p75 mediated apoptosis in neuroblastoma cells is inhibited by expression of TrkA

Upregulation of p75NTR by Histone Deacetylase Inhibitors Sensitizes Human Neuroblastoma Cells to Targeted Immunotoxin-Induced Apoptosis

Histone deacetylase (HDAC) inhibitors are novel chemotherapy agents with potential utility in the treatment of neuroblastoma, the most frequent solid tumor of childhood. Previous studies have shown that the exposure of human neuroblastoma cells to some HDAC inhibitors enhanced the expression of the common neurotrophin receptor p75NTR. In the present study we investigated whether the upregulation of p75NTR could be exploited to render neuroblastoma cells susceptible to the cytotoxic action of an anti-p75NTR antibody conjugated to the toxin saporin-S6 (p75IgG-Sap). We found that two well-characterized HDAC inhibitors, valproic acid (VPA) and entinostat, were able to induce a strong expression of p75NTR in different human neuroblastoma cell lines but not in other cells, with entinostat, displaying a greater efficacy than VPA. Cell pretreatment with entinostat enhanced p75NTR internalization and intracellular saporin-S6 delivery following p75IgG-Sap exposure. The addition of p75IgG-Sap had no effect on vehicle-pretreated cells but potentiated the apoptotic cell death that was induced by entinostat. In three-dimensional neuroblastoma cell cultures, the subsequent treatment with p75IgG-Sap enhanced the inhibition of spheroid growth and the impairment of cell viability that was produced by entinostat. In athymic mice bearing neuroblastoma xenografts, chronic treatment with entinostat increased the expression of p75NTR in tumors but not in liver, kidney, heart, and cerebellum. The administration of p75IgG-Sap induced apoptosis only in tumors of mice that were pretreated with entinostat. These findings define a novel experimental strategy to selectively eliminate neuroblastoma cells based on the sequential treatment with entinostat and a toxin-conjugated anti-p75NTR antibody.

Evaluating larotrectinib for the treatment of advanced solid tumors harboring an NTRK gene fusion

Introduction: Characteristic of some rare pediatric and adult malignancies, addiction to the NTRK oncogene family is also observed in a small fraction of common cancers. Inhibition of their protein products, the Trk kinases, proved a successful treatment strategy for these tumors.Areas covered: The current paper reviews the clinical development of larotrectinib, a selective inhibitor of the Trk kinase family, for the treatment of NTRK fusion-positive cancers. The manuscript includes an overview of the efficacy, safety, pharmacokinetics and pharmacodynamics. The authors sum up by providing the reader with their expert opinion on larotrectinib and its potential future use.Expert opinion: Larotrectinib showed tolerability and high efficacy, regardless of the primary site. In 2018, larotrectinib was granted by the Food and Drug Administration a tissue-agnostic approval for the treatment of solid tumors harboring an NTRK fusion. The major challenges will be the implementation of the screening for NTRK fusions in the general oncologic population, and the incorporation of larotrectinib into the therapeutic algorithms.

Neurotrophin Signaling in Medulloblastoma

Neurotrophins are a family of secreted proteins that act by binding to tropomyosin receptor kinase (Trk) or p75NTR receptors to regulate nervous system development and plasticity. Increasing evidence indicates that neurotrophins and their receptors in cancer cells play a role in tumor growth and resistance to treatment. In this review, we summarize evidence indicating that neurotrophin signaling influences medulloblastoma (MB), the most common type of malignant brain cancer afflicting children. We discuss the potential of neurotrophin receptors as new therapeutic targets for the treatment of MB. Overall, activation of TrkA and TrkC types of receptors seem to promote cell death, whereas TrkB might stimulate MB growth, and TrkB inhibition displays antitumor effects. Importantly, we show analyses of the gene expression profile of neurotrophins and their receptors in MB primary tumors, which indicate, among other findings, that higher levels of NTRK1 or NTRK2 are associated with reduced overall survival (OS) of patients with SHH MB tumors.

