A Brain-Derived Neurotrophic Factor-Based p75NTR Peptide Mimetic Ameliorates Experimental Autoimmune Neuritis Induced Axonal Pathology and Demyelination.

Axonal damage and demyelination are major determinants of disability in patients with peripheral demyelinating neuropathies. The neurotrophin family of growth factors are essential for the normal development and myelination of the peripheral nervous system (PNS), and as such are potential therapeutic candidates for ameliorating axonal and myelin damage. In particular, BDNF promotes peripheral nerve myelination via p75 neurotrophin receptor (p75NTR) receptors. Here, we investigated the therapeutic efficacy of a small structural mimetic of the region of BDNF that binds to p75NTR (cyclo-dPAKKR) in experimental autoimmune neuritis (EAN), an established animal model of peripheral demyelinating neuropathy. Examination of rodents induced with EAN revealed that p75NTR is abundantly expressed in affected peripheral nerves. We found that systemic administration of cyclo-dPAKKR ameliorates EAN disease severity and accelerates recovery. Animals treated with cyclo-dPAKKR displayed significantly better motor performance compared to control animals. Histological assessment revealed that cyclo-dPAKKR administration limits the extent of inflammatory demyelination and axonal damage, and protects against the disruption of nodal architecture in affected peripheral nerves. In contrast, a structural control peptide of cyclo-dPAKKR exerted no influence. Moreover, all the beneficial effects of cyclo-dPAKKR in EAN are abrogated in p75NTR heterozygous mice, strongly suggesting a p75NTR-dependent effect. Taken together, our data demonstrate that cyclo-dPAKKR ameliorates functional and pathological defects of EAN in a p75NTR-dependant manner, suggesting that p75NTR is a therapeutic target to consider for future treatment of peripheral demyelinating diseases and targeting of p75NTR is a strategy worthy of further investigation.

p75NTR: an enhancer of fenretinide toxicity in neuroblastoma.

OBJECTIVE: Neuroblastoma is a common, frequently fatal, neural crest tumor of childhood. Chemotherapy-resistant neuroblastoma cells typically have Schwann cell-like ("S-type") morphology and express the p75 neurotrophin receptor (p75NTR). p75NTR has been previously shown to modulate the redox state of neural crest tumor cells. We, therefore, hypothesized that p75NTR expression level would influence the effects of the redox-active chemotherapeutic drug fenretinide on neuroblastoma cells. METHODS: Transfection and lentiviral transduction were used to manipulate p75NTR expression in these cell lines. Sensitivity to fenretinide was determined by concentration- and time-cell survival studies. Apoptosis incidence was determined by morphological assessment and examination of cleavage of poly-ADP ribose polymerase and caspase-3. Generation and subcellular localization of reactive oxygen species were quantified using species- and site-specific stains and by examining the effects of site-selective antioxidants on cell survival after fenretinide treatment. Studies of mitochondrial electron transport employed specific inhibitors of individual proteins in the electron transport chain. RESULTS: Knockdown of p75NTR attenuates fenretinide-induced accumulation of mitochondrial superoxide and apoptosis. Overexpression of p75NTR has the opposite effects. Pretreatment of cells with 2-thenoyltrifluoroacetone or dehydroascorbic acid uniquely prevents mitochondrial superoxide accumulation and cell death after fenretinide treatment, indicating that mitochondrial complex II is the likely site of fenretinide-induced superoxide generation and p75NTR-induced potentiation of these phenomena. CONCLUSION: Modification of expression of p75NTR in a particular neuroblastoma cell line modifies its susceptibility to fenretinide. Enhancers of p75NTR expression or signaling could be potential drugs for use as adjuncts to chemotherapy of neural tumors.

A neurotrophic rationale for the therapy of neurodegenerative disorders.

The concept and rationale for neuroprotection are presented. Several examples of small molecule neurotrophic agents with favourable drug-like and pharmacological properties are shown. Compound efficacy in acute neurodegenerative models (optic nerve axotomy) and chronic neurodegenerative models (glaucoma, age-associated cognitive impairment, Alzheimer's Disease) are evaluated and discussed. Targeting neurotrophin receptors with ligands that activate survival pathways or inhibit death pathways is an alternative worth pursuing.

Glucocorticoid-induced tumor necrosis factor receptor-related (GITR)-Fc fusion protein inhibits GITR triggering and protects from the inflammatory response after spinal cord injury.

Glucocorticoid-induced tumor necrosis factor receptor-related (GITR) protein is a costimulatory molecule that plays a role in inflammation so that GITR-Fc fusion protein can exert an anti-inflammatory effect. To investigate the mechanism by which GITR-Fc exerts its effects, we first used GITR knock-out (GITR(-/-)) mice to verify whether GITR ligand (GITRL)/GITR system played a pro-inflammatory role in the spinal cord injury (SCI) model. It is noteworthy that less pronounced disease was induced in GITR(-/-) compared with GITR(+/+) mice. We then evaluated the effect of GITR-Fc fusion protein against SCI-induced injuries in GITR(-/-) and wild-type (GITR(+/+)) mice. Administration of GITR-Fc ameliorated SCI-induced inflammation in GITR(+/+) mice as evaluated through: 1) histological damage and apoptosis, 2) modulation of apoptosis-related transduction factors (Bax and Bcl-2), 3) expression of inflammatory markers [nitrotyrosine, inducible nitric-oxide synthase, interleukin (IL)-2, IL-12, and tumor necrosis factor-alpha], and 4) T-lymphocyte infiltration. GITR-Fc was effective in GITR(+/+) but not in GITR(-/-), suggesting that in this experimental model, its anti-inflammatory action was due to inhibition of GITR triggering and not to GITRL activation. In conclusion, GITR plays a role in SCI, and administration of GITR-Fc results in amelioration of SCI severity, prompting further studies on the potential anti-inflammatory properties of GITR-Fc.

