Prostate-specific Membrane Antigen Targeting Research Articles

Targeted Theranostic 111In/Lu-Nanotexaphyrin for SPECT Imaging and Photodynamic Therapy.

Theranostic nanoparticles aim to integrate diagnostic imaging and therapy to facilitate image-guided treatment protocols. Herein, we present a theranostic nanotexaphyrin for prostate-specific membrane antigen (PSMA)-targeted radionuclide imaging and focal photodynamic therapy (PDT) accomplished through the chelation of metal isotopes (In, Lu). To realize nanotexaphyrin's theranostic properties, we developed a rapid and robust 111In/Lu-nanotexaphyrin radiolabeling method using a microfluidic system that achieved a high radiochemical yield (>90%). The optimized metalated nanotexaphyrin displayed excellent chemical, photo, and colloidal stabilities, potent singlet oxygen generation, and favorable plasma circulation half-life in vivo (t1/2 = 6.6 h). Biodistribution, including tumor accumulation, was characterized by NIR fluorescence, SPECT/CT imaging, and γ counting. Inclusion of the PSMA-targeting ligand enabled the preferential accumulation of 111In/Lu-nanotexaphyrin in PSMA-positive (PSMA+) prostate tumors (3.0 ± 0.3%ID/g) at 48 h with tumor vs prostate in a 2.7:1 ratio. In combination with light irradiation, the PSMA-targeting nanotexaphyrin showed a potent PDT effect and successfully inhibited PSMA+ tumor growth in a subcutaneous xenograft model. To the best of our knowledge, this study is the first demonstration of the inherent metal chelation-driven theranostic capabilities of texaphyrin nanoparticles, which, in combination with PSMA targeting, enabled prostate cancer imaging and therapy.

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.

Synthesis and Preliminary Biological Assessment of Carborane-Loaded Theranostic Nanoparticles to Target Prostate-Specific Membrane Antigen.

Boron neutron capture therapy (BNCT) is an encouraging therapeutic modality for cancer treatment. Prostate-specific membrane antigen (PSMA) is a cell membrane protein that is abundantly overexpressed in prostate cancer and can be targeted with radioligand therapies to stimulate clinical responses in patients. In principle, a spatially targeted neutron beam together with specifically targeted PSMA ligands could enable prostate cancer-targeted BNCT. Thus, we developed and tested PSMA-targeted poly(lactide-co-glycolide)-block-poly(ethylene glycol) (PLGA-b-PEG) nanoparticles (NPs) loaded with carborane and tethered to the radiometal chelator deferoxamine B (DFB) for simultaneous positron emission tomography (PET) imaging and selective delivery of boron to prostate cancer. Monomeric PLGA-b-PEGs were covalently functionalized with either DFB or the PSMA ligand ACUPA. Different nanoparticle formulations were generated by nanoemulsification of the corresponding unmodified and DFB- or ACUPA-modified monomers in varying percent fractions. The nanoparticles were efficiently labeled with 89Zr and were subjected to in vitro and in vivo evaluation. The optimized DFB(25)ACUPA(75) NPs exhibited strong in vitro binding to PSMA in direct binding and competition radioligand binding assays in PSMA(+) PC3-Pip cells. [89Zr]DFB(25) NPs and [89Zr]DFB(25)ACUPA(75) NPs were injected to mice with bilateral PSMA(-) PC3-Flu and PSMA(+) PC3-Pip dual xenografts. The NPs demonstrated twofold superior accumulation in PC3-Pip tumors to that of PC3-Flu tumors with a tumor/blood ratio of 25; however, no substantial effect of the ACUPA ligands was detected. Moreover, fast release of carborane from the NPs was observed, resulting in a low boron delivery to tumors in vivo. In summary, these data demonstrate the synthesis, characterization, and initial biological assessment of PSMA-targeted, carborane-loaded PLGA-b-PEG nanoparticles and establish the foundation for future efforts to enable their best use in vivo.

In silico study on radiobiological efficacy of Ac-225 and Lu-177 for PSMA-guided radiotherapy.

The good efficacy of radioligand therapy (RLT) targeting prostate specific-membrane antigen (PSMA) for the treatment of metastatic castration-resistant prostate cancer (mCRPC) has been recently demonstrated in several clinical studies. However, the treatment effect of 177Lu-PSMA-ligands is still suboptimal for a significant fraction of patients. In contrast to external beam radiotherapy, the radiation dose distribution itself is strongly influenced by the heterogeneous tumour microenvironment. Although microdosimetry is critical for RLT treatment outcome, it is difficult to clinically or experimentally establish the quantitative relation. We propose an in silico approach to quantitatively investigate the microdosimetry and its influence on treatment outcome for PSMA-directed RLT of two different radioisotopes 177Lu and 225 Ac. The ultimate goal is optimize the combined 177 Lu and 225 Ac-PSMA therapy and maximize the anti-tumour effect, while minimizing irradiation of off-target tissues.Clinical relevance- With the proposed hybrid model we show that 177Lu-PSMA-ligands treatment assures a more homogeneously distributed dose and a lower dependency of the treatment outcome on the domain vascularisation. On the other hand, the 225Ac-PSMA-ligands treatment shows a much stronger efficacy in killing tumor cells with an equivalent mean dose distribution even in an hypoxic environment.

