PSMA, EpCAM, VEGF and GRPR as imaging targets in locally recurrent prostate cancer after radiotherapy.

In this retrospective pilot study, the expression of the prostate-specific membrane antigen (PSMA), the epithelial cell adhesion molecule (EpCAM), the vascular endothelial growth factor (VEGF) and the gastrin-releasing peptide receptor (GRPR) in locally recurrent prostate cancer after brachytherapy or external beam radiotherapy (EBRT) was investigated, and their adequacy for targeted imaging was analyzed. Prostate cancer specimens were collected of 17 patients who underwent salvage prostatectomy because of locally recurrent prostate cancer after brachytherapy or EBRT. Immunohistochemistry was performed. A pathologist scored the immunoreactivity in prostate cancer and stroma. Staining for PSMA was seen in 100% (17/17), EpCAM in 82.3% (14/17), VEGF in 82.3% (14/17) and GRPR in 100% (17/17) of prostate cancer specimens. Staining for PSMA, EpCAM and VEGF was seen in 0% (0/17) and for GRPR in 100% (17/17) of the specimens' stromal compartments. In 11.8% (2/17) of cases, the GRPR staining intensity of prostate cancer was higher than stroma, while in 88.2% (15/17), the staining was equal. Based on the absence of stromal staining, PSMA, EpCAM and VEGF show high tumor distinctiveness. Therefore, PSMA, EpCAM and VEGF can be used as targets for the bioimaging of recurrent prostate cancer after EBRT to exclude metastatic disease and/or to plan local salvage therapy.

Application of (99m)Technetium-HYNIC(tricine/TPPTS)-Aca-Bombesin(7-14) SPECT/CT in prostate cancer patients: a first-in-man study.

RATIONALE: The peptide bombesin (BBN) and its derivatives exhibit high binding affinity for the gastrin-releasing peptide receptor (GRPR), which is highly expressed in prostate cancer. We used the BBN-based radiopharmaceutical (99m)Technetium-HYNIC(tricine/TPPTS)-Aca-Bombesin(7-14) ((99m)Tc-HABBN) to perform a first-in-man clinical pilot study to evaluate the feasibility of (99m)Tc-HABBN SPECT/CT for detection of prostate cancer in patients. METHODS: Eight patients with biopsy-proven prostate cancer who were scheduled for either radical prostatectomy or external beam radiotherapy underwent (99m)Tc-HABBN scintigraphy and SPECT/CT prior to treatment. Serial blood samples were taken to assess blood radioactivity and to determine in vivo metabolic stability. Clinical parameters were measured and reported side effects, if present, were recorded. Prostate cancer specimens of all patients were immunohistochemically stained for GRPR. RESULTS: (99m)Tc-HABBN was synthesized with high radiochemical yield, purity and specific activity. There were no significant changes in clinical parameters, and there were no adverse or subjective side effects. Low metabolic stability was observed, as less than 20% of (99m)Tc-HABBN was intact after 30 min. Immunohistochemical staining for GRPR was observed in the prostate cancer specimens in all patients. (99m)Tc-HABBN scintigraphy and SPECT/CT did not detect prostate cancer in patients with proven disease. CONCLUSIONS: (99m)Tc-HABBN SPECT/CT for visualization of prostate cancer is safe but hampered by an unexpected low in vivo metabolic stability in man. The difference between the excellent in vitro stability of (99m)Tc-HABBN in human serum samples determined in our previous study regarding (99m)Tc-HABBN and the low in vivo metabolic stability determined in this study, is striking. This issue warrants further study of peptide-based radiopharmaceuticals.

An update of radiolabeled bombesin analogs for gastrin-releasing peptide receptor targeting.

