Direct Delivery Of Oligonucleotide Drugs To The CNS And Common Histopathological Changes - Prisys Events

Understanding the pathological mechanisms of CNS diseases, overcoming the obstacles posed by the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier, and translating preclinical animal model data into clinical success are critical challenges in CNS drug development. The high molecular weight of antisense oligonucleotides (ASOs) hinders their diffusion across the BBB to achieve effective concentrations in the CNS. Studies have shown that less than 1% of ASOs enter the brain following systemic administration.

CNS drug delivery

Main Methods of Direct CNS Delivery for ASOs

To successfully deliver ASOs across the BBB into the CNS, special strategies are necessary. The primary methods of direct CNS delivery include systemic administration, intranasal administration, intracerebroventricular injection, and intrathecal injection (Figure 1). Among these, intrathecal and intracerebroventricular injections are the mainstream clinical routes for ASO delivery into the CNS. These methods allow rapid elevation of drug concentration in the cerebrospinal fluid (CSF) without the need for large doses, maintaining high concentrations within the CNS while minimizing systemic exposure and potential toxicity.

Intrathecal Injection

Intrathecal injection involves directly administering the drug into the subarachnoid space of the spinal cord, allowing the medication to diffuse throughout the cerebrospinal fluid (CSF) and reach the entire ventricular system. This method bypasses the blood-brain barrier (BBB), facilitating the delivery of high concentrations of therapeutic agents to the central nervous system (CNS) while minimizing systemic exposure and potential side effects. Intrathecal injection is particularly advantageous for delivering antisense oligonucleotides (ASOs) because it does not require penetration through the cortical tissues, thereby reducing the risk of local damage. This method is preferred over repetitive intracerebroventricular injections in larger animals like rats and macaques due to its clinical relevance, reduced potential for cortical damage, and ease of repeated administration, making it a preferred method for chronic conditions that necessitate multiple doses.

Intracerebroventricular Injection

Intracerebroventricular (ICV) injection involves administering drugs directly into the brain's ventricular system, ensuring direct delivery to the CNS. This method is particularly useful for small animal models, like mice, where the spinal cord and lumbar cistern are too small for reliable intrathecal administration. ICV injections facilitate the delivery of therapeutic agents across the ependymal cell layer into the brain parenchyma, enabling effective treatment of neurological disorders. However, this method is generally avoided in repetitive dosing due to the high surgical risks and potential for adverse effects such as meningeal adhesions, fibrosis, foreign body reactions, and hemorrhage. Despite these challenges, ICV injection remains a valuable technique in preclinical studies and is instrumental in advancing our understanding of CNS drug delivery mechanisms.

Histopathological Changes from Direct CNS Delivery

Direct CNS delivery methods can lead to local histopathological changes, making it challenging to distinguish between changes caused by the delivery procedure and those caused by the test article itself. Common findings include mild mononuclear or mixed cell infiltration, parenchymal or meningeal hemorrhage, neurofiber degeneration, gliosis, and connective tissue fibrosis at injection sites.

In non-human primates (NHPs), intrathecal injection studies often show leukocyte infiltration in the meninges, choroid plexus, neural parenchyma, and perivascular spaces, along with gliosis and hemorrhage. Similarly, dorsal root ganglia (DRG) and related nerve roots can exhibit autophagy, mononuclear cell infiltration, and calcification.

Conclusion

With the advancement of oligonucleotide drug development, CNS delivery methods have become increasingly important. Safety evaluations pose significant challenges due to the potential overlap between procedure-related and test article-related histopathological changes. Comprehensive toxicity assessments require careful examination of the lesions, considering the nature, incidence, and severity of the changes alongside information about the test article.

For researchers and developers focusing on intracerebroventricular administration of ASOs, understanding these complexities is crucial for advancing the field and ensuring the safe and effective delivery of CNS therapies.

By leveraging advanced direct delivery techniques and thorough histopathological evaluations, the potential for successful CNS drug development increases, paving the way for innovative treatments for neurological disorders.

About Prisys

Prisys is a leading preclinical research organization specializing in pharmacology and efficacy studies in non-human primates (NHPs). With extensive experience in the field, Prisys has efficiently conducted numerous nonclinical studies on CNS delivery of antisense oligonucleotide (ASO) drugs and other novel therapeutic modalities. Their expertise in direct CNS delivery techniques, including intrathecal and intracerebroventricular injections, has been instrumental in advancing the development of new treatments for neurological disorders. Prisys's commitment to high-quality research and precise execution ensures reliable and reproducible results, contributing significantly to the safety evaluation and therapeutic potential of innovative CNS-targeted drugs.