PTEN-deficient Cells Research Articles

Structure-Based Design of Orally Bioavailable 1H-Pyrrolo[3,2-c]pyridine Inhibitors of Mitotic Kinase Monopolar Spindle 1 (MPS1)

The protein kinase MPS1 is a crucial component of the spindle assembly checkpoint signal and is aberrantly overexpressed in many human cancers. MPS1 is one of the top 25 genes overexpressed in tumors with chromosomal instability and aneuploidy. PTEN-deficient breast tumor cells are particularly dependent upon MPS1 for their survival, making it a target of significant interest in oncology. We report the discovery and optimization of potent and selective MPS1 inhibitors based on the 1H-pyrrolo[3,2-c]pyridine scaffold, guided by structure-based design and cellular characterization of MPS1 inhibition, leading to 65 (CCT251455). This potent and selective chemical tool stabilizes an inactive conformation of MPS1 with the activation loop ordered in a manner incompatible with ATP and substrate-peptide binding; it displays a favorable oral pharmacokinetic profile, shows dose-dependent inhibition of MPS1 in an HCT116 human tumor xenograft model, and is an attractive tool compound to elucidate further the therapeutic potential of MPS1 inhibition.

Increased Concentrations of Fructose 2,6-Bisphosphate Contribute to the Warburg Effect in Phosphatase and Tensin Homolog (PTEN)-deficient Cells

Unlike normal differentiated cells, tumor cells metabolize glucose via glycolysis under aerobic conditions, a hallmark of cancer known as the Warburg effect. Cells lacking the commonly mutated tumor suppressor PTEN exhibit a glycolytic phenotype reminiscent of the Warburg effect. This has been traditionally attributed to the hyperactivation of PI3K/Akt signaling that results from PTEN loss. Here, we propose a novel mechanism whereby the loss of PTEN negatively affects the activity of the E3 ligase APC/C-Cdh1, resulting in the stabilization of the enzyme PFKFB3 and increased synthesis of its product fructose 2,6-bisphosphate (F2,6P2). We discovered that when compared with wild-type cells, PTEN knock-out mouse embryonic fibroblasts (PTEN KO MEF) have 2-3-fold higher concentrations of F2,6P2, the most potent allosteric activator of the glycolytic enzyme phosphofructokinase-1 (PFK-1). Reintroduction of either wild-type or phosphatase mutant PTEN in the PTEN KO cells effectively lowers F2,6P2 to the wild-type levels and reduces their lactate production. PTEN KO cells were found to have high protein levels of PFKFB3, which directly contribute to the increased concentrations of F2,6P2. PTEN enhances interaction between PFKFB3 and Cdh1, and overexpression of Cdh1 down-regulates the PFKFB3 protein level in wild-type, but not in PTEN-deficient cells. Importantly, we found that the degradation of endogenous PFKFB3 in PTEN KO cells occurs at a slower rate than in wild-type cells. Our results suggest an important role for F2,6P2 in the metabolic reprogramming of PTEN-deficient cells that has important consequences for cell proliferation.

Association Between S6K1 Phosphorylation and Cytotoxic Efficacy Of S6K1 Inhibitors

S6K1 (ribosomal protein S6 Kinase 1) is emerging as a potential target for counteracting the glucose-dependent survival programs induced by oncogenes. In PTEN-deficient cells, previous analysis revealed that inactivating S6K1 was sufficient to reduce glycolysis and induce programmed cell death. In BCR-ABL+ cells, we found that S6K1 inactivation was cytotoxic when combined with a fatty acid oxidation inhibitor.To begin to translate these findings, we have investigated the cytotoxic efficacy of a panel of S6K1 inhibitors. Although all compounds were efficient inhibitors of S6K1 phosphorylation of downstream substrates, there was one class of inhibitors that strongly induced the phosphorylation of S6K1 itself. These inhibitors were not cytotoxic for PTEN-deficient cells. In contrast, inhibitors that avoided strong phosphorylation of S6K1 overcame the pro-survival program in PTEN-deficient cells. These results suggest that S6K1 inhibition may be beneficial as a chemotherapeutic approach, but that inhibitors should be selected to avoid the phosphorylation of S6K1 itself while also inhibiting kinase activity. Disclosures:No relevant conflicts of interest to declare.

The Potent PI3K-δ,γ Inhibitor, IPI-145, Exhibits Preclinical Activity In Murine and Human T-Cell Acute Lymphoblastic Leukemia

