Jérôme Bignon

Discovery of isoerianin analogues as promising anticancer agents.

The cytotoxic activity of a series of 23 new isoerianin derivatives with modifications on both the A and B rings was studied. Several compounds exhibited excellent antiproliferative activity at nanomolar concentrations against a panel of human cancer cell lines. The most cytotoxic compound, isoerianin (3), strongly inhibits tubulin polymerization in the micromolar range. Moreover, isoerianin leads to G2/M phase cell‐cycle arrest in H1299 and K562 cancer cells, and strongly induces apoptosis. Isoerianin also disrupts the vessel‐like structures formed by human umbilical vein endothelial cells (HUVECs) in vitro, suggesting that this compound may act as a vascular disrupting agent. It clearly appears that in this compound series, the 1,1‐ethane bridge encountered in isoerianin derivatives can replace the 1,2‐ethane bridge of natural erianin with no loss of activity. This reinforces the bioisosteric replacement approach in the combretastatin series previously reported by our research group.

Reduction-Responsive Cholesterol-Based Block Copolymer Vesicles for Drug Delivery

We developed a new robust reduction-responsive polymersome based on the amphiphilic block copolymer PEG-SS-PAChol. The stability and robustness were achieved by the smectic physical cross-linking of cholesterol-containing liquid crystal polymer PAChol in the hydrophobic layer. The reduction-sensitivity was introduced by the disulfide bridge (-S-S-) that links the hydrophilic PEG block and the hydrophobic PAChol block. We used a versatile synthetic strategy based on atom transfer radical polymerization (ATRP) to synthesize the reduction-responsive amphiphilic block copolymers. The reductive cleavage of the disulfide bridge in the block copolymers was first evidenced in organic solution. The partial destruction of PEG-SS-PAChol polymersomes in the presence of a reducing agent was then demonstrated by cryo-electron microscopy. Finally, the calcein release from PEG-SS-PAChol polymersomes triggered by glutathione (GSH) was observed both in PBS suspension and in vitro inside the macrophage cells. High GSH concentrations (≥35 mM in PBS or artificially enhanced in macrophage cells by GSH-OEt pretreatment) and long incubation time (in the order of hours) were, however, necessary to get significant calcein release. These polymersomes could be used as drug carriers with very long circulation profiles and slow release kinetics.

Synthesis, Biological Evaluation of 1,1‐Diarylethylenes as a Novel Class of Antimitotic Agents

The cytotoxic activities of 23 new isocombretastatin A derivatives with modifications on the B‐ring were investigated. Several compounds exhibited excellent antiproliferative activity at nanomolar concentrations against a panel of human cancer cell lines. Compounds isoFCA‐4 (2 e), isoCA‐4 (2 k) and isoNH2CA‐4 (2 s) were the most cytotoxic, and strongly inhibited tubulin polymerization with IC50 values of 4, 2 and 1.5 μM, respectively. These derivatives were found to be 10‐fold more active than phenstatin and colchicine with respect to growth inhibition but displayed similar activities as tubulin polymerization inhibitors. In addition, cell cycle arrest in the G2/M phase and subsequent apoptosis was observed in three cancer cell lines when treated with these compounds. The disruptive effect of 2 e, 2 k and 2 s on the vessel‐like structures formed by human umbilical vein endothelial cells (HUVEC) suggest that these compounds may act as vascular disrupting agents. Both compounds 2 k and 2 s have the potential for further prodrug modification and development as vascular disrupting agents for treatment of solid tumors.

Synthesis and antitumor activity of benzils related to combretastatin A-4.

A series of benzil derivatives related to combretastatin A-4 (CA-4) have been synthesized by oxidation of diarylalkynes promoted by PdI(2) in DMSO. Using this new protocol, 14 benzils were prepared in good to excellent yields and their biological activity has been delineated. Several benzils exhibited excellent antiproliferative activity: for example, 4j and 4k bearing the greatest resemblance to CA-4 and AVE-8062, respectively, were found to inhibit cell growth at the nanomolar level (20-50nM) on four human tumor cell lines. Flow cytometric analysis indicates that these compounds act as antimitotics and arrest the cell cycle in G(2)/M phase. A cell-based assay indicated that compounds 4j and 4k displayed a similar inhibition of tubulin assembly with an IC(50) value similar to CA-4. These results clearly demonstrated that the Z-double bond of CA-4 can be replaced by a 1,2-diketone unit without significant loss of cytotoxicity and inhibition of tubulin assembly potency.