Prostate cancer is a critical public health problem in USA and Europe. New non-invasive imaging methods are urgently needed, due to the low accuracy and specificity of current screen methods and the desire of localizing primary prostate cancer and bone metastasis. Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) are the non-invasive and sensitive imaging methods which have been widely used for diagnosing diseases in the clinic. Lack of suitable radiotracers is the major issue for nuclear imaging of prostate cancer, although radiolabeled bombesin (BN) peptides targeting the Gastrin-Releasing Peptide Receptor (GRPR) on tumor cells are widely investigated. In this review we discuss the recent trends in the development of GRPR-targeted radiopharmaceuticals based on BN analogs with regard to their potential for imaging and therapy of GRPR-expressing malignancies. Following a brief introduction of GRPR and bombesin peptides, we summarize the properties of prostate cancer specific radiolabeled bombesins. New bombesin tracers published in the last five years are reviewed and compared according to their novelties in biomolecules, radionuclides, labeling methods, bifunctional chelators and linkers. Hot topics such as multimerization, application of agonists and antagonists are highlighted in the review. Lastly, a few clinical trials of cancer nuclear imaging with radiolabeled bombesin have been discussed.

Evaluation of a technetium-99m labeled bombesin homodimer for GRPR imaging in prostate cancer.

Multimerization of peptides can improve the binding characteristics of the tracer by increasing local ligand concentration and decreasing dissociation kinetics. In this study, a new bombesin homodimer was developed based on an ε-aminocaproic acid-bombesin(7-14) (Aca-bombesin(7-14)) fragment, which has been studied for targeting the gastrin-releasing peptide receptor (GRPR) in prostate cancer. The bombesin homodimer was conjugated to 6-hydrazinopyridine-3-carboxylic acid (HYNIC) and labeled with (99m)Tc for SPECT imaging. The in vitro binding affinity to GRPR, cell uptake, internalization and efflux kinetics of the radiolabeled bombesin dimer were investigated in the GRPR-expressing human prostate cancer cell line PC-3. Biodistribution and the GRPR-targeting potential were evaluated in PC-3 tumor-bearing athymic nude mice. When compared with the bombesin monomer, the binding affinity of the bombesin dimer is about ten times lower. However, the (99m)Tc labeled bombesin dimer showed a three times higher cellular uptake at 4 h after incubation, but similar internalization and efflux characters in vitro. Tumor uptake and in vivo pharmacokinetics in PC-3 tumor-bearing mice were comparable. The tumor was visible on the dynamic images in the first hour and could be clearly distinguished from non-targeted tissues on the static images after 4 h. The GRPR-targeting ability of the (99m)Tc labeled bombesin dimer was proven in vitro and in vivo. This bombesin homodimer provides a good starting point for further studies on enhancing the tumor targeting activity of bombesin multimers.

CXCR4 inhibition with AMD3100 sensitizes prostate cancer to docetaxel chemotherapy.

Several in vitro and in vivo models have revealed the key role of CXCR4/CXCL12 axis in tumor-stroma interactions. Stromal cells present in the tumor microenvironment express high levels of CXCL12 protein, directly stimulating proliferation and migration of CXCR4-expressing cancer cells. This specific prosurvival influence of stromal cells on tumor cells is thought to protect them from cytotoxic chemotherapy and is postulated as a possible explanation for the minimal residual disease in hematological and solid cancers. Therefore, CXCR4/CXCL12 signaling is an attractive therapeutic target in cancer, as proven in preclinical leukemia mouse models, where CXCR4 inhibition sensitized cancer cells to conventional chemotherapy. This study investigates whether inhibition of CXCR4 with the specific inhibitor AMD3100 sensitizes human prostate cancer cells to docetaxel. We showed that both mouse and human stromal cell lines have a protective effect on PC3-luc cells by promoting their survival after chemotherapy. Furthermore, we demonstrated that AMD3100 sensitizes PC3-luc cells to docetaxel. In a subcutaneous xenograft mouse model of human prostate carcinoma, we showed that a combination of docetaxel and AMD3100 exerts increased antitumor effect compared with docetaxel alone. We concluded that CXCR4 inhibition chemosensitizes prostate cancer cells, both in vitro and in vivo. To explore the relevance of these findings, we analyzed CXCR4 expression levels in human prostate cancer samples. We found that cancer cells present in bone metastatic lesions express higher CXCR4 levels relative to the cells present in primary tumors and lymph node metastatic lesions. These findings underscore the potential of CXCR4 inhibitors as chemosensitizing agents.

