Toxicodynamics of tumour promoters of mouse skin. III. Specific binding of the tumour promoter thapsigargin as measured by the cold-acetone filter assay.
A method is described for measuring rapid, specific, and saturable binding of the skin irritant and tumour-promoting secretagogue thapsigargin (sesquiterpene lactone) to the microsomal fraction from mouse brain. Employing the tritium-labelled compound its apparent dissociation constant, Kd, and the maximal amount of binding Bmax are shown to be 9.8 nM and 1.9 pmol/mg protein respectively. Such a Kd for thapsigargin is similar to (a) its IC50 value for inhibiting Ca2+ uptake in the microsomal fraction from rat brain and (b) its EC50 values for inducing a rise in the cytoplasmic Ca2+ concentration of human platelets and histamine release from rat peritoneal mast cells. A positive correlation is found between the binding affinities of thapsigargin, thapsitranstagin, and trilobolide, their potencies as secretagogues and their lipophilicities. This correlation does not extend to the skin-irritant activities of the compounds thus emphasizing that their mechanism of action is unlike that of 12-O-tetradecanoylphorbol 13-acetate.
Christensen
S B
SB
Department of Organic Chemistry, Royal Danish School of Pharmacy, Copenhagen.
Hergenhahn
M
M
Roeser
H
H
Hecker
E
E
D000818:Animals; D001921:Brain / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002273:Carcinogens / Q000378:metabolism*; D003080:Cold Temperature; D005374:Filtration; D066298:In Vitro Techniques; D051379:Mice; D008861:Microsomes / Q000378:metabolism; D012878:Skin Neoplasms / Q000139:chemically induced*; D013729:Terpenes / Q000378:metabolism*; D019284:Thapsigargin
D002273:Carcinogens; D013729:Terpenes; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases