Impact of FAPI-46/dual-tracer PET/CT imaging on radiotherapeutic management in esophageal cancer.

BACKGROUND: Fibroblast activation protein (FAP) is expressed in the tumor microenvironment (TME) of various cancers. In our analysis, we describe the impact of dual-tracer imaging with Gallium-68-radiolabeled inhibitors of FAP (FAPI-46-PET/CT) and fluorodeoxy-D-glucose (FDG-PET/CT) on the radiotherapeutic management of primary esophageal cancer (EC). METHODS: 32 patients with EC, who are scheduled for chemoradiation, received FDG and FAPI-46 PET/CT on the same day (dual-tracer protocol, 71%) or on two separate days (29%) We compared functional tumor volumes (FTVs), gross tumor volumes (GTVs) and tumor stages before and after PET-imaging. Changes in treatment were categorized as "minor" (adaption of radiation field) or "major" (change of treatment regimen). Immunohistochemistry (IHC) staining for FAP was performed in all patients with available tissue. RESULTS: Primary tumor was detected in all FAPI-46/dual-tracer scans and in 30/32 (93%) of FDG scans. Compared to the initial staging CT scan, 12/32 patients (38%) were upstaged in nodal status after the combination of FDG and FAPI-46 PET scans. Two lymph node metastases were only visible in FAPI-46/dual-tracer. New distant metastasis was observed in 2/32 (6%) patients following FAPI-4 -PET/CT. Our findings led to larger RT fields ("minor change") in 5/32 patients (16%) and changed treatment regimen ("major change") in 3/32 patients after FAPI-46/dual-tracer PET/CT. GTVs were larger in FAPI-46/dual-tracer scans compared to FDG-PET/CT (mean 99.0 vs. 80.3 ml, respectively (p < 0.001)) with similar results for nuclear medical FTVs. IHC revealed heterogenous FAP-expression in all specimens (mean H-score: 36.3 (SD 24.6)) without correlation between FAP expression in IHC and FAPI tracer uptake in PET/CT. CONCLUSION: We report first data on the use of PET with FAPI-46 for patients with EC, who are scheduled to receive RT. Tumor uptake was high and not depending on FAP expression in TME. Further, FAPI-46/dual-tracer PET had relevant impact on management in this setting. Our data calls for prospective evaluation of FAPI-46/dual-tracer PET to improve clinical outcomes of EC.

Dual-tracer PET/CT protocol with [18F]FDG and [68Ga]Ga-FAPI-46 outperforms single-tracer PET/CT with [18F]FDG in different cancer types, resulting in larger functional and gross tumor volume.

PURPOSE: Fibroblast activation protein (FAP) detected by positron-emission tomography (PET) using fibroblast activation protein inhibitor (FAPI) appears to be a promising target for cancer imaging, staging, and therapy, providing added value and strength as a complement to [18F]fluorodeoxyglucose (FDG) in cancer imaging. We recently introduced a combined single-session/dual-tracer protocol with [18F]FDG and [68Ga]Ga-FAPI for cancer imaging and staging. Malignant tissue visualization and target-to-background uptake ratios (TBRs) as well as functional tumor volume (FTV) and gross tumor volume (GTV) were assessed in the present study with single-tracer [18F]FDG PET/computed tomography (CT) and with dual-tracer [18F]FDG&[68Ga]Ga-FAPI-46 PET/CT. METHODS: A total of 19 patients with head and neck and gastrointestinal cancers received initial [18F]FDG-PET/CT followed by dual-tracer PET/CT after additional injection of [68Ga]Ga-FAPI-46 during the same medical appointment (on average 13.9 ± 12.3 min after injection of [18F]FDG). Two readers visually compared detection rate of malignant tissue, TBR, FTV, and GTV for tumor and metastatic tissue in single- and dual-tracer PET/CT. RESULTS: The diagnostic performance of dual-tracer compared to single-tracer PET/CT was equal in 13 patients and superior in 6 patients. The mean TBRs of tumors and metastases in dual-tracer PET/CTs were mostly higher compared to single-tracer PET/CT using maximal count rates (CRmax). GTV and FTV were significantly larger when measured on dual-tracer compared to single-tracer PET/CT. CONCLUSION: Dual-tracer PET/CT with [18F]FDG and [68Ga]Ga-FAPI-46 showed better visualization due to a generally higher TBR and larger FTV and GTV compared to [18F]FDG-PET/CT in several tumor entities, suggesting that [68Ga]Ga-FAPI-46 provides added value in pretherapeutic staging.

