Cutaneous Metastasis From Prostate Cancer on Posttherapeutic 177 Lu-Prostate-Specific Membrane Antigen Scan

ABSTRACT

In this note, we aim to present a patient with a known case of prostate cancer with widespread metastasis to the skeleton and liver who has undergone several cycles of chemoradiotherapy. The patient received 2 doses of 177 Lu-prostate-specific membrane antigen therapy, in which several zones of uptake were detected on the thoracic wall compatible with cutaneous metastatic lesions of prostate cancer.

Advances in Radioligand Theranostics in Oncology

Theranostics with radioligands (radiotheranostics) has played a pivotal role in oncology. Radiotheranostics explores the molecular targets expressed on tumor cells to target them for imaging and therapy. In this way, radiotheranostics entails non-invasive demonstration of the in vivo expression of a molecular target of interest through imaging followed by the administration of therapeutic radioligand targeting the tumor-expressed molecular target. Therefore, radiotheranostics ensures that only patients with a high likelihood of response are treated with a particular radiotheranostic agent, ensuring the delivery of personalized care to cancer patients. Within the last decades, a couple of radiotheranostics agents, including Lutetium-177 DOTATATE (177Lu-DOTATATE) and Lutetium-177 prostate-specific membrane antigen (177Lu-PSMA), were shown to prolong the survival of cancer patients compared to the current standard of care leading to the regulatory approval of these agents for routine use in oncology care. This recent string of successful approvals has broadened the interest in the development of different radiotheranostic agents and their investigation for clinical translation. In this work, we present an updated appraisal of the literature, reviewing the recent advances in the use of established radiotheranostic agents such as radioiodine for differentiated thyroid carcinoma and Iodine-131-labeled meta-iodobenzylguanidine therapy of tumors of the sympathoadrenal axis as well as the recently approved 177Lu-DOTATATE and 177Lu-PSMA for differentiated neuroendocrine tumors and advanced prostate cancer, respectively. We also discuss the radiotheranostic agents that have been comprehensively characterized in preclinical studies and have shown some clinical evidence supporting their safety and efficacy, especially those targeting fibroblast activation protein (FAP) and chemokine receptor 4 (CXCR4) and those still being investigated in preclinical studies such as those targeting poly (ADP-ribose) polymerase (PARP) and epidermal growth factor receptor 2.

A Case Series of Choroidal and Orbital Neuroendocrine Tumors: Metastasis: Two Patients Treated With Peptide Radionuclide Therapy

ABSTRACT

Neuroendocrine tumors (NETs) are rare cancers with heterogeneous histologies, response to treatments, and prognoses. Majority of these cancers originate in the gastrointestinal tract and metastasize to the liver. We report the cases of 5 patients with low-grade NET disease with rare metastases to the choroids. Two of the patients were treated with peptide receptor radionuclide therapy (lutetium 177 [ 177 Lu]). This is the first report confirming peptide radionuclide therapy safety in patients with low-grade NET with ocular metastases.

Peptide receptor radionuclide therapy with 177Lu- or 90Y-SSTR peptides in malignant pheochromocytomas (PCCs) and paragangliomas (PGLs): results from a single institutional retrospective analysis

BACKGROUND

Malignant pheochromocytomas (PCCs) and paragangliomas (PGLs) are rare tumors and available systemic therapies are limited.

AIM

To explore the role of peptide receptor radionuclide therapy (PRRT) with Yttrium-90 (90Y) and Lutetium-177 (177Lu) peptides in pheochromocytomas (PCCs) and paragangliomas (PGLs).

METHODS

We retrospectively analyzed more than 1500 patients with histologically proven neuroendocrine tumors treated with 177Lu- or 90Y-DOTA-TATE or -TOC between 1999 to 2017 at our Institute. Overall, 30 patients with confirmed malignant PCCs and PGLs matched inclusion/exclusion criteria and were considered eligible for this analysis.

RESULTS

Thirty (n = 30) patients were treated: 22 with PGLs and 8 with PCCs (12 M and 18 F, median age 47 [IQR: 35-60 years]). Eighteen patients (n = 18) had head and neck PGLs, 3 patients thoracic PGLs and 1 patient abdominal PGL. Sixteen patients (53%) had locally advanced and fourteen (47%) had metastatic disease. Twenty-seven (90%) patients had disease progression at baseline. Four (13%) patients were treated with 90Y, sixteen (53%) with 177Lu and ten (33%) with 90Y + 177Lu respectively. The median total cumulative activity from treatment with 90Y- alone was 9.45 GBq (range 5.11-14.02 GBq), from 177Lu- alone was 21.9 GBq (7.55-32.12 GBq) and from the combination treatment was 4.94 GBq from 90Y- and 6.83 GBq from 177Lu- (ranges 1.04-10.1 and 2.66-20.13 GBq, respectively). Seven out of 30 (23%) patients had partial response and 19 (63%) stable disease. Median follow up was 8.9 years (IQR: 2.9-12). The 5-y and 10-y PFS was 68% (95% CI: 48-82) and 53% (95% CI: 33-69), respectively, whereas 5-y and 10-y OS was 75% (95% CI: 54-87) and 59% (95% CI: 38-75), respectively. Grade 3 or 4 acute hematological toxicity occurred in three patients, two with leucopenia and one with thrombocytopenia, respectively.

CONCLUSION

PRRT with 177Lu- or 90Y-DOTA-TATE or -TOC is feasible and well tolerated in advanced PGLs and PCCs.

Real-World Experience with 177Lu-PSMA-617 Radioligand Therapy After Food and Drug Administration Approval

We report our initial real-world experience with 177Lu-PSMA-617 radioligand therapy. Methods: We performed a retrospective review of patients treated with 177Lu-PSMA-617. Pretreatment PSMA PET, laboratory findings, overall survival, a fall in prostate-specific antigen by 50% (PSA50), and toxicities were evaluated. Results: Ninety-nine patients were included. Sixty patients achieved a PSA50. Seven of 18 (39%) patients who did not meet the TheraP PSMA imaging criteria achieved a PSA50. Nineteen of 31 (61%) patients who did not meet the VISION laboratory criteria achieved a PSA50. Sixty-three patients had a delay or stoppage in therapy, which was due to a good response in 19 patients and progressive disease in 14 patients. Of 10 patients with a good response who restarted treatment, 9 subsequently achieved a PSA50 on retreatment. The most common toxicities were anemia (33%) and thrombocytopenia (21%). Conclusion: At our center, patients who did not meet the TheraP PSMA imaging criteria or the VISION laboratory criteria benefited from 177Lu-PSMA-617 radioligand therapy.

Lutetium-177 Labelled Anti-PSMA Monoclonal Antibody (Lu-TLX591) Therapy for Metastatic Prostate Cancer: Treatment Toxicity and Outcomes

INTRODUCTION

Whilst prostate cancer is the fourth most common cancer globally, effective therapies for patients with advanced disease are lacking. In recent years, interest in using theranostic agents to treat castrate-resistant prostate cancer (CRPC) and metastatic prostate cancer has emerged. Lu-TLX591 monoclonal antibody is a potential agent of significance; however, to date, reports on its toxicity and efficacy have been limited to small clinical trials in heavily pretreated patients. This retrospective study describes the real-world toxicity and efficacy profile of Lu-TLX591.

METHODS

Eighteen patients received Lu-TLX591 at two private oncology centres in Australia. Patients were eligible if they had CRPC or metastatic prostate cancer and prostate-specific membrane antigen (PSMA)-avid disease confirmed by PSMA-positron emission tomography (PET). Patients received two cycles of Lu-TLX591 monoclonal antibody (177 Lu-DOTA-rosopatamab) each dosed from 1.01-2.85 GBq, 14 days apart. Patient side effects, blood test results and radiology reports were recorded on the patient's electronic medical record (eMR).

RESULTS

Prominent side effects included fatigue (55.6%), anorexia (16.7%), nausea (11.1%), and transfusion reactions (11.1%). All-grade haematological toxicities included lymphopenia (61.1%), anaemia (22.2%), leukopenia (27.8%), neutropenia (27.8%), and thrombocytopenia (27.8%). Grade 4 toxicity included lymphopenia (6.7%) and thrombocytopenia (6.7%). Patients' prostate-specific antigen (PSA) responses were as follows; ≥ 30% PSA decline (27.8%), ≥ 50% PSA decline (11.4%) and any PSA decline (38.9%). Follow-up radiology revealed 54.5% stable disease, 45.4% disease progression and 9.1% disease regression.

CONCLUSION

Lu-TLX591 was safely administered at acceptable toxicity and its efficacy reflects previous clinical trials. Larger studies are required and are underway (NCT04786847; NCT05146973; NCT04876651) to determine Lu-TLX591 effectiveness amongst different prostate cancer populations and compare its efficacy against peptide-based radiopharmaceutical agents.

Dual 177 Lu-Prostate-Specific Membrane Antigen and 177 Lu-DOTATATE Therapy in Metastatic Castration-Resistant Prostate Cancer With Neuroendocrine Differentiation

ABSTRACT

We present an 87-year-old man diagnosed with prostate cancer and neuroendocrine differentiation, posttherapy results to consecutive 177 Lu-prostate-specific membrane antigen and 177 Lu-DOTATATE. Despite hormonal therapy and chemoradiotherapy, the patient progressed rapidly, and multiple liver and bone metastases showed regression after 177 Lu-prostate-specific membrane antigen and 177 Lu-DOTATATE treatment. Prostate cancer with neuroendocrine differentiation is resistant to treatments; however, treatment with the combination of 177 Lu-DOTATATE therapy may be promising.

