Pro-survival role of protein kinase C epsilon in Philadelphia chromosome positive acute leukemia.

Durable responses to imatinib monotherapy are rarely seen in aggressive forms of Philadelphia chromosome positive (Ph+) leukemias. To investigate the possible cause of treatment failure we examined the role of protein kinase C epsilon (PKCE), an oncogene highly implicated in the development of solid tumors and resistance to chemotherapy. We found high levels of PKCE transcripts in Ph+ acute lymphoblastic leukemia (ALL) cells from patients and cell lines, and imatinib resistant chronic myeloid leukemia, which were also less responsive to imatinib-induced apoptosis than Ph+ cells with lower PKCE expression. Furthermore, the siRNA-mediated knockdown or peptide inhibition of PKCE in Ph+ cells increased imatinib-induced apoptosis while overexpression of PKCE reduced imatinib-induced apoptosis, with concomitant increase in the pro-survival factor AKT. Our results suggest PKCE plays a protective role against apoptosis induced by BCR-ABL inhibition in Ph+ leukemias with high PKCE expression, such as Ph+ ALL.

Gene profiling reveals association between altered Wnt signaling and loss of T-cell potential with age in human hematopoietic stem cells.

Functional decline of the hematopoietic system occurs during aging and contributes to clinical consequences, including reduced competence of adaptive immunity and increased incidence of myeloid diseases. This has been linked to aging of the hematopoietic stem cell (HSC) compartment and has implications for clinical hematopoietic cell transplantation as prolonged periods of T-cell deficiency follow transplantation of adult mobilized peripheral blood (PB), the primary transplant source. Here, we examined the gene expression profiles of young and aged HSCs from human cord blood and adult mobilized PB, respectively, and found that Wnt signaling genes are differentially expressed between young and aged human HSCs, with less activation of Wnt signaling in aged HSCs. Utilizing the OP9-DL1 in vitro co-culture system to promote T-cell development under stable Notch signaling conditions, we found that Wnt signaling activity is important for T-lineage differentiation. Examination of Wnt signaling components and target gene activation in young and aged human HSCs during T-lineage differentiation revealed an association between reduced Wnt signal transduction, increasing age, and impaired or delayed T-cell differentiation. This defect in Wnt signal activation of aged HSCs appeared to occur in the early T-progenitor cell subset derived during in vitro T-lineage differentiation. Our results reveal that reduced Wnt signaling activity may play a role in the age-related intrinsic defects of aged HSCs and early hematopoietic progenitors and suggest that manipulation of this pathway could contribute to the end goal of improving T-cell generation and immune reconstitution following clinical transplantation.

Single step synthesis of acetylene-substituted oxacalix[4]arenes.

Oxacalixarenes bearing acetylene groups are synthesized in a single step by nucleophilic aromatic substitution reactions of orcinol with various 1,5-diethynyl-2,4-difluorobenzenes. Thermodynamic equilibration of the cyclooligomer mixtures was accomplished for arylethynyl activating groups, leading to increased yields of the corresponding oxacalix[4]arenes. A 1,3-alternate macrocycle conformation is observed in the solid state, presenting a large V-shaped π-surface.

Evaluation of potential PET imaging probes for the orexin 2 receptors.

A wide range of central nervous system (CNS) disorders, particularly those related to sleep, are associated with the abnormal function of orexin (OX) receptors. Several orexin receptor antagonists have been reported in recent years, but currently there are no imaging tools to probe the density and function of orexin receptors in vivo. To date there are no published data on the pharmacokinetics (PK) and accumulation of some lead orexin receptor antagonists. Evaluation of CNS pharmacokinetics in the pursuit of positron emission tomography (PET) radiotracer development could be used to elucidate the association of orexin receptors with diseases and to facilitate the drug discovery and development. To this end, we designed and evaluated carbon-11 labeled compounds based on diazepane orexin receptor antagonists previously described. One of the synthesized compounds, [(11)C]CW4, showed high brain uptake in rats and further evaluated in non-human primate (NHP) using PET-MR imaging. PET scans performed in a baboon showed appropriate early brain uptake for consideration as a radiotracer. However, [(11)C]CW4 exhibited fast kinetics and high nonspecific binding, as determined after co-administration of [(11)C]CW4 and unlabeled CW4. These properties indicate that [(11)C]CW4 has excellent brain penetrance and could be used as a lead compound for developing new CNS-penetrant PET imaging probes of orexin receptors.

