Development of a quantitative bioassay to assess preventive compounds against inflammation-based carcinogenesis.

Reducing cancer incidence and mortality by use of cancer-chemopreventive agents is an important goal. We have established an in vitro bioassay that is able to screen large numbers of candidate chemicals that are positive for prevention of inflammation-related carcinogenesis. To accomplish this we have added candidate chemicals or vehicles and freshly isolated, fluorescent dye-labeled inflammatory cells that were overlaid on TNF-alpha-stimulated mouse endothelial cells in a 96-well plate. Inhibition of inflammatory cell attachment to the endothelial cells by the chemicals was quantified by the intensity of fluorescence from the adherent inflammatory cells after removing unattached cells. Using this assay, we selected two chemicals, auraptene and turmerones, for further study. As an in vivo test, diets containing these test chemicals were administered to mice with a piece of foreign body, gelatin sponge, that had been implanted to cause inflammation, and we found that the number of inflammatory cells that infiltrated into the subcutaneously implanted gelatin sponge was reduced compared to that found in the mice fed with a control diet. Moreover, diets containing either of the two chemicals prevented inflammation-based carcinogenesis in a mouse model. We found that the compounds reduced not only the number of infiltrating cells but also the expression of inducible nitric oxide synthase (iNOS) or formation of 8-hydroxy-2'-deoxyguanine (8-OHdG) in the infiltrated cells. Moreover, both compounds but not controls sustained the reducing activity in the inflammatory lesion, and this finding was confirmed by using non-invasive in vivo electron spin resonance. The newly established in vitro screening assay will be useful for finding biologically effective chemopreventive agents against inflammation-related carcinogenesis.

Nano-scaled particles of titanium dioxide convert benign mouse fibrosarcoma cells into aggressive tumor cells.

Nanoparticles are prevalent in both commercial and medicinal products; however, the contribution of nanomaterials to carcinogenesis remains unclear. We therefore examined the effects of nano-sized titanium dioxide (TiO(2)) on poorly tumorigenic and nonmetastatic QR-32 fibrosarcoma cells. We found that mice that were cotransplanted subcutaneously with QR-32 cells and nano-sized TiO(2), either uncoated (TiO(2)-1, hydrophilic) or coated with stearic acid (TiO(2)-2, hydrophobic), did not form tumors. However, QR-32 cells became tumorigenic after injection into sites previously implanted with TiO(2)-1, but not TiO(2)-2, and these developing tumors acquired metastatic phenotypes. No differences were observed either histologically or in inflammatory cytokine mRNA expression between TiO(2)-1 and TiO(2)-2 treatments. However, TiO(2)-2, but not TiO(2)-1, generated high levels of reactive oxygen species (ROS) in cell-free conditions. Although both TiO(2)-1 and TiO(2)-2 resulted in intracellular ROS formation, TiO(2)-2 elicited a stronger response, resulting in cytotoxicity to the QR-32 cells. Moreover, TiO(2)-2, but not TiO(2)-1, led to the development of nuclear interstices and multinucleate cells. Cells that survived the TiO(2) toxicity acquired a tumorigenic phenotype. TiO(2)-induced ROS formation and its related cell injury were inhibited by the addition of antioxidant N-acetyl-l-cysteine. These results indicate that nano-sized TiO(2) has the potential to convert benign tumor cells into malignant ones through the generation of ROS in the target cells.