Mansouramycins E-G, Cytotoxic Isoquinolinequinones from Marine Streptomycetes.

Chemical investigation of the ethyl acetate extract from the marine-derived Streptomyces sp. isolate B1848 resulted in three new isoquinolinequinone derivatives, the mansouramycins E-G (1a-3a), in addition to the previously reported mansouramycins A (5) and D (6). Their structures were elucidated by computer-assisted interpretation of 1D and 2D NMR spectra, high-resolution mass spectrometry, and by comparison with related compounds. Cytotoxicity profiling of the mansouramycins in a panel of up to 36 tumor cell lines indicated a significant cytotoxicity and good tumor selectivity for mansouramycin F (2a), while the activity profile of E (1a) was less attractive.

Karamomycins A-C: 2-Naphthalen-2-yl-thiazoles from Nonomuraea endophytica.

Karamomycins A-C (2-4), the first natural 2-naphthalen-2-yl-thiazole derivatives, were isolated along with a plausible precursor molecule, 1-hydroxy-4-methoxy-2-naphthoic acid (1), uracil, 1-acetyl-ß-carboline, and actinomycin C2 from the culture broth of the terrestrial actinomycete strain GW58/450, identified as Nonomuraea endophytica. These compounds were characterized by analysis of their NMR and mass spectrometry (MS) data; the absolute configurations of 2 and 4 were determined by comparison of 13C NMR, NOESY, and circular dichroism (CD) spectra with density functional theory (DFT)-calculated data. In karamomycin C (4), the thiazole of 2 is connected to an unusual iminothiazolo[4,3- c][1,4]thiazepinone, for which we proposed a biosynthetic origin from two cysteine residues. It is closely related to ulbactin F; however, the heterocycle is enantiomeric to the latter and connected to phenol instead of 4-methoxy-1-naphthol. Karamomycins A (2) and C (4) were cytotoxic.

Studies on the constituents of Helleborus purpurascens: analysis and biological activity of the aqueous and organic extracts.

In Southeast Europe, the ethnomedicinal use of Helleborus species has a very long tradition. Cardiac steroids (Hellebrin), cysteine-rich proteins (Hellethionins) and several steroidal saponins have been identified in these plants. Aim of the present work was to investigate the amino acid composition of native extracts from the root and rootstock of Helleborus purpurascens. The amino acids have been identified by the GC-MS technique on the previously derivatised (Phenomenex Faast Kit) extract samples by comparison with the mass spectra and retention-time of the standards. A remarkable finding was a relatively intensive peak attributed to the non-proteinogenic Pipecolic acid (Pic). A cyclisation of the derivatised glutamine was observed during the GC measurement and a mechanistic pathway is described. Samples of the extract and of some isolated fractions have also been tested on; altogether 12 cancer cell lines aimed to identify further potentially cytostatic components which should be less toxic than Hellebrin. The finding of one Hellebrin-free fraction (IC50 = 0.007 mg/L) with higher cytotoxicity than Hellebrin (IC50 = 0.008 mg/L) is remarkable.

Marine Bacteria, XLVII - Psychrotolerant Bacteria from Extreme Antarctic Habitats as Producers of Rare Bis- and Trisindole Alkaloids.

From the gastrointestinal tract of a fish dredged near the South Orkney Islands in Antarctica, we isolated the psychrotolerant bacterial strain T262, which belongs to the species Vibrio splendidus. Investigation of this strain led to the isolation of a series of 15 bis- and trisindole derivatives. Among them, six new indole alkaloids, namely, turbomycin C [4'-n-butoxyphenyl-bis(1H-indol-3-yl)methane, 1a], turbomycin D [4'-n-propoxyphenyl-bis(1H-indol-3-yl)methane, 1b], turbomycin E [4'-ethoxyphenyl-bis(1H-indol-3-yl)methane, 1c], turbomycin F [4'-methoxy-3',5'-dinitrophenyl-bis(1H-indol-3-yl)methane, 2], trisindolal (3a), and 4-(1H-indol-3-yl-sulfanyl)phenol (4). Another new bisindole derivative elucidated as 2-(indol-3-ylmethyl)-indol-3-ylethanol (7a) was obtained together with six known compounds from the psychrotolerant Arthrobacter psychrochitiniphilus strain T406, isolated from the excrement of penguins. Some of the isolated compounds showed activity against both gram-positive and gram-negative bacteria at 10 µg/paper disk. Trisindolal (3a) was active against the peronosporomycetes Botrytis cinerea and Phytophthora infestans, and some of the indole derivatives indicated promising cytotoxicity towards human tumor cell lines. By exhibiting a mean IC50 of 0.45 µg/mL (1.17 µM), trisindolal (3a) showed pronounced potency and selectivity in a panel of 11 human tumor cell lines derived from 10 different tumor histotypes.

