Taccalonolide A is the first microtubule stabilizing agent to be discovered from a plant since identification of the mechanism of action of paclitaxel and it is the first natural product steroid identified to have these cellular effects,with cytotoxic and antimalarial activities. Taccalonolide A causes G2-M accumulation, Bcl-2 phosphorylation and initiation of apoptosis. Taccalonolide A is effective in vitro against cell lines that overexpress P-glycoprotein (Pgp) and multidrug resistance protein 7 (MRP7), with an IC50 of 622 nM for SK-OV-3 cells.

Taccalonolide B is effective in vitro against cell lines that overexpress P-glycoprotein (Pgp) and multidrug-resistance protein (MRP7). Taccalonolide B inhibits growth of SK-OV-3 cells with an IC50 of 208 nM.

Taccalonolide AJ is a microtubule stabilizer; it has excellent and highly persistent antitumor efficacy when administered directly to the tumor, suggesting that the lack of antitumor efficacy seen with systemic administration of AJ is likely due to its sh