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

S31-201 (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 Stat3 beta homodimer. S31-201 inhibits Stat3-Stat3 complex formation and Stat3 DNA-binding and transcriptional activities. Furthermore, S31-201 inhibits growth and induces apoptosis preferentially in tumor cells that contain persistently activated Stat3. Constitutively climerized and active Stat3C and Stat3 SH2 domain rescue tumor cells from S31-201-induced apoptosis. Finally, S31-201 inhibits the expression of the Stat3-regulated genes encoding cyclin D1, BcI-xL, and survivin and inhibits the growth of human breast tumors in vivo. These findings strongly suggest that the antitumor activity of S31-201 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 S31-201 in tumors harboring aberrant Stat3

Inhibition of Shp2/PTPN11 protein tyrosine phosphatase by NSC-87877, NSC-117199 and their analogs

Compounds and associated methods for inhibiting a protein tyrosine phosphatase. By a combination of experimental and virtual screenings of the NCI Diversity Set chemical library, NSC-87877 and NSC-117199 have been identified as Shp2 PTP inhibitors. Significantly, NSC-87877 is active in cell-based assays and has no detectable off-target effects in the EGF-stimulated Erk 1/2 activation pathway. Additionally, a number of analogs of NSC-117199 have been produced. These analogs exhibit enhanced protein tyrosine phosphatase inhibition and are found to be potent and/or selective inhibitors of Shp1 and/or Shp2 protein tyrosine phosphatases

Fendiline Enhances the Cytotoxic Effects of Therapeutic Agents on PDAC Cells by Inhibiting Tumor-Promoting Signaling Events: A Potential Strategy to Combat PDAC

The L-type calcium channel blocker fendiline has been shown to interfere with Ras-dependent signaling in K-Ras mutant cancer cells. Earlier studies from our lab had shown that treatment of pancreatic cancer cells with fendiline causes significant cytotoxicity and interferes with proliferation, survival, migration, invasion and anchorage independent growth. Currently there are no effective therapies to manage PDACs. As fendiline has been approved for treatment of patients with angina, we hypothesized that, if proven effective, combinatorial therapies using this agent would be easily translatable to clinic for testing in PDAC patients. Here we tested combinations of fendiline with gemcitabine, visudyne (a YAP1 inhibitor) or tivantinib (ARQ197, a c-Met inhibitor) for their effectiveness in overcoming growth and oncogenic characteristics of PDAC cells. The Hippo pathway component YAP1 has been shown to bypass K-Ras addiction, and allow tumor growth, in a Ras-null mouse model. Similarly, c-Met expression has been associated with poor prognosis and metastasis in PDAC patients. Our results presented here show that combinations of fendiline with these inhibitors show enhanced anti-tumor activity in Panc1, MiaPaCa2 and CD18/HPAF PDAC cells, as evident from the reduced viability, migration, anchorage-independent growth and self-renewal. Biochemical analysis shows that these agents interfere with various signaling cascades such as the activation of Akt and ERK, as well as the expression of c-Myc and CD44 that are altered in PDACs. These results imply that inclusion of fendiline may improve the efficacy of various chemotherapeutic agents that could potentially benefit PDAC patients

Oxadiazole-isopropylamides as Potent and Noncovalent Proteasome Inhibitors

Screening of the 50 000 ChemBridge compound library led to the identification of the oxadiazole-isopropylamide 1 (PI-1833) which inhibited chymotrypsin-like (CT-L) activity (IC50 = 0.60 μM) with little effects on the other two major proteasome proteolytic activities, trypsin-like (T-L) and postglutamyl-peptide-hydrolysis-like (PGPH-L). LC–MS/MS and dialysis show that 1 is a noncovalent and rapidly reversible CT-L inhibitor. Focused library synthesis provided 11ad (PI-1840) with CT-L activity (IC50 = 27 nM). Detailed SAR studies indicate that the amide moiety and the two phenyl rings are sensitive toward modifications. Hydrophobic residues, such as propyl or butyl in the para position (not ortho or meta) of the A-ring and a m-pyridyl group as B-ring, significantly improve activity. Compound 11ad (IC50 = 0.37 μM) is more potent than 1 (IC50 = 3.5 μM) at inhibiting CT-L activity in intact MDA-MB-468 human breast cancer cells and inhibiting their survival. The activity of 11ad warrants further preclinical investigation of this class as noncovalent proteasome inhibitors