An alternative role for acetylenes: activation of fluorobenzenes toward nucleophilic aromatic substitution.

Acetylenes are increasingly versatile functional groups for a range of complexity-building organic transformations and for the construction of desirable molecular architectures. Herein we disclose a previously underappreciated aspect of arylacetylene reactivity by utilizing alkynes as electron-withdrawing groups (EWG) for promoting nucleophilic aromatic substitution (S(N)Ar) reactions. Reaction rates for the substitution of 4-(fluoroethynyl)benzenes by p-cresol were determined by (1)H NMR spectroscopy, and these rate data were used to determine substituent (Hammett) constants for terminal and substituted ethynyl groups. The synthetic scope of acetylene-activated S(N)Ar reactions is broad; fluoroarenes bearing one or two ethynyl groups undergo high-yielding substitution with a variety of oxygen and arylamine nucleophiles.

Application of palladium-mediated (18)F-fluorination to PET radiotracer development: overcoming hurdles to translation.

New chemistry methods for the synthesis of radiolabeled small molecules have the potential to impact clinical positron emission tomography (PET) imaging, if they can be successfully translated. However, progression of modern reactions from the stage of synthetic chemistry development to the preparation of radiotracer doses ready for use in human PET imaging is challenging and rare. Here we describe the process of and the successful translation of a modern palladium-mediated fluorination reaction to non-human primate (NHP) baboon PET imaging-an important milestone on the path to human PET imaging. The method, which transforms [(18)F]fluoride into an electrophilic fluorination reagent, provides access to aryl-(18)F bonds that would be challenging to synthesize via conventional radiochemistry methods.

Radiosynthesis and evaluation of [11C]EMPA as a potential PET tracer for orexin 2 receptors.

EMPA is a selective antagonist of orexin 2 (OX2) receptors. Previous literature with [(3)H]-EMPA suggest that it may be used as an imaging agent for OX2 receptors; however, brain penetration is known to be modest. To evaluate the potential of EMPA as a PET radiotracer in non-human primate (as a step to imaging in man), we radiolabeled EMPA with carbon-11. Radiosynthesis of [(11)C]N-ethyl-2-(N-(6-methoxypyridin-3-yl)-2-methylphenylsulfonamido)-N-(pyridin-3-ylmethyl)acetamide ([(11)C]EMPA), and evaluation as a potential PET tracer for OX2 receptors is described. Synthesis of an appropriate non-radioactive O-desmethyl precursor was achieved from EMPA with sodium iodide and chlorotrimethylsilane. Selective O-methylation using [(11)C]CH3I in the presence of cesium carbonate in DMSO at room temp afforded [(11)C]EMPA in 1.5-2.5% yield (non-decay corrected relative to trapped [(11)C]CH3I at EOS) with ≥95% chemical and radiochemical purities. The total synthesis time was 34-36min from EOB. Studies in rodent suggested that uptake in tissue was dominated by nonspecific binding. However, [(11)C]EMPA also showed poor uptake in both rats and baboon as measured with PET imaging.

Synthesis and evaluation of methylated arylazepine compounds for PET imaging of 5-HT(2c) receptors.

