An antibody that targets cell-surface glucose-regulated protein-78 inhibits expression of inflammatory cytokines and plasminogen activator inhibitors by macrophages

Glucose-regulated protein-78 (Grp78) is an endoplasmic reticulum chaperone, which is secreted by cells and associates with cell surfaces, where it functions as a receptor for activated α2 -macroglobulin (α2 M) and tissue-type plasminogen activator (tPA). In macrophages, α2 M and tPA also bind to the transmembrane receptor, LDL receptor-related protein-1 (LRP1), activating a cell-signaling receptor assembly that includes the NMDA receptor (NMDA-R) to suppress innate immunity. Herein, we demonstrate that an antibody targeting Grp78 (N88) inhibits NFκB activation and expression of proinflammatory cytokines in bone marrow-derived macrophages (BMDMs) treated with the toll-like receptor-4 (TLR4) ligand, lipopolysaccharide, or with agonists that activate TLR2, TLR7, or TLR9. Pharmacologic inhibition of the NMDA-R or deletion of the gene encoding LRP1 (Lrp1) in BMDMs neutralizes the activity of N88. The fibrinolysis protease inhibitor, plasminogen activator inhibitor-1 (PAI1), has been implicated in diverse diseases including metabolic syndrome, cardiovascular disease, and type 2 diabetes. Deletion of Lrp1 independently increased expression of PAI1 and PAI2 in BMDMs, as did treatment of wild-type BMDMs with TLR agonists. tPA, α2 M, and N88 inhibited expression of PAI1 and PAI2 in BMDMs treated with TLR-activating agents. Inhibiting Src family kinases blocked the ability of both N88 and tPA to function as anti-inflammatory agents, suggesting that the cell-signaling pathway activated by tPA and N88, downstream of LRP1 and the NMDA-R, may be equivalent. We conclude that targeting cell-surface Grp78 may be effective in suppressing innate immunity by a mechanism that requires LRP1 and the NMDA-R.

Activated Alpha 2-Macroglobulin Is a Novel Mediator of Mesangial Cell Profibrotic Signaling in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is caused by the overproduction of extracellular matrix proteins (ECM) by glomerular mesangial cells (MCs). We previously showed that high glucose (HG) induces cell surface translocation of GRP78 (csGRP78), mediating PI3K/Akt activation and downstream ECM production. Activated alpha 2-macroglobulin (α2M*) is a ligand known to initiate this signaling cascade. Importantly, increased α2M was observed in diabetic patients’ serum, saliva, and glomeruli. Primary MCs were used to assess HG responses. The role of α2M* was assessed using siRNA, a neutralizing antibody and inhibitory peptide. Kidneys from type 1 diabetic Akita and CD1 mice and human DKD patients were stained for α2M/α2M*. α2M transcript and protein were significantly increased with HG in vitro and in vivo in diabetic kidneys. A similar increase in α2M* was seen in media and kidneys, where it localized to the mesangium. No appreciable α2M* was seen in normal kidneys. Knockdown or neutralization of α2M/α2M* inhibited HG-induced profibrotic signaling (Akt activation) and matrix/cytokine upregulation (collagen IV, fibronectin, CTGF, and TGFβ1). In patients with established DKD, urinary α2M* and TGFβ1 levels were correlated. These data reveal an important role for α2M* in the pathogenesis of DKD and support further investigation as a potential novel therapeutic target.

Glucose-regulated protein (GRP78) is an important cell surface receptor for viral invasion, cancers, and neurological disorders

The 78 kDa glucose-regulated protein (GRP78) is an endoplasmic reticulum (ER)-resident molecular chaperone. GRP78 is a member of the 70 kDa heat shock family of proteins involved in correcting and clearing misfolded proteins in the ER. In response to cellular stress, GRP78 escapes from the ER and moves to the plasma membrane where it (a) functions as a receptor for many ligands, and (b) behaves as an autoantigen for autoantibodies that contribute to human disease and cancer. Cell surface GRP78 (csGRP78) associates with the major histocompatibility complex class I (MHC-I), and is the port of entry for several viruses, including the predictive binding of the novel SARS-CoV-2. Furthermore, csGRP78 is found in association with partners as diverse as the teratocarcinoma-derived growth factor 1 (Cripto), the melanocortin-4 receptor (MC4R) and the DnaJ-like protein MTJ-1. CsGRP78 also serves as a receptor for a large variety of ligands including activated α₂ -macroglobulin (α₂ M*), plasminogen kringle 5 (K5), microplasminogen, the voltage-dependent anion channel (VDAC), tissue factor (TF), and the prostate apoptosis response-4 protein (Par-4). In this review, we discuss the mechanisms involved in the translocation of GRP78 from the ER to the cell surface, and the role of secreted GRP78 and its autoantibodies in cancer and neurological disorders.

Cell surface GRP78 signaling: An emerging role as a transcriptional modulator in cancer

Cancer cells acquire dysregulated gene expression to establish specific transcriptional dependencies and their underlying mechanisms that are ultimately responsible for this addictions have not been fully elucidated. Glucose-regulated protein 78 (GRP78) is a stress-inducible, multifunctional, prosurvival, endoplasmic reticulum chaperone in the heat shock protein 70 family. Expression of cell surface GRP78 (CS-GRP78) is associated with increased malignant behavior and resistance to chemotherapy and radiotherapy by endowing various cancer cells with increased proliferative ability, altered metabolism, improved survival, and augmented invasive and metastatic potential. Emerging evidence has highlighted an unusual role of CS-GRP78 in regulating transcription factors (TFs) by mediating various signaling pathways involved in malignant transformation, metabolic reprogramming, and tumor progression. During the last decade, we targeted CS-GRP78 with C38 monoclonal antibody (C38 Mab) in numerous studies, which have highlighted the epigenetic interplay between CS-GRP78 and various TFs including c-MYC, Yes-associated protein/transcriptional coactivator with PDZ-binding motif, c-Fos, and histone acetylation to potentiate subsequent modulation of tumorigenesis, invasion, and metastasis. Here, we summarize the current state of knowledge about the role of CS-GRP78 in cancer development and progression, including epigenetic regulation and sheds light on CS-GRP78 as vulnerable target for cancer therapy. Overall, this review focuses on the mechanisms of TFs that are behind the transcriptional dysregulation in cancer and lays the groundwork for rational therapeutic use of C38 Mab based on CS-GRP78 biology.

Adipose stem cell crosstalk with chemo-residual breast cancer cells: implications for tumor recurrence

PURPOSE

Most triple-negative breast cancer (TNBC) patients exhibit an incomplete response to neoadjuvant chemotherapy, resulting in chemo-residual tumor cells that drive tumor recurrence and patient mortality. Accordingly, strategies for eliminating chemo-residual tumor cells are urgently needed. Although stromal cells contribute to tumor cell invasion, to date, their ability to influence chemo-residual tumor cell behavior has not been examined. Our study is the first to investigate cross-talk between adipose-derived stem cells (ASCs) and chemo-residual TNBC cells. We examine if ASCs promote chemo-residual tumor cell proliferation, having implications for tumor recurrence.

METHODS

ASC migration toward chemo-residual TNBC cells was tested in a transwell migration assay. Importance of the SDF-1α/CXCR4 axis was determined using neutralizing antibodies and a small molecule inhibitor. The ability of ASCs to drive tumor cell proliferation was analyzed by culturing tumor cells ± ASC conditioned media (CM) and determining cell counts. Downstream signaling pathways activated in chemo-residual tumor cells following their exposure to ASC CM were studied by immunoblotting. Importance of FGF2 in promoting proliferation was assessed using an FGF2-neutralizing antibody.

RESULTS

ASCs migrated toward chemo-residual TNBC cells in a CXCR4/SDF-1α-dependent manner. Moreover, ASC CM increased chemo-residual tumor cell proliferation and activity of extracellular signal-regulated kinase (ERK). An FGF2-neutralizing antibody inhibited ASC-induced chemo-residual tumor cell proliferation.

CONCLUSIONS

ASCs migrate toward chemo-residual TNBC cells via SDF-1α/CXCR4 signaling, and drive chemo-residual tumor cell proliferation in a paracrine manner by secreting FGF2 and activating ERK. This paracrine signaling can potentially be targeted to prevent tumor recurrence.

A Comparative Study of Crosslinked and Noncrosslinked Fibrin from the Major Classes of Vertebrates

Crosslinked and noncrosslinked fibrin formed by clotting whole plasma in the presence and absence of calcium has been examined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The fibrin from 45 species of vertebrates with representatives from all classes except the Bradyodonti (Chimaeras) and a majority of the subclasses have been compared. Noncrosslinked fibrin from the mammals contained subunits resembling the α, β, and γ chains of human noncrosslinked fibrin. The molecular weight of the α-chains varied greatly, the molecular weight of the β-chains varied slightly, while the molecular weight of the γ-chains was apparently invariant. Nonerosslinked avian fibrins showed clearly resolved γ-chains with a molecular weight slightly smaller than human γ-chains. Avian α- and β-chains were usually not resolved. Nonerosslinked fibrin from the reptiles and amphibians contained a clearly resolved subunit with a molecular weight similar to that of human γ-chain. In crosslinked fibrin from all of the mammals, birds, reptiles, and amphibians the γ-chain was absent and a new band which corresponded to a dimer of the γ-chain was found, while high molecular weight polymers were only found in a few species. Fibrin formed from the plasma of the bony fishes was often difficult because of the problem of fibrinolysis ; however, non crosslinked fibrin from some species of bony fish had three clearly resolved subunits while the crosslinked fibrin from all of the species examined had dimers as the predominant crosslinked forms. The noncrosslinked fibrin from the cartilaginous fish had subunits in the same molecular weight range as the other vertebrate fibrins; however, the crosslinked fibrin was unique to this class because all of the fibrin subunits were involved in the crosslinking process. Dimers appeared to be a transient species, and a large number of different high molecular weight crosslinked species were formed. The crosslinked fibrin from the hagfish contained dimers and no higher molecular weight crosslinked forms. Rapid fibrinolysis complicated the interpretation of the results from all of the classes of fish.

