EJNMMI Radiopharmacy and Chemistry最新文献

Background

 Bladder cancer remains a significant global health challenge, with approximately 75% of cases presenting as non-muscle-invasive bladder cancer. Despite standard treatment with transurethral resection and intravesical Bacillus Calmette-Guérin immunotherapy, up to 40% of patients develop resistance or progress to muscle-invasive disease. Targeted alpha-emitting radionuclide therapy offers promising therapeutic potential through the selective delivery of high linear energy transfer radiation to tumor cells while minimizing damage to healthy tissues. PTK7 is overexpressed in various malignancies, including bladder cancer, and is therefore a viable therapeutic target. This study evaluated the preclinical efficacy of [²¹²Pb]Pb-TCMC-chOI-1, a ²¹²Pb-labeled antibody targeting PTK7, for targeted alpha-emitting radionuclide therapy in bladder cancer using 2D adherent cultures (clonogenic assay) and 3D multicellular spheroid models (spheroid growth inhibition).

Results

 PTK7 expression analysis revealed varying antigen densities across five bladder cancer cell lines, ranging from approximately 10,000 to 70,000 sites per cell. The chimeric anti-PTK7 antibody demonstrated apparent equilibrium dissociation constants of 10–44 nM with moderate binding affinity suitable for therapeutic applications. [²¹²Pb]Pb-TCMC-chOI-1 treatment resulted in activity- and time-dependent cytotoxicity, with enhanced sensitivity observed in cell lines with higher PTK7 levels. In clonogenic assays, the activity concentration required for 50% growth reduction was 48–74 kBq/mL, corresponding to 22–51 bound and 9–16 internalized ²¹²Pb atoms per cell. In 3D models, similar therapeutic effects were observed despite significantly lower activities (values of approximately 1 and 30 kBq/mL for KU-19–19 and 647-V cells, respectively), suggesting a more pronounced cross-fire effect. Flow cytometry demonstrated treatment-induced DNA damage, cell cycle perturbations and cell death, with response patterns correlating with overall treatment sensitivity. RT-112 and KU-19–19 cells showed superior responses compared to 647-V and T-24 cells, consistent with their higher PTK7 expression.

Conclusions

 These findings support PTK7 as a therapeutic target for bladder cancer and demonstrate the potential of [²¹²Pb]Pb-TCMC-chOI-1 for targeted alpha-emitting radionuclide therapy. The results provide a rationale for further preclinical optimization of this therapeutic approach.

Trial registration number (TRN): Not applicable.

Background

Recent EMA and FDA approvals of Lu-DOTATATE and Lu-PSMA-617 have led to increased demand for radiotherapeutic (^{177})Lu, due to its promising potential to treat castration-resistant neuroendocrine cancers. Conventional reactor production methods pose challenges related to cost, waste management, and local availability. In comparison, accelerators produce less waste, have lower maintenance costs, and can be directly integrated into hospital settings. In this study, we evaluate the production of radiotherapeutic (^{177})Lu using a 10 mA, 18 MeV (D^+) compact linear accelerator design. The design consists of a single radio-frequency quadrupole (RFQ) and seven drift tube linacs (DTLs) that achieve a beam efficiency of 98.5% over a total length of (12,text {m}). Deuteron activations on a 99% enriched [(^{176})Yb](hbox {Yb}_2hbox {O}_3) target are estimated using experimental and simulated excitation functions.

Results

A circular target with a radius of 1 cm and 0.36 mm thickness is selected to optimize the yield of (^{177})Lu while minimizing the production of undesirable radioisotopes, including (^{174g+m})Lu and (^{177m})Lu. Model calculations indicate that the accelerator design can produce 11.3 μg of (^{177})Lu per hour. A 5-day irradiation is expected to yield approximately 1.07 mg of (^{177})Lu (4.4 TBq), while a 12-day irradiation can produce up to 1.9 mg (7.8 TBq). Following a 2-day processing period, the specific activity of the 5-day irradiated sample is projected to approach 0.6 TBq/mg, with a radiopurity of approximately 99.8%. The minimal burn-up of the (hbox {Yb}_2hbox {O}_3) target suggests it may be recycled and reused over multiple irradiations.