Exploring the role of combined external beam radiotherapy and targeted radioligand therapy with [177Lu]Lu-PSMA-617 for prostate cancer - from bench to bedside

Management of prostate cancer (PC) might be improved by combining external beam radiotherapy (EBRT) and prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) with lutetium-177 (177Lu)-labeled PSMA inhibitors. We hypothesized a higher efficacy of the combination due to augmentation of the radiation dose to the tumor and interactions of EBRT with PSMA expression potentially increasing radiopharmaceutical uptake. Therefore, this study analyzed the influence of radiation on PSMA expression levels in vitro. The results were translated to evaluate the efficacy of the combination of photon EBRT and [177Lu]Lu-PSMA-617 in a murine PC xenograft model. Finally, a clinical case report on a combined elective field EBRT with RLT dose escalation illustrates a proof-of-concept. Methods: PSMA gene and protein expression were assessed in human PSMA-overexpressing LNCaP cells after irradiation using reverse transcription quantitative polymerase chain reaction (RT-qPCR), flow cytometry and On-Cell Western assays. In the in vivo therapy study, LNCaP tumor-bearing BALB/c nu/nu mice were irradiated once with 2 Gy X-ray EBRT and injected with 40 MBq [177Lu]Lu-PSMA-617 after 4 h or received single or no treatment (n = 10 each). Tumor-absorbed doses by [177Lu]Lu-PSMA-617 were calculated according to the Medical Internal Radiation Dosimetry (MIRD) formalism after deriving time-activity curves using a gamma probe. An exemplified patient case is demonstrated where fractionated EBRT (54 Gy to prostate; 45 Gy to pelvic lymphatics) and three cycles of [177Lu]Lu-PSMA-617 (3.4-6.0 GBq per cycle) were sequentially combined under concurrent androgen deprivation for treating locally advanced PC. Results: At 4 h following irradiation with 2-8 Gy, LNCaP cells displayed a PSMA protein upregulation by around 18% relative to non-irradiated cells, and a stronger upregulation on mRNA level (up to 2.6-fold). This effect was reversed by 24 h when PSMA protein levels were downregulated by up to 22%. Mice treated with the combination therapy showed significantly improved outcomes regarding tumor control and median survival (p < 0.0001) as compared to single or no treatment. Relative to monotherapy with PSMA-RLT or EBRT, the tumor doubling time was prolonged 1.7- or 2.7-fold and the median survival was extended by 24% or 60% with the combination, respectively. Additionally, tumors treated with EBRT exhibited a 14% higher uptake of the radiopharmaceutical as evident from the calculated tumor-absorbed dose, albeit with high variability in the data. Concerning the patient case, the tri-modality treatment was well tolerated and the patient responded with a long-lasting complete biochemical remission for five years following end of PSMA-RLT. The patient then developed a biochemical relapse with oligo-recurrent disease on follow-up imaging. Conclusion: The present preclinical and clinical data demonstrate that the combination of EBRT with dose escalation by PSMA-RLT improves tumor control and potentially prolongs survival. This may pave the way for further clinical investigations of this approach to explore the curative potential of the combination therapy.

Radiation levels outside a patient undergoing177Lu-PSMA radioligand therapy

Understanding the spatial distribution of radiation levels outside of a patient undergoing177Lu radioligand therapy is not only helpful for conducting correct tests for patient release, but also useful for estimation of its potential exposure to healthcare workers, caregivers, family members, and the general public. In this study, by mimicking the177Lu-labeled prostate-specific membrane antigen radioligand therapy for prostate cancers in an adult male, the spatial distribution of radiation levels outside of the phantom was simulated based on the Monte Carlo software of Particle and Heavy Ion Transport System, and verified by a series of measurements. Moreover, the normalized dose rates were further formulized on the three transverse planes representing the heights of pelvis, abdomen and chest. The results showed that the distributions of radiation levels were quite complex. Multi-directional and multi-height measurements are needed to ensure the external dose rate to meet the release criteria. In general, the radiation level was higher at the horizontal plane where the source was located, and the levels in front and behind of the body were higher than those of the left and right sides at the same height. The ratio of simulated dose rates to measured ones ranged from 0.82 to 1.19 within 1 m away from the body surface in all directions. Based on the established functions, the relative root mean square deviation between the calculated and simulated values were 0.21, 0.25 and 0.23 within a radius of 1 m on the pelvis, abdomen and chest transverse planes, respectively. It is expected that the results of this study would be helpful for guiding the test of extracorporeal radiation to determine the patient's release, and of benefit to estimate the radiation exposure to others.

SENTRI: Single-Particle Energy Transducer for Radionuclide Injections for Personalized Targeted Radionuclide Cancer Therapy

PURPOSE

Targeted radionuclide therapy (TRT), whereby a tumor-targeted molecule is linked to a therapeutic beta- or alpha-emitting radioactive nuclide, is a promising treatment modality for patients with metastatic cancer, delivering radiation systemically. However, patients still progress due to suboptimal dosing, driven by the large patient-to-patient variability. Therefore, the ability to continuously monitor the real-time dose deposition in tumors and organs at risk provides an additional dimension of information during clinical trials that can enable insights into better strategies to personalize TRT.

METHODS AND MATERIALS

Here, we present a single beta-particle sensitive dosimeter consisting of a 0.27-mm3 monolithic silicon chiplet directly implanted into the tumor. To maximize the sensitivity and have enough detection area, minimum-size diodes (1 μm2) are arrayed in 64 × 64. Signal amplifiers, buffers, and on-chip memories are all integrated in the chip. For verification, PC3-PIP (prostate-specific membrane antigen [PSMA]+) and PC3-flu (PSMA-) cell lines are injected into the left and right flanks of the mice, respectively. The devices are inserted into each tumor and measure activities at 5 different time points (0-2 hours, 7-9 hours, 12-14 hours, 24-26 hours, and 48-50 hours) after 177Lu-PSMA-617 injections. Single-photon emission computed tomography/computed tomography scans are used to verify measured data.

RESULTS

With a wide detection range from 0.013 to 8.95 MBq/mL, the system is capable of detecting high tumor uptake as well as low doses delivered to organs at risk in real time. The measurement data are highly proportional (R2 > 0.99) to the 177Lu-PSMA-617 activity. The in vivo measurement data agree well with the single-photon emission computed tomography/computed tomography results within acceptable errors (±1.5%ID/mL).

CONCLUSIONS

Given the recent advances in clinical use of TRT in prostate cancer, the proposed system is verified in a prostate cancer mouse model using 177Lu-PSMA-617.

Formulation of patient dose of [177Lu]Lu-Trastuzumab using in-house developed freeze-dried kit: A path forward for clinical translation

Trastuzumab is a US-FDA-approved humanized monoclonal antibody used for the treatment of human epidermal growth factor receptor 2 (HER2)-positive breast cancer. The aim of the present work is to optimize a freeze-dried formulation of DOTA-Trastuzumab conjugate for the preparation of patient doses of [177Lu]Lu-Trastuzumab for radioimmunotherapy of breast cancer. The formulation of [177Lu]Lu-Trastuzumab usually takes a long time, and thus, such a process is not suitable for the routine preparation of this agent in hospital radiopharmacies. To circumvent this, a pre-synthesized DOTA-Trastuzumab conjugate as a freeze-dried formulation is proposed. In the present work, DOTA-Trastuzumab conjugate was subjected to a freeze-drying process after the addition of optimized amounts of radioprotectant and cryoprotectant. [177Lu]Lu-DOTA-Trastuzumab was prepared by incubating the lyophilized powder of the kit vial with medium-specific activity 177LuCl3. The final radiochemical purity of [177Lu]Lu-DOTA-Trastuzumab, prepared using freeze-dried kit, was determined to be >95%. To ascertain the reproducibility of the procedure, six consecutive batches of the freeze-dried formulation were prepared, radiolabeled, and evaluated by carrying out both in vitro and ex vivo studies. The consistency of the results of all the six consecutive batches confirmed the robustness and utility of the in-house optimized freeze-dried formulation for the preparation of patient doses of [177Lu]Lu-Trastuzumab at hospital radiopharmacies.

[177Lu]Lu-labeled anti-claudin-18.2 antibody demonstrated radioimmunotherapy potential in gastric cancer mouse xenograft models

PURPOSE

Gastric cancer (GC), one of the most prevalent and deadliest tumors worldwide, is often diagnosed at an advanced stage with limited treatment options and poor prognosis. The development of a CLDN18.2-targeted radioimmunotherapy probe is a potential treatment option for GC.

METHODS

The CLDN18.2 antibody TST001 (provided by Transcenta) was conjugated with DOTA and radiolabeled with the radioactive nuclide 177Lu. The specificity and targeting ability were evaluated by cell uptake, imaging and biodistribution experiments. In BGC823CLDN18.2/AGSCLDN18.2 mouse models, the efficacy of [177Lu]Lu-TST001 against CLDN18.2-expressing tumors was demonstrated, and toxicity was evaluated by H&E staining and blood sample testing.

RESULTS

[177Lu]Lu-TST001 was labeled with an 99.17%±0.32 radiochemical purity, an 18.50 ± 1.27 MBq/nmol specific activity and a stability of ≥ 94% after 7 days. It exhibited specific and high tumor uptake in CLDN18.2-positive xenografts of GC mouse models. Survival studies in BGC823CLDN18.2 and AGSCLDN18.2 tumor-bearing mouse models indicated that a low dose of 5.55 MBq and a high dose of 11.10 MBq [177Lu]Lu-TST001 significantly inhibited tumor growth compared to the saline control group, with the 11.1 MBq group showing better therapeutic efficacy. Histological staining with hematoxylin and eosin (H&E) and Ki67 immunohistochemistry of residual tissues confirmed tumor tissue destruction and reduced tumor cell proliferation following treatment. H&E showed that there was no significant short-term toxicity observed in the heart, spleen, stomach or other important organs when treated with a high dose of [177Lu]Lu-TST001, and no apparent hematotoxicity or liver toxicity was observed.

CONCLUSION

In preclinical studies, [177Lu]Lu-TST001 demonstrated significant antitumor efficacy with acceptable toxicity. It exhibits strong potential for clinical translation, providing a new promising treatment option for CLDN18.2-overexpressing tumors, including GC.

