177Lu-Labeled Bivalent Ligands of Prostate-Specific Membrane Antigen for Endoradiotherapy of Prostate Cancer.

Recently, we developed a bivalent prostate-specific membrane antigen (PSMA) radioligand ([18F]AlF-Bi-PSMA), which showed higher tumor uptake and retention in PSMA-positive mouse models than the clinically used radioligands, [68Ga]Ga-PSMA-11 and [18F]PSMA-1007. Here, we developed two 177Lu-labeled bivalent PSMA ligands with (DOTA-Alb-Bi-PSMA) or without an albumin-binding motif (DOTA-Bi-PSMA) to enhance radiotherapeutic efficacy with minimal toxicity. The results demonstrated that both 177Lu-labeled bivalent radioligands showed good stability, high binding affinity, and PSMA-targeting specificity in vitro. Compared with [177Lu]Lu-PSMA-617, both [177Lu]Lu-Bi-PSMA and [177Lu]Lu-Alb-Bi-PSMA showed a higher area under the curve (AUC) of tumor accumulation and superior therapeutic efficacy. However, [177Lu]Lu-Alb-Bi-PSMA exhibited a dose-dependent increase in acute damage to kidneys. In terms of the radionuclide therapy efficacy and side effects, [177Lu]Lu-Bi-PSMA exhibited well-balanced action with high tumor-to-organs AUC ratios, resulting in remarkable therapeutic efficacy and negligible side effects. These promising results warrant further investigations to achieve the clinical translation of [177Lu]Lu-Bi-PSMA.

The Dedicated Imaging Post-Prostatectomy for Enhanced Radiotherapy outcomes (DIPPER) trial protocol: a multicentre, randomised trial of salvage radiotherapy versus surveillance for low-risk biochemical recurrence after radical prostatectomy.

BACKGROUND: Salvage radiation therapy (SRT) and surveillance for low-risk prostate-specific antigen (PSA) recurrence have competing risks and benefits. The efficacy of early SRT to the prostate bed with or without pelvic lymph nodes compared to surveillance in patients with PSA recurrence after radical prostatectomy and no identifiable recurrent disease evident on prostate specific membrane antigen-positron emission tomography/computer tomography (PSMA-PET/CT) is unknown. STUDY DESIGN: The Dedicated Imaging Post-Prostatectomy for Enhanced Radiotherapy outcomes (DIPPER) is an open-label, multicentre, randomised Phase II trial. ENDPOINTS: The primary endpoint is 3-year event-free survival, with events comprising one of PSA recurrence (PSA ≥0.2 ng/mL higher than baseline), radiological evidence of metastatic disease, or initiation of systemic or other salvage treatments. Secondary endpoints include patient-reported outcomes, treatment patterns, participant perceptions, and cost-effectiveness. ELIGIBILITY CRITERIA: Eligible participants have PSA recurrence of prostate cancer after radical prostatectomy, defined by serum PSA level of 0.2-0.5 ng/mL, deemed low risk according to modified European Association of Urology biochemical recurrence risk criteria (International Society for Urological Pathology Grade Group ≤2, PSA doubling time >12 months), with no definite/probable recurrent prostate cancer on PSMA-PET/CT. PATIENTS AND METHODS: A total of 100 participants will be recruited from five Australian centres and randomised 1:1 to SRT or surveillance. Participants will undergo 6-monthly clinical evaluation for up to 36 months. Androgen-deprivation therapy is not permissible. Enrolment commenced May 2023. TRIAL REGISTRATION: This trial has been registered with the Australian New Zealand Clinical Trials Registry (ACTRN: ACTRN12622001478707).

Inhibition of Poly(ADP-ribose) Polymerase Sensitizes [177Lu]Lu-DOTAGA.(SA.FAPi)2-Mediated Radiotherapy in Triple-Negative Breast Cancer.

Fibroblast activation protein (FAP) is highly expressed in many tumor types and constitutes a promising target for tumor-specific delivery of therapeutic radionuclides. [177Lu]Lu-DOTAGA.(SA.FAPi)2 is a novel radiopharmaceutical based on a novel bidentate inhibitor of FAP that is excreted more slowly than its monomeric counterparts. Still, the efficacy of radiotherapy is mitigated by cascades of DNA damage repair signaling in tumor cells including those via Poly(ADP-ribose) polymerase (PARP). We hereby aimed to evaluate the efficacy of [177Lu]Lu-DOTAGA.(SA.FAPi)2 in combination with a PARP inhibitor, Olaparib, in the 4T1 murine triple negative breast cancer (TNBC) model. The therapeutic efficacy was visualized using 18F-FDG and [68Ga]Ga-FAPI-04 positron emission imaging/computer tomography (PET/CT). Our results demonstrated that Olaparib suppressed BALB/3T3 fibroblasts in vitro and sensitized the efficacy of [177Lu]Lu-DOTAGA.(SA.FAPi)2 in mice bearing 4T1 tumors via enhancement of DNA damage. Treatment-associated toxicity was tolerable with only mild leukopenia. Therefore, the combination of [177Lu]Lu-DOTAGA.(SA.FAPi)2 and Olaparib is a feasible treatment against TNBC.

