Imaging of cardiac fibroblast activation in a patient after acute myocardial infarction using 68Ga-FAPI-04

Our previous study has demonstrated the feasibility of noninvasive imaging of fibroblast activation protein (FAP)-expression after myocardial infarction (MI) in MI-territory in a rat model with 68Ga-FAPI-04-PET. In the current extended clinical case, we sought to delineate cardiac uptake of 68Ga-FAPI-04 in a patient after MI with clinical indication for the evidence of fibroblast activation. Carcinoma patients without cardiac disease underwent 68Ga-FAPI-04-PET/CT as control. The patient with one-vessel disease underwent dynamic 68Ga-FAPI-04-cardiac-PET/CMR for 60 minutes. Correlation of cardiac 68Ga-FAPI-04 uptake with clinical findings, ECG, echocardiography, coronary-arteriography and enhanced cardiac-MRI with T1 MOLLI and ECV mapping were performed. No uptake was found in normal myocardium and in mature scar. A focal intense 68Ga-FAPI-04 uptake with continuous wash-out in the infarct territory of coronary occlusion correlating with T1 and ECV mapping was observed. The uptake of 68Ga-FAPI-04 extends beyond the actual infarcted area and overestimates the infarct size as confirmed by follow-up CMR.

Synthesis and Preclinical Evaluation of a 68Ga-Labeled Adnectin, 68Ga-BMS-986192, as a PET Agent for Imaging PD-L1 Expression

Blocking the interaction of the immune checkpoint molecule programmed cell death protein-1 and its ligand, PD-L1, using specific antibodies has been a major breakthrough for immune oncology. Whole-body PD-L1 expression PET imaging may potentially allow for a better prediction of response to programmed cell death protein-1-targeted therapies. Imaging of PD-L1 expression is feasible by PET with the adnectin protein ¹⁸F-BMS-986192. However, radiofluorination of proteins such as BMS-986192 remains complex and labeling yields are low. The goal of this study was therefore the development and preclinical evaluation of a ⁶⁸Ga-labeled adnectin protein (⁶⁸Ga-BMS-986192) to facilitate clinical trials. Methods: ⁶⁸Ga labeling of DOTA-conjugated adnectin (BXA-206362) was performed in NaOAc-buffer at pH 5.5 (50°C, 15 min). In vitro stability in human serum at 37°C was analyzed using radio-thin layer chromatography and radio-high-performance liquid chromatography. PD-L1 binding assays were performed using the transduced PD-L1-expressing lymphoma cell line U-698-M and wild-type U-698-M cells as a negative control. Immunohistochemical staining studies, biodistribution studies, and small-animal PET studies of ⁶⁸Ga-BMS-986192 were performed using PD-L1-positive and PD-L1-negative U-698-M-bearing NSG mice. Results: ⁶⁸Ga-BMS-986192 was obtained with quantitative radiochemical yields of more than 97% and with high radiochemical purity. In vitro stability in human serum was at least 95% after 4 h of incubation. High and specific binding of ⁶⁸Ga-BMS-986192 to human PD-L1-expressing cancer cells was confirmed, which closely correlates with the respective PD-L1 expression level determined by flow cytometry and immunohistochemistry staining. In vivo, ⁶⁸Ga-BMS-986192 uptake was high at 1 h after injection in PD-L1-positive tumors (9.0 ± 2.1 percentage injected dose [%ID]/g) and kidneys (56.9 ± 9.2 %ID/g), with negligible uptake in other tissues. PD-L1-negative tumors demonstrated only background uptake of radioactivity (0.6 ± 0.1 %ID/g). Coinjection of an excess of unlabeled adnectin reduced tumor uptake of PD-L1 by more than 80%. Conclusion: ⁶⁸Ga-BMS-986192 enables easy radiosynthesis and shows excellent in vitro and in vivo PD-L1-targeting characteristics. The high tumor uptake combined with low background accumulation at early imaging time points demonstrates the feasibility of ⁶⁸Ga-BMS-986192 for imaging of PD-L1 expression in tumors and is encouraging for further clinical applications of PD-L1 ligands.

