Direct effects of delta opioid receptor agonists on invasion-associated activities of HCT-8/E11 colon cancer cells.

BACKGROUND

Opioids and opioid receptors are an integral part of the tumour microenvironment and hence may influence tumour progression. Studies on direct effects of opioids on invasion-associated cellular activities are equivocal. We wanted to clarify these differences.

MATERIALS AND

METHODS

The direct effects of the delta opioid receptor (DOR) agonists [D-Pen(2), D-Pen(5)]-enkephalin (DPDPE), leu-enkephalin and [D-Ala(2), D-Leu(5)]-enkephalin (DADLE) on invasion-associated activities of HCT-8 myc-DOR and HCT-8 FLAG-DOR colon cancer cells stably overexpressing DOR were studied.

RESULTS

The opioids showed a trend to stimulate invasion of single cells in collagen in one clone, while they did not influence invasion of the other clone. In other invasion assays, no effects were observed. They did not affect cell growth and homotypical cell-cell adhesion. DPDPE at 0.1 muM inhibited directional migration; the other opioids and concentrations tested were inefficient.

CONCLUSION

Opioids differently influence invasion-associated cellular activities, depending on the expression level of DOR, experimental set-up, type and concentration of opioid.