Clinical utility of 67 Gallium-SPECT/CT for determining osteotomy indication in patients with lower-limb osteomyelitis.

Standard non-invasive methods for diagnosing and selecting the best treatment for osteomyelitis in patients with multiple chronic conditions remain to be established. We aimed to evaluate the ability of quantitative 67 Ga-citrate single-photon emission computed tomography (67 Ga-SPECT/CT) to determine the indication for either non-surgical treatment or osteotomy in patients with lower-limb osteomyelitis (LLOM) associated with diabetes mellitus and lower-extremity ischemia, based on monitoring of inflammatory activity in bone tissue. This single-centre prospective study conducted from January 2012 to July 2017 included 90 consecutive patients with suspected LLOM. Regions of interest were drawn on SPECT images during quantification of Ga accumulation. Subsequently, the inflammation-to-background ratio (IBR) was calculated by dividing the maximal accumulated lesion number by the mean number for the distal femur bone marrow of the unaffected side. Osteotomy was performed in 28 of 90 patients (31%). The osteotomy rate was higher for patients with IBR >8.4 (71.4%) than for those with IBR ≤8.4 (5.5%) (p < 0.001, sensitivity: 0.89, specificity: 0.84). In the multivariate Cox regression analysis, IBR >8.4 was an independent risk factor for osteotomy (hazard ratio [HR]: 19.0, 95% confident interval [CI]: 5.6-63.9, p < 0.001). Transcutaneous oxygen tension (TcPO2 ) was identified as an independent risk factor for lower-limb amputation (HR: 0.96, 95% CI: 0.92-0.99, p = 0.01). The current results indicate that quantitative 67 Ga-SPECT/CT is useful for distinguishing patients with LLOM likely to require osteotomy.

In Vivo Trafficking of the Anticancer Drug Tris(8-Quinolinolato) Gallium (III) (KP46) by Gallium-68/67 PET/SPECT Imaging.

KP46 (tris(hydroxyquinolinato)gallium(III)) is an experimental, orally administered anticancer drug. Its absorption, delivery to tumours, and mode of action are poorly understood. We aimed to gain insight into these issues using gallium-67 and gallium-68 as radiotracers with SPECT and PET imaging in mice. [67Ga]KP46 and [68Ga]KP46, compared with [68Ga]gallium acetate, were used for logP measurements, in vitro cell uptake studies in A375 melanoma cells, and in vivo imaging in mice bearing A375 tumour xenografts up to 48 h after intravenous (tracer level) and oral (tracer and bulk) administration. 68Ga was more efficiently accumulated in A375 cells in vitro when presented as [68Ga]KP46 than as [68Ga]gallium acetate, but the reverse was observed when intravenously administered in vivo. After oral administration of [68/67Ga]KP46, absorption of 68Ga and 67Ga from the GI tract and delivery to tumours were poor, with the majority excreted in faeces. By 48 h, low but measurable amounts were accumulated in tumours. The distribution in tissues of absorbed radiogallium and octanol extraction of tissues suggested trafficking as free gallium rather than as KP46. We conclude that KP46 likely acts as a slow releaser of gallium ions which are inefficiently absorbed from the GI tract and trafficked to tissues, including tumour and bone.

Fibroblast activation protein identifies Consensus Molecular Subtype 4 in colorectal cancer and allows its detection by 68Ga-FAPI-PET imaging.

BACKGROUND: In colorectal cancer (CRC), the consensus molecular subtype 4 (CMS4) is associated with therapy resistance and poor prognosis. Clinical diagnosis of CMS4 is hampered by locoregional and temporal variables influencing CMS classification. Diagnostic tools that comprehensively detect CMS4 are therefore urgently needed. METHODS: To identify targets for molecular CMS4 imaging, RNA sequencing data of 3232 primary CRC patients were explored. Heterogeneity of marker expression in relation to CMS4 status was assessed by analysing 3-5 tumour regions and 91.103 single-tumour cells (7 and 29 tumours, respectively). Candidate marker expression was validated in CMS4 peritoneal metastases (PM; n = 59). Molecular imaging was performed using the 68Ga-DOTA-FAPI-46 PET tracer. RESULTS: Fibroblast activation protein (FAP) mRNA identified CMS4 with very high sensitivity and specificity (AUROC > 0.91), and was associated with significantly shorter relapse-free survival (P = 0.0038). Heterogeneous expression of FAP among and within tumour lesions correlated with CMS4 heterogeneity (AUROC = 1.00). FAP expression was homogeneously high in PM, a near-homogeneous CMS4 entity. FAPI-PET identified focal and diffuse PM that were missed using conventional imaging. Extra-peritoneal metastases displayed extensive heterogeneity of tracer uptake. CONCLUSION: FAP expression identifies CMS4 CRC. FAPI-PET may have value in the comprehensive detection of CMS4 tumours in CRC. This is especially relevant in patients with PM, for whom effective imaging tools are currently lacking.

