TAMOXIFEN, 17-BETA-ESTRADIOL AND THE CALMODULIN ANTAGONIST J8 INHIBITHUMAN-MELANOMA CELL INVASION THROUGH FIBRONECTIN

Invasion through stromal extracellular matrix (ECM) is part of the com plex, multistep process of tumour cell invasion and metastasis. Our gr oup has previously demonstrated that calcium and calmodulin are import ant in another step in the metastatic cascade that of attachment of ce lls to ECM. Interestingly, the non-steroidal anti-oestrogen tamoxifen (which also has calmodulin antagonist activity), used in the treatment of breast cancer and now in metastatic cutaneous melanoma, can inhibi t the attachment of normal and neoplastic cells to ECM. In this study, we investigated whether such drugs, known to inhibit cell attachment, could also subsequently reduce their invasion through a layer of huma n fibronectin. We examined the ability of the specific calmodulin anta gonist J8, tamoxifen and its two major metabolites, N-desmethyltamoxif en (N-des) and 4-hydroxytamoxifen (4-OH), as well as the pure anti-oes trogen ICI 182,780 and 17 beta-oestradiol to inhibit invasion of the h uman cutaneous melanoma cell line, A375-SM, uveal melanoma cells and u veal melanocytes. A375-SM cells and uveal melanoma cells showed a high level of invasion (15.2% and 33.7% respectively) compared with melano cytes (around 5%) under the experimental conditions used. Submicromola r concentrations of N-des, tamoxifen, J8 and 17 beta-oestradiol signif icantly reduced the invasiveness of the A375-SM cell line. The uveal m elanoma cells also showed similar inhibition, although at higher conce ntrations of these agents. 4-OH and ICI 182, 780 had little or no effe ct on invasion of A375-SM cells (these were not tested on uveal melano ma cells). All cells used in this study were found to be negative for type nuclear oestrogen receptors, reinforcing the possibility that tam oxifen and 17 beta-oestradiol can act via mechanisms unrelated to bind ing to classical oestrogen receptors to inhibit tumour cell invasion.