apratoxin-a and Neoplasms

Chemical genetics has arisen as a tool for the discovery of pathways and proteins in mammalian systems. This approach, comprising small-molecule screening combined with biochemical and genomic target identification methods, enables one to assess which proteins are involved in regulating a particular phenotype. Applied to cell death, this strategy can reveal novel targets and pathways regulating the demise of mammalian cells. Numerous diseases have been linked to the loss of regulation of cell death. Defining the mechanisms governing cell death in these diseases might lead to the discovery of therapeutic agents and targets and provide a richer understanding of the mortality of living systems. Recent advances include the discovery of novel small molecules regulating cell death pathways -- necrostatin and erastin -- as well as the elucidation of the mechanism of death induced in cancer cells by the cytotoxic agent Apratoxin A.

Topics: Animals; Antineoplastic Agents; Cell Death; Cell Line, Tumor; Depsipeptides; Genetic Techniques; Genome; Humans; Imidazoles; Indoles; Neoplasms; Pharmaceutical Preparations; Phenotype; Piperazines; Proteins

Apratoxin A is a natural product with potent antiproliferative activity against many human cancer cell lines. However, we and other investigators observed that it has a narrow therapeutic window in vivo Previous mechanistic studies have suggested its involvement in the secretory pathway as well as the process of chaperone-mediated autophagy. Still the link between the biologic activities of apratoxin A and its in vivo toxicity has remained largely unknown. A better understanding of this relationship is critically important for any further development of apratoxin A as an anticancer drug. Here, we describe a detailed pathologic analysis that revealed a specific pancreas-targeting activity of apratoxin A, such that severe pancreatic atrophy was observed in apratoxin A-treated animals. Follow-up tissue distribution studies further uncovered a unique drug distribution profile for apratoxin A, showing high drug exposure in pancreas and salivary gland. It has been shown previously that apratoxin A inhibits the protein secretory pathway by preventing cotranslational translocation. However, the molecule targeted by apratoxin A in this pathway has not been well defined. By using a (3)H-labeled apratoxin A probe and specific Sec 61α/β antibodies, we identified that the Sec 61 complex is the molecular target of apratoxin A. We conclude that apratoxin A in vivo toxicity is likely caused by pancreas atrophy due to high apratoxin A exposure. Mol Cancer Ther; 15(6); 1208-16. ©2016 AACR.

Topics: A549 Cells; Animals; Antineoplastic Agents; Cell Line, Tumor; Cell Proliferation; Cell Survival; Depsipeptides; Humans; Maximum Tolerated Dose; MCF-7 Cells; Mice; Neoplasm Transplantation; Neoplasms; Organ Specificity; Pancreas; Protein Binding; Rats; SEC Translocation Channels

This paper describes the synthetic studies conducted on a marine natural product, cyclodepsipeptide apratoxin A. Total synthesis of the oxazoline analogue of apratoxin A was achieved. The conversion of oxazoline to thioamide, as well as thioamide formation from a serine-derived compound, were both unsuccessful. However, thiazoline formation from a cysteine-derived compound led to the total synthesis of apratoxin A. An in vivo study on synthetic apratoxin A revealed that it has potent antitumor activity, but with significant toxicity. Solid-phase synthesis of apratoxin A was accomplished using a preformed thiazoline derivative as a coupling unit. This method was used to synthesize several azido-containing analogues as precursors of molecular probes, and these analogues exhibited potent biological activity.

Topics: Antineoplastic Agents; Biological Products; Depsipeptides; HeLa Cells; Humans; Neoplasms; Oxazoles; Solid-Phase Synthesis Techniques

Two approaches for the solid-phase total synthesis of apratoxin A and its derivatives were accomplished. In synthetic route A, the peptide was prepared by the sequential coupling of the corresponding amino acids on trityl chloride SynPhase Lanterns. After cleavage from the polymer-support, macrolactamization of 10, followed by thiazoline formation, provided apratoxin A. This approach, however, resulted in low yield because the chemoselectivity was not sufficient for the formation of the thiazoline ring though its analogue 33 was obtained. However, in synthetic route B, a cyclization precursor was prepared by solid-phase peptide synthesis by using amino acids 13-15 and 18. The final macrolactamization was performed in solution to provide apratoxin A in high overall yield. This method was then successfully applied to the synthesis of apratoxin analogues. The cytotoxic activity of the synthetic derivatives was then evaluated. The epimer 34 was as potent as apratoxin A, and O-methyl tyrosine can be replaced by 7-azidoheptyl tyrosine without loss of activity. The 1,3-dipolar cycloaddition of 38 with phenylacetylene was performed in the presence of a copper catalyst without affecting the thiazoline ring.

Topics: Antineoplastic Agents; Cell Line, Tumor; Cell Survival; Depsipeptides; Humans; Inhibitory Concentration 50; Molecular Structure; Neoplasms