Pradip De

A Vascular Targeted Pan Phosphoinositide 3-Kinase Inhibitor Prodrug, SF1126, with Antitumor and Antiangiogenic Activity

PTEN and the pan phosphoinositide 3-kinase (PI3K) inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1 benzopyran-4-one (LY294002) exert significant control over tumor-induced angiogenesis and tumor growth in vivo. The LY294002 compound is not a viable drug candidate due to poor pharmacologic variables of insolubility and short half-life. Herein, we describe the development and antitumor activity of a novel RGDS-conjugated LY294002 prodrug, termed SF1126, which is designed to exhibit increased solubility and bind to specific integrins within the tumor compartment, resulting in enhanced delivery of the active compound to the tumor vasculature and tumor. SF1126 is water soluble, has favorable pharmacokinetics, and is well tolerated in murine systems. The capacity of SF1126 to inhibit U87MG and PC3 tumor growth was enhanced by the RGDS integrin (alpha v beta 3/alpha 5 beta 1) binding component, exhibiting increased activity compared with a false RADS-targeted prodrug, SF1326. Antitumor activity of SF1126 was associated with the pharmacokinetic accumulation of SF1126 in tumor tissue and the pharmacodynamic knockdown of phosphorylated AKT in vivo. Furthermore, SF1126 seems to exhibit both antitumor and antiangiogenic activity. The results support SF1126 as a viable pan PI3K inhibitor for phase I clinical trials in cancer and provide support for a new paradigm, the application of pan PI3K inhibitory prodrugs for the treatment of cancer.

The Protein Phosphatase Activity of PTEN Regulates Src Family Kinases and Controls Glioma Migration

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is mutated or lost in 60% to 70% of advanced gliomas and is associated with malignant phenotypic changes such as migration, which contribute to the morbidity and mortality of this disease. Most of the tumor suppressor function of PTEN has been attributed to its ability to dephosphorylate the second messenger, phosphatidylinositol 3,4,5-triphosphate, resulting in the biological control of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. Despite recent work suggesting that the protein phosphatase activity of PTEN controls glioma cell migration, the mechanisms by which this occurs are unclear. Herein, we show using glioma cell lines (U87MG and U373MG) stably transfected with wild-type PTEN or catalytically altered mutants of PTEN that PTEN controls integrin-directed migration in a lipid phosphatase, PI3K/AKT-independent manner. Confirming this observation, we show that the stable overexpression of COOH-terminal Src kinase, the physiologic negative regulator of SRC family kinases (SFK), or treatment with the SFK inhibitor PP1 abrogates glioma migration. The results provide direct evidence that the downstream effect of the protein phosphatase activity of PTEN is to suppress SFK and FYN, and to regulate RAC-GTPase activity after alpha(v) integrin stimulation. Furthermore, studying vitronectin-directed migration using (a) Fyn small interfering RNA and (b) astrocytes from Fyn heterozygous (+/-) mice, Pten heterozygous (+/-) mice, Pten and Fyn double heterozygous (+/-) mice, or Fyn knockout (-/-) mice confirmed a role of FYN in alpha(v) integrin-mediated haptotaxis in glial cells. Our combined results provide direct biochemical and genetic evidence that PTENs protein phosphatase activity controls FYN kinase function in glioma cells and regulates migration in a PI3K/AKT-independent manner.

Molecular Basis for a Direct Interaction between the Syk Protein-tyrosine Kinase and Phosphoinositide 3-Kinase

After engagement of the B cell receptor for antigen, the Syk protein-tyrosine kinase becomes phosphorylated on multiple tyrosines, some of which serve as docking sites for downstream effectors with SH2 or other phosphotyrosine binding domains. The most frequently identified binding partner for catalytically active Syk identified in a yeast two-hybrid screen was the p85 regulatory subunit of phosphoinositide 3-kinase. The C-terminal SH2 domain of p85 was sufficient for mediating an interaction with tyrosine-phosphorylated Syk. Interestingly, this domain interacted with Syk at phosphotyrosine 317, a site phosphorylated in trans by the Src family kinase, Lyn, and identified previously as a binding site for c-Cbl. This site interacted preferentially with the p85 C-terminal SH2 domain compared with the c-Cbl tyrosine kinase binding domain. Molecular modeling studies showed a good fit between the p85 SH2 domain and a peptide containing phosphotyrosine 317. Tyr-317 was found to be essential for Syk to support phagocytosis mediated by FcγRIIA receptors expressed in a heterologous system. These studies establish a new type of p85 binding site that can exist on proteins that serve as substrates for Src family kinases and provide a molecular explanation for observations on direct interactions between Syk and phosphoinositide 3-kinase.

