[161Tb]Tb-PSMA-617 radioligand therapy in patients with mCRPC: preliminary dosimetry results and intra-individual head-to-head comparison to [177Lu]Lu-PSMA-617

Rationale: Evaluation of alternative radionuclides for use in prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) is currently focusing on 161Tb, which may provide advantages by emitting additional Auger and conversion electrons. In this pilot study, we present preliminary dosimetry data for [161Tb]Tb-PSMA-617 RLT in a direct comparison with [177Lu]Lu-PSMA-617. Method: Six patients with metastatic castration-resistant prostate cancer (mCRPC) underwent treatment with [177Lu]Lu-PSMA-617 and subsequently - after inadequate response - with [161Tb]Tb-PSMA-617. Whole-body planar and SPECT imaging-based dosimetry of organs at risk (kidneys and salivary glands) and tumor lesions were calculated using IDAC for 177Lu and OLINDA/EXM for 161Tb. The therapeutic index (TI) of mean tumor-absorbed doses over relevant organs at risk was calculated. Results: Mean absorbed doses to organs at risk of PSMA-RLT were slightly higher for [161Tb]Tb-PSMA-617 compared to [177Lu]Lu-PSMA-617 (kidneys: 0.643 ± 0.247 vs. 0.545 ± 0.231 Gy/GBq, factor 1.18; parotid gland: 0.367 ± 0.198 vs. 0.329 ± 0.180 Gy/GBq, factor 1.10), but markedly higher regarding tumor lesions (6.10 ± 6.59 vs 2.59 ± 3.30 Gy/GBq, factor 2.40, p < 0.001). Consequently, the mean TI was higher for [161Tb]Tb-PSMA-617 compared to [177Lu]Lu-PSMA-617 for both, the kidneys (11.54 ± 9.74 vs. 5.28 ± 5.13, p = 0.002) and the parotid gland (16.77 ± 13.10 vs. 12.51 ± 18.09, p = 0.008). Conclusion: In this intra-individual head-to-head pilot study, [161Tb]Tb-PSMA-617 delivered higher tumor-absorbed doses and resulted in superior TI compared to [177Lu]Lu-PSMA-617. This preliminary data support 161Tb as a promising radionuclide for PSMA-RLT in mCRPC.

[89Zr]Zr-PSMA-617 PET/CT characterization of indeterminate [68Ga]Ga-PSMA-11 PET/CT findings in patients with biochemical recurrence of prostate cancer: lesion-based analysis

BACKGROUND

The state-of-the-art method for imaging men with biochemical recurrence of prostate cancer (BCR) is prostate-specific membrane antigen (PSMA)-targeted positron emission tomography/computed tomography (PET/CT) with tracers containing short-lived radionuclides, e.g., gallium-68 (68Ga; half-life: ∼67.7 min). However, such imaging not infrequently yields indeterminate findings, which remain challenging to characterize. PSMA-targeted tracers labeled with zirconium-89 (89Zr; half-life: ∼78.41 h) permit later scanning, which may help in classifying the level of suspiciousness for prostate cancer of lesions previously indeterminate on conventional PSMA-targeted PET/CT.

METHODS

To assess the ability of [89Zr]Zr-PSMA-617 PET/CT to characterize such lesions, we retrospectively analyzed altogether 20 lesions that were indeterminate on prior [68Ga]Ga-PSMA-11 PET/CT, in 15 men with BCR (median prostate-specific antigen: 0.70 ng/mL). The primary endpoint was the lesions' classifications, and secondary endpoints included [89Zr]Zr-PSMA-617 uptake (maximum standardized uptake value [SUVmax]), and lesion-to-background ratio (tumor-to-liver ratio of the SUVmax [TLR]). [89Zr]Zr-PSMA-617 scans were performed 1 h, 24 h, and 48 h post-injection of 123 ± 19 MBq of radiotracer, 35 ± 35 d post-[68Ga]Ga-PSMA-11 PET/CT.

RESULTS

Altogether, 6/20 previously-indeterminate lesions (30%) were classified as suspicious (positive) for prostate cancer, 14/20 (70%), as non-suspicious (negative). In these two categories, [89Zr]Zr-PSMA-617 uptake and lesional contrast showed distinctly different patterns. In positive lesions, SUVmax and TLR markedly rose from 1 to 48 h, with SUVmax essentially plateauing at high levels, and TLR further steeply increasing, from 24 to 48 h. In negative lesions, uptake, when present, was very low, and decreasing, while contrast was minimal, from 1 to 48 h. No adverse events or clinically-relevant vital signs changes related to [89Zr]Zr-PSMA-617 PET/CT were noted during or ~ 4 weeks after the procedure.

CONCLUSIONS

In men with BCR, [89Zr]Zr-PSMA-617 PET/CT may help characterize as suspicious or non-suspicious for prostate cancer lesions that were previously indeterminate on [68Ga]Ga-PSMA-11 PET/CT.

TRIAL REGISTRATION

Not applicable.

Change in total lesion PSMA (TLP) during [177Lu]Lu-PSMA-617 radioligand therapy predicts overall survival in patients with mCRPC: monocentric evaluation of a prospective registry

PURPOSE

This study investigates imaging response of [177Lu]Lu-PSMA-617 radioligand therapy (RLT) based on the whole-body parameter total lesion PSMA (TLP), derived by PSMA-PET/CT and reflecting the total tumor burden, in patients with metastatic castration-resistant prostate cancer (mCRPC) enrolled in a prospective registry (NCT04833517).

METHODS

A total of n = 102 mCRPC patients received a [68Ga]Ga-PSMA-11 PET/CT at baseline and after two cycles of PSMA-RLT, in which TLP was measured by using a semi-automated tumor segmentation. TLP was defined as the summed products of volume and uptake (∑ Volume × SUVmean) of all tumor lesions. The Kaplan-Meier method was used to determine the most appropriate ∆TLP thresholds for classification into partial remission (PR), stable disease (SD), and progressive disease (PD) regarding overall survival (OS). Furthermore, we analyzed criteria that are also frequently used in established response frameworks, such as the occurrence of new metastases as independent criterion (I) or in combination with change in tumor burden (II), and the change in PSA serum value (III).

RESULTS

For the ∆TLP thresholds -30%/+30% (and also for higher thresholds, -40%/+40% or -50%/+50%), significant differences between all three response categories became apparent (PR/PD: p = 0.001; PR/SD: p = 0.001; SD/PD: p = 0.018). Including the development of new metastases as independent criterion of PD, there was no significant difference in OS between SD and PD (p = 0.455), neither when applied in combination with TLP (p = 0.191). Similarly, significant differentiation between SD and PD was not achieved by PSA serum value (p = 0.973).

CONCLUSION

In the largest monocentric study to date, TLP is shown to be a qualified prognostic biomarker, applying ∆TLP thresholds of -30%/+30%. It significantly differentiated between PR, SD, and PD, whereas other response criteria did not differentiate SD vs. PD. Using TLP, the development of new metastases is not a required information for predicting OS.

Change of glucometabolic activity per PSMA expression predicts survival in mCRPC patients non-responding to PSMA radioligand therapy: introducing a novel dual imaging biomarker

Purpose

The value of [18F]fluorodeoxyglucose ([18F]FDG) PET/CT in monitoring prostate-specific membrane antigen (PSMA) targeted radioligand therapy (RLT) is still unclear. The aim of this study was to identify appropriate prognostic dynamic parameters derived from baseline and follow-up [18F]FDG and dual [18F]FDG/[68Ga]Ga-PSMA-11 PET/CT for monitoring early non-responding mCRPC patients undergoing PSMA-RLT.

