Developing immunotherapeutic strategies to target brain tumors.

INTRODUCTION: Recent years have seen rapid growth in cancer treatments that enhance the anti-tumor activities of the immune system. Collectively known as immunotherapy, modulation of the immune system has shown success treating some hematological malignancies, but has yet to be successfully applied to the treatment of patients with brain tumors. AREAS COVERED: This review highlights mechanistic insights from murine studies and compiled recent clinical trial data, focusing on the most aggressive brain tumor, glioblastoma (GBM). The field has recently accumulated a critical mass of data, and we discuss past treatment failures in the context of newly developed approaches now entering clinical trials. This article provides an overview of the immunotherapeutic armamentarium currently in development for the treatment of patients with GBM, who are in dire need of safe and effective therapies. Expert commentary: Themes that emerge include the importance of mitigating the effects of an immunosuppressive tumor microenvironment and the potential for innate immune cell activation to enhance cytotoxic anti-tumor activity. Consideration of these studies as a collective may inform the design of new immunotherapies, as well as the immune monitoring protocols for patients participating in clinical trials.

Immune evasion mediated by tumor-derived lactate dehydrogenase induction of NKG2D ligands on myeloid cells in glioblastoma patients.

Myeloid cells are key regulators of the tumor microenvironment, governing local immune responses. Here we report that tumor-infiltrating myeloid cells and circulating monocytes in patients with glioblastoma multiforme (GBM) express ligands for activating the Natural killer group 2, member D (NKG2D) receptor, which cause down-regulation of NKG2D on natural killer (NK) cells. Tumor-infiltrating NK cells isolated from GBM patients fail to lyse NKG2D ligand-expressing tumor cells. We demonstrate that lactate dehydrogenase (LDH) isoform 5 secreted by glioblastoma cells induces NKG2D ligands on monocytes isolated from healthy individuals. Furthermore, sera from GBM patients contain elevated amounts of LDH, which correlate with expression of NKG2D ligands on their autologous circulating monocytes. NKG2D ligands also are present on circulating monocytes isolated from patients with breast, prostate, and hepatitis C virus-induced hepatocellular carcinomas. Together, these findings reveal a previously unidentified immune evasion strategy whereby tumors produce soluble factors that induce NKG2D ligands on myeloid cells, subverting antitumor immune responses.

Identification of chemicals inducing cardiomyocyte proliferation in developmental stage-specific manner with pluripotent stem cells.

BACKGROUND: The proliferation of cardiomyocytes is highly restricted after postnatal maturation, limiting heart regeneration. Elucidation of the regulatory machineries for the proliferation and growth arrest of cardiomyocytes is imperative. Chemical biology is efficient to dissect molecular mechanisms of various cellular events and often provides therapeutic potentials. We have been investigating cardiovascular differentiation with pluripotent stem cells. The combination of stem cell and chemical biology can provide novel approaches to investigate the molecular mechanisms and manipulation of cardiomyocyte proliferation. METHODS AND RESULTS: To identify chemicals that regulate cardiomyocyte proliferation, we performed a screening of a defined chemical library based on proliferation of mouse pluripotent stem cell-derived cardiomyocytes and identified 4 chemical compound groups: inhibitors of glycogen synthase kinase-3, p38 mitogen-activated protein kinase, and Ca(2+)/calmodulin-dependent protein kinase II, and activators of extracellular signal-regulated kinase. Several appropriate combinations of chemicals synergistically enhanced proliferation of cardiomyocytes derived from both mouse and human pluripotent stem cells, notably up to a 14-fold increase in mouse cardiomyocytes. We also examined the effects of identified chemicals on cardiomyocytes in various developmental stages and species. Whereas extracellular signal-regulated kinase activators and Ca(2+)/calmodulin-dependent protein kinase II inhibitors showed proliferative effects only on cardiomyocytes in early developmental stages, glycogen synthase kinase-3 and p38 mitogen-activated protein kinase inhibitors substantially and synergistically induced re-entry and progression of cell cycle in neonatal but also as well as adult cardiomyocytes. CONCLUSIONS: Our approach successfully uncovered novel molecular targets and mechanisms controlling cardiomyocyte proliferation in distinct developmental stages and offered pluripotent stem cell-derived cardiomyocytes as a potent tool to explore chemical-based cardiac regenerative strategies.

Human embryonic stem cell-derived cardiomyocytes migrate in response to gradients of fibronectin and Wnt5a.