Abstract Phosphoinositide-3 kinases (PI3Ks) are key cellular signaling proteins that act as a central node for relaying signals from cell surface receptors to downstream mediators, such as AKT. The PI3K-δ and PI3K-γ isoforms are preferentially expressed in normal and malignant leukocytes where they play critical roles in cell differentiation, migration, and proliferation. Constitutive activity of the PI3K pathway is common in T-cell acute lymphoblastic leukemia (T-ALL) and frequently involves the deletion of PTEN, the phosphatase that negatively regulates the PI3K pathway. An important role for the PI3K-δ and PI3K-γ isoforms has been demonstrated in the Pten-deleted genetically engineered murine model of T-ALL in conjunction with PI3K-δ and/or PI3K-γ gene knock outs (Subramanian et al, Cancer Cell, 2012). IPI-145 is a potent inhibitor of PI3K-δ and PI3K-γ currently being studied in a Phase 1 trial (IPI-145-02) in patients with advanced hematologic malignancies, including T-ALL (ClinicalTrials.gov NCT01476657). We performed in vitro studies to address the sensitivity of human and murine T-ALL cell lines to IPI-145 and to additional PI3K inhibitors with defined isoform selectivity. The human T-ALL cells examined were from cell lines that lack PTEN protein expression (Loucy, MOLT-4, CCRF-CEM, CEM/C2, p12 Ichikawa, and Karpas-45) and cell lines that express PTEN protein (MOLT13 and MOLT16). In addition, two murine cell lines derived from a Pten-deleted model of T-ALL (LPN049 and LPN236) were studied. The expression levels of class I PI3K isoforms were determined by western blotting and quantitative RT-PCR, which revealed varying levels of protein and RNA expression across the cell lines. In vitro treatment of human T-ALL cells with IPI-145 resulted in variable degrees of growth inhibition, with the PTEN-deficient Loucy cell line demonstrating the greatest sensitivity with an IC50 of 245 nM. In the cell lines tested, growth inhibition to IPI-145 was only seen in PTEN-deficient human cell lines, whereas all PTEN-expressing human T-ALL cell lines were resistant to IPI-145 (IC50 > 10 uM). However, not all PTEN-deficient human T-ALL cells demonstrated sensitivity to IPI-145 (e.g., CEM/C2), indicating that loss of PTEN does not confer sensitivity to PI3K inhibition in all settings. Inhibition of phospho-AKT (pAKT) correlated with growth inhibition, with an IC50 of 286 nM in the Loucy cell line. Studies to evaluate the mechanism of growth inhibition revealed that IPI-145 treatment resulted in apoptosis of sensitive cells as measured by 7-AAD and Annexin V staining. Cell lines derived from the Pten-deleted murine T-ALL model were also sensitive to IPI-145 with IC50s in the 300-600 nM range as measured by MTT assay. In addition, IPI-145 led to apoptosis, as measured by cleaved Caspase 3 and 7-AAD/Annexin V. Interestingly, Pten-deleted murine T-ALL cell lines showed down-regulation of pAKT and c-MYC expression with IPI-145 in a dose responsive manner that corresponded with increasing activated Caspase-3 expression. In NOTCH1-expressing murine T-ALL cell lines, down regulation of NOTCH1 and activated NOTCH1 was also observed in parallel with c-MYC down-regulation. To explore further the individual contributions of the varying PI3K isoforms on T-ALL cell growth, the effect of IPI-145 on tumor cell growth was compared with PI3K-δ, PI3K-δ,γ, and PI3K-β selective compounds in the Loucy PTEN-deficient T-ALL cell line. These experiments support an anti-leukemic effect for both PI3K-δ and PI3K-γ inhibition and indicate that the greatest effect is seen with combined PI3K-δ and PI3K-γ inhibition. A role for PI3K-β in T-ALL cell survival was not observed. Evaluation of the in vivo activity of IPI-145 on Loucy xenografts, as well as PTEN-expressing MOLT-13 xenografts, is ongoing. Together, these data provide a strong rationale for combined targeted inhibition of PI3K-δ and PI3K-γ in T-ALL. Disclosures: Huang: Infinity Pharmaceuticals, Inc.: Research Funding. Proctor:Infinity Pharmaceuticals, Inc.: Employment. Yang:Infinity Pharmaceuticals, Inc.: Research Funding. Gao:Infinity Pharmaceuticals, Inc.: Research Funding. Zhang:Infinity Pharmaceuticals, Inc.: Research Funding. Huang:Infinity Pharmaceuticals, Inc.: Research Funding. Changelian:Infinity Pharmaceuticals, Inc.: Employment. Kutok:Infinity Pharmaceuticals, Inc.: Employment. McGovern:Infinity Pharmaceuticals, Inc.: Employment. You:Infinity Pharmaceuticals, Inc.: Research Funding.

Abstract C215: Sensitivity of PTEN-deficient prostate carcinoma xenografts to ionizing radiation through inhibition of treatment-induced CXCL8 signaling.

