Loss Of PTEN Activity Research Articles

Abstract A060: Dysregulation of PTEN expression in a subset of Cancer Associated Fibroblasts by Tumor Secreted Factors in PDAC

Abstract Pancreatic Ductal Adenocarcinoma (PDAC) is a deadly malignancy. Cancer associated fibroblasts (CAFs) play a complex role in the PDAC tumor microenvironment (TME), with a subset contributing significantly to tumor progression. Phosphatase and tensin homolog (PTEN) is a tumor suppressor and its loss is associated with increased tumor aggressiveness. Our group previously demonstrated PTEN loss in SMA+ positive CAFS correlated with worsened outcomes in patients and in mouse PDAC models. Our group previously demonstrated the loss of PTEN in CAFS led to activation of Stat3, resulting in an immunosuppressive microenvironment (Lefler et al, 2022 PMID: 35803738). However, little is known of the signals produced by tumor cells or other cell types in the TME that trigger loss of PTEN in CAFs. This study aims to to elucidate the molecular mechanisms underlying PTEN loss in CAFs in PDAC. To address this gap, we employed single cell RNA sequencing of tumors from a mouse PDAC model and identified a (PDRGFRa+Lys6+Stat3+Pten-low) CAF subpopulation. Comparing normal pancreas epithelial cells to tumor cells in this data set, we identified the IL6 family of cytokines, (IL6; Oncostatin-M, OSM; and Leukemia Inhibitory Factor, LIF) and Transforming Growth Factor beta 1 (TGFb1) as potential ligands that regulated PTEN, while myeloid cells were a source of the IL6 family member Oncostatin M (OSM). Treatment of isolated CAFs with these factors revealed no significant difference in PTEN mRNA expression. Thus, we developed an in vitro reporter system in which a PTEN-GFP fusion protein is expressed in CAFs. Treating these CAFs with IL6, OSM and TGFb1 (but not LIF) led to a significant decrease in GFP fluorescence. Analysis of endogenous PTEN by western blot confirmed these results. We posited that expression of PTEN E3 ligases might be increased by treatment with these factors, leading to destruction of PTEN. In support of this hypothesis, the expression of E3 ligases WWP1 and WWP2 was increased by treatment with IL6 and OSM. Additionally, preliminary data has revealed that PTEN is oxidized in isolated CAFs, which causes loss of PTEN activity and potentially increased protein turnover. Current experiments are aimed at testing these potential mechanisms. To conclude, PTEN is dysregulated post-transcriptionally in CAFs. The mechanism of PTEN dysregulation could be via increased expression of E3 ligases that target PTEN and/or PTEN oxidation. Future efforts will be aimed at testing whether inhibition of these pathways can restore PTEN expression in mouse PDAC models. These pathways and interactions could be further exploited for therapeutic benefit in curbing PDAC progression. Citation Format: Ivo N. Woogeng, Lu Han, Samaneh Saberi, Cameron Bumbleburg, Joseph Beaudet, Sudarshana Sharma, Michael Ostrowski. Dysregulation of PTEN expression in a subset of Cancer Associated Fibroblasts by Tumor Secreted Factors in PDAC [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr A060.

Non-invasive PTEN mRNA brain delivery effectively mitigates growth of orthotopic glioblastoma

Messenger RNA (mRNA) based gene therapy holds great promise for treating various brain-related disorders including brain cancer. However, mRNA instability, inability to pass the blood-brain barrier (BBB) and lack of tumour targeting, hindering the further application of mRNA in brain disease therapy. Here we designed a new mRNA nanomedicine (ABNPs@mRNA) and demonstrated that it could effectively address the above challenges by combining three distinct design strategies: ApoE peptide based “two birds, one stone” targeting, cell membrane based biomimetic cloaking and tumour microenvironment responsive controlled drug release. To effectively target to glioblastoma (GBM), we loaded ABNPs@mRNA with phosphatase and tensin homolog deleted on chromosome 10 (PTEN) mRNA, a tumour suppressor that is mutated or inactive in 20–40% of GBM. Loss of PTEN activity in GBM patients correlates with therapeutic resistance, oncogenesis and poor prognosis. Together, our three design elements enabled ABNPs@mRNA to deliver a maximum PTEN mRNA concentration of 7.22% injection dose (ID)/g in brain tumour tissue. In the orthotopic GBM mouse models (U87MG and patient-derived CSC2 GSCs xenograft), treatment with ABNPs@mRNA resulted in a remarkable extension of median survival time relative to mice receiving PBS (49 d versus 23 d in U87MG and 40 d versus 23 d in CSC2 model). Importantly, ABNPs@mRNA nanomedicine caused negligible side effects in major organs including liver and kidney. Considering the stability, safety, non-invasive brain delivery and GBM inhibition efficacy, our new mRNA nanomedicine may unlock a new avenue for mRNA application in GBM inhibition and beyond.