Lung Cancer: EGFR Inhibitors with Low Nanomolar Activity against a Therapy-Resistant L858R/T790M/C797S Mutant.

The treatment of non-small-cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) inhibitors is made challenging by acquired resistance caused by somatic mutations. Third-generation EGFR inhibitors have been designed to overcome resistance through covalent binding to the Cys 797 residue of the enzyme, and these inhibitors are effective against most clinically relevant EGFR mutants. However, the high dependence of these recent EGFR inhibitors on this particular interaction means that additional mutation of Cys 797 results in poor inhibitory activity, which leads to tumor relapse in initially responding patients. A new generation of irreversible and reversible mutant EGFR inhibitors was developed with strong noncovalent binding properties, and these compounds show high inhibitory activities against the cysteine-mutated L858R/T790M/C797S EGFR.

Total synthesis and cytotoxicity of the marine natural product malevamide D and a photoreactive analog.

The marine natural product malevamide D from the cyanobacterium Symploca hydnoides was synthesized for the first time. The final peptide coupling linked the dolaisoleuine and dolaproine subunits. The phenyl group of malevamide D was also functionalized with a photoreactive diazirine moiety, which was carried through seven reaction steps. Comprehensive assessment of the cytotoxicity in a panel of 42 human cancer cell lines revealed a geomean IC70 value of 1.5 nM (IC50 0.7 nM) for malevamide D, whereas the photoreactive derivative proved to be less active by a factor of at least 200. COMPARE analysis indicated tubulin interaction as likely mode of action of malevamide D.

Doubly prenylated tryptamines: cytotoxicity, antimicrobial activity and cyclisation to the marine natural product flustramine A.

The marine natural product flustramine A was synthesised via oxidative cyclisation of Nb-methylated 1-prenyl-2-tert-prenyl-6-bromotryptamine and subsequent reduction of the resulting amidinium salt. Only the tert-prenyl group migrated, whereas the 1-prenyl group remained in place. Interestingly, the 2-tert-prenylated precursor revealed to be the biologically most active of our entire series of 21 compounds. Required for cytotoxicity and antimicrobial activity was the presence of a non-cyclised tryptamine side chain carrying a free secondary amine, whereas the presence of a 6-bromo substituent did not enhance cytotoxicity. In a panel of 42 human tumor cell lines, most sensitive were the lung and mammary cancer cell lines LXFA629L (IC50 1.9 µM) and MAXF401NL (IC50 2.4 µM), respectively. In a serial dilution assay, satisfying IC50 values of 5.9 µM against Micrococcus luteus and 7.7 µM each against Mycobacterium phlei were determined for Nb-methyl-1-prenyl-2-tert-prenyl-6-bromotryptamine.

Synthesis and antiproliferative activity of 2,5-bis(3'-indolyl)pyrroles, analogues of the marine alkaloid nortopsentin.

2,5-bis(3'-Indolyl)pyrroles, analogues of the marine alkaloid nortopsentin, were conveniently prepared through a three step procedure in good overall yields. Derivatives 1a and 1b exhibited concentration-dependent antitumor activity towards a panel of 42 human tumor cell lines with mean IC50 values of 1.54 µM and 0.67 µM, respectively. Investigating human tumor xenografts in an ex-vivo clonogenic assay revealed selective antitumor activity, whereas sensitive tumor models were scattered among various tumor histotypes.

Synthesis and characterization of novel bioactive 1,2,4-oxadiazole natural product analogs bearing the N-phenylmaleimide and N-phenylsuccinimide moieties.