NTRK fusion-positive cancers and TRK inhibitor therapy

NTRK gene fusions involving either NTRK1, NTRK2 or NTRK3 (encoding the neurotrophin receptors TRKA, TRKB and TRKC, respectively) are oncogenic drivers of various adult and paediatric tumour types. These fusions can be detected in the clinic using a variety of methods, including tumour DNA and RNA sequencing and plasma cell-free DNA profiling. The treatment of patients with NTRK fusion-positive cancers with a first-generation TRK inhibitor, such as larotrectinib or entrectinib, is associated with high response rates (>75%), regardless of tumour histology. First-generation TRK inhibitors are well tolerated by most patients, with toxicity profiles characterized by occasional off-tumour, on-target adverse events (attributable to TRK inhibition in non-malignant tissues). Despite durable disease control in many patients, advanced-stage NTRK fusion-positive cancers eventually become refractory to TRK inhibition; resistance can be mediated by the acquisition of NTRK kinase domain mutations. Fortunately, certain resistance mutations can be overcome by second-generation TRK inhibitors, including LOXO-195 and TPX-0005 that are being explored in clinical trials. In this Review, we discuss the biology of NTRK fusions, strategies to target these drivers in the treatment-naive and acquired-resistance disease settings, and the unique safety profile of TRK inhibitors.

Expression of nerve growth factor and brain-derived neurotrophic factor in astrocytomas

Neurotrophic factors (NTFs) are well known to serve critical functions in neural survival, neurite growth and cell differentiation in vivo and in vitro. Previous progress has indicated that nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), two NTF family members, may be involved in the process of tumor progression. In the present study, the expression of NGF and BDNF was detected using immunohistochemistry on 70 adult astrocytoma samples collected from distinct locations as well as of various pathological grades, with an additional 15 samples being collected from normal adult brain tissue to be used as controls. NGF and BDNF were identified to be expressed in all samples, and their positive cell expression rates in astrocytomas demonstrated a significant increase compared with that in the normal controls (P<0.05), particularly in grade III (P<0.05). In addition, the expression of NGF and BDNF exhibited a gradual decrease ranging from the temporal lobe, parietal lobe and cerebellum to the frontal lobe (P<0.05). The results of the present study suggest that the expression of NGF and BDNF is increased in astrocytomas, which is associated with the pathological grade and the astrocytoma location.

Rotary bioreactor culture can discern specific behavior phenotypes in Trk-null and Trk-expressing neuroblastoma cell lines

Neuroblastoma is characterized by biological and genetic heterogeneity that leads to diverse, often unpredictable, clinical behavior. Differential expression of the Trk family of neurotrophin receptors strongly correlates with clinical behavior; TrkA expression is associated with favorable outcome, whereas TrkB with unfavorable outcome. Neuroblastoma cells cultured in a microgravity rotary bioreactor spontaneously aggregate into tumor-like structures, called organoids. We wanted to determine if the clinical heterogeneity of TrkA- or TrkB-expressing neuroblastomas was reflected in aggregation kinetics and organoid morphology. Trk-null SY5Y cells were stably transfected to express either TrkA or TrkB. Short-term aggregation kinetics were determined by counting the number of single (non-aggregated) viable cells in the supernatant over time. Organoids were harvested after 8 d of bioreactor culture, stained, and analyzed morphometrically. SY5Y-TrkA cells aggregated significantly slower than SY5Y and SY5Y-TrkB cells, as quantified by several measures of aggregation. SY5Y and TrkB cell lines formed irregularly shaped organoids, featuring stellate projections. In contrast, TrkA cells formed smooth (non-stellate) organoids. SY5Y organoids were slightly smaller on average, but had significantly larger average perimeter than TrkA or TrkB organoids. TrkA expression alone is sufficient to dramatically alter the behavior of neuroblastoma cells in three-dimensional, in vitro rotary bioreactor culture. This pattern is consistent with both clinical behavior and in vivo tumorigenicity, in that SY5Y-TrkA represents a more differentiated, less aggressive phenotype. The microgravity bioreactor is a useful in vitro tool to rapidly investigate the biological characteristics of neuroblastoma and potentially to assess the effect of cytotoxic as well as biologically targeted drugs.

