PSMA-D4 Radioligand for Targeted Therapy of Prostate Cancer: Synthesis, Characteristics and Preliminary Assessment of Biological Properties.

A new PSMA ligand (PSMA-D4) containing the Glu-CO-Lys pharmacophore connected with a new linker system (L-Trp-4-Amc) and chelator DOTA was developed for radiolabeling with therapeutic radionuclides. Herein we describe the synthesis, radiolabeling, and preliminary biological evaluation of the novel PSMA-D4 ligand. Synthesized PSMA-D4 was characterized using TOF-ESI-MS, NMR, and HPLC methods. The novel compound was subject to molecular modeling with GCP-II to compare its binding mode to analogous reference compounds. The radiolabeling efficiency of PSMA-D4 with 177Lu, 90Y, 47Sc, and 225Ac was chromatographically tested. In vitro studies were carried out in PSMA-positive LNCaP tumor cells membranes. The ex vivo tissue distribution profile of the radioligands and Cerenkov luminescence imaging (CLI) was studied in LNCaP tumor-bearing mice. PSMA-D4 was synthesized in 24% yield and purity >97%. The radio complexes were obtained with high yields (>97%) and molar activity ranging from 0.11 to 17.2 GBq mcmol-1, depending on the radionuclide. In vitro assays confirmed high specific binding and affinity for all radiocomplexes. Biodistribution and imaging studies revealed high accumulation in LNCaP tumor xenografts and rapid clearance of radiocomplexes from blood and non-target tissues. These render PSMA-D4 a promising ligand for targeted therapy of prostate cancer (PCa) metastases.

Selection of the First 99mTc-Labelled Somatostatin Receptor Subtype 2 Antagonist for Clinical Translation-Preclinical Assessment of Two Optimized Candidates.

Recently, radiolabelled antagonists targeting somatostatin receptors subtype 2 (SST2) in neuroendocrine neoplasms demonstrated certain superior properties over agonists. Within the ERA-PerMED project "TECANT" two 99mTc-Tetramine (N4)-derivatized SST2 antagonists (TECANT-1 and TECANT-2) were studied for the selection of the best candidate for clinical translation. Receptor-affinity, internalization and dissociation studies were performed in human embryonic kidney-293 (HEK293) cells transfected with the human SST2 (HEK-SST2). Log D, protein binding and stability in human serum were assessed. Biodistribution and SPECT/CT studies were carried out in nude mice bearing HEK-SST2 xenografts, together with dosimetric estimations from mouse-to-man. [99mTc]Tc-TECANT-1 showed higher hydrophilicity and lower protein binding than [99mTc]-TECANT-2, while stability was comparable. Both radiotracers revealed similar binding affinity, while [99mTc]Tc-TECANT-1 had higher cellular uptake (>50%, at 2 h/37 °C) and lower dissociation rate (<30%, at 2 h/37 °C). In vivo, [99mTc]Tc-TECANT-1 showed lower blood values, kidney and muscles uptake, whereas tumour uptake was comparable to [99mTc]Tc-TECANT-2. SPECT/CT imaging confirmed the biodistribution results, providing the best tumour-to-background image contrast for [99mTc]Tc-TECANT-1 at 4 h post-injection (p.i.). The estimated radiation dose amounted to approximately 6 µSv/MBq for both radiotracers. This preclinical study provided the basis of selection of [99mTc]Tc-TECANT-1 for clinical translation of the first 99mTc-based SST2 antagonist.

Clinical translation of theranostic radiopharmaceuticals: Current regulatory status and recent examples.

With the development of ever more radiopharmaceuticals suitable for theranostic applications, translation of novel compounds from the preclinical stage towards clinical application becomes a bottleneck for the advances in Nuclear Medicine. This review article summarizes the current regulatory framework for clinical trials with radiopharmaceuticals in the European Union, provides a general overview of the documentation required, and addresses quality, safety, and clinical aspects to be considered. By using a recent successful example of translating a theranostic peptide radioligand, namely 111 In-CP04, which targets receptors expressed in medullary thyroid carcinoma, the pathway from the preclinical development over establishing the required pharmaceutical documentation to designing and submitting a clinical trial is reviewed. Details regarding preclinical data, generation of the documentation, and final successful application are described. This article should provide an insight in an ever more complex process to bring innovations in the field of radiopharmaceuticals into patients.

Differential diagnosis of solitary pulmonary nodules based on 99mTc-EDDA/HYNIC-TOC scintigraphy: the effect of tumour size on the optimal method of image assessment.

