Radiofluorinated derivatives of 2-(phosphonomethyl)pentanedioic acid as inhibitors of prostate specific membrane antigen (PSMA) for the imaging of prostate cancer

Construction of C-P Bonds from Free Cyclobutanone Oximes and Chlorophosphines via Radical-Radical Coupling

Herein, we report a catalyst-free reaction of cyclobutanone oximes with chlorophosphines (R2PCl), which forms a fragile C═N-O-PR2 species that undergoes N-O homolysis, fragmentation, and radical-radical coupling, leading to the formation of cyano-containing phosphine oxides in good yields. The reaction features an in situ activation of cyclobutanone oximes for radical generation, in which R2PCl plays a dual role as both an activator and a reactant.

Photoredox-Catalyzed Phosphonocarboxylation of Allenes with Phosphine Oxides and CO2

Phosphonocarboxylation of allenes with diarylphosphine oxides and CO2 via visible-light photoredox catalysis was developed for the first time. This work provided practical and sustainable access to highly valuable but otherwise difficult-to-access linear allylic β-phosphonyl carboxylic acids in moderate yields with exclusive regio- and stereoselectivity. This method was also characterized by step and atom economy and transition-metal free and mild conditions. Preliminary mechanistic studies suggested that allyl-methyl carbanion species are the key intermediates.

Occurrence of Z-2-oxo-4-methyl-3-pentene-1,5-dioic acid and its regioisomer 4-methylene-2-oxo-glutaric acid in tulip tissues

Although Z-2-oxo-4-methyl-3-pentene-1,5-dioic acid (Z-OMPD) has been identified as a major dicarboxylic acid in tulip tissues, its biosynthetic pathway has not been elucidated. Herein, Z-OMPD was isolated from tulip leaves and chemically synthesized. Comparisons of these samples revealed that Z-OMPD exists as a tautomeric mixture at physiological pH. As a regioisomer of Z-OMPD, we enzymatically and chemically prepared 4-methylene-2-oxo-glutaric acid (4-MEOG) for the first time. Using these compounds as standards, the occurrence of Z-OMPD and 4-MEOG in various tissues of the tulip cultivar "Murasakizuisho" was evaluated directly and by 2,4-dinitrophenylhydrazone derivatization. Z-OMPD was found to be abundant in the aerial tissues, whereas 4-MEOG was almost absent from all tissues. Stability analyses of Z-OMPD and 4-MEOG revealed that no double bond isomerization occurred at physiological pH, suggesting that enzyme systems are responsible for Z-OMPD biosynthesis in tulip tissues.

68Ga-labeled ODAP-Urea-based PSMA agents in prostate cancer: first-in-human imaging of an optimized agent

PURPOSE

Prostate-specific membrane antigen (PSMA) is a promising target for prostate cancer imaging and therapy. The most commonly used scaffold incorporates a glutamate-urea (Glu-Urea) function. We recently developed oxalyldiaminopropionic acid-urea (ODAP-Urea) PSMA ligands in an attempt to improve upon the pharmacokinetic properties of existing agents. Here, we report the synthesis of an optimized ⁶⁸Ga-labeled ODAP-Urea-based ligand, [⁶⁸Ga]Ga-P137, and first-in-human results.

METHODS

Twelve ODAP-Urea-based ligands were synthesized and radiolabeled with ⁶⁸Ga in high radiochemical yield and purity. Their PSMA inhibitory capacities were determined using the NAALADase assay. Radioligands were evaluated in mice-bearing 22Rv1 prostate tumors by microPET. Lead compound [⁶⁸Ga]Ga-P137 was evaluated for stability, cell uptake, and biodistribution. PET imaging of [⁶⁸Ga]Ga-P137 was performed in three patients head-to-head compared to [⁶⁸Ga]Ga-PSMA-617.