Evaluation of p-Amidinophenyl Esters as Potential Antithrombotic Agents

Three p-amidinophenyl esters have been synthesized and characterized as irreversible inhibitors of the vitamin-K dependent proteinases; factors IXa, Xa and thrombin (Turner et al. [4])+. In the present report we describe the in vitro and in vivo effects of these agents on standard coagulation tests in vitro and in blood from animals treated with the compounds. At a concentration of 500 μM, the three esters increased the activated partial thromboplastin time (PTT) of pooled human plasma 3 to 5-fold. The prothrombin time increased 1.4 to 3.7-fold under similar conditions. The p-amidinophenyl ester of cinnamic acid (CINN) showed the most pronounced effect on both assays. This ester also is the best inhibitor of human factors IXa and Xa, while the p-amidinophenyl ester of benzoic acid (BENZ) is a slightly better α-thrombin inhibitor (4). The effect of these esters on the thrombin clotting time correlated with in vitro kinetic measurements of α-thrombin inhibition rates. Both BENZ and CINN increased the assay endpoint more than 6-fold. The three esters also were studied using mouse plasma. A comparable effect on the PTT was noted. Intravenous administration of 300 αl of 1 mM CINN as a single bolus in mice caused a 2.3-fold increase in the PTT which remained 1.2-fold normal 2 h later. The BENZ and a-methyl-cinnamic acid (MECINN) esters were somewhat less effective as predicted from their in vitro effect on the PTT. This investigation and previous studies indicate that these compounds demonstrate low toxicity at therapeutic levels. It is concluded that the p-amidinophenyl esters may be useful in antithrombotic therapy.

The Clearance of Human Fibrinogen Fragments X and Y in Mice: A Process Mediated by the Fragment D Receptor

The clearance of radiolabeled human fibrinogen fragments X and Y was studied in the mouse model. Fragment X cleared rapidly from the circulation with less than 10% of the ligand remaining in the circulation at 4 hr. The clearance of fragment Y was somewhat slower, but was identical to the rate of clearance of fragment D,. Competition studies indicated that fragments X, Y, D, and D! dimer clear via the same, saturable pathway. Fragment E did not compete for the clearance of these ligands. Tissue distribution studies demonstrated that the liver was the principal site of clearance of all three ligands. The kidneys also cleared a fraction of each ligand in the order fragment D3>D2>D1 >Y>X. This pattern suggests that renal clearance is a passive phenomenon dependent on the size of the fibrinogen degradation product.

A Unique Pathway for the Plasma Elimination of α2-Antiplasmin-Protease Complexes in Mice

Radiolabeled α2-antiplasmin cleared slowly from the circulation of mice. Complex formation with either plasmin or trypsin resulted in a significant increase in the plasma elimination rate of the protease inhibitor. Approximately 20 min and 14 min were required for 50% of the injected α2-antiplasmin-plasmin and α2-antiplasmin-trypsin to clear from the circulation, respectively. Significant competition was observed when radiolabeled α2-antiplasmin-plasmin was cleared in the presence of a large molar excess of unlabeled α2-antiplasmin-plasmin. α1-Antitrypsin-trypsin failed to compete with radiolabeled α2-antiplasmin-plasmin even when present at 2000 fold molar excess. Organ distribution studies localized the major site of α2-antiplasmin-plasmin clearance in the liver. Microscopic autoradiography data suggested that the cell responsible for the clearance pathway was the hepatocyte.

Serum cholesterol levels and tumor growth in a PTEN-null transgenic mouse model of prostate cancer

Background

Some, but not all, epidemiologic evidence supports a role for cholesterol, the precursor for steroid hormone synthesis, in prostate cancer. Using a PTEN-null transgenic mouse model of prostate cancer, we tested the effect of modifying serum cholesterol levels on prostate tumor development and growth. We hypothesized that serum cholesterol reduction would lower tumor androgens and slow prostate cancer growth.

Methods

PTEN^loxP/loxP-Cre⁺ mice consuming ad libitum high fat, high cholesterol diets (40% fat, 1.25% cholesterol) were randomized after weaning to receive the cholesterol uptake inhibitor, ezetimibe (30 mg/kg/day), or no intervention, and sacrificed at 2, 3 or 4 months of age. Serum cholesterol and testosterone were measured by ELISA and intraprostatic androgens by mass spectrometry. Prostate histology was graded, and proliferation and apoptosis in tumor epithelium and stroma was assessed by Ki67 and TUNEL, respectively.

Results

Ezetimibe-treated mice had lower serum cholesterol at 4 months (p=0.031). Serum cholesterol was positively correlated with prostate weight (p=0.033) and tumor epithelial proliferation (p=0.069), and negatively correlated with tumor epithelial apoptosis (p=0.004). Serum cholesterol was unrelated to body weight (p=0.195). Tumor stromal cell proliferation was reduced in the ezetimibe group (p=0.010). Increased serum cholesterol at 4 months was associated with elevated intraprostatic DHEA, testosterone and androstenedione (p=0.043, p=0.074, p=0.031, respectively). However, cholesterol reduction did not significantly affect adenocarcinoma development at 2, 3 or 4 months of age (0%, 78%, 100% in ezetimibe-treated vs. 0%, 80%, 100% in mice not receiving ezetimibe).

Conclusions

Though serum cholesterol reduction did not significantly affect the rate of adenocarcinoma development in the PTEN-null transgenic mouse model of prostate cancer, it lowered intraprostatic androgens and slowed tumor growth. These findings support a role for serum cholesterol in promoting prostate cancer growth, potentially via enhanced tumor androgen signaling, and may provide new insight into cholesterol-lowering interventions for prostate cancer treatment.

Chemotherapy enriches for an invasive triple-negative breast tumor cell subpopulation expressing a precursor form of N-cadherin on the cell surface

BACKGROUND

Although most triple-negative breast cancer (TNBC) patients initially respond to chemotherapy, residual tumor cells frequently persist and drive recurrent tumor growth. Previous studies from our laboratory and others' indicate that TNBC is heterogeneous, being composed of chemo-sensitive and chemo-resistant tumor cell subpopulations. In the current work, we studied the invasive behaviors of chemo-resistant TNBC, and sought to identify markers of invasion in chemo-residual TNBC.

METHODS

The invasive behavior of TNBC tumor cells surviving short-term chemotherapy treatment in vitro was studied using transwell invasion assays and an experimental metastasis model. mRNA expression levels of neural cadherin (N-cadherin), an adhesion molecule that promotes invasion, was assessed by PCR. Expression of N-cadherin and its precursor form (pro-N-cadherin) was assessed by immunoblotting and flow cytometry. Pro-N-cadherin immunohistochemistry was performed on tumors obtained from patients pre- and post- neoadjuvant chemotherapy treatment.

RESULTS

TNBC cells surviving short-term chemotherapy treatment exhibited increased invasive behavior and capacity to colonize metastatic sites compared to untreated tumor cells. The invasive behavior of chemo-resistant cells was associated with their increased cell surface expression of precursor N-cadherin (pro-N-cadherin). An antibody specific for the precursor domain of N-cadherin inhibited invasion of chemo-resistant TNBC cells. To begin to validate our findings in humans, we showed that the percent cell surface pro-N-cadherin (+) tumor cells increased in patients post- chemotherapy treatment.

CONCLUSIONS

TNBC cells surviving short-term chemotherapy treatment are more invasive than bulk tumor cells. Cell surface pro-N-cadherin expression is associated with the invasive and chemo-resistant behaviors of this tumor cell subset. Our findings indicate the importance of future studies determining the value of cell surface pro-N-cadherin as: 1) a biomarker for TNBC recurrence and 2) a therapeutic target for eliminating chemo-residual disease.

Autoantibodies against the cell surface-associated chaperone GRP78 stimulate tumor growth via tissue factor

Tumor cells display on their surface several molecular chaperones that normally reside in the endoplasmic reticulum. Because this display is unique to cancer cells, these chaperones are attractive targets for drug development. Previous epitope-mapping of autoantibodies (AutoAbs) from prostate cancer patients identified the 78-kDa glucose-regulated protein (GRP78) as one such target. Although we previously showed that anti-GRP78 AutoAbs increase tissue factor (TF) procoagulant activity on the surface of tumor cells, the direct effect of TF activation on tumor growth was not examined. In this study, we explore the interplay between the AutoAbs against cell surface-associated GRP78, TF expression/activity, and prostate cancer progression. First, we show that tumor GRP78 expression correlates with disease stage and that anti-GRP78 AutoAb levels parallel prostate-specific antigen concentrations in patient-derived serum samples. Second, we demonstrate that these anti-GRP78 AutoAbs target cell-surface GRP78, activating the unfolded protein response and inducing tumor cell proliferation through a TF-dependent mechanism, a specific effect reversed by neutralization or immunodepletion of the AutoAb pool. Finally, these AutoAbs enhance tumor growth in mice bearing human prostate cancer xenografts, and heparin derivatives specifically abrogate this effect by blocking AutoAb binding to cell-surface GRP78 and decreasing TF expression/activity. Together, these results establish a molecular mechanism in which AutoAbs against cell-surface GRP78 drive TF-mediated tumor progression in an experimental model of prostate cancer. Heparin derivatives counteract this mechanism and, as such, represent potentially appealing compounds to be evaluated in well-designed translational clinical trials.

Myelin basic protein stimulates plasminogen activation via tissue plasminogen activator following binding to independent l-lysine-containing domains

Myelin basic protein (MBP) is a key component of myelin, the specialized lipid membrane that encases the axons of all neurons. Both plasminogen (Pg) and tissue-type plasminogen activator (t-PA) bind to MBP with high affinity. We investigated the kinetics and mechanisms involved in this process using immobilized MBP and found that Pg activation by t-PA is significantly stimulated by MBP. This mechanism involves the binding of t-PA via a lysine-dependent mechanism to the Lys⁹¹ residue of the MBP NH₂-terminal region Asp⁸² -Pro⁹⁹, and the binding of Pg via a lysine-dependent mechanism to the Lys¹²² residue of the MBP COOH-terminal region Leu¹⁰⁹-Gly¹²⁶. In this context, MBP mimics fibrin and because MBP is a plasmin substrate, our results suggest direct participation of the Pg activation system on MBP physiology.

