Comparison of the promoting activity of pristane and [formula omitted] in skin carcinogenesis with their physical effects on micellar models of biological membranes

Abstract

In 1976 (Horton, A.W., Butts, C.K. and Schuff, A.R. (1976) Colloid Interface Sci. 5, 159–168) we assayed pristance (2,6,10,14-tetramethylpentadecane) in a model interfacial system that has given excellent correlation with cocarcinogenic activity among n- alkanes , as tested in cycloalkane diluents. It was predicted that this branched-chain derivative of the diterpenes would have higher activity than n- C 18H 38 , one of the most cocarcinogenic of the n- alkanes in such diluents. Pristane was compared with n- C 18H 38 and two other n- alkanes for their promoting activities in cyclohexane for C3H male mice after a single application of 7,12-dimethylbenz [a] anthracene . The branched-chain alkane proved to be more active. 20% n- tetracosane in cyclohexane was inactive, which correlated with its effects in this diluent in the physical assay system. The promoting activity of 75% n- octane in cyclohexane, predicted by the physical assay, was confirmed by tests on mice. The combined by-products of the synthesis of tetracosane, including C 12 alkanes and alkenes, C 19 and C 20 alkylbenzenes, and C 24 alkenes, proved to be a very active promoter. However, a mixture in cyclohexane of purified tetracosane with this composite of potential impurities was inactive. From the alkanes behavior in physical systems involving vatious membrane phospholipids and steroids, it is hypothesized that the primary step in their biological activity is a chain-chain interaction with membrane lipids that alters the properties of liquid-crystalline phases at aqueous interfaces. Resulting changes in the microfluidity of the lipid phase and the lateral mobility of critical hormone receptors and enzyme systems, such as the nucleotidyl cyclases, would perturb control systems that maintain the normal behavior of the initiated cell. Thus, its progression to a proliferating neoplasm may be favored.