Prostate-specific membrane antigen in breast cancer: a comprehensive evaluation of expression and a case report of radionuclide therapy

Radioligand Therapy in Metastatic Breast Cancer: Harnessing Precision Oncology

Radioligand therapy (RLT) represents a promising advancement in precision oncology and enables the targeted delivery of radiation to cancer cells. This approach has shown success in other tumor types, such as prostate cancer and neuroendocrine tumors. Its potential in metastatic breast cancer (mBC) is currently under investigation. This review discusses RLT mechanism of action, therapeutic potential, and integration into the existing therapeutic landscape of mBC. While clinical trials have shown promising results, challenges remain regarding target heterogeneity, implementation, and optimizing treatment strategies. Further research is essential to integrate RLT into clinical practice and improve patient outcomes fully.

Unveiling Prostate-Specific Membrane Antigen's Potential in Breast Cancer Management

BACKGROUND

In recent years, the role of prostate-specific membrane antigen (PSMA) in the imaging and treatment of prostate cancer (PCa) has been extensively investigated. However, despite its name, PSMA is not exclusively specific to PCa. It has been found to be expressed in the neo-vasculature of various solid tumors, including breast cancer (BC), in which it is associated with tumor angiogenesis.

METHODS

This review aims to assess the potential of PSMA-based radiopharmaceuticals for BC diagnosis and treatment. It explores the current landscape by analyzing preclinical and clinical studies, as well as ongoing clinical trials, to provide insights into the PSMA-targeted approaches in BC management.

RESULTS

Early studies suggest PSMA-based imaging could improve BC lesion detection, especially in TNBC. The available data remains too preliminary to conclusively assess whether PSMA-based imaging or therapy will offer a significant advantage in BC. However, some preclinical findings suggest that this approach may hold promise as a novel strategy for managing this widespread malignancy.

CONCLUSIONS

PSMA-based strategies show potential for BC diagnosis and treatment, but further research is needed. Ongoing and future clinical trials are expected to provide deeper insights into the potential utility of this approach.

Prostate-specific membrane antigen as target for vasculature-directed therapeutic strategies in solid tumors

Prostate-specific membrane antigen (PSMA) is one of the few biomarkers which has been successfully translated to the clinic as theranostic biomarker for patients with prostate cancer. In the context of prostate cancer, PSMA is overexpressed on the cell membrane of tumor cells, making it a viable target for interventions with urea-based small molecule inhibitors or antibodies conjugated to radioactive isotopes. Interestingly, in several non-prostatic cancers, expression of PSMA appears to be associated with the tumor neovasculature. This offers novel therapeutic opportunities for treatments targeting the vasculature in non-prostatic cancers. In this review, we discuss PSMA and its potential as target for vasculature-directed therapeutic approaches, including radioligand therapy, fusion protein vaccination and CAR T-cell therapy.

Prospective investigation of amino acid transport and PSMA-targeted positron emission tomography for metastatic lobular breast carcinoma

PURPOSE

To explore the feasibility of imaging amino-acid transport and PSMA molecular pathways in the detection of metastatic breast invasive lobular carcinoma (ILC) and if there is superior detection compared to standard-of-care imaging [computed tomography (CT)/bone scan, or 18F-FDG positron-emission-tomography (PET)-CT].

METHODS

20 women with de-novo or suspected metastatic ILC underwent two PET-CT scans with 18F-fluciclovine and 68Ga-PSMA-11 on separate days. Uptake per patient and in 3 regions per patient - ipsilateral axillary lymph node (LN), extra-axillary LN (ipsilateral supraclavicular or internal mammary), or distant sites of disease - was compared to standard-of-care imaging (CT/bone scan in 13 patients and 18F-FDG PET-CT in 7 patients). Results were correlated to a composite standard of truth. Confirmed detection rate (cDR) was compared using McNemar's test. Mean SUVmax of 18F-fluciclovine and 68Ga-PSMA-11 in the most avid lesion for each true positive metastatic region and intact primary lesion were compared by t-test.

RESULTS

The cDR for standard-of-care imaging was 5/20 patients in 5/60 regions. 68Ga-PSMA-11 PET-CT detected metastasis in 7/20 patients in 7/60 regions. 18F-fluciclovine PET-CT detected metastasis in 9/20 patients in 12/60 regions. The cDR for 18F-fluciclovine PET-CT was significantly higher versus standard-of-care imaging on the patient and combined region levels, while there were no significant differences between 68Ga-PSMA-11 and standard-of care imaging. 18F-fluciclovine cDR was also significantly higher than 68Ga-PSMA-11 on the combined region level. Mean SUVmax for true positive metastatic and primary lesions with 18F-fluciclovine (n = 18) was significantly greater than for 68Ga-PSMA-11 (n = 11) [5.5 ± 1.8 versus 3.5 ± 2.7 respectively, p = 0.021].

CONCLUSION

In this exploratory trial, 18F-fluciclovine PET-CT has a significantly higher cDR for ILC metastases compared to standard-of-care imaging and to 68Ga-PSMA-11. Mean SUVmax for true positive malignancy was significantly higher with 18F-fluciclovine than for 68Ga-PSMA-11. Exploratory data from this trial suggests that molecular imaging of amino acid metabolism in patients with ILC deserves further study.

CLINICAL TRIAL REGISTRATION

Early phase (I-II) clinical trial (NCT04750473) funded by the National Institutes of Health (R21CA256280).

Potential of PSMA for breast cancer in nuclear medicine: digital quantitative immunohistochemical analysis and implications for a theranostic approach

BACKGROUND

Further research is still needed to fully understand the potential of prostate-specific membrane antigen (PSMA) in breast cancer (BC) and to develop and optimize targeted therapies and imaging modalities. The objective of this study was to present a comprehensive analysis of immunohistochemistry data on PSMA staining in BC and to discuss its potential value in a theranostic approach.

METHODS

Fifty-eight male and female patients were randomly selected from a retrospective database of patients who underwent surgery for breast cancer between January 2012 and December 2017 and for whom a specimen is available in our tumour library. Immunodetection of PSMA and CD31 was performed on serial slides. The digitized slides were reviewed and analysed by an experienced pathologist. Additionally, the corresponding TIFF images were processed to calculate the percentage of positive neovessels.

RESULTS

Eighteen patients (31.6%) had no expression, 29 (50.9%) had PSMA neovascular expression scored as "1", and 10 (17.5%) had neovascular expression scored as "2". Digital immunohistochemistry analysis for this last specific group of patients showed a median proportion of positive neovessels equal to 5% (range: 3-19). A multivariable logistic regression demonstrated that the odds of PSMA positivity were 4.55 times higher in non-luminal tumours and decreased by a factor of 0.12 in lobular subtypes. There was no association between sex or the presence of a germline BRCA1/2 mutation and PSMA expression in tumours.

CONCLUSIONS

Our study highlights generally low neovascular expression of PSMA in specific histopathological subtypes of breast cancer, which will likely hamper the development of an adequate theranostic strategy.

TRIAL REGISTRATION

The procedure has been retrospectively registered to the French National Institute for Health Data (N° F20220615153900).

Diagnostic Performance of Prostate-Specific Membrane Antigen-Targeted Positron Emission Tomography in Patients Diagnosed with Different Types of Breast Cancer: A Systematic Review

Recent research has proposed using positron emission tomography/computed tomography (PET/CT) along with the administration of prostate-specific membrane antigen (PSMA)-targeting radiopharmaceuticals to identify breast cancer (BC) lesions. An extensive literature review to investigate the possible diagnostic utility of PET/CT with PSMA-targeting radiopharmaceuticals in BC patients was performed. The research comprised different clinical scenarios, including both newly diagnosed BC patients and those who had experienced disease relapse. This updated systematic review encompassed six studies investigating the diagnostic efficacy of PSMA-targeted PET/CT in BC. Throughout all clinical settings investigated, the papers presented data demonstrating a modest diagnostic performance of PSMA-targeted PET/CT in different subtypes of BC. In this setting, PSMA-guided PET/CT showed slightly higher accuracy in patients diagnosed with triple-negative BC. Based on the current literature, PSMA-targeted PET/CT cannot be suggested as a diagnostic tool to assess BC extent in any clinical scenario. However, based on the PSMA expression observed in triple-negative patients, it can be proposed as a tool to evaluate whether BC patients could benefit from PSMA-targeting radioligand therapy.

