Carol A. Jones

Mutagenesis and cytotoxicity in human epithelial cells by far- and near-ultraviolet radiations: action spectra.

Action spectra were determined for cell killing and mutation by monochromatic ultraviolet and visible radiations (254-434 nm) in cultured human epithelial P3 cells. Cell killing was more efficient following radiation at the shorter wavelengths (254-434 nm) than at longer wavelengths (365-434 nm). At 254 nm, for example, a fluence of 11 Jm-2 gave 37% cell survival, while at 365 nm, 17 X 10(5) Jm-2 gave equivalent survival. At 434 nm little killing was observed with fluences up to 3 X 10(6) Jm-2. Mutant induction, determined at the hypoxanthine-guanine phosphoribosyltransferase locus, was caused by radiation at 254, 313, and 365 nm. There was no mutant induction at 334 nm although this wavelength was highly cytotoxic. Mutagenesis was not induced by 434 nm radiation, either. There was a weak response at 405 nm; the mutant frequencies were only slightly increased above background levels. For the mutagenic wavelengths, log-log plots of the mutation frequency against fluence showed linear regressions with positive slopes of 2.5, consistent with data from a previous study using Escherichia coli. The data points of the action spectra for lethality and mutagenesis were similar to the spectrum for DNA damage at wavelengths shorter than 313 nm, whereas at longer wavelengths the lethality spectrum had a shoulder, and the mutagenesis spectrum had a secondary peak at 365 nm. No correlation was observed for the P3 cells between the spectra for cell killing and mutagenesis caused by wavelengths longer than 313 nm and the induction of DNA breakage or the formation of DNA-to-protein covalent bonds in these cells.

Induction of DNA-protein crosslinks in human cells by ultraviolet and visible radiations: action spectrum

Abstract— DNA‐protein crosslinking was induced in cultured human P3 teratocarcinoma cells by irradiation with monochromatic radiation with wavelengths in the range254–434 nm (far‐UV, near‐UV, and blue light). Wavelength 545 nm green light did not induce these crosslinks, using the method of alkaline elution of the DNA from membrane filters. The action spectrum for the formation of DNA‐protein crosslinks revealed two maxima, one in the far‐UV spectrum that closely coincided with the relative spectrum of DNA at 254 and 290 nm, and one in the visible light spectrum at 405 nm, which has no counterpart in the DNA spectrum. The primary events for the formation of DNA‐protein crosslinks by such long‐wavelength radiation probably involve photosensitizers. This dual mechanism for DNA‐protein crosslink formation is in strong contrast to the single mechanism for pyrimidine dimer formation in DNA, which apparently has no component in the visible light spectrum.

Different (direct and indirect) mechanisms for the induction of DNA-protein crosslinks in human cells by far- and near-ultraviolet radiations (290 and 405 nm)

Abstract— Apparent DNA‐protein crosslinking induced by monochromatic 290 and 405 nm Tadiations was measured in cultured human P3 teratocarcinoma cells with DNA alkaline elution techniques. The rates of the induction of crosslinks by 290 nm radiation were the same when the cells were irradiated either aerobically or anaerobically or when the cells were in an H2O or D2O aqueous environment. With 405 nm radiation, anaerobic irradiation reduced the induction of the crosslinks (dose modifying factor is about 0.2), and about twice as many crosslinks were observed when the cells were irradiated in an environment of D2O rather than H2O. The results are consistent with the hypothesis that far‐UV radiation induces DNA‐protein crosslinks by a direct mechanism, whereas near‐UV radiation induces crosslinks via indirect photodynamic photosensitizations in which unidentified cellular endogenous photosensitizers and reactive species of oxygen are used.

