The Theranostic PSMA Ligand PSMA-617 in the Diagnosis of Prostate Cancer by PET/CT: Biodistribution in Humans, Radiation Dosimetry, and First Evaluation of Tumor Lesions

Long-axial field-of-view PET/CT: perspectives and review of a revolutionary development in nuclear medicine based on clinical experience in over 7000 patients

Recently introduced long-axial field-of-view (LAFOV) PET/CT systems represent one of the most significant advancements in nuclear medicine since the advent of multi-modality PET/CT imaging. The higher sensitivity exhibited by such systems allow for reductions in applied activity and short duration scans. However, we consider this to be just one small part of the story: Instead, the ability to image the body in its entirety in a single FOV affords insights which standard FOV systems cannot provide. For example, we now have the ability to capture a wider dynamic range of a tracer by imaging it over multiple half-lives without detrimental image noise, to leverage lower radiopharmaceutical doses by using dual-tracer techniques and with improved quantification. The potential for quantitative dynamic whole-body imaging using abbreviated protocols potentially makes these techniques viable for routine clinical use, transforming PET-reporting from a subjective analysis of semi-quantitative maps of radiopharmaceutical uptake at a single time-point to an accurate and quantitative, non-invasive tool to determine human function and physiology and to explore organ interactions and to perform whole-body systems analysis. This article will share the insights obtained from 2 years' of clinical operation of the first Biograph Vision Quadra (Siemens Healthineers) LAFOV system. It will also survey the current state-of-the-art in PET technology. Several technologies are poised to furnish systems with even greater sensitivity and resolution than current systems, potentially with orders of magnitude higher sensitivity. Current barriers which remain to be surmounted, such as data pipelines, patient throughput and the hindrances to implementing kinetic analysis for routine patient care will also be discussed.

Comparison of 68Ga-PSMA-617 PET/CT and 68Ga-RM2 PET/CT in Patients with Localized Prostate Cancer Who Are Candidates for Radical Prostatectomy: A Prospective, Single-Arm, Single-Center, Phase II Study

Considering the wide range of therapeutic options for localized prostate cancer (e.g., active surveillance, radiation-beam therapy, focal therapy, and radical prostatectomy), accurate assessment of the aggressiveness and localization of primary prostate cancer lesions is essential for treatment decision making. National Comprehensive Cancer Network guidelines recognize prostate-specific membrane antigen (PSMA) PET/CT for use in initial staging of high-risk primary prostate cancer. The gastrin-releasing peptide receptor (GRP-R) is a neuropeptide receptor overexpressed by low-risk prostate cancer cells. We aimed to perform the first (to our knowledge) prospective head-to-head comparison of PSMA- and GRP-R-targeted imaging at initial staging to understand how PSMA PET and GRP-R PET can be used or combined in clinical practice. Methods: This was a prospective, single-center, diagnostic cross-sectional imaging study using anonymized, masked, and independent interpretations of paired PET/CT studies in 22 patients with 68Ga-PSMA-617 (a radiolabeled PSMA inhibitor) and 68Ga-RM2 (68Ga-DOTA-4-amino-1-carboxymethylpiperidine-d-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2, a radiolabeled GRP-R antagonist). We enrolled patients with newly diagnosed, biopsy-proven prostate cancer. None had received neoadjuvant hormone therapy or chemotherapy, and all underwent extended pelvic lymph node dissection. Histologic findings served as a reference. Results: On a lesion-based analysis (including lesions < 0.1 cm3), 68Ga-PSMA-617 PET/CT detected 74.3% (26/35) of all tumor lesions and 68Ga-RM2 PET/CT detected 78.1% (25/32; 1 patient could not be offered 68Ga-RM2 PET/CT). Paired examinations showed positive uptake of the 2 tracers in 21 of 32 lesions (65.6%), negative uptake in 5 of 32 lesions (15.6%), and discordant uptake in 6 of 32 lesions (18.8%). Uptake of 68Ga-PSMA-617 was higher when the International Society of Urological Pathology (ISUP) score was at least 4 versus at least 1 (P < 0.0001) or 2 (P = 0.0002). There were no significant differences in uptake between ISUP scores for 68Ga-RM2. Median 68Ga-RM2 SUVmax was significantly higher than median 68Ga-PSMA-617 SUVmax in the ISUP-2 subgroup (P = 0.01). Conclusion: 68Ga-PSMA-617 PET/CT is useful to depict higher, more clinically significant ISUP score lesions, and 68Ga-RM2 PET/CT has a higher detection rate for low-ISUP tumors. Combining PSMA PET and GRP-R PET allows for better classification of intraprostatic lesions.

Preclinical Evaluation of a Fibroblast Activation Protein and a Prostate-Specific Membrane Antigen Dual-Targeted Probe for Noninvasive Prostate Cancer Imaging

Prostate-specific membrane antigen (PSMA) is a prostate cancer target that plays a crucial role in prostate cancer diagnosis and therapy. Herein, a novel dual-targeted imaging probe, [⁶⁸Ga]Ga-FAPI-PSMA, was prepared by radiolabeling conjugated DOTA-FAPI-PSMA with the short half-life radionuclide gallium-68 (⁶⁸Ga), which is dedicated to prostate cancer diagnostic imaging. In vitro, [⁶⁸Ga]Ga-FAPI-PSMA had higher affinity for the PSMA and FAP high-expressing cell lines 22Rv1 and U87 MG with IC₅₀ values of 4.73 and 2.10 nM, respectively, than in the corresponding negative expression cell lines PC₃ and A549, and significant differences in cell uptake were also observed. In vivo, [⁶⁸Ga]Ga-FAPI-PSMA was rapidly cleared from the body, and the estimated radiation dose was relatively low compared with several other FAPI probes. In 22Rv1 and U87 MG tumor xenografts, [⁶⁸Ga]Ga-FAPI-PSMA rapidly accumulated in tumors after administration, and the best images can be obtained at 1 h postinjection. In conclusion, the dual-targeted probe [⁶⁸Ga]Ga-FAPI-PSMA was successfully prepared for in vivo prostate cancer PET/CT imaging.

[Procedure Guideline for Prostate Cancer Imaging with PSMA-ligand PET/CT]

PSMA-PET/CT for imaging prostate cancer (PC) has spread worldwide since its clinical introduction in 2011. The majority of experiences have been collected for PSMA-PET-imaging of recurrent PC. Data for primary staging of high-risk PC are highly promising. Meanwhile, a plethora of PSMA-ligands are available for clinical use (e. g. ⁶⁸Ga-PSMA-11, ⁶⁸Ga-PSMA-I&T, ⁶⁸Ga-PSMA-617, ¹⁸F-DCFBC, ¹⁸F-DCFPyL, ¹⁸F-PSMA-1007, ¹⁸F-rhPSMA-7 and ¹⁸F-JK-PSMA-7). However, an official approval is available only for ⁶⁸Ga-PSMA-11 (approved by the US FDA in 2020) and ¹⁸F-DCFPyL (approved by the US FDA in 2021).Recommendations for acquisition times vary from 1-2 h p. i. It has been shown that for the majority of tumour lesions, the contrast in PSMA-PET/CT increases with time. Therefore, additional late imaging can help to clarify unclear findings. PSMA-PET/CT should be performed prior to commencing an androgen deprivation therapy (ADT) since (long term) ADT reduces the visibility of PC lesions. Following injection of PSMA-ligands, hydration and forced diuresis are recommended for PSMA-ligands with primarily excretion via the kidneys in order to increase the visibility of tumour lesions adjacent to the urinary bladder.PSMA-ligands are physiologically taken up in multiple normal organs. For some ¹⁸F-labelled PSMA-ligands, presence of unspecific focal bone uptake has been reported. When using these tracers, focal bone uptake without CT-correlate should be interpreted with great caution. Besides prostate cancer, practically all solid tumors express PSMA in their neovasculature thereby taking up PSMA-ligands, although usually at a lower extent compared to PC. Also multiple benign lesions and inflammatory processes (e. g. lymph nodes) take up PSMA-ligands, also usually at lower extent compared to PC.

Theranostic 64Cu-DOTHA2-PSMA allows low toxicity radioligand therapy in mice prostate cancer model

Introduction

We have previously shown that copper-64 (⁶⁴Cu)-DOTHA₂-PSMA can be used for positron emission tomography (PET) imaging of prostate cancer. Owing to the long-lasting, high tumoral uptake of ⁶⁴Cu-DOTHA₂-PSMA, the objective of the current study was to evaluate the therapeutic potential of ⁶⁴Cu-DOTHA₂-PSMA in vivo.

Methods

LNCaP tumor-bearing NOD-Rag1^nullIL2rg^null (NRG) mice were treated with an intraveinous single-dose of ⁶⁴Cu-DOTHA₂-PSMA at maximal tolerated injected activity, ^natCu-DOTHA₂-PSMA at equimolar amount (control) or lutetium-177 (¹⁷⁷Lu)-PSMA-617 at 120 MBq to assess their impact on survival. Weight, well-being and tumor size were followed until mice reached 62 days post-injection or ethical limits. Toxicity was assessed through weight, red blood cells (RBCs) counts, pathology and dosimetry calculations.

Results

Survival was longer with ⁶⁴Cu-DOTHA₂-PSMA than with ^natCu-DOTHA₂-PSMA (p < 0.001). Likewise, survival was also longer when compared to ¹⁷⁷Lu-PSMA-617, although it did not reach statistical significance (p = 0.09). RBCs counts remained within normal range for the ⁶⁴Cu-DOTHA₂-PSMA group. ⁶⁴Cu-DOTHA₂-PSMA treated mice showed non-pathological fibrosis and no other signs of radiation injury. Human extrapolation of dosimetry yielded an effective dose of 3.14 × 10^-2 mSv/MBq, with highest organs doses to gastrointestinal tract and liver.