Genetic implications of PSMA expression variability in breast cancer subtypes with a focus on triple-negative breast cancer

Prostate-specific membrane antigen (PSMA) is a protein frequently found to be overexpressed in various non-prostate cancer types. Our investigation, based on data from the TCGA databases, revealed a wide range of differential PSMA (encoded by FOLH1 gene) mRNA expressions across several cancer types, with notable findings in triple-negative breast carcinoma. This preclinical study delves into the molecular underpinnings of utilizing PSMA-targeting radiopharmaceuticals within specific breast cancer subtypes. We conducted a transcriptomic expression analysis of PSMA across different subtypes of breast cancer, focusing particularly on the triple-negative breast cancer (TNBC) subset. Our analysis encompassed 1100 patients from The Cancer Genome Atlas dataset. We observed a broad distribution of PSMA mRNA expressions across various subgroups within these cancer types. Notably, a subset of triple-negative breast cancer exhibited higher PSMA mRNA expression compared to non-triple-negative breast cancer. Intriguingly, we found that higher PSMA mRNA expression was associated with favorable outcomes in terms of distant metastasis-free and relapse-free survival in patients. Within a subset of TNBC patients, there is a prevalent overexpression of PSMA, which appears to be linked with improved relapse-free and distant metastasis-free survival. Our study succinctly highlights the significance of PSMA overexpression in TNBC and its potential impact on patient outcomes and provides a clear and concise overview of the study's contributions to breast cancer research.

Prostate Specific Membrane Antigen Expression in a Syngeneic Breast Cancer Mouse Model

PURPOSE

Prostate specific membrane antigen (PSMA) has been studied in human breast cancer (BCa) biopsies, however, lack of data on PSMA expression in mouse models impedes development of PSMA-targeted therapies, particularly in improving breast conserving surgery (BCS) margins. This study aimed to validate and characterize the expression of PSMA in murine BCa models, demonstrating that PSMA can be utilized to improve therapies and imaging techniques.

METHODS

Murine triple negative breast cancer 4T1 cells, and human cell lines, MDA-MB-231, MDA-MB-468, implanted into the mammary fat pads of BALB/c mice, were imaged by our PSMA targeted theranostic agent, PSMA-1-Pc413, and tumor to background ratios (TBR) were calculated to validate selective uptake. Immunohistochemistry was used to correlate PSMA expression in relation to CD31, an endothelial cell biomarker highlighting neovasculature. PSMA expression was also quantified by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR).

RESULTS

Accumulation of PSMA-1-Pc413 was observed in 4T1 primary tumors and associated metastases. Average TBR of 4T1 tumors were calculated to be greater than 1.5-ratio at which tumor tissues can be distinguished from normal structures-at peak accumulation with the signal intensity in 4T1 tumors comparable to that in high PSMA expressing PC3-pip tumors. Extraction of 4T1 tumors and lung metastases followed by RT-PCR analysis and PSMA-CD31 co-staining shows that PSMA is consistently localized on tumor neovasculature with no expression in tumor cells and surrounding normal tissues.

CONCLUSION

The selective uptake of PSMA-1-Pc413 in these cancer tissues as well as the characterization and validation of PSMA expression on neovasculature in this syngeneic 4T1 model emphasizes their potential for advancements in targeted therapies and imaging techniques for BCa. PSMA holds great promise as an oncogenic target for BCa and its associated metastases.

Frequent Amplification and Overexpression of PSMA in Basallike Breast Cancer from Analysis of The Cancer Genome Atlas

Prostate-specific membrane antigen (PSMA) is frequently overexpressed in nonprostate malignancies. This preclinical study investigated the molecular basis of the application of PMSA-targeting radiopharmaceuticals in breast cancer subtypes. Methods: The somatic copy number status and the transcriptomic and protein expressions of FOLH1 (gene name of PSMA) were analyzed across breast cancer subtypes in 998 patients from The Cancer Genome Atlas dataset. Results: FOLH1 was frequently amplified in basallike breast cancer (BLBC) (32%) compared with luminal and human epidermal growth factor receptor 2-positive subtypes (16% and 17%, respectively; P < 0.01). FOLH1 expression was higher in BLBC (P < 0.001) and was negatively correlated with estrogen-receptor and progesterone-receptor expressions. Consistently, the PSMA protein level was higher in BLBC (P < 0.05). Interestingly, FOLH1 expression was associated with relapse-free and distant metastasis-free survival in patients with BLBC. Conclusion: The BLBC subtype exhibited frequent amplification and overexpression of PSMA, supporting the exploration of PSMA-targeting radiopharmaceuticals in this aggressive breast cancer subtype.

Evaluation of Prostate-Specific Membrane Antigen (PSMA) Immunohistochemical Expression in Early-Stage Breast Cancer Subtypes

Breast cancer, known for its diverse subtypes, ranks as one of the leading causes of cancer-related deaths. Prostate-specific membrane antigen (PSMA), primarily associated with prostate cancer, has also been identified in breast cancer, though its role remains unclear. This study aimed to evaluate PSMA expression across different subtypes of early-stage breast cancer and investigate its correlation with clinicopathological factors. This retrospective study included 98 breast cancer cases. PSMA expression was examined in both tumor cells and tumor-associated blood vessels. The analysis revealed PSMA expression in tumor-associated blood vessels in 88 cases and in tumor cells in 75 cases. Ki67 expression correlated positively with PSMA expression in blood vessels (p < 0.0001, RSpearman 0.42) and tumor cells (p = 0.010, RSpearman 0.26). The estrogen and progesterone receptor expression correlated negatively with PSMA levels in blood vessels (p = 0.0053, R Spearman -0.26 and p = 0.00026, R Spearman -0.347, respectively). Human epidermal growth factor receptor 2 (HER2) status did not significantly impact PSMA expression. We did not detect any statistically significant differences between breast cancer subtypes. These findings provide evidence for a heterogenous PSMA expression in breast cancer tissue and suggest its correlation with tumor aggressiveness. Despite the limited sample size, the study provides valuable insights into the potential of PSMA as a prognostic, diagnostic, and therapeutic target in the management of breast cancer.

Characterization of FOLH1 Expression in Renal Cell Carcinoma

PURPOSE

Given the emergence of PSMA-targeted diagnostic agents and therapeutics, we sought to investigate patterns of FOLH1 expression in RCC and their impacts on RCC outcomes.

METHODS

We conducted a pooled multi-institutional analysis of patients with RCC having undergone DNA and RNA next-generation sequencing. FOLH1-high/low expression was defined as the ≥75th/<25th percentile of RNA transcripts per million (TPM). Angiogenic, T-effector, and myeloid expression signatures were calculated using previously defined gene sets. Kaplan-Meier estimates were calculated from the time of tissue collection or therapy start.

RESULTS

We included 1,724 patients in the analysis. FOLH1 expression was significantly higher in clear cell (71%) compared to non-clear cell RCC tumors (19.0 versus 3.3 TPM, p < 0.001) and varied by specimen site (45% primary kidney/55% metastasis, 13.6 versus 9.9 TPM, p < 0.001). FOLH1 expression was correlated with angiogenic gene expression (Spearman = 0.76, p < 0.001) and endothelial cell abundance (Spearman = 0.76, p < 0.001). While OS was similar in patients with FOLH1-high versus -low ccRCC, patients with FOLH1-high clear cell tumors experienced a longer time on cabozantinib treatment (9.7 versus 4.6 months, respectively, HR 0.57, 95% CI 0.35-0.93, p < 0.05).

CONCLUSIONS

We observed differential patterns of FOLH1 expression based on histology and tumor site in RCC. FOLH1 was correlated with angiogenic gene expression, increased OS, and a longer duration of cabozantinib treatment.

