Yoko Nagumo

Syntheses and biological evaluation of irciniastatin A and the C1-C2 alkyne analogue.

Syntheses of both natural (+)- and unnatural (-)-irciniastatin A (aka psymberin) as well as a C1-C2 alkyne analogue of (+)-irciniastatin A have been achieved. The key features of the syntheses include a highly regioselective epoxide-opening reaction and a late-stage assembly of C1-C6, C8-C16, and C17-C25 fragments. (+)-Alkymberin retained a high level of cytotoxicity, whereas (-)-irciniastatin A showed almost no activity. These results suggest that (+)-alkymberin could be a useful enantio-differential probe for mode-of-action study.

Trastuzumab and Pertuzumab Produce Changes in Morphology and Estrogen Receptor Signaling in Ovarian Cancer Xenografts Revealing New Treatment Strategies

Purpose: The aim of this study was to investigate the antitumor effects of HER2-directed combination therapy in ovarian cancer xenograft models to evaluate their potential. The combinations of trastuzumab and pertuzumab, and trastuzumab and aromatase inhibitor therapy were investigated. Experimental Design: The effects of trastuzumab, pertuzumab, and letrozole on growth response, apoptosis, morphology, and gene and protein expression were evaluated in the SKOV3 ovarian cancer cell line xenograft and a panel of five human ovarian xenografts derived directly from clinical specimens. Results: The combination of HER2-directed antibodies showed enhanced antitumor activity compared with single antibody therapy in the SKOV3 xenograft model. Apoptosis, morphology, and estrogen-regulated gene expression were modulated by these antibodies in both spatial and temporal manners. A panel of ovarian cancer xenografts showed differential growth responses to the combination of trastuzumab and pertuzumab. High HER2 expression and increasing HER3 protein expression on treatment were associated with growth response. In trastuzumab-treated SKOV3 tumors, there was a change in tumor morphology, with a reduction in frequency of estrogen receptor alpha (ERα)-negative clear cell areas. Trastuzumab, but not pertuzumab, increased expression of ERα in SKOV3 xenografts when analyzed by quantitative immunofluorescence. ERα and downstream signaling targets were modulated by trastuzumab alone and in combination. Trastuzumab enhanced the responsiveness of SKOV3 xenografts to letrozole when given in combination. Conclusions: These data suggest that trastuzumab in combination with pertuzumab could be an effective approach in high HER2-expressing ovarian cancers and could also enhance sensitivity to endocrine therapy in ERα-positive ovarian cancer. Clin Cancer Res; 17(13); 4451–61. ©2011 AACR.

Convergent synthesis of the HIJKLM ring fragment of ciguatoxin CTX3C

Abstract Ciguatoxin CTX3C is a representative congener of the ciguatoxins, which are known to be the principal causative agents of ciguatera food poisoning. The structure of CTX3C spans more than 3xa0nm and is characterized by 13 ether rings. To attain a practical construction of this molecule, efficient supplies of the structural fragments are crucial. Herein we report the convergent synthesis of the HIJKLM ring fragment and present a new carbonyl olefination protocol to cyclize the J ring using low-valent titanium.

Modulation of HER3 Is a Marker of Dynamic Cell Signaling in Ovarian Cancer: Implications for Pertuzumab Sensitivity

