Inhibiting the interaction of cMET and IGF-1R with FAK effectively reduces growth of pancreatic cancer cells in vitro and in vivo

Pancreatic cancer is one of the most lethal diseases with no effective treatment. Previously, we have shown that FAK is overexpressed in pancreatic cancer and plays a key role in cancer cell survival and proliferation. FAK has been shown to interact with growth factor receptors including cMET and IGF-1R. As a novel therapeutic approach, we targeted the protein interaction of FAK with growth factor receptors to block tumor growth, alter signaling pathways and sensitize cells to chemotherapy. We have selected a small molecule compound (INT2-31) that decreases phosphorylation of AKT via disrupting interaction of FAK with cMET and IGF-1R. Our results demonstrate that interaction of a small molecule compound with FAK decreases phosphorylation of FAK Y397 while increasing FAK Y407 phosphorylation, without inhibiting the kinase activity of FAK and dramatically reduces downstream signaling to AKT. Our lead compound, INT2-31, demonstrates significant inhibition of tumor cell growth in two orthotopic models of pancreatic cancer. In addition, INT2-31 increases sensitivity to gemcitabine chemotherapy in a direct fresh biopsy xenograft model of pancreatic cancer growth.

Lysophosphatidic acid acyltransferase beta regulates mTOR signaling

Lysophosphatidic acid acyltransferase (LPAAT-β) is a phosphatidic acid (PA) generating enzyme that plays an essential role in triglyceride synthesis. However, LPAAT-β is now being studied as an important regulator of cell growth and differentiation and as a potential therapeutic target in cancer since PA is necessary for the activity of key proteins such as Raf, PKC-ζ and mTOR. In this report we determine the effect of LPAAT-β silencing with siRNA in pancreatic adenocarcinoma cell lines. We show for the first time that LPAAT-β knockdown inhibits proliferation and anchorage-independent growth of pancreatic cancer cells. This is associated with inhibition of signaling by mTOR as determined by levels of mTORC1- and mTORC2-specific phosphorylation sites on 4E-BP1, S6K and Akt. Since PA regulates the activity of mTOR by modulating its binding to FKBP38, we explored the possibility that LPAAT-β might regulate mTOR by affecting its association with FKBP38. Coimmunoprecipitation studies of FKBP38 with mTOR show increased levels of FKBP38 associated with mTOR when LPAAT-β protein levels are knocked down. Furthermore, depletion of LPAAT-β results in increased Lipin 1 nuclear localization which is associated with increased nuclear eccentricity, a nuclear shape change that is dependent on mTOR, further confirming the ability of LPAAT-β to regulate mTOR function. Our results provide support for the hypothesis that PA generated by LPAAT-β regulates mTOR signaling. We discuss the implications of these findings for using LPAAT-β as a therapeutic target.

Selective disruption of rb-raf-1 kinase interaction inhibits pancreatic adenocarcinoma growth irrespective of gemcitabine sensitivity

Inactivation of the retinoblastoma (Rb) tumor suppressor protein is widespread in human cancers. Inactivation of Rb is thought to be initiated by association with Raf-1 (C-Raf) kinase, and here we determined how RRD-251, a disruptor of the Rb-Raf-1 interaction, affects pancreatic tumor progression. Assessment of phospho-Rb levels in resected human pancreatic tumor specimens by immunohistochemistry (n = 95) showed that increased Rb phosphorylation correlated with increasing grade of resected human pancreatic adenocarcinomas (P = 0.0272), which correlated with reduced overall patient survival (P = 0.0186). To define the antitumor effects of RRD-251 (50 μmol/L), cell-cycle analyses, senescence, cell viability, cell migration, anchorage-independent growth, angiogenic tubule formation and invasion assays were conducted on gemcitabine-sensitive and -resistant pancreatic cancer cells. RRD-251 prevented S-phase entry, induced senescence and apoptosis, and inhibited anchorage-independent growth and invasion (P < 0.01). Drug efficacy on subcutaneous and orthotopic xenograft models was tested by intraperitoneal injections of RRD-251 (50 mg/kg) alone or in combination with gemcitabine (250 mg/kg). RRD-251 significantly reduced tumor growth in vivo accompanied by reduced Rb phosphorylation and lymph node and liver metastasis (P < 0.01). Combination of RRD-251 with gemcitabine showed cooperative effect on tumor growth (P < 0.01). In conclusion, disruption of the Rb-Raf-1 interaction significantly reduces the malignant properties of pancreatic cancer cells irrespective of their gemcitabine sensitivity. Selective targeting of Rb-Raf-1 interaction might be a promising strategy targeting pancreatic cancer.

