The Tyr Phenomenon: A Hypocalcemic Response in High-Volume Treatment Responders to 177Lu-Prostate-Specific Membrane Antigen Therapy

177Lu-prostate-specific membrane antigen (PSMA) is an effective treatment for metastatic castration-resistant prostate cancer. Rarer treatment-related adverse events have not yet been described. Methods: We present case reviews of 2 men with a marked hypocalcemic osteosclerotic response to 177Lu-PSMA-I&T therapy. A clinical dataset of 177Lu-PSMA-I&T therapy was evaluated to estimate the incidence and clinical association with hypocalcemia. Results: Forty-one of the 127 men (32%) had a serum calcium drop, and 6 (5%) developed clinical hypocalcemia during 177Lu-PSMA therapy. The baseline total tumor volume was significantly higher in those who developed hypocalcemia (median, 3,249 cm3 [interquartile range, 1,856-3,852] vs. 465 [interquartile range 135-1,172]; P = 0.002). The mean prostate-specific antigen response in those with hypocalcemia was 78% (SD, 24%). Conclusion: Hypocalcemia may occur in response to 177Lu-PSMA-I&T, particularly with both high-volume bone metastases and a significant prostate-specific antigen response, and may be severe, requiring corticosteroids. Further evaluation of 177Lu-PSMA-induced hypocalcemia is required to better understand mechanisms, optimal treatments, and repercussions from any subsequent osteosclerotic response.

Synthesis and Evaluation of 177Lu-DOTA-PD-L1-i and 225Ac-HEHA-PD-L1-i as Potential Radiopharmaceuticals for Tumor Microenvironment-Targeted Radiotherapy

Current cancer therapies focus on reducing immunosuppression and remodeling the tumor microenvironment to inhibit metastasis, cancer progression, and therapeutic resistance. Programmed death receptor 1 (PD-1) is expressed on immune T cells and is one of the so-called checkpoint proteins that can suppress or stop the immune response. To evade the immune system, cancer cells overexpress a PD-1 inhibitor protein (PD-L1), which binds to the surface of T cells to activate signaling pathways that induce immune suppression. This research aimed to synthesize PD-L1 inhibitory peptides (PD-L1-i) labeled with lutetium-177 (177Lu-DOTA-PD-L1-i) and actinium-225 (225Ac-HEHA-PD-L1-i) and to preclinically evaluate their potential as radiopharmaceuticals for targeted radiotherapy at the tumor microenvironment level. Using PD-L1-i peptide as starting material, conjugation with HEHA-benzene-SCN and DOTA-benzene-SCN was performed to yield DOTA-PD-L1-i and HEHA-PD-L1-I, which were characterized by FT-IR, UV-vis spectroscopy, and HPLC. After labeling the conjugates with 225Ac and 177Lu, cellular uptake in HCC827 cancer cells (PD-L1 positive), conjugate specificity evaluation by immunofluorescence, radiotracer effect on cell viability, biodistribution, biokinetics, and assessment of radiation absorbed dose in mice with in duced lung micrometastases were performed. 225Ac-HEHA-PD-L1-i and 177Lu-DOTA-PD-L1-i, obtained with radiochemical purities of 95 ± 3% and 98.5 ± 0.5%, respectively, showed in vitro and in vivo specific recognition for the PD-L1 protein in lung cancer cells and high uptake in HCC287 lung micrometastases (>30% ID). The biokinetic profiles of 177Lu-DOTA-PD-L1-i and 225Ac-DOTA-PD-L1-i showed rapid blood clearance with renal and hepatobiliary elimination and no accumulation in normal tissues. 225Ac-DOTA-PD-L1-i produced a radiation dose of 5.15 mGy/MBq to lung micrometastases. In the case of 177Lu-DOTA-PD-L1-i, the radiation dose delivered to the lung micrometastases was ten times (43 mGy/MBq) that delivered to the kidneys (4.20 mGy/MBq) and fifty times that delivered to the liver (0.85 mGy/MBq). Therefore, the radiotherapeutic PD-L1-i ligands of 225Ac and 177Lu developed in this research could be combined with immunotherapy to enhance the therapeutic effect in various types of cancer.

Development of [177Lu]Lu-LNC1003 for radioligand therapy of prostate cancer with a moderate level of PSMA expression

PURPOSE

Evans blue as an albumin binder has been widely used to improve pharmacokinetics and enhance tumor uptake of radioligands, including prostate-specific membrane antigen (PSMA) targeting agents. The goal of this study is to develop an optimal Evans blue-modified radiotherapeutic agent that could maximize the absolute tumor uptake and tumor absorbed dose thus the therapeutic efficacy to allow treatment of tumors even with moderate level of PSMA expression.

METHODS

[177Lu]Lu-LNC1003 was synthesized based on PSMA-targeting agent and Evans blue. Binding affinity and PSMA targeting specificity were verified through cell uptake and competition binding assay in 22Rv1 tumor model that has moderate level of PSMA expression. SPECT/CT imaging and biodistribution studies in 22Rv1 tumor-bearing mice were performed to evaluate the preclinical pharmacokinetics. Radioligand therapy studies were conducted to systematically assess the therapeutic effect of [177Lu]Lu-LNC1003.

