In a 2-year rat carcinogenicity study, ritlecitinib increased the incidence of combined benign and malignant thymomas in female rats, and thyroid follicular adenomas and combined follicular adenomas and carcinomas in male rats at 100 mg/kg/day (29 times the MRHD based on AUC comparison). No ritlecitinib-related tumors were noted at doses up to 30 mg/kg/day (6.3 times the MRHD based on AUC comparison). No ritlecitinib-related tumors were noted in a 6-month Tg.rasH2 mouse carcinogenicity study at doses up to 300 mg/kg/day.
Ritlecitinib was not mutagenic in the in vitro bacterial reverse mutation assay (Ames assay). Ritlecitinib was positive in an in vitro micronucleus assay in TK6 cells. However, mechanistic studies determined that ritlecitinib is aneugenic and does not present a clinically relevant genotoxic concern. Additionally, in an in vivo rat bone marrow micronucleus assay, ritlecitinib was not aneugenic or clastogenic at doses up to 400 mg/kg/day.
Ritlecitinib had no effects on female rat fertility at doses up to 200 mg/kg/day (55 times the MRHD based on AUC comparison). Effects on male rat fertility were noted (higher preimplantation loss resulting in lower number of implantation sites and corresponding lower litter size in naïve females mated with ritlecitinib-dosed males) at 200 mg/kg/day (55 times the MRHD based on AUC comparison). No effects on male fertility were noted at doses up to 60 mg/kg/day (14 times the MRHD based on AUC comparison). No effects on spermatogenesis (sperm counts, production rate, motility, or morphology) were noted at any dose.
In two 9-month oral repeat dose toxicity studies in dogs, dose-related reversible axonal dystrophy was noted in the brainstem, spinal cord, sciatic nerve, nerve branches of the vagus nerve, and myenteric/submucosal plexuses of the GI tract at doses ≥20 mg/kg/day (14 times the MRHD based on AUC comparison). At 40 mg/kg/day (33 times the MRHD based on AUC comparison), ritlecitinib-related axonal dystrophy caused adverse reversible hearing loss and waveform deficits in brainstem auditory evoked potential (BAEP) testing. BAEP deficits were first noted during Month 7 of dosing and persisted through the end of dosing. No auditory threshold deficits were noted at 6 months after the end of dosing. No BAEP deficits were noted at doses ≤20 mg/kg/day. Additional mechanistic studies provided preliminary evidence that ritlecitinib-related hearing loss was not directly caused by JAK3 or TEC family kinase inhibition, but did not identify the underlying mechanism of axonal dystrophy in dogs.
In a 2-year rat carcinogenicity study, ritlecitinib increased the incidence of combined benign and malignant thymomas in female rats, and thyroid follicular adenomas and combined follicular adenomas and carcinomas in male rats at 100 mg/kg/day (29 times the MRHD based on AUC comparison). No ritlecitinib-related tumors were noted at doses up to 30 mg/kg/day (6.3 times the MRHD based on AUC comparison). No ritlecitinib-related tumors were noted in a 6-month Tg.rasH2 mouse carcinogenicity study at doses up to 300 mg/kg/day.
Ritlecitinib was not mutagenic in the in vitro bacterial reverse mutation assay (Ames assay). Ritlecitinib was positive in an in vitro micronucleus assay in TK6 cells. However, mechanistic studies determined that ritlecitinib is aneugenic and does not present a clinically relevant genotoxic concern. Additionally, in an in vivo rat bone marrow micronucleus assay, ritlecitinib was not aneugenic or clastogenic at doses up to 400 mg/kg/day.
Ritlecitinib had no effects on female rat fertility at doses up to 200 mg/kg/day (55 times the MRHD based on AUC comparison). Effects on male rat fertility were noted (higher preimplantation loss resulting in lower number of implantation sites and corresponding lower litter size in naïve females mated with ritlecitinib-dosed males) at 200 mg/kg/day (55 times the MRHD based on AUC comparison). No effects on male fertility were noted at doses up to 60 mg/kg/day (14 times the MRHD based on AUC comparison). No effects on spermatogenesis (sperm counts, production rate, motility, or morphology) were noted at any dose.
In two 9-month oral repeat dose toxicity studies in dogs, dose-related reversible axonal dystrophy was noted in the brainstem, spinal cord, sciatic nerve, nerve branches of the vagus nerve, and myenteric/submucosal plexuses of the GI tract at doses ≥20 mg/kg/day (14 times the MRHD based on AUC comparison). At 40 mg/kg/day (33 times the MRHD based on AUC comparison), ritlecitinib-related axonal dystrophy caused adverse reversible hearing loss and waveform deficits in brainstem auditory evoked potential (BAEP) testing. BAEP deficits were first noted during Month 7 of dosing and persisted through the end of dosing. No auditory threshold deficits were noted at 6 months after the end of dosing. No BAEP deficits were noted at doses ≤20 mg/kg/day. Additional mechanistic studies provided preliminary evidence that ritlecitinib-related hearing loss was not directly caused by JAK3 or TEC family kinase inhibition, but did not identify the underlying mechanism of axonal dystrophy in dogs.
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