Expression of NTRK1/TrkA affects immunogenicity of neuroblastoma cells

High levels of the NTRK1/TrkA receptor are expressed in low-stage neuroblastomas, which are characterized by a good patient prognosis and often undergo spontaneous regression. In addition to apoptosis, tumor-immune responses might contribute to this regression. We hypothesized that TrkA expression might enhance the immune response to neuroblastomas. Immunohistochemistry on neuroblastoma tissue microarrays confirmed significantly higher lymphocyte infiltration in low-stage compared with high-stage tumors. Flow cytometry of human SH-SY5Y cells stably transfected with NTRK1/TrkA cDNA revealed significant upregulation of major histocompatibility complex (MHC) class I complexes on TrkA-expressing cells. Corresponding to this upregulation, T cell activity and cytoxicity was enhanced in the presence of SY5Y-TrkA cells or by medium conditioned by them, suggesting the existence of additional soluble factors stimulating the T cell response. Activation of natural killer (NK) cells was only increased in the presence of SY5Y-TrkA conditioned medium (CM) and not in co-culture assays, suggesting a dominant inhibitory effect of upregulated MHC class I as the primary NK cell escape mechanism of TrkA-expressing neuroblastomas. We reanalyzed gene expression data obtained from the cell culture model to identify additional genes involved in the TrkA-mediated modulation of immune responses. Upregulation of selected target genes in SY5Y-TrkA cells was confirmed on transcript and protein levels. However, none of the proteins were detected in medium conditioned by SY5Y-TrkA cells, arguing against these factors as soluble mediators of the TrkA-induced immune response. We here provide evidence that TrkA expression in neuroblastoma leads to an increased immunogenicity that may contribute to a less malignant phenotype and/or spontaneous regression of neuroblastoma cells.

The MYCN oncogene and differentiation in neuroblastoma

Childhood neuroblastoma exhibits a heterogeneous clinical behavior ranging from low-risk tumors with the ability to spontaneously differentiate and regress, to high-risk tumors causing the highest number of cancer related deaths in infants. Amplification of the MYCN oncogene is one of the few prediction markers for adverse outcome. This gene encodes the MYCN transcriptional regulator predominantly expressed in the developing peripheral neural crest. MYCN is vital for proliferation, migration and stem cell homeostasis while decreased levels are associated with terminal neuronal differentiation. Interestingly, high-risk tumors without MYCN amplification frequently display increased c-MYC expression and/or activation of MYC signaling pathways. On the other hand, downregulation of MYCN leads to decreased proliferation and differentiation, emphasizing the importance of MYC signaling in neuroblastoma biology. Furthermore, expression of the neurotrophin receptor TrkA is associated with good prognosis, the ability to differentiate and spontaneous regression while expression of the related TrkB receptor is correlated with bad prognosis and MYCN amplification. Here we discuss the role of MYCN in neuroblastoma with a special focus on the contribution of elevated MYCN signaling for an aggressive and undifferentiated phenotype as well as the potential of using MYCN as a therapeutic target.

The role of nerve growth factor in caspase-dependent apoptosis in human BE(2)C neuroblastoma

PURPOSE

The purpose of the study was to determine if nerve growth factor (NGF) stimulation induces apoptosis in the BE(2)C neuroblastoma cell line in vitro.

METHODS

The LPCX retroviral vector was used to achieve stable transduction of NGF complementary DNA into BE(2)C neuroblastoma cells. Wild-type and NGF-transduced cells were then incubated with varying concentrations of NGF for varying periods. A laddering assay was performed to determine the presence of DNA fragments characteristic of apoptosis. The expression of various cleaved and total caspases was determined by Western immunoblotting.

