Prostate-Specific Membrane Antigen (PSMA)-Targeted Radionuclide Therapies for Prostate Cancer

Preclinical evaluation of 64Cu/177Lu-labelled anti-CD30 monoclonal antibody for theranostics in CD30-positive lymphoma

PURPOSE

CD30 serves as an ideal therapeutic target for lymphoma, but its variable expression and high relapse rate pose challenges in targeted therapy. This study aims to label the anti-CD30 monoclonal antibody with 64Cu/177Lu for immuno-positron emission tomography (immuno-PET) and radioimmunotherapy (RIT).

METHODS

CD30 binding kinetics of anti-CD30-IgG (IMB16) were measured by Biolayer interferometry (BLI). Western blotting screened lymphoma cell lines for CD30 expression. Flow cytometry and immunofluorescence validated the specific binding of IMB16. IMB16 was conjugated to p-SCN-Bn-NOTA(NOTA) and p-SCN-Bn-DOTA(DOTA) for radiolabeling with 64Cu and 177Lu. [64Cu]Cu-NOTA-IMB16 and [177Lu]Lu-DOTA-IMB16 were used for immuno-PET and RIT in subcutaneous lymphoma NSG mouse models.

RESULTS

IMB16 had a strong binding affinity to CD30 according to the BLI. Western blotting revealed high CD30 expression in Karpas299 cells and negative expression in Raji cells. Flow cytometry and immunofluorescence confirmed specific binding of IMB16 to CD30 on cell surface. Radiochemical purity of [64Cu]Cu-NOTA-IMB16 and [177Lu]Lu-DOTA-IMB16 exceeded 95%. In Immuno-PET imaging, CD30-positive Karpas299 tumours had a mean uptake value of 19.2 ± 0.9%ID/g (n = 3) at 24 h post-injection, significantly higher than Karpas299-blocked and Raji-negative groups (P < 0.001). A high radiation dose (300µCi) of [177Lu]Lu-DOTA-IMB16 significantly inhibited tumour growth (80.2 ± 17.6% standardized tumour volume, n = 5) at 10 days post-injection, compared to controls. Ex vivo biodistribution and histological staining supported in vivo PET imaging and RIT results.

CONCLUSIONS

Labelling IMB16 with 64Cu enabled non-invasive assessment of CD30 expression, while 177Lu labelling effectively suppressed tumour growth in CD30-positive lymphoma. CD30-targeted theranostic show promise for patient stratification and treatment enhancement, warranting further clinical evaluation.

Association between DNA damage repair alterations and outcomes to 177Lu-PSMA-617 in advanced prostate cancer

BACKGROUND

177Lu-prostate-specific membrane antigen (PSMA)-617 (LuPSMA) is a radionuclide therapy approved for patients with PSMA-avid metastatic castrate-resistant prostate cancer (mCRPC). We evaluated whether alterations in the DNA damage repair (DDR) pathway were associated with outcomes to LuPSMA.

PATIENTS AND METHODS

We identified an institutional cohort of men (n = 134) treated with ≥2 cycles of LuPSMA who had panel-based germline and/or tumor genomic sequencing. Mutations or two-copy losses in any of BRCA1, BRCA2, ATM, CDK12, PALB2, RAD51, and MSH2 were considered DDR defects. The primary outcome was a ≥50% reduction in the prostate-specific antigen (PSA) level during LuPSMA therapy (PSA50); secondary outcomes were PSA progression-free survival (PSA-PFS) and overall survival (OS). Models were adjusted for age, number of prior systemic therapies, sites of metastasis, and log-transformed PSA at cycle 1.

RESULTS

Thirty-four patients (25%) harbored DDR alterations, most commonly in BRCA2 and ATM (both n = 13). The presence of a DDR defect was not associated with PSA50 [adjusted odds ratio 0.48 (0.20-1.09), P = 0.08], PSA-PFS [adjusted hazard ratio (HR) 1.29 (0.79-2.10), P = 0.30], or OS [adjusted HR 1.42 (0.74-2.72), P = 0.29], with a non-significant trend toward poorer outcomes among DDR-altered patients.

CONCLUSIONS

DDR alterations were not associated with outcomes following LuPSMA. This has implications for treatment sequencing in mCRPC, particularly in patients with DDR alterations.

Emerging conjugation strategies and protein engineering technologies aim to improve ADCs in the fight against cancer

Antibody drug conjugates are an exciting therapeutic modality that combines the targeting specificity of antibodies with potent cytotoxins to selectively kill cancer cells. The targeting component improves efficacy and protects non-target cells from the harmful effects of the payload. To date 15 ADCs have been approved by regulatory agencies for commercial use and shown to be valuable tools in the treatment of cancer.The assembly of an ADC requires the chemical ligation of a linker-payload to an antibody. Conventional conjugation methods targeting accessible lysines and cysteines have produced all the ADCs currently on the market. While successful, technologies aiming to improve the homogeneity and stability of ADCs are being developed and tested.Here we provide a review of developing methods for ADC construction. These include enzymatic methods, oligosaccharide remodelling, and technologies using genetic code expansion techniques. The virtues and limitations of each technology are discussed.Emerging conjugation technologies are being applied to produce new formats of ADCs with enhanced functionality including bispecific ADCs, dual-payload ADCs, and nanoparticles for targeted drug delivery. The benefits of these novel formats are highlighted.