Taking into consideration the biological activity of the only natural products containing a 1,2,4-oxadiazole ring in their structure (quisqualic acid and phidianidines A and B), the natural product analogs 1-(4-(3-tert-butyl-1,2,4-oxadiazol-5-yl)phenyl)pyrrolidine-2,5-dione (4) and 1-(4-(3-tert-butyl-1,2,4-oxadiazol-5-yl)phenyl)-1H-pyrrole-2,5-dione (7) were synthesized starting from 4-(3-tert-butyl-1,2,4-oxadiazol-5-yl)aniline (1) in two steps by isolating the intermediates 4-(4-(3-tert-butyl-1,2,4-oxadiazol-5-yl)phenylamino)-4-oxobutanoic acid (3) and (Z)-4-(4-(3-tert-butyl-1,2,4-oxadiazol-5-yl)phenylamino)-4-oxobut-2-enoic acid (6). The two natural product analogs 4 and 7 were then tested for antitumor activity toward a panel of 11 cell lines in vitro by using a monolayer cell-survival and proliferation assay. Compound 7 was the most potent and exhibited a mean IC50 value of approximately 9.4 µM. Aniline 1 was synthesized by two routes in one-pot reactions starting from tert-butylamidoxime and 4-aminobenzoic acid or 4-nitrobenzonitrile. The structures of compounds 1, 2, 4, 5 and 6 were confirmed by X-ray crystallography.

High In Vitro and In Vivo Activity of BI-847325, a Dual MEK/Aurora Kinase Inhibitor, in Human Solid and Hematologic Cancer Models.

BI-847325 is an ATP-competitive inhibitor of MEK/Aurora kinases with the potential to treat a wide range of cancers. In a panel of 294 human tumor cell lines in vitro, BI-847325 was found to be a highly selective inhibitor that was active in the submicromolar range. The most sensitive cancer types were acute lymphocytic and myelocytic leukemia, melanomas, bladder, colorectal, and mammary cancers. BI-847325 showed a broader range of activity than the MEK inhibitor GDC-0623. The high efficacy of BI-847325 was associated with but not limited to cell lines with oncogenic mutations in NRAS, BRAF, and MAP2K1.The high antiproliferative activity of BI-847325 was validated in vivo using subcutaneous xenograft models. After oral administration of 80 and 40 mg/kg once weekly for 3 or 4 weeks, BI-847325 was highly active in four of five colorectal, two of two gastric, two of two mammary, and one of one pancreatic cancer models (test/control < 25%), and tumor regressions were observed in five of 11 cancer models. The treatment was well tolerated with no relevant lethality or body weight changes. In combination with capecitabine, BI-847325 displayed synergism over single-agent therapies, leading to complete remission in the triple-negative mammary model MAXFTN 401, partial regression in the colon model CXF 1103, and stasis in the gastric models GXA 3011 and GXA 3023. In conclusion, dual MEK/Aurora kinase inhibition shows remarkable potential for treating multiple types of hematologic and solid tumors. The combination with capecitabine was synergistic in colorectal, gastric, and mammary cancer. SIGNIFICANCE: We report the preclinical evaluation of BI-847325, a MEK/Aurora kinase inhibitor. Our data demonstrate that BI-847325 has potent antitumor activity in a broad range of human solid and hematologic cancer models in vitro and in vivo and is well tolerated in animal models. It also shows synergistic effect when combined with capecitabine. These findings provide a strong rationale for further development of BI-847325 as a potential therapeutic for patients with cancer.

Novel inhibitors of epidermal growth factor receptor: (4-(Arylamino)-7H-pyrrolo[2,3-d]pyrimidin-6-yl)(1H-indol-2-yl)methanones and (1H-indol-2-yl)(4-(phenylamino)thieno[2,3-d]pyrimidin-6-yl)methanones.

Several members of the quinazoline class of known tyrosine kinase inhibitors are approved anticancer agents, often showing selectivity for receptors of the HER/ErbB-family. Combining structural elements of this class with the bisindolylmethanone-structure led to a series of novel compounds. These compounds inhibited EGFR in the nanomolar range. Moreover, inhibition of EGFR autophosphorylation in intact A431 cells was shown, with IC(50) values ranging form 0.3-1µM for compound 42, and 0.1-0.3µM for 45. In a panel of 42 human tumor cell lines the sensitivity profile of the novel compounds was shown to be similar to that of the quinazoline class of tyrosine kinase inhibitors lapatinib and erlotinib (Tarceva®).

Histone deacetylase inhibitor MGCD0103 synergizes with gemcitabine in human pancreatic cells.

