Although neurotrophic factors were originally isolated on the basis of their ability to support the survival of neurons, these molecules are now thought to influence many aspects of the development and maintenance of the nervous system. Identifying the receptors for these neurotrophic factors should aid in identifying the cells on which these factors act and in understanding their precise mechanisms of action. A "tagged-ligand panning" procedure was used to clone a receptor for ciliary neurotrophic factor (CNTF). This receptor is expressed exclusively within the nervous system and skeletal muscle. The CNTF receptor has a structure unrelated to the receptors utilized by the nerve growth factor family of neurotrophic molecules, but instead is most homologous to the receptor for a cytokine, interleukin-6. This similarity suggestes that the CNTF receptor, like the interleukin-6 receptor, requires a second, signal-transducing component. In contrast to all known receptors, the CNTF receptor is anchored to cell membranes by a glycosyl-phosphatidylinositol linkage.

Ciliary Neurotrophic Factor (CNTF) was first characterized as a trophic factor for motor neurons in the ciliary ganglion and spinal cord, leading to its evaluation in humans suffering from motor neuron disease. In these trials, CNTF caused unexpected and substantial weight loss, raising concerns that it might produce cachectic-like effects. Countering this possibility was the suggestion that CNTF was working via a leptin-like mechanism to cause weight loss, based on the findings that CNTF acts via receptors that are not only related to leptin receptors, but also similarly distributed within hypothalamic nuclei involved in feeding. However, although CNTF mimics the ability of leptin to cause fat loss in mice that are obese because of genetic deficiency of leptin (ob͞ob mice), CNTF is also effective in diet-induced obesity models that are more representative of human obesity, and which are resistant to leptin. This discordance again raised the possibility that CNTF might be acting via nonleptin pathways, perhaps more analogous to those activated by cachectic cytokines. Arguing strongly against this possibility, we now show that CNTF can activate hypothalamic leptin-like pathways in diet-induced obesity models unresponsive to leptin, that CNTF improves prediabetic parameters in these models, and that CNTF acts very differently than the prototypical cachectic cytokine, IL-1. Further analyses of hypothalamic signaling reveals that CNTF can suppress food intake without triggering hunger signals or associated stress responses that are otherwise associated with food deprivation; thus, unlike forced dieting, cessation of CNTF treatment does not result in binge overeating and immediate rebound weight gain.

Patients with metastatic or unresectable (advanced) pheochromocytoma and paraganglioma (PPGL) have poor prognoses and few treatment options. This multicenter, phase 2 trial evaluated the efficacy and safety of high-specific-activity 131 I-meta-iodobenzylguanidine (HSA 131 I-MIBG) in patients with advanced PPGL. Methods: In this open-label, single-arm study, 81 PPGL patients were screened for enrollment, and 74 received a treatment-planning dose of HSA 131 I-MIBG. Of these patients, 68 received at least 1 therapeutic dose (∼18.5 GBq) of HSA 131 I-MIBG intravenously. The primary endpoint was the proportion of patients with at least a 50% reduction in baseline antihypertensive medication use lasting at least 6 mo. Secondary endpoints included objective tumor response as assessed by Response Evaluation Criteria in Solid Tumors version 1.0, biochemical tumor marker response, overall survival, and safety. Results: Of the 68 patients who received at least 1 therapeutic dose of HSA 131 I-MIBG, 17 (25%; 95% confidence interval, 16%–37%) had a durable reduction in baseline antihypertensive medication use. Among 64 patients with evaluable disease, 59 (92%) had a partial response or stable disease as the best objective response within 12 mo. Decreases in elevated (≥1.5 times the upper limit of normal at baseline) serum chromogranin levels were observed, with confirmed complete and partial responses 12 mo after treatment in 19 of 28 patients (68%). The median overall survival was 36.7 mo (95% confidence interval, 29.9–49.1 mo). The most common treatment-emergent adverse events were nausea, myelosuppression, and fatigue. No patients had drug-related acute hypertensive events during or after the administration of HSA 131 I-MIBG. Conclusion: HSA 131 I-MIBG offers multiple benefits, including sustained blood pressure control and tumor response in PPGL patients.

Ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) each promote the survival and differentiation of developing motor neurons, but do so through distinct cellular signaling pathways. Administration of either factor alone has been shown to slow, but not to arrest, progression of motor neuron dysfunction in wobbler mice, an animal model of motor neuron disease. Because CNTF and BDNF are known to synergize in vitro and in ovo, the efficacy of CNTF and BDNF cotreatment was tested in the same animal mode. Subcutaneous injection of the two factors on alternate days was found to arrest disease progression in wobbler mice for 1 month, as measured by several behavioral, physiological, and histological criteria.

Cytokines can initiate and perpetuate human diseases, and are among the best-validated of therapeutic targets. Cytokines can be blocked by the use of soluble receptors; however, the use of this approach for cytokines such as interleukin (IL)-1, IL-4, IL-6 and IL-13 that use multi-component receptor systems is limited because monomeric soluble receptors generally exhibit low affinity or function as agonists. We describe here a generally applicable method to create very high-affinity blockers called 'cytokine traps' consisting of fusions between the constant region of IgG and the extracellular domains of two distinct cytokine receptor components involved in binding the cytokine. Traps potently block cytokines in vitro and in vivo and represent a substantial advance in creating novel therapeutic candidates for cytokine-driven diseases.