Antoinette Nibbs

Catalytic asymmetric alkylation of substituted isoflavanones.

The asymmetric alkylation of isoflavanones (3-aryl-chroman-4-ones) and protected 3-phenyl-2,3-dihydroquinolin-4(1H)-ones catalyzed by a novel cinchonidine-derived phase transfer catalyst E is reported. This functionalization occurs at the unactivated C3 methine to afford novel products that can easily be functionalized to generate more complex fused ring systems. The process accommodates a variety of isoflavanones and activated electrophiles and installs a stereogenic quaternary center in high yield and with good-to-excellent selectivity. Isoflavanones are a privileged class of natural products with a broad spectrum of biological activities including insecticidal, antimicrobial, antibacterial, estrogenic, antitumor, and anti-HIV activity. (1) Isoflavanones are also precursors for more complex natural products such as pterocarpans and rotenones. (1) Given their therapeutic promise, selective strategies to access new classes of isoflavanones and related structures has high value. (2) The functionalization of the C3 position could promote beneficial interactions with biological targets of interest. Specifically, an alkylation at C3 can rapidly access new members of the general class of biologically active homoisoflavanones. (3).

A Biomimetic Strategy to Access the Silybins: Total Synthesis of (−)-Isosilybin A

We report the first asymmetric, total synthesis of (−)-isosilybin A. A late-stage catalytic biomimetic cyclization of a highly functionalized chalcone is employed to form the characteristic benzopyranone ring. A robust and flexible approach to this chalcone provides an entry to the preparation of the entire isomeric family of silybin natural products.

Abstract 4752: Selective inhibition of cancer metastasis with a novel small therapeutic molecule

Prostate cancer (PCa) is the second most common cause of cancer death in US males. Death is typically caused by metastasis. Naturally occurring isoflavanones have been reported to be a class of compounds that effectively inhibit PCa motility and metastasis. This led us to use these compounds as a synthetic scaffold starting point. By integrating fragment-based diversification synthesis with chemi-driven biological selection, we discovered novel small molecule therapeutics with increased selectivity and potent efficacy. We thereby efficiently synthesized a new class of bioactive compounds that inhibit cell motility in vitro and inhibit human PCa metastasis in a murine model at low nanomolar concentrations. Extensive investigations indicate high specificity at the molecular and cellular levels, and failed to identify toxicity, even at high doses administered over extended periods. Importantly, efficacy against several cancer types was also demonstrated. Target validation studies used our lead as a chemical probe, and point to inhibition of ATM/ATR interaction with specific substrate proteins as important. Together, these studies indicate that we have successfully discovered a novel compound, acting upon a novel pharmacologic target, which selectively inhibits human PCa metastasis. Taken with our favorable preclinical toxicological data, these findings support movement of our lead compound into early phase human trials. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4752. doi:1538-7445.AM2012-4752

Abstract 4751: Structure and inhibition of mitogen-activated protein kinase kinase 4 (MEK4): A prostate cancer pro-invasion protein