Discussion

Collectively, our data showed that ⁶⁴Cu-DOTHA₂-PSMA-directed radioligand therapy was effective for the treatment of LNCaP tumor-bearing NRG mice with acceptable toxicity and dosimetry. The main potential challenge is the hepatic and gastrointestinal irradiation.

Targeted Radiation and Immune Therapies-Advances and Opportunities for the Treatment of Prostate Cancer

Prostate cancer is the most diagnosed malignancy in men in the United States and the second leading cause of cancer-related death. For localized disease, radiation therapy is a standard treatment that is often curative. For metastatic disease, radiation therapy has been primarily used for palliation, however, several newer systemic radiation therapies have been demonstrated to significantly improve patient outcomes and improve survival. In particular, several targeted radionuclide therapies have been approved for the treatment of advanced-stage cancer, including strontium-89, samarium-153, and radium-223 for bone-metastatic disease, and lutetium-177-labeled PSMA-617 for patients with prostate-specific membrane antigen (PSMA)-expressing metastatic castration-resistant prostate cancer (mCRPC). Contrarily, immune-based treatments have generally demonstrated little activity in advanced prostate cancer, with the exception of the autologous cellular vaccine, sipuleucel-T. This has been attributed to the presence of an immune-suppressive prostate cancer microenvironment. The ability of radiation therapy to not only eradicate tumor cells but also potentially other immune-regulatory cells within the tumor immune microenvironment suggests that targeted radionuclide therapies may be well poised to combine with immune-targeted therapies to eliminate prostate cancer metastases more effectively. This review provides an overview of the recent advances of targeted radiation agents currently approved for prostate cancer, and those being investigated in combination with immunotherapy, and discusses the challenges as well as the opportunities in this field.

Dosimetry estimation and preliminary clinical application of [99mTc]Tc-HYNIC-PSMA-XL-2 in prostate cancer

OBJECTIVE

Molecular imaging of prostate-specific membrane antigen (PSMA) inhibitors has become a favorite for prostate cancer (PCa). This study aimed to estimate the dosimetry and the preliminary clinical application of the [^99mTc]Tc-HYNIC-PSMA-XL-2, which is a novel imaging tracer invented by our team that can specifically targets PSMA for PCa and its metastases.

METHODS

The single-photon emission computed tomography (SPECT) whole-body (WB) planar images were collected on 6 patients at 0.5, 1.0, 2.0, 4.0 and 8.0 h after ^99mTc-PSMA-XL-2 injection, respectively. The SPECT/computed tomography (CT) scan was carried out immediately following the WB planar image scan performed after 2.0 h. The volumes of interest (VOIs) of the bladder, heart wall, intestines, kidneys, liver, lungs, and spleen were segmented in the SPECT/CT images. VOIs of the salivary glands and the whole body were drawn in SPECT planar images. The dosimetry toolkit was used to process the data and project the SPECT/CT images onto planar images. The dosimetry analysis was performed using the IDAC-Dose dosimetry software. Furthermore, other PCa patients were enrolled to study the preliminary clinical application of [^99mTc]Tc-HYNIC-PSMA-XL-2.

RESULTS

The clearance of [^99mTc]Tc-HYNIC-PSMA-XL-2 is primarily by the hepatobiliary and intestinal system, due to its lipophilic characteristic. The effective half-life of [99mTc]Tc-HYNIC-PSMA-XL-2 is about 3.90 h. High absorbed doses were observed in the salivary glands (1.93E-02 ± 3.88E-03 mSv/MBq), kidneys (1.63E-02 ± 7.32E-03 mSv/MBq) and spleen (1.21E-02 ± 2.64E-03 mSv/MBq). The total body effective dose was 4.84E-03 ± 9.30E-05 mSv/MBq. The preliminary clinical case indicated that [^99mTc]Tc-HYNIC-PSMA-XL-2 SPECT/CT could detect the primary prostate lesion, lymph node and bone metastases comprehensively.

CONCLUSION

[^99mTc]Tc-HYNIC-PSMA-XL-2 is a safe SPECT/CT tracer, which can detect prostate malignant lesions without interference from the bladder. In addition, the malignant lesions of the lymph node and bone of PCa patients also can be detected efficiently.

Lutetium-177-PSMA-617: A Vision of the Future

In the last decade, many life-prolonging therapeutic options have emerged for metastatic castration-resistant prostate cancer (mCRPC). The recent VISION trial is the first to demonstrate a survival benefit of Lutetium-177[¹⁷⁷Lu]Lu-PSMA-617 in post-chemotherapy mCRPC. This journal club reviews the VISION trial in the context of the earlier TheraP trial of [¹⁷⁷Lu]Lu-PSMA-617 in mCRPC post docetaxel and androgen pathway inhibition, to provide direction for the real-world application of [¹⁷⁷Lu]Lu-PSMA-617. Treatment in the control groups differed significantly between both trials and may have influenced outcomes: TheraP mandated cabazitaxel whereas VISION’s design could not allow it. In both trials, [¹⁷⁷Lu]Lu-PSMA-617 had a good safety profile, with common adverse events being fatigue, nausea, dry mouth, marrow suppression and diarrhea. Given its efficacy and favorable safety even in heavily pre-treated patients, [¹⁷⁷Lu]Lu-PSMA-617 provides hope to mCRPC patients and may be applied to earlier disease stages in future investigations.

Necessity of Pelvic Lymph Node Irradiation in Patients with Recurrent Prostate Cancer after Radical Prostatectomy in the PSMA PET/CT Era: A Narrative Review

The main prostate cancer (PCa) treatments include surgery or radiotherapy (with or without ADT). However, none of the suggested treatments eliminates the risk of lymph node metastases. Conventional imaging methods, including MRI and CT scanning, are not sensitive enough for the diagnosis of lymph node metastases; however, the novel imaging method, PSMA PET/CT scanning, has provided valuable information about the pelvic LN involvement in patients with recurrent PCa (RPCa) after radical prostatectomy. The high sensitivity and negative predictive value enable accurate N staging in PCa patients. In this narrative review, we summarize the evidence on the treatment and extent of radiation in prostate-only or whole-pelvis radiation in patients with positive and negative LN involvement on PSMA PET/CT scans.

Prostate specific membrane antigen binding radiopharmaceuticals: Current data and new concepts

Prostate specific membrane antigen (PSMA) represents a validated target for prostate cancer therapeutics. The phase III VISION study with ¹⁷⁷lutetium (¹⁷⁷Lu)-PSMA-617 represented a pivotal step forward and the FDA has now approved this agent in advanced metastatic castrate-resistant prostate cancer (mCRPC). A number of other PSMA targeted radiopharmaceuticals are now under development. Some of these agents are targeted to PSMA via monoclonal antibodies such as J591 and TLX591. Others are targeted to PSMA via small molecules such as PSMA-617, PSMA I&T, MIP-1095, etc. In addition to the use of various ligands, multiple isotopes are now in clinical trials. Beta emitters in development include ¹⁷⁷Lu, ¹³¹iodide (¹³¹I), and ⁶⁷copper (⁶⁷Cu). Targeted alpha emitters potentially include ²²⁵actinium (²²⁵Ac), ²²⁷thorium (²²⁷Th), and ²¹²lead (²¹²Pb). Phase III trials are underway with both ¹⁷⁷Lu-PSMA-617 and ¹⁷⁷Lu-PSMA I&T in mCRPC. Single dose phase I trials are complete with ²²⁵Ac-J591 but additional data are need to launch a phase III. Data are promising with ²²⁵Ac-PSMA-617 but concerns remain over salivary and renal toxicity. Tandem therapies are also considered combining both beta and alpha-targeted therapy. Taken together the field of PSMA targeted radiopharmaceuticals is rapidly developing. The targeted alpha therapies are particularly promising and several developmental paths forward are being considered in the near future.

From Concept to Regulatory Drug Approval: Lessons for Theranostics

Radiopharmaceutical therapy is an emerging treatment modality that has demonstrated increasing importance as a significant component in the treatment of cancer. Prostate cancer (PCa) remains one of the commonest solid-organ tumors and is associated with significant societal burdens. Despite significant disease heterogeneity, PCa remains an ideal candidate for radiopharmaceutical therapy because of the prolonged disease course, metastatic disease tropism, and sensitivity to radiation therapy. To date, advanced PCa remains one of the most successful arenas for the development and approval of radiopharmaceutical agents. In this review, we aim to summarize the complex processes required to obtain regulatory approval for a novel agent and highlight the limitations and hurdles specific to the approval of radiopharmaceutical agents. In advanced PCa, we outline the importance of a framework for trial design with respect to defining disease state and acceptable outcome measures-as recommended by the Prostate Cancer Clinical Trials Working Group (PCWG). Finally, using the principles mandated by the Food and Drug Administration approval process and the framework provided by the PCWG, we outline experience with the successful approval of the radiopharmaceutical agents ²²³Ra and ¹⁷⁷Lu-PSMA-617.

Lutetium Lu 177 vipivotide tetraxetan for metastatic castration-resistant prostate cancer

INTRODUCTION

¹⁷⁷Lu-vipivotide tetraxetan is a radiopharmaceutical that selectively targets prostate-specific membrane antigen (PSMA) and delivers beta-radiations to kill prostate cancer cells.

AREAS COVERED

Extensive experience outside the United States as well as randomized phase II and phase III data demonstrate that ¹⁷⁷Lu-vipivotide tetraxetan is a safe, generally well tolerated, and effective therapy for men with mCRPC. ¹⁷⁷Lu-vipivotide tetraxetan was approved by the FDA in March 2022 for the treatment of PSMA-positive metastatic castration-resistant prostate cancer (mCRPC) after androgen receptor pathway inhibition and taxane-based chemotherapy based on the results of the VISION trial.