Total chemical synthesis of PSMA-11: API for 68Ga-PSMA-11 used for prostate cancer diagnosis

The imaging of prostate tumours by targeting Prostate Specific Membrane Antigen (PSMA), using binding tracer, 68Ga-PSMA-11, offer lots of promises for specific detection of prostate associated malignancies. The popularity of 68Ga-PSMA-11 as a radioligand tool for prostate cancer diagnosis has gained a major boost upon its FDA approval in December 2020. Development of an economically benign protocol for the synthesis of PSMA-11, using solution phase method, is particularly important to get a better access to this highly important and expensive Active Pharmaceutical Ingredient (API). The PSMA-11 synthesized using the protocol presented here, involves the use of a flow reactor based catalytic hydrogenation as the key step. Using the method portrayed, PSMA-11 with purity >99.5% was achieved, while, radiolabelling with 68Ga afforded 68Ga-PSMA-11 with radiochemical purity >95%, which is appropriate for imaging applications.

Comparison of low-molecular-weight ligand and whole antibody in prostate-specific membrane antigen targeted near-infrared photoimmunotherapy

Near-infrared photoimmunotherapy (NIR-PIT) is a cancer phototherapy that uses antibody-IR700 conjugate (Ab-IR700) and NIR light. Ab-IR700 forms aggregates on the plasma membranes of targeted cancer cells after light exposure, inducing lethal physical damage within the membrane. Low-molecular-weight (LMW) ligands are candidate targeting moieties instead of antibodies, but whether LMW-IR700 conjugates induce cell death by aggregation, the same mechanism as Ab-IR700, is unknown. Thus, we investigated differences in cytotoxicity and mechanisms between LMW-IR700 and Ab-IR700 targeting prostate-specific membrane antigen (PSMA). Both conjugates decreased cell viability to the same degree after light irradiation, but different morphological changes were observed in PSMA-positive LNCaP cells by microscopy. Cell swelling and bleb formation were induced by Ab-IR700, but only swelling was observed in cells treated with LMW-IR700, suggesting the cells were damaged via different cytotoxic mechanisms. However, LMW-IR700 induced bleb formation, a hallmark of NIR-PIT with Ab-IR700, when singlet oxygen was quenched or LMW-IR700 was localized only on the plasma membrane. Moreover, the water-soluble axial ligands of LMW-IR700 were cleaved, consistent with previous reports on Ab-IR700. Thus, the main cytotoxic mechanisms of Ab-IR700 and LMW-IR700 differ, although LMW-IR700 on the plasma membrane can cause aggregation-mediated cytotoxicity as well as Ab-IR700.

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

PurposePreliminary data from retrospective analyses and recent data from large randomized controlled trials suggest safety and efficacy of radioligand therapy (RLT) targeting prostate-specific membrane antigen (PSMA) in men with metastatic castration-resistant prostate cancer (mCRPC). Limited data on this modality have been published regarding large samples treated in everyday practice.MethodsWe analyzed prospectively collected registry data regarding lutetium-177 (177Lu)-PSMA-617 RLT of 254 consecutive men with mCRPC seen in everyday academic practice. Since 177Lu-PSMA-617 was experimental salvage treatment following failure of individually appropriate conventional therapies, patients were generally elderly and heavily pretreated (median age 70 years; prior taxanes 74.0%, 188/254), with late–end-stage disease (visceral metastasis in 32.7%, 83/254). Primary endpoints were response to RLT, defined by changes from baseline serum prostate-specific antigen (PSA) concentration, PSA progression-free survival (PSA-PFS), and overall survival (OS), estimated with Kaplan–Meier statistics, and caregiver-reported and patient-reported safety. Unless noted, median (minimum–maximum) values are given.ResultsPatients received 3 (1–13) 177Lu-PSMA-617 activities (6.5 [2.5–11.6] GBq/cycle) every 5.7 (3.0–11.0) weeks. Best response was ≥ 50% PSA reduction in 52.0% of patients (132/254). PSA-PFS was 5.5 (95% confidence interval [95%CI] 4.4–6.6) months and OS, 14.5 (95%CI 11.5–17.5) months. In multivariable Cox proportional-hazards modeling, response to the initial ≤ 2 RLT administrations was the strongest significant prognosticator related to OS (hazard ratio 3.7 [95%CI 2.5–5.5], p < 0.001). No RLT-related deaths or treatment discontinuations occurred; the most frequent RLT-related Grade 3/4 adverse events were anemia (18/254 patients, 7.1%), thrombocytopenia (11/254, 4.3%), and lymphopenia (7/254, 2.8%). RLT-related xerostomia, all grade 1/2, was noted in 53/254 (20.9%).ConclusionsIn a large, prospectively observed “real-world” cohort with late-stage/end-stage mCRPC and conventional treatment failure, 177Lu-PSMA-617 RLT was effective, safe, and well-tolerated. Early biochemical disease control by such therapy was associated with better OS. Prospective study earlier in the disease course may be warranted.

