Evaluation of the Carcinogenic Potential of Enarodustat (JTZ-951), a Hypoxia-Inducible Factor-Prolyl Hydroxylase Inhibitor, in 26-Week Tg.rasH2 Mouse Study and 2-Year Sprague-Dawley Rat Study

Enarodustat (JTZ-951) is an oral hypoxia-inducible factor-prolyl hydroxylase (HIF-PH) inhibitor for the treatment of anemia with chronic kidney disease. Carcinogenicity of enarodustat was evaluated in a 26-week repeated oral dose study in Transgenic rasH2 (Tg.rasH2) mice and a 2-year repeated oral dose study in Sprague-Dawley (SD) rats. The highest dose levels were set at 6 mg/kg in the Tg.rasH2 mouse study and at 1 mg/kg in the SD rat study based on the maximum tolerated doses in the 3-month and 6-month dose-range finding studies, respectively. Enarodustat did not increase the incidence of any tumors or affect survival in these carcinogenicity studies. Pharmacology-related findings including increases in blood RBC parameters were observed at the highest dose levels for each study. The AUC-based exposure margins as protein-unbound drug base are 16.3-/26.0-fold multiple (males/females) for Tg.rasH2 mice and 1.6-/1.1-fold multiple for SD rats when compared with the estimated exposure in human with chronic kidney disease at 8 mg/day (maximum recommended human dose). In conclusion, enarodustat was considered to have no carcinogenic potential at the clinical dose.

The Antitussive Benzonatate Is Not Tumorigenic in Rodent Carcinogenicity Studies

Benzonatate is a peripheral oral antitussive that dampens the activity of cough stretch receptors. Rodent carcinogenicity studies were performed in Tg.rasH2 mice and Wistar Han rats. Mice were orally gavaged benzonatate at 10, 30, 75, and 100 mg/kg/day for males and 5, 15, and 50 mg/kg/day for females. Rats were gavaged at 10, 30, and 90 mg/kg/day for males and 5, 15, and 50 mg/kg/day for females. Higher doses in males were due to differences in maximum tolerated doses in dose-ranging studies. In both species, benzonatate was not detected in plasma because of rapid ester hydrolysis producing 4-(butylamino) benzoic acid (BBA) and methylated polyethylene glycol polymer. This metabolism was similar in human plasma; therefore, plasma BBA was used to show systemic exposure. Both species had no evidence of a benzonatate-related increase in any neoplasm. A slight increase in nasal cavity exudative inflammation was present in benzonatate-dosed male mice. Retinal atrophy was observed in male rats at ≥30 mg/kg/day, but the incidence was within historical control data range and not related to benzonatate. In conclusion, benzonatate and its 2 major metabolites were not carcinogenic in rodent carcinogenicity studies at BBA exposures of ≥32 and 70 times a 200 mg human benzonatate dose, respectively.

High Background Incidence of Spontaneous Subcapsular Adrenal Gland Hyperplasia of Tg.rasH2 Mice Used in 26-week Carcinogenicity Studies

The Tg.rasH2 model was accepted by regulatory agencies worldwide for 26-week carcinogenicity assays as an alternative to the standard 2-year assays in conventional mice in 2003. Several references documenting spontaneous nonneoplastic findings and incidences of spontaneous tumors in the Tg.rasH2 mice have been published. The purpose of this publication is to add adrenal gland subcapsular hyperplasia to the database pertaining to spontaneous lesions noted in Tg.rasH2 mice, review physiology related to this finding, and discuss its significance. The incidence of spontaneous subcapsular adrenal gland hyperplasia was determined in control Tg.rasH2 mice from nine 26-week carcinogenicity studies carried out within the last 5 years at two contract research organizations. Incidence of this finding ranged from 56% to 79% in males and 88% to 100% in females, with an incidence average of 62% in males and 93% in females. Adrenal gland subcapsular hyperplasia is a common finding in male and female Tg.rasH2 mice that did not progress to neoplasia in Tg.rasH2 mice. In general, it tends to be more frequent and severe in females in comparison to males.