AlphaBet: Combination of Radium-223 and [17 7Lu]Lu-PSMA-I&T in men with metastatic castration-resistant prostate cancer (clinical trial protocol)

Biological determinants of PSMA expression, regulation and heterogeneity in prostate cancer

Prostate-specific membrane antigen (PSMA) is an important cell-surface imaging biomarker and therapeutic target in prostate cancer. The PSMA-targeted theranostic 177Lu-PSMA-617 was approved in 2022 for men with PSMA-PET-positive metastatic castration-resistant prostate cancer. However, not all patients respond to PSMA-radioligand therapy, in part owing to the heterogeneity of PSMA expression in the tumour. The PSMA regulatory network is composed of a PSMA transcription complex, an upstream enhancer that loops to the FOLH1 (PSMA) gene promoter, intergenic enhancers and differentially methylated regions. Our understanding of the PSMA regulatory network and the mechanisms underlying PSMA suppression is evolving. Clinically, molecular imaging provides a unique window into PSMA dynamics that occur on therapy and with disease progression, although challenges arise owing to the limited resolution of PET. PSMA regulation and heterogeneity - including intertumoural and inter-patient heterogeneity, temporal changes, lineage dynamics and the tumour microenvironment - affect PSMA theranostics. PSMA response and resistance to radioligand therapy are mediated by a number of potential mechanisms, and complementary biomarkers beyond PSMA are under development. Understanding the biological determinants of cell surface target regulation and heterogeneity can inform precision medicine approaches to PSMA theranostics as well as other emerging therapies.

Alpha and Beta Radiation for Theragnostics

Targeted radionuclide therapy (TRT) has significantly evolved from its beginnings with iodine-131 to employing carrier molecules with beta emitting isotopes like lutetium-177. With the success of Lu-177-DOTATATE for neuroendocrine tumors and Lu-177-PSMA-617 for prostate cancer, several other beta emitting radioisotopes, such as Cu-67 and Tb-161, are being explored for TRT. The field has also expanded into targeted alpha therapy (TAT) with agents like radium-223 for bone metastases in prostate cancer, and several other alpha emitter radioisotopes with carrier molecules, such as Ac-225, and Pb-212 under clinical trials. Despite these advancements, the scope of TRT in treating diverse solid tumors and integration with other therapies like immunotherapy remains under investigation. The success of antibody-drug conjugates further complements treatments with TRT, though challenges in treatment optimization continue.

Emerging Theranostics for Prostate Cancer and a Model of Prostate-specific Membrane Antigen Therapy

There is increasing demand worldwide to develop diagnostic and therapeutic (theranostic) markers for prostate cancer. One target of interest is prostate-specific membrane antigen (PSMA), a protein which is overexpressed in prostate cancer cells. Over the past decade, a growing body of literature has demonstrated that radiolabeled ligands that target PSMA show favorable clinical response and survival outcomes in patients with advanced prostate cancer. This focused review provides background to the development of PSMA as a target, an overview of key studies informing our current approach to radioligand-based imaging and therapy for prostate cancer, and a model for real-world implementation of PSMA theranostics based on an Australian experience.

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.

Alpha-Emitting Radionuclides: Current Status and Future Perspectives

The use of radionuclides for targeted endoradiotherapy is a rapidly growing field in oncology. In particular, the focus on the biological effects of different radiation qualities is an important factor in understanding and implementing new therapies. Together with the combined approach of imaging and therapy, therapeutic nuclear medicine has recently made great progress. A particular area of research is the use of alpha-emitting radionuclides, which have unique physical properties associated with outstanding advantages, e.g., for single tumor cell targeting. Here, recent results and open questions regarding the production of alpha-emitting isotopes as well as their chemical combination with carrier molecules and clinical experience from compassionate use reports and clinical trials are discussed.