An improved understanding of the factors that regulate the migration of human embryonic stem cell-derived cardiomyocytes (hESC-CMs) would provide new insights into human heart development and suggest novel strategies to improve their electromechanical integration after intracardiac transplantation. Since nothing has been reported as to the factors controlling hESC-CM migration, we hypothesized that hESC-CMs would migrate in response to the extracellular matrix and soluble signaling molecules previously implicated in heart morphogenesis. To test this, we screened candidate factors by transwell assay for effects on hESC-CM motility, followed by validation via live-cell imaging and/or gap-closure assays. Fibronectin (FN) elicited a haptotactic response from hESC-CMs, with cells seeded on a steep FN gradient showing nearly a fivefold greater migratory activity than cells on uniform FN. Studies with neutralizing antibodies indicated that adhesion and migration on FN are mediated by integrins α-5 and α-V. Next, we screened 10 soluble candidate factors by transwell assay and found that the noncanonical Wnt, Wnt5a, elicited an approximately twofold increase in migration over controls. This effect was confirmed using the gap-closure assay, in which Wnt5a-treated hESC-CMs showed approximately twofold greater closure than untreated cells. Studies with microfluidic-generated Wnt5a gradients showed that this factor was chemoattractive as well as chemokinetic, and Wnt5a-mediated responses were inhibited by the Frizzled-1/2 receptor antagonist, UM206. In summary, hESC-CMs show robust promigratory responses to FN and Wnt5a, findings that have implications on both cardiac development and cell-based therapies.

Human ES-cell-derived cardiomyocytes electrically couple and suppress arrhythmias in injured hearts.

Transplantation studies in mice and rats have shown that human embryonic-stem-cell-derived cardiomyocytes (hESC-CMs) can improve the function of infarcted hearts, but two critical issues related to their electrophysiological behaviour in vivo remain unresolved. First, the risk of arrhythmias following hESC-CM transplantation in injured hearts has not been determined. Second, the electromechanical integration of hESC-CMs in injured hearts has not been demonstrated, so it is unclear whether these cells improve contractile function directly through addition of new force-generating units. Here we use a guinea-pig model to show that hESC-CM grafts in injured hearts protect against arrhythmias and can contract synchronously with host muscle. Injured hearts with hESC-CM grafts show improved mechanical function and a significantly reduced incidence of both spontaneous and induced ventricular tachycardia. To assess the activity of hESC-CM grafts in vivo, we transplanted hESC-CMs expressing the genetically encoded calcium sensor, GCaMP3 (refs 4, 5). By correlating the GCaMP3 fluorescent signal with the host ECG, we found that grafts in uninjured hearts have consistent 1:1 host­graft coupling. Grafts in injured hearts are more heterogeneous and typically include both coupled and uncoupled regions. Thus, human myocardial grafts meet physiological criteria for true heart regeneration, providing support for the continued development of hESC-based cardiac therapies for both mechanical and electrical repair.

Neuregulin/ErbB signaling regulates cardiac subtype specification in differentiating human embryonic stem cells.

RATIONALE: Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) exhibit either a "working" chamber or a nodal-like phenotype. To generate optimal hESC-CM preparations for eventual clinical application in cell-based therapies, we will need to control their differentiation into these specialized cardiac subtypes. OBJECTIVE: To demonstrate intact neuregulin (NRG)-1ß/ErbB signaling in hESC-CMs and test the hypothesis that this signaling pathway regulates cardiac subtype abundance in hESC-CM cultures. METHODS AND RESULTS: All experiments used hESC-CM cultures generated using our recently reported directed differentiation protocol. To support subsequent action potential phenotyping approaches and provide a higher-throughput method of determining cardiac subtype, we first developed and validated a novel genetic label that identifies nodal-type hESC-CMs. Next, control hESC-CM preparations were compared to those differentiated in the presence of exogenous NRG-1ß, an anti-NRG-1ß neutralizing antibody, or the ErbB antagonist AG1478. We used 3 independent approaches to determine the ratio of cardiac subtypes in the resultant populations: direct action potential phenotyping under current-clamp, activation of the aforementioned genetic label, and subtype-specific marker expression by RT-PCR. Using all 3 end points, we found that inhibition of NRG-1ß/ErbB signaling greatly enhanced the proportion of cells showing the nodal phenotype. CONCLUSIONS: NRG-1ß/ErbB signaling regulates the ratio of nodal- to working-type cells in differentiating hESC-CM cultures and presumably functions similarly during early human heart development. We speculate that, by manipulating NRG-1ß/ErbB signaling, it will be possible to generate preparations of enriched working-type myocytes for infarct repair, or, conversely, nodal cells for potential use in a biological pacemaker.

Quantitative proteomics analysis reveals that proteins differentially expressed in chronic pancreatitis are also frequently involved in pancreatic cancer.

