Irreversible labelling of the opioid receptors by a melphalan-substituted [Met5]enkephalin-Arg-Phe derivative

Peptidomimetics and Their Applications for Opioid Peptide Drug Discovery

Despite various advantages, opioid peptides have been limited in their therapeutic uses due to the main drawbacks in metabolic stability, blood-brain barrier permeability, and bioavailability. Therefore, extensive studies have focused on overcoming the problems and optimizing the therapeutic potential. Currently, numerous peptide-based drugs are being marketed thanks to new synthetic strategies for optimizing metabolism and alternative routes of administration. This tutorial review briefly introduces the history and role of natural opioid peptides and highlights the key findings on their structure-activity relationships for the opioid receptors. It discusses details on opioid peptidomimetics applied to develop therapeutic candidates for the treatment of pain from the pharmacological and structural points of view. The main focus is the current status of various mimetic tools and the successful applications summarized in tables and figures.

Preparation, characterization, and in vitro efficacy of O-carboxymethyl chitosan conjugate of melphalan

A series of melphalan-O-carboxymethyl chitosan (Mel-OCM-chitosan) conjugates with different spacers were prepared and structurally characterized. All conjugates showed satisfactory water-solubility (160-217 times of Mel solubility). In vitro drug release behaviors by both chemical and enzymatic hydrolysis were investigated. The prodrugs released Mel rapidly within papain and lysosomal enzymes of about 40-75%, while released only about 4-5% in buffer and plasma, which suggested that the conjugates have good plasma stability and the hydrolysis in both papain and lysosomes occurs mostly via enzymolysis. It was found that the spacers have important effect on the drug content, water solubility, drug release properties and cytotoxicity of Mel-OCM-chitosan conjugates. Cytotoxicity studies by MTT assay demonstrated that these conjugates had 52-70% of cytotoxicity against RPMI8226 cells in vitro as compared with free Mel, indicating the conjugates did not lose anti-cancer activity of Mel. Overall these studies indicated Mel-OCM-chitosan conjugates as potential prodrugs for cancer treatment.

Josef Rudinger Memorial Lecture 2002. The chemistry of the opioid receptor binding sites

Since the discovery of the opioid receptors and their endogenous ligands an immense research work has been devoted to the exploration of their specificity, the mechanism of ligand binding and ligand-receptor interactions. One of the main goals has been the location and characterization of the binding sites. The present review compiles the results achieved in this field in the last quarter of a century, and puts some questions concerning the success of these efforts.