Abstract Background: CXCL8 signaling levels are elevated in localized high grade prostate cancer (CaP). We have shown exposure of CaP cells to chemical DNA-damaging agents potentiates CXCL8 signaling, which underpins an autocrine mode of therapeutic resistance. Data from in vitro and in vivo CaP models has shown loss of the tumor suppressor PTEN also increases expression of the pro-inflammatory chemokine CXCL8. Experiments were designed to determine whether exposure to ionising radiation (IR) selectively induced CXC-chemokine signaling in PTEN-deficient CaP cells, and to determine how CXCL8 signaling may modulate their radiosensitivity. Methods: shRNA-directed strategies were used to establish cell-based models of CaP with differential expression of PTEN. These clonal (DU145) and heterogeneous (22Rv1) populations were subjected to IR under normal or hypoxic culture conditions. PTEN was reconstituted in PC3 cells and was driven by tetracycline-regulated expression of the gene. Changes in chemokine expression were analyzed by RT-PCR, immunoblotting and ELISA. Autocrine CXCL8 signaling was attenuated using siRNA to down-regulate gene expression of its receptors, CXCR1 and CXCR2. The effects of modulating chemokine signaling on cell viability following exposure to clinically-relevant doses of IR were assessed by colony formation assays, cell proliferation assays, and analysis of apoptosis and cellular senescence. The effect of CXCL8 signaling inhibition in vivo was determined using a PC3 xenograft model in SCID mice. The cell penetrating pepducin, x1/2pal-i3, was used to attenuate both CXCR1 and CXCR2 and tumor growth was assessed via caliper measurements. Results: Exposure to IR (3 Gy) increased gene expression of CXCL8, CXCR1 and CXCR2 - with PTEN-deficiency enhancing this response. Loss of PTEN expression differentially modulated the radiosensitivty of CaP cell lines: PTEN-depletion conferred relative radioresistance in DU145 cells but made 22RV1 cells more radiosensitive. However, the inhibition of CXCL8 signaling in all PTEN-depleted models resulted in consistently increased radiosensitivity (SER 1.2, 1.13, and 1.39 in DU145, 22RV1, and PC3 CaP cells, respectively; p<0.05). Reconstitution of PTEN expression in PC3 cells abrogated the capacity of CXCL8 signaling blockade to confer radiosensitivity. The combination of IR and CXCL8 signaling-inhibition conferred increased apoptosis in DU145 cells (p53 mutant) but induced premature senescence in 22RV1 cells (p53 WT). In vivo, treatment of PC3 xenografts with x1/2pal-i3 combined with IR (3 Gy) resulted in a significant delay in tumor growth compared to control (median quadrupling time: 42 day x1/2pal-i3 & IR vs. 32 day control & IR; p<0.05). Subsequent analysis of gene expression in these tumors confirmed that CXCL8 signaling inhibition attenuated IR-induced expression of anti-apoptotic proteins Bcl-2 and C-FLIP. Conclusions: Our results demonstrate the role of treatment-induced CXCL8 signaling as a mechanism of resistance to IR in PTEN-depleted CaP cells. Inhibition of IR-induced CXCL8 signaling provides a novel therapeutic opportunity to enhance the radiosensitivity of PTEN-depleted CaP cells. However, mechanistic results indicate that other genetic factors including p53 status dictate the resultant induction of treatment-induced apoptosis. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C215. Citation Format: Chris WD Armstrong, Jonathan A. Coulter, Steven Walker, Richard D. Kennedy, Kevin M. Prise, Joe M. O'Sullivan, David JJ Waugh. Sensitivity of PTEN-deficient prostate carcinoma xenografts to ionizing radiation through inhibition of treatment-induced CXCL8 signaling. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C215.

Abstract B267: Inhibition of PLK4 as a therapeutic strategy for genomically unstable cancers deficient for PTEN.

Abstract The unique Polo-like kinase family member, PLK4, was identified as a novel therapeutic target for breast cancer through a systematic approach that integrated functional RNAi viability profiles with molecular profiling data. PLK4 is a conserved upstream regulator of centriole duplication that is aberrantly expressed in several tumor types. Dysregulation of PLK4 activity causes loss of centrosome numeral integrity, thereby promoting genomic instability, but could also enable cancer cells to tolerate its effects. A drug discovery program was initiated that resulted in the identification of CFI-400945, a first-in-class, potent and selective PLK4 small molecule inhibitor (IC50 = 2.8 nM, Ki = 0.26 nM). CFI-400945 is highly selective towards other PLK family members (PLK1, PLK2 and PLK3 IC50s >50 µM) and numerous other protein and lipid kinase classes. Consistent with PLK4 loss-of-function studies, cancer cells treated with CFI-400945 exhibit dysregulated centriole duplication, mitotic defects and cell death. Oral administration of CFI-400945 as a single agent once daily to mice bearing human cancer-derived cell line xenografts and patient-derived xenografts (PDX) results in significant inhibition of tumor growth at doses that are well-tolerated. Superior antitumor activity in vivo is observed towards PTEN-deficient tumor models compared to PTEN wild-type tumor models. Analysis of tumor xenografts from CFI-400945-treated mice demonstrated an increase in tumor cells with aberrant mitoses compared to vehicle-treated mice, and is consistent with observations from cell culture experiments. Together, these pharmacologic results support observations from functional genetic screening that inhibition of PLK4 kinase activity is lethal for PTEN-deficient cancer cells, and suggest a new mechanism-based approach for the treatment of patients whose tumors have defective PTEN. PLK4 dysregulation may represent an adaptation cancer cells have made to tolerate the effects of genomic instability induced by loss-of-function of PTEN or other mediators, such as TP53, ATM, BRCA1 and BRCA2, and thereby is a vulnerability that may be exploited for the design of cancer cell-selective therapies. The CTA to Health Canada for CFI-400945 received approval in July 2013, and an IND has been filed at the FDA, clearing the way for clinical evaluation of the molecule in the near future. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B267. Citation Format: Jacqueline M. Mason, Dan C.-c. Lin, Xin Wei, Yi Che, Yi Yao, Reza Kiarash, Graham C. Fletcher, Mark R. Bray, Guohua Pan, Tak W. Mak. Inhibition of PLK4 as a therapeutic strategy for genomically unstable cancers deficient for PTEN. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B267.

