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Speicher LA, Laing N, Barone LR, Robbins JD, Seamon KB, Tew KD
Interaction of an Estramustine Photoaffinity Analog with Cytoskeletal Proteins in Prostate Carcinoma-Cells
Molecular Pharmacology (1994) 46:866-872.
Abstract
To identify specific drug targets of the antimitotic drug estramustine, a photoaffinity analogue, 17-O-[[2-[3-(4-azido-3- [I-125]iodophenyl)propionamido]ethyl]carbamyl]estradiol-3-N- bis(2-chloroethyl)carbamate, was synthesized and reacted in competition assays with cytoskeletal protein preparations. By attaching the photoaffinity ligand to the 17 beta-position of the steroid D-ring, the cytotoxic properties of the drug were maintained. In cytoskeletal protein preparations from human prostate carcinoma cells (DU 145) or a clonally selected, estramustine-resistant cell line (E4), the major microtubule- associated protein (MAP) present was MAP4. In both cytoskeletal fractions and reconstituted microtubules, 17-O-[[2-[3-(4-azido- 3-[I-125]iodophenyl)propionamido]ethyl]carbamyl]estradiol-3-N- bis(2-chloroethyl)carbamate bound to both MAP4 and tubulin. From competition assays, the apparent binding constant for MAP4 from DU 145 cells was 15 mu M. Similar calculations for tubulin gave values of 13 mu M (bovine brain), 19 mu M (DU 145 wild- type cells), and 25 mu M (E4 cells). The identification of these cytoskeletal proteins as specific drug targets provides a direct explanation for the antimicrotubule and antimitotic effects of estramustine.
Note
Publication Date: 1994-11-01.
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