Small molecule anticancer drugs approved during 2021-2022: Synthesis and clinical applications

Drugs have structural homology across similar biological targets. Small molecule drugs have the efficacy to target specific molecular targets within the cancer cells with enhanced cell membrane permeability, oral administration, selectivity, and specific affinity. The objective of this review is to highlight the clinical importance and synthetic routes of new small molecule oncology drugs approved by the FDA during the period 2021-2022. These marketed drugs are listed based on the month and year of approval in chronological order. We believed that an in-depth insight into the synthetic approaches for the construction of these chemical entities would enhance the ability to develop new drugs more efficiently.

Preclinical Efficacy of a PSMA-Targeted Actinium-225 Conjugate (225Ac-Macropa-Pelgifatamab): A Targeted Alpha Therapy for Prostate Cancer

PURPOSE

Initially, prostate cancer responds to hormone therapy, but eventually resistance develops. Beta emitter-based prostate-specific membrane antigen (PSMA)-targeted radionuclide therapy is approved for the treatment of metastatic castration-resistant prostate cancer. Here we introduce a targeted alpha therapy (TAT) consisting of the PSMA antibody pelgifatamab covalently linked to a macropa chelator and labeled with actinium-225 and compare its efficacy and tolerability with other TATs.

EXPERIMENTAL DESIGN

The in vitro characteristics and in vivo biodistribution, antitumor efficacy, and tolerability of 225Ac-macropa-pelgifatamab (225Ac-pelgi) and other TATs were investigated in cell line- and patient-derived prostate cancer xenograft models. The antitumor efficacy of 225Ac-pelgi was also investigated in combination with the androgen receptor inhibitor darolutamide.

RESULTS

Actinium-225-labeling of 225Ac-pelgi was efficient already at room temperature. Potent in vitro cytotoxicity was seen in PSMA-expressing (LNCaP, MDA-PCa-2b, and C4-2) but not in PSMA-negative (PC-3 and DU-145) cell lines. High tumor accumulation was seen for both 225Ac-pelgi and 225Ac-DOTA-pelgi in the MDA-PCa-2b xenograft model. In the C4-2 xenograft model, 225Ac-pelgi showed enhanced antitumor efficacy with a T/Cvolume (treatment/control) ratio of 0.10 compared with 225Ac-DOTA-pelgi, 225Ac-DOTA-J591, and 227Th-HOPO-pelgifatamab (227Th-pelgi; all at 300 kBq/kg) with T/Cvolume ratios of 0.37, 0.39, and 0.33, respectively. 225Ac-pelgi was less myelosuppressive than 227Th-pelgi. 225Ac-pelgi showed dose-dependent treatment efficacy in the patient-derived KuCaP-1 model and strong combination potential with darolutamide in both cell line- (22Rv1) and patient-derived (ST1273) xenograft models.

CONCLUSIONS

These results provide a strong rationale to investigate 225Ac-pelgi in patients with prostate cancer. A clinical phase I study has been initiated (NCT06052306).

PSMA-Targeted Therapy: Advancements in Detection and Treatment Modalities with Dr. Scott T. Tagawa

Prostate cancer is one of the most challenging malignancies due to its high incidence and prevalence, as it is the most frequently diagnosed non-skin cancer in men. The timely identification of prostate cancer and its metastasis is paramount for ensuring favorable outcomes for patients. Prostate-specific membrane antigen (PSMA) emerges as a promising biomarker for its detection, due to its specificity. This makes it an ideal target for the early identification of a metastatic phenotype. Situated on the membrane of tumor cells, PSMA facilitates the attachment of PSMA-targeting particles, enabling their detection through positron emission tomography (PET) scans with relative ease. Utilizing these imaging agents in conjunction with PET scans enhances the accuracy of prostate cancer tumor detection compared to PET scans alone. The advancement in prostate cancer imaging has paved the way for innovative treatment modalities. Prostate-specific membrane antigen-targeted radionuclide therapies (PSMA-TRT) exploit PSMA imaging agents to target identified prostate cancer malignancies with precise radiation, thereby reducing or eliminating the tumor mass. PSMA-TRT exhibits significant promise in prostate cancer therapy, evident from the notable declines in prostate-specific antigen (PSA) levels post treatment. However, PSMA-TRT carries both beneficial and adverse effects. While it represents a substantial leap forward in tumor cell imaging, PSMA-based antigens, being larger particles than ligands, offer prolonged imaging capabilities. Yet, the long-term effects of PSMA-TRT remain unknown, with the short-term adverse ones including fatigue, nausea, pain flares, and potential radiation exposure to others.

