Nuclear medicine and biology最新文献

Aim/introduction: Astatine-211 is one of the alpha-particle emitting nuclides investigated for use within Targeted Alpha Therapy (TAT) of disseminated cancer. In previous studies, a difference in blood clearance has been observed when comparing astatinated compounds with their iodinated counterparts. This has been explained by a potentially prolonged retention in the blood by present free astatine. This study examined the spontaneous binding of non-conjugated astatine to albumin under physiological conditions in vitro and compared it to that of iodine. Additionally, the in vivo blood circulation patterns of free astatine were assessed and contrasted with those of iodine.

Materials and methods: Astatine solutions were formulated following dry distillation and evaporation to dryness of astatine solvated in CHCl₃. In vitro evaluation of astatine and iodine association to albumin was mainly performed using size exclusion chromatography applying both disposable columns (PD10 and NAP10) as well as an FPLC system (ÄKTA) with online UV detection and activity fraction collection. Also methanol precipitation and radio-TLC methods were used for analysis. In vivo evaluation was performed using furry BALB/C mice (3/group) with both i.v. and i.p. injection of astatine, followed by sequential blood sampling from the tail vein and biodistribution.

Results: Oxidized and unmodified forms of free astatine display a significantly higher and more rapid association to albumin in vitro compared to reduced forms, with >97% compared to <25% associated after 10 min. Both the corresponding oxidized and reduced forms of iodine display a very low and slow association to albumin with <5% associated after 40 min. Oxidized, unmodified and reduced astatine show very similar blood profiles over time as well as a similar uptake in biodistribution after 20-22 h following i.p. injection. Upon i.v. injection a larger difference in blood profiles between the species could be observed, which in turn was different compared to the curve obtained after i.p. injection. In addition, an unexpected uptake of astatide in stomach was found. In all cases the blood profile and biodistribution of astatine was significantly different compared to iodine, which displayed a greater and more rapid blood clearance and specific accumulation in thyroid.

Conclusion: Different forms of unbound astatine differ in their association to albumin. However, all investigated forms of free astatine associates to albumin to a much higher degree than iodine. This behavior could explain the prolonged blood circulation of free astatine compared to iodine.

Pancreatic ductal adenocarcinoma (PDAC) continues to be deadly and resistant to traditional treatments. Overexpressed in >80% of PDACs, mesothelin is an ideal target for antibody-based α-therapy. Actinium-225 (225Ac) produces high-LET α-particles leading to irreparable DNA damage, but its utility has been compromised by unstable chelation with traditional ligands. Here, we engineered a Macropa-enabled, site-specifically [²²⁵Ac]Ac-Macropa-PEG₆-Amatuximab, a radioimmunoconjugate against mesothelin. Conjugation and labeling were characterized by MALDI-TOF and SEC-HPLC. In vitro stability, immunoreactivity, and kinetics of binding were tested in mesothelin-positive AsPC-1 cells and subsequently in vivo biodistribution, dosimetry, and therapy in AsPC-1 xenograft-bearing nude mice. Conjugation had an average ratio of 3.6 ± 0.1 for chelator per antibody, radiolabeling efficiency of 96.3 ± 1.1%, and radiochemical purity ≥98%. The radioconjugate was >92% stable after 168 h in serum, with immunoreactivity (82.2 ± 2.8%) and affinity (Kd = 4.3 ± 0.9 nM). It exhibited specific, time-dependent internalization in AsPC-1 cells and minimal nonspecific uptake. In vivo, [²²⁵Ac]Ac-Macropa-PEG₆-Amatuximab exhibited prolonged circulation, specific tumor localization (3.9 ± 0.5 to 16.3 ± 2.1% ID/g, 1-168 h), and enhanced tumor-to-blood ratios (0.21-3.40). Blocking with unlabeled Amatuximab decreased tumor uptake by >60%. The tumor absorbed dose (1.82 ± 0.14 Gy/MBq) was 4-20-fold greater than doses to normal organs. Therapeutically, it caused dose-dependent tumor regression (TGI: 58% at 50 kBq; 92% at 150 kBq) and prolonged survival (>60 days vs. 0-1% in controls, p < 0.001). [²²⁵Ac]Ac-Macropa-PEG₆-Amatuximab is stable, selective, and therapeutically effective, demonstrating Macropa-based 225Ac chelation as a stable platform for targeted α-therapy of PDAC.