Single-Time-Point Renal Dosimetry Using Nonlinear Mixed-Effects Modeling and Population-Based Model Selection in [177Lu]Lu-PSMA-617 Therapy

The aim of this study was to investigate the accuracy of single-time-point (STP) renal dosimetry imaging using SPECT/CT data, a nonlinear mixed-effects (NLME) model, and a population-based model selection (PBMS) in a large population for 177Lu-labeled prostate-specific membrane antigen therapy. Methods: Biokinetic data (mean ± SD) of [177Lu]Lu-PSMA-617 in kidneys at time points 1 (1.8 ± 0.8 h), 2 (18.7 ± 0.9 h), 3 (42.6 ± 1.0 h), 4 (66.3 ± 0.9 h), and 5 (160.3 ± 24.2 h) after injection were obtained from 63 patients with metastatic castration-resistant prostate cancer using SPECT/CT. Thirteen functions were derived from various parameterizations of 1- to 5-exponential functions. The function's parameters were fitted in the NLME framework to the all-time-point (ATP) data. The PBMS NLME method was performed using the goodness-of-fit test and Akaike weight to select the best function fitting the data. The best function from ATP fitting was used to calculate the reference time-integrated activity and absorbed doses. In STP dosimetry, the parameters of a particular patient with STP data were fitted simultaneously to the STP data at different time points of that patient with ATP data of all other patients. The parameters from STP fitting were used to calculate the STP time-integrated activity and absorbed doses. Relative deviations (RDs) and root-mean-square errors (RMSEs) were used to analyze the accuracy of the calculated STP absorbed dose compared with the reference absorbed dose obtained from the best-fit ATP function. The performance of STP dosimetry using PBMS NLME modeling was compared with the Hänscheid and Madsen methods. Results: The function [Formula: see text] was selected as the best-fit ATP function, with an Akaike weight of 100%. For STP dosimetry, the STP measurement by SPECT/CT at time point 3 (42.6 ± 1.0 h) showed a relatively low mean RD of -4.4% ± 9.4% and median RD of -0.7%. Time point 3 had the lowest RMSE value compared with those at the other 4 time points. The RMSEs of the absorbed dose RDs for time points 1-5 were 23%, 16%, 10%, 20%, and 53%, respectively. The STP dosimetry using the PBMS NLME method outperformed the Hänscheid and Madsen methods for all investigated time points. Conclusion: Our results show that a single measurement of SPECT/CT at 2 d after injection might be used to calculate accurate kidney-absorbed doses using the NLME method and PBMS.

Dosing lutetium Lu 177-dotatate for a hemodialysis patient

Lu177-dotatate (Lutathera™) is a radioactive drug approved for the treatment of adults with gastro-entero-pancreatic neuroendocrine tumors and is predominantly renally excreted. Currently all patients receive 7400 MBq (200 mCi), and there are no guidelines for treating hemodialysis patients. We measured radioactivity prior to and post administration of two cycles of Lu177-dotatate in a hemodialysis patient, and radiation exposure to staff. We reduced the standard 7400 MBq by 33% for the first cycle and patient radioactivity fell by 40% following postdilution hemodiafiltration started 6 h post dosing, and by 45% for the second cycle and radioactivity fell by 47% with postdilution hemodiafiltration started 5 h post administration. By reducing the initial administered radioactivity, coupled with early dialysis, and choosing postdilution hemodiafiltration we were able to achieve radioactivity retention curves similar to those from patients with normal renal function receiving the standard administration of 7400 MBq.

A simple method to shorten the apparent dead time in the dosimetry of Lu-177 for targeted radionuclide therapy using a gamma camera

BACKGROUND

The dead-time loss reportedly degrades the accuracy of dosimetry using a gamma camera for targeted radionuclide therapy with Lu-177; therefore, the dead-time loss needs to be corrected. However, the correction is challenging. In this study, we propose a novel and simple method to shorten the apparent dead time rather than correcting it through experiments and Monte Carlo simulations.

METHODS

An energy window of 208 keV ± 10 % is generally used for the imaging of Lu-177. Lower-energy gamma photons and X-rays of Lu-177 do not contribute to image formation but lead to dead-time losses. In our proposed method, a thin lead sheet was used to shield gamma photons and X-rays with energies lower than 208 keV, while detecting 208 keV gamma photons that penetrated the thin sheet. We measured and simulated the energy spectra and count rate characteristics of a clinical gamma camera system using a cylindrical phantom filled with a Lu-177 solution. Lead sheets of 1.0- and 0.5-mm thicknesses were used as thin shields, and the dead-time losses in tumour imaging with consumed Lu-177 were simulated.

RESULTS

The apparent dead times with lead sheets of 1.0- and 0.5-mm thicknesses and without a lead sheet were 1.7, 1.9, and 5.8 µs for an energy window of 208 keV ± 10 %, respectively. The dead-time losses could be reduced from 10 % to 1.3 % using the 1.0-mm thick lead sheet in the simulated imaging of tumour.

CONCLUSION

Our method is promising in clinical situations and studies on Lu-177 dosimetry for tumours.

Early response monitoring during [177Lu]Lu-PSMA I&T therapy with quantitated SPECT/CT predicts overall survival of mCRPC patients: subgroup analysis of a Swiss-wide prospective registry study

PURPOSE

To assess early tumor response with quantitated SPECT/CT and to correlate it with clinical outcome in metastatic castration-resistant prostate cancer (mCRPC) patients treated with 177Lutetium-PSMA I&T therapy.

METHODS

Single-center, observational study, part of the prospective Swiss national cancer registry study investigating the safety and efficacy of [177Lu]Lu-PSMA I&T (EKNZ: 2021-01271) in mCRPC patients treated with at least two cycles of [177Lu]Lu-PSMA I&T 6-weekly. After the first and second cycle quantitated SPECT/CT (Symbia Intevo, Siemens) was acquired 48 h after injection (three fields of view from head to thigh, 5 s/frame) and reconstructed using xQuant® (48i, 1 s, 10-mm Gauss). Image analysis: The PSMA-positive total tumor volumes (TTV) were semi-automatically delineated using a SUV threshold of 3 with MIMencore® (version 7.1.3, Medical Image Merge Software Inc.). Changes in TTV, highest tumor SUVmax, and total tumor SUVmean between cycles 1 and 2 were calculated and grouped into a) stable or decrease and b) increase. Serum PSA levels were assessed at each therapy cycle and at follow-up until progression or death. Changes in TTV, PSA, SUVmax, and SUVmean were correlated with PSA-progression-free survival (PSA-PFS) and the overall survival (OS) using the Kaplan-Meier methodology (log-rank test).

RESULTS

Between 07/2020 and 04/2022, 111 patients were screened and 73 finally included in the data analysis. The median follow-up was 8.9 months (range 1.4-26.6 months). Stable or decreased TTV at cycle 2 was associated with longer OS (hazard ratio (HR) 0.28, 95% confidence interval (CI) 0.09-0.86, p < 0.01). Similar, stable, or decreased PSA was associated with longer OS (HR 0.21; CI 0.07-0.62, p < 0.01) and PSA-PFS (HR 0.34; 95% CI 0.16-0.72, p < 0.01). Combining TTV and PSA will result in an augmented prognostic value for OS (HR 0.09; CI 0.01-0.63; p < 0.01) and for PSA-PFS (HR 0.11; CI 0.02-0.68; p < 0.01). A reduction of SUVmax or SUVmean was not prognostically relevant, neither for OS (p 0.88 and 0.7) nor for PSA-PFS (p 0.73 and 0.62, respectively).

CONCLUSION

Six weeks after initiating [177Lu]Lu-PSMA I&T, TTV and serum PSA appear to be good prognosticators for OS. Combined together, TTV + PSA change demonstrates augmented prognostic value and can better predict PSA-PFS. Larger studies using TTV change prospectively as an early-response biomarker are warranted for implementing management change towards a more personalized clinical practice.

The real-world outcomes of Lutetium-177 PSMA-617 radioligand therapy in metastatic castration-resistant prostate cancer: Turkish Oncology Group multicenter study

Metastatic castration-resistant prostate cancer (mCRPC) remains a challenging condition to treat despite recent advancements. This retrospective study aimed to assess the activity and tolerability of Lutetium-177 (Lu-177) PSMA-617 radioligand therapy (RLT) in mCRPC patients across multiple cancer centers in Turkey. The study included 165 patients who received at least one cycle of Lu-177 PSMA-617 RLT, with the majority having bone metastases and undergone prior treatments. Prostate-specific antigen (PSA) levels were assessed before each treatment cycle, and the biochemical response was evaluated in accordance with the Prostate Cancer Work Group 3 Criteria. The PSA decline of ≥50% was classified as a response, while an increase of ≥25% in PSA levels was indicative of progressive disease. Neither response nor progression was considered as stable disease. The Lu-177 PSMA-617 RLT led to a significant PSA response, with 50.6% of patients achieving a >50% decrease in PSA levels. Median overall survival (OS) and progression-free survival were 13.5 and 8.2 months, respectively. Patients receiving Lu-177 PSMA-617 RLT in combination with androgen receptor pathway inhibitors (ARPIs) had a higher OS compared to those receiving Lu-177 PSMA-617 RLT alone (18.2 vs 12.3 months, P = .265). The treatment was generally well-tolerated, with manageable side effects such as anemia and thrombocytopenia. This study provides real-world evidence supporting the effectiveness and safety of Lu-177 PSMA-617 RLT in mCRPC patients, particularly when used in combination with ARPIs. These findings contribute to the growing body of evidence on the potential benefits of PSMA-targeted therapies in advanced prostate cancer.

