Preparation of [(68)Ga]PSMA-11 for PET-CT imaging using a manual synthesis module and organic matrix based (68)Ge/(68)Ga generator

Prostate-Specific Membrane Antigen Targeted StarPEG Nanocarrier for Imaging and Therapy of Prostate Cancer

The tumor uptake of large non-targeted nanocarriers primarily occurs through passive extravasation, known as the enhanced permeability and retention (EPR) effect. Prior studies demonstrated improved tumor uptake and retention of 4-arm 40 kDa star polyethylene glycol (StarPEG) polymers for cancer imaging by adding prostate-specific membrane antigen (PSMA) targeting small molecule ligands. To test PSMA-targeted delivery and therapeutic efficacy, StarPEG nanodrugs with/without three copies of PSMA-targeting ligands, ACUPA, are designed and synthesized. For single-photon emission computed tomography (SPECT) imaging and therapy, each nanocarrier is labeled with 177Lu using DOTA radiometal chelator. The radiolabeled nanodrugs, [177Lu]PEG-(DOTA)1 and [177Lu]PEG-(DOTA)1(ACUPA)3, are evaluated in vitro and in vivo using PSMA+ PC3-Pip and/or PSMA- PC3-Flu cell lines, subcutaneous xenografts and disseminated metastatic models. The nanocarriers are efficiently radiolabeled with 177Lu with molar activities 10.8-15.8 MBq/nmol. Besides excellent in vitro PSMA binding affinity (kD = 51.7 nM), the targeted nanocarrier, [177Lu]PEG-(DOTA)1(ACUPA)3, demonstrated excellent in vivo SPECT imaging contrast with 21.3% ID/g PC3-Pip tumors uptake at 192 h. Single doses of 18.5 MBq [177Lu]PEG-(DOTA)1(ACUPA)3 showed complete resolution of the PC3-Pip xenografts observed up to 138 days. Along with PSMA-targeted excellent imaging contrast, these results demonstrated high treatment efficacy of [177Lu]PEG-(DOTA)1(ACUPA)3 for prostate cancer, with potential for clinical translation.

Prostate-Specific Membrane Antigen Targeted Deep Tumor Penetration of Polymer Nanocarriers

Tumoral uptake of large-size nanoparticles is mediated by the enhanced permeability and retention (EPR) effect, with variable accumulation and heterogenous tumor tissue penetration depending on the tumor phenotype. The performance of nanocarriers via specific targeting has the potential to improve imaging contrast and therapeutic efficacy in vivo with increased deep tissue penetration. To address this hypothesis, we designed and synthesized prostate cancer-targeting starPEG nanocarriers (40 kDa, 15 nm), [89Zr]PEG-(DFB)3(ACUPA)1 and [89Zr]PEG-(DFB)1(ACUPA)3, with one or three prostate-specific membrane antigen (PSMA)-targeting ACUPA ligands. The in vitro PSMA binding affinity and in vivo pharmacokinetics of the targeted nanocarriers were compared with a nontargeted starPEG, [89Zr]PEG-(DFB)4, in PSMA+ PC3-Pip and PSMA- PC3-Flu cells, and xenografts. Increasing the number of ACUPA ligands improved the in vitro binding affinity of PEG-derived polymers to PC3-Pip cells. While both PSMA-targeted nanocarriers significantly improved tissue penetration in PC3-Pip tumors, the multivalent [89Zr]PEG-(DFB)1(ACUPA)3 showed a remarkably higher PC3-Pip/blood ratio and background clearance. In contrast, the nontargeted [89Zr]PEG-(DFB)4 showed low EPR-mediated accumulation with poor tumor tissue penetration. Overall, ACUPA conjugated targeted starPEGs significantly improve tumor retention with deep tumor tissue penetration in low EPR PC3-Pip xenografts. These data suggest that PSMA targeting with multivalent ACUPA ligands may be a generally applicable strategy to increase nanocarrier delivery to prostate cancer. These targeted multivalent nanocarriers with high tumor binding and low healthy tissue retention could be employed in imaging and therapeutic applications.

Synthesis and Preliminary Biological Assessment of Carborane-Loaded Theranostic Nanoparticles to Target Prostate-Specific Membrane Antigen

Boron neutron capture therapy (BNCT) is an encouraging therapeutic modality for cancer treatment. Prostate-specific membrane antigen (PSMA) is a cell membrane protein that is abundantly overexpressed in prostate cancer and can be targeted with radioligand therapies to stimulate clinical responses in patients. In principle, a spatially targeted neutron beam together with specifically targeted PSMA ligands could enable prostate cancer-targeted BNCT. Thus, we developed and tested PSMA-targeted poly(lactide-co-glycolide)-block-poly(ethylene glycol) (PLGA-b-PEG) nanoparticles (NPs) loaded with carborane and tethered to the radiometal chelator deferoxamine B (DFB) for simultaneous positron emission tomography (PET) imaging and selective delivery of boron to prostate cancer. Monomeric PLGA-b-PEGs were covalently functionalized with either DFB or the PSMA ligand ACUPA. Different nanoparticle formulations were generated by nanoemulsification of the corresponding unmodified and DFB- or ACUPA-modified monomers in varying percent fractions. The nanoparticles were efficiently labeled with ⁸⁹Zr and were subjected to in vitro and in vivo evaluation. The optimized DFB(25)ACUPA(75) NPs exhibited strong in vitro binding to PSMA in direct binding and competition radioligand binding assays in PSMA(+) PC3-Pip cells. [⁸⁹Zr]DFB(25) NPs and [⁸⁹Zr]DFB(25)ACUPA(75) NPs were injected to mice with bilateral PSMA(-) PC3-Flu and PSMA(+) PC3-Pip dual xenografts. The NPs demonstrated twofold superior accumulation in PC3-Pip tumors to that of PC3-Flu tumors with a tumor/blood ratio of 25; however, no substantial effect of the ACUPA ligands was detected. Moreover, fast release of carborane from the NPs was observed, resulting in a low boron delivery to tumors in vivo. In summary, these data demonstrate the synthesis, characterization, and initial biological assessment of PSMA-targeted, carborane-loaded PLGA-b-PEG nanoparticles and establish the foundation for future efforts to enable their best use in vivo.

