Introduction: The gastrin-releasing peptide receptor (GRPR) is overexpressed in breast cancer. The present study evaluates GRPR imaging as a novel imaging modality in breast cancer by employing positron emission tomography (PET) and the GRPR antagonist 68Ga-RM2.Methods: Fifteen female patients with biopsy confirmed primary breast carcinoma (3 bilateral tumors; median clinical stage IIB) underwent 68Ga-RM2-PET/CT for pretreatment staging. In vivo tumor uptake of 68Ga-RM2 was correlated with estrogen (ER) and progesterone (PR) receptor expression, HER2/neu status and MIB-1 proliferation index in breast core biopsy specimens.Results: 13/18 tumors demonstrated strongly increased 68Ga-RM2 uptake compared to normal breast tissue (defined as PET-positive). All PET-positive primary tumors were ER- and PR-positive (13/13) in contrast to only 1/5 PET-negative tumors. Mean SUVMAX of ER-positive tumors was 10.6±6.0 compared to 2.3±1.0 in ER-negative tumors (p=0.016). In a multivariate analysis including ER, PR, HER2/neu and MIB-1, only ER expression predicted 68Ga-RM2 uptake (model: r2=0.55, p=0.025). Normal breast tissue showed inter- and intraindividually variable, moderate GRPR binding (SUVMAX 2.3±1.0), while physiological uptake of other organs was considerably less except pancreas. Of note, 68Ga-RM2-PET/CT detected internal mammary lymph nodes with high 68Ga-RM2 uptake (n=8), a contralateral axillary lymph node metastasis (verified by biopsy) and bone metastases (n=1; not detected by bone scan and CT).Conclusion: Our study demonstrates that 68Ga-RM2-PET/CT is a promising imaging method in ER-positive breast cancer. In vivo GRPR binding assessed by 68Ga-RM2-PET/CT correlated with ER expression in primary tumors of untreated patients.

PURPOSE. Retinal ischemia/reperfusion (I/R) injury damages retinal neurons. Carbon monoxide (CO) recently attracted attention as cytoprotective because of its anti-inflammatory and antiapoptotic effects. Rapid preconditioning of retinal neurons by inhaled CO before I/R injury may reduce inflammation and apoptosis in retinal ganglion cells (RGCs). METHODS. I/R injury was performed on the left eyes of rats (n = 8) with or without inhaled CO preconditioning (250 ppm) for 1 hour before ischemia. Densities of fluorogold-prelabeled RGCs were analyzed 7 days after injury in whole-mounts. Retinal tissue was further harvested to analyze protein expression of TNF-alpha, HSP-70, and mitogen-activated protein kinases (MAPKs) pERK1/2 and p-p38. DNA-binding activities of the transcription factors NF-kappaB, AP-1, CREB, and HSF-1 were determined to elucidate a possible pathway of neuroprotection. RESULTS. Seven days after I/R injury, RGC death decreased by 52% in the CO preconditioning group compared with controls receiving room air (P < 0.001). Similarly, CO inhalation resulted in attenuated caspase-3 activity and TNF-alpha protein expression. In contrast, HSP-70 protein expression was elevated in the retina after CO. CREB and HSF-1 showed CO-dependent regulation and p-p38 MAPK. CONCLUSIONS. Rapid preconditioning with CO mediates anti-inflammatory and antiapoptotic effects in retinal I/R injury, thus making it neuroprotective. Further studies are needed to evaluate whether CO posttreatment may represent a therapeutic option counteracting ischemic neuronal injury.

Copper-64 is an attractive radionuclide for PET imaging and is frequently used in clinical applications. The aim of this study was to perform a side-by-side comparison of the in vitro and in vivo performance of 64Cu-NODAGA-JR11 (NODAGA = 1,4,7-triazacyclononane,1-glutaric acid,4,7-acetic acid, JR11 = p-Cl-Phe-cyclo(D-Cys-Aph(Hor)-D-Aph(cbm)-Lys-Thr-Cys)D-Tyr-NH2), a somatostatin receptor 2 antagonist, with the clinically used sst2 agonist 64Cu-DOTA-TATE ((TATE = D-Phe-cyclo(Cys-Tyr-D-Trp-Lys-Thr-Cys)Thr). In vitro studies demonstrated Kd values of 5.7±0.95 nM (Bmax = 4.1±0.18 nM) for the antagonist 64/natCu-NODAGA-JR11 and 20.1±4.4. nM (Bmax = 0.48±0.18 nM) for the agonist 64/natCu-DOTA-TATE. Cell uptake studies showed the expected differences between agonists and antagonists. Whereas 64Cu-DOTA-TATE (the agonist) showed very effective internalization in the cell culture assay (with 50% internalized at 4 hours post-peptide addition under the given experimental conditions), 64Cu-NODAGA-JR11 (the antagonist) showed little internalization but strong receptor-mediated uptake at the cell membrane. Biodistribution studies of 64Cu-NODAGA-JR11 showed rapid blood clearance and tumor uptake with increasing tumor-to-relevant organ ratios within the first 4 hours and in some cases, 24 hours, respectively. The tumor washout was slow or non-existent in the first 4 hours, whereas the kidney washout was very efficient, leading to high and increasing tumor-to-kidney ratios over time. Specificity of tumor uptake was proven by co-injection of high excess of non-radiolabeled peptide, which led to >80% tumor blocking. 64Cu-DOTA-TATE showed less favorable pharmacokinetics, with the exception of lower kidney uptake. Blood clearance was distinctly slower and persistent higher blood values were found at 24 hours. Uptake in the liver and lung was relatively high and also persistent. The tumor uptake was specific and similar to that of 64Cu-NODAGA-JR11 at 1 h, but release from the tumor was very fast, particularly between 4 and 24 hours. Tumor-to-normal organ ratios were distinctly lower after 1 hour. This is indicative of insufficient in vivo stability. PET studies of 64Cu-NODAGA-JR11 reflected the biodistribution data with nicely delineated tumor and low background. 64Cu-NODAGA-JR11 shows promising pharmacokinetic properties for further translation into the clinic.

No abstract