Prostate-specific Membrane Antigen Targeting Research Articles

Prostate-Specific Membrane Antigen-Positron Emission Tomography-Guided Radiomics and Machine Learning in Prostate Carcinoma.

Positron emission tomography (PET) using radiolabeled prostate-specific membrane antigen targeting PET-imaging agents has been increasingly used over the past decade for imaging and directing prostate carcinoma treatment. Here, we summarize the available literature data on radiomics and machine learning using these imaging agents in prostate carcinoma. Gleason scores derived from biopsy and after resection are discordant in a large number of prostate carcinoma patients. Available studies suggest that radiomics and machine learning applied to PSMA-radioligand avid primary prostate carcinoma might be better performing than biopsy-based Gleason-scoring and could serve as an alternative for non-invasive GS characterization. Furthermore, it may allow for the prediction of biochemical recurrence with a net benefit for clinical utilization. Machine learning based on PET/CT radiomics features was also shown to be able to differentiate benign from malignant increased tracer uptake on PSMA-targeting radioligand PET/CT examinations, thus paving the way for a fully automated image reading in nuclear medicine. As for prediction to treatment outcome following 177Lu-PSMA therapy and overall survival, a limited number of studies have reported promising results on radiomics and machine learning applied to PSMA-targeting radioligand PET/CT images for this purpose. Its added value to clinical parameters warrants further exploration in larger datasets of patients.

Synthesis and Evaluation of 99mTc-Labeled DPro-Gly-Containing Tracers Targeting PSMA.

The specific expression of prostate-specific membrane antigen (PSMA) makes it an ideal target for the diagnosis and treatment of prostate cancer. Currently, many 99mTc-labeled PSMA-targeted tracers have been developed. However, the high renal uptake of these 99mTc-labeled tracers is a common problem that limits their clinical application. In this work, the ligand (EUKPG) using DPro-Gly as the linker was synthesized and three 99mTc-labeled complexes ([99mTc]Tc-EUKPG-EDDA, [99mTc]Tc-EUKPG-TPPTS, [99mTc]Tc-EUKPG-TPPMS) with different coligands were prepared and evaluated. Among them, [99mTc]Tc-EUKPG-EDDA showed the most favorable pharmacokinetic properties, with significantly reduced uptake in the kidney (14.04 ± 0.23% ID/g), rapid clearance and low uptake in nontarget organs, thus making it to exhibit high tumor-to-background ratios (tumor/blood: 7.47, tumor/muscle: 12.65). Affinity studies have shown that it has high specificity for PSMA both in vivo and in vitro. Therefore, [99mTc]Tc-EUKPG-EDDA has great potential as a promising molecular tracer to target PSMA for tumor imaging.

Performance of PSMA-targeted radiotheranostics in an experimental model of renal cell carcinoma.

Renal cell carcinoma (RCC) represents cancer originating from the renal epithelium and accounts for > 90% of cancers in the kidney. Prostate-specific membrane antigen (PSMA) is overexpressed in tumor-associated neovascular endothelial cells of many solid tumors, including metastatic RCC. Although studied in several small clinical studies, PSMA-based imaging and therapy have not been pursued rigorously in preclinical RCC. This study aimed to evaluate the preclinical performance of PSMA-based radiotheranostic agents in a relevant murine model. A PSMA-overexpressing murine cell line, PSMA+ RENCA, was developed by lentiviral transduction. PSMA-based theranostic agents, 68Ga-L1/177Lu-L1/225Ac-L1, were synthesized in high radiochemical yield and purity following our reported methods. Immunocompetent BALB/c mice were used for flank and orthotopic tumor inoculation. 68Ga-L1 was evaluated in small animal PET/CT imaging in flank and PET/MR imaging in orthotopic models. Cell viability studies were conducted for 177Lu-L1 and 225Ac-L1. Proof-of-concept treatment studies were performed using 225Ac-L1 (0, 37 kBq, 2 kBq × 37 kBq, 1 week apart) using PSMA+ RENCA in the flank model. Cellular uptake of 68Ga-L1, 177Lu-L1, and 225Ac-L1 confirmed the specificity of the agents to PSMA+ RENCA cells rather than to RENCA (wt) cells, which are low in PSMA expression. The uptake in PSMA+ RENCA cells at 1 h for 68Ga-L1 (49.0% incubated dose [ID] ± 3.6%ID/million cells), 177Lu-L1 (22.1%ID ± 0.5%ID)/million cells), and 225Ac-L1 (4.1% ± 0.2% ID)/million cells), respectively, were higher than the RENCA (wt) cells (~ 1%ID-2%ID/million cells). PET/CT images displayed > 7-fold higher accumulation of 68Ga-L1 in PSMA+ RENCA compared to RENCA (wt) in flank implantation at 1 h. A twofold higher accumulation of 68Ga-L1 was observed in orthotopic tumors than in normal kidneys during 1-3 h postinjection. High lung uptake was observed with 68Ga-L1 PET/MR imaging 3 weeks after orthotopic implantation of PSMA+ RENCA due to spontaneous lung metastases. The imaging data were further confirmed by immunohistochemical characterization. 225Ac-L1 (0-37 kBq) displayed a dose-dependent reduction of cell proliferation in the PSMA+ RENCA cells after 48 h incubation; ~ 40% reduction in the cells with treated 37 kBq compared to vehicle (p < 0.001); however, no effect was observed with 177Lu-L1 (0-3700 kBq) up to 144 h postinoculation, suggesting lower efficacy of β-particle-emitting radiations in cellular studies compared to α-particle-emitting 225Ac-L1. Animals treated with 225Ac-L1 at 1 week posttumor inoculation in flank models displayed significant tumor growth delay (p < 0.03) and longer median survival of 21 days and 24 days for the treatment groups 37 kBq and 2 kBq × 37 kBq, respectively, compared to the vehicle group (12 days). The results suggest that a theranostic strategy targeting PSMA, employing PET and α-emitting radiopharmaceuticals, enabled tumor growth control and enhanced survival in a relevant immunocompetent murine model of RCC. These studies provide the rationale for clinical studies of PSMA-targeted theranostic agents in patients with RCC.

