الفهرس 
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Abstract
Breast cancer is the most common cancer and ranks as the second cause of cancer deaths among women. In Egypt, breast cancer represents about 35.1% of cancer incidence among the females with a mortality rate of 23.8%.
Metastasis, the main cause of death in breast cancer patients, is regulated by several factors and signaling pathways, such as epithelial-mesenchymal transition (EMT). The latter is a reversible biologic process that allows a polarized epithelial cell to undergo multiple biochemical changes that enable it to assume a mesenchymal cell phenotype.
During EMT the expression or function of epithelial genes such as E-cadherin, certain cytokeratins, and zona occludens 1 (ZO-1) is lost during the transition, while the expression of genes that define the mesenchymal phenotype, such as vimentin, fibronectin, N-cadherin, and β1 and β3 integrins, become elevated. E-cadherin is regarded as a gatekeeper of the epithelial state. A delocalization of zonula occludens (ZO-1), tight junction protein, from the cell membrane has been reported during epithelial cell migration. Furthermore, intermediate filaments are shown to switch from cytokeratin to vimentin during EMT. Increased expression of vimentin is used as an EMT marker in cancer and correlates with tumor growth, invasion and poor prognosis.
The mammalian Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway transmits extracellular signals to the nucleus and regulates a variety of cellular activities including apoptosis, differentiation, proliferation and immunological responses. The persistent activation of STAT3/5 on tumor cell survival, proliferation and invasion has been observed in the JAK/STAT pathway, suggesting that JAK/STAT pathway could be a target for drug development and cancer therapy.
Aloin, a natural anthracycline extracted from the leaf exudates of Aloe vera, has been previously reported to possess a cytotoxic effect against different cancer cell lines. The dose-dependent cytotoxic action of aloin was mediated due to multiple modes of action, including inhibition of topoisomerase IIα and cyclin B1 proteins expression, induction of apoptosis via enhancing p53 overexpression, increasing the percentage of S phase fraction and in the proportion of cells cycling at a higher ploidy level (> G2M). The polypolidization indicates that aloin does not inhibit the initiation of DNA synthesis and that cells replicated a full complement of DNA but had a difficulty in M phase.
The present study aimed at investigating the cytotoxic effect of aloin against breast cancer cell line (T47D), compared to an anthracycline analog, doxorubicin. The aim was furtherly extended to elucidate the involvement of some genes expression in EMT in T47D cells in the cytotoxic activities of aloin and doxorubicin.
The human breast adenocarcinoma cell line (T47D) was incubated with multiple concentrations of aloin (20-100 μg/ml) or doxorubicin (0.05-0.2 μg/ml) for 24 and 72 hr. The cytotoxic effects of aloin and doxorubicin were evaluated by MTT and clonogenic assays, from which the IC50 values of aloin and doxorubicin were used to monitor the changes in the gene expression of some epithelial and mesenchymal gene markers involved in EMT in T47D cancer cells, as well as the expression of JAK2 and STAT5a genes.
Results obtained are summarized as follows:
Exposure of T47D cells to aloin for 24 and 72 hr showed a significantly dose-dependent reduction in the percentage of cell viability at higher doses in the 24 hr exposure regimen, and at all tested doses in the continuous exposure regimen, compared to untreated cells.
All implemented aloin doses significantly inhibited the colony formation of T47D cells in both exposure regimens.
On the other hand, all tested doxorubicin doses showed a significantly dose-dependent reduction in the percentage of T47D cell viability and inhibition of colony formation at both exposure regimens.
The continuous exposure of T47D cells to IC50 value of aloin (181.5 μM) significantly downregulated the expression of JAK2 and STAT5a mRNAs, which suggested aloin as a candidate inhibitor of JAK2/STAT5a signaling.
The continuous exposure of T47D cells to the IC50 value of doxorubicin (0.17 μM) did not alter the gene expression of JAK2 and STAT5a.
The continuous exposure of T47D cells to the IC50 value of aloin (181.5 μM) significantly downregulated the gene expression of the mesenchymal marker, vimentin.
The continuous exposure of T47D cells to the IC50 value of doxorubicin (0.17 μM) upregulated the expression of the epithelial marker, E-cadherin gene.