The Triple-Tracer strategy against Metastatic PrOstate cancer (3TMPO) study protocol.

OBJECTIVE: To determine the prevalence of intra-patient inter-metastatic heterogeneity based on positron emission tomography (PET)/computed tomography (CT) in patients with metastatic castration-resistant prostate cancer (mCRPC) and to determine the prevalence of neuroendocrine disease in these patients and their eligibility for radioligand therapies (RLTs). PATIENTS AND METHODS: This multicentre observational prospective clinical study will include 100 patients with mCRPC from five Canadian academic centres. Patients with radiological or biochemical progression and harbouring at least three metastases by conventional imaging will be accrued. Intra-patient inter-metastatic heterogeneity will be determined with triple-tracer imaging using fluorine-18 fluorodeoxyglucose (18 F-FDG), gallium-68-(68 Ga)-prostate-specific membrane antigen (PSMA)-617 and 68 Ga-DOTATATE, which are a glucose analogue, a PSMA receptor ligand and a somatostatin receptor ligand, respectively. The 68 Ga-PSMA-617 and 18 F-FDG PET/CT scans will be performed first. If at least one PSMA-negative/FDG-positive lesion is observed, an additional PET/CT scan with 68 Ga-DOTATATE will be performed. The tracer uptake of individual lesions will be assessed for each PET tracer and patients with lesions presenting discordant uptake profiles will be considered as having inter-metastatic heterogeneous disease and may be offered a biopsy. EXPECTED RESULTS: The proposed triple-tracer approach will allow whole-body mCRPC characterisation, investigating the inter-metastatic heterogeneity in order to better understand the phenotypic plasticity of prostate cancer, including the neuroendocrine transdifferentiation that occurs during mCRPC progression. Based on 68 Ga-PSMA-617 or 68 Ga-DOTATATE PET positivity, the potential eligibility of patients for PSMA and DOTATATE-based RLT will be assessed. Non-invasive whole-body determination of mCRPC heterogeneity and transdifferentiation is highly innovative and might establish the basis for new therapeutic strategies. Comparison of molecular imaging findings with biopsies will also link metastasis biology to radiomic features. CONCLUSION: This study will add novel, biologically relevant dimensions to molecular imaging: the non-invasive detection of inter-metastatic heterogeneity and transdifferentiation to neuroendocrine prostate cancer by using a multi-tracer PET/CT strategy to further personalise the care of patients with mCRPC.

Conductive nanocomposite hydrogel and mesenchymal stem cells for the treatment of myocardial infarction and non-invasive monitoring via PET/CT.

BACKGROUND: Injectable hydrogels have great promise in the treatment of myocardial infarction (MI); however, the lack of electromechanical coupling of the hydrogel to the host myocardial tissue and the inability to monitor the implantation may compromise a successful treatment. The introduction of conductive biomaterials and mesenchymal stem cells (MSCs) may solve the problem of electromechanical coupling and they have been used to treat MI. In this study, we developed an injectable conductive nanocomposite hydrogel (GNR@SN/Gel) fabricated by gold nanorods (GNRs), synthetic silicate nanoplatelets (SNs), and poly(lactide-co-glycolide)-b-poly (ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA). The hydrogel was used to encapsulate MSCs and 68Ga3+ cations, and was then injected into the myocardium of MI rats to monitor the initial hydrogel placement and to study the therapeutic effect via 18F-FDG myocardial PET imaging. RESULTS: Our data showed that SNs can act as a sterically stabilized protective shield for GNRs, and that mixing SNs with GNRs yields uniformly dispersed and stabilized GNR dispersions (GNR@SN) that meet the requirements of conductive nanofillers. We successfully constructed a thermosensitive conductive nanocomposite hydrogel by crosslinking GNR@SN with PLGA2000-PEG3400-PLGA2000, where SNs support the proliferation of MSCs. The cation-exchange capability of SNs was used to adsorb 68Ga3+ to locate the implanted hydrogel in myocardium via PET/CT. The combination of MSCs and the conductive hydrogel had a protective effect on both myocardial viability and cardiac function in MI rats compared with controls, as revealed by 18F-FDG myocardial PET imaging in early and late stages and ultrasound; this was further validated by histopathological investigations. CONCLUSIONS: The combination of MSCs and the GNR@SN/Gel conductive nanocomposite hydrogel offers a promising strategy for MI treatment.

Hydroxypyridinones as a Very Promising Platform for Targeted Diagnostic and Therapeutic Radiopharmaceuticals.

