PGP and ovarian carcinoma: To determine whether the covalent microtubule stabilizer, taccalonolide AF (Figure 1A), retains efficacy in Pgp-expressing, taxane-resistant ovarian cancer models in vitro, we selected two isogenic cell line pairs that have been reported to express high levels of MDR1. The SK-OV-3-MDR-1-6/6 line is derived from transduction of the parental SK-OV-3 ovarian cancer line with MDR1 [33].