الفهرس 
TitleOnly 14 pages are availabe for public view
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Abstract
Breast cancer is the second most common cancer in the world and, by far the most frequent cancer among women. Hormonal therapy is a mainstay in the clinical management of patients with breast tumors that express estrogen receptor (ER). The antitumor efficacy of these endocrine treatments depends on tight regulation of breast tumor cell growth by estrogens and growth factors. However, as these cancers progress, they usually become resistant to antiestrogens, and most patients no longer respond to endocrine therapy. New options for antiestrogen treatment are urgently needed to enhance patient survival and quality of life.
Defining the molecular interactions between estrogen and growth factor receptor signaling pathways that lead to tumor progression is essential to develop novel therapeutics that target this critical signal transduction axis. The concept of nodal protein understanding changed the perspective from an initial static view of a single target in an isolated pathway to the current view of a dynamic landscape encompassing multiple targets and pathways interacting through a complex signaling network.
Co-targeting the estrogen receptor, together with cell survival signaling pathways and the use of single drug-multi-targets was the adopted strategy in this work to enhance endocrine responsiveness.
In order to achieve these aims, MCF-7 (4OHT sensitive) and LCC2 (4OHT resistant) cells and the following kinase inhibitors; lapatinib, linsitinib and dactolisib, in addition to the γ-secretase inhibitor; LY411575 were used. Lapatinib is a potent EGFR and HER2 inhibitor while linsitinib is a selective dual kinase inhibitor of IGF-1R/IR. Dactolisib is a dual ATP-competitive PI3K and mTOR inhibitor and LY411575 is a potent γ-secretase inhibitor.
To determine the possible effects of these drugs, different parameters were determined in the present study including; mitogenic growth factors, cell proliferation, apoptosis, survival, intermediary oncogenic mediators and stemness marker.
Experimental cultures were assigned to six groups, group I included control MCF7 & LCC2 cells treated with DMSO 1% of culture media as vehicle. group II included MCF-7 and LCC2 treated with 200 nM 4-hydroxy tamoxifen in DMSO at a final of concentration 1% v/v of culture media. group III included MCF-7 and LCC2 treated with 200 nM 4-hydroxy tamoxifen and 50 nM dactolisib in DMSO at a final concentration of 1% v/v of culture media. group IV included MCF-7 and LCC2 treated with 200 nM 4-hydroxy tamoxifen and 5 μM lapatinib in DMSO at a final concentration 1% v/v of culture media. group V included MCF-7 and LCC2 treated with 200 nM 4-hydroxy tamoxifen and 1.5 μM linsitinib in DMSO at a final concentration of 1% v/v of culture media. group VI included MCF-7 and LCC2 treated with 200 nM 4-hydroxy
tamoxifen 75 μM LY411575 in DMSO at a final concentration of 1% v/v of culture media.
Results of this study showed that treatment of both cell line models (MCF-7 and LCC2) with 4-OHT, at the selected dose, resulted in a significant increase of the following parameters: NF-κB, IGF-1, Notch-1, HER2, β-catenin, GPER and p-eIF4E. GPER expression increased 8.75 times in MCF-7 (4OHT versus control), whereas in LCC2, it showed a 15-fold increase, emphasizing its role in initiating resistance to endocrine therapy. HER2, another contributor to endocrine resistance, was upregulated in LCC2 approximately 2 times compared to MCF-7 after 4OHT treatment. On the other hand, NF-κB, IGF-1, Notch-1, β-catenin, p-eIF4E were comparably upregulated in both models. The combination of 4OHT with dactolisib, linsitinib, lapatinib and LY411575 significantly reduced expression of these parameters in both MCF-7 and LCC2.
On the other hand, the expression of cyclin D1, Bcl-xL, survivin were differentially regulated by the co-targeted therapies reflecting the redundancy of the signaling pathways that converge on these targets. SOX2, an important marker of stemness and endocrine resistance was found to be downregulated by the co-targeted therapies.
With a bird eye view over the intricate inter-connected signaling network, the dominant effect of GPER in mediating the non-genomic signaling of tamoxifen that impinges on the prominent PI3K/Akt/mTOR pathway was noticed. The latter is mutually cross-talking with Notch where NF-κB is an important intermediate.
Remarkably, dactolisib in combination with 4OHT was found to produce major global effects on different signaling pathways among all used combinations. Dactolisib by targeting such nodal proteins might go beyond single-molecule antagonism and provide pathways inhibition, globally affecting multiple signaling circuits in tumor cell. The point here, is that the co-targeted treatment would not revert the tamoxifen signaling in the resistant models as much as it disrupts the interconnected signaling pathways that had led to such resistance.
In conclusion, dactolisib abrogates the main signaling pathways that provide cells with anti-apoptotic, growth and proliferation stimuli and hence its superiority. Further experimental and/or clinical studies are required to assess the clinical benefit of dactolisib and its combination with 4OHT in improving the response of endocrine therapy in tamoxifen resistant models.