In-silico designing of a potent ligand molecule against PTEN (Phosphatase and tensin homolog) implicated in Breast Cancer

Breast cancer has been attributed to be the second most common malignancy in females worldwide after skin cancer associated with a significantly high mortality rate. Tumor suppressor genes have an indispensable role in maintaining genomic integrity as well as cell cycle regulation. Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is one of the most frequently mutated human tumor suppressor genes, implicated in cell growth, survival, and suppressing tumor formation. As the tumor progresses to more advanced stages, genetic alterations tend to increase one such alteration is the mutation of the PTEN gene which is linked to programmed cell death and maintenance of cell cycle regulation. There is a syndrome known as Cowden syndrome associated with a high risk of breast cancer which is a result of an outcome of germline mutations in the PTEN gene. Loss of PTEN activity, either at the protein or genomic level, has been related to many primary and metastatic malignancies including breast cancer. This study focuses on developing a potential bioavailable ligand inhibitory molecule for PTEN, using a computer-aided drug design approach (CADD). A library of developed ligands consisting of 50 potential molecules was screened to find a potential candidate to be used for second generation drug development. Among them, LIG28 was adjudged as the most effective and potential PTEN inhibitor given its maximum binding affinity of ΔG -5.96Kcal/mole with a lower RMSD value. Carmer’s Rule of toxicity further revealed the compatibility and non-toxicity of the molecule. These observations underscore the importance of PTEN as a target in the development of tumorigenesis and the prognosis of breast cancer.

PTEN Protein Loss and Loss-of-Function Mutations in Gastric Cancers: The Relationship with Microsatellite Instability, EBV, HER2, and PD-L1 Expression.

Inactivation of phosphatase and tensin homolog (PTEN) is caused by multiple mechanisms, and loss of PTEN activity is related to the progression of various cancers. In gastric cancer (GC), the relationship between the loss of PTEN protein expression and various genetic alterations remains unclear. The effects of microsatellite instability (MSI), Epstein–Barr virus (EBV), HER2 overexpression, and PD-L1 expression on PTEN mutation have not been fully explored. We performed comprehensive cancer panel tests with a cohort of 322 tumor samples from patients with advanced GC. Immunohistochemistry for PTEN protein was performed in all cases, and the loss of protein expression was defined as a complete absence of nuclear staining. In total, 34 cases (10.6%) had pathogenic PTEN mutations, of which 19 (55.9%) showed PTEN protein loss. The most common PTEN variants associated with protein loss were p.R130 (n = 4) followed by p.R335, p.L265fs, and deletions (n = 2). All the ten nonsense mutations identified in the samples resulted in PTEN inactivation. In the remaining 288 GC cases with wild-type PTEN, protein loss was found in 35 cases (12.2%). Thus, PTEN mutations were significantly associated with PTEN protein loss (p = 5.232 × 10−10), high MSI (p = 3.936 × 10−8), and EBV-positivity (p = 0.0071). In conclusion, our results demonstrate that loss-of-function mutations in PTEN are a frequent genetic mechanism of PTEN inactivation in GC.

Hypoxic niches are endowed with a protumorigenic mechanism that supersedes the protective function of PTEN.

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy worldwide and is characterized by a fast-paced growth. Like other solid tumors, the HNSCC growth rate results in the development of hypoxic regions identified by the expression of hypoxia-inducible factor 1α (HIF-1α). Interestingly, clinical data have shown that pharmacological induction of intratumoral hypoxia caused an unexpected rise in tumor metastasis and the accumulation of cancer stem cells (CSCs). However, little is known on the molecular circuitries involved in the presence of intratumoral hypoxia and the augmented population of CSCs. Here we explore the impact of hypoxia on the behavior of HNSCC and define that the controlling function of phosphatase and tensin homolog (PTEN) over HIF-1α expression and CSC accumulation are de-regulated during hypoxic events. Our findings indicate that hypoxic niches are poised to accumulate CSCs in a molecular process driven by the loss of PTEN activity. Furthermore, our data suggest that targeted therapies aiming at the PTEN/PI3K signaling may constitute an effective strategy to counteract the development of intratumoral hypoxia and the accumulation of CSCs.-Nascimento-Filho, C. H. V., Webber, L. P., Borgato, G. B., Goloni-Bertollo, E. M., Squarize, C. H., Castilho, R. M. Hypoxic niches are endowed with a protumorigenic mechanism that supersedes the protective function of PTEN.

Prognostic and Predictive Implications of PTEN in Breast Cancer: Unfulfilled Promises but Intriguing Perspectives.

The characterization of tumor biology and consequently the identification of prognostic and predictive biomarkers represent key issues for the translational research in breast cancer (BC). Phosphatase and tensin homolog deleted on chromosome ten (PTEN), the negative regulator of the proto-oncogenic phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) pathway, constitutes one of the most intriguing tumor suppressor genes involved in a series of biological processes, such as cell growth and survival, cellular migration and genomic stability. Loss of PTEN activity, due to protein, genetic or epigenetic alterations, was reported in up to almost half of BC cases. Recently, besides the role of PTEN in the pathogenesis of BC, investigated for over 20 years after the PTEN discovery, several retrospective and prospective translational studies, in the early and advanced setting, reported controversial results regarding the association between PTEN functional status and both clinical outcome and response to various BC treatments. This review explores the pre-clinical and clinical role of PTEN in BC with regard to the potential association of PTEN with prognosis and treatment response or resistance, underlying the complexity of the interpretation of available results and suggesting potential future perspectives.