Unveiling the Potential of Prostate-Specific Membrane Antigen for Precision Diagnosis and Therapy of Prostate Cancer: A Radiopharmaceutical Perspective.

Prostate-specific membrane antigen (PSMA) has proven to be an important target for diagnostic imaging in prostate cancer. As PSMA is overexpressed on the surface of prostate cancer cells, numerous targeted PSMA ligands have been developed. The emergence of PSMA targeting based on small molecules, such as the PSMA-11 ligand (or PSMA-HBED-CC), has led to breakthroughs, such as [68Ga]Ga-PSMA-11, for positron emission tomography (PET) imaging of biochemically recurrent or metastatic castration-resistant prostate cancer (mCRPC). In addition, the recent approval of [177Lu]Lu-PSMA-617 for the treatment of adult patients with PSMA-positive mCRPC represents an important milestone in prostate cancer therapy. These advances underscore the growing confidence in the use of PSMA-targeted radiopharmaceuticals for the diagnosis and treatment of prostate cancer patients. PSMA-targeted radiopharmaceuticals have been shown to significantly impact treatment planning and clinical decision-making and facilitate the customisation of treatment regimens.

Design of 225Ac-PSMA for targeted alpha therapy in prostate cancer.

The first alpha emitting radiopharmaceutical, 223RaCl2, radium dichloride, was approved 10 years ago into the clinical armament of treating bone metastases in metastatic castration-resistant prostate cancer (mCRPC). In addition to this, the first beta-emitting radionuclide Lu-177 chelated with a prostate-specific membrane antigen (PSMA) compound, got last year its marketing approval for the third line treatment of mCRPC. Therefore, there is great excitement about combining alpha-emitters and prostate cancer targeting PSMA compounds. This review describes the clinical history of alpha-emitting PSMA in treating mCRPC. Here, we present the potential, current status, and opportunities for 225Ac-PSMA therapy. The work reviews the basic concepts, current treatment outcome, and toxicity, and areas requiring further investigations such as dosimetric aspects in clinical studies covering more than 400 patients. In general, approximately two-thirds of the patients benefit from this third-line therapy. There is also successful evidence of using 225Ac-PSMA in the second-line of prostate cancer management. The future potential of 225Ac-PSMA therapy and targeted alpha therapy (TAT) of cancer in general is enormous. According to our overview the clinical experience with 225Ac-PSMA therapy to date has shown great benefit and physicians dedicated to theragnostics are anxiously waiting for new applications. Hopefully, this review helps in deeper understanding of the strengths and limitations of TAT and may help in creating effective therapy protocols.

PSMA-targeted combination brusatol and docetaxel nanotherapeutics for the treatment of prostate cancer