The serotonin 5-HT(2c) receptor is implicated in a number of diseases including obesity, depression, anxiety, and schizophrenia. In order to ascribe the role of 5-HT(2c) in these diseases, a method for measuring 5-HT(2c )density and function in vivo, such as with positron emission tomography (PET), must be developed. Many high-affinity and relatively selective ligands exist for 5-HT(2c) but cannot be accessed with current radiosynthetic methods for use as PET radiotracers. We propose that N-methylation of an arylazepine moiety, a frequent structural feature in 5-HT(2c) ligands, may be a suitable method for producing new radiotracers for 5-HT(2c). The impact of N-methylation has not been previously reported. For the agonists that we selected herein, N-methylation was found to increase affinity up to 8-fold without impairing selectivity. Compound 5, an N-methylated azetidine-derived arylazepine, was found to be brain penetrant and reached a brain/blood ratio of 2.05:1. However, our initial test compound was rapidly metabolized within 20 min of administration and exhibited high nonspecific binding. N-Methylation, with 16 ± 3% isolated radiochemical yield (decay corrected), is robust and may facilitate screening other 5-HT(2c) ligands as radiotracers for PET.

T-cell potential of human adult and cord blood hemopoietic stem cells expanded with the use of aryl hydrocarbon receptor antagonists.

BACKGROUND AIMS: Expansion of hemopoietic stem cells (HSCs) in vitro is a potential strategy for improving transplant outcomes, but expansion methods tend to promote differentiation and loss of stem cell potential. Aryl hydrocarbon receptor antagonists (AhRAs) have recently been shown to protect HSC stemness during expansion; however, little is known of the T-cell regenerative capacity of AhRA-expanded HSCs. In this study, we confirm the protective effect of two commercially available AhRA compounds on HSCs from both cord blood (CB) and adult samples and assess the T-lymphocyte potential of the expanded cells. METHODS: Adult mobilized peripheral blood and CB samples were purified to CD34(+) cells, which were expanded in vitro with cytokines and AhRAs. After 14 d, CD34(+) cells were re-isolated and then grown on in OP9Delta co-culture under conditions that allow T-lymphocyte differentiation. Cells were monitored weekly for T-lineage markers by flow cytometry. RESULTS: Both AhRA compounds promoted maintenance of CD34 expression during 2 weeks of proliferation with growth factors, although adult cells proliferated markedly less than CB cells. AhRA-expanded CD34(+) cells from CB differentiated to T cells on OP9Delta co-culture with the same rate and time course as untreated cells. Adult cells, by contrast, had reduced differentiation to T cells, with donor-dependent variable responses. CONCLUSIONS: This study shows that whereas AhRA treatment is effective in CB samples, expansion of adult HSCs is less successful and reflects their inherent poor potential in T-cell generation.

An efficient and practical radiosynthesis of [11C]temozolomide.

Temozolomide (TMZ) is a prodrug for an alkylating agent used for the treatment of malignant brain tumors. A positron emitting version, [(11)C]TMZ, has been utilized to help elucidate the mechanism and biodistribution of TMZ. Challenges in [(11)C]TMZ synthesis and reformulation make it difficult for routine production. A highly reproducible one-pot radiosynthesis of [(11)C]TMZ with a radiochemical yield of 17 ± 5% and ≥97% radiochemical purity is reported.

Notch signalling inhibits CD4 expression during initiation and differentiation of human T cell lineage.

The Delta/Notch signal transduction pathway is central to T cell differentiation from haemopoietic stem cells (HSCs). Although T cell development is well characterized using expression of cell surface markers, the detailed mechanisms driving differentiation have not been established. This issue becomes central with observations that adult HSCs exhibit poor differentiation towards the T cell lineage relative to neonatal or embryonic precursors. This study investigates the contribution of Notch signalling and stromal support cells to differentiation of adult and Cord Blood (CB) human HSCs, using the Notch signalling OP9Delta co-culture system. Co-cultured cells were assayed at weekly intervals during development for phenotype markers using flow cytometry. Cells were also assayed for mRNA expression at critical developmental stages. Expression of the central thymocyte marker CD4 was initiated independently of Notch signalling, while cells grown with Notch signalling had reduced expression of CD4 mRNA and protein. Interruption of Notch signalling in partially differentiated cells increased CD4 mRNA and protein expression, and promoted differentiation to CD4(+) CD8(+) T cells. We identified a set of genes related to T cell development that were initiated by Notch signalling, and also a set of genes subsequently altered by Notch signal interruption. These results demonstrate that while Notch signalling is essential for establishment of the T cell lineage, at later stages of differentiation, its removal late in differentiation promotes more efficient DP cell generation. Notch signalling adds to signals provided by stromal cells to allow HSCs to differentiate to T cells via initiation of transcription factors such as HES1, GATA3 and TCF7. We also identify gene expression profile differences that may account for low generation of T cells from adult HSCs.

