Antinociceptive effects after intrathecal administration of phosphodiester-, 2 '-O-allyl-, and C-5-propyne-modified antisense oligodeoxynucleotides targeting the NMDAR1 subunit in mouse

In the present study, we have compared the antinociceptive effect of three different types of antisense oligodeoxynucleotides targeting the N-methyl-D -aspartate (NMDA) R1-subunit in mice. The probes were administrated intrath ecally three times during a period of 5 days (1, 5 or 25 mug/injection), fo llowed by evaluation using the formalin test. The antinociceptive effect wa s correlated to in vitro receptor binding in spinal cord sections. The tiss ue distribution was studied after a single injection of fluorescein-conjuga ted probes. The phosphodiester probe showed superficial tissue penetration after 30 min and disappeared within 2 h. The probe did however, significant ly reduce both receptor binding in laminae I and II (by 36-44% compared to saline) as well as pain behavior (32% compared to saline), without apparent side effects. The mismatched probe was ineffective at 25 pg, while some re ductions in receptor binding and pain behavior were seen after 5 mug. The C -5-propyne-modified phosphorothioate probe showed pronounced tissue penetra tion and cellular uptake as soon as 30 min after injection which was still detectable after 24 h. Immediately after injection of the highest dose, lon g-lasting hind-limb paralysis was observed. Receptor binding was reduced bu t not in a dose-related manner. Pain behavior was significantly reduced by 40% following 25 mug of antisense probe but not after lower doses or 25 mug of mismatched probe. The 2'-O-allyl-modified probe did not significantly r educe receptor binding or pain behavior. Thus, only the phosphodiester prob e showed a significant correlation between reduction in pain behavior and r eceptor binding. These findings demonstrate that antisense technology is as sociated with specificity problems, but still could provide a valuable tool to study the role of different target proteins in the drug discovery proce ss. (C) 2001 Elsevier Science B.V. All rights reserved.