RESULTS

p75 receptor expression in the NGF-transduced cell line was equivalent to that in the wild-type cell line, but Trk A receptor expression was significantly decreased in BE(2)C-NGF cells. DNA laddering assay demonstrated that only BE(2)C-NGF cells underwent apoptosis after stimulation with exogenous NGF. BE(2)C-NGF cells have increased expression of cleaved caspase-3 when compared with wild-type cells. Cleaved caspase-3 expression is further increased with exogenous NGF stimulation in the transduced cells.

CONCLUSION

This study confirms that NGF stimulation of BE(2)C neuroblastoma cells can induce apoptosis through activation of the caspase cascade in vitro. The differential expression of the receptors Trk A and p75 between the wild-type and NGF-transduced cell lines may explain the differing effects observed.

Necdin and neurotrophin receptors: interactors of relevance for neuronal resistance to oxidant stress

Necdin is a protein known to interact with the neurotrophin receptors, neurotrophic tyrosine kinase receptor type 1 (TrkA) and 75 kD low-affinity neurotrophin receptor (p75NTR). TrkA and p75NTR play roles in development and disease of the nervous system and chemoresistance of nervous system tumors. Necdin deletion is associated with Prader-Willi syndrome. The present studies demonstrate that the effects of necdin on the susceptibility of neuroblastoma cells to oxidant stress are dependent on the ratio of p75NTR to TrkA in the cell. In low p75NTR:TrkA ratio cells, necdin down-regulation decreases sensitivity to oxidant stress and expression of and signaling through TrkA. In high p75NTR:TrkA cells, necdin down-regulation is without effect. The effects of necdin deletion on the developing nervous system may depend on the relative expression of p75NTR and TrkA in the cells of particular regions of the nervous system.

The effect of P75 on Trk receptors in neuroblastomas

Neuroblastomas (NBs) with favorable outcome usually express TrkA, whereas unfavorable NBs frequently express TrkB and its cognate ligand BDNF. P75 (p75(LNTR), NGFR, TNFRSF16) binds NGF-related neurotrophins with low affinity and usually is coexpressed with Trk receptors in NBs. Here, we investigated the importance of p75 coexpression with Trk receptors in NBs. We transfected p75 into two Trk-null NB cell lines, SH-SY5Y and NLF that were also engineered to stably express TrkA or TrkB. Cell numbers were compared between single (Trk alone) and double (Trk+p75) transfectants, and proliferation was assessed by flow cytometry. P75 coexpression had little effect on cell growth in Trk NB cells in the absence of ligand, but it increased sensitivity and greatly enhanced the effect of cognate ligand. Exogenous NGF induced greater phosphorylation of TrkA and AKT. This was associated with increased cell number in TrkA/p75 cells compared to TrkA cells (p<0.01), which was due to increased proliferation in TrkA/p75 cells (p<0.05), followed by differentiation. Exogenous BDNF also increased cell number in TrkB/p75 compared to TrkB cells (p<0.01), due to an increase in proliferation, but without differentiation. Coexpression of p75 also increased specificity of Trk-expressing cells to ligand. NT3-induced phosphorylation of TrkA and AKT was reduced in TrkA/p75 cells. NT3-induced phosphorylation of TrkB (as well as AKT and MAPK) was also reduced with p75 coexpression. Our results suggest that p75 plays an important role in enhancing both the sensitivity of Trk receptors to low levels of ligand, as well as increasing the specificity of Trks to their cognate ligands. It also enhances ligand-induced differentiation in TrkA/p75 but not TrkB/p75 cells.

Necdin and TrkA contribute to modulation by p75NTR of resistance to oxidant stress

The neurotrophin receptor p75NTR provides protection from oxidant stress induced by 6-hydroxydopamine (6-OHDA) and resultant cell death. In the absence of p75NTR, TrkA is upregulated and its signaling pathway effectors are increasingly activated. Necdin, a MAGE protein and known interactor of p75NTR and TrkA, is a potential mediator of this phenomenon. Decreased expression of necdin protein in p75NTR-deficient PC12 cells decreased TrkA expression and increased PC12 cell resistance to 6-OHDA. Inhibition of JNK phosphorylation by SP600125 also resulted in increased resistance to 6-OHDA, suggesting that TrkA signaling underlies the susceptibility of these cells to oxidant stress.