Histone deacetylase inhibitors are a group of recently developed compounds that modulate cell growth and survival. We evaluated the effects of the histone deacetylase inhibitor MGCD0103 on growth of pancreatic carcinoma models following single agent treatment and in combination with gemcitabine. MGCD0103 inhibited tumor cell growth and acted synergistically with gemcitabine to enhance its cytotoxic effects. Gene expression analysis identified the cell cycle pathway as one of the most highly modulated gene groups. Our data suggest that MGCD0103 + gemcitabine might be an effective treatment for gemcitabine-refractory pancreatic cancer.

Molecular editing and assessment of the cytotoxic properties of iejimalide and progeny.

Systematic variation of all substructures embedded into the framework of iejimalide B (2) led to a panel of synthetic analogues of this polyunsaturated macrolide, featuring structural modifications that are not accessible by derivatization of the natural lead compound itself. The assessment of the cytotoxicity of these compounds with the aid of a monolayer proliferation assay (12 human tumor cell lines in vitro) as well as a colony formation assay (24 human tumor xenografts ex vivo) revealed the exceptional potency of 2 and several of its synthetic congeners, with IC(50) values in the picomolar range for the most sensitive cell lines. Whereas structural modifications of the macrocycle or of the side chain generally lead to a decrease in activity, changes of the peptidic terminus are not only well accommodated but engender increased tumor selectivity as well. 2 and two of the most promising analogues were selected for in vivo studies in mice, in which their activity against human tumor xenografts of breast cancer (MAXF 401) and prostate cancer (PRXF PC-3M) was tested. In contrast to a previous report in the literature however, which had claimed in vivo activity for the parent iejimalides, these tests did not show a significant therapeutic effect against the chosen solid tumors upon intraperitoneal administration.

Boshramycinones A-C: New anthracyclinones produced by a marine-derived Streptomyces sp.: isolation, structure elucidation and biological activities.

Boshramycinones A-C (1-3), three new anthracyclinones, were isolated from the culture broth of the marine-derived Streptomyces sp. Mei 16-1,2 together with 2-acetyl-1,8-dihydroxy-3-methyl-anthraquinone (4) and bafilomycins B1, B2, and C1-amide. The isolated compounds were identified by NMR spectroscopy and mass spectrometry, the absolute configuration of 3 was determined by comparison of experimental and ab initio-calculated chiroptical data. The antimicrobial activity of the bacterial extract and the isolated compounds were assayed using a set of microorganisms, and cytotoxic activities were determined against 36 human cancer cell lines.

Synthesis and antitumor activity of 2,5-bis(3'-indolyl)-furans and 3,5-bis(3'-indolyl)-isoxazoles, nortopsentin analogues.

A series of novel 2,5-bis(3'-indolyl)furans and 3,5-bis(3'-indolyl)isoxazoles were synthesized as antitumor agents. The antiproliferative activity was evaluated in vitro toward diverse human tumor cell lines. Initially 5 isoxazoles and 3 furan derivatives were tested against a panel of 10 human tumor cell lines and the most active derivatives 3c and 4a were selected to be evaluated in an extended panel of 29 cell lines. By exhibiting mean IC(50) values of 17.4 microg/mL (3a) and 20.5 microg/mL (4c), in particular 4c showed a high level of tumor selectivity toward the 29 cell lines.

Mode of action of epoxyphomalins A and B and characterization of related metabolites from the marine-derived fungus Paraconiothyrium sp.

Epoxyphomalins A (1) and B (2) are highly potent cytotoxic fungal metabolites. During the course of purifying larger quantities of 1 and 2 from Paraconiothyrium sp. fermentation extracts, three new epoxyphomalins (3-5) were isolated and characterized, showing modifications to the oxidation pattern of the cyclohexene moiety or of C-9 of the decalin system. IC(50) values for cytotoxicity against a panel of 36 human tumor cell lines were determined for all new compounds. Compound 4 was found to be cytotoxic particularly toward prostate PC3M (IC(50) = 0.72 µM) and bladder BXF 1218 L (IC(50) = 1.43 µM) cancer cell lines. In addition, inhibition of chymotrypsin-, caspase-, and trypsin-like activity of purified 20S proteasomes was determined for epoxyphomalins A (1) and B (2). The results indicate that compounds 1 and 2 exert their cytotoxic effect through potent inhibition of the 20S proteasome.