Hydroxypyridinones (HOPOs) have been used in the chelation therapy of iron and actinide metals. Their application in metal-based radiopharmaceuticals has also been increasing in recent years. This review article focuses on how multidentate HOPOs can be used in targeted radiometal-based diagnostic and therapeutic radiopharmaceuticals. The general structure of radiometal-based targeted radiopharmaceuticals, a brief description of siderophores, the basic structure and properties of bidentate HOPO, some representative HOPO multidentate chelating agents, radiopharmaceuticals based on HOPO multidentate bifunctional chelators for gallium-68, thorium-227 and zirconium-89, as well as the future prospects of HOPO multidentate bifunctional chelators in other metal-based radiopharmaceuticals are described and discussed in turn. The HOPO metal-based radiopharmaceuticals that have shown good prospects in clinical and preclinical studies are gallium-68, thorium-227 and zirconium-89 radiopharmaceuticals. We expect HOPO multidentate bifunctional chelators to be a very promising platform for building novel targeted radiometal-based diagnostic and therapeutic radiopharmaceuticals.

Treatment outcomes of metastasis-directed treatment using 68Ga-PSMA-PET/CT for oligometastatic or oligorecurrent prostate cancer: Turkish Society for Radiation Oncology group study (TROD 09-002).

PURPOSE: The aim of this study was to evaluate the outcomes of 68Ga prostate-specific membrane antigen (68Ga-PSMA) positron-emission tomography (PET)/CT-based metastasis-directed treatment (MDT) for oligometastatic prostate cancer (PC). METHODS: In this multi-institutional study, clinical data of 176 PC patients with 353 lesions receiving MDT between 2014 and 2019 were retrospectively evaluated. All patients had biopsy proven PC with ≤5 metastases detected with 68Ga-PSMA-PET/CT. MDT was delivered with conventional fractionation or stereotactic body radiotherapy (SBRT) techniques. CTCAE v4.0 was used for acute and RTOG/EORTC Late Radiation Morbidity Scoring Schema was used for late toxicity evaluation. RESULTS: At the time of MDT, 59 patients (33.5%) had synchronous and 117 patients (66.5%) had metachronous metastases. Median number of metastases was one and the MDT technique was SBRT in 73.3% patients. The 2­year overall survival (OS) and progression-free survival (PFS) rates were 87.6% and 63.1%, respectively. With a median follow-up of 22.9 months, 9 patients had local recurrence at the irradiated site. The 2­year local control rate at the treated oligometastatic site per patient was 93.2%. In multivariate analysis, an increased number of oligometastases and untreated primary PC were negative predictors for OS; advanced clinical tumor stage, untreated primary PC, BED3 value of ≤108 Gy, and MDT with conventional fractionation were negative predictors for PFS. No patient experienced grade ≥3 acute toxicity, but one patient had a late grade 3 toxicity of compression fracture after spinal SBRT. CONCLUSION: 68Ga-PSMA-PET/CT-based MDT is an efficient and safe treatment for oligometastatic PC patients. Proper patient selection might improve treatment outcomes.

Use of gallium-68 prostate-specific membrane antigen positron-emission tomography for detecting lymph node metastases in primary and recurrent prostate cancer and location of recurrence after radical prostatectomy: an overview of the current literature.

OBJECTIVES: To review the literature to determine the sensitivity and specificity of gallium-68 prostate-specific membrane antigen (68 Ga-PSMA) positron-emission tomography (PET) for detecting pelvic lymph node metastases in patients with primary prostate cancer (PCa), and the positive predictive value in patients with biochemical recurrence (BCR) after initial curative treatment, and, in addition, to determine the detection rate and management impact of 68 Ga-PSMA PET in patients with BCR after radical prostatectomy (RP). MATERIALS AND METHODS: We performed a comprehensive literature search. Search terms used in MEDLINE, EMBASE and Science Direct were '(PSMA, 68 Ga-PSMA, 68 Gallium-PSMA, Ga-68-PSMA or prostate-specific membrane antigen)' and '(histology, lymph node, staging, sensitivity, specificity, positive predictive value, recurrence, recurrent or detection)'. Relevant abstracts were reviewed and full-text articles obtained where possible. References to and from obtained articles were searched to identify further relevant articles. RESULTS: Nine retrospective and two prospective studies described the sensitivity and specificity of 68 Ga-PSMA PET for detecting pelvic lymph node metastases before initial treatment, which ranged from 33.3% to 100% and 80% to 100%, respectively. In eight retrospective studies, the positive predictive value of 68 Ga-PSMA PET in patients with BCR before salvage lymph node dissection ranged from 70% to 100%. The detection rate of 68 Ga-PSMA PET in patients with BCR after RP in the PSA subgroups <0.2 ng/mL, 0.2-0.49 ng/mL and 0.5 to <1.0 ng/mL ranged from 11.3% to 50.0%, 20.0% to 72.7% and 25.0% to 87.5%, respectively. CONCLUSION: The review results showed that 68 Ga-PSMA PET had a high specificity for the detection of pelvic lymph node metastases in primary PCa. Furthermore, 68 Ga-PSMA PET had a very high positive predictive value in detecting lymph node metastases in patients with BCR. By contrast, sensitivity was only moderate; therefore, based on the currently available literature, 68 Ga-PSMA PET cannot yet replace pelvic lymph node dissection to exclude lymph node metastases. In the salvage phase, 68 Ga-PSMA PET had both a high detection rate and impact on radiotherapy planning in early BCR after RP.

