The plausible biogenetic mechanism proposed in this communication clarifies the chemical pathway leading to over 60 polycyclic pyrrole‐imidazole marine alkaloids isolated from more than 20 different species of various genera (Agelas, Hymeniacidon, Axinella, Acanthella, Cymbastella, Phakellia...) of sponges. The tautomerism and ambivalent reactivity of 2‐aminoimidazole precursors provide a consistent chemical pathway explaining the intriguing formation of all the compounds of this class. The mechanistic proposal proposed here for the first time is unique in the sense that the chemical pathway is universal and therefore provides fertile intellectual ground for the study of the enzymatic mechanism involved in this system.

A variety of synthetic analogues of taxol, a naturally occurring antitumor diterpene, were examined for their potency to inhibit microtubule disassembly. For some of the compounds, the in vitro cytotoxic properties showed a good correlation with the tubulin assay. This structure-activity relationship study shows that inhibition of microtubule disassembly is quite sensitive to the configuration at C-2' and C-3'. A correlation between the conformation of the side chain at C-13 and the activity is suggested. Of all the compounds examined, one of the most potent in inhibiting microtubule disassembly and in inhibiting murine P388 leukemic cells, N-debenzoyl-N-tert-(butoxycarbonyl)-10-deacetyltaxol, named taxotere, was selected for evaluation as a potential anticancer agent.

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Huntington's disease (HD) is a currently incurable neurodegenerative disease caused by the expansion of a CAG trinucleotide repeat within the huntingtin (HTT) gene. Therapeutic approaches include selectively inhibiting the expression of the mutated HTT allele while conserving function of the normal allele. We have evaluated a series of antisense oligonucleotides (ASOs) targeted to the expanded CAG repeat within HTT mRNA for their ability to selectively inhibit expression of mutant HTT protein. Several ASOs incorporating a variety of modifications, including bridged nucleic acids and phosphorothioate internucleotide linkages, exhibited allele-selective silencing in patient-derived fibroblasts. Allele-selective ASOs did not affect the expression of other CAG repeat-containing genes and selectivity was observed in cell lines containing minimal CAG repeat lengths representative of most HD patients. Allele-selective ASOs left HTT mRNA intact and did not support ribonuclease H activity in vitro. We observed cooperative binding of multiple ASO molecules to CAG repeat-containing HTT mRNA transcripts in vitro. These results are consistent with a mechanism involving inhibition at the level of translation. ASOs targeted to the CAG repeat of HTT provide a starting point for the development of oligonucleotide-based therapeutics that can inhibit gene expression with allelic discrimination in patients with HD.

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The in vitro disassembly of microtubules from mammalian brain and Physarum is inhibited by various derivatives of taxol and baccatine III. Structure-activity relationships of the taxol derivatives were identical for both mammalian brain and Physarum microtubules. This observation suggests that the site of action of taxol has been preserved during the evolution of these two different eukaryotic lines. The substituent at C-13 of taxol was required to prevent disassembly of brain microtubules with or without microtubule-associated proteins. In contrast, both taxol and baccatine III prevented the disassembly of Physarum microtubules to the same extent, showing that the substituent at C-13 was not required in the interaction with Physarum tubulin. The different effects of baccatine III and taxol derivatives indicate that measuring the disassembly of microtubules from different organisms could be a useful parameter in the search for derivatives exhibiting antiparasitic activity.Assembly properties of tubulin are highly preserved along the various evolutionary pathways of eukaryotic cells as illustrated by the in vitro coassembly of tubulin from fungi (1-3), ciliates (4), myxomycetes (5), algae (6, 7), and higher plants (8) with mammalian brain tubulin. In contrast, the sensitivity of eukaryotic cells towards microtubule poisons depends on a selective pharmacological specificity of their tubulin (9-11), allowing the use of spindle or microtubular poisons such as griseofulvin (12-14) and methyl 2-benzimidazolecarbamate derivatives (10,15) (36,37). In order to compare the interaction of taxol on tubulin from two distinct evolutionary lines of eukaryotic cells, we have studied the effects of various taxol derivatives, in particular baccatine III (Fig.

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