Methods

Twenty-three mCRPC patients of a prospective registry (NCT04833517), who were treated with [177Lu]Lu-PSMA-617 RLT and classified as early non-responders were included in this study. All patients received dual PET/CT imaging with [18F]FDG and [68Ga]Ga-PSMA-11 at baseline and after median two cycles of RLT. We tested potential biomarkers representing the "change of glucometabolic activity (cGA)" and "change of glucometabolic activity in relation to PSMA expression (cGAP)" composed of established parameters on [18F]FDG PET/CT as SUVmax, cumulative SUV of five lesions (SUV5), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) and its corresponding parameters on [68Ga]Ga-PSMA-11 PET/CT, respectively, for association with overall survival (OS).

Results

Kaplan-Meier analyses showed no significant association with OS for each tested cGA (cGASUVmaxp = 0.904, cGASUV5, p = 0.747 cGAMTVp = 0.682 and cGATLGp = 0.700), likewise the dual imaging biomarkers cGAPSUVmax (p = 0.136), cGAPSUV5 (p = 0.097), and cGAPTV (p = 0.113) failed significance. In contrast, cGAPTL, which is based on TLG and total lesion PSMA (TLP) showed a significant association with OS (p = 0.004). Low cGAPTL (cut-off 0.7) was associated with significant longer survival (17.6 vs. 12.9 months).

Conclusion

The novel biomarker cGAPTL, which represents the temporal change of whole-body TLG normalized by TLP, predicts overall survival in the challenging cohort of patients non-responding to PSMA-RLT.

Detection efficacy of [89Zr]Zr-PSMA-617 PET/CT in [68Ga]Ga-PSMA-11 PET/CT-negative biochemical recurrence of prostate cancer

RATIONALE

In patients with biochemical recurrence of prostate cancer (BCR), preliminary data suggest that prostate-specific membrane antigen (PSMA) ligand radiotracers labeled with zirconium-89 (89Zr; half-life ~ 78.41 h), which allow imaging ≥ 24 h post-injection, detect suspicious lesions that are missed when using tracers incorporating short-lived radionuclides.

MATERIALS AND METHODS

To confirm [89Zr]Zr-PSMA-617 positron emission tomography/computed tomography (PET/CT) detection efficacy regarding such lesions, and compare quality of 1-h, 24-h, and 48-h [89Zr]Zr-PSMA-617 scans, we retrospectively analyzed visual findings and PET variables reflecting lesional [89Zr]Zr-PSMA-617 uptake and lesion-to-background ratio. The cohort comprised 23 men with BCR post-prostatectomy, median (minimum-maximum) prostate-specific antigen (PSA) 0.54 (0.11-2.50) ng/mL, and negative [68Ga]Ga-PSMA-11 scans 40 ± 28 d earlier. Primary endpoints were percentages of patients with, and classifications of, suspicious lesions.

RESULTS

Altogether, 18/23 patients (78%) had 36 suspicious lesions (minimum-maximum per patient: 1-4) on both 24-h and 48-h scans (n = 33 lesions) or only 48-h scans (n = 3 lesions). Only one lesion appeared on a 1-h scan. Lesions putatively represented local recurrence in 11 cases, and nodal or bone metastasis in 21 or 4 cases, respectively; 1/1 lesion was histologically confirmed as a nodal metastasis. In all 15 patients given radiotherapy based on [89Zr]Zr-PSMA-617 PET/CT, PSA values decreased after this treatment. Comparison of PET variables in 24-h vs 48-h scans suggested no clear superiority of either regarding radiotracer uptake, but improved lesion-to-background ratio at 48 h.

CONCLUSIONS

In men with BCR and low PSA, [89Zr]Zr-PSMA-617 PET/CT seems effective in finding prostate malignancy not seen on [68Ga]Ga-PSMA-11 PET/CT. The higher detection rates and lesion-to-background ratios of 48-h scans versus 24-h scans suggest that imaging at the later time may be preferable. Prospective study of [89Zr]Zr-PSMA-617 PET/CT is warranted.

Tumor Sink Effect with Prostate-Specific Membrane Antigen-Targeted Theranostics in Patients with Metastatic Castration-Resistant Prostate Cancer: Intra-Individual Evaluations

"Tumor sink effects", decreased physiological uptake of radiopharmaceuticals due to sequestration by a tumor, may impact radioligand therapy (RLT) toxicity and dosing. We investigated these effects with prostate-specific membrane antigen (PSMA)-targeted radiopharmaceuticals in the healthy organs-at-risk (the parotid glands, kidneys, liver, and spleen) of 33 patients with metastatic castration-resistant prostate cancer (mCRPC). We retrospectively performed three intra-individual comparisons. First, we correlated changes from baseline to post-RLT (after two 177-lutetium (177Lu)-PSMA-617 cycles) in total lesional PSMA (∆TLP) and organ mean standardized uptake values (∆SUVmean). Second, in 25 RLT responders, we compared the organ SUVmean post-RLT versus that at baseline. Lastly, we correlated the baseline TLP and organ SUVmean. Data were acquired via 68-gallium-PSMA-11 positron emission tomography before the first and after the second 177Lu-PSMA-617 cycle. In the parotid glands and spleen, ∆TLP and ∆SUVmean showed a significant inverse correlation (r = -0.40, p = 0.023 and r = -0.36, p = 0.042, respectively). Additionally, in those tissues, the median organ SUVmean rose significantly from baseline after the response to RLT (p ≤ 0.022), and the baseline TLP and SUVmean were significantly negatively correlated (r = -0.44, p = 0.01 and r = -0.42, p = 0.016, respectively). These observations suggest tumor sink effects with PSMA-targeted radiopharmaceuticals in the salivary glands and spleen of patients with mCRPC.

Benefit of including CT urography in [68Ga]PSMA-11 PET/CT with low-dose CT: first results from a larger prostate cancer cohort analysis

BACKGROUND

Accuracy of [⁶⁸Ga]PSMA-11 PET/CT may be hampered by ureter accumulation, mimicking lymph node metastases depending on localization and configuration. The benefit of CT urography for differentiation of lymph node metastasis from urinary tract activity was evaluated in a "PET/CT with low-dose CT" setting.

METHODS

Retrospective analysis of PET/CT for primary staging, biochemical recurrence or local treatment planning in patients with prostate cancer. For CT urography (CTU), iodinated contrast agent was administered 10 minutes prior to image acquisition. All potential pathologic (peri)ureteral tracer uptake was assigned to excretory ureteral accumulation or pathological lesion. To assess additional provided benefit of CTU all foci were rated with an introduced scoring system (ranging from 0 pts: CTU not needed; up to 3 pts: no differentiation possible without CTU). Success of ureter contrasting was assessed by measurement of Hounsfield units. Besides benefit for reading urography-enhanced PET/CT, the possible impact on subsequent patient treatment was evaluated.

RESULTS

A number of N.=247 patients were included in this study. By CT urography, it was possible to identify each ureter on low-dose CT, with its major part contrasted. In 120/247 (48.6%) patients, urography increased the diagnostic confidence while providing substantial support for interpretation in 60 (24.3%) cases. In 42 (17.0%) patients, urography was clinically relevant (up-/downstaging) with potential impact on subsequent patient care. In 30 of these 42 cases (12.1% of all), discrepant treatment would have resulted from a misdiagnosed tracer accumulation without urography.

