18 F-labeled 1,2,3-triazole-linked Glu-urea-Lys-based PSMA ligands have good pharmacokinetic properties for positron emission tomography imaging of prostate cancer

Comparison of the Effects of DOTA and NOTA Chelators on 64Cu-Cudotadipep and 64Cu-Cunotadipep for Prostate Cancer

BACKGROUND

This study compared the effects of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) as 64Cu-chelating agents in newly developed prostate-specific membrane antigen (PSMA) target compounds, 64Cu-cudotadipep and 64Cu-cunotadipep, on pharmacokinetics.

METHODS

The in vitro stability of the chelators was evaluated using human and mouse serum. In vitro PSMA-binding affinity and cell uptake were compared using human 22Rv1 cells. To evaluate specific PSMA-expressing tumor-targeting efficiency, micro-positron emission tomography (mcroPET)/computed tomography (CT) and biodistribution analysis were performed using PSMA+ PC3-PIP and PSMA- PC3-flu tumor xenografts.

RESULTS

The serum stability of DOTA- or NOTA-conjugated 64Cu-cudotadipep and 64Cu-cunotadipep was >97%. The Ki value of the NOTA derivative, cunotadipep, in the in vitro affinity binding analysis was higher (2.17 ± 0.25 nM) than that of the DOTA derivative, cudotadipep (6.75 ± 0.42 nM). The cunotadipep exhibited a higher cellular uptake (6.02 ± 0.05%/1 × 106 cells) compared with the cudotadipep (2.93 ± 0.06%/1 × 106 cells). In the biodistribution analysis and microPET/CT imaging, the 64Cu-labeled NOTA derivative, 64Cu-cunotadipep, demonstrated a greater tumor uptake and lower liver uptake than the DOTA derivative.

CONCLUSIONS

This study indicates that the PSMA-targeted 64Cu-cunotadipep can be applied in clinical practice owing to its high diagnostic power for prostate cancer.

Evaluation of PSMA target diagnostic PET tracers for therapeutic monitoring of [177Lu]ludotadipep of prostate cancer: Screening of PSMA target efficiency and biodistribution using [18F]DCFPyL and [68Ga]PSMA-11

We have compared the similarity of the in vivo distribution of the prostate-specific membrane antigen (PSMA)-targeted positron emission tomography (PET) imaging agents [¹⁸F]DCFPyL, [⁶⁸Ga]galdotadipep, and [⁶⁸Ga]PSMA-11. This study is designed for a further selection of a PSMA-targeted PET imaging agent for the therapeutic evaluation of [¹⁷⁷Lu]ludotadipep, our previously developed prostate-specific membrane antigen (PSMA)-targeted prostate cancer therapeutic radiopharmaceutical. In vitro cell uptake was performed to evaluate the affinity to PSMA using PSMA + PC3-PIP, and PSMA- PC3-flu was used for the study. MicroPET/CT 60 min dynamic imaging and biodistribution were performed at 1, 2, and 4 h after injection. Autoradiography and immunohistochemistry were performed to evaluate the PSMA + tumor target efficiency. In the microPET/CT image, [⁶⁸Ga]PSMA-11 showed the highest uptake in the kidney among all three compounds. [¹⁸F]DCFPyL and [⁶⁸Ga]PSMA-11 showed similar patterns of in vivo biodistribution and high tumor targeting efficiency, similar to those of[⁶⁸Ga]galdotadipep. All three agents showed high uptake in tumor tissue on autoradiography, and PSMA expression was confirmed by immunohistochemistry. Thus, [¹⁸F]DCFPyL or [⁶⁸Ga]PSMA-11 can be used as a PET imaging agent to monitor [¹⁷⁷Lu]ludotadipep therapy in prostate cancer patients.

