Transient acute neuronal activation response caused by high concentrations of oligonucleotides in the cerebral spinal fluid

Oligonucleotide (ON) therapeutics are promising as disease-modifying therapies for central nervous system (CNS) disorders. Intrathecal ON administration into the cerebral spinal fluid is a safe and effective delivery mode to the CNS. However, preclinical studies have shown acute and transient changes in neurobehavior following high-dose central ON delivery. Here, we characterize a subset of these changes peaking 15 min after ON dosing and resolving after 120 min. Symptoms include shaking, muscle twitching, cramping, hyperactivity, hyperreactivity, vocalizations, tremors, convulsions, and seizures. These are collectively referred to as the acute neuronal activation response. Acute neuronal activation is observed in rats, mice, and nonhuman primates and is quantifiable using a simple scoring system. It is distinct from acute inhibition seen with some phosphorothioate-modified antisense oligonucleotides, characterized by loss of spinal reflexes, ataxia, and sedation. The acute neuronal activation response is largely sequence-independent and is driven by ON chelation of divalent cations, particularly influenced by the divalent cation-to-ON ratio in the dosing solution. Acute neuronal activation can be safely mitigated by adjusting this ratio through magnesium supplementation in the ON formulation. We provide a comprehensive framework for quantifying and mitigating the acute neuronal activation response caused by high concentrations of centrally delivered ON therapeutics in preclinical species.