This study was designed to evaluate the expression of HER receptors as a marker of sensitivity to the humanized anti-HER2 monoclonal antibody pertuzumab in ovarian cancer cells. In a recent clinical trial, low levels of HER3 mRNA have been shown to associate with pertuzumab response when combined with gemcitabine. We sought to define how pertuzumab modulated HER expression levels in ovarian cancer using cell line models to better understand differential and dynamic receptor expression in therapeutic response. Changes in HER3 mRNA expression were also assessed in pertuzumab-treated xenografts. HER3 mRNA and, to a lesser extent, HER2, were down-regulated after stimulation both with heregulin-β1 and epidermal growth factor in a range of ovarian cancer cell lines either growth sensitive or growth resistant to pertuzumab. Pertuzumab reversed this down-regulation and the magnitude of the reversal correlated with pertuzumab sensitivity. The change in HER3 mRNA expression correlated inversely to how much the extracellular signal-regulated kinase and phosphoinositide 3-kinase pathways were dynamically activated with stimulation. Finally, up-regulation of HER3 mRNA was found in cancer xenografts treated with pertuzumab. We conclude that HER3 mRNA is down-regulated by both heregulin-β1 and epidermal growth factor activation. This suggests that in some tumors, low HER3 mRNA expression is driven by, or dependent on, growth factor. HER3 mRNA expression is effectively reversed in pertuzumab-sensitive tumors. These data are consistent with low HER3 mRNA identifying a pertuzumab-sensitive phenotype. (Mol Cancer Res 2009;7(9):1563–71)

Concise synthesis of ciguatoxin ABC-ring fragments and surface plasmon resonance study of the interaction of their BSA conjugates with monoclonal antibodies.

Monoclonal antibodies (mAbs), 4H2 and 6H7, were prepared previously using a protein conjugate of a 1:1 epimeric mixture of the synthetic ABC-ring fragments of ciguatoxin (CTX), 3 and 4. Here, the interactions of these mAbs with the fragments of CTX and CTX3C, 3 and 5, were investigated by surface plasmon resonance (SPR) spectroscopy in an attempt to clarify an antigenic determinant. Compared with the previous synthesis, the fragment 3 possessing the 2S configuration was synthesized from tri-O-acetyl-D-glucal much more effectively. The mAb 4H2 was already known to show a dose-dependent binding to the bovine serum albumin (BSA) conjugate of 3, but not to that of 5. The present SPR study of 4H2 demonstrates that the A-ring side chain of 3 plays a decisive role as an epitope. Therefore, SPR can effectively replace the ELISA method for the analysis of mAbs.

Defining the molecular response to trastuzumab, pertuzumab and combination therapy in ovarian cancer

Background:Trastuzumab and pertuzumab target the Human Epidermal growth factor Receptor 2 (HER2). Combination therapy has been shown to provide enhanced antitumour activity; however, the downstream signalling to explain how these drugs mediate their response is not clearly understood.Methods:Transcriptome profiling was performed after 4 days of trastuzumab, pertuzumab and combination treatment in human ovarian cancer in vivo. Signalling pathways identified were validated and investigated in primary ovarian xenografts at the protein level and across a timeseries.Results:A greater number and variety of genes were differentially expressed by the combination of antibody therapies compared with either treatment alone. Protein levels of cyclin-dependent kinase inhibitors p21 and p27 were increased in response to both agents and further by the combination; pERK signalling was inhibited by all treatments; but only pertuzumab inhibited pAkt signalling. The expression of proliferation, apoptosis, cell division and cell-cycle markers was distinct in a panel of primary ovarian cancer xenografts, suggesting the heterogeneity of response in ovarian cancer and a need to establish predictive biomarkers.Conclusion:This first comprehensive study of the molecular response to trastuzumab, pertuzumab and combined therapy in vivo highlights both common and distinct downstream effects to agents used alone or in combination, suggesting that complementary pathways may be involved.

Pertuzumab for the treatment of ovarian cancer

Importance of the field: Pertuzumab is a humanized monoclonal antibody that inhibits human epidermal growth factor receptor 2 (HER2) heterodimerization and has demonstrated clinical activity against both breast and ovarian cancer. To date, it is the most extensively studied HER2 inhibitor in ovarian cancer. Areas covered in this review: We focus on the published descriptions of preclinical and clinical activity in ovarian cancer and biomarkers associated with response. We compare the activity of pertuzumab with that of other clinically evaluated HER2 inhibitors. What the reader will gain: To date, pertuzumab is the most extensively trialled HER2 inhibitor in ovarian cancer, with almost 400 patients having been treated in three large Phase II studies. Recent clinical trials data indicate that pertuzumab enhances gemcitabines activity in platinum-resistant ovarian cancer and may enhance carboplatins activity in platinum-sensitive disease; moreover the subgroup who benefit from pertuzumab appear to be those with cancers with activated HER2 or low HER3 mRNA expression. This review examines the recent clinical trials results and associated preclinical studies that support the utility of pertuzumab in this disease. Take home message: Pertuzumab may have value for the treatment of ovarian cancer. Further prospective biomarker-led trials are warranted.

