Synthesis and preclinical evaluation of a novel molecular probe [18F]AlF-NOTA-PEG2-Asp2-PDL1P for PET imaging of PD-L1 positive tumor

A novel Al18F-labelled NOTA-modified ubiquicidin 29-41 derivative as a bacterial infection PET imaging agent

The antimicrobial peptide ubiquicidin 29-41 (TGRAKRRMQYNRR) is a potential target for detecting bacterial infection. A novel UBI 29-41 derivative modified with 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) on the amino side of lysine was synthesized and radiolabelled with Al18F, named [18F]AlF-NOTA-UBI 29-41. The novel PET tracer maintained good in vitro stability in saline at room temperature and mouse serum at 37 °C. In vitro bacterial binding experiments indicated that the tracer specifically bound to Staphylococcus aureus. A significant difference in the uptake of [18F]AlF-NOTA-UBI 29-41 between infected muscle and inflamed muscle was observed in biodistribution. A PET imaging study in mouse models with bacterial infection and sterile inflammation showed apparent accumulation at the infection site, suggesting that the complex is a potential PET tracer for distinguishing bacterial infection from sterile inflammation.

Design, Synthesis, and Evaluation of a Novel Positron Emission Tomography Tracer Targeting Fibroblast Activation Protein: From Bench to Bedside

FAPI-PET/CT has become a promising tool for cancer diagnosis. However, the pharmacokinetic properties of FAPI tracers need optimization. Here, we developed a novel FAPI tracer, [18F]AlF-NOTA-SP2A-FAPT, for cancer imaging. NOTA-SP2A-FAPT was successfully synthesized and radiolabeled with a high radiochemical purity. [18F]AlF-NOTA-SP2A-FAPT displayed satisfying stability, hydrophilicity, and affinity to FAP, as well as specific uptake in A549-FAP cells. Micro-PET/CT showed that [18F]AlF-NOTA-SP2A-FAPT is rapidly excreted through the renal system. [18F]AlF-NOTA-SP2A-FAPT exhibited high tumor uptake and excellent retention, showing better tumor delineation compared to [18F]FDG and [18F]AlF-NOTA-FAPI-42. Pilot clinical studies of [18F]AlF-NOTA-SP2A-FAPT and head-to-head comparison with [18F]FDG were performed on 13 cancer patients. Compared to [18F]FDG, [18F]AlF-NOTA-SP2A-FAPT had higher uptake in primary tumor and lymph node metastases as well as favorable distribution and good tumor retention. In conclusion, [18F]AlF-NOTA-SP2A-FAPT demonstrated high tumor accumulation, as well as improved pharmacokinetic properties. [18F]AlF-NOTA-SP2A-FAPT could emerge as a promising alternative to the currently established FAPI tracers.

Synthesis and preclinical evaluation of small molecule-based radiotracers for PET imaging of PD-L1 expression and dynamics

PURPOSE

Small molecule-based radiotracers offer several potential advantages in positron emission tomography (PET) imaging, and are therefore a promising approach for non-invasively and accurately monitoring of programmed death ligand 1 (PD-L1) expression in vivo. In this study, two small-molecule radiotracers were developed to assess PD-L1 expression and dynamics during treatments.

METHODS

[18F]LG-2 and [18F]LG-3 were designed based on a phenoxymethyl-biphenyl scaffold with a tris-(hydroxymethyl)-aminomethane terminal group. The radiolabeling was achieved by a two-step method through the "click" chemistry. Cellular uptake assays in different tumor cells were performed to determine the specificity of the two tracers to PD-L1. The ability of [18F]LG-2 and [18F]LG-3 to detect PD-L1 expression in vivo as well as to monitor PD-L1 dynamics during chemotherapy and immunotherapy was investigated via PET imaging.

RESULTS

The radiolabeling of [18F]LG-2 and [18F]LG-3 was achieved with overall radiochemical yield of 15 ± 3% for [18F]LG-2 and 18 ± 5% for [18F]LG-3. In vitro cell uptake studies in tumor cells with varying PD-L1 levels demonstrated the specific binding of these tracers to PD-L1. PET imaging in mice bearing B16-F10 tumors displayed comparable tumor uptake of 6.45 ± 0.38%ID/mL for [18F]LG-2 and 5.64 ± 0.02%ID/mL for [18F]LG-3, while [18F]LG-3 showed nearly a 50% reduction in uptake in the liver and intestines compared to [18F]LG-2. PET signals of [18F]LG-3 in A375-hPD-L1, A375-hPD-L1/A375 and A375 tumor-bearing mice demonstrated a strong and linear correlation with PD-L1 expression levels. The dynamic of PD-L1 status in tumors after cisplatin and PD-L1 inhibitor treatments were accurately evaluated with [18F]LG-3 PET imaging.

CONCLUSION

The small-molecule radiotracer [18F]LG-3 is a promising candidate for evaluating PD-L1 expression and monitoring the dynamic of PD-L1 status during the treatment process.

Preclinical and first‑in‑human evaluation of [68Ga]Ga-DOTA-PEG2-Asp2-PDL1P PET imaging to assess tumor PD-L1 expression

PURPOSE

PD-L1 PET imaging can provide a non-invasively and real-time assessment of PD-L1 expression status at tumor sites. This study aimed to evaluate the targeting efficacy and biodistribution of a novel peptide-based PD-L1 PET agent, [68Ga]Ga-DOTA-PEG2-Asp2-PDL1P, in preclinical studies and human participants.