CONCLUSIONS

CT urography benefits the interpretation of [⁶⁸Ga]-PSMA-11 PET/CT with low-dose CT and leads to discrepant patient treatment in a small but significant subset of patients (12% in our cohort). The implementation of CT urography into standard protocols of [⁶⁸Ga]PSMA-11 PET/CT with low-dose CT is recommended.

Bioconjugated chelates based on (methylpyridinyl)tacn: synthesis, 64Cu labeling and in vitro evaluation for prostate cancer targeting

Three new bifunctional copper chelators based on the 1,4,7-triazacyclononane (tacn) platform have been synthesized and conjugated to peptide. The first one is constituted of the tacn with two methylpyridinyl and one methylthiazolyl carboxylic acid pendant arms, while, in the second and third ones, the macrocycle is functionalized by three methylpyridinyl groups, with an additional hexynoic acid chain on a carbon of one or two pyridine rings. These three bifunctional chelators have been conjugated to the antagonist JMV594 peptide for targeting the gastrin releasing peptide receptor (GRP-r), which is overexpressed in prostate cancer. The resulting monomeric bioconjugates have shown their efficiency to be radiolabeled with β+ emitter 64Cu, and the hydrophilicity and PC-3 cell internalisation properties of these radiolabeled conjugates have been studied. PC-3 cell binding affinity of mono- and dimeric metal-free and natCu metallated conjugates have been evaluated by IC50 measurements. The results demonstrate the potential of these methylpyridinyl tacn derivatives for radiopharmaceutical applications.

89Zr-PSMA-617 PET/CT May Reveal Local Recurrence of Prostate Cancer Unidentified by 68Ga-PSMA-11 PET/CT

ABSTRACT

For localization of biochemical recurrence of prostate cancer, 68Ga-PSMA-11 PET/CT imaging was performed in a 66-year-old man with no suspicious findings at 1 hour p.i. Additional 89Zr-PSMA-617 PET/CT revealed a small local recurrence in the prostate bed, facilitating consecutive local therapy. This interesting image points to the potential of PET/CT with 89Zr-labeled PSMA ligands, for example, 89Zr-PSMA-617, for identifying the source of biochemical recurrence despite otherwise negative imaging including conventional PSMA PET/CT.

89Zr-labeled PSMA ligands for pharmacokinetic PET imaging and dosimetry of PSMA-617 and PSMA-I&T: a preclinical evaluation and first in man

RATIONALE

Prolonged in vivo evaluation of PSMA tracers could improve tumor imaging and patient selection for ¹⁷⁷Lu-PSMA-617 and ¹⁷⁷Lu-PSMA-I&T. In this study, we present the radiolabeling method of PSMA-617 and PSMA-I&T with the long-lived positron emitter ⁸⁹Zr to enable PET imaging up to 7 days post-injection. We compared the biodistribution of ⁸⁹Zr-PSMA-617 and ⁸⁹Zr-PSMA-I&T to those of ¹⁷⁷Lu-PSMA-617 and ¹⁷⁷Lu-PSMA-I&T, respectively, in a PSMA⁺ xenograft model. Moreover, we provide the first human ⁸⁹Zr-PSMA-617 images.

MATERIALS AND METHODS

PSMA ligands were labeled with 50-55 MBq [⁸⁹Zr]ZrCl₄ using a two-step labeling protocol. For biodistribution, BALB/c nude mice bearing PSMA⁺ and PSMA^- xenografts received 0.6 µg (0.6-1 MBq) of ⁸⁹Zr-PSMA-617, ⁸⁹Zr-PSMA-I&T, ¹⁷⁷Lu-PSMA-617, or ¹⁷⁷Lu-PSMA-I&T intravenously. Ex vivo biodistribution and PET/SPECT imaging were performed up to 168 h post-injection. Dosimetry was performed from the biodistribution data. The patient received 90.5 MBq ⁸⁹Zr-PSMA-617 followed by PET/CT imaging.

RESULTS

⁸⁹Zr-labeled PSMA ligands showed a comparable ex vivo biodistribution to its respective ¹⁷⁷Lu-labeled counterparts with high tumor accumulation in the PSMA⁺ xenografts. However, using a dose estimation model for ¹⁷⁷Lu, absorbed radiation dose in bone and kidneys differed among the ¹⁷⁷Lu-PSMA and ⁸⁹Zr-PSMA tracers. ⁸⁹Zr-PSMA-617 PET in the first human patient showed high contrast of PSMA expressing tissues up to 48 h post-injection.

CONCLUSION

PSMA-617 and PSMA-I&T were successfully labeled with ⁸⁹Zr and demonstrated high uptake in PSMA⁺ xenografts, which enabled PET up to 168 h post-injection. The biodistribution of ⁸⁹Zr-PSMA-I&T and ⁸⁹Zr-PSMA-617 resembled that of ¹⁷⁷Lu-PSMA-I&T and ¹⁷⁷Lu-PSMA-617, respectively. The first patient ⁸⁹Zr-PSMA-617 PET images were of high quality warranting further clinical investigation.

Early molecular imaging response assessment based on determination of total viable tumor burden in [68Ga]Ga-PSMA-11 PET/CT independently predicts overall survival in [177Lu]Lu-PSMA-617 radioligand therapy

Purpose

In patients with metastatic castration-resistant prostate cancer (mCRPC) treated with prostate-specific membrane antigen-targeted radioligand therapy (PSMA-RLT), the predictive value of PSMA PET/CT-derived response is still under investigation. Early molecular imaging response based on total viable tumor burden and its association with overall survival (OS) was explored in this study.

Methods

Sixty-six mCRPC patients who received [¹⁷⁷Lu]Lu-PSMA-617 RLT within a prospective patient registry (REALITY Study, NCT04833517) were analyzed. Patients received a [⁶⁸Ga]Ga-PSMA-11 PET/CT scan before the first and after the second cycle of PSMA-RLT. Total lesion PSMA (TLP) was determined by semiautomatic whole-body tumor segmentation. Molecular imaging response was assessed by change in TLP and modified PERCIST criteria. Biochemical response was assessed using standard serum PSA and PCWG3 criteria. Both response assessment methods and additional baseline parameters were analyzed regarding their association with OS by univariate and multivariable analysis.

Results

By molecular imaging, 40/66 (60.6%) patients showed partial remission (PR), 19/66 (28.7%) stable disease (SD), and 7/66 (10.6%) progressive disease (PD). Biochemical response assessment revealed PR in 34/66 (51.5%) patients, SD in 20/66 (30.3%), and PD in 12/66 (18.2%). Response assessments were concordant in 49/66 (74.3%) cases. On univariate analysis, both molecular and biochemical response (p = 0.001 and 0.008, respectively) as well as two baseline characteristics (ALP and ECOG) were each significantly associated with OS. The median OS of patients showing molecular PR was 24.6 versus 10.7 months in the remaining patients (with SD or PD). On multivariable analysis molecular imaging response remained an independent predictor of OS (p = 0.002), eliminating biochemical response as insignificant (p = 0.515).

Conclusion

The new whole-body molecular imaging–derived biomarker, early change of total lesion PSMA (TLP), independently predicts overall survival in [¹⁷⁷Lu]Lu-PSMA-617 RLT in mCRPC, outperforming conventional PSA-based response assessment. TLP might be considered a more distinguished and advanced biomarker for monitoring PSMA-RLT over commonly used serum PSA.