A Proof-of-Concept Study on the Theranostic Potential of 177 Lu-labeled Biocompatible Covalent Polymer Nanoparticles for Cancer Targeted Radionuclide Therapy

Theranostic nanomedicine combined bioimaging and therapy probably rises more helpful and interesting opportunities for personalized medicine. In this work, 177 Lu radiolabeling and surface PEGylation of biocompatible covalent polymer nanoparticles (CPNs) have generated a new theranostic nanoformulation (177 Lu-DOTA-PEG-CPNs) for targeted diagnosis and treatment of breast cancer. The in vitro anticancer investigations demonstrate that 177 Lu-DOTA-PEG-CPNs possess excellent bonding capacity with breast cancer cells (4T1), inhibiting the cell viability, leading to cell apoptosis, arresting the cell cycle, and upregulating the reactive oxygen species (ROS), which can be attributed to the good targeting ability of the nanocarrier and the strong relative biological effect of the radionuclide labelled compound. Single photon emission computed tomography/ computed tomography (SPECT/CT) imaging and in vivo biodistribution based on 177 Lu-DOTA-PEG-CPNs reveal that notable radioactivity accumulation at tumor site in murine 4T1 models with both intravenous and intratumoral administration of the prepared radiotracer. Significant tumor inhibition has been observed in mice treated with 177 Lu-DOTA-PEG-CPNs, of which the median survival was highly extended. More strikingly, 50 % of mice intratumorally injected with 177 Lu-DOTA-PEG-CPNs was cured and showed no tumor recurrence within 90 days. The outcome of this work can provide new hints for traditional nanomedicines and promote clinical translation of 177 Lu radiolabeled compounds efficiently.

177Lu-Labeled Bivalent Ligands of Prostate-Specific Membrane Antigen for Endoradiotherapy of Prostate Cancer

Recently, we developed a bivalent prostate-specific membrane antigen (PSMA) radioligand ([18F]AlF-Bi-PSMA), which showed higher tumor uptake and retention in PSMA-positive mouse models than the clinically used radioligands, [68Ga]Ga-PSMA-11 and [18F]PSMA-1007. Here, we developed two 177Lu-labeled bivalent PSMA ligands with (DOTA-Alb-Bi-PSMA) or without an albumin-binding motif (DOTA-Bi-PSMA) to enhance radiotherapeutic efficacy with minimal toxicity. The results demonstrated that both 177Lu-labeled bivalent radioligands showed good stability, high binding affinity, and PSMA-targeting specificity in vitro. Compared with [177Lu]Lu-PSMA-617, both [177Lu]Lu-Bi-PSMA and [177Lu]Lu-Alb-Bi-PSMA showed a higher area under the curve (AUC) of tumor accumulation and superior therapeutic efficacy. However, [177Lu]Lu-Alb-Bi-PSMA exhibited a dose-dependent increase in acute damage to kidneys. In terms of the radionuclide therapy efficacy and side effects, [177Lu]Lu-Bi-PSMA exhibited well-balanced action with high tumor-to-organs AUC ratios, resulting in remarkable therapeutic efficacy and negligible side effects. These promising results warrant further investigations to achieve the clinical translation of [177Lu]Lu-Bi-PSMA.

Comparison of PET/CT-based eligibility according to VISION and TheraP trial criteria in end-stage prostate cancer patients undergoing radioligand therapy

BACKGROUND

Two randomized clinical trials demonstrated the efficacy of prostate-specific membrane antigen (PSMA) radioligand therapy (PSMA RLT) in metastatic castration-resistant prostate cancer (mCRPC). While the VISION trial used criteria within PSMA PET/CT for inclusion, the TheraP trial used dual tracer imaging including FDG PET/CT. Therefore, we investigated whether the application of the VISION criteria leads to a benefit in overall survival (OS) or progression-free survival (PFS) for men with mCRPC after PSMA RLT.

METHODS

Thirty-five men with mCRPC who had received PSMA RLT as a last-line option and who had undergone pretherapeutic imaging with FDG and [68Ga]Ga-PSMA I&T or [18F]PSMA-1007 were studied. Therapeutic eligibility was retrospectively evaluated using the VISION and TheraP study criteria.

RESULTS

26 of 35 (74%) treated patients fulfilled the VISION criteria (= VISION+) and only 17 of 35 (49%) fulfilled the TheraP criteria (= TheraP+). Significantly reduced OS and PFS after PSMA RLT was observed in patients rated VISION- compared to VISION+ (OS: VISION-: 3 vs. VISION+: 12 months, hazard ratio (HR) 3.1, 95% confidence interval (CI) 1.0-9.1, p < 0.01; PFS: VISION-: 1 vs. VISION+: 5 months, HR 2.7, 95% CI 1.0-7.8, p < 0.01). For patients rated TheraP-, no significant difference in OS but in PFS was observed compared to TheraP+ patients (OS: TheraP-: 5.5 vs. TheraP+: 11 months, HR 1.6, 95% CI 0.8-3.3, p = 0.2; PFS: TheraP-: 1 vs. TheraP+: 6 months, HR 2.2, 95% CI 1.0-4.5, p < 0.01).

CONCLUSION

Retrospective application of the inclusion criteria of the VISION study leads to a benefit in OS and PFS after PSMA RL, whereas TheraP criteria appear to be too strict in patients with end-stage prostate cancer. Thus, performing PSMA PET/CT including a contrast-enhanced CT as proposed in the VISION trial might be sufficient for treatment eligibility of end-stage prostate cancer patients.

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.

A multicentric, single arm, open-label, phase I/II study evaluating PSMA targeted radionuclide therapy in adult patients with metastatic clear cell renal cancer (PRadR)

BACKGROUND

Despite advancements in managing metastatic clear cell renal carcinoma (mccRCC) through antiangiogenic tyrosine kinase inhibitors and immunotherapy, there remains a demand for novel treatments for patients experiencing progression despite the use of these medications. There is currently no established standard treatment for patients receiving third therapy line. Prostate Specific Membrane Antigen (PSMA) whose high expression has been demonstrated in metastatic aggressive prostate adenocarcinoma is also highly expressed in neovessels of various solid tumors including renal cell carcinoma (RCC): 86% of clear cell RCC, 61% of chromophobe RCC, and 28% of papillary RCC. Therefore, PSMA may be a target expressed in metastatic ccRCC for radionuclide therapy using PSMA ligands radiolabeled with Lutetium-177 (PRLT). 177Lu-PSMA delivers ß-particle radiation to PSMA-expressing cells and the surrounding microenvironment with demonstrated efficacy in metastatic prostate cancer.

METHODS

This is a multicenter phase I/II study designed to assess the tolerability and effectiveness of 177Lu-PSMA-1 in individuals with PSMA-positive metastatic clear cell renal cell carcinoma (ccRCC), identified through 68Ga-PSMA PET, conducted in France (PRadR). 48 patients will be treated with 4 cycles of 7.4 GBq of 177Lu-PSMA-1 every 6 weeks. The primary objective is to evaluate the safety of 177Lu-PSMA-1 (phase I) and the efficacy of 177Lu-PSMA-1 in mccRCC patients (phase II). Primary endpoints are incidence of Severe Toxicities (ST) occurring during the first cycle (i.e. 6 first weeks) and disease Control Rate after 24 weeks of treatment (DCR24w) as per RECIST V1.1. Secondary objective is to further document the clinical activity of 177Lu-PSMA-1 in mccRCC patients (duration of response (DoR), best overall response rate (BORR), progression fee survival (PFS) and overall survival (OS).

DISCUSSION

Our prospective study may lead to new potential indications for the use of 177Lu-PSMA-1 in mccRCC patients and should confirm the efficacy and safety of this radionuclide therapy with limited adverse events. The use of 177Lu-PSMA-1may lead to increase disease control, objective response rate and the quality of life in mccRCC patients.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT06059014.

Promising Therapeutic Activity of 177 Lu-PSMA-617 in Synchronous High-Volume Metastatic Hormone-Sensitive Prostate Cancer : A Pilot Experience

PURPOSE

177 Lu-PSMA-617 has been shown to improve survival outcomes in patients with end-stage metastatic castration-resistant prostate cancer. However, data in earlier lines remain limited. In this study, we intended to evaluate the efficacy and safety of 177 Lu-PSMA-617 in patients with synchronous high-volume metastatic hormone-sensitive prostate cancer (mHSPC).

PATIENTS AND METHODS

Hormone-sensitive prostate cancer patients with synchronous high-volume metastases (defined as ≥4 skeletal metastases with ≥1 extra-axial site or any visceral metastasis) showing high PSMA expression on 68 Ga-PSMA-11 PET/CT and ineligible/unwilling for conventional chemohormonal treatment options were selected. Approximately, ~5.55-7.4 GBq of 177 Lu-PSMA-617 was administered intravenously at 8-12 weeks intervals, up to 6 cycles. All patients underwent concomitant androgen deprivation therapy/orchiectomy. The outcome measures included the proportion of patients achieving an undetectable serum prostate-specific antigen (PSA) (ie, ≤0.2 ng/mL) at any time point after therapy, best PSA response rate, objective radiographic response rate, radiographic progression-free survival, overall survival, and adverse events.

RESULTS

Ten patients with high-volume mHSPC received a median cumulative activity of 32.4 GBq (range, 7.4-44.4) of 177 Lu-PSMA-617 over 1-6 cycles. Five patients (50%) achieved an undetectable PSA with 9 patients (90%) showing a ≥50% decline in PSA from baseline. Nine patients underwent radiological follow-up, of which 7 (77.8%) had an objective response. The median radiographic progression-free survival was 24 months (95% confidence interval, 18-30), whereas the median overall survival was not reached. None of the patients had any grade 3/4 adverse event.

CONCLUSIONS

177 Lu-PSMA-617 seems to be a promising efficacious and safe treatment option for patients with synchronous high-volume mHSPC.

Estimation of absorbed dose to salivary glands in mCRPC patients undergoing 177 Lu- PSMA-617 radioligand therapy using quantitative SPECT-CT at single time point: a single-center feasibility study

OBJECTIVE

177 Lu-PSMA-617-radioligand therapy (RLT) has shown promising therapeutic role in patients with metastatic castration-resistant prostate cancer. However, off-target action in salivary glands often presents with xerostomia. Personalized dosimetry can help in optimizing the treatment, however, has so far been tedious due to multiple time-point imaging. In this prospective study, we intended to estimate the absorbed dose delivered to the salivary glands in patients undergoing 177 Lu-PSMA-617-RLT using quantitative SPECT/CT at a single time point.

