2-methoxyestradiol sensitizes breast cancer cells to taxanes by targeting centrosomes

Effect of 2-methoxyestradiol on mammary tumor initiation and progression

BACKGROUND

The anti-cancer agent 2-methoxyestradiol (2-ME) has been shown to have anti-proliferative and anti-angiogenic properties. Previously, the effect of 2-ME on early- and late-stage breast cancer (BC) was investigated in vivo using a transgenic mouse model (FVB/N-Tg(MMTV-PyVT)) of spontaneous mammary carcinoma. Anti-tumor effects were observed in late-stage BC with no effect on early-stage BC. Given the contrasting results obtained from the different BC stages, we have now investigated the effect of 2-ME when administered before the appearance of palpable tumors.

METHODS

Each mouse received 100 mg/kg 2-ME on day 30 after birth, twice per week for 28 days, while control mice received vehicle only. Animals were terminated on day 59. Lung and mammary tissue were obtained for immunohistochemical analysis of CD163 and CD3 expression, and histological examination was performed to analyze tumor necrosis. Additionally, blood samples were collected to measure plasma cytokine levels.

RESULTS

2-ME increased tumor mass when compared to the untreated animals (p = .0139). The pro-tumorigenic activity of 2-ME was accompanied by lower CD3+ T-cell numbers in the tumor microenvironment (TME) and high levels of the pro-inflammatory cytokine interleukin (IL)-1β. Conversely, 2-ME-treatment resulted in fewer CD163+ cells detectable in the TME, increased levels of tumor necrosis, increased IL-10 plasma levels, and low IL-6 and IL-27 plasma levels.

CONCLUSION

Taken together, these findings suggest that 2-ME promotes early-stage BC development.

Oestrogen receptor-independent actions of oestrogen in cancer

Oestrogen, the primary female sex hormone, plays a significant role in tumourigenesis. The major pathway for oestrogen is via binding to its receptor [oestrogen receptor (ERα or β)], followed by nuclear translocation and transcriptional regulation of target genes. Almost 70% of breast tumours are ER + , and endocrine therapies with selective ER modulators (tamoxifen) have been successfully applied. As many as 25% of tamoxifen-treated patients experience disease relapse within 5 years upon completion of chemotherapy. In such cases, the ER-independent oestrogen actions provide a plausible explanation for the resistance, as well as expands the existing horizon of available drug targets. ER-independent oestrogen signalling occurs via one of the following pathways: signalling through membrane receptors, oxidative catabolism giving rise to genotoxic metabolites, effects on mitochondria and redox balance, and induction of inflammatory cytokines. The current review focuses on the non-classical oestrogen signalling, its role in cancer, and its clinical significance.

2-Methoxyestradiol as an Antiproliferative Agent for Long-Term Estrogen-Deprived Breast Cancer Cells

To identify effective treatment modalities for breast cancer with acquired resistance, we first compared the responsiveness of estrogen receptor-positive breast cancer MCF-7 cells and long-term estrogen-deprived (LTED) cells (a cell model of endocrine therapy-resistant breast cancer) derived from MCF-7 cells to G-1 and 2-methoxyestradiol (2-MeO-E2), which are microtubule-destabilizing agents and agonists of the G protein-coupled estrogen receptor 1 (GPER1). The expression of GPER1 in LTED cells was low (~0.44-fold), and LTED cells displayed approximately 1.5-fold faster proliferation than MCF-7 cells. Although G-1 induced comparable antiproliferative effects on both MCF-7 and LTED cells (IC50 values of >10 µM), 2-MeO-E2 exerted antiproliferative effects selective for LTED cells with an IC50 value of 0.93 μM (vs. 6.79 μM for MCF-7 cells) and induced G2/M cell cycle arrest. Moreover, we detected higher amounts of β-tubulin proteins in LTED cells than in MCF-7 cells. Among the β-tubulin (TUBB) isotype genes, the highest expression of TUBB2B (~3.2-fold) was detected in LTED cells compared to that in MCF-7 cells. Additionally, siTUBB2B restores 2-MeO-E2-mediated inhibition of LTED cell proliferation. Other microtubule-targeting agents, i.e., paclitaxel, nocodazole, and colchicine, were not selective for LTED cells. Therefore, 2-MeO-E2 can be an antiproliferative agent to suppress LTED cell proliferation.

