Toward the discovery and development of PSMA targeted inhibitors for nuclear medicine applications

Background: The rising incidence rate of prostate cancer (PCa) has promoted the development of new diagnostic and therapeutic radiopharmaceuticals during the last decades. Promising im-provements have been achieved in clinical practice using prostate specific membrane antigen (PSMA) labeled agents, including specific antibodies and small molecular weight inhibitors. Focusing on molecular docking studies, this review aims to highlight the progress in the design of PSMA targeted agents for a potential use in nuclear medicine. Results: Although the first development of radiopharmaceuticals able to specifically recognize PSMA was exclusively oriented to macromolecule protein structure such as radiolabeled monoclonal antibodies and derivatives, the isolation of the crystal structure of PSMA served as the trigger for the synthesis and the further evaluation of a variety of low molecular weight inhibitors. Among the nuclear imaging probes and radiotherapeutics that have been developed and tested till today, labeled Glutamate-ureido inhibitors are the most prevalent PSMA-targeting agents for nuclear medicine applications. Conclusion: PSMA represents for researchers the most attractive target for the detection and treatment of patients affected by PCa using nuclear medicine modalities. [99mTc]MIP-1404 is considered the tracer of choice for SPECT imaging and [68Ga]PSMA-11 is the leading diagnostic for PET imaging by general consensus. [18F]DCFPyL and [18F]PSMA-1007 are clearly the emerging PET PSMA candidates for their great potential for a widespread commercial distribution. After paving the way with new imaging tools, academic and industrial R&Ds are now focusing on the development of PSMA inhibitors labeled with alpha or beta minus emitters for a theragnostic application

18F-NaF uptake by atherosclerotic plaque on PET/CT imaging: Inverse correlation between calcification density and mineral metabolic activity

Several studies have highlighted the role of vascular (18)F-NaF uptake as a marker of ongoing calcium deposition. However, accumulation of (18)F-NaF is often inconsistent with localization of arterial plaque. Calcification activity and thus (18)F-NaF uptake might prevail in the earlier plaque stages. To test this hypothesis, we evaluated (18)F-NaF uptake in plaque of 3 different densities, using density as a marker of calcification progression. We also tested whether attenuation-weighted image reconstruction affects (18)F-NaF uptake in the different plaque stages. METHODS: Sixty-four oncologic patients (14 men and 50 women; mean age, 65.3 \ub1 8.2 y; range, 26-81 y) underwent (18)F-NaF PET/CT. A volume of interest was drawn on each plaque within the infrarenal aorta to assess mean standardized uptake value and attenuation (in Hounsfield units [HU]). Plaque was then categorized as light (<210 HU), medium (211-510 HU), or heavy (>510 HU). Standardized uptake value was normalized for blood (18)F-NaF activity to obtain the plaque target-to-background ratio (TBR). During this process, several focal, noncalcified areas of (18)F-NaF were identified (hot spots). The TBR of the hot spots was computed after isocontour thresholding. The TBR of a noncalcified control region was also calculated. In 35 patients, the TBR of non-attenuation-corrected images was calculated. RESULTS: The average TBR was highest in light plaque (2.21 \ub1 0.88), significantly lower in medium plaque (1.59 \ub1 0.63, P < 0.001), and lower still in heavy plaque (1.14 \ub1 0.37, P < 0.0001 with respect to both light and medium plaque). The TBR of the control region was not significantly different from that of heavy plaque but was significantly lower than that of light and medium plaque (P < 0.01). Hot spots had the highest absolute TBR (3.89 \ub1 1.87, P < 0.0001 vs. light plaque). TBRs originating from non-attenuation-corrected images did not significantly differ from those originating from attenuation-corrected images. CONCLUSION: Our results support the concept that (18)F-NaF is a feasible option in imaging molecular calcium deposition in the early stages of plaque formation, when active uptake mechanisms are the main determinants of calcium presence, but that retention of (18)F-NaF progressively decreases with increasing calcium deposition in the arterial wall. Our data suggest that non-attenuation-corrected reconstruction does not significantly affect evaluation of plaque of any thickness

18F-FDG micro-PET imaging for research investigations in the Octopus vulgaris: applications and future directions in invertebrate neuroscience and tissue regeneration

This study aimed at developing a method for administration of 18F-Fludeoxyglucose (18F-FDG) in the common octopus and micro-positron emission tomography (micro-PET) bio-distribution assay for the characterization of glucose metabolism in body organs and regenerating tissues. Methods: Seven animals (two with one regenerating arm) were anesthetized with 3.7% MgCl2 in artificial seawater. Each octopus was injected with 18-30 MBq of isosmotic 18F-FDG by accessing the branchial heart or the anterior vena cava. After an uptake time of ~50 minutes, the animal was sacrificed, placed on a bed of a micro-PET scanner and submitted to 10 min static 3-4 bed acquisitions to visualize the entire body. To confirm the interpretation of images, internal organs of interest were collected. The level of radioactivity of each organ was counted with a \u3b3-counter. Results: Micro-PET scanning documented a good 18F-FDG full body distribution following vena cava administration. A high mantle mass radioactivity facing a relatively low tracer uptake in the arms was revealed. In particular, the following organs were clearly identified and measured for their uptake: brain (standardized uptake value, SUV max of 6.57\ub11.86), optic lobes (SUV max of 7.59\ub11.66) and arms (SUV max of 1.12\ub10.06). Interestingly, 18F-FDG uptake was up to threefold higher in the regenerating arm stumps at the level of highly proliferating areas. Conclusion: This study represents a stepping-stone over the use of non-invasive functional techniques to address questions relevant to invertebrate neuroscience and regenerative medicine

Use of the uteroglobin platform for the expression of a bivalent antibody against oncofetal fibronectin in Escherichia coli.