Abstract 2467: Development of new N-Arylbenzamides as STAT3 dimerization inhibitors

The association of aberrant STAT3 activation with many types of human malignancies and solid tumors makes STAT3 an attractive molecular target for the development of novel cancer therapeutics. STAT3 dimerization via two reciprocal phosphotyrosine (pTyr)-Src-homology 2 (SH2) interaction is required for its binding to specific DNA-response elements in the promoters of target genes. This dimerization process offers a potentially selective way to directly target STAT3. Nevertheless the design of small molecules capable of disrupting protein-protein interactions remains a significant challenge to medicinal chemistry. We describe the development of a new class of small molecule capable of disrupting the STAT3:STAT3 protein-protein interaction. We identified the STAT3 inhibitor S3I-201 (NSC-74859) from the NCI chemical collection by using structure-based virtual screening with a model based on the X-ray crystal structure of the STAT3β homodimer. We developed a series of phosphonic and salicylic acids based on the structure of S3I-201 incorporating an N-arylbenzamide scaffold. The series of phosphonic and salicylic acids with a shorter amide linker lacking the O-tosyl group has improved STAT3 inhibitory activity [as measured by a competitive, fluorescence-polarization (FP)-based assay]. The equivalent in vitro potencies observed by the replacement of phosphonic acid moiety of with 5-amino-2-hydroxybenzoic acid group validates 5-amino-2-hydroxybenzoic acid as a phosphotyrosine mimic in this series. The binding mode of selected compounds, as predicted by molecular modeling, will be discussed. Our docking studies indicated that the phosphonic and salicylic acid groups interact in the pTyr-705 binding site in a broadly similar manner, while the other substituents occupy the STAT3 pY+1 and pY-X hydrophobic pockets. One of the most potent compounds in vitro (in the FP assay) inhibits STAT3 dimerization in intact cells and suppresses malignant transformation in human cancer cells that depend on STAT3. The in vitro and cell based potency of the N-arylbenzamides warrants further development of this scaffold as STAT3 inhibitors.

Citation Format: Nicholas J. Lawrence, Roberta Pireddu, Yiyu Ge, Murali K. Urlam, Xiaolei Zhang, Ying Sun, Harshani R. Lawrence, Wayne C. Guida, Said Sebti. Development of new N-Arylbenzamides as STAT3 dimerization inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2467. doi:10.1158/1538-7445.AM2013-2467

Abstract 2470: Identification and evaluation of small molecule inhibitors of lysophosphatidic acid acyltransferase-beta

Abstract: Lysophosphatidic acid acyltransferase-beta (LPAAT-β) catalyzes the production of phosphatidic acid (PA) from lysophosphatidic acid (LPA). PA is a lipid cofactor that contributes to the activation of c-Raf, BRAF, mTOR and PKC-ζ. LPAAT-β expression is a prognostic factor in gynecologic malignancies and is being investigated as a therapeutic target in a variety of tumor types. We previously reported that knockdown of LPAAT-β by siRNA led to a significant inhibition of both anchorage-dependent and -independent growth in pancreatic cancer cell lines. Having thus established LPAAT-β as a valid therapeutic target in pancreatic cancer, we screened small molecule libraries for compounds which block LPAAT-β enzymatic activity in vitro.

Methods: We utilized a 96-well plate screening assay for LPAAT-β enzymatic activity modified from Aguado and Campbell, J Biol Chem 273(7):4096-4105, 1998. Briefly, compounds were introduced into a mixture containing full-length, recombinant, baculovirus-produced LPAAT-β (Blue Sky Biotechnology), oleoyl-LPA, and oleoyl coenzyme A. The ability of the compound to inhibit the enzyme activity was assayed by the measurement of the reaction of the thiol group of the released coenzyme A with the DTNB, resulting in an increase in the optical density of the sample when read at an absorbance of 413 nm. To rule out non-specific compounds identified from the DTNB plate assay, we confirmed activity using a secondary thin layer chromatography (TLC) assay that directly measures the ability of LPAAT-β to catalyze the synthesis of PA from oleoyl-LPA and a fluorochrome-labeled (NBD) palmitoyl coenzyme A.

Results: We screened a total of ten libraries containing 11204 compounds, and achieved a 1.2% hit rate for inhibition of &gt;50% at the tested concentration (100μM for nine libraries; 10μM for one library). Further testing identified several compounds with IC50s ranging from 0.1-15 μM. One hit identified with an IC50 of 100 nM was chosen for further investigation and for synthesis of analogs to optimize potency and undertake SAR. We verified the activity of this hit and its analogs against LPAAT-β by determining their inhibitory activity of the synthesis of NBD-labeled PA in a TLC assay. Finally, we demonstrated that the best analog from this group inhibited the proliferation of several pancreatic cancer cell lines.

Conclusions: We have developed a library of compounds which show inhibitory activity against LPAAT-β in a screening assay, and have confirmed their ability to inhibit LPAAT-β directly in a TLC assay which monitors the production of PA. These compounds show low micromolar activity against LPAAT-β in vitro, and micromolar activity against the proliferation of pancreatic cancer cell lines in culture.

