Regulation of matrix metalloproteinase genes by E2F transcription factors: Rb-Raf-1 interaction as a novel target for metastatic disease

The retinoblastoma (Rb)-E2F transcriptional regulatory pathway plays a major role in cell-cycle regulation, but its role in invasion and metastasis is less well understood. We find that many genes involved in the invasion of cancer cells, such as matrix metalloproteinases (MMP), have potential E2F-binding sites in their promoters. E2F-binding sites were predicted on all 23 human MMP gene promoters, many of which harbored multiple E2F-binding sites. Studies presented here show that MMP genes such as MMP9, MMP14, and MMP15 which are overexpressed in non-small cell lung cancer, have multiple E2F-binding sites and are regulated by the Rb-E2F pathway. Chromatin immunoprecipitation assays showed the association of E2F1 with the MMP9, MMP14, and MMP15 promoters, and transient transfection experiments showed that these promoters are E2F responsive. Correspondingly, depletion of E2F family members by RNA interference techniques reduced the expression of these genes with a corresponding reduction in collagen degradation activity. Furthermore, activating Rb by inhibiting the interaction of Raf-1 with Rb by using the Rb-Raf-1 disruptor RRD-251 was sufficient to inhibit MMP transcription. This led to reduced invasion and migration of cancer cells in vitro and metastatic foci development in a tail vein lung metastasis model in mice. These results suggest that E2F transcription factors may play a role in promoting metastasis through regulation of MMP genes and that targeting the Rb-Raf-1 interaction is a promising approach for the treatment of metastatic disease.

Abstract A130: Fragment-based discovery and optimization of Rho kinase inhibitors

Using high concentration biochemical assays and fragment-based screening, we designed and optimized a novel class of Rho-kinase inhibitors. Ligand Efficiency (LE) was employed to assess the binding potential of the fragments and to guide the optimization process. In addition, molecular modeling was used to aide the design of potent inhibitors. A series of fragments as hinge binders were designed and synthesized, and screened using high concentration biochemical assays. Both the spacer length and isomeric tail molecules played key roles in both activity and selectivity. Structure activity relationship studies led to optimization of fragments that yielded potent and selective ROCK 1 and ROCK 2 inhibitors. For instance, compound 24 was highly potent and selective for ROCK 2 (IC50 = 100 nM) over ROCK 1 (IC50 = 1690 nM) whereas compound 18 was potent and selective for ROCK 1 (IC50 = 460 nM) over ROCK 2 (IC50 = 700nM). Compound 24 but not its inactive stereoisomer 23, and compound 18 but not its inactive analog 11 inhibited the phosphorylation of Rho Kinase substrates in intact human cancer cells.

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 A130.

Abstract 3239: Shp2 inhibitor activity of estramustine phosphate and its triterpenoid analogues

Shp2 is a non-receptor protein tyrosine phosphatase (PTP) encoded by the PTPN11 gene. Shp2 mediates proliferative signaling induced by growth factors. Gain-of-function PTPN11 mutations that encode constitutively active Shp2 are leukemic oncogenes. In a continuing effort to identify new Shp2 PTP inhibitors, we screened a small molecule library comprising the National Cancer Institute (NCI) Approved Oncology Drug set and the NIH Clinical Collection. After evaluation of initial hits, estramustine phosphate was verified as a Shp2 PTP inhibitor. A focused structure-activity relationship study indicated that the 17-phosphate group is required for the Shp2 PTP inhibitor activity of estramustine phosphate. A search for estramustine phosphate analogs led to identification of two triperpenoids, enoxolone and celastrol, having Shp2 PTP inhibitor activity. With the previously reported PTP1B inhibitor trodusquemine, our study reveals steroids and triterpenoids with negatively charged phosphate, carboxylate, or sulfonate groups as novel pharmacophores of selective PTP inhibitors. These findings point to a rich natural source for discovery of lead compounds of novel PTP inhibitors.

