Opioids and migration, chemotaxis, invasion, and adhesion of human cancer cells

This study was designed to examine the role of opioids on cell migration, chemotaxis, invasion, and adhesion, with an emphasis on whether the opioid growth factor (OGF, [Met⁵]-enkephalin) or the opioid antagonist naltrexone (NTX) impacts any or all of these processes. Drug concentrations of OGF and NTX known to depress or stimulate, respectively, cell proliferation and growth were analyzed. Three different human cancers (pancreatic, colon, and squamous cell carcinoma of the head and neck), represented by seven different cancer cell lines (PANC-1, MIA PaCa-2, BxPC-3, CAL-27, SCC-1, HCT-116, and HT-29), were evaluated. In addition, the influence of a variety of other natural and synthetic opioids on cell motility, invasion, and adhesion was assessed. Positive and negative controls were included for comparison. OGF and NTX at concentrations of 10^-4 to 10^-6 M, and dynorphin A1-8, β-endorphin, endomorphin-1, endomorphin-2, leucine enkephalin, [D-Pen^2,5]-enkephalin (DPDPE), [D-Ala², MePhe⁴, Glycol⁵]-enkephalin (DAMGO), morphine, and U69,593 at concentrations of 10^-6 M, did not alter cell migration, chemotaxis, or invasion of any cancer cell line. OGF and NTX at a concentration of 10^-6 M, and incubation for 24 or 72 h, did not change adhesion of these cancer cells to collagen I, collagen IV, fibronectin, laminin, or vitronectin. Moreover, all other opioids tested at 10^-6 M concentrations and for 24 h had no effect on adhesion. These results indicate that the inhibitory or stimulatory actions of OGF and NTX, respectively, on cell replication and growth are independent of cell migration, chemotaxis, invasion, and adhesive properties. Moreover, a variety of other exogenous and endogenous opioids, many specific for the μ, δ, or κ opioid receptors, also did not alter these biological processes, consonant with previous observations of a lack of effects of these compounds and their receptors on the biology of cancer cells.