Citation Format: Michelle A. Blaskovich, Harsukh Gevariya, Nicholas J. Lawrence, Saïd Sebti, Gregory Springett. Identification and evaluation of small molecule inhibitors of lysophosphatidic acid acyltransferase-beta. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2470. doi:10.1158/1538-7445.AM2013-2470

Abstract 350: Inhibition of SHP2 impairs oncogenic activity of EGFR mutants in non-small cell lung cancer

Activating mutations of epidermal growth factor receptor (EGFR) are found in 5-15% of non small cell lung carcinomas (NSCLC) and are targets of NSCLC treatment. However, most patients treated with EGFR tyrosine kinase inhibitors eventually acquire drug resistance, pointing to the need of evaluating other molecules as potential targets for developing new therapy for NSCLC. The protein tyrosine phosphatase (PTP) SHP2 mediates signaling of growth factor receptors including that of EGFR. SHP2 is activated by EGFR mutants in lung adenocarcinoma. Inhibition of SHP2 with the SHP2 PTP inhibitor SPI-112Me or SHP2 knockdown suppressed proliferation of EGFR-dependent HCC827 and H1975 cells. To assess the role of Shp2 in the transgenic mouse model of EGFR mutant-driven lung cancer, we generated transgenic mice carrying a doxycycline (dox)-inducible, PTP-defective SHP2 (tetO-SHP2CSDA). Bitransgenic CCSP-rtTA/tetO-SHP2CSDA mice were crossed with tetO-EGFRL858R mice. F1 offspring of dox-induced transgenic mice were analyzed. Erk1/2 and Src were activated by EGFRL858R in bitransgenic CCSP-rtTA/tetO-EGFRL858R mice. Both of them were suppressed by SHP2CSDA in CCSP-rtTA/tetO-EGFRL858R/tetO-SHP2CSDA tritransgenic mice. Importantly, expression of SHP2CSDA significantly inhibited EGFRL858R-induced lung tumor in the tritransgenic mice. These results suggest that SHP2 is critical for lung tumorigenesis mediated by EGFR mutations.

Citation Format: Valentina E. Schneeberger, Yuan Ren, Noreen Luetteke, Hartmut Berns, Liwei Chen, Harshani R. Lawrence, Nicholas J. Lawrence, Alex S. Lopez, Eric B. Haura, Domenico Coppola, Jie Wu. Inhibition of SHP2 impairs oncogenic activity of EGFR mutants in non-small cell lung cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 350. doi:10.1158/1538-7445.AM2013-350

Abstract 3254: Discovery of S3I-1757, a STAT3-STAT3 dimerization disruptor that inhibits STAT3 activity, tumor survival, migration and invasion

The ability of STAT3 to translocate to the nucleus, bind DNA and transcriptionally regulate STAT3 target genes depends on tyrosine phosphorylation STAT3-STAT3 dimerization. Our chemistry efforts led to the discovery of S3I-1757 that disrupts STAT3-STAT3 dimerization. Fluorescence polarization assays and molecular modeling show that S3I-1757 interacts with Y-705 binding site in the STAT3-SH2 domain and displaces fluorescein-labelled GpYLPQTV phosphotyrosine peptide from binding to STAT3. Furthermore, using co-immunoprecipitation and co-localization studies we show that S3I-1757 inhibits STAT3 dimerization and STAT3-EGF receptor binding in intact cells. Treatment of human cancer cells with S3I-1757 (but not a closely related analogue, S3I-1756, that does not inhibit STAT3 dimerization), inhibits selectively the phosphorylation of STAT3 over Akt and Erk1/2, nuclear accumulation of P-Y705-STAT3, STAT3-DNA binding and transcriptional activation and suppresses the expression levels of STAT3 target genes such as Bcl-xL, survivin, cyclin D1 and MMP9. Furthermore, S3I-1757 but not S3I-1756 inhibits anchorage-dependent and -independent growth, migration and invasion of human cancer cells which depend on STAT3 selectively over those that do not. Finally, STAT3-C, a genetically engineered mutant of STAT3 that forms a constitutively dimerized STAT3, rescues from S3I-1757 effects. Our results warrant further development of S3I-1757 as a STAT3-STAT3 dimerization inhibitor capable of blocking hyper activated STAT3 and suppressing malignant transformation of STAT3-dependent human tumors.

