Tyr1-ψ[( Z)CF═CH]-Gly2 Fluorinated Peptidomimetic Improves Distribution and Metabolism Properties of Leu-Enkephalin

Abstract

Opioid peptides are key regulators in cellular and intercellular physiological responses, and could be therapeutically useful for modulating several pathological conditions. Unfortunately, the use of peptide-based agonists to target centrally located opioid receptors is limited by poor physicochemical (PC), distribution, metabolic, and pharmacokinetic (DMPK) properties that restrict penetration across the blood-brain barrier via passive diffusion. To address these problems, the present paper exploits fluorinated peptidomimetics to simultaneously modify PC and DMPK properties, thus facilitating entry into the central nervous system. As an initial example, the present paper exploited the Tyr¹-ψ[( Z)CF═CH]-Gly² peptidomimetic to improve PC druglike characteristics (computational), plasma and microsomal degradation, and systemic and CNS distribution of Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu). Thus, the fluoroalkene replacement transformed an instable in vitro tool compound into a stable and centrally distributed in vivo probe. In contrast, the Tyr¹-ψ[CF₃CH₂-NH]-Gly² peptidomimetic decreased stability by accelerating proteolysis at the Gly³-Phe⁴ position.

Keywords: Leu-enkephalin; Opioid peptides; fluorination; peptide CNS-distribution; peptide stability; peptidomimetics.

Figure 1. Hypothesis: FPMs Should Stabilize and Increase Distribution of Leu-Enkephalin

(HAC = Heavy Atom Count, HBD = Hydrogen-Bond Donors, HBA = Hydrogen-Bond Acceptors, TPSA = Topological Polar Surface Area, ACE = Angiotensin Converting Enzyme, AP-N = Aminopeptidase N)

Figure 2. Tyr¹-ψ[(Z)CF=CH]-Gly² Substitution Improves Plasma Stability of Leu-Enkephalin

( ) = Tyr¹-ψ[(Z)CF=CH]-Gly²-Leu-Enkephalin ( ) = Leu-Enkephalin

Figure 3. Tyr¹-ψ[(Z)CF=CH]-Gly² Substitution Improves Microsomal Stability

( ) = Tyr¹-ψ[(Z)CF=CH]-Gly²-Leu-Enkephalin, ( ) = Leu-Enkephalin, (▲) = Diphenhydramine (Mouse and Rat) or Verapamil (Human).

Figure 4. Tyr¹-ψ[CF₃CH₂–NH]-Gly² Substitution Worsens Plasma and Microsomal Stability

( ) = Leu-Enkephalin (1), ( ) = Tyr¹-ψ[(R)-CF₃CH₂–NH]-Gly²-Leu-enkephalin (3), ( ) = Tyr¹-ψ[(S)-CF₃CH₂–NH]-Gly²-Leu-enkephalin (4), (●) = Diphenhydramine

Figure 5. Tyr¹-ψ[(Z)CF=CH]-Gly²-Leu-Enkephalin Is Orally Available and Distributes into the CNS

( ) = IV 50 mg/kg Tyr¹-ψ[(Z)CF=CH]-Gly²-Leu-Enkephalin, ( ) = PO 400 mg/kg Tyr¹-ψ[(Z)CF=CH]-Gly²-Leu-Enkephalin