The Role of PTEN in Innate and Adaptive Immunity.

The lipid and protein phosphatase and tensin homolog (PTEN) controls the differentiation and activation of multiple immune cells. PTEN acts downstream from T- and B-cell receptors, costimulatory molecules, cytokine receptors, integrins, and also growth factor receptors. Loss of PTEN activity in human and mice is associated with cellular and humoral immune dysfunction, lymphoid hyperplasia, and autoimmunity. Although most patients with PTEN hamartoma tumor syndrome (PHTS) have no immunological symptoms, a subclinical immune dysfunction is present in many, and clinical immunodeficiency in few. Comparison of the immune phenotype caused by PTEN haploinsufficiency in PHTS, phosphoinositide 3-kinase (PI3K) gain-of-function in activated PI3K syndrome, and mice with conditional biallelic Pten deletion suggests a threshold model in which coordinated activity of several phosphatases control the PI3K signaling in a cell-type-specific manner. Emerging evidence highlights the role of PTEN in polygenic autoimmune disorders, infection, and the immunological response to cancer. Targeting the PI3K axis is an emerging therapeutic avenue.

Abstract 4826: Enhancement of PTEN activity via peptidomimetics

Abstract Compromised PTEN function is associated with multiple cancers. As per the continuum model, variable degree of PTEN inactivation drives distinct cancer phenotypes. Loss of PTEN activity, via genomic/non-genomic mechanisms, leads to enhanced oncogenic PI3K signaling. While kinase inhibitors have proved effective in the clinic, they are increasingly met with off-target effects and therapy-resistance due to compensatory feedback mechanisms. Although PTEN restoration therapy has proved promising in experimental models; implementation of these therapies in the clinic remains challenging. To fill this therapy gap, we have targeted endogenous PTEN for activation via peptidomimetics, mitigating PI3K signaling. Our selected peptidomimetics reduced cell proliferation, migration and cell cycle activity after treatment of non-small cell lung cancer cells expressing endogenous PTEN. Computational studies utilizing PTEN crystal structures revealed a binding site at the interface of the Phosphatase Domain (PD) and C2 Domain (C2D). Induced fit docking indicated that a unique functional group is responsible for peptidomimetic-mediated enhancement of PTEN activity. Molecular dynamics analysis revealed energetically favorable binding of our lead peptidomimetic at the PD/C2D interface, which allosterically modulated the conformation of the active site. Binding of our peptidomimetic altered the active site orientation of PIP3, increasing its binding affinity. In summary, we have developed the first-known direct PTEN activators and analyzed their effects in suppressing oncogenic activities in lung cancer. Refinement of our peptidomimetics, complemented with in vivo studies, will provide a novel clinical rationale to reduce doses of standard therapy and their associated toxicities, decreasing morbidity and mortality observed in the clinic. Citation Format: Emily Palumbo, Peng Teng, Prerna Malaney, Jacob Wilson, Fiona Kearns, Michael T. Kemp, Zhi Tian, Vladimir Uversky, Diane Allen-Gipson, Yu Chen, H. Lee Woodcock, Jianfeng Cai, Vrushank Dave. Enhancement of PTEN activity via peptidomimetics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4826.

Phase 1 Trial Testing Single Agent CUDC-907, a Novel, Oral Dual Inhibitor of Histone Deacetylase (HDAC) and PI3K: Initial Assessment of Patients with Relapsed or Refractory (RR) Diffuse Large B-Cell Lymphoma (DLBCL), Including Double Expressor (DE) Lymphoma