RESULTS

Ligands were synthesized in 11.1-44.4% yield and > 95% purity. They have high affinity to PSMA (K_i of 0.13 to 5.47 nM). [⁶⁸Ga]Ga-P137 was stable and hydrophilic. [⁶⁸Ga]Ga-P137 showed higher uptake than [⁶⁸Ga]Ga-PSMA-617 in tumor-bearing mice at 6.43 ± 0.98%IA/g vs 3.41 ± 1.31%IA/g at 60-min post-injection. In human studies, the normal organ biodistribution of [⁶⁸Ga]Ga-P137 was grossly equivalent to that of [⁶⁸Ga]Ga-PSMA-617 except for within the urinary tract, in which [⁶⁸Ga]Ga-P137 demonstrated lower uptake.

CONCLUSION

The optimized ODAP-Urea-based ligand [⁶⁸Ga]Ga-P137 can image PSMA in xenograft models and humans, with lower bladder accumulation to the Glu-Urea-based agent, [⁶⁸Ga]Ga-PSMA-617, in a preliminary, first-in-human study.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04560725, Registered 23 September 2020. https://clinicaltrials.gov/ct2/show/NCT04560725.

Transition metal-free phosphonocarboxylation of alkenes with carbon dioxide via visible-light photoredox catalysis

Catalytic difunctionalization of alkenes has been an ideal strategy to generate structurally complex molecules with diverse substitution patterns. Although both phosphonyl and carboxyl groups are valuable functional groups, the simultaneous incorporation of them via catalytic difunctionalization of alkenes, ideally from abundant, inexpensive and easy-to-handle raw materials, has not been realized. Herein, we report the phosphonocarboxylation of alkenes with CO2 via visible-light photoredox catalysis. This strategy is sustainable, general and practical, providing facile access to important β-phosphono carboxylic acids, including structurally complex unnatural α-amino acids. Diverse alkenes, including enamides, styrenes, enolsilanes and acrylates, undergo such reactions efficiently under mild reaction conditions. Moreover, this method represents a rare example of redox-neutral difunctionalization of alkenes with H-P(O) compounds, including diaryl- and dialkyl- phosphine oxides and phosphites. Importantly, these transition-metal-free reactions also feature low catalyst loading, high regio- and chemo-selectivities, good functional group tolerance, easy scalability and potential for product derivatization.

Development and characterization of a theranostic multimodal anti-PSMA targeting agent for imaging, surgical guidance, and targeted photodynamic therapy of PSMA-expressing tumors

Rationale: Prostate cancer (PCa) recurrences after surgery frequently occur. To improve the outcome after surgical resection of the tumor, the theranostic multimodal anti-PSMA targeting agent ¹¹¹In-DTPA-D2B-IRDye700DX was developed and characterized for both pre- and intra-operative tumor localization and eradication of (residual) tumor tissue by PSMA-targeted photodynamic therapy (tPDT), which is a highly selective cancer treatment based on targeting molecules conjugated to photosensitizers that can induce cell destruction upon exposure to near-infrared (NIR) light.

Methods: The anti-PSMA monoclonal antibody D2B was conjugated with IRDye700DX and DTPA and subsequently radiolabeled with ¹¹¹In. To determine the optimal dose and time point for tPDT, BALB/c nude mice with PSMA-expressing (PSMA⁺) s.c. LS174T-PSMA xenografts received the conjugate (24-240 µg/mouse) intravenously (8 MBq/mouse) followed by µSPECT/CT, near-infrared fluorescence imaging, and ex vivo biodistribution at 24, 48, 72 and 168 h p.i. Tumor growth of LS174T-PSMA xenografts and overall survival of mice treated with 1-3 times of NIR light irradiation (50, 100, 150 J/cm²) 24 h after injection of 80 µg of DTPA-D2B-IRDye700DX was compared to control conditions.

