Eric M. Green

Four fraction palliative radiotherapy for osteosarcoma in 24 dogs.

Twenty-four dogs underwent palliative radiotherapy consisting of four 8 gray (Gy) fractions of 60Co radiation on days 0, 7, 14, and 21 at 26 sites for axial (n=11) or appendicular (n=15) osteosarcoma. Response was noted in 92% of sites treated. Seventeen dogs were euthanized due to local or metastatic disease, one dog died of metastatic disease, five dogs died of unrelated causes, and one dog is alive. The four fraction protocol is effective for palliation of clinical signs associated with axial or appendicular osteosarcoma and may result in a higher response rate and longer survival time than three fraction palliative protocols.

Radiation therapy for incompletely excised grade II canine mast cell tumors.

Forty-five dogs with incompletely excised grade II mast cell tumors were treated with radiation using a cobalt 60 teletherapy unit (15 fractions of 3.2 Gy for a total of 48 Gy). Twenty-four of the dogs underwent prophylactic regional lymph node irradiation. Three (6.7%) dogs had tumor recurrence, two (4.4%) dogs developed metastasis, and 14 (31%) dogs developed a second cutaneous mast cell tumor. No difference in overall survival rate was observed between the dogs receiving and not receiving prophylactic irradiation of the regional lymph node.

A Small Molecule Inhibitor of Sarcomere Contractility Acutely Relieves Left Ventricular Outflow Tract Obstruction in Feline Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an inherited disease of the heart muscle characterized by otherwise unexplained thickening of the left ventricle. Left ventricular outflow tract (LVOT) obstruction is present in approximately two-thirds of patients and substantially increases the risk of disease complications. Invasive treatment with septal myectomy or alcohol septal ablation can improve symptoms and functional status, but currently available drugs for reducing obstruction have pleiotropic effects and variable therapeutic responses. New medical treatments with more targeted pharmacology are needed, but the lack of preclinical animal models for HCM with LVOT obstruction has limited their development. HCM is a common cause of heart failure in cats, and a subset exhibit systolic anterior motion of the mitral valve leading to LVOT obstruction. MYK-461 is a recently-described, mechanistically novel small molecule that acts at the sarcomere to specifically inhibit contractility that has been proposed as a treatment for HCM. Here, we use MYK-461 to test whether direct reduction in contractility is sufficient to relieve LVOT obstruction in feline HCM. We evaluated mixed-breed cats in a research colony derived from a Maine Coon/mixed-breed founder with naturally-occurring HCM. By echocardiography, we identified five cats that developed systolic anterior motion of the mitral valve and LVOT obstruction both at rest and under anesthesia when provoked with an adrenergic agonist. An IV MYK-461 infusion and echocardiography protocol was developed to serially assess contractility and LVOT gradient at multiple MYK-461 concentrations. Treatment with MYK-461 reduced contractility, eliminated systolic anterior motion of the mitral valve and relieved LVOT pressure gradients in an exposure-dependent manner. Our findings provide proof of principle that acute reduction in contractility with MYK-461 is sufficient to relieve LVOT obstruction. Further, these studies suggest that feline HCM will be a valuable translational model for the study of disease pathology, particularly LVOT obstruction.

Cutaneous and systemic blastomycosis, hypercalcemia, and excess synthesis of calcitriol in a domestic shorthair cat.

A 9 yr old domestic shorthair cat was diagnosed with cutaneous and pulmonic blastomycosis. Severe persistent ionized hypercalcemia and excess circulating concentration of calcitriol were documented in association with blastomycosis. Ionized hypercalcemia resolved when the granulomatous lesions of blastomycosis resolved and the calcitriol levels decreased.

Chemotherapy and Radiotherapy for Treatment of Cutaneous Lymphoma in a Ground Cuscus (Phalanger gymnotis)

Abstract A 15-year-old female ground cuscus (Phalanger gymnotis) was presented with an isolated ulcerated, nonhealing lesion on the lateral thorax. Histopathology and immunohistochemistry were diagnostic for cutaneous T-cell lymphoma with incomplete excision. Oral chemotherapy with CCNU (lomustine) resulted in clinical remission that lasted 255 days, with no appreciable toxicity. Tumor recurrence was treated with radiation therapy, which resulted in 120 additional days of clinical remission. Subsequently, the tumor developed at a distant site and the cuscus was humanely euthanized. A slight decrease in appetite early in disease progression was the only adverse effect noted throughout the treatment period. Oral, minimally invasive chemotherapy, and adjunct radiation therapy were viable treatment options for this ground cuscus and should be considered for treatment of neoplasia in other nontraditional species.

Effects of extensive circumferential periosteal stripping on the microstructure and mechanical properties of the murine femoral cortex.

Extensive periosteal stripping (PS) is a risk factor for post‐radiation pathologic fracture following surgery for extremity soft tissue tumors. The purpose of this study was to determine the effects of PS on bone structure and mechanical properties. Thirty‐one skeletally mature mice underwent PS, with circumferential removal of periosteum from an 8‐mm segment of the mid‐diaphysis of the left femur. Thirty‐one control mice underwent sham surgery in which the femur was isolated without manipulation of the periosteum. At 2, 6, 12, or 26 weeks following surgery, the left femora were examined by micro‐CT to quantify cortical thickness (CtTh), cross‐sectional area (CSA), bone volume (BV), and polar moment of inertia (PMI). Three‐point mechanical bend testing was performed and peak load, stiffness, and energy to failure were determined. PS resulted in significantly decreased CtTh, CSA, BV, and PMI at all time points. Peak load, stiffness, and energy to failure were significantly reduced at 2, 6, and 12 weeks. There were no significant differences in mechanical properties at 26 weeks. In this mouse model, extensive circumferential PS resulted in sustained changes in bone structure that were still evident after 6 months, accompanied by reductions in bone strength that persisted for at least 3 months.