Threshold for defining PSMA-positivity prior to 177Lu-PSMA therapy: a comparison of [68Ga]Ga-PSMA-11 and [18F]F-DCFPyL in metastatic prostate cancer.

BACKGROUND: In 2022, the American Food and Drug Administration and the European Medicines Agency approved [177Lu]Lu-PSMA-617 (PLUVICTO™, Novartis AG, Basel, Switzerland) for radionuclide therapy with prostate-specific membrane antigen (PSMA) ligands in metastatic prostate cancer. Theranostics require appropriate patients to be identified by positron emission tomography (PET) prior to radionuclide therapy, usually employing [68Ga]Ga-PSMA-11. Alternatively, several 18F-labelled PSMA-PET tracers are available and may increasingly replace 68Ga-labelled compounds, with respect to their image quality, availability and other practical advantages. However, alternative tracers may differ in uptake behaviour, and their comparability with regard to patient selection for [177Lu]Lu-PSMA therapy has not yet been established. Here, we analysed whether tumour-to-background ratios determined by PET using the 18F-labelled PSMA-specific radiopharmaceutical [18F]F-DCFPyL were comparable to those determined by PET using [68Ga]Ga-PSMA-11. RESULTS: No differences could be observed between [68Ga]Ga-PSMA-11-PET and [18F]F-DCFPyL-PET regarding tumour-to-liver ratios or tumour-to-mediastinum ratios (e. g. tumour-to-liver ratios using maximum SUV of the tumour lesion for ultra-high definition reconstructed PET images with a median of 2.5 (0.6-9.0) on [68Ga]Ga-PSMA-11-PET vs. 2,0 (0.6-11.4) on [18F]F-DCFPyL-PET). However, significant differences were observed in terms of contrast-to-noise ratios, thereby demonstrating the better image quality obtained with [18F]F-DCFPyL-PET. CONCLUSIONS: Our data showed that [18F]F-DCFPyl-PET and [68Ga]Ga-PSMA-11-PET provide comparable tumour-to-liver and tumour-to-mediastinum ratios. Therefore, a tumour uptake of [18F]F-DCFPyL above the liver background, like using [68Ga]Ga-PSMA-11, can be considered as equally suitable for defining PSMA-positivity by a semiquantitative assessment based on the liver background, e. g. prior to radioligand therapy with 177Lu-labelled PSMA ligands. In addition, our data suggest a tending advantage of [18F]F-DCFPyL in terms of lesion detectability.

Synthesis and evaluation of radioiodinated estrogens for diagnosis and therapy of male urogenital tumours.

The preparation of 24 estrogens, their estrogen receptor (ER) affinity and studies of radioiodinated estrogen binding to ER-positive male bladder tumor cells (HTB9) are described. The estrogens with the highest affinity were selected using fluorescence anisotropy assays. A 2,2,2-trifluoroethyl group at the 11ß-position caused particularly promising affinity. (Radio)iodination was performed on the 17α-vinyl group. Binding studies on HTB9 cells revealed picomolar affinities of radioconjugates 19 and 31, indicating promising ability for targeting of urogenital tumors.

First Clinical Experience With [68Ga]Ga-FAPI-46-PET/CT Versus [18F]F-FDG PET/CT for Nodal Staging in Cervical Cancer.