DLBCL, the most common lymphoid malignancy in adults, is an aggressive form of non-Hodgkin lymphoma (NHL) with significant heterogeneity in terms of gene expression, prognosis and response to treatment. Certain histone modifications and HDAC expression patterns have been implicated in the pathobiology of DLBCL and other cancers. Aberrant PTEN/PI3K/AKT signaling is also frequently observed in a variety of human cancers including DLBCL, where loss of PTEN activity and/or activating mutations in PI3K and AKT have been shown to reduce apoptosis and promote cell proliferation. Synergistic anti-tumor effects achieved with HDAC and PI3K inhibitor combinations in various DLBCL xenograft models have provided a strong rationale for testing a highly potent dual HDAC and PI3K inhibitor, CUDC-907. Significant anti-tumor effects have been observed across a wide range of DLBCL models exposed to CUDC-907, including the U2932 ABC DLBCL model that harbors BCL2 translocation and over-expresses cMYC and BCL6, and the WSU-DLCL-2 GCB DLBCL model that harbors EZH2 mutation. These disease mechanisms and preclinical data have led to testing of CUDC-907 in an ongoing Phase 1 trial in patients (pts) with various hematologic cancers.Sixty-three heavily pre-treated pts with lymphoma or multiple myeloma have received CUDC-907 in 21-day cycles according to once daily (QD), intermittent (BIW or TIW), or five days on/two days off (5/2) dosing schedules. CUDC-907 was escalated in 30 mg increments such that pts received 30-60 mg QD, 60-150 mg intermittently, or 60 mg 5/2. A dose expansion using the 60 mg 5/2 dose and schedule is ongoing. Thus far, CUDC-907 has demonstrated a manageable side effect profile and sustained clinical efficacy, particularly in the subset of pts with RR DLBCL.The most common treatment-related adverse events (AEs) were diarrhea (54%; 5% Grade ≥3), fatigue (37%; 3% Grade ≥3), nausea (22%) and thrombocytopenia (18%; 14% Grade ≥3), with dose limiting toxicities of hyperglycemia (QD and BIW schedules) and diarrhea (QD and TIW schedules). Side effects were reversible and manageable. Among 11/18 subjects with RR DLBCL who were evaluable for disease response, 6/11 (55%) achieved objective responses (2 CRs and 4 PRs); lasting a median of 119 days (range: 48 - 354+). Of 7 pts with sufficient tissue, 3 response-evaluable pts were found to over-express MYC and BCL2 by IHC, meeting criteria applied to "double-expressor" (DE) DLBCL. On CUDC-907 monotherapy, 2/3 confirmed pts with DE DLBCL have attained objective responses: 1 ongoing CR (followed by autologous stem cell transplant) and 1PR (lasting 132 days). The third response-evaluable pt with DE DLBCL has experienced lengthy stabilization of disease (171+ days).Signals emerging from preclinical and clinical studies suggest that pts with DLBCL, including those with particularly aggressive disease, may derive benefit from treatment with CUDC-907. Enrollment of pts with RR DLBCL is ongoing into the expansion phase of the Phase 1 trial that is testing CUDC-907 on the 60 mg 5/2 RP2D as monotherapy and in combination with rituximab. Tissue obtained from pts with RR DLBCL treated with CUDC-907 will be assessed for MYC, BCL2, and other genetic aberrations that will be correlated with clinical outcomes observed in the trial. A Phase 2 trial of CUDC-907 in RR NHL is currently being planned, with emphasis on MYC aberrations. DisclosuresYounes:Celgene: Honoraria; Incyte: Honoraria; Janssen: Honoraria; Seattle Genetics: Honoraria, Research Funding; Bayer: Honoraria; Bristol Meyer Squibb: Honoraria; Novartis: Research Funding; Sanofi-Aventis: Honoraria; Johnson and Johnson: Research Funding; Curis: Research Funding; Takeda Millenium: Honoraria. Berdeja:Acetylon: Research Funding; Onyx: Research Funding; Abbvie: Research Funding; Curis: Research Funding; Celgene: Research Funding; Takeda: Research Funding; MEI: Research Funding; Novartis: Research Funding; Janssen: Research Funding; BMS: Research Funding; Array: Research Funding. Flinn:Celgene Corporation: Research Funding. Clancy:Curis: Employment, Equity Ownership. Ma:Curis: Employment, Equity Ownership. Sun:Curis: Employment, Equity Ownership. Tian:Curis: Employment, Equity Ownership. Wang:Curis: Employment, Equity Ownership. Viner:Curis: Employment, Equity Ownership.

β-Catenin activation synergizes with Pten loss and Myc overexpression in Notch-independent T-ALL

AbstractWnt signaling is important for T-cell differentiation at the early CD4−CD8− stage and is subsequently downregulated with maturation. To assess the importance of this downregulation, we generated a mouse line (R26-βcat) in which high levels of active β-catenin are maintained throughout T-cell development. Young R26-βcat mice show a differentiation block at the CD4+CD8+ double-positive (DP) stage. These DP cells exhibit impaired apoptosis upon irradiation or dexamethasone treatment. All R26-βcat mice develop T-cell leukemias at 5 to 6 months of age. R26-βcat leukemias remain dependent on β-catenin function but lack Notch pathway activation. They exhibit recurrent secondary genomic rearrangements that lead to Myc overexpression and loss of Pten activity. Because β-catenin activation and Myc translocations were previously found in murine T-cell acute lymphoblastic leukemias (T-ALLs) deficient for Pten, our results suggest that activation of the canonical Wnt pathway is associated with a subtype of Notch-independent T-ALLs that bear Myc gene rearrangements and Pten mutations.