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 3239. doi:10.1158/1538-7445.AM2011-3239

Abstract 3248: New inhibitors of the Shp2 phosphatase

The Shp2 protein tyrosine phosphatase (PTP) mediates signal transduction of growth factor receptors and regulates cellular activities critical to tumor growth and metastasis. In the basal state, the interactions between the N-SH2 and PTP domains keep the phosphatase in an auto inhibited closed conformation. Upon growth factor or cytokine stimulation, the SH2 domains of Shp2 binds to tyrosine phosphorylated docking proteins such as Gab1 and Gab2, which activates Src, Ras, and the Erk1/2 (Erk) mitogen-activated protein (MAP) kinase pathway. Shp2 gain-of-function mutations are found in leukemias and solid tumors and are linked to Noonan syndrome. Although Shp2 is involved in pathogenesis of human cancers, it is not clear how Shp2 mediates tumorigenesis. Shp2 is therefore believed to be an important enzyme for targeted cancer therapy. Since no potent and selective Shp2 PTP inhibitor is currently available for chemical biology studies and experimental therapy, we and others have been actively engaged in the search for such agents. In our continuing efforts to develop potent and selective Shp2 inhibitors to serve as both chemical probes to further our understanding of the role and signaling mechanisms of Shp2 in human diseases and as potential drugs for cancer therapy.

We will report the screening of a focused library of a set of commercially available salicylic acid derivatives using the in vitro DIFMUP phosphatase assay for their ability to inhibit the Shp2 phosphatase domain. Activity of hits was confirmed using the Biomol Green assay to determine inhibition of dephosphorylation of a Shp2 peptide substrate derived from EphR. One such hit was a thiazole containing salicylic acid that inhibits Shp2 with an IC50 (DIFMUP) of 100 µM. We will report the design and synthesis of salicylic acid libraries along with their benzoic acid counterparts. The most potent compound to date is HM2-08-4 which has an IC50 (DIFMUP) 1.1 µM. Emerging structure-activity relationships as well as modeling and X-ray studies will be discussed. The preliminary use of selected compounds as tools to probe the pharmacological inhibition of Shp2 and elucidate its role in cancer will be described.

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 3248. doi:10.1158/1538-7445.AM2011-3248

Abstract 3253: Novel oxindole inhibitors of Aurora A kinase: Structure based hit-to-lead approach

The M-phase of cell division is controlled by phosphorylation events performed by several mitotic serine/threonine kinases. For example, the three human isoforms of Aurora kinase (A, B, and C) have been amply investigated as they are essential for the execution of numerous mitotic events and required for genome integrity and stability. Studies have shown that Aurora A and B are frequently over-expressed in various cancer cells. Aurora A also acts as an oncogene inducing malignant transformation when over-expressed. Since the discovery of the Aurora kinases and their association with cancer, there has been great interest in developing small molecule inhibitors of Aurora kinases as potential anticancer drugs.In-house screening campaign directed toward the discovery of novel Aurora A inhibitors, led to the identification of a new and potent class of oxindole derivatives as inhibitors of Aurora-A kinase. The initial hit HL1-058-1 was identified as an inhibitor of histone H3-Ser10 phosphorylation (IC50 1-5 μM).

By using a Z’-lyte kinase assay kit, the inhibitory effect of HL1-058-1 was shown to be the direct consequence of the Aurora kinase inhibition (IC50 of 2.7 ± 0.3 µM). Based on the preliminary data, HL1-058-1 was selected for further study. Synthesis of a focused library of analogs based on this hit revealed RPM305 and RPM304 as potent inhibitors of Aurora A (IC50 0.020 ± 0.005 μM, and 0.038 ± 0.018 μM, respectively). Interestingly, compound RPM304 showed 26 fold selectivity over Aurora B (IC50 0.99 ± 0.08 μM).

A coupled enzyme assay was also used to carry out further structure activity relationship studies of the most potent analogs.

One of the lead compounds was co-crystallized with the kinase domain of Aurora A. The design and synthesis of further focused libraries of oxindoles, based on this X-ray structure will be described. Details of the cell activity of this class of compound to inhibit Aurora A activity and tumor cell growth will be described.