The effective treatment of pancreatic cancer relies on the diagnosis of the disease at an early stage, a difficult challenge. One major obstacle in the development of diagnostic biomarkers of early pancreatic cancer has been the dual expression of potential biomarkers in both chronic pancreatitis and cancer. To better understand the limitations of potential protein biomarkers, we used ICAT technology and tandem mass spectrometry-based proteomics to systematically study protein expression in chronic pancreatitis. Among the 116 differentially expressed proteins identified in chronic pancreatitis, most biological processes were responses to wounding and inflammation, a finding consistent with the underlining inflammation and tissue repair associated with chronic pancreatitis. Furthermore 40% of the differentially expressed proteins identified in chronic pancreatitis have been implicated previously in pancreatic cancer, suggesting some commonality in protein expression between these two diseases. Biological network analysis further identified c-MYC as a common prominent regulatory protein in pancreatic cancer and chronic pancreatitis. Lastly five proteins were selected for validation by Western blot and immunohistochemistry. Annexin A2 and insulin-like growth factor-binding protein 2 were overexpressed in cancer but not in chronic pancreatitis, making them promising biomarker candidates for pancreatic cancer. In addition, our study validated that cathepsin D, integrin beta1, and plasminogen were overexpressed in both pancreatic cancer and chronic pancreatitis. The positive involvement of these proteins in chronic pancreatitis and pancreatic cancer will potentially lower the specificity of these proteins as biomarker candidates for pancreatic cancer. Altogether our study provides some insights into the molecular events in chronic pancreatitis that may lead to diverse strategies for diagnosis and treatment of these diseases.

Comparison of pancreas juice proteins from cancer versus pancreatitis using quantitative proteomic analysis.

OBJECTIVES: Pancreatitis is an inflammatory condition of the pancreas. However, it often shares many molecular features with pancreatic cancer. Biomarkers present in pancreatic cancer frequently occur in the setting of pancreatitis. The efforts to develop diagnostic biomarkers for pancreatic cancer have thus been complicated by the false-positive involvement of pancreatitis. METHODS: In an attempt to develop protein biomarkers for pancreatic cancer, we previously use quantitative proteomics to identify and quantify the proteins from pancreatic cancer juice. Pancreatic juice is a rich source of proteins that are shed by the pancreatic ductal cells. In this study, we used a similar approach to identify and quantify proteins from pancreatitis juice. RESULTS: In total, 72 proteins were identified and quantified in the comparison of pancreatic juice from pancreatitis patients versus pooled normal control juice. Nineteen of the juice proteins were overexpressed, and 8 were underexpressed in pancreatitis juice by at least 2-fold compared with normal pancreatic juice. Of these 27 differentially expressed proteins in pancreatitis, 9 proteins were also differentially expressed in the pancreatic juice from pancreatic cancer patient. CONCLUSIONS: Identification of these differentially expressed proteins from pancreatitis juice provides useful information for future study of specific pancreatitis-associated proteins and to eliminate potential false-positive biomarkers for pancreatic cancer.

Palladin mutation causes familial pancreatic cancer and suggests a new cancer mechanism.

BACKGROUND: Pancreatic cancer is a deadly disease. Discovery of the mutated genes that cause the inherited form(s) of the disease may shed light on the mechanism(s) of oncogenesis. Previously we isolated a susceptibility locus for familial pancreatic cancer to chromosome location 4q32-34. In this study, our goal was to discover the identity of the familial pancreatic cancer gene on 4q32 and determine the function of that gene. METHODS AND FINDINGS: A customized microarray of the candidate chromosomal region affecting pancreatic cancer susceptibility revealed the greatest expression change in palladin (PALLD), a gene that encodes a component of the cytoskeleton that controls cell shape and motility. A mutation causing a proline (hydrophobic) to serine (hydrophilic) amino acid change (P239S) in a highly conserved region tracked with all affected family members and was absent in the non-affected members. The mutational change is not a known single nucleotide polymorphism. Palladin RNA, measured by quantitative RT-PCR, was overexpressed in the tissues from precancerous dysplasia and pancreatic adenocarcinoma in both familial and sporadic disease. Transfection of wild-type and P239S mutant palladin gene constructs into HeLa cells revealed a clear phenotypic effect: cells expressing P239S palladin exhibited cytoskeletal changes, abnormal actin bundle assembly, and an increased ability to migrate. CONCLUSIONS: These observations suggest that the presence of an abnormal palladin gene in familial pancreatic cancer and the overexpression of palladin protein in sporadic pancreatic cancer cause cytoskeletal changes in pancreatic cancer and may be responsible for or contribute to the tumor's strong invasive and migratory abilities.