Browsing by Author "Palma, Gabriella Bianca Henriques"

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    Investigating the potential of acetyl plumbagin to reduce cancer-related drug resistance in various breast cancer cell lines
    (2019) Palma, Gabriella Bianca Henriques
    Breast cancer (BC) is the second most common malignancy comprising of 21.78% of all cancers in women. Death rates have decreased significantly from BC due to improved use of adjuvant Tamoxifen (Tam) and chemotherapy. However, given the improvement of survival rates due to endocrine therapies, many patients relapse with acquired resistance at later times after initial response. Thus a greater understanding of the mechanisms involved in cancerrelated drug resistance is needed along with the identification of new compounds that could help overcome drug resistance in cancer cells. The aim of this investigation was to test Acetyl Plumbagin (AP) as an adjuvant compound in various estrogen receptor positive (ER+) BC cell lines to reduce cholesterol accumulation and cancer-related resistance. This study observed the changes in pathways affected in two BC cell lines when AP was added alone and when AP was added in combination with Tam. This allowed for the observation of enhanced efficacy of Tam in inhibiting cell growth in MCF7 and long-term estrogen deprived (LTED) cells by 500% and 300% respectively. A significant increase in early-stage apoptosis was observed when cells were treated with the combination therapy as compared to single treatments. Cholesterol depletion was observed in both cell lines indicating that Tam and AP work in a synergistic manner in inducing apoptosis via cholesterol depletion in cell membranes. AP significantly enhanced the sensitivity of ER+ BC cells to Tam treatment. This indicates that AP could act as an anti-cancer lead compound for future drug development, targeting cholesterol accumulation and Tam resistance in BC.
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    The roles of miRNA-128 and miRNA-223 in cholesterol-mediated drug resistance in breast cancer
    (2024) Palma, Gabriella Bianca Henriques
    Breast cancer (BC) is the most prevalent cancer in women, with 70% of BC cases being hormone responsive (estrogen receptor positive (ER+)). This ER+ BC subtype relies on estrogen for enhanced cell proliferation and survival. The main therapeutic strategy to prevent hormone responsive BC recurrence is with the use of endocrine therapy such as Tamoxifen (TAM). Despite the success in reducing mortality rates of BC patients with the use of adjuvant TAM and chemotherapy, cancer drug resistance remains a significant challenge. A major contributor to this resistance is the dysregulation of cholesterol homeostasis in these cells. BC cells have elevated intracellular cholesterol levels, which is associated with cancer progression. In our previous research, we observed that the use of a cholesterol depleting agent, Acetyl Plumbagin (AP) in combination with TAM, led to the induction of cell death via cholesterol depletion. These results therefore warranted further investigation into the molecular mechanisms in which TAM + AP are involved in. MicroRNAs (miRNAs) regulate cholesterolrelated and cancer drug resistance pathways, and the aberrant expression of these miRNAs are often associated with increased cancer proliferation and resistance. It was therefore predicted that manipulating the expression of these target miRNAs could lead to a reduction in BC related drug resistance via cholesterol depletion. Thus, we aimed at investigating the roles of miRNA128 and miRNA-223 in cholesterol-mediated TAM resistance. Three BC cell lines (MCF-7 (estrogen-dependent), MDA-MB-231 (estrogen-independent), and Long-Term Estrogen Deprived (LTED)) were treated with a combination of 1 µM TAM and 10 µM AP following transfection with a miR-128 inhibitor or a miR-223 mimic. Cell viability and cholesterol levels were assessed following treatments. In addition, gene and protein expression levels involved in cancer drug resistance and cholesterol homeostasis were also assessed. It was found that the combination treatment with altered miRNA expression led to reduced cell viability and proliferation due to a reduction in free cholesterol, cholesteryl esters, and lipid rafts in all three BC cell lines. Moreover, miR-128 inhibition lowered the expression of genes involved in cholesterol synthesis and transport (HMGCR, HMGCS1, SREBF1/2, CETP, LCAT, and LDLR), drug resistance (ABCC5 and UGCG), and cell signalling (ESR1, EGFR, and IGF1R) in MCF7 cells. Whereas overexpression of miR-223 led to decreased expression in EGFR, ESR1, ABCC5, CETP, LCAT, LDLR, HMGCR, SREBF1, and SREBF2, with increased expression in ABCG1, PTEN, and TP53 in MDA-MB-231 cells. Therefore, the current study demonstrated that miR-128 and miR-223 could be potential targets in reducing TAM resistance through the depletion of excess cholesterol.