Abstract IA22: Rationale and current status of development of PI3K/TOR pathway inhibitors

Abstract The PI3K/AKT pathway is the most frequently mutated pathway in breast cancer, with mutation and/or amplification of the genes encoding the PI3K catalytic subunits p110α (PIK3CA) and p110β (PIK3CB), the PI3K regulatory subunit p85α (PIK3R1), receptor tyrosine kinases (RTKs) such as HER2 (ERBB2) and FGFR1, the PI3K activator K-Ras, the PI3K effectors AKT1, AKT2, and PDK1, and loss of the lipid phosphatases PTEN and INPP4B. The three genes PIK3CA, PIK3CB, and PIK3CD encode the homologous p110α , p110β, and p110δ isozymes, respectively. Expression of p110δ; is largely restricted to immune and hematopoietic cells, whereas p110α and p110β are ubiquitously expressed. The p110α isozyme is essential for signaling and growth of tumors driven by PIK3CA mutations, RTKs, and/or mutant Ras, whereas p110β lies downstream of GPCRs and has been shown to mediate tumorigenesis in PTEN-deficient cells. PIK3CA mutations are the most common genetic alterations of this pathway, where ≥80% occur within the helical (E542K and E545K) and kinase (H1047R) domains of p110α. Such mutations confer increased catalytic activity through different mechanisms, but both induce characteristics of cellular transformation including growth factor- and anchorage-independent growth, and resistance to anoikis. Several drugs targeting multiple levels of the PI3K network (i.e., PI3K, AKT, mTOR) have been developed (Table 1). A number of ATP-mimetics that bind competitively and reversibly to the ATP-binding pocket of p110 are in early clinical development. These include the pan-PI3K inhibitors BKM120, XL-147, PX-866, PKI-587, and GDC-0941, the p110α-specific inhibitors BYL719, GDC-0032, and INK-1117, the p110δ-specific inhibitor CAL-101, and the dual PI3K/mTOR inhibitors BEZ235, BGT226, PF-4691502, GDC-0980, and XL-765. The pan-PI3K and p110α-specific inhibitors are equally potent against oncogenic p110α mutants. The rationale for the development of isozyme-specific antagonists is to allow higher doses of anti-p110α and anti-p110β drugs to be delivered without incurring side-effects caused by pan-PI3K inhibitors. Recently completed phase I trials with BKM120, BEZ235, and XL-147 showed that treatment partially inhibited PI3K as measured by levels of P-S6 and P-AKT in patients' skin or tumors, and 2-deoxy-2-[18F]fluoro-D-glucose (FDG) uptake measured by PET. Main toxicities were rash, hyperglycemia, diarrhea, fatigue and, mood alterations. Few clinical responses were observed in patients with and without detectable PI3K pathway mutations, although screening for genetic lesions in this pathway was not comprehensive. Both allosteric and ATP-competitive pan-inhibitors of the three isoforms of AKT are also being developed. AZD5363, GDC-0068, GSK2141795, and GSK690693 are ATP-competitive compounds which have shown antitumor activity in preclinical models and recently entered phase I trials. Allosteric inhibitors such as MK-2206 bind to the AKT PH domain and/or hinge region to promote an inactive conformation of the AKT protein that is unable to bind to the plasma membrane. MK-2206 inhibits AKT signaling in vivo, and suppresses growth of breast cancer xenografts harboring PIK3CA mutations or ERBB2 amplification. Phase I data showed that treatment with MK-2206 decreases levels of P-AKT, P-PRAS40, and P-GSK3β in tumor cells, peripheral blood mononuclear cells, and hair follicles. Another approach to block this pathway has been the development of ATP-competitive inhibitors of the mTOR kinase, which block both mTORC1 and mTORC2. Several dual TORC1/2 inhibitors have been identified, including INK128 (Intellikine), CC223 (Celgene), AZD2014 (AstraZeneca), and Palomid 529 (Paloma Pharmaceuticals). Dual PI3K/mTOR inhibitors have also been developed in the hope of overcoming the loss of feedback inhibition or PI3K activation observed with rapalogs. The mTORC1 pathway is one of the prominent negative feedback regulators of the PI3K pathway; inhibition of mTORC1 can release this feedback inhibition and activate the PI3K pathway19. BEZ235, a dual PI3K/mTOR inhibitor, showed higher anti-proliferative activity than rapamycin in a preclinical study trastuzumab-resistant and –sensitive human breast cancer cell lines. In breast cancer, dual PI3K/mTOR inhibitors are being combined with everolimus, endocrine therapies (exemestane and letrozole), chemotherapy (paclitaxel), and anti-HER2 therapy (trastuzumab). Citation Format: Carlos L. Arteaga. Rationale and current status of development of PI3K/TOR pathway inhibitors. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr IA22.