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 3253. doi:10.1158/1538-7445.AM2011-3253

Abstract 3242: New chemical tools for disrupting the MDM2/p53 protein-protein interaction: Identification, synthesis and biological evaluation of a novel class of MDM2/p53 inhibitors

MDM2 and MDMX function as key regulators of p53 by binding to its N terminus, inhibiting its transcriptional activity, and promoting its degradation. In particular, MDM2 is overexpressed in some of human tumors, and with MDMX contributes directly to loss of p53 function during the development of nearly 50% of human cancers. Due to p53 inactivation, MDM2 in many tumors confers tumor survival; therefore it is an important molecular target for anticancer therapy. Several studies showed that reactivation of wild type p53 in tumor cells can be obtained by disrupting the MDM2/p53 interaction with peptidic, peptidomimetic, and small molecule p53-mimetics. Specific successful examples include the Nutlins and spirooxindole analogs (MI-219 and MI-63). Amongst the peptidic and peptidomimetic inhibitors examined to date, none is nearly as effective as Nutlins and MI-219 in tumor killing in vitro. Hence, new inhibitors against MDM2 and/or MDMX are needed: as cell permeable chemical probes of the p53 pathway in cancer biology, and as templates for structure-based rational design of p53 activators for future therapeutic use. As part of our drug discovery program to identify antagonists of the p53/MDM2 and p53/MDMx protein-protein interactions, a high-throughput in-silico screen of a 3.2 millions virtual library of compounds (from Schrödinger, Inc.). A physical restraint was applied during the screen, in order to mimic binding to the hydrophobic cleft of MDM2 normally occupied by three p53 side chains (F19, W23, and L26) that are critical for MDM2/p53 binding. The top highest ranked 160 compounds were then assessed for their ability to block p53 interaction with MDM2 and MDMx in an ELISA assay. This resulted in the identification of E12/DP3-117, a small molecule disruptor of the p53/MDM2 protein-protein interaction with an IC50 value of 47 ± 14 μM. We will report the synthesis and biological evaluation of focused libraries based on the initial hit and on compounds showing improved activity. Structure activity relationship studies around the hits will be disclosed as well as the outcomes of further rounds of chemical design and biological assessment. Binding of E12/DP3-117 to MDM2 is currently being assessed via co-crystallization and other biophysical techniques. We will describe the use of the crystal structure of p53-like mutant peptides in complex with the N-terminal domains of Mdm2, as the basis for rational design of more potent MDM2 small-molecule/peptide hybrid inhibitors.

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 3242. doi:10.1158/1538-7445.AM2011-3242

Abstract 3243: Discovery of novel Rho kinase inhibitors: Hit generation and lead optimization

Rho associated protein kinases (ROCKs) are Ser/Thr kinases which require activation by small GTPases of the Rho family. ROCK is often found to be over expressed in ovarian, testicular, bladder, and pancreatic cancers. ROCK has been implicated in cell motility, adhesion, smooth muscle contraction and stress fiber formation. Inhibition of Rho kinase is a novel approach for the treatment of cardiovascular disease, CNS disorders, and, more recently, cancer. ROCK has received increased attention for its affect on cell adhesion and invasion, two key steps in metastasis. We detail the development of ROCK inhibitors from initial small molecule library screening and in-house HTS screening data. We report on the identification and resynthesis of one screening hit (ROCK1 IC50 38.5 ± 3.4 µM). Focused chemical libraries were developed and structure activity relationships will be described. All compounds have been screened in a Z-lyte kinase assay to determine their activity against both ROCK1 and ROCK2. Hit-to-lead optimization and SAR studies resulted in compounds capable of inhibiting ROCK1 at low nanomolar concentrations, RPM1510 (ROCK1 IC50 0.15 ± 0.02 µM) and RPM1533 (ROCK1 IC50 0.12 ± 0.02 µM). Progress in obtaining structural information by X-ray crystallography will be reported along with ROCK inhibitory data. Trends in isoform and kinase selectivity and potency will also be discussed. Members of this class have been shown to inhibit potently, in human lung cancer cells, the phosphorylation of MYPT1, a surrogate for ROCK activity in vivo.

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 3243. doi:10.1158/1538-7445.AM2011-3243

Critical role of IRF-8 in negative regulation of TLR3 expression by Src homology 2 domain-containing protein tyrosine phosphatase-2 activity in human myeloid dendritic cells