Results: Highest specific tumor uptake was observed at conjugate doses of 80 µg/mouse. Biodistribution revealed no significant difference in tumor uptake in mice at 24, 48, 72 and 168 h p.i. PSMA⁺ tumors were clearly visualized with both µSPECT/CT and NIR fluorescence imaging. Overall survival in mice treated with 80 µg of DTPA-D2B-IRDye700DX and 1x 150 J/cm² of NIR light at 24 h p.i. was significantly improved compared to the control group receiving neither conjugate nor NIR light (73 days vs. 16 days, respectively, p=0.0453). Treatment with 3x 150 J/cm² resulted in significantly prolonged survival compared to treatment with 3x 100 J/cm² (p = 0.0067) and 3x 50 J/cm² (p = 0.0338).

Principal conclusions:¹¹¹In-DTPA-D2B-IRDye700DX can be used for pre- and intra-operative detection of PSMA⁺ tumors with radionuclide and NIR fluorescence imaging and PSMA-targeted PDT. PSMA-tPDT using this multimodal agent resulted in significant prolongation of survival and shows great potential for treatment of (metastasized) prostate cancer.

Procedures for the GMP-Compliant Production and Quality Control of [18F]PSMA-1007: A Next Generation Radiofluorinated Tracer for the Detection of Prostate Cancer

Radiolabeled tracers targeting the prostate-specific membrane antigen (PSMA) have become important radiopharmaceuticals for the PET-imaging of prostate cancer. In this connection, we recently developed the fluorine-18-labelled PSMA-ligand [18F]PSMA-1007 as the next generation radiofluorinated Glu-ureido PSMA inhibitor after [18F]DCFPyL and [18F]DCFBC. Since radiosynthesis so far has been suffering from rather poor yields, novel procedures for the automated radiosyntheses of [18F]PSMA-1007 have been developed. We herein report on both the two-step and the novel one-step procedures, which have been performed on different commonly-used radiosynthesisers. Using the novel one-step procedure, the [18F]PSMA-1007 was produced in good radiochemical yields ranging from 25 to 80% and synthesis times of less than 55 min. Furthermore, upscaling to product activities up to 50 GBq per batch was successfully conducted. All batches passed quality control according to European Pharmacopoeia standards. Therefore, we were able to disclose a new, simple and, at the same time, high yielding production pathway for the next generation PSMA radioligand [18F]PSMA-1007. Actually, it turned out that the radiosynthesis is as easily realised as the well-known [18F]FDG synthesis and, thus, transferable to all currently-available radiosynthesisers. Using the new procedures, the clinical daily routine can be sustainably supported in-house even in larger hospitals by a single production batch.

Integrated 68Ga-HBED-CC-PSMA-PET/MRI in patients with suspected recurrent prostate cancer

AIM

Evaluate the diagnostic accuracy of ⁶⁸Ga-labeled HBED-CC-PSMA-PET/MRI for detection of recurrent PCa in comparison to PET/CT.

METHODS

48 patients with suspected recurrent PCa underwent PET/CT after injection of the ⁶⁸Ga-HBED-CC-PSMA ligand followed by integrated PET/MRI. Image analysis was performed by nuclear medicine physicians and radiologists with respect to the detection of lymph node metastases, bone metastases and local recurrence of the tumour. Image quality was evaluated visually based on a three-point ordinal scale.

RESULTS

From 48 patients initially examined, 25 were finally eligible for qualitative and quantitative image evaluation. In 14 patients, neither PET/CT nor PET/MRI found tumour lesions, and 9 patients were excluded from image analysis due to a pronounced extinction artifact around the urinary bladder (halo). In comparison to ⁶⁸Ga-HBED-CC-PSMA-PET/CT, ⁶⁸Ga-HBED-CC-PSMA-PET/MRI identified 14 vs. 9 local recurrences in the prostate bed and 23 vs. 20 PET-positive lymph nodes, and 4 vs. 4 PET-positive bone lesions, respectively. While the improved detection of suspicious lymph nodes was primarily attributable to the PET component, the advantageous detection of tumour recurrences in the prostate bed was chiefly referable to the superior soft-tissue contrast of the MR component of integrated PET/MRI. Analysis of SUV_max revealed that ⁶⁸Ga-HBED-CC-PSMA-PET/MRI provided significantly higher SUV_max compared to ⁶⁸Ga-HBED-CC-PSMA-PET/CT (17.6, range 2.0-49.6, and 15.1, range 3.5-36.8, respectively, p = 0.0019).