Trk receptor expression and inhibition in neuroblastomas

Neuroblastoma, the most common and deadly solid tumor in children, exhibits heterogeneous clinical behavior, from spontaneous regression to relentless progression. Current evidence suggests that the TRK family of neurotrophin receptors plays a critical role in these diverse behaviors. Neuroblastomas expressing TrkA are biologically favorable and prone to spontaneous regression or differentiation, depending on the absence or presence of its ligand (NGF) in the microenvironment. In contrast, TrkB-expressing tumors frequently have MYCN amplification and are very aggressive and often fatal tumors. These tumors also express the TrkB ligand (BDNF), resulting in an autocrine or paracrine survival pathway. Exposure to BDNF promotes survival, drug resistance, and angiogenesis of TrkB-expressing tumors. Here we review the role of Trks in normal development, the different functions of Trk isoforms, and the major Trk signaling pathways. We also review the roles these receptors play in the heterogeneous biological and clinical behavior of neuroblastomas, and the activation of Trk receptors in other cancers. Finally we address the progress that has been made in developing targeted therapy with Trk-selective inhibitors to treat neuroblastomas and other tumors with activated Trk expression.

The low-affinity neurotrophin receptor, p75, is upregulated in ganglioneuroblastoma/ganglioneuroma and reduces tumorigenicity of neuroblastoma cells in vivo

Neuroblastoma, the most common extracranial tumor of childhood, is derived from neural crest progenitor cells that fail to differentiate along their predefined route to sympathetic neurons or sympatho-adrenergic adrenal cells. Although expression of the high-affinity neurotrophin receptors, TrkA and TrkB, is of major importance in neuroblastoma, the significance of the expression of the low-affinity neurotrophin receptor, p75, is unclear. Here, we analyzed immunohistochemically expression of p75 on a tissue microarray of 93 primary neuroblastic tumors and assessed the functional consequences of p75 expression in neuroblastoma cell lines. We found the p75 receptor protein to be expressed in neuroblastic cells of ganglioneuromas/ganglioneuroblastomas as well as differentiating neuroblastomas, but not in poorly differentiated neuroblastomas. In an unrelated cohort of 110 neuroblastic tumors, p75 mRNA expression levels correlated with differentiation, and patients with tumors that expressed p75 at high levels had an increased event-free and overall survival. In addition, we did not detect p75 expression in 8 established neuroblastoma cell lines examined with FACS analysis. These cell lines exhibited an undifferentiated morphology, and were all derived from aggressive, high-stage neuroblastomas. Ectopic p75 expression in the SH-SY5Y neuroblastoma cell line significantly reduced proliferation, increased the fraction of apoptotic cells in vitro and resulted in a loss of tumorigenicity in nude mice. Taken together, our data suggest that expression of the p75 low-affinity neurotrophin receptor is correlated with a reduced level of tumorigenicity, and that induction of p75 expression may be an option to revert features of an aggressive tumor phenotype.

Peroxynitrite mediates retinal neurodegeneration by inhibiting nerve growth factor survival signaling in experimental and human diabetes

OBJECTIVE

Recently we have shown that diabetes-induced retinal neurodegeneration positively correlates with oxidative stress and peroxynitrite. Studies also show that peroxynitrite impairs nerve growth factor (NGF) survival signaling in sensory neurons. However, the causal role of peroxynitrite and the impact of tyrosine nitration on diabetes-induced retinal neurodegeneration and NGF survival signaling have not been elucidated.