Synthetic Lethal Targeting of PTEN-Deficient Cancer Cells Using Selective Disruption of Polynucleotide Kinase/Phosphatase

A recent screen of 6,961 siRNAs to discover possible synthetic lethal partners of the DNA repair protein polynucleotide kinase/phosphatase (PNKP) led to the identification of the potent tumor suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Here, we have confirmed the PNKP/PTEN synthetic lethal partnership in a variety of different cell lines including the PC3 prostate cancer cell line, which is naturally deficient in PTEN. We provide evidence that codepletion of PTEN and PNKP induces apoptosis. In HCT116 colon cancer cells, the loss of PTEN is accompanied by an increased background level of DNA double-strand breaks, which accumulate in the presence of an inhibitor of PNKP DNA 3'-phosphatase activity. Complementation of PC3 cells with several well-characterized mutated PTEN cDNAs indicated that the critical function of PTEN required to prevent toxicity induced by an inhibitor of PNKP is most likely associated with its cytoplasmic lipid phosphatase activity. Finally, we show that modest inhibition of PNKP in a PTEN knockout background enhances cellular radiosensitivity, suggesting that such a "synthetic sickness" approach involving the combination of PNKP inhibition with radiotherapy may be applicable to PTEN-deficient tumors.

Blockade of reactive oxygen species and Akt activation is critical for anti-inflammation and growth inhibition of metformin in phosphatase and tensin homolog-deficient RAW264.7 cells

Context: Metformin is widely used for treatment of type 2 diabetes and has a potential application on the treatment of inflammation and cancer. Phosphatase and tensin homolog (PTEN) plays a critical role in cancer cell growth and inflammation; however, precise mechanisms remain unclear.Objective: We aimed to investigate the possible mechanisms of how PTEN regulates metformin against cell growth and inflammation.Materials and methods: We established PTEN knockdown in RAW264.7 murine macrophages (shPTEN cells) to detect inflammatory mediators using commercial kits, production of reactive oxygen species (ROS) by flow cytometry, cell growth by MTT assay and phosphorylated levels of signal molecules by western blot.Results: The shPTEN cells had a significant large amount of inflammatory mediators, such as inducible nitric oxide synthase (iNOS)/nitric oxide (NO) and cyclooxygenase-2 (COX-2)/prostaglandin E2 (PGE2); and also elevated the production of ROS and increased cell proliferation. These effects were accompanied with the activation of Akt and p38 mitogen-activated protein kinase (MAPK), and the inactivation of an AMP-activated protein kinase (AMPK) activator and extracellular signal-regulated kinase 1/2. Pretreatment with metformin not only blocked these inflammatory mediators, but also caused growth inhibition induced by significant apoptosis. Furthermore, inactivation of Akt, blockade of ROS generation and independence of activations of AMPK and MAPK by metformin were also observed.Conclusion: Macrophages with PTEN deficiency developed a continuous inflammatory microenvironment, which further aggravated tumor cell growth. Moreover, metformin affected PTEN-deficient cells dependent of inhibition of ROS production and Akt activation against enlarged inflammatory mediators and/or cell growth in shPTEN cells.

BAD Dephosphorylation and Decreased Expression of MCL-1 Induce Rapid Apoptosis in Prostate Cancer Cells

PTEN loss and constitutive activation of the PI3K signaling pathway have been associated with advanced androgen-independent prostate cancer. PTEN-deficient prostate cancer C42Luc cells survive in serum-free media and show relative resistance to apoptosis even in the presence of the PI3K inhibitor ZSTK474. Yet, when ZSTK474 is combined with the translation inhibitor cycloheximide, C42Luc cells undergo apoptosis within 6 hours. We identified dephosphorylation of BAD (Bcl2-associated death promoter) as a main apoptosis-regulatory molecule downstream from PI3K, and loss of MCL-1 (Myeloid cell leukemia -1) as a major target of cycloheximide. The combination of MCL-1 knockdown and expression of phosphorylation-deficient mutant BAD2SA is sufficient to trigger rapid apoptosis in prostate cancer cells. These results establish the mechanism for the synergistic induction of apoptosis by the combination of a PI3K inhibitor and of a protein synthesis inhibitor in PTEN-deficient prostate cancer cells.

