Castration Determines the Efficacy of ETAR Blockade in a Mouse Model of Prostate Cancer Bone Metastasis.

Bone metastasis is a painful complication of advanced prostate cancer. Endothelin-1 is a tumor-secreted factor that plays a central role in osteoblast activation and the osteosclerotic response of prostate cancer metastatic to bone. Antagonists that block the activation of the endothelin A receptor (ETAR), located on osteoblasts, reduce osteoblastic bone lesions in animal models of bone metastasis. However, ETAR antagonists demonstrated limited efficacy in clinical trials of men with advanced prostate cancer who also received standard androgen deprivation therapy (ADT). Previous data from our group suggested that, in a mouse model, ETAR antagonists might only be efficacious when androgen signaling in the osteoblast is lowered beyond the ability of standard ADT. This notion was tested in a mouse model of prostate cancer bone metastasis. Castrated and sham-operated male athymic nude mice underwent intracardiac inoculation of the ARCaPM castration-resistant prostate cancer cell line. The mice were then treated with either the ETAR antagonist zibotentan or a vehicle control to generate four experimental groups: vehicle+sham (Veh+Sham), vehicle+castrate (Veh+Castr), zibotentan+sham (Zibo+Sham), and zibotentan+castrate (Zibo+Castr). The mice were monitored radiographically for the development of skeletal lesions. The Zibo+Castr group had significantly longer survival and a single incidental lesion. Mice in the Zibo+Sham group had the shortest survival and the largest number of skeletal lesions. Survival and skeletal lesions of the Veh+Sham and Veh+Castr groups were intermediate compared with the zibotentan-treated groups. We report a complex interaction between ETAR and androgen signaling, whereby ETAR blockade was most efficacious when combined with complete androgen deprivation.

Variation in Bacterial Contamination of Microisolation Cage Tops According to Rodent Species and Housing System.

The Guide recommends sanitizing cage components, including microisolation cage tops (MCT), at a minimum of every 2 wk. Previously published data demonstrated that mouse MCT microbial loads do not increase until at least 2 wk and that sanitation can be delayed past 2 wk. How microbial loads differ on mouse compared with rat MCT, as well as across different ventilation systems, remains unclear. We hypothesized that MCT microbial loads would be higher in tops from rats compared with mice and would differ according to IVC ventilation system. We evaluated bacterial loads on MCT at serial time points to 90 d from static cages housing mice or rats and from rat and mouse cages on several ventilation systems (mice, 6; rats, 4). MCT were determined to have sufficiently elevated bacterial loads to necessitate changing based on either statistically significant changes in bacterial loads or values greater than 50 cfu. Across all ventilation systems, bacterial counts at 14 d were significantly higher on rat MCT compared with mouse MCT. Across the ventilation systems examined, rat MCT cfu remained similarly elevated from 14 d through 90 d. Mouse MCT total cfu were also stable across multiple ventilation systems yet remained lower than 50 cfu until at least 90 d. Patterns of bacterial species isolated from rat MCT were relatively consistent over time and ventilation system, whereas mice showed greater variability in both contexts. We found that 14 d is an appropriate sanitization time point for rat MCT, whereas the interval at which mouse MCT are cleaned can be extended to 90 d at least. Our data highlight interspecies differences in the accumulation of bacteria on MCT and that mouse MCT sanitation intervals for several housing systems can be extended beyond 14 d.

The Endothelin-A Receptor Antagonist Zibotentan Induces Damage to the Nasal Olfactory Epithelium Possibly Mediated in Part through Type 2 Innate Lymphoid Cells.

Zibotentan, an endothelin-A receptor antagonist, has been used in the treatment of various cardiovascular disorders and neoplasia. Castrated athymic nude mice receiving zibotentan for a preclinical xenograft efficacy study experienced weight loss, gastrointestinal bloat, and the presence of an audible respiratory click. Human side effects have been reported in the nasal cavity, so we hypothesized that the nasal cavity is a target for toxicity in mice receiving zibotentan. Lesions in the nasal cavity predominantly targeted olfactory epithelium in treated mice and were more pronounced in castrated animals. Minimal lesions were present in vehicle control animals, which suggested possible gavage-related reflux injury. The incidence, distribution, and morphology of lesions suggested direct exposure to the nasal mucosa and a possible systemic effect targeting the olfactory epithelium, driven by a type 2 immune response, with group 2 innate lymphoid cell involvement. Severe nasal lesions may have resulted in recurrent upper airway obstruction, leading to aerophagia and associated clinical morbidity. These data show the nasal cavity is a target of zibotentan when given by gavage in athymic nude mice, and such unanticipated and off-target effects could impact interpretation of research results and animal health in preclinical studies.