Radiation-induced cancer cell repopulation: a possible mechanism implied by experiments using transplantable mouse-derived sarcoma cell line.

PURPOSE: Treatment with any cytotoxic agent can trigger surviving cells in a tumor to divide faster than before. This phenomenon is widely recognized as "repopulation". To better clarify the mechanism, gene expression profiling and pathological experiments were performed. MATERIALS AND METHODS: A mouse fibrosarcoma cell line, QRsP, was used. Cells were irradiated with 10 Gy. Colony assay and cloning were performed. Six clones were established. cDNA analysis was performed on the clone that showed the largest number of colonies on the 2nd 10 Gy irradiation. Mouse transplantation experiment was then carried out. RESULTS: cDNA analysis showed that cyclin-dependent kinase inhibitors, p16 and p57 were down-regulated; 14.8- and 12.0-fold, respectively for the tolerant clone. Matrix metalloproteinase 3 and 13 were up-regulated; 22.5- and 25.8-fold, respectively. Transplantation ratio was 100% (5/5) for the tolerant clone whereas it was 40% (2/5) for the parent. Under light microscope, the mean mitotic cell number was 4.0+/-3.9 for the parent, and 12.8+/-3.4 for the tolerant clone (p<0.01, Student's t-test). CONCLUSIONS: This study implies that repopulation is not a temporary reaction to irradiation. It is caused probably by "clonal" gene-expression changes, though it remains unknown whether the changes are attributable to tolerant cell selection or to gene mutation/modification.

Determination of nitrobenzene in water and ice samples collected from the Songhua River after an explosion of a petrochemical plant and investigation on enclosing behavior of nitrobenzene into ice.

In this study, nitrobenzene in water and ice samples collected from the Songhua River after the explosion of a petrochemical plant was determined by GC/MS. The results showed that nitrobenzene was detected in most of the water and ice samples taken from the Songhua River. However, the concentration of nitrobenzene in all water and ice samples was from 0 to 0.65 microg L(-1); this range was sufficiently lower than the permissible level (0.017 mg L(-1)) for drinking water in China. The enclosing behavior of nitrobenzene in ice was also investigated. The amount of nitrobenzene enclosed in ice was lower than that reported by UNEP.