Synthetic Biology Design as a Paradigm Shift toward Manufacturing Affordable Adeno-Associated Virus Gene Therapies

Gene therapy has demonstrated enormous potential for changing how we combat disease. By directly engineering the genetic composition of cells, it provides a broad range of options for improving human health. Adeno-associated viruses (AAVs) represent a leading gene therapy vector and are expected to address a wide range of conditions in the coming decade. Three AAV therapies have already been approved by the FDA to treat Leber's congenital amaurosis, spinal muscular atrophy, and hemophilia B. Yet these therapies cost around $850,000, $2,100,000, and $3,500,000, respectively. Such prices limit the broad applicability of AAV gene therapy and make it inaccessible to most patients. Much of this problem arises from the high manufacturing costs of AAVs. At the same time, the field of synthetic biology has grown rapidly and has displayed a special aptitude for addressing biomanufacturing problems. Here, we discuss emerging efforts to apply synthetic biology design to decrease the price of AAV production, and we propose that such efforts could play a major role in making gene therapy much more widely accessible.

Systemic checkpoint blockade by PD-L1 single-chain antibody confers potent anti-tumor immunity and long-term survival

Immune checkpoint inhibitors (ICIs) are promising in adjuvant settings for solid tumors and hematologic malignancies. They are currently used in the treatment as monoclonal antibodies in high concentrations, raising concerns of toxicity and adverse side effects. Among various checkpoint molecules, targeting the program cell death protein-1 (PD-1)-programmed death-ligand 1 (PD-L1) axis has garnered more clinical utility than others have. In order to develop a physiologically relevant and systemically stable level of ICIs from a one-time application by genetic antibody engineering, we endeavored using a non-pathogenic, replication-deficient recombinant adeno-associated vector (rAAV), expressing single-chain variable fragments (scFv) of PD-L1 antibody and tested in syngeneic mouse therapy models of MC38 colorectal and EMT6 breast tumors. Results of this study indicated a significant protection against PD-L1-mediated inhibition of CD8+ T cell function, against the growth of primary and secondary tumors, and durable antitumor cytotoxic T lymphocytes activity by adoptive CD8+ T cell transfer. Stable maintenance of PD-L1 scFv in vivo resulted in an increase in PD-1- CD8+ T cells, and a concomitant decrease in regulatory T cells, M2 macrophages and myeloid-derived suppressor cells in the tumor microenvironment. Overall, these data demonstrate the potential of rAAV-PD-L1-scFv as an alternative to mAb targeting of PD-L1 for tumor therapy.

Abstract 2103: Hedgehog signaling regulates metabolism and polarization of mammary tumor-associated macrophages

In the United States, a woman has a 12% chance of developing breast cancer, and current treatments offer little relief to patients diagnosed with metastatic disease. Tumorigenesis and successful establishment of metastases depend upon tumor cell interactions with the surrounding immune microenvironment. Elevated tumor infiltration of immunosuppressive (M2) macrophages correlates with poor prognosis of breast cancer patients. The tumor microenvironment remarkably orchestrates molecular mechanisms that program these macrophages toward the M2 phenotype. Also, metabolic programming is instrumental in orchestrating the polarization of macrophages to assume an M1 (tumor-eradicating) or an M2 (tumor-promoting) phenotype. Aberrant activation of Hedgehog (Hh) signaling in breast cancer cells enables them to survive, proliferate, and metastasize, thus making it a promising target for breast cancer treatment. Hh signaling also enables a crosstalk between breast cancer cells and cells in their milieu, thus contributing to M2 macrophage polarization. We used two immunocompetent orthotopic mouse models of mammary tumors to test the effect of inhibiting Hh signaling on tumor-associated macrophages, and discovered that treatment with the pharmacologic Hh inhibitor, Vismodegib, induced a significant shift in the profile of tumor-infiltrating macrophages. We hypothesized that Hh activity calibrates the metabolism in macrophages, leading to enhanced M2 phenotype and function within the tumor microenvironment. Using a mass spectrometry-enabled untargeted metabolomics approach, we identified that inhibiting Hh signaling reduces flux through the hexosamine biosynthetic pathway, resulting in reduced cellular O-GlcNAcylation in M2 macrophages. This impinges upon diminished STAT6 O-GlcNAcylation, which consequently decreases fatty acid oxidation and ultimately enacts a metabolic cascade including lipid utilization, cellular bioenergetics, and mitochondrial dynamics. As such, inhibiting Hh activity mitigates the metabolomic and bioenergetic underpinnings of the immunosuppressive program of M2 macrophages, resulting in macrophages that are functionally and phenotypically reminiscent of inflammatory, anti-tumor macrophages. In conclusion, we discovered a novel role for Hh signaling in promoting polarization of tumor-associated macrophages to the M2 type through recalibrating their metabolic circuitries, ultimately leading to diminished M2 phenotype and function within the tumor microenvironment. This is the first evidence highlighting the relevance of Hh signaling in controlling a complex metabolic network in immune cells. This knowledge will help us to better understand how to target and diminish the pro-tumorigenic functions of tumor-infiltrating macrophages.

Citation Format: Dominique C. Hinshaw, Ann Hanna, Tshering Lama-Sherpa, Brandon Metge, Sarah C. Kammerud, Gloria A. Benavides, Atul Kumar, Heba A. Alsheikh, Mateus Mota, Dongquan Chen, Scott Ballinger, Jeffrey C. Rathmell, Selvarangan Ponnazhagan, Victor Darley-Usmar, Rajeev S. Samant, Lalita A. Shevde. Hedgehog signaling regulates metabolism and polarization of mammary tumor-associated macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2103.

Indoleamine 2, 3-Dioxygenase Promotes Aryl Hydrocarbon Receptor-Dependent Differentiation Of Regulatory B Cells in Lung Cancer

Regulatory B cells (Breg) are IL-10 producing subsets of B cells that contribute to immunosuppression in the tumor microenvironment (TME). Breg are elevated in patients with lung cancer; however, the mechanisms underlying Breg development and their function in lung cancer have not been adequately elucidated. Herein, we report a novel role for Indoleamine 2, 3- dioxygenase (IDO), a metabolic enzyme that degrades tryptophan (Trp) and the Trp metabolite L-kynurenine (L-Kyn) in the regulation of Breg differentiation in the lung TME. Using a syngeneic mouse model of lung cancer, we report that Breg frequencies significantly increased during tumor progression in the lung TME and secondary lymphoid organs, while Breg were reduced in tumor-bearing IDO deficient mice (IDO^-/-). Trp metabolite L-Kyn promoted Breg differentiation in-vitro in an aryl hydrocarbon receptor (AhR), toll-like receptor-4-myeloid differentiation primary response 88, (TLR4-MyD88) dependent manner. Importantly, using mouse models with conditional deletion of IDO in myeloid-lineage cells, we identified a significant role for immunosuppressive myeloid-derived suppressor cell (MDSC)-associated IDO in modulating in-vivo and ex-vivo differentiation of Breg. Our studies thus identify Trp metabolism as a therapeutic target to modulate regulatory B cell function during lung cancer progression.

Hedgehog signaling regulates metabolism and polarization of mammary tumor-associated macrophages

Elevated infiltration of immunosuppressive alternatively polarized (M2) macrophages is associated with poor prognosis in cancer patients. The tumor microenvironment remarkably orchestrates molecular mechanisms that program these macrophages. Here we identify a novel role for oncogenic Hedgehog (Hh) signaling in programming signature metabolic circuitries that regulate alternative polarization of tumor-associated macrophages. Two immunocompetent orthotopic mouse models of mammary tumors were used to test the effect of inhibiting Hh signaling on tumor-associated macrophages. Treatment with the pharmacological Hh inhibitor Vismodegib induced a significant shift in the profile of tumor-infiltrating macrophages. Mass spectrometry-based metabolomic analysis showed Hh inhibition induced significant alterations in metabolic processes, including metabolic sensing, mitochondrial adaptations, and lipid metabolism. In particular, inhibition of Hh in M2 macrophages reduced flux through the UDP-GlcNAc biosynthesis pathway. Consequently, O-GlcNAc-modification of STAT6 decreased, mitigating the immune suppressive program of M2 macrophages, and the metabolically demanding M2 macrophages shifted their metabolism and bioenergetics from fatty acid oxidation to glycolysis. M2 macrophages enriched from Vismodegib-treated mammary tumors showed characteristically decreased O-GlcNAcylation and altered mitochondrial dynamics. These Hh-inhibited macrophages are reminiscent of inflammatory (M1) macrophages, phenotypically characterized by fragmented mitochondria. This is the first report highlighting the relevance of Hh signaling in controlling a complex metabolic network in immune cells. These data describe a novel immunometabolic function of Hh signaling that can be clinically exploited.

Extracellular Vesicle Mediated Tumor-Stromal Crosstalk Within an Engineered Lung Cancer Model

Tumor-stromal interactions within the tumor microenvironment (TME) influence lung cancer progression and response to therapeutic interventions, yet traditional in vitro studies fail to replicate the complexity of these interactions. Herein, we developed three-dimensional (3D) lung tumor models that mimic the human TME and demonstrate tumor-stromal crosstalk mediated by extracellular vesicles (EVs). EVs released by tumor cells, independent of p53 status, and fibroblasts within the TME mediate immunomodulatory effects; specifically, monocyte/macrophage polarization to a tumor-promoting M2 phenotype within this 3D-TME. Additionally, immune checkpoint inhibition in a 3D model that included T cells showed an inhibition of tumor growth and reduced hypoxia within the TME. Thus, perfused 3D tumor models incorporating diverse cell types provide novel insights into EV-mediated tumor-immune interactions and immune-modulation for existing and emerging cancer therapies.

Computational Simulation of Exosome Transport in Tumor Microenvironment

Cellular exosome-mediated crosstalk in tumor microenvironment (TME) is a critical component of anti-tumor immune responses. In addition to particle size, exosome transport and uptake by target cells is influenced by physical and physiological factors, including interstitial fluid pressure, and exosome concentration. These variables differ under both normal and pathological conditions, including cancer. The transport of exosomes in TME is governed by interstitial flow and diffusion. Based on these determinants, mathematical models were adapted to simulate the transport of exosomes in the TME with specified exosome release rates from the tumor cells. In this study, the significance of spatial relationship in exosome-mediated intercellular communication was established by treating their movement in the TME as a continuum using a transport equation, with advection due to interstitial flow and diffusion due to concentration gradients. To quantify the rate of release of exosomes by biomechanical forces acting on the tumor cells, we used a transwell platform with confluent triple negative breast cancer cells 4T1.2 seeded in BioFlex plates exposed to an oscillatory force. Exosome release rates were quantified from 4T1.2 cells seeded at the bottom of the well following the application of either no force or an oscillatory force, and these rates were used to model exosome transport in the transwell. The simulations predicted that a larger number of exosomes reached the membrane of the transwell for 4T1.2 cells exposed to the oscillatory force when compared to controls. Additionally, we simulated the interstitial fluid flow and exosome transport in a 2-dimensional TME with macrophages, T cells, and mixtures of these two populations at two different stages of a tumor growth. Computational simulations were carried out using the commercial computational simulation package, ANSYS/Fluent. The results of this study indicated higher exosome concentrations and larger interstitial fluid pressure at the later stages of the tumor growth. Quantifying the release of exosomes by cancer cells, their transport through the TME, and their concentration in TME will afford a deeper understanding of the mechanisms of these interactions and aid in deriving predictive models for therapeutic intervention.

A conserved aromatic moiety in the ectodomain is a key determinant for structural integrity and protein trafficking of TNFR superfamily

Extracellular trafficking of tumor necrosis factor receptor superfamily (TNFRSF) is tightly regulated, disruption of which triggers various autoinflammatory disorders, including TNF receptor-associated periodic syndrome (TRAPS). Here, we provide thus far unraveled molecular basis of noncysteine mutations in TNFR1 ectodomain where loss of an aromatic moiety in cysteine-rich domain (CRD) 2 results in TRAPS disease-associated phenotype. Our study characterized that a missense mutation on phenylalanine residue located in CRD2 (TNFR1F60V ) causes a delay in TNFR1 transport to cell membrane, leading to sustained receptor responsiveness and downstream NF-κB activation, characteristic of clinical manifestation of a prolonged fever. By creating and characterizing identical mutations on structurally conserved ectodomains of osteoprotegerin (OPG) and decoy receptor 3, other two secreted forms of TNFRSF, we further identified that a conserved aromatic residue at the A1 submodule of CRD2 (A1CRD2) confers structural integrity of ectodomain where aromatic sidechain deletion increases thermal instability, interfering with efficient posttranslational modification and subsequent receptor secretion. Interestingly, our functional analyses indicated that this particular noncysteine mutation is not associated with either protein misfolding or loss of function. Finally, by using a synthetic agonist, we demonstrated gain-of-function of the trafficking defect, suggesting the possibility of rescuing affected pathology in related disorders. Given the structural and topological similarities present in the ectodomains of TNFRSF members, our findings provide mechanistic insights of defects in subcellular trafficking of TNF receptors, reported in various TNFRSF-associated diseases.

RANKL-Targeted Combination Therapy with Osteoprotegerin Variant Devoid of TRAIL Binding Exerts Biphasic Effects on Skeletal Remodeling and Antitumor Immunity

Complexities in treating breast cancer with bone metastasis are enhanced by a vicious protumorigenic pathology, involving a shift in skeletal homeostasis toward aggressive osteoclast activity and polarization of immune cells supporting tumor growth and immunosuppression. Recent studies signify the role of receptor activator of NF-κB ligand (RANKL) beyond skeletal pathology in breast cancer, including tumor growth and immunosuppression. By using an osteoprotegerin (OPG) variant, which we developed recently through protein engineering to uncouple TNF-related apoptosis-inducing ligand (TRAIL) binding, this study established the potential of a cell-based OPG^Y49R therapy for both bone damage and immunosuppression in an immunocompetent mouse model of orthotopic and metastatic breast cancers. In combination with agonistic death receptor (DR5) activation, the OPG^Y49R therapy significantly increased both bone remolding and long-term antitumor immunity, protecting mice from breast cancer relapse and osteolytic pathology. With limitations, cost, and toxicity issues associated with the use of denosumab, bisphosphonates, and chemotherapy for bone metastatic disease, use of OPG^Y49R combination could offer a viable alternate therapeutic approach.

Adeno-Associated Virus D-Sequence-Mediated Suppression of Expression of a Human Major Histocompatibility Class II Gene: Implications in the Development of Adeno-Associated Virus Vectors for Modulating Humoral Immune Response

A 20-nt long sequence, termed the D-sequence, in the adeno-associated virus (AAV) inverted terminal repeat was observed to share a partial sequence homology with the X-box in the regulatory region of the human leukocyte antigen DRA (HLA-DRA) promoter of the human major histocompatibility complex class II (MHC-II) genes. The D-sequence was also shown to specifically interact with the regulatory factor binding to the X-box (RFX), binding of which to the X-box is a critical step in the MHC-II gene expression, suggesting that D-sequence might compete for RFX transcription factor binding, thereby suppressing expression from the MHC-II promoter. In DNA-mediated transfection experiments, using a reporter gene under the control of the HLA-DRA promoter, D-sequence oligonucleotides were found to inhibit expression of the reporter gene expression in HeLa and 293 cells by ∼93% and 96%, respectively. No inhibition was observed when nonspecific synthetic oligonucleotides were used. D-sequence oligonucleotides had no effect on expression from the cytomegalovirus immediate-early gene promoter. Interferon-γ-mediated activation of MHC-II gene expression was also inhibited by D-sequence oligonucleotides as well as after infection with either the wild-type AAV or transduction with recombinant AAV vectors. These studies suggest that the D-sequence-mediated downregulation of the MHC-II gene expression may be exploited toward the development of novel AAV vectors capable of dampening the host humoral response, which has important implication in the optimal use of these vectors in human gene therapy.

Runx2 Deficiency in Osteoblasts Promotes Myeloma Progression by Altering the Bone Microenvironment at New Bone Sites

Multiple myeloma is a plasma cell malignancy that thrives in the bone marrow (BM), with frequent progression to new local and distant bone sites. Our previous studies demonstrated that multiple myeloma cells at primary sites secrete soluble factors and suppress osteoblastogenesis via the inhibition of Runt-related transcription factor 2 (Runx2) in pre- and immature osteoblasts (OB) in new bone sites, prior to the arrival of metastatic tumor cells. However, it is unknown whether OB-Runx2 suppression in new bone sites feeds back to promote multiple myeloma dissemination to and progression in these areas. Hence, we developed a syngeneic mouse model of multiple myeloma in which Runx2 is specifically deleted in the immature OBs of C57BL6/KaLwRij mice (OB-Runx2-/- mice) to study the effect of OB-Runx2 deficiency on multiple myeloma progression in new bone sites. In vivo studies with this model demonstrated that OB-Runx2 deficiency attracts multiple myeloma cells and promotes multiple myeloma tumor growth in bone. Mechanistic studies further revealed that OB-Runx2 deficiency induces an immunosuppressive microenvironment in BM that is marked by an increase in the concentration and activation of myeloid-derived suppressor cells (MDSC) and the suppression and exhaustion of cytotoxic CD8+ T cells. In contrast, MDSC depletion by either gemcitabine or 5-fluorouracil treatment in OB-Runx2-/- mice prevented these effects and inhibited multiple myeloma tumor growth in BM. These novel discoveries demonstrate that OB-Runx2 deficiency in new bone sites promotes multiple myeloma dissemination and progression by increasing metastatic cytokines and MDSCs in BM and inhibiting BM immunity. Importantly, MDSC depletion can block multiple myeloma progression promoted by OB-Runx2 deficiency.Significance: This study demonstrates that Runx2 deficiency in immature osteoblasts at distant bone sites attracts myeloma cells and allows myeloma progression in new bone sites via OB-secreted metastatic cytokines and MDSC-mediated suppression of bone marrow immunity.

Revisiting Immunotherapy: A Focus on Prostate Cancer

Therapeutic interventions to harness the immune system against tumor cells have provided mixed results in the past for several solid tumors and hematologic malignancies. However, immunotherapy has advanced considerably over the last decade and is becoming an integral combination for treating patients with advanced solid tumors. In particular, prostate cancer immunotherapy has shown modest efficacy for patients in the past. With several key discoveries on immune mechanisms and advanced molecular diagnostic platforms recently, immunotherapy is re-emerging as a viable option for prostate cancer, especially castration-resistant prostate cancer (CRPC), to stimulate antitumor immunity. Combination of patient-tailored immunotherapy and immune checkpoint blockers with conventional cytotoxic agents and androgen receptor-targeted therapies should move the field forward. With a recent adaptation that the application of immune checkpoint inhibitors has been successful in the treatment of more than a dozen solid tumors, including melanoma, lymphoma, liver, cervical, gastrointestinal, and breast cancers, it is a timely endeavor to harness immunotherapy for prostate cancer. Here, we provide an account on the progression of immunotherapy with new discoveries and precision approaches for tumors, in particular CRPC, from mechanistic standpoint to emerging limitations and future directions.

Structural determinants and genetic modifications enhance BMP2 stability and extracellular secretion

The short half-life and use of recombinant bone morphogenetic protein (BMP)-2 in large doses poses major limitations in the clinic. Events regulating post-translational processing and degradation of BMP2 in situ, linked to its secretion, have not been understood. Towards identifying mechanisms regulating intracellular BMP2 stability, we first discovered that inhibiting proteasomal degradation enhances both intracellular BMP2 level and its extracellular secretion. Next, we identified BMP2 degradation occurs through an ubiquitin-mediated mechanism. Since ubiquitination precedes proteasomal turnover and mainly occurs on lysine residues of nascent proteins, we systematically mutated individual lysine residues within BMP2 and tested them for enhanced stability. Results revealed that substitutions on four lysine residues within the pro-BMP2 region and three in the mature region increased both BMP2 turnover and extracellular secretion. Structural modeling revealed key lysine residues involved in proteasomal degradation occupy a lysine cluster near proprotein convertase cleavage site. Interestingly, mutations within these residues did not affect biological activity of BMP2. These data suggest preventing intracellular proteasomal loss of BMP2 through genetic modifications can overcome limitations related to its short half-life.

Structural determinants and genetic modifications enhance BMP2 stability and extracellular secretion

The short half-life and use of recombinant bone morphogenetic protein (BMP)-2 in large doses poses major limitations in the clinic. Events regulating post-translational processing and degradation of BMP2 in situ, linked to its secretion, have not been understood. Towards identifying mechanisms regulating intracellular BMP2 stability, we first discovered that inhibiting proteasomal degradation enhances both intracellular BMP2 level and its extracellular secretion. Next, we identified BMP2 degradation occurs through an ubiquitin-mediated mechanism. Since ubiquitination precedes proteasomal turnover and mainly occurs on lysine residues of nascent proteins, we systematically mutated individual lysine residues within BMP2 and tested them for enhanced stability. Results revealed that substitutions on four lysine residues within the pro-BMP2 region and three in the mature region increased both BMP2 turnover and extracellular secretion. Structural modeling revealed key lysine residues involved in proteasomal degradation occupy a lysine cluster near proprotein convertase cleavage site. Interestingly, mutations within these residues did not affect biological activity of BMP2. These data suggest preventing intracellular proteasomal loss of BMP2 through genetic modifications can overcome limitations related to its short half-life.

Recombinant AAV-CEA Tumor Vaccine in Combination with an Immune Adjuvant Breaks Tolerance and Provides Protective Immunity

Carcinoembryonic antigen (CEA) is a human glycoprotein involved in cellular adhesion and expressed during human fetal development. Although expression of CEA largely ceases prior to birth, several human epithelial cancers, including colorectal, gastric, squamous esophageal, and breast carcinomas have been known to overexpress CEA, suggesting its potential as an immunotherapeutic target. Using a transgenic mouse model constitutively expressing human CEA in a spatiotemporal manner as a self-protein and a syngeneic mouse colon cancer cell line, MC38-CEA, overexpressing CEA, we tested the potential of a novel genetic immunotherapy approach against CEA-expressing tumors, using recombinant adeno-associated virus vector encoding CEA (rAAV-CEA) and appropriately timed immune adjuvant application. Results of the study demonstrated breaking of immune tolerance for CEA with this vaccine regimen and an anti-tumor response, resulting in tumor-free survival. Furthermore, tumor challenge of CEA-vaccinated mice with parental MC38 cells not expressing CEA did not result in protection from tumor development, confirming that the protection against tumor development is CEA specific. The study illustrates the feasibility of utilizing rAAV vectors in combination with an immunostimulatory adjuvant to break tolerance to weakly immunogenic self-antigens and for an anti-tumor response.

Pathology, Chemoprevention, and Preclinical Models for Target Validation in Barrett Esophagus

Despite esophageal adenocarcinoma (EAC) being the most widespread among gastrointestinal cancers, with an 11-fold increase in the risk of cancer for patients with Barrett esophagus (BE), its prognosis is still poor. There is a critical need to better perceive the biology of cancer progression and identification of specific targets that are the hallmark of BE's progression. This review explores the established animal models of BE, including genetic, surgical and nonsurgical approaches, potential chemoprevention targets, and the reasoning behind their applications to prevent Barrett-related EAC. The key methodological features in the design feasibility of relevant studies are also discussed. Cancer Res; 78(14); 3747-54. ©2018 AACR.

Abstract 4690: FoxP3+T cells program/re-program the prostatic tumor microenvironment

Foxp3+ T cells play a critical role in maintaining immunological tolerance by regulating functions of other immune cells, thus preventing autoimmunity. Previous studies have demonstrated the importance of Foxp3+ T cells in the tumor, however, the role increasingly recruited FoxP3+ T cells in the programming of prostatic tumor microenvironment is not well illustrated. Therefore, in this study, we have investigated the role of Foxp3+ T cells in the prostatic tumor microenvironment with the notion that increased Foxp3+ T cells facilitate tumor growth. To accomplish this, we carried out tumor induction studies in C57/BL-6 mice using transgenic adenocarcinoma of mouse prostate (TRAMP cell lines: -C1, -C2 and -C3) as tumor models. Mice were administered with TRAMP (C1-3) cells using the Matrigel system. TRAMP-C3 cells are non-tumorigenic while TRAMP-C1 and TRAMP-C2 cells form tumors. Mice were sacrificed by cervical dislocation when tumor sizes reached ~18-20mm in diameter. To prepare single cell suspension, spleen and tumor were dissected out and cells were stained with various cell surface as well as intracellular immune markers to determine the number of Foxp3+ T cells and other immune cells in the prostatic tumor microenvironment. Our findings suggest that the high number of Foxp3+ T cells was found in the spleen and tumor of TRAMP-C1 and TRAMP-C2 mice than the spleen and tiny tumor of TRAMP-C3 mice. Furthermore, the number of cytotoxic T lymphocytes and NK cells were also observed to be low in the tumorigenic TRAMP-C1 and -C2 mice as compared to non-tumorigenic mice (TRAMP-C3). Therefore, our findings suggest that the number of Foxp3+ T cells may play a critical role in shaping the prostatic tumor microenvironment.

Citation Format: Sanjay Kumar, James Stoke III, Shalie Malik, Udai P. Singh, Selvarangan Ponnazhagan, Upender Manne, Manoj K. Mishra. FoxP3+T cells program/re-program the prostatic tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4690.

Myeloid-Derived Suppressor Cells Impair B Cell Responses in Lung Cancer through IL-7 and STAT5

Myeloid-derived suppressor cells (MDSCs) are known suppressors of antitumor immunity, affecting amino acid metabolism and T cell function in the tumor microenvironment. However, it is unknown whether MDSCs regulate B cell responses during tumor progression. Using a syngeneic mouse model of lung cancer, we show reduction in percentages and absolute numbers of B cell subsets including pro-, pre-, and mature B cells in the bone marrow (BM) of tumor-bearing mice. The kinetics of this impaired B cell response correlated with the progressive infiltration of MDSCs. We identified that IL-7 and downstream STAT5 signaling that play a critical role in B cell development and differentiation were also impaired during tumor progression. Global impairment of B cell function was indicated by reduced serum IgG levels. Importantly, we show that anti-Gr-1 Ab-mediated depletion of MDSCs not only rescued serum IgG and IL-7 levels but also reduced TGF-β1, a known regulator of stromal IL-7, suggesting MDSC-mediated regulation of B cell responses. Furthermore, blockade of IL-7 resulted in reduced phosphorylation of downstream STAT5 and B cell differentiation in tumor-bearing mice and administration of TGF-β-blocking Ab rescued these IL-7-dependent B cell responses. Adoptive transfer of BM-derived MDSCs from tumor-bearing mice into congenic recipients resulted in significant reductions of B cell subsets in the BM and in circulation. MDSCs also suppressed B cell proliferation in vitro in an arginase-dependent manner that required cell-to-cell contact. Our results indicate that tumor-infiltrating MDSCs may suppress humoral immune responses and promote tumor escape from immune surveillance.

Regulatory T cells modulate immune cells and promote tumor growth in prostatic tumor microenvironment

Several tumors express antigens that can be recognized by T lymphocytes, suggesting that T cell-mediated immune response may play a critical role in anti-tumor immunity. Studies demonstrated that Regulatory T cells (TR) suppress the functions of immune cells, which are capable to recognized and eliminate tumor cells. However, there exists an utmost demand for further research how immune cells (CD8+ cells, NK cells, etc.) fail to suppress tumor growth and proliferation in the prostatic tumor microenvironment. To investigate this, tumor induction studies in C57/BL-6 mice using transgenic adenocarcinoma of mouse prostate (TRAMP cell lines: -C1, -C2 and -C3) as tumor models were performed. TRAMP-C3 did not form tumor while TRAMP-C1 and TRAMP-C2 cells are tumorigenic. For tumor induction, mice were administered with TRAMP (C1-3) cells. Mice were sacrificed by cervical dislocation when tumor sizes reached ~18–20mm in diameter. A single cell suspension (obtained from spleen, draining lymph node, and tumor) was stained with various cell surface/intracellular immune markers/cytokines to enumerate CD8+ T/TR/NK/Ly6G/Ly6C+ -MDSC cells. Additionally, the expression of TGF-β, IFN-γ, IL-4, IL-17, PD-1 and PDL-1 and cell cycle analysis for CD8+ T cells was also carried out. Our findings suggest that recruitment of suppressive TR and Ly6G/Ly6C+ -MDSC cells and high expression TGF-β and PD-1 and lower expression of NKG2D and IFN-γ and low number of NK and CD8+ cytotoxic T cells in spleen, draining LN and tumor of TRAMP-C1 and TRAMP-C2 (as compared to TRAMP-C3 mice) facilitated tumor growth. Therefore, the expression of PD-1 and TGF-β on TR suggest that TR might be playing a significant role in facilitating tumor growth and progression.

Osteoclast proton pump regulator Atp6v1c1 enhances breast cancer growth by activating the mTORC1 pathway and bone metastasis by increasing V-ATPase activity

It is known that V-ATPases (vacuolar H⁺-ATPase) are involved in breast cancer growth and metastasis. Part of this action is similar to their role in osteoclasts, where they’re involved in extracellular acidification and matrix destruction; however, the roles of their subunits in cancer cell proliferation, signaling, and other pro-tumor actions are not well established. Analysis of TCGA data shows that V-ATPase subunit Atp6v1c1 is overexpressed or amplified in 34% of human breast cancer cases, with a 2-fold decrease in survival at 12 years. Whereas other subunits, such as Atp6v1c2 and Atp6v0a3, are overexpressed or genomically amplified less often, 6% each respectively, and have less impact on survival. Experiments show that lentiviral-shRNA mediated ATP6v1c1 knockdown in 4T1 mouse mammary cancer cells significantly reduces orthotopic and intraosseous tumor growth. ATP6v1c1 knockdown also significantly reduces tumor stimulated bone resorption through osteoclastogenesis at the bone and metastasis in vivo, as well as V-ATPase activity, proliferation, and mTORC1 activation in vitro. To generalize the effects of ATP6v1c1 knockdown on proliferation and mTORC1 activation we used human cancer cell lines - MCF-7, MDA-MB-231, and MDA-MB-435s. ATP6V1C1 knockdown reduced cell proliferation and impaired mTORC1 pathway activation in cancer cells but not in the untransformed cell line C3H10T1/2. Our study reveals that V-ATPase activity may be mediated through mTORC1 and that ATP6v1c1 can be knocked down to block both V-ATPase and mTORC1 activity.

Indoleamine 2,3-dioxygenase regulates anti-tumor immunity in lung cancer by metabolic reprogramming of immune cells in the tumor microenvironment

Indoleamine 2,3-dioxygenase (IDO) has been implicated in immune evasion by tumors. Upregulation of this tryptophan (Trp)-catabolizing enzyme, in tumor cells and myeloid-derived suppressor cells (MDSCs) within the tumor microenvironment (TME), leads to Trp depletion that impairs cytotoxic T cell responses and survival; however, exact mechanisms remain incompletely understood. We previously reported that a combination therapy of gemcitabine and a superoxide dismutase mimetic promotes anti-tumor immunity in a mouse model of lung cancer by inhibiting MDSCs, enhancing polyfunctional response of CD8⁺ memory T cells, and extending survival. Here, we show that combination therapy targets IDO signaling, specifically in MDSCs, tumor cells, and CD8⁺ T cells infiltrating the TME. Deficiency of IDO caused significant reduction in tumor burden, tumor-infiltrating MDSCs, GM-CSF, MDSC survival and infiltration of programmed death receptor-1 (PD-1)-expressing CD8⁺ T cells compared to controls. IDO^−/− MDSCs downregulated nutrient-sensing AMP-activated protein kinase (AMPK) activity, but IDO^−/− CD8⁺ T cells showed AMPK activation associated with enhanced effector function. Our studies provide proof-of-concept for the efficacy of this combination therapy in inhibiting IDO and T cell exhaustion in a syngeneic model of lung cancer and provide mechanistic insights for IDO-dependent metabolic reprogramming of MDSCs that reduces T cell exhaustion and regulates anti-tumor immunity.

Effects of Cellular Methylation on Transgene Expression and Site-Specific Integration of Adeno-Associated Virus

DNA methylation is a major epigenetic event that affects not only cellular gene expression but that also has the potential to influence bacterial and viral DNA in their host-dependent functions. Adeno-associated virus (AAV) genome contains a high degree of CpG sequences capable of methylation in its terminal repeat sequences, which are the sole elements retained in AAV-based vectors used in gene therapy. The present study determined the influence of methylation status of the host cell on wild type (wt) AAV integration and recombinant (r) AAV transgene expression in HeLa cells. Results of the study indicated that hypo-methylation significantly enhanced both wtAAV chromosomal integration and transgene expression of rAAV. A direct influence of methylation on AAV integration was further confirmed by methylating the AAVS1 integration sites prior to viral infection with DNA trans-complementation assay. These results signify the importance of epigenetic status of target cells as one of the key factors in long-term transgene expression in AAV gene therapy.

Abstract 2955: Gr1-MDSCs and Tregs modulate the prostate cancer progression

Myeloid-derived suppressor cells (MDSCs) and Regulatory T cells (Tregs) are the major components of immunosuppressive network that play a critical role in tumor immune evasion. The mechanisms by which tumors induce expansion of suppressive cells and the crosstalk between Gr1-MDSCs (Gr1+, CD11b+, F4/80+) and Tregs relative to TGF-β secretion remain incompletely defined. Prior studies have suggested that MDSCs may contribute to Treg recruitment in cancer. Herein, the goal of this investigation is to examine the role of TGF-β mediated generation of Tregs and Gr1-MDSCs during prostate cancer progression and clearance. To achieve this goal, matrigel system was used along with transgenic adenocarcinoma of mouse prostate (TRAMP-C1, C2 and C3 cell) in C57BL/6 mice. Interestingly, TRAMP-C3 cells are characterized as non-tumorigenic; however, TRAMP-C1 and TRAMP-C2 cells do form tumor. Mice were administered with serial log concentration of TRAMP (C1, C2 and C3) cells along with the matrigel. After three weeks, matrigels along with or without tumor were excised from tumor bearing mice, single cell suspensions was prepared and cells were flow analyzed for GR1-MDSCs and Tregs. Additionally, the TGF-β level was also estimated (colorimetric) in culture supernatant in context to MDSCs and Treg expansion. Our initial findings suggest that the expression of Gr1-MDSCs (Gr1+, CD11b+, F4/80+) and Foxp3+ Tregs increased in TRAMP-C1 and C2 as compared to TRAMP-C3 bearing C57BL/6 mice. These findings indicate that the modulation of Gr1-MDSCs and Tregs could help in tumor suppression.

Citation Format: Sanjay Kumar, James Stokes, Udai Singh, Karyn Scissum Gunn, Upender Manne, Selvarangan Ponnazhagan, Manoj K. Mishra. Gr1-MDSCs and Tregs modulate the prostate cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2955. doi:10.1158/1538-7445.AM2017-2955

PD-1 expression on Foxp3+ Treg cells modulates CD8+ T cell function in prostatic tumor microenvironment

Regulatory T (Treg) cells act as terminators of T cell immune response during prostate cancer progression and development. However, their role and immunosuppressive mechanism(s) in context to programmed death 1 (PD-1) is not completely understood. The present investigation is aimed to determine the role of PD-1 on Treg cells and their impact on CD8+ T cell function in prostatic tumor microenvironment using transgenic adenocarcinoma of the mouse prostate (TRAMP) cells (TRAMP C1, C2 and C3) as a model system. To execute the above aim, tumor induction studies were performed. Briefly, the C57BL/6 mice were administered with serial log concentrations of TRAMP (C1-3) cells. Interestingly, the TRAMP-C3 cells do not form tumor, however, TRAMP-C1 and TRAMP-C2 cells do form tumor. After tumor development, mice were sacrificed by cervical dislocation; tumor, lung, spleen, and draining lymph nodes were harvested when the tumor size reached approximately 20mm. Single cell suspensions were prepared from different organs, cells were then stained with specific antibodies, and flow analyzed for the expression of different immune markers. Our preliminary findings demonstrated that PD-1 expression on Foxp3+ Treg cells displayed greater suppressive capacity against CD8+ T cell function in tumor, lung, spleen, and draining lymph node when compared to the control. More importantly, Foxp3+ Treg(high) PD-1(high) interaction with PDL-1 induced immunosuppression by blocking CD8+ T cells function in prostatic tumor microenvironment. In conclusion, Foxp3+ Treg(high), PD-1(high), and CD8+(low) T cells may enhance tumor progression; thus, targeting the PD-1 on Treg cells may be a possible therapy to treat prostate cancer.

Location of tumor affects local and distant immune cell type and number

INTRODUCTION

Tumors comprise heterogeneous populations of cells, including immune infiltrates that polarize during growth and metastasis. Our preclinical studies on breast cancer (BCa) identified functional differences in myeloid-derived suppressor cells based on tumor microenvironment (TME), prompting variations in host immune response to tumor growth, and dissemination based on tissue type.

METHODS

In order to understand if such variations existed among other immune cells, and if such alteration occurs in response to tumor growth at the primary site or due to bone dissemination, we characterized immune cells, examining localized growth and in the tibia. In addition, immune cells from the spleen were examined from animals of both tumor locations by flow cytometry.

RESULTS

The study demonstrates that location of tumor, and not simply the tumor itself, has a definitive role in regulating immune effectors. Among all immune cells characterized, macrophages were decreased and myeloid dendritic cell were increased in both tumor locations. This difference was more evident in subcutaneous tumors. Additionally, spleens from mice with subcutaneous tumors contained greater increases in both macrophages and myeloid dendritic cells than in mice with bone tumors. Furthermore, in subcutaneous tumors there was an increase in CD4+ and CD8+ T-cell numbers, which was also observed in their spleens.

CONCLUSIONS

These data indicate that alterations in tumor-reactive immune cells are more pronounced at the primary site, and exert a similar change at the major secondary lymphoid organ than in the bone TME. These findings could provide translational insight into designing therapeutic strategies that account for location of metastatic foci.

Endostatin inhibits androgen-independent prostate cancer growth by suppressing nuclear receptor-mediated oxidative stress

Androgen-deprivation therapy has been identified to induce oxidative stress in prostate cancer (PCa), leading to reactivation of androgen receptor (AR) signaling in a hormone-refractory manner. Thus, antioxidant therapies have gained attention as adjuvants for castration-resistant PCa. Here, we report for the first time that human endostatin (ES) prevents androgen-independent growth phenotype in PCa cells through its molecular targeting of AR and glucocorticoid receptor (GR) and downstream pro-oxidant signaling. This reversal after ES treatment significantly decreased PCa cell proliferation through down-regulation of GR and up-regulation of manganese superoxide dismutase and reduced glutathione levels. Proteome and biochemical analyses of ES-treated PCa cells further indicated a significant up-regulation of enzymes in the major reactive oxygen species (ROS) scavenging machinery, including catalase, glutathione synthetase, glutathione reductase, NADPH-cytochrome P450 reductase, biliverdin reductase, and thioredoxin reductase, resulting in a concomitant reduction of intracellular ROS. ES further augmented the antioxidant system through up-regulation of glucose influx, the pentose phosphate pathway, and NAD salvaging pathways. This shift in cancer cell redox homeostasis by ES significantly decreased the effect of protumorigenic oxidative machinery on androgen-independent PCa growth, suggesting that ES can suppress GR-induced resistant phenotype upon AR antagonism and that the dual targeting action of ES on AR and GR can be further translated to PCa therapy.-Lee, J. H., Kang, M., Wang, H., Naik, G., Mobley, J. A., Sonpavde, G., Garvey, W. T., Darley-Usmar, V. M., Ponnazhagan, S. Endostatin inhibits androgen-independent prostate cancer growth by suppressing nuclear receptor-mediated oxidative stress.

Immature myeloid cells are critical for enhancing bone fracture healing through angiogenic cascade

Bone fractures heal with overlapping phases of inflammation, cell proliferation, and bone remodeling. Osteogenesis and angiogenesis work in concert to control many stages of this process, and when one is impaired it leads to failure of bone healing, termed a nonunion. During fracture repair, there is an infiltration of immune cells at the fracture site that not only mediate the inflammatory responses, but we hypothesize they also exert influence on neovasculature. Thus, further understanding the effects of immune cell participation throughout fracture healing will reveal additional knowledge as to why some fractures heal while others form nonunions, and lead to development of novel therapeutics modulating immune cells, to increase fracture healing and prevent nonunions. Using novel femoral segmental and critical-size defect models in mice, we identified a systemic and significant increase in immature myeloid cell (IMC) infiltration during the initial phase of fracture healing until boney union is complete. Using gemcitabine to specifically ablate the IMC population, we confirmed delayed bone healing. Further, adoptive transfer of IMC increased bone growth in a nonunion model, signifying the role of this unique cell population in fracture healing. We also identified IMC post-fracture have the ability to increase endothelial cell migration, and tube formation, signaling the essential communication between the immune system and angiogenesis as a requirement for proper bone healing. Based on this data we propose that IMC may play a significant role in fracture healing and therapeutic targeting of IMC after fracture would minimize the chances of eventual nonunion pathology.

Abstract 1011: Endostatin regulates androgen receptor-mediated metabolic and oxido-reductive pathways in prostate cancer cells

Endostatin (ES) has been recognized for decades as an endogenous protein with antiangiogenic function. Recent findings, however, indicate the pleiotropic effects of ES in different tissue and cell types, ensuing further investigation on unidentified molecular mechanisms of action. Previously, we have shown that ES exerts a direct role in suppressing prostate cancer cell proliferation by inhibiting androgen receptor (AR) activity, signifying therapeutic potential of ES for targeting both tumor epithelia and endothelia. Subsequent to this finding, we identified robust glucose influx and significant reduction of intracellular ROS levels in LNCaP cells upon ES treatment. The ES mutants with low AR binding did not promote glucose uptake through GLUT1 augmentation, suggesting that AR-targeted effects of ES include modulation of downstream metabolic pathways. Surprisingly, global proteome analysis showed that the levels of major metabolic enzymes either in glycolytic pathway or TCA cycle were not changed upon ES treatment. Instead, ES markedly increased the levels of G6PD (5-fold), NAMPT (2.5-fold), and NAPRT (5-fold), indicating upregulation of the late-limiting steps in NAD biosynthesis and pentose phosphate pathway (PPP). Further proteome analysis of ES-treated LNCaP cells strongly indicated upregulation of ROS scavenging machinery, including SOD2 (3- fold), CAT (2-folds), GSS (2-fold), GSR (1.8-fold), and POR (4.6-fold). Overall, these data suggest that ES can modulate intracellular ROS levels by augmenting glucose uptake, NAD biosynthesis, and the NADPH levels by shunting metabolic pathways to PPP. Given that basal ROS levels are known to increase upon disease progression to higher grade prostate tumors, ES effect of promoting ROS scavenging machinery can be employed as an adjuvant to re-sensitize prostate cancer cells to ROS-inducing chemo- and radiation therapies.

Abbreviations: CAT: catalase, GLUT1: glucose transporter isoform 1, G6PD: glucose-6-phosphate dehydrogenase, GSS: glutathione synthase, GSR: glutathione reductase, NAMPT: nicotinamide phosphoribosyltransferase, NAPRT: nicotinate phosphoribosyltransferase, POR: NADPH-cytochrome P450 reductase, ROS: reactive oxygen species, SOD2: manganese superoxide dismutase, TCA: tricarboxylic acid

Citation Format: Joo Hyoung Lee, Minsung Kang, James A. Mobley, Guru Sonpavde, W. Timothy Garvey, Victor M. Darley-Usmar, Selvarangan Ponnazhagan. Endostatin regulates androgen receptor-mediated metabolic and oxido-reductive pathways in prostate cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1011.

Abstract 1457: Regulatory T cells and its impact on prostate cancer development and clearance

Prostate Cancer (PCa) is the most common non-skin malignancy and the most commonly diagnosed cancer in men in United States. The immunotherapeutic role of immune cells in regulation of PCa have been studied but still the specific roles of regulatory T cells needs further investigation. In this study, the role of immune cells, particularly the role of regulatory T cells, in tumor development and progression was analyzed using TRAMP (transgenic adenocarcinoma of mouse prostate) model system. TRAMP cells (TRAMP C1, C2 and C3) were used to induce tumor in C57/B6 mouse. Interestingly, the TRAMP-C3 is non-tumorigenic whileTRAMP-C1 and TRAMP-C2 are tumorigenic. Briefly, tumor induction studies were performed on different groups of mice. Mice were inoculated with these three cell lines, tumors were analyzed at different time points, and the percentage and absolute number of different immune cells (CD4, CD8, NK, NKT, Macrophages, regulatory T cells, and Dendritic cells) were analyzed. Our data demonstrated that the capacity of TRAMP-C1 and TRAMP-C2 cells to form tumors and the inability of TRAMP-C3 cells to induce tumors is mediated by number of regulatory T cells in the tumor microenvironment. Therefore, the data suggest an understanding of function and effect of regulatory T cells during tumor progression and clearance is needed to successfully develop a targeted therapy to modulate the number of immune cells in the tumor microenvironment.

Citation Format: Sanjay Kumar, James Stokes III, Karyn Scissum Gunn, Udai Singh, Selvarangan Ponnazhagan, Manoj K. Mishra. Regulatory T cells and its impact on prostate cancer development and clearance. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1457.

Abstract 2539: Cell cycle regulation influences the phenotype of breast and prostate cancer stem cells in vitro

The dissemination of metastases from the primary tumor accounts for over 90% of cancer-associated mortality. Despite advances on treatment modalities involving chemotherapeutic drugs, radiotherapy, and surgery, metastasis almost invariably arises by persistence of unresolved cancer cells following initial treatment. One intriguing explanation for this resiliency is the cancer stem-cell (CSC) hypothesis. According to the CSC model, phenotypic heterogeneity exists within the tumor, and a minority fraction of cells are able to reconstitute the tumor following ablation by current treatments. In like manner to their “normal” stem-cell counterparts, CSCs are capable of unlimited self-renewal, and the ability to “differentiate” to reconstitute the phenotypic heterogeneity of the initial tumor. Recent studies have sought to identify cancer stem cells in numerous types of solid tumors, including breast and prostate. Among the cell surface antigens utilized to identify the CSC subpopulations are CD24, CD44, CD133, and other factors associated with epithelial-to-mesenchymal transition (EMT).

In this study, we sought to investigate the phenotypic changes associated with cell-cycle in breast (BCa-SC) and prostate (PCa-SC) cancer. We characterized in vitro the malignant and osteolytic human breast cancer cell line MDA-MB-231 and human prostate cancer cell line PC3, with the goal of identifying an optimal checkpoint where the CSC subpopulation would be most vulnerable to subsequent targeted chemotherapy. We found that common CSC markers are expressed in a time-dependent manner due to changes in the cell cycle. Our hypothesis is that temporal inhibition of the cell cycle when the CSC phenotype is least prominent will circumvent the chemo-resistance inherent to CSC.

Citation Format: Joseph Feduska, Carnellia Lee, Selvarangan Ponnazhagan. Cell cycle regulation influences the phenotype of breast and prostate cancer stem cells in vitro. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2539.

Abstract 4328: Resveratrol inhibits NO-mediated oxidative stress in murine prostate cancer cells

Background: Nitric oxide (NO) is an important signaling molecule in the immune, nervous and cardiovascular systems. NO involves in the regulation of cellular behavior as well as cytotoxic events. Studies demonstrated that resveratrol (RES) (a polyphenolic compound in the skin of red fruits) at high concentration (≥50μM) induces NO production in endothelial F-2 cells and in human umbilical vein endothelial cells. However, the impact of RES on the biological functions of NO are still poorly understood. Therefore, the goal of this study was to investigate the impact of RES on NO-mediated oxidative stress at mitochondria level in mouse prostate cancer (PCa) cells.

Experimental Procedures: The transgenic adenocarcinoma of the mouse prostate (TRAMP) cells (mirrors the pathogenesis of human prostate cancer) were cultured in Dulbecco's Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum (FBS), penicillin 100 IU/ml, streptomycin 100 μg/ml, 0.005mg/ml bovine insulin, and 10nM Dehydroisoandrosterone in 5% CO2 at 370C. Cells were harvested by trypsinization after 80% confluency (at 4-5 pass), counted (105/ml), and incubated with RES (50uM), RES (50uM) + Deta-NONOate (750uM), Deta-NONOate (750uM), RES (50uM) +L-NMMA (750uM), and L-NMMA (750uM). Deta-NONOate was used as nitric oxide donor while L-NMMA was used as nitric oxide inhibitor. Thereafter, cell viability, NO-estimation in culture supernatant, mitochondrial membrane potential (MMP), total ROS-production in mitochondria and cytoplasm, and apoptotic assay (Annexin-V and caspase-3/7) were carried out.

Results and Conclusion: PCa cells incubated with RES showed decreased cell viability, decreased NO production in culture supernatant, decreased MMP, and decreased level of ROS in mitochondria. However, PS-externalization, and total ROS in cytoplasm were found high after normalization with control cells. Further, treatment with Deta-NONOate results in decreased cell viability, decreased total ROS in the cytoplasm, and decreased MMP, while mitochondrial ROS and NO production in culture supernatant were observed highly significant as compared control cells. Furthermore, cells were also exposed to the combination of RES and NO which suggest that RES reduced NO-mediated cell killing and reactive oxygen species generation in TRAMP cells. However, no significant changes were observed after L-NMMA exposure to TRAMP cells. The result demonstrates that RES protect cells from NO-mediated cell killing and induced NO-independent apoptosis in PCa cells. This suggests that role of RES as a potential therapeutic agent to control cancer. However, further investigation is needed to explore potential mechanism of action of RES in controlling cancer proliferation.

Citation Format: Sanjay Kumar, James Stokes, Karyn Scissum Gunn, Selvarangan Ponnazhagan, Upender Manne, Manoj K. Mishra. Resveratrol inhibits NO-mediated oxidative stress in murine prostate cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4328.

Prostate cancer-derived cathelicidin-related antimicrobial peptide facilitates macrophage differentiation and polarization of immature myeloid progenitors to protumorigenic macrophages

BACKGROUND

A growing body of evidence indicates a positive correlation between expression of human antimicrobial peptide leucin leucin 37 (LL-37) and progression of epithelial cancers, including prostate cancer (PCa). Although the molecular mechanisms for this correlation has not yet been elucidated, the primary function of LL-37 as a chemotactic molecule for innate immune effector cells suggests its possible association in coordinating protumorigenic mechanisms, mediated by tumor-infiltrating immune cells.

METHODS

To investigate protumorigenic role(s) of cathelicidin-related antimicrobial peptide (CRAMP), a murine orthologue of LL-37, the present study compared tumor growth kinetics between mouse PCa cell lines with and without CRAMP expression (TRAMP-C1 and TRAMP-C1(CRAMP-sh) , respectively) in immunocompetent mice. CRAMP-mediated chemotaxis of different innate immune cell types to the tumor microenvironment (TME) was observed in vivo and confirmed by in vitro chemotaxis assay. The role of CRAMP in differentiation and polarization of immature myeloid progenitors (IMPs) to protumorigenic type 2 macrophages (M2) in TME was determined by adoptive transfer of IMPs into mice bearing CRAMP(+) and CRAMP(-) tumors. To differentiate protumorigenic events mediated by tumor-derived CRAMP from host immune cell-derived CRAMP, tumor challenge study was performed in CRAMP-deficient mice. To identify mechanisms of CRAMP function, macrophage colony stimulating factor (M-CSF) and monocyte chemoattractant protein 1 (MCP-1) gene expression was analyzed by QRT-PCR and STAT3 signaling was determined by immunoblotting.

RESULTS

Significantly delayed tumor growth was observed in wild-type (WT) mice implanted with TRAMP-C1(CRAMP-sh) cells compared to mice implanted with TRAMP-C1 cells. CRAMP(+) TME induced increased number of IMP differentiation into protumorigenic M2 macrophages compared to CRAMP(-) TME, indicating tumor-derived CRAMP facilitates differentiation and polarization of IMPs toward M2. Tumor challenge study in CRAMP deficient mice showed comparable tumor growth kinetics with WT mice, suggesting tumor-derived CRAMP plays a crucial role in PCa progression. In vitro study demonstrated that overexpressed M-CSF and MCP-1 in TRAMP-C1 cells through CRAMP-mediated autocrine signaling, involving p65, regulates IMP-to-M2 differentiation/polarization through STAT3 activation.

CONCLUSION

Altogether, the present study suggests that overexpressed CRAMP in prostate tumor initially chemoattracts IMPs to TME and mediates differentiation and polarization of early myeloid progenitors into protumorigenic M2 macrophages during PCa progression. Thus, selective downregulation of CRAMP in tumor cells in situ may benefit overcoming immunosuppressive mechanisms in PCa.

Regulatory T cells modulate tumor progression and clearance

Regulatory T (Treg) cells, a distinct lineage of T cells, are required to maintain immunological tolerance. However, the molecular mechanism(s) by which Treg cells modulate tumor growth and clearance needs further investigation. Thus, the goal of this study is to analyze the absolute number and role of Treg cells during tumorigenesis. To achieve this goal, tumor induction studies were performed on C57/B6 mice using transgenic adenocarcinoma mouse prostate (TRAMP) cell lines C1, C2 and C3. Interestingly, TRAMP C1 and C2 are tumorigenic while TRAMP C3 fail to form tumor. C57/B6 mice treated with different tumorigenic concentrations of TRAMP (C1, C2, and C3) cells. The experimental design also included appropriate controls. Developing tumors, spleen and draining lymph nodes were dissected out and single cell suspensions were prepared. Cells were stained with the specific antibodies such as NK cells, NKT cells, CD4, CD8, macrophages, B cells and Treg cells and analyzed using a 13-color flowcytometer. Preliminary data revealed that development of tumors by TRAMP C1 and TRAMP C2 cells and non-tumorigenesis by TRAMP C3 cells was dependent on number of Treg cells in tumor microenvironment. Therefore, the data suggest that the number of Treg cells present in tumor microenvironment may have a direct impact on tumor progression and clearance. Thus, modulating the number of Treg cells in tumor microenvironment may be a successful therapeutic strategy to control tumor progression

Abstract 434: Prostate cancer cell-derived cathelicidin-related antimicrobial peptide regulates MCP-1 and CXCL1/2 through autocrine signaling

Prostate cancer (PCa) is the most commonly diagnosed cancer and the second leading cause of cancer deaths among males in the United States. Even with conventional therapies PCa metastasizes to advanced stage in many patients, suggesting a need for alternate therapeutic targets to increase patient survival. We have recently shown that elevated levels of the human antimicrobial peptides, leucin leucin-37 (LL-37) and its murine orthologue, cathelicidin-related antimicrobial peptide (CRAMP), were positively associated with PCa progression. In addition, we have observed that PCa-derived CRAMP chemoattracts protumorigenic immune cells, including macrophages, neutrophils, and myeloid-derived suppressor cells (MDSCs) to the tumor microenvironment. To further understand possible protumorigenic immune mechanisms of CRAMP during PCa growth, we studied a relationship between CRAMP and formyl peptide receptor 2 (FPR2) in mouse PCa cell lines. Interestingly, we observed that TRAMP-C1 cells, which express high-level of CRAMP, also express high levels of its receptor, FPR2, whereas its cloned derivative, TRAMP-C1shRNA cells with targeted down-regulation of CRAMP, display decreased level of FPR2 both in mRNA and protein levels. We further characterized downstream target genes of CRAMP-FPR2 signaling pathway. Quantitative real-time PCR results indicated that TRAMP-C1 cells have increased expression of both monocyte chemotactic protein-1 (MCP-1), known to chemoattract monotyes/macrophages, and CXCL1/2, known to chemoattract neutrophils and MDSCs, whereas TRAMP-C1shRNA cells exhibited low levels of MCP-1 and CXCL1/2 mRNA. Moreover, results indicated elevated gene expression of FPR2, MCP-1, and CXCL1/2 in TRAMP-C1shRNA cells following stimulation with exogenous CRAMP peptide in culture. In a separate experiment, we also observed down-regulation of MCP-1 and CXCL1/2 in TRAMP-C1 cells after the blockade of FPR2 by FPR2 inhibitor, suggesting a possible association between CRAMP and FPR2 in TRAMP-C1 cells, influencing the levels of MCP-1 and CXCL1/2 during PCa progression. Chemokines including MCP-1 and CXCL1/2 play a significant role in PCa development by recruiting protumorigenic immune effectors, such as MDSCs, tumor-associated macrophages and neutrophils to the tumor microenvironment. Thus, understanding the role of CRAMP in stimulating PCa cells to produce protumorigenic chemokines will define the immunomodulatory role of CRAMP during PCa progression.

Altogether, the data suggest that PCa-derived CRAMP triggers pro-tumorigenic stimuli by influencing levels of protumorigenic chemokines through autocrine and paracrine FPR2 signaling. Ongoing studies to identify transcriptional regulators influenced by CRAMP-FPR2 signaling will further define the precise mechanisms of action of CRAMP, to possibly extend the findings in PCa patients as a potential therapeutic target.

Citation Format: Ha-Ram Cha, Jonathan Hensel, Selvarangan Ponnazhagan. Prostate cancer cell-derived cathelicidin-related antimicrobial peptide regulates MCP-1 and CXCL1/2 through autocrine signaling. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 434. doi:10.1158/1538-7445.AM2015-434

Abstract 5050: Proteome-based combined treatment strategies synergizing antagonism of androgen receptor function in prostate cancer

Acquired resistance to second-generation androgen receptor (AR)-targeted therapies compels the development of novel therapeutic agents for castration-resistant prostate cancer (CRPC). We have recently reported a novel function of endostatin (ES) through direct binding and inhibition of AR in human prostate cancer (PCa) cells. Molecular characterization of the putative mechanisms of ES function on AR-positive PCa cells by global proteomic analysis revealed dramatic upregulation of CYP51A1 expression in LNCaP cells, suggesting that the increases in cholesterol biosynthesis and the resultant steroidogenesis may provide survival mechanism for PCa cells through the augmentation of androgen-AR axis. To validate this hypothesis, anti-proliferative effects of combined treatment of ES with Lovastatin or Fluconazole, inhibitor of HMG-CoA reductase or CYP5A1, were analyzed in vitro using AR-positive LNCaP cells. Results indicated a significantly enhanced ES-mediated growth inhibition on LNCaP cells by targeting both the ligand biosynthesis and receptor function. Proteomic profiling further indicated that ES significantly decreased the levels of AR, coactivator Ran (ARA24) and downregulated AR-driven expression of MCM complex 2, 3, 4 and 6, MDC1 and STMN1, suggesting that AR-targeted effects of ES include disruption of DNA replication, cell cycle propagation and cell division. We found that dual inhibition of AR nuclear transport and AR-mediated cell division by co-treatment of ES and Taxol greatly decreased PCa cell proliferation. Together, this interdisciplinary approach integrating proteomics with PCa cell function possibly suggests that antagonism of AR, which is the principal drug target for the PCa treatment, can be potentiated by the combination of ES with currently used chemotherapy agents and adjuvants. These findings further provide new insights into proteome-based approach as a useful tool to design and optimize effective therapeutic regimens for individual patients with CRPC.

Citation Format: Joo Hyoung Lee, James A. Mobley, Selvarangan Ponnazhagan. Proteome-based combined treatment strategies synergizing antagonism of androgen receptor function in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5050. doi:10.1158/1538-7445.AM2015-5050

SOCS3 Deficiency in Myeloid Cells Promotes Tumor Development: Involvement of STAT3 Activation and Myeloid-Derived Suppressor Cells

Suppressor of cytokine signaling (SOCS) proteins are negative regulators of the JAK/STAT pathway and generally function as tumor suppressors. The absence of SOCS3 in particular leads to heightened activation of the STAT3 transcription factor, which has a striking ability to promote tumor survival while suppressing antitumor immunity. We report for the first time that genetic deletion of SOCS3, specifically in myeloid cells, significantly enhances tumor growth, which correlates with elevated levels of myeloid-derived suppressor cells (MDSC) in the tumor microenvironment, and diminishes CD8(+) T-cell infiltration in tumors. The importance of MDSCs in promoting tumor growth is documented by reduced tumor growth upon depletion of MDSCs. Furthermore, SOCS3-deficient bone-marrow-derived cells exhibit heightened STAT3 activation and preferentially differentiate into the Gr-1(+)CD11b(+)Ly6G(+) MDSC phenotype. Importantly, we identify G-CSF as a critical factor secreted by the tumor microenvironment that promotes development of MDSCs via a STAT3-dependent pathway. Abrogation of tumor-derived G-CSF reduces the proliferation and accumulation of Gr-1(+)CD11b(+) MDSCs and inhibits tumor growth. These findings highlight the critical function of SOCS3 as a negative regulator of MDSC development and function via inhibition of STAT3 activation.

Variants of Osteoprotegerin Lacking TRAIL Binding for Therapeutic Bone Remodeling in Osteolytic Malignancies

Osteolytic bone damage is a major cause of morbidity in several metastatic pathologies. Current therapies using bisphosphonates provide modest improvement, but cytotoxic side effects still occur prompting the need to develop more effective therapies to target aggressive osteoclastogenesis. Increased levels of receptor activator of NF-κB ligand (TNFSF11/RANKL), leading to RANKL-RANK signaling, remain the key axis for osteoclast activation and bone resorption. Osteoprotegerin (TNFRSF11B/OPG), a decoy receptor for RANKL, is significantly decreased in patients who present with bone lesions. Despite its potential in inhibiting osteoclast activation, OPG also binds to TNF-related apoptosis-inducing ligand (TNFSF10/TRAIL), making tumor cells resistant to apoptosis. Toward uncoupling the events of TRAIL binding of OPG and to improve its utility for bone remodeling without inducing tumor resistance to apoptosis, OPG mutants were developed by structural homology modeling based on interactive domain identification and by superimposing models of OPG, TRAIL, and its receptor DR5 (TNFRSF10B) to identify regions of OPG for rational design. The OPG mutants were purified and extensively characterized for their ability to decrease osteoclast damage without affecting tumor apoptosis pathway both in vitro and in vivo, confirming their potential in bone remodeling following cancer-induced osteolytic damage.

IMPLICATIONS

OPG variants were developed that lack TRAIL binding, yet retain RANKL binding and suggest new possibilities for therapeutic targeting in osteolytic malignancies.

Myeloid-derived suppressor cells as a novel target for the control of osteolytic bone disease

Myeloid-derived suppressor cells (MDSC) from mice bearing bone metastases differentiate into functional osteoclasts in vitro and in vivo, through a signaling pathway that relies on nitric oxide. In addition, MDSC-targeting drugs have been shown to robustly inhibit osteolysis. Thus, MDSC stand out as novel osteoclast progenitors and hence as candidate targets for the control of osteolytic bone disease.

Role of plasmacytoid dendritic cells in breast cancer bone dissemination

Elevated levels of plasmacytoid dendritic cells (pDC) have been observed as breast cancer disseminates to the bone. The selective depletion of pDC in mice led to a total abrogation of bone metastasis as well as to an increase in T_H1 antitumor response, suggesting that pDC may be considered as a potential therapeutic target for metastatic breast cancer.

Abstract 612: Endostatin is a novel inhibitor of androgen receptor function in prostate cancer

Abnormalities in androgen-androgen receptor (AR) axis have long been recognized for their roles in promoting prostate tumor growth and metastasis. Conventional therapies targeting androgen ablation show transient tumor regression, however, when the tumor recurs during castration-refractory metastatic stage, the current treatment options are very limited. Although the precise mechanism by which prostate cancer (PCa) cells circumvent the androgen deprivation is unclear, recurring tumors have been shown to retain AR activity and upregulation of AR-target gene expression such as prostate specific antigen (PSA), suggesting that targeting AR remains a key component of developing novel therapeutic strategies. Here, we show a profound effect of endostatin, an endogenous angiogenesis inhibitor, on proliferation and invasion of AR-positive PCa cells by targeting AR function. The present study identified that intracellular trafficking of endostatin and direct interaction with AR disrupts AR nuclear translocation and the consequent transcriptional activation of PSA gene. In addition, our structural modeling and site-directed mutagenesis studies suggest that the binding mechanism may include the interaction of bulky side chains (F31 and F34) present in endostatin with the co-activator binding interface (AF-2) in AR ligand-binding domain (LBD). Regarding drug resistance to the second-generation androgen antagonists in patients with metastatic PCa, recent studies revealed that a missense mutation in AR LBD (F876L) and the consequential antagonist-to-agonist switch confers continued AR activity. In this context, our study suggests that endostatin can be recognized as an endogenous AR inhibitor where its molecular interaction with AR may prevent from agonistic switch of AR function by fully masking the AF-2 subdomain. Overall, the current finding provides new insights into endostatin whose anti-cancer activity is not only limited to inhibiting angiogenesis, but can also be expanded to suppressing AR-mediated PCa progression by disrupting AR transactivation.

Citation Format: Joo Hyoung Lee, Tatyana Isayeva, Matthew Larson, Diptiman Chanda, Igor Chesnokov, Selvarangan Ponnazhagan. Endostatin is a novel inhibitor of androgen receptor function in prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 612. doi:10.1158/1538-7445.AM2014-612

Abstract 162: Immunomodulatory role of CRAMP (cathelicidin-related antimicrobial peptide) in prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed cancer and the second leading cause of cancer deaths among males in the United States. Successful treatments for patients with metastatic PCa are limited suggesting a need for alternate targets. Recently, we identified that antimicrobial peptides in human (LL-37) and mouse (CRAMP) are positively correlated with PCa progression in humans and mice, respectively. As a host defense peptide, LL-37/CRAMP functions against microbial pathogens, and in chemotaxis of leukocytes at sites of inflammation. Preliminary studies pertaining to immunomodulation of PCa cell-derived CRAMP in situ indicated that CRAMP chemoattracts myeloid-derived suppressor cells (MDSC), a heterogeneous population of myeloid precursors that induce T cell suppression, to tumor microenvironment (TME) indicating the significance of CRAMP in pro-tumorigenic immune cell functions during PCa progression. The present study further evaluated role of CRAMP as an immunomodulator during PCa growth using transplantable mouse PCa cell line, TRAMP-C1, containing varying CRAMP expression in wild-type and CRAMP loss of function mouse (Cnlp-/-) models. Results of the study indicated targeted down-regulation of CRAMP in mouse PCa cells delays tumorigenesis in syngenic immunocompetent mouse model suggesting significance of CRAMP in PCa development. Whereas implantation of PCa cells abrogated of CRAMP resulted in retention of neutrophils and macrophages in spleen at significantly elevated levels, mice bearing CRAMP-expressing tumors displayed decreased number of neutrophils and macrophages in spleen, but increased infiltration toward TME. These results suggest tumor-derived CRAMP possibly mediates infiltration of neutrophils and macrophages toward TME from spleen. Whether the infiltrated neutrophils and macrophages correlate to pro-tumorigenic N2 and M2 cells, respectively, needs to be confirmed. Since host immune cells, mainly neutrophils, produce CRAMP and recruit additional innate effectors to inflammatory sites, we further analyzed whether host immune cell-derived CRAMP exert synergistic effects in PCa growth together with tumor-derived CRAMP by using Cnlp-/- mice. Results indicated not only comparable tumor growth kinetics, but also comparable levels of MDSC and neutrophils in TME between Cnlp-/- and wild-type mice, suggesting that tumor is a key source of CRAMP that functions as a chemoattractant of MDSC and neutrophils. Taken together, present study proposes that tumor-produced CRAMP functions as a chmoattractant for infiltration of pro-tumorigenic immune cells; MDSC, neutrophils, and macrophages that facilitate tumor growth.

Citation Format: Ha-Ram Cha, Anandi Sawant, Jonathan Hensel, Carnella Lee, Selvarangan Ponnazhagan. Immunomodulatory role of CRAMP (cathelicidin-related antimicrobial peptide) in prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 162. doi:10.1158/1538-7445.AM2014-162

Anterior gradient protein-2 is a regulator of cellular adhesion in prostate cancer

Anterior Gradient Protein (AGR-2) is reported to be over-expressed in many epithelial cancers and promotes metastasis. A clear-cut mechanism for its observed function(s) has not been previously identified. We found significant upregulation of AGR-2 expression in a bone metastatic prostate cancer cell line, PC3, following culturing in bone marrow-conditioned medium. Substantial AGR-2 expression was also confirmed in prostate cancer tissue specimens in patients with bone lesions. By developing stable clones of PC3 cells with varying levels of AGR-2 expression, we identified that abrogation of AGR-2 significantly reduced cellular attachment to fibronectin, collagen I, collagen IV, laminin I and fibrinogen. Loss of cellular adhesion was associated with sharp decrease in the expression of α4, α5, αV, β3 and β4 integrins. Failure to undergo apoptosis following detachment is a hallmark of epithelial cancer metastasis. The AGR-2-silenced PC3 cells showed higher resistance to Tumor necrosis factor-related apoptosis- inducing ligand (TRAIL) induced apoptosis in vitro. This observation was also supported by significantly reduced Caspase-3 expression in AGR-2-silenced PC3 cells, which is a key effector of both extrinsic and intrinsic death signaling pathways. These data suggest that AGR-2 influence prostate cancer metastasis by regulation of cellular adhesion and apoptosis.

Detection of Merkel cell polyomavirus in formalin-fixed, paraffin-embedded tissue of Merkel cell carcinoma and correlation with prognosis

Merkel cell carcinoma (MCC) is a rare, but highly aggressive primary cutaneous malignancy, showing neuroendocrine differentiation. In 2008, a novel member of the polyomavirus family, named Merkel cell polyomavirus (MCPyV) was identified in the genome of MCC tumors raising the possibility of an involvement in its pathogenesis. Due to the rarity of this tumor and current pathology practices, the most readily available tissue is archival formalin-fixed, paraffin-embedded (FFPE) material. In this study, we evaluated the presence of MCPyV in FFPE tissue and correlated its presence with tumor progression. Representative FFPE specimens from 18 tumors belonging to 14 patients with a diagnosis of MCC spanning the period from 2003 to 2008 were retrieved. Following DNA extraction, we performed PCR amplification and sequencing with four different MCPyV-specific primer pairs mapping within the T antigen and VP1 region. Overall, we detected MCPyV amplicons in 8/18 (44.4%) analyzed tumors from 7/14 (50%) cases. Two-year survival rate and median survival for the MCPyV-positive MCCs were 48% and 22.5 months, respectively and for the negative ones 69% and 51.3 months, respectively; however, the difference did not reach statistical significance (p=0.8). There was no significant correlation between the presence of the virus and the stage at presentation; however, tumors in the head and neck area had a lower frequency of viral positivity compared to those arising in the extremities suggesting a MCPyV-independent oncogenetic pathway perhaps, dependent on UV exposure, in a subset of these cases.

The dual targeting of immunosuppressive cells and oxidants promotes effector and memory T-cell functions against lung cancer

We have recently demonstrated that the combination of gemcitabine and a superoxide dismutase mimetic protects mice against lung cancer by suppressing the functions of myeloid-derived suppressor cells and by activating memory CD8⁺ T-cell responses. Persistent memory cells exhibited a glycolytic metabolism, which may have directly enhanced their effector functions. This combinatorial therapeutic regimen may reduce the propensity of some cancer patients to relapse.

Enhancement of antitumor immunity in lung cancer by targeting myeloid-derived suppressor cell pathways

Chemoresistance due to heterogeneity of the tumor microenvironment (TME) hampers the long-term efficacy of first-line therapies for lung cancer. Current combination therapies for lung cancer provide only modest improvement in survival, implicating necessity for novel approaches that suppress malignant growth and stimulate long-term antitumor immunity. Oxidative stress in the TME promotes immunosuppression by tumor-infiltrating myeloid-derived suppressor cells (MDSC), which inhibit host protective antitumor immunity. Using a murine model of lung cancer, we demonstrate that a combination treatment with gemcitabine and a superoxide dismutase mimetic targets immunosuppressive MDSC in the TME and enhances the quantity and quality of both effector and memory CD8(+) T-cell responses. At the effector cell function level, the unique combination therapy targeting MDSC and redox signaling greatly enhanced cytolytic CD8(+) T-cell response and further decreased regulatory T cell infiltration. For long-term antitumor effects, this therapy altered the metabolism of memory cells with self-renewing phenotype and provided a preferential advantage for survival of memory subsets with long-term efficacy and persistence. Adoptive transfer of memory cells from this combination therapy prolonged survival of tumor-bearing recipients. Furthermore, the adoptively transferred memory cells responded to tumor rechallenge exerting long-term persistence. This approach offers a new paradigm to inhibit immunosuppression by direct targeting of MDSC function, to generate effector and persistent memory cells for tumor eradication, and to prevent lung cancer relapse.

Myeloid-derived suppressor cells as osteoclast progenitors: a novel target for controlling osteolytic bone metastasis

Immune cells and their secreted growth factors play major roles in tumor growth and metastasis. Interplay between the growing tumor and infiltrating immune cells determines the nature of immune response and ultimately, tumor fate. Increased infiltration of protumorigenic immune cells promotes tumor growth as well as dissemination to distant sites. These cells induce immunosuppression that inhibits proliferation and functions of cells of antitumor immune response. One population of immunosuppressive cells that is increasingly gaining attention is myeloid-derived suppressor cells (MDSC). MDSCs are immature myeloid progenitors that suppress T-cell effector functions and promote angiogenesis. MDSC numbers are elevated at both the primary tumor and metastatic sites, including bone. In addition to immunosuppressive functions of MDSCs, we and others have recently discovered a novel function for MDSCs as osteoclast progenitors. Osteolysis is a common complication in the carcinomas of breast, lung, prostate, and multiple myeloma with poor prognosis. Therefore, targeting the functions of MDSCs may exert dual therapeutic effects on immunosuppression and bone pathology. Cancer Res; 73(15); 4606-10. ©2013 AACR.

Abstract 250: Growth characteristics of breast cancer stem cells in vitro and in vivo

Breast cancer (BCa) is the most common malignancy in United States women, accounting for greater than 40,000 deaths each year. Studies have attributed the presence of cancer stem cells (CSC) with resistance to chemotherapy as a key component of refractories of treatments in BCa. Breast cancer stem cells (BCa-SC) are characterized by CD24lo and CD44hi phenotype with mesenchymal properties, which differ from the epithelial CD24hi and CD44hi phenotype expressed in the majority of BCa cells. Thus, further understanding properties of BCa-SC may lead to the development of novel treatment options towards treating refractory cancer cells. Fundamental to this, further characterization of BCa-SC will be needed to identify therapeutic targets based CSC biology. To this end, we sought to characterize the plasticity of BCa-SC based on cell cycle in vitro and growth kinetics in vivo. A murine BCa cell line, 4T1, was cultured in CSC medium and analyzed every 6 hrs for CD24 and CD44 expression by flow cytometry. Results of this analysis indicated that specific BCa-SC markers peaked every 24 hours. This data supports a possible reprogramming of BCa-SC based on cell cycle regulation, suggesting the use of cell cycle inhibitors to block cells in particular stages of the cell cycle, which may improve therapeutic approaches to induce cell death. The stemness of these cells was further confirmed by real-time PCR. BCa-SC showed increased expression of ALDH1, TWIST, and TGF-β3 with decreased E-Cadherin and CD24 levels correlating to the phenotypic changes observed with CD24 and CD44 expression. To further examine the role of BCa-SC in tumor growth in vivo, BALB/c mice were subcutaneously implanted with populations of 4T1 cells that constituted CSC and non- cancer stem cells (NCSC) in different combinations and tumor growth was analyzed. Results showed that the growth kinetics CSC and NCSC when used alone was significantly lower in vivo compared to mixed populations containing both CSC and NCSC, suggesting CSC may attribute for the repopulation of the disease but an aggressive growth requires differentiated non-stem cells in the tumor microenvironment.

Citation Format: Carnella M. Lee, Anandi Sawant, Ha-Ram Cha, Selvarangan Ponnazhagan. Growth characteristics of breast cancer stem cells in vitro and in vivo. [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 250. doi:10.1158/1538-7445.AM2013-250

Myeloid-derived suppressor cells function as novel osteoclast progenitors enhancing bone loss in breast cancer

Enhanced bone destruction is a hallmark of various carcinomas such as breast cancer, where osteolytic bone metastasis is associated with increased morbidity and mortality. Immune cells contribute to osteolysis in cancer growth, but the factors contributing to aggressive bone destruction are not well understood. In this study, we show the importance of myeloid-derived suppressor cells (MDSC) in this process at bone metastatic sites. Because MDSC originate from the same myeloid lineage as macrophages, which are osteoclast precursors, we hypothesized that MDSC may undergo osteoclast differentiation and contribute to enhanced bone destruction and tumor growth. Using an immunocompetent mouse model of breast cancer bone metastasis, we confirmed that MDSC isolated from the tumor-bone microenvironment differentiated into functional osteoclasts both in vitro and in vivo. Mechanistic investigations revealed that nitric oxide signaling was critical for differentiation of MDSC into osteoclasts. Remarkably, osteoclast differentiation did not occur in MDSC isolated from control or tumor-bearing mice that lacked bone metastasis, signifying the essential cross-talk between tumor cells and myeloid progenitors in the bone microenvironment as a requirement for osteoclast differentiation of MDSC. Overall, our results identify a wholly new facet to the multifunctionality of MDSC in driving tumor progression, in this case as a novel osteoclast progenitor that specifically drives bone metastasis during cancer progression.

Polyglutamate directed coupling of bioactive peptides for the delivery of osteoinductive signals on allograft bone

Allograft bone is commonly used as an alternative to autograft, however allograft lacks many osteoinductive factors present in autologous bone due to processing. In this study, we investigated a method to reconstitute allograft with osteoregenerative factors. Specifically, an osteoinductive peptide from collagen I, DGEA, was engineered to express a heptaglutamate (E7) domain, which binds the hydroxyapatite within bone mineral. Addition of E7 to DGEA resulted in 9× greater peptide loading on allograft, and significantly greater retention after a 5-day interval with extensive washing. When factoring together greater initial loading and retention, the E7 domain directed a 45-fold enhancement of peptide density on the allograft surface. Peptide-coated allograft was also implanted subcutaneously into rats and it was found that E7DGEA was retained in vivo for at least 3 months. Interestingly, E7DGEA peptides injected intravenously accumulated within bone tissue, implicating a potential role for E7 domains in drug delivery to bone. Finally, we determined that, as with DGEA, the E7 modification enhanced coupling of a bioactive BMP2-derived peptide on allograft. These results suggest that E7 domains are useful for coupling many types of bone-regenerative molecules to the surface of allograft to reintroduce osteoinductive signals and potentially advance allograft treatments.