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Endogenous opioid systems regulate growth of neural tumor cells in culture
1Department of Anatomy, M.S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
Abstract:
Endogenous opioid systems (i.e., opioids and opioid receptors) play a role in neural cancer. Using a tissue culture system of S20Y murine neuroblastoma to assess the effects of opioids on growth, [Met5]-enkephalin was the most potent compound to influence cell replication. With a median effective concentration of 10(-10) M, this peptide inhibited cell proliferation in a stereospecific and naloxone-reversible manner. [Met5]-Enkephalin depressed both DNA synthesis and mitosis. [Met5]-Enkephalin was detected in neuroblastoma cells by radioimmunoassay, and was found to increase in concentration in culture media over time, suggesting that these cells produced the peptide. Immunocytochemistry showed [Met5]-enkephalin-like activity in the cortical cytoplasm, but not the cell nucleus, of neuroblastoma cells. Binding of [3H]-[Met5]-enkephalin specific and saturable, and Scatchard analysis yielded a Kd of 1.2 +/- 0.1 nM and a binding capacity of 50.2 +/- 4.3 fmol/mg protein. [Met5]-Enkephalin also depressed the growth of N115 murine neuroblastoma, SK-N-MC human neuroblastoma, and HT-1080 human fibrosarcoma. These results indicate that [Met5]-enkephalin, a naturally occurring pentapeptide that is derived from proenkephalin A, is a potent inhibitor of cell growth. Since cancer cells produce [Met5]-enkephalin, and contain a binding site to this ligand, endogenous opioid systems appear to control cell proliferation by an autocrine mechanism.
Insights
[Met5]-enkephalin, a naturally occurring peptide, potently inhibits cancer cell growth by acting on endogenous opioid systems. Neuroblastoma cells produce and respond to this peptide, suggesting an autocrine control mechanism for cell proliferation.
Area of Science:
- Neuroscience
- Cancer Biology
- Endocrinology
Background:
- Endogenous opioid systems, including opioids and their receptors, are implicated in neural cancer.
- Understanding the role of these systems in cancer cell proliferation is crucial for developing novel therapeutic strategies.
Purpose of the Study:
- To investigate the effects of endogenous opioids on neuroblastoma cell growth using a tissue culture system.
- To identify specific opioid peptides that influence cancer cell replication and elucidate their mechanism of action.
Main Methods:
- Utilized S20Y murine neuroblastoma cell cultures to assess opioid effects on cell growth.
- Employed radioimmunoassay and immunocytochemistry to detect and localize [Met5]-enkephalin.
- Performed binding assays with [3H]-[Met5]-enkephalin to characterize receptor interactions.
- Tested the effects of [Met5]-enkephalin on various cancer cell lines, including murine neuroblastoma, human neuroblastoma, and human fibrosarcoma.
Main Results:
- [Met5]-enkephalin demonstrated potent inhibition of cell proliferation at a median effective concentration of 10(-10) M.
- This inhibition was stereospecific and reversible by naloxone, affecting DNA synthesis and mitosis.
- [Met5]-enkephalin was detected within neuroblastoma cells and increased in culture media, indicating endogenous production.
- Specific and saturable binding sites for [Met5]-enkephalin were identified in cancer cells.
- [Met5]-enkephalin also inhibited the growth of other neuroblastoma and fibrosarcoma cell lines.
Conclusions:
- [Met5]-enkephalin, a naturally occurring pentapeptide, acts as a potent inhibitor of cancer cell growth.
- Cancer cells produce [Met5]-enkephalin and possess binding sites for it, suggesting an autocrine mechanism controlling proliferation via endogenous opioid systems.