METHODS

[68Ga]Ga-DOTA-PEG2-Asp2-PDL1P was synthesized and the probe stability was analyzed in vitro and in vivo. Cellular uptake of the probe was evaluated using tumor cell lines with different PD-L1 expression levels. Small animal PET imaging and semi-quantitative studies were conducted in PC3, H1975 and A549 tumor-bearing mice models, with tumor PD-L1 expression confirmed through immunofluorescence and immunohistochemistry. Furthermore, [68Ga]Ga-DOTA-PEG2-Asp2-PDL1P PET imaging was performed in 1 healthy volunteer and 14 lung cancer patients to assess biodistribution and PD-L1 expression at tumor sites.

RESULTS

[68Ga]Ga-DOTA-PEG2-Asp2-PDL1P exhibited a radiochemical purity of > 99% and had good stability both in vitro and in vivo. In vitro cellular uptake and in vivo small animal PET imaging revealed the probe binding to PD-L1 with high affinity and specificity, consistent with the results of immunofluorescence and immunohistochemistry. In the clinical study involving 15 participants, [68Ga]Ga-DOTA-PEG2-Asp2-PDL1P was proven safe with demonstrating low uptake in normal organs and physiologically excreting via the urinary system. Lung cancer patients with high PD-L1 expression (TPS 70-90%) exhibited higher tumor uptake and tumor-to-background ratios than those with negative or low PD-L1 expression (TPS < 1-10%), with SUVmax of 1.89-2.27 vs. 0.87-1.01, tumor-to-lung ratios of 4.73-7.68 vs. 1.61-2.35, and tumor-to-muscle ratios of 6.73-12.61 vs. 4.35-5.61.

CONCLUSION

[68Ga]Ga-DOTA-PEG2-Asp2-PDL1P showed promising as a PET agent to assess tumor PD-L1 expression in preclinical and first-in-human studies, offering a non-invasive, real-time and accurate tool to address clinical challenges in predicting and assessing the efficacy of immunotherapy.

Comparative study of [18F]AlF-PAI-PDL1p and [68Ga]Ga-PAI-PDL1p as novel PD-L1 targeting PET probes for tumor imaging

PD-L1 is expressed in many tumors but rarely in normal tissues, therefore, it can be a target of PET imaging. In this work, we developed new peptide-based PET probes [18F]AlF-PAI-PDL1p and [68Ga]Ga-PAI-PDL1p with yields of 20-25 % and 40-55 %, respectively. [18F]AlF-PAI-PDL1p and [68Ga]Ga-PAI-PDL1p were synthesized within 30 min with high molar activities. [18F]AlF-PAI-PDL1p and [68Ga]Ga-PAI-PDL1p showed good stability in vivo and in vitro. In vitro cell studies showed [18F]AlF-PAI-PDL1p and [68Ga]Ga-PAI-PDL1p target PD-L1 specifically, with high uptake of 61.52 ± 4.39 and 19.29 ± 2.17 %ID/1 million cells in B16F10 cells at 60 min, respectively. Biodistribution results showed that both [18F]AlF-PAI-PDL1p and [68Ga]Ga-PAI-PDL1p had lower liver accumulation. In vivo PET imaging results showed that [18F]AlF-PAI-PDL1p had a high tumor uptake of 4.23 ± 0.81 %ID/g at 2 h and increased uptake of 6.60 ± 1.01 %ID/g at 12 h. [68Ga]Ga-PAI-PDL1p also showed high tumor uptake of 2.30 ± 0.20 %ID/g at 2 h and slightly increased uptake of 3.80 ± 0.26 %ID/g at 6 h. In conclusion, [18F]AlF-PAI-PDL1p and [68Ga]Ga-PAI-PDL1 seemed to be potential tracers for PET imaging of PD-L1 expression.

Synthesis and preclinical evaluation of a novel probe [18F]AlF-NOTA-IPB-GPC3P for PET imaging of GPC3 positive tumor

Glypican-3 (GPC3) is markedly overexpressed in hepatocellular carcinoma (HCC) and not expressed in normal liver tissues. In this study, a novel peptide PET imaging agent ([18F]AlF-NOTA-IPB-GPC3P) was developed to target GPC3 expressed in tumors. The overall radiochemical yield of [18F]AlF-NOTA-IPB-GPC3P was 10-15 %, and its lipophilicity, expressed as the logD value at a pH of 7.4, was -1.18 ± 0.06 (n = 3). Compared to the previously reported tracer [18F]AlF-GP2633, [18F]AlF-NOTA-IPB-GPC3P exhibited higher cellular uptake (15.13 vs 5.96) and internalized rate (80.63 % vs 35.93 %) in Huh7 cells at 120 min. Micro-PET/CT and biodistribution studies further demonstrated that [18F]AlF-NOTA-IPB-GPC3P exhibited significantly increased tumor uptake and prolonged tumor residence in Huh7 tumors compared to [18F]AlF-GP2633 (4.66 ± 0.22 % ID/g vs 0.72 ± 0.09 % ID/g at 60 min, p < 0.001; 5.05 ± 0.23 % ID/g vs 0.35 ± 0.08 % ID/g at 120 min, p < 0.001, respectively). Furthermore, the tumor-to-organ ratios of [18F]AlF-NOTA-IPB-GPC3P surpassed those of [18F]AlF-GP2633. Our results support the utilization of [18F]AlF-NOTA-IPB-GPC3P as a PET imaging agent targeting the GPC3 receptor for tumor detection.