177 Lu-PSMA-617 radioligand therapy of metastatic castration-resistant prostate cancer: Initial 254-patient results from a prospective registry (REALITY Study)

Purpose

Preliminary data from retrospective analyses and recent data from large randomized controlled trials suggest safety and efficacy of radioligand therapy (RLT) targeting prostate-specific membrane antigen (PSMA) in men with metastatic castration-resistant prostate cancer (mCRPC). Limited data on this modality have been published regarding large samples treated in everyday practice.

Methods

We analyzed prospectively collected registry data regarding lutetium-177 (¹⁷⁷Lu)-PSMA-617 RLT of 254 consecutive men with mCRPC seen in everyday academic practice. Since ¹⁷⁷Lu-PSMA-617 was experimental salvage treatment following failure of individually appropriate conventional therapies, patients were generally elderly and heavily pretreated (median age 70 years; prior taxanes 74.0%, 188/254), with late–end-stage disease (visceral metastasis in 32.7%, 83/254). Primary endpoints were response to RLT, defined by changes from baseline serum prostate-specific antigen (PSA) concentration, PSA progression-free survival (PSA-PFS), and overall survival (OS), estimated with Kaplan–Meier statistics, and caregiver-reported and patient-reported safety. Unless noted, median (minimum–maximum) values are given.

Results

Patients received 3 (1–13) ¹⁷⁷Lu-PSMA-617 activities (6.5 [2.5–11.6] GBq/cycle) every 5.7 (3.0–11.0) weeks. Best response was ≥ 50% PSA reduction in 52.0% of patients (132/254). PSA-PFS was 5.5 (95% confidence interval [95%CI] 4.4–6.6) months and OS, 14.5 (95%CI 11.5–17.5) months. In multivariable Cox proportional-hazards modeling, response to the initial ≤ 2 RLT administrations was the strongest significant prognosticator related to OS (hazard ratio 3.7 [95%CI 2.5–5.5], p < 0.001). No RLT-related deaths or treatment discontinuations occurred; the most frequent RLT-related Grade 3/4 adverse events were anemia (18/254 patients, 7.1%), thrombocytopenia (11/254, 4.3%), and lymphopenia (7/254, 2.8%). RLT-related xerostomia, all grade 1/2, was noted in 53/254 (20.9%).

Conclusions

In a large, prospectively observed “real-world” cohort with late-stage/end-stage mCRPC and conventional treatment failure, ¹⁷⁷Lu-PSMA-617 RLT was effective, safe, and well-tolerated. Early biochemical disease control by such therapy was associated with better OS. Prospective study earlier in the disease course may be warranted.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05525-7.

Response Assessment and Prediction of Progression-Free Survival by 68Ga-PSMA-11 PET/CT Based on Tumor-to-Liver Ratio (TLR) in Patients with mCRPC Undergoing 177Lu-PSMA-617 Radioligand Therapy

At present, little is known about the molecular imaging-based response assessment of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy with ¹⁷⁷Lutetium (¹⁷⁷Lu-PSMA-617 RLT) in metastatic castration-resistant prostate cancer (mCRPC). Our study evaluated the response to RLT using both molecular imaging and biochemical response assessments, and their potential prediction of progression-free survival (PFS). Fifty-one consecutive patients given two cycles of RLT at 6-week intervals were analyzed retrospectively. ⁶⁸Ga-PSMA-11 PET/CT was obtained about 2 weeks prior to the first and 4–6 weeks after the second cycle. Molecular imaging-based response using SUV_peak and tumor-to-liver ratio (TLR) was determined by modified PERCIST criteria. ∆TLR and ∆SUV were significantly correlated with ∆PSA (p < 0.001, each). After a median follow-up of 49 months, the median PFS (95% CI) was 8.0 (5.9–10.1) months. In univariate analysis, responders showing partial remission (PR_PSA and PR_TLR) had significantly (p < 0.001, each) longer PFS (median: 10.5 and 9.3 months) than non-responders showing either stable or progressive disease (median: 4.0 and 3.5 months). Response assessment using SUV_peak failed to predict survival. In multivariable analysis, response assessment using TLR was independently associated with PFS (p < 0.001), as was good performance status (p = 0.002). Molecular imaging-based response assessment with ⁶⁸Ga-PSMA-11 PET/CT using normalization of the total lesion PSMA over healthy liver tissue uptake (TLR) could be an appropriate biomarker to monitor RLT in mCRPC patients and to predict progression-free survival (PFS) of this treatment modality.

Efficacy and Safety of [225Ac]Ac-PSMA-617 Augmented [177Lu]Lu-PSMA-617 Radioligand Therapy in Patients with Highly Advanced mCRPC with Poor Prognosis

The use of ²²⁵Ac in prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT), either as monotherapy or in combination with ¹⁷⁷Lu, is a promising therapy approach in patients with metastatic castration-resistant prostate carcinoma (mCRPC). In this study, we report the efficacy and safety of [²²⁵Ac]Ac-PSMA-617 augmented [¹⁷⁷Lu]Lu-PSMA-617 RLT in ¹⁷⁷Lu-naive mCRPC patients (n = 15) with poor prognosis (presence of visceral metastases, high total tumor burden with diffuse bone metastases or a short PSA doubling time of <2 months). Biochemical (by PSA serum value) and molecular imaging response (by [⁶⁸Ga]Ga-PSMA-11 PET/CT) was assessed after two cycles of [¹⁷⁷Lu]Lu-PSMA-617 RLT, with at least one [²²⁵Ac]Ac-PSMA-617 augmentation. In addition, PSA-based progression-free survival (PSA-PFS), overall survival (OS) and toxicity (according to CTCAE) were analyzed. We observed a biochemical- and molecular imaging-based partial remission in 53.3% (8/15) and 66.7% (10/15) of patients, respectively. The median PSA-PFS and OS was 9.1 and 14.8 months, respectively. No serious acute adverse events were recorded. Two out of fifteen patients experienced grade 3 anemia. No other grade 3/4 toxicities were observed. RLT-related xerostomia (grade 1/2) was recorded in 2/15 patients. Our data showed a high clinical efficacy with a favorable side effects profile of [²²⁵Ac]Ac-PSMA-617 augmented [¹⁷⁷Lu]Lu-PSMA-617 RLT in this highly challenging patient cohort.

Comparison of different methods for post-therapeutic dosimetry in [177Lu]Lu-PSMA-617 radioligand therapy

Background

Dosimetry is of high importance for optimization of patient-individual PSMA-targeted radioligand therapy (PSMA-RLT). The aim of our study was to evaluate and compare the feasibility of different approaches of image-based absorbed dose estimation in terms of accuracy and effort in clinical routine.

Methods

Whole-body planar images and SPECT/CT images were acquired from 24 patients and 65 cycles at 24h, 48h, and ≥96h after administration of a mean activity of 6.4 GBq [¹⁷⁷Lu]Lu-PSMA-617 (range 3–10.9 GBq). Dosimetry was performed by use of the following approaches: 2D planar-based dosimetry, 3D SPECT/CT-based dosimetry, and hybrid dosimetry combining 2D and 3D data. Absorbed doses were calculated according to IDAC 2.1 for the kidneys, the liver, the salivary glands, and bone metastases.