RESULTS

LNC1003 showed high binding affinity (IC50 = 10.77 nM) to PSMA in vitro, which was comparable with that of PSMA-617 (IC50 = 27.49 nM) and EB-PSMA-617 (IC50 = 7.91 nM). SPECT imaging of [177Lu]Lu-LNC1003 demonstrated significantly improved tumor uptake and retention as compared with [177Lu]Lu-EB-PSMA and [177Lu]Lu-PSMA-617, making it suitable for prostate cancer therapy. Biodistribution studies further confirmed the remarkably higher tumor uptake of [177Lu]Lu-LNC1003 (138.87 ± 26.53%ID/g) over [177Lu]Lu-EB-PSMA-617 (29.89 ± 8.86%ID/g) and [177Lu]Lu-PSMA-617 (4.28 ± 0.25%ID/g) at 24 h post-injection. Targeted radioligand therapy results showed noteworthy inhibition of 22Rv1 tumor growth after administration of a single dose of 18.5 MBq [177Lu]Lu-LNC1003. There was no obvious antitumor effect after [177Lu]Lu-PSMA-617 treatment under the same condition.

CONCLUSION

In this study, [177Lu]Lu-LNC1003 was successfully synthesized with high radiochemical purity and stability. High binding affinity and PSMA targeting specificity were identified in vitro and in vivo. With greatly enhanced tumor uptake and retention, [177Lu]Lu-LNC1003 has the potential to improve therapeutic efficacy using significantly lower dosages and less cycles of 177Lu that promises clinical translation to treat prostate cancer with various levels of PSMA expression.

[177Lu]Lu-PSMA-617 theranostic probe for hepatocellular carcinoma imaging and therapy

PURPOSE

This study aimed to explore the feasibility of using [177Lu]Lu-prostate-specific membrane antigen (PSMA)-617 and [177Lu]Lu-Evans blue (EB)-PSMA-617 for in vivo radioligand therapy by single-dose administration in a PSMA-positive hepatocellular carcinoma (HCC) xenograft mouse model.

METHODS

[177Lu]Lu-PSMA-617 and [177Lu]Lu-EB-PSMA-617 were prepared, and labelling efficiency and radiochemical purity were determined. A HepG2 human HCC subcutaneous xenograft mouse model was established. After intravenous injection of [177Lu]Lu-PSMA-617 or [177Lu]Lu-EB-PSMA-617 (37 MBq) into the mouse model, single-photon emission computed tomography/computed tomography (SPECT/CT) was performed. Biodistribution studies were conducted to verify targeting specificity and pharmacokinetics. In the radioligand therapy study, mice were randomized into 4 groups: 37 MBq [177Lu]Lu-PSMA-617, 18.5 MBq [177Lu]Lu-PSMA-617, 7.4 MBq [177Lu]Lu-EB-PSMA-617, and saline (control). A single-dose administration was applied at the beginning of therapy studies. Tumor volume, body weight, and survival were monitored every 2 days. After the end of therapy, mice were euthanized. Tumors were then weighed, and systemic toxicity was evaluated via blood testing and histological examination of healthy organs.

RESULTS

[177Lu]Lu-PSMA-617 and [177Lu]Lu-EB-PSMA-617 were successfully prepared with high purity and stability. SPECT/CT and biodistribution showed that tumor uptake was higher and persisted longer for [177Lu]Lu-EB-PSMA-617 compared with [177Lu]Lu-PSMA-617. [177Lu]Lu-PSMA-617 was rapidly cleared from the blood, while [177Lu]Lu-EB-PSMA-617 persisted for significantly longer. In radioligand therapy studies, tumor growth was significantly suppressed in the 37 MBq [177Lu]Lu-PSMA-617, 18.5 MBq [177Lu]Lu-PSMA-617, and 7.4 MBq [177Lu]Lu-EB-PSMA-617 groups compared to the saline group. Median survival was 40, 44, 43, and 30 days, respectively. No healthy organ toxicity was observed in safety and tolerability evaluation.

CONCLUSIONS

Radioligand therapy using [177Lu]Lu-PSMA-617 and [177Lu]Lu-EB-PSMA-617 significantly suppressed tumor growth and prolonged survival time in PSMA-positive HCC xenograft mice without obvious toxicity. These radioligands appear promising for clinical use in humans, and future studies are warranted.

Joint EANM/SNMMI procedure guideline for the use of 177Lu-labeled PSMA-targeted radioligand-therapy (177Lu-PSMA-RLT)

Prostate-specific membrane antigen (PSMA) is expressed by the majority of clinically significant prostate adenocarcinomas, and patients with target-positive disease can easily be identified by PSMA PET imaging. Promising results with PSMA-targeted radiopharmaceutical therapy have already been obtained in early-phase studies using various combinations of targeting molecules and radiolabels. Definitive evidence of the safety and efficacy of [177Lu]Lu-PSMA-617 in combination with standard-of-care has been demonstrated in patients with metastatic castration-resistant prostate cancer, whose disease had progressed after or during at least one taxane regimen and at least one novel androgen-axis drug. Preliminary data suggest that 177Lu-PSMA-radioligand therapy (RLT) also has high potential in additional clinical situations. Hence, the radiopharmaceuticals [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMA-I&T are currently being evaluated in ongoing phase 3 trials. The purpose of this guideline is to assist nuclear medicine personnel, to select patients with highest potential to benefit from 177Lu-PSMA-RLT, to perform the procedure in accordance with current best practice, and to prepare for possible side effects and their clinical management. We also provide expert advice, to identify those clinical situations which may justify the off-label use of [177Lu]Lu-PSMA-617 or other emerging ligands on an individual patient basis.