Despite extensive studies that unraveled ligands and signal transduction pathways triggered by TLRs, little is known about the regulation of TLR gene expression. TLR3 plays a crucial role in the recognition of viral pathogens and induction of immune responses by myeloid DCs. IFN regulatory factor (IRF)-8, a member of the IRF family, is a transcriptional regulator that plays essential roles in the development and function of myeloid lineage, affecting different subsets of myeloid DCs. In this study, we show that IRF-8 negatively controls TLR3 gene expression by suppressing IRF-1- and/or polyinosinic-polycytidylic acid-stimulated TLR3 expression in primary human monocyte-derived DCs (MDDCs). MDDCs expressed TLR3 increasingly during their differentiation from monocytes to DCs with a peak at day 5, when TLR3 expression was further enhanced upon stimulation with polyinosinic-polycytidylic acid and then was promptly downregulated. We found that both IRF-1 and IRF-8 bind the human TLR3 promoter during MDDC differentiation in vitro and in vivo but with different kinetic and functional effects. We demonstrate that IRF-8-induced repression of TLR3 is specifically mediated by ligand-activated Src homology 2 domain-containing protein tyrosine phosphatase association. Indeed, Src homology 2 domain-containing protein tyrosine phosphatase-dephosphorylated IRF-8 bound to the human TLR3 promoter competing with IRF-1 and quashing its activity by recruitment of histone deacetylase 3. Our findings identify IRF-8 as a key player in the control of intracellular viral dsRNA-induced responses and highlight a new mechanism for negative regulation of TLR3 expression that can be exploited to block excessive TLR activation.

Effect of Ack1 tyrosine kinase inhibitor on ligand-independent androgen receptor activity

BACKGROUND

Androgen receptor (AR) plays a critical role in the progression of both androgen-dependent and androgen-independent prostate cancer (AIPC). Ligand-independent activation of AR in AIPC or castration resistant prostate cancer (CRPC) is often associated with poor prognosis. Recently, tyrosine kinase Ack1 has been shown to regulate AR activity by phosphorylating it at tyrosine 267 and this event was shown to be critical for AIPC growth. However, whether a small molecule inhibitor that can mitigate Ack1 activation is sufficient to abrogate AR activity on AR regulated promoters in androgen-depleted environment is not known.

METHODS

We have generated two key resources, antibodies that specifically recognize pTyr267-AR and synthesized a small molecule inhibitor of Ack1, 4-amino-5,6-biaryl-furo[2,3-d]pyrimidine (named here as AIM-100) to test whether AIM-100 modulates ligand-independent AR activity and inhibits prostate cell growth.

RESULTS

Prostate tissue microarray analysis indicates that Ack1 Tyr284 phosphorylation correlates positively with disease progression and negatively with the survival of prostate cancer patients. Interestingly, neither pTyr267-AR expression nor its transcriptional activation was affected by anti-androgens in activated Ack1 expressing or EGF stimulated prostate cells. However, the Ack1 inhibitor, AIM-100, not only inhibited Ack1 activation but also able to suppress pTyr267-AR phosphorylation, binding of AR to PSA, NKX3.1, and TMPRSS2 promoters, and inhibit AR transcription activity.

CONCLUSION

Ack1 Tyr284 phosphorylation is prognostic of progression of prostate cancer and inhibitors of Ack1 activity could be novel therapeutic agents to treat AIPC.

Inhibition of cellular Shp2 activity by a methyl ester analog of SPI-112

The protein tyrosine phosphatase (PTP) Shp2 (PTPN11) is an attractive target for anticancer drug discovery because it mediates growth factor signaling and its gain-of-function mutants are causally linked to leukemias. We previously synthesized SPI-112 from a lead compound of Shp2 inhibitor, NSC-117199. In this study, we demonstrated that SPI-112 bound to Shp2 by surface plasmon resonance (SPR) and displayed competitive inhibitor kinetics to Shp2. Like some other compounds in the PTP inhibitor discovery efforts, SPI-112 was not cell permeable, precluding its use in biological studies. To overcome the cell permeation issue, we prepared a methyl ester SPI-112 analog (SPI-112Me) that is predicted to be hydrolyzed to SPI-112 upon entry into cells. Fluorescence uptake assay and confocal imaging suggested that SPI-112Me was taken up by cells. Incubation of cells with SPI-112Me inhibited epidermal growth factor (EGF)-stimulated Shp2 PTP activity and Shp2-mediated paxillin dephosphorylation, Erk1/2 activation, and cell migration. SPI-112Me treatment also inhibited Erk1/2 activation by a Gab1-Shp2 chimera. Treatment of Shp2(E76K) mutant-transformed TF-1 myeloid cells with SPI-112Me resulted in inhibition of Shp2(E76K)-dependent cell survival, which is associated with inhibition of Shp2(E76K) PTP activity, Shp2(E76K)-induced Erk1/2 activation, and Bcl-XL expression. Furthermore, SPI-112Me enhanced interferon-gamma (IFN-gamma)-stimulated STAT1 tyrosine phosphorylation, ISRE-luciferase reporter activity, p21 expression, and the anti-proliferative effect. Thus, the SPI-112 methyl ester analog was able to inhibit cellular Shp2 PTP activity.