PTEN deficiency is associated with reduced sensitivity to mTOR inhibitor in human bladder cancer through the unhampered feedback loop driving PI3K/Akt activation

Background:Preclinical studies have shown that PTEN loss enhances sensitivity to mammalian target of Rapamycin (mTOR) inhibitors because of facilitated PI3K (phosphatidylinositol-3 kinase)/Akt activation and consecutive stimulation of the mTOR pathway. In patients with advanced transitional cell carcinoma (TCC) treated with the mTOR inhibitor everolimus, PTEN loss was, however, associated with resistance to treatment.Methods:Transitional cell carcinoma specimens, human bladder cancer cells and derived mouse xenografts were used to evaluate how the PTEN status influences the activity of mTOR inhibitors.Results:Transitional cell carcinoma patients with a shorter progression-free survival under everolimus exhibited PTEN deficiency and increased Akt activation. Moreover, PTEN-deficient bladder cancer cells were less sensitive to rapamycin than cells expressing wild-type PTEN, and rapamycin strikingly induced Akt activation in the absence of functional PTEN. Inhibition of Akt activation by the PI3K inhibitor wortmannin interrupted this rapamycin-induced feedback loop, thereby enhancing the antiproliferative effects of the mTOR inhibitor both in vitro and in vivo.Conclusion:Facilitation of Akt activation upon PTEN loss can have a more prominent role in driving the feedback loop in response to mTOR inhibition than in promoting the mTOR pathway. These data support the use of both PI3K and mTOR inhibitors to treat urothelial carcinoma, in particular in the absence of functional PTEN.

Regulation of the Tumor Suppressor PTEN through Exosomes: A Diagnostic Potential for Prostate Cancer

PTEN is a potent tumor-suppressor protein. Aggressive and metastatic prostate cancer (PC) is associated with a reduction or loss of PTEN expression. PTEN reduction often occurs without gene mutations, and its downregulation is not fully understood. Herein, we show that PTEN is incorporated in the cargo of exosomes derived from cancer cells. PTEN is not detected in exosomes derived from normal, noncancerous cells. We found that PTEN can be transferred to other cells through exosomes. In cells that have a reduction or complete loss of PTEN expression, the transferred PTEN is competent to confer tumor-suppression activity to acceptor cells. In PC patients, we show that PTEN is incorporated in the cargo of exosomes that circulate in their blood. Interestingly, normal subjects have no PTEN expression in their blood exosomes. Further, we found that the prostate-specific antigen (PSA) is incorporated in PC patients’ and normal subjects’ blood exosomes. These data suggest that exosomal PTEN can compensate for PTEN loss in PTEN deficient cells, and may have diagnostic value for prostate cancer.

PTEN loss defines a PI3K/AKT pathway-dependent germinal center subtype of diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) represents a heterogeneous diagnostic category with distinct molecular subtypes that can be defined by gene expression profiling. However, even within these defined subtypes, heterogeneity prevails. To further elucidate the pathogenesis of these entities, we determined the expression of the tumor suppressor phosphatase and tensin homolog (PTEN) in 248 primary DLBCL patient samples. These analyses revealed that loss of PTEN was detectable in 55% of germinal center B-cell-like (GCB) DLBCLs, whereas this abnormality was found in only 14% of non-GCB DLBCL patient samples. In GCB DLBCL, the PTEN status was inversely correlated with activation of the oncogenic PI3K/protein kinase B (AKT) pathway in both DLBCL cell lines and primary patient samples. Reexpression of PTEN induced cytotoxicity in PTEN-deficient GCB DLBCL cell line models by inhibiting PI3K/AKT signaling, indicating an addiction to this pathway in this subset of GCB DLBCLs. PI3K/AKT inhibition induced down-regulation of the transcription factor MYC. Reexpression of MYC rescued GCB DLBCL cells from PTEN-induced toxicity, identifying a regulatory mechanism of MYC expression in DLBCL. Finally, pharmacologic PI3K inhibition resulted in toxicity selectively in PTEN-deficient GCB DLBCL lines. Collectively, our results indicate that PTEN loss defines a PI3K/AKT-dependent GCB DLBCL subtype that is addicted to PI3K and MYC signaling and suggest that pharmacologic inhibition of PI3K might represent a promising therapeutic approach in these lymphomas.

Blockade of Glioma Proliferation Through Allosteric Inhibition of JAK2

The gene that encodes the epidermal growth factor receptor (EGFR) is frequently overexpressed or mutated in human cancers, including glioblastoma. However, the efficacy of EGFR-targeted small-molecule inhibitors or monoclonal antibodies in glioblastomas that also have mutation or deletion of the gene encoding phosphatase and tensin homolog (PTEN) has been modest. We found that EGFR signaling was blocked by a small molecule (G5-7) that selectively inhibited Janus kinase 2 (JAK2)-mediated phosphorylation and activation of EGFR and STAT3 (signal transducer and activator of transcription 3) by binding to JAK2, thereby decreasing the activity of downstream signaling by mTOR (mammalian target of rapamycin) and inducing cell cycle arrest. G5-7 inhibited the proliferation of PTEN-deficient glioblastoma cell lines harboring a constitutively active variant of EGFR (U87MG/EGFRvIII) and human glioblastoma explant neurosphere cultures, but the drug only weakly inhibited the proliferation of either glioblastoma cell lines that were wild type for EGFR and stably transfected with PTEN (U87MG/PTEN) or normal neural progenitor cells and astrocytes. Additionally, G5-7 reduced vascular endothelial growth factor (VEGF) secretion and endothelial cell migration and induced apoptosis in glioblastoma xenografts, thereby suppressing glioblastoma growth in vivo. Furthermore, G5-7 was more potent than EGFR or JAK2 inhibitors that interfere with either ligand or adenosine 5'-triphosphate (ATP) binding at impeding glioblastoma cell proliferation, demonstrating that this allosteric JAK2 inhibitor may be an effective clinical strategy.