Background: CTT1403 (¹⁷⁷Lu-CTT2001), an irreversible phosphoramidate PSMA inhibitor developed by Cancer Targeted Technology, was initially synthesized using a two-step radiolabeling method and has previously been evaluated in first-in-human studies. This two-step approach protected the phosphoramidate pharmacophore-containing a temperature- and pH-labile PN bond-from the harsh conditions required for lutetium-177 (¹⁷⁷Lu) chelation. Although the final chemical structure of CTT1403 is identical regardless of the radiolabeling route, it was not clear that CTT2001 could tolerate one-step labeling conditions while preserving PSMA-binding integrity. Therefore, the aim of the study was to develop, optimize, and automate a one-step radiolabeling method for CTT1403 and to confirm that the resulting product is biologically equivalent and exhibits comparable in vitro and in vivo behavior to CTT1403 produced by the original two-step process.

Methods: CTT2001 was synthesized and radiolabeled with ¹⁷⁷Lu using an optimized one-step procedure that was subsequently automated on a Trasis AllinOne synthesizer. Radiochemical purity, stability, cellular uptake/internalization, and biodistribution in PC3-PIP tumor-bearing mice were evaluated.

Results: CTT1403 synthesized via the one-step method demonstrated cellular uptake and internalization in PC3-PIP cells, as well as in vivo biodistribution in PC3-PIP tumor-bearing mice, that were comparable to those of the two-step-labeled product. The one-step procedure was successfully automated on the Trasis All-in-One synthesizer, producing CTT1403 with a radiochemical yield of 86.5 ± 4.27% (n = 3), a molar activity of 30.3 ± 1.11 MBq/nmol, and a radiochemical purity of 97.6 ± 0.80% (n = 3) in a total synthesis time of 38 min. The final product remained stable for at least 24 h at -4 °C and -20 °C.

Conclusions: The one-step radiolabeling method yields CTT1403 that is biologically equivalent to the two-step product and can be reliably produced using fully automated synthesis. This streamlined, efficient, and reproducible approach supports routine clinical manufacturing of CTT1403.

Background: [¹⁸F]Fluoropivalate ([¹⁸F]FPIA), also known as ¹⁸F-pivalate or ¹⁸F-RAD101, is the fluorinated analogue of pivalic acid and has shown promise in ongoing clinical trials for the detection of brain metastases. The original synthesis of [¹⁸F]FPIA involved a two-step procedure that was not fully automated, limiting its suitability for large-scale or GMP production. A subsequent report described an improved two-step, one-pot synthesis on a cassette-based module, although with certain limitations. Here, we present an optimized two-step, one-pot synthesis of [¹⁸F]FPIA using a vial-based automated synthesizer and demonstrate its successful implementation under GMP conditions. We also report [¹⁸F]FPIA-PET imaging in prostate cancer patient-derived xenograft (PDX) models.

Results: [¹⁸F]FPIA was successfully produced with the optimized synthetic strategy with a total synthesis time of 75 min and a 25.4 ± 3.8% (n = 9) activity yield at end of synthesis (EOS), with >99% radiochemical purity. In a GMP setting, the scale-up synthesis was successful with a 37 ± 9% (n = 37) activity yield at EOS and a > 99% radiochemical purity. In the proof-of-concept PET imaging study of [¹⁸F]FPIA in androgen receptor (AR)-negative and -positive prostate cancer PDX animal models, uptake was observed in both groups when the tumor reached a size of 50-300 mm³. The AR-negative group showed significantly higher [¹⁸F]FPIA uptake compared to the AR-positive group, with average tumor-to-muscle ratios of 1.6 and 1.2, respectively.

Conclusions: In summary, an optimized one-pot, two-step synthesis of [¹⁸F]FPIA on a vial-based automated synthesizer was successful and a seamless transition into a GMP facility is reported, enabling a streamlined transition to clinical production. Furthermore, we have demonstrated the use of [¹⁸F]FPIA for noninvasive metabolic imaging in prostate cancer and its potential to distinguish between different prostate cancer subtypes.