Blocking mitotic exit as a potential target for combination therapy with anti-mitotic drugs

Recent efforts in cancer therapy investigations have been focused on developing a rational strategy to specifically target cancer cells to reduce toxic side effects. Uncontrolled cell division (mitosis) is a hallmark of cancer cells. Classical anti-mitotic drugs such as Taxanes and Vinca alkaloids work by disrupting microtubule dynamics, which results in a block in cell division and induction of mitotic arrest. This prolonged mitotic arrest can trigger cell death, which is often curative in some cancer patients. However, despite the success of these chemotherapies, many patients have innate or develop acquired resistance. Furthermore, higher doses of these drugs cause toxicities, which limit the efficacy of these compounds. To overcome these limitations research has focused on finding novel drug combinations that enhance the effects of mitotic chemotherapies. Recently, blocking mitotic exit has emerged as a promising strategy for killing cancer cells and enhancing mitotic chemotherapy response. In order to find novel regulators of mitotic exit, we analysed published genome wide RNA interference screens and online-databases to identify novel genes whose knockdown increased mitotic index and raised the sensitivity of cells to Taxol. In this thesis, we explored two of these potential new target genes, STK16 (serine/threonine kinase 16) and Protein phosphatase 2 A (PP2A). The effects of targeting STK16 and PP2A (using specific siRNA or chemical inhibitors) were examined in combinations with Taxol. HeLa cells stably expressing histone H2B fused to red fluorescent protein (H2B-mCherry) were treated with combination of drugs and monitored by live cell imaging systems. Phenotypes of the cells were tracked during the treatment to measure duration of mitotic arrest and percentage of dead cells. Knockdown of STK16 failed to affect mitotic progression or the duration of mitotic arrest in combination with Taxol. In contrast, siRNA knockdown of the B55 subunit of PP2A and inhibit