Citation Format: Xiaolei Zhang, Ying Sun, Roberta Pireddu, Hua Yang, Murali K. Urlam, Harshani R. Lawrence, Wayne C. Guida, Nicholas J. Lawrence, Said M. Sebti. Discovery of S3I-1757, a STAT3-STAT3 dimerization disruptor that inhibits STAT3 activity, tumor survival, migration and invasion. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3254. doi:10.1158/1538-7445.AM2013-3254

A novel inhibitor of STAT3 homodimerization selectively suppresses STAT3 activity and malignant transformation

STAT3-STAT3 dimerization, which involves reciprocal binding of the STAT3-SH2 domain to phosphorylated tyrosine-705 (Y-705), is required for STAT3 nuclear translocation, DNA binding, and transcriptional regulation of downstream target genes. Here, we describe a small molecule S3I-1757 capable of disrupting STAT3-STAT3 dimerization, activation, and malignant transforming activity. Fluorescence polarization assay and molecular modeling suggest that S3I-1757 interacts with the phospho-Y-705-binding site in the SH2 domain and displaces fluorescein-labeled GpYLPQTV phosphotyrosine peptide from binding to STAT3. We generated hemagglutinin (HA)-tagged STAT3 and FLAG-tagged STAT3 and showed using coimmunoprecipitation and colocalization studies that S3I-1757 inhibits STAT3 dimerization and STAT3-EGF receptor (EGFR) binding in intact cells. Treatment of human cancer cells with S3I-1757 (but not a closely related analog, S3I-1756, which does not inhibit STAT3 dimerization), inhibits selectively the phosphorylation of STAT3 over AKT1 and ERK1/2 (MAPK3/1), nuclear accumulation of P-Y705-STAT3, STAT3-DNA binding, and transcriptional activation and suppresses the expression levels of STAT3 target genes, such as Bcl-xL (BCL2L1), survivin (BIRC5), cyclin D1 (CCND1), and matrix metalloproteinase (MMP)-9. Furthermore, S3I-1757, but not S3I-1756, inhibits anchorage-dependent and -independent growth, migration, and invasion of human cancer cells, which depend on STAT3. Finally, STAT3-C, a genetically engineered mutant of STAT3 that forms a constitutively dimerized STAT3, rescues cells from the effects of S3I-1757 inhibition. Thus, we have developed S3I-1757 as a STAT3-STAT3 dimerization inhibitor capable of blocking hyperactivated STAT3 and suppressing malignant transformation in human cancer cells that depend on STAT3.

Development of new N-Arylbenzamides as STAT3 Dimerization Inhibitors

The O-tosylsalicylamide S3I-201 (10) was used as a starting point for design and synthesis of novel STAT-3 dimerization inhibitors with improved drug-like qualities. The phosphonic acid 12d and salicylic acids 13f, 13g with a shorter amide linker lacking the O-tosyl group had improved STAT-3 inhibitory activity. The equivalent potencies observed by the replacement of phosphonic acid moiety of 12d with 5-amino-2-hydroxybenzoic acid group as in 13f further validates 5-amino-2-hydroxybenzoic acid as a phosphotyrosine mimic. The salicylic acid 13f displayed improved whole cell activity. The focused library of salicylic acids 13 with benzamide linker indicated that hydrophobic heptyl and cyclohexyl are the best tolerated R groups and a biphenyl ether (as the Ar group) significantly contributes to STAT3 inhibitory activity. Our docking studies indicated that the acidic groups of 12d, 13f and 13g interact in the p-Tyr-705 binding site in a broadly similar manner, while the phenoxybenzoyl group and the cyclohexylbenzyl group occupying pY+1 and pY-X hydrophobic pockets respectively. The in vitro and cell based potency of 13f warrants further development of this scaffold as STAT3 inhibitors.

Regulation of interlocking gene regulatory network subcircuits by a small molecule inhibitor of retinoblastoma protein (RB) phosphorylation: cancer cell expression of HLA-DR

The induction of the major histocompatibility (MHC), antigen-presenting class II molecules by interferon-gamma, in solid tumor cells, requires the retinoblastoma tumor suppressor protein (Rb). In the absence of Rb, a repressosome blocks the access of positive-acting, promoter binding proteins to the MHC class II promoter. However, a complete molecular linkage between Rb expression and the disassembly of the MHC class II repressosome has been lacking. By treating A549 lung carcinoma cells with a novel small molecule that prevents phosphorylation-mediated, Rb inactivation, we demonstrate that Rb represses the synthesis of an MHC class II repressosome component, YY1. The reduction in YY1 synthesis correlates with the advent of MHC class II inducibility; with loss of YY1 binding to the promoter of the HLA-DRA gene, the canonical human MHC class II gene; and with increased Rb binding to the YY1 promoter. These results support the concept that the Rb gene regulatory network (GRN) subcircuit that regulates cell proliferation is linked to a GRN subcircuit regulating a tumor cell immune function.