PURPOSE: The aim of the study was to determine an optimal method for the evaluation of scintigrams obtained with (99m)Tc-EDDA/HYNIC-TOC for the purpose of differential diagnosis of solitary pulmonary nodules (SPNs) and to assess the diagnostic value of the method. METHODS: Eighty-five patients (48 males and 37 females, mean age 57 years, range 34-78 years) were enrolled in the study. Patients underwent (99m)Tc-EDDA/HYNIC-TOC scintigraphy for the purpose of differential diagnosis of SPNs (size between 1 and 4 cm). Images of all patients were evaluated visually in a prospective manner. RESULTS: Positive scintigraphic results were found in 37 out of 40 (93%) patients with malignant SPNs including 34 out of 35 (97%) patients with primary lung carcinoma. Two remaining false negative cases turned out to be metastatic lesions of malignant melanoma and leiomyosarcoma. Among 45 benign tumours, negative results were obtained in 31 cases (69%) and positive results in 14. The accuracy of the method was 80%. Analysis of the results of the visual assessment of scintigrams revealed a significantly higher frequency of false positive results among larger nodules (diameter at least 1.4 cm). Uptake of the tracer in those nodules was therefore assessed semi-quantitatively (using the tumour-to-background ratio), in expectation of an improvement in the low specificity of the visual method. The semi-quantitative assessment reduced the total number of false positive results in a subgroup of larger nodules from 13 to six, while preserving the high sensitivity of the method. CONCLUSION: The combination of visual analysis (for lesions smaller than 1.4 cm in diameter) and semi-quantitative assessment (for larger lesions) provided a high sensitivity of the method and significantly improved its specificity (84%) and accuracy (88%) in comparison with visual analysis (p<0.05).

Short communication: Semiquantitative assessment of 99mTc-EDDA/HYNIC-TOC scintigraphy in differentiation of solitary pulmonary nodules--a complementary role to visual analysis.

UNLABELLED: The aim of this study was the assessment of a value of a semiquantitative analysis of scintigrams obtained with (99m)Tc-EDDA/HYNIC-TOC as a radiopharmaceutical (RPH) in differential diagnosis of solitary pulmonary nodules (SPNs), as a method complementary to visual evaluation of scintigrams. MATERIAL AND METHODS: Scintigraphic images of 59 patients (33 males and 26 females between 34 and 78 years of age, mean value, 57) with SPN on chest radiographs (39 malignant and 20 benign) were retrospectively assessed semiquantitatively. Visual scintigram analysis was made earlier, prospectively. Nodule diameters ranged from 1 to 4 (mean 2.2) cm. A single photon emission computed tomography (SPECT) acquisition was performed at 2-4 hours after administration of 740 to 925 MBq of a RPH. Verification of scintigraphic results was based on a pathological examination of tumor samples (histopathology or cytology) and, in some cases, on bacteriological studies. As an additional criterion for tumor benignity, its stable size in a time interval not shorter than 3 years was accepted. A simple, semiquantitative method for assessment of radiopharmaceutical uptake in SPNs was used, based on "count sample" taken from tumor center (T) in relation to radiopharmaceutical concentration in the background (B) measured in the contralateral lung. A criterion for optimal differentiation between malignant and benign nodules (T/B ratio threshold value) was introduced, based on a receiver operating characteristic (ROC) curve. Additionally, a value of T/B ratio was searched for, excluding tumor benignity with high probability. RESULTS: Visual analysis of scintigrams revealed enhanced uptake of RPH at 36 of 39 (92%) sites, corresponding to locations of malignant nodules (including 34 of 35-97% cases of lung cancer). In 13 of 20 (65%) benign nodules, true negative results were obtained. Accuracy of the method equalled 83%. Optimal differentiation between malignant and benign nodules was found for a value of a T/B ratio amounting to 2. The semiquantitative method gave true positive results in 35 of 39 (90%) malignant nodules (as in visual method in 34 of 35-97% cases of lung cancer). True negative results were obtained in 17 of 20 (85%) benign cases. Accuracy of the method reached 88%. A T/B ratio exceeding 4 excluded tumor benignity with high probability. CONCLUSIONS: A simple method, of quantitatively assessing 99mTc-EDDA/HYNICTOC uptake in solitary pulmonary nodules by means of a T/B ratio can play a role that is complementary to the visual evaluation of scintigrams. It improves low specificity of the method in the detection of malignant nodules, without significant reduction of its sensitivity and provides a T/B ratio excluding tumor benignity with high probability.

A visual and semi-quantitative assessment of (99m)Tc-EDDA/HYNIC-TOC scintigraphy in differentiation of solitary pulmonary nodules.

