Preclinical Evaluation of the Toxicological Effects of a Novel Constrained Ethyl Modified Antisense Compound Targeting Signal Transducer and Activator of Transcription 3 in Mice and Cynomolgus Monkeys

Abstract

ISIS 481464 is a constrained ethyl (cEt) modified phosphorothioate antisense oligonucleotide (ASO) targeting signal transducer and activator of transcription 3 (STAT3) studied in mice and monkey to support oncology clinical trials. Six-week toxicology studies were performed in mice and cynomolgus monkey (up to 70 and 30 mg/kg/week respectively). Reduction in STAT3 protein up to 90% of control was observed in monkey. Cynomolgus monkey was considered the most relevant species to human with respect to pharmacokinetic properties, but mice are useful in their relative sensitivity to the potential proinflammatory and hepatic effects of oligonucleotides. In monkeys, there was no impact on organ function at doses up to 30 mg/kg/week for 6 weeks. Minimal to slight proximal tubular epithelial cell degeneration and regeneration within the kidney was observed, which had no impact on renal function and showed reversibility at the end of the treatment-free period. Additionally, mild and transient activated partial thromboplastin time elevations and mild increases in complement Bb were observed at the higher doses by intravenous dosing only. In mice, the alterations at 70 mg/kg/week included spleen weight increase up to 1.4-fold relative to control, increases in alanine aminotransferase and aspartate aminotransferase up to 1.8-fold over control, interleukin-10 increases up to 3.7-fold, and monocyte chemoattractant protein-1 increase up to 1.9-fold over control. No significant clinical pathology or histopathology changes were seen in mice at 20 mg/kg/week or less. The toxicity profile of ISIS 481464 is consistent with effects observed with phosphorothioate ASOs containing 2'-O-methoxyethylribose modifications instead of cEt.

Generation 2.5 Antisense Oligonucleotides Targeting the Androgen Receptor and Its Splice Variants Suppress Enzalutamide-Resistant Prostate Cancer Cell Growth

“…Short tissue half-life of first-generation phosphorothioate ASO, along with in vivo delivery of siRNA, remain significant barriers to clinical development of ASO or siRNA targeting the AR. In this study, we used a panel of highly optimized, next-generation constrained-ethyl (cEt) modified ASOs (Gen 2.5), which demonstrated favorable physicochemical, biochemical, and pharmacokinetic properties in vivo (47,48). The improved resistance against nuclease-mediated metabolism results in a significantly improved tissue half-live in vivo, resulting in a longer duration of action and a more intermittent dosing schedule.…”

Antisense Oligonucleotide Therapies

“…The shorter basepair length of most LNA gapmers (based on their higher binding efficiency) seems to reduce their proinflammatory potential as compared to other backbones. The basis for the sequence specificity in rodents are sequence motifs that are recognized by pathogen-associated molecular pattern (PAMP) receptors, such as the nucleic acidsensing TLR receptors (Agrawal and Kandimalla 2004;Senn, Burel, and Henry 2005;Richardt-Pargmann and Vollmer 2009;Burel et al 2012;Burel et al 2013). These attributes have been exploited for immunomodulatory drug indications by industry (Krieg 1998(Krieg , 1999Henry et al 1999).…”

Systemic Administration of a Cyclic Signal Transducer and Activator of Transcription 3 (STAT3) Decoy Oligonucleotide Inhibits Tumor Growth without Inducing Toxicological Effects

“…WHI-P131, a potent and selective inhibitor of JAK3, was well tolerated in a study with three cynomolgus monkeys at a dose level ranging from 20 to 100 mg/kg (15). The toxicological effects of ISIS 481464, a constrained ethyl modified phosphorothioate antisense oligonucleotide targeting STAT3, have been studied both in mice and cynomolgus monkeys (16). The toxicity profile of ISIS 481464 was similar to the antisense oligonucleotide containing 2′-Omethoxyethylribose modification, and no new toxicity was revealed (16).…”

“…The toxicological effects of ISIS 481464, a constrained ethyl modified phosphorothioate antisense oligonucleotide targeting STAT3, have been studied both in mice and cynomolgus monkeys (16). The toxicity profile of ISIS 481464 was similar to the antisense oligonucleotide containing 2′-Omethoxyethylribose modification, and no new toxicity was revealed (16). The toxicity study of the linear STAT3 decoy oligonucleotide conducted in a nonhuman primate model demonstrated no acute toxicity, and the no-observable adverse-effect level was >3.2 mg/kg, suggesting that direct injection of the STAT3 decoy does not cause local or systemic abnormalities (4).…”