EXPERT OPINION

This review discusses the development and studies leading to the approval of ¹⁷⁷Lu-vipivotide tetraxetan. In all, ¹⁷⁷Lu-vipivotide tetraxetan is an exciting new tool in the arsenal for men with mCRPC after novel androgen pathway inhibitors and at least one taxane chemotherapy. Optimal selection of patients, sequencing of ¹⁷⁷Lu-vipivotide tetraxetan with the other agents available to treat mCRPC, and the use of dosimetry are current areas of interest with great potential and opportunities for further individual patient optimization using the tools of theranostics.

Comparison of Internal Dosimetry of 18 F-PSMA-1007 and 68 Ga-PSMA-11-HBED-CC

BACKGROUND

Prostate cancer (PCa) is the most common cancer in men worldwide. Targeting prostate-specific membrane antigen (PSMA) using radiopharmaceuticals has shown promising results for PCa imaging as well as theranostics. 68 Ga-based PSMA imaging is limited by production of small quantities by generator, and it has led to quest for cyclotron produced 18 F-based PSMA ligands. In the current study, we evaluated the biodistribution and internal dosimetry of 18 F-PSMA-1007 and compared it with 68 Ga-PSMA-11-HBED-CC.

MATERIALS AND METHODS

A total of 8 patients with histopathologically proven PCa were included in the study, of whom 4 patients underwent 18 F-PSMA-1007, and the other 4 patients underwent 68 Ga-PSMA-11-HBED-CC PET/CT. The biodistribution of both tracers was quantified for different organs by computing SUVs. All the patients underwent 5-point serial imaging to compute equivalent dose to essential organs and whole-body effective dose using OLINDA-based dosimetry.

RESULTS

The radiotracer uptake in brain, lacrimal gland, salivary gland, heart, lung, liver, gallbladder, spleen, pancreas, intestine, gluteal muscle, and bone marrow were found to be higher in 18 F-PSMA-1007 PET as compared with 68 Ga PSMA-11 PET. Kidney and urinary bladder showed higher SUV value on 68 Ga-PSMA-11-HBED-CC as compared with 18 F-PSMA-1007.The whole-body effective dose from 18 F-PSMA-1007 (1.46E-02 mSv/MBq) was higher than 68 Ga-PSMA-11-HBED-CC (1.03E-02 mSv/MBq). The highest mean equivalent dose from 18 F-PSMA-1007 was observed in the kidneys (1.48E-01 mGy/MBq), followed by spleen (mean, 1.06E-01 mGy/MBq) and liver (6.80E-02 mGy/MBq), whereas 68 Ga-PSMA-11-HBED-CC equivalent dose was maximum in the kidneys (2.13E-01 mGy/MBq), followed by liver (3.03E-02 mGy/MBq), spleen (2.90E-02 mGy/MBq), adrenals (2.67E-02 mGy/MBq), and urinary bladder (1.89E-02 mGy/MBq).

CONCLUSION

Whole-body effective dose from 18 F-PSMA-1007 is higher compared with 68 Ga-PSMA-11-HBED-CC. 18 F-PSMA-1007 shows lesser urinary bladder clearance compared with 68 Ga-PSMA-11-HBED-CC, which can allow better interpretation of prostatic bed without significant radioactive urine interference. 18 F-PSMA-1007 is a cyclotron-produced alternative to generator-produced 68 Ga-PSMA-11-HBED-CC and can emerge as a good diagnostic surrogate for patients planned for 177 Lu-PSMA-617 therapy.

[177Lu]Lu-PSMA-617 (PluvictoTM): The First FDA-Approved Radiotherapeutical for Treatment of Prostate Cancer

In March 2022, [¹⁷⁷Lu]Lu-PSMA-617 (Pluvicto^TM) was approved by the FDA for the treatment of prostate cancer patients. Until now, the approval has been limited to patients with PSMA-positive metastatic castration-resistant prostate cancer who have previously received other therapy options (such as inhibition of the androgen receptor pathway and taxane-based chemotherapy). [¹⁷⁷Lu]Lu-PSMA-617, which combines a PSMA-specific peptidomimetic with a therapeutical radionuclide, is used in a radioligand therapy that selectively delivers ionizing radiation to tumor cells, causing their death, while sparing the surrounding healthy tissue. In numerous clinical trials, the efficacy of [¹⁷⁷Lu]Lu-PSMA-617 was demonstrated.

A Review of 177Lutetium-PSMA and 225Actinium-PSMA as Emerging Theranostic Agents in Prostate Cancer

The development of prostate-specific membrane antigen (PSMA) ligands labeled with radionuclides is a ground-breaking achievement in the management of prostate cancer. With the increasing use of ⁶⁸Gallium-PSMA and ¹⁸F-DCFPyL (Pylarify) and their approval by the Food and Drug Administration (FDA), other PSMA agents and their unique characteristics are also being studied. Two other PSMA agents, namely ¹⁷⁷Lutetium-PSMA (¹⁷⁷Lu-PSMA) and ²²⁵Actinium-PSMA (²²⁵Ac-PSMA), are currently drawing the researcher’s attention mainly due to their theranostic importance. Studies focusing on the essential characteristics of these two emerging radiotracers are relatively lacking. Hence, this review article, beginning with a brief introduction, intends to provide insights on the mechanism, efficacy, adverse effects, usefulness, including theranostic implications, and limitations of these two emerging PSMA agents. The ¹⁷⁷Lu-PSMA is commercially accessible, is well tolerated, and has been found to lower prostate-specific antigen (PSA) levels while improving patients’ quality of life. It also reduces pain and the requirement for analgesics and is safe for advanced diseases. However, despite its potential advantages, around one-third of patients do not respond satisfactorily to this costly treatment; it is still challenging to personalize this therapy and predict its outcome. Similarly, ²²⁵Ac is compatible with antibody-based targeting vectors, releasing four extremely hazardous high-energy emissions with a longer half-life of 10 days. It has made ²²⁵Ac-PSMA therapy useful for tumors resistant to standard treatments, with a better response than ¹⁷⁷Lu-PSMA. Dosimetry studies show a good biochemical response without toxicity in patients with advanced metastatic castration-resistant prostate cancer (mCRPC). However, it can potentially cause significant damage to healthy tissues if not retained at the tumor site. Encapsulating radionuclides in a nano-carrier, hastening the absorption by tumor cells, and local delivery might all help reduce the harmful consequences. Both have advantages and disadvantages. The choice of PSMA agents may rely on desired qualities, cost, and convenience, among other factors. Further research is warranted in order to better understand their ideal use in clinical settings.

Determination of pharmacokinetics and tissue distribution of a novel lutetium-labeled PSMA-targeted ligand, 177Lu-DOTA-PSMA-GUL, in rats by using LC–MS/MS

Prostate specific membrane antigen (PSMA) is known to be overexpressed in prostate cancer cells, providing as a diagnostic and therapeutic target for prostate cancer. A lutetium-labeled PSMA targeted ligand, ¹⁷⁷Lu-DOTA-PSMA-GUL is a novel radiopharmaceutical, which has been developed for the treatment of prostate cancer. While the GUL domain of ¹⁷⁷Lu-DOTA-PSMA-GUL binds to the antigen, the beta-emitting radioisotope, ¹⁷⁷Lu-labeled DOTA, interacts with prostate cancer cells. However, the in vivo pharmacokinetics of intact ¹⁷⁷Lu-DOTA-PSMA-GUL has never been characterized. This study aimed to evaluate the pharmacokinetics and tissue distribution of the radiopharmaceutical in rats by using its stable isotope-labeled analog, ¹⁷⁵Lu-DOTA-PSMA-GUL. A sensitive liquid chromatography-tandem mass spectrometry (LC–MS/MS) analysis of ¹⁷⁵Lu-DOTA-PSMA-GUL was developed and validated. Following intravenous injection, the plasma concentration–time profiles of ¹⁷⁵Lu-DOTA-PSMA-GUL showed a multi-exponential decline with the average elimination half-life of 0.30 to 0.33 h. Systemic exposure increased with the dose and renal excretion is the major elimination route. Tissue distribution of ¹⁷⁵Lu-DOTA-PSMA-GUL was most substantial in kidneys, followed by the prostate. The developed LC–MS/MS assay and the in vivo pharmacokinetic data of ¹⁷⁵Lu-DOTA-PSMA-GUL would provide helpful information for further clinical studies to be developed as a novel therapeutic agent for prostate cancer.

A prospective phase II study of prostate-specific antigen-guided salvage radiotherapy and 68Ga-PSMA-PET for biochemical relapse after radical prostatectomy - The PROPER 1 trial

Background and purpose

The treatment of biochemical recurrence (BCR) after prostatectomy is challenging as the site of the recurrence is often undetectable. Our aim was to test a personalised treatment concept for BCR based on PSA kinetics during salvage radiotherapy (SRT) combined with prostate-specific membrane antigen positron emission tomography (PSMA-PET).

Materials and methods

This phase II trial included 100 patients with BCR. PSMA-PET was performed at baseline. PSA was measured weekly during SRT. Initially, 70 Gy in 35 fractions was prescribed to the prostate bed. Radiotherapy was adapted after 50 Gy. Non-responders (PSA still ≥ 0.15 ng/mL) received sequential lymph node irradiation with a boost to PSMA-PET positive lesions, while responders (PSA < 0.15 ng/mL) continued SRT as planned. PET-findings were only taken into consideration for treatment planning in case of PSA non-response after 50 Gy.

Results

Data from 97 patients were eligible for analysis. Thirty-four patients were classified as responders and 63 as non-responders. PSMA-PET was positive in 3 patients (9%) in the responder group and in 22 (35%) in the non-responder group (p = 0.007). The three-year failure-free survival was 94% for responders and 68% for non-responders (median follow-up 38 months). There were no significant differences in physician-reported urinary and bowel toxicity. Patient-reported diarrhoea at end of SRT was more common among non-responders.

Conclusion

This new personalised treatment concept with intensified SRT based on PSA response demonstrated a high tumour control rate in both responders and non-responders. These results suggest a clinically significant effect with moderate side effects in a patient group with otherwise poor prognosis. PSMA-PET added limited value. The treatment approach is now being evaluated in a phase III trial.Clinical trial registration numbers: NCT02699424&ISRCTN45905321.