Lutetium-177-PSMA-617 in Metastatic Castration-resistant Prostate Cancer: Limitations of the VISION Trial

Lu-PSMA was approved in the USA for patients with prostate-specific membrane antigen-positive metastatic castration-resistant prostate cancer already treated with androgen receptor pathway inhibition and taxane-based chemotherapy on the basis of results from VISION. Three limitations affected the control arm in VISION: choice of the standard of care was limited, some patients initially deemed ineligible for taxane later received it, and there was a high attrition rate. VISION is an example of the many challenges in modern oncology trials. The direct and indirect costs of Lu-PSMA also mean that this therapy is likely to be out of reach for many nations, deepening global inequities in health care access.

Adoption of Lutetium-177 PSMA radioligand therapy for metastatic castration resistant prostate cancer: a total population analysis in Germany from 2016 to 2020

PURPOSE

This study is to investigate the adoption and current trends of Lutetium-177 PSMA RLT for mCRPC in Germany.

METHODS

We analyzed data from the reimbursement.INFO tool based on German hospitals' quality reports for Lutetium-177 PSMA RLT from 2016 to 2020 and from the nationwide German hospital billing database (Destatis) for general therapy with open radionuclides in combination with prostate cancer from 2006 to 2020. For validation of these billing data, we included the 177Lu-PSMA RLT cycles from two participating institutions from 2016 to 2020. For detection of trends over time we applied linear regression models.

RESULTS

General therapy with open radionuclides increased from 2006 to 2020. We identified a total of 12,553 177Lu-PSMA RLT cycles. The number of 177Lu-PSMA RLTs steadily increased from a total of 1026 therapies in 2016 to 3328 therapies in 2020 (+ 576 RLT/year; p < 0.005). In 2016, 25 departments of nuclear medicine offered this treatment, which increased to 44 nuclear medicine departments in 2020. In 2016, 16% of nuclear medicine departments (4/25) performed more than 100 177Lu-PSMA RLTs, which increased to 36% (16/44) in 2020 (p < 0.005). In 2016, 88% (22/25) of 177Lu-PSMA RLTs were performed at a university hospital, which decreased to 70% (31/44) in 2020. The proportion of patients older than 65 years receiving 177Lu-PSMA RLT increased from 78% in 2016 to 81% in 2020.

CONCLUSION

Treatment of mCRPC with 177Lu-PSMA RLT has been rapidly increasing in Germany in the recent years providing an additional therapy option. This development is remarkable, because of outstanding formal EMA approval.

FDA Approval Summary: Lutetium Lu 177 Vipivotide Tetraxetan for Patients with Metastatic Castration-Resistant Prostate Cancer

On March 23, 2022, the FDA approved Pluvicto (lutetium Lu 177 vipivotide tetraxetan, also known as 177Lu-PSMA-617) for the treatment of adult patients with prostate-specific membrane antigen (PSMA)-positive metastatic castration-resistant prostate cancer (mCRPC) who have been treated with androgen receptor pathway inhibition and taxane-based chemotherapy. The recommended 177Lu-PSMA-617 dose is 7.4 gigabecquerels (GBq; 200 mCi) intravenously every 6 weeks for up to six doses, or until disease progression or unacceptable toxicity. The FDA granted traditional approval based on VISION (NCT03511664), which was a randomized (2:1), multicenter, open-label trial that assessed the efficacy and safety of 177Lu-PSMA-617 plus best standard of care (BSoC; n = 551) or BSoC alone (n = 280) in men with progressive, PSMA-positive mCRPC. Patients were required to have received ≥1 androgen receptor pathway inhibitor, and one or two prior taxane-based chemotherapy regimens. There was a statistically significant and clinically meaningful improvement in overall survival (OS), with a median OS of 15.3 months in the 177Lu-PSMA-617 plus BSoC arm and 11.3 months in the BSoC arm, respectively (HR: 0.62; 95% confidence interval: 0.52-0.74; P < 0.001). The most common adverse reactions (≥20%) occurring at a higher incidence in patients receiving 177Lu-PSMA-617 were fatigue, dry mouth, nausea, anemia, decreased appetite, and constipation. The most common laboratory abnormalities that worsened from baseline in ≥30% of patients receiving 177Lu-PSMA-617 were decreased lymphocytes, decreased hemoglobin, decreased leukocytes, decreased platelets, decreased calcium, and decreased sodium. This article summarizes the FDA review of data supporting traditional approval of 177Lu-PSMA-617 for this indication.

New Horizons in Radioligand Therapy: 161Tb-PSMA-617 in Advanced mCRPC

ABSTRACT

An 85-year-old man with advanced metastatic castration-resistant prostate cancer and progression after 8 cycles of 177 Lu-prostate-specific membrane antigen (PSMA)-617 radioligand therapy (RLT) received 1 cycle of 161 Tb-PSMA RLT. This one administration of 6.5 GBq 161 Tb-PSMA-617 resulted in impressive partial remission with a PSA decline by 53.4% (from 474 to 221 ng/mL) and a concomitant decrease in tumor burden on PSMA PET/CT imaging. The presented case provides stunning initial evidence of the therapeutic potential of 161 Tb-PSMA RLT in metastatic castration-resistant prostate cancer, even in patients progressing after extensive 177 Lu-based RLT. 161 Tb-labeled PSMA ligands may thus offer a promising alternative to standard PSMA RLT.