Conclusions

The study confirms the feasibility of accelerator-based (^{177})Lu production as an alternative to existing reactor-based methods. The 10 mA, 18 MeV (D^+) RFQ-DTL design achieves an exceptionally high (^{177})Lu radiopurity and a competitive overall yield, which can meet the dose requirements of thousands of patients.

Background

Fibroblast activation protein (FAP)-targeting radioligands have gained attention for the ability to image multiple tumor types. Current FAP-targeting radioligands are labeled with ⁶⁸Ga and ¹⁸F, but their short half-lives limit distribution range after production and later time-point imaging. This study describes the development Kalios, a novel class of NODAGA-conjugated FAP-targeting radioligands labeled with the cyclotron-produced Copper-61 (t_1/2 = 3.33 h), for greater temporal range for FAP-targeted imaging.

Results

Four Kalios ligands were synthesized and radiolabeled with [⁶¹Cu]CuCl₂ in high yield and radiochemical purity within 5 min at room temperature. All radioligands demonstrated high hydrophilicity and strong affinity for FAP, and were primarily internalized after incubation with FAP-positive cells. PET/CT images obtained at 0–1 h and 4 h post-injection (p.i.) illustrated accumulation of all radioligands in FAP-positive tumors. Biodistribution studies of [⁶¹Cu]Cu-Kalios-02 demonstrated stable tumor uptake between 1 and 4 h p.i., with washout from normal tissues at 4 h, resulting in improved tumor-to-background ratios.

Conclusions

Kalios ligands represent a new class of FAP-targeting ⁶¹Cu-labeled radioligands. The half-life of ⁶¹Cu allowed delayed 4-h imaging with improved tumor-to-background ratios. The improved delayed imaging and greater distribution range of these ⁶¹Cu-labeled FAP-targeting radioligands demonstrates their clear potential for clinical translation, while combination with the therapeutic twin ⁶⁷Cu allows for truly paired Kalios theranostics.

Background

Mesothelin is a glycoprotein overexpressed in various cancers, with limited expression in healthy tissues. The single-domain antibody (sdAb, or nanobody) A1-His has previously successfully been validated in mice for the SPECT imaging of mesothelin positive tumors following radiolabeling with ^99mTc. Our objective was to radiolabel this sdAb with ⁶⁸Ga for PET imaging, exhibiting superior sensitivity and resolution than SPECT in clinical practice. To this aim, it was conjugated to NOTA chelator that is commonly employed for ⁶⁸Ga labeling of antibody-derived tracers. In addition, the high affinity and specificity of A1-His sdAb position it as a promising candidate for theranostic applications. In anticipation of future radiolabeling with beta-emitting radionuclides, DOTA-conjugated A1-His was also evaluated. Given the high thermal stability of sdAbs, this DOTA-conjugated sdAb could potentially be implemented in future studies as a theranostic agent with beta-emitting radionuclides.

Results

A1-His was successfully conjugated to p-SCN-Bn-DOTA and p-SCN-Bn-NOTA under optimized conditions, achieving chelator-to-sdAb ratios of 1.8 and 1.3, respectively. NOTA-A1-His allowed rapid radiolabeling with ⁶⁸Ga at room temperature, achieving high radiochemical purity (> 98%) within 5 min. Using DOTA, similar purity was obtained at 60 °C for 15 min. Both radiotracers demonstrated stability over 4 h in the radiolabeling medium and 2 h in human blood. However, some instability was observed in murine blood. Biodistribution and imaging studies in mice bearing mesothelin-expressing tumors showed specific tumor targeting for both tracers. Notably, [68Ga]Ga-DOTA-A1-His exhibited twofold lower kidney uptake compared to [68Ga]Ga-NOTA-A1-His, potentially enhancing imaging contrast and reducing renal radiation exposure. His-tag removal, further improves the biodistribution profile of the 2 tracers.

Conclusions

Both p-SCN-Bn-DOTA and p-SCN-Bn-NOTA chelators can be effectively conjugated to the A1 sdAb and radiolabeled with ⁶⁸Ga, producing stable radiotracers with specific tumor-targeting capabilities. NOTA chelator offers advantages in rapid, room-temperature radiolabeling. However, DOTA would offer the advantage to be employed for theranostic approaches using β⁻ emitters such as ¹⁷⁷Lu or ¹⁶¹Tb. The lower kidney retention of DOTA-A1 also suggests that its dosimetry, a key factor in theranostic, would be more favorable.