INTRODUCTION: In several solid tumors, fibroblast activation protein (FAP) is overexpressed by cancer-associated fibroblasts in the tumor microenvironment. Preliminary evidence suggests that detection and staging are feasible with PET/CT imaging using [68Ga]-radiolabeled inhibitors of FAP also in cervical cancer (CC). Our study aims to explore the accuracy of [68Ga]Ga-fibroblast activation protein inhibitor (FAPI)-46 PET/CT and [18F]F-FDG PET/CT compared with histopathological results of surgical lymph node (LN) staging before primary chemoradiation. METHODS: Seven consecutive women with treatment-naive and biopsy-proven locally advanced CC underwent both whole-body [68Ga]Ga-FAPI-46- and [18F]F-FDG PET/CT, for imaging nodal staging before systematic laparoscopic lymphadenectomy of the pelvic and para-aortic region. Location and number of suspicious LNs in PET imaging were recorded and compared with the results of histopathological analysis, including immunohistochemical staining for FAP. RESULTS: All 7 patients had focal uptake above background in their tumor lesions in [68Ga]Ga-FAPI-46 PET/CT. [68Ga]Ga-FAPI-46 PET/CT showed a higher tumor-to-background ratio (TBR) in primary tumor as well as in LN metastasis. Median TBRmax values using liver were 32.02 and 5.15 for [68Ga]Ga-FAPI-46 PET/CT and [18F]F-FDG PET/CT, respectively. Median TBRmax using blood pool was 18.45 versus 6.85 for [68Ga]Ga-FAPI-46 PET/CT and [18F]F-FDG PET/CT, respectively. Higher TBR also applies for nodal metastasis: TBRmax was 14.55 versus 1.39 (liver) and 7.97 versus 1.8 (blood pool) for [68Ga]Ga-FAPI-46 PET/CT and [18F]F-FDG PET/CT, respectively. Overall, [68Ga]Ga-FAPI-46 PET/CT detected more lesions compared with [18F]F-FDG PET/CT. Following surgical staging, a total of 5 metastatic LNs could be pathologically confirmed, of which 2 and 4 were positive by [18F]F-FDG PET/CT and [68Ga]Ga-FAPI-46 PET/CT, respectively. CONCLUSION: [68Ga]Ga-FAPI-46 PET/CT seems useful to improve detection of nodal metastasis in patients with CCs. Future studies should aim to compare [68Ga]Ga-FAPI-46 PET/CT to surgical staging of pelvic and para-aortic LNs in patients with locally advanced CC.

From Bench to Bedside: Patient-Oriented Radiopharmaceutical Development in Nuclear Medicine Based on the Example of [89Zr]Zr-PSMA-DFO.

The interdisciplinary possibilities inherent in nuclear medicine offer an opportunity for the patient-centered development of radioactive pharmaceuticals based on specific research questions. This approach provides radiopharmaceutical manufacturers with a robust scientific foundation on which to navigate the regulatory requirements for drug approval laid down by the law. A vivid illustration of this interdisciplinary cooperation has been the development of a Zr-89-labeled PSMA ligand where reliable results have been obtained across various domains, including chemistry, radiochemistry, biochemistry, and preclinical research. This comprehensive process extended to feasibility studies conducted with carefully selected patients from a single nuclear medicine clinic. The approach demonstrates how far close collaboration between different disciplines within nuclear medicine can further the move towards patient-oriented radiopharmaceutical treatments while simultaneously meeting regulatory demands. With such a strategy, innovative radiopharmaceutical solutions can be brought to the market more swiftly and efficiently, in line with the needs of patients.

Correction: Click functionalized biocompatible gadolinium oxide core-shell nanocarriers for imaging of breast cancer cells.

[This corrects the article DOI: 10.1039/D2RA00347C.].

Click functionalized biocompatible gadolinium oxide core-shell nanocarriers for imaging of breast cancer cells.

Site-specific delivery using functionalized nanocarriers is in high demand in imaging applications of modern clinical research. To improve the imaging capabilities of conventionally used contrast agents and expand the targeting accuracy, functional gadolinium oxide based nanocarriers originated from homogeneous core shells structures (Gd2O3@SiO2@Fe3O4) were developed using a multilayer formation approach. The synthesis and chemical configuration for the covalent binding of macrocyclic chelating agents and estrogen targeting molecules on these nanocarriers were designed by a two-step chemical synthesis method. Initially, SiO2@Fe3O4 structures were prepared and encapsulated with a homogenous thin Gd2O3 overlayer. The exterior surface of the as-prepared carriers offered chemical binding with a breast cancer specific estrogen molecule, covalently grafted through a Click-Chemistry protocol. In the next step, to enhance the diagnostic imaging capabilities of these carriers, thiocyanate-linked chelator molecule, DOTA, was attached to the surface of estrogen bound Gd2O3@SiO2@Fe3O4 using basic reaction conditions. The active amino groups before and after conjugation of estrogen molecules on the surface were quantified using a fluorescamine based approach. Due to the covalent binding of the macrocyclic chelator to the Gd2O3@SiO2@Fe3O4 surface, core shell carriers showed potential radiolabeling efficiency using positron emitter radionuclide, gallium-68 (68Ga). Intracellular uptake of estrogen-conjugated carriers was evaluated with MCF7 breast cancer cell lines using confocal laser scanning microscopy and fluorescent flow cytometry. In addition, in vitro cytotoxicity studies of functional nanocarriers as compared to bare nanoparticles showed reduced toxicity to HEK-293 cells demonstrating the role of surface attached molecules in preventing direct exposure of the Gd2O3 surface to the cells. The as-developed gadolinium based nanocarriers presented excellent capabilities as biocompatible target-specific imaging probes which indicates great potential in the field of dual-mode contrast agents.