Is Hypoxia a Factor Influencing PSMA-Directed Radioligand Therapy?-An In Silico Study on the Role of Chronic Hypoxia in Prostate Cancer.

Simple SummaryTumor hypoxia is considered a critical factor associated with the resistance of conventional radiotherapy, where the X-ray-induced free radicals lead to DNA damage in a manner that is strongly dependent on the tissue oxygenation. The emerging PSMA-directed radioligand therapy (RLT) employs the or particles emitted by the radiopharmaceuticals to kill the tumor cells. In contrast to conventional therapy, the induced DNA damage is less dependent on the oxygenation status. Less attention has been paid to investigating whether tumor hypoxia will influence the efficacy of PSMA-directed RLT. We propose a histology-driven in silico model to quantitatively investigate the influence of tumor hypoxia on the treatment outcome for PSMA-directed RLT with Lu and Ac. Our finding suggests that hypoxia is a factor to be considered for the application of PSMA-directed RLT.Radioligand therapy (RLT) targeting prostate specific-membrane antigen (PSMA) is an emerging treatment for metastatic castration-resistant prostate cancer (mCRPC). It administrates Ac- or Lu-labeled ligands for the targeted killing of tumor cells. Differently from X- or -ray, for the emitted or particles the ionization of the DNA molecule is less dependent on the tissue oxygenation status. Furthermore, the diffusion range of electrons in a tumor is much larger than the volume typically spanned by hypoxic regions. Therefore, hypoxia is less investigated as an influential factor for PSMA-directed RLT, in particular with emitters. This study proposes an in silico approach to theoretically investigate the influence of tumor hypoxia on the PSMA-directed RLT. Based on mice histology images, the distribution of the radiopharmaceuticals was simulated with an in silico PBPK-based convection–reaction–diffusion model. Three anti-CD31 immunohistochemistry slices were used to simulate the tumor microenvironment. Ten regions of interest with varying hypoxia severity were analyzed. A kernel-based method was developed for dose calculation. The cell survival probability was calculated according to the linear-quadratic model. The statistical analysis performed on all the regions of interest (ROIs) shows more heterogeneous dose distributions obtained with Ac compared to Lu. The higher homogeneity of Lu-PSMA-ligand treatment is due to the larger range covered by the emitted particles. The dose-to-tissue histogram (DTH) metric shows that in poorly vascularized ROIs only 10% of radiobiological hypoxic tissue receives the target dose using Lu-PSMA-ligand treatment. This percentage drops down to 5% using Ac. In highly vascularized ROIs, the percentage of hypoxic tissue receiving the target dose increases to more than 85% and 65% for the Lu and Ac-PSMA-ligands, respectively. The in silico study demonstrated that the reduced vascularization of the tumor strongly influences the dose delivered by PSMA-directed RLT, especially in hypoxic regions and consequently the treatment outcome.

Antibodies targeting Prostate-Specific Membrane Antigen positive prostate cancer: from diagnostic imaging to theranostics.

Targeting Prostate-Specific Membrane Antigen (PSMA) has paved the way for personalized medicine in prostate cancer (PCa) patients. This review aims to highlight the role of PSMA targeting antibodies in PCa, for diagnostic and therapeutic purposes. PSMA Positron Emission Tomography/Computed Tomography has been a game changer in the diagnosis of PCa in the recent decade. Two anti-PSMA monoclonal antibodies have been studied in PCa: 7E11-C35 (limited use) and J591. J591 antibody was used for diagnostic purposes coupled with different radionuclides. Most importantly, it was combined to numerous therapeutic radionuclides such as Lutetium-177 (177Lu), Yttrium-90 (90Y), Indium-111 (111In), and Actinium-225 (225Ac). It was also conjugated to drugs forming antibody-drug conjugates (e.g. MLN2704 and PSMA-ADC). These compounds were tested in recent phase I/II clinical trials. PSMA targeting antibodies are very promising for further clinical investigation and continue to be a momentous research area, for both imaging and therapeutic settings. Although some clinical trials resulted in unfavorably safety profiles for some antibodies, they validated PSMA as a crucial immunoconjugate target.

