The Use of 117mSn (Tin) Colloid for Treatment of Naturally Occurring Grade 3 Elbow Osteoarthritis in Client Dogs


 BackgroundThe pathology associated with elbow dysplasia is progressive and irreversible and long-term prognosis is poor. Evidence has revealed the important role synovitis plays in the pathophysiology of osteoarthritis. The use of radiosynoviothesis has been proposed as an alternative in early therapeutic intervention to prevent, delay or limit joint disease progression. The aim of this study was to evaluate the effect and duration of improvement following intra-articular injection of 117mSn colloid on naturally occurring Grade 3 elbow osteoarthritis in dogs. Dog elbows (15 dogs/27 elbows) were injected with 117mSn colloid and cohorts followed check point assessments on Days 90, 180, 270 and 365 post treatment. Effectiveness was evaluated using: 1) Canine Brief Pain Inventory (CBPI) assessed by the caretaker, and 2) clinician-assessed lameness. Complete blood count, chemistry panel, joint fluid analysis and urinalysis were assessed for safety.ResultsAt least half the dogs showed success at each study time check point (Days 90, 180, 270 and 365) compared with baseline, using the validated CBPI User Guide criteria. Day 270 provided the largest percentage (70%) of successes when compared with baseline. These CBPI findings were corroborated by statistical agreement with success of clinician-assessed lameness. The mean Pain Severity Score (PSS) improved significantly at Days 90, 270 and 365 compared to baseline, while the mean Pain Interference Score (PIS) improved significantly at Day 270 compared to baseline. Safety assessments did not reveal concerns for the study duration.ConclusionsDogs diagnosed with Grade 3 osteoarthritis in at least one elbow benefited by either not worsening or improving over 365 days after treatment with 117mSn colloid. No 117mSn colloid-related safety concerns were observed.


Background
It has been suggested that as many as 20% of dogs over 1 year of age are a icted with osteoarthritis (OA). 1 Canine elbow OA occurs most commonly as a sequela to elbow dysplasia. 2 Elbow dysplasia has been shown to occur more frequently in medium and large sized dogs, such as the German shepherd, Labrador retriever and Rottweiler. 3,4 The current approach to treatment of elbow OA is multimodal, consisting of a combination of weight management, non-steroidal anti-in ammatory drugs (NSAIDs), nutraceuticals, nutrition, intraarticular therapies, and surgical treatment. 5 Because the pathology associated with elbow dysplasia is progressive and irreversible, longterm prognosis is poor and treating the resulting OA is aimed at the management of pain and alleviation of associated clinical signs. 4,5,6,7 Mounting evidence has revealed the important role synovitis plays in the pathophysiology of OA. 8,9 Catabolic and proin ammatory mediators produced by in ammation of the synovial membrane are associated with OA pathogenesis. 1,10,11 The Multicenter Osteoarthritis Study (MOST) following 514 human subjects with magnetic resonance imaging (MRI)-detected effusion synovitis of the knee over 30 months found that subjects had a 2.7-fold greater risk (p = 0.002) of cartilage loss compared with individuals without synovitis. 12 In addition, low-grade synovitis appears to persist long term following surgical treatments of joints, predisposing the patient to insidious progression of OA. 13 A number of conservative therapies currently used to treat OA, including NSAIDs and corticosteroids, are thought to work by reducing synovitis in those joints. 8,14,15,16 Elevation of cytokines in early human OA patients suggests activation of the immune response in the synovial membrane. 11 It has been proposed that early therapeutic intervention targeting the synovium may alleviate clinical signs of joint disease and may even prevent, delay or limit progression. 10,11 One such alternative is the use of radiosynoviorthesis, using a low-energy ionizing radiation (conversion electrons) emitted by a radiotherapeutic radionuclide to penetrate the synovial membrane. The ionizing radiation emission causes macrophage apoptosis and ablation of in ammatory cytokines and growth factors within the joint lining synovium. 17 Studies of both human and canid subjects diagnosed with chronic synovitis (human) 18 or OA (canine) 19 revealed that radiation therapy is an effective therapy and was associated with a favorable clinical outcome over a period of one year.
Rodent experimental models evaluating the use of 117m Sn colloid in the treatment of OA were used in pre-canine studies conducted by J Simón et al. 20,21 During this sequential staged investigational process, no signi cant safety concerns were observed. Such ndings led the authors to conduct this canine study on the intended target species, i.e., dogs with naturally occurring elbow OA. The Nuclear Regulatory Commission has released a technical evaluation report regarding the use of 117m Sn colloid to treat dogs with OA. (https://adams.nrc.gov/wba/ Oct 30, 2020, Exubrion Technical Evaluation Report; ML20269A274).
The purpose of this study was to determine both the change and duration of change in visual lameness and Canine Brief Pain Inventory (CBPI) score 22,23 following intra-articular injection of 117m Sn (tin) colloid (Synovetin OA®, Exubrion Therapeutics, Buford, GA) on naturally occurring canine Grade 3 elbow OA.

