Prostate-specific membrane antigen theranostics in advanced prostate cancer: an evolving option

An integrated bioinformatic investigation of kallikrein gene family members in kidney renel cell carcinoma

BACKGROUNDS

KLKs have been proved to be key regulators of the tumor microenvironment. In this study, we explored the potential of Kallikrein-related peptidases (KLKs) as clinical diagnostic and prognostic markers in patients with kidney renal clear cell carcinoma (KIRC) as well as their relationship with common immuno-inhibitor and immune cell infiltration in the tumor microenvironment to provide new targets and novel ideas for KIRC therapy.

METHODS

Oncomine, Gene Expression Profiling Interactive Analysis (GEPIA), UCSC Xena, Genotype-Tissue Expression (GTEx), Kaplan-Meier plotter, cBioPortal, STRING, GeneMANIA, and TISIDB were used to analyze the differential expression, prognostic value, gene changes, molecular interaction, and immune infiltration of KLKs in patients with KIRC.

RESULTS

From the gene expression level, it can be determined that KLK1, KLK6, and KLK7 are differentially expressed in KIRC and normal tissues. From the perspective of clinical prognosis, KLK1, KLK13, and KLK14 are highly correlated with the clinical prognosis of KIRC. The expression of KLKs is regulated by various immunosuppressive agents, with KDR, PVRL2, and VTCN1 being the most significant. The expression of KLKs is significantly correlated with the infiltration of various immune cells, of which Eosinophils and Neutrophils are the most significant.

CONCLUSIONS

KLK1, KLK6, KLK7, KLK13, and KLK14 have potential as diagnostic and prognostic biomarkers, among which KLK1 is the most significant. This study may provide detailed immune information and promising targets for KIRC immunotherapy to assist in designing new immunotherapies.

Imaging and therapy in prostate cancer using prostate specific membrane antigen radioligands

Prostate specific membrane antigen (PSMA) directed PET imaging has rapidly transformed prostate cancer workup over the past decade and paved the way for a theranostic approach using 177Lu-labelled PSMA radioligand therapy (RLT). This review gives an overview of the underlying principles behind PSMA as a target; the current use of PSMA PET in prostate cancer imaging and benefits compared to conventional imaging; and therapeutic applications including optimisation of patient selection. It also explores the evidence base of PSMA PET for other indications not in routine clinical use and the future of PSMA-directed RLT.

Clinical Experience with [225Ac]Ac-PSMA Treatment in Patients with [177Lu]Lu-PSMA-Refractory Metastatic Castration-Resistant Prostate Cancer

For patients with advanced-stage metastatic castration-resistant prostate cancer (mCRPC) who do not respond to [177Lu]Lu-PSMA therapy, there are limited treatment options. Clinical results obtained with [225Ac]Ac-PSMA are promising. We retrospectively analyzed the outcomes of patients treated with [225Ac]Ac-PSMA between December 2018 and October 2022. Methods: We evaluated the treatment results of 23 patients (mean age, 70.3 ± 8.8 y) with mCRPC who were refractory to treatment with [177Lu]Lu-PSMA (2-9 cycles). The safety profile was assessed according to Common Technology Criteria for Adverse Events version 5.0. Treatment efficacy was assessed using prostate-specific membrane antigen PET progression criteria and prostate-specific antigen (PSA) response according to Prostate Cancer Working Group 2 criteria after the first cycle of [225Ac]Ac-PSMA treatment. Results: All patients received androgen-deprivation therapy, whereas 22 (96%) and 19 (83%) patients received chemotherapy and second-generation antiandrogen therapy, respectively. One patient received 4 cycles, 2 received 3 cycles, 8 received 2 cycles, and 12 received 1 cycle of [225Ac]Ac-PSMA. The median interval between cycles was 13 wk (range, 8-28 wk). [225Ac]Ac-PSMA was administered with a mean activity of 7.6 MBq (range, 6.2-10.0 MBq) in each cycle. Patients were at an advanced stage of disease, and tumor burden was very high. Although the best PSA response was observed in 5 patients (26%) after [225Ac]Ac-PSMA treatment, there was at least some level of decline in PSA observed in 11 patients (58%; n = 19). Treatment response was assessed in patients who underwent [68Ga]Ga-PSMA PET/CT imaging. After the first cycle of treatment (n = 18), 50% of patients (n = 9) showed disease progression according to prostate-specific membrane antigen PET progression criteria, and the disease control rate was calculated to be 50%. Median progression-free survival was 3.1 mo, and median overall survival was 7.7 mo. Grade 3 hematologic toxicity occurred in 1 patient, and grade 3 nephrotoxicity was observed in another patient. Parotid SUVmax decreased by 33%, although all patients complained of dry mouth before treatment. Conclusion: We observed that [225Ac]Ac-PSMA therapy was safe and showed potential even in cases with advanced-stage mCRPC in which all other treatment options were completed.

