ANTIESTROGENS INDUCE APOPTOSIS OF MULTIPLE-MYELOMA CELLS

Previous studies have suggested that multiple myeloma (MM) cells expre ss estrogen receptors (ER). In the present study, we characterized the effects of estrogen agonists and antagonists (anti-estrogens [AE]) on growth of MM cell lines and MM patient cells. In addition to antagoni zing estrogen binding to ER, AE can trigger apoptosis. Hence, we also determined whether estrogens or AE altered MM cell survival. Immunoblo tting showed that ER-a is expressed in 4 of 5 MM cell lines (ARH-77, R PMI 8226, S6B45, and U266, but not OCl-My-5 cells), as well as in fres hly isolated MM cells from 3 of 3 patients. 17 beta-estradiol (E2) did not significantly alter proliferation of MM cell lines or MM patient cells. In contrast, two structurally distinct AE, tamoxifen (TAM) and ICI 182,780 (ICI), significantly inhibited the proliferation of all 5 MM cell lines and MM cells from 2 of 2 patients (IC50, 2 to 4 mu mol/L ). Proliferation of these cell lines was also inhibited by the hydroxy lated TAM derivative, 4-hydroxytamoxifen (4HTAM), although this deriva tive was less potent than TAM (IC50, 3 to 25 mu mol/L). In contrast, t he dehalogenated TAM derivative toremifene (TOR) did not inhibit MM ce ll proliferation. We next examined the effects of these agents on MM c ell survival. TAM, ICI, and, to a lesser extent; 4HTAM and TOR trigger ed apoptosis in both ER-alpha-positive as well as ER-alpha-negative MM cell lines and patient MM cells, evidenced both by fluorescence-activ ated cell sorting (FACS) analysis using propidium iodide staining and the TUNEL assay. TAM-induced growth inhibition and apoptosis of ER-alp ha-positive S6B45 NIM cells was not blocked by coculture with excess E 2. TAM-induced apoptosis of S6B45 MM cells was also unaffected by addi tion of exogenous interleukin-6. Importantly, both the inhibition of M M cell proliferation and the induction of MM cell apoptosis were achie ved at concentrations of TAM (0.5 and 5.0 mu mol/L) that did not signi ficantly alter in vitro growth of normal hematopoietic progenitor cell s. Similar plasma levels of TAM have been achieved using high-dose ora l TAM therapy, with an acceptable toxicity profile. These studies ther efore provide the rationale for trials to define the utility of AE the rapy in MM. (C) 1998 by The American Society of Hematology.