Head-to-Head Comparison of [68 Ga]Ga-FAPI-46-PET/CT and [18F]F-FDG-PET/CT for Radiotherapy Planning in Head and Neck Cancer.

INTRODUCTION: In head and neck cancers (HNCs), fibroblast activation protein (FAP) is expressed by cancer-associated fibroblasts (CAFs) in the tumor microenvironment. Preliminary evidence suggests that detection and staging is feasible with positron emission tomography (PET/CT) imaging using [68 Ga]-radiolabeled inhibitors of FAP ([68 Ga]Ga-FAPI-46) in HNCs. This study aims to compare [68 Ga]Ga-FAPI-46 PET/CT and [18F]-fluorodeoxy-D-glucose ([18F]F-FDG) PET/CT with a focus on improved target volume definition and radiotherapy planning in patients with HNC referred for chemoradiation. METHODS: A total of 15 patients with HNCs received both [68 Ga]Ga-FAPI-46 PET/CT and [18F]F-FDG PET/CT with a thermoplastic mask, in addition to initial tumor staging by conventional imaging with contrast-enhanced CT and/or MRI. Mean intervals between FAPI/FDG and FAPI/conventional imaging were 4 ± 20 and 17 ± 18 days, respectively. Location and number of suspicious lesions revealed by the different procedures were recorded. Subsequently, expert-generated gross tumor volumes (GTVs) based on conventional imaging were compared to those based on [18F]F-FDG and [68 Ga]Ga-FAPI-46 PET/CT to measure the impact on subsequent radiation planning. RESULTS: All patients had focal FAPI uptake above background in tumor lesions. Compared to FDG, tumor uptake (median SUVmax 10.2 vs. 7.3, p = 0.008) and tumor-to-background ratios were significantly higher with FAPI than with FDG (SUVmean liver: 9.3 vs. 3.2, p < 0.001; SUVmean bloodpool: 6.9 vs. 4.0, p < 0.001). A total of 49 lesions were recorded. Of these, 40 (82%) were FDG+ and 41 (84%) were FAP+. There were 5 (10%) FAP+/FDG- lesions and 4 (8%) FAP-/FDG+ lesions. Volumetrically, a significant difference was found between the GTVs (median 57.9 ml in the FAPI-GTV, 42.5 ml in the FDG-GTV, compared to 39.2 ml in the conventional-GTV). Disease stage identified by FAPI PET/CT was mostly concordant with FDG PET/CT. Compared to conventional imaging, five patients (33%) were upstaged following imaging with FAPI and FDG PET/CT. CONCLUSION: We demonstrate that [68 Ga]Ga-FAPI-46 -PET/CT is useful for detecting tumor lesions in patients with HNCs. There is now a need for prospective randomized studies to confirm the role of [68 Ga]Ga-FAPI-46 PET/CT in relation to [18F]F-FDG PET/CT in HNCs and to evaluate its impact on clinical outcome.

Dual-Tracer PET/CT Protocol with [18F]-FDG and [68Ga]Ga-FAPI-46 for Cancer Imaging: A Proof of Concept.

Imaging studies with PET tracers acting as fibroblast activation protein inhibitors (FAPIs) show promising results that could usefully complement [18F]-FDG in cancer imaging. Methods: All patients received [18F]-FDG PET/CT and dual-tracer PET/CT after an additional injection of [68Ga]Ga-FAPI-46 after the [18F]-FDG PET/CT. Two readers visually compared detection rate and analyzed target-to-background ratios for tumor and metastatic tissue in single- and dual-tracer PET/CT. Results: Detection rate in dual-tracer PET/CT was visually as good as that in single-tracer PET/CT in 4 patients and superior in 2 patients, whereas target-to-background ratios were significantly higher in dual-tracer PET/CT. Conclusion: Dual-tracer [18F]-FDG/[68Ga]Ga-FAPI-46 PET/CT within a single session is feasible and has potential. The dual-tracer approach may have superior sensitivity to [18F]-FDG PET/CT alone without compromising individual assessment of either scan.

Translational Development of a Zr-89-Labeled Inhibitor of Prostate-specific Membrane Antigen for PET Imaging in Prostate Cancer.