CONCLUSION

⁶⁸Ga-HBED-CC-PSMA-PET/MRI was found to be superior as compared to ⁶⁸Ga-HBED-CC-PSMA-PET/CT in the detection of PSMA-expressing prostate bed recurrences.

Gallium-68 Prostate-Specific Membrane Antigen PET Imaging

The role of gallium-68 (⁶⁸Ga) prostate-specific membrane antigen (PSMA) PET imaging is evolving and finding its place in the imaging armamentarium for prostate cancer (PCa). Despite the progress of conventional imaging strategies, significant limitations remain, including identification of small-volume disease and assessment of bone. Clinical studies have demonstrated that ⁶⁸Ga-PSMA is a promising tracer for detection of PCa metastases, even in patients with low prostate-specific antigen. To provide an accurate interpretation of ⁶⁸Ga-PSMA PET/computed tomography, nuclear medicine specialists and radiologists should be familiar with physiologic ⁶⁸Ga-PSMA uptake, common variants, patterns of locoregional and distant spread of PCa, and inherent pitfalls.

Clinical Experience with 18F-Labeled Small Molecule Inhibitors of Prostate-Specific Membrane Antigen

Prostate cancer (PCa) is the most common noncutaneous malignancy diagnosed in men. Despite the large number of men who will suffer from PCa at some point during their lives, conventional imaging modalities for this important disease (contrast-enhanced computed tomography, bone scan, and MR imaging) have provided only marginal to moderate success in appropriately guiding patient management in certain clinical contexts. In this review, the authors discuss radiofluorinated small molecule radiotracers that have been developed to bind to the transmembrane glycoprotein prostate-specific membrane antigen, a target that is nearly universally overexpressed on PCa epithelial cells.

The therapeutic and diagnostic potential of the prostate specific membrane antigen/glutamate carboxypeptidase II (PSMA/GCPII) in cancer and neurological disease

Prostate specific membrane antigen (PSMA) otherwise known as glutamate carboxypeptidase II (GCPII) is a membrane bound protein that is highly expressed in prostate cancer and in the neovasculature of a wide variety of tumours including glioblastomas, breast and bladder cancers. This protein is also involved in a variety of neurological diseases including schizophrenia and ALS. In recent years, there has been a surge in the development of both diagnostics and therapeutics that take advantage of the expression and activity of PSMA/GCPII. These include gene therapy, immunotherapy, chemotherapy and radiotherapy. In this review, we discuss the biological roles that PSMA/GCPII plays, both in normal and diseased tissues, and the current therapies exploiting its activity that are at the preclinical stage. We conclude by giving an expert opinion on the future direction of PSMA/GCPII based therapies and diagnostics and hurdles that need to be overcome to make them effective and viable.

Optimization of Acquisition time of 68Ga-PSMA-Ligand PET/MRI in Patients with Local and Metastatic Prostate Cancer

Objective

The aim of this optimization study was to minimize the acquisition time of ⁶⁸Ga-HBED-CC-PSMA positron emission tomography/magnetic resonance imaging (PET/MRI) in patients with local and metastatic prostate cancer (PCa) to obtain a sufficient image quality and quantification accuracy without any appreciable loss.