Installation and Optimization of 68Ga Synthesis Module for Clinical Use: An Institutional Experience

Introduction:

With advent of gallium-labeling somatostatin analogs and its evaluation under positron emission tomography–computed tomography, there has been a tremendous surge in its application. Gallium 68 can be made available either from onsite cyclotron production or in the form of ready-to-use ⁶⁸Ge/⁶⁸Ga generators. Wherein setting up and running of cyclotron amounts to huge investment and dedicated team, the ⁶⁸Ge/⁶⁸Ga generator has proved to be a better option and viable project. Moreover, due to long half-life of ⁶⁸Ge, i.e. 271 days, it enables the usage of generator for several months. The preparation of gallium-labeled peptides is much simpler in comparison to 18F radiochemistry, but the radiation exposure has always been an area of concern owing to high-energy annihilation photon of 511 keV.

Materials and Methods:

In this study, we share our experience of self-installation of ⁶⁸Ge/⁶⁸Ga generator during lockdown and the various steps involved in installation of fully automated peptide-labeling system in customized mini hot cell module, synthesis steps, and quality control steps of gallium-based radiopharmaceutical.

Results:

The installation was successfully completed with online assistance during the pandemic situation. The average elution yield met company specification (>80%), and ⁶⁸Ga-labeled peptides were prepared with high radiochemical purity (>95%). The overall exposure in single batch of production and quality control never exceeded 3 μSv as shielding was well-taken care of with customized mini hot cell.

Conclusion:

With the described experience and validation process, one can easily think of making an installation at his/her center and cater to the needs of society with a new radiopharmaceutical.

Physiological PSMA Uptake in the Tubarial Salivary Glands and Its Implications in the PARIS Protocol-A First Study of Its Kind!

OBJECTIVES

Because prostate-specific membrane antigen (PSMA) expression is universal in juvenile nasal angiofibroma (JNA), PSMA PET/CT is commonly used in the postoperative setting using the postoperative angiofibroma radionuclide imaging study protocol. Our study aims to illustrate physiological PSMA ligand uptake distribution characteristics in the salivary glands, specifically the tubarial glands with tumor, to aid in accurate PSMA PET/CT analysis.

STUDY DESIGN

Forty-three consecutive patients who underwent a dedicated head and neck spot PSMA PET/CT for JNA were evaluated retrospectively. PSMA SUVmax values in the tumor, tubarial, parotid, submandibular, and sublingual salivary glands were determined visually and quantitatively.

RESULTS

All the tumors and the salivary glands showed increased tracer uptake. The median SUVmax ± SD ratios of the tumor, right and left tubarial gland, right and left parotid gland, right and left submandibular gland, and right and left sublingual gland were 2.7 ± 0.8 (range, 0.5-7.5), 3.8 ± 1.9 (range, 0.9-8.1), 4.7 ± 2.1 (range, 0.8-7.4), 9.5 ± 4.8 (range, 3.2-21.9), 9.2 ± 4.7 (range, 2.9-18.9), 10.4 ± 5.7 (range, 3.5-25.4), 10.4 ± 5.5 (range, 3.7-26.4), 6 ± 4.1 (range, 1.3-20.6), and 6.5 ± 4.2 (range, 1.8-19.7), respectively. The uptake in the tubarial glands was comparable with that of the tumor but less compared with other major salivary glands.

CONCLUSIONS

Ours is the first study demonstrating the quantitative uptake of tubarial salivary glands in detail. Because the tubarial glands uptake and the anatomical location are similar to that of the tumor, these physiological uptakes must be borne in mind to circumvent false-positive interpretations and care must be given during the planning of stereotactic radiotherapy for JNAs.

PET/CT using 68 Ga-PSMA-617 versus 18 F-fluorodeoxyglucose to differentiate low- and high-grade gliomas

BACKGROUND AND PURPOSE

To compare and characterize metabolic features of high- and low-grade glioma tumors using ⁶⁸ Ga-PSMA-617 and ¹⁸ F-FDG positron emission tomography/computed tomography (PET/CT).

METHODS

Thirty patients who underwent both ⁶⁸ Ga-PSMA-617 and ¹⁸ F-FDG PET/CT over 2 consecutive days and then underwent surgical treatment were retrospectively identified. All tumors were diagnosed histologically. This report includes 16 high-grade glioma (HGG) and 14 low-grade glioma (LGG) tumors. Standard uptake value (SUV) and target to nontarget (T/NT) were quantitatively investigated through the entire tumor region. Statistical analyses were performed using area under the curve (AUC) and comparison of two means.

