In vitro cell cultures as tools in the study of free radicals and free radical modifiers in carcinogenesis

Evidence for increased non-ceruloplasmin copper in early-stage human breast cancer serum

We measured total serum copper and ceruloplasmin levels in pre- and postmenopausal Stage I and II breast cancer (BC) patients and omnivorous and vegetarian controls. The omnivorous groups included 14 premenopausal women [33 +/- 6 (SD) yrs] and 11 postmenopausal women (57 +/- 5 yrs), and the vegetarian groups were comprised of 12 premenopausal subjects (34 +/- 7 yrs) and 11 postmenopausal subjects (59 +/- 5 yrs). There were 13 premenopausal BC patients (39 +/- 7 yrs) and 10 postmenopausal BC patients (66 +/- 6 yrs). Fasting serum samples were taken on three consecutive days, typically four times in the year. Serum ceruloplasmin levels (g/l) were measured by nephelometry utilizing monoclonal antiserum, and total serum copper levels (mumol/l) were determined by proton-induced X-ray emission analysis. Premenopausal patients had higher serum copper levels than their controls (mean 18.7 vs. 16.6, p less than 0.03). For ceruloplasmin, the postmenopausal BC patients had significantly lower levels than pooled postmenopausal controls (0.309 vs. 0.370, p less than 0.001). The copper-to-ceruloplasmin ratio was significantly higher in the pooled cancer groups than in the pooled control groups (3.69 vs. 3.21, p less than 0.001), with similar patterns in both pre- and postmenopausal classes. This high serum copper-to-ceruloplasmin ratio in BC patients may reflect disordered copper metabolism in this disease, which could also have implications for the origin of, or the response to, the cancer process.

Long-chain (sphingoid) bases inhibit multistage carcinogenesis in mouse C3H/10T1/2 cells treated with radiation and phorbol 12-myristate 13-acetate

Sphingosine and other long-chain (sphingoid) bases inhibit protein kinase C, the putative cellular receptor for the tumor promoter phorbol 12-myristate 13-acetate (PMA), and exert potent effects on diverse cell functions. We tested the ability of long-chain bases to modulate multistage carcinogenesis in mouse C3H/10T1/2 cells exposed to gamma-rays and PMA. Sphingosine and sphinganine completely blocked the enhancement of radiation-induced transformation by PMA (promotion) and partially suppressed transformation by radiation alone. N-Acetylsphingosine, a ceramide analog, did not inhibit transformation. Sphingosine was rapidly taken up by the cells and metabolized; hence, the long-chain bases were added daily to achieve prolonged inhibition. Long-chain bases inhibited protein kinase C activity in C3H/10T1/2 cells and suppressed the down-regulation of this enzyme by PMA. Our results establish that long-chain bases are highly effective inhibitors of carcinogenesis in this model. Our results also indicate that the suppressive effects may be mediated, in part, by inhibition of protein kinase C. The data suggest that sphingosine and other long-chain bases derived from complex sphingolipids may act as cancer-preventative agents.

Distinctive transforming genes in x-ray-transformed mammalian cells

DNAs from hamster embryo cells and mouse C3H/10T1/2 cells transformed in vitro by x-irradiation into malignant cells transmit the radiation transformation phenotype by producing transformed colonies (transfectants) in two mouse recipient lines, the NIH 3T3 and C3H/101/2 cells, and in a rat cell line, the Rat-2 cells. DNAs from unirradiated cells or irradiated and visibly untransformed cells do not produce transformed colonies. The transfectants grow in agar and form tumors in nude mice. Treatment of the DNAs with restriction endonucleases prior to transfection indicates that the same transforming gene (oncogene) is present in each of the transformed mouse cells and is the same in each of the transformed hamster cells. Southern blot analysis of 3T3 or Rat-2 transfectants carrying oncogenes from radiation-transformed C3H/10T1/2 or hamster cells indicates that the oncogenes responsible for the transformation of 3T3 cells are not the Ki-ras, Ha-ras, or N-ras genes, nor are they neu, trk, raf, abl, or fms, although quick blot analysis using 11 oncogene probes detected increased transcripts of c-abl and c-fms in the 3T3 transformants containing oncogenic sequences from the x-ray-transformed C3H/10T1/2 cells. The work demonstrates that DNAs from mammalian cells transformed into malignancy by direct exposure in vitro to radiation contain genetic sequences with detectable transforming activity in three recipient cell lines. The results provide evidence that DNA is the target of radiation carcinogenesis induced at a cellular level in vitro. The experiments indicate that malignant radiogenic transformation in vitro of hamster embryo and mouse C3H/10T1/2 cells involves the activation of unique non-ras transforming genes, which heretofore have not been described.