Methods

Twenty patients with PCa were administered intravenously with the ⁶⁸Ga-HBED-CC-PSMA ligand (mean activity 99 MBq/patient, range 76–148 MBq) and subsequently underwent PET/MRI at, on average, 168 min (range 77–320 min) after injection. PET and MR imaging data were acquired simultaneously. PET acquisition was performed in list mode and PET images were reconstructed at different time intervals (1, 2, 4, 6, 8, and 10 min). Data were analyzed regarding radiotracer uptake in tumors and muscle tissue and PET image quality. Tumor uptake was quantified in terms of the maximum and mean standardized uptake value (SUV_max, SUV_mean) within a spherical volume of interest (VOI). Reference VOIs were drawn in the gluteus maximus muscle on the right side. PET image quality was evaluated by experienced nuclear physicians/radiologists using a five-point ordinal scale from 5–1 (excellent—insufficient).

Results

Lesion detectability linearly increased with increasing acquisition times, reaching its maximum at PET acquisition times of 4 min. At this image acquisition time, tumor lesions in 19/20 (95%) patients were detected. PET image quality showed a positive correlation with increasing acquisition time, reaching a plateau at 4–6 min image acquisition. Both SUV_max and SUV_mean correlated inversely with acquisition time and reached a plateau at acquisition times after 4 min.

Conclusion

In the applied image acquisition settings, the optimal acquisition time of ⁶⁸Ga-PSMA-ligand PET/MRI in patients with local and metastatic PCa was identified to be 4 min per bed position. At this acquisition time, PET image quality and lesion detectability reach a maximum while SUV_max and SUV_mean do not change significantly beyond this time point.

Alterations in androgen deprivation enhanced prostate-specific membrane antigen (PSMA) expression in prostate cancer cells as a target for diagnostics and therapy

BACKGROUND

Prostate-specific membrane antigen (PSMA) is a promising target for diagnostics and therapy of prostate carcinoma (PCa). Based on the hypothesis that PSMA expression can be modulated by variations in androgen deprivation therapy (ADT), we investigated the binding of a PSMA-directed radiopharmaceutical in vitro in order to get an insight of the interactions between altered premedication and PSMA expression before repetitive PSMA-directed PET/CT for therapy response and targeted therapy implementation.

METHODS

The human castration-resistant PCa cell line VCaP (CRPC) was treated with either 1 nmol/L testosterone (T) over 20 passages yielding the androgen-sensitive cell line (revCRPC) or with 5 μmol/L abiraterone acetate (AA) generating the abiraterone-tolerant subtype CRPCAA. In these cell lines, T and AA were varied by either supply or withdrawal of T and AA. PSMA expression of the three cell culture models was detected by Western blot and immunohistochemical staining. For quantitative measurement of tracer uptake, 0.3 nmol/L (68)Ga-labelled PSMA-HBED-CC peptide (100-300 kBq/ml) was added to different treated parallel cultures (n = 9 each). Time-dependent uptake per 10(6) cells of each culture was calculated and evaluated. PSMA mRNA expression was investigated by qPCR.

RESULTS

PSMA expression increased dependently on intensified ADT in all three basic cell lines. (68)Ga-PSMA-HBED-CC uptake almost doubled during 3 h in all cell lines (p < 0.01). Compared to the basic cells, pre-incubation with abiraterone for 48 h resulted in a significant increased uptake in CRPC (p < 0.001). In revCRPC, 48-h AA pre-incubation resulted in an eightfold higher uptake after 3 h (p < 0.001). Additional withdrawal of external testosterone increased the uptake up to tenfold (p < 0.01). The increase of PSMA expression upon ADT and AA treatments was confirmed by qPCR and Western blot data. Furthermore, in CRPCAA, 48-h AA withdrawal increased the uptake up to fivefold (p < 0.01).

CONCLUSIONS

The investigated three PCa cell culture subtypes represent a serial preclinical model of androgen deprivation therapy as a proxy for clinical situations with differing basal PSMA expression. The uptake of PSMA-binding tracers could be stimulated by therapeutic effective short-term variation in premedication in all stages of ADT response. These complex interactions have to be considered in the interpretation of diagnostic imaging using PSMA ligands as well as in the optimal timing of PSMA-based therapies.

