Histone deacetylases (HDACs) are validated targets for anticancer therapy as attested by the approval of suberoylanilide hydroxamic acid (SAHA) and romidepsin (FK228) for treating cutaneous T cell lymphoma. We recently described the bioassay-guided isolation, structure determination, synthesis, and target identification of largazole, a marine-derived antiproliferative natural product that is a prodrug that releases a potent HDAC inhibitor, largazole thiol. Here, we characterize the anticancer activity of largazole by using in vitro and in vivo cancer models. Screening against the National Cancer Institute's 60 cell lines revealed that largazole is particularly active against several colon cancer cell types. Consequently, we tested largazole, along with several synthetic analogs, for HDAC inhibition in human HCT116 colon cancer cells. Enzyme inhibition strongly correlated with the growth inhibitory effects, and differential activity of largazole analogs was rationalized by molecular docking to an HDAC1 homology model. Comparative genomewide transcript profiling revealed a close overlap of genes that are regulated by largazole, FK228, and SAHA. Several of these genes can be related to largazole's ability to induce cell cycle arrest and apoptosis. Stability studies suggested reasonable bioavailability of the active species, largazole thiol. We established that largazole inhibits HDACs in tumor tissue in vivo by using a human HCT116 xenograft mouse model. Largazole strongly stimulated histone hyperacetylation in the tumor, showed efficacy in inhibiting tumor growth, and induced apoptosis in the tumor. This effect probably is mediated by the modulation of levels of cell cycle regulators, antagonism of the AKT pathway through insulin receptor substrate 1 down-regulation, and reduction of epidermal growth factor receptor levels.

We discovered new structural diversity to a prevalent, yet medicinally underappreciated, cyanobacterial protease inhibitor scaffold and undertook comprehensive protease profiling to reveal potent and selective elastase inhibition. SAR and X-ray cocrystal structure analysis allowed a detailed assessment of critical and tunable structural elements. To realize the therapeutic potential of these cyclodepsipeptides, we probed the cellular effects of a novel and representative family member, symplostatin 5 (1), which attenuated the downstream cellular effects of elastase in an epithelial lung airway model system, alleviating clinical hallmarks of chronic pulmonary diseases such as cell death, cell detachment and inflammation. This compound attenuated the effects of elastase on receptor activation, proteolytic processing of the adhesion protein ICAM-1, NF-κB activation and transcriptomic changes, including the expression of pro-inflammatory cytokines IL1A, IL1B and IL8. Compound 1 exhibited activity comparable to the clinically-approved elastase inhibitor sivelestat in short-term assays and demonstrated superior sustained activity in longer-term assays.