METHODS

Patients undergoing 177 Lu-PSMA-617 RLT were included in this prospective study. Post-therapy whole-body images and regional quantitative single time-point SPECT/CT were acquired at 24 h with high-energy collimator. The data was processed and analyzed using Q.Metrix software. A scaling factor, that is, the time-integrated activity conversion factor was applied for the image acquired at 24 h. Absorbed doses were computed using MIRD scheme and OLINDA software.

RESULTS

A total of 21 patients (mean age: 66 ± 9 years) were included. The value of mean absorbed dose for the parotid glands was 1.90 ± 1.31Gy (range: 0.26-6.23) and that for the submandibular glands was 1.37 ± 0.94Gy (range: 0.16-3.65). The mean absorbed doses per administered activity for the parotid and submandibular glands were 0.26 ± 0.18 Gy/GBq and 0.19 ± 0.12 Gy/GBq, respectively. The absorbed doses were estimated for one cycle of therapy and were well within acceptable limits. None of the patients experienced dryness of mouth.

CONCLUSION

Single time-point dosimetry with quantitative SPECT/CT is feasible and can be standardized to estimate the absorbed dose to salivary glands instead of multiple time-point acquisitions.

Dosimetric Analysis of a Phase I Study of PSMA-Targeting Radiopharmaceutical Therapy With [177Lu]Ludotadipep in Patients With Metastatic Castration-Resistant Prostate Cancer

OBJECTIVE

177Lutetium [Lu] Ludotadipep is a novel prostate-specific membrane antigen targeting therapeutic agent with an albumin motif added to increase uptake in the tumors. We assessed the biodistribution and dosimetry of [177Lu]Ludotadipep in patients with metastatic castration-resistant prostate cancer (mCRPC).

MATERIALS AND METHODS

Data from 25 patients (median age, 73 years; range, 60-90) with mCRPC from a phase I study with activity escalation design of single administration of [177Lu]Ludotadipep (1.85, 2.78, 3.70, 4.63, and 5.55 GBq) were assessed. Activity in the salivary glands, lungs, liver, kidneys, and spleen was estimated from whole-body scan and abdominal SPECT/CT images acquired at 2, 24, 48, 72, and 168 h after administration of [177Lu]Ludotadipep. Red marrow activity was calculated from blood samples obtained at 3, 10, 30, 60, and 180 min, and at 24, 48, and 72 h after administration. Organ- and tumor-based absorbed dose calculations were performed using IDAC-Dose 2.1.

RESULTS

Absorbed dose coefficient (mean ± standard deviation) of normal organs was 1.17 ± 0.81 Gy/GBq for salivary glands, 0.05 ± 0.02 Gy/GBq for lungs, 0.14 ± 0.06 Gy/GBq for liver, 0.77 ± 0.28 Gy/GBq for kidneys, 0.12 ± 0.06 Gy/GBq for spleen, and 0.07 ± 0.02 Gy/GBq for red marrow. The absorbed dose coefficient of the tumors was 10.43 ± 7.77 Gy/GBq.

CONCLUSION

[177Lu]Ludotadipep is expected to be safe at the dose of 3.7 GBq times 6 cycles planned for a phase II clinical trial with kidneys and bone marrow being the critical organs, and shows a high tumor absorbed dose.

177 Lu-PSMA-617 Therapy in a Case of Metastatic Castration-Resistant Prostate Cancer

ABSTRACT

We report a 65-year-old man with metastatic castration-resistant prostate cancer who was treated with 2 cycles of 177 Lu-PSMA-617 therapy. PET/CT imaging of 68 Ga-PSMA-11 revealed a complete metabolic response (PERCIST1.0) after therapy. The prostate-specific antigen concentration drastically decreased (97.7% down).

Critical Challenges in Pluvicto Therapy: Incontinent and Anticoagulated Patients

As molecular therapy continues to grow, unanticipated challenges may arise, requiring the institution's therapeutic team to reevaluate its therapeutic protocol to identify and address potential situations and challenges that may occur. This practical pointer will focus on the novel prostate cancer therapy Pluvicto (177Lu-vipivotide tetraxetan) and 2 unique situations and challenges of treating patients at the Theranostic Center at Carilion Clinic, an outpatient facility dedicated to targeted molecular therapy.

Image-Guided Fine-Needle Aspiration Cytology for BRCA Mutation Assessment of PSMA-Positive Lymph Node Metastases in a Patient With Metastatic Castration-Resistant Prostate Cancer

ABSTRACT

A 64-year-old man with metastatic castration-resistant prostate cancer presented for prostate-specific membrane antigen (PSMA) PET/CT in preparation for 177 Lu-PSMA radioligand therapy. For precedent BRCA mutation assessment, fine-needle aspiration cytology of 2 PSMA-positive lymph node metastases was conducted. The acquired material was suitable for next-generation sequencing-based gene panel diagnostics and did not show a BRCA1 / 2 mutation, thus PSMA radioligand therapy was initiated. Fine-needle aspiration cytology of lymph node metastases may be a viable option in evaluating further therapeutic alternatives.

Estimation of the relative biological effectiveness (RBE) of the Lu-DOTA-iPSMA177<!--Q1:CorrectlyacknowledgingtheprimaryfundersandgrantIDsofyourresearchisimportanttoensurecompliancewithfunderpolicies.Pleasemakesurethatfundersarementionedaccordingly.--> radiopharmaceutical

Relative biological effectiveness is a radiobiological parameter relevant in radiotherapy planning and useful in evaluating the physiological impact of radiation in different tissues. Targeted radionuclide therapy allows the selective and specific deposition of higher radiation doses in a noninvasive way and without collateral effects through the administration of radiopharmaceuticals. Lu-DOTA-177(hydrazinylnicotinoyl-Lys-(Nal)-NH-CO-NH-Glu) also called Lu-iPSMA177 is a third generation radiopharmaceutical composed by a peptide that recognizes the prostate-specific membrane antigen (PSMA), a membrane protein overexpressed in several types of cancer and that mediates the radiopharmaceutical's recognition of cancer cells. The present study reports radiobiological parameters of Lu-iPSMA177 and demonstrates the superiority of targeted radiopharmaceuticals over external radiotherapy treatment options in terms of their relative biological effectiveness. The relative biological effectiveness value of 1.020±0.003 for the LINAC, estimated by fitting the linear-quadratic model equation to the resulting survival curves, was like those of 1.25±0.04,1.060±0.005and1.00±0.04 obtained by an alternative method in relation to the mean lethal doses at 90, 80 or 60 survival percent respectively. While the relative biological effectiveness values of 5.65±0.13,4.72±0.27and2.87±0.19 estimated for Lu-iPSMA177 were significantly higher than those for the LINAC. The results confirm that the biological effect produced by the deposition of a radiation absorbed dose delivered by the LINAC can be induced with a quarter of that dose using Lu-iPSMA177 due to the energy distribution, dose-rate and energy fluence.

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.

Gadolinium-Based Nanoparticles Sensitize Ovarian Peritoneal Carcinomatosis to Targeted Radionuclide Therapy

Ovarian cancer (OC) is the most lethal gynecologic malignancy (5-y overall survival rate, 46%). OC is generally detected when it has already spread to the peritoneal cavity (peritoneal carcinomatosis). This study investigated whether gadolinium-based nanoparticles (Gd-NPs) increase the efficacy of targeted radionuclide therapy using [177Lu]Lu-DOTA-trastuzumab (an antibody against human epidermal growth factor receptor 2). Gd-NPs have radiosensitizing effects in conventional external-beam radiotherapy and have been tested in clinical phase II trials. Methods: First, the optimal activity of [177Lu]Lu-DOTA-trastuzumab (10, 5, or 2.5 MBq) combined or not with 10 mg of Gd-NPs (single injection) was investigated in athymic mice bearing intraperitoneal OC cell (human epidermal growth factor receptor 2-positive) tumor xenografts. Next, the therapeutic efficacy and toxicity of 5 MBq of [177Lu]Lu-DOTA-trastuzumab with Gd-NPs (3 administration regimens) were evaluated. NaCl, trastuzumab plus Gd-NPs, and [177Lu]Lu-DOTA-trastuzumab alone were used as controls. Biodistribution and dosimetry were determined, and Monte Carlo simulation of energy deposits was performed. Lastly, Gd-NPs' subcellular localization and uptake, and the cytotoxic effects of the combination, were investigated in 3 cancer cell lines to obtain insights into the involved mechanisms. Results: The optimal [177Lu]Lu-DOTA-trastuzumab activity when combined with Gd-NPs was 5 MBq. Moreover, compared with [177Lu]Lu-DOTA-trastuzumab alone, the strongest therapeutic efficacy (tumor mass reduction) was obtained with 2 injections of 5 mg of Gd-NPs/d (separated by 6 h) at 24 and 72 h after injection of 5 MBq of [177Lu]Lu-DOTA-trastuzumab. In vitro experiments showed that Gd-NPs colocalized with lysosomes and that their radiosensitizing effect was mediated by oxidative stress and inhibited by deferiprone, an iron chelator. Exposure of Gd-NPs to 177Lu increased the Auger electron yield but not the absorbed dose. Conclusion: Targeted radionuclide therapy can be combined with Gd-NPs to increase the therapeutic effect and reduce the injected activities. As Gd-NPs are already used in the clinic, this combination could be a new therapeutic approach for patients with ovarian peritoneal carcinomatosis.

Radioligand Therapy With 177 Lu-PSMA-I&T in Patients With Metastatic Prostate Cancer : Oncological Outcomes and Toxicity Profile

INTRODUCTION

This study aimed to investigate the oncological outcomes and toxicity profile of 177 Lu-PSMA-I&T radioligand therapy (RLT) in patients with metastatic castration-resistant prostate cancer (mCRPC), as well as our initial experience in metastatic hormone-sensitive prostate cancer (mHSPC).