First In-Human Medical Imaging with a PASylated 89Zr-Labeled Anti-HER2 Fab-Fragment in a Patient with Metastatic Breast Cancer

Purpose

PASylation® offers the ability to systematically tune and optimize the pharmacokinetics of protein tracers for molecular imaging. Here we report the first clinical translation of a PASylated Fab fragment (⁸⁹Zr∙Df-HER2-Fab-PAS₂₀₀) for the molecular imaging of tumor-related HER2 expression.

Methods

A patient with HER2-positive metastatic breast cancer received 37 MBq of ⁸⁹Zr∙Df-HER2-Fab-PAS₂₀₀ at a total mass dose of 70 μg. PET/CT was carried out 6, 24, and 45 h after injection, followed by image analysis of biodistribution, normal organ uptake, and lesion targeting.

Results

Images show a biodistribution typical for protein tracers, characterized by a prominent blood pool 6 h p.i., which decreased over time. Lesions were detectable as early as 24 h p.i. ⁸⁹Zr∙Df-HER2-Fab-PAS₂₀₀ was tolerated well.

Conclusion

This study demonstrates that a PASylated Fab tracer shows appropriate blood clearance to allow sensitive visualization of small tumor lesions in a clinical setting.

Molecular Imaging of Fibroblast Activity After Myocardial Infarction Using a 68Ga-Labeled Fibroblast Activation Protein Inhibitor, FAPI-04

Heart failure remains a major source of late morbidity and mortality after myocardial infarction (MI). The temporospatial presence of activated fibroblasts in the injured myocardium predicts the quality of cardiac remodeling after MI. Therefore, monitoring of activated fibroblasts is of great interest for studying cardiac remodeling after MI. Fibroblast activation protein (FAP) expression is upregulated in activated fibroblasts. This study investigated the feasibility of imaging activated fibroblasts with a new ⁶⁸Ga-labeled FAP inhibitor (⁶⁸Ga-FAPI-04) for PET imaging of fibroblast activation in a preclinical model of MI. Methods: MI and sham-operated rats were scanned with ⁶⁸Ga-FAPI-04 PET/CT (1, 3, 6, 14, 23, and 30 d after MI) and with ¹⁸F-FDG (3 d after MI). Dynamic ⁶⁸Ga-FAPI-04 PET and blocking studies were performed on MI rats 7 d after coronary ligation. After in vivo scans, the animals were euthanized and their hearts harvested for ex vivo analyses. Cryosections were prepared for autoradiography, hematoxylin and eosin (H&E), and immunofluorescence staining. Results: ⁶⁸Ga-FAPI-04 uptake in the injured myocardium peaked on day 6 after coronary ligation. The tracer accumulated intensely in the MI territory, as identified by decreased ¹⁸F-FDG uptake and confirmed by PET/MR and H&E staining. Autoradiography and H&E staining of cross-sections revealed that ⁶⁸Ga-FAPI-04 accumulated mainly at the border zone of the infarcted myocardium. In contrast, there was only minimal uptake in the infarct of the blocked rats, comparable to the uptake in the remote noninfarcted myocardium (PET image-derived ratio of infarct uptake to remote uptake: 6 ± 2). Immunofluorescence staining confirmed the presence of FAP-positive myofibroblasts in the injured myocardium. Morphometric analysis of the whole-heart sections demonstrated 3- and 8-fold higher FAP-positive fibroblast density in the border zone than in the infarct center and remote area, respectively. Conclusion: ⁶⁸Ga-FAPI-04 represents a promising radiotracer for in vivo imaging of post-MI fibroblast activation. Noninvasive imaging of activated fibroblasts may have significant diagnostic and prognostic value, which could aid clinical management of patients after MI.

Radiosynthesis and pre-clinical evaluation of [68Ga] labeled antimicrobial peptide fragment GF-17 as a potential infection imaging PET radiotracer

