Biodistribution and Radiation Dosimetry for 68Ga-DOTA-CCK-66, a Novel CCK2R-Targeting Compound for Imaging of Medullary Thyroid Cancer.

ABSTRACT: Cholecystokinin 2 receptor (CCK2R) is a promising target for imaging and treatment of medullary thyroid cancer due to its overexpression in over 90% of tumor cells. 68Ga-DOTA-CCK-66 is a recently introduced PET tracer selective for CCK2R, which has shown favorable pharmacokinetics in vivo in preclinical experiments. In order to further investigate safety and suitability of this tracer in the human setting, whole-body distribution and radiation dosimetry were evaluated. PATIENTS AND METHODS: Six patients with a history of medullary thyroid cancer were injected intravenously with 169 ± 19 MBq of 68Ga-DOTA-CCK-66. Whole-body PET/CT scans were acquired at 10 minutes, 1 hour, 2 hours, and 4 hours after tracer injection. Time-activity curves per organ were determined, and mean organ-absorbed doses and effective doses were calculated using OLINDA/EXM. RESULTS: Injection of a standard activity of 150 MBq of 68Ga-DOTA-CCK-66 results in an effective dose of 4.5 ± 0.9 mSv. The highest absorbed organ doses were observed in the urinary bladder wall (40 mGy) and the stomach (15 mGy), followed by the kidneys (6 mGy), as well as the liver and the spleen (3 mGy each). CCK2R-expressing tumor manifestations could be detected in 2 of the 6 patients, including lymph node, bone, and liver metastases. CONCLUSIONS: 68Ga-DOTA-CCK-66 exhibits a favorable dosimetry. Beyond physiologic receptor expression of the stomach, no other relevant tracer accumulation could be observed, rendering this organ at risk in case of subsequent radioligand therapy using 177Lu-DOTA-CCK-66.

[Modern TARE 2023 - from palliative care to a curative treatment alternative]. / Die moderne TARE 2023 ­ von der Palliativversorgung zur kurativen Behandlungsalternative.

Selective internal radiotherapy (SIRT) or transarterial radioembolisation (TARE) is an alternative treatment for hepatocellular carcinoma (HCC) or hepatic metastatic colorectal carcinoma (mCRC) and is now anchored in many guidelines. The article summarises the current guidelines on SIRT/TARE in HCC and mCRC.

[Unclear cause of unilateral blindness with normal inflammation parameters]. / Unklare Ursache einseitiger Erblindung bei normwertigen Entzündungsparametern.

A 70-year-old female patient presented with unilateral blindness of the right eye. As C­reactive protein (CRP) and the erythrocyte sedimentation rate (ESR) were inconspicuous, a nonarteritic embolic occlusion was assumed; however, after detailed anamnesis large vessel vasculitis (LVV) appeared more likely, which was confirmed by the subsequent imaging diagnostics. This rare case of LVV without an increase in one of the inflammatory parameters CRP or ESR highlights the importance of the medical history and targeted diagnostic procedures.

Safety and Efficacy of Extended Therapy with [177Lu]Lu-PSMA: A German Multicenter Study.