Abstract 732: Targeting the Bcl-2/BH3 protein-protein interaction: Identification, design, and synthesis of new selective inhibitors of the Mcl-1/BH3 interaction

It is well accepted that escape of apoptosis is a major mechanism for cancer progression and drug resistance. Anti-apoptotic members of the Bcl-2 protein family, such as Bcl-2, Bcl-xL and Mcl-1, are among the most effective inhibitors of apoptosis and are frequently upregulated in various types of human cancer. A number of pro-apoptotic proteins share only the BH3 domain with other members of the Bcl-2 family, so called BH3-only proteins, and appear to function essentially as transdominant inhibitors by binding to anti-apoptotic Bcl-2 family proteins and neutralizing their cell-survival activity. The development of small molecules to mimic the BH3 proteins has been an intense area of research. It is clear from the development of ABT737 (and its orally available relative ABT-263) that targeting of Bcl-2/Bcl-xL by small molecule BH3-mimetics is a promising strategy for the development of a new class of anticancer drugs. However the clinical potential of ABT737 may be limited since it does not inhibit the pro-survival Bcl-2 family protein Mcl-1. To date available Bcl-2 family proteins inhibitors are either pan-inhibitors such as (-)-gossypol (which simultaneously inhibits Bcl-xl/BH3, Bcl-2/BH3 and Mcl-1/BH3 interactions) or are selective for the Bcl-xl/BH3 and Bcl-2/BH3 interactions. Hence a selective Mcl-1/BH3 inhibitor would greatly aid investigating the role of Mcl-1 in cancer and in drug resistance and complement the activity of ABT737. Our current study is centered on the identification and the synthesis of small molecule selective inhibitors of the Mcl-1/BH3 interaction. To this aim we interrogated the hit-list from inhibitors of the MLSCN screen of the Mcl-1-NOXA interaction [(Emory, AID 1022) TR-FRET screen for Mcl-1-NOXA inhibitors]. We docked 2100 of the experimental 2100 MLSCN hits with Mcl-1 protein structure derived from the Mcl-1-NOXA X-ray crystal structure. We then examined the top 375 compounds. We then ranked them by docking score, the number of MLSCN biological assays tested and number of hits in these assays. We then selected compounds that docked well and had been tested in many MLSCN assays for which they were not hits. Selected compounds were purchased and assessed for activity in an Alphascreen and ELISA assay, to reveal the hit HL5-026 (IC50 = 46 µM). HL5-026 is an inhibitor of the Mcl-1/Bim-BH3 interaction that has four-fold selectivity over Bcl-xl/Bim-BH3. HL5-026 binding to Mcl-1 is currently being assessed via co-crystallization and other biophysical techniques. We will report the synthesis and biological evaluation of focused libraries based on the initial hit and designed by modeling and docking to Mcl-1. First generation libraries have revealed compounds of improved activity. Structure activity relationships around the hits will be disclosed as well as the outcomes of further rounds of chemical design and biological assessment.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 732.

Abstract 734: Development of small molecule inhibitors of the phosphatase Shp2 by fragment screening

