Pure antiestrogen‐induced G1‐arrest in myeloma cells results from the reduced kinase activity of cyclin D3/CDK6 complexes whereas apoptosis is mediated by endoplasmic reticulum‐dependent caspases

Abstract

Multiple myeloma (MM) is a malignancy characterized by the accumulation of tumoral plasma cells in bone marrow. This disease remains incurable and the development of new therapeutic strategies is urgently required. We have studied the effects of 2 selective estrogen receptor disrupters (SERDs), RU 58668 (RU) and ICI 182,780 (ICI) or pure antiestrogens (AEs) on MM cell lines. Both compounds have antimyeloma activity through either cell cycle arrest or induction of apoptosis. To analyze the molecular mechanisms of SERD action, we choose 2 differently responding cell lines as models. In LP-1 cells, RU blocked cell cycle at the G1 phase. RU treatment induced a rapid decrease of c-Myc, an upregulation of p27 Kip1 , and the subsequent decreased activity of cyclin-dependent kinase, CDK6 and associated cyclin D3, impairing the inactivation of the retinoblastoma protein (pRb). In RPMI 8226 cells, RU induced apoptosis by recruiting endoplasmic reticulum-as well as mitochondria-associated caspases. Moreover, RU interfered with the NF-jB survival pathway, often deregulated in MM malignancy. Antimyeloma activities were observed in dexamethasone (Dex)-and RU-resistant cells when RU was combined with bortezomib; Dex and bortezomib being frequently used in MM therapy. RU induced the death of CD1381 cells purified from MM patients but not CD191 normal cells obtained from tonsils. Therefore, RU mediates the inhibition of survival, the activation of apoptosis and finally potentiates anticancer drug. Those combinatory effects provide a basis for the potential use of pure AEs in MM treatment. ' 2008 Wiley-Liss, Inc.Key words: multiple myeloma; pure antiestrogen; apoptosis; antiestrogenic therapy; survival pathway Multiple myeloma (MM) is a B-cell malignancy characterized by the accumulation of clonal tumor cells in the bone marrow. This accumulation of malignant plasma cells that synthesize immunoglobulins causes hyperproteinemia, renal dysfunction, bone lesions and immunodeficiency. 1 This disease, which accounts for 2% of all cancer deaths per year and nearly 20% of deaths caused by hematological malignancies in the western world, remains largely incurable despite novel therapeutic approaches targeting both myeloma cells and bone marrow environment. 2,3 Selective estrogen receptor modulators (SERMs) and selective estrogen receptors disruptors (SERDs) or pure antiestrogens (AEs) may provide a new strategy in myeloma therapy. MM cell lines and primary cells express estrogen receptors (ERs). This has been described 20 years ago using binding assays 4,5 and more recently using western blotting. 6 We and others have previously reported that SERMs inhibited cell proliferation and induced apoptosis in MM cells. [6][7][8][9] Using several MM cell lines, we demonstrated that 4-hydroxytamoxifen (4-HT) inhibits proliferation through 2 independent but concomitant processes: a block at the G0/G1-phase and the triggering of a mitochondrial death pathway. We further investigated the effects of 2 steroid-like pure AEs, RU 58668 (RU) and ICI 182...

Therapeutic Potential of New 4-hydroxy-tamoxifen-Loaded pH-gradient Liposomes in a Multiple Myeloma Experimental Model

“…This effect was found at a lower extent after treatment with free 4HT. This supports a greater extent of cellular uptake of the liposomeencapsulated AE and may reflect an enhanced reticulum endothelium-mediated caspase apoptosis process as indicated previously (18). These results are in agreement with the enhancement of the cellular capture of the other AE RU once entrapped in liposomes, a process also reported to bypass the extrusion capacity of Pgps (33).…”

“…Depending on the cell line, different AEs arrest progression of the cell cycle and/or induce apoptosis (15)(16)(17). For examples, 4HT arrests cell cycle and induces apoptosis in LP-1 MM cells, while the selective estrogen receptor down-regulators (SERDs) RU 58668 (RU) and Faslodex® induce only apoptosis in RPMI8266 MM cells (17)(18)(19). Raloxifen acts like 4HT for arresting cell proliferation and inducing apoptosis in MM cells (20).…”

Antiestrogen-binding site ligands induce autophagy in myeloma cells that proceeds through alteration of cholesterol metabolism

“…We have previously reported that AEs belonging to both SERD and SERM classes display anti-proliferative and/or pro-apoptotic properties on MM cell lines and primary cells [ 5 , 7 ]; these effects are dependent on AEs and cell lines ( Supplementary Table 1 ). Roughly, OHT induces both G1 arrest and apoptosis in responsive HMCLs, while pure AEs such as RU 58668 and fulvestrant induce either G1 arrest or apoptosis, suggesting that each AE subtype does not affect identical pathways.…”

“…Selective estrogen receptor modulators (SERMs) and selective estrogen receptors disruptors (SERDs) or pure antiestrogens (AEs) may provide a potent strategy in myeloma therapy. Indeed, several groups, including our, have previously reported that SERMs and SERDs inhibited cell proliferation and/or induced apoptosis of MM cells [ 3 - 7 ]. Although myeloma cells express estrogen receptors (ER) belonging to both α and β isotypes [ 4 , 5 ],it is not clear if AEs signal through canonical ERs.…”