177Lu-PSMA Therapy for Metastatic Castration-Resistant Prostate Cancer: A Mini-Review of State-of-the-Art

BACKGROUND

Prostate specific membrane antigen (PSMA) ligand labeled with Lutetium-177 (177Lu) is a promising therapeutic option for metastatic castration-resistant prostate cancer (mCRPC). Several prospective and retrospective studies as well as clinical trials are completed or underway. This has ultimately led to the approval of this therapy by the US Food and Drug Administration (FDA) on March 23 2022. Our work aims to present a mini-review of the most recent research performed and the potential future directions of 177Lu-PSMA-radioligand therapy (RLT) for mCRPC patients.

MAIN BODY

For patients with mCRPCwho have met the eligibility criteria for 177Lu-PSMA RLT, numerous studies and trials are either ongoing or have been completed. The studies included in this review have reported overall biochemical response, defined as a prostate-specific antigen (PSA) decline of at least 50%, in at least 44% of patients with mCRPC. The median ranges of overall survival (OS) and radiographic progression-free survival (rPFS) were reported within 10.7-56 and 3.6-16 months, respectively. With data from several retrospective and prospective studies published, the safety of 177Lu-PSMA RLT in mCRPC has been confirmed and demonstrated by its low toxicity profile. Various studies have published pharmacokinetic/pharmacodynamic models to better understand the absorption, distribution, metabolism, and excretion of the RLT in this patient population. Findings have been published for 177Lu-PSMA RLT alone and in combination with other agents. We summarize their findings in our review.

CONCLUSIONS

The efficacy of 177Lu-PSMA RLT for patients with mCRPC has been proven thus far with promising results: PSA response, OS and rPFS when used alone or in combination with other treatment options, relative to the standard treatment options alone. The low toxicity profile noted also proves the safety of 177Lu-PSMA RLT in these patients.

Site-Specific Intact N-Linked Glycopeptide Characterization of Prostate-Specific Membrane Antigen from Metastatic Prostate Cancer Cells

The composition of N-linked glycans that are conjugated to the prostate-specific membrane antigen (PSMA) and their functional significance in prostate cancer progression have not been fully characterized. PSMA was isolated from two metastatic prostate cancer cell lines, LNCaP and MDAPCa2b, which have different tissue tropism and localization. Isolated PSMA was trypsin-digested, and intact glycopeptides were subjected to LC-HCD-EThcD-MS/MS analysis on a Tribrid Orbitrap Fusion Lumos mass spectrometer. Differential qualitative and quantitative analysis of site-specific N-glycopeptides was performed using Byonic and Byologic software. Comparative quantitative analysis demonstrates that multiple glycopeptides at asparagine residues 51, 76, 121, 195, 336, 459, 476, and 638 were in significantly different abundance in the two cell lines (p < 0.05). Biochemical analysis using endoglycosidase treatment and lectin capture confirm the MS and site occupancy data. The data demonstrate the effectiveness of the strategy for comprehensive analysis of PSMA glycopeptides. This approach will form the basis of ongoing experiments to identify site-specific glycan changes in PSMA isolated from disease-stratified clinical samples to uncover targets that may be associated with disease progression and metastatic phenotypes.