Prospective results have demonstrated favorable safety and efficacy of [177Lu]Lu-PSMA radiopharmaceutical therapy for up to 6 cycles in men with metastatic castration-resistant prostate cancer. However, no systematic data are available outlining the feasibility of extended therapy beyond 6 cycles. We aim to evaluate the safety and efficacy of extended [177Lu]Lu-PSMA radiopharmaceutical therapy in patients who have received more than 6 cycles. Methods: In total, 111 patients were included in this multicenter retrospective analysis. Based on individual decisions, patients underwent uninterrupted continuation of therapy (continuous treatment) or reexposure after a therapy break (rechallenge treatment) between 2014 and 2023. Overall survival, 50% prostate-specific antigen (PSA) decline (measured 8-12 wk after treatment initiation or rechallenge), PSMA PET response, and grades per Common Terminology Criteria for Adverse Events were assessed. χ2 tests, multivariable Cox regression analysis, and log-rank tests were applied for statistical analyses. Results: Patients received extended treatment with [177Lu]Lu-PSMA, either as a continuous treatment (43/111, 38.7%) or as a rechallenge (68/111, 61.3%) treatment, with median cumulative doses of 57.4 or 60.8 GBq, respectively. Overall survival from the initiation of [177Lu]Lu-PSMA was 31.3, 23.2, and 40.2 mo for the entire cohort, the continuous treatment group, and the rechallenge treatment group, respectively. The initial 50% PSA decline was significantly higher in the retreated group than in the continuous group (57/63 [90.4%] vs. 26/42 [61.9%]; P = 0.006). A 50% PSA decline was observed in 23 of 62 patients (37.1%) after the first rechallenge. The rate of grades 3-4 toxicity was comparable between continuous and rechallenge treatments (anemia, 7/43 [16.3%] vs. 13/68 [19.1%)], P = 0.6; leukocytopenia, 1/43 [2.3%] vs. 2/67 [3.0%], P = 0.3; thrombocytopenia, 3/43 [7.0%] vs. 3/68 [4.4%], P = 0.3; renal, 2/43 [4.7%] vs. 5/68 [7.4%], P = 0.2). Conclusion: Extended therapy with [177Lu]Lu-PSMA is safe and has not been associated with increased grades 3-4 toxicity. Patient candidates for extended treatment experienced a favorable median survival of 31.3 mo from the first administration. Response under [177Lu]Lu-PSMA rechallenge demonstrated preserved efficacy of [177Lu]Lu-PSMA after a treatment break.

Biodistribution and radiation dosimetry of [99mTc]Tc-N4-BTG in patients with biochemical recurrence of prostate cancer.

BACKGROUND: In patients with prostate cancer (PCa), imaging with gastrin-releasing peptide receptor (GRPR) ligands is an alternative to PSMA-targeted tracers, particularly if PSMA expression is low or absent. [99mTc]Tc-N4-BTG is a newly developed GRPR-directed probe for conventional scintigraphy and single photon emission computed tomography (SPECT) imaging. The current study aims to investigate the safety, biodistribution and dosimetry of [99mTc]Tc-N4-BTG in patients with biochemical recurrence (BCR) of PCa. RESULTS: No adverse pharmacologic effects were observed. Injection of [99mTc]Tc-N4-BTG resulted in an effective dose of 0.0027 ± 0.0002 mSv/MBq. The urinary bladder was the critical organ with the highest mean absorbed dose of 0.028 ± 0.001 mGy/MBq, followed by the pancreas with 0.0043 ± 0.0015 mGy/MBq, osteogenic cells with 0.0039 ± 0.0005 mGy/MBq, the kidneys with 0.0034 ± 0.0003 mGy/MBq, and the liver with 0.0019 ± 0.0004 mGy/MBq, respectively. No focal tracer uptake suggestive of PCa recurrence could be revealed for any of the patients. CONCLUSION: [99mTc]Tc-N4-BTG appears to be a safe diagnostic agent. Compared to GRPR-targeted PET tracers, this 99mTc-labelled SPECT agent could contribute to a broader application and better availability of this novel approach. Further research to assess its clinical value is warranted.

First Safety and Efficacy Data with the Radiohybrid 177Lu-rhPSMA-10.1 for the Treatment of Metastatic Prostate Cancer.

We recently published the first dosimetry data, to our knowledge, for the radioligand therapy agent 177Lu-rhPSMA-10.1, providing an intrapatient comparison with 177Lu-PSMA-I&T in patients with metastatic prostate cancer. Here, we report efficacy and safety findings from these patients. Methods: Four consecutive patients with prostate-specific membrane antigen (PSMA)-positive metastatic prostate cancer received up to 6 cycles of 177Lu-rhPSMA-10.1 (7.4-7.7 GBq per cycle). Efficacy (prostate-specific antigen response according to Prostate Cancer Working Group 3 criteria and the Response Evaluation Criteria in PSMA PET/CT), progression-free survival, and overall survival were evaluated. Adverse events were recorded from the first dose until 16-24 mo after treatment. Results: The patients received a total activity of 29.6-59.4 GBq (4-6 cycles). Prostate-specific antigen was reduced by 100%, 99%, 88%, and 35%. Progression-free survival was not reached for 2 patients at 24 and 18 mo of follow-up and was 15 and 12 mo for the other 2 patients. One patient had a sustained complete response with 2 y of follow up. All patients were alive at the last time point of data collection. No serious adverse events were reported. Conclusion: 177Lu-rhPSMA-10.1 demonstrated encouraging preliminary efficacy and was well tolerated. Formal clinical trials are now under way to evaluate its potential prospectively (NCT05413850).