Results
Fifteen dogs were enrolled in the study and a total of 27 elbows were treated via intra-articular injection of 117m Sn colloid. Mean age of the dogs was 8.47 years (range 1.5-12.9 years). Mean baseline weight of the dogs was 31.57 kg (range 19.8-45.7 kg). Of the 15 dogs enrolled, 8 dogs were male (two intact) and seven dogs were spayed females. All 15 dogs (27 elbows) were analyzed with respect to the intent-to-treat (ITT) criteria, de ned as all dogs originally entered into the study. One dog was excluded from the per protocol (PP) analysis, de ned as those dogs that completed the treatment originally intended, as the injected dose was >20% under the intended dose.
Effectiveness data were analyzed using the PP population. Using the criterion of CPBI success, at least 50% of the dogs showed success at all timepoints compared with baseline. Day 270 provided the largest percentage (70%) of successes when compared with baseline.
Success was not generally seen when compared with the previous visit (e.g., Day 270 vs Day 365) ( Table 1). Both PSS and PIS showed improvement of ³ 1 or ³ 2 integers, consecutively, in at least 57% of the dogs from baseline to all time-points ( Clinician-assessed lameness was used to evaluate dogs at a walk, trot and for the greater lameness at walk or trot (worst lameness score) ( Table 3). Dogs were walked by a trained handler in a consistent manner. The CBPI ndings were corroborated with statistical agreement between clinician-assessed lameness success and CBPI success (Table 4).
Of the 25 PP population elbows, 19 had follow-up radiographs at Day 365. Radiographic imaging of a majority (78.9%) of the 19 elbows radiographed at Day 365 showed a progression (worsening) of the conditions (p<0.01). Computed tomography (CT) results for the categorical variables (Table 5) showed no signi cant differences between baseline scores and scores at Day 365. Most scores for other CT variables did not change from baseline to Day 365.
MRI of the cranial joint pouch width showed least square mean values at both Days 180 and 365 were signi cantly lower than the mean at baseline (Tables 6 and 7). There were no signi cant differences for any other continuous or categorical variables between time points.
When comparing clinical success and change seen in radiographs, there was signi cant (p<0.01) lack of agreement between the two variables. More dogs exhibited clinical success and radiologic failure than showed clinical failure and radiologic success. When comparing other imaging variables (CT success, MRI Day 180 success and MRI Day 365 success), there was apparent agreement between clinical success and each of the imaging variables (p>0.05), using McNemar's test of agreement.
Safety assessments were performed on the ITT population (15 dogs/27 elbows). Independent laboratory assessments of joint uid, urinalysis, and bloodwork did not reveal any safety concerns over the 365-day study duration. No adverse device events (ADEs) were related to 117m Sn colloid.

