Cebranopadol: novel dual opioid/NOP receptor agonist analgesic.

WHAT IS KNOWN AND OBJECTIVE: Chronic pain presents a difficult clinical challenge because of the limited efficacy, the limiting adverse-effect profile or the abuse potential of current analgesic options. Cebranopadol is a novel new agent in clinical trials that combines dual agonist action at opioid and nociceptin/orphanin FQ peptide (NOP) receptors. It is the first truly unique, centrally acting analgesic in several years. We here review the basic and clinical pharmacology of cebranopadol. METHODS: Published literature and Internet sources were searched to identify information related to the basic science (pharmacology and medicinal chemistry) and development (clinical trial) information on the mechanism of dual opioid and NOP receptor pharmacologic action in general, and for cebranopadol in particular. The identified sources were reviewed and the information synthesized. RESULTS: The preclinical testing of cebranopadol has characterized it as a dual opioid and NOP receptor agonist that displays antinociceptive and antihyperalgesic action in a variety of acute and chronic pain models in animals. Unlike most current traditional opioids, it is generally more potent against neuropathic than nociceptive pain. Several phase 2 clinical trials have been completed. WHAT IS NEW AND CONCLUSION: Despite the medical need, a truly novel centrally acting analgesic has not been developed in many years. Cebranopadol represents a truly novel mechanistic approach. Its actual place in pain pharmacotherapy awaits the results of phase 3 clinical trials.

Pre-clinical evaluation and efficacy studies of a melanin-binding IgM antibody labeled with 188Re against experimental human metastatic melanoma in nude mice.

PURPOSE: Currently there is no satisfactory treatment for metastatic melanoma. Radioimmunotherapy (RIT) uses the antigen-antibody interaction to deliver lethal radiation to target cells. Recently we established the feasibility of targeting melanin in tumors with 188-Rhenium ((188)Re)-labeled 6D2 mAb to melanin. Here we carried out pre-clinical development of (188)Re-6D2 to accrue information necessary for a Phase I trial in patients with metastatic melanoma. RESULTS: TCEP proved to be effective in generating a sufficient number of -SH groups on 6D2 to ensure high radiolabeling yields with (188)Re and preserved its structural integrity. (188)Re-6D2 was quickly cleared from the blood with the half-life of approximately 5 hrs and from the body--with the half-life of 10 hr. The doses of 0.5, 1.0 and 1.5 mCi significantly (p < 0.05) slowed down A2058 tumor growth in nude mice, also causing release of melanin into the extracellular space which could provide additional target for repeated treatments. Transient effects of RIT on WBC and platelet counts resolved by Day 14 post-treatment. EXPERIMENTAL DESIGN: Tris(2-Carboxyethyl) Phosphine Hydrochloride (TCEP) was evaluated as potential agent for generation of -SH groups on 6D2 mAb. TCEP-treated 6D2 mAb was radiolabeled with (188)Re and its radiochemical purity and stability was measured by ITLC and HPLC and its immunoreactivity--by melanin-binding ELISA. The pharmacokinetics, therapeutic efficacy and acute hematologic toxicity studies were performed in nude mice bearing lightly pigmented A2058 human metastatic melanoma tumors. CONCLUSIONS: We have developed radiolabeling and quality control procedures for melanin-binding (188)Re-6D2 mAb which made possible currently an on-going Phase I clinical trial in patients with metastatic melanoma.

Structure and function of the xenobiotic substrate binding site of a glutathione S-transferase as revealed by X-ray crystallographic analysis of product complexes with the diastereomers of 9-(S-glutathionyl)-10-hydroxy-9,10-dihydrophenanthrene.

