PSMA-targeted Radionuclide Therapy Research Articles

Abstract 7582: Descriptive analysis of patients with mCRPC and liver metastases receiving alpha and beta PSMA targeted radionuclide therapy (PSMA-TRT)

Abstract Introduction: Predictors of outcomes after PSMA-TRT are still being established. Liver metastases (mets) have been associated with poor response. Mutations in genes encoding DNA damage repair (DDR) and TP53 affect radiosensitivity. Here we describe a cohort of patients with mCRPC and liver metastases treated on clinical trials of PSMA-TRT. Methods: 39 patients with liver mets were enrolled on phase I/II PSMA-TRT studies between Jan 2006 to Apr 2022. Patients received alpha therapy (225Ac-J591), beta therapy (fractionated 177Lu-PSMA-617, single-dose and fractionated 177Lu-J591) or a combination of both (225Ac-591 and 177Lu-PSMA-I&T). All patients included in this analysis had CT imaging; patients enrolled after 2017 had PSMA-PET imaging. 15 patients also had genomic analysis completed. Results: Median age was 69 (range 55-93), PSA 85.7 (2.45-9614). 39 (100%) bone mets, 33 (84.6%) LN, 9 (23.1%) lung. 22 (56.4%) greater than 1 ARPI, 23 (59.0%) greater thanc 1 chemo, 13 (33.3%) sip-T, 7 (17.9%) Ra-223, 4 (10.2%) prior TRT (with concurrent liver mets). Of the 19 with both CT and PSMA PET, 18 (94.7%) were identified on PSMA PET (including 8 PET only), 10 (55.6%) on CT (1 CT only, i.e. non-PSMA PET avid). Median whole body PSMA-imaging score (PSMA-IS) was 4 (range 1-4), with 7 (17.9%) 1-2 and 32 (82.1%) 3-4. 9 (23.0%) received alpha-TRT, 26 (66.7%) beta-TRT, and 4 (10.3%) combo-TRT. Somatic or germline analysis was completed in 15 (38.5%) of 39 patients. 8 (53.3%) had mutations in DNA repair pathways (3 in BRCA2, 3 in CHEK 2, 1 in FANC, 1 in MSH2). 7 (46.7%) had mutations in TP53. 31 patients (79.5%) had PSA decline, with 15 (38.5%) achieving PSA 50. 26 (66.7%) had baseline CTC measured; 19 (73.0%) had detectable CTC at baseline. Of these 19, 3 (15.8%) converted to undetectable after therapy and 2 (10.5%) converted to favorable CTC. PSA50 rate in alpha-TRT was 4 (44.4%), beta-TRT 8 (30.7%), combo-TRT 3 (75%). PSA50 in patients with PSMA-IS 1-2 was 1 (14.2%) compared to 14 (43.9%) in PSMA-IS 3-4. 3 (37.5%) of 8 patients with mutDDR achieved PSA50, compared to 3 (42.9%) with mutTP53. Conclusions: This dataset adds to the collective literature of two subgroups of patients with mCRPC receiving TRT: those with liver disease and those with mutations in DNA repair pathways. The results of this study suggest higher rates of response in patients receiving alpha therapy, either alone or in combination with beta therapy, and in patients with high radiotracer uptake on PSMA-PET, based on PSMA-imaging score of 3 or 4. Genomic alterations in DRR proteins did not have clear implications. Citation Format: Samuel Ruder, Michael Sun, Andres Ricaurte Fajardo, Jones Nauseef, Zachary Davidson, Joseph Thomas, Sandra Huicochea Castellanos, Ana Molina, Cora Sternberg, Amie Patel, Escarleth Fernandez, Sarah Yuan, Edward Fung, Vasilios Avlonitis, Elisabeth O'Dwyer, David Nanus, Joseph Osborne, Neil Bander, Scott Tagawa. Descriptive analysis of patients with mCRPC and liver metastases receiving alpha and beta PSMA targeted radionuclide therapy (PSMA-TRT) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7582.

68Ga Prostate-specific Membrane Antigen Uptake in Metastatic Medullary Thyroid Carcinoma.

We present the case of a 58-year-old man with advanced medullary thyroid carcinoma who had a treatment history with different types of modalities. In the follow-up, the patient had rising calcitonin and CEA levels. Metastatic lymph nodes, liver, and bone metastases with varying degrees of uptake were detected on 18F-fluorodeoxyglucose (FDG) and 68Ga-DOTATATE positron emission tomography/computed tomography (PET/CT). 68Ga prostate-specific membrane antigen (PSMA) PET/CT was performed to explore whether the patient might have a chance for PSMA-targeted radionuclide therapy, and increased PSMA expression was noted in most of the metastatic lesions, even some of which have higher PSMA uptake than 18F-FDG and 68Ga-DOTATATE.

Comparison of adverse event rate of prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy (TRT) with antibody or small molecule ligand targeting vector.