Results

Mean absorbed doses estimated by 3D dosimetry (the reference method) were 0.54 ± 0.28 Gy/GBq for the kidneys, 0.10 ± 0.05 Gy/GBq for the liver, 0.81 ± 0.34 Gy/GBq for the parotid gland, 0.72 ± 0.39 Gy/GBq for the submandibular gland, and 1.68 ± 1.32 Gy/GBq for bone metastases. Absorbed doses of normal organs estimated by hybrid dosimetry showed small, non-significant differences (median up to 4.0%) to the results of 3D dosimetry. Using 2D dosimetry, in contrast, significant differences (median up to 10.9%) were observed. Regarding bone metastases, small, but significant differences (median up to 7.0%) of absorbed dose were found for both, 2D dosimetry and hybrid dosimetry. Bland-Altman analysis revealed high agreement between hybrid dosimetry and 3D dosimetry for normal organs and bone metastases, but substantial differences between 2D dosimetry and 3D dosimetry.

Conclusion

Hybrid dosimetry provides high accuracy in estimation of absorbed dose in comparison to 3D dosimetry for all important organs and is therefore feasible for use in individualized PSMA-RLT.

Molecular imaging and biochemical response assessment after a single cycle of [225Ac]Ac-PSMA-617/[177Lu]Lu-PSMA-617 tandem therapy in mCRPC patients who have progressed on [177Lu]Lu-PSMA-617 monotherapy

Rationale: Despite the promising results of prostate-specific membrane antigen (PSMA)-targeted ¹⁷⁷Lu radioligand therapy in metastatic castration-resistant prostate carcinoma (mCRPC), some patients do not respond and other patients with initially good response develop resistance to this treatment. In this study, we investigated molecular imaging and biochemical responses after a single cycle of [²²⁵Ac]Ac-PSMA-617/[¹⁷⁷Lu]Lu-PSMA-617 tandem therapy in patients who had progressed on [¹⁷⁷Lu]Lu-PSMA-617 monotherapy.

Methods: Seventeen patients with mCRPC were included in a retrospective, monocenter study. Molecular imaging-based response was assessed by modified PERCIST criteria using the whole-body total lesion PSMA (TLP) and molecular tumour volume (MTV) derived from [⁶⁸Ga]Ga-PSMA-11 PET/CT. Biochemical response was evaluated according to PCWG3 criteria using the prostate-specific antigen (PSA) serum value. Concordance and correlation statistics as well as survival analyses were performed.

Results: Based on the molecular imaging-based response assessment, 5 (29.4%) patients showed partial remission and 7 (41.2%) had stable disease. The remaining 5 (29.4%) patients had further progression, four with an increase in TLP/MTV of >30% and one with stable TLP/MTV but appearance of new metastases. Based on the biochemical response assessment, 5 (29.4%), 8 (47.1%), and 4 (23.5%) patients showed partial remission, stable disease, and progressive disease, respectively. A comparison of the response assessment methods showed a concordance of 100% (17/17) between TLP and MTV and 70.6% (12/17) between TLP/MTV and PSA. Patients with partial remission, independently assessed by each method, had better overall survival (OS) than patients with either stable or progressive disease. The difference in OS was statistically significant for the molecular imaging response assessment (median OS not reached vs. 8.3 m, p = 0.044), but not for the biochemical response assessment (median OS 18.1 m vs. 9.4 m, p = 0.468).

Conclusion: Based on both assessment methods, [²²⁵Ac]Ac-PSMA-617/[¹⁷⁷Lu]Lu-PSMA-617 tandem therapy is an effective treatment for the highly challenging cohort of patients with mCRPC who have progressed on [¹⁷⁷Lu]Lu-PSMA-617 monotherapy. Molecular imaging response and biochemical PSA response were mostly concordant, though a considerable number of cases (29.4%) were discordant. Molecular imaging response reflecting the change in total viable tumour burden appears to be superior to PSA change in estimating survival outcome after tandem therapy.

Neuron-specific enolase has potential value as a biomarker for [18F]FDG/[68Ga]Ga-PSMA-11 PET mismatch findings in advanced mCRPC patients

BACKGROUND

PSMA-targeted radioligand therapy (PSMA-RLT) yielded impressive results in the metastasized castration-resistant prostate carcinoma (mCRPC) setting. High expression of PSMA is essential for successful PSMA-RLT. However, some patients develop [18F]FDG-avid lesions with low or no PSMA expression ([18F]FDG/[68Ga]Ga-PSMA-11 mismatch findings on PET/CT) in the course of treatment. Those lesions are not affected by PSMA-RLT and a change in therapy management is needed. To enable early mismatch detection, possible blood parameters as indicators for the occurrence of [18F]FDG/[68Ga]Ga-PSMA-11 mismatch findings on PET/CT were evaluated.

METHODS

Retrospective study of N = 66 advanced mCRPC patients with dual [68Ga]Ga-PSMA-11 and [18F]FDG PET/CT imaging within 4 weeks, who were referred for or received [177Lu]Lu-PSMA-617 radioligand therapy. Prostate-specific antigen (PSA), neuron-specific enolase (NSE), gamma-glutamyltransferase (GGT), and alkaline phosphatase (ALP) were tested as indicators for the occurrence of [18F]FDG/[68Ga]Ga-PSMA-11 mismatch findings. Additional to absolute values, relative changes (ΔPSA, ΔNSE, ΔGGT, ΔALP) over a period of 4 ± 1 weeks prior to [18F]FDG PET/CT were analyzed.

RESULTS

In total, 41/66 (62%) patients revealed at least one [18F]FDG/[68Ga]Ga-PSMA-11 mismatch finding on PET/CT. These mismatch findings were detected in 13/41 (32%) patients by screening for and in 28/41 (68%) patients during PSMA-RLT. NSE serum level (55.4 ± 44.6 μg/l vs. 18.5 ± 8 μg/l, p < 0.001) and ΔNSE (93.8 ± 124.5% vs. 2.9 ± 39.5%, p < 0.001) were significantly higher in the mismatch group than in the non-mismatch group. No significant differences were found for serum PSA (p = 0.424), ΔPSA (p = 0.417), serum ALP (p = 0.937), ΔALP (p = 0.611), serum GGT (p = 0.773), and ΔGGT (p = 0.971). For NSE and ΔNSE, the maximum value of the Youden index in ROC analysis was at a cut-off level of 26.8 μg/l (sensitivity 78%, specificity 96%) and at + 13.9% (sensitivity 84%, specificity 75%), respectively. An introduced scoring system of both parameters achieved a sensitivity of 90% and a specificity of 88% for the occurrence of [18F]FDG/[68Ga]Ga-PSMA-11 mismatch.

CONCLUSION

We observed a significantly higher absolute serum concentration and a higher relative increase of NSE in advanced mCRPC patients with [18F]FDG-avid and insufficient PSMA expressing metastases ([18F]FDG/[68Ga]Ga-PSMA-11 mismatch findings on PET/CT) in our cohort. NSE might be used as a potential laboratory indicator for [18F]FDG/[68Ga]Ga-PSMA-11 mismatch findings, if this observation is confirmed in future, ideally prospective, studies in larger patient cohorts.

Response and outcome of liver metastases in patients with metastatic castration-resistant prostate cancer (mCRPC) undergoing 177Lu-PSMA-617 radioligand therapy

PURPOSE

Little is known about the efficacy of prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) against liver metastases of metastatic castration-resistant prostate cancer (mCRPC). We retrospectively analyzed efficacy-related outcomes of ¹⁷⁷Lu-PSMA-617 RLT in this setting and potential predictors of those outcomes.