Discussion
Elbow dysplasia typically results in progressive OA, 24 clinically characterized by signs of pain and lameness. 1,5 Signs of pain and lameness may be di cult to see in dogs with bilaterally symmetrical disease necessitating additional diagnostic techniques. Accordingly, dogs that clinically improve following a given treatment are considered favorable outcomes from that treatment.
It is conventionally accepted that elbow dysplasia is most commonly a bilateral condition. 6 Twelve of the 15 client-owned dogs enrolled were treated bilaterally for naturally occurring Grade 3 elbow OA (27 elbows) and followed over a 12-month period. In this study CBPI was used to assess effectiveness using the combined criteria (≥1 integer improvement for PSS and ≥2 integers improvement for PIS) for the successful treatment of an individual patient. Using these criteria, success was achieved in at least half of the dogs at Days 90, 180, 270 and 365 (compared with baseline), with Day 270 identi ed as the time of highest success (70%) within the year following a treatment.
Two factors in the intended use of CBPI as a subjective measurement of a dog's pain differed from its use in this study. CBPI is typically used for the validation of systemic treatment modalities and this study was a one-time local treatment of either one or two elbows. 25,26,27 The use of CBPI to assess the effect of treatment in individual dogs typically requires, and has been used for, a much larger sample size than was used in this smaller study of a novel treatment. 25,26,27 Based on these considerations and the fact that CBPI was developed as a scale analogous to that used in human chronic pain studies to capture an owner's perception of both pain severity and how pain interfered with daily life, 23 we examined the PSS and PIS individually from baseline to each time-point (Table 2). PSS signi cantly improved at all time points, except for Day 180, which although not signi cant compared to baseline, was still improved compared with baseline. PIS signi cantly improved at Day 270, however, although not signi cant, there was improvement in PIS scores at all other timepoints compared to baseline. Using the individual criteria for successful treatment, the highest rate of improvement in PSS (72.7%) was measured at Day 365 and in PIS (90%) at Day 270, compared with baseline.
Statistical assessment by McNemar's test of agreement between the CBPI and clinician-assessed lameness yielded p-values ≥ 0.05 for many comparisons from baseline to each visit, indicating agreement. Although the two assessments were conducted by different sets of individuals (dog caregivers and clinical investigators) using different assessment parameters, both of the assessments are focused toward measurement of compromised activity or movement. Corroboration of these assessed parameters and their statistical agreement validate the results of treatment success. The high degree of agreement between the two assessments indicates that both the dogs' caregivers and clinicians were able to evaluate consistent improvement in the treated dogs' lameness. Smaller incremental improvements in the dogs' lameness over the study period (12 months) were evident by the caretakers' ability to document them using the CBPI survey.
Various imaging modalities were used over the 12-month study period. Clinical success was de ned by whether the dog improved or showed no change when compared with CBPI baseline assessments. The poor correlation (as high as 69% incidence of false-negative radiographic diagnosis) between radiographic and clinical ndings of dogs with osteoarthritis is well recognized. 28 In this study, regardless the CBPI outcome, radiographic indices worsened over the course of the study, resulting in a lack of correlation between radiographic results and treatment outcome assessments.
Magnetic resonance imaging showed statistically signi cant changes in the cranial joint pouch width (JPW) when comparing Day 180 and Day 365 images to baseline. The statistically signi cant reduction in cranial JPW from baseline over time to Day 180 and Day 365 follow-up time points is consistent with a reduction in joint effusion. In general, the cranial JPW MRI variable tends to be smaller in magnitude than the caudal JPW, explaining why small changes in magnitude for this variable may have been more easily detected.
There was agreement, based on McNemar's test of agreement, between CT (all time points) and MRI (Day 180 and Day 365) imagining variables and clinical success (p > 0.05). Given that the total number of dogs with both clinical and imaging variables was very small (10 to 12 dogs), it is possible that lack of agreement may have been shown if the sample size was larger.
Favorable results seen across all laboratory safety assessments demonstrate the lack of clinically signi cant safety concerns related to the use of 117m Sn colloid over the duration of the 12-month study period. Therefore, a good safety pro le was demonstrated for 117m Sn colloid under the prescribed conditions for use.

Conclusion
From the results of this study we conclude that the use of 117m Sn colloid has been proved advantageous for the treatment of dogs with Grade 3 osteoarthritis in the elbow. Dogs a icted with this progressive degenerative disease bene ted by either not worsening or improving over the 365-day study period. No device-related safety concerns were observed following treatment with 117m Sn colloid over the study period, demonstrating a good safety pro le for the device under the prescribed conditions for use.