Cigarette smoke condensate induces centrosome clustering in normal lung epithelial cells

BACKGROUND

Unlike normal cells, cancer cells frequently have multiple centrosomes that can cluster to form bipolar mitotic spindles and allow for successful cell division. Inhibiting centrosome clustering, therefore, holds therapeutic promise to promote cancer cell-specific cell death.

METHODS

We used confocal microscopy, real-time PCR, siRNA knockdown, and western blot to analyze centrosome clustering and declustering using normal lung bronchial epithelial and nonsmall-cell lung cancer (NSCLC) cell lines. Also, we used Ingenuity Pathway Analysis software to identify novel pathways associated with centrosome clustering.

RESULTS

In this study, we found that exposure to cigarette smoke condensate induces centrosome amplification and clustering in human lung epithelial cells. We observed a similar increase in centrosome amplification and clustering in unexposed NSCLC cell lines which may suggest a common underlying mechanism for lung carcinogenesis. We identified a cyclin D2-mediated centrosome clustering pathway that involves a sonic hedgehog-forkhead box protein M1 axis which is critical for mitosis. We also observed that cyclin D2 knockdown induced multipolar mitotic spindles that could eventually lead to cell death.

CONCLUSIONS

Here we report a novel role of cyclin D2 in the regulation of centrosome clustering, which could allow the identification of tumors sensitive to cyclin D2 inhibitors. Our data reveal a pathway that can be targeted to inhibit centrosome clustering by interfering with the expression of cyclin D2-associated genes.

Self-Nanoemulsifying Drug Delivery System of 2-Methoxyestradiol Exhibits Enhanced Anti-Proliferative and Pro-Apoptotic Activities in MCF-7 Breast Cancer Cells

(1) Background: 2-Methoxyestradiol (2ME) is a metabolite of estrogens and possesses promising anti-proliferative and cytotoxic activities. However, it suffers unfavorable pharmacokinetic characteristics such as absorption after oral administration. The aim of this study was to prepare an optimized 2ME self-nanoemulsifying drug delivery system (2ME-SNEDDS) and evaluate its cytotoxicity and pro-apoptotic activities in MCF-7 breast cancer cells. (2) Methods: For optimization of the 2ME-SNEDDS, a three-component system was used in the D-optimal mixture experimental study. MCF-7 cells were incubated with the 2ME-SNEDDS and subjected to an assessment of growth inhibition, cell cycle progression, annexin V staining, caspase-3 concentration, Bax, Bcl-2, and cyclin D1 mRNA expression, and reactive oxygen species (ROS) generation. (3) Results: The optimized formula had a globule size of 94.97 ± 4.35 nm. Zeta potential was found to be −3.4 ± 1.2 mV with a polydispersity index (PDI) of 0.34. In addition, 96.3  ± 4.3% of 2ME was released from the 2ME-SNEDDS within 24 h using the activated analysis bag technique. Moreover, the prepared 2ME-SNEDDS exhibited a significant enhancement of the anti-proliferative activity against MCF-7 cells in comparison to raw 2ME. This was associated with cyclin D1 expression down-regulation and the accumulation of cells in the G0/G1 and G2/M phases. The pro-apoptotic activities of the 2ME-SNEDDS were confirmed by annexin V staining, which indicated enhanced early and late cell death. This accompanied modulation of the mRNA expression of Bax and Bcl-2 in favor of apoptosis. The 2ME-SNEDDS significantly enhanced cleaved caspase-3 concentration in comparison to raw 2ME. In addition, the 2ME-SNEDDS significantly increased the generation of ROS in MCF-7 cells. (4) Conclusions: The 2ME-SNEDDS exhibits enhanced cytotoxicity and pro-apoptotic activity in MCF-7 cells. This is mediated by, at least partially, ROS generation.