Rap1a null mice have altered myeloid cell functions suggesting distinct roles for the closely related Rap1a and 1b proteins

The Ras-related GTPases Rap1a and 1b have been implicated in multiple biological events including cell adhesion, free radical production, and cancer. To gain a better understanding of Rap1 function in mammalian physiology, we deleted the Rap1a gene. Although loss of Rap1a expression did not initially affect mouse size or viability, upon backcross into C57BL/6J mice some Rap1a−/− embryos died in utero. T cell, B cell, or myeloid cell development was not disrupted in Rap1a −/− mice. However, macrophages from Rap1a null mice exhibited increased haptotaxis on fibronectin and vitronectin matrices that correlated with decreased adhesion. Chemotaxis of lymphoid and myeloid cells in response to CXCL12 or CCL21 was significantly reduced. In contrast, an increase in FcR-mediated phagocytosis was observed. Because Rap1a was previously copurified with the human neutrophil NADPH oxidase, we addressed whether GTPase loss affected superoxide production. Neutrophils from Rap1a−/− mice had reduced fMLP-stimulated superoxide production as well as a weaker initial response to phorbol ester. These results suggest that, despite 95% amino acid sequence identity, similar intracellular distribution, and broad tissue distribution, Rap1a and 1b are not functionally redundant but rather differentially regulate certain cellular events.

Wnt signaling in triple negative breast cancer is associated with metastasis

BackgroundTriple Negative subset of (TN) Breast Cancers (BC), a close associate of the basal-like subtype (with limited discordance) is an aggressive form of the disease which convey unpredictable, and poor prognosis due to limited treatment options and lack of proven effective targeted therapies.MethodsWe conducted an expression study of 240 formalin-fixed, paraffin-embedded (FFPE) primary biopsies from two cohorts, including 130 TN tumors, to identify molecular mechanisms of TN disease.ResultsThe annotation of differentially expressed genes in TN tumors contained an overrepresentation of canonical Wnt signaling components in our cohort and others. These observations were supported by upregulation of experimentally induced oncogenic Wnt/β-catenin genes in TN tumors, recapitulated using targets induced by Wnt3A. A functional blockade of Wnt/β-catenin pathway by either a pharmacological Wnt-antagonist, WntC59, sulidac sulfide, or β-catenin (functional read out of Wnt/β-catenin pathway) SiRNA mediated genetic manipulation demonstrated that a functional perturbation of the pathway is causal to the metastasis- associated phenotypes including fibronectin-directed migration, F-actin organization, and invasion in TNBC cells. A classifier, trained on microarray data from β-catenin transfected mammary cells, identified a disproportionate number of TNBC breast tumors as compared to other breast cancer subtypes in a meta-analysis of 11 studies and 1,878 breast cancer patients, including the two cohorts published here. Patients identified by the Wnt/β-catenin classifier had a greater risk of lung and brain, but not bone metastases.ConclusionThese data implicate transcriptional Wnt signaling as a hallmark of TNBC disease associated with specific metastatic pathways.

CSK Controls Retinoic Acid Receptor (RAR) Signaling: a RAR-c-SRC Signaling Axis Is Required for Neuritogenic Differentiation