Hematological and renal toxicity in mice after three cycles of high activity [177Lu]Lu-PSMA-617 with or without human α1-microglobulin

Radioligand therapy with [177Lu]Lu-PSMA-617 can be used to prolong life and reduce tumor burden in terminally ill castration resistant prostate cancer patients. Still, accumulation in healthy tissue limits the activity that can be administered. Therefore, fractionated therapy is used to lower toxicity. However, there might be a need to reduce toxicity even further with e.g. radioprotectors. The aim of this study was to (i). establish a preclinical mouse model with fractionated high activity therapy of three consecutive doses of 200 MBq [177Lu]Lu-PSMA-617 in which we aimed to (ii). achieve measurable hematotoxicity and nephrotoxicity and to (iii). analyze the potential protective effect of co-injecting recombinant α1-microglobulin (rA1M), a human antioxidant previously shown to have radioprotective effects. In both groups, three cycles resulted in increased albuminuria for each cycle, with large individual variation. Another marker of kidney injury, serum blood urea nitrogen (BUN), was only significantly increased compared to control animals after the third cycle. The number of white and red blood cells decreased significantly and did not reach the levels of control animals during the experiment. rA1M did reduce absorbed dose to kidney but did not show significant protection here, but future studies are warranted due to the recent clinical studies showing a significant renoprotective effect in patients.

Evaluation of prostate-specific membrane antigen expression in locally advanced or metastatic breast carcinoma with 68 Ga-PSMA-11 positron-emission tomography/computed tomography imaging for potential theranostics

BACKGROUND AND AIM

Prostate-specific membrane antigen (PSMA) is ubiquitously expressed in tumor-associated neovasculature and may be a potential theranostic in many solid cancers, including breast carcinoma (BC). Herein, we analyzed the presence of PSMA in BC, through qualitative and quantitative parameters on 68 Ga-PSMA-11 positron-emission tomography/computed tomography (PET/CT), across various hormonal subtypes.

METHODS

This study examined 41 female patients of BC. All underwent 68 Ga-PSMA-11 PET/CT. For qualitative analysis, a visual estimation of PSMA expression was performed as per miPSMA scoring system (VISION trial) and a score ≥2 was considered eligible for lutetium-177 ( 177 Lu)-PSMA-617 radioligand therapy (Lu-PRLT). For quantitative analysis, maximum standardized uptake values (SUVmax) were determined and ratios >1 for SUVmax lesion to SUVmax liver were considered eligible for Lu-PRLT. PSMA expression was correlated with hormonal status using Chi-square test. The sensitivity, specificity and area under curve (AUC) of PSMA expression were determined using receiver-operating characteristics analysis ( P < 0.05).

RESULTS

A total of 19 patients (46.3%) and 15 patients (36.7%) in stage IV were found eligible for Lu-PRLT based on qualitative and quantitative analyses, respectively. Strong PSMA expression was detected in triple-negative and hormonal receptors-negative/human epidermal growth factor receptor 2-positive status on qualitative PSMA expression analysis. A sensitivity of 65.5%, specificity of 93.3% and AUC of 0.857 for SUVmax 6.5 on 68 Ga-PSMA-11 PET/CT were detected for PSMA expression for considering Lu-PRLT.

CONCLUSION

We found a modest number of BC patients suited for Lu-PRLT, indicating that PSMA PET/CT imaging may be a valuable modality for selecting theranostics in a carefully selected group of breast carcinoma.

The prostate-specific membrane antigen holds potential as a vascular target for endogenous radiotherapy with [177Lu]Lu-PSMA-I&T for triple-negative breast cancer

INTRODUCTION

Overexpression of prostate-specific membrane antigen (PSMA) on the vasculature of triple-negative breast cancer (TNBC) presents a promising avenue for targeted endogenous radiotherapy with [177Lu]Lu-PSMA-I&T. This study aimed to assess and compare the therapeutic efficacy of a single dose with a fractionated dose of [177Lu]Lu-PSMA-I&T in an orthotopic model of TNBC.

METHODS

Rj:NMRI-Foxn1nu/nu mice were used as recipients of MDA-MB-231 xenografts. The single dose group was treated with 1 × 60 ± 5 MBq dose of [177Lu]Lu-PSMA-I&T, while the fractionated dose group received 4 × a 15 ± 2 MBq dose of [177Lu]Lu-PSMA-I&T at 7 day intervals. The control group received 0.9% NaCl. Tumor progression was monitored using [18F]FDG-PET/CT. Ex vivo analysis encompassed immunostaining, TUNEL staining, H&E staining, microautoradiography, and autoradiography.

RESULTS

Tumor volumes were significantly smaller in the single dose (p < 0.001) and fractionated dose (p < 0.001) groups. Tumor growth inhibition rates were 38% (single dose) and 30% (fractionated dose). Median survival was notably prolonged in the treated groups compared to the control groups (31d, 28d and 19d for single dose, fractionated dose and control, respectively). [177Lu]Lu-PSMA-I&T decreased the size of viable tumor areas. We further demonstrated, that [177Lu]Lu-PSMA-I&T binds specifically to the tumor-associated vasculature.

CONCLUSION

This study highlights the potential of [177Lu]Lu-PSMA-I&T for endogenous radiotherapy of TNBC.

Head-to-Head Comparison of [18F]PSMA-1007 and [18F]FDG PET/CT in Patients with Triple-Negative Breast Cancer

BACKGROUND

Triple-negative breast cancer (TNBC) exhibits high aggressiveness and a notably poorer prognosis at advanced stages. Nuclear medicine offers new possibilities, not only for diagnosis but also potentially promising therapeutic strategies. This prospective study explores the potential of prostate-specific membrane antigen (PSMA) as a diagnostic and therapeutic target in TNBC.

METHODS

the research investigates PSMA expression in vivo among TNBC patients using [18F]PSMA-1007 PET/CT and compares it head-to-head with the standard-of-care [18F]FDG PET/CT.

RESULTS

The study involves 10 TNBC patients, revealing comparable uptake of [18F]PSMA-1007 and [18F]FDG in primary and metastatic lesions. Nodal metastases were found in eight patients, showing similar SUVmax values in both modalities. Two patients had uncountable lung metastases positive in both [18F]FDG and [18F]PSMA-1007 scans. PET-positive bone metastases were identified by 18F-PSMA in four patients, while elevated [18F]FDG uptake was found only in three of them. Distant metastases displayed higher SUVmax values in the [18F]PSMA-1007 PET/CT, as compared to [18F]FDG. Additionally, brain metastases were exclusively detected using [18F]PSMA-1007.

CONCLUSIONS

the findings provide valuable insights into the expression of PSMA in TNBC and underscore the potential clinical significance of [18F]PSMA-1007 PET/CT in enhancing both diagnostic and therapeutic approaches for this aggressive breast cancer subtype.

Hotspots and frontiers in PSMA research for prostate cancer: a bibliometric and visualization analysis over the past 20 years

BACKGROUND

Prostate-specific membrane antigen (PSMA)-targeted imaging and therapy have significantly changed the management of patients with prostate cancer (PCa) at different disease stages. This advancement has attracted the attention of scholars, leading to a prolific output of scholarly publications. This study comprehensively outlines the knowledge framework associated with PSMA-based diagnosis and treatment of PCa through the application of bibliometric analysis, and discusses the potential research trends and foci.

METHODS

Articles and reviews related to PSMA for prostate cancer from 2003 to 2022 were retrieved from Web of Science Core Collection. VOSviewer, Citespace, and R-bibliometrix were primarily employed to execute and visually represent co-authorship, co-citation, and co-occurrence analysis of countries, institutions, authors, references and keywords in this field.

RESULTS

A total of 3830 papers were included. The papers on the field of PSMA-based PCa therapy and imaging had been continuously increased since 2003, but the rate has slowed from 2020. The United States made the largest contribution in this field, in terms of publications 997 (26.03%), H-index (110) and total citations (53,167 times). We identified the most productive institution were Technical University of Munich, and Australian institutions had become very active in recent years. Journal of Nuclear Medicine was the most prominent journal in this field. Professors Matthias Eiber and Martin G Pomper made great achievements, while Ali Afshar-Oromieh was the most co-cited author. According to the result of keywords and topics analysis, "ga-68 labeled psma ligand", "radiation dosimetry" and "HBED-CC" were major research areas in the near future, while "Extended pelvic lymph node dissection" was considered to be the future research foci.

CONCLUSIONS

The field of psma-based PCa therapy and imaging is in the stage of vigorous development and has a bright prospect. The United States and Germany have achieved outstanding results in this area, while Australia has recently developed rapidly. It is foreseeable that more research foci will be lied in the early detection of pelvic lymph nodes and the multimodal imaging-guided surgery.

