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High nuclear expression of G protein‐coupled receptors, including kinin B1 receptors (B1R), has been observed in several human cancers, but the clinical significance of this is unknown. We put forward the hypothesis that these "nuclearized" kinin B1R contribute to tumorigenicity and can be a new target in anticancer strategies. Our initial immunostaining and ultrastructural electron microscopy analyses demonstrated high B1R expression predominantly located at internal/nuclear compartments in the MDA‐MB‐231 triple‐negative breast cancer (TNBC) cell line as well as in clinical samples of patients with TNBC. On the basis of these findings, in the present study, we evaluated the anticancer therapeutic potential of newly identified, cell‐permeable B1R antagonists in MDA‐MB‐231 cells (ligand–receptor binding/activity assays and LC‐MS/MS analyses). We found that these compounds (SSR240612, NG67, and N2000) were more toxic to MDA‐MB‐231 cells in comparison with low‐ or non‐B1R expressing MCF‐10A normal human mammary epithelial cells and COS‐1 cells, respectively (clonogenic, MTT proliferative/cytocidal assays, and fluorescence‐activated cell‐sorting (FACS)‐based apoptosis analyses). By comparison, the peptide B1R antagonist R954 unable to cross cell membrane failed to produce anticancer effects. Furthermore, the putative mechanisms underlying the anticancer activities of cell‐penetrant B1R antagonists were assessed by analyzing cell cycle regulation and signaling molecules related to cell survival and apoptosis (FACS and western blot). Finally, drug combination experiments showed that cell‐penetrant B1R antagonists can cooperate with suboptimal doses of chemotherapeutic agents (doxorubicin and paclitaxel) to promote TNBC death. This study provides evidence on the potential value of internally acting kinin B1R antagonists in averting growth of breast cancer. High nuclear localization of G protein‐coupled receptors (GPCRs) has been observed in several human cancers, but the clinical significance of this remains unknown. Here, we provided in vitro evidence for the existence of a novel intracrine signaling pathway mediated by nuclear kinin B1 receptors, critical for the growth of triple‐negative breast cancer (TNBC) cells, and identifed new chemical entities that enable to target the corresponding intracellular GPCRs. In sum, our results highlight the need to target a given GPCR in relation to its subcellular localization to achieve therapeutic outcomes. [ABSTRACT FROM AUTHOR]

Abstract: Treatment of malignant glioma with chemotherapy is limited mostly because of delivery impediment related to the blood–brain barrier (BBB). One approach for transporting drugs across the BBB involves the activation of bradykinin-B2 receptors (BK-B2R). Our objective was to pharmacologically characterize the BBB permeability induced by the synthetic biostable BK-B2R analogue [Phe8 ψ(CH2NH)Arg9]-BK (R523) in F98 glioma-implanted Fischer rats. On day 10 post-inoculation, we detected the presence of B2R in the tumor cells and the peritumoral microvasculature (RT-PCR and immunohistochemistry). We assessed BBB permeability before and after the intracarotid (i.c.) infusion of R523 (0.1ml/min for 5min; 2.5, 10, and 50nmol/kg/min) using non-invasive dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with the different sized-contrast agents Gd-DTPA (0.5kDa) and Gadomer (17kDa) (0.25mmol/kg via the caudal vein). T 1-weighted images were analyzed for the presence or absence of contrast enhancement within and surrounding the tumor area and mathematically processed to yield a contrast agent distribution volume (CADV), which was used as an indicator of vascular permeability. Our results showed that the agonist R523 increased, in a dose-dependent manner, the CADV indexes of Gd-DTPA and Gadomer, with a maximum 2-fold increase in brain uptake of both CA. The increase in CADV induced by R523 (10nmol/kg/min) was prevented by the B2R antagonist HOE140 (20nmol/kg/min, i.c.) and the nitric oxide synthase inhibitor L-NA (5mg/kg, i.v.) but not by the B1R antagonist R892 (20nmol/kg/min, i.c.) or the cyclooxygenase inhibitor Meclofenamate (5mg/kg, i.v.). The BBB permeabilizing effect of R523 (10nmol/kg/min) lasted for <1h and was accompanied by a dose-related fall in arterial blood pressure. We concluded that R523 allows the extravasation of hydrophilic macromolecular agents (⩽17kDa) into tumor tissues by inducing selective tumor BBB permeability via B2R- and NO-dependent mechanisms. [Copyright &y& Elsevier]