ETS factors reprogram the androgen receptor cistrome and prime prostate tumorigenesis in response to PTEN loss

Studies of ETS-mediated prostate oncogenesis have been hampered by the lack of suitable experimental systems. Here we describe a new conditional mouse model which gives robust, homogenous ERG expression throughout the prostate. When combined with homozygous Pten loss, mice developed accelerated, highly penetrant invasive prostate cancer. In mouse prostate tissue, ERG significantly increased androgen receptor (AR) binding. Robust ERG-mediated transcriptional changes, observed only in the setting of Pten loss, included restoration of AR transcriptional outut and genes involved in cell death, migration, inflammation and angiogenesis. Similarly, ETV1 positively regulated AR cistrome and transcriptional output in ETV1-translocated, PTEN-deficient human prostate cancer cells. In two large clinical cohorts, ERG and ETV1 expression correlated with higher AR transcriptional output in PTEN-negative prostate cancer specimens. We propose that ETS factors cause prostate-specific transformation by altering the AR cistrome, priming the prostate epithelium to respond to aberrant upstream signals such as PTEN loss.

THU0117 Loss of PTEN in Myeloid Cells Controls Inflammatory Bone Destruction by Regulating the Osteoclastogenic Potential of Myeloid Cells

BackgroundLocal bone destruction in rheumatoid arthritis, psoriasisarthritis or ankylosing spondylitis is a serious health burden and the major cause of disability and severely reduced quality of life in these diseases....

The influence of growth hormone/insulin-like growth factor deficiency on prostatic dysplasia in pbARR2-Cre, PTEN knockout mice

Elevated insulin-like growth factor-I (IGF-I) serum levels and phosphatase and tensin homolog (PTEN) loss are prostate cancer (PCa) risk factors that enhance androgen-responsive and castration-resistant PCa xenografts growth. The impact of suppressed growth hormone (GH)/IGF-I levels on neoplastic initiation of PTEN-deficient prostate epithelia was assessed histologically and by epithelial-to-mesenchymal marker expression in Ghrhr D60G homozygous (lit/lit) and heterozygous (lit/+) pbARR2-Cre, PTEN(fl/fl) (PTEN-/-) mice. How suppressed GH/IGF-I levels impacted growth of PTEN-/- mouse-derived prostate cells (MPPK) was examined by growth and survival signaling of cells cultured in lit/+ or lit/lit serum. Body weight, prostate weight and serum GH and IGF-I levels were reduced in lit/lit relative to lit/+ PTEN-/- littermates. While the anterior lobes of lit/+ PTEN-/- prostates consistently presented swollen, indicative of ductal blockage, the degree of prostatic dysplasia in 15- and 20-week-old lit/lit and lit/+ PTEN-/- mice was indistinguishable as measured by normalized prostatic weight, tissue histology, or probasin, PSP94, E-cadherin, N-cadherin and vimentin expression. However, growth and AKT activation of MPPK cells was decreased when cultured in lit/lit serum as compared with lit/+ serum and restored in lit/lit serum supplemented with IGF-I and, to a lesser extent, GH. These results suggest that initiation of prostate carcinogenesis by loss of PTEN is not influenced by germline variation of genes encoding signaling molecules in the GH/IGF-I axis, but suggests that these factors may affect the progression of dysplastic phenotype and supports previous studies, indicating that the GH/IGF milieu does impact the growth of PTEN-deficient dysplastic prostatic cells once transformed.

Odontogenic ameloblast-associated protein (ODAM) inhibits growth and migration of human melanoma cells and elicits PTEN elevation and inactivation of PI3K/AKT signaling

BackgroundThe Odontogenic Ameloblast-associated Protein (ODAM) is expressed in a wide range of normal epithelial, and neoplastic tissues, and we have posited that ODAM serves as a novel prognostic biomarker for breast cancer and melanoma. Transfection of ODAM into breast cancer cells yields suppression of cellular growth, motility, and in vivo tumorigenicity. Herein we have extended these studies to the effects of ODAM on cultured melanoma cell lines.MethodsThe A375 and C8161 melanoma cell lines were stably transfected with ODAM and assayed for properties associated with tumorigenicity including cell growth, motility, and extracellular matrix adhesion. In addition, ODAM–transfected cells were assayed for signal transduction via AKT which promotes cell proliferation and survival in many neoplasms.ResultsODAM expression in A375 and C8161 cells strongly inhibited cell growth and motility in vitro, increased cell adhesion to extracellular matrix, and yielded significant cytoskeletal/morphologic rearrangement. Furthermore, AKT activity was downregulated by ODAM expression while an increase was noted in expression of the PTEN (phosphatase and tensin homolog on chromosome 10) tumor suppressor gene, an antagonist of AKT activation. Increased PTEN in ODAM-expressing cells was associated with increases in PTEN mRNA levels and de novo protein synthesis. Silencing of PTEN expression yielded recovery of AKT activity in ODAM-expressing melanoma cells. Similar PTEN elevation and inhibition of AKT by ODAM was observed in MDA-MB-231 breast cancer cells while ODAM expression had no effect in PTEN-deficient BT-549 breast cancer cells.ConclusionsThe apparent anti-neoplastic effects of ODAM in cultured melanoma and breast cancer cells are associated with increased PTEN expression, and suppression of AKT activity. This association should serve to clarify the clinical import of ODAM expression and any role it may serve as an indicator of tumor behavior.