Development of o-chlorophenyl substituted pyrimidines as exceptionally potent aurora kinase inhibitors

The o-carboxylic acid substituted bisanilinopyrimidine 1 was identified as a potent hit (Aurora A IC(50) = 6.1 ± 1.0 nM) from in-house screening. Detailed structure-activity relationship (SAR) studies indicated that polar substituents at the para position of the B-ring are critical for potent activity. X-ray crystallography studies revealed that compound 1 is a type I inhibitor that binds the Aurora kinase active site in a DFG-in conformation. Structure-activity guided replacement of the A-ring carboxylic acid with halogens and incorporation of fluorine at the pyrimidine 5-position led to highly potent inhibitors of Aurora A that bind in a DFG-out conformation. B-Ring modifications were undertaken to improve the solubility and cell permeability. Compounds such as 9m with water-solubilizing moieties at the para position of the B-ring inhibited the autophosphorylation of Aurora A in MDA-MB-468 breast cancer cells.

RKI-1447 is a potent inhibitor of the Rho-associated ROCK kinases with anti-invasive and antitumor activities in breast cancer

The Rho-associated kinases ROCK1 and ROCK2 are critical for cancer cell migration and invasion, suggesting they may be useful therapeutic targets. In this study, we describe the discovery and development of RKI-1447, a potent small molecule inhibitor of ROCK1 and ROCK2. Crystal structures of the RKI-1447/ROCK1 complex revealed that RKI-1447 is a Type I kinase inhibitor that binds the ATP binding site through interactions with the hinge region and the DFG motif. RKI-1447 suppressed phosphorylation of the ROCK substrates MLC-2 and MYPT-1 in human cancer cells, but had no effect on the phosphorylation levels of the AKT, MEK, and S6 kinase at concentrations as high as 10 μmol/L. RKI-1447 was also highly selective at inhibiting ROCK-mediated cytoskeleton re-organization (actin stress fiber formation) following LPA stimulation, but does not affect PAK-meditated lamellipodia and filopodia formation following PDGF and Bradykinin stimulation, respectively. RKI-1447 inhibited migration, invasion and anchorage-independent tumor growth of breast cancer cells. In contrast, RKI-1313, a much weaker analog in vitro, had little effect on the phosphorylation levels of ROCK substrates, migration, invasion or anchorage-independent growth. Finally, RKI-1447 was highly effective at inhibiting the outgrowth of mammary tumors in a transgenic mouse model. In summary, our findings establish RKI-1447 as a potent and selective ROCK inhibitor with significant anti-invasive and antitumor activities and offer a preclinical proof-of-concept that justify further examination of RKI-1447 suitability as a potential clinical candidate.

HG-829 is a potent noncompetitive inhibitor of the ATP-binding cassette multidrug resistance transporter ABCB1

Transmembrane drug export mediated by the ATP-binding cassette (ABC) transporter P-glycoprotein contributes to clinical resistance to antineoplastics. In this study, we identified the substituted quinoline HG-829 as a novel, noncompetitive, and potent P-glycoprotein inhibitor that overcomes in vitro and in vivo drug resistance. We found that nontoxic concentrations of HG-829 restored sensitivity to P-glycoprotein oncolytic substrates. In ABCB1-overexpressing cell lines, HG-829 significantly enhanced cytotoxicity to daunorubicin, paclitaxel, vinblastine, vincristine, and etoposide. Coadministration of HG-829 fully restored in vivo antitumor activity of daunorubicin in mice without added toxicity. Functional assays showed that HG-829 is not a Pgp substrate or competitive inhibitor of Pgp-mediated drug efflux but rather acts as a noncompetitive modulator of P-glycoprotein transport function. Taken together, our findings indicate that HG-829 is a potent, long-acting, and noncompetitive modulator of P-glycoprotein export function that may offer therapeutic promise for multidrug-resistant malignancies.

Pyridylthiazole-based ureas as inhibitors of Rho associated protein kinases (ROCK1 and 2)

Potent ROCK inhibitors of a new class of 1-benzyl-3-(4-pyridylthiazol-2-yl)ureas have been identified. Remarkable differences in activity were observed for ureas bearing a benzylic stereogenic center. Derivatives with hydroxy, methoxy and amino groups at the meta position of the phenyl ring give rise to the most potent inhibitors (low nM). Substitutions at the para position result in substantial loss of potency. Changes at the benzylic position are tolerated resulting in significant potency in the case of methyl and methylenehydroxy groups. X-Ray crystallography was used to establish the binding mode of this class of inhibitors and provides an explanation for the observed differences of the enantiomer series. Potent inhibition of ROCK in human lung cancer cells was shown by suppression of the levels of phosphorylation of the ROCK substrate MYPT-1.

