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Background: Tropomyosin receptor kinases (TrkA, TrkB, TrkC) are a family of tyrosine kinases primarily expressed in neuronal cells of the brain. Identification of oncogenic alterations in Trk expression as a driver in multiple tumor types has increased interest in their role in human cancers. Recently, first- and second-generation 11C and 18F-labeled Trk inhibitors, e.g., [18F]TRACK, have been developed. The goal of the present study was to analyze the direct interaction of [18F]TRACK with peripheral Trk receptors in vivo to prove its specificity for use as a functional imaging probe. Methods: In vitro uptake and competition experiments were carried out using the colorectal cancer cell line KM12. Dynamic PET experiments were performed with [18F]TRACK, either alone or in the presence of amitriptyline, an activator of Trk, entrectinib, a Trk inhibitor, or unlabeled reference compound TRACK in KM12 tumor-bearing athymic nude mice as well as B6129SF2/J and corresponding B6;129S2-Ntrk2tm1Bbd/J mice. Western blot and immunohistochemistry experiments were done with KM12 tumors, brown adipose tissue (BAT), and brain tissue samples. Results: Uptake of [18F]TRACK was increasing over time reaching 208 ± 72% radioactivity per mg protein (n = 6/2) after 60 min incubation time. Entrectinib and TRACK competitively blocked [18F]TRACK uptake in vitro (IC50 30.9 ± 3.6 and 29.4 ± 9.4 nM; both n = 6/2). [18F]TRACK showed uptake into KM12 tumors (SUVmean,60 min 0.43 ± 0.03; n = 6). Tumor-to-muscle ratio reached 0.9 (60 min) and 1.2 (120 min). In TrkB expressing BAT, [18F]TRACK uptake reached SUVmean,60 min 1.32 ± 0.08 (n = 7). Activation of Trk through amitriptyline resulted in a significant radioactivity increase of 21% in KM12 tumor (SUVmean,60 min from 0.53 ± 0.01 to 0.43 ± 0.03; n = 6; p < 0.05) and of 21% in BAT (SUVmean,60 min from 1.32 ± 0.08; n = 5 to 1.59 ± 0.07; n = 6; p < 0.05) respectively. Immunohistochemistry showed TrkB > TrkA expression on BAT fat cells, but TrkA > TrkB in whole brain. WB analysis showed sevenfold higher TrkB expression in BAT versus KM12 tumor tissue. Conclusion: The present data show that radiotracer [18F]TRACK can target peripheral Trk receptors in human KM12 colon cancer as well as brown adipose tissue as confirmed through in vitro and in vivo blocking experiments. Higher TrkB versus TrkA protein expression was detected in brown adipose tissue of mice confirming a peripheral functional role of brain-derived neurotrophic factor in adipose tissue. [ABSTRACT FROM AUTHOR]

Inflammation is associated with production of cytokines and chemokines that recruit and activate inflammatory cells. Interleukin (IL) 12 produced by macrophages in response to various stimuli is a potent inducer of interferon (IFN) [Gamma] production. IFN-[Gamma], in turn, markedly enhances IL-12 production. Although the immune response is typically self-limiting, the mechanisms involved are unclear. We demonstrate that IFN-[Gamma], inhibits production of chemokines (macrophage inflammatory proteins MIP-1[Alpha] and MIP-1[Beta]). Furthermore, pre-exposure to tumor necrosis factor (TNF) inhibited IFN-[Gamma] priming for production of high levels of IL-12 by macrophages in vitro. Inhibition of IL-12 by TNF can be mediated by both IL-10-dependent and IL-10-independent mechanisms. To determine whether TNF inhibition of IFN-[Gamma]-induced IL-12 production contributed to the resolution of an inflammatory response in vivo, the response of [TNF.sup.+/+] and [TNF.sup.-/-] mice injected with Corynebacterium parvum were compared. [TNF.sup.-/-] mice developed a delayed, but vigorous, inflammatory response leading to death, whereas [TNF.sup.+/+] mice exhibited a prompt response that resolved. Serum IL-12 levels were elevated 3-fold in C. parvum-treated [TNF.sup.-/-] mice compared with [TNF.sup.+/+] mice. Treatment with a neutralizing anti-IL-12 antibody led to resolution of the response to C. parvum in [TNF.sup.-/-] mice. We conclude that the role of TNF in limiting the extent and duration of inflammatory responses in vivo involves its capacity to regulate macrophage IL-12 production. IFN-[Gamma] inhibition of chemokine production and inhibition of IFN-[Gamma]-induced IL-12 production by TNF provide potential mechanisms by which these cytokines can exert anti-inflammatory/repair function(s).