Small molecule neurotrophin receptor ligands: novel strategies for targeting Alzheimer's disease mechanisms.

A number of factors limit the therapeutic application of neurotrophin proteins, such as nerve growth factor (NGF) and brain-derived growth factor (BDNF), for Alzheimer's and other neurodegenerative diseases. These factors include unfavorable pharmacological properties typical of proteins and the pleiotropic effects mediated by protein-ligand interactions with p75(NTR), Trk, and sortilin neurotrophin receptors. Targeted modulation of p75(NTR) provides a strategy for preventing degeneration without promoting TrkA-mediated deleterious effects, and targeted activation of TrkB might achieve more favorable neurotrophic effects than those achieved by concomitant activation of p75(NTR) and TrkB. The discovery of small molecules functioning as ligands at specific neurotrophin receptors has made possible for the first time approaches for modulating selected components of neurotrophin signaling processes for the purpose of modulating underlying Alzheimer's disease mechanisms.

4-1BB and OX40 dual costimulation synergistically stimulate primary specific CD8 T cells for robust effector function.

CD40, 4-1BB, and OX40 are costimulatory molecules belonging to the TNF/nerve growth factor superfamily of receptors. We examined whether simultaneous costimulation affected the responses of T cells using several different in vivo tracking models in mice. We show that enforced dual costimulation through 4-1BB and OX40, but not through CD40, induced profound specific CD8 T cell clonal expansion. In contrast, the response of specific CD4 T cells to dual costimulation was additive rather than synergistic. The synergistic response of the specific CD8 T cells persevered for several weeks, and the expanded effector cells resided throughout lymphoid and nonlymphoid tissue. Dual costimulation through 4-1BB and OX40 did not increase BrdU incorporation nor an increase in the number of rounds of T cell division in comparison to single costimulators, but rather enhanced accumulation in a cell-intrinsic manner. Mechanistically speaking, we show that CD8 T cell clonal expansion and effector function did not require T help, but accumulation in (non)lymphoid tissue was predominantly CD4 T cell dependent. To determine whether this approach would be useful in a physiological setting, we demonstrated that dual costimulation mediated rejection of an established murine sarcoma. Importantly, effector function directed toward established tumors was CD8 T cell dependent while being entirely CD4 T cell independent, and the timing of enforced dual costimulation was exquisitely regulated. Collectively, these data suggest that simultaneous dual costimulation through 4-1BB and OX40 induces a massive burst of CD8 T cell effector function sufficient to therapeutically treat established tumors even under immunocompromising conditions.

Chimeric receptors with 4-1BB signaling capacity provoke potent cytotoxicity against acute lymphoblastic leukemia.

To develop a therapy for drug-resistant B-lineage acute lymphoblastic leukemia (ALL), we transduced T lymphocytes with anti-CD19 chimeric receptors, consisting of an anti-CD19 single-chain variable domain (reactive with most ALL cases), the hinge and transmembrane domains of CD8alpha, and the signaling domain of CD3zeta. We compared the antileukemic activity mediated by a novel receptor ('anti-CD19-BB-zeta') containing the signaling domain of 4-1BB (CD137; a crucial molecule for T-cell antitumor activity) to that of a receptor lacking costimulatory molecules. Retroviral transduction produced efficient and durable receptor expression in human T cells. Lymphocytes expressing anti-CD19-BB-zeta receptors exerted powerful and specific cytotoxicity against ALL cells, which was superior to that of lymphocytes with receptors lacking 4-1BB. Anti-CD19-BB-zeta lymphocytes were remarkably effective in cocultures with bone marrow mesenchymal cells, and against leukemic cells from patients with drug-resistant ALL: as few as 1% anti-CD19-BB-zeta-transduced T cells eliminated most ALL cells within 5 days. These cells also expanded and produced interleukin-2 in response to ALL cells at much higher rates than those of lymphocytes expressing equivalent receptors lacking 4-1BB. We conclude that anti-CD19 chimeric receptors containing 4-1BB are a powerful new tool for T-cell therapy of B-lineage ALL and other CD19+ B-lymphoid malignancies.

Therapeutic potential of 4-1BB (CD137) as a regulator for effector CD8(+) T cells.

A fundamental problem of antitumor immunity is tumor-induced immunosuppression. Tumor cells often down-regulate expression of co-stimulatory molecules, tumor antigens, and major histocompatibility complex (MHC) molecules on tumor cells, secrete immunosuppressive substance such as transforming growth factor-beta (TGF-beta) or interleukin-4 (IL-4), and induce apoptosis of effector T cells to escape surveillance. A major goal of antitumor or antivirus immunotherapy is to generate long-lived protective T cells that enable killing of target cells. In this review, we discuss the importance of 4-1BB for development or survival of functionally active effector CD8(+) T cells against tumors, virus infection, and allogeneic immune responses and for potential therapeutic application.