Ack1-mediated androgen receptor phosphorylation modulates radiation resistance in castration-resistant prostate cancer

Androgen deprivation therapy has been the standard of care in prostate cancer due to its effectiveness in initial stages. However, the disease recurs, and this recurrent cancer is referred to as castration-resistant prostate cancer (CRPC). Radiotherapy is the treatment of choice; however, in addition to androgen independence, CRPC is often resistant to radiotherapy, making radioresistant CRPC an incurable disease. The molecular mechanisms by which CRPC cells acquire radioresistance are unclear. Androgen receptor (AR)-tyrosine 267 phosphorylation by Ack1 tyrosine kinase (also known as TNK2) has emerged as an important mechanism of CRPC growth. Here, we demonstrate that pTyr(267)-AR is recruited to the ATM (ataxia telangiectasia mutated) enhancer in an Ack1-dependent manner to up-regulate ATM expression. Mice engineered to express activated Ack1 exhibited a significant increase in pTyr(267)-AR and ATM levels. Furthermore, primary human CRPCs with up-regulated activated Ack1 and pTyr(267)-AR also exhibited significant increase in ATM expression. The Ack1 inhibitor AIM-100 not only inhibited Ack1 activity but also was able to suppress AR Tyr(267) phosphorylation and its recruitment to the ATM enhancer. Notably, AIM-100 suppressed Ack1 mediated ATM expression and mitigated the growth of radioresistant CRPC tumors. Thus, our study uncovers a previously unknown mechanism of radioresistance in CRPC, which can be therapeutically reversed by a new synergistic approach that includes radiotherapy along with the suppression of Ack1/AR/ATM signaling by the Ack1 inhibitor, AIM-100.

A novel mechanism by which small molecule inhibitors induce the DFG flip in Aurora A

Most protein kinases share a DFG (Asp-Phe-Gly) motif in the ATP site that can assume two distinct conformations, the active DFG-in and the inactive DFG-out states. Small molecule inhibitors able to induce the DFG-out state have received considerable attention in kinase drug discovery. Using a typical DFG-in inhibitor scaffold of Aurora A, a kinase involved in the regulation of cell division, we found that halogen and nitrile substituents directed at the N-terminally flanking residue Ala273 induced global conformational changes in the enzyme, leading to DFG-out inhibitors that are among the most potent Aurora A inhibitors reported to date. The data suggest an unprecedented mechanism of action, in which induced-dipole forces along the Ala273 side chain alter the charge distribution of the DFG backbone, allowing the DFG to unwind. As the ADFG sequence and three-dimensional structure is highly conserved, DFG-out inhibitors of other kinases may be designed by specifically targeting the flanking alanine residue with electric dipoles.

Abstract 3904: Pyridylthiazole-based ureas as inhibitors of Rho-associated protein kinases

Rho GTPase is a small G-protein which plays a critical role in signaling pathways and controls 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 target proteins involved in various signal transduction pathways. Rho and the Rho-kinase signalling pathways are implicated in cell morphology, motility, smooth muscle contraction, formation of stress fibres, focal adhesion and cell transformation. ROCKs have been subject to growing attention, having been implicated in a range of therapeutic areas including cardiovascular diseases, CNS disorders, and 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. Potent ROCK inhibitors of a new class of 1-benzyl-3-(4-pyridylthiazol-2-yl)ureas have been identified. Remarkable differences in activity were observed for ureas bearing a benzylic stereogenic center. Derivatives with hydroxy, methoxy and amino groups at the meta position of the phenyl ring give rise to the most potent inhibitors (low nM). Substitutions at the para position result in substantial loss of potency. Changes at the benzylic position are tolerated resulting in significant potency in the case of methyl and methylenehydroxy groups. X-ray crystallography was used to establish the binding mode of this class of inhibitors and provides an explanation for the observed differences of the enantiomer series. Potent inhibition of ROCK in human lung cancer cells was shown by suppression of the phosphorylation levels of the ROCK substrate MYPT-1. One of the series, RKI-1447 inhibits migration, invasion and anchorage-independent tumor growth of breast cancer cells and is discussed in an accompanying poster.

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 3904. doi:1538-7445.AM2012-3904

Abstract 2942: RKI-1447, a potent ROCK inhibitor with anti-tumor and anti-invasive activities in breast cancer

Rho-associated kinases 1 and 2 (ROCKs) are intimately involved in metastasis and this prompted the development of ROCK inhibitors (RKIs) as anti-metastatic agents. Here, we describe the development of RKI-1447 which inhibits ROCK 1 and 2 potently in vitro (IC50s; 14 and 6 nM, respectively) and suppresses the phosphorylation of ROCK substrates MLC2 and MYPT1 in human breast cancer cells (IC50; 100 nM). The crystal structure of the RKI-1447-ROCK1 complex reveals that RKI-1447 binds the hinge region in the ATP binding site. RKI-1447 is highly selective and does not affect the phosphorylation levels of Akt, Erk, Mek and S6. RKI-1447 is also highly selective at inhibiting ROCK-mediated cytoskeleton re-organization (actin stress fiber formation) following LPA stimulation, but does not affect PKA-meditated lamelipodia and filopodia formation following PDGF and bradykinin stimulation, respectively. RKI-1447 inhibits migration, invasion and anchorage-independent tumor growth of breast cancer cells. A structurally-related analog RKI-1313 that is inactive against ROCKs in vitro (IC50 &gt; 10 µM) has little effects on migration, invasion and anchorage-independent growth. Finally, RKI-1447 is highly effective at inhibiting the growth of ErbB2-driven breast tumors in a transgenic animal model.