161 Background: PSMA-targeted radionuclide therapy (PSMA-TRT) has been established with use of either monoclonal antibodies (mAb) or small molecule ligands (SML) as the targeting vectors for delivery of 177Lu to PSMA-expressing prostate cancer. mAb and SML differ in their molecular weight, pharmacokinetics, and biodistribution which is predicted to result in different adverse effect profiles. Methods: In this study with written informed consent, we compare the adverse effects from individual patients receiving PSMA-TRT for mCRPC using mAb (J591) vs SML (PSMA-617 or PSMA I&T) for delivering 177Lu in prospective clinical trials or registry. All-grade treatment-emergent adverse events (TEAEs) were extracted from trial databases. Adverse effects were graded 0-5. Pearson’s Chi-squared test was used to assess TEAEs and association with treatment type. Multivariable logistic regression was used to compare TEAEs after adjusting for administered radioactivity dose and CALGB (Halabi) prognostic score. Results: 248 patients with mCRPC were treated from March 2001 to February 2023. 166 (67.7%) received mAb (177Lu-J591), 81 received SML [76 (30.6%) 177Lu-PSMA-617, 5 (2%) 177Lu-PSMA-I&T)]. The median age was 70.9 years (44.5 yrs to 93.8 yrs). At the time of trial enrollment, 137 (55.2% [68% SML and 49% mAb]) patients had exposure to chemotherapy, 112 (45.1%) had exposure to androgen-receptor pathway therapy, 193 (77.8%) had bone metastases, 120 (48.3%) LN mets, 42 (16.9%) lung mets, and 20 (8.0%) liver mets. 142 (57.2%) had Halabi score high disease. All-grade hematologic TEAEs were more common with mAb: neutropenia in 122 (74%) patients vs 16 (20%) (p<0.001), anemia in 122 (73%) vs 26 (33%) (P<0.001), and thrombocytopenia in 145 (87%) vs 25 (32%) (p<0.001). Gr >3 neutropenia occurred in 79 (47%) and Gr >3 thrombocytopenia in 98 (59%) receiving mAb. All-grade non-hematologic TEAEs were generally more common with SML: fatigue in 31 (53%) vs 79 (48%) (p=0.5), pain in 32 (54%) vs 73 (44%) (p=0.2), nausea in 21 (36%) vs 34 (20%) (p=0.02) and xerostomia in 36 (61%) vs 1 (0.6%) (p<0.001). After adjusting for administered dose and Halabi score, treatment with 177Lu via SML vector was associated with less neutropenia (OR 0.04, 95% CI 0.02-0.09, p<0.001), anemia (OR 0.11, 95% CI 0.06-0.22, p<0.001), and thrombocytopenia (OR 0.04, 95% CI 0.02-0.09, p<0.001) but more nausea (OR 3.2, 95% CI 1.54-6.72, p=0.002) and xerostomia (NA due to low event rate in mAb). Conclusions: As predicted, PSMA-TRT with mAb vs SML is associated with different toxicity profiles. PSMA-TRT with the mAb 177Lu-J591 is more commonly associated with hematologic toxicities compared to the SML 177Lu-PSMA-617 and 177Lu-PSMA-I&T, which are more commonly associated with non-hematologic toxicities.

Precision strikes: PSMA-targeted radionuclide therapy in prostate cancer - a narrative review.

Radio-ligand targeted therapy is a new and promising concept of treatment Castration resistant prostate cancer (CRPC). Only a few radio-pharmaceutics were approved for usage in treating prostate cancer, among the multiple others tested. We aimed to review and summarize the literature on the therapeutic isotopes specific for PSMA. We performed a scoping literature review of PubMed from January 1996 to December 2022. 98 publications were selected for inclusion in this review. The studies contained in publications allowed to summarize the data on pharmacokinetics, therapeutic effects, side effects and the medical use of 225Ac and 177Lu radionuclides. The review also presents new research directions for specific PSMA radionuclides. Radioligand targeted therapy is a new and promising concept where Lu-177-PSMA-617 have promising outcomes in treatment according to standard of care.

177Lu-PSMA radioligand therapy for patients with recurrent/metastatic (R/M) salivary gland cancer (SGC): A phase II pilot study.

6099 Background: New treatments are warranted due to limited systemic treatment options for SGC patients (pts). Gallium [68Ga]Ga prostate-specific membrane antigen (PSMA) PET imaging results in SGC pts have demonstrated PSMA expression of SGC and thus indicated that PSMA radionuclide therapy may be a useful option, especially in the case of adenoid cystic carcinoma (AdCC) and salivary duct carcinoma (SDC) subtypes. Therefore, this study (EudraCT number 2019-003857-27) evaluated the safety and efficacy of PSMA-targeted radionuclide therapy in AdCC and SDC pts. Methods: This was a single-center, single-arm, phase II pilot study. R/M AdCC (n = 10) and SDC (n = 5) pts with sufficient PSMA tracer uptake on [68Ga]Ga-PSMA PET imaging, i.e., ≥1 lesion ≥1.5cm with PSMA expression above mean liver level, were treated with 2-4 cycles of 7.4 GBq [177Lu]Lu-PSMA-I&T, with an interval of 6±1 weeks. Baseline imaging was repeated for evaluation 4 weeks after cycle 2; in case of progressive disease (PD) per RECIST 1.1 the treatment was discontinued; otherwise, pts received the full treatment (4 cycles). All pts received whole body post-therapeutic imaging after 1, 24, 48, 72 h and 7d after each cycle. The primary endpoint was safety. Secondary endpoints include the objective response rate, progression-free survival (PFS), and overall survival (OS). Results: Between 6-2020 and 2-2023, 15 AdCC pts and 10 SDC pts were screened for eligibility. Five AdCC pts and 8 SDC pts were screen failures due to insufficient PSMA expression in 11 pts (AdCC n = 4; SDC n = 7) or due to brain metastases in 2 pts (AdCC n = 1; SDC n = 1). Ten AdCC and 2 SDC pts received at least one cycle of 7.4 GBq [177Lu]Lu-PSMA-I&T. The most observed adverse events (grade 1-2) included: nausea (75%), dry mouth (75%), fatigue (67%), and anemia (58%). Two pts (17%) developed grade 3 toxicity; lymphocytopenia (n = 1) and hyponatremia (n = 1). No grade 4-5 toxicities were observed. Two pts (AdCC n = 1; SDC n = 1) received only 1 treatment cycle due to early PD. The interim-treatment evaluation resulted in the discontinuation of treatment after 2 cycles in an additional 3 AdCC and the second SDC pts due to PD. Six AdCC pts received the full treatment (4 cycles); no responses were observed; 3 pts (75%) showed stable disease of more than 3 months after treatment completion (5, 15 and 21 months); 3 pts showed PD at 3 months after treatment completion. Median PFS in 10 AdCC pts was 6.7 months (95%CI: 0.0-15.1); OS was not reached after a median follow-up of 11.9 months. Conclusions: [177Lu]Lu-PSMA-I&T treatment in SGC pts is well-tolerated. The efficacy in AdCC was limited; only stable disease was achieved in 3 out of 10 pts. In most screened SDC pts, PSMA expression was insufficient to undergo [177Lu]Lu-PSMA-I&T treatment; the 2 SDC pts included showed early PD. Dosimetry analyses will be performed to calculate the delivered radiation doses to organs at risk as well as tumor lesions. Clinical trial information: EUCTR2019-003857-27.

