First preclinical SPECT/CT imaging and biodistribution of [165Er]ErCl3 and [165Er]Er-PSMA-617
Bibliographic record
Abstract
Abstract Background 165 Er (t 1/2 = 10.4 h, E x-ray = 47.1 keV (59.4%) and 54.3 keV (14.3%)) is a promising radionuclide suitable for targeted Auger electron therapy of cancer. 165 Er can be produced at a relatively low cost, high yield, and high purity using small medical cyclotrons. As a late lanthanide, 165 Er is easy to label and can be used as a surrogate for other lanthanides or Ac in proof-of-concept studies. In this report, we explore the radiochemistry, in vitro, and in vivo behavior of [ 165 Er]ErCl 3 and [ 165 Er]Er-PSMA-617 to showcase the application of this radionuclide. Particularly, we report the first phantom and preclinical SPECT imaging of this radionuclide leveraging its characteristic X-ray photon emissions. Results The 165 Ho(p,n) 165 Er nuclear reaction using a 13 MeV cyclotron demonstrated production yields of up to 25 ± 5 MBq. µA −1 h −1 at the end of the bombardment. After the purification (4.0 ± 0.5 h) using a sequential combination of cation exchange and extraction chromatography, 4-h irradiation produced up to 1.5 GBq of [ 165 Er]ErCl 3 . High molar activity [ 165 Er]Er-PSMA-617 was prepared (~ 200 MBq/nmol). [ 165 Er]Er-PSMA-617 showed a Log D 7.4 value of -2.34 ± 0.24 meaning high hydrophilicity of the complex as expected. The stability of [ 165 Er]Er-PSMA-617 in saline, human, and mouse serum was studied and showed intact tracer after 12 h in all three cases. [ 165 Er]ErCl 3 and [ 165 Er]Er-PSMA-617 were both taken up by LNCaP cells. PSMA-617 has IC 50 at nanomolar range for [ 165 Er]Er-PSMA-617 in LNCaP cells. SPECT images with preclinical phantoms showed good uniformity, spatial resolution, and quantitative accuracy. SPECT/CT imaging in LNCaP tumor-bearing mice injected with [ 165 Er]Er-PSMA-617 showed high tumor uptake and quantitative accuracy when comparing the results to ex vivo biodistribution %IA/g values. Mice injected with [ 165 Er]ErCl 3 showed uptake in bone structures and excretion through both liver and kidneys. Conclusions This study demonstrated the preclinical use of 165 Er for the first time. Using [ 165 Er]ErCl 3 and [ 165 Er]Er-PSMA-617 as examples, the radiochemistry, cell, and animal studies showed that 165 Er can be used as a tool for evaluating targeted radiopharmaceuticals. The X-ray emission from 165 Er can be used for quantitative SPECT imaging in mice.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".