Li, YanAgyapong, Kofi Effah2026-01-122026-01-122025http://hdl.handle.net/10292/20476Breast cancer continues to represent one of the most common causes of cancer-related morbidity and mortality globally and in New Zealand. Chemotherapy as a routine therapy remains an effective strategy not only in early-stage breast cancer patients but in advanced breast cancer patients when resistance to endocrine therapy occurs, such as oestrogen receptor-positive (ER⁺) disease. Taxane-based agents (e.g., docetaxel) have been extensively applied because they modulate microtubule dynamics and suppress the growth of tumour cells. Yet, the treatment response of docetaxel is often impeded by the development of chemoresistance. Multidrug resistance (MDR) represents a significant obstacle to the success of chemotherapy, which is largely associated with ATP-binding cassette (ABC) transporters that actively remove cytotoxic drugs from cancer cells, thereby inhibiting intracellular drug accumulation. Of these transporters, ABCC10 (also known as MRP7) has been associated with resistance to taxanes such as docetaxel, but its role in chemoresistance in ER⁺ breast cancer remains unclear. Here, we hypothesise that gene knockout of ABCC10 in ER⁺ breast cancer cell line MCF-7 would improve cellular sensitivity to docetaxel. In order to evaluate this, liposomal transfection of CRISPR-Cas9 ribonucleoprotein complexes targeting exon 3 of ABCC10 in MCF-7 cells was used. Polymerase chain reaction and T7 endonuclease I assay indicated successful gene disruption of the gene with ∼36% genomic cleavage efficiency. To limit clonal heterogeneity, the following single knockout clone was chosen (D4-F8) and functionally characterized. Loss of ABCC10 led to increased sensitivity to docetaxel, with a 35-fold reduction in IC50 values compared to wild-type MCF7 cells (p < 0.05). In addition, ABCC10 knockout cells suffered significantly from impaired clonogenic survival and plating efficiency, while basal metabolic activity was still intact, demonstrating impaired long-term proliferative capacity. These observations highlight that ABCC10 is a functional regulator of docetaxel resistance in ER⁺ breast cancer cells. This study is the first CRISPR-Cas9-mediated knockout of ABCC10 in MCF-7 cells and provides mechanistic evidence that ABCC10 is a potential therapeutic target against taxane resistance. This work underlines the utility of precision genome-editing approaches in defining chemotherapy resistance mechanisms, thus providing an understanding of effective cytotoxic resistance mechanisms and informing treatment strategy in ER⁺ breast cancer.enThesisOpenAccess