Fission-neutron-induced Expression of a Tumour-associated Antigen in Human Cell Hybrids (HeLa × Skin Fibroblast): Evidence for Increased Expression at Low Dose Rate

The induction of a tumour-associated antigen in a human cell hybrid line (HeLa x skin fibroblast) following exposure to fission neutrons of average energy 0.85 MeV (Janus reactor, Argonne National Laboratory) at two dose rates, 0.086 and 10.3 cGy/min, has been examined. The dose-response data obtained indicate the lower dose rate to be 2.9-fold more effective than the higher in inducing expression of the tumour-associated antigen, while there was no significant dose-rate effect in terms of cell killing. These results are qualitatively in agreement with previous observations using neutrons from the Janus reactor for the neoplastic transformation of C3H10T1/2 cells and Syrian hamster embryo cells.

The Multistage Concept of Carcinogenesis

The recognition of carcinogenesis as a complex multievent process has developed from evidence gained over the past 50 years of research in experimental oncology demonstrating that tumors can be induced in high yield by the combined administration of agents that may have little or no carcinogenic activity when given singly. Three major types of tumorigenic enhancement may be defined on the basis of the types of inducing agents used and of the temporal relationships of their administration: 1. Syncarcinogenesis: Synergistic enhancement of tumor formation by simultaneous1 or sequential treatment2 with two carcinogens that separately may have relatively little carcinogenic activity 2. Cocarcinogenesis: Enhancement of tumor formation by simultaneous administration of a carcinogen and an additional agent (cocarcinogen) that has no intrinsic carcinogenic activity but facilitates carcinogen action3–8 3. Two-stage, or initiation-promotion carcinogenesis: Enhancement of tumor formation by the sequential administration of a carcinogen (initiator) and an additional agent (promoter) that has no intrinsic carcinogenic activity but facilitates expression of prior carcinogen-induced cryptic cellular changes.3 In this context, an initiating agent is exemplified by a subcarcinogenic dose of carcinogen, i.e., one that will not elicit neoplasms within the life span of an animal but that will produce an irreversible fundamental change (i.e., mutation) in the cells of a target organ or tissue so as to predispose them to neoplastic transformation when they are further subjected to an appropriate tumor promoting stimulus. A tumor promoter, exemplified by certain plant products, hormones, and xenobiotics acts to affect gene expression and to stimulate a hyperplastic expansion of the initiated cell population. This process ultimately results in the development of persistent precancerous nodules, papillomas, or polyps within the target tissue or organ. Some of these lesions can then undergo progression to malignant neoplasms (see Chapter 10).

Inhibition of metabolic cooperation in Chinese hamster V79 cells by 1α,25-dihydroxycholecalciferol, the active metabolite of vitamin D3

The biologically active metabolite of vitamin D3, 1 alpha, 25-dihydroxycholecalciferol (1,25-(OH)2D3), inhibited the metabolic cooperation between cocultivated Chinese hamster V79 cells that are either susceptible or resistant to the cytotoxic effect of 6-thioguanine (TG). This inhibition was characterized by an increased survival of TG-resistant cells when they are cocultured with susceptible cells in the presence of TG. TG-resistant cells in the absence of susceptible cells and after treatment with TG yielded a cloning efficiency of about 90%. Cocultivation of these cells with the susceptible cells reduced this cloning efficiency to about 30%. At 0.5 microgram/ml, 1,25-(OH)2D3 restored the cloning efficiency of the TG-resistant cells in the cocultures to 62%. Phorbol 12-myristate 13-acetate (PMA), a known inhibitor of metabolic cooperation, at 0.5 microgram/ml restored the cloning efficiency to a similar extent. Vitamin D3, 24,25-dihydroxycholecalciferol (24,25-(OH)2D3, and phorbol were ineffective in inhibiting this metabolic cooperation. 1,25-(OH)2D3, unlike PMA, did not inhibit the binding of [3H]phorbol 12,13-dibutyrate (PDBu) to its cellular receptors in either the TG-susceptible or resistant cells. These results indicate that 1,25-(OH)2D3 resembles tumor-promoting agents such as PMA in its capacity to inhibit metabolic cooperation, but this capacity is not mediated through phorbol diester receptors.