RESULTS

SUV_max and SUV_mean were the most effective (AUC, 0.96 and 0.94 for PSMA PET; AUC, 0.79 and 0.74 for FDG PET, respectively) for differentiating HGGs from LGGs. These methods distinguished between HGG and LGG effectively (PSMA PET: SUV_max , 5.766 ± 3.945 vs. 0.7364 ± 0.5295, p < 0.0001; SUV_mean , 1.666 ± 1.680 and 0.1514 ± 0.1534, p < 0.0001, respectively) (FDG PET: SUV_max , 11.67 ± 3.639 and 9.118 ± 6.612; SUV_mean , 5.648 ± 2.114 and 4.435 ± 2.872; p = 0.0083, 0.0262, respectively). The Youden index for SUV_max and SUV_mean of ⁶⁸ Ga-PSMA-617 and ¹⁸ F-FDG were 0.82 and 0.79 and 0.54 and 0.61, separately. T/NT_max was helpful for visual inspection of ⁶⁸ Ga-PSMA-617-PET images (T/NT_max : 1.291 ± 0.9553 in grade II, 5.25 ± 2.435 in grade III, and 13.61 ± 13.84 in grade IV). T/NT_max differed significantly between LGG and HGG and between subtypes of LGG.

CONCLUSION

PET/CT with ⁶⁸ Ga-PSMA-617 and ¹⁸ F-FDG may help distinguish between HGG and LGG, and ⁶⁸ Ga-PSMA-617 PET/CT is superior to¹⁸ F-FDG in differentiating HGG and LGG.

Optimized Application of 68Ga-Prostate-Specific Membrane Antigen-617 Whole-Body PET/CT and Pelvic PET/MR in Prostate Cancer Initial Diagnosis and Staging

Purpose: To analyze ⁶⁸Ga-PSMA-617 PET/CT or PET/MR and delayed PET/MR images in patients diagnosed with or suspicion of prostate cancer, and to explore the optimal use of PET/CT and PET/MR for initial diagnosis and staging in prostate cancer.

Methods: Images from conventional scan by ⁶⁸Ga-PSMA whole-body PET/CT or PET/MR followed by delayed pelvic PET/MR were retrospectively analyzed. Prostatic ⁶⁸Ga-PSMA uptake was measured as SUVmax1 (conventional scan 1 h post injection) and SUVmax2 (delayed scan 3 h post injection). Age, PSA levels, and SUVmax were compared between benign and malignant cases. The correlation of SUVmax1 and SUVmax2 was analyzed. Diagnostic performance was evaluated by ROC analysis.

Results: Fifty-six patients with 41 prostate cancers and 15 benign prostate lesions were enrolled. Fifty-three patients had paired conventional and delayed scans. Age, tPSA, fPSA levels, and SUVmax were significantly different between benign and malignant cases. A good correlation was found between SUVmax1 and SUVmax2. There was significant difference between SUVmax1 and SUVmax2 in the malignant group (p = 0.001). SUVmax1 had superior diagnostic performance than SUVmax2, SUVmax difference and PSA levels, with a sensitivity of 85.4%, a specificity of 100% and an AUC of 0.956. A combination of SUVmax1 with nodal and/or distant metastases and MR PI-RADS V2 score had a sensitivity and specificity of 100%. Delayed pelvic PET/MR imaging in 33 patients were found to be redundant because these patients had nodal and/or distant metastases which can be easily detected by PET/CT. PET/MR provided incremental value in 8 patients at early-stage prostate cancer based on precise anatomical localization and changes in lesion signal provided by MR.

Conclusion: Combined ⁶⁸Ga-PSMA whole-body PET/CT and pelvic PET/MR can accurately differentiate benign prostate diseases from prostate cancer and accurately stage prostate cancer. Whole-body PET/CT is sufficient for advanced prostate cancer. Pelvic PET/MR contributes to diagnosis and accurate staging in early prostate cancer. Imaging at about 1 h after injection is sufficient in most patients.

ClinicalTrials.gov: NCT03756077. Registered 27 November 2018—Retrospectively registered, https://clinicaltrials.gov/show/NCT03756077.

Validation of Postoperative Angiofibroma Radionuclide Imaging Study (PARIS) Protocol Using PSMA PET/CT-A Proof of Concept Study

OBJECTIVES

Juvenile nasopharyngeal angiofibroma (JNA) expresses prostate-specific membrane antigen (PSMA), and PSMA PET/CT scan may be used for its imaging. Also, the precise diagnosis of residual/recurrent JNA after surgical treatment remains difficult with conventional contrast MRI and/or CT; functional imaging with PSMA PET/CT promises greater accuracy in the detection or exclusion of recurrent/residual JNA.

PATIENTS AND METHODS

In this prospective study, 22 postoperative JNA patients who underwent a PSMA PET/CT scan both preoperatively and postoperatively from January 2018 to September 2020 were included. All patients underwent a low-dose head and neck spot PET/CT imaging. Abnormal postcontrast enhancement of a definite lesion was considered residual/recurrent tumor in contrast-enhanced MRI (CEMRI). In PSMA PET/CT, any abnormal uptake apart from physiological sites in the head and neck was considered as residual lesions. Radiological results were categorized as negative, suspicious for residual lesions, or definite residual/recurrent tumors. PSMA PET/CT findings were considered as the radiological standard, and patients were managed accordingly. The sensitivity, specificity, positive predictive value, and negative predictive value were separately calculated for CEMRI and PSMA PET/CT for diagnosing residual lesions.

