Apoptosis is a basic biological process that promotes survival of the organism at the expense of individual cells (Kerr et al., 1972). Apoptosis is widely used by multi-cellular organisms to remove unwanted cells.

Apoptosis plays a role in various diseases such as diabetes, cancer, AIDS and cardiovascular disorders and even in neurological disorders of the brain such as Parkinson's, Alzheimer's, and Creutzfeldt-Jakob's disease. In diabetes, the insulin producing b-cells are obliterated through apoptosis.

The apoptotic machinery is often impaired in cancer cells (Reed, 1999; Wyllie et al., 1999). Whereas cell division and apoptosis usually are in balance in benign tumors, the rate of cell division is greater than the rate of apoptosis in malignant tumors. When cancer cells are not removed in adequate numbers through apoptosis, the size of the tumor increases. Treatment with radiation and/or anti-cancer drugs may, when successful, stimulate apoptosis leading to eradication of the tumor.

Many of the events that occur in the apoptotic cell are mediated by a family of cysteine aspartyl proteases called caspases (Salvesen and Dixit, 1997). Caspases are initially synthesized as inactive pro-enzymes, which are cleaved to active enzymes by various stimuli. Activation of caspases occurs early during the apoptotic process, prior to exposure of phosphatidyl serine (p.s.) affecting the outer surface of the plasma membrane (detected by binding of annexin V). Caspase substrates are widely dispersed in the nucleus, cytoplasm and cytoskeleton. One such substrate is the intermediate filament protein cytokeratin 18 (Caulin et al., 1997; Leers et al., 1999). The proteolytic cleavage events of various cellular proteins, mediated by caspases, account for the biochemical and morphological changes observed during apoptosis.

Caspase activation is the end result of various stimuli. These can be pathological and include damage to cell membranes, mitochondria or DNA. The intracellular mechanisms leading to activation of pro-caspases are complex and often involve release of cytochrome C from mitochondria (Li et al., 1997). Little is known about the mechanisms by which anti-cancer agents induce changes at the level of mitochondria and the subsequent release of cytochrome C.

The Bcl-2 protein family represent one of the major families of apoptosis-regulatory proteins. There are at least 16 members of this group (Zamzami et al., 1998). The Bcl-2 gene was discovered as a proto-oncogene adjacent to chromosome translocations in low-grade B-cell non-Hodgkin´s lymphoma. Bcl-2 is an apoptosis-suppressor, and the activity of Bcl-2 in B-cell lymphoma leads to decreased apoptosis and an increase in the tumor cell population.

The success of cancer treatment using radiation or chemotherapy is highly variable. Some tumors respond well to treatment, others do not. Methods which can determine if apoptosis has been stimulated may assist in monitoring the effectiveness of therapy. A simple test method for this diagnosis has been missing. Measuring caspase cleavage products using M30-Apoptosense® in patient sera (For Research Only) is one approach to this problem.

REFERENCES

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Kerr, J. F., Wyllie, A. H., and Currie, A. R. (1972). Apoptosis: a basic biological phenomenon with wide-ranging implications in tissue kinetics. Br J Cancer 26, 239-57.

Leers, M. P., Kölgen W., Björklund, V.. Bergman, T., Tribbick, G., Persson, B., Björklund, P., Ramaekers, F. C., Björklund, B., Nap, M., Jörnvall H, Schütte, B. (1999) Immunocytochemical detection and mapping of a cytokeratin 18 neo- epitope exposed during early apoptosis. J. Pathology 187, 567-572.

Li, P., Nijhawan, D., Budihardjo, I., Srinivasula, S. M., Ahmad, M., Alnemri, E. S., and Wang, X. (1997). Cytochrome c and dATP-dependent formation of Apaf-1/caspase-9 complex initiates an apoptotic protease cascade. Cell 91, 479-89.

Reed, J. C. (1999). Mechanisms of apoptosis avoidance in cancer. Curr Opin Oncol 11, 68-75.

Salvesen, G. S., and Dixit, V. M. (1997). Caspases: intracellular signaling by proteolysis. Cell 91, 443-6.

Wyllie, A. H., Bellamy, C. O., Bubb, V. J., Clarke, A. R., Corbet, S., Curtis, L., Harrison, D. J., Hooper, M. L., Toft, N., Webb, S., and Bird, C. C. (1999). Apoptosis and carcinogenesis. Br J Cancer 80 Suppl 1, 34-7.

Zamzami, N., Brenner, C., Marzo, I., Susin, S. A., and Kroemer, G. (1998). Subcellular and submitochondrial mode of action of Bcl-2-like oncoproteins. Oncogene 16, 2265-82.