Alterations in Wnt–β‐catenin and Pten signalling play distinct roles in endometrial cancer initiation and progression

Endometrioid endometrial cancer arises through a gradual series of histological changes, each accompanied by specific alterations in gene expression and activity. Activation of the Wnt-β-catenin pathway and loss of PTEN activity are frequently observed in endometrial cancers. However, the specific roles played by alterations in these pathways in the initiation and progression of endometrial cancer are currently unclear. Here, we investigated the effects of loss of Pten and Apc gene function in the mouse endometrium by employing tissue-specific and inducible mutant alleles, followed by immunohistochemical (IHC) and loss of heterozygosity (LOH) analysis of their corresponding cancerous lesions. Loss of the Apc function in the endometrium leads to cytoplasmic and nuclear β-catenin accumulation in association with uterine hyperplasia and squamous cell metaplasia, but without malignant transformation. Loss of Pten function also resulted in squamous metaplasia but, in contrast to loss of Apc function, it initiates endometrial cancer. On the other hand, loss of Apc function in the endometrium accelerates Pten-driven endometrial tumourigenesis. Analysis of compound heterozygous mice confirmed that somatic loss of the wild-type Pten allele represents the rate-limiting initiation step in endometrial cancer. Simultaneous loss of Pten and Apc resulted in endometrial cancer characterized by earlier onset and a more aggressive malignant behaviour. These observations are indicative of the synergistic action between the Wnt-β-catenin and Pten signalling pathways in endometrial cancer onset and progression.

Abstract 5719: Improvement of radiotherapy for glioblastoma by co-targeting PI3K and HSP90

Abstract Introduction: Glioblastoma (GBM) tumors frequently contain mutations in the tumor suppressor gene, PTEN, leading to loss of PTEN activity. PTEN loss causes overactivation of the PI3K pathway, inducing inhibition of apoptosis and radioresistance. Heat-shock protein 90 (HSP90) is a molecular chaperone that is over-expressed in GBM and that has among its client proteins, PI3K and Akt. It was hypothesized that dual inhibition of Hsp90 and PI3K signaling would additively or synergistically radiosensitize GBM through inhibition of radiation-induced PI3K/Akt signaling, leading to enhanced apoptosis. This study investigated the radiosensitizing effect of the HSP 90 inhibitor, HSP990 in combination with the PI3K inhibitor, BKM-120 in U87 GBM xenografts. Methods: Human U87 (GBM) cells, null for PTEN, were studied. Radiosensitivity was determined by apoptotic assays (Annexin V kit) in vitro and by tumor growth delay studies in vivo. Immunoblots were performed to assess pAkt levels. HSP990 and BKM 120 were provided by Novartis Pharmaceuticals. Results: Apoptotic assays revealed the following percentages of cells undergoing apoptosis 48 hrs after treatments: radiation alone: 57%; HSP990 alone: 75%; HSP990 + radiation (RT): 86%; BKM120 alone: 59%; BKM120+ RT: 42%. The combination of BKM120 + HSP990 induced the highest percentage of apoptosis (89% of cell population). The addition of radiation to the combined drug treatment did not increase the percentage of cells undergoing apoptosis (66% for triple modality treatment vs. 89% for HSP990 + BKM120 treatment). In vivo, each individual treatment (RT, HSP990 or BKM120) slowed the rate of tumor growth compared with the control group and all pairs of treatments performed better than either of the component treatments alone (p<0.0001 for all comparisons). The combination of all three treatments performed significantly better than BKM+RTX and HSP+RTX (p=0.01 for both) but was not significantly better than BKM+HSP (p=0.06). Conclusions: The response of U87 glioblastoma to radiotherapy was enhanced in the presence of BKM120 and HSP990. Enhanced apoptosis contributed to the mechanism of cell death. This work was supported by a grant from Novartis Pharmaceuticals. 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 5719. doi:1538-7445.AM2012-5719

Abstract 231: Development of an ELISA for quantification of in vitro and cellular PTEN phosphatase activity

Abstract Phosphatase and Tensin Homolog deleted on Chromosome 10 (PTEN) is a 3′ phosphoinositide phosphatase that converts PI(3,4,5)P3 to PI(4,5)P2 thus opposing PKB/Akt activation by PI 3-Kinase. PTEN is involved in neuronal stem cell proliferation and self-renewal, cardiac myocyte hypertrophy and contractility, and a wide range of developmental processes. However, PTEN is best known for its role as a tumor suppressor. Loss of PTEN activity results in accumulation of PI(3,4,5)P3, abnormal activation of PKB/Akt, unregulated cell growth, suppression of apoptosis, and increased tumorigenesis in a number of human tissues. It has also been proposed that PTEN is a candidate for targeted chemotherapy because certain anti-cancer agents preferentially destroy tumors with PTEN mutations. In addition to this direct role in cancer, PTEN has recently been shown to regulate cancer-associated pathways including VEGF-mediated angiogenesis and others. Consequently interest in PTEN as a cancer target is still high. Traditionally, quantification of PTEN phosphatase activity has required the use of radioactivity, organic solvents, and chromatography. In addition, detection of free phosphate released from the PTEN activity is commonly used for quantification. However, this latter method has limited sensitivity and dynamic range, and is susceptible to contamination from other sources of inorganic phosphate which can give incorrect results. To address the need for a better quantification method, we have developed a PTEN activity assay using a standard competitive ELISA format. Rather than detecting free phosphate, the assay detects the PTEN product, PI(4,5)P2, giving much more accurate quantification, improved sensitivity, and eliminates possible errors from phosphate contamination. We have shown that the assay can successfully quantify PTEN activity using both recombinant and immunoprecipitated enzyme. Several cell lines were tested for PTEN activity including the human breast cancer cell lines MDA-MB-231 and MDA-MB-468 (PTEN deficient). 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 231. doi:1538-7445.AM2012-231