ROS-independent Nrf2 activation in prostate cancer

In prostate cancer, oxidative stress and the subsequent Nrf2 activation promote the survival of cancer cells and acquired chemoresistance. Nrf2 links prostate cancer to endoplasmic reticulum stress, an event that triggers the unfolded protein response, aiming to restore cellular homeostasis as well as an adaptive survival mechanism. Glucose-regulated protein of 78 kD /immunoglobulin heavy chain binding protein (GRP78/BiP) is a key molecular chaperone in the endoplasmic reticulum that, when expressed at the cell surface, acts as a receptor for several signaling pathways enhancing antiapoptotic and proliferative signals. We showed GRP78/BiP translocation to PC3 cell surface in the presence of tunicamycin, an ER stress inductor, and demonstrated the existence of a GRP78/BiP-dependent non-canonical Nrf2 activation, responsible for increased resistance to ER-stress induced apoptosis. We found that, even in the absence of ROS production, tunicamycin causes Nrf2 activation, and activates Akt signaling, events bulnted by anti-GRP78/BiP antibody treatment. The presence of GRP78/BiP at the cell surface might be exploited for the immunotherapeutic strategy of prostate cancer since its blockage by anti-GRP78/BiP antibodies might promote cancer death by suppressing some of the several molecular protective mechanisms found in aggressive cancer cells.

Evidence for Feedback Regulation Following Cholesterol Lowering Therapy in a Prostate Cancer Xenograft Model

BACKGROUND

Epidemiologic data suggest cholesterol-lowering drugs may prevent the progression of prostate cancer, but not the incidence of the disease. However, the association of combination therapy in cholesterol reduction on prostate or any cancer is unclear. In this study, we compared the effects of the cholesterol lowering drugs simvastatin and ezetimibe alone or in combination on the growth of LAPC-4 prostate cancer in vivo xenografts.

METHODS

Proliferation assays were conducted by MTS solution and assessed by Student's t-test. 90 male nude mice were placed on a high-cholesterol Western-diet for 7 days then injected subcutaneously with 1 × 10⁵ LAPC-4 cells. Two weeks post-injection, mice were randomized to control, 11 mg/kg/day simvastatin, 30 mg/kg ezetimibe, or the combination and sacrificed 42 days post-randomization. We used a generalized linear model with the predictor variables of treatment, time, and treatment by time (i.e., interaction term) with tumor volume as the outcome variable. Total serum and tumor cholesterol were measured. Tumoral RNA was extracted and cDNA synthesized from 1 ug of total RNA for quantitative real-time PCR.

RESULTS

Simvastatin directly reduced in vitro prostate cell proliferation in a dose-dependent, cell line-specific manner, but ezetimibe had no effect. In vivo, low continuous dosing of ezetimibe, delivered by food, or simvastatin, delivered via an osmotic pump had no effect on tumor growth compared to control mice. In contrast, dual treatment of simvastatin and ezetimibe accelerated tumor growth. Ezetimibe significantly lowered serum cholesterol by 15%, while simvastatin had no effect. Ezetimibe treatment resulted in higher tumor cholesterol. A sixfold induction of low density lipoprotein receptor mRNA was observed in ezetimibe and the combination with simvastatin versus control tumors.

CONCLUSIONS

Systemic cholesterol lowering by ezetimibe did not slow tumor growth, nor did the cholesterol independent effects of simvastatin and the combined treatment increased tumor growth. Despite lower serum cholesterol, tumors from ezetimibe treated mice had higher levels of cholesterol. This study suggests that induction of low density lipoprotein receptor is a possible mechanism of resistance that prostate tumors use to counteract the therapeutic effects of lowering serum cholesterol. Prostate 77:446-457, 2017. © 2016 Wiley Periodicals, Inc.

BRG1 and BRM SWI/SNF ATPases redundantly maintain cardiomyocyte homeostasis by regulating cardiomyocyte mitophagy and mitochondrial dynamics in vivo

There has been an increasing recognition that mitochondrial perturbations play a central role in human heart failure. Mitochondrial networks, whose function is to maintain the regulation of mitochondrial biogenesis, autophagy ('mitophagy') and mitochondrial fusion/fission, are new potential therapeutic targets. Yet our understanding of the molecular underpinning of these processes is just emerging. We recently identified a role of the SWI/SNF ATP-dependent chromatin remodeling complexes in the metabolic homeostasis of the adult cardiomyocyte using cardiomyocyte-specific and inducible deletion of the SWI/SNF ATPases BRG1 and BRM in adult mice (Brg1/Brm double mutant mice). To build upon these observations in early altered metabolism, the present study looks at the subsequent alterations in mitochondrial quality control mechanisms in the impaired adult cardiomyocyte. We identified that Brg1/Brm double-mutant mice exhibited increased mitochondrial biogenesis, increases in 'mitophagy', and alterations in mitochondrial fission and fusion that led to small, fragmented mitochondria. Mechanistically, increases in the autophagy and mitophagy-regulated proteins Beclin1 and Bnip3 were identified, paralleling changes seen in human heart failure. Evidence for perturbed cardiac mitochondrial dynamics included decreased mitochondria size, reduced numbers of mitochondria, and an altered expression of genes regulating fusion (Mfn1, Opa1) and fission (Drp1). We also identified cardiac protein amyloid accumulation (aggregated fibrils) during disease progression along with an increase in pre-amyloid oligomers and an upregulated unfolded protein response including increased GRP78, CHOP, and IRE-1 signaling. Together, these findings described a role for BRG1 and BRM in mitochondrial quality control, by regulating mitochondrial number, mitophagy, and mitochondrial dynamics not previously recognized in the adult cardiomyocyte. As critical to the pathogenesis of heart failure, epigenetic mechanisms like SWI/SNF chromatin remodeling seem more intimately linked to cardiac function and mitochondrial quality control mechanisms than previously realized.

Actions of thrombin in the interstitium

Thrombin is a pleiotropic enzyme best known for its contribution to fibrin formation and platelet aggregation during vascular hemostasis. There is increasing evidence to suggest a role for thrombin in the development of interstitial fibrosis, but interstitial thrombin has not been demonstrated by the direct determination of activity. Rather its presence is inferred by products of thrombin action such as fibrin and activated fibroblasts. This review will focus on possible mechanisms of thrombin formation in the interstitial space, the possible actions of thrombin, processes regulating thrombin activity in the interstitial space, and evidence supporting a role for thrombin in fibrosis.

Abstract POSTER-THER-1420: Ascites drives ovarian cancer stem-like cell growth: therapeutic opportunities

Background: A significant literature suggests that cancer stem-like cells drive the aggressive behavior of ovarian cancer. Cancer stem-like cells are distinct from bulk tumor cells in possessing self-renewing/tumor-initiating activity and exhibiting therapy resistance. Accordingly, targeting cancer stem-like cells is a logical approach to developing an effective ovarian cancer therapy.

The presence of ascites in ovarian cancer patients is associated with decreased five-year survival. Ascites promotes anti-apoptotic signaling in ovarian cancer cells. However, an ability of ascites to drive cancer stem-like behavior has not been tested.

Glucose-regulated protein of 78 kDa (GRP78) is expressed on the surface of a variety of tumor types. This receptor is an ideal therapeutic target because it promotes tumor cell survival(Li and Lee, 2006) and is not detected in normal tissues. In head and neck cancer, cell surface GRP78-positive tumor cells exhibit cancer stem-like behaviors (Wu et al., 2010. Mol Cancer. 9:283.). However, it remains unknown if targeting cell surface GRP78 is an efficient strategy for killing cancer stem-like cells.

We have produced and characterized a unique set of monoclonal antibodies specific for the carboxy-terminus (C-terminus) of GRP78. These antibodies inhibit Akt signaling and suppress melanoma growth (Misra et al. , 2010. Cancer biology & therapy. 9:142-152; de Ridder et al. 2012. Melanoma Res. 22:225-235). Neither the ability of these antibodies to target cancer stem-like cells, nor their therapeutic potential for ovarian cancer has been previously assessed.

Purpose of the current studies: 1) Address the hypothesis that ascites fluid enriches for therapy-resistant ovarian cancer stem-like cells, 2) Determine efficacy of targeting cell surface GRP78 to eliminate ascites-enriched ovarian cancer stem-like cells.

Experimental Procedures: Ovarian cancer cells (murine and human) were incubated with acellular ascites fluid obtained from an ovarian cancer mouse model or from ovarian cancer patients. Ability of these cells to grow as self-renewing spheres in vitro and to initiate tumor growth in a mouse model were measured. Stem cell marker (CD133, Oct4) and cell surface GRP78 expression were assessed by flow cytometry. Effects of anti-GRP78 antibodies on cancer stem-like cell behaviors in vitro and on tumor growth in vivo were measured.

Data Summary: Incubation of ovarian cancer cells with ascites enriched for tumor cells with increased self-renewing/tumor initiating activity and increased cell surface GRP78 expression. A C-terminal anti-GRP78 antibody suppressed ascites-enriched ovarian cancer stem-like cells by inhibiting Akt signaling. Ovarian cancer bearing mice receiving the C-terminal anti-GRP78 antibody survived significantly longer than those receiving an IgG control.

Conclusions: Acellular ascites fluid enriches for therapy-resistant cancer stem-like cells that express cell surface GRP78. An antibody specific for the C-terminus of GRP78 suppresses ascites-enriched ovarian cancer stem-like cells. We are currently testing the ability of this antibody to increase chemotherapy sensitivity of ovarian cancer by eliminating therapy-resistant cancer stem-like cells. These studies are expected to lay the groundwork for future clinical trials investigating if a humanized form of this anti- GRP78 antibody +/- chemotherapy reduces incidence of ovarian cancer mortality.