PATIENTS AND METHODS

A total of 38 consecutive patients with metastatic prostate cancer (33 mCRPC and 5 mHSPC) received 177 Lu-PSMA-I&T RLT, with a median of 2 cycles per patient (range, 1-7). Response to RLT was evaluated based on prostate-specific antigen (PSA) changes and imaging response. Clinical progression-free survival and overall survival were used to report oncological outcomes. Toxicity was assessed using the Common Toxicity Criteria for Adverse Events criteria.

RESULTS

In mCRPC, 22 (69%), 18 (56%), and 11 (34%) patients achieved any PSA decline, PSA response of ≥30%, and PSA response of ≥50%, respectively. The clinical progression-free survival and overall survival after the first cycle of RLT were 6.3 and 21.4 months, respectively. In mHSPC, 177 Lu-PSMA-I&T RLT resulted in excellent PSA response (93.0%-99.9%) in all cases. Clinical progression and cancer-related mortality occurred in only 1 case. Toxicity profile was favorable in both mHSPC and mCRPC.

CONCLUSIONS

177 Lu-PSMA-I&T RLT demonstrated favorable PSA response (≥30%) in over half of the patients with mCRPC and excellent PSA response in all patients with mHSPC. Toxicity profile was favorable in both mHSPC and mCRPC settings. Further studies are needed to evaluate the role of 177 Lu-PSMA-I&T RLT in the management of metastatic prostate cancer.

177Lu-Prostate-Specific Membrane Antigen Therapy in Patients with Metastatic Castration-Resistant Prostate Cancer and Prior 223Ra (RALU Study)

223Ra-dichloride (223Ra) and 177Lu-prostate-specific membrane antigen (PSMA) are approved treatments for metastatic castration-resistant prostate cancer (mCRPC). The safety and effectiveness of sequential use of 223Ra and 177Lu-PSMA in patients with mCRPC are not well described. This study aimed to evaluate 177Lu-PSMA safety and efficacy in patients with mCRPC previously treated with 223Ra. Methods: The radium→lutetium (RALU) study was a multicenter, retrospective, medical chart review. Participants had received at least 1 223Ra dose and, in any subsequent therapy line, at least 1 177Lu-PSMA dose. Primary endpoints included the incidence of adverse events (AEs), serious AEs, grade 3-4 hematologic AEs, and abnormal laboratory values. Secondary endpoints included overall survival, time to next treatment/death, and change from baseline in serum prostate-specific antigen and alkaline phosphatase levels. Results: Data were from 133 patients. Before 177Lu-PSMA therapy, 56% (75/133) of patients received at least 4 life-prolonging therapies; all patients received 223Ra (73% received 5-6 injections). Overall, 27% (36/133) of patients received at least 5 177Lu-PSMA infusions. Any-grade treatment-emergent AEs were reported in 79% (105/133) of patients and serious AEs in 30% (40/133). The most frequent grade 3-4 laboratory abnormalities were anemia (30%, 40/133) and thrombocytopenia (13%, 17/133). Median overall survival was 13.2 mo (95% CI, 10.5-15.6 mo) from the start of 177Lu-PSMA. Conclusion: In this real-world setting, 223Ra followed by 177Lu-PSMA therapy in heavily pretreated patients with mCRPC was clinically feasible, with no indication of impairment of 177Lu-PSMA safety or effectiveness.

Radiobiological Assessment of Targeted Radionuclide Therapy with [177Lu]Lu-PSMA-I&T in 2D vs. 3D Cell Culture Models

In vitro therapeutic efficacy studies are commonly conducted in cell monolayers. However, three-dimensional (3D) tumor spheroids are known to better represent in vivo tumors. This study used [177Lu]Lu-PSMA-I&T, an already clinically applied radiopharmaceutical for targeted radionuclide therapy against metastatic castrate-resistant prostate cancer, to demonstrate the differences in the radiobiological response between 2D and 3D cell culture models of the prostate cancer cell lines PC-3 (PSMA negative) and LNCaP (PSMA positive). After assessing the target expression in both models via Western Blot, cell viability, reproductive ability, and growth inhibition were assessed. To investigate the geometric effects on dosimetry for the 2D vs. 3D models, Monte Carlo simulations were performed. Our results showed that PSMA expression in LNCaP spheroids was highly preserved, and target specificity was shown in both models. In monolayers of LNCaP, no short-term (48 h after treatment), but only long-term (14 days after treatment) radiobiological effects were evident, showing decreased viability and reproductive ability with the increasing activity. Further, LNCaP spheroid growth was inhibited with the increasing activity. Overall, treatment efficacy was higher in LNCaP spheroids compared to monolayers, which can be explained by the difference in the resulting dose, among others.

Comparative Analysis of Morphological and Functional Effects of 225Ac- and 177Lu-PSMA Radioligand Therapies (RLTs) on Salivary Glands

Most Prostate Specific Membrane Antigens (PSMAs) targeting small molecules accumulate in the salivary glands (SGs), raising concerns about SG toxicity, especially after repeated therapies or therapy with 225Ac-labeled ligands. SG toxicity is assessed clinically by the severity of patient-reported xerostomia, but this parameter can be challenging to objectively quantify. Therefore, we explored the feasibility of using SG volume as a biomarker for toxicity. In 21 patients with late-stage metastatic resistant prostate cancer (mCRPC), the PSMA volume and ligand uptake of SG were analyzed retrospectively before and after two cycles of 177Lu-PSMA (LuPSMA; cohort A) and before and after one cycle of 225Ac-PSMA-617 (AcPSMA, cohort B). Mean Volume-SG in cohort A was 59 ± 13 vs. 54 ± 16 mL (-10%, p = 0.4), and in cohort B, it was 50 ± 13 vs. 40 ± 11 mL (-20%, p = 0.007), respectively. A statistically significant decrease in the activity concentration in the SG was only observed in group B (SUVmean: 9.2 ± 2.8 vs. 5.3 ± 1.8, p < 0.0001; vs. A: SUVmean: 11.2 ± 3.3 vs. 11.1 ± 3.5, p = 0.8). SG volume and PSMA-ligand uptake are promising markers to monitor the SG toxicity after a PSMA RLT.

Prognostic role of neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, systemic immune-inflammation index, and pan-immune-inflammation value in metastatic castration-resistant prostate cancer patients who underwent 177Lu-PSMA-617

This study is aimed to investigate the prognostic significance of inflammation indices, including neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), and pan-immune-inflammation value (PIV) in metastatic castration-resistant prostate cancer (mCRPC) patients who had received lutetium labeled prostate-specific membrane antigen (177Lu-PSMA-617) therapy. Sixty-one mCRPC patients who received 177Lu-PSMA-617 treatment and followed up in Kocaeli University were included. The relationship between overall survival (OS) and progression-free survival (PFS) and clinical and laboratory parameters was analyzed by multivariate analyses. The mean age was 69.8 ± 6.9 years. The mean follow-up time was 53.2 ± 24 months. The median OS was 14 (95% CI: 8.8-18.1) and the median PFS was 10.4 (95% CI: 4.7-17.2) months. NLR ≥ 2.7, PLR ≥ 134.27, SII ≥ 570.39, PIV ≥ 408.59 were considered as elevated levels. In the multivariate analysis for OS, baseline ECOG performance score (HR: 1.92, 95% CI: 1.01-3.65, P = .046), high albümin (HR: 0.36, 95% CI: 0.16-0.82, P = .015), primary resistant total prostate-specific-antigen (PSA) (HR: 4.37, 95% CI: 1.84-10.35, P = .001), high NLR (HR: 3.32, 95% CI: 1.66-6.65, P = .001), high MLR (HR: 2.53, 95% CI: 1.35-4.76, P = .004), high PLR (HR: 2.47, 95% CI: 1.23-4.96, P = .01), and high SII (HR: 2.17, 95% CI: 1.09-4.32, P = .027) were associated with shorter OS. However, PIV was not associated with survival (P = .69). No factor other than the primer-resistant PSA could be identified as having an impact on PFS (for the PSA, HR: 4.52, 95% CI: 1.89-10.76, P = .001). In this study, pretreatment NLR, MLR, PLR, and SII demonstrate as powerful independent prognostic indices predicting survival in patients with mCRPC receiving 177Lu-PSMA-617 therapy.

Prognostic Value of End-of-Treatment PSMA PET/CT in Patients Treated with 177Lu-PSMA Radioligand Therapy: A Retrospective, Single-Center Analysis

Our objective was to evaluate the prognostic value of end-of-treatment prostate-specific membrane antigen (PSMA) PET/CT (PSMA-PET) in patients with metastatic castration-resistant prostate cancer (mCRPC) treated with 177Lu-PSMA radioligand therapy (PSMA-RLT). Methods: This was a single-center retrospective study. mCRPC patients who underwent PSMA-RLT with available baseline PSMA-PET (bPET) and end-of-treatment PSMA-PET (ePET) within 6 mo of the last PSMA-RLT cycle were eligible. Overall survival (OS) and prostate-specific antigen (PSA) progression status at the time of ePET (by Prostate Cancer Clinical Trials Working Group 3 criteria) were collected. PSMA-PET tumor segmentation was performed to obtain whole-body PSMA tumor volume (PSMA-VOL) and define progressive (≥20% increase) versus nonprogressive disease. Pairs of bPET and ePET were interpreted for appearance of new lesions. Response Evaluation Criteria in PSMA-PET/CT (RECIP) 1.0 were also applied to define progressive versus nonprogressive disease. The associations between changes in PSMA-VOL, new lesions, RECIP 1.0, and PSA progression status at the time of ePET with OS were evaluated by Kaplan-Meier analysis. Results: Twenty mCRPC patients were included. The median number of treatment cycles was 3.5 (interquartile range [IQR], 2-4). The median time between bPET and cycle 1 of PSMA-RLT was 1.0 mo (IQR, 0.7-1.8 mo). The median time between the last cycle of PSMA-RLT and ePET was 1.9 mo (IQR, 1.2-3.5 mo). Twelve of 20 patients (60%) had died at the last follow-up. The median follow-up time from ePET for survivors was 31.2 mo (IQR, 6.8-40.7 mo). The median OS from ePET was 11.4 mo (IQR, 6.8-30.7 mo). Patients with new lesions on ePET had shorter OS than those without new lesions (median OS, 10.7 mo [95% CI, 9.2-12.2] vs. not reached; P = 0.002). Patients with progressive PSMA-VOL had shorter OS than those with nonprogressive PSMA-VOL (median OS, 10.7 mo [95% CI: 9.7-11.7 mo] vs. not reached; P = 0.007). Patients with progressive RECIP had shorter OS than those with nonprogressive RECIP (median OS, 10.7 mo [95% CI, 9.7-11.7 mo] vs. not reached; P = 0.007). PSA progression at the time of ePET was associated with shorter OS (median, 10.9 mo [95% CI, 9.4-12.4 mo] vs. not reached; P = 0.028). Conclusion: In this retrospective study of 20 mCRPC patients treated with PSMA-RLT, progression on ePET by the appearance of new lesions, changes in PSMA-VOL, and RECIP 1.0 was prognostic for OS. Validation in larger, prospective multicentric clinical trials is warranted.