177Lu-Prostate-Specific Membrane Antigen Therapy in Patients with Metastatic Castration-Resistant Prostate Cancer and Prior 223Ra (RALU Study)

223Ra-dichloride (223Ra) and 177Lu-prostate-specific membrane antigen (PSMA) are approved treatments for metastatic castration-resistant prostate cancer (mCRPC). The safety and effectiveness of sequential use of 223Ra and 177Lu-PSMA in patients with mCRPC are not well described. This study aimed to evaluate 177Lu-PSMA safety and efficacy in patients with mCRPC previously treated with 223Ra. Methods: The radium→lutetium (RALU) study was a multicenter, retrospective, medical chart review. Participants had received at least 1 223Ra dose and, in any subsequent therapy line, at least 1 177Lu-PSMA dose. Primary endpoints included the incidence of adverse events (AEs), serious AEs, grade 3-4 hematologic AEs, and abnormal laboratory values. Secondary endpoints included overall survival, time to next treatment/death, and change from baseline in serum prostate-specific antigen and alkaline phosphatase levels. Results: Data were from 133 patients. Before 177Lu-PSMA therapy, 56% (75/133) of patients received at least 4 life-prolonging therapies; all patients received 223Ra (73% received 5-6 injections). Overall, 27% (36/133) of patients received at least 5 177Lu-PSMA infusions. Any-grade treatment-emergent AEs were reported in 79% (105/133) of patients and serious AEs in 30% (40/133). The most frequent grade 3-4 laboratory abnormalities were anemia (30%, 40/133) and thrombocytopenia (13%, 17/133). Median overall survival was 13.2 mo (95% CI, 10.5-15.6 mo) from the start of 177Lu-PSMA. Conclusion: In this real-world setting, 223Ra followed by 177Lu-PSMA therapy in heavily pretreated patients with mCRPC was clinically feasible, with no indication of impairment of 177Lu-PSMA safety or effectiveness.

Emerging Role of Nuclear Medicine in Prostate Cancer: Current State and Future Perspectives

Prostate cancer is the most frequent epithelial neoplasia after skin cancer in men starting from 50 years and prostate-specific antigen (PSA) dosage can be used as an early screening tool. Prostate cancer imaging includes several radiological modalities, ranging from ultrasonography, computed tomography (CT), and magnetic resonance to nuclear medicine hybrid techniques such as single-photon emission computed tomography (SPECT)/CT and positron emission tomography (PET)/CT. Innovation in radiopharmaceutical compounds has introduced specific tracers with diagnostic and therapeutic indications, opening the horizons to targeted and very effective clinical care for patients with prostate cancer. The aim of the present review is to illustrate the current knowledge and future perspectives of nuclear medicine, including stand-alone diagnostic techniques and theragnostic approaches, in the clinical management of patients with prostate cancer from initial staging to advanced disease.

Novel therapies for metastatic prostate cancer

INTRODUCTION

Patients with metastatic prostate cancer, especially in the castrate-resistant setting, have a poor prognosis. Many agents have been approved for metastatic prostate cancer, such as androgen receptor pathway inhibitors, taxane-based chemotherapy, radiopharmaceuticals, and immunotherapy. However, prostate cancer remains the leading cause of cancer deaths in nonsmoking men. Fortunately, many more novel agents are under investigation.

AREAS COVERED

We provide an overview of the broad group of novel therapies for metastatic prostate cancer, with an emphasis on active and recruiting clinical trials that have been recently published and/or presented at national or international meetings.

EXPERT OPINION

The future for patients with metastatic prostate cancer is promising, with further development of novel therapies such as radiopharmaceuticals. Based on a growing understanding of prostate cancer biology, novel agents are being designed to overcome resistance to approved therapies. There are many trials using novel agents either as monotherapy or in combination with already approved agents with potential to further improve outcomes for men with advanced prostate cancer.

