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BACKGROUND: Animal, epidemiological and clinical studies have demonstrated the anti-tumor activity of pharmacological proteasome inhibitors and the cancer-preventive effects of green tea consumption. Previously, one of our laboratories reported that natural ester bond-containing green tea polyphenols (GTPs), such as (-)-epigallocatechin-3-gallate [(-)-EGCG] and (-)-gallocatechin-3-gallate [(-)-GCG], are potent and specific proteasome inhibitors. Another of our groups, for the first time, was able to enantioselectively synthesize (-)-EGCG as well as other analogs of this natural GTP. Our interest in designing and developing novel synthetic GTPs as proteasome inhibitors and potential cancer-preventive agents prompted our current study. MATERIALS AND METHODS: GTP analogs, (+)-EGCG, (+)-GCG, and a fully benzyl-protected (+)-EGCG [Bn-(+)-EGCG], were prepared by enantioselective synthesis. Inhibition of the proteasome or calpain (as a control) activities under cell-free conditions were measured by fluorogenic substrate assay. Inhibition of intact tumor cell proteasome activity was measured by accumulation of some proteasome target proteins (p27, I kappa B-alpha and Bax) using Western blot analysis. Inhibition of tumor cell proliferation and induction of apoptosis by synthetic GTPs were determined by G(1) arrest and caspase activation, respectively. Finally, inhibition of the transforming activity of human prostate cancer cells by synthetic GTPs was measured by a colony formation assay. RESULTS: (+)-EGCG and (+)-GCG potently and specifically inhibit the chymotrypsin-like activity of purified 20S proteasome and the 26S proteasome in tumor cell lysates, while Bn-(+)-EGCG does not. Treatment of leukemic Jurkat T or prostate cancer LNCaP cells with either (+)-EGCG or (+)-GCG accumulated p27 and IkappaB-alpha proteins, associated with an increased G(1) population. (+)-EGCG treatment also accumulated the pro-apoptotic Bax protein and induced apoptosis in LNCaP cells expressing high basal levels of Bax, but not prostate cancer DU-145 cells with low Bax expression. Finally, synthetic GTPs significantly inhibited colony formation by LNCaP cancer cells. CONCLUSIONS: Enantiomeric analogs of natural GTPs, (+)-EGCG and (+)-GCG, are able to potently and specifically inhibit the proteasome both, in vitro and in vivo, while protection of the hydroxyl groups on (+)-EGCG renders the compound completely inactive.

Our ongoing efforts to validate kinases for cancer therapy led to the novel finding that ectopic expression of JAK2 and Aurora A together is more effective than each alone at inducing normal cells to grow in an anchorage-independent manner and to invade. In addition, siRNA silencing or pharmacological inhibition of JAK2 and Aurora A with Ruxolitinib and Alisertib, respectively, is more effective than blocking each kinase alone at suppressing anchorage-dependent and -independent growth and invasion as well as at inducing apoptosis. This led us to develop dual Aurora and JAK inhibitors, AJI-214 and AJI-100, which potently inhibit the activities of Aurora A, Aurora B and JAK2 in vitro. In human cancer cells, these dual inhibitors block the auto-phosphorylation of Aurora A (Thr-288) and the phosphorylation of the Aurora B substrate histone H3 (Ser-10) and the JAK2 substrate STAT3 (Tyr-705). Furthermore, AJI-214 and AJI-100 inhibit anchorage dependent and independent cell growth and invasion and induce G2/M cell cycle accumulation and apoptosis. Finally, the more soluble AJI-100 was effective at inducing tumor regression of human xenografts in mice. Taken together, our genetic and pharmacological studies indicate that targeting Aurora A and JAK2 together is a more effective approach than each alone at inhibiting malignant transformation and warrant further advanced pre clinical investigations of dual Aurora A/JAK2 inhibitors as potential anti tumor agents. Citation Format: Said M. Sebti, Hua Yang, Harshani Lawrence, Aslamuzzaman Kazi, Harsukh Gervaria, Ronil Patel, Yunting Luo, Uwe Rix, Ernst Schonbrunn, Nicholas Lawrence. Combined blockade of Aurora A and JAK2 kinase is highly effective at inhibiting malignant transformation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1750. doi:10.1158/1538-7445.AM2014-1750

Numerous cell cycle, apoptosis and angiogenesis-regulatory proteins undergo ubiquitin proteasome-dependent proteolysis. A proteasome inhibitor Velcade was approved for the treatment of multiple myeloma. However, Velcade is a covalent and slowly reversible inhibitor and is associated with undesired side effects. Non-covalent inhibitors with potentially less toxicity are desirable. In this abstract we report on a family of non-covalent inhibitors that resulted from our HTS screen of a 50,000 compound library against the chymotrypsin-like (CT-L) activity of purified 20S proteasome. Our initial hit PI-1833 (IC50 value = 0.5 uM) was used as a starting point for structure activity relationship studies that led to highly potent (IC50 value = 20 nM) and cell permeable derivatives. In addition to inhibiting CT-L in human breast cancer cells, these derivatives also induced the accumulation of two proteasome target proteins Bax and p27KIP, indicating their ability to inhibit proteasome activity in intact cells. Furthermore, these proteasome inhibitors also induced apoptosis and inhibited tumor cell growth. Further mechanistic studies as well as in vivo anti-tumor efficacy studies are ongoing. 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 2778. doi:1538-7445.AM2012-2778

