Overcoming drug resistance: targeting the BCL-2 family and the long non-coding RNA HCP5 in medulloblastoma and colorectal cancer

Colorectal cancer (CRC) is one of the most common cancers in the UK and medulloblastoma is a common cancer found in children. While there has been a progressive improvement in treatment outcomes, success has been marred by drug resistance and severe side effects. Therefore, this project focused on two aspects of chemotherapeutic drug resistance, the first using the antimitotic agent vincristine in combination with inhibitors of the anti-apoptotic Bcl-2 family proteins, while the second investigated the role of the long non-coding RNA (lncRNA), HCP5 in the resistance of cells to genotoxic agents. In the first part, three medulloblastoma cell lines (DAOY, MB03, ONS76) were analysed for the expression of Bcl-xL and ONS76 cells found to have the highest level of this anti-apoptotic protein. Subsequent results indicated that Bcl-xL encourages mitotic slippage and stemness and that knockdown of Bcl-xL in the high expressing ONS76 cells, reduces these and sensitizes the cells to the anti-mitotic agent vincristine. Thus, pharmacological inhibition of Bcl-xL should sensitize medulloblastoma cells to low doses of vincristine. Regarding the lncRNA HCP5, results showed that HCP5 was generally more highly expressed in a panel of CRC cell lines than the three medulloblastoma cell lines, corroborating data from an in-silico analysis for the corresponding tumours. One function of HCP5 is to translocate the multifunctional YB-1 protein from the cytoplasm to the nucleus where it carries out many of its functions. Knockdown of HCP5 followed by immunofluorescence indicated a reduction in the amount of YB-1 in the nucleus, confirming this function. Subsequently, HCP5 silencing sensitized all cell lines tested to the DNA damaging agents, cisplatin, oxaliplatin and tert-butyl hydroperoxide and also resulted in an increase in double-strand breaks as determined by H2AX formation. Finally, fluorescence activated cell sorting using Annexin V and propidium iodide confirmed a decrease in cell viability in HCP5 knockdown cells following treatment with genotoxic agents and that this was mirrored by an increased apoptotic fraction. Together, these studies indicate the possibilities of using novel therapeutics to increase the functionality of existing treatments to combat acquired drug resistance in cancer patients