Irciniastatin A induces JNK activation that is involved in caspase-8-dependent apoptosis via the mitochondrial pathway.

Irciniastatin A (ISA)/psymberin, a pederin-type natural product isolated from marine sponge, exhibits extremely potent and selective cytotoxicity against certain human cancer cell lines, but its molecular target and cytotoxic mechanisms are still unknown. Here we show that ISA is a potent inhibitor of protein translation, and induces apoptosis accompanied with activation of the stress-activated protein kinases via the mitochondrial pathway in human leukemia Jurkat cells. ISA potently inhibited protein translation, and induced a slow but prolonged activation of the stress-activated protein kinases, JNK and p38, at between 1h and 6h after treatment. In Bcl-x(L)-transfected cells, the activation of JNK and p38 by ISA was shortened. The same results were obtained in the cells treated with N-acetyl-L-cysteine, suggesting that the prolonged activation of JNK and p38 by ISA is mediated by reactive oxygen species generated from mitochondria. ISA strongly induced apoptosis, which was partially suppressed by the JNK inhibitor SP600125, but not by the p38 inhibitor SB202190. Apoptosis induction by ISA was partially reduced, but not suppressed by SP600125 in caspase-8-deficient Jurkat cells. These results suggest that ISA activates stress-activated kinases by a mitochondria-mediated mechanism, and that activation of JNK is required for caspase-8-dependent apoptosis.

Critical Contribution of Aromatic Rings to Specific Recognition of Polyether Rings THE CASE OF CIGUATOXIN CTX3C-ABC AND ITS SPECIFIC ANTIBODY 1C49

To address how proteins recognize polyether toxin compounds, we focused on the interaction between the ABC ring compound of ciguatoxin 3C and its specific antibody, 1C49. Surface plasmon resonance analyses indicated that Escherichia coli-expressed variable domain fragments (Fv) of 1C49 had the high affinity constants and slow dissociation constants typical of antigen-antibody interactions. Linear vant Hoff analyses suggested that the interaction is enthalpy-driven. We resolved the crystal structure of 1C49 Fv bound to ABC ring compound of ciguatoxin 3C at a resolution of 1.7Å. The binding pocket of the antibody had many aromatic rings and bound the antigen by shape complementarity typical of hapten-antibody interactions. Three hydrogen bonds and many van der Waals interactions were present. We mutated several residues of the antibody to Ala, and we used surface plasmon resonance to analyze the interactions between the mutated antibodies and the antigen. This analysis identified Tyr-91 and Trp-96 in the light chain as hot spots for the interaction, and other residues made incremental contributions by conferring enthalpic advantages and reducing the dissociation rate constant. Systematic mutation of Tyr-91 indicated that CH-π and π-π interactions between the aromatic ring at this site and the antigen made substantial contributions to the association, and van der Waals interactions inhibited dissociation, suggesting that aromaticity and bulkiness are critical for the specific recognition of polyether compounds by proteins.

Construction of Multidrug-Sensitive Yeast with High Sporulation Efficiency

Budding yeast is often used in chemical genetics for screening, target identification, and compound verification, but its high-level drug resistance has made the analysis of compounds difficult. Here we report the construction of 12geneΔ0HSR, a strain that lacks eight efflux pumps located on the plasma membrane and four transcription factors involved in expression of efflux pumps, and contains the RME1(ins-308A) mutation. This strain retained sufficient transformation, mating, and sporulation efficiency for genetic analysis in addition to hypersensitivity against several compounds. 12geneΔ0HSR is a useful tool for chemical biology, not only in chemical screening but in target identification and verification of bioactive compounds.