The current role of nuclear medicine in breast cancer

Breast cancer is the most common cancer in females worldwide. Nuclear medicine plays an important role in patient management, not only in initial staging, but also during follow-up. Radiopharmaceuticals to study breast cancer have been used for over 50 years, and several of these are still used in clinical practice, according to the most recent guideline recommendations.In this critical review, an overview of nuclear medicine procedures used during the last decades is presented. Current clinical indications of each of the conventional nuclear medicine and PET/CT examinations are the focus of this review, and are objectively provided. Radionuclide therapies are also referred, mainly summarising the methods to palliate metastatic bone pain. Finally, recent developments and future perspectives in the field of nuclear medicine are discussed. In this context, the promising potential of new radiopharmaceuticals not only for diagnosis, but also for therapy, and the use of quantitative imaging features as potential biomarkers, are addressed.Despite the long way nuclear medicine has gone through, it looks like it will continue to benefit clinical practice, paving the way to improve healthcare provided to patients with breast cancer.

PSMA-targeted therapy for non-prostate cancers

Radioligand therapy (RLT) agents are demonstrating a crucial role in the clinical approach to aggressive malignancies such as metastatic castrate-resistant prostate cancer (m-CRPC). With the recent FDA approval of prostate-specific membrane antigen (PSMA)-targeted RLT for m-CRPC, the field has broadened its gaze to explore other cancers that express PSMA in the tumor parenchyma or tumor neovasculature. In this review article, we discuss current progress in the clinical use of PSMA RLTs in non-prostate cancers such salivary gland cancers, renal cell carcinoma, high grade glioma, and soft tissue sarcoma. We highlight early reports in small case series and clinical trials indicating promise for PSMA-targeted RLT and highlighting the importance of identifying patient cohorts who may most benefit from these interventions. Further study is indicated in non-prostate cancers investigating PSMA RLT dosimetry, PSMA PET/CT imaging as a biomarker, and assessing PSMA RLT safety and efficacy in these cancers.

Theranostics in breast cancer

Introduction

Breast cancer is a complex disease and constitutes the leading cause of cancer in women globally. Conventional treatment modalities include surgery, chemotherapy, radiation therapy, and hormonal therapy; all of these have their limitations and often result in significant side effects or toxicity. Targeted radionuclide therapy based on a theranostic approach has been successfully applied in several malignancies, such as prostate cancer, thyroid cancer, and neuro-endocrine tumours. Several studies have also highlighted the potential of theranostic applications in breast cancer.

Aim

This review aims to provide an overview of the most promising current and future theranostic approaches in breast cancer.

Discussion

The discussion includes pre-clinical as well as clinical data on some of the most successful targets used to date. Examples of potential theranostic approaches include those targeting the Human epidermal growth factor receptor 2 (HER2) expression, angiogenesis, aspects of the tumour microenvironment, Gastrin-releasing peptide receptor (GRPR), Prostate-specific membrane antigen (PSMA) and Chemokine receptor 4 (CXCR-4) expression. Several challenges to widespread clinical implementation remain, which include regulatory approval, access to the various radiopharmaceuticals and imaging technology, cost-effectiveness, and the absence of robust clinical data.

Conclusion

Theranostic approaches have the potential to greatly improve diagnosis, treatment, and outcomes for patients with breast cancer. More research is needed to fully explore the potential of such approaches and to identify the best potential targets, considering feasibility, costs, efficacy, side effects and outcomes.

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.

The GRPR Antagonist [99mTc]Tc-maSSS-PEG2-RM26 towards Phase I Clinical Trial: Kit Preparation, Characterization and Toxicity

Gastrin-releasing peptide receptors (GRPRs) are overexpressed in the majority of primary prostate tumors and in prostatic lymph node and bone metastases. Several GRPR antagonists were developed for SPECT and PET imaging of prostate cancer. We previously reported a preclinical evaluation of the GRPR antagonist [^99mTc]Tc-maSSS-PEG₂-RM26 (based on [D-Phe⁶, Sta¹³, Leu¹⁴-NH₂]BBN(6-14)) which bound to GRPR with high affinity and had a favorable biodistribution profile in tumor-bearing animal models. In this study, we aimed to prepare and test kits for prospective use in an early-phase clinical study. The kits were prepared to allow for a one-pot single-step radiolabeling with technetium-99m pertechnetate. The kit vials were tested for sterility and labeling efficacy. The radiolabeled by using the kit GRPR antagonist was evaluated in vitro for binding specificity to GRPR on PC-3 cells (GRPR-positive). In vivo, the toxicity of the kit constituents was evaluated in rats. The labeling efficacy of the kits stored at 4 °C was monitored for 18 months. The biological properties of [^99mTc]Tc-maSSS-PEG₂-RM26, which were obtained after this period, were examined both in vitro and in vivo. The one-pot (gluconic acid, ethylenediaminetetraacetic acid, stannous chloride, and maSSS-PEG₂-RM26) single-step radiolabeling with technetium-99m was successful with high radiochemical yields (>97%) and high molar activities (16-24 MBq/nmol). The radiolabeled peptide maintained its binding properties to GRPR. The kit constituents were sterile and non-toxic when tested in living subjects. In conclusion, the prepared kit is considered safe in animal models and can be further evaluated for use in clinics.

The roles of 68 Ga-PSMA PET/CT and 18 F-FDG PET/CT imaging in patients with triple-negative breast cancer and the association of tissue PSMA and claudin 1, 4, and 7 levels with PET findings

AIM

Aim of study is to compare the results of Gallium-68-prostate-specific membrane antigen ( 68 Ga-PSMA) and 18 F-fluorodeoxyglucose ( 18 F-FDG) positron emission tomography(PET)/computed tomography (CT), to evaluate the correlation between PET findings and the level of PSMA, Claudin (Clau) 1, 4, and 7 receptors obtained by immunohistochemical (IHC) analysis, and to determine potential predictive and prognostic values in TNBC.

METHODS

Forty-seven lesions of 42 subjects diagnosed TNBC both underwent PET/CT scan for preoperative staging/restaging were prospectively included study. PSMA, Clau 1, 4, and 7 expressions were IHC evaluated from the biopsy samples of the primary tumor (PT). Maximum standardized uptake value(SUV max) of the PT, lymph node, and distant organ metastases (DOMs) on 18 F-FDG and 68 Ga-PSMA PET/CT were compared with PSMA, Clau 1, 4, and 7 receptor expressions.

RESULTS

IHC analyses on 29 BC lesions to demonstrate Clau expression showed 86% (25/29) Clau 1, 86% (25/29) Clau 4, 45% (13/29) Clau 7, and 48% (14/29) PSMA-positive. The mean DOM (SUVmax) was 15.5 ± 11.6 for 18 F-FDG and 6.0 ± 2.9 for 68 Ga-PSMA. Axial diameter of BC PT had a significant positive correlation with 18 F-FDG SUVmax, 68 Ga-PSMA SUVmax, and PSMA scores. BC lesions 68 Ga-PSMA SUVmax had a significant negative correlation with the Ki-67 index. Axial diameter of the primary tumor had significant negative correlation with Clau 7 scores ( r  = -0.409, P  = 0.034). Absence of Clau 1 expression found to significantly increase the rate of DOM (100% vs. 28%) ( P  = 0.014). All patients with axillary lymph node (ALN) metastases ( n  = 17, 100%) exhibited Clau 4 positivity ( P  = 0.021). The presence of PSMA expression observed to significantly increase the rate of ALN metastases (64.7% vs. 25%) ( P  = 0.035).

CONCLUSION

Confirming PSMA expression with PET imaging would be significant as PSMA, a theranostic agent, may be a considerable potential agent for radionuclide treatment strategies, in addition to its additional diagnostic contribution to FDG, especially in patients with metastatic TNBC, which is an aggressive, heterogeneous disease.

Incidental Diagnosis of Metastatic Breast Cancer in a Man With 99m Tc-PSMA SPECT/CT

ABSTRACT

Breast cancer in men is a rare and unsuspected malignancy. A 48-year-old man begins with disabling low back pain. The CT scan reported a compression fracture in L2 and diffuse skeletal lesions suggestive of metastatic disease. The serum prostate-specific antigen was 6.2 ng/mL. He was referred for SPECT/CT with 99m Tc-EDDA/HYNIC-inhibitor prostate-specific membrane antigen due to clinical suspicion of prostate cancer. SPECT/CT with 99m Tc-EDDA/HYNIC-inhibitor prostate-specific membrane antigen showed a primary lesion in the left breast and multiple bone lesions. Biopsy confirmed infiltrating ductal carcinoma with positive hormone receptors and indeterminate HER2 (human epidermal growth factor receptor 2).

