title: Reversible lipidization for the oral delivery of leu-enkephalin.
abstract: The endogenous opioid peptide leu-enkephalin (ENK) was chemically modified by a method known as reversible aqueous lipidization (REAL) with a novel amine-reacting lipophilic dimethylmaleic anhydride analog, 3,4-bis(decylthiomethyl)-2,5-furandione. The binding affinity of the product, REAL-ENK, to opioid receptors was greatly reduced. This prodrug was stable in neutral and basic phosphate buffers but underwent rapid hydrolysis under acidic conditions in the presence of 50% acetonitrile. It also showed increased stability toward enzymatic degradations in various tissue preparations. The half-lives of REAL-ENK in mouse small intestinal mucosal homogenate and liver homogenate were 12 and 80 min, representing a 12- and 32-fold increase over those of ENK itself. In contrast to ENK (t(1/2) 6.7 min), REAL-ENK was stable in mouse plasma. More importantly, REAL-ENK produced significant and sustained antinociception mediated by peripheral opioid receptors in a rodent inflammatory pain model. Pharmacokinetic studies employing a radioimmunoassay (RIA) demonstrated that significantly higher and sustained plasma peptide levels were detected up to 24 h following the oral administration of REAL-ENK in normal mice. The peak concentration and area under the curve of oral REAL-ENK were 4.4 and 21 times higher than that of oral ENK. Our results indicate that like its disulfide-based counterpart, amine-based REAL may be an enabling technology which can be applied to enhance metabolic stability, increase oral absorption, and preserve and possibly prolong the pharmacological activity of peptide drugs.
authors.affiliation: College of Pharmacy, Western University of Health Sciences, Department of Pharmaceutical Sciences, Pomona, CA 91766, USA. jwangwesternu.edu
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Wang
authors.forename: Derk J
authors.initials: DJ
authors.lastname: Hogenkamp
authors.forename: Minhtam
authors.initials: M
authors.lastname: Tran
authors.forename: Wen-Yen
authors.initials: WY
authors.lastname: Li
authors.forename: Ryan F
authors.initials: RF
authors.lastname: Yoshimura
authors.forename: Timothy B C
authors.initials: TB
authors.lastname: Johnstone
authors.forename: Wei-Chiang
authors.initials: WC
authors.lastname: Shen
authors.forename: Kelvin W
authors.initials: KW
authors.lastname: Gee
mesh_terms: D000284:Administration, Oral; D000818:Animals; D018938:Caco-2 Cells; D004743:Enkephalin, Leucine / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics; D006207:Half-Life; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism; D008055:Lipids / Q000737:chemistry*; D008099:Liver / Q000378:metabolism; D051379:Mice; D011863:Radioimmunoassay; D014018:Tissue Distribution
chemical_list: D008055:Lipids; D004743:Enkephalin, Leucine