Protein tyrosine phosphorylation, which is controlled by tyrosine kinase (PTK) and tyrosine phosphatase (PTP), regulates numerous cellular processes, including proliferation, survival, differentiation, migration and apoptosis. Accumulating evidence has shown that defective function of PTPs leads to aberrant protein phosphorylation, which is associated with many humane diseases, including cancer. Src homology 2 phosphatase-2 (Shp2) is a cytoplasmic, nonreceptor protein tyrosine phophatase. It is the first proto-oncogene identified in the PTP superfamily. The structure of Shp2 consists of two SH2 (N-SH2 and C-SH2) domains, a single PTP region and a C-terminal hydrophilic tail. In the basal state, Shp2 displays a low catalytic activity due to close interactions between the N-SH2 and PTP domains that keep the phosphatase in an autoinhibited closed conformation. Upon growth factor or cytokine stimulation, the SH2 domains of Shp2 binds to tyrosine phosphorylated docking proteins such as Gab1 and Gab2, which activates Src, Ras, and the Erk1/2 (Erk) mitogen-activated protein (MAP) kinase pathway. Shp2 gain-of-function mutations are found in leukemias and solid tumors and are linked to Noonan syndrome. Although Shp2 is involved in pathogenesis of human cancers, it is not clear how Shp2 mediates tumorigenesis. To aid chemical biology studies and ultimately experimental therapy, we have been actively engaged in the search potent and selective Shp2 inhibitors. We will describe the results of a fragment-based screen as a method for identifying Shp2 inhibitors. The fragment libraries were both purchased and constructed in-house with a bias towards compounds that would potentially function as phosphotyrosine mimics. This has revealed compounds with moderate to low activity (IC50 200-500 µM) that have served as the starting pints for fragment-to-lead development. The emerging structure-activity relationships will be discussed as well as synthesis, modeling and X-ray studies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 734.

Abstract 733: Synthesis and biological evaluation of inhibitors of Rho protein kinase

Rho GTPases are small G-proteins which play a critical role in signaling pathways and control cell growth and division. Rho-associated protein kinase (known as ROCK or Rho kinase) is a Ser/Thr protein kinase activated by GTP-bound Rho and phosphorylates important signalling proteins. Rho/ROCK mediated signalling pathways are implicated in cell morphology, moltility, smooth muscle contraction, formation of stress fiber, focal adhesion, cell transformation and cytokineses. ROCKs have been subject to growing attention, having been implicated in a range of therapeutic areas including cancer. Further, the pharmacological inhibition of ROCKs has been suggested as a promising strategy in the prevention of cell invasion, a central event in the process of metastasis.

We describe the identification of potent ROCK inhibitors from data mining of the Molecular Libraries Screening Center Network (MLSCN) data available through PubChem and in-house HTS screening. Libraries of compounds have been designed to aid the hit-to-lead process and probe structure activity relationships. Molecular modeling and crystallography have been used to aid the design of potent ROCK inhibitors. Compounds were first assessed for in vitro ROCK1 inhibitory activity using a Z-lyte kinase assay. Selected compounds were also screened against the isoform ROCK2. Selectivity trends will be discussed. The overall process has led to the improvement of activity of compounds from high micromolar activity to low nanomolar activity. Structure activity relationship studies led to the identification of highly potent and cell-permeable analogues that were shown to inhibit selected substrates of ROCK such as MYPT1 in cell assays and are the subject of ongoing antitumor studies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 733.

Abstract 761: The development of cell permeable Shp2 PTP inhibitors

Protein tyrosine phosphorylation affects cellular activities that control tumor growth and progression. Protein tyrosine phosphorylation, a key regulatory process of signal transduction pathways, is controlled by the action protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Kinases are now a clinically proven anticancer drug target. The development of PTP inhibitors is, by comparison, a relatively new field. Since PTPs do not require a small molecule cofactor they generally show a low propensity to bind a small molecule inhibitor. Nevertheless there are now examples of highly potent PTP inhibitors that provide promising proof-of-principle that PTPs are druggable. Most PTP inhibitors have a charged or highly polar functional group that mimics the phosphotyrosine residue, that often leads to poor ADME and cell permeability properties.

We will report our efforts to address the problems of cell permeability we have encountered in our Shp2 PTP inhibitor program. We have previously reported a series of isatin based Shp2 inhibitors based on a compound (NSC-117199) identified from screen of the NCI Diversity Set. We synthesized >100 analogs of NSC-117199 in our lead optimization effort, which yielded several compounds with approximately 50-fold increase in potency and > 10-fold increase in selectivity (Shp2 versus Shp1). However, these Shp2 PTP inhibitors have either a polar nitro or carboxyl group and have no detectable cellular activity. We will report three approaches to address this problem. The first approach was to prepare neutral ester prodrugs. Several compounds have clearly demonstrable activity against Shp2 in cells. A series of esters has also been designed to also improve the water solubility of the PTP inhibitor. A second approach taken was to further modify the isatin scaffold that does not necessitate the use of a prodrug strategy. We will report the discovery of new isatins related to NSC-117199 that have new modifications that result in cell active Shp2 inhibitors. Finally we will report the discovery and preliminary optimization of new classes of cell active Shp2 inhibitors based on alternative scaffolds.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 761.