Animals
Companion dogs treated in this study resided in their caretaker's household during and after completion of the study. Prior to any studyrelated procedure, caretakers signed a consent agreeing to participation, treatment and follow-up evaluations through month 12 post treatment. Study-eligible dogs were at least 1 year of age and weighed 4.54 kg (10 lbs.) or more, exhibited clinically evident weightbearing lameness of Grade +1 on a Lameness Scoring System, 29 regardless of NSAID therapy, located in one or both elbows, and had radiographic evidence of Grade 3 OA in at least one elbow. Ongoing NSAID therapy was acceptable, provided the dog was initially lame at baseline evaluation while being treated with an NSAID. Additional criteria included MRI or CT evidence of osseous osteoarthritis changes and a grade 3+ for both questions 1 and 5 of the CBPI survey. Dogs were excluded from the study if they had comorbidities likely to preclude a one-year survival post treatment, evidence of bone neoplasia, severe osteochondritis dissecans (OCD) lesions, septic arthritis, a recently ruptured synovial cyst that communicated with the articular cavity, were pregnant or lactating, or had a known hypersensitivity to the active substance or excipients. This study protocol was approved by the Louisiana State University Institutional Animal Care and Use Committee (IACUC Protocol #16-008) and all methods were carried out in accordance with relevant guidelines and regulations outlined here.

Dose Determination
Dogs were treated with a 1.75 mCi 117m Sn colloid intra-articular dose, which was normalized by body weight based on a standard intraarticular dose for a 22.72 kg (50 lb) dog (Table 8). At the time of this study dose calibration standards for 117 Sn had not been determined by the National Institute of Standards and Technology. The amount of radionuclide delivered was determined by the manufacturer based on rate constants, the date of manufacture, and the date the dose was to be administered. Enrollments were assessed with respect to the delivered dose of 117m Sn colloid in comparison to the intended dose. If the injected dose was >20% under or over the intended dose, the subject was excluded from the PP analysis.

Baseline Assessments
Baseline assessments were obtained within 30 days of treatment. A history and physical examination were performed at baseline and Days 1, 90, 180, 270 and 365. Blood was assessed by CBC and serum chemistry at baseline, Day 180 and Day 365. Urine was collected for urinalysis via free catch or ultrasound-guided cystocentesis at baseline, daily during the post-treatment hospitalization and on Days 180 and 365.

Imaging Procedures
Digital radiography, CT and MRI were each performed at baseline and Day 365. MRI was also performed at Day 180.

Standard Treatment Protocol
Dogs were anesthetized and placed into right or left lateral recumbency depending on the clinician's approach to the target elbow. Hair overlying the elbow joint was clipped and the skin was surgically prepared by scrubbing with povidone iodine or chlorhexidine, beginning at the injection site and spiraling outward. The elbow was covered with a sterile surgical drape. The procedure was performed using either a lateral or medial approach, depending on the surgeon's preference. For the lateral approach, with the elbow exed at 90 degrees, a sterile 22G 1½-inch diamond-tipped spinal needle was inserted caudolaterally between the lateral condyle of the humerus and the triceps tendon, then directed distal and slightly medial along the cranio-lateral aspect of the ulnar anconeus into the supratrochlear foramen of the humerus. For a medial approach, the needle was inserted approximately 1 cm distal to the medial epicondyle and directed perpendicular into the joint. Following needle placement, 0.5 to 1.0 mL of joint uid was aspirated into a sterile syringe. This syringe was removed and a different sterile syringe containing the 117m Sn colloid was attached to the same positioned needle. The colloid was injected slowly into the joint, followed by approximately 0.3 mL of air to clear as much of the colloid from the syringe and needle as possible. The needle was removed from the joint and direct pressure was applied to the injection site for 2 minutes to prevent leaking of the radioisotope and encourage hemostasis.

Imaging Assessments
A radiographic osteoarthritis grade was assigned to each elbow joint, for each dog, as previously described. 30 Scoring at Day 365 was made as related to the initial score and the immediately previous examination. Scoring was: -1 (worsening), 0 (static) or +1 (improvement).
The CT scan for each patient was evaluated for speci c continuous and categorical variables (Table 5). Categorical variables were assigned a grade of 0 to 3 based on subjective assessment for severity of changes, where 0 indicated an absence of the metric and 3 indicated the presence of severe changes. One and 2 indicated mild and moderate severity, respectively. MRI studies were performed using different sequences at each site owing to the difference in equipment between sites. Each investigator followed a pre-determined quantitative morphometric protocol for MRI evaluation. Cranial and caudal JPW was measured on sagittal T2W sequences. The sagittal proton density (PD) was used to assess for the presence of hypointense synovial bodies surrounded by hyperintense synovial uid. A positive change was considered when an increase in uid over time and a decrease in the synovial body size occurred. The presence of synovial uid heterogeneity that could be created by brin strands, was considered a negative change. Subchondral changes in bone intensity were assessed in sagittal and dorsal reformatted images using the 3D sequences optimized for each site. Sclerosis of the subchondral bone was assessed at the ulna at the base of the medial coronoid process and trochlear sulcus.
Cartilage erosions were assessed by determining if the cartilage covered the joint uniformly and was assessed in the PD weighted sequences. The thickness of the joint capsule medial and lateral to the joint was measured on dorsal multiplanar reconstructed 3D scans. Images were evaluated by the radiologist investigator using eFilm viewing software (IBM Watson Health, Armonk, NY). The image for each patient was evaluated for speci c continuous and categorical variables (Table 9).