Citation Format: Lihong Mo, Margaret Kennedy, Andrew Berchuck, George Cianciolo, Robin E. Bachelder, Salvatore V. Pizzo. Ascites drives ovarian cancer stem-like cell growth: therapeutic opportunities [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-THER-1420.

Catalytic autoantibodies against myelin basic protein (MBP) isolated from serum of autistic children impair in vitro models of synaptic plasticity in rat hippocampus

Autoantibodies from autistic spectrum disorder (ASD) patients react with multiple proteins expressed in the brain. One such autoantibody targets myelin basic protein (MBP). ASD patients have autoantibodies to MBP of both the IgG and IgA classes in high titers, but no autoantibodies of the IgM class. IgA autoantibodies act as serine proteinases and degrade MBP in vitro. They also induce a decrease in long-term potentiation in the hippocampi of rats either perfused with or previously inoculated with this IgA. Because this class of autoantibody causes myelin sheath destruction in multiple sclerosis (MS), we hypothesized a similar pathological role for them in ASD.

Nuclear basic fibroblast growth factor regulates triple-negative breast cancer chemo-resistance

INTRODUCTION

Chemotherapy remains the only available treatment for triple-negative (TN) breast cancer, and most patients exhibit an incomplete pathologic response. Half of patients exhibiting an incomplete pathologic response die within five years of treatment due to chemo-resistant, recurrent tumor growth. Defining molecules responsible for TN breast cancer chemo-resistance is crucial for developing effective combination therapies blocking tumor recurrence. Historically, chemo-resistance studies have relied on long-term chemotherapy selection models that drive genetic mutations conferring cell survival. Other models suggest that tumors are heterogeneous, being composed of both chemo-sensitive and chemo-resistant tumor cell populations. We previously described a short-term chemotherapy treatment model that enriches for chemo-residual TN tumor cells. In the current work, we use this enrichment strategy to identify a novel determinant of TN breast cancer chemotherapy resistance [a nuclear isoform of basic fibroblast growth factor (bFGF)].

METHODS

Studies are conducted using our in vitro model of chemotherapy resistance. Short-term chemotherapy treatment enriches for a chemo-residual TN subpopulation that over time resumes proliferation. By western blotting and real-time polymerase chain reaction, we show that this chemotherapy-enriched tumor cell subpopulation expresses nuclear bFGF. The importance of bFGF for survival of these chemo-residual cells is interrogated using short hairpin knockdown strategies. DNA repair capability is assessed by comet assay. Immunohistochemistry (IHC) is used to determine nuclear bFGF expression in TN breast cancer cases pre- and post- neoadjuvant chemotherapy.

RESULTS

TN tumor cells surviving short-term chemotherapy treatment express increased nuclear bFGF. bFGF knockdown reduces the number of chemo-residual TN tumor cells. Adding back a nuclear bFGF construct to bFGF knockdown cells restores their chemo-resistance. Nuclear bFGF-mediated chemo-resistance is associated with increased DNA-dependent protein kinase (DNA-PK) expression and accelerated DNA repair. In fifty-six percent of matched TN breast cancer cases, percent nuclear bFGF-positive tumor cells either increases or remains the same post- neoadjuvant chemotherapy treatment (compared to pre-treatment). These data indicate that in a subset of TN breast cancers, chemotherapy enriches for nuclear bFGF-expressing tumor cells.

CONCLUSION

These studies identify nuclear bFGF as a protein in a subset of TN breast cancers that likely contributes to drug resistance following standard chemotherapy treatment.

Syngeneic Murine Ovarian Cancer Model Reveals That Ascites Enriches for Ovarian Cancer Stem-Like Cells Expressing Membrane GRP78

Patients with ovarian cancer are generally diagnosed at FIGO (International Federation of Gynecology and Obstetrics) stage III/IV, when ascites is common. The volume of ascites correlates positively with the extent of metastasis and negatively with prognosis. Membrane GRP78, a stress-inducible endoplasmic reticulum chaperone that is also expressed on the plasma membrane ((mem)GRP78) of aggressive cancer cells, plays a crucial role in the embryonic stem cell maintenance. We studied the effects of ascites on ovarian cancer stem-like cells using a syngeneic mouse model. Our study demonstrates that ascites-derived tumor cells from mice injected intraperitoneally with murine ovarian cancer cells (ID8) express increased (mem)GRP78 levels compared with ID8 cells from normal culture. We hypothesized that these ascites-associated (mem)GRP78(+) cells are cancer stem-like cells (CSC). Supporting this hypothesis, we show that (mem)GRP78(+) cells isolated from murine ascites exhibit increased sphere forming and tumor initiating abilities compared with (mem)GRP78(-) cells. When the tumor microenvironment is recapitulated by adding ascites fluid to cell culture, ID8 cells express more (mem)GRP78 and increased self-renewing ability compared with those cultured in medium alone. Moreover, compared with their counterparts cultured in normal medium, ID8 cells cultured in ascites, or isolated from ascites, show increased stem cell marker expression. Antibodies directed against the carboxy-terminal domain of GRP78: (i) reduce self-renewing ability of murine and human ovarian cancer cells preincubated with ascites and (ii) suppress a GSK3α-AKT/SNAI1 signaling axis in these cells. Based on these data, we suggest that (mem)GRP78 is a logical therapeutic target for late-stage ovarian cancer.

Binding of tissue-type plasminogen activator to the glucose-regulated protein 78 (GRP78) modulates plasminogen activation and promotes human neuroblastoma cell proliferation in vitro

The glucose-regulated protein 78 (GRP78) is a plasminogen (Pg) receptor on the cell surface. In this study, we demonstrate that GRP78 also binds the tissue-type plasminogen activator (t-PA), which results in a decrease in K(m) and an increase in the V(max) for both its amidolytic activity and activation of its substrate, Pg. This results in accelerated Pg activation when GRP78, t-PA, and Pg are bound together. The increase in t-PA activity is the result of a mechanism involving a t-PA lysine-dependent binding site in the GRP78 amino acid sequence (98)LIGRTWNDPSVQQDIKFL(115). We found that GRP78 is expressed on the surface of neuroblastoma SK-N-SH cells where it is co-localized with the voltage-dependent anion channel (VDAC), which is also a t-PA-binding protein in these cells. We demonstrate that both Pg and t-PA serve as a bridge between GRP78 and VDAC bringing them together to facilitate Pg activation. t-PA induces SK-N-SH cell proliferation via binding to GRP78 on the cell surface. Furthermore, Pg binding to the COOH-terminal region of GRP78 stimulates cell proliferation via its microplasminogen domain. This study confirms previous findings from our laboratory showing that GRP78 acts as a growth factor-like receptor and that its association with t-PA, Pg, and VDAC on the cell surface may be part of a system controlling cell growth.

Model of tumor dormancy/recurrence after short-term chemotherapy

Although many tumors regress in response to neoadjuvant chemotherapy, residual tumor cells are detected in most cancer patients post-treatment. These residual tumor cells are thought to remain dormant for years before resuming growth, resulting in tumor recurrence. Considering that recurrent tumors are most often responsible for patient mortality, there exists an urgent need to study signaling pathways that drive tumor dormancy/recurrence. We have developed an in vitro model of tumor dormancy/recurrence. Short-term exposure of tumor cells (breast or prostate) to chemotherapy at clinically relevant doses enriches for a dormant tumor cell population. Several days after removing chemotherapy, dormant tumor cells regain proliferative ability and establish colonies, resembling tumor recurrence. Tumor cells from “recurrent” colonies exhibit increased chemotherapy resistance, similar to the therapy resistance of recurrent tumors in cancer patients. Previous studies using long-term chemotherapy selection models identified acquired mutations that drive tumor resistance. In contrast, our short term chemotherapy exposure model enriches for a slow-cycling, dormant, chemo-resistant tumor cell sub-population that can resume growth after drug removal. Studying unique signaling pathways in dormant tumor cells enriched by short-term chemotherapy treatment is expected to identify novel therapeutic targets for preventing tumor recurrence.

Resveratrol worsens survival in SCID mice with prostate cancer xenografts in a cell-line specific manner, through paradoxical effects on oncogenic pathways

BACKGROUND

Resveratrol increases lifespan and decreases the risk of many cancers. We hypothesized resveratrol will slow the growth of human prostate cancer xenografts.

METHODS

SCID mice were fed Western diet (40% fat, 44% carbohydrate, 16% protein by kcal). One week later, human prostate cancer cells, either LAPC-4 (151 mice) or LNCaP (94 mice) were injected subcutaneously. Three weeks after injection, LAPC-4 mice were randomized to Western diet (control group), Western diet plus resveratrol 50 mg/kg/day, or Western diet plus resveratrol 100 mg/kg/day. The LNCaP mice were randomized to Western diet or Western diet plus resveratrol 50 mg/kg/day. Mice were sacrificed when tumors reached 1,000 mm(3). Survival differences among groups were assessed using Cox proportional hazards. Serum insulin and IGF axis were assessed using ELISAs. Gene expression was analyzed using Affymetrix gene arrays.

RESULTS

Compared to control in the LAPC-4 study, resveratrol was associated with decreased survival (50 mg/kg/day--HR 1.53, P = 0.04; 100 mg/kg/day--HR 1.22, P = 0.32). In the LNCaP study, resveratrol did not change survival (HR 0.77, P = 0.22). In combined analysis of both resveratrol 50 mg/kg/day groups, IGF-1 was decreased (P = 0.05) and IGFBP-2 was increased (P = 0.01). Resveratrol induced different patterns of gene expression changes in each xenograft model, with upregulation of oncogenic pathways E2F3 and beta-catenin in LAPC-4 tumors.