ABSTRACT Herein, we report the first evidence that c-SRC is required for retinoic acid (RA) receptor (RAR) signaling, an observation that suggests a new paradigm for this family of nuclear hormone receptors. We observed that CSK negatively regulates RAR functions required for neuritogenic differentiation. CSK overexpression inhibited RA-mediated neurite outgrowth, a result which correlated with the inhibition of the SFK c-SRC. Consistent with an extranuclear effect of CSK on RAR signaling and neurite outgrowth, CSK overexpression blocked the downstream activation of RAC1. The conversion of GDP-RAC1 to GTP-RAC1 parallels the activation of c-SRC as early as 15 min following all-trans-retinoic acid treatment in LA-N-5 cells. The cytoplasmic colocalization of c-SRC and RARγ was confirmed by immunofluorescence staining and confocal microscopy. A direct and ligand-dependent binding of RAR with SRC was observed by surface plasmon resonance, and coimmunoprecipitation studies confirmed the in vivo binding of RARγ to c-SRC. Deletion of a proline-rich domain within RARγ abrogated this interaction in vivo. CSK blocked the RAR-RA-dependent activation of SRC and neurite outgrowth in LA-N-5 cells. The results suggest that transcriptional signaling events mediated by RA-RAR are necessary but not sufficient to mediate complex differentiation in neuronal cells. We have elucidated a nongenomic extranuclear signal mediated by the RAR-SRC interaction that is negatively regulated by CSK and is required for RA-induced neuronal differentiation.

PHA665752, a small-molecule inhibitor of c-Met, inhibits hepatocyte growth factor-stimulated migration and proliferation of c-Met-positive neuroblastoma cells

Backgroundc-Met is a tyrosine kinase receptor for hepatocyte growth factor/scatter factor (HGF/SF), and both c-Met and its ligand are expressed in a variety of tissues. C-Met/HGF/SF signaling is essential for normal embryogenesis, organogenesis, and tissue regeneration. Abnormal c-Met/HGF/SF signaling has been demonstrated in different tumors and linked to aggressive and metastatic tumor phenotypes. In vitro and in vivo studies have demonstrated inhibition of c-Met/HGF/SF signaling by the small-molecule inhibitor PHA665752. This study investigated c-Met and HGF expression in two neuroblastoma (NBL) cell lines and tumor tissue from patients with NBL, as well as the effects of PHA665752 on growth and motility of NBL cell lines. The effect of the tumor suppressor protein PTEN on migration and proliferation of tumor cells treated with PHA665752 was also evaluated.MethodsExpression of c-Met and HGF in NBL cell lines SH-EP and SH-SY5Y and primary tumor tissue was assessed by immunohistochemistry and quantitative RT-PCR. The effect of PHA665752 on c-Met/HGF signaling involved in NBL cell proliferation and migration was evaluated in c-Met-positive cells and c-Met-transfected cells. The transwell chemotaxis assay and the MTT assay were used to measure migration and proliferation/cell-survival of tumor cells, respectively. The PPAR-γ agonist rosiglitazone was used to assess the effect of PTEN on PHA665752-induced inhibition of NBL cell proliferation/cell-survival and migrationResultsHigh c-Met expression was detected in SH-EP cells and primary tumors from patients with advanced-stage disease. C-Met/HGF signaling induced both migration and proliferation of SH-EP cells. Migration and proliferation/cell-survival were inhibited by PHA665752 in a dose-dependent manner. We also found that induced overexpression of PTEN following treatment with rosiglitazone significantly enhanced the inhibitory effect of PHA665752 on NBL-cell migration and proliferation.Conclusionc-Met is highly expressed in most tumors from patients with advanced-stage, metastatic NBL. Furthermore, using the NBL cell line SH-EP as a model, PHA665752 was shown to inhibit cMet/HGF/SF signaling in vitro, suggesting c-Met inhibitors may have efficacy for blocking local progression and/or metastatic spread of c-Met-positive NBL in vivo. These are novel findings for this disease and suggest that further studies of agents targeting the c-Met/HGF axis in NBL are warranted

Molecular determinants of trastuzumab efficacy: What is their clinical relevance?

Trastuzumab-containing therapy is a standard of care for human epidermal growth factor receptor-2 (HER2)-positive breast cancer. In pre-clinical models, a wide range of molecular mechanisms have been associated with reduced sensitivity to trastuzumab in vitro. These include expression of the truncated HER2 receptor fragment p95HER2, activating mutation of the gene encoding the class 1A catalytic subunit of phosphatidylinositol 3-kinase (PIK3CA), loss of phosphatase and tensin homolog (PTEN), activation of other downstream signal transducers, prevention of cell cycle arrest, increased signaling through alternative (HER or non-HER) tyrosine kinase receptors, and resistance to antibody-dependent cellular cytotoxicity. However, the clinical significance of these mechanisms as determinants of trastuzumab efficacy in vivo has been unclear. Here, we review clinical studies of potential predictive biomarkers of trastuzumab efficacy in HER2-positive breast cancer and consider whether evaluation of such markers might inform patient selection for therapy. We find that clinical evidence relating to potential predictive biomarkers is mostly limited to small, retrospective studies, many of which have yielded conflicting findings. Some trends are evident in the retrospective data and in biomarker analyses from randomized clinical trials, particularly relating to activation of the phosphatidylinositol 3-kinase pathway, but none is sufficiently strong to form a basis for patient selection. This may be explained by the fact that multiple mechanisms of action determine the clinical efficacy of trastuzumab. In the absence of novel, validated biomarkers of efficacy, trastuzumab eligibility should continue to be based on evaluation of HER2 status according to standard methods.