A Step-by-Step Guide for the Novel Radiometal Production for Medical Applications: Case Studies with 68Ga, 44Sc, 177Lu and 161Tb.

The production of novel radionuclides is the first step towards the development of new effective radiopharmaceuticals, and the quality thereof directly affects the preclinical and clinical phases. In this review, novel radiometal production for medical applications is briefly elucidated. The production status of the imaging nuclide 44Sc and the therapeutic ß--emitter nuclide 161Tb are compared to their more established counterparts, 68Ga and 177Lu according to their targetry, irradiation process, radiochemistry, and quality control aspects. The detailed discussion of these significant issues will help towards the future introduction of these promising radionuclides into drug manufacture for clinical application under Good Manufacturing Practice (GMP).

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

BACKGROUND: Triple-negative breast cancer has extremely high risk of relapse due to the lack of targeted therapies, intra- and inter-tumoral heterogeneity, and the inherent and acquired resistance to therapies. In this study, we evaluate the potential of prostate-specific membrane antigen (PSMA) as target for radio-ligand therapy (RLT). METHODS: Tube formation was investigated after incubation of endothelial HUVEC cells in tumor-conditioned media and monitored after staining using microscopy. A binding study with 68Ga-labeled PSMA-addressing ligand was used to indicate targeting potential of PSMA on tumor-conditioned HUVEC cells. For mimicking of the therapeutic application, tube formation potential and vitality of tumor-conditioned HUVEC cells were assessed following an incubation with radiolabeled PSMA-addressing ligand [177Lu]-PSMA-617. For in vivo experiments, NUDE mice were xenografted with triple-negative breast cancer cells MDA-MB231 or estrogen receptor expressing breast cancer cells MCF-7. Biodistribution and binding behavior of [68Ga]-PSMA-11 was investigated in both tumor models at 30 min post injection using µPET. PSMA- and CD31-specific staining was conducted to visualize PSMA expression and neovascularization in tumor tissue ex vivo. RESULTS: The triple-negative breast cancer cells MDA-MB231 showed a high pro-angiogenetic potential on tube formation of endothelial HUVEC cells. The induced endothelial expression of PSMA was efficiently addressed by radiolabeled PSMA-specific ligands. 177Lu-labeled PSMA-617 strongly impaired the vitality and angiogenic potential of HUVEC cells. In vivo, as visualized by µPET, radiolabeled PSMA-ligand accumulated specifically in the triple-negative breast cancer xenograft MDA-MB231 (T/B ratio of 43.3 ± 0.9), while no [68Ga]-PSMA-11 was detected in the estrogen-sensitive MCF-7 xenograft (T/B ratio of 1.1 ± 0.1). An ex vivo immunofluorescence analysis confirmed the localization of PSMA on MDA-MB231 xenograft-associated endothelial cells and also on TNBC cells. CONCLUSIONS: Here we demonstrate PSMA as promising target for two-compartment endogenous radio-ligand therapy of triple-negative breast cancer.

Improving the Theranostic Potential of Exendin 4 by Reducing the Renal Radioactivity through Brush Border Membrane Enzyme-Mediated Degradation.

As highly expressed in insulinomas, the glucagon-like peptide-1 receptor (GLP-1R) is believed to be an attractive target for diagnosis, localization, and treatment with radiolabeled exendin 4. However, the high and persistent radioactivity accumulation of exendin 4 in the kidneys limits accurate diagnosis and safe, as well as effective, radiotherapy in insulinomas. In this study, we intend to reduce the renal accumulation of radiolabeled exendin 4 through degradation mediated by brush border membrane enzymes. A new exendin 4 ligand NOTA-MVK-Cys40-Leu14-Exendin 4 containing Met-Val-Lys (MVK) linker between the peptide and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) chelator was synthesized and labeled with 68Ga. The in vitro mouse serum stability and cell binding affinity of the tracer were evaluated. Initial in vitro cleavage of the linker was determined by incubation of a model compound Boc-MVK-Dde with brush border membrane vesicles (BBMVs) with and without the inhibitor of neutral endopeptidase (NEP). Further cleavage studies were performed with the full structure of NOTA-MVK-Cys40-Leu14-Exendin 4. Kidney and urine samples were collected in the in vivo metabolism study after intravenous injection of 68Ga-NOTA-MVK-Cys40-Leu14-Exendin 4. The microPET images were acquired in INS-1 tumor model at different time points; the radioactivity uptake of 68Ga-NOTA-MVK-Cys40-Leu14-Exendin 4 in tumor and kidneys were determined and compared with the control radiotracer without MVK linker. 68Ga-NOTA-MVK-Cys40-Leu14-Exendin 4 was stable in mouse serum. The MVK modification did not affect the affinity of NOTA-MVK-Cys40-Leu14-Exendin 4 toward GLP-1R. The in vitro cleavage study and in vivo metabolism study confirmed that the MVK sequence can be recognized by BBM enzymes and cleaved at the amide bond between Met and Val, thus releasing the small fragment containing Met. MicroPET images showed that the tumor uptake of 68Ga-NOTA-MVK-Cys40-Leu14-Exendin 4 was comparable to that of the control, while the kidney uptake was significantly reduced. As a result, more favorable tumor to kidney ratios were achieved. In this study, a novel exendin 4 analogue, NOTA-MVK-Cys40-Leu14-Exendin 4, was successfully synthesized and labeled with 68Ga. With the cleavable MVK sequence, this ligand could be cleaved by the enzymes on kidneys, and releasing the fragment of 68Ga-NOTA-Met-OH, which will rapidly excrete from urine. As the high and consistent renal radioactivity accumulation could be significantly reduced, NOTA-MVK-Cys40-Leu14-Exendin 4 shows great potential in the diagnosis and radiotherapy for insulinoma.