Increased PSMA Expression in 177 Lu-PSMA-617 Scan in Metastatic Castrate-Resistant Prostate Cancer Patient Treated With PSMA Radioligand Therapy and Enzalutamide : A Potential Game-Changer

ABSTRACT

Androgen deprivation therapy plays an integral role in the treatment algorithm of advanced prostate cancer. Enzalutamide has shown great benefit in castrate-sensitive as well as resistant prostate cancer. Few studies have shown that enzalutamide can potentially increase the PSMA expression on 68 Ga-PSMA-11 PET/CT imaging in patients with metastatic castrate-resistant prostate cancer. We present an interesting case where addition of short course of enzalutamide resulted in increased localization of 177 Lu-PSMA-617 in metastatic lesions on posttherapy scan pointing to the added benefit of PSMA RLT.

Peritoneal Metastases From Prostate Carcinoma Treated With 177 Lu-PSMA-I&T

ABSTRACT

A 71-year-old man was referred for 177 Lu-PSMA therapy. He had metastatic castration-resistant prostate cancer, progressive on several treatment lines, with current PSA 260 μg/L and deteriorating condition. CT showed ascites with omental and peritoneal metastases, all positive on PSMA PET/CT. He was treated with 4 cycles of 7.4 GBq (0.2 Ci) 177 Lu-PSMA-I&T. Posttherapy scans showed good targeting of all metastases. After 4 cycles, PSA had dropped to 44 μ/L. Four months after the fourth cycle, the patients' general condition had significantly improved, and PSA had decreased to 7.0 μg/L.

Short-Interval, Low-Dose [ 177 Lu]Lu-Prostate-Specific Membrane Antigen in the Treatment of Refractory Glioblastoma

ABSTRACT

Prostate-specific membrane antigen (PSMA) is expressed on the neovasculature as well as to some extent on the glioblastoma cells. With this background, we report the case of a 34-year-old man with recurrent glioblastoma who was treated with 2 cycles of low-dose [ 177 Lu]Lu-PSMA after exhausting all available treatment options in the state sector. Baseline imaging demonstrated intense PSMA signal in the known lesion, which was amenable to therapy. The prospect of [ 177 Lu]Lu-PSMA-based therapy for glioblastoma is warranted going forward.

Logistical, technical, and radiation safety aspects of establishing a radiopharmaceutical therapy program: A case in Lutetium-177 prostate-specific membrane antigen (PSMA) therapy

Prostate-specific membrane antigen (PSMA) is a cell surface protein highly expressed in nearly all prostate cancers, with restricted expression in some normal tissues. The differential expression of PSMA from tumor to non-tumor tissue has resulted in the investigation of numerous targeting strategies for therapy of patients with metastatic prostate cancer. In March of 2022, the FDA granted approval for the use of lutetium-177 PSMA-617 (Lu-177-PSMA-617) for patients with PSMA-positive metastatic castration-resistant prostate cancer (mCRPC) who have been treated with androgen receptor pathway inhibition and taxane-based chemotherapy. Therefore, the use of Lu-177-PSMA-617 is expected to increase and become more widespread. Herein, we describe logistical, technical, and radiation safety considerations for implementing a radiopharmaceutical therapy program, with particular focus on the development of operating procedures for therapeutic administrations. Major steps for a center in the U.S. to implement a new radiopharmaceutical therapy (RPT) program are listed below, and then demonstrated in greater detail via examples for Lu-177-PSMA-617 therapy.

Clinical Best Practices for Radiation Safety During Lutetium-177 Therapy

IMPORTANCE

177 Lu therapy as part of theranostic treatment for cancer is expanding but it can be a challenge for sites with limited radiation protection staff to implement the radiation safety program required for therapeutic nuclear medicine.

OBJECTIVE

To increase the adoption of 177 Lu therapy, especially in smaller centers and clinics, by providing a collection of radiation safety best practices and operational experience. To provide a resource for radiation safety officers supporting the implementation of a 177 Lu therapy program.

METHODS

A panel of 11 radiation safety professionals representing sites across Canada and the United States with experience delivering 177 Lu therapy was assembled and discussed their responses to a list of questions focused on the following radiation safety topics: facility layout and design; radiation safety program; and drug management and patient care.

RESULTS

A comprehensive set of best practice guidelines for clinical radiation safety during 177 Lu therapy has been developed based on the collective operational experience of a group of radiation safety professionals. Significant findings included that 177 Lu therapy is often safely administered in unshielded rooms, that staff radiation exposure associated with 177 Lu therapy is minimal relative to other nuclear medicine programs, and that some relatively simple preparation in advance including papering of common surfaces and planning for incontinence can effectively control contamination during therapy.

CONCLUSION

The guidance contained in this paper will assist radiation safety professionals in the implementation of safe, effective 177 Lu therapy programs, even at smaller sites with limited to no experience in therapeutic nuclear medicine.

Genomic characterization of metastatic castration-resistant prostate cancer patients undergoing PSMA radioligand therapy: A single-center experience

BACKGROUND

Genomic defects in DNA-damage repair (DDR) mechanisms have been proposed to affect the radiosensitivity of prostate cancers. In this study, we intended to evaluate the prevalence of genetic alterations in a cohort of metastatic castration-resistant prostate cancer (mCRPC) patients undergoing radioligand therapy (RLT) with prostate-specific membrane antigen (PSMA)-inhibitors as well as the impact of such mutations on treatment outcomes.