PURPOSE: We present here a Zr-89-labeled inhibitor of prostate-specific membrane antigen (PSMA) as a complement to the already established F-18- or Ga-68-ligands. PROCEDURES: The precursor PSMA-DFO (ABX) was used for Zr-89-labeling. This is not an antibody, but a peptide analogue of the precursor for the production of [177Lu]Lu-PSMA-617. The ligand [89Zr]Zr-PSMA-DFO was compared with [68Ga]Ga-PSMA-11 and [18F]F-JK-PSMA-7 in vitro by determination of the Kd value, cellular uptake, internalization in LNCaP cells, biodistribution studies with LNCaP prostate tumor xenografts in mice, and in vivo by small-animal PET imaging in LNCaP tumor mouse models. A first-in-human PET was performed with [89Zr]Zr-PSMA-DFO on a patient presenting with a biochemical recurrence after brachytherapy and an ambiguous intraprostatic finding with [18F]F-JK-PSMA-7 but histologically benign cells in a prostate biopsy 7 months previously. RESULTS: [89Zr]Zr-PSMA-DFO was prepared with a radiochemical purity ≥ 99.9% and a very high in vitro stability for up to 7 days at 37 °C. All radiotracers showed similar specific cellular binding and internalization, in vitro and comparable tumor uptake in biodistribution experiments during the first 5 h. The [89Zr]Zr-PSMA-DFO achieved significantly higher tumor/background ratios in LNCaP tumor xenografts (tumor/blood: 309 ± 89, tumor/muscle: 450 ± 38) after 24 h than [68Ga]Ga-PSMA-11 (tumor/blood: 112 ± 57, tumor/muscle: 58 ± 36) or [18F]F-JK-PSMA-7 (tumor/blood: 175 ± 30, tumor/muscle: 114 ± 14) after 4 h (p < 0.01). Small-animal PET imaging demonstrated in vivo that tumor visualization with [89Zr]Zr-PSMA-DFO is comparable to [68Ga]Ga-PSMA-11 or [18F]F-JK-PSMA-7 at early time points (1 h p.i.) and that PET scans up to 48 h p.i. clearly visualized the tumor at late time points. A late [89Zr]Zr-PSMA-DFO PET scan on a patient with biochemical recurrence (BCR) had demonstrated intensive tracer accumulation in the right (SUVmax 13.25, 48 h p.i.) and in the left prostate lobe (SUV max 9.47), a repeat biopsy revealed cancer cells on both sides. CONCLUSION: [89Zr]Zr-PSMA-DFO is a promising PSMA PET tracer for detection of tumor areas with lower PSMA expression and thus warrants further clinical evaluation.

An 89Zr-Labeled PSMA Tracer for PET/CT Imaging of Prostate Cancer Patients.

The short half-life of existing prostate-specific membrane antigen (PSMA) tracers limits their time for internalization into tumor cells after injection, which is an essential prerequisite for robust detection of tumor lesions with low PSMA expression on PET/CT scans. Because of its longer half-life, the 89Zr-labeled ligand 89Zr-PSMA-DFO allows acquisition of PET scans up to 6 d after injection, thereby overcoming the above limitation. We investigated whether 89Zr-PSMA-DFO allowed more sensitive detection of weak PSMA-positive prostate cancer lesions. Methods: We selected 14 prostate cancer patients with biochemical recurrence who exhibited no PSMA-positive lesions on a PET scan acquired with existing PSMA tracers (68Ga-PSMA-11, 18F-JK-PSMA-7). Within 5 wk after the negative scan result, we obtained a second PSMA PET scan using 89Zr-PSMA-DFO (117 ± 16 MBq, PET acquisition within 6 d of injection). Results:89Zr-PSMA-DFO detected 15 PSMA-positive lesions in 8 of 14 patients, who had a PET-negative reading of their initial PET scans with existing tracers. In these 8 patients, the new scans revealed localized recurrence of disease (3/8), metastases in lymph nodes (3/8), or lesions at distant sites (2/8). On the basis of these results, patients received lesion-targeted radiotherapies (5/8), androgen deprivation therapies (2/8), or no therapy (1/8). The plausibility of 14 of 15 lesions was supported by histology, clinical follow-up after radiotherapy, or subsequent imaging. Furthermore, comparison of the 15 89Zr-PSMA-DFO-positive lesions with their correlates on the original PET scan revealed that established tracers exhibited mild accumulation in 7 of 15 lesions; however, contrast-to-noise ratios were too low for robust detection of these lesions (contrast-to-noise ratios, 2.4 ± 3.7 for established tracers vs. 10.2 ± 8.5 for 89Zr-PSMA-DFO, P = 0.0014). The SUVmax of the 15 89Zr-PSMA-DFO-positive lesions (11.5 ± 5.8) was significantly higher than the SUVmax on the original PET scans (4.7 ± 2.8, P = 0.0001). Kidneys were the most exposed organ, with doses of 3.3 ± 0.7 mGy/MBq. The effective dose was 0.15 ± 0.04 mSv/MBq. Conclusion: In patients with weak PSMA expression, a longer period of time might be needed for ligand internalization than that offered by existing PSMA tracers to make lesions visible on PET/CT scans. Hence, 89Zr-PSMA-DFO might be of significant benefit to patients in whom the search for weak PSMA-positive lesions is challenging. Radiation exposure should be weighed against the potential benefit of metastasis-directed therapy or salvage radiotherapy, which we initiated in 36% (5/14) of our patients based on their 89Zr-PSMA-DFO PET scans.