Kit-based preparation of [68Ga]Ga-P16-093 (PSMA-093) using different commercial 68Ge/68Ga generators

PURPOSE

Prostate-specific membrane antigen (PSMA) is an important biomarker for molecular imaging and a target for radionuclide therapy of prostate cancer. Recently, U.S. Food and Drug Administration (FDA) has approved [68Ga]Ga-PSMA-11 as a PSMA-targeted positron emission tomography (PET) imaging agent for the diagnosis of prostate cancer. As an alternative PSMA imaging agent, [68Ga]Ga-P16-093 ([68Ga]Ga-PSMA-093) showed excellent blood clearance and rapid tumor uptake, desirable in vivo properties for avidly detecting primary tumor and metastatic lesions in patients. To improve the availability and test the robustness of radiolabeling reaction, eluents of 68Ga/HCl from different sources of generators were evaluated.

PROCEDURES

Commercially available 68Ge/68Ga generators from Eckert & Ziegler, ITG and iThemba were eluted with varying molarities of hydrochloric acid (0.05-0.6 M, as recommended by each company) and reacted with P16-093 kits. Radiolabeling yields, in vitro stabilities, in vitro cell uptakes and drug release criteria of different preparations were investigated. PET/computed tomography (CT) imaging of prostate cancer patients with [68Ga]Ga-P16-093 produced by using different sources of 68Ga were performed.

RESULTS

Optimized P16-093 kit containing 15 μg of P16-093 (precursor) and 68 mg of sodium acetate trihydrate (buffer), a formulation previously tested in humans, was successfully labeled with eluents from Eckert & Ziegler, ITG and iThemba's generators. In vitro cell uptake studies showed that [68Ga]Ga-P16-093, formulated with ITG and iThemba's generators, exhibited equivalent PSMA-specific uptakes. Clinical studies in prostate cancer patients exhibited exceedingly comparable maximum standardized uptake value (SUVmax) for each lesion regardless of source of the generator used in preparation.

CONCLUSION

Using different vendors' generator and lyophilized P16-093 kits, [68Ga]Ga-P16-093 could be conveniently and reliably prepared by a simple one-step reaction with excellent yields. Clinically useful doses of [68Ga]Ga-P16-093 imaging tracer could be made available using different 68Ge/68Ga generators.

Efficacy and Safety of 225Ac-PSMA-617-Targeted Alpha Therapy in Metastatic Castration-Resistant Prostate Cancer: A Systematic Review and Meta-Analysis

Objective

To conduct a meta-analysis of the efficacy and safety of ²²⁵Ac-PSMA-617 in the treatment of metastatic castration-resistant prostate cancer based on existing clinical evidence.

Methods

Search for retrospective studies about ²²⁵Ac-PSMA-617 in the treatment of metastatic castration-resistant prostate cancer from establishment to July 2021 in PubMed and EMBASE. The primary endpoint was ²²⁵Ac-PSMA-617 biochemical response evaluation criteria after treatment [any prostate specific antigen (PSA) decrease and PSA decrease >50% from baseline] to evaluate the treatment effect. Secondary endpoints included assessment of overall survival (OS), progression-free survival (PFS), molecular response, and toxicity for all studies. Two researchers conducted literature screening, data extraction and quality evaluation according to the inclusion and exclusion criteria. Use stata16.0 software for analysis, fixed-effects model for data merging and forest plots for display.