Active targeting to cancer involves exploiting specific interactions between receptors on the surface of cancer cells and targeting moieties conjugated to the surface of vectors such that site-specific delivery is achieved. Prostate specific membrane antigen (PSMA) has proved to be an excellent target for active targeting to prostate cancer. We report the synthesis and use of a PSMA-specific ligand (Glu-NH-CO-NH-Lys) for the site-specific delivery of brusatol- and docetaxel-loaded poly(lactide-co-glycolide) (PLGA) nanoparticles to prostate cancer. The PSMA targeting ligand covalently linked to PLGA-PEG3400 was blended with methoxyPEG-PLGA to prepare brusatol- and docetaxel-loaded nanoparticles with different surface densities of the targeting ligand. Flow cytometry was used to evaluate the impact of different surface densities of the PSMA targeting ligand in LNCaP prostate cancer cells at 15 min and 2 h. Cytotoxicity evaluations of the targeted nanoparticles reveal differences based on PSMA expression in PC-3 and LNCaP cells. In addition, levels of reactive oxygen species (ROS) were measured using the fluorescent indicator, H2DCFDA, by flow cytometry. PSMA-targeted nanoparticles loaded with docetaxel and brusatol showed increased ROS generation in LNCaP cells compared to PC-3 at different time points. Furthermore, the targeted nanoparticles were evaluated in male athymic BALB/c mice implanted with PSMA-producing LNCaP cell tumors. Evaluation of the percent relative tumor volume show that brusatol-containing nanoparticles show great promise in inhibiting tumor growth. Our data also suggest that the dual drug-loaded targeted nanoparticle platform improves the efficacy of docetaxel in male athymic BALB/c mice implanted with PSMA-producing LNCaP cell tumors.

Evaluation of a bimodal, matched pair theranostic agent targeting prostate-specific membrane antigen

BackgroundProstate cancer affects 1 in 6 men, and it is the second‑leading cause of cancer-related death in American men. Surgery is one of the main treatment modalities for prostate cancer, but it often results in incomplete resection margins or complete resection that leads to nerve damage and undesirable side effects. In the present work, we have developed a new bimodal tracer, NODAGA-sCy7.5 PSMAi (prostate-specific membrane antigen inhibitor), labeled with the true matched theranostic pair 64Cu/67Cu and a near-infrared fluorescent dye. This agent could potentially be used for concomitant PET imaging, optical surgical navigation, and targeted radiopharmaceutical therapy. MethodsA prostate-specific membrane antigen (PSMA)-targeting urea derivative was conjugated to NODAGA for copper radiolabeling and to the near-infrared fluorophore sulfo-Cy7.5 (sCy7.5). Binding studies were performed in PSMA-positive PC-3 PIP cells, as well as uptake and internalization assays in PC-3 PIP cells and PSMA-negative PC-3 wild type cells. Biodistribution studies of the 64Cu-labeled compound were performed in PC-3 PIP- and PC-3 tumor-bearing mice, and 67Cu biodistributions of the agent were obtained in PC-3 PIP tumor-carrying mice. PET imaging and fluorescence imaging were also performed, using the same molar doses, in the two mouse models. ResultsThe PSMA conjugate bound with high affinity to PSMA-positive prostate cancer cells, as opposed to cells that were PSMA-negative. Uptake and internalization were rapid and PSMA-mediated in PC-3 PIP cells, while only minimal non-specific uptake was observed in PC-3 cells. Biodistribution studies showed specific uptake in PC-3 PIP tumors, while accumulation in PC-3 tumor-bearing mice was low. Furthermore, tumor uptake of the 67Cu-labeled agent in the PC-3 PIP model was statistically equivalent to that of 64Cu. PET and fluorescence imaging at 0.5 nmol per mouse also demonstrated that PC-3 PIP tumors could be clearly detected, while PC-3 tumors showed no tumor accumulation. ConclusionsNODAGA-sCy7.5-PSMAi was specific and selective in detecting PSMA-positive, as opposed to PSMA-negative, tumors in mouse models of prostate cancer. This bioconjugate could potentially be used for PET staging with 64Cu, targeted radiopharmaceutical therapy with 67Cu, and/or image-guided surgery with sCy7.5.

Lutetium-177-Prostate-Specific Membrane Antigen Radioligand Therapy: What Is the Value of Post-Therapeutic Imaging?

Lutetium-177 (Lu-177)-labelled radioligand therapies (RLT) targeting prostate-specific membrane antigen (PSMA) present a promising treatment for patients with progressive metastasized castration-resistant prostate cancer (mCRPC). Personalized dosimetry, facilitated by post-therapeutic imaging, offers the potential to enhance treatment efficacy by customizing radiation doses to individual patient needs, thereby maximizing therapeutic benefits while minimizing toxicity to healthy tissues. However, implementing personalized dosimetry is resource-intensive, requiring multiple single-photon emission-computed tomography (SPECT)/CT scans and posing significant logistical challenges for both healthcare facilities and patients. Despite these challenges, personalized dosimetry can lead to optimized radiation delivery, improved safety, and better management of complex cases. Nevertheless, the financial and resource burdens complicate its adoption in routine clinical practice. While the European Association of Nuclear Medicine (EANM) supports personalized dosimetry, standardization is lacking due to these practical constraints. Further research and streamlined methodologies are essential to balance the benefits and feasibility of personalized dosimetry, potentially improving treatment outcomes for mCRPC patients.

