Regulation of carcinogenic food additives and drugs in the US.

The four components of the process by which a decision is made about the acceptability of human exposure to a chemical are outlined. The quantity and quality of the data that are required have increased considerably in recent years, and the standards governing the conduct of the studies done to obtain them have become more stringent. Thus, many chemicals now in widespread use were admitted on the basis of evidence that is now considered woefully inadequate; the steps being taken in the US to remedy this situation are described. Since such testing is long and expensive, four regulatory agencies have joined together to develop guidelines that can be used by each. The interpretation of data presents yet another problem. Further, what constitutes adequate evidence for safety is a matter subject to wide ranges of opinion: this is illustrated by the example of cyclamate. The difficulties of extrapolating results to actual situations are outlined; and the limitations of the usefulness of experimental testing are pointed out. Determination of an acceptable ratio between benefits and risks depends on a wide variety of factors, and regulatory decisions in this regard thus depend on several kinds of scientific judgements and on policy decisions based on cultural aspects.

Effects of methylation of the beta-galactosidase genome upon in vitro synthesis of beta-galactosidase.

A template DNA from phage lambdah80dlacp5 coding for the in vitro synthesis of beta-galactosidase was used to study the effect of DNA methylation by the alkylating agent, dimethyl sulfate (DMS). Increasing the levels of DMS up to 50 mM concentration in the incubation medium led to an increase of DNA methylation. When incubated for 10 min at 37 degrees C, 3-4% Of nucleotides were methylated. The increase was linear to about 0.6% nucleotide methylation level. A higher yield was obtained at 37 degrees C incubation temperature than at 20 degrees C. Methylation of lambdah80dlacp5 DNA alone without methylation of other factors in the incubation mixture caused inhibition of the synthesis of beta-galactosidase in vitro. Increasing levels of DNA methylation caused greater inhibition of the newly synthesized enzyme activity. Total protein and RNA synthesis was inhibited by the methylated DNA to a much lesser extent than the inhibition of enzyme activity. When the level of nucleotide methylation was 0.74%, only 2% of enzyme activity remained, but total protein and RNA synthetic activities were found to be 72% and 44%, respectively.

Organ culture of rodent prostate. Effects of polyamines and testosterone.

Prostate organs were maintained in culture for 14 days on a plasma clot to which insulin, testosterone, spermine, and spermidine were added. Explants cultured in the control medium (embryo extract and chicken plasma) showed regressive changes and there was complete necrosis by the 5th day. When cultured in the presence of testosterone plus the control medium the explants continued to maintain their epithelial height and stromal characteristics after 5 days. By the 7th day regressive changes similar to those seen for explants cultured in the absence of testosterone were observed. With spermine and spermidine in the medium along with insulin and testosterone, the stromal and epithelial integrity of the explants was kept intact for 14 days. When either testosterone or spermine was omitted from this list of additives, survival and maintenance of normal morphology were greatly impaired. Omission of spermidine did not affect results if the other chemicals were added. No attempts were made to maintain cultures beyond 14 days.

Transplantations of isologous prostatic tissue in cleared mammary fat pads of BALB/c mice and F344 rats.

The cleared inguinal (mammary) fat-pad of male and female BALB/c mice and F344 rats was found to be a suitable site for maintaining prostate transplants. Uncastrated syngeneic hosts were stimulated by testosterone propionate pellets implanted under their dorsal skin. Transplants survived in testosterone-stimulated male and female hosts for as long as 21 months, at which time the experiment was terminated. However, transplants did not survive in unstimulated female hosts. Histological examination of transplants in stimulated animals showed that the epithelial height was maintained and there was increased secretory activity. Attempts to maintain prostate transplants in spleen, kidney capsule, and in scapulat fat-pad for long periods were unsuccessful. Transplants at these sites survived for less than 1 year, the epithelium was low and irregular, and palpation of the transplants was difficult. The prolonged viability of prostate transplants in cleared inguinal mammary fat-pads should facilitate the study of the effects of carcinogens and/or hormones on the prostate.

Chemical carcinogenesis and the pancreas.

Although carcinoma of the pancreas is an increasingly prevalent form of human cancer, there has been relatively little experimental work on the etiology of this tumor until recently, probably because of the lack of adequate experimental models. However, at least two good experimental systems are now available. Several epidemiologic investigations suggest that chemical carcinogens may induce cancer of the pancreas in humans. If this is so, chemicals must reach the pancreas either through the blood supply or by reflux into the pancreatic duct from bile or duodenal contents. The route of exposure may vary according to the chemical and physical characteristics of different chemical carcinogens. Additional work is needed to determine the ability of different classes of chemicals to reach the pancreatic duct by these routes and the presence of enzymes required for activation of carcinogens in the pancreas. Levels of such enzymes as well as the response of cells of the pancreatic duct to carcinogens may be affected by the physiologic state of the pancreas or pathologic conditions within it. Research is needed to investigate these possibilities.

Teratogenic evaluation of 2,4,5-T.

The herbicide 2,4,5-trichlorophenoxyacetic acid is teratogenic and fetocidal in two strains of mice when administered either subcutaneously or orally and in one strain of rats when administered orally. The incidences of both cystic kidney and cleft palate were increased in the C57BL/6 mice as well as the incidence of cleft palate in the AKR mice. The incidence of cystic kidney was also increased in the rats. In addition, an increase in the ratio of liver weight to body weight in the mouse fetus and the occurrence of hemorrhagic gastrointestinal tract in the rat fetus suggest that this compound also has fetotoxic properties.