Abstract 3680: The Akt activation inhibitor TCN-P inhibits Akt phosphorylation by binding to the PH domain of Akt and blocking its recruitment to the plasma membrane

Persistently activated hyper-phosphorylated Akt contributes to human oncogenesis and tumor resistance. TCN-P, the active metabolite of the Akt phosphorylation inhibitor triciribine (TCN), is in clinical trials in patients whose tumors contain hyper-phosphorylated Akt, but the mechanism by which TCN-P, inhibits Akt phosphorylation is not known. In this manuscript, we show that in vitro, TCN-P inhibits neither Akt kinase activity nor the phosphorylation of Akt S473 and T308 by mTOR or PDK1, respectively. However, in intact cells, immunofluorescence and subcellular fractionation experiments demonstrate that TCN inhibits EGF-stimulated Akt recruitment to the plasma membrane and subsequent phosphorylation of Akt on Ser473 and Thr308. Surface plasmon resonance (SPR) demonstrates that TCN-P, but not TCN, binds to full-length, non-phosphorylated (inactive) Akt. However, neither TCN-P nor TCN interacts with full-length, phosphorylated (active) Akt. Furthermore, TCN-P, but not TCN, binds Akt-derived pleckstrin homology (PH) domain with KD values of 690 nM and 1.4 µM as demonstrated by SPR and isothermal calorimetry (ITC), respectively. Consistent with these data, nuclear magnetic resonance (NMR) spectroscopy shows that TCN-P, but not TCN, binds to the PH domain engaging amino acid residues in the vicinity of the PIP3 binding pocket. Thus, SPR, NMR, as well as biochemical studies indicate that the anti-cancer drug TCN-P inhibits Akt function by binding to the PH domain of Akt, blocking its recruitment to the plasma membrane and subsequent phosphorylation, suggesting that this drug may be beneficial to patients whose tumors express persistently activated Akt.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3680.

Combretastatin-like chalcones as inhibitors of microtubule polymerisation. Part 2: Structure-based discovery of alpha-aryl chalcones

Tubulin is an important molecular target in cancer chemotherapy. Antimitotic agents able to bind to the protein are currently under study, commonly used in the clinic to treat a variety of cancers and/or exploited as probes to investigate the protein's structure and function. Here we report the binding modes for a series of colchicinoids, combretastatin A4 and chalcones established from docking studies carried out on the structure of tubulin in complex with colchicine. The proposed models, in agreement with published biochemical data, show that combretastatin A4 binds to the colchicine site of beta-tubulin and that chalcones assume an orientation similar to that of podophyllotoxin. The models can be used to design a new class of podophyllotoxin mimics, the alpha-aryl chalcones, capable of binding to the colchicine-binding site of beta-tubulin with higher affinity.

Identification of a disruptor of the MDM2-p53 protein-protein interaction facilitated by high-throughput in silico docking

NSC 333003 has been identified from the NCI Diversity Set as an inhibitor of the MDM2-p53 protein-protein interaction by in silico docking (virtual screening). Its potency and chemical characteristics render it well suited for lead optimization studies that can result in more potent analogs with improved drug-like properties. Its synthesis was achieved using an acid catalyzed condensation reaction from commercially available benzothiazole hydrazine and pyridyl phenyl ketone in refluxing methanol. Stereochemical implications for this compound are described.

Inhibitors of Src homology-2 domain containing protein tyrosine phosphatase-2 (Shp2) based on oxindole scaffolds

Screening of the NCI diversity set of compounds has led to the identification of 5 (NSC-117199), which inhibits the protein tyrosine phosphatase (PTP) Shp2 with an IC50 of 47 microM. A focused library incorporating an isatin scaffold was designed and evaluated for inhibition of Shp2 and Shp1 PTP activities. Several compounds were identified that selectively inhibit Shp2 over Shp1 and PTP1B with low to submicromolar activity. A model for the binding of the active compounds is proposed.