Genetically Engineered Membrane-Coated Nanoparticles forEnhanced Prostate-Specific Membrane Antigen Targeting and Ferroptosis Treatment of Castration-Resistant Prostate Cancer.

Conventional androgen deprivation therapy (ADT) targets the androgen receptor (AR) inhibiting prostate cancer (PCa) progression; however, it can eventually lead to recurrence as castration-resistant PCa (CRPC), which has high mortality rates and lacks effective treatment modalities. The study confirms the presence of high glutathione peroxidase 4 (GPX4) expression, a key regulator of ferroptosis (i.e., iron-dependent program cell death) in CRPC cells. Therefore, inducing ferroptosis in CRPC cells might be an effective therapeutic modality for CRPC. However, nonspecific uptake of ferroptosis inducers can result in undesirable cytotoxicity in major organs. Thus, to precisely induce ferroptosis in CRPC cells, a genetic engineering strategy is proposed to embed a prostate-specific membrane antigen (PSMA)-targeting antibody fragment (gy1) in the macrophage membrane, which is then coated onto mesoporous polydopamine (MPDA) nanoparticles to produce a biomimetic nanoplatform. The results indicate that the membrane-coated nanoparticles (MNPs) exhibit high specificity and affinity toward CRPC cells. On further encapsulation with the ferroptosis inducers RSL3 and iron ions, MPDA/Fe/RSL3@M-gy1 demonstrates superior synergistic effects in highly targeted ferroptosis therapy eliciting significant therapeutic efficacy against CRPC tumor growth and bone metastasis without increased cytotoxicity. In conclusion, a new therapeutic strategy is reported for the PSMA-specific, CRPC-targeting platform for ferroptosis induction with increased efficacy and safety.

Enhanced Prostate-specific Membrane Antigen Targeting by Precision Control of DNA Scaffolded Nanoparticle Ligand Presentation.

Targeted nanoparticles have been extensively explored for their ability to deliver their payload to a selective cell population while reducing off-target side effects. The design of actively targeted nanoparticles requires the grafting of a ligand that specifically binds to a highly expressed receptor on the surface of the targeted cell population. Optimizing the interactions between the targeting ligand and the receptor can maximize the cellular uptake of the nanoparticles and subsequently improve their activity. Here, we evaluated how the density and presentation of the targeting ligands dictate the cellular uptake of nanoparticles. To do so, we used a DNA-scaffolded PLGA nanoparticle system to achieve efficient and tunable ligand conjugation. A prostate-specific membrane antigen (PSMA) expressing a prostate cancer cell line was used as a model. The density and presentation of PSMA targeting ligand ACUPA were precisely tuned on the DNA-scaffolded nanoparticle surface, and their impact on cellular uptake was evaluated. It was found that matching the ligand density with the cell receptor density achieved the maximum cellular uptake and specificity. Furthermore, DNA hybridization-mediated targeting chain rigidity of the DNA-scaffolded nanoparticle offered ∼3 times higher cellular uptake compared to the ACUPA-terminated PLGA nanoparticle. Our findings also indicated a ∼ 3.7-fold reduction in the cellular uptake for the DNA hybridization of the non-targeting chain. We showed that nanoparticle uptake is energy-dependent and follows a clathrin-mediated pathway. Finally, we validated the preferential tumor targeting of the nanoparticles in a bilateral tumor xenograft model. Our results provide a rational guideline for designing actively targeted nanoparticles and highlight the application of DNA-scaffolded nanoparticles as an efficient active targeting platform.

Prostate-Specific Membrane Antigen Targeted StarPEG Nanocarrier for Imaging and Therapy of Prostate Cancer.

The tumor uptake of large non-targeted nanocarriers primarily occurs through passive extravasation, known as the enhanced permeability and retention (EPR) effect. Prior studies demonstrated improved tumor uptake and retention of 4-arm 40 kDa star polyethylene glycol (StarPEG) polymers for cancer imaging by adding prostate-specific membrane antigen (PSMA) targeting small molecule ligands. To test PSMA-targeted delivery and therapeutic efficacy, StarPEG nanodrugs with/without three copies of PSMA-targeting ligands, ACUPA, are designed and synthesized. For single-photon emission computed tomography (SPECT) imaging and therapy, each nanocarrier is labeled with 177Lu using DOTA radiometal chelator. The radiolabeled nanodrugs, [177Lu]PEG-(DOTA)1 and [177Lu]PEG-(DOTA)1(ACUPA)3, are evaluated in vitro and in vivo using PSMA+ PC3-Pip and/or PSMA- PC3-Flu cell lines, subcutaneous xenografts and disseminated metastatic models. The nanocarriers are efficiently radiolabeled with 177Lu with molar activities 10.8-15.8 MBq/nmol. Besides excellent in vitro PSMA binding affinity (kD = 51.7nM), the targeted nanocarrier, [177Lu]PEG-(DOTA)1(ACUPA)3, demonstrated excellent in vivo SPECT imaging contrast with 21.3% ID/g PC3-Pip tumors uptake at 192h. Single doses of 18.5MBq [177Lu]PEG-(DOTA)1(ACUPA)3 showed complete resolution of the PC3-Pip xenografts observed up to 138days. Along with PSMA-targeted excellent imaging contrast, these results demonstrated high treatment efficacy of [177Lu]PEG-(DOTA)1(ACUPA)3 for prostate cancer, with potential for clinical translation.