Chemistry, antiproliferative properties, tumor selectivity, and molecular mechanisms of novel gold(III) compounds for cancer treatment: a systematic study.

The antiproliferative properties of a group of 13 structurally diverse gold(III) compounds, including six mononuclear gold(III) complexes, five dinuclear oxo-bridged gold(III) complexes, and two organogold(III) compounds, toward several human tumor cell lines were evaluated in vitro using a systematic screening strategy. Initially all compounds were tested against a panel of 12 human tumor cell lines, and the best performers were tested against a larger 36-cell-line panel. Very pronounced antiproliferative properties were highlighted in most cases, with cytotoxic potencies commonly falling in the low micromolar--and even nanomolar--range. Overall, good-to-excellent tumor selectivity was established for at least seven compounds, making them particularly attractive for further pharmacological evaluation. Compare analysis suggested that the observed antiproliferative effects are caused by a variety of molecular mechanisms, in most cases "DNA-independent," and completely different from those of platinum drugs. Remarkably, some new biomolecular systems such as histone deacetylase, protein kinase C/staurosporine, mammalian target of rapamycin/rapamycin, and cyclin-dependent kinases were proposed for the first time as likely biochemical targets for the gold(III) species investigated. The results conclusively qualify gold(III) compounds as a promising class of cytotoxic agents, of outstanding interest for cancer treatment, while providing initial insight into their modes of action.

Molecular editing and biological evaluation of amphidinolide X and Y.

Scarce and precious: A collection of compounds with deep-seated structural "point mutations" within the framework of the marine natural products amphidinolide X and Y was prepared by "diverted total synthesis". The resulting products provided first insights into the cytotoxicity profile of these extremely scarce macrolides.Deliberate deviations from the previously described total syntheses of amphidinolide X (1) and Y (2) allowed a collection of seven designed analogues of these extremely scarce marine natural products to be obtained. These fully synthetic "natural product-like" compounds enabled first insights into the previously unknown structure-activity relationships governing this series. Although the average cytotoxicity is moderate, it was found that certain bladder, colon and prostate cancer cell lines are fairly sensitive, and that the best synthetic analogues are more active than the natural products themselves. The syntheses rely on the 9-MeO-9-BBN variant of the Suzuki coupling for the formation of the carbon frameworks, as well as on Yamaguchi lactonization reactions for the cyclization of the macrocyclic rings.

Mansouramycins A-D, cytotoxic isoquinolinequinones from a marine streptomycete.

Chemical screening of the ethyl acetate extract from the marine-derived Streptomyces sp. isolate Mei37 resulted in five isoquinolinequinones, four new derivatives, mansouramycin A-D (1, 3-5), and the known 3-methyl-7-(methylamino)-5,8-isoquinolinedione (2). Their structures were elucidated by NMR and MS techniques and by comparison with related compounds. Cytotoxicity profiling of the mansouramycins in a panel of up to 36 tumor cell lines indicated significant cytotoxicity of several derivatives, with pronounced selectivity for non-small cell lung cancer, breast cancer, melanoma, and prostate cancer cells.

Plasticity in gilvocarcin-type C-glycoside pathways: discovery and antitumoral evaluation of polycarcin V from Streptomyces polyformus.

Gilvocarcin-type polyketide glycosides represent some of the most powerful antitumor therapeutics. Bioactivity-guided fractionation of a culture extract of Streptomyces polyformus sp. nov. (YIM 33176) yielded the known gilvocarcin V (2) and a novel related compound, polycarcin V (1). Structure elucidation by NMR and chemical derivatization revealed that the congener (1) features a C-glycosidically linked alpha-L-rhamnopyranosyl moiety in lieu of the D-fucofuranose. The concomitant production of two distinct furanosyl and pyranosyl C-glycosides that share the same aglycone is unprecedented in bacteria. A conversion of both isoforms via a quinone methide intermediate can be ruled out, thus pointing to two individual C-glycosylation pathways. Cytotoxicity profiling of polycarcin V in a panel of 37 tumor cell lines indicated significant antitumoral activity with a pronounced selectivity for non-small-cell lung cancer, breast cancer and melanoma cells. As the antiproliferative fingerprint is identical to that of actinomycin D, the known DNA interaction of gilvocarcins was established as a general principle of antitumorigenic activity.