Exposure to siRNA-GalNAc Conjugates in Systems of the Standard Test Battery for Genotoxicity.

Registration of pharmaceuticals requires an assessment of their genotoxic potential using in vitro and in vivo tests outlined in the International Conference on Harmonisation (ICH) guidance S2(R1). We have evaluated numerous siRNA-N-acetylgalactosamine (GalNAc) conjugates containing phosphorothioate linkages and various combinations of 2'-fluoro and 2'-O-methyl ribose modifications of multiple nucleotides in the ICH battery of assays, all of which have uniformly yielded negative results. To verify these negative genotoxicity results, in this study we confirm test article exposure using toolkit small interfering RNAs (siRNAs) representative of those in the clinic. In the Ames test, the highest uptake of the siRNA-GalNAc conjugates occurred at 1 h postdose in all bacterial strains independent of siRNA sequence or chemistry (up to ∼14,000 siRNA molecules per cell), followed by metabolic degradation of the parent siRNA at 6, 24, and 48 h postdose. siRNA-GalNAc conjugates were internalized by bacteria as assessed by protection from the addition of nucleases to the culture media following uptake and by the requirement of cell lysis for detection of the siRNA. In the in vitro chromosome aberration assay, uptake was observed in Chinese hamster ovary cells (up to ∼5,500 siRNA molecules per cell at 21 h postdose) and in CD3+ human peripheral blood lymphocytes (up to ∼500 siRNA molecules per cell at 21 h postdose). In the in vivo micronucleus assay in rat bone marrow, exposure to parent siRNA was 100-350 µg of antisense strand per gram of protein at 24 and 48 h postlimit dose of 2 g/kg. Loss of terminal nucleotides was detected in bone marrow by mass spectrometry, indicating exposure to monomer metabolites as well. Negative genotoxicity results were also confirmed in an in vitro double-strand DNA break assay in HeLa and HepG2 cells where exposure was maximized using transfection reagents. Thus negative genotoxicity assay results for siRNA-GalNAc conjugates were valid and not the result of poor or no intracellular exposure.

Historical milestones and discoveries that shaped the toxicology sciences.

Knowledge of the toxic and healing properties of plants, animals, and minerals has shaped civilization for millennia. The foundations of modern toxicology are built upon the significant milestones and discoveries of serendipity and crude experimentation. Throughout the ages, toxicological science has provided information that has shaped and guided society. This chapter examines the development of the discipline of toxicology and its influence on civilization by highlighting significant milestones and discoveries related to toxicology. The examples shed light on the beginnings of toxicology, as well as examine lessons learned and re-learned. This chapter also examines how toxicology and the toxicologist have interacted with other scientific and cultural disciplines, including religion, politics, and the government. Toxicology has evolved to a true scientific discipline with its own dedicated scientists, educational institutes, sub-disciplines, professional societies, and journals. It now stands as its own entity while traversing such fields as chemistry, physiology, pharmacology, and molecular biology. We invite you to join us on a path of discovery and to offer our suggestions as to what are the most significant milestones and discoveries in toxicology. Additional information is available on the history section of Toxipedia (www.toxipedia.org).