Carcinogenicity assessment of inotersen in Tg.rasH2 mice and Sprague-Dawley rats: Implications for 2'-MOE antisense oligonucleotides

Inotersen, a 2'-O-(2-methoxyethyl) modified antisense oligonucleotide (2'-MOE ASO), is approved for the treatment of hereditary transthyretin-mediated amyloidosis (hATTR). It underwent a comprehensive nonclinical safety evaluation, including safety pharmacology, repeat-dose toxicity, genotoxicity, reproductive and development toxicity, and carcinogenicity studies. Tumorigenic potential was assessed through dedicated carcinogenicity studies in transgenic rasH2 (Tg.rasH2) mice and Sprague Dawley (SD) rats. In the 26-week Tg.rasH2 mouse study, inotersen and a mouse-active surrogate (ISIS 401724) were administered as weekly subcutaneous (SC) doses up to 80 mg/kg and 30 mg/kg, respectively. Proinflammatory effects and ASO accumulation in the liver and kidney, both well-documented class effects, were observed; however, no treatment-related neoplasms were noted. Similarly, the mouse surrogate did not induce any treatment-related neoplasms. In the 2-year SD rat carcinogenicity study, inotersen was administered as weekly SC doses up to 6 mg/kg. The primary dose-limiting effect at doses ≥2 mg/kg/week was an increased incidence of chronic progressive nephropathy (CPN), which contributed to decreased survival at the 6 mg/kg/week dose level. Notably, no renal neoplasia was associated with the increased CPN. Increasing mononuclear cell infiltrates at the injection site were linked to an increased incidence of subcutaneous fibrosarcoma at doses ≥2 mg/kg/week. This inflammation-associated injection site tumor in rats administered inotersen has limited relevance for humans. Additionally, the long-term assessment of ASO effects in rats is somewhat limited due to the ASO exacerbation of CPN and its impact on survival. There was no evidence of genotoxicity in vitro or in vivo at limit doses. Collectively, these data support a conclusion that a single carcinogenicity assessment in the Tg.rasH2 mouse, along with data from chronic toxicology studies in the rodent and nonrodent, is sufficient to assess carcinogenic potential for this drug class.