Kappa-opioid receptor binding varies inversely with tumor grade in human gliomas.

BACKGROUND: Opioid agonists can inhibit cell proliferation in various neural tumor cell lines, including rat gliomas. Because opioid antimitogenic effects are mediated by opioid receptors, it was of interest to the authors to determine opioid receptor levels in human brain tumors. METHODS: Specimens obtained at craniotomy from 30 patients with glioma and nonneoplastic brain disorders were evaluated for their kappa-opioid receptor binding. Kd and Bmax values were estimated from homologous competition binding curves with the kappa1-selective radioligand [3H]U69,593. RESULTS: Receptor binding density was greatest in nonneoplastic brain tissue, less in Grade 2 and 3 astrocytoma, and least in glioblastoma multiforme. CONCLUSIONS: These results suggest that opioid receptor-based stratification of grade may have clinical utility in distinguishing glioblastoma multiforme from lower grade astrocytomas, and thereby may facilitate diagnosis and treatment.

Overexpression of sigma receptors in nonneural human tumors.

Previous data indicated that opioid receptors occur in both neural and nonneural human tumors. However, it has recently been shown that some of the putative opioid binding may be attributable to sigma sites. In this study the occurrence of sigma and opioid receptors in nonneural human tumors was assessed. The neoplasms included renal and colon carcinomas and a sarcoma. [3H]1,3-di-o-tolylguanidine was used to assay sigma receptors by homologous competition binding assays, which when analyzed provided dissociation constant and receptor density values. Opioid binding was measured with [3H]-(-)-ethylketocyclazocine, a ligand which interacts with mu, delta, and kappa subtypes. Fresh surgical specimens were obtained from 9 human neoplasms, selected for their large size, and compared with nonmalignant tissues. All 9 tumors contained sigma sites, and dissociation constant values were within the range of 27-83 nM. Occasionally, two-site fit the data better than one-site binding, suggesting the presence of multiple sigma sites. Opioid binding was not detected. Intratumoral variability was evaluated by sampling several locations on the periphery of the mass and one in the center. Each of the samples was bisected, with a portion reserved for histological examination to correlate morphological features with receptor data. Changes in sigma binding were not associated with the extent of fibrosis, viability, or necrosis. Receptor density values displayed moderate intra- and intertumoral variation (coefficients of variation, 8-39 and 27-49%, respectively). More important, sigma binding in tumors was found to be greater than or equal to 2-fold higher than that of control nonmalignant tissue.

Sigma and opioid receptors in human brain tumors.

Human brain tumors (obtained as surgical specimens) and nude mouse-borne human neuroblastomas and gliomas were analyzed for sigma and opioid receptor content. Sigma binding was assessed using [3H]1,3-di-o-tolylguanidine (DTG), whereas opoid receptor subtypes were measured with tritiated forms of the following: mu, [D-ala2,mePhe4,gly-ol5]enkephalin (DAMGE); kappa, ethylketocyclazocine (EKC) or U69,593; delta, [D-pen2,D-pen5]enkephalin (DPDPE) or [D-ala2,D-leu5]enkephalin (DADLE) with mu suppressor present. Binding parameters were estimated by homologous displacement assays followed by analysis using the LIGAND program. Sigma binding was detected in 15 of 16 tumors examined with very high levels (pmol/mg protein) found in a brain metastasis from an adenocarcinoma of lung and a human neuroblastoma (SK-N-MC) passaged in nude mice. kappa opioid receptor binding was detected in 4 of 4 glioblastoma multiforme specimens and 2 of 2 human astrocytoma cell lines tested but not in the other brain tumors analyzed.