Phase I results of a phase I/II study of pembrolizumab and AR signaling inhibitor (ARSI) with 225Ac-J591.

181 Background: Only a small fraction of patients with PC respond to immunotherapy; radiation increases responses. PSMA targeted radionuclide therapy (PSMA-TRT) radiates multiple sites of disease simultaneously. ARSI can lead to radiosensitization and upregulate PSMA and PD-L1 expression. We hypothesize that the addition of potent alpha-PSMA-TRT (225Ac-J591) will lead to double-stranded DNA breaks, cell death, and subsequent release of neoantigens, thereby increasing the response proportion and duration to pembrolizumab plus ARSI. Here, we present preliminary phase I results of a phase I/II study, including an unexpected cytokine release syndrome (CRS). Methods: Eligibility: Progressive mCRPC by PCWG3 criteria (at least one ARSI, no chemotherapy in the mCRPC setting). Patients received ARSI of physician’s choice, pembrolizumab (400mg every 6 weeks), and single infusion of 225Ac-J591 at two different dose levels (65 or 80 KBq/kg). The primary endpoint for phase I is determination of 225Ac-J591 dose for phase II in a pick-the-winner design. Results: 12 patients were treated (6 at 65 KBq/kg, 6 at 80 KBq/kg). 7 (58%) received enzalutamide, 3 (25%) apalutamide, and 2 (17%) darolutamide. Median age 66.5, median PSA 7.75 ng/mL, 6 (50%) CALGB intermediate risk, 4 (33%) low risk, 11 (92%) with bone metastases, 3 (25%) with nodal metastases. 7 (58%) with prior abiraterone, 6 (50%) prior enzalutamide, 5 (42%) sip-T. All patients experienced PSA decline following therapy, 6 (50%) with >50% decline. With >6 months follow-up, 4 (33%; all at 80 KBq/kg) remain progression-free and on study. Of note, 7 (58%) developed an unexpected CRS 7-14 days following treatment characterized by morbilliform rash, fever >101F, and low blood counts. Inflammatory markers were elevated: IL-6 (2.1-7.7 pg/mL), D-Dimer (306-2378 ng/mL), ferritin (361.3-513.4 ng/mL), fibrinogen (386-461 mg/dL), ESR (16-42 mm/hr). After pausing the ARSI, this reaction improved within 1 week. Thrombocytopenia and/or neutropenia occurred during this syndrome, then typically improved before counts fell again at expected nadir 4 weeks after 225Ac-J591. Overall AEs on study include: 9 (75%) thrombocytopenia (3 with g≥3; 1 g4 with PC marrow infiltration), 7 (58%) neutropenia (none g≥3), 6 (50%) nausea, 7 (58%) g1-2 fatigue, 9 (75%) g1-2 xerostomia, 7 (58%) g1 AST. In contrast to heme AEs with unexpected initial occurrence during CRS followed by typical nadir from TRT, the described non-hematologic AEs were generally independent of CRS. 4 (33%) developed typical irAEs: 2 with rash (D60, D62) and 2 hypothyroidism (D77, D82). Conclusions: Combination therapy with alpha-PSMA-TRT, ARSI, and pembrolizumab demonstrates efficacy in the phase I run-in. A key safety signal that has emerged with triplet therapy is CRS that can be managed supportively. The randomized phase II component is accruing with additional safety visits and sample collection for cytokine analysis. Clinical trial information: NCT04946370 .