Multimerization improves targeting of peptide radio-pharmaceuticals.

Multimerization offers unique kinetic and thermodynamic properties to molecules. Multimeric ligands, characterized by multiple similar or different monomeric molecules tethered together, can bind several receptors simultaneously. Multimerization occurs also in nature. This process can be used to develop molecules with high diagnostic and therapeutic value. By altering parameters as linkers` length and flexibility, scaffold and backbones insertion, and ligands-receptors recognition, it is possible to provide high selectivity and binding affinity. The resultant multimeric ligand has a more favorable binding affinity than corresponding monomeric ligands.

(99m)technetium-HYNIC(tricine/TPPTS)-Aca-bombesin(7-14) as a targeted imaging agent with microSPECT in a PC-3 prostate cancer xenograft model.

The peptide bombesin (BN) and derivates thereof show high binding affinity for the gastrin-releasing peptide receptor (GRPR), which is highly expressed in primary and metastasized prostate cancer. We have synthesized a new BN-based radiopharmaceutical (99m)technetium-HYNIC(tricine/TPPTS)-Aca-BN(7-14) ((99m)Tc-HABN) and evaluated its GRPR targeting properties in vitro and in a xenograft tumor model for human prostate cancer in athymic mice. (99m)Tc-HABN was synthesized, and its lipophilicity and stability were investigated. The IC(50), internalization and efflux properties were determined in vitro using the GRPR expressing human prostate cancer cell line PC-3. (99m)Tc-HABN biodistribution and microSPECT imaging were performed in PC-3 tumor-bearing athymic mice. (99m)Tc-HABN was prepared with high labeling yield (>90%), high radiochemical purity (>95%) and a specific activity of ~19.8 MBq/nmol. The partition coefficient log D value was -1.60 ± 0.06. (99m)Tc-HABN proved to be stable in human serum for 6 h. The IC50 of HYNIC-Aca-BN(7-14) was 12.81 ± 0.14 nM. Incubation of PC-3 cells with (99m)Tc-HABN demonstrated rapid cellular internalization and a long intracellular retention time. When mice were injected with (99m)Tc-HABN, the activity was predominantly cleared via the kidneys. Uptake in the tumor was 2.24 ± 0.64% ID/g after 30 min, with a steady decrease during the 4 h study period. In vivo experiments with a blocking agent showed GRPR mediated uptake. (99m)Tc-HABN microSPECT imaging resulted in clear delineation of the tumor. (99m)Tc-HABN is a novel BN-based radiopharmaceutical that proved to be suitable for targeted imaging of prostate cancer with microSPECT using the human prostate cancer cell line PC-3 in a xenograft mouse model.

Transfer of cysto-urethroscopy skills from a virtual-reality simulator to the operating room: a randomized controlled trial.

OBJECTIVE: To assess whether real-time cysto-urethroscopy (CUS) performance improves by simulator-based training (criterion or predictive validity), addressing the research question 'Does practical skills training on the URO Mentor (UM, Simbionix USA Corp., Cleveland, OH, USA) virtual-reality simulator improve the performance of flexible CUS in patients'. SUBJECTS AND METHODS: Participants (71 interns from Catharina Hospital Eindhoven, CHE, and 29 from University Medical Centre Groningen, UMCG) were randomized to carry out CUS in a patient after training on the UM (UM-trained, 50) or without training on UM (control, 50). The assessment of real-time performance consisted of scoring on a Global Rating Scale (GRS) by supervisors unaware of training status. Data were analysed using stepwise multiple linear regression. The effect size (ES) indication for correlations was used to interpret the magnitude of a standard regression coefficient (beta); an ES of 0.10, 0.30 and 0.50 were considered small, moderate and large, respectively. The study was approved by the Medical Review Ethics Committees of the participating hospitals. RESULTS: Overall, the group that received training performed significantly better than the controls (P < or = 0.003, beta range 0.30-0.47). There was no effect of training for participants with a specific preference for a surgical speciality in two of five GRS scores. Participants from CHE obtained higher GRS 3 scores than those from UMCG. Significantly more UMCG trainees indicated having had stress than those from CHE (P < 0.001). CONCLUSIONS: The results showed that interns who had trained on UM outperformed controls for a CUS procedure in a patient. Training for CUS on the UM is to be recommended for learning to respect tissue, procedural knowledge, flow of procedure and forward planning. Use of the UM to train interns with a specific interest in a surgical speciality in handling instruments, and time and motion, seems to be of limited value.

