-) mice with ranolazine, a broadly acting Na(+) channel inhibitor that should increase NCX1 forward-mode operation, reduced muscular pathology.

      PMID:24662047 | PMC:PMC4019055 | DOI:10.1128/MCB.00339-14

      View details for PubMedID 24662047
  • Overexpression of the Na+/K+ ATPase α2 but not α1 isoform attenuates pathological cardiac hypertrophy and remodeling Circulation research
    Correll RN, Eder P, Burr AR, Despa S, Davis J, Bers DM, Molkentin JD
    2014 Jan 17;114(2):249-256. doi: 10.1161/CIRCRESAHA.114.302293. Epub 2013 Nov 11.
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      RATIONALE: The Na+ / K+ ATPase (NKA) directly regulates intracellular Na+ levels, which in turn indirectly regulates Ca2+ levels by proximally controlling flux through the Na+ / Ca2+ exchanger (NCX1). Elevated Na+ levels have been reported during heart failure, which permits some degree of reverse-mode Ca2+ entry through NCX1, as well as less efficient Ca2+ clearance.

      OBJECTIVE: To determine whether maintaining lower intracellular Na+ levels by NKA overexpression in the heart would enhance forward-mode Ca2+ clearance and prevent reverse-mode Ca2+ entry through NCX1 to protect the heart.

      METHODS AND RESULTS: Cardiac-specific transgenic mice overexpressing either NKA-α1 or NKA-α2 were generated and subjected to pressure overload hypertrophic stimulation. We found that although increased expression of NKA-α1 had no protective effect, overexpression of NKA-α2 significantly decreased cardiac hypertrophy after pressure overload in mice at 2, 10, and 16 weeks of stimulation. Remarkably, total NKA protein expression and activity were not altered in either of these 2 transgenic models because increased expression of one isoform led to a concomitant decrease in the other endogenous isoform. NKA-α2 overexpression but not NKA-α1 led to significantly faster removal of bulk Ca2+ from the cytosol in a manner requiring NCX1 activity. Mechanistically, overexpressed NKA-α2 showed greater affinity for Na+ compared with NKA-α1, leading to more efficient clearance of this ion. Furthermore, overexpression of NKA-α2 but not NKA-α1 was coupled to a decrease in phospholemman expression and phosphorylation, which would favor greater NKA activity, NCX1 activity, and Ca2+ removal.

      CONCLUSIONS: Our results suggest that the protective effect produced by increased expression of NKA-α2 on the heart after pressure overload is due to more efficient Ca2+ clearance because this isoform of NKA preferentially enhances NCX1 activity compared with NKA-α1.

      PMID:24218169 | PMC:PMC4001807 | DOI:10.1161/CIRCRESAHA.114.302293

      View details for PubMedID 24218169
  • Bax and Bak function as the outer membrane component of the mitochondrial permeability pore in regulating necrotic cell death in mice eLife
    Karch J, Kwong JQ, Burr AR, Sargent MA, Elrod JW, Peixoto PM, Martinez-Caballero S, Osinska H, Cheng EH, Robbins J, Kinnally KW, Molkentin JD
    2013 Aug 27;2:e00772. doi: 10.7554/eLife.00772.
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      A critical event in ischemia-based cell death is the opening of the mitochondrial permeability transition pore (MPTP). However, the molecular identity of the components of the MPTP remains unknown. Here, we determined that the Bcl-2 family members Bax and Bak, which are central regulators of apoptotic cell death, are also required for mitochondrial pore-dependent necrotic cell death by facilitating outer membrane permeability of the MPTP. Loss of Bax/Bak reduced outer mitochondrial membrane permeability and conductance without altering inner membrane MPTP function, resulting in resistance to mitochondrial calcium overload and necrotic cell death. Reconstitution with mutants of Bax that cannot oligomerize and form apoptotic pores, but still enhance outer membrane permeability, permitted MPTP-dependent mitochondrial swelling and restored necrotic cell death. Our data predict that the MPTP is an inner membrane regulated process, although in the absence of Bax/Bak the outer membrane resists swelling and prevents organelle rupture to prevent cell death. DOI:

      PMID:23991283 | PMC:PMC3755340 | DOI:10.7554/eLife.00772

      View details for PubMedID 23991283
  • A TRPC6-dependent pathway for myofibroblast transdifferentiation and wound healing in vivo Developmental cell
    Davis J, Burr AR, Davis GF, Birnbaumer L, Molkentin JD
    2012 Oct 16;23(4):705-15. doi: 10.1016/j.devcel.2012.08.017. Epub 2012 Sep 27.
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      After injury or cytokine stimulation, fibroblasts transdifferentiate into myofibroblasts, contractile cells that secrete extracellular matrix for wound healing and tissue remodeling. Here, a genome-wide screen identified TRPC6, a Ca(2+) channel necessary and sufficient for myofibroblast transformation. TRPC6 overexpression fully activated myofibroblast transformation, while fibroblasts lacking Trpc6 were refractory to transforming growth factor β (TGF-β) and angiotensin II-induced transdifferentiation. Trpc6 gene-deleted mice showed impaired dermal and cardiac wound healing after injury. The profibrotic ligands TGF-β and angiotensin II induced TRPC6 expression through p38 mitogen-activated protein kinase (MAPK) serum response factor (SRF) signaling via the TRPC6 promoter. Once induced, TRPC6 activates the Ca(2+)-responsive protein phosphatase calcineurin, which itself induced myofibroblast transdifferentiation. Moreover, inhibition of calcineurin prevented TRPC6-dependent transdifferentiation and dermal wound healing. These results demonstrate an obligate function for TRPC6 and calcineurin in promoting myofibroblast differentiation, suggesting a comprehensive pathway for myofibroblast formation in conjunction with TGF-β, p38 MAPK, and SRF.

      PMID:23022034 | PMC:PMC3505601 | DOI:10.1016/j.devcel.2012.08.017

      View details for PubMedID 23022034
  • Regulation of angiogenesis by a non-canonical Wnt-Flt1 pathway in myeloid cells Nature
    Stefater JA, Lewkowich I, Rao S, Mariggi G, Carpenter AC, Burr AR, Fan J, Ajima R, Molkentin JD, Williams BO, Wills-Karp M, Pollard JW, Yamaguchi T, Ferrara N, Gerhardt H, Lang RA
    2011 May 29;474(7352):511-5. doi: 10.1038/nature10085.
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      Myeloid cells are a feature of most tissues. Here we show that during development, retinal myeloid cells (RMCs) produce Wnt ligands to regulate blood vessel branching. In the mouse retina, where angiogenesis occurs postnatally, somatic deletion in RMCs of the Wnt ligand transporter Wntless results in increased angiogenesis in the deeper layers. We also show that mutation of Wnt5a and Wnt11 results in increased angiogenesis and that these ligands elicit RMC responses via a non-canonical Wnt pathway. Using cultured myeloid-like cells and RMC somatic deletion of Flt1, we show that an effector of Wnt-dependent suppression of angiogenesis by RMCs is Flt1, a naturally occurring inhibitor of vascular endothelial growth factor (VEGF). These findings indicate that resident myeloid cells can use a non-canonical, Wnt-Flt1 pathway to suppress angiogenic branching.