Esophageal diverticulum associated with a trichobezoar in a cat.

A 9-year-old, castrated male, domestic longhaired cat was evaluated for persistent regurgitation over the previous month. The cat had presented 9 months earlier and was diagnosed with esophageal obstruction secondary to a trichobezoar. The trichobezoar had been removed endoscopically, and the cat was subsequently fed a canned prescription diet. The owners noted only infrequent regurgitation over the following 9 months. After signs recurred, contrast radiography with fluoroscopy revealed an esophageal diverticulum at the thoracic inlet, with an ovoid filling defect. Decreased esophageal motility was noted distal to the diverticulum. Esophagoscopy confirmed the presence of a trichobezoar within an esophageal diverticulum. Following removal of the trichobezoar and therapy to prevent trichobezoar formation, the cat did well for 2 months until it died suddenly with signs of hyperventilation and open-mouth breathing.

ACCURACY OF COMPUTED TOMOGRAPHY IN DETERMINING LESION SIZE IN CANINE APPENDICULAR OSTEOSARCOMA

Multidetector contrast enhanced computed tomography with acquisition of 0.625-mm thick transverse images was used to measure the extent of appendicular osteosarcoma in 10 dogs. The measured length of tumor based on CT was compared to the true length of tumor using histopathology. There was a statistically significant association with good correlation between the true length of osteosarcoma compared to the length of intramedullary/endosteal abnormalities on CT with a mean overestimation of 1.8% (SD = 15%). There was not a statistically significant association between the true tumor length and the length of periosteal proliferation on CT with a mean overestimation of 9.7% (SD = 30.3%). There was a statistically significant association, but with poor correlation, between the true tumor length compared to the length of abnormal contrast enhancement with a mean overestimation of 9.6% (SD = 34.8%). The extent of intramedullary/endosteal CT abnormalities assessed from submillimeter transverse images may be of value in assessing patient candidacy and surgical margins for limb-sparing surgery.

Intra- and interobserver variability of board-certified veterinary radiologists and veterinary general practitioners for pulmonary nodule detection in standard and inverted display mode images of digital thoracic radiographs of dogs.

OBJECTIVE To determine intra- and interobserver variability of 2 veterinary radiologists and 2 veterinary general practitioners for detection of pulmonary nodules in standard and inverted (reversed grayscale) displays of digital thoracic radiographs of dogs. DESIGN Evaluation study. SAMPLE 114 sets of 3-view (right lateral, left lateral, and ventrodorsal or dorsoventral views) digital thoracic radiographs from 114 dogs. PROCEDURES 2 experienced board-certified veterinary radiologists and 2 experienced veterinary general practitioners individually evaluated 114 randomized sets of radiographs. Pulmonary nodules were present in radiographs of 60 of 114 dogs. Each reviewer examined all images in standard or inverted display mode and scored nodule detection on a confidence scale of 1 to 5. After ≥ 2 months, the same individuals evaluated the same images in the remaining display mode. Intraobserver agreement for each display mode was determined via a κ statistic; results between the 2 groups of reviewers were compared via receiver operator curve analysis. RESULTS There was no significant intraobserver variability in pulmonary nodule detection between the 2 display modes. Detection accuracy for board-certified radiologists was significantly greater than that of veterinary general practitioners for both display modes. Near-perfect intraobserver agreement was detected between the 2 display modes for board-certified radiologists, whereas moderate to slight intraobserver agreement was detected for the veterinary general practitioners. CONCLUSIONS AND CLINICAL RELEVANCE Detection of pulmonary nodules in digital thoracic radiographs was comparable, whether a standard or inverted mode was used for evaluations. However, the board-certified radiologists had greater detection accuracy than did veterinary general practitioners.

Deciphering the super relaxed state of human β-cardiac myosin and the mode of action of mavacamten from myosin molecules to muscle fibers

Significance Cardiac muscle contraction is powered by ATP hydrolysis during cycles of interaction between myosin-containing thick filaments and actin-containing thin filaments. This generates force in the cardiac muscle necessary for pumping blood through the body. Mutations in myosin alter this force generation leading to hypercontractility and hypertrophic cardiomyopathy (HCM). An energy-conserving, super relaxed state (SRX) of myosin, which has a very low ATPase activity, has previously been described in muscle fibers. Destabilization of the SRX has been proposed to be a chief cause of HCM. This work sheds light on the biochemical and molecular nature of SRX and demonstrates the mechanism of action of mavacamten, a cardiac inhibitor in phase 2 clinical trials. Mavacamten exerts its effects primarily by stabilizing the SRX of β-cardiac myosin. Mutations in β-cardiac myosin, the predominant motor protein for human heart contraction, can alter power output and cause cardiomyopathy. However, measurements of the intrinsic force, velocity, and ATPase activity of myosin have not provided a consistent mechanism to link mutations to muscle pathology. An alternative model posits that mutations in myosin affect the stability of a sequestered, super relaxed state (SRX) of the protein with very slow ATP hydrolysis and thereby change the number of myosin heads accessible to actin. Here we show that purified human β-cardiac myosin exists partly in an SRX and may in part correspond to a folded-back conformation of myosin heads observed in muscle fibers around the thick filament backbone. Mutations that cause hypertrophic cardiomyopathy destabilize this state, while the small molecule mavacamten promotes it. These findings provide a biochemical and structural link between the genetics and physiology of cardiomyopathy with implications for therapeutic strategies.