Cytotoxic and tubulin-interactive hemiasterlins from Auletta sp. and Siphonochalina spp. sponges

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Abstract

Chemical and biological investigations of extracts from the sponge genus Auletta and two collections of Siphonochalina sp. have shown these organisms to be producers of the potent hemiasterlin class of antitumor agents. In addition to the previously known hemiasterlin (1) and hemiasterlin A (2), a new analogue, hemiasterlin C (3), was isolated and identified. The structures of 1 and 2 were assigned based on comparison to literature values, and 3 was identified on the basis of 1H NMR, 13C NMR, COSY, HSQC, and HMBC experiments. The cytotoxic and antitubulin activities of 1, 1, 1 were evaluated. In a comparative assay for inhibition of tubulin polymerization, the hemiasterlins were more potent than dolastatin 15 and equipotent with cryptophycin 1, but were somewhat less potent than dolastatin 10.

Introduction

In our continuing investigation of marine organisms as a source of potential antitumor compounds, our attention was drawn to three species of sponge which had been collected off the coast of Papua New Guinea and evaluated in the NCI 60 human tumor cell line primary assay.1 One of these organisms was identified as an Auletta sp., while the other two were identified as Siphonochalina spp. COMPARE correlations1 as high as 0.7 or greater were observed among extracts of these three organisms (Table 1). Further, COMPARE correlation analyses of the extract screening data referenced to the NCI standard agents database1 suggested that the activity of these extracts might be due to tubulin-interactive constituents (Table 2). A literature search revealed that the only metabolites of Siphonochalina reported to date were a variety of acetylenic compounds and a number of novel triterpenes.2, 3, 4, 5, 6 In contrast, there was only one previous report of Auletta in the chemical literature, documenting the isolation of milnamide (4), a highly modified tripeptide.7

Section snippets

Results

Bioassay-guided fractionation of the nBuOH partition of the Auletta sp. aqueous extract led to the isolation and identification of hemiasterlin (1) and hemiasterlin A (2). These assignments were supported by comparisons with the published data for these compounds obtained from Hemiasterella minor8 and Cymbastela sp.9 These compounds are closely related to milnamide,7 but had not previously been reported from Auletta. The nBuOH partition fraction from the aqueous extract of Siphonochalina sp.

Discussion

Dolastatin 10, an analogue of dolastatin 15 (Cemadotin), and an analogue of cryptophycin 1 (cryptophycin 52) are all currently in early clinical trials. The structures of these larger peptides are considerably more complex than those of the hemiasterlins. The structural motif of the hemiasterlins would appear to be readily amenable to the rapid generation of analogues by combinatorial chemistry as a potential route to lead-optimization for further preclinical development.

With the identification

General

NMR spectra were recorded on a Varian VXR 500 spectrometer, and chemical shifts were referenced relative to the residual undeuterated solvent signal. Proton-detected heteronuclear correlations were measured using HSQC (optimized for 1JHC=140 Hz) and HMBC (optimized for nJHC=8 Hz) pulse sequences. Whenever possible, proton–proton connectivities were confirmed by COSY 45 NMR experiments. Infrared spectra were obtained on a Perkin–Elmer Spectrum 2000 FT-IR spectrometer. Optical rotations were

Acknowledgements

We thank the Coral Reef Foundation (P. Colin) and Natural Products Branch (D. John Newman) for the sponge collections, T. McCloud for extractions, A. Monks and D. Scudiero for screening support, and J. Michael for technical assistance.

References (19)

  • U. Shmueli et al.

    Tetrahedron Lett.

    (1981)
  • S. Carmely et al.

    Tetrahedron Lett.

    (1983)
  • R. Talpir et al.

    Tetrahedron Lett.

    (1994)
  • J.E. Coleman et al.

    Tetrahedron

    (1995)
  • E.D. de Silva et al.

    Tetrahedron Lett.

    (1990)
  • R. Bai et al.

    J. Biol. Chem.

    (1990)
  • C.D. Smith et al.

    J. Biol. Chem.

    (1996)
  • R. Bai et al.

    Biochem. Pharmacol.

    (1992)
  • M.R. Boyd et al.

    Drug Dev. Res.

    (1995)
There are more references available in the full text version of this article.

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Dedicated to the memory of Anna P. Talarico, who lost her battle with a brain tumor on 2 October, 1997.

Werner Kirsten High School Student Intern Program 1995-96; Summer Research Training Program, 1997.

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