Phase I Clinical Trial of Prostate-Specific Membrane Antigen-Targeting 68Ga-NGUL PET/CT in Healthy Volunteers and Patients with Prostate Cancer

OBJECTIVE

68Ga-NGUL is a novel prostate-specific membrane antigen (PSMA)-targeting tracer based on Glu-Urea-Lys derivatives conjugated to a 1,4,7-triazacyclononane-N, N', N″-triacetic acid (NOTA) chelator via a thiourea-type short linker. This phase I clinical trial of 68Ga-NGUL was conducted to evaluate the safety and radiation dosimetry of 68Ga-NGUL in healthy volunteers and the lesion detection rate of 68Ga-NGUL in patients with prostate cancer.

MATERIALS AND METHODS

We designed a prospective, open-label, single-arm clinical trial with two cohorts comprising six healthy adult men and six patients with metastatic prostate cancer. Safety and blood test-based toxicities were monitored throughout the study. PET/CT scans were acquired at multiple time points after administering 68Ga-NGUL (2 MBq/kg; 96-165 MBq). In healthy adults, absorbed organ doses and effective doses were calculated using the OLINDA/EXM software. In patients with prostate cancer, the rates of detecting suspicious lesions by 68Ga-NGUL PET/CT and conventional imaging (CT and bone scintigraphy) during the screening period, within one month after recruitment, were compared.

RESULTS

All 12 participants (six healthy adults aged 31-32 years and six prostate cancer patients aged 57-81 years) completed the clinical trial. No drug-related adverse events were observed. In the healthy adult group, 68Ga-NGUL was rapidly distributed, with the highest uptake in the kidneys. The median effective dose coefficient was calculated as 0.025 mSv/MBq, and cumulative activity in the bladder had the highest contribution. In patients with metastatic prostate cancer, 229 suspicious lesions were detected using either 68Ga-NGUL PET/CT or conventional imaging. Among them, 68Ga-NGUL PET/CT detected 199 (86.9%) lesions and CT or bone scintigraphy detected 114 (49.8%) lesions.

CONCLUSION

68Ga-NGUL can be safely applied clinically and has shown a higher detection rate for the localization of metastatic lesions in prostate cancer than conventional imaging. Therefore, 68Ga-NGUL is a valuable option for prostate cancer imaging.

Prostate specific membrane antigen positron emission tomography in primary prostate cancer diagnosis: First-line imaging is afoot

Prostate specific membrane antigen positron emission tomography (PSMA PET) is an excellent molecular imaging technique for prostate cancer. Currently, PSMA PET for patients with primary prostate cancer is supplementary to conventional imaging techniques, according to guidelines. This supplementary function of PSMA PET is due to a lack of systematic review of its strengths, limitations, and potential development direction. Thus, we review PSMA ligands, detection, T, N, and M staging, treatment management, and false results of PSMA PET in clinical studies. We also discuss the strengths and challenges of PSMA PET. PSMA PET can greatly increase the detection rate of prostate cancer and accuracy of T/N/M staging, which facilitates more appropriate treatment for primary prostate cancer. Lastly, we propose that PSMA PET could become the first-line imaging modality for primary prostate cancer, and we describe its potential expanded application.

Optimized 68Ga-Labeled Urea-Based PSMA-Targeted PET Tracers for Prostate Cancer

Prostate-specific membrane antigen (PSMA)-targeting radiopharmaceuticals have become some of the most promising tools for the diagnosis and therapy prostate cancer (PCa). The structure of existing PSMA-targeted PET tracers still needs to be optimized to improve their pharmacokinetic properties and tumor-to-background ratio. In this study, we modified the structure of a well-studied PSMA tracer, and six novel tracers with variable hydrophilicity and pharmacokinetics were developed and evaluated both in vitro and in vivo. All of the novel tracers showed high hydrophilicity (log p = −2.99 ± 0.33 to −3.49 ± 0.01), rapid clearance rates (elimination half-times = 15.55 to 35.97 min), and high affinity for PSMA (Ki = 8.11 ± 0.49 to 42.40 ± 2.11 nM) in vitro. Specific cell binding and micro-PET experiments showed that [⁶⁸Ga]Ga-PSMA-Q displayed the highest specific PSMA+ cell uptake (3.75 ± 0.35 IA%/10⁶ at 60 min), tumor uptake (SUVmax = 0.97 ± 0.24 at 60 min p.i.), and tumor-to-muscle ratio (59.33 ± 5.72 at 60 min p.i.), while the tumor-to-muscle ratio was much higher than that of [⁶⁸Ga]Ga-PSMA-617. The results of this study validate the clinical potential of [⁶⁸Ga]Ga-PSMA-Q for PET imaging and further targeted therapy of prostate cancer.

Refined Chelator Spacer Moieties Ameliorate the Pharmacokinetics of PSMA-617

Prostate-specific membrane antigen (PSMA) binding tracers are promising agents for the targeting of prostate tumors. To further optimize the clinically established radiopharmaceutical PSMA-617, novel PSMA ligands for prostate cancer endoradiotherapy were developed. A series of PSMA binding tracers that comprise a benzyl group at the chelator moiety were obtained by solid-phase synthesis. The compounds were labeled with ⁶⁸Ga or ¹⁷⁷Lu. Competitive cell-binding assays and internalization assays were performed using the cell line C4-2, a subline of the PSMA positive cell line LNCaP (human lymph node carcinoma of the prostate). Positron emission tomography (PET) imaging and biodistribution studies were conducted in a C4-2 tumor bearing BALB/c nu/nu mouse model. All ⁶⁸Ga-labeled ligands were stable in human serum over 2 h; ¹⁷⁷Lu-CA030 was stable over 72 h. The PSMA ligands revealed inhibition potencies [K_i] (equilibrium inhibition constants) between 4.8 and 33.8 nM. The percentage of internalization of the injected activity/10⁶ cells of ⁶⁸Ga-CA028, ⁶⁸Ga-CA029, and ⁶⁸Ga-CA030 was 41.2 ± 2.7, 44.3 ± 3.9, and 53.8 ± 5.4, respectively; for the comparator ⁶⁸Ga-PSMA-617, 15.5 ± 3.1 was determined. Small animal PET imaging of the compounds showed a high tumor-to-background contrast. Organ distribution studies revealed high specific uptake in the tumor, that is, approximately 34.4 ± 9.8% of injected dose per gram (%ID/g) at 1 h post injection for ⁶⁸Ga-CA028. At 1 h p.i., ⁶⁸Ga-CA028 and ⁶⁸Ga-CA030 demonstrated lower kidney uptake than ⁶⁸Ga-PSMA-617, but at later time points, kidney time–activity curves converge. In line with the preclinical data, first diagnostic PET imaging using ⁶⁸Ga-CA028 and ⁶⁸Ga-CA030 revealed high-contrast detection of bone and lymph node lesions in patients with metastatic prostate cancer. The novel PSMA ligands, in particular CA028 and CA030, are promising agents for targeting PSMA-positive tumor lesions as shown in the preclinical evaluation and in a first patient, respectively. Thus, clinical translation of ⁶⁸Ga-CA028 and ⁶⁸Ga/¹⁷⁷Lu-CA030 for diagnostics and endoradiotherapy of prostate cancer in larger cohorts of patients is warranted.

[89Zr]Zr-PSMA-617 PET/CT in biochemical recurrence of prostate cancer: first clinical experience from a pilot study including biodistribution and dose estimates

Purpose

Prostate-specific membrane antigen (PSMA)-targeted PET/CT has become increasingly important in the management of prostate cancer, especially in localization of biochemical recurrence (BCR). PSMA-targeted PET/CT imaging with long-lived radionuclides as ⁸⁹Zr (T_1/2 = 78.4 h) may improve diagnostics by allowing data acquisition on later time points. In this study, we present our first clinical experience including preliminary biodistribution and dosimetry data of [⁸⁹Zr]Zr-PSMA-617 PET/CT in patients with BCR of prostate cancer.

Methods

Seven patients with BCR of prostate cancer who revealed no (n = 4) or undetermined (n = 3) findings on [⁶⁸Ga]Ga-PSMA-11 PET/CT imaging were referred to [⁸⁹Zr]Zr-PSMA-617 PET/CT. PET/CT imaging was performed 1 h, 24 h, 48 h, and 72 h post injection (p.i.) of 111 ± 11 MBq [⁸⁹Zr]Zr-PSMA-617 (mean ± standard deviation). Normal organ distribution and dosimetry were determined. Lesions visually considered as suggestive of prostate cancer were quantitatively analyzed.

Results

Intense physiological uptake was observed in the salivary and lacrimal glands, liver, spleen, kidneys, intestine and urinary tract. The parotid gland received the highest absorbed dose (0.601 ± 0.185 mGy/MBq), followed by the kidneys (0.517 ± 0.125 mGy/MBq). The estimated overall effective dose for the administration of 111 MBq was 10.1 mSv (0.0913 ± 0.0118 mSv/MBq). In 6 patients, and in particular in 3 of 4 patients with negative [⁶⁸Ga]Ga-PSMA-11 PET/CT, at least one prostate cancer lesion was detected in [⁸⁹Zr]Zr-PSMA-617 PET/CT imaging at later time points. The majority of tumor lesions were first visible at 24 h p.i. with continuously increasing tumor-to-background ratio over time. All tumor lesions were detectable at 48 h and 72 h p.i.

Conclusion

[⁸⁹Zr]Zr-PSMA-617 PET/CT imaging is a promising new diagnostic tool with acceptable radiation exposure for patients with prostate cancer especially when [⁶⁸Ga]Ga-PSMA-11 PET/CT imaging fails detecting recurrent disease. The long half-life of ⁸⁹Zr enables late time point imaging (up to 72 h in our study) with increased tracer uptake in tumor lesions and higher tumor-to-background ratios allowing identification of lesions non-visible on [⁶⁸Ga]Ga-PSMA-11 PET/CT imaging.

