Spin-labeled phorbol esters and their interactions with cellular membranes. III. Skin irritant and tumor-promoting activities of spin-labeled phorbol-12,13-diesters and relationships to their particular structures

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Abstract
Sixteen ‘doxy’ spin-labeled 12, 13-(acetate, acylates) of phoebol were assayed in NMRI mice for irritant and for tumor-promoting activity. The spin-labeled positionally isomeric ( n , m )PA-and AP( n , m )-type esters carry straight aliphatic acyl chains of different overall lengths N (number of C atoms). Within the chains the ‘doxy’ label is located in different positions ( nm ). The potency of some of the esters as irritants and as promoters is comparable to or even higher than that of the prototype diterpene ester promoter 12- O -tetradecanoylphorbol-13-acetate and its positional isomer 12- O -acetylphorbol-13-tetradecanoate. Their irritancies on the ear and their promoting activities on the back skin depend strongly on the structural features of the acyl chain carrying the spin label. Based upon the bioactivities of individual esters biologically meaningful probes were defined for investigations of the molecular interaction of phorbol-ester-type promoters with cellular targets for electron paramagenetic resonance.