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 2942. doi:1538-7445.AM2012-2942

Abstract 3902: Development of Aurora A inhibitors with ortho-halophenyl substituted pyrimidines: Unusual potency, SAR and X-ray crystallography studies

The Aurora kinases are a family of serine-threonine kinases that play an important role in the regulation of cell division. The three members of the Aurora family Aurora A, B and C share a high degree of structural homology in their kinase domain but each kinase plays a different role in the control of mitosis. Aurora A and B have received the most attention to date as anticancer targets. Detailed studies have shown Aurora A and B are over expressed in a variety of cancers and are implicated in many aspects of tumor development. Aurora A is frequently over-expressed in tumors and cancer cell lines and has characteristics of an oncogene. Aurora B is also over expressed in many cancer types but does not have oncogenic properties. Aurora B plays important roles in M phase to ensure correct chromosome-microtubule alignment and attachment and chromosomal cytokinesis. Therefore, inhibition of Aurora kinase A and B is emerging as target-based therapy in cancer treatment. From our previous work HLM-8598 was identified from an in-house chemical library as a potent and highly selective inhibitor for Aurora A (IC50 value of 0.073 ± 0.002 μM) over Aurora B (IC50 = 5.4 ± 1.8 μM). X-ray crystallography studies of HLM-8598 bound to Aurora A confirmed HLM-8598 is a type-1 kinase inhibitor that interacts with the ATP binding site of the enzyme. The HLM-8598 bound to Aurora A structure-assisted synthesis of new analogs with IC50 &lt; 2.5 nM affinity. We will present the synthesis of new analogs that contain an ortho-halogen substituted phenyl moiety, structure activity relationship studies as a part of our efforts to identify unusually potent Aurora A kinase inhibitors. We will discuss the use of kinase structural elements to rationally guide compound synthesis and improve design strategy. The in vitro and in vivo activities of ortho-halogen phenyl substituted pyrimidines will be presented as unusually potent Aurora A inhibitors and 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 3902. doi:1538-7445.AM2012-3902

Abstract 1854: Lysophosphatidic Acid Acyltransferase-Beta contributes to proliferation and anchorage-independent growth in pancreatic adenocarcinoma

Abstract: Lysophosphatidic acid acyltransferase-beta (LPAAT-α) catalyzes the production of phosphatidic acid (PA) from lysophosphatidic acid (LPA). PA is a lipid cofactor that contributes to the activation of c-Raf, BRAF, mTOR and PKC-α. LPAAT-α expression is a prognostic factor in gynecologic malignancies and is being investigated as a therapeutic target in a variety of tumor types. We previously reported that LPAAT-α is expressed in pancreatic cancer cell lines and in human pancreatic adenocarcinoma tissues. We employed siRNA knockdown of LPAAT-α expression in pancreatic cancer cells in vitro. We find that reduction in the expression of LPAAT-α protein is associated with decreased proliferation and impairment in anchorage dependent growth of pancreatic cancer cells. Methods: MiaPaCa and Panc-1 cells were transfected with two different siRNAs targeted to LPAAT-α at 10 nM and 25 nM for 48 hrs and 72 hrs. A non-targeting siRNA was used as a control. The cells were then plated on tissue culture dishes or in soft agar and allowed to proliferate. Proliferation on plastic dishes was measured using Alamar Blue. Colony formation in soft agar was determined by directly counting macroscopic colonies. Results: Transfection of MiaPaCa and Panc-1 cells with siRNA at 25 nM for 72 hours achieved almost 100% inhibition of LPAAT-α protein expression by Western blotting. Under these conditions there was a 50% reduction in proliferation and colony formation. Studies to determine the effects of depleting LPAAT-α on the levels of p-PKC-α, p-MEK, p-4E-BP1 and p-S6Kinase are ongoing and will be presented. Conclusions: Suppression of expression of LPAAT-α protein in pancreatic cancer cell lines reduces proliferation and anchorage independent growth. This contributes to the validation of LPAAT-α as a therapeutic target in pancreatic cancer.

