Disorazol A1, a highly effective antimitotic agent acting on tubulin polymerization and inducing apoptosis in mammalian cells

Methanolysis products of disorazole A1

Two new disorazole analogues were synthesized by acid-promoted methanolysis of disorazole A1 (1). Structural elucidation of both products (2 and 3), through 1D and 2D NMR experiments, verified that each resulted from epoxide cleavage. With antiproliferative activities in susceptible cell lines comparable to that of disorazole A1, these methanolysis products indicate that the C-9-C-10 epoxide is not an essential structural component for biological activity.

The biosynthetic genes for disorazoles, potent cytotoxic compounds that disrupt microtubule formation

Disorazoles are polyketides produced by the myxobacterium Sorangium cellulosum So ce12. Their mode of action is to inhibit tubulin polymerization and destabilize microtubules. Using transposon mutagenesis, two mutant strains were identified that produced no disorazoles. Sequencing the DNA flanking the insertions revealed a polyketide synthase gene cluster that would encode three polypeptides, DszA, DszB, and DszC, with DszC containing both nonribosomal peptide synthetase and polyketide synthase modules. The disorazole polyketide synthase modules lack an acyltransferase domain. Instead, a separate gene, dszD, encodes an AT protein, thus revealing that the disorazole gene cluster falls into the trans-AT Type I family of PKS enzymes.

Production of the Tubulin Destabilizer Disorazol in Sorangium cellulosum: Biosynthetic Machinery and Regulatory Genes

Myxobacteria show a high potential for the production of natural compounds that exhibit a wide variety of antibiotic, antifungal, and cytotoxic activities. The genus Sorangium is of special biotechnological interest because it produces almost half of the secondary metabolites isolated from these microorganisms. We describe a transposon-mutagenesis approach to identifying the disorazol biosynthetic gene cluster in Sorangium cellulosum So ce12, a producer of multiple natural products. In addition to the highly effective disorazol-type tubulin destabilizers, S. cellulosum So ce12 produces sorangicins, potent eubacterial RNA polymerase inhibitors, bactericidal sorangiolides, and the antifungal chivosazoles. To obtain a transposon library of sufficient size suitable for the identification of the presumed biosynthetic gene clusters, an efficient transformation method was developed. We present here the first electroporation protocol for a strain of the genus Sorangium. The transposon library was screened for disorazol-negative mutants. This approach led to the identification of the corresponding trans-acyltransferase core biosynthetic gene cluster together with a region in the chromosome that is likely to be involved in disorazol biosynthesis. A third region in the genome harbors another gene that is presumed to be involved in the regulation of disorazol production. A detailed analysis of the biosynthetic and regulatory genes is presented in this paper.