TNFα Potentiates 2-Methoxyestradiol-Induced Mitochondrial Death Pathway

Modulation of adjuvant arthritis in the rat by 2-methoxyestradiol: an effect independent of an anti-angiogenic action

Angiogenesis is a prominent feature in rheumatoid arthritis. 2-methoxyestradiol (2ME2) inhibits endothelial cell proliferation, and angiogenesis in vivo. We evaluated the effect of 2ME2 in rats with adjuvant arthritis (AA), an autoimmune T-cell-dependent polyarticular arthritis induced by immunization with Mycobacterium organisms. Rats were immunized with Mycobacterium butyricum and arthritis was assessed clinically, by radiolabeled blood neutrophil (PMNL) migration to joints and by histology. Treatment with 2ME2 (30 mg/kg/d or 100 mg/kg/d) from day 6 post-immunization inhibited arthritis severity on day 14 (vehicle clinical score=11.2; 2ME2 groups=7-8, p<0.05). When treatment was delayed until signs of clinical arthritis on day 10 post-immunization, 2ME2 treatment still inhibited arthritis severity. PMNL migration to the joints was significantly inhibited (by 35-40%; p<0.01) by early 2ME2 treatment (day 6-14). Treatment with 2ME2 inhibited PMNL migration to dermal inflammation induced by TNF-alpha but not by LPS or C5a. Joint histology revealed decrease in leukocyte infiltration and especially in cartilage damage. However, synovial vascularity was not affected by 2ME2 treatment. The marked splenomegaly, splenitis and lymphoid hyperplasia associated with AA were prevented by 2ME2 therapy. Furthermore, the ex vivo proliferative response to mycobacterial antigen (PPD) of lymphocytes from 2ME2-treated rats with AA was markedly diminished, although response to mitogens was unaffected. Thus 2ME2 has anti-arthritic properties with a disease-modifying action, separate from its anti-angiogenic properties. The selective inhibition of TNF-alpha-induced leukocyte recruitment, lymphoid hyperplasia and attenuated recall response to antigen suggests both immunomodulatory and anti-inflammatory actions of 2ME2.

Targeting human 8-oxoguanine DNA glycosylase to mitochondria protects cells from 2-methoxyestradiol-induced-mitochondria-dependent apoptosis

2-Methoxyestradiol (2-ME), an endogenous estrogen metabolite of 17beta-estradiol, is known to induce mitochondria-mediated apoptosis through several mechanisms. We sought to study the effect of mitochondrialy targeted hOGG1 (MTS-hOGG1) on HeLa cells exposed to 2-ME. MTS-hOGG1-expressing cells exposed to 2-ME showed increased cellular survival and had significantly less G(2)/M cell cycle arrest compared to vector-only-transfected cells. In addition, 2-ME exposure resulted in an increase in mitochondrial membrane potential, increased apoptosis, accompanied by higher activation of caspase-3, -9, cleavage of Bid to tBid and protein poly(ADP-ribose) polymerase (PARP) cleavage in HeLa cells lacking MTS-hOGG1. Fas inhibitors cerulenin or C75 inhibited 2-ME-induced caspase activation, PARP cleavage, apoptosis and reversed mitochondrial membrane hyperpolarization, thereby recapitulating the increased expression of MTS-hOGG1. Hence, MTS-hOGG1 plays an important protective role against 2-ME-mediated mitochondrial damage by blocking apoptosis induced through the Fas pathway.

Crosstalk between extrinsic and intrinsic cell death pathways in pancreatic cancer: synergistic action of estrogen metabolite and ligands of death receptor family

2-Methoxyestradiol is a physiologic metabolite of 17beta-estradiol. This orally active compound can inhibit tumor growth or metastasis in tumor models without inducing any clinical sign of toxicity. Our previous studies indicated that 2-methoxyestradiol-mediated apoptosis involves the disappearance of intact 21-kDa Bid protein, cytochrome c release, and predominant procaspase-3 cleavage. Here, using MIA PaCa-2 cells as a model, we investigated whether this estrogen metabolite induces apoptosis by converging two major pathways: the death receptor-mediated extrinsic and the mitochondrial intrinsic pathway. Exogenous expression of dominant-negative caspase-8 or dominant-negative FADD reverts the effect of 2-methoxyestradiol-mediated cell death. In parallel with this observation, Z-IETD-FMK, a cell permeable irreversible inhibitor of caspase-8, can render significant protection against 2-methoxyestradiol-induced apoptosis. RNase protection assay and cell surface receptor analysis by flow cytometry show the up-regulation of members of death receptor family in 2-methoxyestradiol-exposed pancreatic cancer cells. Our mechanistic studies also implicate that oxidative stress precedes 2-methoxyestradiol-mediated c-Jun NH2-terminal kinase activation, leading to elevated Fas level. Because 2-methoxyestradiol is able to trigger death receptor signaling, we were interested in examining the effects of 2-methoxyestradiol and Fas ligand (FasL)/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) together on pancreatic cancer cell death. Interestingly, the endogenous angiogenesis inhibitor 2-methoxyestradiol augments FasL/TRAIL-induced apoptosis in these cells. Moreover, the combination of 2-methoxyestradiol and TRAIL reduces the tumor burden in vivo in MIA PaCa-2 tumor xenograft model by caspase-3 activation.

2-methoxyestradiol inhibits differentiation and is cytotoxic to osteoclasts

2-Methoxyestradiol (2-ME), a naturally occurring metabolite of 17beta-estradiol, is highly cytotoxic to a wide range of tumor cells but is harmless to most normal cells. However, 2-ME prevented bone loss in ovariectomized rats, suggesting it inhibits bone resorption. These studies were performed to determine the direct effects of 2-ME on cultured osteoclasts. 2-ME (2 microM) reduced osteoclast number by more than 95% and induced apoptosis in three cultured osteoclast model systems (RAW 264.7 cells cultured with RANKL, marrow cells co-cultured with stromal support cells, and spleen cells cultured without support cells in media supplemented with RANKL and macrophage colony stimulating factor (M-CSF)). The 2-ME-mediated effect was ligand specific; 2-hydroxyestradiol (2-OHE), the immediate precursor to 2-ME, exhibited less cytotoxicity; and 2-methoxyestrone (2-MEOE1) the estrone analog of 2-ME, was not cytotoxic. Co-treatment with ICI 182,780 did not antagonize 2-ME, suggesting that the cytotoxicity was not estrogen receptor-dependent. 2-ME-induced cell death in RAW 264.7 cells coincided with an increase in gene expression of cytokines implicated in inhibition of differentiation and induction of apoptosis. In addition, the 2-ME-mediated decrease in cell survival was partially inhibited by anti-lymphotoxin(LT)beta antibodies, suggesting that 2-ME-dependent effects involve LTbeta. These results suggest that 2-ME could be useful for treating skeletal diseases in which bone resorption is increased, such as postmenopausal osteoporosis and cancer metastasis to bone.