[68Ga]Ga/[177Lu]Lu-BL01, a Novel Theranostic Pair for Targeting C-X-C Chemokine Receptor 4.

C-X-C chemokine receptor type 4 (CXCR4) is overexpressed in hematological and solid malignancies. LY2510924 is a potent peptide antagonist of CXCR4. A derivative of LY2510924, BL01, was evaluated for theranostic applications targeting CXCR4. Methods: BL01 was synthesized by solid phase approach. A Lys(ivDde) residue was added at the C-terminus of LY2510924 (cyclo[Phe-Tyr-Lys(iPr)-d-Arg-2-Nal-Gly-d-Glu]-Lys(iPr)-NH2). A DOTA chelator was conjugated to the side chain of the deprotected exogenous Lys residue. The binding affinity of Ga/Lu-BL01 was determined by competitive radioligand binding assays. BL01 was radiolabeled with 68GaCl3 or 177LuCl3. Biodistribution studies were performed in mice bearing Daudi Burkitt's lymphoma tumor xenografts at selected time points. PET imaging studies were performed with [68Ga]Ga-BL01, with blocking experiments performed with preinjection of LY2510924. The stability of [68Ga]Ga/[177Lu]Lu-BL01 was assessed in mouse plasma. Results: Ga-BL01 and Lu-BL01 have nanomolar affinity for CXCR4. [68Ga]Ga-BL01 was obtained in 58 ± 5% decay-corrected radiochemical yields and >99% radiochemical purity with a molar activity of 40 ± 11 GBq/µmol, while [177Lu]Lu-BL01 was obtained in 65 ± 6% decay-corrected radiochemical yields and >99% radiochemical purity with a molar activity of 120 ± 21 GBq/µmol. [68Ga]Ga-BL01 and [177Lu]Lu-BL01 were excreted primarily through the renal pathway. Daudi xenografts were clearly delineated in PET images with good contrast. On the basis of biodistribution data, tumor uptake of [68Ga]Ga-BL01 was 10.2 ± 2.56% injected dose per gram (%ID/g) at 1 h postinjection (p.i.). Spleen (12.6 ± 2.36 %ID/g) and lungs (13.2 ± 2.98 %ID/g), organs that express CXCR4, had high uptake as well. Preinjection of LY2510924 reduced average uptake of [68Ga]Ga-BL01 in tumors by 88%, demonstrating target specificity. The uptake of [68Ga]Ga-BL01 in tumor increased to 15.3 ± 1.86 %ID/g at 2 h p.i., with improved contrast. [177Lu]Lu-BL01 has similar pharmacokinetics as [68Ga]Ga-BL01 at 1 h p.i. The highest uptake was observed in tumor (14.0 ± 1.11 %ID/g), followed by the lungs (13.0 ± 1.27 %ID/g) and spleen (11.6 ± 1.78 %ID/g). The tumor uptake increased to 16.2 ± 2.69 %ID/g at 4 h p.i., before declining slightly to 10.1 ± 1.41 %ID/g at 24 h p.i. Both compounds were stable in vivo, as no metabolites were observed at 5 min p.i. Conclusions: [68Ga]Ga-BL01 and [177Lu]Lu-BL01 are a promising theranostic pair for imaging and endoradiotherapy of CXCR4-expressing malignancies.

Design and development of the theranostic pair 177 Lu-OPS201/68 Ga-OPS202 for targeting somatostatin receptor expressing tumors.