Targeted therapy is increasingly used to manage metastatic papillary thyroid cancer. The focus of the present study was to examine glucose metabolism an d tumor responses for thyroid cancer xenografts expressing the glycolytic pathway modulators platelet-derived growth factor receptor (PDGFR) and BRAFV600E. Radiolabelled glucose derivative [18F] FDG was used to analyze the effects of PDGFR blockade with imati nib, BRAF blockade with vemurafenib, as well as combined PDGFR and BRAF blockade in vitro and in vivo with PET. Dynamic PET data was correlated with immunohistochemistry staining and kinetic analysis for facilitative glucose transporter 1 (GLUT1) and hexokinase-II (HK2). Vemurafenib decreased [18F]FDG uptake in BCPAP cells in vitro; however, it was increased by ~70% with imatinib application to BCPAP cells. This metabolic response to tyrosine kinase inhibition required BRAFV600E as it was not seen in cell lines lacking mutated BRAF (TPC1). In xenografts, imatinib therapy in BCPAP thyroid tumour-bearing mice significantly increased [18F]FDG uptake and retention (>30%) in BCPAP tumours with PDGFRβ or both (α+β) isoforms. Kinetic analysis revealed that the increased glucose uptake is a consequence of increased phosphorylation and intracellular trapping of [18F]FDG confirmed by an increase in HK2 protein expression and act ivity, but not GLUT1 activity. BRAF inhibition alone, or combined PDGFR and BRAF inhibition, reduced (~60%) [18F]FDG uptake in both types of BCPAP (β or α+β) tumours. In terms of tumour growth, combination therapy with imatinib and vemurafenib led to a near abolition of the tumors (~90% reduction), but single therapy for BCPAP with PDGFRα expression was much less effective. In summary, imatinib led to a paradoxical increase of [18F]FDG uptake in xenografts that was reversed through BRAFV600E inhibition. The present data show that metabolic reprogramming in thyroid cancer occurs as a consequence of BRAF-mediated upregulation of HK2 expression that may permit tumour growth with isolated blockade of upstream tyrosine kinase receptors. [ABSTRACT FROM AUTHOR]

Allergic asthma is an inflammatory disease of the airways characterized by eosinophilic inflammation and airway hyper-reactivity. Cytokines and chemokines specific for Th2-type inflammation predominate in asthma and in animal models of this disease. The role of Th1-type inflammatory mediators in asthma remains controversial. IFN-gamma-inducible protein 10 (IP-10; CXCL10) is an IFN-gamma-inducible chemokine that preferentially attracts activated Th1 lymphocytes. IP-10 is up-regulated in the airways of asthmatics, but its function in asthma is unclear. To investigate the role of IP-10 in allergic airway disease, we examined the expression of IP-10 in a murine model of asthma and the effects of overexpression and deletion of IP-10 in this model using IP-10-transgenic and IP-10-deficient mice. Our experiments demonstrate that IP-10 is up-regulated in the lung after allergen challenge. Mice that overexpress IP-10 in the lung exhibited significantly increased airway hyperreactivity, eosinophilia, IL-4 levels, and CD8(+) lymphocyte recruitment compared with wild-type controls. In addition, there was an increase in the percentage of IL-4-secreting T lymphocytes in the lungs of IP-10-transgenic mice. In contrast, mice deficient in IP-10 demonstrated the opposite results compared with wild-type controls, with a significant reduction in these measures of Th2-type allergic airway inflammation. Our results demonstrate that IP-10, a Th1-type chemokine, is up-regulated in allergic pulmonary inflammation and that this contributes to the airway hyperreactivity and Th2-type inflammation seen in this model of asthma.