Long-Term Nephrotoxicity of 177Lu-PSMA Radioligand Therapy.

ß-emitting 177Lu targeting prostate-specific membrane antigen (PSMA) is an approved treatment option for metastatic castration-resistant prostate cancer. Data on its long-term nephrotoxicity are sparse. This study aimed to retrospectively evaluate post-177Lu-PSMA estimated glomerular filtration rate (eGFR) dynamics for at least 12 mo in a cohort of metastatic castration-resistant prostate cancer patients. Methods: The institutional databases of 3 German tertiary referral centers identified 106 patients who underwent at least 4 cycles of 177Lu-PSMA and had at least 12 mo of eGFR follow-up data. eGFR (by the Chronic Kidney Disease Epidemiology Collaboration formula) at 3, 6, and 12 mo after 177Lu-PSMA radioligand therapy was estimated using monoexponentially fitted curves through available eGFR data. eGFR changes were grouped (≥15%-<30%, moderate; ≥30%-<40%, severe; and ≥40%, very severe). Associations between eGFR changes (%) and nephrotoxic risk factors, prior treatment lines, and number of 177Lu-PSMA cycles were analyzed using multivariable linear regression. Results: At least moderate eGFR decreases were present in 45% (48/106) of patients; of those, nearly half (23/48) had a severe or very severe eGFR decrease. A higher number of risk factors at baseline (-4.51, P = 0.03) was associated with a greater eGFR decrease. Limitations of the study were the retrospective design, lack of a control group, and limited number of patients with a follow-up longer than 1 y. Conclusion: A considerable proportion of patients may experience moderate or severe decreases in eGFR 1 y from initiation of 177Lu-PSMA. A higher number of risk factors at baseline seems to aggravate loss of renal function. Further prospective trials are warranted to estimate the nephrotoxic potential of 177Lu-PSMA.

Preclinical Evaluation of Minigastrin Analogs and Proof-of-Concept [68Ga]Ga-DOTA-CCK-66 PET/CT in 2 Patients with Medullary Thyroid Cancer.