RESEARCH DESIGN AND METHODS

Expression of NGF and its receptors was examined in retinas from human and streptozotocin-induced diabetic rats and retinal ganglion cells (RGCs). Diabetic animals were treated with FeTPPS (15 mg x kg(-1) x day(-1) ip), which catalytically decomposes peroxynitrite to nitrate. After 4 weeks of diabetes, retinal cell death was determined by TUNEL assay. Lipid peroxidation and nitrotyrosine were determined using MDA assay, immunofluorescence, and Slot-Blot analysis. Expression of NGF and its receptors was determined by enzyme-linked immunosorbent assay (ELISA), real-time PCR, immunoprecipitation, and Western blot analyses.

RESULTS

Analyses of retinal neuronal death and NGF showed ninefold and twofold increases, respectively, in diabetic retinas compared with controls. Diabetes also induced increases in lipid peroxidation, nitrotyrosine, and the pro-apoptotic p75(NTR) receptor in human and rat retinas. These effects were associated with tyrosine nitration of the pro-survival TrkA receptor, resulting in diminished phosphorylation of TrkA and its downstream target, Akt. Furthermore, peroxynitrite induced neuronal death, TrkA nitration, and activation of p38 mitogen-activated protein kinase (MAPK) in RGCs, even in the presence of exogenous NGF. FeTPPS prevented tyrosine nitration, restored NGF survival signal, and prevented neuronal death in vitro and in vivo.

CONCLUSIONS

Together, these data suggest that diabetes-induced peroxynitrite impairs NGF neuronal survival by nitrating TrkA receptor and enhancing p75(NTR) expression.

High nerve growth factor receptor (p75NTR) expression is a favourable prognostic factor in paediatric B cell precursor-acute lymphoblastic leukaemia

Nerve growth factor (NGF) plays a pivotal role in cellular survival/death decisions with the low affinity receptor p75NTR predominately transmitting anti-proliferative signals. In spite of its established role in B-cell function and identification as a prognostically favourable marker in a number of malignancies, little is known about the expression pattern and prognostic significance of p75NTR in B cell precursor-acute lymphoblastic leukaemia (BCP-ALL). p75NTR expression was prospectively studied on primary ALL-blasts in a cohort of paediatric patients with common ALL (n = 86) and preB-ALL (n = 34) treated within the Co-operative study group for childhood acute lymphoblastic leukaemia (CoALL) protocol, CoALL06-97. Flow cytometric analysis showed that almost half of the patients expressed no or negligible amounts of p75NTR (<10%). The median expression in patients expressing p75NTR beyond that threshold was 49% (range 11-100%). In patients classified as low-risk at diagnosis, p75NTR expression was significantly higher than in high-risk patients (P = 0.001). Of note, p75NTR expression was lower in the 21 patients who subsequently developed relapse compared with those remaining in remission (P = 0.038). Accordingly, relapse-free survival was significantly better in patients expressing high surface p75NTR (P = 0.041). Thus, in this prospective analysis, high p75NTR expression was a strong prognostic marker that identified a group of paediatric ALL patients with favourable outcome.

Overexpressions of nerve growth factor and its tropomyosin-related kinase A receptor on chordoma cells

STUDY DESIGN

Immunohistochemistry and in situ apoptosis detection assay were performed on chordoma and notochordal cells.

OBJECTIVES

To investigate the expression levels of nerve growth factor (NGF) and its 2 receptors, tropomyosin-related kinase A (TrkA) and p75, as well as proliferation potential and apoptosis indexes in chordoma and notochordal cells.

SUMMARY OF BACKGROUND DATA

Chordomas arise from primitive notochordal remnants. Why these notochordal remnants undergo malignant transformation to chordoma remains unknown. The binding of NGF to the TrkA receptor promotes cell survival, while its binding to the p75 receptor triggers apoptosis. If there is simultaneous expression of both receptors, the effect of TrkA supersedes and the cells survive.

METHODS

We examined 10 surgically obtained sacral chordoma tissue samples to determine the expressions of NGF and TrkA and p75 receptors as well as markers of cellular proliferation and apoptosis. As controls, we used notochordal cells of L4-L5 discs obtained from ten 1-month old rats. We quantified the expressions of NGF and TrkA and p75 receptors as well as markers of cellular proliferation and apoptosis for both groups, respectively.