METHODS

Twenty-eight consecutive mCRPC patients with liver metastases given ¹⁷⁷Lu-PSMA-617 RLT were analyzed retrospectively. Their planned regimen was 4-6 cycles at 6 ± 2-week intervals; the mean activity/cycle was 6.5 ± 0.5 GBq. Hepatic response was determined by modified positron emission tomography response criteria in solid tumors; association of such response with overall survival (OS) was tested, as were relationships of the selected patient, disease, and treatment characteristics with hepatic progression-free survival (PFS_hep) and OS. Survival analyses used Kaplan-Meier curves, log-rank test at p < 0.05 significance, and Cox proportional-hazards modeling.

RESULTS

Median (minimum-maximum) follow-up was 37.5 (2.3-50.6) months. In liver metastases, complete or partial response was observed in 6 patients (21%) each, and stable disease in 1 (4%), for hepatic disease control in 46%. Overall, median (95% confidence interval) PFS_hep was 5.7 (2.2-9.2) months, and OS, 11.7 (3.0-20.4) months. Patients with hepatic disease control did not reach the median OS, while those with hepatic progressive disease had median OS (95% confidence interval) of 6.4 (1.6-11.1) months. In multivariate analysis, hepatic disease control by ¹⁷⁷Lu-PSMA-617 RLT was significantly independently associated with OS, as was a prostate-specific antigen decline of ≥ 50% after 2 RLT cycles, and good baseline performance status (Eastern Cooperative Oncology Group 0-1). Hepatic tumor burden (≤ 25% vs. > 25% of liver volume) had no apparent relationship with hepatic tumor response, PFS_hep, or OS.

CONCLUSION

¹⁷⁷Lu-PSMA-617 RLT frequently controlled liver metastases, resulting in long PFS_hep and significantly improved OS. Hepatic tumor burden appeared to lack any relationship with treatment efficacy, supporting ¹⁷⁷Lu-PSMA-617 RLT of late-stage/end-stage mCRPC with liver metastases.

Results from extended lymphadenectomies with [111In]PSMA-617 for intraoperative detection of PSMA-PET/CT-positive nodal metastatic prostate cancer

Purpose

Identification of suspicious PSMA-PET/CT-positive lymph node (LN) metastases (LNM) from prostate cancer (PCa) during lymphadenectomy (LA) is challenging. We evaluated an ¹¹¹In-labelled PSMA ligand (DKFZ-617, referred to as [¹¹¹In]PSMA-617) as a γ-emitting tracer for intraoperative γ-probe application for resected tissue samples in PCa patients. Forty-eight hours prior to LA, [¹¹¹In]PSMA-617 was administered intravenously in 23 patients with suspected LNM on PSMA-PET/CT (n = 21 with biochemical relapse, n = 2 at primary therapy). Resected tissue samples (LN, LNM and fibrofatty tissue) were measured ex situ by a γ-probe expressed as counts per second (CPS_norm). [¹¹¹In]PSMA-617 tissue sample uptake was measured by a germanium detector for verification and calculated as %IA_lbm (percent injected activity per kilogram lean body mass at time of surgery). Based on a clinical requirement for a specificity > 95%, thresholds for both ex situ measurements were chosen accordingly. Correlation of the results from PET/CT, γ-probe and germanium detector with histopathology was done.

Results

Eight hundred sixty-four LNs (197 LNM) were removed from 275 subregions in 23 patients, on average 8.6 ± 14.9 LNM per patient. One hundred four of 275 tissue samples showed cancer. Median γ-probe and germanium detector results were significantly different between tumour-affected (33.5 CPS_norm, 0.71 %IA_lbm) and tumour-free subregions (3.0 CPS_norm, 0.03 %IA_lbm) (each p value < 0.0001). For the chosen γ-probe cut-off (CPS_norm > 23) and germanium detector cut-off (%IA_lbm > 0.27), 64 and 74 true-positive and 158 true-negative samples for both measurements were identified. Thirty-nine and 30 false-negative and 6 and 5 false-positive tissue samples were identified by γ-probe and germanium detector measurements.

Conclusion

[¹¹¹In]PSMA-617 application for LA is feasible in terms of an intraoperative real-time measurement with a γ-probe for detection of tumour-affected tissue samples. γ-probe results can be confirmed by precise germanium detector measurements and were significantly different between tumour-affected and tumour-free samples.

225Ac-PSMA-617/177Lu-PSMA-617 tandem therapy of metastatic castration-resistant prostate cancer: pilot experience

PURPOSE

Up to 30% of patients with prostate-specific membrane antigen (PSMA)-positive metastatic castration-resistant prostate cancer (mCRPC) never respond or develop resistance to ¹⁷⁷Lu-labeled PSMA-targeted radioligand monotherapy. Single-agent PSMA-targeted radioligand therapy (PRLT) with the alpha-emitter ²²⁵Ac showed promise against mCRPC but may cause severe and/or persistent xerostomia, which may substantially impair patients' quality-of-life. We hypothesized that when ¹⁷⁷Lu-PSMA ligand alone is ineffective, tandem therapy with low-activity ²²⁵Ac-PSMA ligand plus full activity of the beta emitter may enhance efficacy while minimizing xerostomia severity.

METHODS

We retrospectively analyzed pilot experience with 1 course of ²²⁵Ac-PSMA-617/¹⁷⁷Lu-PSMA-617 tandem therapy in our first 20 patients with mCRPC receiving this intervention after insufficiently responding to ¹⁷⁷Lu-PSMA-617 monotherapy. This cohort had late-stage/end-stage disease with high baseline prostate-specific antigen (PSA) concentration (median 215 ng/mL), heavy pre-treatment (abiraterone and/or enzalutamide, and ¹⁷⁷Lu-PRLT [median cumulative activity, 26.3 GBq] in 20/20 patients, 100%; docetaxel and/or cabazitaxel in 13/20 patients, 65%), and frequent Eastern Cooperative Oncology Group performance status of 2 (8/20 patients, 40%).

RESULTS

Median (minimum-maximum) administered activities were ²²⁵Ac-PSMA-617, 5.3 (1.5-7.9) MBq, and ¹⁷⁷Lu-PSMA-617, 6.9 (5.0-11.6) GBq. Significant responders to tandem therapy received ¹⁷⁷Lu-PSMA-617 monotherapy as maintenance (median [minimum-maximum]: 1 [0-5] cycle). After a median (minimum-maximum) 22 (14-63) weeks' follow-up, 13/20 patients (65%) had as best biochemical response a PSA decline > 50%. Median (95% confidence interval) progression-free survival was 19 (12-26) weeks, and overall survival was 48 (4-92) weeks post-tandem therapy administration. Xerostomia was reported as grade 1 (very mild) in 8/20 patients (40%), grade 2 (mild) in 5/20 (25%), and grade 3/4 in 0/20.

CONCLUSIONS

Our results suggest that a single course of tandem therapy with low-activity ²²⁵Ac-PSMA-617/full-activity ¹⁷⁷Lu-PSMA-617 may safely enhance response to PRLT in men with late-stage/end-stage mCRPC while minimizing xerostomia severity. Formal study of this combination is warranted.