METHODS

Data of consecutive mCRPC patients from 2017 to 2021 who were treated with PSMA-RLT and underwent next-generation sequencing (NGS) were collected and analyzed for response and survival outcomes.

RESULTS

In 95 patients of mCRPC treated with PSMA-RLT, 15 patients (median age: 66 years, range: 50-73 years; [¹⁷⁷ Lu]Lu-PSMA-617, n = 12; [²²⁵ Ac]Ac-PSMA-617, n = 3) underwent NGS. The median progression-free survival (PFS) of this cohort was 3 months (95% confidence interval: 1.6-4.4 months). On NGS, 21 genetic alterations were reported in 10/15 (67%) patients, of which 13 were DDR-associated alterations involving the genes: ATM (n = 3), BRCA2 (n = 3), TP53 (n = 2), PTEN (n = 2), FANCD2 (n = 1), FANCM (n = 1), and NBN (n = 1). Overall, 5/15 (33%) patients harbored six pathogenic variants (BRCA2, n = 2; ATM, n = 1; TP53, n = 1; PTEN, n = 2). No significant difference was noted for the biochemical response, radiological response, PFS, and overall survival between the patients with and without genetic alterations.

CONCLUSIONS

Patients of mCRPC undergoing PSMA-RLT were frequently seen to harbor DDR-associated aberrations, albeit with no significant impact on treatment outcomes. Large prospective trials comparing PSMA-RLT-related outcomes in DDR-deficient and -proficient patients are required to bring out the differences, if any, in a more observable manner.

Cross-reactivity to glutamate carboxypeptidase III causes undesired salivary gland and kidney uptake of PSMA-targeted small-molecule radionuclide therapeutics

PURPOSE

Recently, Pluvicto™ ([177Lu]Lu-PSMA-617), a small-molecule prostate-specific membrane antigen (PSMA) radioligand therapeutic, has been approved by the FDA in metastatic castration-resistant prostate cancer. Pluvicto™ and other PSMA-targeting radioligand therapeutics (RLTs) have shown side effects due to accumulation in certain healthy tissues, such as salivary glands and kidney. Until now, the molecular mechanism underlying the undesired accumulation of PSMA-targeting RLTs had not been elucidated.

METHODS

We compared the sequence of PSMA with the entire human proteome to identify proteins closely related to the target. We have identified glutamate carboxypeptidase III (GCPIII), N-acetylated alpha-linked acidic dipeptidase like 1 (NAALADL-1), and transferrin receptor 1 (TfR1) as extracellular targets with the highest similarity to PSMA. The affinity of compound 1 for PSMA, GCPIII, NAALADL-1, and TfR1 was measured by fluorescence polarization. The expression of the putative anti-target GCPIII was assessed by immunofluorescence on human salivary glands and kidney, using commercially available antibodies.

RESULTS

A fluorescent derivative of Pluvicto™ (compound 1) bound tightly to PSMA and to GCPIII in fluorescence polarization experiments, while no interaction was observed with NAALADL-1 and TfR1. Immunofluorescence analysis revealed abundant expression of GCPIII both in healthy human kidney and salivary glands.

CONCLUSION

We conclude that the membranous expression of GCPIII in kidney and salivary gland may be the underlying cause for unwanted accumulation of Pluvicto™ and other Glu-ureido PSMA radio pharmaceuticals in patients.

Individual radiosensitivity reflected by γ-H2AX and 53BP1 foci predicts outcome in PSMA-targeted radioligand therapy

PURPOSE

γ-H2AX and 53BP1 are fundamental for cellular DNA damage response (DDR) after radiation exposure and are linked to cell repair, arrest, or apoptosis. We aimed to evaluate whether DDR-markers in peripheral blood lymphocytes (PBLs) may have predictive potential for outcome in metastatic castration-resistant prostate cancer (mCRPC) patients receiving [177Lu]Lu-prostate-specific membrane antigen (PSMA) radioligand therapy (RLT).

METHODS

We prospectively enrolled 20 men with advanced mCRPC scheduled for PSMA-targeted RLT. Prior to the first cycle of [177Lu]Lu-PSMA RLT, all patients underwent [18F]F-PSMA-1007 positron emission tomography (PET)/computed tomography (CT) for assessment of tumor PSMA expression (assessing maximum standardized uptake value (SUVmax) of all tumor lesions). Blood samples were collected prior to, + 1 h after, and + 24 h after administration of [177Lu]Lu-PSMA, and DDR-markers γ-H2AX and 53BP1 were determined in PBLs through immunocytofluorescence. We then tested the predictive performance of DDR-markers relative to clinical and PET-based parameters for progressive disease (PSA-PD) after 2 cycles. In addition, the predictive value for progression-free survival (PSA-PFS, provided as median and 95% confidence interval [CI]) was explored.

RESULTS

Low baseline 53BP1 and γ-H2AX foci (P = 0.17) tended to predict early PSA-PD, whereas low SUVmax was significantly associated with higher risk for PSA-PD (P = 0.04). In Kaplan-Meier analysis, there was a trend towards prolonged PSA-PFS in patients with higher baseline 53BP1 of 6 months (mo; 95%CI, 4-9 mo) compared to 3 mo in patients with low 53BP1 (95% CI, 2-3 mo; P = 0.12). Comparable results were recorded for higher γ-H2AX expression (6 mo [95% CI, 3-9 mo] relative to 3 mo [95% CI, 2-4 mo] in patients with low γ-H2AX; P = 0.12). SUVmax, however, did not demonstrate predictive value (P = 0.29). Consistently, in univariate Cox-regression analysis, baseline 53BP1 foci demonstrated borderline significance for predicting PSA-PFS under [177Lu]Lu-PSMA RLT (P = 0.05).