Lutetium-177 PSMA for the treatment of metastatic castrate resistant prostate cancer: a systematic review

INTRODUCTION

Metastatic castrate resistant prostate cancer (mCPRC) remains an aggressive form of prostate cancer that no longer responds to traditional hormonal treatment alone. Despite the advent of novel anti-androgen medications, many patients continue to progress, and as a result, there is a growing need for additional treatment options.

AREAS COVERED

Lutetium-177 (177Lu) - PSMA-617 has become one of the new frontline treatment options for refractory metastatic castrate resistant prostate cancer after the failure of novel anti-androgen therapy and chemotherapy. Lu-177 has been used in real-world prospective trials and is now becoming utilized in newer phase III clinical trials. Here, we present a comprehensive overview of the current literature, covering retrospective studies, prospective studies, and clinical trials that established Lutetium-177-PSMA-617 (177Lu-PSMA-617) for the treatment of mCRPC.

EXPERT OPINION

177Lu - PSMA-617 has been approved for treatment of mCRPC based on positive phase III studies. While this treatment is tolerable and effective, biomarkers are necessary to determine which patients will benefit. In the future, radioligand treatments will likely be utilized in earlier lines of therapy and potentially in combination with other prostate cancer treatments.

Determinants of outcome following PSMA-based radioligand therapy and mechanisms of resistance in patients with metastatic castration-resistant prostate cancer

[177Lu]Lu-PSMA has recently been approved for use in the post-taxane, post-novel hormonal-agent setting in patients with metastatic castration-resistant prostate cancer. As a beta-emitting radioligand targeting prostate-specific membrane antigen (PSMA), it delivers radiation to cells expressing PSMA on their surface. In pivotal clinical trials, patients were selected for this treatment based on positron emission tomography (PET)/CT imaging, requiring PSMA-avid disease with no evidence of discordant disease on 2-[18F]fluoro-2-deoxy-D-glucose PET/CT or contrast CT scan. Despite exhibiting an optimal imaging phenotype, the response for many patients is not durable, and a minority do not respond to [177Lu]Lu-PSMA at all. Disease progression is inevitable even for those who achieve an exceptional initial response. Reasons for both primary and acquired resistance are largely unknown; however, they are likely due to the presence of underlying PSMA-negative disease not identified on imaging, molecular factors conferring radioresistance, and inadequate delivery of lethal radiation, particularly to sites of micrometastatic disease. Biomarkers are urgently needed to optimize patient selection for treatment with [177Lu]Lu-PSMA by identifying those who are most and least likely to respond. Retrospective data support using several prognostic and predictive baseline patient- and disease-related parameters; however, robust prospective data is required before these can be translated into widespread use. Further, early on-treatment clinical parameters (in addition to serial prostate-specific antigen [PSA] levels and conventional restaging imaging) may serve as surrogates for predicting treatment response. With little known about the efficacy of treatments given after [177Lu]Lu-PSMA, optimal treatment sequencing is paramount, and biomarker-driven patient selection will hopefully improve treatment and survival outcomes.

Nanoparticle-Based Radioconjugates for Targeted Imaging and Therapy of Prostate Cancer

Prostate cancer is the second most frequent malignancy in men worldwide and the fifth leading cause of death by cancer. Although most patients initially benefit from therapy, many of them will progress to metastatic castration-resistant prostate cancer, which still remains incurable. The significant mortality and morbidity rate associated with the progression of the disease results mainly from a lack of specific and sensitive prostate cancer screening systems, identification of the disease at mature stages, and failure of anticancer therapy. To overcome the limitations of conventional imaging and therapeutic strategies for prostate cancer, various types of nanoparticles have been designed and synthesized to selectively target prostate cancer cells without causing toxic side effects to healthy organs. The purpose of this review is to briefly discuss the selection criteria of suitable nanoparticles, ligands, radionuclides, and radiolabelling strategies for the development of nanoparticle-based radioconjugates for targeted imaging and therapy of prostate cancer and to evaluate progress in the field, focusing attention on their design, specificity, and potential for detection and/or therapy.