THE GP-130 FAMILY CYTOKINES IL-6, LIF AND OSM BUT NOT IL-11 CAN REVERSE THE ANTIPROLIFERATIVE EFFECT OF DEXAMETHASONE ON HUMAN MYELOMA CELLS

In order to understand the mechanisms supporting steroid escape in pat ients with multiple myeloma (MM), three IL-6 autocrine human myeloma c ell lines, LP1, OPM2 and L363, have been treated with dexamethasone in the presence or absence of cytokines belonging to the gp 130 family: IL-6, LIF, OSM and IL-11, With pharmacological doses of dexamethasone, a dramatic growth arrest was observed in all the cell lines. IL-6 com pletely reversed this inhibition. Of note, this IL-6 induced reversion was still seen with very low amounts of IL-6 (12 pg/ml), Finally, whe reas LIF and OSM had clear growth-promoting effects on OPM2 only, both cytokines (but not IL-11) reversed the dexamethasone-induced growth a rrest in all the cell lines. Therefore the high levels of IL-6 (ng/ml) observed in the MM intermediate milieu and the putative presence of L IF and OSM can easily counteract the effects of dexamethasone in vivo.