Abstract 3056: Alpha particle radiobiology and the treatment of prostate adenocarcinoma

Abstract Background: Castration-resistant prostate cancer (CRPC) is treated with the androgen receptor (AR) antagonist Enzalutamide (ENZA). However, early positive outcomes are later reversed by acquired resistance, ultimately leading to lethal AR-independent disease progression. High linear energy transfer (LET) alpha particle emitting drugs targeting Prostate Specific Membrane Antigen (e.g., [Actinium-225]-PSMA617) are potent and specific, yielding radiological and biomarker disease regression, but are not curative. DNA damage responses (DDR) in irradiated cells repair double strand breaks (DSB) allowing CRPC to escape. We are exploring the pharmacological effect of AR signaling on alpha particle therapy. AR signaling has a significant role in DDR and a better understanding of the alpha radiobiology is necessary to better deploy these potent drugs in combination. Methods: Alpha particle-induced DDR was investigated using readouts of clonogenic survival, cell cycle, apoptosis, and gene expression in AR-positive LNCaP-AR and AR-negative DU145 cells that were also treated with ENZA and an ATM inhibitor (ATMi, KU59403). Briefly, cells were seeded on mylar, treated with ENZA and ATMi and subsequently irradiated with alpha particles. Clonogenic survival was quantified at 10 days post alpha-irradiation. DNA damage was confirmed by imaging gamma-H2AX foci. Flow cytometry was used to analyze cell cycle arrest and apoptosis. Relative gene expression was quantified from RNA extracted immediately after and 10 days post-irradiation via RT-qPCR. Results: We observed the formation of increased DNA DSB (gamma-H2AX foci) versus controls after irradiation. ENZA radiosensitized LNCaP-AR versus untreated cells as evidenced by the D0 values obtained from clonogenic assays. However, combination of ENZA and alpha particles also upregulated expression of DDR genes. LNCaP-AR were in G2 arrest with increased apoptosis following irradiation. An ATMi was added to the regimen to address the upregulated DDR and increased apoptosis was observed. Altogether, these results indicate that cells are radiosensitized by ENZA but concomitant activation of DDR requires ATMi to improve therapy. Conclusion: DNA damage caused by alpha particles alone does not eradicate CRPC because some cells can repair DSB. Cell control from ENZA treatment alone is transient, leading to development of acquired resistance and disease relapse. Combining alpha particles and ENZA radiosensitizes AR-dependent prostate cancer cells, but DDR rescues a fraction of cells. Inhibiting the ATM pathway in AR-antagonized cells, in combination with high LET alpha irradiation, is a better approach to overcome prostate cancer cell resistance mechanisms. Combination ENZA/ATMi/alpha particles is a strategy designed to address the radioresistant subpopulation and could avoid CRPC progression to the more lethal, non-treatable stage of this disease. Citation Format: Barbara P. Mello, Ekaterina Revskaya, David A. Scheinberg, Michael R. McDevitt. Alpha particle radiobiology and the treatment of prostate adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3056.

Abstract 910: Amanitin-based ADCs targeting PSMA as novel therapeutic modality for prostate cancer therapy

Abstract Background: Antibody-targeted amanitin conjugates (ATACs) comprise a new class of antibody-drug conjugates (ADCs) using amanitin as toxic payload. Amanitin binds to the RNA pol II and thereby efficiently inhibits the cellular transcription process. In the current study, in vitro and in vivo data of an ATAC targeting PSMA (prostate specific membrane antigen) are presented. PSMA is a type II integral membrane glycoprotein and used as tumor marker due to its predominant expression on malignant prostate cells in prostate carcinoma. As PSMA expression increases with tumor aggressiveness, metastatic and disease recurrence, it is considered an ideal target for amanitin-based ADCs. Material and methods: Cell lines: PSMA+ cell lines: LNCap, 22RV1; PSMA- cell line: PC3 Antibody: cysteine engineered monoclonal anti-PSMA antibody (Albert Ludwig University Freiburg, medical center; derivatization and production at Heidelberg Pharma) Toxic warhead: Cysteine reactive amanitin-linker constructs were synthesized at Heidelberg Pharma and conjugated site-specifically to engineered cysteine residues of the anti-PSMA antibody yielding ATACs with a DAR of 2. Cell proliferation assay: Quantitative determination of cell viability was performed by BrdU-based chemiluminescent cell proliferation ELISA (Roche). Animal models: Subcutaneous Mouse xenograft tumor models with PSMA-positive cell lines 22RV1 and LNCap were performed in single-dose experiments. Tolerability was assessed in mice and non-human primates (NHP). Results: All anti-PSMA ATACs with optimized amanitin-linker variants for use in solid tumors showed favorable in vitro cytotoxicity with nano- to picomolar activity on PSMA+ cell lines and no cytotoxic activity on PSMA- cells. In mouse xenograft models, the optimized anti-PSMA ATACs caused dose-dependent tumor regression in LNCap s.c. xenografts. Complete remission was achieved after a single i.v. dose of ¼ MTD with 100% overall survival for the full duration of the studies (&amp;gt;160 days). The tolerability of the tested ATACs in mice differed between 15 and &amp;gt; 80 mg/kg Safety profiling in Cynomolgus monkeys revealed a good tolerability and therapeutic index for all selected amanitin-linker variants. Hematology and clinical chemistry parameters were unaffected except liver enzymes and LDH: A moderate and transient increase was observed. Low off target toxicity was confirmed by a non-binding ATAC. Conclusions: Targeted cytotoxic drug delivery to PSMA positive cell lines was achieved by using anti-PSMA ATACs optimized for the use in solid tumors. The mode of action of the payload amanitin led to an efficient anti-tumor potential in vitro and in vivo with good tolerability in non-human primates. Using ATACs in the therapy of PSMA positive prostate cancer is a promising approach, especially by using a cytotoxic agent whose mode of action differs from other commonly used toxins. Citation Format: Alexandra Braun, Aniko Palfi, Christoph Mueller, Torsten Hechler, Andreas Pahl, Michael Kulke. Amanitin-based ADCs targeting PSMA as novel therapeutic modality for prostate cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 910.

