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.

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.

Hyperkalemia in patients treated with endoradiotherapy combined with amino acid infusion is associated with severe metabolic acidosis.

BACKGROUND: Amino acid co-infusion for renal protection in endoradiotherapy (ERT) applied as prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) or peptide receptor radionuclide therapy (PRRT) has been shown to cause severe hyperkalemia. The pathophysiology behind the rapid development of hyperkalemia is not well understood. We hypothesized that the hyperkalemia should be associated with metabolic acidosis. RESULTS: Twenty-two patients underwent ERT. Prior to the first cycle, excretory kidney function was assessed by mercapto-acetyltriglycine (MAG-3) renal scintigraphy, serum biochemistry, and calculated glomerular filtration rate (eGFR). All patients received co-infusion of the cationic amino acids L-arginine and L-lysine for nephroprotection. Clinical symptoms, electrolytes, and acid-base status were evaluated at baseline and after 4 h. No patient developed any clinically relevant side effects. At baseline, acid base status and electrolytes were normal in all patients. Excretory kidney function was normal or only mildly impaired in all except two patients with stage 3 renal insufficiency. All patients developed hyperkalemia. Base excess and HCO3- were significantly lower after 4 h. In parallel, mean pH dropped from 7.36 to 7.29. There was a weak association between calculated (r = - 0.21) as well as MAG-3-derived GFR (r = - 0.32) and the rise in potassium after 4 h. CONCLUSION: Amino acid co-infusion during ERT leads to severe metabolic acidosis which induces hyperkalemia by potassium hydrogen exchange. This novel finding implies that commercially available bicarbonate solutions might be an easy therapeutic option to correct metabolic acidosis rapidly.

Radiation Dosimetry for 177Lu-PSMA I&T in Metastatic Castration-Resistant Prostate Cancer: Absorbed Dose in Normal Organs and Tumor Lesions.

Prostate-specific membrane antigen (PSMA)-targeted radioligand therapy is increasingly used in metastatic castration-resistant prostate cancer. We aimed to estimate the absorbed doses for normal organs and tumor lesions using 177Lu-PSMA I&T (I&T is imaging and therapy) in patients undergoing up to 4 cycles of radioligand therapy. Results were compared with pretherapeutic Glu-NH-CO-NH-Lys-(Ahx)-[68Ga(HBEDCC)] (68Ga-PSMA-HBED-CC) PET. Methods: A total of 34 cycles in 18 patients were analyzed retrospectively. In 15 patients the first, in 9 the second, in 5 the third, and in 5 the fourth cycle was analyzed, respectively. Whole-body scintigraphy was performed at least between 30-120 min, 24 h, and 6-8 d after administration. Regions of interest covering the whole body, organs, and up to 4 tumor lesions were drawn. Organ and tumor masses were derived from pretherapeutic 68Ga-PSMA-HBED-CC PET/CT. Absorbed doses for individual cycles were calculated using OLINDA/EXM. SUVs from pretherapeutic PET were compared with absorbed doses and with change of SUV. Results: The mean whole-body effective dose for all cycles was 0.06 ± 0.03 Sv/GBq. The mean absorbed organ doses were 0.72 ± 0.21 Gy/GBq for the kidneys; 0.12 ± 0.06 Gy/GBq for the liver; and 0.55 ± 0.14 Gy/GBq for the parotid, 0.64 ± 0.40 Gy/GBq for the submandibular, and 3.8 ± 1.4 Gy/GBq for the lacrimal glands. Absorbed organ doses were relatively constant among the 4 different cycles. Tumor lesions received a mean absorbed dose per cycle of 3.2 ± 2.6 Gy/GBq (range, 0.22-12 Gy/GBq). Doses to tumor lesions gradually decreased, with 3.5 ± 2.9 Gy/GBq for the first, 3.3 ± 2.5 Gy/GBq for the second, 2.7 ± 2.3 Gy/GBq for the third, and 2.4 ± 2.2 Gy/GBq for the fourth cycle. SUVs of pretherapeutic PET moderately correlated with absorbed dose (r = 0.44, P < 0.001 for SUVmax; r = 0.43, P < 0.001 for SUVmean) and moderately correlated with the change of SUV (r = 0.478, P < 0.001 for SUVmax, and r = 0.50, P < 0.001 for SUVmean). Conclusion: Organ- and tumor-absorbed doses for 177Lu-PSMA I&T are comparable to recent reports and complement these with information on an excellent correlation between the 4 therapy cycles. With the kidneys representing the critical organ, a cumulative activity of 40 GBq of 177Lu-PSMA I&T appears to be safe and justifiable. The correlation between pretherapeutic SUV and absorbed tumor dose emphasizes the need for PSMA-ligand PET imaging for patient selection.

Biodistribution and radiation dosimetry of (68)Ga-PSMA HBED CC-a PSMA specific probe for PET imaging of prostate cancer.

PURPOSE: Positron emission tomography (PET) agents targeting the prostate-specific membrane antigen (PSMA) are currently under broad clinical and scientific investigation. (68)Ga-PSMA HBED-CC constitutes the first (68)Ga-labelled PSMA-inhibitor and has evolved as a promising agent for imaging PSMA expression in vivo. The aim of this study was to evaluate the whole-body distribution and radiation dosimetry of this new probe. METHODS: Five patients with a history or high suspicion of prostate cancer were injected intravenously with a mean of 139.8 ± 13.7 MBq of (68)Ga-PSMA HBED-CC (range 120-158 MBq). Four static skull to mid-thigh scans using a whole-body fully integrated PET/MR-system were performed 10 min, 60 min, 130 min, and 175 min after the tracer injection. Time-dependent changes of the injected activity per organ were determined. Mean organ-absorbed doses and effective doses (ED) were calculated using OLINDA/EXM. RESULTS: Injection of a standard activity of 150 MBq (68)Ga-PSMA HBED-CC resulted in a median effective dose of 2.37 mSv (Range 1.08E-02 - 2.46E-02 mSv/MBq). The urinary bladder wall (median absorbed dose 1.64E-01 mGv/MBq; range 8.76E-02 - 2.91E-01 mGv/MBq) was the critical organ, followed by the kidneys (median absorbed dose 1.21E-01 mGv/MBq; range 7.16E-02 - 1.75E-01), spleen (median absorbed dose 4.13E-02 mGv/MBq; range 1.57E-02 - 7.32E-02 mGv/MBq) and liver (median absorbed dose 2.07E-02 mGv/MBq; range 1.80E-02 - 2.57E-02 mGv/MBq). No drug-related pharmacological effects occurred. CONCLUSION: The use of (68)Ga-PSMA HBED-CC results in a relatively low radiation exposure, delivering organ doses that are comparable to those of other (68)Ga-labelled PSMA-inhibitors used for PET-imaging. Total effective dose is lower than for other PET-agents used for prostate cancer imaging (e.g. (11)C- and (18)F-Choline).