Assessment Parameters
The CBPI was used at each visit to assess changes in pain and activity (www.caninebpi.com). 22,23 The pain severity score (PSS) was calculated as the mean of questions 1 through 4. The pain interference score (PIS) was calculated as the mean of questions 5 through 10. Improvement was assessed by comparing each visit with baseline and comparing each visit to the most recent visit. Success was de ned, using the criteria for successful treatment of an individual patient 23 , as the improvement of one or more full integer change for the PSS and improvement of two or more full integer changes for the PIS.
Clinician assessment was used to evaluate lameness during walk and trot based on a six-point scale with Grade 0 representing no lameness and Grade 5 representing continuous non-weight-bearing lameness. The worse value (highest) of the two assessments (walk or trot) at a follow-up visit was also collected and statistically analyzed.

Safety Data Analyses
A CBC, serum chemistry, urinalysis and joint uid analysis at baseline and on Days 180 and 365 were performed by an independent laboratory. In addition, joint uid parameters were reviewed with respect to safety-related considerations.

Statistical Analysis
Data analyses were performed with statistical analysis software (SAS, version 9.4, SAS Institute Inc, Cary, NC). For those variables that were assessed for each elbow, the elbow was the experimental unit. For those variables that could only be evaluated for the whole animal, the dog was the experimental unit. For effectiveness, tests of statistical signi cance were completed at a two-sided alpha level of 0.05. For the CBPI assessment, success was presented as the number and percentage of dogs meeting each criterion for baseline compared with Days 90, 180, 270 and 365, and for each visit compared with the most recent visit. For the clinician assessment of lameness, descriptive statistics (number of dogs, mean, standard error of the mean (SEM), minimum, 1 st quartile median, 3 rd quartile and maximum values) were compared with baseline and Days 90, 180, 270 and 365. The same descriptive statistics were also compared with change from baseline for each visit and for change from the previous visit to the current visit. Within group p-values were generated by the paired t-test or Wilcoxon signed rank test, depending on the distribution of the data, for clinical lameness assessments. The CBPI success criteria data was compared with the clinical lameness assessments of walk and trot for each dog. Lameness success was de ned as an improvement from baseline of one or more integers. Two-by-two tables for success/failure were constructed for each visit. McNemar's test of agreement was applied to each metric. P-values ≥ 0.05 indicate agreement. Data for the categorical variables for both CT and MRI were analyzed using the Sign Test to compare baseline with post-treatment scores for each animal and treated elbow. The pre-and posttreatment MRI data for continuous variables were analyzed using repeated measures ANOVA with dog/leg as the replicate and time as the main effect. Least-squares means were calculated for each time point Owners signed a written consent form following a detailed verbal explanation of the study protocol.

Consent for publication
Not applicable.

Availability of data and materials
Not applicable.

Competing interests
The primary author (J. Donecker) is an employee of Exubrion Therapeutics. Drs. Aulakh, Hudson and Fabiani are members of the Exubrion Therapeutics advisory board.

Funding
Funding was provided by Exubrion Therapeutics. Employees of Exubrion Therapeutics were involved in the study design, analysis and writing of this manuscript.
Authors' contributions MF and LG oversaw the safe use and administration of Synovetin OA®, which contains the radioisotope tin 117m. MF and KA recruited and evaluated dogs throughout the study. JMD oversaw the execution of this study. Dr. Karen Aiken of Embark Consulting Group provided technical writing assistance for this report.     and humeral radial joints were made from speci c panels based on a previous study.