الفهرس 
Review of LiteratureOnly 14 pages are availabe for public view
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Abstract
Breast cancer is a complex disease encompassing multipletumor entities, each characterized by distinct morphology, behavior and clinical implications. Triple negative breast cancer (TNBC) is the most lethal subtype of breast cancer owing to high heterogeneity, aggressive nature and lack of treatment options. Although, the chemotherapy remains the standard of care for TNBC treatment, patients frequently develop resistance. Chemotherapy resistance presents a significant hurdle for successful cancer treatment, especially in the metastatic setting, where it accounts for 90% of therapy failure.
Mitosis is a critical and highly orchestrated event in the cell cycle. Errors in the choreography of this event may lead to uncontrolled proliferation, aneuploidy and genetic instability culminating in cancer development. Aurora kinases play a prominent role as essential regulators of the mitotic spindle and have been attributed to a wide range of functions in the mitotic control, including regulation of spindle assembly checkpoint pathway, function of centrosomes and cytoskeleton, and cytokinesis. Overexpression of aurora kinases is generally detected in a wide variety of human cancers.
The chromosomal passenger complex (CPC) is composed of aurora kinase B, INCENP, survivin and borealin. This highly conserved complex targets to different locations during mitosis, where it regulates key mitotic events: correction of chromosome microtubule attachment errors, activation of the spindle assembly checkpoint, and construction and regulation of the contractile apparatus that drives cytokinesis. Perturbation of this complex in cultured cells gives rise to chromosome segregation errors and cytokinesis failure, and as a consequence the ploidy status of the next generation of cells is changed.
In addition, mitotic regulators including centromere protein A (CENP-A) and mitotic centromere-associated kinesin (MCAK) are involved in achieving correct spindle assembly and positioning, and accurate kinetochore-microtubule attachments to prevent genomic instability. Alterations in this mitotic regulators signaling are associated with mitotic errors that may lead to cancer.
Antimitotic drugs inhibit polymerization dynamics of microtubules by activating the spindle assembly checkpoint (SAC) and blocking transition from metaphase to anaphase. Subsequently, cells undergo mitotic arrest, and since the compounds disrupt spindle formation and chromosome orientation, cells remain either in a prolonged arrest state with subsequent apoptosis induction or in a senescence-like G1 state. These drugs generally target specific components of mitotic regulation that are exclusively expressed during cell division, such as kinases, motor proteins and multiprotein complexes. Examples of antimitotic drugs in the market with potent chemotherapeutic efficacy are docetaxel, paclitaxel, vinblastine and vindesine. Novel compounds with antimitotic activity are currently in preclinical studies and clinical trials, and some of these are products or derivatives from natural sources.
Aloin, a natural phytoanthracycline extracted from the leaf exudate of Aloe vera, has been previously reported to possess a cytotoxic effect against different cancer cell lines. The dose-dependent cytotoxic action of aloin against different tumor cell lines was mediated due to multiple modes of action, including repressed protein expression of topoisomerase llα and cyclin B1, and conversely enhanced p53 protein overexpression. The most prominent action of aloin was the increased proportion of the tumor 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.
These previous findings strived exploring the putative mechanistic action of aloin on the expression of some mitotic regulating genes in estrogen receptor-dependent (T47D) and -independent (MDA-MB-231) breast tumor cells. Experimentation of the effect of doxorubicin was carried out in parallel as a reference compound.
T47D and MDA-MB-231 tumor cells were exposed to increasing concentrations of aloin (20-140 μg/ml and 50-500 μg/ml, respectively) for 24 and 72 h. On the other hand, continuous exposure of T47D and MDA-MB-231 tumor cells to doxorubicin at multiple increments (0.05-0.4 μg/ml and 0.2-1.4 μg/ml, respectively) was explored. The antitumor activity of the adopted concentrations of aloin and doxorubicin was judged by determination of the percentage of cell viability using MTT assay, from which IC50 values were calculated by GraphPad Prism software. The IC50 value of aloin was sharply higher in MDA-MB-231 (310.8 μg/ml) than in T47D cells (72.26 μg/ml). In parallel, the IC50 values of doxorubicin were recorded as 0.1992 and 0.7485 in T47D and MDA-MB-231 cell lines, respectively. The effect of aloin and doxorubicin at their IC50 values on the expression of some genes involved in the regulation of the mitotic machinery were emphasized.
Results obtained are summarized as follows:
The addition of multiple increments of aloin (20-140 μg/ml) in the culture medium of estrogen receptor-dependent breast tumor cells (T47D) produced a dose-dependent reduction in the percentage of cell viability, reaching a minimum of 39.25 and 25.22% at the highest dose (140 μg/ml) in the 24 and 72 h regimens, respectively.
The continuous exposure of T47D cells to doxorubicin produced a significant reduction in the percentage of cell viability attaining a minimum of 20.4% at the highest dose (0.4 μg/ml).
Aloin inhibited the proliferation of triple negative breast cancer cells (MDA-MB-231) in a time- and dose-dependent manner. A gradual reduction in the percentage of cell viability was obtained, reaching a minimum of 56.95 and 23.17% at the highest dose (500 μg/ml) in 24 and 72 h exposure assays, respectively.
On the other hand, continuous exposure of MDA-MB-231 cells to doxorubicin produced a significant reduction in the percentage of cell viability attaining a minimum of 13.85% at the highest dose (1.4 μg/ml).
T47D and MDA-MB-231 tumor cells exposed to different increments of aloin (20-100 and 100-500 μg/ml, respectively), showed a significantly gradual increase in the percentage of inhibition of colony formation, which reached 11.62 and 10.61% at the lowest doses (20 and 100 μg/ml, respectively), whereas achieved a complete inhibition of colony formation (100%) at the highest doses (100 and 500 μg/ml, respectively), compared to control cells. As for doxorubicin, a complete inhibition of colony formation for T47D and MDA-MB-231 tumor cells was recorded at all tested doses.
Exposure of T47D and MDA-MB-231 tumor cells to aloin or doxorubicin for 72 h at their respective IC50 values significantly down-regulated the protein expression of INCENP, survivin and CENP-A in the two breast cancer cell lines, as well as the relative mRNA expression of aurora kinases A and B and MCAK in the T47D cell line only, whereas aurora kinases A and B and MCAK mRNA expressions were up-regulated in the MDA-MB-231 cells.
The promising results of this study suggest that extensive research is required on different breast cancer subtypes to confirm the action of aloin as a potent inhibitor of aurora kinases. Also, experimenting the effect of aloin on the expression of other mitotic regulators, such as cyclin-dependent kinases (CDK4, CDK6 and CDK2) and polo-like kinase 1 (PLK1) is recommended.