The antimicrobial peptide fragment GF-17 was synthesized in-house and conjugated with DOTA and measured molecular mass of DOTA-GF-17 conjugate was 2489 Da. The peptide conjugate was purified and labeled with [⁶⁸Ga]. The best radiolabeling efficiency (95.0%) of [⁶⁸Ga]DOTA-GF-17 was achieved at pH 4 with peptide conjugate amount of 20.0 nmol with 30 min of heating at 95 °C. The product remained stable for up to 3 h. The plasma protein binding and lipophilicity for [⁶⁸Ga]DOTA-GF-17 were 80.98% and -3.12 respectively. The uptake studies with [⁶⁸Ga]DOTA- GF-17 in S.aureus and P.aeruginosa bacterial strains demonstrated binding of 69.08% and 43.69% respectively. The animal bio-distribution and PET imaging studies were in agreement showing similar pattern for organs' tracer distribution and renal excretion. The tracer had rapid blood clearance and uptake in bone marrow and muscles was very low. The highest uptake of [⁶⁸Ga]DOTA-GF-17 was observed at 45 min and 120 min in S.aureus and P.aeruginosa infections respectively. [⁶⁸Ga]DOTA-GF-17 could be a promising PET tracer and holds a great scope for taking the product further to perform extensive PET studies in animal infection (using gram negative/positive strains) models to prove the diagnostic utility of this novel PET tracer for futuristic clinical applications.

Single Lesion on Prostate-specific Membrane Antigen-ligand Positron Emission Tomography and Low Prostate-specific Antigen Are Prognostic Factors for a Favorable Biochemical Response to Prostate-specific Membrane Antigen-targeted Radioguided Surgery in Recurrent Prostate Cancer

BACKGROUND

Prostate-specific membrane antigen (PSMA)-ligand positron emission tomography (PET) allows detection of metastatic prostate cancer (PC) lesions at low prostate-specific antigen (PSA) values. To facilitate their intraoperative detection during salvage surgery, we recently introduced PSMA-targeted radioguided surgery (RGS).

OBJECTIVE

To describe the outcome of a large cohort of patients treated with PSMA-targeted RGS and to establish prognostic factors.

DESIGN, SETTING, AND PARTICIPANTS

A total of 121 consecutive patients with recurrent PC as defined by PSMA-ligand PET (median PSA: 1.13ng/ml) underwent PSMA-targeted RGS.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The frequency of a complete biochemical response (cBR; PSA <0.2ng/ml) without additional treatment and the duration of biochemical recurrence-free survival (bRFS, time from PSMA-targeted RGS with PSA <0.2ng/ml without further treatment) were evaluated and correlated with preoperatively available clinical variables.

RESULTS AND LIMITATIONS

In almost all patients (120/121, 99%) metastatic tissue could be removed. A cBR was achieved in 77 patients (66%). The chance of cBR was highest in patients with both low preoperative PSA and a single lesion (38/45: 84%). Median bRFS was 6.4mo in the whole patient cohort and 19.8mo for patients with cBR. Significantly longer median bRFS was observed in patients with a low preoperative PSA value (p=0.004, hazard ratio 1.48, 95% confidence interval 1.13-1.93) and with a single lesion in preoperative PSMA-ligand PET (14.0 vs 2.5mo, p=0.002).

CONCLUSIONS

PSMA-targeted RGS leads to a remarkable interval of bRFS in a subset of patients. The frequency of cBR and the duration of bRFS were highest in patients with a low preoperative PSA value and a single lesion on PSMA-ligand PET.

PATIENT SUMMARY

Prostate-specific membrane antigen radioguided surgery delays disease progression in selected patients with recurrent prostate cancer after radical prostatectomy. Patients with a single lesion of recurrence and a low prostate-specific antigen value had the best outcome.

Synthesis and in vitro and in vivo evaluation of urea-based PSMA inhibitors with increased lipophilicity

Background

Several radiolabeled prostate-specific membrane antigen (PSMA) inhibitors based on the lysine-urea-glutamate (KuE) motif as the pharmacophore proved to be suitable tools for PET/SPECT imaging of the PSMA expression in prostate cancer patients. PSMA I&T, a theranostic tracer developed in our group, was optimized through alteration of the peptidic structure in order to increase the affinity to PSMA and internalization in PSMA-expressing tumor cells. However, further structural modifications held promise to improve the pharmacokinetic profile.