Impact of Clinical Factors on 18F-Flotufolastat Detection Rates in Men With Recurrent Prostate Cancer: Exploratory Analysis of the Phase 3 SPOTLIGHT Study

18F-Flotufolastat (18F-rhPSMA-7.3) is a newly approved prostate-specific membrane antigen targeting radiopharmaceutical for diagnostic imaging of prostate cancer (PCa). SPOTLIGHT (National Clinical Trials 04186845) evaluated 18F-flotufolastat in men with suspected PCa recurrence. Here, we present results of predefined exploratory endpoints from SPOTLIGHT to evaluate the impact of clinical factors on 18F-flotufolastat detection rates (DR). The impact of baseline prostate-specific antigen (PSA), PSA doubling time (PSAdt), and International Society of Urologic Pathology Grade Group (GG) on 18F-flotufolastat DR was evaluated among all SPOTLIGHT patients with an evaluable scan, with DR stratified according to the patients' prior treatment (radical prostatectomy ± radiation therapy [RP] or radiation therapy only [RT]). The patients underwent positron emission tomography 50 to 70 minutes after receiving 18F-flotufolastat (296 MBq IV), and scans were read by 3 blinded central readers, with the majority read representing agreement between ≥2 readers. In total, 389 men (median PSA: 1.10 ng/mL) were evaluable. By majority read, 18F-flotufolastat identified distant lesions in 39% and 43% of patients treated with prior RP or RT, respectively. The overall DR broadly increased with increasing PSA (<0.2 ng/mL: 33%; ≥10 ng/mL: 100%). Among patients with PSA <1 ng/mL, 68% had positive scans, and 27% had extrapelvic findings. PSAdt was available for 145/389 (37%) patients. PSAdt did not appear to influence 18F-flotufolastat DR (77%-90% across all PSAdt categories). Among patients with prior RP, DR ranged from 70% to 83% across PSAdt categories, and 100% DR was reported for all post-RT patients. In total, 362/389 (93%) patients had baseline GG data. Overall DRs were uniformly high (75%‒95%) across all GG. When stratified by prior treatment, DRs across all GG were 69% to 89% in patients with prior RP and ≥96% in patients with prior RT. 18F-Flotufolastat-positron emission tomography enabled the accurate detection of recurrent PCa lesions across a wide range of PSA, PSAdt, and International Society of Urologic Pathology GG, thus supporting its clinical utility for a broad range of patients with recurrent PCa.

Au/Doc/Quer@PDA/A10-3.2 Nanoparticles for targeted treatment of docetaxel-resistant prostate cancer

Docetaxel (Doc), as a first-line chemotherapy drug for prostate cancer (PC), often loses its therapeutic efficacy due to acquired resistance and lack of targeting specificity. Therefore, there is a need to develop a novel drug that can overcome Doc resistance and enhance its targeting ability to inhibit PC progression. In this study, we prepared Au/Doc/Quer@PDA/A10-3.2 nanoparticles (NPs) composite drug by encapsulating Doc and quercetin (Quer) within polydopamine (PDA)-coated Au NPs and further modifying them with RNA oligonucleotide aptamer A10-3.2. A10-3.2 was used for specific targeting of prostate-specific membrane antigen (PSMA)-positive PC cells (LNCaP). Quer was employed to reverse the resistance of Doc-resistant cell line (LNCaP/R) to Doc. Physical characterization using ultraviolet-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR) confirmed the successful preparation of Au/Doc/Quer@PDA/A10-3.2 NPs. Fluorescence imaging and flow cytometry experiments demonstrated the targeting ability of Au/Doc/Quer@PDA/A10-3.2 NPs towards PSMA-positive LNCaP/R cells. Cell proliferation, apoptosis, invasion, and migration experiments revealed that Quer reversed the resistance of LNCaP/R cells to Doc. Immunoblotting experiments further confirmed the mechanism behind sensitization of chemotherapy by Quer. Finally, we evaluated the therapeutic efficacy of Au/Doc/Quer@PDA/A10-3.2 NPs in a mouse model of PC. In conclusion, this study synthesized and validated a novel nano-composite drug (Au/Doc/Quer@PDA/A10-3.2 NPs) for combating Doc-resistant PC, which could potentially be applied in clinical treatment of PC.