PSMA Ligands for Radionuclide Imaging and Therapy of Prostate Cancer: Clinical Status

Prostate cancer (PCa) is the most common malignancy in men worldwide, leading to substantial morbidity and mortality. At present, imaging of PCa has become increasingly important for staging, restaging, and treatment selection. Until recently, choline-based positron emission tomography/computed tomography (PET/CT) represented the state-of-the-art radionuclide imaging technique for these purposes. However, its application is limited to patients with high PSA levels and Gleason scores. Prostate-specific membrane antigen (PSMA) is a promising new target for specific imaging of PCa, because it is upregulated in the majority of PCa. Moreover, PSMA can serve as a target for therapeutic applications. Currently, several small-molecule PSMA ligands with excellent in vivo tumor targeting characteristics are being investigated for their potential in theranostic applications in PCa. Here, a review of the recent developments in PSMA-based diagnostic imaging and therapy in patients with PCa with radiolabeled PSMA ligands is provided.

Selective CNS Uptake of the GCP-II Inhibitor 2-PMPA following Intranasal Administration

Glutamate carboxypeptidase II (GCP-II) is a brain metallopeptidase that hydrolyzes the abundant neuropeptide N-acetyl-aspartyl-glutamate (NAAG) to NAA and glutamate. Small molecule GCP-II inhibitors increase brain NAAG, which activates mGluR3, decreases glutamate, and provide therapeutic utility in a variety of preclinical models of neurodegenerative diseases wherein excess glutamate is presumed pathogenic. Unfortunately no GCP-II inhibitor has advanced clinically, largely due to their highly polar nature resulting in insufficient oral bioavailability and limited brain penetration. Herein we report a non-invasive route for delivery of GCP-II inhibitors to the brain via intranasal (i.n.) administration. Three structurally distinct classes of GCP-II inhibitors were evaluated including DCMC (urea-based), 2-MPPA (thiol-based) and 2-PMPA (phosphonate-based). While all showed some brain penetration following i.n. administration, 2-PMPA exhibited the highest levels and was chosen for further evaluation. Compared to intraperitoneal (i.p.) administration, equivalent doses of i.n. administered 2-PMPA resulted in similar plasma exposures (AUC_{0-t, i.n}./AUC_{0-t, i.p.} = 1.0) but dramatically enhanced brain exposures in the olfactory bulb (AUC_{0-t, i.n}./AUC_{0-t, i.p.} = 67), cortex (AUC_{0-t, i.n}./AUC_{0-t, i.p.} = 46) and cerebellum (AUC_{0-t, i.n}./AUC_{0-t, i.p.} = 6.3). Following i.n. administration, the brain tissue to plasma ratio based on AUC_0-t in the olfactory bulb, cortex, and cerebellum were 1.49, 0.71 and 0.10, respectively, compared to an i.p. brain tissue to plasma ratio of less than 0.02 in all areas. Furthermore, i.n. administration of 2-PMPA resulted in complete inhibition of brain GCP-II enzymatic activity ex-vivo confirming target engagement. Lastly, because the rodent nasal system is not similar to humans, we evaluated i.n. 2-PMPA also in a non-human primate. We report that i.n. 2-PMPA provides selective brain delivery with micromolar concentrations. These studies support intranasal delivery of 2-PMPA to deliver therapeutic concentrations in the brain and may facilitate its clinical development.