The Potential of PSMA as a Vascular Target in TNBC

Recent studies proving prostate-specific membrane antigen (PSMA) expression on triple-negative breast cancer (TNBC) cells and adjacent endothelial cells suggest PSMA as a promising target for therapy of until now not-targetable cancer entities. In this study, PSMA and its isoform expression were analyzed in different TNBC cells, breast cancer stem cells (BCSCs), and tumor-associated endothelial cells. PSMA expression was detected in 91% of the investigated TNBC cell lines. The PSMA splice isoforms were predominantly found in the BCSCs. Tumor-conditioned media from two TNBC cell lines, BT-20 (high full-length PSMA expression, PSMAΔ18 expression) and Hs578T (low full-length PSMA expression, no isoform expression), showed significant pro-angiogenic effect with induction of tube formation in endothelial cells. All TNBC cell lines induced PSMA expression in human umbilical vein endothelial cells (HUVEC). Significant uptake of radiolabeled ligand [⁶⁸Ga]Ga-PSMA was detected in BCSC1 (4.2%), corresponding to the high PSMA expression. Moreover, hypoxic conditions increased the uptake of radiolabeled ligand [¹⁷⁷Lu]Lu-PSMA in MDA-MB-231 (0.4% vs. 3.4%, under hypoxia and normoxia, respectively) and MCF-10A (0.3% vs. 3.0%, under normoxia and hypoxia, respectively) significantly (p < 0.001). [¹⁷⁷Lu]Lu-PSMA-induced apoptosis rates were highest in BT-20 and MDA-MB-231 associated endothelial cells. Together, these findings demonstrate the potential of PSMA-targeted therapy in TNBC.

68 Ga-Prostate-Specific Membrane Antigen PET/CT in Ovarian Tumors : Potential to Differentiate Benign and Malignant Tumors Before Surgery: A Preliminary Report

PURPOSE OF THE REPORT

Ovarian cancer is usually diagnosed in an advanced stage of disease due to the absence of specific symptoms and a lack of sensitive diagnostic methods. Prostate-specific membrane antigen (PSMA) is expressed on prostate cancer cells but can be found in other tumors such as ovarian cancer.The aim of this pilot study was to evaluate the feasibility of using 68 Ga-PSMA-11 PET/CT in detection of ovarian neoplasm before surgical treatment.

PATIENTS AND METHODS

Eight women with mean age of 56.0 ± 16.2 years were included in the study. All patients underwent transvaginal ultrasound followed by CT scan of the chest and abdomen as qualification for surgery. Within a 1-week interval, PET/CT was performed on a Siemens Biograph scanner, 60 minutes after injection of 2 MBq/kg 68 Ga-PSMA-11.

RESULTS

In 3 cases (37.5%), the 68 Ga-PSMA-11 PET/CT was positive, whereas histological examination confirmed 2 serous ovarian cancer cases and 1 ovarian borderline tumor. The SUV max in the serous ovarian cancer was 8.7 and 4.1, and in the borderline ovarian tumor, it was 13.8. No correlation was found between antigen CA-125 level and 68 Ga-PSMA expression. Range of tumor SUV max was not correlated with stage of disease. The remaining 62.5% (5/8) were negative in 68 Ga-PSMA-11 PET/CT, and histopathology confirmed benign pelvic tumor.

CONCLUSIONS

The initial experience supports the potential to use 68 Ga-PSMA-11 in ovarian cancer to differentiate malignant and benign tumors before surgery.This study was approved by the Ethical Committee of the Medical University of Warsaw (KB/2/A/2018).

The Role of Theragnostics in Breast Cancer: A Systematic Review of the Last 12 Years

BACKGROUND

Breast cancer is the most common malignancy in women, with high morbidity and mortality. Molecular alterations in breast cancer involve the expression or upregulation of various molecular targets that can be used for diagnostic nuclear medicine imaging and radiopharmaceutical treatment. Theragnostics is based on the binding of radionuclides to molecular targets. These radionuclides can induce a cytotoxic effect on the specific tumor cell (target) or its vicinity, thus allowing a personalized approach to patients with effective treatment and comparably small side effects.

AIM

This review aims to describe the most promising molecular targets currently under investigation for theragnostics and precision oncology in breast cancer.

METHODS

A comprehensive literature search of studies on theragnostics in breast cancer was performed in the PubMed, PMC, Scopus, Google Scholar, Embase, Web of Science, and Cochrane library databases, between 2010 and 2022, using the following terms: breast neoplasm*, breast, breast cancer*, theragnostic*, theranostic*, radioligand therap*, RLT, MET, FLT, FMISO, FES, estradiol, trastuzumab, PD-L1, PSMA, FAPI, FACBC, fluciclovine, FAZA, GRPR, DOTATOC, DOTATATE, CXC4, endoglin, gastrin, mucin1, and syndecan1.

RESULTS

Fifty-three studies were included in the systematic review and summarized in six clinical sections: 1) human epidermal growth factor receptor 2 (HER2); 2) somatostatin receptors (SSTRS); 3) prostate-specific membrane antigen radiotracers (PSMA); 4) fibroblast activation protein-α targeted radiotracers; 5) gastrin-releasing peptide receptor-targeted radiotracers; 6) other radiotracers for theragnostics.

CONCLUSION

The theragnostic approach will progressively allow better patient selection, and improve the prediction of response and toxicity, avoiding unnecessary and costly treatment.

Prostate-specific membrane antigen expression predicts recurrence of papillary thyroid carcinoma after total thyroidectomy

BACKGROUND

Prostate-specific membrane antigen (PSMA) overexpression has been observed in the endothelial neovasculature of several solid malignancies. This study aimed to identify PSMA expression in the primary tumor of classical papillary thyroid carcinoma (PTC) and assess the correlation between the degree of PSMA expression and recurrence.

METHODS

We reviewed the electronic medical records of patients who underwent total thyroidectomy and central neck dissection, with or without lateral neck dissection, for classical PTC between 2009 and 2014 at our institution. Recurrence was defined as a structural disease based on histological confirmation on follow-up. Fifty-one patients with the recurrent structural disease were matched, using a propensity score matching method, to patients with no disease evidence during follow-up. Clinicopathological and follow-up data were collected for 102 patients. The monoclonal mouse anti-human PSMA/FOLH1/NAALADase I antibody was used for staining the primary tumor. The score of PSMA expression was classified as negative (< 5% positivity), weak (5-10 % positivity), moderate (11-49% positivity), and strong (more than 50% positivity). Clinicopathological factors were compared between patients with low and high PSMA expression. Moreover, whether the degree of PSMA expression and clinicopathological factors could predict recurrence was investigated. Cox proportional hazard regression models were used to evaluate the risk of recurrence.

RESULTS

There was no significant difference in clinicopathological factors between low (negative or weak) and high (moderate or strong) PSMA expression. Gross extrathyroidal extension (ETE), absence of chronic lymphocytic thyroiditis, and high PSMA expression were all associated with lower recurrence-free survival (RFS) rate in a univariate analysis. In multivariate analysis, gross ETE (hazard ratio [HR], 2.279; 95% confidence interval [CI], 1.257-4.132; p = 0.007) and high PSMA expression (HR, 1.895; 95% CI, 1.073-3.348; p = 0.028) were associated with poor RFS.

CONCLUSIONS

High PSMA expression in the primary tumor was a significant factor in predicting recurrence in classic PTC. PSMA could be a potential biomarker for personalized management for PTC.

PSMA Expression in Solid Tumors beyond the Prostate Gland: Ready for Theranostic Applications?

In the past decades, the expanding use of prostate-specific membrane antigen (PSMA) imaging for prostate cancer has led to the incidental detection of a lot of extra-prostatic malignancies showing an increased uptake of PSMA. Due to these incidental findings, the increasing amount of immunohistochemistry studies and the deeper knowledge of the mechanisms of expression of this antigen, it is now clear that “PSMA” is a misnomer, since it is not specific to the prostate gland. Nevertheless, this lack of specificity could represent an interesting opportunity to bring new insights on the biology of PSMA and its sites of expression to image and treat new conditions, particularly several cancers. In this review, we will describe the main extra-prostatic cancers that exhibit PSMA expression and that can be studied with PSMA-based positron emission tomography–computed tomography (PET/CT) as an additional or alternative tool to conventional imaging. In particular, we will focus on cancers in which a radioligand therapy with ¹⁷⁷lutetium has been attempted, aiming to provide an overview of the possible future theragnostic applications of PSMA.

