N-
alkanes from C12 to C28 were tested for their cocarcinogenic or promoting activities to evaluate a correlation of their
biologic activity with their effects on transport properties of
phospholipid micelles. On this basis, we had predicted that the C18 and C20 homologues would be more active than the better known
dodecane. The C12, C16, C18, and C20 n-
alkanes, at various dilutions from 6 to 40% by volume in
decahydronaphthalene (
Decalin), were tested for their relative activity in a cocarcinogenic relationship to
benzo[a]pyrene. At a 20%
alkane concentration level, the solutions containing
octadecane and
eicosane induced
tumors most rapidly. A 40%
dodecane concentration was required to produce this level of cocarcinogenic activity. The activity of
octadecane paralleled its physical effects on transport kinetics closely in the 6-40% (by volume) concentration. The C18, C20, and C28 n-
alkanes and the C30
olefin squalene at dilutions from 10 to 40% in
Decalin (by volume) were tested for their relative promoting activity after a single application of 7,12-dimethylbenz[a]
anthracene in
benzene. At comparable mole fractions in
Decalin, the three n-
alkanes had essentially the same promoting activity;
squalene, at 20%, showed only borderline activity. Thus the high
biologic activity of the C18, C20, and C28 n-
alkanes correlated well with their physical effects on the structure of
phospholipid micelles (chain-chain interactions of the
alkanes with the acyl chains of the
lipid). This correlation was interpreted as a strong indication that the liquid crystalline region of the
phospholipid assembly (adjacent to the aqueous interface) in the membranes of latent (initiated)
cancer cells was the site of action of
hydrocarbon cocarcinogens. Application of a modified physical model to
pristane, a branched-chain C19
alkane from
coal and Colorado shale, indicated higher cocarcinogenic activity than that of n-C18H38. Applied to purified samples of
docosane and
tetracosane, activity comparable to that of
octadecane was indicated.