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Introduction: Metastasis of Prostate Cancer (PCa) represents the second highest cause of death due to cancer among men in the United States. If this unregulated movement of cells can be inhibited, mortality arising from PCa will be greatly reduced. Our group has shown that Mitogen-activated protein kinase kinase 4 (MAP2K4/MEK4), a 399 amino acid protein, activates pro-invasion signaling pathways in human PCa. Further, we have shown that 4,5,7-trihydroxyisoavone (genistein) inhibits MEK4 kinase activity, cell invasion and metastasis of human PCa cells in a murine model. While therapeutically effective, genistein represents a non-chemically optimized natural product with additional undesired effects such as estrogenic receptor stimulation. Recognizing that MEK4 represents a novel and important therapeutic target, we have sought to characterize its structure, biochemical function and have synthesized genistein analogs designed to target it. Summary of Results: Using X-ray crystallography we have obtained a 3.38A resolution structure of the MEK4 catalytic domain. We are in the process of improving our resolution, and of deriving 3D structures with inhibitors bound to MEK4. We have evaluated biophysical interactions between MEK4 and ligands (i.e., genistein and its analogs). Ligand binding to a protein tends to increase its stability, thereby increasing the temperature of denaturation, or melting. Using a fluorescence thermal shift (FTS) assay, we demonstrated that genistein and 6 of 39 novel analogs thermally stabilized MEK4 in a concentration dependent manner, consistent with MEK4 binding. We identified a similar pattern in 5 compounds from a commercial library, one of which was staurosporine - a broad spectrum protein kinase inhibitor. We developed and characterized a novel in vitro MEK4 kinase assay, using kinase dead p38MAPK (K53A) as substrate. In human PCa cells, MEK4 activates the p38 MAPK pro-invasion pathway. To date, we have used this assay system to demonstrate that staurosporine inhibits MEK4 with nanomolar IC50 values. Conclusions and Future Directions: MEK4 is a novel target for therapeutic intervention in PCa. Our ultimate goal is to synergistically utilize structural and biochemical information to inform the synthesis of inhibitors that specifically and selectively act upon MEK4 to inhibit human PCa metastasis in man. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4751. doi:1538-7445.AM2012-4751

Abstract C177: Chemical-driven biological probing: Discovery of a novel antimetastatic drug.

Chemicals constitute richly informative probes, have high resolving potential and are able to uncover complex biological processes. Harnessing this potential provides an avenue for the discovery of new therapeutics that act via novel mechanisms. We focused these principles upon an intractable problem: cancer metastasis. We started with a chemical scaffold with broad bioactivity, with desirable drug-like properties and that would support synthetic diversification. Initially focusing upon human prostate cancer (PCa) we then coupled fragment-diversification and novel synthetic routes to upfront positive selection screens (inhibition of cell motility) and negative selection screens (cell toxicity) in an iterative fashion. We thereby efficiently synthesized a new class of bioactive compounds that inhibits systemic PCa metastasis at low nanomolar concentrations. Efficacy against other cancer types was demonstrated. Extensive investigations indicate high specificity and no toxicity. Target validation studies point to inhibition of protein-protein interaction motifs. Together, these studies support the notion that this approach is powerful, can be broadly applied across biological systems, and constitutes a paradigm. Specifically, they have led to the discovery of a novel acting drug that inhibits human cancer metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C177.

Abstract B58: Discovery of a novel drug KBU2046 that inhibits conversion of human prostate cancer to a metastatic phenotype

Epidemiological evidence, preclinical studies and prospective phase II studies in humans indicate that the isoflavone, genistein, will inhibit the conversion of human prostate cells to an invasive, and ultimately, a metastatic phenotype. Though promising, genistein exerts many additional effects that have the potential for future toxicity in humans. We therefore sought to discover a new drug with improved efficacy and most importantly, with high specificity. Starting from an isoflavone chemical scaffold, we employed a fragment-based chemical synthesis diversification approach, and coupled it to three in vitro screens: 1) cell invasion (efficacy), 2) cell growth inhibition (an indicator of general toxicity), and 3) several measures of estrogenic activity. From multiple synthesis/biological assay iterations we developed a refined structure-activity relationship map, thereby leading us to discover KBU2046. KBU2046 represents a new and chemically distinct class of bioactive compounds. It has greater anti-invasion efficacy than genistein, and more importantly, no cell toxicity or estrogenic activity. Extensive toxicity studies in mice were negative. At low nanomolar blood concentrations, KBU2046 will prevent orthotopically implanted human prostate cancer cells from forming metastasis in a dose-responsive fashion. In summary, we have successfully discovered and developed a compound that prevents progression to a metastatic phenotype for human prostate cancer. We are in the process of bringing KBU2046 into the clinic, with the goal of preventing death from the second most common cause of cancer related death in men. Citation Information: Cancer Prev Res 2010;3(12 Suppl):B58.