Resistance to antimitotic drugs in Chinese hamster ovary cells correlates with changes in the level of polymerized tubulin

Combinations of pacliataxel and vinblastine and their effects on tublin polymerization and cellular cytotoxicity: Characterization of a synergistic schedule

“…The availability of 2 classes of tubulin acting agents (taxanes and vincas) with a similar target but separate effects remains to be exploited efficiently. In vitro evidence suggests that when the resistance is mediated by tubulin, collateral sensitivity can be expected for the alternate class of tubulin targeting agents (Minotti et al, 1991). While this offers the possibility of exploiting any emerging resistance by means of an agent to which such cells may be collaterally sensitive, the present results suggest that the schedule of administration must be carefully considered.…”

“…To quantitate tubulin polymerization we developed a simple assay by modifying a method originally described by Minotti et al (1991). Cells grown to confluency in 24-well plates were treated with drug for a specified time.…”

“…The percent of polymerized tubulin (%P) was determined by dividing the value of polymerized tubulin by the total tubulin content (soluble and polymerized). Although most tubulin exists in the soluble form in untreated cells (Minotti et al, 1991), the distribution of tubulin between the soluble and polymerized fractions could be altered to some degree by the experimental conditions. We determined that the presence of PTX in the lysis buffer or an increase in the temperature during harvesting increased the amount of tubulin in the polymerized fraction.…”

Resistance To Taxanes

“…GTP binding and hydrolysis is an essential regulatory mechansm of microtubule stability. The way that mutations would alter the stability is explained as follows (39). Normally, cells control the ratio of polymerized microtubules to depolymerized tubulin.…”

“…Therefore, paclitaxel-resistant cells may shift the equilibrium towards the depolymerized form of tubulin. This may explain why some paclitaxel-resistant cells with tubulin mutations actually become dependent on paclitaxel for growth (31,35,38,39) because the drug would be required to restore the set point ratio for proper cell growth. It would also explain why some paclitaxel-resistant cells display increase sensitivity to depolymerizing agents.…”