Radiolabeled somatostatin receptor (sstr) antagonists have shown superiority in different preclinical and clinical settings compared with the well-established and clinically used agonists for targeting sstr-expressing tumors, with regard to pharmacokinetics, tumor uptake, and retention. The theranostic pair 177 Lu-OPS201/68 Ga-OPS202, based on the sstr2 antagonist JR11 (Cpa-c[d-Cys-Aph(Hor)-d-Aph(Cbm)-Lys-Thr-Cys]-d-Tyr-NH2 ), is the most advanced pair of the antagonist family in terms of preclinical development and is currently under clinical evaluation. OPS201 and OPS202 share the same amino acid sequence (JR11) but feature different conjugated chelators needed for radiolabeling, DOTA for OPS201 and NODAGA for OPS202. In this review, the design and development of the peptidic analog, JR11, and the selection of chelators and radiometals that led to 177 Lu-OPS201/68 Ga-OPS202 are discussed. Furthermore, the preclinical evaluation of both radiolabeled analogs from bench to bedside and the clinical trials involving the theranostic pair are presented.

Comparison of Ga-68 PSMA positron emission tomography/computerized tomography with Tc-99m MDP bone scan in prostate cancer patients

Background/aim: The aim of our study was to compare Tc-99m MDP bone scan and Ga-68 PSMA PET/CT in terms of detection of bone metastasis in prostate cancer patients. Materials and methods: A total of 28 prostate cancer patients with bone scan and PSMA PET/CT performed within 90 days were retrospectively included in our analysis. All bone lesions were scored as negative (score-0), positive (score-1), or suspicious (score-2) for metastasis by two experienced nuclear medicine physicians. Both patient-based and region-based analyses were made for all osseous lesions. Results: On per-patient analysis; sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were 72.7%, 52.9%, 50%, 75%, and 60.7%, respectively, for bone scan and 90.9%, 100%, 100%, 94.4%, and 96.4%, respectively, for PSMA PET/CT. On per-region analysis; sensitivity, specificity, PPV, NPV, and accuracy were 76.2%, 80.9%, 57.1%, 91.1%, and 79.8%, respectively, for bone scan and 85.7%, 100%, 100%, 95.5%, and 95.4%, respectively, for PSMA PET/CT. Conclusion: Ga-68 PSMA PET/CT has higher sensitivity, specificity, and accuracy compared to bone scan in terms of bone metastasis detection in prostate cancer patients. Therefore, it might be the modality of choice for patients with suspicion for metastatic disease, despite negative bone scan and conventional imaging results

A prospective randomized multicentre study of the impact of gallium-68 prostate-specific membrane antigen (PSMA) PET/CT imaging for staging high-risk prostate cancer prior to curative-intent surgery or radiotherapy (proPSMA study): clinical trial protocol.

BACKGROUND: Accurate staging of patients with prostate cancer (PCa) is important for therapeutic decision-making. Relapse after surgery or radiotherapy of curative intent is not uncommon and, in part, represents a failure of staging with current diagnostic imaging techniques to detect disease spread. Prostate-specific membrane antigen (PSMA) positron-emission tomography (PET)/computed tomography (CT) is a new whole-body scanning technique that enables visualization of PCa with high contrast. The hypotheses of this study are that: (i) PSMA-PET/CT has improved diagnostic performance compared with conventional imaging; (ii) PSMA-PET/CT should be used as a first-line diagnostic test for staging; (iii) the improved diagnostic performance of PSMA-PET/CT will result in significant management impact; and (iv) there are economic benefits if PSMA-PET/CT is incorporated into the management algorithm. OBJECTIVES AND METHODS: The proPSMA trial is a prospective, multicentre study in which patients with untreated high-risk PCa will be randomized to gallium-68-PSMA-11 PET/CT or conventional imaging, consisting of CT of the abdomen/pelvis and bone scintigraphy with single-photon emission CT/CT. Patients eligible for inclusion are those with newly diagnosed PCa with select high-risk features, defined as International Society of Urological Pathology grade group ≥3 (primary Gleason grade 4, or any Gleason grade 5), prostate-specific antigen level ≥20 ng/mL or clinical stage ≥T3. Patients with negative, equivocal or oligometastatic disease on first line-imaging will cross over to receive the other imaging arm. The primary objective is to compare the accuracy of PSMA-PET/CT with that of conventional imaging for detecting nodal or distant metastatic disease. Histopathological, imaging and clinical follow-up at 6 months will define the primary endpoint according to a predefined scoring system. Secondary objectives include comparing management impact, the number of equivocal studies, the incremental value of second-line imaging in patients who cross over, the cost of each imaging strategy, radiation exposure, inter-observer agreement and safety of PSMA-PET/CT. Longer-term follow-up will also assess the prognostic value of a negative PSMA-PET/CT. OUTCOME AND SIGNIFICANCE: This trial will provide data to establish whether PSMA-PET/CT should replace conventional imaging in the primary staging of select high-risk localized PCa, or whether it should be used to provide incremental diagnostic information in selected cases.

Effect of Cyclosporin H on ischemic injury and neutrophil infiltration in cerebral infarct model of rats via PET imaging.

