A compound of simple structure,
2,4-dichlorobenzyl thiocyanate (DCBT), is an
antimitotic agent with a number of unusual properties. The
drug causes an extreme reorganization of microtubules in cells in culture. Most normal microtubules disappear, and remaining
tubulin-containing structures appear to be bundled or aggregated. DCBT irreversibly inhibits in vitro polymerization of purified
tubulin, but only after a prolonged preincubation of the
protein with the
drug. Binding of radiolabeled DCBT to
tubulin similarly requires a long incubation time, with the reaction not being complete even after 6 hr at 37 degrees C. A specific interaction with
tubulin is also shown by the crossresistance to DCBT of
Colcemid-resistant cells with an altered
beta-tubulin. A human KB
carcinoma cell line and a Chinese hamster ovary cell line selected for crossresistance to multiple chemotherapeutic agents, including most
antimitotic drugs, are sensitive to DCBT. Initial structure-function studies have demonstrated weak
antimitotic and antitubulin activity with the parent compound
benzyl thiocyanate. Chlorination at either position 2 or position 4 of the phenyl ring produces compounds of intermediate activity (4-chlorobenzyl
thiocyanate is more active than 2-chlorobenzyl
thiocyanate). The
thiocyanate moiety appears to be essential for activity.