Results

Among the investigated compounds 1–9, the PSMA inhibitors 5 and 6 showed the highest PSMA affinity (lowest IC₅₀ values) after the introduction of a naphthylalanine modification. The affinity was up to three times higher compared to the reference PSMA I&T. Extended aromatic systems such as the biphenylalanine residue in 4 impaired the interaction with the lipophilic binding pocket of PSMA, resulting in a tenfold lower affinity. The IC₅₀ of DOTAGA-conjugated 10 was slightly increased compared to the acetylated analog; however, efficient PSMA-mediated internalization and 80% plasma protein binding of ⁶⁸Ga-10 resulted in effective tumor targeting and low uptake in non-target tissues of LNCaP tumor-bearing CD-1 nu/nu mice at 1 h p.i., as determined by small-animal PET imaging and biodistribution studies. For prolonged tumor retention, the plasma protein binding was increased by insertion of 4-iodo-d-phenylalanine resulting in 97% plasma protein binding and 16.1 ± 2.5% ID/g tumor uptake of ¹⁷⁷Lu-11 at 24 h p.i.

Conclusions

Higher lipophilicity of the novel PSMA ligands 10 and 11 proved to be beneficial in terms of affinity and internalization and resulted in higher tumor uptake compared to the parent compound. Additional combination with para-iodo-phenylalanine in the spacer of ligand 11 elevated the plasma protein binding and enabled sustained tumor accumulation over 24 h, increasing the tumor uptake almost fourfold compared to ¹⁷⁷Lu-PSMA I&T. However, high renal uptake remains a drawback and further studies are necessary to elucidate the responsible mechanism behind it.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0440-2) contains supplementary material, which is available to authorized users.

Synthesis and preclinical evaluation of novel 18F-labeled Glu-urea-Glu-based PSMA inhibitors for prostate cancer imaging: a comparison with 18F-DCFPyl and 18F-PSMA-1007

Background

Due to its high and consistent expression in prostate cancer (PCa), the prostate-specific membrane antigen (PSMA) represents an ideal target for molecular imaging and targeted therapy using highly specific radiolabeled PSMA ligands. To address the continuously growing clinical demand for ¹⁸F-labeled PSMA-probes, we developed two novel Glu-urea-Glu-(EuE)-based inhibitors, EuE-k-¹⁸F-FBOA (1) and EuE-k-β-a-¹⁸F-FPyl (2), both with optimized linker structure and different ¹⁸F-labeled aromatic moieties. The inhibitors were evaluated in a comparative preclinical study with ¹⁸F-DCFPyl and ¹⁸F-PSMA-1007.

Results

Radiolabeling procedures allowed preparation of (1) and (2) with high radiochemical yields (67 ± 7 and 53 ± 7%, d.c.) and purity (> 98%). When compared with ¹⁸F-DCFPyl (IC₅₀ = 12.3 ± 1.2 nM) and ¹⁸F-PSMA-1007 (IC₅₀ = 4.2 ± 0.5 nM), both metabolically stable EuE-based ligands showed commensurable or higher PSMA affinity (IC₅₀ = 4.2 ± 0.4 nM (1), IC₅₀ = 1.1 ± 0.2 nM (2)). Moreover, 1.4- and 2.7-fold higher internalization rates were observed for (1) and (2), respectively, resulting in markedly enhanced tumor accumulation in LNCaP-tumor-bearing mice ((1) 12.7 ± 2.0% IA/g, (2) 13.0° ± 1.0% IA/g vs. 7.3 ± 1.0% IA/g (¹⁸F-DCFPyl), 7.1 ± 1.5% IA/g (¹⁸F-PSMA-1007), 1 h p.i.). In contrast to (1), (2) showed higher kidney accumulation and delayed clearance kinetics. Due to the high hydrophilicity of both compounds, almost no unspecific uptake in non-target tissue was observed. In contrast, due to the less hydrophilic character (logP = − 1.6) and high plasma protein binding (98%), ¹⁸F-PSMA-1007 showed uptake in non-target tissue and predominantly hepatobiliary excretion, whereas, ¹⁸F-DCFPyl exhibited pharmacokinetics quite similar to those obtained with (1) and (2).

Conclusion

Both ¹⁸F-labeled EuE-based PSMA ligands showed excellent in vitro and in vivo PSMA-targeting characteristics. The substantially higher tumor accumulation in mice compared to recently introduced ¹⁸F-PSMA-1007 and ¹⁸F-DCFPyl suggests their high value for preclinical studies investigating the effects on PSMA-expression. In contrast to (2), (1) seems to be more promising for further investigation, due to the more reliable ¹⁸F-labeling procedure, the faster clearance kinetics with comparable high tumor uptake, resulting therefore in better high-contrast microPET imaging as early as 1 h p.i.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0382-8) contains supplementary material, which is available to authorized users.