Oncogenic JAK2V617F causes PD-L1 expression, mediating immune escape in myeloproliferative neoplasms

Recent evidence has revealed that oncogenic mutations may confer immune escape. A better understanding of how an oncogenic mutation affects immunosuppressive programmed death ligand 1 (PD-L1) expression may help in developing new therapeutic strategies. We show that oncogenic JAK2 (Janus kinase 2) activity caused STAT3 (signal transducer and activator of transcription 3) and STAT5 phosphorylation, which enhanced PD-L1 promoter activity and PD-L1 protein expression in JAK2^V617F-mutant cells, whereas blockade of JAK2 reduced PD-L1 expression in myeloid JAK2^V617F-mutant cells. PD-L1 expression was higher on primary cells isolated from patients with JAK2^V617F-myeloproliferative neoplasms (MPNs) compared to healthy individuals and declined upon JAK2 inhibition. JAK2^V617F mutational burden, pSTAT3, and PD-L1 expression were highest in primary MPN patient-derived monocytes, megakaryocytes, and platelets. PD-1 (programmed death receptor 1) inhibition prolonged survival in human MPN xenograft and primary murine MPN models. This effect was dependent on T cells. Mechanistically, PD-L1 surface expression in JAK2^V617F-mutant cells affected metabolism and cell cycle progression of T cells. In summary, we report that in MPN, constitutive JAK2/STAT3/STAT5 activation, mainly in monocytes, megakaryocytes, and platelets, caused PD-L1-mediated immune escape by reducing T cell activation, metabolic activity, and cell cycle progression. The susceptibility of JAK2^V617F-mutant MPN to PD-1 targeting paves the way for immunomodulatory approaches relying on PD-1 inhibition.

Combination treatment with hypofractionated radiotherapy plus IL-2/anti-IL-2 complexes and its theranostic evaluation

Background

Immunogenic radiotherapy (RT) can act synergistically with immune checkpoint blockers (ICBs). However, alternatives are needed for non-responding patients and those with pre-existing or ICB-induced autoimmune symptoms. Combination of RT with IL-2 could be an alternative. But IL-2 has a short half-life, and, by binding to its high-affinity receptor, it strongly stimulates immunosuppressive CD4+ Tregs and seems to promote potentially life-threatening vascular leakage. IL-2/anti-IL-2 complexes (IL-2c), which bind to the low-affinity receptor, have been reported to circumvent these disadvantages but they have not yet been thoroughly tested in conjunction with radiotherapy.

Methods

We evaluated, in three mouse models, the antitumoral effects induced by hypofractionated RT (hRT) plus IL-2c. We also used non-invasive imaging with a newly developed PET tracer based on therapeutically active IL-2c and a PD-L1 PET tracer for the theranostic evaluation of the treatment and its side effects.

Results

Treatment of mice bearing established B16 melanomas with hRT + IL-2c was superior to hRT + uncomplexed IL-2 or hRT alone; IL-2c alone was not effective. hRT + IL-2c was also synergistic in mice bearing C51 colon carcinomas or 4T1 mammary carcinomas. The better antitumor response correlated with increased tumor-specific CD8+ T cells and NK cells, but not CD4+ Tregs, in the irradiated tumor and in lymphoid organs. With the new PET tracer, we visualized the whole-body distribution of IL-2c and the bound receptors in naïve mice and tumor-bearing mice. Surprisingly, the tumor uptake was non-specific and only moderate. This prompted experiments demonstrating that specific IL-2c binding in the tumor is limited by IL-2 secreted by tumor-resident effector cells and that extratumorally expanded T and NK cells can infiltrate the irradiated tumor, which suggests that systemic immune activation considerably contributed to the reduction of tumor growth. Lastly, we show that a side effect of IL-2c treatment – a quite dramatic non-specific expansion of CD8+ T and NK cells – is only transient, and we visualized the associated splenomegaly as well as side effects on liver and lung by contrast-enhanced CT and PD-L1 PET.

Conclusions

Our results show that the combination of immunogenic RT with IL-2c that are directed towards the low-affinity IL-2 receptor can be synergistic and more effective than the combination with uncomplexed IL-2. In addition, our theranostic evaluation provided insights into the mechanism of action and the side effects of IL-2c treatment.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0537-9) contains supplementary material, which is available to authorized users.

Performance of 111In-labelled PSMA ligand in patients with nodal metastatic prostate cancer: correlation between tracer uptake and histopathology from lymphadenectomy

PURPOSE

Intraoperative identification of lymph node (LN) metastases (LNM) detected on preoperative PSMA PET/CT may be facilitated by PSMA radioguided surgery with the use of a gamma probe. We evaluated the uptake of ¹¹¹In-labelled PSMA ligand DKFZ-617 (referred to as ¹¹¹In-PSMA-617) in unaffected LN and LNM at the level of single LN.

METHODS

Six patients with prostate cancer (PCa) with suspicion of LNM on preoperative PSMA PET/CT underwent ¹¹¹In-PSMA-617-guided lymphadenectomy (LA; four salvage LA and two primary LA). ¹¹¹In-PSMA-617 (109 ± 5 MBq). was injected Intravenously 48 h prior to surgery Template LAs were performed in small subregions: common, external, obturator and internal iliac vessels, and presacral and retroperitoneal subregions (n = 4). Samples from each subregion were isolated aiming at the level of single LN. Uptake was measured ex situ using a germanium detector. Receiver operating characteristic (ROC) analysis was performed based on ¹¹¹In-PSMA-617 uptake expressed as standardized uptake values normalized to lean body mass (SUL).

RESULTS

Overall 310 LN (mean 52 ± 19.7) were removed from 74 subregions (mean 12 ± 3.7). Of the 310 LN, 35 turned out to be LNM on histopathology. Separation of the samples from all subregions resulted in 318 single specimens: 182 PCa-negative LN samples with 275 LN, 35 single LNM samples, 3 non-nodal PCa tissue samples and 98 fibrofatty tissue samples. The median SULs of nonaffected LN (0.16) and affected LN (13.2) were significantly different (p < 0.0001). Based on 38 tumour-containing and 182 tumour-free specimens, ROC analysis revealed an area under the curve of 0.976 (95% CI 0.95-1.00, p < 0.0001). Using a SUL cut-off value of 1.136, sensitivity, specificity, positive predictive value, negative predictive value and accuracy in discriminating affected from nonaffected LN were 92.1% (35/38), 98.9% (180/182), 94.6% (35/37), 98.4% (180/183) and 97.7% (215/220), respectively.

CONCLUSION

Ex situ analysis at the level of single LN showed that ¹¹¹In-PSMA-617 had excellent ability to discriminate between affected and nonaffected LN in our patients with PCa. This tracer characteristic is a prerequisite for in vivo real-time measurements during surgery.