Brain-penetrant LSD1 inhibitors can block memory consolidation.

Modulation of histone modifications in the brain may represent a new mechanism for brain disorder therapy. Post-translational modifications of histones regulate gene expression, affecting major cellular processes such as proliferation, differentiation, and function. An important enzyme involved in one of these histone modifications is lysine specific demethylase 1 (LSD1). This enzyme is flavin-dependent and exhibits homology to amine oxidases. Parnate (2-phenylcyclopropylamine (2-PCPA); tranylcypromine) is a potent inhibitor of monoamine oxidases and derivatives of 2-PCPA have been used for development of selective LSD1 inhibitors based on the ability to form covalent adducts with flavin adenine dinucleotide (FAD). Here we report the synthesis and in vitro characterization of LSD1 inhibitors that bond covalently to FAD. The two most potent and selective inhibitors were used to demonstrate brain penetration when administered systemically to rodents. First, radiosynthesis of a positron-emitting analog was used to obtain preliminary bio-distribution data and whole brain time-activity curves. Second, we demonstrate that this series of LSD1 inhibitors is capable of producing a cognitive effect in a mouse model. By using a memory formation paradigm, novel object recognition, we show that LSD1 inhibition can abolish long-term memory formation without affecting short-term memory, providing further evidence for the importance of reversible histone methylation in the function of the nervous system.

Urokinase signal transduction and its role in cell migration.

Urokinase and its receptor uPAR play a role in cell migration that is being actively characterized. We previously reported that urokinase potentiates cell migration in human airway smooth muscle cells only where there is some primary migratory stimulus such as PDGF or recent exposure to growth medium. In this study, we examined the signaling of urokinase through its receptor, which lacks an intracellular domain and is presumed to act through associations with other membrane proteins. Whereas PDGF (30 min) and PDGF with urokinase increased the amount of the tyrosine dephosphorylase SHP2 in the membrane fraction, urokinase alone (30 min) decreased membrane SHP2. Analysis of the time course of urokinase stimulation showed that SHP2 was brought into association with the urokinase receptor uPAR between 2.5 and 20 min of urokinase, and later dissociated from it. Focal adhesion kinase was steadily lost from association with uPAR during urokinase stimulation, but its phosphorylation state increased and it became cleaved to smaller molecules. Association of uPAR with caveolin also decreased during urokinase stimulation. In contrast, the tyrosine kinase Src increased in the membrane fraction in response to urokinase stimulation. Disruption of raft structures by cyclodextrin treatment led to potentiation of PDGF chemotaxis, similar to urokinase action. Blocking of dephosphorylase activity with vanadate reduced basal cell migration and blocked the action of urokinase on PDGF chemotaxis. These observations support a role for urokinase in altering the phosphorylation state of focal adhesions, leading to breakdown of their structure and facilitation of cell motility.-Carlin, S. M., Resink, T. J., Tamm, M., Roth, M. Urokinase signal transduction and its role in cell migration.

Detection and characterization of OX40 ligand expression in human airway smooth muscle cells: a possible role in asthma?

