Characterization of human and rat immortalized clones parotid acinar cells with respect to specific proteins and their mRNAs, and receptor-linked adenylate cyclase

Vitamin E (d-alpha-tocopheryl succinate) decreases mitotic accumulation in gamma-irradiated human tumor, but not in normal, cells

Previous studies have shown that treatment of tumor cells in vitro with d-alpha-tocopheryl succinate (alpha-TS), a most effective form of vitamin E, alone or in combination with X-irradiation, reduced the growth of these cells more than that produced by individual agents. However, it is unknown whether alpha-TS, alone or in combination with gamma-irradiation, would produce similar effects on normal cells. To study this, we have compared the effects of alpha-TS on three human tumor cell lines, HeLa (cervical carcinoma), OVGI (ovarian carcinoma), and A549 (lung carcinoma), with the effects on three human normal fibroblast lines, GM2149, AG1522, and HF19. Results showed that alpha-TS treatment of HeLa cells for 20 hours caused inhibition of growth in a dose-dependent manner, but normal human fibroblasts treated similarly with alpha-TS did not show such an effect. alpha-TS treatment for 20 hours also decreased mitotic accumulation in all three tumor cell lines but did not produce such an effect in any of the normal fibroblasts. As expected, gamma-irradiation with 1 Gy decreased mitotic accumulation in human tumor cells and normal fibroblasts; however, alpha-TS treatment for 24 hours before, during, and after irradiation for the entire experimental period further decreased mitotic accumulation in human tumor cells but not in normal cells. These data suggest that effects of alpha-TS, alone or in combination with gamma-irradiation, are selective for tumor cells. Therefore, existing fear that antioxidants such as vitamin E may protect cancer cells from free radical damage during radiation therapy is not justified.

Characterization of immortalized rabbit lacrimal gland epithelial cells

To establish an immortalized lacrimal gland epithelial cell line, the orbital lacrimal glands of normal New Zealand White rabbits were multiply injected with an immortalizing amphotropic retroviral vector (LXSN16E6E7) containing the E6 and E7 genes of human papillomavirus type 16. Lacrimal glands were removed after 2 d and acinar epithelial cells were isolated and cultured on Matrigel-coated 60 mm2 plates containing DMEM-F12 supplemented with 5% Nu-serum V. Transformed cells were selected in G418 sulfate for 7 d and passaged. Morphology of the immortalized cells was similar to that described for normal acinar cells both in vivo and in vitro, with rough endoplasmic reticulum and secretory granules. These characteristics remained unchanged and the cells continued to exhibit typical polygonal epithelioid structure. The cells have been maintained in culture for 14 mo. and have gone through 58 passages without loss of proliferation or epithelial cell characteristics. Immunohistochemistry and Western blots showed positive reactivity to secretory component, transferrin, and transferrin receptor, which are typical proteins found in the lacrimal gland. Functional analysis by stimulation with a cholinergic agonist, carbachol (100 microM), resulted in a significant release of protein. This is the first report of an immortalized rabbit lacrimal epithelial cell. These cells will provide a valuable tool for the molecular analysis of lacrimal gland epithelial cell functions.

Effect of adenosine 3',5'-cyclic monophosphate (cAMP) on human non-tumorigenic and tumorigenic parotid acinar cells in culture

Adenosine 3',5'-cyclic monophosphate (cAMP) regulates growth and/or differentiation of some tumor cells in culture. The effects of cAMP on human parotid acinar cells have never been studied. Results showed that 2HPC8 (non-tumorigenic cells derived from human pleomorphic parotid adenoma) were more sensitive to dibutyryl cAMP, an analog of cAMP, and RO20-1724, an inhibitor of cyclic nucleotide phosphodiesterase, than 2HP1G cells (derived from spontaneous transformation of 2HPC8 cells), suggesting that human parotid adenoma cells maintain a higher degree of cAMP-responsiveness than parotid carcinoma cells. Prostaglandin E1 (PGE1), a stimulator of adenylate cyclase, which increased cAMP levels in 2HPC8 cells, but not in 2HP1G cells, caused a greater degree of growth inhibition in 2HP1G cells than in 2HPC8 cells, suggesting that this effect of PGE1 on tumorigenic cells is not related to cAMP. In the normal parotid and parotid adenoma cell cultures, about 5-10% of cells were small and round, whereas in tumorigenic cell cultures, all cells were small and round. Some indirect evidence suggests that these round cells may be the primary target for transformation. These tumor cells formed cytoplasmic processes of variable length after treatment with cAMP stimulating agents and prostaglandin E1.

Effect of individual and multiple antioxidant vitamins on growth and morphology of human nontumorigenic and tumorigenic parotid acinar cells in culture

The effects of individual and multiple antioxidant vitamins on growth and morphology of human nontumorigenic (2HPC8) and tumorigenic (2HP1G) parotid acinar cells in culture have not been investigated. Our study showed that tumorigenic acinar cells were more sensitive than nontumorigenic acinar cells to individual vitamins such as vitamin C, beta-carotene (BC), d-alpha-tocopheryl succinate (alpha-TS), and retinoic acid (RA) and a mixture of four vitamins (vitamin C, BC, alpha-TS, and RA). The effect of individual vitamins on tumorigenic acinar cells depended on the dose and the type of vitamins. Vitamin C at a low concentration stimulated growth, but at a high concentration it inhibited growth. BC was most effective in reducing growth, and it alone caused extensive morphological changes in tumorigenic acinar cells. A mixture of four vitamins at appropriate doses was more effective than a mixture of two or three vitamins at the same doses in reducing the growth of tumorigenic acinar cells. The extent of growth inhibition depended on the dose and the type of vitamins. Our results suggest that the use of multiple antioxidant vitamins is essential for a maximal reduction in cancer incidence among a high-risk population. The use of one or two vitamins may be ineffective or even harmful.