Escherichia coli is a robust, economic and rapid expression system for the production of recombinant therapeutic proteins. However, the expression in bacterial systems of complex molecules such as antibodies and fusion proteins is still affected by several drawbacks. We have previously described a procedure based on uteroglobin (UG) for the engineering of very soluble and stable polyvalent and polyspecific fusion proteins in mammalian cells (Ventura et al. 2009. J. Biol. Chem. 284∶26646-26654.) Here, we applied the UG platform to achieve the expression in E. coli of a bivalent human recombinant antibody (L19) toward the oncofetal fibronectin (B-FN), a pan-tumor target. Purified bacterial L19-UG was highly soluble, stable, and, in all molecules, the L19 moiety maintained its immunoreactivity. About 50-70% of the molecules were covalent homodimer, however after refolding with the redox couple reduced-glutathione/oxidized-glutathione (GSH/GSSG), 100% of molecules were covalent dimers. Mass spectrometry studies showed that the proteins produced by E. coli and mammalian cells have an identical molecular mass and that both proteins are not glycosylated. L19-UG from bacteria can be freeze-dried without any loss of protein and immunoreactivity. In vivo, in tumor-bearing mice, radio-iodinated L19-UG selectively accumulated in neoplastic tissues showing the same performance of L19-UG from mammalian cells. The UG-platform may represent a general procedure for production of various biological therapeutics in E. coli

Concomitant Prostate Cancer and Hodgkin Lymphoma: A Differential Diagnosis Guided by a Combined 68Ga-PSMA-11 and 18F-FDG PET/CT Approach

Here we report the case of concomitant favorable-risk prostate cancer and Hodgkin Lymphoma in a 38-year old male. 68Ga-Prostate Specific Membrane Antigen-11 Positron Emission Tomography/Computed Tomography (68Ga-PSMA-11 PET/CT) was performed for staging purposes, showing the focal PSMA prostatic uptake as well as the presence of enlarged low-PSMA expressing mediastinal lymphadenopathies, thus raising the suspicion of another malignancy. A subsequent 18F-Fluorodeoxyglucose (18F-FDG) PET/CT demonstrated a high FDG-avidity by mediastinal lymphadenopathies as opposed to the low prostate cancer FDG uptake. Of note, both tumor entities were clearly detected by the two scans. However, different ranges in terms of Maximum Standardized Uptake Value (SUVmax) uptake allowed the discrimination between the two tumor entities. At the subsequent mediastinal lymph nodal biopsy, the coexistence of Hodgkin lymphoma was documented. The present case suggests that even if specific for prostate cancer, 68Ga-PSMA-11 PET/CT may raise the suspicion of other concurrent malignancies thanks to its non-receptor bounding mechanism. Further, it shows that in certain cases, the combination of 18F-FDG and 68Ga-PSMA PET/CT imaging may non-invasively guide the clinical management, optimizing the diagnostic process and the subsequent therapeutic interventions

Uteroglobin platform.

<p>A) The cDNA encoding the variable heavy (VH) and variable light (VL) domains of immunoglobulins composing a single chain fragment variable (scFv) is fused to the 5′ end of uteroglobin (UG) cDNA. The covalent dimerization of the UG moiety within the fusion protein scFv-UG allows the generation of a divalent antibody. B) The cDNA encoding for an scFv is fused to both the 5′ and 3′ ends of UG. The resulting fusion protein is a tetravalent antibody. C) Two different cDNAs encoding for two different antibody fragments or an antibody fragment and a therapeutic molecule, such as a cytokine, are fused to the 5′ and 3′ ends of UG. The resulting protein is dual specific and tetravalent <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0082878#pone.0082878-Ventura1" target="_blank">[26]</a>.</p

Mass spectrometry analysis of L19-UG from mammalian cells and <i>E.coli.</i>

<p>Mass spectrometry analysis of reduced L19-UG obtained from CHO cells (<b>A</b>, <b>C</b>) and from <i>E. coli</i> (<b>B</b>, <b>D</b>). The raw (<b>A</b>–<b>B</b>) and deconvoluted (<b>C</b>–<b>D</b>) mass spectra relative to the chromatographic peaks at 32.5 minutes are reported. The calculated average neutral mass of monomeric form of L19-UG is 34670,3 Da for the protein produced in CHO cells and 34670,6 Da for the protein produced in <i>E. coli</i>.</p

Biodistribution experiments of ¹²⁵I-L19-UG in F9 tumor-bearing mice.

<p>The percentage of the injected dose per gram of tissue (%ID/g) ± SD in the different organs, at the indicated time post ¹²⁵I-L19-UG i.v. administration, are reported.</p

Immunoreactivity of L19-UG from <i>E.coli</i>.

<p><b>A)</b> Different concentrations of L19-UG purified from <i>E. coli</i> (black circles) and CHO cells (black diamonds) were tested for binding to the recombinant fragment 7.ED-B.8.9 FN by ELISA. To verify the specificity of the binding, different concentrations of L19-UG from <i>E. coli</i> were pre-incubated with a molar excess (1,2 milligrams per ml) of the recombinant ED-B and then tested in ELISA for its binding to 7.ED-B.8.9 (white circles). The mean absorbances at λ = 405 nm ± SD are indicated. <b>B)</b> A shift in the column retention volume of L19-UG in SEC (Superdex 200) was obtained after incubating L19-UG with a molar excess of the recombinant FN fragment B-8. Left panel: SEC profile of L19-UG showing a single peak at 15.14 ml. Right panel: SEC profile of L19-UG pre-incubated with a molar excess of B-8 rFN showing an elution peak at 13.65 ml, which corresponds to the immunocomplex L19-UG/B-8 rFN, and an elution peak at 16 ml, which corresponds to the excess unbound B-8 rFN.</p