Rat Mammary carcinoma susceptibility 3 (Mcs3) pleiotropy, socioenvironmental interaction, and comparative genomics with orthologous human 15q25.1-25.2

Genome-wide association studies of breast cancer susceptibility have revealed risk-associated genetic variants and nominated candidate genes; however, the identification of causal variants and genes is often undetermined by genome-wide association studies. Comparative genomics, utilizing Rattus norvegicus strains differing in susceptibility to mammary tumor development, is a complimentary approach to identify breast cancer susceptibility genes. Mammary carcinoma susceptibility 3 (Mcs3) is a Copenhagen (COP/NHsd) allele that confers resistance to mammary carcinomas when introgressed into a mammary carcinoma susceptible Wistar Furth (WF/NHsd) genome. Here, Mcs3 was positionally mapped to a 7.2-Mb region of RNO1 spanning rs8149408 to rs107402736 (chr1:143700228-150929594, build 6.0/rn6) using WF.COP congenic strains and 7,12-dimethylbenz(a)anthracene-induced mammary carcinogenesis. Male and female WF.COP-Mcs3 rats had significantly lower body mass compared to the Wistar Furth strain. The effect on female body mass was observed only when females were raised in the absence of males indicating a socioenvironmental interaction. Furthermore, female WF.COP-Mcs3 rats, raised in the absence of males, did not develop enhanced lobuloalveolar morphologies compared to those observed in the Wistar Furth strain. Human 15q25.1-25.2 was determined to be orthologous to rat Mcs3 (chr15:80005820-82285404 and chr15:83134545-84130720, build GRCh38/hg38). A public database search of 15q25.1-25.2 revealed genome-wide significant and nominally significant associations for body mass traits and breast cancer risk. These results support the existence of a breast cancer risk-associated allele at human 15q25.1-25.2 and warrant ultrafine mapping of rat Mcs3 and human 15q25.1-25.2 to discover novel causal genes and variants.

Ga-68 Prostate-Specific Membrane Antigen-HBED-CC Positron Emission Tomography/Computed Tomography in Anaplastic Thyroid Carcinoma

Purpose

Anaplastic thyroid carcinoma (ATC) is the most aggressive thyroid cancer and there is no established treatment that works well. The study was conducted to see prostate-specific membrane antigen (PSMA) expression in ATC as a stepping stone to study its role in potential theranostics.

Materials and Methods

Pathologically proven ATC patients were prospectively included in this study. Ga-68-PSMA positron emission tomography/computed tomography (PET/CT) was done to look for PSMA expression in local and distant sites 45-60 mins after injecting 2-3mCi of tracer.

Results

Twenty patients were enrolled in this study. Nodal metastases were seen in all patients, while distant metastases were seen in 17/20. The mean SUVmax of primary lesion was 6.72 ± 4.6. Mean SUVmax of node and lung lesions was 5.7 ± 5.6 and 2.9 ± 1.98, respectively. Mean SUVmax of liver, mediastinum, and parotid gland was 5.95 ± 3.03, 1.54 ± 0.68, and 9.03 ± 3.75, respectively. Mean Tumor to background ratio (liver = TBRl; mediastinum = TBRm; parotid = TBRp) were 1.21, 4.49 and 0.78, respectively.

Conclusion

ATC showed variable PSMA expression on Ga-68-PSMA-PET/CT and this attribute may be potentially useful in ATC theranostics.

Imaging Characteristics of Coexisting Metastatic Papillary Thyroid Cancer and Prostate Cancer on 18 F-Fluciclovine and 68 Ga-PSMA-11 PET/CT

ABSTRACT

A 76-year-old man with biopsy-proven metastatic papillary thyroid cancer in a mediastinal nodule status post total thyroidectomy is on surveillance. The patient also had prostate cancer and received prostatectomy and androgen deprivation treatment. An 18 F-fluciclovine PET revealed avid lesions in the mediastinal nodule and a sclerotic focus at L5 with concurrent prostate-specific antigen level of 0.4 ng/mL. The L5 lesion was later biopsied and confirmed as metastasis from prostate cancer. A 68 Ga-PSMA-11 PET 2 months later showed avid radiotracer uptake within L5 metastasis but not the mediastinal nodule. The patient received radiation therapy to the L5 lesion and responded well.

PSMA Radioligand Uptake as a Biomarker of Neoangiogenesis in Solid Tumours: Diagnostic or Theragnostic Factor?

Due to its overexpression on the surface of prostate cancer cells, prostate-specific membrane antigen (PSMA) is a relatively novel effective target for molecular imaging and radioligand therapy (RLT) in prostate cancer. Recent studies reported that PSMA is expressed in the neovasculature of various types of cancer and regulates tumour cell invasion as well as tumour angiogenesis. Several authors explored the role of diagnostic and therapeutic PSMA radioligands in various malignancies. In this narrative review, we describe the current status of the literature on PSMA radioligands' application in solid tumours other than prostate cancer to explore their potential role as diagnostic or therapeutic agents, with particular regard to the relevance of PSMA radioligand uptake as neoangiogenetic biomarker. Hence, a comprehensive review of the literature was performed to find relevant articles on the applications of PSMA radioligands in non-prostate solid tumours. Data on the general, methodological and clinical aspects of all included studies were collected. Forty full-text papers were selected for final review, 8 of which explored PSMA radioligand PET/CT performances in gliomas, 3 in salivary gland malignancies, 6 in thyroid cancer, 2 in breast cancer, 16 in renal cell carcinoma and 5 in hepatocellular carcinoma. In the included studies, PSMA radioligand PET showed promising performance in patients with non-prostate solid tumours. Further studies are needed to better define its potential role in oncological patients management, especially in those undergoing antineoangiogenic therapies, and to assess the efficacy of PSMA-RLT in this clinical context.

Advances in PSMA theranostics

•

PSMA is an appealing target for theranostic because it is a transmembrane protein with a known substrate that is overexpessed on prostate cancer cells and internalizes upon ligand binding.

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There are a number of PSMA theranostic ligands in clinical evaluation, clinical trial, or clinically approved.

•

PSMA theranostic ligands increase progression-free survival, overall survival, and pain in patients with metastatic castration resistant prostate cancer.

•

A major obstacle to PSMA-targeted radioligand therapy is off-target toxicity in salivary glands.

The validation of prostate specific membrane antigen (PSMA) as a molecular target in metastatic castration-resistant prostate cancer has stimulated the development of multiple classes of theranostic ligands that specifically target PSMA. Theranostic ligands are used to image disease or selectively deliver cytotoxic radioactivity to cells expressing PSMA according to the radioisotope conjugated to the ligand. PSMA theranostics is a rapidly advancing field that is now integrating into clinical management of prostate cancer patients. In this review we summarize published research describing the biological role(s) and activity of PSMA, highlight the most clinically advanced PSMA targeting molecules and biomacromolecules, and identify next generation PSMA ligands that aim to further improve treatment efficacy. The goal of this review is to provide a comprehensive assessment of the current state-of-play and a roadmap to achieving further advances in PSMA theranostics.

Non-conventional and Investigational PET Radiotracers for Breast Cancer: A Systematic Review

Breast cancer is one of the most common malignancies in women, with high morbidity and mortality rates. In breast cancer, the use of novel radiopharmaceuticals in nuclear medicine can improve the accuracy of diagnosis and staging, refine surveillance strategies and accuracy in choosing personalized treatment approaches, including radioligand therapy. Nuclear medicine thus shows great promise for improving the quality of life of breast cancer patients by allowing non-invasive assessment of the diverse and complex biological processes underlying the development of breast cancer and its evolution under therapy. This review aims to describe molecular probes currently in clinical use as well as those under investigation holding great promise for personalized medicine and precision oncology in breast cancer.