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

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

Preclinical Study of Therapeutic Efficacy of a New Russian Radiopharmaceutical 177Lu-DOTA-PSMA

The therapeutic efficacy of a Russian radiopharmaceutical 177Lu-DOTA-PSMA was studied in vivo using male BALB/c nu/nu (nude) mice with prostate carcinoma 22Rv1 xenografts by tumor growth inhibition criterion. The mean tumor volumes in mice treated with 177Lu-DOTA-PSMA were significantly lower than in animals of the control group. There were no significant differences in the values of tumor growth inhibition between the groups of animals receiving 3.7 or 7.4 MBq of 177Lu-DOTA-PSMA.

Current Status of Radiolabeled Monoclonal Antibodies Targeting PSMA for Imaging and Therapy

Prostate cancer (PCa) is one of the most prevalent cancer diagnoses among men in the United States and in several other developed countries. The prostate specific membrane antigen (PSMA) has been recognized as a promising molecular target in PCa, which has led to the development of specific radionuclide-based tracers for imaging and radiopharmaceuticals for PSMA targeted therapy. These compounds range from small molecule ligands to monoclonal antibodies (mAbs). Monoclonal antibodies play a crucial role in targeting cancer cell-specific antigens with a high degree of specificity while minimizing side effects to normal cells. The same mAb can often be labeled in different ways, such as with radionuclides suitable for imaging with Positron Emission Tomography (β+ positrons), Gamma Camera Scintigraphy (γ photons), or radiotherapy (β- electrons, α-emitters, or Auger electrons). Accordingly, the use of radionuclide-based PSMA-targeting compounds in molecular imaging and therapeutic applications has significantly grown in recent years. In this article, we will highlight the latest developments and prospects of radiolabeled mAbs that target PSMA for the detection and treatment of prostate cancer.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

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

Optimized Therapeutic 177Lu-Labeled PSMA-Targeted Ligands with Improved Pharmacokinetic Characteristics for Prostate Cancer

Clinical trials have shown the significant efficacy of [¹⁷⁷Lu]Lu-PSMA-617 for treating prostate cancer. However, the pharmacokinetic characteristics and therapeutic performance of [¹⁷⁷Lu]Lu-PSMA-617 still need further improvement to meet clinical expectations. The aim of this study was to evaluate the feasibility and therapeutic potential of three novel ¹⁷⁷Lu-labeled ligands for the treatment of prostate cancer. The novel ligands were efficiently synthesized and radiolabeled with non-carrier added ¹⁷⁷Lu; the radiochemical purity of the final products was determined by Radio-HPLC. The specific cell-binding affinity to PSMA was evaluated in vitro using prostate cancer cell lines 22Rv1and PC-3. Blood pharmacokinetic analysis, biodistribution experiments, small animal SPCET imaging and treatment experiments were performed on normal and tumor-bearing mice. Among all the novel ligands developed in this study, [¹⁷⁷Lu]Lu-PSMA-Q showed the highest uptake in 22Rv1 cells, while there was almost no uptake in PC-3 cells. As the SPECT imaging tracer, [¹⁷⁷Lu]Lu-PSMA-Q is highly specific in delineating PSMA-positive tumors, with a shorter clearance half-life and higher tumor-to-background ratio than [¹⁷⁷Lu]Lu-PSMA-617. Biodistribution studies verified the SPECT imaging results. Furthermore, [¹⁷⁷Lu]Lu-PSMA-Q serves well as an effective therapeutic ligand to suppress tumor growth and improve the survival rate of tumor-bearing mice. All the results strongly demonstrate that [¹⁷⁷Lu]Lu-PSMA-Q is a PSMA-specific ligand with significant anti-tumor effect in preclinical models, and further clinical evaluation is worth conducting.

Construction of a 124I-Labeled Specific Antibody for the Noninvasive Detection of Mesothelin-Overexpressing Tumors

