peloruside-a and zampanolide

Marine sponges are an excellent source of bioactive secondary metabolites with potential therapeutic value in the treatment of diseases. One group of compounds of particular interest is the microtubule-stabilizing agents, the most well-known compound of this group being paclitaxel (Taxol), an anti-cancer compound isolated from the bark and leaves of the Pacific yew tree. This review focuses on two of the more recent additions to this important class of drugs, peloruside A and zampanolide, both isolated from marine sponges. Peloruside A was isolated from Mycale hentscheli collected in New Zealand coastal waters, and it already shows promising anti-cancer activity. Two other potent bioactive compounds with different modes of action but isolated from the same sponge, mycalamide A and pateamine, will also be discussed. The fourth compound, zampanolide, most recently isolated from the Tongan sponge Cacospongia mycofijiensis, has only recently been added to the microtubule-stabilizing group of compounds, and further work is in progress to determine its activity profile relative to peloruside A and other drugs of this class.

Topics: Animals; Antineoplastic Agents; Bridged Bicyclo Compounds, Heterocyclic; Epoxy Compounds; Humans; Lactones; Macrolides; Microtubules; Neoplasms; Porifera; Pyrans; Thiazoles

The marine natural product zampanolide and analogues thereof constitute a new chemotype of taxoid site microtubule-stabilizing agents with a covalent mechanism of action. Zampanolide-ligated tubulin has the switch-activation loop (M-loop) in the assembly prone form and, thus, represents an assembly activated state of the protein. In this study, we have characterized the biochemical properties of the covalently modified, activated tubulin dimer, and we have determined the effect of zampanolide on tubulin association and the binding of tubulin ligands at other binding sites. Tubulin activation by zampanolide does not affect its longitudinal oligomerization but does alter its lateral association properties. The covalent binding of zampanolide to β-tubulin affects both the colchicine site, causing a change of the quantum yield of the bound ligand, and the exchangeable nucleotide binding site, reducing the affinity for the nucleotide. While these global effects do not change the binding affinity of 2-methoxy-5-(2,3,4-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-one (MTC) (a reversible binder of the colchicine site), the binding affinity of a fluorescent analogue of GTP (Mant-GTP) at the nucleotide E-site is reduced from 12 ± 2 × 10

Topics: Animals; Binding Sites; Biological Products; Bridged-Ring Compounds; Cattle; Colchicine; Humans; Ligands; Macrolides; Microtubules; Nucleotides; Taxoids; Tubulin

Zampanolide, first discovered in a sponge extract in 1996 and later identified as a microtubule-stabilizing agent in 2009, is a covalent binding secondary metabolite with potent, low nanomolar activity in mammalian cells. Zampanolide was not susceptible to single amino acid mutations at the taxoid site of β-tubulin in human ovarian cancer 1A9 cells, despite evidence that it selectively binds to the taxoid site. As expected, it did not synergize with other taxoid site microtubule-stabilizing agents (paclitaxel, ixabepilone, discodermolide), but surprisingly also did not synergize in 1A9 cells with laulimalide/peloruside binding site agents either. Efforts to generate a zampanolide-resistant cell line were unsuccessful. Using a standard wound scratch assay in cell culture, it was an effective inhibitor of migration of human umbilical vein endothelial cells (HUVEC) and fibroblast cells (D551). These properties of covalent binding, the ability to inhibit cell growth in paclitaxel and epothilone resistant cells, and the ability to inhibit cell migration suggest that it would be of interest to investigate zampanolide in preclinical animal models to determine if it is effective in vivo at preventing tumor growth and metastasis.

Topics: Bridged Bicyclo Compounds, Heterocyclic; Cell Line, Tumor; Cell Movement; Cell Proliferation; Drug Resistance, Neoplasm; Female; Fibroblasts; Human Umbilical Vein Endothelial Cells; Humans; Lactones; Macrolides; Microtubules; Taxoids; Tubulin; Tubulin Modulators

In this chapter, we describe the methods used to determine the binding site and binding profile of zampanolide, a novel microtubule-stabilizing agent (MSA) that binds covalently to tubulin. These methods can be applied to other novel MSAs in which the binding site and mechanism of binding are unknown. Using the described methods, we have shown that zampanolide binds to the taxoid site on β-tubulin, but unlike most other MSAs is able to covalently modify this site. The purpose of this chapter is to provide a step-by-step protocol for determining the binding site of a novel MSA.

Topics: Animals; Binding Sites; Brain; Bridged Bicyclo Compounds, Heterocyclic; Cattle; Lactones; Macrolides; Microtubules; Paclitaxel; Polycyclic Compounds; Protein Binding; Tubulin Modulators