CONCLUSION

In this prospective study investigating mCRPC patients undergoing [177Lu]Lu-PSMA RLT, low baseline DDR-markers in PBLs tended to predict poor outcome. Although the study group was small and results need further confirmation, these preliminary findings lay the foundation for exploring additive radiosensitizing or treatment intensification in future studies with high-risk individuals scheduled for RLT.

Is18F-FDG PET needed to assess177Lu-PSMA Therapy Eligibility? A VISION-like, Single-Center Analysis

¹⁸F-FDG and prostate-specific membrane antigen (PSMA) PET have been used to assess eligibility for PSMA-targeted therapy by some centers. However, it remains unclear whether both examinations are needed as a part of workup in the clinical practice or whether PSMA PET alone, as was done in the positive phase 3 VISION trial, is sufficient to identify suitable candidates. The aim was to reanalyze all patients who underwent both ¹⁸F-FDG and PSMA PET for PSMA-targeted therapy eligibility assessment using the VISION trial criteria. Methods: Eighty-nine men with metastatic castration-resistant prostate cancer referred to ¹⁷⁷Lu-PSMA therapy from June 2019 to October 2021 who underwent both ¹⁸F-FDG and PSMA PET (using either ⁶⁸Ga-PSMA-11 or ¹⁸F-PSMA-1007) examinations within 2 wk were included in this analysis. Eligibility status was determined in accordance with either knowledge of both ¹⁸F-FDG and PSMA PET (clinical routine) or VISION criteria with PSMA PET-only (study reassessment, done twice with liver only for PSMA-11 and liver/spleen as reference for PSMA-1007). A metastasis seen on ¹⁸F-FDG PET or CT but not on PSMA PET was denoted as a mismatch finding and led to exclusion from ¹⁷⁷Lu-PSMA therapy. On the basis of clinical assessment, 52 patients received ¹⁷⁷Lu-PSMA therapy, and 37 did not; all patients were reassessed. Results: Patients treated with ¹⁷⁷Lu-PSMA therapy had significantly longer overall survival than those not treated (12.4 vs. 6.8 mo, P < 0.01). PSMA-only analysis (spleen/liver reference) and ¹⁸F-FDG/PSMA mismatch reads had substantial agreement (Cohen κ = 0.73). Eighteen percent (n = 16/89) of patients had a mismatch finding based on ¹⁸F-FDG/PSMA PET. With the liver/spleen reference, a minor fraction of patients who had no mismatch finding (and were therefore treated) would have been withheld from therapy by PSMA-only analysis (3%). Three percent (n = 3) of all patients had an ¹⁸F-FDG/PSMA mismatch finding not detected by PSMA PET-only (VISION-like) analysis. For patients not receiving PSMA therapy, the overall survival was not statistically significantly different comparing ¹⁸F-FDG/PSMA mismatch versus nonmismatch (P = 0.61) patients. Conclusion: ¹⁸F-FDG and PSMA PET provide complementary information, yet less than 5% of patients had mismatch findings not detected using PSMA PET-only. Based on our data, ¹⁸F-FDG/PSMA mismatch examination and PSMA-only analysis have a substantial level of agreement.

Cure of disseminated human lymphoma with [177Lu]Lu-ofatumumab in a preclinical model

Although immunotherapies that target CD20 on most non-Hodgkin lymphoma (NHL) cells have improved patient outcomes, current therapies are inadequate because many cases are, or become, refractory or undergo relapse. Here, we labelled the third-generation human anti-CD20 antibody ofatumumab with ¹⁷⁷Lu, determined the in vitro characteristics of [¹⁷⁷Lu]Lu-ofatumumab, estimated human dosimetry, and assayed tumor targeting and therapeutic efficacy in a murine model of disseminated NHL. Methods: CHX-A″-diethylenetriaminepentaacetic acid-[¹⁷⁷Lu]Lu-ofatumumab was prepared. We evaluated radiochemical yield, purity, in vitro immunoreactivity, stability, (n = 7), affinity, and killing of CD20-expressing Raji cells (n = 3). Human dosimetry was estimated from biodistribution studies as percentage injected activity per gram using C57BL/6N mice. Tissue and organ biodistribution was determined in R2G2 immunodeficient mice with subcutaneous Raji-cell tumors. Therapy studies used R2G2 mice with disseminated human Raji-luc tumor cells (n = 10 mice/group). Four days after cell injection, the mice were left untreated or were treated with ofatumumab, 8.51 MBq of [¹⁷⁷Lu]Lu-IgG, or 0.74 or 8.51 MBq of [¹⁷⁷Lu]Lu-ofatumumab. Survival, weight, and bioluminescence were tracked. Results: Radiochemical yield was 93% ± 2%, radiochemical purity was 99% ± 1%, and specific activity was 401 ± 17 MBq/mg. Immunoreactivity was substantially preserved, and more than 75% of ¹⁷⁷Lu remained chelated after 7 d in serum. [¹⁷⁷Lu]Lu-ofatumumab specifically killed Raji-luc cells in vitro (P < 0.05). Dosimetry estimated that an effective dose for human administration is 0.36 mSv/MBq and that marrow may be the dose-limiting organ. Biodistribution in subcutaneous tumors 1, 3, and 7 d after [¹⁷⁷Lu]Lu-ofatumumab injection was 11, 15, and 14 percentage injected activity per gram, respectively. In the therapy study, median survival of untreated mice was 19 d, not statistically different from mice treated with 8.51 MBq of [¹⁷⁷Lu]Lu-IgG (25 d). Unlabeled ofatumumab increased survival to 46 d, similar to 0.74 MBq of [¹⁷⁷Lu]Lu-ofatumumab (59 d), with both being superior to no treatment (P < 0.0003). Weight loss and increased tumor burden preceded death or killing of the animal for cause. In contrast, treatment with 8.51 MBq of [¹⁷⁷Lu]Lu-ofatumumab dramatically increased median survival (>221 d), permitted weight gain, eliminated detectable tumors, and was curative in 9 of 10 mice. Conclusion: [¹⁷⁷Lu]Lu-ofatumumab shows favorable in vitro characteristics, localizes to tumor, and demonstrates curative therapeutic efficacy in a disseminated lymphoma model, showing potential for clinical translation to treat NHL.