Abstract C64: Adult murine prostate basal and luminal cells are self-sustained lineages that can both serve as targets for prostate cancer initiation

Abstract The prostate epithelial lineage hierarchy and the cellular origin for prostate cancer remain inadequately defined. We sought to utilize a lineage tracing approach to define the epithelial lineage hierarchy in the prostate. A previously reported K14-CreER transgenic mouse line was bred with a fluorescent reporter line to specifically label the prostate basal cell lineage. In parallel, the prostate luminal cell lineage was labeled with fluorescence using a novel K8-CreERT2 transgenic mouse line generated in our own lab. Using this lineage tracing approach, we show that adult rodent prostate basal and luminal cells are independently self-sustained in vivo. We then sought to characterize the cells of origin for prostate cancer in the context of loss of function of Pten, which occurs frequently in primary and advanced human prostate cancer. We bred the K14-CreER and K8-CreERT2 mouse lines with Ptenfl/fl mice separately so that Pten expression can be disrupted specifically in prostate basal and luminal cells, respectively. Disrupting Pten in either lineage led to prostate cancer initiation. However, the cellular composition and onset dynamics of the resulting tumors are distinctive. Prostate luminal cells are more responsive to Pten null-induced mitogenic signaling. In contrast, basal cells are resistant to direct transformation. Instead, loss of Pten activity induces the capability of basal cells to differentiate into transformation-competent luminal cells. These studies suggest that deregulation of the normal prostate epithelial differentiation program is a critical step for initiation of human prostate cancer with a basal cell origin. Furthermore, suppressing signaling pathways that induce basal-luminal differentiation may provide an efficient approach to prevent prostate cancer initiation. Citation Format: Nahyun Choi, Boyu Zhang, Li Zhang, Michael Ittmann, Li Xin. Adult murine prostate basal and luminal cells are self-sustained lineages that can both serve as targets for prostate cancer initiation [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr C64.

Features of the reversible sensitivity-resistance transition in PI3K/PTEN/AKT signalling network after HER2 inhibition

Systems biology approaches that combine experimental data and theoretical modelling to understand cellular signalling network dynamics offer a useful platform to investigate the mechanisms of resistance to drug interventions and to identify combination drug treatments. Extending our work on modelling the PI3K/PTEN/AKT signalling network (SN), we analyse the sensitivity of the SN output signal, phospho-AKT, to inhibition of HER2 receptor. We model typical aberrations in this SN identified in cancer development and drug resistance: loss of PTEN activity, PI3K and AKT mutations, HER2 overexpression, and overproduction of GSK3β and CK2 kinases controlling PTEN phosphorylation. We show that HER2 inhibition by the monoclonal antibody pertuzumab increases SN sensitivity, both to external signals and to changes in kinetic parameters of the proteins and their expression levels induced by mutations in the SN. This increase in sensitivity arises from the transition of SN functioning from saturation to non-saturation mode in response to HER2 inhibition. PTEN loss or PIK3CA mutation causes resistance to anti-HER2 inhibitor and leads to the restoration of saturation mode in SN functioning with a consequent decrease in SN sensitivity. We suggest that a drug-induced increase in SN sensitivity to internal perturbations, and specifically mutations, causes SN fragility. In particular, the SN is vulnerable to mutations that compensate for drug action and this may result in a sensitivity-to-resistance transition. The combination of HER2 and PI3K inhibition does not sensitise the SN to internal perturbations (mutations) in the PI3K/PTEN/AKT pathway: this combination treatment provides both synergetic inhibition and may prevent the SN from acquired mutations causing drug resistance. Through combination inhibition treatments, we studied the impact of upstream and downstream interventions to suppress resistance to the HER2 inhibitor in the SN with PTEN loss. Comparison of experimental results of PI3K inhibition in the PTEN upstream pathway with PDK1 inhibition in the PTEN downstream pathway shows that upstream inhibition abrogates resistance to pertuzumab more effectively than downstream inhibition. This difference in inhibition effect arises from the compensatory mechanism of an activation loop induced in the downstream pathway by PTEN loss. We highlight that drug target identification for combination anti-cancer therapy needs to account for the mutation effects on the upstream and downstream pathways.