Selenium and vitamin E inhibit radiogenic and chemically induced transformation in vitro via different mechanisms

Results from in vivo and in vitro studies showing that antioxidants may act as anticarcinogens support the role of active oxygen in carcinogenesis and provide impetus for exploring the functions of dietary antioxidants in cancer prevention by using in vitro models. We examined the single and combined effects of selenium, a component of glutathione peroxidase, and vitamin E, a known antioxidant, on cell transformation induced in C3H/10T-1/2 cells by x-rays, benzo[a]pyrene, or tryptophan pyrolysate and on the levels of cellular scavenging systems and peroxide destruction. Incubation of C3H/10T-1/2 cells with 2.5 microM Na2SeO3 (selenium) or with 7 microM alpha-tocopherol succinate (vitamin E) 24 hr prior to exposure to x-rays or the chemical carcinogens resulted in an inhibition of transformation by each of the antioxidants with an additive-inhibitory action when the two nutrients were combined. Cellular pretreatment with selenium resulted in increased levels of cellular glutathione peroxidase, catalase, and nonprotein thiols (glutathione) and in an enhanced destruction of peroxide. Cells pretreated with vitamin E did not show these biochemical effects, and the combined pretreatment with vitamin E and selenium did not augment the effect of selenium on these parameters. The results support our earlier studies showing that free radical-mediated events play a role in radiation and chemically induced transformation. They indicate that selenium and vitamin E act alone and in additive fashion as radioprotecting and chemopreventing agents. The results further suggest that selenium confers protection in part by inducing or activating cellular free-radical scavenging systems and by enhancing peroxide breakdown while vitamin E appears to confer its protection by an alternate complementary mechanism.

Antagonistic action of a tumor promoter and a poly(adenosine diphosphoribose) synthesis inhibitor in radiation-induced transformation in vitro

Transformation of mouse C3H 10T1/2 cells by X-irradiation in vitro was blocked by the addition of 1 mM 3-aminobenzamide, an inhibitor of polyadenosine diphosphoribose (poly[ADP-ribose]) synthesis immediately after irradiation. 3-Aminobenzamide also inhibited an increase in the frequency of transformants caused by the addition of the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate, 7 days after irradiation. These results demonstrate a role for poly(ADP-ribose) synthesis during the initiation and promotion stages of transformation. From previous studies it is known that poly(ADP-ribose) synthesis is stimulated by the DNA damage caused by X rays during initiation. During promotion, however, 12-O-tetradecanoylphorbol-13-acetate acted as a mitogen but did not induce detectable DNA damage, and we could detect no stimulation of poly(ADP-ribose) synthetase. The roles of poly(ADP-ribose) during initiation and during promotion must, therefore, be significantly different.

Sodium bisulfite protects against radiogenic and chemically induced transformation in hamster embryo and mouse C3H/10T-1/2 cells

Pretreatment of hamster embryo cells or mouse C3H/10T-1/2 cells with sodium bisulfite (0.5, 2.5, 5.0 and 100 ppm) inhibits the oncogenic transformation of the cells following their exposure to x-rays or benzo(a)pyrene. The results suggest that low doses of bisulfite, a widely used food additive, can serve as a radioprotective and chemopreventive agent with anticarcinogenic potential.