HER2 Mediates PSMA/mGluR1-Driven Resistance to the DS-7423 Dual PI3K/mTOR Inhibitor in PTEN Wild-type Prostate Cancer Models

Prostate cancer remains a major cause of male mortality. Genetic alteration of the PI3K/AKT/mTOR pathway is one of the key events in tumor development and progression in prostate cancer, with inactivation of the PTEN tumor suppressor being very common in this cancer type. Extensive evaluation has been performed on the therapeutic potential of PI3K/AKT/mTOR inhibitors and the resistance mechanisms arising in patients with PTEN-mutant background. However, in patients with a PTEN wild-type phenotype, PI3K/AKT/mTOR inhibitors have not demonstrated efficacy, and this remains an area of clinical unmet need. In this study, we have investigated the response of PTEN wild-type prostate cancer cell lines to the dual PI3K/mTOR inhibitor DS-7423 alone or in combination with HER2 inhibitors or mGluR1 inhibitors. Upon treatment with the dual PI3K/mTOR inhibitor DS-7423, PTEN wild-type prostate cancer CWR22/22RV1 cells upregulate expression of the proteins PSMA, mGluR1, and the tyrosine kinase receptor HER2, while PTEN-mutant LNCaP cells upregulate androgen receptor and HER3. PSMA, mGluR1, and HER2 exert control over one another in a positive feedback loop that allows cells to overcome treatment with DS-7423. Concomitant targeting of PI3K/mTOR with either HER2 or mGluR1 inhibitors results in decreased cell survival and tumor growth in xenograft studies. Our results suggest a novel therapeutic possibility for patients with PTEN wild-type PI3K/AKT-mutant prostate cancer based in the combination of PI3K/mTOR blockade with HER2 or mGluR1 inhibitors.

Expression of Prostate Specific Membrane Antigen (PSMA) in Breast Cancer

Background Prostate specific membrane antigen (PSMA) is a promising protein for breast cancer patients. It has not only been detected in prostate cancer but is also expressed by tumor cells and the endothelial cells of tumor vessels in breast cancer patients. PSMA plays a role in tumor progression and tumor angiogenesis. For this reason, a number of diagnostic and therapeutic methods to target PSMA have been developed. Method This paper provides a general structured overview of PSMA and its oncogenic potential, with a special focus on its role in breast cancer. This narrative review is based on a selective literature search carried out in PubMed and the library of Freiburg University Clinical Center. The following key words were used for the search: "PSMA", "PSMA and breast cancer", "PSMA PET/CT", "PSMA tumor progression". Relevant articles were explicitly read through, processed, and summarized. Conclusion PSMA could be a new diagnostic and therapeutic alternative, particularly for triple-negative breast cancer. It appears to be a potential predictive and prognostic marker.

Novel Tracers and Radionuclides in PET Imaging

The use of PET imaging agents in oncology, cardiovascular disease, and neurodegenerative disease shows the power of this technique in evaluating the molecular and biological characteristics of numerous diseases. These agents provide crucial information for designing therapeutic strategies for individual patients. Novel PET tracers are in continual development and many have potential use in clinical and research settings. This article discusses the potential applications of tracers in diagnostics, the biological characteristics of diseases, the ability to provide prognostic indicators, and using this information to guide treatment strategies including monitoring treatment efficacy in real time to improve outcomes and survival.

PSMA radioligand therapy for solid tumors other than prostate cancer: background, opportunities, challenges, and first clinical reports

In the past decade, a growing body of literature has reported promising results for prostate-specific membrane antigen (PSMA)-targeted radionuclide imaging and therapy in prostate cancer. First clinical studies evaluating the efficacy of [¹⁷⁷Lu]Lu-PSMA radioligand therapy (PSMA-RLT) demonstrated favorable results in prostate cancer patients. [¹⁷⁷Lu]Lu-PSMA is generally well tolerated due to its limited side effects. While PSMA is highly overexpressed in prostate cancer cells, varying degrees of PSMA expression have been reported in other malignancies as well, particularly in the tumor-associated neovasculature. Hence, it is anticipated that PSMA-RLT could be explored for other solid cancers. Here, we describe the current knowledge of PSMA expression in other solid cancers and define a perspective towards broader clinical implementation of PSMA-RLT. This review focuses specifically on salivary gland cancer, glioblastoma, thyroid cancer, renal cell carcinoma, hepatocellular carcinoma, lung cancer, and breast cancer. An overview of the (pre)clinical data on PSMA immunohistochemistry and PSMA PET/CT imaging is provided and summarized. Furthermore, the first clinical reports of non-prostate cancer patients treated with PSMA-RLT are described.

177Lu-PSMA-617 Therapy in Mice, with or without the Antioxidant α1-Microglobulin (A1M), Including Kidney Damage Assessment Using 99mTc-MAG3 Imaging

Anti-prostate specific membrane antigen (PSMA) radioligand therapy is promising but not curative in castration resistant prostate cancer. One way to broaden the therapeutic index could be to administer higher doses in combination with radioprotectors, since administered radioactivity is kept low today in order to avoid side-effects from a high absorbed dose to healthy tissue. Here, we investigated the human radical scavenger α₁-microglobulin (A1M) together with 177-Lutetium (¹⁷⁷Lu) labeled PSMA-617 in preclinical models with respect to therapeutic efficacy and kidney toxicity. Nude mice with subcutaneous LNCaP xenografts were injected with 50 or 100 MBq of [¹⁷⁷Lu]Lu-PSMA-617, with or without injections of recombinant A1M (rA1M) (at T = 0 and T = 24 h). Kidney absorbed dose was calculated to 7.36 Gy at 4 days post a 100 MBq injection. Activity distribution was imaged with Single-Photon Emission Computed Tomography (SPECT) at 24 h. Tumor volumes were measured continuously, and kidneys and blood were collected at termination (3–4 days and 3–4 weeks after injections). In a parallel set of experiments, mice were given [¹⁷⁷Lu]Lu-PSMA-617 and rA1M as above and dynamic technetium-99m mercaptoacetyltriglycine ([^99mTc]Tc-MAG3) SPECT imaging was performed prior to injection, and 3- and 6-months post injection. Blood and urine were continuously sampled. At termination (6 months) the kidneys were resected. Biomarkers of kidney function, expression of stress genes and kidney histopathology were analyzed. [¹⁷⁷Lu]Lu-PSMA-617 uptake, in tumors and kidneys, as well as treatment efficacy did not differ between rA1M and vehicle groups. In mice given rA1M, [^99mTc]Tc-MAG3 imaging revealed a significantly higher slope of initial uptake at three months compared to mice co-injected with [¹⁷⁷Lu]Lu-PSMA-617 and vehicle. Little or no change compared to control was seen in urine albumin, serum/plasma urea levels, RT-qPCR analysis of stress response genes and in the kidney histopathological evaluation. In conclusion, [^99mTc]Tc-MAG3 imaging presented itself as a sensitive tool to detect changes in kidney function revealing that administration of rA1M has a potentially positive effect on kidney perfusion and tubular function when combined with [¹⁷⁷Lu]Lu-PSMA-617 therapy. Furthermore, we could show that rA1M did not affect anti-PSMA radioligand therapy efficacy.

Development of Radiotracers for Breast Cancer-The Tumor Microenvironment as an Emerging Target

Molecular imaging plays an increasingly important role in the diagnosis and treatment of different malignancies. Radiolabeled probes enable the visualization of the primary tumor as well as the metastases and have been also employed in targeted therapy and theranostic approaches. With breast cancer being the most common malignancy in women worldwide it is of special interest to develop novel targeted treatments. However, tumor microenvironment and escape mechanisms often limit their therapeutic potential. Addressing tumor stroma associated targets provides a promising option to inhibit tumor growth and angiogenesis and to disrupt tumor tissue architecture. This review describes recent developments on radiolabeled probes used in diagnosis and treatment of breast cancer especially in triple negative type with the focus on potential targets offered by the tumor microenvironment, like tumor associated macrophages, cancer associated fibroblasts, and endothelial cells.

Prior therapies as prognostic factors of overall survival in metastatic castration-resistant prostate cancer patients treated with [177Lu]Lu-PSMA-617. A WARMTH multicenter study (the 617 trial)

Introduction

The impact of prior therapies, especially chemotherapy, on overall survival (OS) in patients with castration-resistant prostate cancer (CRPC) receiving [¹⁷⁷Lu]Lu-PSMA-617 therapy has been the subject of controversy. Therefore, WARMTH decided to plan a multicenter retrospective analysis (the “617 trial”) to evaluate response rate and OS as well as the impact of prior therapies on OS in more than 300 patients treated with ¹⁷⁷Lu-PSMA-617.

