**Safety Evaluation of an Alpha-Emitter Bismuth-213 Labeled Antibody to (1**→**3)-**β**-Glucan in Healthy Dogs as a Prelude for a Trial in Companion Dogs with Invasive Fungal Infections**

**Muath Helal 1,**† **, Kevin J. H. Allen 1,**† **, Hilary Burgess <sup>2</sup> , Rubin Jiao <sup>1</sup> , Mackenzie E. Malo <sup>1</sup> , Matthew Hutcheson <sup>3</sup> , Ekaterina Dadachova 1,\* ,**‡ **and Elisabeth Snead 2,**‡


Academic Editors: Alessandra Boschi and Petra Martini Received: 3 July 2020; Accepted: 6 August 2020; Published: 8 August 2020

**Abstract: Background**: With the limited options available for therapy to treat invasive fungal infections (IFI), radioimmunotherapy (RIT) can potentially offer an effective alternative treatment. Microorganism-specific monoclonal antibodies have shown promising results in the experimental treatment of fungal, bacterial, and viral infections, including our recent and encouraging results from treating mice infected with *Blastomyces dermatitidis* with <sup>213</sup>Bi-labeled antibody 400-2 to (1→3)-β-glucan. In this work, we performed a safety study of <sup>213</sup>Bi-400-2 antibody in healthy dogs as a prelude for a clinical trial in companion dogs with acquired invasive fungal infections and later on in human patients with IFI. **Methods**: Three female beagle dogs (≈6.1 kg body weight) were treated intravenously with 155.3, 142.5, or 133.2 MBq of <sup>213</sup>Bi-400-2 given as three subfractions over an 8 h period. RBC, WBC, platelet, and blood serum biochemistry parameters were measured periodically for 6 months post injection. **Results**: No significant acute or long-term side effects were observed after RIT injections; only a few parameters were mildly and transiently outside reference change value limits, and a transient atypical morphology was observed in the circulating lymphocyte population of two dogs. **Conclusions**: These results demonstrate the safety of systemic <sup>213</sup>Bi-400-2 administration in dogs and provide encouragement to pursue evaluation of RIT of IFI in companion dogs.

**Keywords:** radioimmunotherapy; bismuth-213; invasive fungal infections; 1-3-beta-glucan; dogs