The three-dimensional structures of isoenzyme 3-3 of glutathione (GSH) transferase complexed with (9R,10R)- and (9S,10S)-9-(S-glutathionyl)-10-hydroxy-9,10-dihydrophenanthrene [(9R,10R)-2 and (9S,10S)-2], which are the products of the addition of GSH to phenanthrene 9,10-oxide, have been determined at resolutions of 1.9 and 1.8 A, respectively. The structures indicate that the xenobiotic substrate binding site is a hydrophobic cavity defined by the side chains of Y6, W7, V9, and L12 from domain I (the GSH binding domain) and I111, Y115, F208, and S209 in domain II of the protein. All of these residues are located in variable-sequence regions of the primary structure of class mu isoenzymes. Three of the eight residues (V9, I111, and S209) of isoenzyme 3-3 that are in direct van der Waals contact with the dihydrophenanthrenyl portion of the products are mutated (V9I, I111A, and S209A) in the related isoenzyme 4-4. These three residues are implicated in control of the stereoselectivity of the class mu isoenzymes. The hydroxyl group of Y115 is found to be hydrogen-bonded to the 10-hydroxyl group of (9S,10S)-2, a fact suggesting that this residue could act as an electrophile to stabilize the transition state for the addition of GSH to epoxides. The Y115F mutant isoenzyme 3-3 is about 100-fold less efficient than the native enzyme in catalyzing the addition of GSH to phenanthrene 9,10-oxide and about 50-fold less efficient in the Michael addition of GSH to 4-phenyl-3-buten-2-one. The side chain of Y115 is positioned so as to act as a general-acid catalytic group for two types of reactions that would benefit from electrophilic assistance. The results are consistent with the notion that domain II, which harbors most of the variability in primary structure, plays a crucial role in defining the substrate specificity of class mu isoenzymes.

Formation of the 1-(S-glutathionyl)-2,4,6-trinitrocyclohexadienate anion at the active site of glutathione S-transferase: evidence for enzymic stabilization of sigma-complex intermediates in nucleophilic aromatic substitution reactions.

Formation of the Meisenheimer complex or sigma-complex [1-(S-glutathionyl)-2,4,6-trinitrocyclohexadienate] between glutathione (GSH) and 1,3,5-trinitrobenzene (TNB) can be observed at the active sites of isoenzymes 3-3 and 4-4 of rat liver GSH transferase. The spectroscopic properties (UV-visible and CD) of the enzyme-bound sigma-complex are consistent with a 1:1 complex in an asymmetric environment. Competitive inhibitors which occupy the GSH binding site (e.g., gamma-L-glutamyl-D,L-2-aminomalonylglycine) inhibit sigma-complex formation. The apparent formation constants of the sigma-complex (M) with enzyme-bound GSH (E.GS- + TNB in equilibrium E.M) at pH 7.5 are 5 x 10(4) M-1 and 7 x 10(2) M-1 for isoenzymes 3-3 and 4-4, respectively. Both values are much greater than that in aqueous solution (GS- + TNB in equilibrium M), where Kf = 28 M-1. Isoenzyme 3-3 is roughly an order of magnitude more efficient than 4-4 in catalyzing nucleophilic aromatic substitutions, a fact that appears to correlate with the ability of each enzyme to stabilize the sigma-complex. The pH dependence of Kf(app) for isoenzyme 3-3 is used to probe the ionization behavior of enzyme-bound GSH. The results are consistent with a double-ionization scheme (e.g., H+E.GSH in equilibrium H+E.GS- in equilibrium E.GS-) with pK's of 5.7 and 7.6, which are assigned to the thiol pK and the pK of a protonated base in the active site, respectively. Formation of the sigma-complex is also observed in single crystals of isoenzyme 3-3, providing a clear demonstration of the chemical competence of the crystallized enzyme. The results are discussed with respect to catalytic efficiency and the ability of the enzyme to stabilize sigma-complex intermediates in nucleophilic aromatic substitution reactions.

Crystallization and a preliminary X-ray diffraction study of isozyme 3-3 of glutathione S-transferase from rat liver.

Crystals of the homodimeric isozyme 3-3 of glutathione S-transferase from rat liver have been obtained with the hanging drop method of vapor diffusion from ammonium sulfate solutions. The successful crystallization of the enzyme required the presence of both the enzyme inhibitor (9R, 10R)-9, 10-dihydro-9-(S-glutathionyl)-10-hydroxyphenanthrene and the detergent beta-octylglucopyranoside. The crystals belong to the monoclinic space group C2, with cell dimensions of a = 88.24(8) A, b = 69.44(4) A, c = 81.28(5) A, beta = 106.01(6) degrees, and contain four dimeric enzyme molecules per unit cell. The crystals diffract to at least 2.2 A and are suitable for X-ray crystallographic structure determination at high resolution.