Role of alterations in the apoptotic machinery in sensitivity of cancer cells to treatment.

Apoptosis is a genetically controlled and evolutionarily conserved form of cell death of critical importance for normal embryonic development and for the maintenance of tissue homeostasis in the adult organism. The malfunction of the death machinery may play a primary or secondary role in various diseases, with essentially too little or too much apoptosis leading to proliferative or degenerative diseases, respectively. The machinery responsible for killing and degradation of the cell via apoptosis is expressed constitutively and become activated through various stimuli. Apoptotic mechanisms are operating during spontaneous regression of tumors as well as in response to treatment with anti-neoplastic drugs. The therapeutic goal in cancer treatment is to trigger tumor-selective cell death. However, resistance to treatment is a concern for many types of cancer. Since many anti-neoplastic agents induce an apoptotic type of death in susceptible cells, it is likely that defects or dysregulation of different steps of the apoptotic pathways might be an important determinant of resistance to anticancer drugs. These defects might appear at the initiation and/or execution stages of apoptosis and result in the insufficient elimination of tumor cells, which might lead either to acquired resistance to treatment, or to uncontrolled migration of cancer cells and metastasis. Hence, identification and targeting of the disabled pathway, which is most efficiently inactivated in a particular type of tumor might be the most successful approach in the future. Here we review current knowledge concerning function of apoptotic machinery in cancer cells, and how this information can be used to increase the efficiency of tumor treatment.