A single-arm, low-dose, prospective study of177Lu-EB-PSMA radioligand therapy in patients with metastatic castration-resistant prostate cancer

We aimed to investigate the safety and therapeutic efficacy of radioligand therapy (RLT) of ¹⁷⁷Lu-EB-prostate-specific membrane antigen (PSMA) in patients with metastatic castration-resistant prostate cancer. Methods: Thirty men with progressive metastatic castration-resistant prostate cancer previously treated with taxane-based chemotherapy and second-generation androgen deprivation therapy were enrolled. All patients received up to 3 cycles of approximately 2.0 GBq (55 mCi) of ¹⁷⁷Lu-EB-PSMA per cycle at 8-wk intervals. The primary endpoint was therapeutic safety, including changes in hematologic status, liver function, and renal function. An additional primary endpoint was therapeutic efficacy, including prostate-specific antigen (PSA) response and molecular imaging response. The secondary endpoints were PSA progression-free survival (PFS) and overall survival (OS). Another endpoint was patient-reported health-related quality of life. Results: From January 2019 to December 2021, 30, 22, and 11 patients received 1, 2, or 3 cycles of ¹⁷⁷Lu-EB-PSMA RLT, respectively. During the entire follow-up period, 33.3% of patients experienced grade 3 hematologic adverse events. Seventeen (56.7%) patients achieved a PSA reduction of at least 50%. The median PSA PFS was 4.6 mo (95% CI, 2.7-6.5 mo), and the median OS was 12.6 mo (95% CI, 8.1-17.1 mo). A higher whole-body PSMA SUV_mean correlated with a better PSA response, higher baseline alkaline phosphatase and larger total PSMA-positive tumor volume were associated with worse PSA PFS, and the existence of visceral metastases and higher PSA value at baseline were significant prognosticators of worse OS. Health-related quality-of-life outcomes improved significantly after ¹⁷⁷Lu-EB-PSMA RLT. Conclusion: RLT based on approximately 2.0 GBq of ¹⁷⁷Lu-EB-PSMA for up to 3 cycles may achieve a PSA response and hematologic toxicity comparable to those from 7.4-GBq doses of ¹⁷⁷Lu-PSMA-617 for up to 4-6 cycles. Further studies with more cycles of ¹⁷⁷Lu-EB-PSMA RLT are needed to evaluate the potential benefits in terms of PFS and OS.

Novel Framework for Treatment Response Evaluation Using PSMA PET/CT in Patients with Metastatic Castration-Resistant Prostate Cancer (RECIP 1.0): An International Multicenter Study

Our objective was to develop version 1.0 of a novel framework for response evaluation criteria in prostate-specific membrane antigen (PSMA) PET/CT (RECIP) and a composite response classification that combines responses by prostate-specific antigen (PSA) measurements and by RECIP 1.0 (PSA + RECIP). Methods: This was an international multicenter, retrospective study. One hundred twenty-four men with metastatic castration-specific prostate cancer (mCRPC) who underwent 177Lu-PSMA therapy and received PSMA PET/CT at baseline and at an interim time point of 12 wk were included. Pairs of baseline interim PET/CT scans were interpreted by consensus among 3 masked readers for appearance of new lesions. Tumor lesions were segmented, and total PSMA-positive tumor volume (PSMA-VOL) was obtained. Appearance of new lesions and changes in PSMA-VOL were combined to develop RECIP 1.0, which included classifications of complete response (RECIP-CR: absence of any PSMA-ligand uptake on interim PET/CT), partial response (RECIP-PR: decline ≥ 30% in PSMA-VOL and no appearance of new lesions), progressive disease (RECIP-PD: increase ≥ 20% in PSMA-VOL and appearance of new lesions), and stable disease (RECIP-SD: any condition but RECIP-PR or RECIP-PD). Changes in PSA levels at 12 wk by Prostate Cancer Working Group Criteria 3 were recorded. PSA + RECIP results were defined as response (PSA decline ≥ 50% or RECIP-PR/CR) or progression (PSA increase ≥ 25% or RECIP-PD). The study's primary outcome measure was the prognostic value of RECIP 1.0 for overall survival (OS). The secondary outcome measure was the prognostic accuracy (C-index) of PSA + RECIP versus PSA responses. Results: Patients with RECIP-PD (n = 39; 8.3 mo) had a shorter OS than patients with stable disease (RECIP-SD) (n = 47; 13.1 mo; P < 0.001) or RECIP-PR (n = 38; 21.7 mo; P < 0.001). In identifying responders and progressors, PSA + RECIP had C-indices superior to those of PSA only: 0.65 versus 0.62 (P = 0.028) and 0.66 versus 0.63 (P = 0.044), respectively. Conclusion: PSMA PET/CT by RECIP 1.0 is prognostic for OS and can be used as a response biomarker to monitor early efficacy of 177Lu-PSMA in men with mCRPC. PSA + RECIP may be used as a novel composite endpoint in mCRPC clinical trial design.