1390P Circulating tumor DNA (ctDNA) and prognosis with PSMA-targeted radionuclide therapy (TRT)

PSMA-TRT is approved for mCRPC based upon demonstrated overall survival (OS) advantage. However, even after pre-selection by PSMA imaging, not all patients respond (54% without PSA50 response in the VISION study). In addition to dose (which is likely related to both target expression and amount of radioactivity administered), prognostic genomic factors that may relate to radiosensitivity exist. Collection of real-time tissue biopsies in the setting of mCRPC presents challenges that might be overcome with the use of ctDNA. Germline control + plasma DNA were obtained prior to treatment in 2 prospective trials of PSMA-TRT and assayed utilizing the PCF SELECT (Specific Evaluation in Liquid biopsies of Established prostate Cancer Targets) platform. Variables of interest included AR copy number (wild-type vs gain), homologous recombination repair (HRR) gene copy number (wild-type vs loss), and allele-specific ploidy (asP; diploid vs high). asP is a novel metric for genomic instability and loss of heterozygosity, computed as the weighted mean of the allele-specific copy number of homologous chromosomes (Ciani et al. Cell Systems 2022). Cox regression modelling was used to assess the association of these variables with clinical outcome measures of >50% PSA response (PSA50) and OS. 80 patients received PSMA-TRT (177Lu-PSMA-617 n=50; 225Ac-J591 n=30). High asP was associated with poorer OS (HR 2.14, 95% CI 1.15-4, p=0.017) and a trend to lower rates of achieving PSA50 (OR 0.48, 95% CI 0.16-1.47, p=0.20). AR copy number gain was associated with poorer OS (HR 2.69, 95% CI 1.40-5.18, p=0.003) and lower rates of PSA50 (OR 0.47, 95% CI 0.14-1.49, p=0.20). In this study, HRR gene copy number loss was not associated with differential responses or OS. Similar results as this combined study were obtained when individual studies of 177Lu-PSMA-617 or 225Ac-J591 were analyzed for AR copy number and asP. ctDNA analysis, a non-invasive technique, in patients undergoing PSMA-TRT demonstrate that AR copy number gain and high allele-specific ploidy, reflecting genomic instability and complex karyotype, are associated with poorer prognosis.

A High Separation Factor for 165Er from Ho for Targeted Radionuclide Therapy.

Background: Radionuclides emitting Auger electrons (AEs) with low (0.02–50 keV) energy, short (0.0007–40 µm) range, and high (1–10 keV/µm) linear energy transfer may have an important role in the targeted radionuclide therapy of metastatic and disseminated disease. Erbium-165 is a pure AE-emitting radionuclide that is chemically matched to clinical therapeutic radionuclide 177Lu, making it a useful tool for fundamental studies on the biological effects of AEs. This work develops new biomedical cyclotron irradiation and radiochemical isolation methods to produce 165Er suitable for targeted radionuclide therapeutic studies and characterizes a new such agent targeting prostate-specific membrane antigen. Methods: Biomedical cyclotrons proton-irradiated spot-welded Ho(m) targets to produce 165Er, which was isolated via cation exchange chromatography (AG 50W-X8, 200–400 mesh, 20 mL) using alpha-hydroxyisobutyrate (70 mM, pH 4.7) followed by LN2 (20–50 µm, 1.3 mL) and bDGA (50–100 µm, 0.2 mL) extraction chromatography. The purified 165Er was radiolabeled with standard radiometal chelators and used to produce and characterize a new AE-emitting radiopharmaceutical, [165Er]PSMA-617. Results: Irradiation of 80–180 mg natHo targets with 40 µA of 11–12.5 MeV protons produced 165Er at 20–30 MBq·µA−1·h−1. The 4.9 ± 0.7 h radiochemical isolation yielded 165Er in 0.01 M HCl (400 µL) with decay-corrected (DC) yield of 64 ± 2% and a Ho/165Er separation factor of (2.8 ± 1.1) · 105. Radiolabeling experiments synthesized [165Er]PSMA-617 at DC molar activities of 37–130 GBq·µmol−1. Conclusions: A 2 h biomedical cyclotron irradiation and 5 h radiochemical separation produced GBq-scale 165Er suitable for producing radiopharmaceuticals at molar activities satisfactory for investigations of targeted radionuclide therapeutics. This will enable fundamental radiation biology experiments of pure AE-emitting therapeutic radiopharmaceuticals such as [165Er]PSMA-617, which will be used to understand the impact of AEs in PSMA-targeted radionuclide therapy of prostate cancer.

629P Patient-reported outcomes in prostate cancer patients receiving PSMA-targeted radionuclide therapy

Prostate-specific membrane antigen (PSMA) targeted radionuclide therapy (TRT) is a promising investigational therapy for patients with progressive metastatic castration-resistant prostate cancer. PSMA TRT conjugates a radionuclide emitting alpha radiation (e.g., Actinium-225) or beta radiation (e.g., Lutetium-177) to a small molecule ligand (e.g., PSMA-617) or a monoclonal antibody (e.g., J591) that has affinity for PSMA. Treatment is generally well-tolerated, but adverse events have been reported.

Radionuclide Therapy in Prostate Cancer: from standalone to combination PSMA theranostics.

Despite significant advances in prostate cancer therapeutic development over the last two decades, metastatic prostate cancer remains a lethal disease. Prostate-specific membrane antigen (PSMA), which is markedly overexpressed by prostate cancer cells, including at metastatic sites, but have low normal tissue expression, has emerged as an important theranostic target for these diseases. Both beta-emitting and alpha-emitting PSMA-targeted radionuclide therapy (RNT) are in clinical development. Several of these agents have already shown promising activity, however, a significant subset of patients have primary resistant disease and secondary resistance invariably occurs. Further, the effect of these therapies on healthy organs limit their therapeutic window. Elucidating the biology of PSMA as well as characterising the pharmacokinetic and pharmacodynamic properties of PSMA-targeted RNT will facilitate therapeutic approaches aimed at improving efficacy and safety. In this review, we provide an overview of existing PSMA-targeting RNT and an update on novel combinatorial approaches.