Results

A total of 6 retrospective studies, namely, 201 patients, were included in the final analysis. The pooled proportions of patients with decreased PSA and PSA decreased by more than 50% were 87.0% (95% confidence interval, 0.820 to 0.920) and 66.1% (95% confidence interval, 0.596 to 0.726), respectively. The pooled proportions of OS and PFS were 12.5 months (95%CI: 6.2–18.8 months) and 9.1 months (95%CI: 2.6–15.7 months). The patients showing molecular responses were 54% (95% confidence interval: 25–84%). In all studies, the most common side effect of ²²⁵Ac-PSMA-617 TAT was xerostomia, with any degree of xerostomia occurring in 77.1% (155 out of 201), and grade III only accounted for 3.0%. The second was 30.3% (61 out of 201) anemia of any degree, and grade III accounts for 7.5% (15 out of 201). Grade III leukopenia and thrombocytopenia were 4.5% (9 out of 201) and 5.5% (11 out of 201), respectively. Only 6 (3.0%) of 201 patients had Grade III nephrotoxicity.

Conclusion

²²⁵Ac-PSMA-617 is an effective and safe treatment option for mCRPC patients, and the toxicity caused by it is relatively low. However, future randomized controlled trials and prospective trials are required in the future to judge the therapeutic effects and survival benefits compared with existing clinical treatments.

Systematic Review Registration

PROSPERO: CRD42021281967.

Novel Selectively Targeted Multifunctional Nanostructured Lipid Carriers for Prostate Cancer Treatment

Prostate cancer (PC) is the most common cancer in men over 50 and the 4th most prevalent human malignancy. PC treatment may include surgery, androgen deprivation therapy, chemotherapy, and radiation therapy. However, the therapeutic efficacy of systemic chemotherapy is limited due to low drug solubility and insufficient tumor specificity, inflicting toxic side effects and frequently provoking the emergence of drug resistance. Towards the efficacious treatment of PC, we herein developed novel selectively PC-targeted nanoparticles (NPs) harboring a cytotoxic drug cargo. This delivery system is based upon PEGylated nanostructured lipid carriers (NLCs), decorated with a selective ligand, targeted to prostate-specific membrane antigen (PSMA). NPs loaded with cabazitaxel (CTX) displayed a remarkable loading capacity of 168 ± 3 mg drug/g SA-PEG, encapsulation efficiency of 67 ± 1%, and an average diameter of 159 ± 3 nm. The time-course of in vitro drug release from NPs revealed a substantial drug retention profile compared to the unencapsulated drug. These NPs were selectively internalized into target PC cells overexpressing PSMA, and displayed a dose-dependent growth inhibition compared to cells devoid of the PSMA receptor. Remarkably, these targeted NPs exhibited growth-inhibitory activity at pM CTX concentrations, being markedly more potent than the free drug. This selectively targeted nano-delivery platform bears the promise of enhanced efficacy and minimal untoward toxicity.

Treatment outcome and identification of factors influencing overall survival after Lu-177-PSMA-617 radioligand therapy in metastatic prostate cancer

OBJECTIVE

To examine the clinical benefit of Lu-177-PSMA-617 radioligand therapy for patients with metastatic castration-resistant prostate cancer (mCRPC).

PATIENTS AND METHODS

Between November 2014 and December 2018, a total of 56 consecutive patients (median age 69.5 years; range 55-84 years) with mCRPC were included in this retrospective analysis. Patients received between 1 and 4 therapy cycles with a mean activity of 6.8 GBq per cycle. Biochemical response was evaluated using Prostate Cancer Working Group Criteria 3 (PCWG 3). Survival was assessed using Kaplan-Meier estimates and Cox proportional hazards regression analysis. This retrospective study was approved by the local ethics committee.

RESULTS

A total of 139 treatment cycles with Lu-177-PSMA-617 were performed. A decline of 50% or more of prostate-specific antigen (PSA) level occurred in 54% and a PSA decline of any amount in 65% of patients. The estimated median overall survival (OS) was 16 months, in the chemotherapy subgroup 14 months. A longer OS was associated with a PSA-decline ≥50%, more than 2 cycles of therapy, cumulative activity >15 GBq and an initial alkaline phosphatase ≤ 220 [U/l]. These identified predictors remained significant on uni- and multivariate Cox regression analysis. Moreover, 40% of the patients who were non-responders after the first therapy cycle turned into responders after the second one.