Abstract 1573: Combinatorial antitumor effects of CD3-based trispecific T cell activating constructs (TriTACs) and checkpoint inhibitors in preclinical models

Abstract Tri-specific T Cell-Activating Constructs (TriTACs) are T-cell engagers that have been developed to redirect T cells to kill tumor cells. TriTAC molecules are currently being investigated in multiple phase 1/2 clinical trials in solid tumors, including HPN424 targeting prostate-specific membrane antigen (PSMA) in prostate cancer (NCT03577028), HPN536 targeting mesothelin (MSLN) in multiple malignancies (NCT03872206) and HPN328 targeting Delta Like Canonical Notch Ligand 3 (DLL3) in small cell lung cancer (SCLC) (NCT04471727). TriTAC molecules consist of a single domain antibody (sdAb) specific for a tumor antigen, a sdAb specific for serum albumin for half-life extension, and a single chain Fv (scFv) specific for the CD3ϵ subunit of the T cell receptor (TCR) complex for T cell engagement. In the presence of antigen expressing tumor cells, TriTAC treatment leads to potent T cell activation, production of proinflammatory cytokines, and re-directed tumor cell killing. Upregulation of co-stimulatory and/or inhibitory receptors during activation can potentially affect the cytolytic functions of TriTAC-activated T cells. We demonstrate that PD-1 can be readily detected on T cells subsequent to the engagement of the TCR by the TriTAC molecules HPN424, HPN536, and HPN328 in the presence of tumor cells expressing the target antigens PSMA, MSLN, and DLL3, respectively. We also demonstrate that TriTAC molecules upregulate PD-L1 on T cells in a dose-dependent manner. While induction of PD-1 on T cells suggests that cytolytic activity of TriTAC-activated T cells may be down-modulated by PD-L1-expressed by target tumor cells, simultaneous upregulation of PD-L1 on T cells suggests a second mechanism through which the functions of TriTAC-activated T cells could be further regulated by the PD1/PD-L1 axis in the tumor microenvironment through T cell-T cell interactions. In addition, in the MSLN-expressing NCI-H292 lung cancer model that co-expresses constitutive, high levels of PD-L1, both anti-PD1 and anti-PDL1 antibodies significantly enhanced the antitumor effects of the MSLN-targeting TriTAC HPN536 in vivo. Together these results demonstrate the potential utility of PD1/PDL1 blockade to enhance the potency of TriTAC-mediated tumor cell killing, supporting further investigation of these combinatorial approaches in patients. Citation Format: Mary Ellen Molloy, Laura B. Valenzuela, Priyanka E. Basak, Che-Leung Law. Combinatorial antitumor effects of CD3-based trispecific T cell activating constructs (TriTACs) and checkpoint inhibitors in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1573.

64Cu-PSMA-BCH: a new radiotracer for delayed PET imaging of prostate cancer.