Antimony-119 (¹¹⁹Sb, t_1/2 = 38.19 h) is an Auger electron emitting radionuclide of interest for radiopharmaceutical therapy. It can be directly produced by proton bombardment of tin-119 using low energy cyclotrons. The radiochemical separation methods available for recovering ¹¹⁹Sb from the bulk Sn target material are lacking, particularly with respect to matrix suitability for further applications.

Eight new resins were successfully synthesized, evaluating combinations of two different resin support materials with three different chain lengths of ethers (dibutyl, dipentyl, dioctyl) as well as fluorinated alcohol as the impregnated extractant. All resins showed good stability, losing less than 1% of functional groups in HCl and water. Seven out of eight synthesized resins showed excellent capacity, retaining tens to hundreds of milligrams of Sb per gram of resin. Seven out of eight synthesized resins, as well as one of the resin supports showed good separation between Sb and Sn based on the distribution coefficient studies as well as dynamic elution studies.

Our tested resins may be applied for the separation of radiotracer amounts of Sb from bulk Sn target material. We propose the dibutyl ether functionalized divinylbenzene copolymer resin support (DBE-300 resin) as the best candidate, based on the following characteristics: (1) quantitative, concentrated elution of Sn offering compatibility with recycling of enriched ¹¹⁹Sn material; (2) near-quantitative (98%), concentrated recovery of ¹¹⁹Sb in ethanol, providing a matrix resistant to hydrolysis, easy to convert by evaporation, as well as toxicologically insignificant pre-clinically and even clinically.

Background

The aim of this work was to demonstrate the suitability of AAZTA chelator conjugated to a FAPI-46-derived FAP inhibitor and labelled with gallium-68 as a potential PET tracer.

Results

Gallium-68 radiolabelling was achieved with high radiochemical yield at room temperature. The new tracer was stable in different media, showing specific binding to FAP-protein both in vitro and in vivo, and a suitable biodistribution and clearance. High tumor uptake of the tracer (1.01 ± 0.12 SUV 35 min p.i.) was found in 4T1-tumor bearing mice, and blocking experiments demonstrated the high target specificity.

Conclusion

The substitution of the DOTA chelator with the AAZTA ligand on FAPI-46 moiety allowed a fast radiolabelling at room temperature of the PET tracer without influencing the biodistribution properties, such as clearance and FAP-mediated tumor uptake, but rather expanding the tracer applicability.

Background

[²¹¹At]m-Astatobenzylguanidine ([²¹¹At]MABG) has demonstrated potent antitumor efficacy in preclinical models of malignant neuroendocrine tumours including neuroblastoma and pheochromocytoma/paraganglioma. The high linear energy transfer and short tissue penetration range of alpha particles enable highly localized cytotoxic effects, potentially overcoming therapeutic limitations associated with conventional beta-emitting radiopharmaceuticals. However, under clinical-scale (i.e., high radioactivity) conditions, the efficient and stable production of [²¹¹At]MABG has been hindered by radiolytic degradation during the manufacturing process limiting the availability of reliable methods offering high radiochemical yield and purity. In this study, we aimed to develop a scalable production methodology for [²¹¹At]MABG suitable for clinical translation.

Results

²¹¹At was produced via the ²⁰⁹Bi(α,2n)²¹¹At nuclear reaction using a cyclotron, with ²¹⁰At formation minimised by precise control of the alpha particle energy. The resulting product was purified using an automated dry distillation system. [²¹¹At]MABG was synthesised using the COSMiC-Mini automated synthesiser in 28.2 ± 2.8 min from initial ²¹¹At activities of up to 586.1 MBq. The radiochemical yield and purity were 80.3 ± 4.4% (decay-corrected RCY: 84.0 ± 4.5%) and 99.0 ± 0.7%, respectively (n = 6). The addition of sodium ascorbate as a radical scavenger contributed to maintaining a high radiochemical yield and purity during large-scale production. The final product was obtained as a sterile solution.

Conclusions

In this study, we established a reliable and scalable production methodology for [²¹¹At]MABG, consistently achieving high radiochemical yield and purity across a wide range of radioactivity levels through optimization of the automated radiosynthesis process and the use of radiolytic stabilizers. This approach provides a solid technical foundation for the clinical application of [²¹¹At]MABG in targeted alpha therapy.

