How does radiation kill cells?

Translational upregulation of X-linked inhibitor of apoptosis (XIAP) increases resistance to radiation induced cell death

Inhibitory regulators of apoptosis play a critical role in the responsiveness of tumour cells to cytotoxic agents. The X-linked inhibitor of apoptosis protein (XIAP) is a member of a novel family of Inhibitor of Apoptosis (IAP) proteins. Here we show that acute low dose ionizing irradiation results in the translational upregulation of XIAP that correlates with an increased resistance to radiation in non-small cell lung carcinoma. This upregulation is mediated by an internal ribosome binding mechanism via an IRES element located within a XIAP 5' UTR. Transient overexpression of XIAP rendered human carcinoma cells resistant to low dose gamma-irradiation. By contrast, the antisense targeting of XIAP resulted in increased cell death following irradiation advocating a distinct role for XIAP in radiation resistant phenotype of human cancers. Oncogene (2000) 19, 4174 - 4177

Clinical applications of telomerase in cancer treatment

Telomerase activity has been found in most cancer cells, but not in the majority of normal differentiated tissues. Therefore, telomerase has been considered a relatively selective and widely expressed tumor marker to be used as a diagnostic tool, and in some cases, as a potential prognostic indicator. Telomerase activity can also be used to evaluate chemosensitivity of neoplastic cells obtained from cancer patients, by measuring residual telomerase activity after drug treatment. Finally, telomerase has been considered to represent a suitable target for designing new anticancer strategies. This review focuses on present and future clinical applications of telomerase studies in cancer management. Copyright 2000 Harcourt Publishers Ltd.

Chromosomal breakage-fusion-bridge events cause genetic intratumor heterogeneity

It has long been known that rearrangements of chromosomes through breakage-fusion-bridge (BFB) cycles may cause variability of phenotypic and genetic traits within a cell population. Because intercellular heterogeneity is often found in neoplastic tissues, we investigated the occurrence of BFB events in human solid tumors. Evidence of frequent BFB events was found in malignancies that showed unspecific chromosome aberrations, including ring chromosomes, dicentric chromosomes, and telomeric associations, as well as extensive intratumor heterogeneity in the pattern of structural changes but not in tumors with tumor-specific aberrations and low variability. Fluorescence in situ hybridization analysis demonstrated that chromosomes participating in anaphase bridge formation were involved in a significantly higher number of structural aberrations than other chromosomes. Tumors with BFB events showed a decreased elimination rate of unstable chromosome aberrations after irradiation compared with normal cells and other tumor cells. This result suggests that a combination of mitotically unstable chromosomes and an elevated tolerance to chromosomal damage leads to constant genomic reorganization in many malignancies, thereby providing a flexible genetic system for clonal evolution and progression.

Radiation-induced centrosome overduplication and multiple mitotic spindles in human tumor cells

The centrosome is a highly regulated organelle and its proper duplication is indispensable for the formation of bipolar mitotic spindles and balanced chromosome segregation. To elucidate a possible linkage between centrosome duplication and radiation-induced nuclear damage, we examined centrosome dynamics in U2-OS osteosarcoma cells following gamma-irradiation. Nearly all control cells contained one or two centrosomes, and at mitosis more than 97% of the cells displayed typical bipolar spindles. In contrast, over 20% of cells at 48 h after 10 Gy gamma-irradiation contained more than two centrosomes, and 60% of the mitotic cells showed aberrant spindles organized by multiple poles. Remarkably, the cells with multiple centrosomes frequently exhibited changes in size and/or morphology of the nucleus, including micronuclei formation. We conclude that abnormal centrosome duplication could be one of the key events involved in nuclear fragmentation and perhaps even cell death following irradiation.