Management of Dry Eye Toxicity After Treatment With 177Lu-PSMA-617 Radioligand Therapy

Treatment options for patients with metastatic castration-resistant prostate cancer include use of radioligand therapy with 177Lu-PSMA-617. 177Lu-PSMA-617 is used to target prostate cancer cells selectively by targeting prostate specific membrane antigen (PSMA); however, PSMA is also expressed on lacrimal glands among other tissues. Herein, we report on a case of a Common Terminology Criteria for Adverse Events version 5 grade 3 dry eye event with concomitant blepharitis after administration of 177Lu-PSMA-617. The patient was managed with neomycin-polymyxin-dexamethasone 3.5-10000-0.1 ophthalmic suspension, artificial tears, lubricating ointments, lid scrubs, and oral antihistamines.

Assessment of PSMA Expression of Healthy Organs in Different Stages of Prostate Cancer Using [68Ga]Ga-PSMA-11-PET Examinations.

The efficacy of radioligand therapy (RLT) targeting prostate-specific membrane antigen (PSMA) is currently being investigated for its application in patients with early-stage prostate cancer (PCa). However, little is known about PSMA expression in healthy organs in this cohort. Collectively, 202 [68Ga]Ga-PSMA-11 positron emission tomography (PET) scans from 152 patients were studied. Of these, 102 PET scans were from patients with primary PCa and hormone-sensitive biochemically recurrent PCa and 50 PET scans were from patients with metastatic castration-resistant PCa (mCRPC) before and after three cycles of [177Lu]Lu-PSMA-RLT. PSMA-standardized uptake values (SUV) were measured in multiple organs and PSMA-total tumor volume (PSMA-TTV) was determined in all cohorts. The measured PET parameters of the different cohorts were normalized to the bloodpool and compared using t- or Mann-Whitney U tests. Patients with early-stage PCa had lower PSMA-TTVs (10.39 mL vs. 462.42 mL, p < 0.001) and showed different SUVs in the thyroid, submandibular glands, heart, liver, kidneys, intestine, testes and bone marrow compared to patients with advanced CRPC, with all tests showing p < 0.05. Despite the differences in the PSMA-TTV of patients with mCRPC before and after [177Lu]Lu-PSMA-RLT (462.42 mL vs. 276.29 mL, p = 0.023), no significant organ differences in PET parameters were detected. These suggest different degrees of PSMA-ligand binding among patients with different stages of PCa that could influence radiotoxicity during earlier stages of disease in different organs when PSMA-RLT is administered.

Targeted interleukin-2 enhances the in vivo anti-cancer activity of Pluvicto™.

Pluvicto™ ([177Lu]Lu-PSMA-617), a radioligand therapeutic targeting prostate-specific membrane antigen (PSMA), has been recently approved for the treatment of metastatic castration-resistant prostate cancer (mCRPR). The drug suffers from salivary gland and kidney uptake that prevents its dose escalation to potentially curative doses. In this work, we sought to potentiate the in vivo anti-cancer activity of Pluvicto™ by combining it with L19-IL2, a clinical-stage investigational medicinal product based on tumor-targeted interleukin-2. We established a new PSMA-expressing model (HT-1080.hPSMA) and validated it using a fluoresceine analogue of PSMA-617 (compound 1). The HT-1080.hPSMA model was used to study the saturation and tumor retention of Pluvicto™ (compound 2) and to run combination therapy studies with L19-IL2. To complement our understanding of the mechanism of action of this novel combination, we conducted proteomics experiments on tumor samples after therapy with Pluvicto™ alone or in combination with the immunocytokine. High, selective, and long-lived tumor uptake was observed for Pluvicto™ (2) in the novel HT-1080.hPSMA model. Therapy studies in HT-1080.hPSMA tumor-bearing mice revealed that the combination of Pluvicto™ (2) plus L19-IL2 mediated curative and durable responses in all animals. Potent in vivo anti-cancer activity was observed solely for the combination modality, at doses that were well tolerated by treated animals. Proteomics studies indicated that L19-IL2 boosts the activation of the immune system in animals pre-treated with Pluvicto™. The therapeutic efficacy of Pluvicto™ at low radioactive doses can be effectively enhanced by the combination with L19-IL2. Our findings warrant further clinical exploration of this novel combination modality.