Any decline in prostate-specific antigen levels identifies survivors scheduled for prostate-specific membrane antigen-directed radioligand therapy

BACKGROUND

Prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) is increasingly incorporated in the therapeutic algorithm of patients with metastatic castration-resistant prostate cancer (mCRPC). We aimed to elucidate the predictive performance of early biochemical response for overall survival (OS).

MATERIALS AND METHODS

In this bicentric analysis, we included 184 mCRPC patients treated with ¹⁷⁷ Lu-PSMA RLT. Response to treatment was defined as decrease in prostate-specific antigen (PSA) levels 8 weeks after the first cycle of RLT (any decline or >50% according to Prostate Cancer Working Group 3). OS of responders and nonresponders was then compared using Kaplan-Meier curves and log-rank comparison.

RESULTS

A total of 114/184 patients (62.0%) showed any PSA decline (PSA response >50%, 55/184 [29.9%]). For individuals exhibiting a PSA decline >50%, OS of 19 months was significantly longer relative to nonresponders (13 months; hazard ratio of death [HR] = 0.64, 95% confidence interval [95% CI] = 0.44-0.93; p = 0.02). However, the difference was even more pronounced for any PSA decline, with an OS of 19 months in responders, but only 8 months in nonresponders (HR = 0.39, 95% CI = 0.25-0.60; p < 0.001).

CONCLUSIONS

In mCRPC patients scheduled for RLT, early biochemical response was tightly linked to prolonged survival, irrespective of the magnitude of PSA decline. As such, even in patients with PSA decrease of less than 50%, RLT should be continued.

Lutetium-177 Radiopharmeceutical Therapy Extravasation Lessons Learned

Lutetium-177 ( 177 Lu) dotatate has been offered at Fox Chase Cancer Center since 2017 as part of a clinical trial and then in 2018 as a commercially available cancer therapy, and we thought we were prepared for most 177 Lu issues by the fall of 2020. A single phone call identified that the Radiation Safety Department had not been prepared to address extravasations. Fortunately for the patient and Radiation Safety, the 177 Lu therapies are administered by an infusion nurse and Fox Chase Cancer Center has a robust infusion center. The expertise of our infusion center team helped to quickly identify specific mitigation efforts to employ. A team of radiation safety and diagnostic medical physicists worked together to estimate a tissue dose. Research was also started with the aim of identifying therapeutic 177 Lu extravasations as early as possible. The lessons we learned and plans for future early identification of 177 Lu dotatate extravasations are the basis of this paper.

Outcome of 177 Lu-PSMA Radionuclide Treatment in Advanced Prostate Cancer and Its Association With Clinical Parameters : A Single-Center Experience

PURPOSE

This study was set out to analyze the efficacy and safety of 177 Lu-PSMA-617 (LuPSMA) treatment in metastatic castration-resistant prostate cancer (mCRPC) patients.

PATIENTS AND METHODS

Progressive mCRPC patients who received at least 1 cycle of LuPSMA therapy were evaluated retrospectively. Demographic, clinic, and histopathological data were documented. Treatment efficacy was determined based on biochemical response criteria (Prostate Cancer Clinical Trial Working Group 3), and toxicity rates were defined based on CTCAE v4.03. The prognostic significance of laboratory/clinical data and 68 Ga-PSMA PET/CT quantitative results were analyzed using SPSS Version 24.0.

RESULTS

One hundred patients (median prostate-specific antigen [PSA] level, 75.7 ng/mL) who met the eligibility criteria were identified. The median number of cycles received per patient was 3 (range, 1-9). After the first cycles of LuPSMA, biochemical partial response, biochemical stable disease, and biochemical progressive disease were observed in 31%, 36%, and 33% of patients, respectively. Any PSA decline was determined in 60% of patients. After the fourth cycle of treatment, biochemical partial response, biochemical stable disease, and biochemical progressive disease were defined in 48%, 26%, and 26% of patients, respectively. The median overall survival (OS) from the first cycle of LuPSMA was 14 months. Patients who had any PSA response after the first cycle had significantly longer OS than nonresponders (median OS: 17 vs 9 months; P ≤ 0.001). Total PSMA-derived tumor volume ( P = 0.004), total PSMA activity per lesion ( P = 0.01), PSA ( P = 0.007), alkaline phosphatase ( P = 0.002), lactate dehydrogenase ( P < 0.001), and hemoglobin ( P < 0.001) were significant prognostic factors for OS in univariate Cox regression analysis.

CONCLUSIONS

LuPSMA therapy is a favorable treatment for mCRPC with remarkable therapeutic efficacy and low toxicity rates, even in progressive disease under standard therapies. Baseline PSMA-based tumor burden, PSA, alkaline phosphatase, lactate dehydrogenase, and hemoglobin were significant predictors of OS and can be useful for selection of the best candidate for LuPSMA therapy.