Abstract 2199: A murine insertional mutagenesis screen to identify oncogenes and tumor suppressor genes involved in Schwann cell tumorigenesis

Abstract Introduction: Schwann cell tumors can occur sporadically, or in association with inherited tumor pre-disposition syndromes, such as Neurofibromatosis type 1 and type 2. A common feature of Schwann cell neoplasia is overexpression of the epidermal growth factor receptor (EGFR) and loss of p53 pathway function. To gain more insight into the genetic basis of neoplastic Schwann cell diseases we are using the conditional Sleeping Beauty (SB) transposon-based somatic mutagenesis system. Methods: To create mutations in Schwann cells and their precursors, five transgenes were introduced into mice. The first transgene conditionally expresses the Sleeping Beauty (SB11) transposase enzyme when Cre recombinase is also expressed1,2. The second transgene is an oligodendritic and Schwann cell specific Cre-recombinase controlled by the CNP (3’-cyclic nucleotide 3’-phosphodiesterase) promoter. The third transgene is a concatomer of oncogenic transposons (T2/Onc) capable of activating and/or disrupting endogenous gene expression. Since loss of p53 function and/or overexpression of epidermal growth factor receptor (EGFR) are associated with Malignant Peripheral Nerve Sheath Tumors (MPNSTs), CNP-EGFR and conditional dominant negative p53R270H alleles are also included3,4. Mice possessing all five transgenes experience transposition and insertional mutations in Schwann cell lineage cells. Results: SB is expressed and active in the Schwann cell lineage with variegated expression in other tissue types. Mice that harbor both a conditional dominant negative p53 allele and CNP-EGFR transgene develop nervous tissue tumors at 70% penetrance. These tumors are primarily neurofibromas, but in addition, there are Schwannomas, oculomotor nerve tumors, and dermal MPNSTs. Preliminary data indicate that MPNSTs develop more frequently in mice that are also undergoing SB transposon mutagenesis. Initial analysis of transposon insertion sites showed over 10 common sites of transposon insertion (CIS), implicating new genes in the pathogenesis of Schwann cell tumors. Among the CIS were the Neurofibromatosis type 1 and type 2 genes (Nf1 and Nf2), validating the screen. The Pten gene was also often targeted, consistent with the hypothesis that loss of Pten activity could play a major role in Schwann cell tumor progression. These and other CIS-associated genes will be discussed. Conclusions: Expression of EGFR at high levels cooperates with loss of function mutations in the p53 gene to induce Schwann cell tumors. SB insertional mutagenesis can contribute to Schwann cell tumorigenesis and identify new candidates in tumor progression. 1. Keng, V.W., et al. (2009). Nat Biotechnol. 3:264-74 2. Starr, T.K., et al. (2009). Science. 323:1747-50 3. Rasheed, B.K., et al. (1994). Cancer Res. 54:1324-1330 4. Perry, A., et al. (2002). Jour. Neuropathol. Exp. Neurol. 61:702-709 Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2199.

Abstract 5713: Omega-3 fatty acid molecular and cellular modulation of in vitro models of high-risk breast cancer

Abstract Omega-3 (n-3) fatty acids, especially the long-chain polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaonoic acid (DHA), have been shown to have potential antitumor effects for a wide range of cancer types, including breast. Multiple and widely diverse mechanisms have been purported through which n-3 fatty acids act as antitumor agents. Due to this wide range of effects, the n-3 fatty acids EPA and DHA in particular have been extrapolated to be possible chemo-preventive agents. Recent epidemiological studies have demonstrated that high intake of n-3 fatty acids from fish is inversely correlated with breast cancer risk. In this current study, we explore the molecular and cellular effects of EPA and DHA in breast cancer cells demonstrating abnormalities similar to those found in high risk patient populations, including MCF-7 cells with stable suppression of PTEN expression, MDA-MB-231 cells that mimic the triple negative phenotype and mouse epithelial cells that are derived from MMTV-erbB2 mouse breast tumors. Loss of PTEN activity has been reported in as much as 50% of all breast cancers. Triple negative disease exhibits an aggressive and early pattern of metastasis, with limited treatment options and a poor prognosis. ErbB2 is overexpressed in 30% of breast tumors and has been associated with a more aggressive and a pro-inflammatory disease. Based upon the highly inflammatory nature of these three cell types, we hypothesized that omega-3 fatty acids would be effective in modulating cellular processes that promote the more aggressive phenotype associated with these abnormalities. We are investigating the effect of EPA and DHA on survival, proliferation and apoptosis of the three modulated cell lines in comparison to less aggressive cell lines, and the molecular changes that correlate with response. Preliminary data suggest that cell proliferation is not modulated by exposure to either EPA or DHA. However, both EPA and DHA effectively suppressed NF-kB transcriptional activity in these cells. These data suggest that one important mechanism by which omega-3 fatty acids may function as anti-tumor and possibly chemo-preventive agents is through regulation of NF-kB-induced inflammation. Studies are currently on-going to evaluate if modulation of NF-kB is critical for mediating the protective effects of omega-3 fatty acids on breast cancer development and progression and if reduction of inflammatory responses will correlate with a less aggressive disease in these cells that closely reflect high risk patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5713.