Acquisition of flexible cystoscopy skills on a virtual reality simulator by experts and novices.

OBJECTIVE: To assess the construct validity of the URO Mentor (Simbionix Corp., Cleveland, OH, USA) virtual reality training model for several variables of skills training in cysto-urethroscopy, addressing two research questions: (i) Does training on the URO Mentor significantly improve novices' performance in terms of time, trauma, areas inspected and Global Rating Scale (GRS) score?; (ii) is discrimination between different levels of expertise possible using the URO Mentor? METHODS: Thirty experts and 50 novices performed seven tasks on the URO Mentor during one training session. The first, fourth and seventh tasks were 'test tasks' to evaluate participants' performance. The simulator recorded procedure time and trauma; a supervisor scored which areas were inspected and gave scores on the GRS. A two-way analysis of variance with repeated-measures test was used to analyse experts' and novices' performances, with P < 0.05 considered to indicate statistical significance. Effect sizes (ES) were calculated to quantify the practical significance of the results; ES of 0.10, 0.30, and 0.50 were considered small, medium and large, respectively. RESULTS: Novices' performances showed a significant improvement with large ES in time (linear trend of learning curve P < 0.001, ES 0.66) and mean GRS score (linear trend P < 0.001, ES 0.84, quadratic trend P = 0.018, ES 0.24). There was a medium improvement for trauma (linear trend P < 0.001, ES 0.40) and a small improvement in areas inspected (linear trend P = 0.032, ES 0.21). That the 95% confidence intervals of the measures on the first task of experts and novices did not coincide indicates that differentiation between experts and novices on the four variables measured can be achieved using the URO Mentor. CONCLUSIONS: Training on the URO Mentor appears to result in a medium to large improvement of novices' performances for time, trauma, areas inspected and GRS scores. Moreover, discrimination between different levels of expertise is possible using this simulator.

Expression of the gastrin-releasing peptide receptor, the prostate stem cell antigen and the prostate-specific membrane antigen in lymph node and bone metastases of prostate cancer.

OBJECTIVE: Cell membrane antigens like the gastrin-releasing peptide receptor (GRPR), the prostate stem cell antigen (PSCA), and the prostate-specific membrane antigen (PSMA), expressed in prostate cancer, are attractive targets for new therapeutic and diagnostic applications. Therefore, we investigated in this study whether these antigens are expressed in metastasized prostate cancer. METHODS: Formalin-fixed, paraffin-embedded specimens of 15 patients with uni- or bilateral lymph node metastases of prostate cancer (totaling 21 cases) and 17 patient-cases of bone metastases were processed for immunohistochemistry with anti-GRPR, anti-PSCA, and anti-PSMA antibodies. A pathologist blinded to clinical and pathological data scored the immunoreactivity for these antibodies on a four-point scale (0 = no staining; 1+ = weak staining; 2+ = moderate staining; 3+ = strong staining) and documented the distribution pattern. RESULTS: GRPR staining in lymph node metastases was seen in 85.7% of cases (18 of 21 cases), PSCA in 95.2% (20/21), and PSMA in 100% (21/21). GRPR in bone metastases was seen in 52.9% of cases (9/17), PSCA in 94.1% (16/17), and PSMA in 100% (17/17). CONCLUSION: We have shown for the first time that GRPR is expressed in the vast majority of lymph node metastases and in 52.9% of bone metastases of prostate cancer. PSCA and PSMA are both highly expressed in lymph node and bone metastases. Although PSCA and PSMA are mostly expressed in prostate cancer metastases, GRPR offers an interesting alternative target as it can be targeted relatively easy with peptide-based (radio)pharmaceuticals.