Because of the need for radiolabeled theranostics for the detection and treatment of medullary thyroid cancer (MTC), and the yet unresolved stability issues of minigastrin analogs targeting the cholecystokinin-2 receptor (CCK-2R), our aim was to address in vivo stability, our motivation being to develop and evaluate DOTA-CCK-66 (DOTA-γ-glu-PEG3-Trp-(N-Me)Nle-Asp-1-Nal-NH2, PEG: polyethylene glycol) and DOTA-CCK-66.2 (DOTA-glu-PEG3-Trp-(N-Me)Nle-Asp-1-Nal-NH2), both derived from DOTA-MGS5 (DOTA-glu-Ala-Tyr-Gly-Trp-(N-Me)Nle-Asp-1-Nal-NH2), and clinically translate [68Ga]Ga-DOTA-CCK-66. Methods: 64Cu and 67Ga labeling of DOTA-CCK-66, DOTA-CCK-66.2, and DOTA-MGS5 was performed at 90°C within 15 min (1.0 M NaOAc buffer, pH 5.5, and 2.5 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer, respectively). 177Lu labeling of these 3 compounds was performed at 90°C within 15 min (1.0 M NaOAc buffer, pH 5.5, 0.1 M sodium ascorbate). CCK-2R affinity of natGa/natCu/natLu-labeled DOTA-CCK-66, DOTA-CCK-66.2, and DOTA-MGS5 was examined on AR42J cells. The in vivo stability of 177Lu-labeled DOTA-CCK-66 and DOTA-MGS5 was examined at 30 min after injection in CB17-SCID mice. Biodistribution studies at 1 h ([67Ga]Ga-DOTA-CCK-66) and 24 h ([177Lu]Lu-DOTA-CCK-66/DOTA-MGS5) after injection were performed on AR42J tumor-bearing CB17-SCID mice. In a translation to the human setting, [68Ga]Ga-DOTA-CCK-66 was administered and whole-body PET/CT was acquired at 120 min after injection in 2 MTC patients. Results: Irrespective of the metal or radiometal used (copper, gallium, lutetium), high CCK-2R affinity (half-maximal inhibitory concentration, 3.6-6.0 nM) and favorable lipophilicity were determined. In vivo, increased numbers of intact peptide were found for [177Lu]Lu-DOTA-CCK-66 compared with [177Lu]Lu-DOTA-MGS5 in murine urine (23.7% ± 9.2% vs. 77.8% ± 2.3%). Overall tumor-to-background ratios were similar for both 177Lu-labeled analogs. [67Ga]Ga-DOTA-CCK-66 exhibited accumulation (percentage injected dose per gram) that was high in tumor (19.4 ± 3.5) and low in off-target areas (blood, 0.61 ± 0.07; liver, 0.31 ± 0.02; pancreas, 0.23 ± 0.07; stomach, 1.81 ± 0.19; kidney, 2.51 ± 0.49) at 1 h after injection. PET/CT examination in 2 MTC patients applying [68Ga]Ga-DOTA-CCK-66 confirmed multiple metastases. Conclusion: Because of the high in vivo stability and favorable overall preclinical performance of [nat/67Ga]Ga-/[nat/177Lu]Lu-DOTA-CCK-66, a proof-of-concept clinical investigation of [68Ga]Ga-DOTA-CCK-66 was completed. As several lesions could be identified and excellent biodistribution patterns were observed, further patient studies applying [68Ga]Ga- and [177Lu]Lu-DOTA-CCK-66 are warranted.

An Intrapatient Dosimetry Comparison of 177Lu-rhPSMA-10.1 and 177Lu-PSMA-I&T in Patients with Metastatic Castration-Resistant Prostate Cancer.

As the use of radioligand therapy moves earlier in the prostate cancer timeline, minimizing the absorbed dose to normal organs while maintaining high tumor radiation doses becomes more clinically important because of the longer life expectancy of patients. We performed an intrapatient comparison of pretherapeutic dosimetry with the novel radiohybrid prostate-specific membrane antigen-targeting radiopharmaceutical 177Lu-rhPSMA-10.1, along with 177Lu-PSMA-I&T, in patients with metastatic castration-resistant prostate cancer. Methods: Four consecutive patients with advanced histologically proven metastatic castration-resistant prostate cancer who were scheduled for radioligand therapy were evaluated. Before undergoing therapy, each patient received 1.06 ± 0.05 GBq of 177Lu-rhPSMA-10.1 and 1.09 ± 0.02 GBq of 177Lu-PSMA-I&T at least 7 d apart. For dosimetric assessment, whole-body planar scintigraphy was performed after 5 min, 4 h, 1 d, 2 d, and 7 d. In addition, SPECT/CT images were acquired over the thorax and the abdomen, 4 h, 1 d, 2 d, and 7 d after injection. Dosimetry of the whole body and salivary glands was based on the evaluation of the counts in whole-body planar imaging. Dosimetry of the kidneys, liver, spleen, bone marrow, and tumor lesions (≤4 per patient) was based on the activity in volumes drawn on SPECT/CT images. Doses were calculated using OLINDA/EXM version 1.0. The therapeutic index (TI), or ratio between mean dose of the metastases and mean dose of the kidneys, was calculated for each patient. Results: We found the dose to the kidneys to be higher with 177Lu-rhPSMA-10.1 than with 177Lu-PSMA-I&T (0.68 ± 0.30 vs. 0.46 ± 0.10 mGy/MBq); however, 177Lu-rhPSMA-10.1 delivered an average of a 3.3 times (range, 1.2-8.3 times) higher absorbed radiation dose to individual tumor lesions. Consequently, intraindividual comparison revealed a 1.1-3.1 times higher TI for 177Lu-rhPSMA-10.1 than for 177Lu-PSMA-I&T in all evaluated patients. The effective whole-body dose was 0.038 ± 0.008 mSv/MBq for 177Lu-rhPSMA-10.1 and 0.022 ± 0.005 mSv/MBq for 177Lu-PSMA-I&T. Conclusion: Using 177Lu-rhPSMA-10.1 can significantly increase the tumor-absorbed dose and improve the TI compared with 177Lu-PSMA-I&T. An improved TI gives the flexibility to maximize tumor-absorbed doses up to a predefined renal dose limit or, in earlier disease, to reduce the radiation exposure to the kidney while still achieving an effective tumor dose. The function of at-risk organs such as the kidneys is being assessed in a prospective clinical trial.