Selective chemical probe inhibitor of Stat3, identified through structure-based virtual screening, induces antitumor activity

S3I-201 (NSC 74859) is a chemical probe inhibitor of Stat3 activity, which was identified from the National Cancer Institute chemical libraries by using structure-based virtual screening with a computer model of the Stat3 SH2 domain bound to its Stat3 phosphotyrosine peptide derived from the x-ray crystal structure of the Stat3beta homodimer. S3I-201 inhibits Stat3.Stat3 complex formation and Stat3 DNA-binding and transcriptional activities. Furthermore, S3I-201 inhibits growth and induces apoptosis preferentially in tumor cells that contain persistently activated Stat3. Constitutively dimerized and active Stat3C and Stat3 SH2 domain rescue tumor cells from S3I-201-induced apoptosis. Finally, S3I-201 inhibits the expression of the Stat3-regulated genes encoding cyclin D1, Bcl-xL, and survivin and inhibits the growth of human breast tumors in vivo. These findings strongly suggest that the antitumor activity of S3I-201 is mediated in part through inhibition of aberrant Stat3 activation and provide the proof-of-concept for the potential clinical use of Stat3 inhibitors such as S3I-201 in tumors harboring aberrant Stat3.

Effects of alpha-substitutions on structure and biological activity of anticancer chalcones

Chalcones are known to exhibit antimitotic properties caused by inhibition of tubulin polymerisation. We describe here the effects of different alpha-substitutions, in particular alpha-fluorination, on the structure and biological activity of a series of chalcones.

Discovery of a Novel Shp2 Protein Tyrosine Phosphatase Inhibitor

Shp2 is a nonreceptor protein tyrosine phosphatase (PTP) encoded by the PTPN11 gene. It is involved in growth factorinduced activation of mitogen-activated protein (MAP) kinases Erk1 and Erk2 (Erk1/2) and has been implicated in the pathogenicity of the oncogenic bacterium Helicobacter pylori. Moreover, gain-of-function Shp2 mutations have been found in childhood leukemias and Noonan syndrome. Thus, small molecule Shp2 PTP inhibitors are much needed reagents for evaluation of Shp2 as a therapeutic target and for chemical biology studies of Shp2 function. By screening the National Cancer Institute (NCI) Diversity Set chemical library, we identified 8-hydroxy-7-(6-sulfonaphthalen-2-yl)diazenyl-quinoline-5-sulfonic acid (NSC-87877) as a potent Shp2 PTP inhibitor. Molecular modeling and site-directed mutagenesis studies suggested that NSC-87877 binds to the catalytic cleft of Shp2 PTP. NSC-87877 cross-inhibited Shp1 in vitro, but it was selective for Shp2 over other PTPs (PTP1B, HePTP, DEP1, CD45, and LAR). It is noteworthy that NSC-87877 inhibited epidermal growth factor (EGF)-induced activation of Shp2 PTP, Ras, and Erk1/2 in cell cultures but did not block EGF-induced Gab1 tyrosine phosphorylation or Gab1-Shp2 association. Furthermore, NSC-87877 inhibited Erk1/2 activation by a Gab1-Shp2 chimera but did not affect the Shp2-independent Erk1/2 activation by phorbol 12-myristate 13-acetate. These results identified NSC-87877 as the first PTP inhibitor capable of inhibiting Shp2 PTP in cell cultures without a detectable off-target effect. Our study also provides the first pharmacological evidence that Shp2 mediates EGF-induced Erk1/2 MAP kinase activation.

Mice with skin-specific DNA repair gene (Ercc1) inactivation are hypersensitive to ultraviolet irradiation-induced skin cancer and show more rapid actinic progression

Ercc1 has an essential role in the nucleotide excision repair (NER) pathway that protects against ultraviolet (UV)-induced DNA damage and is also involved in additional repair pathways. The premature death of simple Ercc1 mouse knockouts meant that we were unable to study the role of Ercc1 in the skin. To do this, we have used the Cre-lox system to generate a skin-specific Ercc1 knockout. With a Cre transgene under control of the bovine keratin 5 promoter we achieved 100% recombination of the Ercc1 gene in the epidermis. Hairless mice with Ercc1-deficient skin were hypersensitive to the short-term effects of UV irradiation, showing a very low minimal erythemal dose and a dramatic hyperproliferative response. Ultraviolet-irradiated mice with Ercc1-deficient skin developed epidermal skin tumours much more rapidly than controls. These tumours appeared to arise earlier in actinic progression and grew more rapidly than tumours on control mice. These responses are more pronounced than have been reported for other NER-deficient mice, demonstrating that Ercc1 has a key role in protecting against UV-induced skin cancer.