RESULTS

On postoperative CEMRI evaluation, 12 patients had residual tumors, 2 had normal suspicious scans, and 8 had normal postoperative scans. On PSMA PET/CT, only 7 patients had residual tumors and 15 had normal postoperative scans. In 1 patient with a residual tumor on both scans, a discrepancy was noted concerning tumor extent, and PSMA PET/CT accurately mapped the tumor. The sensitivity, specificity, positive predictive value, and negative predictive value of CEMRI were 100%, 53.33%, 41.67%, and 100%, respectively. The sensitivity, specificity, positive predictive value, and negative predictive value of PSMA PET/CT were 100% for all parameters.

CONCLUSIONS

Because CEMRI is oversensitive and less specific compared with PSMA PET/CT, Postoperative Angiofibroma Radionuclide Imaging Study (PARIS) protocol should be used always. In residual tumors, PSMA PET/CT has an outright advantage over CEMRI in the diagnosis, tumor mapping, decision making, planning stereotactic radiation, and aiding in future follow-ups.

Standardization of the [68Ga]Ga-PSMA-11 Radiolabeling Protocol in an Automatic Synthesis Module: Assessments for PET Imaging of Prostate Cancer

Prostate-specific membrane antigen (PSMA) is a glycoprotein present in the prostate, that is overexpressed in prostate cancer (PCa). Recently, PSMA-directed radiopharmaceuticals have been developed, allowing the pinpointing of tumors with the Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT) imaging techniques. The aim of the present work was to standardize and validate an automatic synthesis module-based radiolabeling protocol for [⁶⁸Ga]Ga-PSMA-11, as well as to produce a radiopharmaceutical for PET imaging of PCa malignancies. [⁶⁸Ga]Ga-PSMA-11 was evaluated to determine the radiochemical purity (RCP), stability in saline solution and serum, lipophilicity, affinity to serum proteins, binding and internalization to lymph node carcinoma of the prostate (LNCaP) cells, and ex vivo biodistribution in mice. The radiopharmaceutical was produced with an RCP of 99.06 ± 0.10%, which was assessed with reversed-phase high-performance liquid chromatography (RP-HPLC). The product was stable in saline solution for up to 4 h (RCP > 98%) and in serum for up to 1 h (RCP > 95%). The lipophilicity was determined as -3.80 ± 0.15, while the serum protein binding (SPB) was <17%. The percentages of binding to LNCaP cells were 4.07 ± 0.51% (30 min) and 4.56 ± 0.46% (60 min), while 19.22 ± 2.73% (30 min) and 16.85 ± 1.34% (60 min) of bound material was internalized. High accumulation of [⁶⁸Ga]Ga-PSMA-11 was observed in the kidneys, spleen, and tumor, with a tumor-to-contralateral-muscle ratio of >8.5 and a tumor-to-blood ratio of >3.5. In conclusion, an automatic synthesis module-based radiolabeling protocol for [⁶⁸Ga]Ga-PSMA-11 was standardized and the product was evaluated, thus verifying its characteristics for PET imaging of PCa tumors in a clinical environment.

Automated radiosynthesis of [68 Ga]Ga-PSMA-11 and [177 Lu]Lu-PSMA-617 on the iPHASE MultiSyn module for clinical applications

Prostate-specific membrane antigen (PSMA)-targeted imaging and therapy of prostate cancer using theranostic pairs is rapidly changing clinical practice. To facilitate clinical trials, fully automated procedures for the radiosyntheses of [68 Ga]Ga-PSMA-11 and [177 Lu]Lu-PSMA-617 were developed from commercially available precursors using the cassette based iPHASE MultiSyn module. Formulated and sterile radiopharmaceuticals were obtained in 76 ± 3% (n = 20) and 91 ± 4% (n = 15) radiochemical yields after 17 and 20 min, respectively. Radiochemical purity was always >95% and molar activities exceeded 792 ± 100 and 88 ± 6 GBq/μmol, respectively. Quality control showed conformity with all relevant release criteria and radiopharmaceuticals were used in the clinic.

Lesion-to-background ratio threshold value of SUVmax of simultaneous [68Ga]Ga-PSMA-11 PET/MRI imaging in patients with prostate cancer

Purpose

This study aimed to calculate an applicable relative ratio threshold value instead of the absolute threshold value for simultaneous ⁶⁸Ga prostate-specific membrane antigen/positron emission tomography ([⁶⁸Ga]Ga-PSMA-11 PET) in patients with prostate cancer (PCa).

Materials and methods

Our study evaluated thirty-two patients and 170 focal prostate lesions. Lesions are classified into groups according to Prostate Imaging Reporting and Data System (PI-RADS). Standardized uptake values maximum (SUVmax), corresponding lesion-to-background ratios (LBRs) of SUVmax, and LBR distributions of each group were measured based on regions of interest (ROI). We examined LBR with receiver operating characteristic analysis to determine threshold values for differentiation between multiparametric magnetic resonance imaging (mpMRI)-positive and mpMRI-negative lesions.

