Novel Drug Delivery System to Bone Using Acidic Oligopeptide: Pharmacokinetic Characteristics and Pharmacological Potential

Abstract

We synthesized fifteen oligopeptides consisting of Asp or Glu conjugated with a fluorescent probe, 9- fluorenylmethylchloroformate (Fmoc). In the in vitro binding assay to putative hydroxyapatite (HA), the affinities of these conjugates depended only on the number of amino acid residues, not on their optical characters (L or D) or their species (Asp or Glu). In an in vivo experiment involving a single i.v. injection of Fmoc-D-Asp oligopeptides into mice, peptides consisting of over six Asp residues were selectively distributed to the bone. Then, we synthesized estradiol-17 beta-succinate-(L-Asp)6 [E2-(L-Asp)6] and studied its pharmacokinetic characteristics and its antiosteoporotic effects on ovariectomized (OVX) mice. Although the distribution volume of E2-(L-Asp)6 was significantly smaller than that of E2, E2-(L-Asp)6 was selectively distributed in the bone after i.v. injection and gradually decreased during 7 days. E2-(L-Asp)6 effectively prevented OVX-induced bone loss, without altering the uterine weight, in the dosage range of 0.11 to 1.1 mumol/kg once a week, while E2 increased both the bone mineral density and uterine weight at 0.37 mumol/kg every third day. The results suggest that acidic oligopeptide may be useful for drug delivery to bone and E2-(L-Asp)6 is a good candidate as an anti-osteoporosis drug without the adverse side effects of E2.

Enhancement of drug delivery to bone: Characterization of human tissue-nonspecific alkaline phosphatase tagged with an acidic oligopeptide

“…The uptake level in soft tissues was less than in estradiol. Thus, estradiol with at least six residues of L-Asp was observed to prevent bone loss in ovariectomized (osteoporosis) mice without causing liver damage or increasing uterine weight [61]. Bone density improved with fewer adverse effects, suggesting that estradiol tagged with the acidic oligopeptide is a potential drug to treat a postmenopausal osteoporosis [43].…”

Therapies for the bone in mucopolysaccharidoses

“…A drug attached to HA is released during bone resorption processes and targeting a drug to HA is a potential strategy for a selective drug delivery to bone [73,74]. Kasugai et al, 2000 showed that they could enhance estradiol uptake by bone and prevent osteoporosis by tagging the hormone to Glu 6 (E6) [75,76]. We and others have recently applied this new bone-targeting system to a large molecule, an enzyme (tissue nonspecific alkaline phosphatase), showing that the tagged enzymes are delivered more efficiently to bone [77][78][79] and that the tagged enzyme improves clinical and pathological effects of a mouse model of a systemic bone disease, hypophosphatasia, better than untagged native enzyme [80].…”

Bone-Targeting of Quinolones Conjugated with an Acidic Oligopeptide

“…The 3-carboxylate and 4-carbonyl groups in quinolone are known to be responsible for potential chelating property with divalent metals such as calcium existing in bone, and these groups remain intact in NFLX-D 6 , but not in LVFX-D 6 (32). It is also known that the extension of the number of acidic amino acid increases the bone accumulating property of acidic oligopeptide in vivo (21). Thus, it was hypothesized that the intact 3-carboxylate and 4-carbonyl groups in NFLX-D 6 further augmented the affinity of L-Asp hexapeptide to bone.…”

“…To determine the binding affinity of acidic oligopeptides to hydroxyapatite, homopeptides consisting of two to ten residues of acidic amino acids were conjugated with 9-fluorenylmethylchloroformate and the binding affinities were investigated in vitro. The results indicated that the dissociation constants of the acidic oligopeptides decreased with increasing numbers of acidic amino acid residues, and the maximal binding rates reached a plateau at six residues, which were independent of acidic amino acid specie (Asp or Glu) and optical isomeric form (L or D) (21). In vivo, fluorescein-labeled L-Asp hexapeptide accumulated specifically in bone at 24 h after systemic administration in mice and was not detected in other tissues.…”