Agelastatin A: a novel inhibitor of osteopontin-mediated adhesion, invasion, and colony formation.

Effective inhibitors of osteopontin (OPN)-mediated neoplastic transformation and metastasis are still lacking. (-)-Agelastatin A is a naturally occurring oroidin alkaloid with powerful antitumor effects that, in many cases, are superior to cisplatin in vitro. In this regard, past comparative assaying of the two agents against a range of human tumor cell lines has revealed that typically (-)-agelastatin A is 1.5 to 16 times more potent than cisplatin at inhibiting cell growth, its effects being most pronounced against human bladder, skin, colon, and breast carcinomas. In this study, we have investigated the effects of (-)-agelastatin A on OPN-mediated malignant transformation using mammary epithelial cell lines. Treatment with (-)-agelastatin A inhibited OPN protein expression and enhanced expression of the cellular OPN inhibitor, Tcf-4. (-)-Agelastatin A treatment also reduced beta-catenin protein expression and reduced anchorage-independent growth, adhesion, and invasion in R37 OPN pBK-CMV and C9 cell lines. Similar effects were observed in MDA-MB-231 and MDA-MB-435s human breast cancer cell lines exposed to (-)-agelastatin A. Suppression of Tcf-4 by RNA interference (short interfering RNA) induced malignant/invasive transformation in parental benign Rama 37 cells; significantly, these events were reversed by treatment with (-)-agelastatin A. Our study reveals, for the very first time, that (-)-agelastatin A down-regulates beta-catenin expression while simultaneously up-regulating Tcf-4 and that these combined effects cause repression of OPN and inhibition of OPN-mediated malignant cell invasion, adhesion, and colony formation in vitro. We have also shown that (-)-agelastatin A inhibits cancer cell proliferation by causing cells to accumulate in the G(2) phase of cell cycle.

Glycogen synthase kinase 3 is a potential drug target for African trypanosomiasis therapy.

Development of a safe, effective, and inexpensive therapy for African trypanosomiasis is an urgent priority. In this study, we evaluated the validity of Trypanosoma brucei glycogen synthase kinase 3 (GSK-3) as a potential drug target. Interference with the RNA of either of two GSK-3 homologues in bloodstream-form T. brucei parasites led to growth arrest and altered parasite morphology, demonstrating their requirement for cell survival. Since the growth arrest after RNA interference appeared to be more profound for T. brucei GSK-3 "short" (Tb10.161.3140) than for T. brucei GSK-3 "long" (Tb927.7.2420), we focused on T. brucei GSK-3 short for further studies. T. brucei GSK-3 short with an N-terminal maltose-binding protein fusion was cloned, expressed, and purified in a functional form. The potency of a GSK-3-focused inhibitor library against the recombinant enzyme of T. brucei GSK-3 short, as well as bloodstream-form parasites, was evaluated with the aim of determining if compounds that inhibit enzyme activity could also block the parasites' growth and proliferation. Among the compounds active against the cell, there was an excellent correlation between activity inhibiting the T. brucei GSK-3 short enzyme and the inhibition of T. brucei growth. Thus, there is reasonable genetic and chemical validation of GSK-3 short as a drug target for T. brucei. Finally, selective inhibition may be required for therapy targeting the GSK-3 enzyme, and a molecular model of the T. brucei GSK-3 short enzyme suggests that compounds that selectively inhibit T. brucei GSK-3 short over the human GSK-3 enzymes can be found.

New total synthesis of the marine antitumor alkaloid (-)-agelastatin A.

[reaction: see text] A new total synthesis of (-)-agelastatin A (1) has been achieved from the chiral oxazolidinone (-)-3. Although enone transposition was problematic when the Michael ring closure of 2 was attempted with strong base, the desired cyclization could be effected with Hunig's base after the pyrrole nucleus was brominated. Subsequent reduction and monobromination afforded synthetic (-)-agelastatin A (1).

Enantiospecific formal total synthesis of the tumor and GSK-3 beta inhibiting alkaloid, (-)-agelastatin A.

[reaction: see text] An enantiospecific total synthesis of Weinreb's advanced intermediate 2 for (-)-agelastatin A has been achieved from the Hough-Richardson aziridine 8. Noteworthy reactions in our sequence include the highly regioselective trans-diaxial ring-opening of 8 with azide ion to set up the vicinal diamido functionality present within (-)-2 and the Grubbs-Hoveyda ring-closing metathesis (RCM) reaction that was used to construct its cyclopentene core.

Total syntheses of the telomerase inhibitors dictyodendrin B, C, and E.

Concise and flexible total syntheses of the pyrrolo[2,3-c]carbazole alkaloids dictyodendrin B (2), C (3), and E (5) are described. These polycyclic telomerase inhibitors of marine origin derive from the common intermediate 18 which was prepared on a multigram scale by a sequence comprising a TosMIC cycloaddition with formation of the pyrrole A-ring, a titanium-induced reductive oxoamide coupling reaction to generate an adjacent indole nucleus, and a photochemical 6pi-electrocyclization/aromatization tandem to forge the pyrrolocarbazole core. Conversion of 18 into dictyodendrin C required selective manipulations of the lateral protecting groups and oxidation with peroxoimidic acid to form the vinylogous benzoquinone core of the target. Zinc-induced reductive cleavage of the trichloroethyl sulfate ester then completed the first total synthesis of 3. Its relatives 2 and 5 also originate from compound 18 by a selective bromination of the pyrrole entity followed by elaboration of the resulting bromide 27 via metal-halogen exchange or cross-coupling chemistry, respectively. Particularly noteworthy in this context is the generation of the very labile p-quinomethide motif of dictyodendrin E by a palladium-catalyzed benzyl cross-coupling reaction followed by vinylogous oxidation of the resulting product 41 with DDQ. The Suzuki step could only be achieved with the aid of the borate complex 40 formed in situ from p-methoxybenzylmagnesium chloride and 9-MeO-9-BBN, whereas alternative methods employing benzylic boronates, -trifluoroborates, or -stannanes met with failure.

Total synthesis of dictyodendrin B.

A concise total synthesis of dictyodendrin B (1) is reported, a scarce marine alkaloid endowed with promising telomerase inhibitory activity. Key steps of the chosen route are a reductive cyclization of ketoamide 11 to indole 12 mediated by low-valent titanium (from TiCl3 and KC8) followed by a photochemical 6pi-electrocyclization, which was performed in the presence of Pd/C and nitrobenzene to effect concomitant dehydrogenation/aromatization of the product initially formed. Regioselective bromination of the resulting pyrrolocarbazole 13 followed by lithium/bromine exchange and quenching of the resulting organolithium species with p-methoxybenzaldehyde installed the side chain at C2. Oxidation of the benzylic alcohol 15 thus obtained to ketone 17 was best achieved with catalytic amounts of tetra-n-propylammonium perruthenate (TPAP) and N-methylmorpholine-N-oxide (NMO) in dilute CH2Cl2 solution to avoid the formation of undue amounts of the unsymmetrical dimer 16. Ketone 17 was elaborated into the natural product by selective cleavage of the isopropyl ether with BCl3, introduction of the sulfate moiety with the aid of trichloroethyl chlorosulfuric acid ester, deprotection of all lateral methyl ether groups, and final reductive cleavage of the trichloroethyl ester moiety. The spectroscopic data of synthetic dictyodendrin B thus formed matched those of an authentic sample in all regards. Moreover, it was shown that global deprotection of the peripheral -OH groups in pyrrolo[2,3-c]carbazole 13 is accompanied by spontaneous air-oxidation to form the quinone core of dictyodendrin C.