Preclinical Development Peloruside- and Laulimalide-Resistant Human Ovarian Carcinoma Cells Have bI-Tubulin Mutations and Altered Expression of bII- and bIII-Tubulin Isotypes

Peloruside A and laulimalide are potent microtubule-stabilizing natural products with a mechanism of action similar to that of paclitaxel. However, the binding site of peloruside A and laulimalide on tubulin remains poorly understood. Drug resistance in anticancer treatment is a serious problem. We developed peloruside Aand laulimalide-resistant cell lines by selecting 1A9 human ovarian carcinoma cells that were able to grow in the presence of one of these agents. The 1A9-laulimalide resistant cells (L4) were 39-fold resistant to the selecting agent and 39-fold cross-resistant to peloruside A, whereas the 1A9-peloruside A resistant cells (R1) were 6-fold resistant to the selecting agent while they remained sensitive to laulimalide. Neither cell line showed resistance to paclitaxel or other drugs that bind to the taxoid site on b-tubulin nor was there resistance to microtubule-destabilizing drugs. The resistant cells exhibited impaired peloruside A/ laulimalide-induced tubulin polymerization and impaired mitotic arrest. Tubulin mutations were found in the bI-tubulin isotype, R306H or R306C for L4 and A296T for R1 cells. This is the first cell-based evidence to support a b-tubulin–binding site for peloruside A and laulimalide. To determine whether the different resistance phenotypes of the cells were attributable to any other tubulin alterations, the b-tubulin isotype composition of the cells was examined. Increased expression of bIIand bIII-tubulin was observed in L4 cells only. These results provide insight into how alterations in tubulin lead to unique resistance profiles for two drugs, pelorusideA and laulimalide, that have a similarmode of action.Mol Cancer Ther; 10(8); 1419–29. 2011