[99mTc]Tc-PentixaTec: development, extensive pre-clinical evaluation, and first human experience.

PURPOSE: The clinical success non-invasive imaging of CXCR4 expression using [68 Ga]Ga-PentixaFor-PET warrants an expansion of the targeting concept towards conventional scintigraphy/SPECT with their lower cost and general availability. To this aim, we developed and comparatively evaluated a series of 99mTc-labeled cyclic pentapeptides based on the PentixaFor scaffold. METHODS: Six mas3-conjugated CPCR4 analogs with different 4-aminobenzoic acid (Abz)-D-Ala-D-Arg-aa3 linkers (L1-L6) as well as the corresponding HYNIC- and N4-analogs of L6-CPCR4 were synthesized via standard SPPS. Competitive binding studies (IC50 and IC50inv) were carried out using Jurkat T cell lymphoma cells and [125I]FC-131 as radioligand. Internalization kinetics were investigated using hCXCR4-overexpressing Chem-1 cells. Biodistribution studies and small animal SPECT/CT imaging (1 h p.i.) were carried out using Jurkat xenograft bearing CB17/SCID mice. Based on the preclinical results, [99mTc]Tc-N4-L6-CPCR4 ([99mTc]Tc-PentixaTec) was selected for an early translation to the human setting. Five patients with hematologic malignancies underwent [99mTc]Tc-N4-L6-CPCR4 SPECT/planar imaging with individual dosimetry. RESULTS: Of the six mas3-conjugated peptides, mas3-L6-CPCR4 (mas3-dap-r-a-Abz-CPCR4) showed the highest CXCR4 affinity (IC50 = 5.0 ± 1.3 nM). Conjugation with N4 (N4-L6-CPCR4) further improved hCXCR4 affinity to 0.6 ± 0.1 nM. [99mTc]Tc-N4-L6-CPCR4 also showed the most efficient internalization (97% of total cellular activity at 2 h) and the highest tumor accumulation (8.6 ± 1.3% iD/g, 1 h p.i.) of the compounds investigated. Therefore, [99mTc]Tc-N4-L6-CPCR4 (termed [99mTc]Tc-PentixaTec) was selected for first-in-human application. [99mTc]Tc-PentixaTec was well tolerated, exhibits a favorable biodistribution and dosimetry profile (2.1-3.4 mSv per 500 MBq) and excellent tumor/background ratios in SPECT and planar imaging. CONCLUSION: The successive optimization of the amino acid composition of the linker structure and the N-terminal 99mTc-labeling strategies (mas3 vs HYNIC vs N4) has provided [99mTc]Tc-PentixaTec as a novel, highly promising CXCR4-targeted SPECT agent for clinical application. With its excellent CXCR4 affinity, efficient internalization, high uptake in CXCR4-expressing tissues, suitable clearance/biodistribution characteristics, and favorable human dosimetry, it holds great potential for further clinical use.

In-Vivo Somatostatin-Receptor Expression in Small Cell Lung Cancer as a Prognostic Image Biomarker and Therapeutic Target.