BACKGROUND: The airway smooth muscle (ASM) cell, originally thought of as a passive structural cell, is now well recognized as an active participant in the pathologic events that occur during persistent asthma. Cell-surface molecules play an important role in the development of an immune response. A number of cell-surface molecules are expressed on ASM cells, and these might contribute to the inflammatory reaction. OBJECTIVE: The purpose of this study was to determine whether OX40 ligand (OX40L), a molecule known to be involved in T-cell activation, was present on the ASM cell surface. METHODS: We used real-time RT-PCR to detect mRNA expression and flow cytometry, ELISA, and immunoprecipitation to detect the presence of cell-surface protein on ASM cells isolated from asthmatic and nonasthmatic individuals. ELISAs and Western blotting were used to determine the functional outcomes of engagement of OX40L. RESULTS: OX40L was present on both asthmatic and nonasthmatic ASM cells. Engagement of OX40L with recombinant OX40:Fc resulted in a significantly greater increase in release of IL-6 from ASM cells of asthmatic patients than from ASM cells of nonasthmatic patients (P<.01). Ligation of OX40L resulted in a rapid translocation of protein kinase C beta2 to the cell membrane. CONCLUSION: Because the receptor for OX40L, OX40, is expressed on CD4+ T cells within 48 hours of stimulation through the T-cell receptor, elucidation of the cross-talk between OX40 and OX40L could be very important in understanding the interaction of cells present in the inflamed airways of an asthmatic patient.

PAR-2 activation, PGE2, and COX-2 in human asthmatic and nonasthmatic airway smooth muscle cells.

The protease-activated receptor-2 (PAR-2) is present on human airway smooth muscle (ASM) cells and can be activated by mast cell tryptase, trypsin, or an activating peptide (AP). Trypsin induced significant increases in PGE2 release from human ASM cells after 6 and 24 h and also induced cyclooxygenase (COX)-2 mRNA expression and COX-2 protein. Tryptase and the PAR-2 AP did not alter PGE2 release or COX-2 protein levels, suggesting a lack of PAR-2 involvement. When we compared results in asthmatic and nonasthmatic muscle cells, both trypsin and bradykinin induced less PGE2 from asthmatic ASM cells, and bradykinin induced significantly less COX-2 mRNA in asthmatic cells. Significantly less PGE2 was released from proliferating ASM cells from asthmatic patients. In conclusion, trypsin induces PGE2 release and COX-2 in human ASM cells, which is unlikely to be via PAR-2 activation. In addition, ASM cells from asthmatic patients produce significantly less PGE2 and COX-2 compared with nonasthmatic cells. These findings may contribute to the increase in muscle mass evident in asthmatic airways.

Urokinase potentiates PDGF-induced chemotaxis of human airway smooth muscle cells.

We investigated the chemotactic action of PDGF and urokinase on human airway smooth muscle (HASM) cells in culture. Cells were put in collagen-coated transwells with 8-micro m perforations, incubated for 4 h with test compounds, then fixed, stained, and counted as migrated nuclei by microscopy. Cells from all culture conditions showed some basal migration (migration in the absence of stimuli during the assay), but cells preincubated for 24 h in 10% FBS or 20 ng/ml PDGF showed higher basal migration than cells quiesced in 1% FBS. PDGF(BB), PDGF(AA), and PDGF(AB) were all chemotactic when added during the assay. PDGF chemotaxis was blocked by the phosphatidyl 3'-kinase inhibitor LY-294002, the MEK inhibitor U-0126, PGE(2), formoterol, pertussis toxin, and the Rho kinase inhibitor Y-27632. Urokinase alone had no stimulatory effect on migration of quiescent cells but caused a dose-dependent potentiation of chemotaxis toward PDGF. Urokinase also potentiated the elevated basal migration of cells pretreated in 10% FBS or PDGF. This potentiating effect of urokinase appears to be novel. We conclude that PDGF and similar cytokines may be important factors in airway remodeling by redistribution of smooth muscle cells during inflammation and that urokinase may be important in potentiating the response.