Collections of the marine cyanobacterium Lyngbya bouillonii from shallow patch reefs in Apra Harbor, Guam, afforded three hitherto undescribed analogues of the glycosidic macrolide lyngbyaloside, namely 2-epi-lyngbyaloside (1) and the regioisomeric 18E-and 18Z-lyngbyalosides C (2 and 3). Concurrently we discovered two new analogues of the cytoskeletal actin-disrupting lyngbyabellins, 27-deoxylyngbyabellin A (4) and lyngbyabellin J (5), a novel macrolide of the laingolide family, laingolide B (6), and a linear modified peptide, lyngbyapeptin D (7), along with known lyngbyabellins A and B, lyngbyapeptin A, and lyngbyaloside. The structures of 1-7 were elucidated by a combination of NMR spectroscopic and mass spectrometric analysis. Compounds 1-6 were either brominated (1-3) or chlorinated (4-6), consistent with halogenation being a hallmark of many marine natural products. All extracts derived from these L. bouillonii collections were highly cytotoxic due to the presence of apratoxin A or also apratoxin C. Compounds 1-5 showed weak to moderate cytotoxicity to HT29 colorectal adenocarcinoma and HeLa cervical carcinoma cells.Marine cyanobacteria have been attracting increasing attention for probe and drug discovery due to the high incidence of structurally novel bioactive secondary metabolites that complement those known from terrestrial sources. These natural products are predominantly modified peptides and depsipeptides, polyketides and peptide-polyketide hybrids, many of which are cyclic and oftentimes halogenated.1 One intriguing characteristic of marine cyanobacteria is that a single organism commonly produces several distinct classes of natural products so that up to 10% of the genome may be dedicated to secondary metabolism. One example of such a "superproducer" is Lyngbya bouillonii.2 , 3 Various collections carried out over the past two decades have consistently yielded apratoxin A,4 lyngbyabellin A,5 lyngbyapeptin A6 and, with variable reproducibility, also lyngbyastatin 2,7 , 8 lyngbyabellin B,6 apratoxin B9 and apramides A-G.10 Recently we found that the secondary metabolite content of L. bouillonii may be depth-dependent, because at the same site (Finger's Reef, Guam) but at greater depth (14 m instead of 2 m) apratoxin E rather than apratoxin A was the major apratoxin produced by a morphologically identical * To whom correspondence should be addressed. Tel.: (352) Fax: (352) 273-7741, luesch@cop.ufl.edu. ‡ Contributed equally.Supporting Information Available: NMR spectra for compounds 1-7. This material is available free of charge via the Internet at http://pubs.acs.org. NIH Public AccessAuthor Manuscript J Nat Prod. Author manuscript; available in PMC 2011 September 24. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript cyanobacterium.8 The latter, however, lacked the usually co-existing snapping shrimp Alpheus frontalis that is known to use L. bouillonii as food and tubular shelter.11 -13Previous investigations of L. bouillonii from Finger's Reef in Apra Harbor we...

Inspired by marine cyanobacterial natural products, we synthesized modified peptides with a central statine-core unit, characteristic for aspartic protease inhibition. A series of tasiamide B analogues inhibited BACE1, a therapeutic target in Alzheimer's disease. We probed the stereospecificity of target engagement and determined additional structure-activity relationships with respect to BACE1 and related aspartic proteases, cathepsins D and E. We cocrystallized selected inhibitors with BACE1 to reveal the structural basis for the activity. Hybrid molecules that combine features of tasiamide B and an isophthalic acid moiety-containing sulfonamide showed nanomolar cellular activity. Compounds were screened in a series of rigorous complementary cell-based assays. We measured secreted APP ectodomain (sAPPβ), membrane bound carboxyl terminal fragment (CTF), levels of β-amyloid (Aβ) peptides and selectivity for β-secretase (BACE1) over γ-secretase. Prioritized compounds showed reasonable stability in vitro and in vivo, and our most potent inhibitor showed efficacy in reducing Aβ levels in the rodent brain.

Cytotoxicity-directed purification of a Symploca cf. hydnoides sample from Cetti Bay, Guam, afforded seven new cyclic depsipeptides, veraguamides A–G (1–7), together with the known compound dolastatin 16. The planar structures of 1–7 were elucidated using NMR and MS experiments, while enantioselective HPLC and Mosher's analysis of acid and base hydrolysates, respectively, were utilized to assign the absolute configurations of the stereocenters. Veraguamides A–G (1–7) are characterized by the presence of an invariant proline residue, multiple N-methylated amino acids, an α-hydroxy acid, and a C8-polyketide derived β-hydroxy acid moiety with a characteristic terminus as either an alkynyl bromide, alkyne, or vinyl group. These compounds and a semisynthetic analog (8) showed moderate to weak cytotoxic activity against HT29 colorectal adenocarcinoma and HeLa cervical carcinoma cell lines. Preliminary structure-activity relationship analysis identified several sensitive positions in the veraguamide scaffold that affect the cytotoxic activity of this compound class. Dolastatin 16 showed only weak cytotoxic activity on both cell lines tested. The complete stereostructure of dolastatin 16 was proposed for the first time through degradation followed by a combination of advanced Marfey's analysis and modified Mosher's analysis using phenylglycine methyl ester as a chiral anisotropic reagent.