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 1854. doi:1538-7445.AM2012-1854

Abstract 2912: Development of potent SHP2 inhibitors for in vivo studies

The Src homology-2 domain-containing protein tyrosine phosphatase-2 (SHP2) is a positive transducer of growth factor, cytokine, integrin, and hormone signaling pathways which regulates processes such as cell proliferation, differentiation, adhesion, migration, and apoptosis and plays a pivotal role in growth factor and cytokine signaling. Gain-of-function SHP2 mutations are associated with various kinds of leukemia, and solid tumors. This makes SHP2 an attractive target for anticancer therapy. We are developing SHP2 inhibitors as novel anticancer drugs. Previously, we have reported on SPI-112 and its methyl ester prodrug SPI-112Me. However, the poor solubility of SPI-112Me has become an obstacle for in vivo studies. In ongoing study, we generate SPI-112 analogs to further improve physicochemical properties of these SHP2 inhibitors, such as solubility and cell permeability. To this aim, we synthesized SPI-112 derivatives containing various phosphotyrosine mimics and their prodrugs. SPI-112 derivatives of SHP2 inhibitors having improved properties have been obtained in this effort.

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 2912. doi:1538-7445.AM2012-2912

Fragment-based and structure-guided discovery and optimization of Rho kinase inhibitors

Using high concentration biochemical assays and fragment-based screening assisted by structure-guided design, we discovered a novel class of Rho-kinase inhibitors. Compound 18 was equipotent for ROCK1 (IC(50) = 650 nM) and ROCK2 (IC(50) = 670 nM), whereas compound 24 was more selective for ROCK2 (IC(50) = 100 nM) over ROCK1 (IC(50) = 1690 nM). The crystal structure of the compound 18-ROCK1 complex revealed that 18 is a type 1 inhibitor that binds the hinge region in the ATP binding site. Compounds 18 and 24 inhibited potently the phosphorylation of the ROCK substrate MLC2 in intact human breast cancer cells.

Ack1 tyrosine kinase activation correlates with pancreatic cancer progression

Pancreatic cancer is a significant cause of cancer mortality worldwide as the disease has advanced significantly in patients before symptoms are evident. The signal transduction pathways that promote this rapid progression are not well understood. Ack1 or TNK2, an ubiquitously expressed oncogenic non-receptor tyrosine kinase, integrates signals from ligand-activated receptor tyrosine kinases to modulate intracellular signaling cascades. In the present study, we investigated the Ack1 activation profile in a pancreatic cancer tumor microarray, and observed that expression levels of activated Ack1 and pTyr284-Ack1 positively correlated with the severity of disease progression and inversely correlated with the survival of patients with pancreatic cancer. To explore the mechanisms by which Ack1 promotes tumor progression, we investigated the role of AKT/PKB, an oncogene and Ack1-interacting protein. Ack1 activates AKT directly in pancreatic and other cancer cell lines by phosphorylating AKT at Tyr176 to promote cell survival. In addition, the Ack1 inhibitor AIM-100 not only inhibited Ack1 activation but also suppressed AKT tyrosine phosphorylation, leading to cell cycle arrest in the G1 phase. This effect resulted in a significant decrease in the proliferation of pancreatic cancer cells and induction of apoptosis. Collectively, our data indicate that activated Ack1 could be a prognostic marker for ascertaining early or advanced pancreatic cancer. Thus, Ack1 inhibitors hold promise for therapeutic intervention to inhibit pancreatic tumor growth.

Nicotine-mediated induction of E-selectin in aortic endothelial cells requires Src kinase and E2F1 transcriptional activity

Smoking is highly correlated with enhanced likelihood of atherosclerosis by inducing endothelial dysfunction. In endothelial cells, various cell-adhesion molecules including E-selectin, are shown to be upregulated upon exposure to nicotine, the addictive component of tobacco smoke; however, the molecular mechanisms underlying this induction are poorly understood. Here we demonstrate that nicotine-induced E-selectin transcription in human aortic endothelial cells (HAECs) could be significantly blocked by α7-nAChR subunit inhibitor, α-BT, Src-kinase inhibitor, PP2, or siRNAs against Src or β-Arrestin-1 (β-Arr1). Further, chromatin immunoprecipitations show that E-selectin is an E2F1 responsive gene and nicotine stimulation results in increased recruitment of E2F1 on E-selectin promoter. Inhibiting E2F1 activity using RRD-251, a disruptor of the Rb-Raf-1 kinase interaction, could significantly inhibit the nicotine-induced recruitment of E2F1 to the E-selectin promoter as well as E-selectin expression. Interestingly, stimulation of HAECs with nicotine results in increased adhesion of U937 monocytic cells to HAECs and could be inhibited by pre-treatment with RRD-251. Similarly, depletion of E2F1 or Src using RNAi blocked the increased adhesion of monocytes to nicotine-stimulated HAECs. These results suggest that nicotine-stimulated adhesion of monocytes to endothelial cells is dependent on the activation of α7-nAChRs, β-Arr1 and cSrc regulated increase in E2F1-mediated transcription of E-selectin gene. Therefore, agents such as RRD-251 that can target activity of E2F1 may have potential therapeutic benefit against cigarette smoke induced atherosclerosis.