Preclinical indication for subcutaneously delivered interleukin-1 receptor antagonist in stroke: pharmacokinetics, penetration and protection.

Andrew Greenhalgh, James Galea, Pippa Tyrrell, Nancy Rothwell. University of Manchester, Manchester, United Kingdom.

Interleukin-1 (IL-1) is a pro-inflammatory cytokine that has been suggested as a key mediator of neuronal death in cerebral ischaemia. IL-1’s naturally occurring antagonist, interleukin-1 receptor antagonist (IL-1RA), is neuroprotective in many experimental models of cerebral ischaemia. Brain penetration of IL-1RA might be expected to be limited due to the fact it is a large (17 KDa), hydrophilic protein. However, repeated high doses of IL-1RA, administered subcutaneously (SC), have been shown to be neuroprotective in rodents and intravenous delivery of IL-1RA leads to high cerebrospinal fluid (CSF) concentrations in subarachnoid haemorrhage patients.

The aim of this study was to investigate the pharmacokinetics, brain tissue penetration and neuroprotective effects of IL-1RA after a single SC administration in the rat. Focal cerebral ischaemia was induced in SD rats by transient (90 min) middle cerebral artery occlusion (MCAo). IL-1RA was administered to naïve or MCAo animals at occlusion (single SC dose of 100 mg/kg).

After injection of IL-1RA in naïve animals, concentrations in plasma increased rapidly to 10350ng/ml (± 2940ng/ml) in 15 min and were sustained above this level until 8 h (9530 ± 630 ng/ml). CSF concentrations increased more slowly to 100 ng/ml (± 65ng/mL) at 1 h, and were maintained at a mean concentration of 170 ng/mL (± 50 ng/mL) between 1 and 8 h. The pharmacokinetic profile of MCAo animals did not differ significantly from naive animals. Immunohistochemistry with a specific antibody directed against IL-1RA revealed extensive parenchymal penetration of IL-1RA only following blood brain barrier breakdown in stroke and not in naïve animals. This dose also reduced infarct volume by 33% compared to placebo treated animals.

Ultimately, these results suggest drug concentration in CSF is not predictive of its brain penetration. Moreover they indicate IL-1RA is a potential candidate for clinical development since it reaches the brain, via a dosing regime that is practical in the clinic.