Probucol is anti-hyperalgesic in a mouse peripheral nerve injury model of neuropathic pain.

2,6-di-tert-butylphenol (2,6-DTBP) ameliorates mechanical allodynia and thermal hyperalgesia produced by partial sciatic nerve ligation in mice, and selectively inhibits HCN1 channel gating. We hypothesized that the clinically utilized non-anesthetic dimerized congener of 2,6-DTBP, probucol (2,6-di-tert-butyl-4-[2-(3,5-di-tert-butyl-4-hydroxyphenyl)sulfanylpropan-2-ylsulfanyl]phenol), would relieve the neuropathic phenotype that results from peripheral nerve damage, and that the anti-hyperalgesic efficacy in vivo would correlate with HCN1 channel inhibition in vitro. A single oral dose of probucol (800 mg/kg) relieved mechanical allodynia and thermal hyperalgesia in a mouse spared-nerve injury neuropathic pain model. While the low aqueous solubility of probucol precluded assessment of its possible interaction with HCN1 channels, our results, in conjunction with recent data demonstrating that probucol reduces lipopolysaccharide-induced mechanical allodynia and thermal hyperalgesia, support the testing/development of probucol as a non-opioid, oral antihyperalgesic albeit one of unknown mechanistic action.

[18F]RPS-544: A PET tracer for imaging the chemokine receptor CXCR4.

INTRODUCTION: CXCR4 specific [18F]-labeled positron emission tomography (PET) imaging agents are needed which would enable general distribution of the radiotracer for clinical investigation. We sought to synthesize, radiolabel and evaluate [18F]RPS-544, a novel non-peptide CXCR4 antagonist as a CXCR4 specific probe. We compared [18F]RPS-544 with the previously published [18F]-3 ([18F]RPS-510 in this paper) in a bi-lateral tumor model of differential CXCR4 expression for its ability to selectively target CXCR4 expression. METHODS: Radiolabeling of [18F]RPS-544 and [18F]RPS-510 was performed by aromatic substitution on a 6-nitropyridyl group using no-carrier-added [18F]fluoride under basic conditions. 18F incorporation was determined by radioHPLC. Semi-preparative HPLC was used to purify the final product prior to reformulation. Imaging and biodistribution was performed in nude mice with bilateral PC3 (CXCR4+ and WT) xenograft tumors at 1, 2 and 4 h post injection. RESULTS: RPS-544 bound CXCR4 with an IC50 of 4.9 ±â€¯0.3 nM. [18F]RPS-544 showed preferential uptake in CXCR4+ tumors, with a CXCR4/WT ratio of 3.3 ±â€¯1.3 at 1 h p.i. and 2.3 ±â€¯0.5 at 2 h p.i. Maximum uptake in the CXCR4+ tumors was 3.4 ±â€¯1.2%ID/g at 1 h p.i., significantly greater (p = 0.003) than the uptake in the WT tumor. Tumor/blood ratios were 2.5 ±â€¯0.4 and 3.6 ±â€¯0.3 at 1 and 2 h p.i. Tumor/muscle ratios were >4 at all time-points. Tumor/lung ratios were >2 at 1 h and 2 h p.i. Substantial uptake was observed in the liver (15-25%ID/g), kidneys (25-35%ID/g), the small intestine (1-7%ID/g) and the large intestine (1-12%ID/g). Blood concentrations varied over time (0.5-2%ID/g). All other organs showed uptake of <1%ID/g at all time points studied with clearance profiles similar to blood clearance. CONCLUSIONS: Here we present, to the best of our knowledge, the first high affinity [18F]-labeled tracer, suitable for in vivo PET imaging of CXCR4. [18F]RPS-544 displayed high affinity for CXCR4 and good tumor uptake with a maximum uptake at 1 h p.i.. CXCR4 dependent uptake was demonstrated using bilateral tumors with differential CXCR4 expression as well as pharmacological blockade using the known CXCR4 antagonist, AMD-3100. Tissue contrast as judged by tumor to normal tissue ratios was positive in several key tissues. The structural and pharmacological similarities between [18F]RPS-544 and the approved drug AMD-3465, combined with the ease of synthesis and high molar activity (>185 GBq/µmol) achieved during radiosynthesis could lead to accelerated translation into the clinic.

Discovery and biological characterization of 1-(1H-indol-3-yl)-9H-pyrido[3,4-b]indole as an aryl hydrocarbon receptor activator generated by photoactivation of tryptophan by sunlight.

Activation of the aryl hydrocarbon receptor (AHR) by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is required for AHR dependent transcriptional activation and TCDD toxicity. We previously reported that aqueous tryptophan exposed to sunlight through window glass (aTRP) contains multiple photoproducts, including the well characterized 6-formylindolo[3,2-b]carbazole (FICZ), capable of activating the AHR and inducing CYP1A and CYP1A-mediated enzyme activities. We report here the isolation from aTRP and chemical characterization and synthesis of 1-(1H-indol-3-yl)-9H-pyrido[3,4-b]indole (IPI), a compound previously identified as a natural product of marine ascidia and now shown to be a TRP photoproduct with AHR-inducing properties. IPI, FICZ and TCDD produced equieffective induction of CYP1A-mediated 7-ethoxyresorufin deethylase (EROD) activity in chick embryo primary hepatocytes and mammalian Hepa1c1c7 cells. EROD induction by IPI was markedly curtailed in AHR-defective c35 cells, supporting the AHR dependence of the IPI response. Although IPI had a higher EC(50) for EROD induction than FICZ, the much larger amount of IPI than FICZ in aTRP makes IPI a prominent contributor to EROD induction in aTRP. IPI was detected in TRP-containing culture medium under ambient laboratory conditions but not in TRP-free medium, consistent with its production from TRP. Cotreatment of hepatocytes with submaximal EROD-inducing doses of IPI and FICZ or TCDD produced additive increases in EROD without synergistic or inhibitory interactions. IPI and FICZ were readily metabolized by cultured hepatocytes. In addition to increasing CYP1A4 mRNA and EROD, IPI and FICZ decreased hepatocyte phosphoenolpyruvate carboxykinase mRNA expression and glucose output, biological effects associated with TCDD metabolic dysregulation. The findings underscore a role for sunlight in generating AHR-activating bioactive molecules.