Develop a 64Cu labeled radiopharmaceutical targeting prostate specific membrane antigen (PSMA) and investigate its application for prostate cancer imaging. 64Cu-PSMA-BCH was prepared and investigated for stability, PSMA specificity, and micro-PET imaging. With the approval of Ethics Committee of Beijing Cancer Hospital (No. 2017KT97), PET/CT imaging in 4 patients with suspected prostate cancer was performed and the radiation dosimetry was estimated. Then, PSMA PET-ultrasound image-guided biopsies were performed on 3 patients and the fine needle aspirates were further performed for autoradiography and immunohistochemistry analysis. 64Cu-PSMA-BCH was prepared with high radiochemical yield and stability. In vivo study showed higher uptake in PSMA ( +) 22Rv1 cells than PSMA ( -) PC-3 cells (5.59 ± 0.36 and 1.97 ± 0.22 IA%/106 cells at 1h). It accumulated in 22Rv1 tumor with increasing radioactivity uptake and T/N ratios from 1 to 24h post-injection. In patients with suspected prostate cancer, SUVmax and T/N ratios increased within 24h post-injection. Compared with image at 1h post-injection, more tumor lesions were detected at 6h and 24h post-injection. The human organ radiation dosimetry showed gallbladder wall was most critical, liver and kidneys were followed, and the whole-body effective dose was 0.0292mSv/MBq. Two fine needle aspirates obtained by PET-ultrasound-guided targeted biopsy showed high radioactive signal by autoradiography, with 100% PSMA expression in cytoplasm and 30% expression in nucleus. 64Cu-PSMA-BCH was PSMA specific and showed high stability in vivo with lower uptake in liver than 64Cu-PSMA-617. Biodistribution in mice and PCa patients showed similar profile compared with other PSMA ligands and it was safe with moderate effective dosimetry. The increased tumor uptake and T/N ratios by delayed imaging may facilitate the detection of small lesions and guiding targeted biopsies.

Renal Safety of [177Lu]Lu-PSMA-617 Radioligand Therapy in Patients with Compromised Baseline Kidney Function.

Simple SummaryRadioligand therapy (RLT) targeting prostate-specific membrane antigen (PSMA) is an effective antitumor-treatment in metastatic castration-resistant prostate carcinoma (mCRPC). Concerns of potential nephrotoxicity are based on renal tubular PSMA expression and the resulting radiopharmaceutical retention during RLT, but data confirming clinically significant renal toxicity are still lacking. In this study, n = 22 patients treated within a prospective patient registry (REALITY Study) with significantly impaired baseline kidney function were investigated for treatment-associated nephrotoxicity and the potential relationship with administered activities of [177Lu]Lu-PSMA-617. As opposed to prevailing concerns, glomerular filtration rate (GFR) improved significantly in our cohort of patients and no significant correlation between change in GFR and administered activities were found. As pre-treatment chronic kidney failure did not lead to detectable RLT-induced deterioration of renal function in our study, the nephrotoxic potential of [177Lu]Lu-PSMA-617 RLT may be overestimated. We suggest not to categorically exclude patients from enrolment to PSMA-RLT due to renal impairment.Background: Radioligand therapy (RLT) targeting prostate-specific membrane antigen (PSMA) is an effective antitumor-treatment in metastatic castration-resistant prostate carcinoma (mCRPC). Concerns of potential nephrotoxicity are based on renal tubular PSMA expression and the resulting radiopharmaceutical retention during RLT, but data confirming clinically significant renal toxicity are still lacking. In this study, patients with significantly impaired baseline kidney function before initiation of therapy were investigated for treatment-associated nephrotoxicity and the potential relationship with administered activities of [177Lu]Lu-PSMA-617. Methods: Twenty-two mCRPC patients with impaired renal function (glomerular filtration rate (GFR) ≤ 60 mL/min) who received more than two cycles of [177Lu]Lu-PSMA-617 RLT (median 5 cycles and median 6-week time interval between consecutive cycles) were analyzed in this study. Patients were treated within a prospective patient registry (REALITY Study, NCT04833517). Cumulative administered activities ranged from 17.1 to 85.6 GBq with a median activity of 6.5 GBq per cycle. Renal function was closely monitored during and after PSMA-RLT. Results: Mean pre-treatment GFR was 45.0 ± 10.7 mL/min. After two (22/22 patients), four (20/22 patients), and six cycles (10/22 patients) of RLT, a significant increase of GFR was noted (each p < 0.05). End-of-treatment GFR (54.1 ± 16.7 mL/min) was significantly higher than baseline GFR (p = 0.016). Only one patient experienced deterioration of renal function (change of CTCAE grade 2 to 3). The remaining patients showed no significant reduction of GFR, including follow-up assessments (6, 9, and 12 months), and even showed improved (10/22 patients) or unchanged (11/22 patients) CTCAE-based renal impairment grades during and after the end of PSMA-RLT. No significant correlation between the change in GFR and per-cycle (p = 0.605) or cumulative (p = 0.132) administered activities were found. Conclusions: As pre-treatment chronic kidney failure did not lead to detectable RLT-induced deterioration of renal function in our study, the nephrotoxic potential of [177Lu]Lu-PSMA-617 RLT may be overestimated and not of clinical priority in the setting of palliative treatment in mCRPC. We suggest not to categorically exclude patients from enrolment to PSMA-RLT due to renal impairment.

An Improved 211At-Labeled Agent for PSMA-Targeted α-Therapy.