Lesion Dosimetry for [177Lu]Lu-PSMA-617 Radiopharmaceutical Therapy Combined with Stereotactic Body Radiotherapy in Patients with Oligometastatic Castration-Sensitive Prostate Cancer

A single-institution prospective pilot clinical trial was performed to demonstrate the feasibility of combining [177Lu]Lu-PSMA-617 radiopharmaceutical therapy (RPT) with stereotactic body radiotherapy (SBRT) for the treatment of oligometastatic castration-sensitive prostate cancer. Methods: Six patients with 9 prostate-specific membrane antigen (PSMA)-positive oligometastases received 2 cycles of [177Lu]Lu-PSMA-617 RPT followed by SBRT. After the first intravenous infusion of [177Lu]Lu-PSMA-617 (7.46 ± 0.15 GBq), patients underwent SPECT/CT at 3.2 ± 0.5, 23.9 ± 0.4, and 87.4 ± 12.0 h. Voxel-based dosimetry was performed with calibration factors (11.7 counts per second/MBq) and recovery coefficients derived from in-house phantom experiments. Lesions were segmented on baseline PSMA PET/CT (50% SUVmax). After a second cycle of [177Lu]Lu-PSMA-617 (44 ± 3 d; 7.50 ± 0.10 GBq) and an interim PSMA PET/CT scan, SBRT (27 Gy in 3 fractions) was delivered to all PSMA-avid oligometastatic sites, followed by post-PSMA PET/CT. RPT and SBRT voxelwise dose maps were scaled (α/β = 3 Gy; repair half-time, 1.5 h) to calculate the biologically effective dose (BED). Results: All patients completed the combination therapy without complications. No grade 3+ toxicities were noted. The median of the lesion SUVmax as measured on PSMA PET was 16.8 (interquartile range [IQR], 11.6) (baseline), 6.2 (IQR, 2.7) (interim), and 2.9 (IQR, 1.4) (post). PET-derived lesion volumes were 0.4-1.7 cm3 The median lesion-absorbed dose (AD) from the first cycle of [177Lu]Lu-PSMA-617 RPT (ADRPT) was 27.7 Gy (range, 8.3-58.2 Gy; corresponding to 3.7 Gy/GBq, range, 1.1-7.7 Gy/GBq), whereas the median lesion AD from SBRT was 28.1 Gy (range, 26.7-28.8 Gy). Spearman rank correlation, ρ, was 0.90 between the baseline lesion PET SUVmax and SPECT SUVmax (P = 0.005), 0.74 (P = 0.046) between the baseline PET SUVmax and the lesion ADRPT, and -0.81 (P = 0.022) between the lesion ADRPT and the percent change in PET SUVmax (baseline to interim). The median for the lesion BED from RPT and SBRT was 159 Gy (range, 124-219 Gy). ρ between the BED from RPT and SBRT and the percent change in PET SUVmax (baseline to post) was -0.88 (P = 0.007). Two cycles of [177Lu]Lu-PSMA-617 RPT contributed approximately 40% to the maximum BED from RPT and SBRT. Conclusion: Lesional dosimetry in patients with oligometastatic castration-sensitive prostate cancer undergoing [177Lu]Lu-PSMA-617 RPT followed by SBRT is feasible. Combined RPT and SBRT may provide an efficient method to maximize the delivery of meaningful doses to oligometastatic disease while addressing potential microscopic disease reservoirs and limiting the dose exposure to normal tissues.

[177Lu]Lu-PSMA-617 Versus Docetaxel in Chemotherapy-Naïve Metastatic Castration-Resistant Prostate Cancer: Final Survival Analysis of a Phase 2 Randomized, Controlled Trial

The prostate-specific membrane antigen (PSMA) inhibitor [177Lu]Lu-PSMA-617 has been previously demonstrated to be noninferior to docetaxel in achieving a biochemical response in chemotherapy-naïve metastatic castration-resistant prostate cancer patients. Here, we report the final analysis of overall survival (OS) for a phase 2 randomized, controlled trial. Methods: Forty chemotherapy-naïve, PSMA-positive metastatic castration-resistant prostate cancer patients were randomly assigned to [177Lu]Lu-PSMA-617 (n = 20) or docetaxel (n = 20). Thirty-five patients received treatment per the protocol. Survival analysis was done using Kaplan-Meier curves and the Cox regression model. Results: The mean follow-up duration was 33.4 mo. In intention-to-treat analysis, the median OS for the [177Lu]Lu-PSMA-617 and docetaxel arms was 15.0 mo (95% CI, 9.5-20.5 mo) and 15.0 mo (95% CI, 8.1-21.9 mo), respectively (P = 0.905). In per-protocol analysis, the median OS was 19.0 mo (95% CI, 12.3-25.7 mo) versus 15.0 mo (95% CI, 8.1-21.9 mo), respectively (P = 0.712). No significant difference in OS was observed between the 2 arms across the analyzed subgroups. Conclusion: Long-term outcomes with [177Lu]Lu-PSMA-617 administered earlier in the prechemotherapy setting are comparable to those with docetaxel.

Prediction of Resistance to 177Lu-PSMA Therapy by Assessment of Baseline Circulating Tumor DNA Biomarkers

177Lu-PSMA-617 and 177Lu-PSMA I&T (collectively termed 177Lu-PSMA) are currently being used for the treatment of selected metastatic castration-resistant prostate cancer (mCRPC) patients with PSMA PET-positive disease, but biomarkers for these agents remain incompletely understood. Methods: Pretreatment circulating tumor DNA (ctDNA) samples were collected from 44 mCRPC patients receiving 177Lu-PSMA treatment. Prostate-specific antigen responders and nonresponders were assessed relative to the ctDNA findings at baseline. Results: The ctDNA findings indicated that nonresponders were more likely to have gene amplifications than were responders (75% vs. 39.2%, P = 0.03). In particular, amplifications in FGFR1 (25% vs. 0%, P = 0.01) and CCNE1 (31.2% vs. 0%, P = 0.001) were more likely to be present in nonresponders. CDK12 mutations were more likely to be present in nonresponders (25% vs. 3.6%, P = 0.05). Conclusion: Our analyses indicate that ctDNA assays may contain specific biomarkers predictive of response or resistance for 177Lu-PSMA-treated mCRPC patients. Additional confirmatory studies are required before clinicians can use these findings to make personalized treatment decisions.

Improved Quality of Life in Metastatic Castration-Resistant Prostate Cancer Patients Receiving Consecutive Cycles of 177Lu-PSMA I&T

The aim of this retrospective analysis was to evaluate health-related quality of life (HRQoL) for patients with metastatic castration-resistant prostate cancer (mCRPC) receiving consecutive cycles of 177Lu-prostate-specific membrane antigen (PSMA) radioligand therapy (RLT) using the reliable and validated European Organisation for Research and Treatment of Cancer core quality-of-life (QoL) questionnaire. In addition, differences in HRQoL between patients with early discontinuation of treatment because of disease progression and patients who were defined as eligible for treatment continuation were analyzed. Methods: In total, 60 mCRPC patients were included in this analysis. The European Organisation for Research and Treatment of Cancer core QoL questionnaire was completed at baseline, before each treatment cycle up to the sixth treatment cycle, and at the time of PSMA-ligand PET/CT scans after the second and fourth treatment cycles. QoL assessment included global health status, functional scales, and symptom burden during treatment. Results: Global health was significantly improved at the second and fourth cycles of 177Lu-PSMA RLT (P = 0.014 and P = 0.039, respectively). In line with this, role and emotional functioning showed significant improvements at the second and fourth treatment cycles (role functioning, P = 0.045 and P = 0.048, respectively, and emotional functioning, P = 0.035 and P = 0.007, respectively). In addition, compared with baseline, fatigue and pain were significantly alleviated at the second and fourth treatment cycles (pain, P = 0.035 and P = 0.034, respectively, and fatigue, P = 0.042 and P = 0.041, respectively). Other aspects of HRQoL, even if not significantly improved, remained stable over time, except for deterioration of fatigue at the study's end (P = 0.014) and reduction of dyspnea at the second treatment cycle (P = 0.012). Patients with early discontinuation of treatment showed a concordant decline in HRQoL. Conclusion: mCRPC patients showed significant improvement in HRQoL in the course of treatment with 177Lu-PSMA RLT. Furthermore, patients with early discontinuation of treatment showed an analogous decline in HRQoL.