Materials and methods

The data of 631 metastatic CRPC (mCRPC) patients from 11 different clinics were evaluated. According to the inclusion and exclusion criteria, all patients had to have received at least abiraterone or enzalutamide prior to [¹⁷⁷Lu]Lu-PSMA-617 therapy. The patients were divided into three groups: patients who had received prior chemotherapy, patients who avoided chemotherapy, and patients for whom a chemotherapy was contraindicated.

Results

The analysis included the data of 416 patients, with a median age of 71.9 years. At the time of analysis, 87 patients (20,9%) were still alive. A total of 53.6% of patients had received both abiraterone and enzalutamide; 75.5% and 26.4% had a history of chemotherapy with docetaxel and cabazitaxel, respectively. A total of 20.4% had had Ra-223. The median OS was 11.1 months. Prior chemotherapy, the existence of bone and liver metastases, as well as Eastern Cooperative Oncology Group (ECOG) status, were significant prognosticators of worse overall survival in both univariate and multivariate analyses. Patients without any prior chemotherapy showed a significantly longer OS (14.6 months). The median OS in patients who received one or two lines of chemotherapy with docetaxel or docetaxel followed by cabazitaxel, respectively, was 10.9 months and 8.9 months. There was no difference in OS between patients who had not received chemotherapy and patients for whom chemotherapy was contraindicated. The other prior therapies did not have any significant impact on OS.

Conclusion

In the present multicenter analysis, chemotherapy-naïve mCRPC patients receiving [¹⁷⁷Lu]Lu-PSMA-617 therapy had a significantly longer OS than patients with a history of chemotherapy. This remained independent in the multivariate analysis besides presence of bone and liver metastases as negative prognosticators for survival, whereas an ECOG of 0–1 is associated with a longer OS.

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04797-9) contains supplementary material, which is available to authorized users.

PSMA expression on neovasculature of solid tumors

The use of prostate specific membrane antigen (PSMA) binding agents, labelled with diagnostic and therapeutic radio-isotopes is opening the potential for a new era of personalized management of prostate carcinoma. A wide variety of immunohistochemistry studies have shown PSMA also to be upregulated on the endothelial cells of the neovasculature of a wide variety of other solid tumors where it may facilitate endothelial cell sprouting and invasion through its regulation of lytic proteases that have the ability to cleave the extracellular matrix. Similar to the introduction of PSMA-targeting theranostics in prostate carcinoma, overexpression of PSMA on newly formed tumor vessels may serve as a target for imaging and subsequent treatment of cancer through the use of agents that are capable of blocking PSMA in its function or through PSMA-mediated delivery of chemotherapeutics or radiation agents. In this review, the available data on PSMA expression on tumor neovasculature in human solid tumors assessed by using immunohistochemistry are discussed.

Looking for Drugs in All the Wrong Places: Use of GCPII Inhibitors Outside the Brain

In tribute to our friend and colleague Michael Robinson, we review his involvement in the identification, characterization and localization of the metallopeptidase glutamate carboxypeptidase II (GCPII), originally called NAALADase. While Mike was characterizing NAALADase in the brain, the protein was independently identified by other laboratories in human prostate where it was termed prostate specific membrane antigen (PSMA) and in the intestines where it was named Folate Hydrolase 1 (FOLH1). It was almost a decade to establish that NAALADase, PSMA, and FOLH1 are encoded by the same gene. The enzyme has emerged as a therapeutic target outside of the brain, with the most notable progress made in the treatment of prostate cancer and inflammatory bowel disease (IBD). PSMA-PET imaging with high affinity ligands is proving useful for the clinical diagnosis and staging of prostate cancer. A molecular radiotherapy based on similar ligands is in trials for metastatic castration-resistant prostate cancer. New PSMA inhibitor prodrugs that preferentially block kidney and salivary gland versus prostate tumor enzyme may improve the clinical safety of this radiotherapy. The wide clinical use of PSMA-PET imaging in prostate cancer has coincidentally led to clinical documentation of GCPII upregulation in a wide variety of tumors and inflammatory diseases, likely associated with angiogenesis. In IBD, expression of the FOLH1 gene that codes for GCPII is strongly upregulated, as is the enzymatic activity in diseased patient biopsies. In animal models of IBD, GCPII inhibitors show substantial efficacy, suggesting potential theranostic use of GCPII ligands for IBD.

Targeting of prostate-specific membrane antigen for radio-ligand therapy of triple-negative breast cancer

Background

Triple-negative breast cancer has extremely high risk of relapse due to the lack of targeted therapies, intra- and inter-tumoral heterogeneity, and the inherent and acquired resistance to therapies. In this study, we evaluate the potential of prostate-specific membrane antigen (PSMA) as target for radio-ligand therapy (RLT).

Methods

Tube formation was investigated after incubation of endothelial HUVEC cells in tumor-conditioned media and monitored after staining using microscopy. A binding study with ⁶⁸Ga-labeled PSMA-addressing ligand was used to indicate targeting potential of PSMA on tumor-conditioned HUVEC cells. For mimicking of the therapeutic application, tube formation potential and vitality of tumor-conditioned HUVEC cells were assessed following an incubation with radiolabeled PSMA-addressing ligand [¹⁷⁷Lu]-PSMA-617. For in vivo experiments, NUDE mice were xenografted with triple-negative breast cancer cells MDA-MB231 or estrogen receptor expressing breast cancer cells MCF-7. Biodistribution and binding behavior of [⁶⁸Ga]-PSMA-11 was investigated in both tumor models at 30 min post injection using μPET. PSMA- and CD31-specific staining was conducted to visualize PSMA expression and neovascularization in tumor tissue ex vivo.

Results

The triple-negative breast cancer cells MDA-MB231 showed a high pro-angiogenetic potential on tube formation of endothelial HUVEC cells. The induced endothelial expression of PSMA was efficiently addressed by radiolabeled PSMA-specific ligands. ¹⁷⁷Lu-labeled PSMA-617 strongly impaired the vitality and angiogenic potential of HUVEC cells. In vivo, as visualized by μPET, radiolabeled PSMA-ligand accumulated specifically in the triple-negative breast cancer xenograft MDA-MB231 (T/B ratio of 43.3 ± 0.9), while no [⁶⁸Ga]-PSMA-11 was detected in the estrogen-sensitive MCF-7 xenograft (T/B ratio of 1.1 ± 0.1). An ex vivo immunofluorescence analysis confirmed the localization of PSMA on MDA-MB231 xenograft-associated endothelial cells and also on TNBC cells.

Conclusions

Here we demonstrate PSMA as promising target for two-compartment endogenous radio-ligand therapy of triple-negative breast cancer.

Prostate-specific membrane antigen expression in hepatocellular carcinoma: potential use for prognosis and diagnostic imaging

Aim

The prostate-specific membrane antigen (PSMA) is currently being established as a potent diagnostic marker in many tumor types. So far, its evidence in hepatocellular carcinoma (HCC) is sparse. The aim of our study was a comprehensive evaluation of PSMA expression and its prognostic role in patients with hepatocellular carcinoma as well as feasibility test of PSMA as an agent for diagnostic imaging.

Methods

The cohort for immunohistochemistry consisted of 153 patients with HCC. For validation purposes the HCC cohort (n = 359) of The Cancer Genome Atlas was analyzed on transcript level as well.

Results

On immunohistochemistry, non-tumorous liver tissue showed PSMA expression on canalicular membranes in all cases. In tumor tissue two patterns of expression, with a canalicular (41.1% of tumors) and a neovascular (89.9% of tumors) staining were seen. Completely negative for both two patterns were only 4.1% of tumors; conversely, 79.2% of the tumors showed high levels of PSMA protein expression at any location. At mRNA level higher FOLH1 (PSMA) expression rates were statistically significant and independently associated with longer overall survival times.Additionally, a case report of successful diagnostic ⁶⁸Ga-PSMA-11 PET/CT in a patient with HCC progression on multiple therapy lines is provided.

Conclusions

Majority of hepatocellular carcinomas show high levels of PSMA expression on tumor vessels and on canalicular membrane of the tumor cells. Putative diagnostic, prognostic and therapeutic value of PSMA in HCC warrants further clinically oriented investigations.