α-Particle emitters targeting the prostate-specific membrane antigen (PSMA) proved effective in treating patients with prostate cancer who were unresponsive to the corresponding β-particle therapy. 211At is an α-emitter that may engender less toxicity than other α-emitting agents. We synthesized a new 211At-labeled radiotracer targeting PSMA that resulted from the search for a pharmacokinetically optimized agent. Methods: A small series of 125I-labeled compounds was synthesized from tin precursors to evaluate the effect of the location of the radiohalogen within the molecule and the presence of lutetium in the chelate on biodistribution. On that basis, 211At-3-Lu was selected and evaluated in cell uptake and internalization studies, and biodistribution and PSMA-expressing (PSMA+) PC3 PIP tumor growth control were evaluated in experimental flank and metastatic (PC3-ML-Luc) models. A long-term (13-mo) toxicity study was performed for 211At-3-Lu, including tissue chemistries and histopathology. Results: The radiochemical yield of 211At-3-Lu was 17.8% ± 8.2%. Lead compound 211At-3-Lu demonstrated total uptake within PSMA+ PC3 PIP cells of 13.4 ± 0.5% of the input dose after 4 h of incubation, with little uptake in control cells. In SCID mice, 211At-3-Lu provided uptake that was 30.6 ± 4.8 percentage injected dose per gram (%ID/g) in PSMA+ PC3 PIP tumor at 1 h after injection, and this uptake decreased to 9.46 ± 0.96 %ID/g by 24 h. Tumor-to-salivary gland and tumor-to-kidney ratios were 129 ± 99 at 4 h and 130 ± 113 at 24 h, respectively. Deastatination was not significant (stomach, 0.34 ± 0.20 %ID/g at 4 h). Dose-dependent survival was demonstrated at higher doses (>1.48 MBq) in both flank and metastatic models. There was little off-target toxicity, as demonstrated by hematopoietic stability, unchanged tissue chemistries, weight gain rather than loss throughout treatment, and favorable histopathologic findings. Conclusion: Compound 211At-3-Lu or close analogs may provide limited and acceptable toxicity while retaining efficacy in management of prostate cancer.

PSMA-PET/CT Registry for Recurrent Prostate Cancer (PREP): Initial findings from a single center.

5064 Background: Several lesion-targeted therapies exist for locally recurrent or limited stage metastatic prostate cancer (PCa) post-radiotherapy (RT) and radical prostatectomy (RP). However, detection of disease sites is limited using conventional imaging (CI) including computed tomography (CT) and bone scan. Prostate specific membrane antigen (PSMA) targeting PET radiopharmaceuticals like [18F]DCFPyL may help detect disease not seen on CI. Our objective was to assess the ability of PSMA targeted PET/CT to detect sites of disease recurrence and impact on patient management. Methods: This multi-center prospective registry study included six Ontario centers. Eligible patients in 1 of 7 clinical cohorts (Table) were identified and approved by Cancer Care Ontario (CCO) to have restaging with PSMA targeted PET/CT. Referring physicians were asked to complete a form indicating whether a change in management strategy would occur based on the PET/CT results. At 6 months post-PET/CT, actual patient management will be confirmed via provincial registries. These interim results are from a single center. Results: 253 patients were enrolled and had a PSMA targeted PET/CT. At baseline, median age was 71 years (range 50-102 years) and median PSA was 2.7 ng/mL (range 0.04-134.0 ng/mL). The majority of patients (n=59; 23.3%) were in cohort 2 (biochemical failure post-RP). In patients with negative CI, PSMA targeted PET/CT detected disease sites in 68.5% (170/248), resulting in a change in management for 67.8% (137/202) overall and 72.1% and 64.3% post-RT and post-RP, respectively. Conclusions: PSMA targeted PET/CT detected occult lesions on CI in the majority of patients enrolled, leading to a high rate of change in management. Our institutional results are in keeping with preliminary results reported for the provincial cohort. Clinical trial information: NCT03718260. [Table: see text]

Phase I study of CCW702, a bispecific small molecule-antibody conjugate targeting PSMA and CD3 in patients with metastatic castration-resistant prostate cancer (mCRPC).

TPS5094 Background: CCW702 is a novel bispecific antibody comprised of a small molecule imaging agent ligand (DUPA) with specificity for prostate specific membrane antigen (PSMA) conjugated to an anti-CD3 antibody via an unnatural amino acid. This format has the structure of an antibody drug conjugate with the activity of a CD3-engaging bispecific antibody. The design of CCW702 was leveraged to optimize the structure and function of T cell redirected cytotoxicity against PSMA-positive prostate cancer tumors in preclinical development. Methods: This is a first-in-human, open-label, multi-center phase 1 study evaluating the safety and tolerability of CCW702 when administered via subcutaneous (SC) injection in men with mCPRC. This study will be conducted in two parts: Part I, a dose escalation to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (R2PD); Part II, a dose expansion to determine efficacy at the R2PD. Safety, pharmacokinetics (PK), pharmacodynamics (PD), immunogenicity, and preliminary efficacy will be evaluated. Efficacy will be assessed by change in circulating tumor cells (CTC), PSA50 response rate, and objective tumor response by RECIST v1.1. Key biomarkers include characterization of CTC, T cell phenotyping in peripheral blood, chemokines and cytokines over time, and evaluation of available tumor biopsies by IHC. Key inclusion criteria include men age ≥ 18 years with histologically or cytologically confirmed adenocarcinoma who, in the metastatic setting, have progressed on at least one novel AR-targeted therapy. Up to 1 prior chemotherapy regimen is allowed. This study will enroll 20-30 patients in Part 1 and approximately 40 patients in Part 2. The study opened in December 2019 and is currently enrolling in the dose escalation phase. Clinical trial information: NCT04077021.