PSMA-Targeting Radiopharmaceuticals for Prostate Cancer Therapy: Recent Developments and Future Perspectives.

Simple SummaryOne of the most frequently diagnosed cancer in men is adenocarcinoma of the prostate. Once the disease is metastatic, only very limited treatment options are available, resulting in a very short median survival time of 13 months; however, this reality is gradually changing due to the discovery of prostate-specific membrane antigen (PSMA), a protein that is present in cancerous prostate tissue. Researchers have developed pharmaceuticals specific for PSMA, ranging from antibodies (mAb) to low-molecular weight molecules coupled to beta minus and alpha-emitting radionuclides for their use in targeted radionuclide therapy (TRT). TRT offers the possibility of selectively removing cancer tissue via the emission of radiation or radioactive particles within the tumour. In this article, the major milestones in PSMA ligand research and the therapeutic developments are summarised, together with a future perspective on the enhancement of current therapeutic approaches.Prostate cancer (PC) is the second most common cancer among men, with 1.3 million yearly cases worldwide. Among those cancer-afflicted men, 30% will develop metastases and some will progress into metastatic castration-resistant prostate cancer (mCRPC), which is associated with a poor prognosis and median survival time that ranges from nine to 13 months. Nevertheless, the discovery of prostate specific membrane antigen (PSMA), a marker overexpressed in the majority of prostatic cancerous tissue, revolutionised PC care. Ever since, PSMA-targeted radionuclide therapy has gained remarkable international visibility in translational oncology. Furthermore, on first clinical application, it has shown significant influence on therapeutic management and patient care in metastatic and hormone-refractory prostate cancer, a disease that previously had remained immedicable. In this article, we provide a general overview of the main milestones in the development of ligands for PSMA-targeted radionuclide therapy, ranging from the firstly developed monoclonal antibodies to the current state-of-the-art low molecular weight entities conjugated with various radionuclides, as well as potential future efforts related to PSMA-targeted radionuclide therapy.

Prostate-Specific Membrane Antigen Expression in Patients With Differentiated Thyroid Cancer With Thyroglobulin Elevation and Negative Iodine Scintigraphy Using 68Ga-PSMA-HBED-CC PET/CT.

Prostate-specific membrane antigen (PSMA) is a member of superfamily of zinc-dependent exopeptidases that is robustly expressed in prostate cancer cells and nonprostatic solid tumor neovasculature including microvessels of thyroid tumors. Its expression in differentiated thyroid cancer (DTC) has been confirmed in many recent studies, but systematic studies exploring PSMA expression in patients with DTC with thyroglobulin elevation and negative iodine scintigraphy (TENIS) are lacking. The aim of the present study was to evaluate the role of PSMA scan in TENIS patients with DTC. Nine consecutive patients with DTC with proven TENIS syndrome (6 men and 3 women with age range 29-68 years and mean age of 48 years) underwent 18F-FDG PET/CT as per the institution protocol. Thereafter, they were subjected to 68Ga-PSMA-HBED-CC PET/CT as per the institution protocol within a week of FDG PET imaging. Prostate-specific membrane antigen expression (SUVmax) in the lesions was compared with 18F-FDG PET and CT scan findings. In 5 of 9 patients with TENIS, the metastatic lesions showed PSMA expression. A total of 14 lesions were seen on the CT scan. Prostate-specific membrane antigen PET detected 9 of 14 lesions (64.28%) (SUVmax ranging from 10.1 to 45.67; median SUVmax of 16.31), whereas FDG PET was positive in 11 of 14 lesions (78.57%). The lesions that showed PSMA uptake was localized to bones (5 of 9) and lungs (4 of 9). Two lesions that were localized to iliac crest and acetabulum were missed on FDG PET but were seen on CT and PSMA PET scan. The results of this pilot study indicate that 68Ga-HBED-CC-PSMA PET/CT demonstrates PSMA expression in TENIS patients with lesions being localized to the bones and lungs. 68Ga-PSMA PET/CT could be useful for the identification of TENIS patients who might benefit from PSMA-targeted radionuclide therapy.

Patient-reported outcomes (PRO) from a phase I/II dose-escalation study of fractionated dose 177Lu-PSMA-617 for progressive metastatic castration-resistant prostate cancer (mCRPC).