CONCLUSION

Resveratrol was associated with significantly worse survival with LAPC-4 tumors, but unchanged survival with LNCaP. Based on these preliminary data that resveratrol may be harmful, caution should be advised in using resveratrol for patients until further studies can be conducted.

Abstract 5248: Tunneling nanotubes connect melanoma cells and mediate transfer of mitochondria and GRP78

Background: Recently, exciting reports have outlined the existence and function of very thin, membranous conduits between cells that span significant distances, termed tunneling nanotubes (TnTs). TnTs have been observed in neoplastic and normal cells, and may transport soluble proteins, such as P-glycoprotein (MDR1), lipids, and whole organelles, including mitochondria and Golgi vesicles, between cells. Furthermore, TnTs mediate intercellular Ca2+ signals and transmit electrical potentials. However, their functional characterization remains incomplete.

Objectives: Our objective is to describe TnT formation and function in melanoma cell lines and primary tumor samples.

Methods: We describe the presence and composition of TnTs between cells in the melanoma cell lines SK-Mel-31, DM440, DM443, DM738, and DM598 in vitro with a combination of brightfield and fluorescent microscopy techniques. TnT formation is assessed in response to hypoxia, glucose stress, and low pH. Bulk intercellular transport of mitochondria is quantified via flow cytometry using MitotrackerTM dyes, and GFP-GRP78 fusion proteins are used for studies of protein transport. Additional flow cytometric studies include JC-1 staining to measure mitochondrial membrane potential, annexin V binding to measure apoptosis, and 7-AAD exclusion for live/dead staining. Fluorescent ATP assays are used to measure general metabolic capacity, and confocal microscopy of primary melanoma specimens is performed using melanosome-specific (P100) and dsDNA (H33342) stains.

Results All tested cell lines formed TnT-like structures with variable F-actin and tubulin composition. Mitochondria and Golgi vesicles were visible within live and fixed TnTs, which were formed constitutively and were further induced by hypoxia, glucose stress, and low pH. In an actin-dependent process, cells rapidly transferred labeled mitochondria, achieving homogeneity within 24 h as measured by flow cytometry. Transfer of healthy mitochondria from unstressed cells significantly mitigated the acute toxicity of chemotherapeutically damaged cells. GRP78 was also rapidly transferred between cells, and the transfer of GRP78 from healthy donor cells rescued cells damaged by chemotherapeutics as measured by a decreased apoptotic rate.

Conclusions: Here, we report for the first time, the characterization of TnTs between melanoma cells. Moreover, melanoma cells acquired primary and secondary chemotherapeutic resistance to alkylating agents melphalan and temozolomide and the BRAFV600E inhibitor, vemurafenib, via bulk intercellular transfer of functional mitochondria and the ER stress protein, GRP78. TnT inhibitors would represent a novel class of chemotherapeutics with implications for invasion, metastasis, and chemotherapeutic resistance.

Citation Format: Gustaaf G. de Ridder, Rupa Ray, Salvatore V. Pizzo. Tunneling nanotubes connect melanoma cells and mediate transfer of mitochondria and GRP78. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5248. doi:10.1158/1538-7445.AM2013-5248

Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

Abstract 3698: Inhibition of cholesterol uptake with ezetimibe reduces intra-tumoral testosterone levels and slows tumor growth in transgenic mouse models of prostate cancer

Introduction: Western countries have 6 fold higher incidence of prostate cancer (PC). Dietary composition, in addition to other factors, may contribute to this geographic disparity. Cholesterol, the precursor for de novo steroid hormone synthesis, has been hypothesized to promote PC growth via multiple pathways including intratumoral steroidogenesis. While lowering serum cholesterol slows xenograft PC growth, this has not been tested in transgenic models, which allow testing of PC prevention as well as modulating PC growth in an orthotopic position. We determined the effect of cholesterol uptake inhibition, using ezetimibe, on PC growth in Hi-Myc and PTEN transgenic mice.

Methods: We randomized 50 c-myc/wt (Hi-Myc) mice and 30 PTENloxP/loxP-Cre+ (PTEN) to one of two diets: high fat high cholesterol (HFHC; 40% fat, 17% protein, 43% carbohydrate, 1.25% cholesterol), or HFHC with ezetimibe (30 mg/kg food) (HFHC+Z). Mice were fed ad libitum starting right after weaning and body weights measured twice weekly. Prostate, liver, spleen, adipose tissue and serum were harvested from Hi-Myc and PTEN mice at age 6 and 4 months, respectively. Serum cholesterol and testosterone (T) and tumor T were measured in Hi-Myc mice and are ongoing in PTEN mice.

Results: In Hi-Myc mice, body weights were significantly greater in the HFHC+Z group at sacrifice, relative to the HFHC group (p=0.04), but there were no differences in prostate weight between groups with adjustment for body weight (p=0.84). In PTEN mice, there was no difference in body weights between groups, but prostate weight was significantly lower in the HFHC+Z group, relative to the HFHC group (p=0.046). In Hi-Myc mice, while serum T levels did not vary between groups (p=0.93), tumor T, dihydrotestosterone (DHT) and androstenedione concentrations were significantly reduced in the HFHC+Z group, relative to the HFHC group (p=0.01, p=0.01, p=0.006, respectively).

Discussion: Reduction of serum cholesterol levels using cholesterol uptake inhibitor, ezetimibe, significantly reduced prostate weight in PTEN mice consuming a HFHC diet. Furthermore, supplementation of the HFHC diet with ezetimibe significantly reduced tumor concentrations of T, DHT and androstenedione in Hi-Myc mice, although there was no effect on prostate weight. These findings highlight a potentially critical role for cholesterol in PC progression by providing evidence that reduction of hypercholesterolemia may reduce intratumoral de novo steroidogenesis and slow PC growth. This study may provide new insight into the use of cholesterol-lowering drugs for PC prevention and treatment.

Citation Format: Emma H. Allott, Elizabeth M. Masko, Alexa Choy, Alexis R. Gaines, Keith R. Solomon, Salvatore V. Pizzo, Stephen J. Freedland. Inhibition of cholesterol uptake with ezetimibe reduces intra-tumoral testosterone levels and slows tumor growth in transgenic mouse models of prostate cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3698. doi:10.1158/1538-7445.AM2013-3698

Abstract 1247: Development of GRP78 scFv-Subtilase fusion proteins for sensitization of melanoma to chemotherapeutics

GRP78 is an important molecular chaperone in the endoplasmic reticulum (ER). However, GRP78 is aberrantly expressed on the surface of melanoma cells. Our objective is to characterize cell-surface GRP78 in melanoma and determine whether immunoconjugates against GRP78 are a viable treatment strategy. We have demonstrated that cleavage of ER GRP78 by Subtilase (SubAB), a GRP78-specific protease, sensitizes melanoma cell lines of different genotypes to melphalan, vemurafenib, and temozolomide. Our data indicate that SubAB cleavage of GRP78 sensitizes melanoma cells to melphalan and vemurafenib. We then coupled the catalytic domain of SubAB, SubA, to GRP78-single chain variable fragments derived from anti-GRP78 mouse monoclonal antibodies. We have previously published that these antibodies target GRP78+ mouse melanomas in a syngeneic mouse melanoma model. These GRP78 scFv-SubA fusion proteins are internalized by cell-surface GRP78 and the SubA moiety cleaves ER GRP78 inside the cell, leading to tumor cell sensitization to chemotherapeutics, and in some instances, tumor cell death. To determine the mechanism by which ER GRP78 cleavage sensitizes melanoma cells to chemotherapeutics, the NH2-terminal 28 kDa and COOH-terminal 50 kDa SubA cleavage products were overexpressed in melanoma cells, and pull-down experiments were performed to identify binding partners. Microarray analyses were also performed on chemotherapy-treated and GRP78 scFv-SubA fusion protein-treated melanoma cells to obtain a broad view of cellular events that occurred subsequent to ER GRP78 cleavage by SubAB or GRP78 scFv-SubA fusion proteins. These fusion proteins will then be tested in mouse melanoma models to determine whether they sensitize cancer cells to chemotherapeutics in vivo. These results of these studies may lead to the development of novel melanoma therapeutics.

Citation Format: Rupa Ray, Gustaaf de Ridder, Salvatore V. Pizzo. Development of GRP78 scFv-Subtilase fusion proteins for sensitization of melanoma to chemotherapeutics. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1247. doi:10.1158/1538-7445.AM2013-1247

The effect of carbohydrate restriction on prostate cancer tumor growth in a castrate mouse xenograft model

BACKGROUND

No- and low-carbohydrate diets delay tumor growth compared to western diet (WD) in prostate cancer (PCa) xenograft studies. The effect of these diets in concert with androgen deprivation is unknown.

METHODS

A total of 160 male SCID mice were injected with 1× 10(5) LAPC-4 human PCa cells. Of these, 150 mice were castrated and randomized to an ad libitum WD or fed via a paired-feeding protocol with a no-carbohydrate ketogenic diet (NCKD), 10% carbohydrate diet, or 20% carbohydrate diet. The remaining 10 mice were not castrated and were fed an ad libitum WD. The mice were sacrificed once volumes reached 1,000 mm3 and survival tested using the log-rank test. Serum from the median surviving 8 mice/group was assayed for insulin, IGF-1, and IGFBP-3.

RESULTS

Body weights were roughly equal among groups. The 10 non-castrated mice experienced accelerated tumor growth. Among castrated mice, WD had the most rapid tumor growth; 20% carbohydrate diet the slowest (P = 0.046). Survival was not significantly different among the various carbohydrate restricted groups (P = 0.51). When pooled, there was a non-significant trend (P = 0.11) in improved survival among the carbohydrate restricted diets versus WD. No significant difference in serum insulin, IGF-1, and IGFBP-3 levels was noted among all groups at pre-randomization or at sacrifice.

CONCLUSIONS

A 20% carbohydrate diet slowed tumor growth versus a WD. Though the benefit of carbohydrate restriction was somewhat less than in prior studies in non-castrate mice, these data still suggest diets achievable in humans may play a role in PCa management.