RGS16 Inhibits Breast Cancer Cell Growth by Mitigating Phosphatidylinositol 3-Kinase Signaling

Aberrant activity of the phosphatidylinositol 3-kinase (PI3K) pathway supports growth of many tumors including those of breast, lung, and prostate. Resistance of breast cancer cells to targeted chemotherapies including tyrosine kinase inhibitors (TKI) has been linked to persistent PI3K activity, which may in part be due to increased membrane expression of epidermal growth factor (EGF) receptors (HER2 and HER3). Recently we found that proteins of the RGS (regulator of G protein signaling) family suppress PI3K activity downstream of the receptor by sequestering its p85alpha subunit from signaling complexes. Because a substantial percentage of breast tumors have RGS16 mutations and reduced RGS16 protein expression, we investigated the link between regulation of PI3K activity by RGS16 and breast cancer cell growth. RGS16 overexpression in MCF7 breast cancer cells inhibited EGF-induced proliferation and Akt phosphorylation, whereas shRNA-mediated extinction of RGS16 augmented cell growth and resistance to TKI treatment. Exposure to TKI also reduced RGS16 expression in MCF7 and BT474 cell lines. RGS16 bound the amino-terminal SH2 and inter-SH2 domains of p85alpha and inhibited its interaction with the EGF receptor-associated adapter protein Gab1. These results suggest that the loss of RGS16 in some breast tumors enhances PI3K signaling elicited by growth factors and thereby promotes proliferation and TKI evasion downstream of HER activation.

Mutations in the phosphatidylinositol-3-kinase pathway predict for antitumor activity of the inhibitor PX-866 whereas oncogenic Ras is a dominant predictor for resistance.

The novel phosphatidylinositol-3-kinase (PI3K) inhibitor PX-866 was tested against 13 experimental human tumor xenografts derived from cell lines of various tissue origins. Mutant PI3K (PIK3CA) and loss of PTEN activity were sufficient, but not necessary, as predictors of sensitivity to the antitumor activity of the PI3K inhibitor PX-866 in the presence of wild-type Ras, whereas mutant oncogenic Ras was a dominant determinant of resistance, even in tumors with coexisting mutations in PIK3CA. The level of activation of PI3K signaling measured by tumor phosphorylated Ser(473)-Akt was insufficient to predict in vivo antitumor response to PX-866. Reverse-phase protein array revealed that the Ras-dependent downstream targets c-Myc and cyclin B were elevated in cell lines resistant to PX-866 in vivo. Studies using an H-Ras construct to constitutively and preferentially activate the three best-defined downstream targets of Ras, i.e., Raf, RalGDS, and PI3K, showed that mutant Ras mediates resistance through its ability to use multiple pathways for tumorigenesis. The identification of Ras and downstream signaling pathways driving resistance to PI3K inhibition might serve as an important guide for patient selection as inhibitors enter clinical trials and for the development of rational combinations with other molecularly targeted agents.

Phosphatase and tensin homolog (PTEN) regulates hepatic lipogenesis, microsomal triglyceride transfer protein, and the secretion of apolipoprotein B–containing lipoproteins

Hepatic apolipoprotein B (apoB) lipoprotein production is metabolically regulated via the phosphoinositide 3-kinase cascade; however, the role of the key negative regulator of this pathway, the tumor suppressor phosphatase with tensin homology (PTEN), is unknown. Here, we demonstrate that hepatic protein levels of apoB100 and microsomal triglyceride transfer protein (MTP) are significantly down-regulated (73% and 36%, respectively) in the liver of PTEN liver-specific knockout (KO) mice, and this is accompanied by increased triglyceride (TG) accumulation and lipogenic gene expression, and reduced hepatic apoB secretion in freshly isolated hepatocytes. MTP protein mass and lipid transfer activity were also significantly reduced in liver of PTEN KO mice. Overexpression of the dominant negative mutant PTEN C/S124 (adenovirus expressing PTEN C/S mutant [AdPTENC/S]) possessing constitutive phospoinositide 3-kinase activity in HepG2 cells led to significant reductions in both secreted apoB100 and cellular MTP mass (76% and 34%, respectively), and increased messenger RNA (mRNA) levels of sterol regulatory element binding protein 1c (SREBP-1c), fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC). Reduced apoB100 secretion induced by AdPTENC/S was associated with increased degradation of newly-synthesized cellular apoB100, in a lactacystin-sensitive manner, suggesting enhanced proteasomal degradation. AdPTENC/S also reduced apoB-lipoprotein production in McA-RH7777 and primary hamster hepatocytes. Our findings suggest a link between PTEN expression and hepatic production of apoB-containing lipoproteins. We postulate that perturbations in PTEN not only may influence hepatic insulin signaling and hepatic lipogenesis, but also may alter hepatic apoB-lipoprotein production and the MTP stability. On loss of PTEN activity, increased lipid substrate availability in the face of reduced hepatic lipoprotein production capacity can rapidly lead to hepatosteatosis and fatty liver.