Abstract IA17: Exploiting the synthetic lethal properties of selective PI3K-β inhibition in PTEN deficient cells with GSK2636771

Abstract The phosphoinositide 3-kinase (PI3K) pathway is among the most commonly mutated pathways in human cancer. The majority of first-generation PI3K inhibitors currently in clinical trials inhibit multiple PI3K isoforms. The PIK3CB gene encodes p110β isoform, which has been reported to be required for pathway activation in phosphatase and tensin homolog (PTEN) deficient cancer cells. The observed dependence of PTEN-deficient tumors on p110β provides an opportunity for identification of a novel isoform-selective therapeutic with a synthetic lethal effect. During an extensive knowledge-based lead identification and optimization effort, we identified substituted benzimidazole GSK2636771 as a potent, orally bioavailable, PI3Kβ-selective inhibitor. The observed enzymatic potency for PI3Kβ is approximately 1000 and 10 fold higher than the potency against PI3Kα and PI3δ respectively. Pre-clinical data demonstrate the synthetic lethal relationship between PTEN deficiencies and PI3K-β inhibition. PTEN-deficient cells dosed with GSK2636771 show concentration dependent decreases in cellular levels of phosphorylated AKT (pAKT), and PRAS40 both in-vitro and in-vivo. A 3-day proliferation assay performed on a large panel of cell lines (n=80) grown in-vitro demonstrates selective growth inhibition in PTEN-deficient cells at lower concentrations of GSK2636771. In-vivo studies in PTEN-deficient prostate cancer models also show dose dependent tumor growth delay. PTEN is commonly mutated, deleted, or epigenetically silenced in a wide range of solid tumors. Loss of PTEN protein is particularly frequent in prostate (50%), endometrial (57%), and triple negative breast cancers (30%). Prospective selection of patients with this protein loss serves as a development path through the course of study P3B115717 (NCT01458067), a Phase I/IIa first-time-in-human study with GSK2363771. This study is currently in dose-escalation.β Citation Format: Joel Greshock. Exploiting the synthetic lethal properties of selective PI3K-β inhibition in PTEN deficient cells with GSK2636771. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Synthetic Lethal Approaches to Cancer Vulnerabilities; May 17-20, 2013; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(5 Suppl):Abstract nr IA17.

Abstract A23: Genome-wide discovery of synthetic lethal interactions in PTEN-deficient human mammary epithelial cells

Abstract PTEN is one of the most frequently dysregulated tumor suppressor genes in human cancers, and PTEN deficiency is common in breast tumors, particularly those that belong to the aggressive basal-like breast cancer (BLBC) subtype. Because the BLBC subtype is itself very heterogeneous and basal-like tumors lack expression of cancer drug targets like HER2, there is currently no targeted therapy available for effective treatment. To systematically and comprehensively explore potential vulnerabilities in PTEN-deficient BLBC, we sought to discover genes that are synthetic lethal to PTEN loss using a functional genomics approach. We carried out a synthetic lethal siRNA screen in a pair of isogenic cell lines: an untransformed, non-tumorigenic human mammary epithelial cell line with molecular characteristics that closely mimic BLBCs (MCF10A), and a derivative cell line that harbored a targeted deletion of exon 2 in the PTEN gene (MCF10A-PTEN-/-). For greater sensitivity in detecting synthetic lethal effects, we used a high content screening system to determine total cell numbers by direct counting of stained cell nuclei after siRNA knock-down. Through the discovery of synthetic lethal interactions in these PTEN-deficient cell lines, we aim to identify novel components of the PTEN signaling network and uncover vulnerabilities in PTEN-deficient tumors. We first completed a pilot screen of kinase and phosphatase genes and identified synthetic lethal hits which were subsequently confirmed using multiple siRNA sequences for each gene. Our top candidate synthetic lethal genes were not directly involved in the PI3K-Akt signaling pathway, consistent with studies showing that therapeutic targeting of the PI3K pathway in PTEN-deficient cancers is not always effective. Using the strongest hit from the pilot screen as a positive synthetic lethal control, we further completed a whole-genome screen in the same pair of isogenic cell lines. We are currently validating the top candidate synthetic lethal genes and will explore if these putative synthetic lethal interactions are present in other PTEN-deficient breast cancer cell lines belonging to the BLBC subtype. Citation Format: Yew Chung Tang, John McPherson, Elisabeth Tan, Germaine Goh, Frederic Bard, Steve Rozen. Genome-wide discovery of synthetic lethal interactions in PTEN-deficient human mammary epithelial cells. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Synthetic Lethal Approaches to Cancer Vulnerabilities; May 17-20, 2013; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(5 Suppl):Abstract nr A23.