Antitumor efficacy of 90Y-NM600 targeted radionuclide therapy and PD-1 blockade is limited by regulatory T cells in murine prostate tumors

Background

Systemic radiation treatments that preferentially irradiate cancer cells over normal tissue, known as targeted radionuclide therapy (TRT), have shown significant potential for treating metastatic prostate cancer. Preclinical studies have demonstrated the ability of external beam radiation therapy (EBRT) to sensitize tumors to T cell checkpoint blockade. Combining TRT approaches with immunotherapy may be more feasible than combining with EBRT to treat widely metastatic disease, however the effects of TRT on the prostate tumor microenvironment alone and in combinfation with checkpoint blockade have not yet been studied.

Methods

C57BL/6 mice-bearing TRAMP-C1 tumors and FVB/NJ mice-bearing Myc-CaP tumors were treated with a single intravenous administration of either low-dose or high-dose ⁹⁰Y-NM600 TRT, and with or without anti-PD-1 therapy. Groups of mice were followed for tumor growth while others were used for tissue collection and immunophenotyping of the tumors via flow cytometry.

Results

⁹⁰Y-NM600 TRT was safe at doses that elicited a moderate antitumor response. TRT had multiple effects on the tumor microenvironment including increasing CD8 +T cell infiltration, increasing checkpoint molecule expression on CD8 +T cells, and increasing PD-L1 expression on myeloid cells. However, PD-1 blockade with TRT treatment did not improve antitumor efficacy. Tregs remained functional up to 1 week following TRT, but CD8 +T cells were not, and the suppressive function of Tregs increased when anti-PD-1 was present in in vitro studies. The combination of anti-PD-1 and TRT was only effective in vivo when Tregs were depleted.

Conclusions

Our data suggest that the combination of ⁹⁰Y-NM600 TRT and PD-1 blockade therapy is ineffective in these prostate cancer models due to the activating effect of anti-PD-1 on Tregs. This finding underscores the importance of thorough understanding of the effects of TRT and immunotherapy combinations on the tumor immune microenvironment prior to clinical investigation.

Reconstructed SPECT images of 177Lu homogeneous cylindrical phantom used for calibration and texture analysis

In a clinical contest, it is common to use dedicated phantoms to perform quality assurance test to check the performance of a SPECT system. Some of these phantoms are also used to calibrate the system for dosimetric evaluation of patients undergoing radiometabolic cancer therapy. In this work, a 3D-OSEM reconstructed ¹⁷⁷Lu SPECT dataset of a homogeneous cylindrical phantom is described. This dataset was acquired to investigate the variation of the SPECT calibration factor, counts convergence, noise and uniformity by varying the number of subsets and iterations. In particular, the dataset is composed of images reconstructed using five different numbers of subsets and sixteen different numbers of iterations, for a total of 80 different configurations. The dataset is suitable for comparison with other reconstruction algorithms (e.g. FBP, MLEM, etc.) and radionuclides (e.g. technetium, yttrium). In regards to the uniformity issue, the same dataset allows the user to perform radiomic investigations on the influence of the border effect on the reconstructed images.

Measurement(s)	Calibration Factor • coefficient of variation • Texture Descriptor
Technology Type(s)	Single Photon Emission Computed Tomography • Image Feature

Diagnostic Accuracy of PET/CT or PET/MRI Using PSMA-Targeting Radiopharmaceuticals in High-Grade Gliomas: A Systematic Review and a Bivariate Meta-Analysis

Background: Several studies proposed the use of positron emission tomography (PET) with Prostate Specific Membrane Antigen (PSMA)-targeting radiopharmaceuticals in brain tumors. Our aim is to calculate the diagnostic accuracy of these methods in high-grade gliomas (HGG) with a bivariate meta-analysis. Methods: A comprehensive literature search of studies on the diagnostic accuracy of PET/CT or PET/MRI with PSMA-targeting radiopharmaceuticals in HGG was performed. Original articles evaluating these imaging methods both in the differential diagnosis between HGG and low-grade gliomas (LGG) and in the assessment of suspicious HGG recurrence were included. Pooled sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR-), and diagnostic odds ratio (DOR) including 95% confidence intervals (95% CI) were calculated. Statistical heterogeneity was also assessed using the I² test. Results: The meta-analysis of six selected studies (157 patients) provided the following results about PET/CT or PET/MRI with PSMA-targeting radiopharmaceuticals in the diagnosis of HGG: sensitivity 98.2% (95% CI: 75.3–99.9%), specificity 91.2% (95% CI: 68.4–98.1%), LR+ 4.5 (95% CI: 2.2–9.3), LR− 0.07 (95% CI: 0.04–0.15), and DOR 70.1 (95% CI: 19.6–250.9). No significant statistical heterogeneity among the included studies was found (I² = 0%). Conclusions: the quantitative data provided demonstrate the high diagnostic accuracy of PET/CT or PET/MRI with PSMA-targeting radiopharmaceuticals for HGG detection. However, more studies are needed to confirm the promising role of PSMA-targeted PET in this clinical setting.

A Pilot Study of Dynamic 18F-DCFPyL PET/CT Imaging of Prostate Adenocarcinoma in High-Risk Primary Prostate Cancer Patients

PURPOSE

The primary aim of this study was to investigate the pharmacokinetics of 18F-DCFPyL, an 18F-labeled PSMA-based ligand, and to explore the utility of early time point positron emission tomography (PET) imaging extracted from PET data to distinguish malignant primary prostate from benign prostate tissue.

PROCEDURES

Ten consecutive patients with biopsy-proven high-risk prostate cancer underwent a dynamic 18F-DCFPyL PET/CT scan of the pelvis for the first 45 min post-injection (p.i.) followed by a static PET/CT at 2 h p.i. 18F-DCFPyL uptake values and kinetics were compared between benign prostate tissue and prostate cancer, including quantitative pharmacokinetic PET parameters extracted from 18F-DCFPyL time activity curves generated from dynamic data using a two-tissue compartment model and Patlak plots.

RESULTS

18F-DCFPyL uptake values were significantly higher in primary prostate tumors than those in benign prostatic hyperplasia (BPH) and normal prostate tissue at 5 min, 30 min, and 120 min p.i. (P = 0.0002), when examining both SUVmax and SUVmean values. The two-tissue compartment model found an overall influx value (Ki) of 0.063 in primary prostate cancer, demonstrating a Ki over 15-fold higher in malignant prostate tissue compared with BPH (Ki = 0.004) and normal prostate tissue (Ki = 0.005) (P = 0.0001).

CONCLUSION

High-risk primary prostate cancer is readily identified on dynamic and static, delayed, 18F-DCFPyL PET images. The tumor-to-background ratio increases over time, with optimal 18F-DCFPyL PET/CT imaging at 120 min p.i. for evaluation of prostate cancer, but not necessarily ideal for clinical application. Primary prostate cancer demonstrates different uptake kinetics in comparison to BPH and normal prostate tissue. The 15-fold difference in Ki between prostate cancer and non-cancer (BPH and normal) tissues translates to an ability to distinguish prostate cancer from normal tissue at time points as early as 5 to 10 min p.i.

Diagnostic accuracy of [18F]PSMA-1007 PET/CT in biochemical recurrence of prostate cancer

AIM

Despite increasing use for the detection of biochemically recurrent prostate cancer (rPC), the diagnostic accuracy of positron emission tomography/computed tomography (PET/CT) with [18F]PSMA-1007 remains only partially investigated. The aim of this study was to determine the sensitivity (SE), specificity (SP), positive predictive value (PPV), and negative predictive value (NPV) for PC-local recurrence and metastases on a per region basis.

MATERIALS AND METHODS

One hundred seventy-seven consecutive patients undergoing [18F]PSMA-1007 PET/CT for rPC were retrospectively analysed. Six body regions were defined: prostate fossa, pelvic lymph nodes (LN), retroperitoneal LN, supradiaphragmatic LN, bones, and soft tissue. A region was counted positive if at least one PSMA-positive lesion suspicious for PC was observed. Confirmation of a true-positive PSMA-avid lesion was defined as positive by histopathology, fall in serum prostate-specific antigen (PSA) (> 50%) after targeted therapy or confirmatory further CT, MRI, PET/CT, or bone scan imaging. Regions where additional imaging was able to confirm the absence of suspicious PC lesions or regions outside exclusively targeted RT with serum PSA decline (> 50%) were counted as true-negative regions. SE, SP, PPV, and NPV were calculated for all six regions.

RESULTS

The overall PET-positivity rate was 91%. Conclusive follow-up for affirmation or refutation of a PSMA-positive lesion was available for 81/152 patients on a per region basis. In this subgroup, overall sensitivity, specificity, PPV, and NPV were 95% (CI: 0.90-0.98), 89% (CI: 0.83-0.93), 86% (0.80-0.90), and 96% (CI: 0.92-0.98), respectively. On a per region basis, PPV was 97% (CI: 0.83-0.99) for local recurrence, 93% (CI: 0.78-0.98) for pelvic LN, 87% (CI: 0.62-0.96) for retroperitoneal LN, 82% (CI: 0.52-0.95) for supradiaphragmatic LN, and 79% (0.65-0.89) for bone lesions. The number of solid organ metastases (n = 6) was too small for an accurate statistical analysis.

CONCLUSION

The known high PET-positivity rate of [18F]PSMA-1007 PET/CT in rPC was confirmed, with corresponding high (> 90%) sensitivity and NPV on a per region basis. However, overall PPV was limited (86%), particularly for bone lesions (79%), which are a potential diagnostic weaknesses when using this tracer.