Tandem Isotope Therapy with 225Ac- and 177Lu-PSMA-617 in a Murine Model of Prostate Cancer

Radionuclide therapy targeting prostate-specific membrane antigen (PSMA) is a promising option for metastatic castration-resistant prostate cancer. Clinical experience using 177Lu or 225Ac has demonstrated encouraging treatment responses; however, responses are not durable. Dual-isotope combinations, or "tandem" approaches, may improve tolerability while retaining a high tumor dose. In this study, we directly compared α- versus β-particle treatment, as well as a combination thereof, at different stages of disease in a murine model of disseminated prostate cancer. Methods: First, to determine comparable injected activities from 177Lu- and 225Ac-PSMA-617, ex vivo biodistribution studies were performed at 5 time points after treatment of C4-2 subcutaneous tumor-bearing NSG mice. To establish a more representative model of metastatic prostate cancer, NSG mice were inoculated with luciferase-expressing C4-2 cells in the left ventricle, leading to disseminated visceral and bone lesions. At either 3 or 5 wk after inoculation, the mice were treated with equivalent tumor dose-depositing activities of 177Lu- or 225Ac-PSMA-617 alone or in combination (35 MBq of 177Lu, 40 kBq of 225Ac, or 17 MBq of 177Lu + 20 kBq 225Ac; 10/group). Disease burden was assessed by weekly bioluminescence imaging. Treatment efficacy was evaluated using whole-body tumor burden and overall survival. Results: The ex vivo biodistribution studies revealed that 35 MBq of 177Lu and 40 kBq of 225Ac yield equivalent absorbed tumor doses in a subcutaneous C4-2 model. The disease burden of mice treated at 3 wk after inoculation (microscopic disease) with 177Lu was not significantly different from that of untreated mice. However, 225Ac-PSMA-617 both as a single agent and in combination with 177Lu (17 MBq of 177Lu + 20 kBq of 225Ac) were associated with significant whole-body tumor growth retardation and survival benefit (overall survival, 8.3 wk for nontreatment, 9.4 wk for 177Lu, 15.3 wk for 225Ac alone, and 14.1 wk for tandem therapy). When treated at 5 wk after inoculation (macroscopic disease), all treatment groups showed retarded tumor growth and improved survival, with no significant differences between 225Ac alone and administration of half the 225Ac activity in tandem with 177Lu (overall survival, 7.9 wk for nontreatment, 10.3 wk for 177Lu, 14.6 wk for 225Ac alone, and 13.2 wk for tandem therapy). Conclusion: Treatment of a disseminated model of prostate cancer with simultaneous 225Ac- and 177Lu-PSMA-617 results in significantly decreased tumor growth compared with 177Lu, which was ineffective as a single agent against microscopic lesions. Mice treated later in the disease progression and bearing macroscopic, millimeter-sized lesions experienced significant tumor growth retardation and survival benefit in both monoisotopic and tandem regimens of 177Lu and 225Ac. Although the greatest benefits were observed with the single agent 225Ac, the tandem arm experienced no significant difference in disease burden or survival benefit, suggesting that the reduced activity of 225Ac was adequately compensated in the tandem arm. The superior therapeutic efficacy of 225Ac in this model suggests a preference for α-emitters alone, or possibly in combination, in the microscopic disease setting.

Prediction of Response to 177Lu-PSMA Therapy Based on Tumor-to-Kidney Ratio on Pretherapeutic PSMA PET/CT and Posttherapeutic Tumor-Dose Evaluation in mCRPC

The aim of this study was to analyze the absorbed dose of 177Lu-PSMA in osseous versus lymphatic metastases in patients with metastatic castration-resistant prostate cancer across therapy cycles and to relate those data to therapeutic success. In addition, pretherapeutic prostate-specific membrane antigen (PSMA) PET/CT was evaluated for its ability to predict response behavior. Methods: The study comprised 30 patients with metastatic castration-resistant prostate cancer, each receiving at least 3 cycles of 177Lu-PSMA therapy. Prostate-specific antigen (PSA) values between baseline and 6 wk after the third therapy cycle were used to classify the patients as responders (PSA decline ≥ 50%) or nonresponders (unchanged or increasing PSA level). Quantitative SPECT/CT images were acquired 24, 48, and 168 h after application of 177Lu-PSMA. The absorbed dose for tumor lesions was calculated with dosimetry software. From the pretherapeutic PET/CT scan, the tumor-to-kidney uptake ratio was determined for different SUVs. Results: Regardless of patient response, the kidneys received a mean dose of 0.55 ± 0.20 Gy/GBq per cycle. In the first therapy cycle, the lymph node lesions received a mean dose of 3.73 ± 1.65 Gy/GBq in responders and 1.86 ± 1.25 Gy/GBq in nonresponders (P < 0.01). For bone lesions, the respective mean doses were 3.47 ± 2.00 Gy/GBq and 1.48 ± 0.95 Gy/GBq (P < 0.01). When successive therapy cycles were compared, the mean dose was found to have been reduced from the first to the second cycle by 27% for lymph nodes and by 33% for bone lesions. A significant difference (P < 0.01) in the ratio of lymph node and bone lesion uptake to kidney uptake between responders and nonresponders could be deduced from the pretherapeutic PET/CT scan. Conclusion: Significantly higher doses were achieved for lymph node and bone lesions in responders. The highest absorbed dose, for both lymphatic and osseous lesions, was achieved in the first cycle, decreasing in the second therapy cycle thereafter despite unchanged therapy activities. It may be possible to estimate the response to therapy from the ratio of tumor uptake to kidney uptake obtained from the pretherapeutic PSMA PET/CT scans.

Theranostic Nuclear Medicine with Gallium-68, Lutetium-177, Copper-64/67, Actinium-225, and Lead-212/203 Radionuclides

Molecular changes in malignant tissue can lead to an increase in the expression levels of various proteins or receptors that can be used to target the disease. In oncology, diagnostic imaging and radiotherapy of tumors is possible by attaching an appropriate radionuclide to molecules that selectively bind to these target proteins. The term "theranostics" describes the use of a diagnostic tool to predict the efficacy of a therapeutic option. Molecules radiolabeled with γ-emitting or β+-emitting radionuclides can be used for diagnostic imaging using single photon emission computed tomography or positron emission tomography. Radionuclide therapy of disease sites is possible with either α-, β-, or Auger-emitting radionuclides that induce irreversible damage to DNA. This Focus Review centers on the chemistry of theranostic approaches using metal radionuclides for imaging and therapy. The use of tracers that contain β+-emitting gallium-68 and β-emitting lutetium-177 will be discussed in the context of agents in clinical use for the diagnostic imaging and therapy of neuroendocrine tumors and prostate cancer. A particular emphasis is then placed on the chemistry involved in the development of theranostic approaches that use copper-64 for imaging and copper-67 for therapy with functionalized sarcophagine cage amine ligands. Targeted therapy with radionuclides that emit α particles has potential to be of particular use in late-stage disease where there are limited options, and the role of actinium-225 and lead-212 in this area is also discussed. Finally, we highlight the challenges that impede further adoption of radiotheranostic concepts while highlighting exciting opportunities and prospects.

Early biochemical and radiographic response after one cycle of [177Lu]Lu-PSMA I&T radioligand therapy in metastatic castration-resistant prostate cancer patients

PURPOSE

The aim of this study was to investigate very early radiographic PSMA PET response after one cycle of [177Lu]Lu-PSMA I&T radioligand therapy (RLT) of metastatic castration-resistant prostate cancer (mCRPC) and to assess its role in predicting overall response and survival.

METHODS

This retrospective study enrolled 40 mCRPC patients who were treated with a median of 3 (2-9) [177Lu]Lu-PSMA I&T RLT cycles. Biochemical response was based on the relative change of serum PSA according to PCWG3 criteria, while radiographic response referred to the relative change of PSMA-derived total viable tumor volumes expressed as total lesion PSMA (TLP).

RESULTS

After one cycle of RLT, biochemical partial response (PR) was seen in 8/40 (20.0%), stable disease (SD) in 22/40 (55.0%), and progressive disease (PD) in 10/40 (25%) patients. In PSMA PET, very early molecular PR was observed in 12 (30.0%), SD in 19 (47.5%), and PD in 9 (22.5%) subjects. The PSA and TLP nadir were achieved after a median of 1 (1-5) and 2 (1-6) cycles, respectively. Nineteen (47.5%) patients showed overall biochemical PR, 11 (27.5%) had SD, and 10 (25%) experienced PD. In PSMA-directed PET, 4 patients experienced molecular complete response (CR), 24 (60.0%) had PR, 4 (10.0%) SD, and 8 (20.0%) PD. Early biochemical or radiographic response was not associated with longer overall survival (OS). Overall biochemical responders had a nearly significantly longer median OS (22.7 months) than non-responders (14.4 months, p = 0.08). Early PSA progression was associated with shorter OS (12.2 months), compared to biochemical SD/PR (18.7 months, p = 0.09).

CONCLUSION

In this retrospective cohort, there was no association between early PSMA PET radiographic response and overall survival; hence, treatment should not be prematurely discontinued. In contrast, early PSA progression after one cycle of [177Lu]Lu-PSMA I&T RLT was an indicator of overall progression and poor clinical outcome.

177Lu-PSMA Treatment Monitoring Through Serial Fast Whole-Body Tomoscintigraphies Recorded With a Latest-Generation CZT-Camera

ABSTRACT

The tomoscintigraphy monitoring of 177Lu-prostate-specific membrane antigen (PSMA) treatment may be helpful for quality control and predicting therapeutic response. Furthermore, the drawbacks of relatively low image quality and extended recording times can be overcome by new CZT-cameras providing fast, high-quality, whole-body recordings. Although still requiring further larger-scale confirmation, the current case report demonstrates that these CZT-cameras have the potential to provide straightforward and comprehensive 177Lu-PSMA treatment monitoring, that is, <20-minute whole-body tomoscintigraphy recording, tumor activities concordant with those from 68Ga-PSMA PET, and no requirement for any additional tracer injection.