Mesothelin (MSLN) is a molecular biomarker of many types of solid tumors, such as mesothelioma, pancreatic cancer, and colon cancer. Owing to the significant difference in expression between cancer cells and normal cells, mesothelin has been widely used as a key target in cancer immunotherapy. In this study, we used iodine isotope (^nat/124/125I)-labeled mesothelin antibodies to noninvasively detect MSLN expression in mice with LS174T colon cancer. The ¹²⁴I-labeled MSLN antibody showed a high radiochemical purity (RCP, >99%) and specific activity (20.8-67.8 GBq/μmol) after purification and was stable in 5% HSA and PBS (>95% RCP at 8 days). Western blot analysis indicated that the LS174T cells showed a higher MSLN protein level than the HepG2 cells. The half maximal effective concentration (EC₅₀) values of the MSLN antibody and ^natI-anti-MSLN were 34.77 ± 3.72 ng/mL and 32.60 ± 2.52 ng/mL (P = 0.63), respectively. The dissociation constant of ¹²⁴I-anti-MSLN binding to MSLN protein was 16.0 nM. The radiotracer showed a significantly higher uptake in LS174T cells than in HepG2 tumor cells (1.56 ± 0.09 vs 0.81 ± 0.03, P = 0.0016) 2 days postinjection. The LS174T mouse models showed extremely low organ uptake and high tumor uptake 96 h after the injection of ¹²⁴I-anti-MSLN, and the T/M values were much higher than those of the other imaging groups (10.56 ± 1.20 for ¹²⁴I-anti-MSLN in LS174T mice vs 3.27 ± 0.20 for ¹²⁴I-anti-MSLN in HepG2 mice vs 3.53 ± 0.2 for ¹²⁴I-IgG in LS174T mice). The immunochemical histology results showed that LS174T tumors were strongly positive (+++) for MSLN, while those in the HepG2 group showed slight expression (+). The dosimetry estimation study showed that the effective dose of ¹²⁴I-anti-MSLN was 0.185 mSv/MBq, which is within the range of acceptable doses for further nuclear medicine translational research. Taken together, these results suggest that this radiotracer has the potential for detecting mesothelin-overexpressing tumors.

Development and Functional Characterization of a Versatile Radio-/Immunotheranostic Tool for Prostate Cancer Management

Simple Summary

In previous studies, we described a modular Chimeric Antigen Receptor (CAR) T cell platform which we termed UniCAR. In contrast to conventional CARs, the interaction of UniCAR T cells does not occur directly between the CAR T cell and the tumor cell but is mediated via bispecific adaptor molecules so-called target modules (TMs). Here we present the development and functional characterization of a novel IgG4-based TM, directed to the tumor-associated antigen (TAA) prostate stem cell antigen (PSCA), which is overexpressed in prostate cancer (PCa). We show that this anti-PSCA IgG4-TM cannot only be used for (i) redirection of UniCAR T cells to PCa cells but also for (ii) positron emission tomography (PET) imaging, and (iii) alpha particle-based endoradiotherapy. For radiolabeling, the anti-PSCA IgG4-TM was conjugated with the chelator DOTAGA. PET imaging was performed using the ⁶⁴Cu-labeled anti-PSCA IgG4-TM. According to PET imaging, the anti-PSCA IgG4-TM accumulates with high contrast in the PSCA-positive tumors of experimental mice without visible uptake in other organs. For endoradiotherapy the anti-PSCA IgG4-TM-DOTAGA conjugate was labeled with ²²⁵Ac³⁺. Targeted alpha therapy resulted in tumor control over 60 days after a single injection of the ²²⁵Ac-labeled TM. The favorable pharmacological profile of the anti-PSCA IgG4-TM, and its usage for (i) imaging, (ii) targeted alpha therapy, and (iii) UniCAR T cell immunotherapy underlines the promising radio-/immunotheranostic capabilities for the diagnostic imaging and treatment of PCa.

Abstract

Due to its overexpression on the surface of prostate cancer (PCa) cells, the prostate stem cell antigen (PSCA) is a potential target for PCa diagnosis and therapy. Here we describe the development and functional characterization of a novel IgG4-based anti-PSCA antibody (Ab) derivative (anti-PSCA IgG4-TM) that is conjugated with the chelator DOTAGA. The anti-PSCA IgG4-TM represents a multimodal immunotheranostic compound that can be used (i) as a target module (TM) for UniCAR T cell-based immunotherapy, (ii) for diagnostic positron emission tomography (PET) imaging, and (iii) targeted alpha therapy. Cross-linkage of UniCAR T cells and PSCA-positive tumor cells via the anti-PSCA IgG4-TM results in efficient tumor cell lysis both in vitro and in vivo. After radiolabeling with ⁶⁴Cu²⁺, the anti-PSCA IgG4-TM was successfully applied for high contrast PET imaging. In a PCa mouse model, it showed specific accumulation in PSCA-expressing tumors, while no uptake in other organs was observed. Additionally, the DOTAGA-conjugated anti-PSCA IgG4-TM was radiolabeled with ²²⁵Ac³⁺ and applied for targeted alpha therapy. A single injection of the ²²⁵Ac-labeled anti-PSCA IgG4-TM was able to significantly control tumor growth in experimental mice. Overall, the novel anti-PSCA IgG4-TM represents an attractive first member of a novel group of radio-/immunotheranostics that allows diagnostic imaging, endoradiotherapy, and CAR T cell immunotherapy.