Abstract 6037: Copper-67 as a next-generation radioconjugate warhead for cancer therapy

Abstract Background and Purpose: Antibody drug conjugates (ADCs) have shown promise as cancer treatments. However, the efficacy of ADCs has been limited in solid tumors and can come with significant toxicities. Radioconjugates utilize various radionuclides that are chelated and can be conjugated to small molecules, peptides and antibodies. We propose Targeted Copper Theranostics (TCTs) which use copper-64 to image tumors and beta-emitting copper-67 to irradiate and kill cancer cells using various molecular targets of oncological relevance. We have evaluated the efficacy of copper-67 based therapy in three formats; peptides, antibodies, and pre-targeting of antibody conjugates in relevant tumor mouse models. Benefits of copper-67 [half-life, 61.8 h; 100% β- energy in the range of 0.18-0.56 MeV] include high purity, high specific activity, manufacturing in a centralized distribution model at high yields on electron accelerators, and half-life suitable to various targeting formats. Copper-64 and copper-67 provide multiple logistical benefits relative to other radionuclides including Ga-68, F-18 and Lu-177. Methods: We evaluated three tumor-targeting moieties conjugated to a sarcophagine bifunctional chelator (SAR), including: a peptide dimer targeting prostate specific membrane antigen (SAR-bisPSMA); an antibody 5B1, targeting the PDAC-specific biomarker carbohydrate antigen-19-9 (CA19-9); and a Tz-TCO IDEEA huA33 antibody/sarcophagine tetrazine conjugate targeting transmembrane glycoprotein A33. Various doses were administered of [67Cu]Cu-SAR-bisPSMA in LNCAP xenografts; [67Cu]Cu-SAR-5B1 (~10 μg) in FC1245 Ft2Ab PDAC tumor-bearing C57BL/6 mice; and [67Cu]Cu-MeCOSAR-Tz in athymic nude mice bearing A33 antigen-expressing SW1222 human colorectal carcinoma xenografts 72 hours after administration of huA33-TCO. Results: Administration of either 7.5, 15 or 30 MBq of [67Cu]Cu-SAR-bisPSMA increased overall survival relative to the control group. Similarly, after administration of 4, 11, 18 MBq of [67Cu]Cu-5B1, treated groups enhanced overall survival to 32 days compared to control (14 days). Pre-targeting using ~18.5, 37.0 or 55.5 MBq or fractionated dosing of two 27.8 MBq doses of [67Cu]Cu-MeCOSAR-Tz showed efficient tumor growth reduction with enhanced overall survival for treated mice pre-administered huA33-TCO, from 68 days to &amp;gt;200 days (dose dependent) compared to control (21 days). Conclusion: We report the inhibition of tumor growth with minimal radiotoxicity and each format demonstrated significantly improved overall survival compared to controls. Collectively our results demonstrated that TCTs using the sarcophagine chelator with copper-67 are effective radioconjugates across multiple formats with an acceptable safety profile. Copper-67-based TCTs are being translated in multiple theranostic clinical trials in the USA and Australia. Citation Format: Matt Harris, Kurt Gehlsen, Lachlan McInnes, Jason Lewis. Copper-67 as a next-generation radioconjugate warhead for cancer therapy [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 6037.

Abstract 6725: NTX-470, a novel multispecific T cell engager expressed from mRNA targets PSMA and STEAP1 prostate cancer antigens to generate enhanced functional activity

Abstract Prostate cancer is the most common cancer in American men and the second leading cause of cancer death in men in western countries. Most metastatic patients develop castration resistant prostate cancer, which despite advances in immunotherapy, is limited in treatment options and represents a critical unmet need. Bi-specific T cell engagers (TCEs) targeting prostate cancer antigens represent a modality that has demonstrated preliminary clinical activity. Clinically validated antigens that are highly expressed in prostate cancers include Prostate-Specific Membrane Antigen (PSMA) and Six Transmembrane Epithelial Antigen of the Prostate 1 (STEAP1). TCEs targeting either PSMA or STEAP1 individually have shown promising clinical activity, but challenges with durability and toxicity have been reported, potentially attributable to antigen escape, target-independent T cell activation (bystander activation) and specificity issues. Contrary to its name, PSMA expression is not exclusive to prostate cells and can be found in several other tissues and/or conditions, including normal nonprostatic epithelial cells, inflammation/infection, nonprostatic neoplastic cells and nonprostatic tumor-associated neovasculature. The widespread expression of PSMA may limit the therapeutic window of PSMA-specific TCEs and drive immunotoxicity by increased on-target, off-tumor binding. To address these issues, Nutcracker Therapeutics (NTX) has developed novel and highly complex multispecific TCE molecules that target both PSMA and STEAP1, which can be expressed using NTX’s proprietary mRNA therapeutics platform. A wide library of molecules was designed with attenuated PSMA and CD3 binding to mitigate on-target, off-tumor binding and target-independent T cell activation. Molecules were screened and selected based on their propensity to cause bystander T cell activation and the strength of PSMA binding. We identified a small number of molecules that are capable of engaging CD3 T cells but display minimal activity in the absence of STEAP1 or PSMA expressing target cells, including molecules that retain low bystander activity and attenuated PSMA binding yet maintain robust target cell killing. These molecules include NTX-470, which targets both STEAP1 and PSMA on tumor cells with minimal bystander activity. Citation Format: Chris Rae, Sudha Adusumilli, Srinivasa Bandi, Shruti Lal, Pragyesh Dhungel, Kimmy Ferry, Shima Gholizadeh, Anushtha Sharma, Adrienne Sallets, Weiqun Liu, Evan McCartney-Melstad, Pei-Ken Hsu, Ray Low, Colin McKinlay, Meredith Leong, David Y. Oh, Lawrence Fong, Guna Kannan, Samuel Deutsch, Ole Haabeth. NTX-470, a novel multispecific T cell engager expressed from mRNA targets PSMA and STEAP1 prostate cancer antigens to generate enhanced functional activity [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 6725.