CONCLUSION

PSA-decline ≥50%, a cumulative activity >15 GBq and an initial alkaline phosphatase ≤ 220 [U/l] were identified as key predictors of prolonged OS in patients with mCRPC. In contrast rapid clinical deterioration mostly due to skeletal carcinomatosis resulted in early treatment failure.

Tumor-Specificity Growth Factor Combined with Tumor Markers in Nuclear Medicine Imaging to Identify Prostate Cancer Osteonosus

Objective

This study has explored the application value of malignant tumor SPE growth factor (TSGF) combined with tumor markers (TM) (TSGF + TM) in nuclear medicine imaging to identify prostate cancer osteonosus (PCO).

Methods

A retrospective analysis for 70 patients with prostate cancer and bone disease admitted to our hospital was performed, 30 healthy persons in the same period were selected as the control group, and the advantages and disadvantages of various examinations were analyzed. All patients were diagnosed with PET whole body bone imaging. Suspicious lesions could be examined by MRI or CT. According to the results of imaging examination, patients were divided into 40 cases of malignant prostate cancer and 30 cases of benign prostate cancer. All the patients underwent 18F-FDG-PET imaging, alpha-fetoprotein (AFP), and TSGF + TM determination. The case diagnosis results were compared and analyzed, and the sensitivity (SEN), specificity (SPE), and accuracy (ACC) of various detection methods were calculated. The SEN, SPE, and ACC of positron emission tomography (PET) were 90.9%, 57.8%, and 81.2%, respectively; those of TM were 79.2%, 94.6%, and 69.8%, respectively; and those of TSGF + TM were 95.9%, 100%, and 97.3%, respectively. The accuracy of combined diagnosis of tumors can reach 100%. The AFP and TSGF levels of serum TM were compared and analyzed, and it was found that the benign lesion group and the malignant lesion group showed significant increases compared with the control group, and the difference between the malignant lesion group and the control group was obvious (P < 0.05). SGF combined with TM could obtain a more definite diagnosis in PCO.

Conclusion

TSGF + TM combined with 18F-FDG-PET imaging showed important clinical value to diagnose the PCO. The imaging accuracy of TSGF + TM combined with 18F-FDG-PET is 97.3%, and the specificity of tumor diagnosis is 100%. Therefore, the TSGF + TM applied in medical imaging and identification of PCO was worthy of clinical promotion.

Theranostic Advances in Breast Cancer in Nuclear Medicine

The implication of 'theranostic' refers to targeting an identical receptor for diagnostic and therapeutic purposes, by the same radioligand, simultaneously or separately. In regard to extensive efforts, many considerable theranostic tracers have been developed in recent years. Emerging evidence strongly demonstrates the tendency of nuclear medicine towards therapies based on a diagnosis. This review is focused on the examples of targeted radiopharmaceuticals for the imaging and therapy of breast cancer.

UpFrontPSMA: a randomized phase 2 study of sequential 177 Lu-PSMA-617 and docetaxel vs docetaxel in metastatic hormone-naïve prostate cancer (clinical trial protocol)

OBJECTIVE

To assess the activity and safety of sequential lutetium-177 (¹⁷⁷ Lu)-PSMA-617 and docetaxel vs docetaxel on a background of androgen deprivation therapy (ADT) in men with de novo metastatic hormone-naïve prostate cancer (mHNPC).