Beyond Surgical Treatment in Adenoid Cystic Carcinoma of the Head and Neck: A Literature Review

Introduction

Adenoid cystic carcinoma (AdCC) is a rare tumour as it accounts for about 10% of all salivary gland neoplasms. It occurs in all age groups with a predominance of women, but no risk factors have been identified to date. Although AdCC behaves as a slow-growing tumour, it is characterized by multiple and late recurrences. Therefore, we aim to update the knowledge of the treatment options in advanced and recurrent cases.

Materials and Methods

We performed a systematic literature review to provide a synthesis of the practical knowledge required for AdCC non-surgical management. Altogether, 99 out of the 1208 available publications were selected for analysis.

Results

AdCC is described as a basaloid tumour consisting of epithelial and myoepithelial cells. Immunohistochemistry is useful for diagnosis (PS100, Vimentin, CD117, CKit, muscle actin, p63) and for prognosis (Ki67). Identified mutations could lead to therapeutic opportunities (MYB-NFIB, Notch 1). The work-up is mainly based on neck and chest CT scan and MRI, and PET-CT with 18-FDG or PSMA can be considered. Surgical treatment remains the gold standard in resectable cases. Post-operative intensity modulated radiotherapy is the standard of care, but hadron therapy may be used in specific situations. Based on the available literature, no standard chemotherapy regimen can be recommended.

Conclusion

There is currently no consensus on the use of chemotherapy in AdCC, either concomitantly to RT in a postoperative setting or at a metastatic stage. Further, the available targeted therapies do not yet provide significant tumour response.

Advances in PSMA theranostics

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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.

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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.

[99mTc]Tc-iFAP Radioligand for SPECT/CT Imaging of the Tumor Microenvironment: Kinetics, Radiation Dosimetry, and Imaging in Patients

Tumor microenvironment fibroblasts overexpress the fibroblast activation protein (FAP). We recently reported the preclinical evaluation of [99mTc]Tc-iFAP as a new SPECT radioligand capable of detecting FAP. This research aimed to evaluate the kinetic and dosimetric profile of [99mTc]Tc-iFAP in healthy volunteers, and to assess the radioligand uptake by different solid tumors in three cancer patients. [99mTc]Tc-iFAP was obtained from lyophilized formulations prepared under GMP conditions with >98% radiochemical purity. Whole-body scans of six healthy subjects were obtained at 0.5, 2, 4, and 24 h after [99mTc]Tc-iFAP (740 MBq) administration. A 2D-planar/3D-SPECT hybrid activity quantitation method was used to fit the biokinetic models of the source organs (volume of interest: VOI) as exponential functions (A(t)VOI). The total nuclear transformations (N) that occurred in the source organs were calculated from the mathematical integration (0,∞) of A(t)VOI. The OLINDA code was used to estimate the radiation doses. Three treatment-naive patients (breast, lung, and cervical cancer) with a prior [18F]FDG PET/CT scan underwent whole-body, chest, and abdominal SPECT/CT scanning after [99mTc]Tc-iFAP (740 MBq) administration. Both imaging methods were compared visually and quantitatively. Oncological diagnoses were performed histopathologically. The results showed favorable [99mTc]Tc-iFAP biodistribution and kinetics due to rapid blood activity removal (t1/2α = 2.22 min and t1/2β = 90 min) and mainly renal clearance. The mean radiation equivalent doses were 5.2 ± 0.8 mSv for the kidney and 1.7 ± 0.3 mSv for the liver after administration of 740 MBq. The effective dose was 2.3 ± 0.4 mSv/740 MBq. [99mTc]Tc-iFAP demonstrated high and reliable uptake in the primary tumor lesions and lymph node metastases in patients with breast, cervical, and lung cancer, which correlated with that detected by [18F]FDG PET/CT. The tumor microenvironment molecular imaging from cancer patients obtained in this research validates the performance of additional clinical studies to determine the utility of [99mTc]Tc-iFAP in the diagnosis and prognosis of different types of solid tumors.

Investigation of Tumor Cells and Receptor-Ligand Simulation Models for the Development of PET Imaging Probes Targeting PSMA and GRPR and a Possible Crosstalk between the Two Receptors

Prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) have both been used in nuclear medicine as targets for molecular imaging and therapy of prostate (PCa) and breast cancer (BCa). Three bioconjugate probes, the PSMA specific: [⁶⁸Ga]Ga-1, ((HBED-CC)-Ahx-Lys-NH-CO-NH Glu or PSMA-11), the GRPR specific: [⁶⁸Ga]Ga-2, ((HBED-CC)-4-amino-1-carboxymethyl piperidine-[D-Phe⁶, Sta¹³]BN(6-14), a bombesin (BN) analogue), and 3 (the BN analogue: 4-amino-1-carboxymethyl piperidine-[(R)-Phe⁶, Sta¹³]BN(6-14) connected with the fluorescent dye, BDP-FL), were synthesized and tested in vitro with PCa and BCa cell lines, more specifically, with PCa cells, PC-3 and LNCaP, with BCa cells, T47D, MDA-MB-231, and with the in-house created PSMA-overexpressing PC-3^(PSMA), T47D^(PSMA), and MDA-MB-231^(PSMA). In addition, biomolecular simulations were conducted on the association of 1 and 2 with PSMA and GRPR. The PSMA overexpression resulted in an increase of cell-bound radioligand [⁶⁸Ga]Ga-1 (PSMA) for PCa and BCa cells and also of [⁶⁸Ga]Ga-2 (GRPR), especially in those cell lines already expressing GRPR. The results were confirmed by fluorescence-activated cell sorting with a PE-labeled PSMA-specific antibody and the fluorescence tracer 3. The docking calculations and molecular dynamics simulations showed how 1 enters the PSMA funnel region and how pharmacophore Glu-urea-Lys interacts with the arginine patch, the S1', and S1 subpockets by forming hydrogen and van der Waals bonds. The chelating moiety of 1, that is, HBED-CC, forms additional stabilizing hydrogen bonding and van der Waals interactions in the arene-binding site. Ligand 2 is diving into the GRPR transmembrane (TM) helical cavity, thereby forming hydrogen bonds through its amidated end, water-mediated hydrogen bonds, and π-π interactions. Our results provide valuable information regarding the molecular mechanisms involved in the interactions of 1 and 2 with PSMA and GRPR, which might be useful for the diagnostic imaging and therapy of PCa and BCa.

Where Do We Stand in the Management of Oligometastatic Prostate Cancer? A Comprehensive Review

Simple Summary

Oligometastatic prostate cancer is an intermediate stage between localised and metastatic disease. Today, there are many advances in the diagnosis of this stage of the disease, with the appearance of new imaging techniques and treatments, thanks to the development of new modalities, both local and systemic therapies, the emergence of personalised medicine, and theragnostics.

Abstract

Oligometastatic prostate cancer (OMPC) is an intermediate state between localised disease and widespread metastases that includes a spectrum of disease biology and clinical behaviours. This narrative review will cover the current OMPC scenario. We conducted comprehensive English language literature research for original and review articles using the Medline database and grey literature through December 2021. OMPC is a unique clinical state with inherently more indolent tumour biology susceptible to multidisciplinary treatment (MDT). With the development of new imaging techniques, patients with OMPC are likely to be identified at an earlier stage, and the paradigm for treatment is shifting towards a more aggressive approach to treating potentially curable patients. Multimodal management is necessary to improve patient outcomes due to the combination of available therapies, such as local therapy of primary tumour, metastasis directed therapy or systemic therapy, to reduce tumour load and prevent further disease progression. Additional prospective data are needed to select patients most likely to benefit from a given therapeutic approach.

Synthesis, preclinical evaluation, and first-in-human study of Al18F-PSMA-Q for prostate cancer imaging

PURPOSE

To investigate the potential of a novel Al¹⁸F-labeled PSMA-targeted radiotracer for PCa diagnosis through both preclinical and pilot clinical studies.

METHODS

Al¹⁸F-PSMA-Q was prepared automatically. The binding affinity to PSMA was evaluated in vitro using the 22Rv1 (PSMA +) and PC-3 (PSMA -) cell lines. Pharmacokinetics evaluation, biodistribution study, Micro-PET imaging of Al¹⁸F-PSMA-Q in normal mice and tumor-bearing mice, and a comparison with ¹⁸F-DCFPyL were performed. PET/CT imaging was performed on 8 healthy volunteers and 20 newly diagnosed PCa patients at 1 h post-injection (p.i.). The biodistribution in human and preliminary diagnostic efficacy of Al¹⁸F-PSMA-Q were evaluated, and the radiation dosimetry was estimated using OLINDA/EXM 2.0 software.

RESULT

Qualified Al¹⁸F-PSMA-Q was efficiently prepared with a non-decay-corrected radiochemical yield (RCY) of 22.0-28.3%, a specific activity (SA) of > 50 GBq/μmol. The hydrophilicity was comparably high with a log P value of - 3.69 ± 0.39. Al¹⁸F-PSMA-Q was found to bind to PSMA specifically with a Ki value of 17.05 ± 1.14 nM. The distribution and elimination half-lives of Al¹⁸F-PSMA-Q were 3.93 min and 14.22 min, respectively, which were shorter than those of ¹⁸F-DCFPyL. Micro-PET imaging of Al¹⁸F-PSMA-Q can clearly differentiate 22Rv1 tumors from PC-3 tumors and background with a high SUVmax of 2.17 ± 0.42 and a tumor-to-muscle ratio of 84.37 ± 31.62, which were higher than those of ¹⁸F-DCFPyL (1.79 ± 0.39 and 13.25 ± 1.65). The uptake of Al¹⁸F-PSMA-Q in 22Rv1 cells and tumors can be substantially blocked by 2-PMPA. High level accumulation of Al¹⁸F-PSMA-Q was observed in organs physiologically expressing PSMA. Twenty-six tumor lesions were detected in 20 PCa patients, and the mean SUVmax values of primary tumors, lymph node metastasis, bone metastases, and tumor-muscle ratios were 19.71 ± 16.52, 5.11, 31.30 ± 29.85, and 44.77 ± 22.29, respectively. The mean SUVmax of tumors in patients with PSA > 10 ng/mL was significantly higher than that in patients with PSA ≤ 10 ng/mL (25.97 ± 18.64 vs. 10.33 ± 3.74). Meanwhile, the mean SUVmax of tumors in patients with a Gleason score ≥ 8 was significantly higher than that in patients with a Gleason score < 8 (31.85 ± 22.09 vs. 13.18 ± 11.58). The kidneys received the highest estimated dose of 0.098 ± 0.006 mGy/MBq, and the effective dose was calculated as 0.0128 ± 0.007 mGy/MBq.