Synthesis, proteolytic stability, and in vitro evaluation of DOTA conjugated p160 peptide based radioconjugates: [177Lu]Lu-DOTA-p160.

In this work, we describe the synthesis, in vitro stability, and preliminary biological evaluation of [177Lu]Lu-DOTA-p160 peptide-based radiopharmaceuticals. Our findings highlight that all DOTA-p160-peptide radioconjugates exhibit favorable proteolytic and enzymatic stability with a prolonged half-life in human plasma and serum. Cell uptake studies carried out on MCF-7 cell line revealed saturable binding of the radioconjugates in the nanomolar range, thereby demonstrating their promising potential in the imaging and therapy of breast tumors.

Uptake in non-affected bone tissue does not differ between [18F]-DCFPyL and [68Ga]-HBED-CC PSMA PET/CT.

INTRODUCTION: [68Ga]PSMA-HBED-CC and [18F]DCFPyL show a high potential for the detection of recurrent prostate cancer. While 18F-based tracers have several advantages in availability and image resolution, their sensitivity in the skeleton might be impaired by released [18F]fluoride due to its high bone affinity. In turn, chemically unbound trivalent 68Ga might also accumulate in osseous tissue, in cases of occupied binding sites of plasma proteins and thereby influence bone signal. METHODS: A comparison of average bone SUV was performed in 17 bone-negative and 4 bone-positive patients. All patients underwent PET/CT 125 minutes after application of [18F]DCFPyL and 73 minutes after application of [68Ga]PSMA-HBED-CC at another date. RESULTS: Native SUVs in unaffected bone tissue and SUVs relative to liver uptake were lower in [18F]DCFPyL (0.49) than in [68Ga]PSMA-HBED-CC scans (0.52). SUVs relative to gluteal muscles did not differ between the two tracers. Average lesional SUVs did not differ between tracers. CONCLUSION: No difference of average bone signal intensity was observed for [18F]DCFPyL-PET/CT in comparison to [68Ga]PSMA-HBED-CC scans indicating that diagnostic assessment of the skeleton is not affected by non-specific accumulation of free [18F]fluoride or 68Ga.

PSA-Stratified Performance of 18F- and 68Ga-PSMA PET in Patients with Biochemical Recurrence of Prostate Cancer.