Nitric oxide activates an Nrf2/sulfiredoxin antioxidant pathway in macrophages

Peroxiredoxins (Prxs) are a family of peroxidases that maintain thiol homeostasis by catalyzing the reduction of organic hydroperoxides, H₂O₂, and peroxynitrite. Under conditions of oxidative stress, eukaryotic Prxs can be inactivated by the substrate-dependent oxidation of the catalytic cysteine to sulfinic acid, which may regulate the intracellular messenger function of H₂O₂. A small redox protein, sulfiredoxin (Srx), conserved only in eukaryotes, has been shown to reduce sulfinylated 2-Cys Prxs, adding to the complexity of the H₂O₂ signaling network. In this study, we addressed the regulation of Srx expression in immunostimulated primary macrophages that produce both reactive oxygen species (ROS) and nitric oxide (NO(•)). We present genetic evidence that NO-mediated Srx up-regulation is mediated by the transcription factor nuclear factor erythroid 2-related factor (Nrf2). We also show that the NO(•)/Srx pathway inhibits generation of ROS. These results reveal a link between innate immunity and H₂O₂ signaling. We propose that an NO(•)/Nrf2/Srx pathway participates in the maintenance of redox homeostasis in cytokine-activated macrophages and other inflammatory settings.

B-ring-modified isocombretastatin A-4 analogues endowed with interesting anticancer activities.

A novel class of isocombretastatin A‐4 (isoCA‐4) analogues with modifications at the 3′‐position of the B‐ring by replacement with C‐linked substituents was studied. Exploration of the structure–activity relationships of theses analogues led to the identification of several compounds that exhibit excellent antiproliferative activities in the nanomolar concentration range against H1299, MDA‐MB231, HCT116, and K562 cancer cell lines; they also inhibit tubulin polymerization with potency similar to that of isoCA‐4. 1,1‐Diarylethylenes 8 and 17, respectively with (E)‐propen‐3‐ol and propyn‐3‐ol substituents at the 3′‐position of the B‐ring, proved to be the most active in this series. Both compounds led to the arrest of various cancer cell lines at the G2/M phase of the cell cycle and strongly induced apoptosis. Docking of compounds 8 and 17 in the colchicine binding site indicated that their C3′ substituents guide the positioning of the B‐ring in a manner different from that observed for isoCA‐4.

Tandem One-Pot Palladium-Catalyzed Coupling of Hydrazones, Haloindoles, and Amines: Synthesis of Amino-N-vinylindoles and Their Effect on Human Colon Carcinoma Cells

The synthesis of amino-substituted N-vinylazoles was achieved by a new palladium-assisted tandem catalytic reaction involving N-tosylhydrazones, halo-substituted azoles, and amines. Accordingly, two Csp(2)-N bonds were formed through two mechanistically distinct reactions using a single Pd(II)/Pd(0) catalyst system in a one-pot fashion. This work paves the way for the design of biological relevant compounds in an amino-substituted N-vinylindole series. Among several polyoxygenated derivatives evaluated, compounds 5e and 5u were found to exhibit good antiproliferative activity.

Palladium-Catalyzed One-Pot Reaction of Hydrazones, Dihaloarenes, and Organoboron Reagents: Synthesis and Cytotoxic Activity of 1,1-Diarylethylene Derivatives

A new three-component assembly reaction between N-tosylhydrazones, dihalogenated arenes, and boronic acids or boronate esters was developed, producing highly substituted 1,1-diarylethylenes in good yields. The two C-C bonds formed through this coupling have been catalyzed by a single Pd-catalyst in a one-pot fashion. It is noted that the one-pot pinacol boronate cross-coupling reaction generally provides products in high yields, offers an expansive substrate scope, and can address a broad range of aryl, styrene, vinyl, and heterocyclic olefinic targets. The scope of this one-pot coupling has been also extended to the synthesis of the 1,1-diarylethylene skeleton of the natural product ratanhine. The new compounds were evaluated for their cytotoxic activity, and this allowed the identification of compound 4ab that exhibits excellent antiproliferative activity in the nanomolar concentration range against HCT116 cancer cell lines.

Regioselective hydrostannation of diarylalkynes directed by a labile ortho bromine atom: An easy access to stereodefined triarylolefins, hybrids of combretastatin A-4 and isocombretastatin A-4

A series of triarylolefins bearing the combretastatin A-4 and the isocombretastatin A-4 cores were synthesized and evaluated. The cooperative ortho-effect of a labile bromine atom in the regioselective hydrostannation of unsymmetrical diarylalkynes leading to stereodefined triarylolefins is presented.

Overexpression of the natural tetrapeptide acetyl‐N‐ser‐asp‐lys‐pro derived from thymosin β4 in neoplastic diseases

The natural tetrapeptide acetyl‐ser‐asp‐lys‐pro (AcSDKP) is formed in vivo by enzymatic cleavage of the N terminus of thymosin β4 by prolyl oligopeptidase (POP). Recently, AcSDKP was shown to promote angiogenesis. Because of the critical role of neovascularization in cancer development, the levels of AcSDKP and POP activity in a number of different malignant tissues were investigated. Our studies revealed that AcSDKP levels were markedly elevated in neoplastic diseases including hematologic malignancies and solid neoplasms. Consistent with this finding, the enhanced activity of POP was also detected in all analyzed specimens of cancer tissues. Both these novel findings are in concert with the previously reported overexpression of thymosin β4 in a large variety of malignant tumors and with its potential role in cancerogenesis. The physiological relevance of these findings awaits further studies; however, our first results strongly suggest a key role for AcSDKP in the pathogenesis of cancer.