Peloruside B, a potent antitumor macrolide from the New Zealand marine sponge Mycale hentscheli: isolation, structure, total synthesis, and bioactivity

Peloruside B (2), a natural congener of peloruside A (1), was isolated in sub-milligram quantities from the New Zealand marine sponge Mycale hentscheli. Peloruside B promotes microtubule polymerization and arrests cells in the G(2)M phase of mitosis similar to paclitaxel, and its bioactivity was comparable to that of peloruside A. NMR-directed isolation, structure elucidation, structure confirmation by total synthesis and bioactivity of peloruside B are described in this article. The synthesis features Sharpless dihydroxylation, Brown's asymmetric allylboration reaction, reductive aldol coupling, Yamaguchi macrolactonization and selective methylation

Synergistic effects of peloruside A and laulimalide with taxoid site drugs, but not with each other, on tubulin assembly

Previous studies on the drug content of pelleted tubulin polymers suggest that peloruside A binds in the laulimalide site, which is distinct from the taxoid site. In a tubulin assembly system containing microtubule-associated proteins and GTP, however, peloruside A was significantly less active than laulimalide, inducing assembly in a manner that was most similar to sarcodictyins A and B. Because peloruside A thus far seems to be the only compound that mimics the action of laulimalide, we examined combinations of microtubule-stabilizing agents for synergistic effects on tubulin assembly. We found that peloruside A and laulimalide showed no synergism but that both compounds could act synergistically with a number of taxoid site agents [paclitaxel, epothilones A/B, discodermolide, dictyostatin, eleutherobin, the steroid derivative 17β-acetoxy-2-ethoxy-6-oxo-B-homo-estra-1,3,5(10)-trien- 3-ol, and cyclostreptin]. None of the taxoid site compounds showed any synergism with each other. From an initial study with peloruside A and cyclostreptin, we conclude that the synergism phenomenon derives, at least in part, from an apparent lowering of the tubulin critical concentration with drug combinations compared with single drugs. The apparent binding of peloruside A in the laulimalide site led us to attempt construction of a pharmacophore model based on superposition of an energy-minimized structure of peloruside A on the crystal structure of laulimalide. Although the different sizes of the macrocycles limited our ability to superimpose the two molecules, atom correspondences that were observed were consistent with the difficulty so far experienced in creation of fully active analogs of laulimalide

Peloruside- and laulimalide-resistant human ovarian carcinoma cells have βI-tubulin mutations and altered expression of βII- and βIII-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 A- and 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 β-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 βI-tubulin isotype, R306H or R306C for L4 and A296T for R1 cells. This is the first cell-based evidence to support a β-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 β-tubulin isotype composition of the cells was examined. Increased expression of βII- and βIII-tubulin was observed in L4 cells only. These results provide insight into how alterations in tubulin lead to unique resistance profiles for two drugs, peloruside A and laulimalide, that have a similar mode of action