45 Background: We performed the 1st dose-escalation study of PSMA-targeted radionuclide therapy with 177Lu-PSMA-617. Using dose-fractionation, we intended to deliver a dose-intense regimen designed to minimize radioresistance due to repopulation. Radionuclide therapy may be able to treat symptoms due to tumor and therefore may be associated with improvement in PRO. Methods: Inclusion: progressive mCRPC following potent AR-pathway inhibitor (ARPI, e.g. abi/enza) and taxane (or unfit/refuse chemo) without limit of # prior therapies, adequate organ function, ECOG performance status 0-2, without preselection for PSMA expression. Treatment was a single cycle of fractionated dose 177Lu-PSMA-617 on D1 and D15 (7.4 to 22 GBq in phase 1; 22.2 GBq in phase 2). PRO tools included FACT-P and BPI-SF at baseline and follow up. Results: 44 men with median age 69 (range 55-91), median PSA 182.97 (range 0.89-5541) were treated. 93% with bone, 45% nodal, 18% lung, 9% liver, 9% other visceral metastases. 55% with at least 1 prior chemo regimen, 52% >2 prior ARPI, 27% with Ra223, 30% sip-T, 5% 177Lu-J591. 59.1% with >50% PSA decline (66.7% at 22.2 GBq, n=21), median overall survival 16 months (95% CI 11-NR). High grade (Gr) toxicity was rare with 6.8% Gr 3 anemia and 2.3% Gr 3 platelets. Gr 1/2 treatment-emergent AE’s include 81.8% with pain flare, 61.4% xerostomia, 29.5% fatigue, 25% platelets, 25% anemia, 25% pain, 15.5% nausea. FACT-P scores tended to improve in all categories by D22 (1 week later), with overall FACT-P scores improving by mean of 8.9 points (p=0.07) at D22 and remaining improved at 12 wks. All BPI scores also improved, with BPI overall severity score improving by mean of 3.0 at D22 (p=0.008) and remained better than baseline at 12 wks. There was no clear association with any AE and PRO changes, but those with PSA decline tended to have improved pain scores (p=0.1). Conclusions: A single cycle of up to 22.2 GBq of 177Lu-PSMA-617 is safe with fractionated (D1 & D15) dosing, with encouraging early efficacy signals in a population unselected for PSMA expression and improved quality of life and pain scores by validated PRO instruments. Clinical trial information: NCT03042468.

The Future of PSMA-Targeted Radionuclide Therapy: An Overview of Recent Preclinical Research.

Prostate specific membrane antigen (PSMA) has become a major focus point in the research and development of prostate cancer (PCa) imaging and therapeutic strategies using radiolabeled tracers. PSMA has shown to be an excellent target for PCa theranostics because of its high expression on the membrane of PCa cells and the increase in expression during disease progression. Therefore, numerous PSMA-targeting tracers have been developed and (pre)clinically studied with promising results. However, many of these PSMA-targeting tracers show uptake in healthy organs such as the salivary glands, causing radiotoxicity. Furthermore, not all patients respond to PSMA-targeted radionuclide therapy (TRT). This created the necessity of additional preclinical research studies in which existing tracers are reevaluated and new tracers are developed in order to improve PSMA-TRT by protecting the (PSMA-expressing) healthy organs and improving tumor uptake. In this review we will give an overview of the recent preclinical research projects regarding PCa-TRT using PSMA-specific radiotracers, which will give an indication of where the PSMA-TRT research movement is going and what we can expect in future clinical trials.

Abstract 4865: Prognostic value of BRCA2 and AR gene alterations in advanced prostate cancer patients treated with PSMA-targeted radionuclide therapies

Abstract Background: PSMA-targeted radionuclide therapy (TRT) is being developed for treatment of pts with prostate cancer (PC). Several targeting agents were shown to be active and tolerable in early phase studies & randomized trials are underway. Because of the DNA damaging effects of ionizing radiation and the relationship between AR pathway & PSMA expression, we hypothesized that pts with germline or somatic gene alterations in DNA damage repair (DDR) & crosstalk pathways (AR, MYC) treated with PSMA-TRT may demonstrate differential treatment responses & outcomes. Methods: We examined a single-institution cohort of advanced PC pts with available germline (targeted) or/and somatic (targeted or whole exome) DNA testing, clinical data (Halabi CALGB prognostic factors) & outcome. The Kaplan-Meier method & Cox regression analysis were used to evaluate the associations of mutations/copy number alterations (CNA) with PSA response (≥50%,≥30%,any), radiographic response, PFS and OS. Stepwise forward-selection was used in the multivariable regression model & p for entry was set at 0.1. For final analyses, p≤0.05 was used for significance. Results: We analyzed 53 pts treated with PSMA-TRT. 16 (30.2%) received 177Lu-J591, 28 (56.6%) 177Lu-PSMA-617, 4 (7.5%) had both concurrently, 2 (3.8%) 225Ac-J591 (3 additional received >1 agent sequentially & are analyzed based upon 1st drug). 6 (11.3%) had pathogenic germline DDR mutations while 31 (58.5%) had ≥1 mutation/CNA in DDR genes. The most frequently affected genes were: TP53 (n=21, 39.6%), BRCA2 (n=14, 26.4%), CHEK2 (n=10, 18.9%), FANCA (n=10, 18.9%), RB1 (n=9, 16.9%), ATM (n=5, 9.4%), ERCC5 (n=5, 9.4%), ERCC3 (n=3, 5.7%), ERCC2 (n=2, 3.8%), BRCA1(n=2, 3.8%), MSH6 (n=2, 3.8%), FANCD2 (n=2, 3.8%), FANCF (n=2, 3.8%). AR amplifications (ampl) or resistance-mutations were found in 22 pts (41.5%), and MYC ampl in 9 pts (16.9%). 19 (35.8%) pts had ≥50% PSA decline, 24 (45.3%) experienced ≥30% decline & 39 (73.6%) had any PSA decline. 4 pts experienced a PR while 18 had SD. BRCA2 inactivating mutations, deletions or losses were associated with any PSA decline (p=0.011). PFS was significantly longer in patients with RB1 deletion or loss (5 vs 3 mos, p=0.003). BRCA2 alterations were predictive of longer OS vs wild-type (49 vs 17 mos, p=0.09). AR ampl or mutations and MYC ampl predicted shorter OS (AR: 13 vs 63 mos, p=0.02; MYC: 8 vs 24 mos, p=0.06). On multivariate analysis after adjusting for Halabi prognostic groups (low vs high risk), BRCA2 & AR alterations retained their significance as independent prognosticators of OS (BRCA2 HR 0.1 [0.02-0.42], p=0.002; AR HR 7.2 [2.09-25.14], p=0.002). Conclusions: Knowledge of molecular alterations in BRCA2, AR and RB1 genes may have potential utility for prediction of clinical outcomes in pts being considered for PSMA-TRT. These findings merit further testing and validation in larger prospective trials. Citation Format: Panagiotis J. Vlachostergios, Vincenza Conteduca, Amy L. Hackett, Jyothi Manohar, Aileen Lee, Aidan Case, Michael Sun, Muhammad J. Niaz, Olivier Elemento, Ana M. Molina, David M. Nanus, Himisha Beltran, Neil H. Bander, Scott T. Tagawa. Prognostic value of BRCA2 and AR gene alterations in advanced prostate cancer patients treated with PSMA-targeted radionuclide therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4865.