Improving Theranostic Gallium-68/Lutetium-177-Labeled PSMA Inhibitors with an Albumin Binder for Prostate Cancer

We developed a novel therapeutic radioligand, [177Lu]1h, with an albumin binding motif and evaluated it in a prostate-specific membrane antigen (PSMA)-expressing tumor xenograft mouse model. Fourteen PSMA target candidates were synthesized, and binding affinity was evaluated with an in vitro competitive binding assay. First, four compound candidates were selected depending on binding affinity results. Next, we selected four compounds ([68Ga]1e, [68Ga]1g, [68Ga]1h, and [68Ga]1k) were screened for tumor targeting efficiency by micro-positron emission tomography/computed tomography (micro-PET/CT) imaging. Finally, [177Lu]1h compound was evaluated the tumor targeting efficiency and therapeutic efficiency by micro-single-photon emission computed tomography/computed tomography (micro-SPECT/CT), biodistribution, and radiotherapy studies. Estimated human effective dose was calculated by biodistribution data. Compound 1h showed a high binding affinity (Ki value = 4.08 ± 0.08 nmol/L), and [177Lu]1h showed extended blood circulation (1 hour = 10.32 ± 0.31, 6 hours = 2.68 ± 1.07%ID/g) compared to [177Lu]PSMA-617 (1 h = 0.17 ± 0.10%ID/g). [177Lu]1h was excreted via the renal pathway and showed high tumor uptake (24.43 ± 3.36%ID/g) after 1 hour, which increased over 72 hours (72 hours = 51.39 ± 9.26%ID/g). Mice treated with 4 and 6 MBq of [177Lu]1h showed a median survival rate of >61 days. In particular, all mice treated with 6 MBq of [177Lu]1h survived for the entire monitoring period. The estimated human effective dose of [177Lu]1h was 0.07 ± 0.01 and 0.03 ± 0.00 mSv/MBq in total body and kidney, respectively. The current study indicates that [177Lu]1h has the potential for further investigation of metastatic castration-resistant prostate cancer (mCRPC) therapy in clinical trials.

KSNM60 in Non-thyroidal Radionuclide Therapy: Leaping into the Future

This year, the Korean Society of Nuclear Medicine (KSNM) is celebrating its 60th anniversary. Treatment, as well as diagnosis, has played a very important role in the development of nuclear medicine. Since I-131 was used for thyroid therapy in 1959, other radionuclide therapy is still being used, and attempts to use new radionuclide are increasing. In this review, we briefly summarize and introduce the therapies such as radioimmunotherapy, transarterial radioembolization, radionuclide therapy for neuroendocrine tumors, peptide receptor radionuclide therapy, control of metastatic bone pain, radiation synovectomy, radionuclide brachytherapy, alpha particle therapy, and boron neutron capture therapy, which has been being attempted so far in the field of nuclear medicine.

Research on preparation and in vitro evaluation of the dendrimer-peptide nuclear acid conjugate for amplification pretargeting

Amplification pretargeting has the potential to increase the tracer's accumulation in the tumor. This study aimed to develop a three-step amplification pretargeting strategy in nuclear medicine with a polymer conjugated with multiple copies of peptide nuclear acid (PNA). In this study, the tracer ¹⁸ F-labeled complementary PNA (¹⁸ F-cPNA) was prepared by click-chemistry with high radiochemical purity (>99%) and great stability in vitro. The PAMMA dendrimer generation 4 (G4) was conjugated with multiple copies of PNAs. The average number of PNA groups in the G4-PNA conjugate was determined by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and the accessibility to the ¹⁸ F-cPNA was identified by size-exclusion high-performance liquid chromatography (SE-HPLC). There were approximately 11.7 of 64 carboxyl groups modified with PNAs, of which more than 99% were accessible to ¹⁸ F-cPNA. ¹⁸ F-cPNA was added to a mixture of CC49-cPNA and G4-PNA, and the complex exhibited a single peak on high-performance liquid chromatography (HPLC) as evidence of complete hybridization between ¹⁸ F-cPNA and CC49-cPNA/G4-PNA. The LS174T tumor cells were incubated with CC49-cPNA followed by G4-PNA as an amplification platform before ¹⁸ F-cPNA was added to hybridize with CC49-cPNA/G4-PNA. Compared with conventional pretargeting without G4-PNA, the radioactivity signal was amplified about four times, which demonstrated that the dendrimer-PNA conjugate plays a crucial role in signal amplification.