Receptor-recognized α₂-macroglobulin binds to cell surface-associated GRP78 and activates mTORC1 and mTORC2 signaling in prostate cancer cells

OBJECTIVE

Tetrameric α(2)-macroglobulin (α(2)M), a plasma panproteinase inhibitor, is activated upon interaction with a proteinase, and undergoes a major conformational change exposing a receptor recognition site in each of its subunits. Activated α(2)M (α(2)M*) binds to cancer cell surface GRP78 and triggers proliferative and antiapoptotic signaling. We have studied the role of α(2)M* in the regulation of mTORC1 and TORC2 signaling in the growth of human prostate cancer cells.

METHODS

Employing immunoprecipitation techniques and Western blotting as well as kinase assays, activation of the mTORC1 and mTORC2 complexes, as well as down stream targets were studied. RNAi was also employed to silence expression of Raptor, Rictor, or GRP78 in parallel studies.

RESULTS

Stimulation of cells with α(2)M* promotes phosphorylation of mTOR, TSC2, S6-Kinase, 4EBP, Akt(T308), and Akt(S473) in a concentration and time-dependent manner. Rheb, Raptor, and Rictor also increased. α(2)M* treatment of cells elevated mTORC1 kinase activity as determined by kinase assays of mTOR or Raptor immunoprecipitates. mTORC1 activity was sensitive to LY294002 and rapamycin or transfection of cells with GRP78 dsRNA. Down regulation of Raptor expression by RNAi significantly reduced α(2)M*-induced S6-Kinase phosphorylation at T389 and kinase activity in Raptor immunoprecipitates. α(2)M*-treated cells demonstrate about a twofold increase in mTORC2 kinase activity as determined by kinase assay of Akt(S473) phosphorylation and levels of p-Akt(S473) in mTOR and Rictor immunoprecipitates. mTORC2 activity was sensitive to LY294002 and transfection of cells with GRP78 dsRNA, but insensitive to rapamycin. Down regulation of Rictor expression by RNAi significantly reduces α(2)M*-induced phosphorylation of Akt(S473) phosphorylation in Rictor immunoprecipitates.

CONCLUSION

Binding of α(2)M* to prostate cancer cell surface GRP78 upregulates mTORC1 and mTORC2 activation and promotes protein synthesis in the prostate cancer cells.

The voltage-dependent anion channel (VDAC) binds tissue-type plasminogen activator and promotes activation of plasminogen on the cell surface

The voltage-dependent anion channel (VDAC), a major pore-forming protein in the outer membrane of mitochondria, is also found in the plasma membrane of a large number of cells where in addition to its role in regulating cellular ATP release and volume control it is important for maintaining redox homeostasis. Cell surface VDAC is a receptor for plasminogen kringle 5, which promotes partial closure of the channel. In this study, we demonstrate that VDAC binds tissue-type plasminogen activator (t-PA) on human neuroblastoma SK-N-SH cells. Binding of t-PA to VDAC induced a decrease in K(m) and an increase in the V(max) for activation of its substrate, plasminogen (Pg). This resulted in accelerated Pg activation when VDAC, t-PA, and Pg were bound together. VDAC is also a substrate for plasmin; hence, it mimics fibrin activity. Binding of t-PA to VDAC occurs between a t-PA fibronectin type I finger domain located between amino acids Ile(5) and Asn(37) and a VDAC region including amino acids (20)GYGFG(24). These VDAC residues correspond to a GXXXG repeat motif commonly found in amyloid β peptides that is necessary for aggregation when these peptides form fibrillar deposits on the cell surface. Furthermore, we also show that Pg kringle 5 is a substrate for the NADH-dependent reductase activity of VDAC. This ternary complex is an efficient proteolytic complex that may facilitate removal of amyloid β peptide deposits from the normal brain and cell debris from injured brain tissue.

Upregulation of mTORC2 activation by the selective agonist of EPAC, 8-CPT-2Me-cAMP, in prostate cancer cells: assembly of a multiprotein signaling complex

Ligation of cell surface-associated GRP78 by activated α(2) -macroglobulin triggers pro-proliferative cellular responses. In part, this results from activation of adenylyl cyclase leading to an increase in cAMP. We have previously employed the cAMP analog 8-CPT-2Me-cAMP to probe these responses. Here we show in 1-LN prostate cancer cells that 8-CPT-2Me-cAMP causes a dose-dependent increase in Epac1, p-Akt(T308) , p-Akt(S473) , but not p-CREB. By contrast, the PKA activator 6-Benz-cAMP caused a dose-dependent increase in p-CREB, but not Epac1. We measured mTORC2-dependent Akt phosphorylation at S473 in immunoprecipitates of mTOR or Rictor from 1-LN cells. 8-CPT-2Me-cAMP caused a two-threefold increase in p-Akt(S473) and Akt(S473) kinase activity in Rictor immunoprecipitates. By contrast, there was only a negligible effect on p-Akt(T308) in Rictor immunoprecipitates. Silencing Rictor gene expression by RNAi significantly suppressed 8-CPT-2Me-cAMP-induced phosphorylation of Akt at Ser(473) . These studies represent the first report that Epac1 mediates mTORC2-dependent phosphorylation of Akt(S473) . Pretreatment of these cells with the PI 3-Kinase inhibitor LY294002 significantly suppressed 8-CPT-2Me-cAMP-dependent p-Akt(S473) and p-Akt(S473) kinase activities, and both effects were rapamycin insensitive. This treatment caused a two to threefold increase in S6 Kinase and 4EBP1 phosphorylation, indices of mTORC1 activation. Pretreatment of the cells with LY294002 and rapamycin significantly suppressed 8-CPT-2Me-cAMP-induced phosphorylation of S6 Kinase and 4EBP1. We further demonstrate that in 8-CPT-2Me-cAMP-treated cells, Epac1 co-immunoprecipitates with AKAP, Raptor, Rictor, PDE3B, and PDE4D suggesting thereby that during Epac1-induced activation of mTORC1 and mTORC2, Epac1 may have an additional function as a "scaffold" protein.

The Escherichia coli subtilase cytotoxin A subunit specifically cleaves cell-surface GRP78 protein and abolishes COOH-terminal-dependent signaling

GRP78, a molecular chaperone with critical endoplasmic reticulum functions, is aberrantly expressed on the surface of cancer cells, including prostate and melanoma. Here it functions as a pro-proliferative and anti-apoptotic signaling receptor via NH(2)-terminal domain ligation. Auto-antibodies to this domain may appear in cancer patient serum where they are a poor prognostic indicator. Conversely, GRP78 COOH-terminal domain ligation is pro-apoptotic and anti-proliferative. There is no method to disrupt cell-surface GRP78 without compromising the total GRP78 pool, making it difficult to study cell-surface GRP78 function. We studied six cell lines representing three cancer types. One cell line per group expresses high levels of cell-surface GRP78, and the other expresses low levels (human hepatoma: Hep3B and HepG2; human prostate cancer: PC3 and 1-LN; murine melanoma: B16F0 and B16F1). We investigated the effect of Escherichia coli subtilase cytoxin catalytic subunit (SubA) on GRP78. We report that SubA specifically cleaves cell-surface GRP78 on HepG2, 1-LN, and B16F1 cells without affecting intracellular GRP78. B16F0 cells (GRP78(low)) have lower amounts of cleaved cell-surface GRP78. SubA has no effect on Hep3B and PC3 cells. The predicted 28-kDa GRP78 COOH-terminal fragment is released into the culture medium by SubA treatment, and COOH-terminal domain signal transduction is abrogated, whereas pro-proliferative signaling mediated through NH(2)-terminal domain ligation is unaffected. These experiments clarify cell-surface GRP78 topology and demonstrate that the COOH-terminal domain is necessary for pro-apoptotic signal transduction occurring upon COOH-terminal antibody ligation. SubA is a powerful tool to specifically probe the functions of cell-surface GRP78.

Abstract 3220: The effects of cholesterol treatment drugs alone and in combination on prostate tumor xenograft growth

Background: Epidemiologic data suggest cholesterol-lowering drugs may prevent the progression of prostate cancer (PC), but not the incidence of the disease. This may occur by lowering levels of low-density lipoproteins (LDL). Statins and cholesterol-uptake inhibitors like ezetimibe lower serum LDL and are commonly prescribed for patients with high cholesterol. In this study, we determined the therapeutic role of simvastatin, ezetimibe, or both in vitro using several PC cell lines and in vivo using a LAPC-4 xenograft model. Methods: We treated 4 PC cell lines (LAPC-4, CWR22rv1, PC-3, and DU145) with varying concentrations of simvastatin (0-1000nM) or ezetimibe (0-100μM) for 0-5 days. MTS assays were performed to determine cell proliferation, and the IC50 was calculated using BioDataFit 1.02. For our in vivo study, a total of 90 athymic male nude mice were fed a high-fat, high-cholesterol diet (HFHC; 40% fat, 17% protein, 43% carbohydrates, 1.25% cholesterol), subcutaneously injected with 1 x 10^5 LAPC-4 cells, and randomized 2 weeks later to 1 of 4 treatments: vehicle control, 11mg/kg/day simvastatin (delivered via osmotic pump), 30mg/kg diet ezetimibe (delivered in the food), or simvastatin + ezetimibe. Mice remained on study for 42 days post-randomization, at which point they were harvested and samples analyzed. Results: In vitro, simvastatin directly reduced PC cell proliferation in a dose-dependent, cell line-specific manner, but ezetimibe had no inhibitory effect. In vivo, treatment of low continuous dosing of simvastatin or ezetimibe for 42 days had no effect on tumor growth compared to control. However, relative to control, the combination of simvastatin and ezetimibe accelerated tumor growth (p=0.01). The simvastatin-ezetimibe mice also showed lower fat infiltration in the liver and lower serum cholesterol, but higher tumor cholesterol levels than control. Conclusions: Our results suggest that low continuous dosing of simvastatin or ezetimibe may have no effect on PC growth in a slow-growing LAPC-4 xenograft model, but the combination of simvastatin and ezetimibe may accelerate PC growth, possibly by stimulating cholesterol uptake within the tumor. This novel finding may be important in implementing new treatments for men with slow growing PC and high cholesterol.

