Combinatorial PX‐866 and Raloxifene Decrease Rb Phosphorylation, Cyclin E2 Transcription, and Proliferation of MCF‐7 Breast Cancer Cells

Abstract

As a potential means to reduce proliferation of breast cancer cells, a multiple-pathway approach with no effect on control cells was explored. The human interactome being constructed by the Center for Cancer Systems Biology will prove indispensable to understanding composite effects of multiple pathways, but its discovered protein–protein interactions require characterization. Accordingly, we explored the effects of regulators of one protein on downstream targets of the other protein. MCF-7 estrogen receptor-positive (ER+) breast cancer cells were treated with raloxifene to upregulate the TGF-β pathway and PX-866 to down-regulate the PI3K/Akt pathway. This resulted in highly significant downstream reduction of cell cycle proliferation in breast cancer cells with no significant proliferation reduction following similar treatment of noncancerous MCF10A breast epithelial cells. Reduced phosphorylation of p107 and substantial reduction of Rb phosphorylation were observed in response. The effects of reduced Rb and p107 phosphorylation were reflected in significant decline in E2F-1 transcriptional activity, which is dependent on pocket protein phosphorylation status. The reduced proliferation was related to decreased expression of cyclins, including E2F-1-regulated Cyclin E2, which was also in response to raloxifene and PX-866. All combinations of raloxifene and PX-866 produced significant or highly significant results for reduced MCF-7 cell proliferation, reduced Cyclin E2 transcription, and reduced Rb phosphorylation. These studies demonstrated that uncontrolled proliferation of ER+ breast cancer cells can be significantly reduced by combinational targeting of two relevant pathways.

p53‐dependent up‐regulation of CDKN1A and down‐regulation of CCNE2 in response to beryllium

“…Recently, a similar phenomenon was reported in MCF‐7 human breast cancer cells. In MCF‐7, combination therapy with a PI‐3‐kinase inhibitor and a selective oestrogen receptor modulator caused a large decrease in CCNE2 mRNA but very little change in cyclin E2 protein abundance …”

Down-regulation of hTERT and Cyclin D1 transcription via PI3K/Akt and TGF-β pathways in MCF-7 Cancer cells with PX-866 and Raloxifene

“…We previously reported the highly significant decrease of proliferation of MCF-7 cells after three days of treatment with 1.0 μM raloxifene alone or in combination with 0.1, 0.4 or 0.8 μM PX-866 and the absence of any significant decrease of MCF10A cell proliferation following identical treatment [57]. As documented, there are few cellular or intracellular functions even remotely related to cell division, growth or cancer that are hTERT-independent, and this includes gene expression, signaling, survival, mitochondrial function and migration [9].…”

“…We previously reported that IL-11 transcription was significantly decreased by raloxifene in combination with PX-866 in MCF-7 cells [57]. Recognized contributions of IL-11 to cancer include development, apoptosis evasion, angiogenesis, progression and metastasis in multiple cancer cell types [67].…”

Inhibitors of phosphoinositide 3-kinase (PI3K) and phosphoinositide 3-kinase-related protein kinase family (PIKK)

“…As a result, the therapeutic potential of these combination therapies is restricted 59–62 . When raloxifene and sonolisib are combined, the expansion of breast cancer cells is significantly reduced, proving that the combination therapy has certain potential for patients with breast cancer 63 . In recent studies, sonolisib has been shown to inhibit temozolomide-induced autophagy and promote apoptosis in GBM cells, thereby enhancing antitumor efficacy.…”