Short-term assays for detection of conditional cancerogens. I. Construction of DR-CAT Raji cells and some of their characteristics as tester cells

A number of agents including the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) (TPA) can induce an abortive virus cycle in the EBV-non-producer Burkitt's-lymphoma line Raji. Two distant regions, DL and DR, of the EBV genome with almost complete homology carry strong promoters which are induced in an abortive or lytic cycle and additionally function as lytic origins of viral DNA replication. To set up a system in which the activity of EBV-inducing agents can be measured in a quantitative and reproducible fashion, we generated a cell line which carries multiple copies of a DR-promoter chloramphenicol-acetyltransferase (CAT) construct on an episomal vector. CAT activity is low in untreated cells, but high upon treatment of the cells with various EBV-inducing agents. Combinations of different agents can produce an over-additive effect. The Raji-DR-CAT cell line may provide a simple quantitative and reproducible test system for EBV-inducing agents, especially for tumor promoters which activate protein kinases C.

Toxicodynamics of tumour promoters of mouse skin. II. Binding to protein kinase C of some new diterpene esters and induction of luminol-enhanced chemoluminescence in mouse peritoneal neutrophils

In binding competition assays using a protein kinase C preparation from mouse brain (particulate fraction) 3H-labelled 12-O-tetradecanoylphorbol-13-acetate (TPA), for a series of new diterpene esters (DTE) the relative binding affinity [rba = Kia(TPA)/Kia(DTE)] in relation to TPA was determined. A wide range of values was noticed, some of the DTE binding more strongly than TPA (rba greater than 1), others binding less strongly than TPA (rba less than 1) In comparative terms, competition for specific binding sites appears to correlate better with irritant than with promoting activity of the DTE. Using mouse peritoneal neutrophils, binding of [3H]-TPA was determined by a modification of the "cold-acetone filter assay"; saturation of high-affinity sites (Kda = 0.2 nM) was obtained at concentrations less than or equal to 1 nM, but there was also evidence for specific binding at "low-affinity" sites (Kda = 26 nM). Induction of chemoluminescence in the presence of luminol in mouse peritoneal neutrophils with a set of DTE usually elecited two peaks; at concentrations greater than or equal to 10 nM DTE a short-lived, "spike-like" response lasting only from 0 to about 5 min (phase A) its followed by a "plateau" response from about 5-120 min (phase B). This latter phase of chemoluminescence stimulation with luminol correlated well with the irritant potential of the DTE used. The sequence of the two phases can be inverted partially by using first TPA at 2,5 nM followed by a quick concentration increase to 100 nM; this indicates two different concentration-dependent events. As regards the intensity of the chemoluminescent response, quantitative but not qualitative differences between DTE were observed, which show some correlation with strong and weak tumour-promoting activity. Inhibition studies suggest the involvement of the myeloperoxidase/H2O2/Cl- system in the luminogenic response; it is suggested that the release of hypochlorite or a closely related oxidant may be instrumental in tumour promotion.

Induction of Epstein-Barr virus early antigens by tumor promoters of the diterpene ester type in Raji cells and specific (receptor) binding as compared to irritant and promoting activities

Sixteen new diterpene esters (DTE) of the tigliane, ingenane, daphnane, and 1 alpha-alkyldaphnane types were investigated in two in vitro assays: as inhibitors of specific binding of 3H-labeled 12-O-tetradecanoylphorbol 13-acetate (TPA) to protein kinase C in a receptor preparation from mouse brain, and as inducers of Epstein-Barr virus (EBV) early antigens in Raji cells. Inhibition of binding of [3H]TPA to the receptor preparation by tigliane and ingenane DTE correlates with irritant activity in vivo, while some daphnane and 1 alpha-alkyldaphnane DTE inhibit binding of [3H]TPA in a less pronounced manner but still are very irritant. Tumor-promoting activity does not correlate consistently with the receptor-binding data. To test the hypothesis that early antigen induction in Raji cells by DTE is coupled to functional DTE receptors (protein kinase C), the latter were searched on these Raji cells by a 'cold acetone-filter assay' and shown to be present. The dependence of the early antigen induction rate on the concentration of the DTE tested was demonstrated. At a given concentration of DTE, differences in the induction rate between various DTE are seen. However, a clear quantitative correlation either between early antigen induction and receptor binding data in vitro, or early-antigen-inducing activity in vitro versus irritancy and tumor-promoting activity in vivo was not observed.