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 3220. doi:1538-7445.AM2012-3220

Carbohydrate restriction and lactate transporter inhibition in a mouse xenograft model of human prostate cancer

What's known on the subject? and What does the study add? It is known that both lactate inhibition and carbohydrate restriction inhibit tumour growth. What is unknown is whether the two work synergistically together. This study adds that though the combination of lactate inhibition and carbohydrate restriction did not synergistically slow tumour growth in our model, we confirmed that carbohydrate restriction started after tumour inoculation slowed tumour growth. Moreover, lactate inhibition resulted in changes in the tumour microenvironment that may have implications for future metabolic targeting of prostate cancer growth.

OBJECTIVE

To determine if a no-carbohydrate ketogenic diet (NCKD) and lactate transporter inhibition can exert a synergistic effect on delaying prostate tumour growth in a xenograft mouse model of human prostate cancer.

MATERIALS AND METHODS

120 nude athymic male mice (aged 6-8 weeks) were injected s.c. in the flank with 1.0 × 10(5) LAPC-4 prostate cancer cells. • Mice were randomized to one of four treatment groups: Western diet (WD, 35% fat, 16% protein, 49% carbohydrate) and vehicle (Veh) treatment; WD and mono-carboxylate transporter-1 (MCT1) inhibition via α-cyano-4-hydroxycinnamate (CHC) delivered through a mini osmotic pump; NCKD (84% fat, 16% protein, 0% carbohydrate) plus Veh; or NCKD and MCT1 inhibition. • Mice were fed and weighed three times per week and feed was adjusted to maintain similar body weights. • Tumour size was measured twice weekly and the combined effect of treatment was tested via Kruskal-Wallis analysis of all four groups. Independent effects of treatment (NCKD vs WD and CHC vs Veh) on tumour volume were tested using linear regression analysis. • All mice were killed on Day 53 (conclusion of pump ejection), and serum and tumour sections were analysed for various markers. Again, combined and independent effects of treatment were tested using Kruskal-Wallis and linear regression analysis, respectively.

RESULTS

There were no significant differences in tumour volumes among the four groups (P= 0.09). • When testing the independent effects of treatment, NCKD was significantly associated with lower tumour volumes at the end of the experiment (P= 0.026), while CHC administration was not (P= 0.981). However, CHC was associated with increased necrotic fraction (P < 0.001).

CONCLUSIONS

Differences in tumour volumes were observed only in comparisons between mice fed a NCKD and mice fed a WD. • MCT1 inhibition did not have a significant effect on tumour volume, although it was associated with increased necrotic fraction.

Loss of cell surface TFII-I promotes apoptosis in prostate cancer cells stimulated with activated α₂ -macroglobulin

Receptor-recognized forms of α₂ -macroglobulin (α₂ M) bind to cell surface-associated GRP78 and initiate pro-proliferative and anti-apoptotic signaling. Ligation of GRP78 with α₂ M also upregulates TFII-I, which binds to the GRP78 promoter and enhances GRP78 synthesis. In addition to its transcriptional functions, cytosolic TFII-I regulates agonist-induced Ca(2+) entry. In this study we show that down regulation of TFII-I gene expression by RNAi profoundly impairs its cell surface expression and anti-apoptotic signaling as measured by significant reduction of GRP78, Bcl-2, and cyclin D1 in 1-Ln and DU-145 human prostate cancer cells stimulated with α₂ M. In contrast, this treatment significantly increases levels of the pro-apoptotic proteins p53, p27, Bax, and Bak and causes DNA fragmentation. Furthermore, down regulation of TFII-I expression activates agonist-induced Ca(2+) entry. In plasma membrane lysates p-PLCγ1, TRPC3, GRP78, MTJ1, and caveolin co-immunoprecipitate with TFII-I suggesting multimeric complexes of these proteins. Consistent with this hypothesis, down regulating TFII-I, MTJ1, or GRP78 expression by RNAi greatly attenuates cell surface expression of TFII-I. In conclusion, we demonstrate that not only does cell surface GRP78 regulate apoptosis, but it also regulates Ca(2+) homeostasis by controlling cell surface localization of TFII-I.

Abstract 4602: Cholesterol and ezetimibe: Effects on tumor growth and survival outcomes: An interim analysis

Introduction and Objectives: Prostate cancer (PC) is affected by cholesterol metabolism and cholesterol-mediating medications. Ezetimibe, a gut cholesterol-uptake inhibitor, inhibits angiogenesis in human PC xenografts when given as preventive therapy. We investigated the effect of ezetimibe on PC growth when given as treatment therapy.

Methods: We randomized 125 SCID mice into three initial diets: a high-fat, low-cholesterol diet (HFLC) (40% fat, 43% carbohydrates, 17% protein, 0.21% cholesterol), a high-fat, high-cholesterol diet (HFHC) (40% fat, 43% carbohydrates, 17% protein, 1.25% cholesterol), and a high-fat, high-cholesterol diet supplemented with ezetimibe (30mg/kg) (HFHC+Z). Mice were fed ad libitum. After two weeks, we injected 106 LNCaP cells into the flanks, with 5-10 mice/group serving as non-injected controls. At two weeks post-injection, half the injected and control mice in the HFHC diet group had ezetimibe added to their diet (HFHC+delayed Z). Tumor volumes and body weights were measured twice weekly. Mice were sacrificed once tumors reached 1000mm3. Body weights and tumor volumes were compared across groups using Kruskal-Wallis test. Interim survival outcomes for this on-going study up to 86 days post-injection were evaluated with Cox proportional hazards.

Results: At 1 day prior to injection, there were no significant differences in body weights across groups. At post-injection day (PD) 2, HFHC+Z mice with tumors were significantly lighter vs. all other mice (p=0.009). By PD 21, HFHC+delayed Z mice with tumors also became significantly lighter vs. the HFLC and HFHC mice with tumors (p&lt;0.001). At PD 86, all mice with tumors were significantly lighter than their control counterparts without tumors (all p&lt;0.013). Tumor volumes were not significantly different across groups (p=0.280). Likewise, survival was not significantly different across groups at PD 86 (p=0.125).

Conclusion: Preliminary evidence from this on-going study demonstrates that ezetimibe is associated with weight loss, but only in mice with PC xenografts. The administration of ezetimibe as preventive vs. treatment therapy does not appear to affect tumor growth or survival. Future studies to explore the interplay between cholesterol metabolism and PC include comparing serum levels of cholesterol, insulin, IGF-1, and IGFBP-3, and tumor markers of proliferation and angiogenesis including akt, pakt, mTOR, VEGF, HIF, CD31 (microvessel density) and ki67 (proliferation). Moreover, we are continuing to follow the mice for any differences in tumor growth or survival.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4602. doi:10.1158/1538-7445.AM2011-4602

Modulation of the unfolded protein response by GRP78 in prostate cancer

The unfolded protein response (UPR) is an adaptive survival mechanism through which cells can weather the stress of misfolded protein accumulation induced by a wide variety of pathophysiologic and pharmacologic insults. The ER chaperone GRP78 is a central modulator of the UPR both through its protein-binding capacity and its direct regulation of the UPR signaling molecules IRE1α, PERK, and ATF6. Recent reports have revealed the presence of GRP78 on the surface of cancer cells. Biological roles for cell-surface GRP78 include competing NH(2)-domain and COOH-domain agonist receptor activities that induce opposite effects on proliferation and apoptosis. Modulation of the UPR impacts both of these processes directly and indirectly. Here, we outline methods that we use to investigate UPR modulation via direct ligation of cell-surface GRP78. Specifically, we review methods of cell culture, cell-signaling analysis with emphasis on UPR components, and ultimately, the impact that these have on cell proliferation, survival, and apoptosis.

Ligation of prostate cancer cell surface GRP78 activates a proproliferative and antiapoptotic feedback loop: a role for secreted prostate-specific antigen

GRP78, a well characterized chaperone in the endoplasmic reticulum, is critical to the unfolded protein response. More recently, it has been identified on the cell surface, where it has many roles. On cancer cells, it functions as a signaling receptor coupled to proproliferative/antiapoptotic and promigratory mechanisms. In the current study, we demonstrate that ligation of prostate cancer cell surface GRP78 by its natural ligand, activated α(2)-macroglobulin (α(2)M*), results in a 2-3-fold up-regulation in the synthesis of prostate-specific antigen (PSA). The PSA is secreted into the medium as an active proteinase, where it binds to native α(2)M. The resultant α(2)M·PSA complexes bind to GRP78, causing a 1.5-2-fold increase in the activation of MEK1/2, ERK1/2, S6K, and Akt, which is coupled with a 2-3-fold increase in DNA and protein synthesis. PSA is a marker for the progression of prostate cancer, but its mechanistic role in the disease is unclear. The present studies suggest that PSA may be involved in a signal transduction-dependent feedback loop, whereby it promotes a more aggressive behavior by human prostate cancer cells.

Re-examination of CD91 function in GRP94 (glycoprotein 96) surface binding, uptake, and peptide cross-presentation

GRP94 (gp96)-peptide complexes can be internalized by APCs and their associated peptides cross-presented to yield activation of CD8(+) T cells. Investigations into the identity (or identities) of GRP94 surface receptors have yielded conflicting results, particularly with respect to CD91 (LRP1), which has been proposed to be essential for GRP94 recognition and uptake. To assess CD91 function in GRP94 surface binding and endocytosis, these parameters were examined in mouse embryonic fibroblast (MEF) cell lines whose expression of CD91 was either reduced via RNA interference or eliminated by genetic disruption of the CD91 locus. Reduction or loss of CD91 expression abrogated the binding and uptake of receptor-associated protein, an established CD91 ligand. Surface binding and uptake of an N-terminal domain of GRP94 (GRP94.NTD) was unaffected. GRP94.NTD surface binding was markedly suppressed after treatment of MEF cell lines with heparin, sodium chlorate, or heparinase II, demonstrating that heparin sulfate proteoglycans can function in GRP94.NTD surface binding. The role of CD91 in the cross-presentation of GRP94-associated peptides was examined in the DC2.4 dendritic cell line. In DC2.4 cells, which express CD91, GRP94.NTD-peptide cross-presentation was insensitive to the CD91 ligands receptor-associated protein or activated α(2)-macroglobulin and occurred primarily via a fluid-phase, rather than receptor-mediated, uptake pathway. These data clarify conflicting data on CD91 function in GRP94 surface binding, endocytosis, and peptide cross-presentation and identify a role for heparin sulfate proteoglycans in GRP94 surface binding.

