Antisense Oligonucleotide-Related Macrovesicular Vacuolation of Hippocampal Neurons in Nonhuman Primates. (February 2022)

• Record Type: Journal Article
• Authors: Lamb, Martin; Engelhardt, Jeffery A.; Grubor, Branka; Meier, William A.; Magee, Tom F.; Henry, Scott P.; Fikes, James D.
• Is Part Of: Toxicologic pathology. Volume 50:Number 2(2022)
• Page Start: 197
• Page End: 210
• Publication Date: 2022-02
• Subjects: antisense oligonucleotide -- neuron -- brain -- vacuolation -- processing artifact -- nonhuman primate; Pathology -- Periodicals; Toxicology -- Periodicals; Pathology; Toxicology; 615.9
• DOI: 10.1177/01926233211063831
• Languages: English
• ISSNs: 0192-6233

Abstract

2′-methoxyethyl (MOE) antisense oligonucleotides (ASOs) tested in multidose intrathecal nonhuman primate (NHP) toxicity studies have consistently revealed the presence of single large vacuoles in pyramidal neurons of the hippocampus in the absence of any cellular response. Termed "macrovesicular, " these vacuoles were characterized by immunohistochemistry and transmission electron microscopy which showed that these vacuoles are dilated lysosomes in neurons containing accumulated ASO. Additionally, two NHP studies were conducted to investigate the role of tissue fixation on their histogenesis. In Fixation Study 1, 6 doses of 5 mg 2′-MOE ASO with a full phosphorothioate backbone were administered by lumbar puncture over 5 weeks; in Fixation Study 2, 5 doses of 35 mg 2′-MOE ASO with a mixed phosphorothioate/phosphodiester backbone were administered over 12 weeks. At necropsy in each study, brain slices were either immersion fixed in neutral buffered 10% formalin or Carnoy's fixative; frozen at −80 °C; or perfusion fixed with modified Karnovsky's fixative. Fixed samples were processed to paraffin, sectioned, and stained with hematoxylin and eosin (H&E) and compared with H&E cryosections prepared from the frozen tissue of the same brain. The presence of vacuoles in fixed brain tissue but never in fresh frozen tissue showed that they arose during postmortem tissue fixation, and as such represent a processing artifact that is not relevant to human safety assessment of intrathecally administered 2′-MOE ASOs.