Results

We analyzed a total of 170 focal prostate lesions. Lesions number of PI-RADS 2 to 5 was 70, 16, 46, and 38. LBR of SUVmax of each PI-RADS scores was 1.5 (0.9, 2.4), 2.5 (1.6, 3.4), 3.7 (2.6, 4.8), and 6.7 (3.5, 12.7). Based on an optimal threshold ratio of 2.5 to be exceeded, lesions could be classified into MRI-positive lesion on [⁶⁸Ga]Ga-PSMA PET with a sensitivity of 85.2%, a specificity of 72.0%, with the corresponding area under the receiver operating characteristic curve (AUC) of 0.83, p < 0.001. This value matches the imaging findings better.

Conclusion

The ratio threshold value of SUVmax, LBR, has improved clinical and research applicability compared with the absolute value of SUVmax. A higher threshold value than the background’s uptake can dovetail the imaging findings on MRI better. It reduces the bias from using absolute background uptake value as the threshold value.

Correlation between Intraprostatic PSMA Uptake and MRI PI-RADS of [68Ga]Ga-PSMA-11 PET/MRI in Patients with Prostate Cancer: Comparison of PI-RADS Version 2.0 and PI-RADS Version 2.1

PURPOSE

We aimed to evaluate the correlation between PSMA uptake and magnetic resonance imaging (MRI) PI-RADS of simultaneous [68Ga]Ga-PSMA-11 PET/MRI regarding PI-RADS version 2.0 and 2.1 respectively and compared the difference between these two versions.

MATERIALS AND METHODS

We retrospectively analyzed a total of forty-six patients with biopsy-proven prostate cancer who underwent simultaneous [68Ga]Ga-PSMA-11 PET/MRI. We classified the lesions regarding PI-RADS version 2.0 and 2.1, peripheral zone (PZ), and transitional zone (TZ), respectively. Based on regions of interest (ROI), standardized uptake values maximum (SUVmax), and corresponding lesion-to-background ratios (LBR) of SUVmax of each category, PI-RADS score 1 to 5, were measured. A comparison between PI-RADS version 2.0 and PI-RADS version 2.1 was performed.

RESULTS

A total of 215 focal prostate lesions were analyzed, including two subgroups, 125 TZ and 90 PZ. Data are reported as median and interquartile range (IQR). Regarding PI-RADS version 2.1, TZ SUVmax of each category were 1.5 (0.5, 1.9), 1.9 (0.8, 2.3), 3.3 (2.1, 4.6), 4.2 (3.1, 5.7), 7.3 (5.2, 9.7). PZ SUVmax of each category were 1.0 (0.8, 1.6), 2.5 (1.5, 3.2), 3.3 (1.9, 4.5), 4.3 (3.0, 5.4), 7.4 (5.0, 9.3). Regarding the inter-reader agreement of the overall PI-RADS assessment category, the kappa value was 0.723 for version 2.0 and 0.853 for version 2.1.

CONCLUSION

Revisions of PI-RADS version 2.1 results in variations in lesions classification. Lesions with the PI-RADS category of 3, 4, and 5 present relatively higher intraprostatic PSMA uptake, while lesions with the PI-RADS category of 1 and 2 present relatively lower and similar uptake. Version 2.1 has higher inter-reader reproducibility than version 2.0.

Gallium-68 prostate-specific membrane antigen ([68Ga]Ga-PSMA-11) PET for imaging of thyroid cancer: a feasibility study

Background

Prostate-specific membrane antigen (PSMA) is expressed in the microvasculature of thyroid cancer. This suggests the potential use of PSMA as a diagnostic agent in patients with aggressive forms of thyroid cancer. The purpose of the current study was to determine the feasibility and utility of [⁶⁸Ga]Ga-PSMA-11 PET/MRI in thyroid cancer patients.

Methods

Eligible patients for this prospective pilot study were adults with a history of pathology-proven thyroid cancer who had abnormal radiotracer uptake on an 2-[¹⁸F]FDG PET and/or ¹³¹I scintigraphy performed in the 12 months prior to study enrollment. Patients underwent a [⁶⁸Ga]Ga-PSMA-11 PET/MRI, and comparison was made to the prior qualifying 2-[¹⁸F]FDG PET CT/MRI for lesion location and relative intensity.

Results

Twelve patients underwent [⁶⁸Ga]Ga-PSMA-11 PET/MRI, one of which was excluded from analysis due to debulking surgery prior to the PSMA PET. Of the remaining patients, 7/11 had differentiated disease (3 papillary, 2 follicular, 2 Hurthle cell) and 4/11 had dedifferentiated disease (2 poorly differentiated papillary, 2 anaplastic). Out of 43 lesions, 41 were visually 2-[¹⁸F]FDG positive (uptake greater than background, detection rate 95.3%) and 28 were PSMA positive (uptake greater than background, detection rate 65.1%). Uptake was heterogeneous between patients, and in some cases within patients. 3/11 patients (1 poorly differentiated papillary, 2 follicular) had PSMA uptake which was greater than FDG uptake. For the remaining 8 patients, 2-[¹⁸F]FDG uptake was greater than PSMA. Using one eligibility guideline in the prostate cancer literature for PSMA radioligand therapy (RLT), 8/11 could be considered eligible for possible future PSMA RLT. This was not predictable based on thyroid cancer subtype.

Conclusions

[⁶⁸Ga]Ga-PSMA-11 PET demonstrated lower detection rate when compared to 2-[¹⁸F]FDG PET for thyroid cancer lesion visualization. Thyroid cancer subtype alone may not be sufficient to predict PSMA uptake, and radiotracer uptake may vary between patients and even within patients.