      PMID:21623369 | PMC:PMC3214992 | DOI:10.1038/nature10085

      View details for PubMedID 21623369
  • Actin-binding cleft closure in myosin II probed by site-directed spin labeling and pulsed EPR Proceedings of the National Academy of Sciences of the United States of America
    Klein JC, Burr AR, Svensson B, Kennedy DJ, Allingham J, Titus MA, Rayment I, Thomas DD
    2008 Sep 2;105(35):12867-72. doi: 10.1073/pnas.0802286105. Epub 2008 Aug 25.
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      We present a structurally dynamic model for nucleotide- and actin-induced closure of the actin-binding cleft of myosin, based on site-directed spin labeling and electron paramagnetic resonance (EPR) in Dictyostelium myosin II. The actin-binding cleft is a solvent-filled cavity that extends to the nucleotide-binding pocket and has been predicted to close upon strong actin binding. Single-cysteine labeling sites were engineered to probe mobility and accessibility within the cleft. Addition of ADP and vanadate, which traps the posthydrolysis biochemical state, influenced probe mobility and accessibility slightly, whereas actin binding caused more dramatic changes in accessibility, consistent with cleft closure. We engineered five pairs of cysteine labeling sites to straddle the cleft, each pair having one label on the upper 50-kDa domain and one on the lower 50-kDa domain. Distances between spin-labeled sites were determined from the resulting spin-spin interactions, as measured by continuous wave EPR for distances of 0.7-2 nm or pulsed EPR (double electron-electron resonance) for distances of 1.7-6 nm. Because of the high distance resolution of EPR, at least two distinct structural states of the cleft were resolved. Each of the biochemical states tested (prehydrolysis, posthydrolysis, and rigor), reflects a mixture of these structural states, indicating that the coupling between biochemical and structural states is not rigid. The resulting model is much more dynamic than previously envisioned, with both open and closed conformations of the cleft interconverting, even in the rigor actomyosin complex.

      PMID:18725645 | PMC:PMC2529091 | DOI:10.1073/pnas.0802286105

      View details for PubMedID 18725645
  • Structure and dynamics of the force-generating domain of myosin probed by multifrequency electron paramagnetic resonance Biophysical journal
    Nesmelov YE, Agafonov RV, Burr AR, Weber RT, Thomas DD
    2008 Jul;95(1):247-56. doi: 10.1529/biophysj.107.124305. Epub 2008 Mar 13.
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      Spin-labeling and multifrequency EPR spectroscopy were used to probe the dynamic local structure of skeletal myosin in the region of force generation. Subfragment 1 (S1) of rabbit skeletal myosin was labeled with an iodoacetamide spin label at C707 (SH1). X- and W-band EPR spectra were recorded for the apo state and in the presence of ADP and nucleotide analogs. EPR spectra were analyzed in terms of spin-label rotational motion within myosin by fitting them with simulated spectra. Two models were considered: rapid-limit oscillation (spectrum-dependent on the orientational distribution only) and slow restricted motion (spectrum-dependent on the rotational correlation time and the orientational distribution). The global analysis of spectra obtained at two microwave frequencies (9.4 GHz and 94 GHz) produced clear support for the second model and enabled detailed determination of rates and amplitudes of rotational motion and resolution of multiple conformational states. The apo biochemical state is well-described by a single structural state of myosin (M) with very restricted slow motion of the spin label. The ADP-bound biochemical state of myosin also reveals a single structural state (M*, shown previously to be the same as the post-powerstroke ATP-bound state), with less restricted slow motion of the spin label. In contrast, the extra resolution available at 94 GHz reveals that the EPR spectrum of the S1.ADP.V(i)-bound biochemical state of myosin, which presumably mimics the S1.ADP.P(i) state, is resolved clearly into three spectral components (structural states). One state is indistinguishable from that of the ADP-bound state (M*) and is characterized by moderate restriction and slow motion, with a mole fraction of 16%. The remaining 84% (M**) contains two additional components and is characterized by fast rotation about the x axis of the spin label. After analyzing EPR spectra, myosin ATPase activity, and available structural information for myosin II, we conclude that post-powerstroke and pre-powerstroke structural states (M* and M**) coexist in the S1.ADP.V(i) biochemical state. We propose that the pre-powerstroke state M** is characterized by two structural states that could reflect flexibility between the converter and N-terminal domains of myosin.

      PMID:18339764 | PMC:PMC2426653 | DOI:10.1529/biophysj.107.124305

      View details for PubMedID 18339764




Contact Information

Adam Burr, MD, PhD

600 Highland Avenue,
Madison, WI 53792