Deep Neural Network for Automatic Characterization of Lesions on 68Ga-PSMA PET/CT Images.

The emerging PSMA-targeted radionuclide therapy provides an effective method for the treatment of advanced metastatic prostate cancer. To optimize the therapeutic effect and maximize the theranostic benefit, there is a need to identify and quantify target lesions prior to treatment. However, this is extremely challenging considering that a high number of lesions of heterogeneous size and uptake may distribute in a variety of anatomical context with different backgrounds. This study proposes an end-to-end deep neural network to characterize the prostate cancer lesions on PSMA imaging automatically. A 68Ga-PSMA-11 PET/CT image dataset including 71 patients with metastatic prostate cancer was collected from three medical centres for training and evaluating the proposed network. For proof-of-concept, we focus on the detection of bone and lymph node lesions in the pelvic area suggestive for metastases of prostate cancer. The preliminary test on pelvic area confirms the potential of deep learning methods. Increasing the amount of training data may further enhance the performance of the proposed deep learning method.

Terbium-161 for PSMA-targeted radionuclide therapy of prostate cancer

PurposeThe prostate-specific membrane antigen (PSMA) has emerged as an interesting target for radionuclide therapy of metastasized castration-resistant prostate cancer (mCRPC). The aim of this study was to investigate 161Tb (T1/2 = 6.89 days; Eβ͞av = 154 keV) in combination with PSMA-617 as a potentially more effective therapeutic alternative to 177Lu-PSMA-617, due to the abundant co-emission of conversion and Auger electrons, resulting in an improved absorbed dose profile.Methods161Tb was used for the radiolabeling of PSMA-617 at high specific activities up to 100 MBq/nmol. 161Tb-PSMA-617 was tested in vitro and in tumor-bearing mice to confirm equal properties, as previously determined for 177Lu-PSMA-617. The effects of 161Tb-PSMA-617 and 177Lu-PSMA-617 on cell viability (MTT assay) and survival (clonogenic assay) were compared in vitro using PSMA-positive PC-3 PIP tumor cells. 161Tb-PSMA-617 was further investigated in therapy studies using PC-3 PIP tumor-bearing mice.Results161Tb-PSMA-617 and 177Lu-PSMA-617 displayed equal in-vitro properties and tissue distribution profiles in tumor-bearing mice. The viability and survival of PC-3 PIP tumor cells were more reduced when exposed to 161Tb-PSMA-617 as compared to the effect obtained with the same activities of 177Lu-PSMA-617 over the whole investigated concentration range. Treatment of mice with 161Tb-PSMA-617 (5.0 MBq/mouse and 10 MBq/mouse, respectively) resulted in an activity-dependent increase of the median survival (36 vs 65 days) compared to untreated control animals (19 days). Therapy studies to compare the effects of 161Tb-PSMA-617 and 177Lu-PSMA-617 indicated the anticipated superiority of 161Tb over 177Lu.Conclusion161Tb-PSMA-617 showed superior in-vitro and in-vivo results as compared to 177Lu-PSMA-617, confirming theoretical dose calculations that indicate an additive therapeutic effect of conversion and Auger electrons in the case of 161Tb. These data warrant more preclinical research for in-depth investigations of the proposed concept, and present a basis for future clinical translation of 161Tb-PSMA-617 for the treatment of mCRPC.

Association of noninvasive, radiographic measurement of prostate-specific membrane antigen (PSMA) expression with response to PSMA-targeted radionuclide therapy (TRT).