Optimization of the radiosynthesis of [68Ga]Ga-PSMA-11 using a Trasis MiniAiO synthesizer: do we need to heat and purify?

INTRODUTION:: [Ga]Ga-prostate specific membrane antigen (PSMA)-11 showed a clear gain in sensitivity for lesion detection in the biological recurrence of prostate cancer as compared to the standard [F]fluorocholine radiopharmaceutical. To meet the strong demand for [Ga]Ga-PSMA-11, we aimed to optimize an automated radiolabeling process by evaluating the influence of different key parameters on radiochemical purity and radiochemical yield.

METHODS

The radiosynthesis of [Ga]Ga PSMA-11 was performed using a Trasis MiniAio synthesizer and a Ge/Ga GalliaPharm generator supplied by Eckert & Ziegler, Berlin, Germany. Optimized labeling parameters were evaluated by variation of sodium acetate concentrations and temperature of radiolabeling as well as the purification process.

RESULTS

For each condition tested, radiochemical purity was higher than 99% in the final vial without batch failure, indicating a robust and fast radiosynthesis process. Radiosynthesis without the solid phase extraction purification process at room temperature in less than 5 min resulted in a radiolabeling efficiency of over 99% and remained stable at least 4 h without manual processing to limit operator radiation exposure.

CONCLUSION

The procedure was completely automated and provided a high radiochemical yield. It can be performed several times a day, facilitating the clinical demand of this radiopharmaceutical.

Synthesis and Initial Biological Evaluation of Boron-Containing Prostate-Specific Membrane Antigen Ligands for Treatment of Prostate Cancer Using Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a therapeutic modality which has been used for the treatment of cancers, including brain and head and neck tumors. For effective treatment via BNCT, efficient and selective delivery of a high boron dose to cancer cells is needed. Prostate-specific membrane antigen (PSMA) is a target for prostate cancer imaging and drug delivery. In this study, we conjugated boronic acid or carborane functional groups to a well-established PSMA inhibitor scaffold to deliver boron to prostate cancer cells and prostate tumor xenograft models. Eight boron-containing PSMA inhibitors were synthesized. All of these compounds showed a strong binding affinity to PSMA in a competition radioligand binding assay (IC₅₀ from 555.7 to 20.3 nM). Three selected compounds 1a, 1d, and 1f were administered to mice, and their in vivo blocking of ⁶⁸Ga-PSMA-11 uptake was demonstrated through a positron emission tomography (PET) imaging and biodistribution experiment. Biodistribution analysis demonstrated boron uptake of 4-7 μg/g in 22Rv1 prostate xenograft tumors and similar tumor/muscle ratios compared to the ratio for the most commonly used BNCT compound, 4-borono-l-phenylalanine (BPA). Taken together, these data suggest a potential role for PSMA targeted BNCT agents in prostate cancer therapy following suitable optimization.

Single-Center Prospective Evaluation of 68Ga-PSMA-11 PET in Biochemical Recurrence of Prostate Cancer

OBJECTIVE. The purpose of this study was to determine the diagnostic accuracy of ⁶⁸Ga-labeled prostate-specific membrane antigen 11 (PSMA-11) PET for disease detection in patients with prostate cancer who have biochemically recurrent disease after radiation therapy or prostatectomy. SUBJECTS AND METHODS. One hundred fifty patients underwent ⁶⁸Ga-PSMA-11 PET/CT or PET/MRI, and the images were interpreted by two blinded board-certified radiologists. Each reader evaluated for the presence or absence of PSMA-positive disease within the prostate bed, pelvic lymph nodes, bones, and soft tissues (extrapelvic lymph nodes and visceral structures). The presence or absence of disease was confirmed by histopathologic analysis if available. For patients who did not have pathologic analysis, a composite of imaging and clinical follow-up was used as the reference standard. RESULTS. The median prostate-specific antigen level was 2.1 ng/mL. Forty-three patients had pathologic correlation, and for 29 patients a composite of imaging and follow-up was used to determine the presence or absence of disease. With substantial to almost perfect interreader reliability by region (κ = 0.78-0.87), ⁶⁸Ga-PSMA-11 PET had high sensitivity per region (up to 100%) and per patient (up to 89.8%). It also had high positive predictive value per region (up to 100%) and per patient (up to 91.5%). Sensitivity was highest for bone metastases and lowest for soft-tissue metastases. Positive predictive value was highest for bone metastases and lowest for prostate bed recurrence. CONCLUSION. Gallium-68-labeled PSMA-11 PET is sensitive for prostate cancer metastases in patients with biochemically recurrent prostate cancer. It has high positive predictive value and substantial to almost perfect interrater reliability.