BACKGROUND: The aim of the study was the assessment of the clinical usefulness of scintigraphy with (99m)Tc-EDDA/HYNIC-TOC for purposes of a differential diagnosis of SPNs by means of a visual inspection and semi-quantitative assessment of uptake intensity of the radiopharmaceutical (RPh). MATERIAL AND METHODS: In 53 patients (32 males and 21 females at the ages between 38 and 78 years, mean value 57) with SPN on chest radiographs or CT scans, of diameters from 1 to 5.5 (mean 2.3) cm a SPECT acquisition was performed, 2-4 h after administration of 740 MBq of RPh. Additionally, aiming at the implementation of a correction of a partial volume effect resulting from finite resolution of this technique, the measurement of the resolution of this technique was performed on an thorax phantom. Scintigraphic studies were inspected visually visually and semi-quantitatively, restoring real concentration of the RPh in nodules in comparison with the peritumoral background (tumour-to-background ratio) by the application of resolution recovery coefficients for the respective nodule diameters. The threshold values of tumour-to-background ratio providing optimal differentiation between malignant and benign nodules of sizes smaller and larger than 2 cm in diameter were determined. Verification of scintigraphic results was based on pathological examinations of tumour samples (histopathology or cytology) and in some cases on bacteriological studies. The additional criterion of tumour benignity was accepted, based on its stable size in a time interval no shorter than 3 years. RESULTS: In 32 patients the following malignant tumours were diagnosed: 12 adenocarcinomas, 6 squamous cell carcinomas, 6 non-small cell lung cancers of unspecified more detailed morphology, 2 large cell carcinomas, 2 small cell lung cancers, 2 carcinoids and 2 metastatic lesions (malignant melanoma and leiomyosarcoma). In 21 patients benign etiologies were found: 6 tuberculomas, 2 other granuloma, 4 hamartomas, 2 non-specific inflammatory infiltrate, 1 alien body with inflammatory reaction and 1 suppurating inflammatory lesion, 1 abscesses, 1 peripheral carcinoid of morphological features of a benign tumour, 2 tumours of unspecified etiology with sizes stable over 3 and 5 years, and 1 ectopic lesion of thyroid tissue. A visual inspection of scintigrams revealed enhanced uptake of RPh at 29 of 32 sites corresponding to locations of malignant nodules, in 2 cases (1 adenocarcinoma and 1 metastatic lesion of malignant melanoma) results were negative and in 1 (metastatic leiomyosarcoma) equivocal; in 13 of 21 benign nodules true negative results were obtained, in 4--positive (foreign body with inflammatory reaction, abscess, suppurating inflammatory lesion and tuberculoma), in the next 4--equivocal (2 tuberculomas, 1 hamartoma, 1 tumour of unspecified aetiology, but with a stable size over 3 years). The mean values of tumour-to-back-ground ratio without resolution recovery in malignant and benign nodules equalled 4.6 (sd 5.9) and 1.8 (sd 1.2), resp. (p = 7 x 10(-4)), while after resolution recovery coefficients--7.8 (sd 7.2) and 2.7 (sd 2.8), resp. (p = 2 x 10(-4)). The semi-quantitative method resulted in true positive results in 29/32 malignant cases and true negative in 15/21 benign cases. CONCLUSIONS: (99m)Tc-EDDA/HYNIC-TOC scintigraphy is a very promising method for the differentiation of SPNs. The semi-quantitative method using resolution recovered tumour-to-background ratio enables the differentiation of malignant and benign SPNs based on the intensity of RPh uptake and facilitates the making of a decision as to the positive or negative scintigraphic character of the equivocal lesions.

Assessment of clinical usefulness of 131I alpha-methyl-tyrosine and fused SPECT/MRI imaging for diagnostics of recurrent cerebral gliomas.

BACKGROUND: Early detection and diagnostic differentiation of neoplastic tissue from necrotic changes and scars following the treatment of cerebral gliomas is essential for determining further therapy and prognosis. The primary technique used for the diagnostics of recurrent neoplastic growth is the magnetic resonance imaging (MRI), which in some cases, however, does not allow one to identify the character of cerebral lesions. Recently, MRI has been supplemented with single-photon emission computed tomography (SPECT) or positron emission tomography (PET) employing radiolabelled amino acids. e.g. tyrosine or methionine. The aim of the project was to assess the diagnostic potential of SPECT when iodine-131 alpha-methyl tyrosine (IMT), a Polish make of radiopharmaceutical (OBRI--POLATOM, Otwock-Rwierk, Poland), was applied. The use of 131I as a substitute for the more costly, imported iodine-123 has been justified in view of the nature and significance of the diagnostic problem on the one hand, and the possibility of 131-iodine application on a larger scale in CEE countries, on the other. MATERIAL AND METHODS: MRI and SPECT were performed in 24 patients with a history of surgical treatment and radiotherapy of cerebral glioma (WHO grade II/IV). A SPECT was carried out 15 min after an i.v. injection of 74-111 MBq IMT. The tomograms were evaluated visually and in quantitative terms. The fused SPET/MR images were also analyzed. The obtained results were verified against histopathological findings, control MRI examinations and the clinical course of disease within 7-28 months of monitoring. RESULTS: In 19 patients, an increased IMT uptake indicative of a recurrent tumour was found, and the presence of the tumour was confirmed. In five patients no hot spots were detected which would indicate the neoplastic growth and verification did not provide any evidence for relapse. CONCLUSIONS: The examination employing iodine-131 IMT made it possible to confirm or exclude tumour recurrence in all the subjects, also in the cases when the CT/MR images were inconclusive. The MRI/SPECT fusion made it possible to more accurately identify the location of tumour recurrence as well as determine the area for spectroscopic MR analysis, for stereotactic biopsy and radiotherapy.