Lysophosphatidic Acid Acyltransferase Beta Regulates mTOR Signaling

<div><p>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. </p></div

Development of Novel ACK1/TNK2 Inhibitors Using a Fragment-Based Approach

The tyrosine kinase ACK1, a critical signal transducer regulating survival of hormone-refractory cancers, is an important therapeutic target, for which there are no selective inhibitors in clinical trials to date. This work reports the discovery of novel and potent inhibitors for ACK1 tyrosine kinase (also known as TNK2) using an innovative fragment-based approach. Focused libraries were designed and synthesized by selecting fragments from reported ACK inhibitors to create hybrid structures in a mix and match process. The hybrid library was screened by enzyme-linked immunosorbent assay-based kinase inhibition and 33P HotSpot assays. Systematic structure–activity relationship studies led to the identification of compound (R)-9b, which shows potent in vitro (IC50 = 56 nM, n = 3, 33P HotSpot assay) and in vivo (IC50 \u3c 2 μM, human cancer cell lines) ACK1 inhibition. Both (R)-9b and (S)-9b were stable in human plasma and displayed a long half-life (t1/2 \u3e 6 h)

Development of Novel ACK1/TNK2 Inhibitors Using a Fragment-Based Approach

The tyrosine kinase ACK1, a critical signal transducer regulating survival of hormone-refractory cancers, is an important therapeutic target, for which there are no selective inhibitors in clinical trials to date. This work reports the discovery of novel and potent inhibitors for ACK1 tyrosine kinase (also known as TNK2) using an innovative fragment-based approach. Focused libraries were designed and synthesized by selecting fragments from reported ACK inhibitors to create hybrid structures in a mix and match process. The hybrid library was screened by enzyme-linked immunosorbent assay-based kinase inhibition and 33P HotSpot assays. Systematic structure–activity relationship studies led to the identification of compound (R)-9b, which shows potent in vitro (IC50 = 56 nM, n = 3, 33P HotSpot assay) and in vivo (IC50 \u3c 2 μM, human cancer cell lines) ACK1 inhibition. Both (R)-9b and (S)-9b were stable in human plasma and displayed a long half-life (t1/2 \u3e 6 h)

Oxadiazole-isopropylamides as Potent and Noncovalent Proteasome Inhibitors

Screening of the 50 000 ChemBridge compound library led to the identification of the oxadiazole-isopropylamide 1 (PI-1833) which inhibited chymotrypsin-like (CT-L) activity (IC50 = 0.60 μM) with little effects on the other two major proteasome proteolytic activities, trypsin-like (T-L) and postglutamyl-peptide-hydrolysis-like (PGPH-L). LC–MS/MS and dialysis show that 1 is a noncovalent and rapidly reversible CT-L inhibitor. Focused library synthesis provided 11ad (PI-1840) with CT-L activity (IC50 = 27 nM). Detailed SAR studies indicate that the amide moiety and the two phenyl rings are sensitive toward modifications. Hydrophobic residues, such as propyl or butyl in the para position (not ortho or meta) of the A-ring and a m-pyridyl group as B-ring, significantly improve activity. Compound 11ad (IC50 = 0.37 μM) is more potent than 1 (IC50 = 3.5 μM) at inhibiting CT-L activity in intact MDA-MB-468 human breast cancer cells and inhibiting their survival. The activity of 11ad warrants further preclinical investigation of this class as noncovalent proteasome inhibitors

LPAAT-β siRNA treatment results in increased nuclear eccentricity.

<p>MiaPaCa2 cells were treated (A) for 24 hr with 500 nM Torin-1 (* p < 0.0001), 10 nM rapamycin, or DMSO vehicle and (B) for 72 hr with 25 nM LP-4 (* p = 0.05) or non-targeting (nt) siRNA. Nuclei were stained with antibody to Lamin A to highlight the nuclear membrane as well as counterstained with DAPI. Analysis of the images using Definiens Tissue Studio software generated the length and width of individual nuclei, which were then analyzed for enhanced nuclear eccentricity as described in Materials and Methods. Graphs show the frequency distribution of nuclear eccentricity and nuclear l/w normalized to cell number. Statistical significance was determined using Student’s t-test. Results are representative of four independent experiments.</p