Radiochemistry and Preclinical PET Imaging of 68Ga-Desferrioxamine Radiotracers Targeting Prostate-Specific Membrane Antigen

Radiotracers incorporating the urea-based Glu-NH-C(O)-NH-Lys group have gained prominence due to their role in targeting prostate-specific membrane antigen (PSMA)-a clinical biomarker of prostate cancer. Here, the synthesis, radiolabeling, and in vitro and in vivo characterization of two ⁶⁸Ga-radiolabeled Glu-NH-C(O)-NH-Lys radiotracers conjugated to the desferrioxamine B (DFO) chelate were evaluated. Two linker groups based on amide bond and thiourea coupling chemistries were employed to develop ⁶⁸Ga-DFO-Nsucc-PSMA (⁶⁸Ga-4) and ⁶⁸Ga-DFO- pNCS-Bn-PSMA (⁶⁸Ga-7), respectively. Radiosynthesis proceeded quantitatively at room temperature with high radiochemical yields, chemical/radiochemical purities, and specific activities. Pharmacokinetic profiles of ⁶⁸Ga-4 and ⁶⁸Ga-7 were assessed using positron-emission tomography (PET) in mice bearing subcutaneous LNCaP tumors. Data were compared to the current clinical benchmark radiotracer ⁶⁸Ga-HBED-CC-PSMA (⁶⁸Ga-1) (HBED = N,N'-Bis(2-hydroxy-5-(ethylene-beta-carboxy)benzyl)ethylenediamine N,N'-diacetic acid). Results indicated that the target binding affinity, protein association, blood pool and background organ clearance properties, and uptake in PSMA-positive lesions are strongly dependent on the nature of the chelate, the linker, and the spacer groups. Protein dissociation constants ( K_d values) were found to be predictive of pharmacokinetics in vivo. Compared to ⁶⁸Ga-1, ⁶⁸Ga-4 and ⁶⁸Ga-7 resulted in decreased tumor uptake but enhanced blood pool clearance and reduced residence time in the kidney. The study highlights the importance of maximizing protein binding affinity during radiotracer optimization.

Gastrin-releasing Peptide Receptor Imaging in Breast Cancer Using the Receptor Antagonist (68)Ga-RM2 And PET

Introduction: The gastrin-releasing peptide receptor (GRPR) is overexpressed in breast cancer. The present study evaluates GRPR imaging as a novel imaging modality in breast cancer by employing positron emission tomography (PET) and the GRPR antagonist ⁶⁸Ga-RM2.

Methods: Fifteen female patients with biopsy confirmed primary breast carcinoma (3 bilateral tumors; median clinical stage IIB) underwent ⁶⁸Ga-RM2-PET/CT for pretreatment staging. In vivo tumor uptake of ⁶⁸Ga-RM2 was correlated with estrogen (ER) and progesterone (PR) receptor expression, HER2/neu status and MIB-1 proliferation index in breast core biopsy specimens.

Results: 13/18 tumors demonstrated strongly increased ⁶⁸Ga-RM2 uptake compared to normal breast tissue (defined as PET-positive). All PET-positive primary tumors were ER- and PR-positive (13/13) in contrast to only 1/5 PET-negative tumors. Mean SUV_MAX of ER-positive tumors was 10.6±6.0 compared to 2.3±1.0 in ER-negative tumors (p=0.016). In a multivariate analysis including ER, PR, HER2/neu and MIB-1, only ER expression predicted ⁶⁸Ga-RM2 uptake (model: r²=0.55, p=0.025). Normal breast tissue showed inter- and intraindividually variable, moderate GRPR binding (SUV_MAX 2.3±1.0), while physiological uptake of other organs was considerably less except pancreas. Of note, ⁶⁸Ga-RM2-PET/CT detected internal mammary lymph nodes with high ⁶⁸Ga-RM2 uptake (n=8), a contralateral axillary lymph node metastasis (verified by biopsy) and bone metastases (n=1; not detected by bone scan and CT).

Conclusion: Our study demonstrates that ⁶⁸Ga-RM2-PET/CT is a promising imaging method in ER-positive breast cancer. In vivo GRPR binding assessed by ⁶⁸Ga-RM2-PET/CT correlated with ER expression in primary tumors of untreated patients.

[μ-N,N,N′,N′-Tetrakis(2-pyridylmethyl)butane-1,4-diamine]bis[dibromidocopper(II)]

The title dinuclear copper complex, [Cu₂Br₄(C₂₈H₃₂N₆)], is located on an inversion center. The unique Cu^II ion is in a slightly distorted square-pyramidal environment in which the N atoms of a dipicolyl­amine group and a bromide ligand form the basal plane. The apical site is occupied by a second Br atom. While the Cu—N distances involving the pyridine N atoms are the same within experimental error, the Cu—N distance involving the tertiary N atom is slightly elongated. Due to the typical Jahn–Teller distortion of copper(II) complexes, the apical Cu—Br distance is elongated.

[μ-N,N,N',N'-Tetra-kis(2-pyridyl-meth-yl)butane-1,4-diamine]-bis-[dichlorido-copper(II)] trihydrate

The title dinuclear copper complex, [Cu₂Cl₄(C₂₈H₃₂N₆)]·3H₂O, is located on a crystallographic inversion center. The unique Cu^II ion is coordinated in a slightly distorted square-pyramidal environment in which the N atoms of the dipicolyl­amine group and a chloride ligand form the basal plane. The apical position is occupied by a second chloride atom. While the Cu—N distances of the pyridine N atoms are the same within expermental error, the Cu—N distance to the tertiary N atom is slightly elongated. The apical Cu—Cl distance is elongated due to typical Jahn–Teller distortion. One of the water O atoms was refined as disordered over two sites with occupancies 0.734 (17):0.266 (17) and another with half occupancy. H atoms for the disordered solvent atoms were not included in the refinement.

[μ-N,N,N',N'-Tetra-kis(2-pyridyl-meth-yl)butane-1,4-diamine]-bis-[dinitratocadmium(II)]

The title dinuclear cadmium complex, [Cd₂(NO₃)₄(C₂₈H₃₂N₆)], is located on an inversion center. The unique Cd^II ion displays a 5 + 2 coordination. A distorted square-pyramidal geometry is formed by the dipicolyl­amine group of the ligand via the N atoms in a meridional fashion and two O atoms of the nitrate ligands with short Cd—O distances. The coordination is completed by two loosely bound O atoms of the nitrate ligands.

[μ-N,N,N',N'-Tetra-kis-(2-pyridyl-meth-yl)pentane-1,5-diamine]-bis-[dichlorido-copper(II)] sesquihydrate

In the title dinuclear copper complex, [Cu(2)Cl(4)(C(29)H(34)N(6))]·1.5H(2)O, both Cu(II) ions are coordinated in a slightly distorted square-pyramidal environment in which the N atoms of the dipicolyl-amine group and a chloride ligand form the basal plane. The apical position is occupied by a second chloride atom. The Cu-N distances involving the pyridine N atoms differ slightly from each other and the Cu-N distance involving the tertiary N atom is the longest. The apical Cu-Cl distance is elongated compared to its basal counterpart due to typical Jahn-Teller distortion. In the crystal structure, complex and water mol-ecules are linked via inter-molecular O-H⋯O and O-H⋯Cl hydrogen bonds into chains along [001]. One of the water mol-ecules was refined with half occupancy.

[μ-N,N,N',N'-Tetra-kis(2-pyridyl-meth-yl)butane-1,4-diamine]-bis-[diacetato-cadmium(II)] nona-hydrate

The title dinuclear complex, [Cd₂(CH₃CO₂)₄(C₂₈H₃₂N₆)]·9H₂O, is located on a crystallographic inversion center. The unique Cd^II ion displays a 5 + 2 coordination. A distorted square-pyramidal geometry is formed by the dipicolyl­amine unit of the ligand via the N atoms in a meridional fashion and two O atoms of the acetate ligands with short Cd—O distances. The coordination is completed by two loosely bound O atoms of the acetate ligands. The Cd—N distances involving the pyridine N atoms differ slightly from each other and the Cd—N distance involving the tertiary N atom is the longest. In the crystal structure, complex mol­ecules and solvent water mol­ecules are connected into a three-dimensional network via inter­molecular O—H⋯O hydrogen bonds. One of the water mol­ecules lies on a twofold rotation axis.