Background

Bombesin analogues are gaining popularity as GRPR-targeting theranostic agents aiming to provide molecular tools for a patient-tailored management. We previously reported on two series of DOTAGA-bearing GRPR-antagonists, based on either [NMe-Gly¹¹]RM26 (DOTAGA-X-DPhe-Gln-Trp-Ala-Val-NMe-Gly-His-Sta-Leu-NH₂) or on DB15 (DOTAGA-X-SAR; SAR: DPhe-Gln-Trp-Ala-Val-NMe-Gly-His-Leu-NHEt) motifs, which were preclinically screened after labelling with In-111. In the current study, we aimed to evaluate in vitro and in vivo the four best-performing agents, AU-RM26-M2 (X: PEG2-Pip; Pip: 4-amino-1-carboxymethyl-piperidine), AU-RM26-M4 (X: Arg-Arg-Pip), AU-SAR-M1 (X: AMA-DIG; AMA: p-amino methylaniline, DIG: diglycolate) and AU-SAR-M2 (Arg-AMA-DIG), this time labelled with the therapeutic radionuclide Lu-177.

Results

All four [¹⁷⁷Lu]Lu-peptide radioligands displayed highly GRPR-mediated cellular uptake, showing the typical profile of radioantagonists, with the bulk of cell-associated radioactivity being membrane-bound. The analogues demonstrated good in vivo stability, which was however further improved by in situ stabilization induced by pretreatment of animals with Entresto as the source of the potent neprilysin (NEP)-inhibitor sacubitrilat. The biodistribution profile of the four radiopeptides was determined in prostate cancer PC-3 xenograft-bearing mice at 4 h and 23 h pi, after Entresto pre-treatment. All peptide radioligands had a rapid clearance from the background tissues, with the highest activity uptake found in the implanted tumours, the kidneys and to a lesser extent the GRPR-rich pancreas. The activity in the pancreas and, on a smaller scale, in the kidneys was washed out by 23 h pi, while being highly retained in the tumours. Among the tested analogues, [¹⁷⁷Lu]Lu-AU-SAR-M1 displayed the overall most favourable properties, combining the lowest retention in the kidneys with high and prolonged activity accumulation in the tumours. As a result, [¹⁷⁷Lu]Lu-AU-SAR-M1 provided the best area under the curve (AUC) ratio between tumour and kidneys (5.4), in comparison with [¹⁷⁷Lu]Lu-AU-SAR-M2 (3.8), [¹⁷⁷Lu]Lu-AU-RM26-M4 (3.4), and [¹⁷⁷Lu]Lu-AU-RM26-M2 (1.1).

Conclusions

In conclusion, these results qualify [¹⁷⁷Lu]Lu-AU-SAR-M1 as the candidate of choice for further evaluation in a dedicated preclinical radiotherapy study.

Background

Stable ²⁰⁸Pb will accumulate over time in all ²¹²Pb generators, forming an increasing proportion of the Pb atoms and potentially impacting the efficiency of chelation of ²¹²Pb. This paper models the accumulation of ²⁰⁸Pb in ²¹²Pb-parent generators with time, calculates the optimal elution time with respect to effective specific activity (ESA) of the ²¹²Pb produced, and considers whether the presence of ²⁰⁸Pb could prevent the required molar activities (A_m) being achieved. A matrix calculation was utilised to model the decay of ²²⁴Ra and ²²⁸Th parents in generators and the associated accumulation of ²⁰⁸Pb with time. This model was used to calculate the optimal elution times for each generator with respect to ESA and A_m.

Results

The optimal elution time with respect to A_m of ²¹²Pb is 16.5 h for a ²²⁴Ra generator (61.0% of ²²⁴Ra starting activity, A_m = 6997 MBq ²¹²Pb/nmol total Pb) and 19.2 h for a ²²⁸Th generator (71.4% of ²²⁸Th starting activity, A_m = 6566 MBq ²¹²Pb/nmol total Pb).

Conclusions

The limited data available in literature shows the level of ²⁰⁸Pb present in these studies does not prevent attainment of the required molar activities for pre-clinical or clinical work. However, with other chelators and under other conditions this may not be the case. The authors would encourage others to measure and report the level of ²⁰⁸Pb in ²¹²Pb generator eluates alongside radiolabelling results and the max A_m of the radiopharmaceutical ²¹²Pb (vector molecule (VM)) achieved.