Synthesis and biological evaluation of copper-64 radiolabeled [DUPA-6-Ahx-(NODAGA)-5-Ava-BBN(7-14)NH2], a novel bivalent targeting vector having affinity for two distinct biomarkers (GRPr/PSMA) of prostate cancer

Gastrin-releasing peptide receptors (GRPr) and prostate-specific membrane antigen (PSMA) are two identifying biomarkers expressed in very high numbers on prostate cancer cells and could serve as a useful tool for molecular targeting and diagnosis of disease via positron-emission tomography (PET). The aim of this study was to produce the multipurpose, bivalent [DUPA-6-Ahx-((64)Cu-NODAGA)-5-Ava-BBN(7-14)NH2] radioligand for prostate cancer imaging, where DUPA = (2-[3-(1,3-dicarboxypropyl)-ureido]pentanedioic acid), a small-molecule, PSMA-targeting probe, 6Ahx = 6-aminohexanoic acid, 5-Ava = 5-aminovaleric acid, NODAGA = [2-(4,7-biscarboxymethyl)-1,4,7-(triazonan-1-yl)pentanedioic acid] (a derivative of NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid)), and BBN(7-14)NH2 = bombesin, a GRPr-specific peptide targeting probe.

METHODS

The PSMA/GRPr dual targeting ligand precursor [DUPA-6-Ahx-K-5-Ava-BBN(7-14)NH2], was synthesized by solid-phase and manual peptide synthesis, after which NODAGA was added via manual conjugation to the ε-amine of lysine (K). The new bivalent GRPr/PSMA targeting vector was purified by reversed-phase high performance liquid chromatography (RP-HPLC), characterized by electrospray-ionization mass spectrometry (ESI-MS), and metallated with (64)CuCl2 and (nat)CuCl2. The receptor binding affinity was evaluated in human, prostate, PC-3 (GRPr-positive) and LNCaP (PSMA-positive) cells and the tumor-targeting efficacy determined in severe combined immunodeficient (SCID) and athymic nude mice bearing PC-3 and LNCaP tumors. Whole-body maximum intensity microPET/CT images of PC-3/LNCaP tumor-bearing mice were obtained 18 h post-injection (p.i.).

RESULTS

Competitive binding assays in PC-3 and LNCaP cells indicated high receptor binding affinity for the [DUPA-6-Ahx-((nat)Cu-NODAGA)-5-Ava-BBN(7-14)NH2] conjugate. MicroPET scintigraphy in PC-3/LNCaP tumor-bearing mice indicated that xenografted tumors were visible at 18h p.i. with collateral, background radiation also being observed in non-target tissue.

CONCLUSIONS

DUPA-6-Ahx-((64)Cu-NODAGA)-5-Ava-BBN(7-14)NH2] targeting vector, as described herein, is the first example of a dual GRPr-/PSMA-targeting radioligand for molecular of imaging prostate tumors. Detailed in vitro studies and microPET molecular imaging investigations of [DUPA-6-Ahx-((64)Cu-NODAGA)-5-Ava-BBN(7-14)NH2 in tumor-bearing mice indicate that further studies are necessary to optimize uptake and retention of tracer in GRPr- and PSMA-positive tissues.

Strategies for imaging androgen receptor signaling pathway in prostate cancer: implications for hormonal manipulation and radiation treatment

Prostate cancer (Pca) is a heterogeneous disease; its etiology appears to be related to genetic and epigenetic factors. Radiotherapy and hormone manipulation are effective treatments, but many tumors will progress despite these treatments. Molecular imaging provides novel opportunities for image-guided optimization and management of these treatment modalities. Here we reviewed the advances in targeted imaging of key biomarkers of androgen receptor signaling pathways. A computerized search was performed to identify all relevant studies in Medline up to 2013. There are well-known limitations and inaccuracies of current imaging approaches for monitoring biological changes governing tumor progression. The close integration of molecular biology and clinical imaging could ease the development of new molecular imaging agents providing novel tools to monitor a number of biological events that, until a few years ago, were studied by conventional molecular assays. Advances in translational research may represent the next step in improving the oncological outcome of men with Pca who remain at high risk for systemic failure. This aim may be obtained by combining the anatomical properties of conventional imaging modalities with biological information to better predict tumor response to conventional treatments.