RESULTS

Chordoma and notochordal cells both expressed NGF as well as TrkA and p75 receptors. While the mean percentage of p75 receptor expression was very similar between chordoma and notochordal cells (P = 0.394), the mean percentages of TrkA and NGF expressions were significantly higher in chordoma cells than in notochordal cells (both P = 0.002). The mean proliferation potential index of chordoma cells was significantly higher than in notochordal cells (P < 0.01). Conversely, the mean apoptosis index of chordoma cells was significantly lower compared with that of notochordal cells (P = 0.03).

CONCLUSION

The current results suggest that increased expressions of NGF and TrkA receptor in chordoma cells might be a possible mechanism of malignant transformation of notochordal remnants to chordoma by negating apoptotic signal of p75 receptor.

Role of nerve growth factor and its receptors in non-nervous cancer growth: efficacy of a tyrosine kinase inhibitor (AG879) and neutralizing antibodies antityrosine kinase receptor A and antinerve growth factor: an in-vitro and in-vivo study

Neurotrophins, originally identified as neuronal survival and differentiation factors, exert their actions through tyrosine kinase receptors such as TrKA, in the case of the nerve growth factor. Neurotrophins also interact with p75, a common receptor devoid of kinase activity and connected to apoptosis. Here we show that nerve growth factor, TrKA and p75 are expressed in cell lines of human cancers of various non-neuronal lineages, including a panel of muscular sarcomas, and we show that all cell lines investigated actively release nerve growth factor into the medium. Treatment by AG879 (a tyrosine kinase inhibitor that inhibits TrKA phosphorylation, but not TrKB and TrKC) or by neutralizing antibodies anti-nerve growth factor and anti-TrKA dramatically decreases their proliferation with a variable increase in apoptosis. Similarly, p75 transfection induced a significant increase in apoptosis. Furthermore, for the first time we have determined by high-performance liquid chromatography the pharmacokinetic profile of a novel preparation of AG879 and we have established an optimal plasmatic concentration for in-vivo administration. Treatment with AG879 in immunodepressed mice grafted with leiomyosarcoma or promyelocytic leukemia cells resulted in dramatic reductions in tumor sizes. In conclusion, our data have a novel preclinical potential for revealing a possible therapeutical utility in targeting in-vivo nerve growth factor/TrKA by AG879 or neutralizing antibody anti-TrKA in cancer proliferation and in muscle sarcomas, in particular.

Cell Renewing in Neuroblastoma: Electrophysiological and Immunocytochemical Characterization of Stem Cells and Derivatives

We explored the stem cell compartment of the SH-SY5Y neuroblastoma (NB) clone and its development by a novel approach, integrating clonal and immunocytochemical investigations with patch-clamp measurements of ion currents simultaneously expressed on single cells. The currents selected were the triad IHERG, IKDR, INa, normally expressed at varying mutual ratios during development of neural crest stem cells, from which NB derives upon neoplastic transformation. These ratios could be used as electrophysiological clusters of differentiation (ECDs), identifying otherwise indistinguishable stages in maturation. Subcloning procedures allowed the isolation of highly clonogenic substrate-adherent (S-type) cells that proved to be p75- and nestinpositive and were characterized by a nude electrophysiological profile (ECDS0). These cells expressed negligible levels of the triad and manifested the capacity of generating the two following lineages: first, a terminally differentiating, smooth muscular lineage, positive for calponin and smooth muscle actin, whose electrophysiological profile is characterized by a progressive diminution of IHERG, the increase of IKDR and INa, and the acquisition of IKIR (ECDS2); second, a neuronal abortive pathway (NF-68 positive), characterized by a variable expression of IHERG and IKDR and a low expression of INa (ECDNS). This population manifested a vigorous amplification, monopolizing the stem cell compartment at the expense of the smooth muscular lineage to such an extent that neuronal-like (N-type) cells must be continuously removed if the latter are to develop.