Diagnostic Accuracy of 68Ga-PSMA-11 PET/MRI Compared with Multiparametric MRI in the Detection of Prostate Cancer

Purpose To compare the diagnostic accuracy of gallium 68 (⁶⁸Ga)-labeled prostate-specific membrane antigen (PSMA)-11 PET/MRI with that of multiparametric MRI in the detection of prostate cancer. Materials and Methods The authors performed a retrospective study of men with biopsy-proven prostate cancer who underwent simultaneous ⁶⁸Ga-PSMA-11 PET/MRI before radical prostatectomy between December 2015 and June 2017. The reference standard was whole-mount pathologic examination. Readers were blinded to radiologic and pathologic findings. Tumor localization was based on 30 anatomic regions. Region-specific sensitivity and specificity were calculated for PET/MRI and multiparametric MRI by using raw stringent and alternative neighboring approaches. Maximum standardized uptake value (SUV_max) in the tumor and Prostate Imaging Reporting and Data System (PI-RADS) version 2 grade were compared with tumor Gleason score. Generalized estimating equations were used to estimate population-averaged sensitivity and specificity and to determine the association between tumor characteristics and SUV_max or PI-RADS score. Results Thirty-two men (median age, 68 years; interquartile range: 62-71 years) were imaged. The region-specific sensitivities of PET/MRI and multiparametric MRI were 74% (95% confidence interval [CI]: 70%, 77%) and 50% (95% CI: 45%, 0.54%), respectively, with the alternative neighboring approach (P < .001 for both) and 73% (95% CI: 68%, 79%) and 69% (95% CI: 62%, 75%), respectively, with the population-averaged generalized estimating equation (P = .04). Region-specific specificity of PET/MRI was similar to that of multiparametric MRI with the alternative neighboring approach (88% [95% CI: 85%, 91%] vs 90% [95% CI: 87%, 92%], P = .99) and in population-averaged estimates (70% [95% CI: 64%, 76%] vs 70% [95% CI: 64%, 75%], P = .99). SUV_max was associated with a Gleason score of 7 and higher (odds ratio: 1.71 [95% CI: 1.27, 2.31], P < .001). Conclusion The sensitivity of gallium 68-labeled prostate-specific membrane antigen-11 PET/MRI in the detection of prostate cancer is better than that of multiparametric MRI. © RSNA, 2018 See also the editorial by Civelek in this issue.

Preparation of 68Ga-PSMA-11 with a Synthesis Module for Micro PET-CT Imaging of PSMA Expression during Prostate Cancer Progression

Objective

To synthesize ⁶⁸Ga-Glu-urea-Lys(Ahx)-HBED-CC (⁶⁸Ga-PSMA-11) with a synthesis module and investigate PET-CT imaging to monitor PSMA expression during prostate cancer (PCa) progression and tumor growth in mice bearing subcutaneous PCa xenografts.

Method

The radiochemical purity and stability of  ⁶⁸Ga-PSMA-11 were determined via radio-HPLC. The PCa cell lines of different PSMA expression levels (PC3, VCAP±, CWR22RV1+, and LNCaP++) were selected to mimic the PCa progression. ⁶⁸Ga-PSMA-11 biodistribution was studied by dissection method and in vivo imaging with micro PET-CT. The expression levels of PSMA in tumor cells and tissues were analyzed by immunofluorescence, flow cytometry, and western blot. The correlation between PSMA expression and radio-uptake was also evaluated. 2-PMPA preadministration served as a block group.

Results

The radiochemical purity of  ⁶⁸Ga-PSMA-11 was 99.6 ± 0.1% and stable in vitro for 2 h. The equilibrium binding constant (Kd) of  ⁶⁸Ga-PSMA-11 to LNCaP, CWR22Rv1, PC-3, and VCAP cells was 4.3 ± 0.8 nM, 16.4 ± 1.3 nM, 225.3 ± 20.8 nM, and 125.6 ± 13.1 nM, respectively. Results of tumor uptake (% ID and % ID/g or % ID/cm³) of  ⁶⁸Ga-PSMA-11 in biodistribution and micro PET imaging were LNCaP > CWR22RV1 > PC-3 and VCAP due to different PSMA expression levels. It was confirmed by flow cytometry, western blot, and immunofluorescence. Tumor uptake (% ID/cm³) of  ⁶⁸Ga-PSMA-11 increased with the tumor anatomical volume in quadratic polynomial fashion and reached the peak (when tumor volume was 0.5 cm³) earlier than tumor uptake (% ID). Tumor uptake (% ID/cm³) of  ⁶⁸Ga-PSMA-11 based on functional volume correlated well with the PSMA expression in a linear manner (y = 9.35x + 2.59, R² = 0.8924, and p < 0.0001); however, low dose 2-PMPA causes rapid renal clearance of increased tumor/kidney uptake of  ⁶⁸Ga-PSMA-11.

Conclusions

The ⁶⁸Ga-PSMA-11 PET-CT imaging could invasively evaluate PSMA expression during PCa progression and tumor growth with % ID/cm³ (based on functional volume) as an important index. Low dose 2-PMPA preadministration might be a choice to decrease kidney uptake of  ⁶⁸Ga-PSMA-11.

Scatter Artifact with Ga-68-PSMA-11 PET: Severity Reduced With Furosemide Diuresis and Improved Scatter Correction

PURPOSE

To assess the utility of furosemide diuresis and the role of an improved scatter correction algorithm in reducing scatter artifact severity on Ga-68- Prostate-specific membrane antigen (PSMA)-11 positron emission tomography (PET).

MATERIALS AND METHODS

A total of 139 patients underwent Ga-68-PSMA-11 PET imaging for prostate cancer: 47 non-time-of-flight (non-TOF) PET/computed tomography, 51 PET/magnetic resonance imaging (MRI) using the standard TOF scatter correction algorithm, and 41 PET/MRI using an improved TOF scatter correction algorithm. Whole-body PET acquisitions were subdivided into 3 regions: around kidneys; between kidneys and bladder; and around bladder. The images were reviewed, and scatter artifact severity was rated using a Likert-type scale.