Low-carbohydrate diets and prostate cancer: how low is "low enough"?

Previous studies indicate that carbohydrate intake influences prostate cancer biology, as mice fed a no-carbohydrate ketogenic diet (NCKD) had significantly smaller xenograft tumors and longer survival than mice fed a Western diet. As it is nearly impossible for humans to consume and maintain NCKD, we determined whether diets containing 10% or 20% carbohydrate kcal showed similar tumor growth as NCKD. A total of 150 male severe combined immunodeficient mice were fed a Western diet ad libitum, injected with the human prostate cancer cell line LAPC-4, and then randomized 2 weeks later to one of three arms: NCKD, 10% carbohydrate, or 20% carbohydrate diets. Ten mice not injected were fed an ad libitum low-fat diet (12% fat kcal) serving as the reference in a modified-paired feeding protocol. Mice were sacrificed when tumors reached 1,000 mm(3). Despite consuming extra calories, all mice receiving low-carbohydrate diets were significantly lighter than those receiving a low-fat diet (P < 0.04). Among the low-carbohydrate arms, NCKD-fed mice were significantly lighter than the 10% or 20% carbohydrate groups (P < 0.05). Tumors were significantly larger in the 10% carbohydrate group on days 52 and 59 (P < 0.05), but at no other point during the study. Diet did not affect survival (P = 0.34). There were no differences in serum insulin-like growth factor-I or insulin-like growth factor binding protein-3 at sacrifice among the low-carbohydrate arms (P = 0.07 and P = 0.55, respectively). Insulin was significantly lower in the 20% carbohydrate arm (P = 0.03). LAPC-4 xenograft mice fed a low-carbohydrate diet (10-20% carbohydrate kcal) had similar survival as mice consuming NCKD (0% carbohydrate kcal).

Binding of anti-GRP78 autoantibodies to cell surface GRP78 increases tissue factor procoagulant activity via the release of calcium from endoplasmic reticulum stores

The increased risk of venous thromboembolism in cancer patients has been attributed to enhanced tissue factor (TF) procoagulant activity (PCA) on the surface of cancer cells. Recent studies have shown that TF PCA can be modulated by GRP78, an endoplasmic reticulum (ER)-resident molecular chaperone. In this study, we investigated the role of cell surface GRP78 in modulating TF PCA in several human cancer cell lines. Although both GRP78 and TF are present on the cell surface of cancer cells, there was no evidence of a stable interaction between recombinant human GRP78 and TF, nor was there any effect of exogenously added recombinant GRP78 on cell surface TF PCA. Treatment of cells with the ER stress-inducing agent thapsigargin, an inhibitor of the sarco(endo)plasmic reticulum Ca(2+) pump that causes Ca(2+) efflux from ER stores, increased cytosolic [Ca(2+)] and induced TF PCA. Consistent with these findings, anti-GRP78 autoantibodies that were isolated from the serum of patients with prostate cancer and bind to a specific N-terminal epitope (Leu(98)-Leu(115)) on cell surface GRP78, caused a dose-dependent increase in cytosolic [Ca(2+)] and enhanced TF PCA. The ability to interfere with cell surface GRP78 binding, block phospholipase C activity, sequester ER Ca(2+), or prevent plasma membrane phosphatidylserine exposure resulted in a significant decrease in the TF PCA induced by anti-GRP78 autoantibodies. Taken together, these findings provide evidence that engagement of the anti-GRP78 autoantibodies with cell surface GRP78 increases TF PCA through a mechanism that involves the release of Ca(2+) from ER stores. Furthermore, blocking GRP78 signaling on the surface of cancer cells attenuates TF PCA and has the potential to reduce the risk of cancer-related venous thromboembolism.

Abstract 2816: Low-carbohydrate diets and prostate cancer growth: How low is “low enough”

Introduction: Previous dietary studies indicate carbohydrate intake may influence prostate cancer biology, as LAPC-4 and LNCaP xenograft mice fed a no-carbohydrate ketogenic diet (NCKD; 84% fat-0% carbohydrate-16% protein kcal) had significantly smaller tumors and longer survival times compared to mice fed a Western diet (40% fat-44% carbohydrate-16% protein kcal). The NCKD mice were also found to have higher levels of circulating IGFBP-3 and the lowest levels of insulin, IGF-1, and IGF-1:IGFBP-3 ratio despite consuming more calories than the Western group. As it is nearly impossible for a human to consume and maintain a no-carbohydrate diet similar to that in the previous xenograft studies, we sought to determine whether diets containing 10% or 20% kcal from carbohydrates could slow tumor growth in a similar manner to the NCKD in a xenograft model.

METHODS: A total of 150 male SCID mice were injected with LAPC-4 cells and placed on a Western diet (35% fat-49% carbohydrate-16% protein kcal) ad libitum. Two weeks post-injection, all mice were randomized to one of three arms: NCKD, 10% carbohydrate, or 20% carbohydrate. Ten mice not injected with tumor were fed an ad libitum low-fat diet (12% fat-72% carbohydrate-16% protein kcal) and served as the reference group in a modified-paired feeding protocol for the other three groups. Calorie intake and body weights were measured thrice weekly and tumor volumes twice per week. Mice were sacrificed when tumors reached 1,000mm3.

RESULTS: Despite consuming 5-10% extra calories on average, all mice receiving low-carbohydrate diets were significantly lighter than the mice consuming the low-fat diet (p&lt;0.04). Overall, the mice fed a NCKD were significantly lighter than the other two arms at multiple time points (p&lt;0.05). There were no significant differences in tumor volumes among groups at any time except at Day 52 and 59, where 10% carbohydrate mice had larger tumors (p&lt;0.05). However, after adjusting for the fact that tumor volumes were compared at multiple time points (i.e. multiple comparisons), these were no longer significant. Dietary treatment did not impact overall survival (p=0.34). NCKD mice had significantly higher glucose levels at sacrifice compared to the mice fed 10% and 20% carbohydrates (p=0.001), but similar levels of urinary ketones (p=0.37).

CONCLUSIONS: LAPC-4 xenograft mice fed a low-carbohydrate diet (10-20% carbohydrate kcal) had similar survival to mice consuming a NCKD (0% carbohydrate kcal). Thus, the survival benefit of a NCKD may be achievable with less restrictive low-carbohydrate diets.

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 2816.

Ligation of cell surface GRP78 with antibody directed against the COOH-terminal domain of GRP78 suppresses Ras/MAPK and PI 3-kinase/AKT signaling while promoting caspase activation in human prostate cancer cells

We have previously shown that treatment of prostate cancer and melanoma cells expressing GRP78 on their cell surface with antibody directed against the COOH-terminal domain of GRP78 upregulates and activates p53 causing decreased cell proliferation and upregulated apoptosis. In this report, we demonstrate that treatment of 1-LN prostate cancer cells with this antibody decreases cell surface expression of GRP78, Akt(Thr308) and Akt(Ser473) kinase activities and reduces phosphorylation of FOXO, and GSK3beta. This treatment also suppresses activation of ERK1/2, p38 MAPK and MKK3/6; however, it upregulates MKK4 activity. JNK, as determined by its phosphorylation state, is subsequently activated, triggering apoptosis. Incubation of cells with antibody reduced levels of anti-apoptotic Bcl-2, while elevating pro-apoptotic BAD, BAX and BAK expression as well as cleaved caspases-3, -7, -8 and -9. Silencing GRP78 or p53 gene expression by RNAi prior to antibody treatment abrogated these effects. We conclude that antibody directed against the COOH-terminal domain of GRP78 may prove useful as a pan suppressor of proliferative/survival signaling in cancer cells expressing GRP78 on their cell surface.

Inhibition of NF-kappaB1 and NF-kappaB2 activation in prostate cancer cells treated with antibody against the carboxyl terminal domain of GRP78: effect of p53 upregulation

Ligation of cancer cell surface GRP78 by activated alpha2-macroglobulin (alpha2M*) triggers pro-proliferative and anti-apoptotic signaling pathways. Cancer patients who develop autoantibodies to the alpha2M* binding site in GRP78 have a poor prognosis since these antibodies are receptor agonists. The NF-kappaB family of transcription factors induces expression of genes affecting cell growth and differentiation. NF-kappaB1 plays a major regulatory role in controlling innate immunity and inflammation, whereas NF-kappaB2 plays a greater role in cancer cell proliferation. Here we report that treatment of prostate cancer cells with antibody directed against the carboxyl terminal domain of GRP78 inhibits alpha2M*-induced activation of NF-kappaB2 by approximately 50% while exerting a lesser effect of approximately 20% on NF-kappaB1 activation. Treatment of these cells nearly abolished alpha2M*-induced activation of IKKalpha involved in the activation of NF-kappaB2. This antibody also suppressed alpha2M*-induced phosphorylation of IKKalpha, IKKalpha/beta, IkappaBalpha, and IkappaBbeta as well as levels of NIK. Antibody treatment of cancer cells elevated pro-apoptotic p21WAF and p27kip while reducing cyclin D1 levels. These studies demonstrate that antibody directed against the carboxyl terminal domain of GRP78 inhibits the pro-proliferative NF-kappaB signaling cascade in cancer cells.