The development of proteosome inhibitors for CT-L activity has been the subject of considerable interest in the treatment of cancer due to its critical role in maintaining homeostasis and hence its key position in many cellular processes. Proteosome inhibitors are classified as reversible or irreversible inhibitors according to their chemical structure and their mechanism of inhibition. Irreversible inhibitors possess a chemically reactive group, such as aldehydes, boronic acids, epoxy ketones that react with catalytic Thr1-O covalently, where as reversible inhibitors inhibit proteosome non-covalently via H-bond interactions (electrostatic and/or van der Waals). Bortezomib, a peptide boronic acid analog, is the first clinically approved proteosome inhibitor and is found to be an irreversible or slow reversible inhibitor that forms covalent bond with the N-terminal nucleophilic Thr1 in the β5 subunit of the proteasome. Reversible proteosome inhibitors (peptidic molecules) reported to date inhibit the proteosome non-covalently. Similar to Bortezomib, MLN9708 is a modified dipeptidyl boronic acid, which hydroylses immediately in plasma to MLN2238, is a potent, reversible and specific inhibitor of the chymotrypsin-like subunit of the proteasome. Small molecules as reversible proteosome inhibitors are less extensively investigated. In this study, we present the discovery of PI-184, non-peptidic small molecule with a pyridine and oxadiazole pharmacore as a reversible, potent and a novel proteasome inhibitor. Structure Activity relationship (SAR) guided synthesis of analogs around PI-184 led to the discovery of highly potent compounds with in-vivo chymotrypsin-like inhibitory activity. Here we present the detailed SAR, in-vitro and in-vivo proteasome activity of PI-184 class of compounds as potential anti-cancer agents. 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 3894. doi:1538-7445.AM2012-3894

Many low molecular weight GTPases such as Ras, Ral and Rho require posttranslational farnestylation or geranylgeranylation for mediating malignant transformation. This prompted the development of farnesyltransferase (FT) inhibitors (FTI) and geranylgeranyltransferase-I (GGT-1) inhibitors (GGTI) as potential anticancer agents. However, when cancer cells are treated with FTIs, K-Ras becomes geranylgeranylated suggesting that inhibition of both FT and GGT-1 may be required to inhibit tumors harboring K-Ras mutations. Recently our group has developed a series of dual FT and GGT-1 inhibitors based on an ethylenediamine scaffold. Among these dual inhibitors FGTI-2734 was most potent in vitro (FT IC50 = 250±190 nM and GGT-1 IC50 = 520±90 nM). In human cancer cells FGTI-2734 inhibits potently HDJ-2 farnesylation, Rap 1A geranylgeranylation and K-Ras prenylation. Furthermore, FGTI-2734 inhibits the phosphorylation of Erk1/2, Akt and S6K, induces p27 accumulation and inhibits potently tumor cell growth. Finally, FGTI-2734 significantly reduces survivin protein levels, and reduction of survivin levels is associated with induction of apoptosis. Thus, this single molecule with dual FT and GGT-1 inhibitory activities may have distinct advantage over selective FTIs and GGTIs and warrants further advanced pre-clinical studies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 620. doi:10.1158/1538-7445.AM2011-620

The ubiquitin-proteasome pathway plays a critical role in the regulated degradation of proteins involved in cell cycle control and tumor growth. Proteasome inhibitors cause selective apoptosis of malignant cells and represent a new class of antineoplastic agents. In 2003 Bortezomib (peptide boronate), a proteasome inhibitor was approved by FDA for treatment of multiple myeloma. Toxicity and tumor cell resistance against Bortezomib demand development of less toxic proteasome inhibitors with broader spectrum of tumor activity. Our aim is to develop non-peptidic small drug-like molecules as proteasome inhibitors. To this end, we have identified through in-house screening efforts HLM-030376 as a small molecule proteasome inhibitor with phenanthridine pharmacophore. HLM-030376 showed in-vitro chymotrypsin like, trypsin like and PGPH inhibitory activities with IC50 values 0.26, 0.19 and 2.07 µM respectively. Extensive synthetic modifications around the HLM-030376 pharmacophore were undertaken to aid the cell activity of this class of compounds. We will describe the synthesis and activity of analogs of HLM-030376 as potent proteasome inhibitors. The analogs of HLM-030376 showed in-vivo CT-L inhibitory activities (IC50 between 0.6-6.0 µM) against MDA-MB 468 breast cancer cell line as well as improved (IC50 between 70-200 nM) in-vitro CT-L inhibitory activities. The detailed in-vitro structure activity relationship (SAR) data of HLM-030376 and analogs will be discussed to understand the structural moieties responsible for proteasome activity. The whole cell activity data of HLM-030376 as well as in-silico docking studies will be presented as potential proteasome inhibitors for further development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1362. doi:10.1158/1538-7445.AM2011-1362