The biodistribution and tumour uptake of a series of 16α-[18F]fluoroestradiol ([18F]FES) derivatives was determined in oestrogen receptors-positive (ER+) tumour-bearing mice to assess the impact of substituents, formulation and specific activity on target tissue uptake. MC4-L2 and MC7-L1 murine ER+ cells were inoculated in Balb/c mice. The animals were injected with various [18F]FES derivatives substituted with 2- or 4-fluorine and/or an 11β-methoxy group. The radiopharmaceuticals were formulated in 10% ethanol/saline or 10% ethanol/lipid emulsion. The organs were counted, and radioactivity concentrations were expressed as the percentage of the injected dose per gram tissue (%ID/g). To estimate the effect of specific activity on tumour uptake, the 4-fluoro-11β-methoxy-16α-[18F]-fluoroestradiol (4F-M[18F]FES) was co-injected with different concentrations of non-radioactive estradiol to give an in vivo competitive inhibition curve. 4F-M[18F]FES exhibited the highest average uterine uptake (%ID/g = 15.7 ± 2.1). The highest uptake by the two mammary tumours was observed with [18F]FES (%ID/g = 3.1 and 3.4 ± 0.3) and 11β-methoxy-16α[18F]-fluoroestradiol (M-[18F]FES) (%ID/g = 3.2 and 3.3 ± 0.6), followed by 4F-M[18F]FES (%ID/g = 2.5 and 2.3 ± 0.3). The formulation had little influence on the biodistribution pattern. Co-injection with a total mass of estradiol >10−10 mol blocked 4F-M[18F]FES tumour uptake. All of the radiolabelled estradiol derivatives achieved significant target tissue uptake in vivo, both in ER+ tumours and the uterus. The formulation had little impact on the biodistribution of these compounds but some compounds (4F-M[18F]FES, M-[18F]FES and [18F]FES) had more favourable target tissue uptake and target-to-background ratios. [ABSTRACT FROM AUTHOR]

Purpose: A significant positive correlation has been observed between ketone body availability and their uptake by tumor cells. Our objective was to evaluate [11C]acetoacetate as a potential tracer of ketone body utilization by breast and prostate tumors and to compare it with [11C]acetate.Methods: Biodistribution studies were performed with [11C]acetoacetate and [11C]acetate in mice bearing breast or prostate tumors. The percentage of the injected dose accumulated per gram of tissue was determined. These results were complemented by dynamic positron emission tomography (PET) imaging of the radiotracer uptake and dosimetry calculations.Results: [11C]Acetoacetate uptake was optimal between 5 and 30 min, with maximal uptake of 2.72, 2.42, 2.54, and 2.19% injected dose (%ID)/g for MC7-L1, MC4-L2, PC3, and LN-CaP tumors respectively. Tumor retention for [11C]acetoacetate tended to be higher than [11C]acetate, but this did not reach statistical significance. [11C]Acetate uptake was reached within 15 min with optimal uptake of 1.25, 2.30, and 0.96%ID/g for MC7-L1, MC4-L2, and PC-3 tumors, respectively.Conclusions: We observed a moderate uptake of [11C]acetoacetate in breast and prostate tumors with low background activity due to rapid elimination of this tracer. Further studies are warranted to determine if this tracer can detect slow-growing breast and prostate cancers in the clinical setting. [ABSTRACT FROM AUTHOR]