RESULTS

The worst scatter occurred when using non-TOF scatter correction without furosemide, where 42.1% of patients demonstrated severe scatter artifacts in 1 or more regions. Improved TOF scatter correction resulted in the smallest percentage of studies with severe scatter (6.5%). Scatter ratings by region were lowest using improved TOF scatter correction. Furosemide reduced mean scatter severity when using non-TOF and standard TOF.

CONCLUSIONS

Both furosemide and scatter correction algorithm play a role in reducing scatter in PSMA PET. Improved TOF scatter correction resulted in the lowest scatter severity.

Impact of 68Ga-PSMA-11 PET on Management in Patients with Biochemically Recurrent Prostate Cancer

The purpose of this prospective study was to estimate the effect of ⁶⁸Ga-labeled prostate-specific membrane antigen (PSMA)-11 PET on the intended management of patients with biochemically recurrent prostate cancer. Methods: Pre- and postimaging surveys were filled out by the referring providers for patients with biochemical recurrence who were imaged using ⁶⁸Ga-PSMA-11 PET. The inclusion criterion for this study was a prostate-specific antigen (PSA) doubling time of less than 12 mo after initial treatment (NCT02611882). Of the 150 consecutive patients imaged, 126 surveys were completed (84% response rate). The responses were categorized as major change, minor change, no change, or unknown change. Results: There were 103 patients (82%) with disease detected on ⁶⁸Ga-PSMA-11 PET. On the basis of the survey results, there were 67 patients (53.2%) with major changes in management and 8 patients (6.4%) with minor changes. The proportion of cases resulting in a change in management did not significantly differ by baseline PSA level. In patients with PSA levels below 0.2 ng/dL, 7 of 12 patients had disease detected on ⁶⁸Ga-PSMA-11 PET, 5 of whom had a major change in management. Conclusion:⁶⁸Ga-PSMA-11 PET resulted in a major change in management in 53% of patients with biochemical recurrence. Further studies are warranted to investigate whether PSMA-based management strategies result in improved outcomes for patients.

Diagnostic Value of 68Ga PSMA-11 PET/CT Imaging of Brain Tumors-Preliminary Analysis

OBJECTIVE

To evaluate the feasibility of using Ga PSMA-11 PET/CT for imaging brain lesions and its comparison with F-FDG.

METHODS

Ten patients with brain lesions were included in the study. Five patients were treated cases of glioblastoma with suspected recurrence. F-FDG and Ga PSMA-11 brain scans were done for these patients. Five patients were sent for assessing the nature (primary lesion/metastasis) of space occupying lesion in brain. They underwent whole body F-FDG PET/CT scan and a primary site elsewhere in the body was ruled out. Subsequently they underwent Ga PSMA-11 brain PET/CT imaging. Target to background ratios (TBR) for the brain lesions were calculated using contralateral cerebellar uptake as background.

RESULTS

In five treated cases of glioblastoma with suspected recurrence the findings of Ga PSMA-11 PET/CT showed good correlation with that of F-FDG PET/CT scan. Compared to the F-FDG, Ga PSMA-11 PET/CT showed better visualization of the recurrent lesion (presence/absence) owing to its significantly high TBR. Among the five cases evaluated for lesion characterization glioma and atypical meningioma patients showed higher SUVmax in the lesion with Ga PSMA-11 than with F-FDG and converse in cases of lymphoma. TBR was better with Ga PSMA PET/CT in all cases.

CONCLUSION

Ga PSMA-11 PET/CT brain imaging is a potentially useful imaging tool in the evaluation of brain lesions. Absence of physiological uptake of Ga PSMA-11 in the normal brain parenchyma results in high TBR values and consequently better visualization of metabolically active disease in brain.

Radiolabeled enzyme inhibitors and binding agents targeting PSMA: Effective theranostic tools for imaging and therapy of prostate cancer

Because of the broad incidence, morbidity and mortality associated with prostate-derived cancer, the development of more effective new technologies continues to be an important goal for the accurate detection and treatment of localized prostate cancer, lymphatic involvement and metastases. Prostate-specific membrane antigen (PSMA; Glycoprotein II) is expressed in high levels on prostate-derived cells and is an important target for visualization and treatment of prostate cancer. Radiolabeled peptide targeting technologies have rapidly evolved over the last decade and have focused on the successful development of radiolabeled small molecules that act as inhibitors to the binding of the N-acetyl-l-aspartyl-l-glutamate (NAAG) substrate to the PSMA molecule. A number of radiolabeled PSMA inhibitors have been described in the literature and labeled with SPECT, PET and therapeutic radionuclides. Clinical studies with these agents have demonstrated the improved potential of PSMA-targeted PET imaging agents to detect metastatic prostate cancer in comparison with conventional imaging technologies. Although many of these agents have been evaluated in humans, by far the most extensive clinical literature has described use of the ⁶⁸Ga and ¹⁷⁷Lu agents. This review describes the design and development of these agents, with a focus on the broad clinical introduction of PSMA targeting motifs labeled with ⁶⁸Ga for PET-CT imaging and ¹⁷⁷Lu for therapy. In particular, because of availability from the long-lived ⁶⁸Ge (T_1/2=270days)/⁶⁸Ga (T_1/2=68min) generator system and increasing availability of PET-CT, the ⁶⁸Ga-labeled PSMA targeted agent is receiving widespread interest and is one of the fastest growing radiopharmaceuticals for PET-CT imaging.