Several studies outlined the sensitivity of 68Ga-labeled PET tracers against the prostate-specific membrane antigen (PSMA) for localization of relapsed prostate cancer in patients with renewed increase in the prostate-specific antigen (PSA), commonly referred to as biochemical recurrence. Labeling of PSMA tracers with 18F offers numerous advantages, including improved image resolution, longer half-life, and increased production yields. The aim of this study was to assess the PSA-stratified performance of the 18F-labeled PSMA tracer 18F-DCFPyL and the 68Ga-labeled reference 68Ga-PSMA-HBED-CC. Methods: We examined 191 consecutive patients with biochemical recurrence according to standard acquisition protocols using 18F-DCFPyL (n = 62, 269.8 MBq, PET scan at 120 min after injection) or 68Ga-PSMA-HBED-CC (n = 129, 158.9 MBq, 60 min after injection). We determined PSA-stratified sensitivity rates for both tracers and corrected our calculations for Gleason scores using iterative matched-pair analyses. As an orthogonal validation, we directly compared tracer distribution patterns in a separate cohort of 25 patients, sequentially examined with both tracers. Results: After prostatectomy (n = 106), the sensitivity of both tracers was significantly associated with absolute PSA levels (P = 4.3 × 10-3). Sensitivity increased abruptly, when PSA values exceeded 0.5 µg/L (P = 2.4 × 10-5). For a PSA less than 3.5 µg/L, most relapses were diagnosed at a still limited stage (P = 3.4 × 10-6). For a PSA of 0.5-3.5 µg/L, PSA-stratified sensitivity was 88% (15/17) for 18F-DCFPyL and 66% (23/35) for 68Ga-PSMA-HBED-CC. This significant difference was preserved in the Gleason-matched-pair analysis. Outside of this range, sensitivity was comparably low (PSA < 0.5 µg/L) or high (PSA > 3.5 µg/L). After radiotherapy (n = 85), tracer sensitivity was largely PSA-independent. In the 25 patients examined with both tracers, distribution patterns of 18F-DCFPyL and 68Ga-PSMA-HBED-CC were strongly comparable (P = 2.71 × 10-8). However, in 36% of the PSMA-positive patients we detected additional lesions on the 18F-DCFPyL scan (P = 3.7 × 10-2). Conclusion: Our data suggest that 18F-DCFPyL is noninferior to 68Ga-PSMA-HBED-CC, while offering the advantages of 18F labeling. Our results indicate that imaging with 18F-DCFPyL may even exhibit improved sensitivity in localizing relapsed tumors after prostatectomy for moderately increased PSA levels. Although the standard acquisition protocols, used for 18F-DCFPyL and 68Ga-PSMA-HBED-CC in this study, stipulate different activity doses and tracer uptake times after injection, our findings provide a promising rationale for validation of 18F-DCFPyL in future prospective trials.

Characterization of a Cell-Penetrating Peptide with Potential Anticancer Activity.

Cell-penetrating peptides (CPPs) are still an interesting and viable alternative for drug delivery applications. CPPs contain considerably high amounts of positively charged amino acids, imparting them with cationic character. Tumor cells are characterized by an enhanced anionic nature of their membrane surface, a property that could be used by CPPs to target these cells. We recently identified a branched CPP that displays a high internalization capacity while exhibiting selectivity for certain tumor cell types. In this study we elucidated this observation in greater detail by investigating the underlying mechanism behind the cellular uptake of this peptide. An additional cytotoxicity screen against several cancer cell lines indeed demonstrates high cytotoxic activity against cancer cells over normal fibroblasts. Furthermore, we show that this feature can be used for delivering the anticancer drug actinomycin D with high efficiency in the MCF-7 cancer cell line.

Comparison of [(18)F]DCFPyL and [ (68)Ga]Ga-PSMA-HBED-CC for PSMA-PET Imaging in Patients with Relapsed Prostate Cancer.

PURPOSE: Gallium-68 (Ga-68)-labeled tracers for imaging expression of the prostate-specific membrane antigen (PSMA) such as the [(68)Ga]Ga-PSMA-HBED-CC have already demonstrated high potential for the detection of recurrent prostate cancer. However, compared to Ga-68, a labeling with fluorine-18 (F-18) would offer advantages with respect to availability, production amount, and image resolution. [(18)F]DCFPyL is a promising F-18-labeled candidate for PSMA-positron emission tomography (PET) imaging that has been recently introduced. In the current study, we aimed to compare [(68)Ga]Ga-PSMA-HBED-CC and [(18)F]DCFPyL for clinical use in biochemically relapsed prostate cancer. PROCEDURES: In 14 selected patients with PSA relapse of prostate cancer, [(18)F]DCFPyL PET/X-ray computed tomography (CT) was performed in addition to [(68)Ga]Ga-PSMA-HBED-CC PET/CT. A systematic comparison was carried out between results obtained with both tracers with regard to the number of detected PSMA-positive lesions, the standardized uptake value (SUV)max and the lesion to background ratios. RESULTS: All suspicious lesions identified by [(68)Ga]Ga-PSMA-HBED-CC were also detected with [(18)F]DCFPyL. In three patients, additional lesions were observed using [(18)F]DCFPyL PET/CT. The mean SUVmax in the concordant [(18)F]DCFPyL PSMA-positive lesions was significantly higher as compared to [(68)Ga]Ga-PSMA-HBED-CC (14.5 vs. 12.2, p = 0.028, n = 15). The mean tumor to background ratios (n = 15) were significantly higher for [(18)F]DCFPyL compared to [(68)Ga]Ga-PSMA-HBED-CC using kidney, spleen, or parotid as reference organs (p = 0.006, p = 0.002, p = 0.008), but no significant differences were found using the liver (p = 0.167) or the mediastinum (p = 0.363) as reference organs. CONCLUSION: [(18)F]DCFPyL PET/CT provided a high image quality and visualized small prostate lesions with excellent sensitivity. [(18)F]DCFPyL represents a highly promising alternative to [(68)Ga]Ga-PSMA-HBED-CC for PSMA-PET/CT imaging in relapsed prostate cancer.