BACKGROUND: Brain ischemia-reperfusion injury is a complex process, and neuroinflammation is an important secondary contributing pathological event. Neutrophils play major roles in ischemic neuroinflammation. Once activated, neutrophils express formyl peptide receptors (FPRs), which are special receptors of a class of chemoattractants and may be potential targets to regulate the activity of neutrophils and control cerebral ischemic injury. This study was aimed to explore the ameliorating effect of Cyclosporin H (CsH), a potent FPR antagonist, on brain ischemic injury by inhibiting the activation and migration of neutrophils, and improving cerebral blood flow. METHODS: We employed a middle cerebral artery occlusion (MCAO) Model on rats and performed behavioral, morphological, and microPET imaging assays to investigate the potential restoring efficacy of CsH on cerebral ischemic damages. Peptide N-cinnamoyl-F-(D)L-F-(D)L-F (cFLFLF), an antagonist to the neutrophil FPR with a high binding affinity, was used for imaging neutrophil distribution. RESULTS: We found that CsH had similar effect with edaravone on improving the neurobehavioral deficient symptoms after cerebral ischemia-reperfusion, and treatment with CsH also alleviated ischemic cerebral infarction. Compared with the MCAO Model group, [18F]FDG uptake ratios of the CsH and edaravone treatment groups were significantly higher. The CsH-treated groups also showed significant increases in [18F]FDG uptake at 144 h when compared with that of 24 h. This result indicates that like edaravone, treatment with both doses of CsH promoted the recovery of blood supply after cerebral ischemic event. Moreover, MCAO-induced cerebral ischemia significantly increased the radiouptake of [68Ga]Ga-cFLFLF at 72 h after ischemia-reperfusion operation. Compared with MCAO Model group, radiouptake values of [68Ga]-cFLFLF in both doses of CsH and edaravone groups were all decreased significantly. These results showed that both doses of CsH resulted in a similar therapeutic effect with edaravone on inhibiting neutrophil infiltration in cerebral infarction. CONCLUSION: Potent FPR antagonist CsH is promisingly beneficial in attenuating neuroinflammation and improving neurobehavioral function against cerebral infarction. Therefore, FPR may become a novel target for regulating neuroinflammation and improving prognosis for ischemic cerebrovascular disorders.

Development of FAPI Tetramers to Improve Tumor Uptake and Efficacy of FAPI Radioligand Therapy.

Radiolabeled fibroblast activation protein (FAP) inhibitors (FAPIs) have shown promise as cancer diagnostic agents; however, the relatively short tumor retention of FAPIs may limit their application in radioligand therapy. In this paper, we report the design, synthesis, and evaluation of a FAPI tetramer. The aim of the study was to evaluate the tumor-targeting characteristics of radiolabeled FAPI multimers in vitro and in vivo, thereby providing information for the design of FAP-targeted radiopharmaceuticals based on the polyvalency principle. Methods: FAPI tetramers were synthesized on the basis of FAPI-46 and radiolabeled with 68Ga, 64Cu, and 177Lu. In vitro FAP-binding characteristics were identified using a competitive cell-binding experiment. To evaluate their pharmacokinetics, small-animal PET, SPECT, and ex vivo biodistribution analyses were performed on HT-1080-FAP and U87MG tumor-bearing mice. In addition, the 2 tumor xenografts received radioligand therapy with 177Lu-DOTA-4P(FAPI)4, and the antitumor efficacy of the 177Lu-FAPI tetramer was evaluated and compared with that of the 177Lu-FAPI dimer and monomer. Results: 68Ga-DOTA-4P(FAPI)4 and 177Lu-DOTA-4P(FAPI)4 were highly stable in phosphate-buffered saline and fetal bovine serum. The FAPI tetramer exhibited high FAP-binding affinity and specificity both in vitro and in vivo. 68Ga-, 64Cu-, and 177Lu-labeled FAPI tetramers exhibited higher tumor uptake, longer tumor retention, and slower clearance than FAPI dimers and FAPI-46 in HT-1080-FAP tumors. The uptake (percentage injected dose per gram) of 177Lu-DOTA-4P(FAPI)4, 177Lu-DOTA-2P(FAPI)2, and 177Lu-FAPI-46 in HT-1080-FAP tumors at 24 h was 21.4 ± 1.7, 17.1 ± 3.9, and 3.4 ± 0.7, respectively. Moreover, 68Ga-DOTA-4P(FAPI)4 uptake in U87MG tumors was approximately 2-fold the uptake of 68Ga-DOTA-2P(FAPI)2 (SUVmean, 0.72 ± 0.02 vs. 0.42 ± 0.03, P < 0.001) and more than 4-fold the uptake of 68Ga-FAPI-46 (0.16 ± 0.01, P < 0.001). In the radioligand therapy study, remarkable tumor suppression was observed with the 177Lu-FAPI tetramer in both HT-1080-FAP and U87MG tumor-bearing mice. Conclusion: The satisfactory FAP-binding affinity and specificity, as well as the favorable in vivo pharmacokinetics of the FAPI tetramer, make it a promising radiopharmaceutical for theranostic applications. Improved tumor uptake and prolonged retention of the 177Lu-FAPI tetramer resulted in excellent characteristics for FAPI imaging and radioligand therapy.