Pascal Verdier-Pinard

Comparison of the activities of the truncated halichondrin B analog NSC 707389 (E7389) with those of the parent compound and a proposed binding site on tubulin.

The complex marine natural product halichondrin B was compared with NSC 707389 (E7389), a structurally simplified, synthetic macrocyclic ketone analog, which has been selected for clinical trials in human patients. NSC 707389 was invariably more potent than halichondrin B in its interactions with tubulin. Both compounds inhibited tubulin assembly, inhibited nucleotide exchange on β-tubulin, and were noncompetitive inhibitors of the binding of radiolabeled vinblastine and dolastatin 10 to tubulin. Neither compound seemed to induce an aberrant tubulin assembly reaction, as occurs with vinblastine (tight spirals) or dolastatin 10 (aggregated rings and spirals). We modeled the two compounds into a shared binding site on tubulin consistent with their biochemical properties. Of the two tubulin structures available, we selected for modeling the complex of a stathmin fragment with two tubulin heterodimers with two bound colchicinoid molecules and a single bound vinblastine between the two heterodimers (Nature (Lond) 435:519-522, 2005). Halichondrin B and NSC 707389 fit snugly between the two heterodimers adjacent to the exchangeable site nucleotide. Fitting the compounds into this site, which was also close to the vinblastine site, resulted in enough movement of amino acid residues at the vinblastine site to cause the latter compound to bind less well to tubulin. The model suggests that halichondrin B and NSC 707389 most likely form highly unstable, small aberrant tubulin polymers rather than the massive stable structures observed with vinca alkaloids and antimitotic peptides.

Curacin d, an antimitotic agent from the marine cyanobacterium Lyngbya majuscula

Curacin D is a novel brine shrimp toxic metabolite isolated from a Virgin Islands collection of the marine cyanobacterium Lyngbya majuscula. Structure elucidation of curacin D was accomplished through multidimensional NMR, GC/MS, and comparisons with curacin A. Curacin D provides new insights into structure-activity relationships in this natural product class as well as some aspects of the likely biosynthetic pathway of the curacins.

Antitumor agents—CLXXV. Anti-tubulin action of (+)-thiocolchicine prepared by partial synthesis☆

(+)-Thiocolchicine (2b) was prepared from (+/-)-colchicine (1) in a five-step reaction sequence that included chromatographic separation of appropriate camphanylated diastereomers. Acid hydrolysis of the (+)-diastereomer, followed by acetylation, yielded the desired product 2b. (+)-Thiocolchicine has 15-fold lower inhibitory activity against tubulin polymerization than (-)-thiocolchicine, and is 29-fold less potent for inhibiting growth of human Burkitt lymphoma cells. The enantiomer 2a, prepared from the (-)-camphanylated diastereomer, had potent activity in all assays comparable to that of (-)-thiocolchicine prepared by other methods. These results support the hypothesis that the proper configuration of colchicine-related compounds is an important requirement for their anti-tubulin action.

Antifungal and cancer cell growth inhibitory activities of 1-(3′,4′,5′-trimethoxyphenyl)-2-nitro-ethylene

Summary. The antifungal and cancer cell growth inhibitory activities of 1‐(3′,4′,5′‐trimethoxyphenyl)‐2‐nitro‐ethylene (TMPN) were examined. TMPN was fungicidal for the majority of 132 reference strains and clinical isolates tested, including those resistant to fluconazole, ketoconazole, amphotericin B or flucytosine. Minimum fungicidal concentration/minimum inhibitory concentration (MFC/MIC) ratios were ≤2 for 96% of Cryptococcus neoformans clinical isolates and 71% of Candida albicans clinical isolates. TMPN was fungicidal for a variety of other basidiomycetes, endomycetes and hyphomycetes, and its activity was unaffected by alterations in media pH. The frequency of occurrence of fungal spontaneous mutations to resistance was <10−6. Kill‐curve analyses confirmed the fungicidal action of TMPN, and demonstrated that killing was concentration‐ and time‐dependent. At sub‐MIC exposure to TMPN, C. albicans did not exhibit yeast/hyphae switching. TMPN was slightly cytotoxic for murine and human cancer cell lines (GI50=1–4 µg ml−1), and weakly inhibited mammalian tubulin polymerization (IC50=0.60 µg ml−1).