CONCLUSION

The novel qualified PSMA-targeted radiotracer Al¹⁸F-PSMA-Q was conveniently prepared with favorable yield and SA. The results of preclinical and pilot clinical studies exhibited a high specific uptake in PCa lesions and an excellent tumor-to-background ratio with a reasonable radiation exposure, which indicated the great potential of Al¹⁸F-PSMA-Q for PCa imaging.

TRIAL REGISTRATION

Chinese Clinical trial registry ChiCTR2100053507, Registered 23 November 2021, retrospectively registered.

Preliminary Evaluation of 68Ga-P16-093, a PET Radiotracer Targeting Prostate-Specific Membrane Antigen in Prostate Cancer

PURPOSE

Prostate-specific membrane antigen (PSMA) is a promising molecular target for imaging of prostate adenocarcinoma. ⁶⁸Ga-P16-093, a small molecule PSMA ligand, previously showed equivalent diagnostic performance compared to ⁶⁸Ga-PSMA-11 PET/CT in a pilot study of prostate cancer patients with biochemical recurrence (BCR). We performed a pilot study for further characterization of ⁶⁸Ga-P16-093 including comparison to conventional imaging.

PROCEDURES

Patients were enrolled into two cohorts. The biodistribution cohort included 8 treated prostate cancer patients without recurrence, who underwent 6 whole body PET/CT scans with urine sampling for dosimetry using OLINDA/EXM. The dynamic cohort included 15 patients with BCR and 2 patients with primary prostate cancer. Two patients with renal cell carcinoma were also enrolled for exploratory use. A dynamic PET/CT was followed by 2 whole body scans for imaging protocol optimization based on bootstrapped replicates. ⁶⁸Ga-P16-093 PET/CT was compared for diagnostic performance against available ¹⁸F-fluciclovine PET/CT, ^99mTc-MDP scintigraphy, diagnostic CT, and MRI.

RESULTS

⁶⁸Ga-P16-093 deposited similar effective dose (0.024 mSv/MBq) and lower urinary bladder dose (0.064 mSv/MBq) compared to ⁶⁸Ga-PSMA-11. The kidneys were the critical organ (0.290 mSv/MBq). While higher injected activities were preferable, lower injected activities at 74-111 MBq (2-3 mCi) yielded 80% retention in signal-to-noise ratio. The optimal injection-to-scan interval was 60 min, with acceptable delay up to 90 min. ⁶⁸Ga-P16-093 PET/CT showed superior diagnostic performance over conventional imaging with overall patient-level lesion detection rate of 71%, leading to a change in management in 42% of the patients.

CONCLUSIONS

Based on its favorable imaging characteristics and diagnostic performance in prostate cancer, ⁶⁸Ga-P16-093 PET/CT merits further investigation in larger clinical studies.

EANM dosimetry committee recommendations for dosimetry of 177Lu-labelled somatostatin-receptor- and PSMA-targeting ligands

The purpose of the EANM Dosimetry Committee is to provide recommendations and guidance to scientists and clinicians on patient-specific dosimetry. Radiopharmaceuticals labelled with lutetium-177 (177Lu) are increasingly used for therapeutic applications, in particular for the treatment of metastatic neuroendocrine tumours using ligands for somatostatin receptors and prostate adenocarcinoma with small-molecule PSMA-targeting ligands. This paper provides an overview of reported dosimetry data for these therapies and summarises current knowledge about radiation-induced side effects on normal tissues and dose-effect relationships for tumours. Dosimetry methods and data are summarised for kidneys, bone marrow, salivary glands, lacrimal glands, pituitary glands, tumours, and the skin in case of radiopharmaceutical extravasation. Where applicable, taking into account the present status of the field and recent evidence in the literature, guidance is provided. The purpose of these recommendations is to encourage the practice of patient-specific dosimetry in therapy with 177Lu-labelled compounds. The proposed methods should be within the scope of centres offering therapy with 177Lu-labelled ligands for somatostatin receptors or small-molecule PSMA.

High SUVs Have More Robust Repeatability in Patients with Metastatic Prostate Cancer: Results from a Prospective Test-Retest Cohort Imaged with 18F-DCFPyL

Objectives

In patients with prostate cancer (PC) receiving prostate-specific membrane antigen- (PSMA-) targeted radioligand therapy (RLT), higher baseline standardized uptake values (SUVs) are linked to improved outcome. Thus, readers deciding on RLT must have certainty on the repeatability of PSMA uptake metrics. As such, we aimed to evaluate the test-retest repeatability of lesion uptake in a large cohort of patients imaged with ¹⁸F-DCFPyL.

Methods

In this prospective, IRB-approved trial (NCT03793543), 21 patients with history of histologically proven PC underwent two ¹⁸F-DCFPyL PET/CTs within 7 days (mean 3.7, range 1 to 7 days). Lesions in the bone, lymph nodes (LN), and other organs were manually segmented on both scans, and uptake parameters were assessed (maximum (SUV_max) and mean (SUV_mean) SUVs), PSMA-tumor volume (PSMA-TV), and total lesion PSMA (TL-PSMA, defined as PSMA − TV × SUV_mean)). Repeatability was determined using Pearson's correlations, within-subject coefficient of variation (wCOV), and Bland-Altman analysis.

Results

In total, 230 pairs of lesions (177 bone, 38 LN, and 15 other) were delineated, demonstrating a wide range of SUV_max (1.5–80.5) and SUV_mean (1.4–24.8). Including all sites of suspected disease, SUVs had a strong interscan correlation (R² ≥ 0.99), with high repeatability for SUV_mean and SUV_max (wCOV, 7.3% and 12.1%, respectively). High SUVs showed significantly improved wCOV relative to lower SUVs (P < 0.0001), indicating that high SUVs are more repeatable, relative to the magnitude of the underlying SUV. Repeatability for PSMA-TV and TL-PSMA, however, was low (wCOV ≥ 23.5%). Across all metrics for LN and bone lesions, interscan correlation was again strong (R² ≥ 0.98). Moreover, LN-based SUV_mean also achieved the best wCOV (3.8%), which was significantly reduced when compared to osseous lesions (7.8%, P < 0.0001). This was also noted for SUV_max (wCOV, LN 8.8% vs. bone 12.0%, P < 0.03). On a compartment-based level, wCOVs for volumetric features were ≥22.8%, demonstrating no significant differences between LN and bone lesions (PSMA-TV, P =0.63; TL-PSMA, P =0.9). Findings on an entire tumor burden level were also corroborated in a hottest lesion analysis investigating the SUV_max of the most intense lesion per patient (R², 0.99; wCOV, 11.2%).

Conclusion

In this prospective test-retest setting, SUV parameters demonstrated high repeatability, in particular in LNs, while volumetric parameters demonstrated low repeatability. Further, the large number of lesions and wide distribution of SUVs included in this analysis allowed for the demonstration of a dependence of repeatability on SUV, with higher SUVs having more robust repeatability.

A New Class of PSMA-617-Based Hybrid Molecules for Preoperative Imaging and Intraoperative Fluorescence Navigation of Prostate Cancer

The development of PSMA-targeting low-molecular-weight hybrid molecules aims at advancing preoperative imaging and accurate intraoperative fluorescence guidance for improved diagnosis and therapy of prostate cancer. In hybrid probe design, the major challenge is the introduction of a bulky dye to peptidomimetic core structures without affecting tumor-targeting properties and pharmacokinetic profiles. This study developed a novel class of PSMA-targeting hybrid molecules based on the clinically established theranostic agent PSMA-617. The fluorescent dye-bearing candidates of the strategically designed molecule library were evaluated in in vitro assays based on their PSMA-binding affinity and internalization properties to identify the most favorable hybrid molecule composition for the installation of a bulky dye. The library’s best candidate was realized with IRDye800CW providing the lead compound. Glu-urea-Lys-2-Nal-Chx-Lys(IRDye800CW)-DOTA (PSMA-927) was investigated in an in vivo proof-of-concept study, with compelling performance in organ distribution studies, PET/MRI and optical imaging, and with a strong PSMA-specific tumor uptake comparable to that of PSMA-617. This study provides valuable insights about the design of PSMA-targeting low-molecular-weight hybrid molecules, which enable further advances in the field of peptidomimetic hybrid molecule development.

PSMA-Targeting Imaging and Theranostic Agents-Current Status and Future Perspective

In the past two decades, extensive efforts have been made to develop agents targeting prostate-specific membrane antigen (PSMA) for prostate cancer imaging and therapy. To date, represented by two recent approvals of [⁶⁸Ga]Ga-PSMA-11 and [¹⁸F]F-DCFPyL by the United States Food and Drug Administration (US-FDA) for positron emission tomography (PET) imaging to identify suspected metastases or recurrence in patients with prostate cancer, PSMA-targeting imaging and theranostic agents derived from small molecule PSMA inhibitors have advanced to clinical practice and trials of prostate cancer. The focus of current development of new PSMA-targeting agents has thus shifted to the improvement of in vivo pharmacokinetics and higher specific binding affinity with the aims to further increase the detection sensitivity and specificity and minimize the toxicity to non-target tissues, particularly the kidneys. The main strategies involve systematic chemical modifications of the linkage between the targeting moiety and imaging/therapy payloads. In addition to a summary of the development history of PSMA-targeting agents, this review provides an overview of current advances and future promise of PSMA-targeted imaging and theranostics with focuses on the structural determinants of the chemical modification towards the next generation of PSMA-targeting agents.