BACKGROUND: Given the dismal prognosis of small cell lung cancer (SCLC), novel therapeutic targets are urgently needed. We aimed to evaluate whether SSTR expression, as assessed by positron emission tomography (PET), can be applied as a prognostic image biomarker and determined subjects eligible for peptide receptor radionuclide therapy (PRRT). METHODS: A total of 67 patients (26 females; age, 41-80 years) with advanced SCLC underwent SSTR-directed PET/computed tomography (somatostatin receptor imaging, SRI). SRI-avid tumor burden was quantified by maximum standardized uptake values (SUVmax) and tumor-to-liver ratios (T/L) of the most intense SCLC lesion. Scan findings were correlated with progression-free (PFS) and overall survival (OS). In addition, subjects eligible for SSTR-directed radioligand therapy were identified, and treatment outcome and toxicity profile were recorded. RESULTS: On a patient basis, 36/67 (53.7%) subjects presented with mainly SSTR-positive SCLC lesions (>50% lesions positive); in 10/67 patients (14.9%), all lesions were positive. The median SUVmax was found to be 8.5, while the median T/L was 1.12. SRI-uptake was not associated with PFS or OS, respectively (SUVmax vs. PFS, ρ = 0.13 with p = 0.30 and vs. OS, ρ = 0.00 with p = 0.97; T/L vs. PFS, ρ = 0.07 with p = 0.58 and vs. OS, ρ = -0.05 with p = 0.70). PRRT was performed in 14 patients. One patient succumbed to treatment-independent infectious complications immediately after PRRT. In the remaining 13 subjects, disease control was achieved in 5/13 (38.5%) with a single patient achieving a partial response (stable disease in the remainder). In the sub-group of responding patients, PFS and OS were 357 days and 480 days, respectively. CONCLUSIONS: SSTR expression as detected by SRI is not predictive of outcome in patients with advanced SCLC. However, it might serve as a therapeutic target in selected patients.

177 Lu-rhPSMA-10.1 Induces Tumor Response in a Patient With mCRPC After PSMA-Directed Radioligand Therapy With 177 Lu-PSMA-I&T.

ABSTRACT: 177 Lu-rhPSMA-10.1 is a novel PSMA-targeting radiopharmaceutical that has been optimized in terms of pharmacological and pharmacokinetic properties and may be therefore advantageous in treatment of metastatic castrate-resistant prostate cancer. In this image, we present the case of an 86-year-old man with metastastic castrate-resistant prostate cancer undergoing 177 Lu-PSMA-I&T treatment. After initial partial response to radioligand therapy, another 2 treatment cycles resulted in a rising serum PSA level that could be correlated with increasingly PSMA-positive as well as a new bone lesion. Consequently, the patient was changed to 177 Lu-rhPSMA-10.1 treatment on a compassionate use basis achieving a renewed tumor response.

Lung perfusion assessed by SPECT/CT after a minimum of three months anticoagulation therapy in patients with SARS-CoV-2-associated acute pulmonary embolism: a retrospective observational study.

BACKGROUND: Anticoagulant treatment is recommended for at least three months after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-related acute pulmonary embolism (PE), but the persistent pulmonary clot burden after that time is unknown. METHODS: Lung perfusion was assessed by ventilation-perfusion (V/Q) SPECT/CT in 20 consecutive patients with SARS-CoV-2-associated acute PE after a minimum of three months anticoagulation therapy in a retrospective observational study. RESULTS: Remaining perfusion defects after a median treatment period of six months were observed in only two patients. All patients (13 men, seven women, mean age 55.6 ± 14.5 years) were on non-vitamin K direct oral anticoagulants (DOACs). No recurrent venous thromboembolism or anticoagulant-related bleeding complications were observed. Among patients with partial clinical recovery, high-risk PE and persistent pulmonary infiltrates were significantly more frequent (p < 0.001, respectively). INTERPRETATION: Temporary DOAC treatment seems to be safe and efficacious for resolving pulmonary clot burden in SARS-CoV-2-associated acute PE. Partial clinical recovery is more likely caused by prolonged SARS-CoV-2-related parenchymal lung damage rather than by persistent pulmonary perfusion defects.