Differential activation of Wnt-β-catenin pathway in triple negative breast cancer increases MMP7 in a PTEN dependent manner.

Mutations of genes in tumor cells of Triple Negative subset of Breast Cancer (TNBC) deregulate pathways of signal transduction. The loss of tumor suppressor gene PTEN is the most common first event associated with basal-like subtype (Martins, De, Almendro, Gonen, and Park, 2012). Here we report for the first time that the functional upregulation of secreted-MMP7, a transcriptional target of Wnt-β-catenin signature pathway in TNBC is associated to the loss of PTEN. We identified differential expression of mRNAs in several key-components genes, and transcriptional target genes of the Wnt-β-catenin pathway (WP), including beta-catenin, FZD7, DVL1, MMP7, c-MYC, BIRC5, CD44, PPARD, c-MET, and NOTCH1 in FFPE tumors samples from TNBC patients of two independent cohorts. A similar differential upregulation of mRNA/protein for beta-catenin, the functional readout of WP, and for MMP7, a transcriptional target gene of beta-catenin was observed in TNBC cell line models. Genetic or pharmacological attenuation of beta-catenin by SiRNA or WP modulators (XAV939 and sulindac sulfide) and pharmacological mimicking of PTEN following LY294002 treatment downregulated MMP7 levels as well as enzymatic function of the secreted MMP7 in MMP7 positive PTEN-null TNBC cells. Patient data revealed that MMP7 mRNA was high in only a subpopulation of TNBC, and this subpopulation was characterized by a concurrent low expression of PTEN mRNA. In cell lines, a high expression of casein-zymograph-positive MMP7 was distinguished by an absence of functional PTEN. A similar inverse relationship between MMP7 and PTEN mRNA levels was observed in the PAM50 data set (a correlation coefficient of -0.54). The PAM50 subtype and outcome data revealed that the high MMP7 group had low pCR (25%) and High Rd (74%) in clinical stage T3 pathologic response in contrast to the high pCR (40%) and low residual disease (RD) (60%) of the low MMP7 group.

PI3K-AKT-mTOR inhibitors in breast cancers: From tumor cell signaling to clinical trials.

&NA; Breast cancer (BC) is the most common women cancer and second most common cause of cancer death in women. A woman living in the United States has 12.3% lifetime risk of being diagnosed with BC. From the genomics point of view, the most common three subtypes of BC encountered in clinics are HR +, HER2 +, and TNBC or basal‐like BC. Estrogen receptor (ER) status or HER2 amplification or chemotherapy is not sufficient to understand the underlying mechanisms of disease progression and resistance (de novo or acquire). Although hormonal therapy and HER2‐directed therapies have produced a considerable positive outcome in HR + and HER2 + BC respectively, there are no established targeted agents for TNBC and basal‐like BC. While PARP inhibitors have shown promising activity in BRCA‐related cancers, its value in the treatment of TNBC remains to be demonstrated. The PI3K‐AKT‐mTOR signaling pathway plays a crucial role in the initiation and progress in tumorigenesis including breast tumorigenesis and regulates critical cellular functions including survival, proliferation, and metabolism. This article aims to understand the role of PI3K‐mTORC1/C2 alterations in determining the clinical outcome in the specific breast cancer subtypes. The understanding of the tumor cell signaling will help us in the decision‐making the process for obtaining the treatment modalities towards further advancement of the precision medicine. In this review, we will restrict our discussion to a basic understanding of the biology of subtype‐specific BC and several targeted agents under development for the treatment of BC.