enkephalin--ala(2)-mephe(4)-gly(5)- and carfentanil

In this work, we studied a series of carfentanyl amide-based opioid derivatives targeting the mu opioid receptor (μOR) and the delta opioid receptor (δOR) heteromer as a credible novel target in pain management therapy. We identified a lead compound named

Topics: Analgesics; Animals; Cell Line; Fentanyl; Humans; Male; Mice; Mice, 129 Strain; Mice, Inbred C57BL; Mice, Knockout; Pain Measurement; Rats; Rats, Long-Evans; Receptors, Opioid, delta

Fentanyl and its derivatives are considered among the most potent opiate analgesic/euphoriants. The pharmacological literature generally supports a mu opiate receptor site of action for the fentanyl derivatives, but some observations suggest that other sites of action may be involved in producing the extremely potent fentanyl effects. In order to investigate the mechanism of action of fentanyl-like drugs further, [3H]carfentanil was used as a radioligand to image high-affinity carfentanil binding sites in slidemounted sections of the rat brain (receptor autoradiography). In parallel studies the prototypical mu opiate agonist radioligand [3H]DAMGO ([D-Ala2-MePhe4-Gly-ol5]enkephalin) was also used. The working hypothesis was that if carfentanil was acting through another high-affinity site besides the mu opiate receptor, the distribution pattern of the autoradiographic image produced by [3H]carfentanil should be significantly different than the autoradiographic pattern displayed by the well-characterized and selective mu opiate [3H]DAMGO. Thirty-five brain regions were examined for specific [3H]carfentanil and [3H]DAMGO binding. The absolute and relative densities of the sites were essentially identical. The highest levels of binding were observed in the "patch" areas of the striatum (131 +/- 5 fmol/mg T.E. for [3H]carfentanil; 162 +/- 13 fmol/mg T.E. for [3H]DAMGO). The lowest levels were observed in the cerebellum where no specific binding of either radioligand was observed. The overall distribution pattern of the two radioligands produced a correlation coefficient of 0.95; the distribution pattern was prototypical for the mu opiate receptor as reported previously by other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Autoradiography; Brain; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Fentanyl; Guanosine 5'-O-(3-Thiotriphosphate); Rats; Rats, Sprague-Dawley; Receptors, Opioid, mu; Tissue Distribution; Tritium

SH-SY5Y (human neuroblastoma) cultured cells, known to have mu-opioid receptors, have been used to assess and compare the ability of eight representative mu-selective compounds from diverse opioid families to recognize and activate these receptors. A wide range of receptor affinities spanning a factor of 10,000 was found between the highest affinity fentanyl analogs (Ki = 0.1nM) and the lowest affinity analog, meperidine (Ki = 1 microM). A similar range was found for inhibition of PGE1-stimulated cAMP accumulation with a rank order of activities that closely paralleled binding affinities. Maximum inhibition of cAMP accumulation by each compound was about 80%. Maximum stimulation of GTPase activity (approximately 50%) was also similar for all compounds except the lowest affinity meperidine. Both effects were naloxone reversible. These results provide further evidence that mu-receptors are coupled to inhibition of adenylate cyclase and that the SH-SY5Y cell line is a good system for assessment of mu-agonists functional responses.

Topics: Alprostadil; Analgesics; Cyclic AMP; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Fentanyl; GTP Phosphohydrolases; Humans; Meperidine; Morphinans; Naloxone; Narcotics; Oxymorphone; Receptors, Opioid; Receptors, Opioid, mu; Tumor Cells, Cultured