Radiolabeling of PSMA-617 with 89Zr: A novel use of DMSO to improve radiochemical yield and preliminary small-animal PET results

INTRODUCTION

Novel diagnostic and therapeutic options are urgently needed for patients with metastatic castration-resistant prostate cancer (CRPC). PSMA-617 is one of the most promising ligands that bind to prostate specific membrane antigen (PSMA), the cell surface biomarker of CRPC. Of the radiolabeled PSMA ligands developed to date, [⁶⁸Ga]Ga-PSMA-617 is most commonly used for PSMA positron emission tomography (PET) prior to radioligand therapy (RLT) with [¹⁷⁷Lu]Lu-PSMA-617. However, the presence of ⁶⁸Ga radioactivity (half-life 68 m) in urine at the early PET imaging time point complicates optimization of the therapeutic dose of PSMA-617 labeled with ¹⁷⁷Lu (half-life 6.7 d). Thus, PET imaging with the long-lived positron emitter ⁸⁹Zr (half-life 3.3 d) would be better suited in order to optimize the dose of [¹⁷⁷Lu]Lu-PSMA-617 as ⁸⁹Zr PET allows scans after excretion of the radioactive urine. Until now, PSMA-617 could not be radiolabeled with ⁸⁹Zr with high radiochemical yield due to poor incorporation of ⁸⁹Zr into 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). Here we report a novel method for radiolabeling PSMA-617 with ⁸⁹Zr and the preliminary results of small-animal PET with [⁸⁹Zr]Zr-PSMA-617.

METHODS

We labeled PSMA-617 with ⁸⁹Zr in a 1:1 mixture of DMSO and HEPES buffer at 90 °C for 30 min, followed by quality control analysis by HPLC. We then determined the dissociation constant (K_d) and logD values of [⁸⁹Zr]Zr-PSMA-617. We obtained PET images of [⁸⁹Zr]Zr-PSMA-617 at 24 h in mice bearing both LNCaP (PSMA-positive) and PC-3 (PSMA-negative) tumors (N = 5). The ex vivo [⁸⁹Zr]Zr-PSMA-617 biodistribution was then examined separately using tissue samples of LNCaP-bearing mice at 2 h (N = 4) and 24 h (N = 4).

RESULTS

[⁸⁹Zr]Zr-PSMA-617 was prepared with a radiochemical yield of 70 ± 9%. The K_d value was 6.8 ± 3.5 nM. The logD value was -4.05 ± 0.20. PET images showed the highest uptake in LNCaP tumors (maximum standardized uptake value, SUV_max = 0.98 ± 0.32) and low uptake in kidneys (SUV_max = 0.18 ± 0.7) due to the absence of urine radioactivity.

CONCLUSION

[⁸⁹Zr]Zr-PSMA-617 was successfully prepared using DMSO and HEPES buffer. [⁸⁹Zr]Zr-PSMA-617 visualized PSMA-positive LNCaP tumors in the absence of radioactive urine 24 h p.i.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

This method of radiolabeling PSMA-617 with ⁸⁹Zr using DMSO would be suitable for future clinical trials. Prediction of radiation dose by using [⁸⁹Zr]Zr-PSMA-617 leads to the safe and effective RLT with [¹⁷⁷Lu]Lu-PSMA-617.

Differences in Distribution and Detection Rate of the [68Ga]Ga-PSMA Ligands PSMA-617, -I&T and -11-Inter-Individual Comparison in Patients with Biochemical Relapse of Prostate Cancer

The biochemical relapse of prostate cancer is diagnostically challenging but of high clinical impact for subsequent patient treatment. PET/CT with radiolabeled PSMA ligands outperforms conventional diagnostic methods in the detection of tumor recurrence. Several radiopharmaceuticals were and are available for use. The aim of this study was to investigate whether the routinely applied [⁶⁸Ga]Ga-PSMA ligands PSMA-617, -I&T and -11 (HBED-CC) differ in physiological and pathological distribution, or in tumor detection rate. A retrospective evaluation of 190 patients (39 patients received PSMA-617, 68 patients PSMA-I&T and 83 patients PSMA-11) showed significant differences in tracer accumulation within all organs examined. The low retention within the compartments blood pool, bone and muscle tissue is a theoretical advantage of PSMA-11. Evaluation of tumor lesion uptake and detection rate did not reveal superiority of one of the three radiopharmaceuticals, neither in the whole population, nor in particularly challenging subgroups like patients with very low PSA levels. We conclude that all three [⁶⁸Ga]Ga-PSMA ligands are equally feasible in this clinically important scenario, and may replace each other in case of unavailability or production restrictions.

Radiolabeled PSMA Inhibitors

PSMA has shown to be a promising target for diagnosis and therapy (theranostics) of prostate cancer. We have reviewed developments in the field of radio- and fluorescence-guided surgery and targeted photodynamic therapy as well as multitargeting PSMA inhibitors also addressing albumin, GRPr and integrin αvβ3. An overview of the regulatory status of PSMA-targeting radiopharmaceuticals in the USA and Europe is also provided. Technical and quality aspects of PSMA-targeting radiopharmaceuticals are described and new emerging radiolabeling strategies are discussed. Furthermore, insights are given into the production, application and potential of alternatives beyond the commonly used radionuclides for radiolabeling PSMA inhibitors. An additional refinement of radiopharmaceuticals is required in order to further improve dose-limiting factors, such as nephrotoxicity and salivary gland uptake during endoradiotherapy. The improvement of patient treatment achieved by the advantageous combination of radionuclide therapy with alternative therapies is also a special focus of this review.

Patient-Specific Dosimetry in Radioligand Therapy (RLT) for Metastatic Prostate Cancer Using 177Lu-DKFZ-PSMA-617

Purpose

¹⁷⁷Lu-DKFZ-PSMA-617 is a promising treatment for patients with metastatic prostate cancer. Specific dosimetry for each patient is an important factor in planning the patient's treatment process. This study aimed to perform an image-based absorbed dose calculation for the treatment of metastatic prostate cancer with ¹⁷⁷Lu-DKFZ-PSMA-617.

Methods

The individualized patient dosimetry calculations were based on whole-body planar scintigraphy images acquired in 10 patients with a mean age of 71.4 ± 6.07 years (range 63-85 years) at approximately 0-2 h, 4-6 h, 18-24 h, and 36-48 h after administration of the mean 6253 ± 826.4 MBq (range 5500-7400 MBq) of ¹⁷⁷Lu-DKFZ-PSMA-617. Time-activity curves were generated for various organs. For count conversion to activities, calibration factors were calculated. Finally, the absorbed dose for an individual cycle was calculated using IDIAC-DOSE 2.1 software.

Results

On average, the calculated absorbed dose for the kidneys and salivary glands were 0.46 ± 0.09 mGy/MBq and 0.62 ± 0.07 mGy/MBq, respectively.

Conclusions

Based on the results, the¹⁷⁷Lu-PSMA-617 therapy is a safe method for the treatment of castration-resistant prostate cancer patients. Large inter-individual variations in organ dose were found, demonstrating the need for patient-specific dosimetry and treatment planning.

Intraindividual comparison of [68 Ga]-Ga-PSMA-11 and [18F]-F-PSMA-1007 in prostate cancer patients: a retrospective single-center analysis

BACKGROUND

The analysis aimed to compare the radiotracers [⁶⁸Ga]-Ga-PSMA-11 and [¹⁸F]-F-PSMA-1007 intraindividually in terms of malignant lesions, mi(molecular-imaging)TNM staging and presumable unspecific lesions retrospectively as used in routine clinical practice.

METHODS

A retrospective analysis of 46 prostate cancer patients (median age: 71 years) who underwent consecutive [⁶⁸Ga]-Ga-PSMA-11- and [¹⁸F]-F-PSMA-1007-PET/CT or PET/MRI within a mean of 12 ± 8.0 days was performed. MiTNM staging was performed in both studies by two nuclear medicine physicians who were blinded to the results of the other tracer. After intradisciplinary and interdisciplinary consensus with two radiologists was reached, differences in both malignant and presumable nonspecific tracer accumulation were analyzed.

RESULTS

Differences in terms of miTNM stages in both studies occurred in nine of the 46 patients (19.6%). The miT stages differed in five patients (10.9%), the miN stages differed in three patients (6.5%), and different miM stages occurred only in one patient who was upstaged in [¹⁸F]-F-PSMA-1007 PET. Concordant miTNM stages were obtained in 37 patients (80.4%). There was no significant difference between [¹⁸F]-F-PSMA-1007 and [⁶⁸Ga]-Ga-PSMA-11 in the SUV_max locally (31.5 vs. 32.7; p = 0.658), in lymph node metastases (28.9 vs. 24.9; p = 0.30) or in bone metastases (22.9 vs. 27.6; p = 0.286). In [¹⁸F]-F-PSMA-1007 PET, more patients featured presumable unspecific uptake in the lymph nodes (52.2% vs. 28.3%; p: < 0.001), bones (71.7% vs. 23.9%; p < 0.001) and ganglia (71.7% vs. 43.5%; p < 0.001). Probable unspecific, exclusively [¹⁸F]-F-PSMA-1007-positive lesions mainly occurred in the ribs (58.7%), axillary lymph nodes (39.1%) and cervical ganglia (28.3%).

CONCLUSION

In terms of miTNM staging, both tracers appeared widely exchangeable, as no tracer relevantly outperformed the other. The differences between the two tracers were far more common in presumable unspecific lesions than in malignant spots. A routinely performed two-tracer study could not be shown to be superior. Since it seems at least challenging for most nuclear medicine departments to provide both [¹⁸F]-F-PSMA-1007 and [⁶⁸Ga]-Ga-PSMA-11, it appears reasonable to choose the PSMA radiotracer depending on local availability with attention to the greater occurrence of nonspecific bone findings with [¹⁸F]-F-PSMA-1007.