Advancements in PSMA ligand radiolabeling for diagnosis and treatment of prostate cancer: a systematic review.

Prostate cancer(PCa), a leading global health concern, profoundly impacts millions of men worldwide. Progressing through two stages, it initially develops within the prostate and subsequently extends to vital organs such as lymph nodes, bones, lungs, and the liver. In the early phases, castration therapy is often employed to mitigate androgen effects. However, when prostate cancer becomes resistant to this treatment, alternative strategies become imperative. As diagnostic and treatment methodologies for prostate cancer continually advance, radioligand therapy (RLT) has emerged as a promising avenue, yielding noteworthy outcomes. The fundamental principle of RLT involves delivering radionuclide drugs to cancerous lesions through specific carriers or technologies. Subsequently, these radionuclide drugs release radioactive energy, facilitating the destruction of cancer cell tissues. At present, the positron emission tomography (PET) targeting PSMA has been widely developed for the use of diagnosis and staging of PCa. Notably, FDA-approved prostate-specific membrane antigen (PSMA) targeting agents, such as 68Ga-PSMA-11 and 177Lu-PSMA-617, represent significant milestones in enhancing diagnostic precision and therapeutic efficacy. This review emphasizes the current research status and outcomes of various radionuclide-labeled PSMA ligands. The objective is to provide valuable insights for the continued advancement of diagnostic and therapeutic approaches in the realm of prostate cancer.

Exploration of commercial cyclen-based chelators for mercury-197m/g incorporation into theranostic radiopharmaceuticals.

A comprehensive investigation of the Hg2+ coordination chemistry and 197m/gHg radiolabeling capabilities of cyclen-based commercial chelators, namely, DOTA and DOTAM (aka TCMC), along with their bifunctional counterparts, p-SCN-Bn-DOTA and p-SCN-Bn-TCMC, was conducted to assess the suitability of these frameworks as bifunctional chelators for the 197m/gHg2+ theranostic pair. Radiolabeling studies revealed that TCMC and DOTA exhibited low radiochemical yields (0%-6%), even when subjected to harsh conditions (80°C) and high ligand concentrations (10-4M). In contrast, p-SCN-Bn-TCMC and p-SCN-Bn-DOTA demonstrated significantly higher 197m/gHg radiochemical yields (100% ± 0.0% and 70.9% ± 1.1%, respectively) under the same conditions. The [197m/gHg]Hg-p-SCN-Bn-TCMC complex was kinetically inert when challenged against human serum and glutathione. To understand the differences in labeling between the commercial chelators and their bifunctional counterparts, non-radioactive natHg2+ complexes were assessed using NMR spectroscopy and DFT calculations. The NMR spectra of Hg-TCMC and Hg-p-SCN-Bn-TCMC suggested binding of the Hg2+ ion through the cyclen backbone framework. DFT studies indicated that binding of the Hg2+ ion within the backbone forms a thermodynamically stable product. However, competition can form between isothiocyanate binding and binding through the macrocycle, which was experimentally observed. The isothiocyanate bound coordination product was dominant at the radiochemical scale as, in comparison, the macrocycle bound product was seen at the NMR scale, agreeing with the DFT result. Furthermore, a bioconjugate of TCMC (TCMC-PSMA) targeting prostate-specific membrane antigen was synthesized and radiolabeled, resulting in an apparent molar activity of 0.089 MBq/nmol. However, the complex demonstrated significant degradation over 24h when exposed to human serum and glutathione. Subsequently, cell binding assays were conducted, revealing a Ki value ranging from 19.0 to 19.6nM. This research provides crucial insight into the effectiveness of current commercial chelators in the context of 197m/gHg2+ radiolabeling. It underscores the necessity for the development of specific and customized chelators to these unique "soft" radiometals to advance 197m/gHg2+ radiopharmaceuticals.