5013 Background: Prostate surface membrane antigen (PSMA) is usually overexpressed in PC and is enriched in castration-resistant tumors. PSMA-TRT is of increasing interest to the field. Many in the field of theranostics have assumed that PSMA uptake on imaging is a pre-requisite for response. We have conducted a number of trials which have incorporated PSMA imaging, but have not selected patients for treatment based upon imaging results and performed an analysis examining the relationship between imaging and response. Methods: Men with mCRPC had either planar radiolabeled J591 imaging (111In-J591 and/or 177Lu-J591) or 68Ga-PSMA11 PET/CT. Visual scores were assigned based upon PSMA uptake in tumors compared to liver uptake and scored on a 0-4 scale. Imaging scores were associated with PSA decline (≥30%, ≥50%) using Cox regression analysis. As several studies were dose-escalation in nature with prior demonstration of dose-response, we controlled for dose administered. Results: 216 men with metastatic CRPC, median PSA 72.45ng/dl, were treated with PSMA-TRT as follows: 177Lu-J591 (n=136), 177Lu-PSMA-617 (n=38), Lu-J591 + Lu-PSMA-617 combination (n=6), 225Ac-J591 (n=7), 90Y-J591 (n=29). 116 (53.7%) pts received low dose and 100 (46.3%) high dose as previously defined in the individual studies. 55 (25.5%) pts had low PSMA expression by imaging (VS 0-1) whereas 161 (74.5%) had high PSMA (VS 2-4). High PSMA expression was associated with more frequent PSA decline (≥30%: 39.2 vs 17.9% p=0.003; ≥50%: 27.5 vs 8.9% p=0.004). When controlling for dose level, this association remained significant for low (≥30%: 25 vs 8.6% p=0.04) and high doses of radionuclide therapy (≥50%: 34.9 vs 9.5% p=0.02). 13 (6%) pts with no PSMA uptake (VS=0) had PSA declines. Conclusions: This is the first study to formally analyze response to PSMA-TRT by PSMA imaging expression in an unselected patient population. The level of PSMA expression measured by imaging is associated with the chance of response. However, a subset of patients without any significant PSMA uptake on imaging did demonstrate response to PSMA-TRT, indicating that imaging cannot exclude all patients that might benefit. Clinical trial information: NCT03545165, NCT03276572, NCT03042468, NCT02552394.

Differential Uptake of 68Ga-PSMA-HBED-CC (PSMA-11) in Low-Grade Versus High-Grade Gliomas in Treatment-Naive Patients.

Prostate-specific membrane antigen (PSMA) is a type II membrane glycoprotein, which is not only overexpressed in prostate cancers but also in variety of solid tumors including glioblastoma multiforme. The aim of the present study was to demonstrate PSMA expression in gliomas using Ga-PSMA-HBED-CC(PSMA 11) PET/CT. Ten patients with initially MRI suspected and eventually histopathologically proven gliomas [8 males (age range 30-73 yr; mean age 51.8 yr); 2 females aged 39 and 55 years] were subjected preoperatively to regional brain PET scan with Ga-PSMA-11 and F-FDG PET/CT. Final histopathology of brain lesions, their MIB-1 proliferation index (MIB-1 PI) were compared with PSMA and FDG PET findings. FDG PET/CT showed distinct FDG uptake in high-grade gliomas, whereas low-grade gliomas were non-FDG-avid amidst physiological tracer uptake. In vivo PSMA expression was seen in all patients with glioma. Of these, the 7 patients of glioblastoma harboring 8 lesions showed significantly higher PSMA expression than those with low-grade gliomas, average SUVmax being 16.93 and 2.93, respectively. Similarly, average tumor-to-background ratios (13.95 and 3.42, respectively) and MIB-1 PI (17.31 and 3.3, respectively) were substantially more in high-grade versus low-grade gliomas. The results of this pilot study show that Ga-HBED-CC-PSMA PET/CT can be used to characterize the PSMA expression in gliomas, high-grade ones demonstrating higher SUVmax, MIB-1 PI tumor-to-background ratio than the low-grade ones. With these results as basis, certain patients may benefit from potential PSMA-targeted radionuclide therapy.

Evidence of Prostate-Specific Membrane Antigen Expression in Metastatic Differentiated Thyroid Cancer Using 68Ga-PSMA-HBED-CC PET/CT

Prostate-specific membrane antigen (PSMA) overexpression is not restricted to prostate cancer, but it has also been demonstrated in gliomas, lung cancer, and in tumor neovasculature. Systematic studies exploring PSMA uptake in thyroid tumors are lacking. The aim of this pilot study was to assess PSMA expression in patients with metastatic differentiated thyroid cancer (mDTC). Ten patients of mDTC harboring 32 lesions (5 men; age range, 38-65 years; mean age, 50 years) underwent prospective evaluation with radioiodine (I), F-FDG PET, and Ga-PSMA-HBED-CC PET scans as per the institution protocol. PSMA expression (SUVmax) was compared with F-FDG and I scan findings in all patients. Lesions were radioiodine avid in 8 patients, whereas 2 were classified as thyroglobulin elevation with negative iodide scintigraphy (TENIS) patients. All patients with iodine-avid metastatic disease showed substantial PSMA uptake. PSMA PET detected 30/32 total lesions (93.75%; SUVmax ranging from 4.86 to 101.81 with median SUVmax of 31.35), whereas FDG PET/CT was positive in 23/32 lesions (81.85%). Twenty-one (70%) of 30 lesions that showed PSMA expression were localized to the bones. PSMA localized a lesion in each of the 2 TENIS patients similar to FDG PET scan. Ga-PSMA-HBED-CC PET/CT is a potentially useful imaging modality in patients of mDTC with most (70%) of PSMA expressing metastasis being localized to the bones. PSMA PET/CT could be useful for identifying patients with limited therapeutic options (eg, TENIS) who might benefit from PSMA-targeted radionuclide therapy.