Characterization of SnO2-based (68)Ge/ (68)Ga generators and (68)Ga-DOTATATE preparations: radionuclide purity, radiochemical yield and long-term constancy.

BACKGROUND: With the increasing utilization of (68)Ge-(68)Ga radionuclide generators, (68)Ga labelled peptides like DOTATATE are receiving more attention in nuclear medicine. On the one hand, the long half-life of the parent nuclide (68)Ge is an enormous advantage for routine applications, but the question of the long-term stability of the (68)Ge breakthrough arises, which up to now has scarcely been investigated. METHOD: A sum of 123 eluates from four different (68)Ge-(68)Ga generators (iThemba Labs, Faure, South Africa) and 115 samples of the prepared radiopharmaceutical (68)Ga-DOTATATE were measured first with a dose calibrator and again after decay of the eluted (68)Ga via gamma-ray spectrometry. A complete decay curve was recorded for one sample eluate. A further three eluates were eluted in ten fractions of 0.5 ml in order to obtain detailed information concerning the distribution of the two nuclides within the eluates. The influences of factors such as the amount of DOTATATE, addition of Fe(3+) salts and replacement of HEPES buffer with sodium acetate on the radiochemical synthesis were also tested. RESULTS: The content of long-lived (68)Ge breakthrough increases over the entire period of use to more than 100 ppm. The labelling process with the chelator DOTA removes (68)Ge efficiently. The maximum activity found in the residues of the radiopharmaceuticals investigated in this study was below 10 Bq in nearly all cases. In many cases (12% of the labelled substance), the long-lived parent nuclide could not be identified at all. The labelling process is still viable for reduced amounts of the chelator and with acetate buffer. CONCLUSION: Effective doses received by the patient from (68)Ge in the injected radiopharmaceutical (68)Ga-DOTATATE are lower than 0.1 µSv and are therefore practically negligible, especially when compared with the contribution of the PET radiopharmaceutical itself. Gamma-ray spectrometry as recommended by the European Pharmacopeia is suitable for quantification of radionuclidic impurities.

Cellular response on Auger- and Beta-emitting nuclides: human embryonic stem cells (hESC) vs. keratinocytes.

PURPOSE: We studied the response of human embryonic stem cells (hESC) to the ß-emitter (131)I, which affects the entire cell and to the Auger electron emitter (125)I-deoxyuridine ((125)I-dU), primarily affecting the deoxyribonuleic acid (DNA). The effects were also studied in keratinocytes as a prototype for somatic cells. METHODS: HESC (H1) and human keratinocytes (HaCaT, human) were exposed to (125)I-dU (5 × 10(-5) - 5 MBq/ml) and (131)I-iodide (5 × 10(-5) - 12.5 MBq/ml) and apoptosis was measured by DNA-fragmentation. Cell morphology was studied by light microscopy and electron microscopy. Transcriptional profiling was done on the Agilent oligonucleotide microarray platform. RESULTS: Auger-process induced no apoptosis but a strong transcriptional response in hESC. In contrast, HaCaT cells showed a pronounced induction of apoptosis but only a moderate transcriptional response. Transcriptional response of hESC was similar after (125)I-dU and (131)I treatments, whereas HaCaT cells expressed a much more pronounced response to (125)I-dU than to (131)I. A striking radiation-induced down-regulation of pluripotency genes was observed in hESC whereas in keratinocytes the enriched gene annotations were related primarily to apoptosis, cell division and proliferation. CONCLUSIONS: Human embryonic stem cells respond to ionizing radiation by (125)I-dU and (131)I in a different way compared to keratinocytes. Transcriptional response and gene expression appear to facilitate an escape from programmed cell death by striking a new path which probably leads to cell differentiation.