PATIENTS AND METHODS

UpFrontPSMA (NCT04343885) is an open-label, randomized, multicentre, phase 2 trial, recruiting 140 patients at 12 Australian centres. Key eligibility criteria include: prostate cancer with a histological diagnosis within 12 weeks of screening commencement; prostate-specific antigen (PSA) >10 ng/mL at diagnosis; ≤4 weeks on ADT; evidence of metastatic disease on computed tomography (CT) and/or bone scan; high-volume prostate-specific membrane antigen (PSMA)-avid disease with a maximum standardized uptake value >15; and absence of extensive discordant fluorodeoxyglcuose (FDG)-positive, PSMA-negative disease. ⁶⁸ Ga-PSMA-11 and ¹⁸ F-FDG positron-emission tomography (PET)/CT undergo central review to determine eligibility. Patients are randomized 1:1 to experimental treatment, Arm A (¹⁷⁷ Lu-PSMA-617 7.5GBq q6w × 2 cycles followed by docetaxel 75 mg/m² q3w × 6 cycles), or standard-of-care treatment, Arm B (docetaxel 75 mg/m² q3w × 6 cycles). All patients receive continuous ADT. Patients are stratified based on disease volume on conventional imaging and duration of ADT at time of registration. The primary endpoint is the proportion of patients with undetectable PSA (≤0.2 ng/L) at 12 months after study treatment commencement. Secondary endpoints include safety, time to castration resistance, overall survival, PSA and radiographic progression-free survival, objective tumour response rate, early PSMA PET response, health-related quality of life, and frequency and severity of adverse events. Enrolment commenced in April 2020.

RESULTS AND CONCLUSIONS

The results of this trial will generate data on the activity and safety of ¹⁷⁷ Lu-PSMA-617 in men with de novo mHNPC in a randomized phase 2 design.

The CDCP1 Signaling Hub: A Target for Cancer Detection and Therapeutic Intervention

CUB-domain containing protein 1 (CDCP1) is a type I transmembrane glycoprotein that is upregulated in malignancies of the breast, lung, colorectum, ovary, kidney, liver, pancreas, and hematopoietic system. Here, we discuss CDCP1 as an important hub for oncogenic signaling and its key roles in malignant transformation and summarize approaches focused on exploiting it for cancer diagnosis and therapy. Elevated levels of CDCP1 are associated with progressive disease and markedly poorer survival. Predominantly located on the cell surface, CDCP1 lies at the nexus of key tumorigenic and metastatic signaling cascades, including the SRC/PKCδ, PI3K/AKT, WNT, and RAS/ERK axes, the oxidative pentose phosphate pathway, and fatty acid oxidation, making important functional contributions to cancer cell survival and growth, metastasis, and treatment resistance. These findings have stimulated the development of agents that target CDCP1 for detection and treatment of a range of cancers, and results from preclinical models suggest that these approaches could be efficacious and have manageable toxicity profiles.

Optimizing PSMA Radioligand Therapy for Patients with Metastatic Castration-Resistant Prostate Cancer. A Systematic Review and Meta-Analysis

The aim of the review was to evaluate patient and treatment characteristics for patients with metastatic castration-resistant prostate cancer (mCRPC) treated with PSMA radioligand therapy (PRLT) associated with above-average outcome. The systematic review and meta-analysis followed recommendations by the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA). We searched for publications in PubMed, Embase, and ClinicalTrials.gov up to 31 September 2020. Thirty-six publications and four duplicates reported 2346 patients. Nearly two-thirds of the patients had bone metastases. Median overall survival (OS) was 16 months. Asymptomatic patients and patients with only lymph node metastases lived longer than symptomatic patients and patients with more extensive metastases. Patients treated with an intensified schedule of ¹⁷⁷Lu PRLT lived longer than those treated with a conventional schedule. Half of the patients obtained a PSA decline ≥ 50% and these patients lived longer than those with less PSA decline. Approximately 10% of the patients developed hematologic toxicity with anemia grade 3 as the most severe adverse effect. Characteristics for patients, cancer, restaging, and PRLT predict above average overall survival following treatment with PRLT.