Mitose assoziierter Zelltod nach Chemotherapie vermittelter Durchbrechung des G2-Zellzyklus-Kontrollpunktes

Deficiency in cell cycle checkpoint function is a characteristic of tumour cells that enables to high proliferation and mutation rates. In particular, deficiency of p53-dependent signalling networks gives rise to such malignant traits while on the other hand making cells more dependent on the DNA damage recovery system in the G2-phase of the cell cycle to repair DNA damage. A new concept of combinational chemotherapy is the combination of a classical DNA damaging drug with an inhibitor of the CHK1-kinase, resulting in abrogation of the DNA damage recovery pathway in G2-phase. P53-deficient cells can therefore no longer arrest in G1 or G2 and enter mitosis with the introduced DNA damage, which leads to a mitotic arrest and high rates of cell death. The pathways linking DNA damage, mitotic arrest and apoptosis are not known in detail and are further studied in this work. I showed that in cells, arrested in mitosis after treatment with Adriamycin and UCN-01, antiapoptotic pathways are activated, although mitochondrial apoptosis is induced. Under these conditions a reduction in the protein level of the active conformation of the proapoptotic protein bax and a hyperphosphorylation of the antiapoptotic protein Bcl-2 can be observed. Cell death is further enhanced by addition of the CDK1 inhibitor roscovitine, conceivably due to an antiapoptotic function of CDK1 in mitosis or an activation of apoptotic pathways triggered by mitotic exit. A similar effect can be seen by addition of ZM447439, a small molecule inhibitor of Aurora-B kinase. Forcing cells with DNA damage into mitosis and manipulating activated mitotic and apoptotic pathways to enhance cell death, might therefore be a promising therapeutic strategy. Whether a combination treatment with a DNA damaging drug, a CHK1 inhibitor and a CDK1-inhibitor shows similar effects in other p53-deficient tumour cell lines and if it is tolerated by benign somatic tissues, should be tested in further experiments. Small molecule inhibitors of CHK1 and CDK1 are already in clinical trials as single treatment or in combination with various established chemotherapeutic agents.