Abstract
The analgesic potency of morphine-6-glucuronide (M6G) has been shown to be 50-fold higher than morphine after intracerebral injection. However, the brain penetration of M6G is significantly lower than morphine, thus limiting its usefulness in pain management. Here, we created new entities by the conjugation of the Angiopep-2 peptide (An2) that crosses the blood-brain-barrier (BBB) by LRP1 receptor-mediated transcytosis, with either morphine or M6G. We demonstrated improvement of BBB permeability of these new entities compared with that of unconjugated M6G and morphine. Intravenous or subcutaneous administration of the An2-M6G conjugate exerted greater and more sustained analgesic activity than equivalent doses of either morphine or M6G. Likewise, subcutaneous An2-morphine induced a delayed but prolonged antinociceptive effect. The effects of these conjugates on the gastrointestinal tract motility were also evaluated. An2-morphine significantly reduced the intestinal transit time while An2-M6G exhibited a reduced constipation profile, as compared to morphine. In summary, we have developed new brain-penetrant opioid conjugates exhibiting improved analgesia to side-effect ratios. These results thus support the use of An2 carrier peptides as an innovative BBB targeting technology to deliver effective drugs such as M6G for the pain management.
SIGNIFICANCE STATEMENT The metabolite M6G does not cross efficiently the blood-brain barrier. The LRP1 peptide ligand Angiopep-2 may serve as an effective drug delivery system to the brain. Here, we demonstrated that the coupling of M6G to An2 improves its brain penetration and significantly increases its analgesic potency. The An2-M6G conjugate has a favorable side-effect profile that includes reduction of developing constipation. An2-M6G exhibits a unique pharmacodynamic profile with a better therapeutic window than morphine.
- The American Society for Pharmacology and Experimental Therapeutics