IFN-gamma-inducible protein 10 (IP-10, CXCL10), a chemokine secreted from cells stimulated with type I and II IFNs and LPS, is a chemoattractant for activated T cells. Expression of IP-10 is seen in many Th1-type inflammatory diseases, where it is thought to play an important role in recruiting activated T cells into sites of tissue inflammation. To determine the in vivo function of IP-10, we constructed an IP-10-deficient mouse (IP-10(-/-)) by targeted gene disruption. Immunological analysis revealed that IP-10(-/-) mice had impaired T cell responses. T cell proliferation to allogeneic and antigenic stimulation and IFN-gamma secretion in response to antigenic challenge were impaired in IP-10(-/-) mice. In addition, IP-10(-/-) mice exhibited an impaired contact hypersensitivity response, characterized by decreased ear swelling and reduced inflammatory cell infiltrates. T cells recovered from draining lymph nodes also had a decreased proliferative response to Ag restimulation. Furthermore, IP-10(-/-) mice infected with a neurotropic mouse hepatitis virus had an impaired ability to control viral replication in the brain. This was associated with decreased recruitment of CD4(+) and CD8(+) lymphocytes into the brain, reduced levels of IFN-gamma and the IFN-gamma-induced chemokines monokine induced by IFN-gamma (Mig, CXCL9) and IFN-inducible T cell alpha chemoattractant (I-TAC, CXCL11) in the brain, decreased numbers of virus-specific IFN-gamma-secreting CD8(+) cells in the spleen, and reduced levels of demyelination in the CNS. Taken together, our data suggest a role for IP-10 in both effector T cell generation and trafficking in vivo.

A pathological hallmark of Alzheimer's disease is the senile plaque, composed of beta-amyloid fibrils, microglia, astrocytes, and dystrophic neurites. We reported previously that class A scavenger receptors mediate adhesion of microglia and macrophages to beta-amyloid fibrils and oxidized low-density lipoprotein (oxLDL)-coated surfaces. We also showed that CD36, a class B scavenger receptor and an oxLDL receptor, promotes H(2)O(2) secretion by macrophages adherent to oxLDL-coated surfaces. Whether CD36 is expressed on microglia, and whether it plays a role in secretion of H(2)O(2) by microglia interacting with fibrillar beta-amyloid is not known. Using fluorescence-activated cell sorting analysis and immunohistochemistry, we found that CD36 is expressed on human fetal microglia, and N9-immortalized mouse microglia. We also found that CD36 is expressed on microglia and on vascular endothelial cells in the brains of Alzheimer's disease patients. Bowes human melanoma cells, which normally do not express CD36, gained the ability to specifically bind to surfaces coated with fibrillar beta-amyloid when transfected with a cDNA encoding human CD36, suggesting that CD36 is a receptor for fibrillar beta-amyloid. Furthermore, two different monoclonal antibodies to CD36 inhibited H(2)O(2) production by N9 microglia and human macrophages adherent to fibrillar beta-amyloid by approximately 50%. Our data identify a role for CD36 in fibrillar beta-amyloid-induced H(2)O(2) production by microglia, and imply that CD36 can mediate binding to fibrillar beta-amyloid. We propose that similar to their role in the interaction of macrophages with oxLDL, class A scavenger receptors and CD36 play complimentary roles in the interactions of microglia with fibrillar beta-amyloid.