Design,Synthesis And Pharmacological Studies Of Dendritic Opioid Peptide Analogues

Opioid drugs have been widely used for the relief of pain as clinical analgesics,however unintended side effects,including constipation and the development of tolerance usually associated with their use,which constrained the clinical use of opioid analgesics.Therefore,design of novel opioid analogues have important significance.Endomorphin-2(EM-2)and Biphalin as efficient opioid receptor agonists,have been extensive studied.The present study was conducted to design and sysnthesis two types of new opioid peptides analogues of dendritic modification:(1)The dendritic peptides EKP and BKP were acylated EM-2 and Biphalin analogues,where palmitic acid was covalently attached to the pharmacophore of EM-2 or Biphalin.Such modification was made to enhance proteolytic stability while retaining or increasing biological activity.(2)On the basis of that NPFF receptor antagonist RF9 completely prevents the development of opioid tolerance when coinjected with heroin,we have designed two dendritic peptide EKR and RKE,where both opioid and RF9 pharmacophores were fused.Such bifunctional compounds were expected to induce potent antinociception with lower side effects.The above four opioid peptides analogues were synthesized by manual solid-phase synthesis.In vitro agonist activities of these peptides were firstly characterized in c AMP functional assay.Furthermore,the antinociceptive profiles of these compounds and their related CNS side effects were also evaluated in vivo.The pharmacological roles of the dendritic peptides EKP and BKP were evaluated by the in vitro and in vivo activity assays.In vitro c AMP assays suggested that EKP and BKP acted as agonists at κ-opioid receptor.Both EKP and BKP exhibit potent antinociceptive effects in the mouse tail-flick,formalin-induced paw licking,the acetic acid-induced writhing and carrageenan induced inflammation assay after intracerebroventricular(i.c.v.)administration.To characterize the biological activity of the dendritic peptides EKR and RKE,in vitro c AMP functional assays and in vivo tail-flick assay were conducted.Our results showed that: In in vitro c AMP assay,EKR and RKE functioned as agonists of μ-opioid receptor.In the tail-flick test,intracerebroventricularly(i.c.v.)injection of EKR and RKE produced significant antinociception,which were blocked by μ-opioid receptor selective antagonist.Most importantly,i.c.v.administration of high-dose EKR and RKE attenuated tolerance during 8 days,compared with Morphin.Moreover,supraspinal administration of EKR and RKE had no inhibitory effect on gastrointestinal motility.Taken together,the dendritic peptides EKR and RKE produced a potent antinociception with limited side effects.