Originally purified as a major lipid component of a strain of the cyanobacterium Lyngbya majuscula isolated in Curaçao, curacin A is a potent inhibitor of cell growth and mitosis, binding rapidly and tightly at the colchicine site of tubulin. Because its molecular structure differs so greatly from that of colchicine and other colchicine site inhibitors, we prepared a series of curacin A analogs to determine the important structural features of the molecule. These modifications include reduction and E-to-Z transitions of the olefinic bonds in the 14-carbon side chain of the molecule; disruption of and configurational changes in the cyclopropyl moiety; disruption, oxidation, and configurational reversal in the thiazoline moiety; configurational reversal and substituent modifications at C13; and demethylation at C10. Inhibitory effects on tubulin assembly, the binding of colchicine to tubulin, and the growth of MCF-7 human breast carcinoma cells were examined. The most important portions of curacin A required for its interaction with tubulin seem to be the thiazoline ring and the side chain at least through C4, the portion of the side chain including the C9-C10 olefinic bond, and the C10 methyl group. Only two modifications totally eliminated the tubulin-drug interaction. The inactive compounds were a segment containing most of the side chain, including its two substituents, and analogs in which the methyl group at the C13 oxygen atom was replaced by a benzoate residue. Antiproliferative activity comparable with that observed with curacin A was only reproduced in compounds that were potent inhibitors of the binding of colchicine to tubulin. Molecular modeling and quantitative structure-activity relationship studies demonstrated that most active analogs overlapped extensively with curacin A but failed to provide an explanation for the apparent structural analogy between curacin A and colchicine.

The successful synthesis of dolastatin 11, a depsipeptide originally isolated from the mollusk Dolabella auricularia, permitted us to study its effects on cells. The compound arrested cells at cytokinesis by causing a rapid and massive rearrangement of the cellular actin filament network. In a dose-and time-dependent manner, F-actin was rearranged into aggregates, and subsequently the cells displayed dramatic cytoplasmic retraction. The effects of dolastatin 11 were most similar to those of the sponge-derived depsipeptide jasplakinolide, but dolastatin 11 was about 3-fold more cytotoxic than jasplakinolide in the cells studied. Like jasplakinolide, dolastatin 11 induced the hyperassembly of purified actin into filaments of apparently normal morphology. Dolastatin 11 was qualitatively more active than jasplakinolide and, in a quantitative assay we developed, dolastatin 11 was twice as active as jasplakinolide and 4-fold more active than phalloidin. However, in contrast to jasplakinolide and phalloidin, dolastatin 11 did not inhibit the binding of a fluorescent phalloidin derivative to actin polymer nor was it able to displace the phalloidin derivative from polymer. Thus, despite its structural similarity to other agents that induce actin assembly (all are peptides or depsipeptides), dolastatin 11 may interact with actin polymers at a distinct drug binding site.

The endogenous estrogen metabolite 2-methoxyestradiol has modest antimitotic activity that may result from a weak interaction at the colchicine binding site of tubulin, but it nevertheless has in vivo antitumor activity. Synthetic efforts to improve activity led to compounds that increased inhibitory effects on cell growth, tubulin polymerization, and binding of colchicine to tubulin. This earlier work was directed at modifications in the steroid A ring, which is probably analogous to the colchicine tropolonic C ring. One of the most active analogs prepared was 2-ethoxyestradiol (2EE). We report here that different modifications in the steroid B ring of 2EE yield compounds with two apparently distinct modes of action. Simple expansion of the B ring to seven members resulted in a compound comparable to 2EE in its ability to inhibit tubulin polymerization and colchicine binding to tubulin. Acetylation of the hydroxyl groups in this analog and in 2EE essentially abolished these inhibitory properties. The introduction of a ketone functionality at C6, together with acetylation of the hydroxyls at positions 3 and 17, produced a compound with activity similar to that of paclitaxel, in that the agent enhanced tubulin polymerization into polymers that were partially stable at 0 degrees C. The acetyl group at C17, but not that at C3, was essential for this paclitaxel-like activity.

Eine Bibliothek von Epothilon‐A und ‐B‐Analoga, die durch kombinatorische Festphasensynthese mit SMART‐Mikroreaktoren sowie durch konventionelle Chemie in Lösung hergestellt wurde, wurde in zwei unterschiedlichen Tubulin‐Bindungs‐Assays untersucht. Ausgewählte Verbindungen wurden darüber hinaus hinsichtlich ihrer Cytotoxizität gegen mehrere Krebszellinien, einschließlich taxolresistenter, bewertet. Daraus wurden wichtige Struktur‐Wirkungs‐Beziehungen gewonnen, die den Weg für weitere Entdeckungen und Entwicklungen auf dem Gebiet der Krebsforschung ebnen werden.

Septins are cytoskeletal proteins conserved from algae and protists to mammals. A unique feature of septins is their presence as heteromeric complexes that polymerize into filaments in solution and on lipid membranes. Although animal septins associate extensively with actin-based structures in cells, whether septins organize as filaments in cells and if septin organization impacts septin function is not known. Customizing a tripartite split-GFP complementation assay, we show that all septins decorating actin stress fibers are octamer-containing filaments. Depleting octamers or preventing septins from polymerizing leads to a loss of stress fibers and reduced cell stiffness. Super-resolution microscopy revealed septin fibers with widths compatible with their organization as paired septin filaments. Nanometer-resolved distance measurements and single-protein tracking further showed that septin filaments are membrane bound and largely immobilized. Finally, reconstitution assays showed that septin filaments mediate actin–membrane anchoring. We propose that septin organization as octamer-based filaments is essential for septin function in anchoring and stabilizing actin filaments at the plasma membrane.

Septins, a family of GTP-binding proteins assembling into higher order structures, interface with the membrane, actin filaments and microtubules, which positions them as important regulators of cytoarchitecture. Septin 9 (Sept9), which is frequently overexpressed in tumors and mutated in hereditary neuralgic amyotrophy (HNA), mediates the binding of septins to microtubules, but the molecular determinants of this interaction remained uncertain. We demonstrate that a short MAP-like motif unique to Sept9 isoform 1 (Sept9_i1) drives septin octamer-microtubule interaction in cells and in vitro reconstitutions. Septin-microtubule association requires polymerizable septin octamers harboring Sept9_i1. Although outside of the MAP-like motif, HNA mutations abrogates this association, identifying a putative regulatory domain. Removal of this domain from Sept9_i1 sequesters septins on microtubules, promotes microtubule stability and alters actomyosin fiber distribution and tension. Thus, we identify key molecular determinants and potential regulatory roles of septin-microtubule interaction, paving the way to deciphering the mechanisms underlying septin associated pathologies.

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are prepared from compound (III) via optical resolution of the corresponding camphanates followed by hydrolysis and acylation reactions. Key intermediate (II) is derived from known thiocolchicone (I) by ring contraction. With exception of (-)-(IVc) all compounds show strong inhibitory effects on the tubulin polymerization reaction. Compounds (II) and (-)-(IVa) also exhibit potent antitumor activity against most cell lines in NCI's in vitro screening. -(SHI, Q.; CHEN, K.; CHEN, X.; BROSSI, A.; VERDIER-PINARD, P.; HAMEL, E.; MCPHAIL, A. T.; TROPSHA, A.; LEE, K.-H.; J.