Investigation of Intrathecal Injection Method and Animal Parameters with the Aim of Improving Drug Delivery to the Cisterna Magna in Cynomolgus Monkeys

Abstract

Intrathecal (IT) injection allows drug delivery to the central nervous system circumventing the blood-brain barrier; however, before refining our method in cynomolgus monkeys, we observed marked differences in cerebrospinal fluid (CSF) drug concentrations between animals, despite no difference in plasma drug concentration. Insufficient drug delivery to the cisterna magna (CM) in some animals is also reported in the literature. In light of this, we refined our lumbar IT injection method based on previous researches, and identified conditions that can suppress differences in CM CSF drug concentration between individuals. Lumbar IT injection of 4.2 mg/mL dye (Evans blue) solution at 2.4mL/body and 2 mL/min was performed in 12 anesthetized monkeys [age: 3 to 6 years, body weight (BW): 2.4 to 7.0 kg]. CM CSF was collected 1 hour after injection, and absorbance at 620 nm was measured to obtain CSF dye concentration. In addition, 3 monkeys received a 2nd injection after a 1-week recovery period to verify the reproducibility of the experiment results. CSF dye concentrations showed above 10000 ng/mL in 9 monkeys; 2 monkeys 5000 ng/mL and 1 monkey 150 ng/mL. When classified by BW, dye delivery to the CM was favorable in lower BW monkeys, whereas CSF dye concentration decreased in higher BW monkeys. The reproducibility of the results was confirmed in the 2nd IT injection in 3 monkeys. These results imply that, incorporating the animal BW parameter in our refined method can suppress differences in CM CSF drug concentration.