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Opioids and the apoptotic pathway in human cancer cells
Ian S Zagon1, Patricia J McLaughlin
1Department of Neuroscience and Anatomy, The Milton S. Hershey Medical Center, The Pennsylvania State University, College of Medicine, 500 University Drive, H-109, Hershey, PA 17033, USA. iszl@psu.edu
Abstract:
This study was designed to examine the role of opioids in cell survival, with an emphasis on the mechanism of opioid growth factor (OGF, [Met(5)]-enkephalin)-dependent growth inhibition. Using three human cancer cell lines: MIA PaCa-2 pancreatic adenocarcinoma, HT-29 colon adenocarcinoma, and CAL-27 squamous cell carcinoma of the head and neck, and OGF and the opioid antagonist naltrexone (NTX) at a dosage (10(-6)M) selected because it is known to repress or increase, respectively, cell replication, the effects on apoptosis (TUNEL, Annexin V) and necrosis (trypan blue) were investigated on days 2, 5, and 7 of exposure. In addition, the influence of a variety of other natural and synthetic opioids on apoptosis and necrosis was examined at a dosage of 10(-6)M. OGF, NTX, naloxone, [D-Pen(2,5)]-enkephalin, [Leu(5)]-enkephalin, dynorphin A1-8, beta-endorphin, endomorphin-1 and -2, and methadone at concentrations of 10(-6)M did not alter cell viability of any cancer cell line. Exposure of cultures to [D-Ala(2),MePhe(4),Glycol(5)]-enkephalin (DAMGO), morphine, or etorphine at 10(-6)M significantly increased the number of adherent cells positively stained for TUNEL and Annexin V, as well as the number of necrotic cells in the supernatant, from control levels at all time points studied. The effects of DAMGO, morphine, and etorphine on apoptosis/necrosis were not fully blocked by concomitant administration of naloxone. Despite the increase in cell death in some opioid-treated groups, the number of apoptotic and necrotic adherent cells, and the number of necrotic cells in the supernatant, was no more than 1-2% of the total cell population. These results indicate that the inhibitory (OGF) or stimulatory (NTX) action on cell growth in tissue culture is not due to alterations in apoptotic or necrotic pathways. Moreover, although some opioids increased cell death, and dose-effect relationships need to be established, this activity was not of great magnitude and supports the previously reported lack of growth inhibition of many of these compounds.
Insights
Opioid growth factor (OGF) and naltrexone (NTX) do not affect cancer cell death pathways. Some opioids like DAMGO, morphine, and etorphine slightly increase apoptosis and necrosis, but not significantly impacting overall cell survival.
Area of Science:
- Oncology
- Pharmacology
- Cell Biology
Background:
- Opioid peptides play diverse roles in cellular functions.
- Opioid growth factor (OGF) is known to inhibit cell growth.
- The precise mechanisms by which opioids influence cancer cell death remain incompletely understood.
Purpose of the Study:
- To investigate the role of OGF and other opioids in cancer cell survival.
- To determine if OGF-dependent growth inhibition involves apoptosis or necrosis.
- To examine the effects of various opioids on apoptosis and necrosis in human cancer cell lines.
Main Methods:
- Utilized three human cancer cell lines: MIA PaCa-2, HT-29, and CAL-27.
- Assessed apoptosis using TUNEL and Annexin V assays.
- Measured necrosis via trypan blue staining following exposure to various opioids at 10(-6)M.
Main Results:
- OGF and naltrexone (NTX) did not alter cell viability or induce apoptosis/necrosis.
- DAMGO, morphine, and etorphine significantly increased markers of apoptosis and necrosis.
- The observed increase in cell death was minimal (1-2%) and not fully reversible by naloxone.
Conclusions:
- OGF's growth inhibitory effects are not mediated by apoptosis or necrosis.
- While some opioids can induce minor cell death, this does not significantly impact overall cancer cell survival.
- Further research is needed to establish dose-effect relationships for opioid-induced cell death.