More Than Meets the Eye: Scientific Rationale behind Molecular Imaging and Therapeutic Targeting of Prostate-Specific Membrane Antigen (PSMA) in Metastatic Prostate Cancer and Beyond.

Simple SummaryProstate-specific membrane antigen (PSMA) is a transmembrane protein that is overexpressed in prostate cancer and correlates with the aggressiveness of the disease. PSMA is a promising target for imaging and therapeutics in prostate cancer patients validated in prospective trials. However, the role of PSMA in prostate cancer progression is poorly understood. In this review, we discuss the biology and scientific rationale behind the use of PSMA and other targets in the detection and theranostics of metastatic prostate cancer.Prostate cancer is the second most common cancer type in men globally. Although the prognosis for localized prostate cancer is good, no curative treatments are available for metastatic disease. Better diagnostic methods could help target therapies and improve the outcome. Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that is overexpressed on malignant prostate tumor cells and correlates with the aggressiveness of the disease. PSMA is a clinically validated target for positron emission tomography (PET) imaging-based diagnostics in prostate cancer, and during recent years several therapeutics have been developed based on PSMA expression and activity. The expression of PSMA in prostate cancer can be very heterogeneous and some metastases are negative for PSMA. Determinants that dictate clinical responses to PSMA-targeting therapeutics are not well known. Moreover, it is not clear how to manipulate PSMA expression for therapeutic purposes and develop rational treatment combinations. A deeper understanding of the biology behind the use of PSMA would help the development of theranostics with radiolabeled compounds and other PSMA-based therapeutic approaches. Along with PSMA several other targets have also been evaluated or are currently under investigation in preclinical or clinical settings in prostate cancer. Here we critically elaborate the biology and scientific rationale behind the use of PSMA and other targets in the detection and therapeutic targeting of metastatic prostate cancer.

Fully human antibody VH domains to generate mono and bispecific CAR to target solid tumors

BackgroundChimeric antigen receptor (CAR) T cells are effective in B-cell malignancies. However, heterogeneous antigen expression and antigen loss remain important limitations of targeted immunotherapy in solid tumors. Therefore, targeting multiple...

Preclinical Evaluation of a Fluorine-18 Labeled Probe for the Detection of the Expression of PSMA Level in Cancer.

Prostate-specific membrane antigen (PSMA) is a prospect biomarker for the treatment of prostate cancer. Meanwhile, positron emission tomography (PET) is being developed as a significant imaging modality in cancer diagnosis. A new PET probe Glu-ureido-Lys-naphthylalanine-tranexamic acid-Gly(AMBF3)-triiodobenzoic acid (18F-GLNTGT) was radiosynthesized by a one-step 18F-labeled method. 18F-GLNTGT was obtained with a radioactivity yield (RCY) of 12.16 ± 6.4% and a good radiochemical purity (RCP > 96%). The cell uptakes of 18F-GLNTGT were determined to be 15.9 ± 0.43% ID and 9.47 ± 1.26% ID at 15 min in LNCaP cells and PC-3 cells, respectively. The cell internalization of 18F-GLNTGT was determined to be 12.89 ± 0.94% ID and 5.34 ± 0.15% ID at 15 min in LNCaP cells and PC-3 cells, respectively. It is suggested that the probe has good specificity targeting PSMA. From the results of 18F-GLNTGT binding affinity with PSMA, it has a higher affinity and a Ki value of 0.49 nM (95% confidence interval (CI): 0.35–0.67 nM). In PET imaging, 18F-GLNTGT showed the highest tumor uptake of 3.51 ± 0.15% ID/g at 45 min and the maximum tumor/muscle (T/Mmax) ratio of 3.68 ± 0.29 at 60 min post-injection (p.i.) in LNCaP tumors. The control probe 18F-AlF-NOTA-RGD2 presented the highest tumor uptake of 4.2 ± 0.54% ID/g at 7.5 min and the T/Mmax ratio of 2.72 ± 0.63 at 45 min p.i. in LNCaP tumors. The results showed that the probe has a higher tumor/muscle ratio compared with the control probe 18F-AlF-NOTA-RGD2. Although the probe 18F-GLNTGT has some limitations for CT signal detection both in cells and in vivo, it is still a promising PET probe for targeting PSMA membrane protein.