Positron-Emission Tomography of HER2-Positive Breast Cancer Xenografts in Mice with <sup>89</sup>Zr-Labeled Trastuzumab-DM1: A Comparison with <sup>89</sup>Zr-Labeled Trastuzumab
Bibliographic record
Abstract
Our aim was to synthesize 89Zr-labeled trastuzumab-emtansine (89Zr-DFO-T-DM1) to probe the delivery of trastuzumab-emtansine (T-DM1) to HER2-positive breast cancer (BC) by positron emission tomography (PET). We further aimed to compare the tumor and normal tissue uptake of 89Zr-DFO-T-DM1 with 89Zr-DFO-trastuzumab. T-DM1 was modified with 3.0 ± 0.2 desferrioxamine (DFO) chelators for complexing 89Zr by reaction with a 14-fold molar excess of p-NCS-Bz-DFO. The number of DFO chelators per T-DM1 molecule was quantified spectrophotometrically at 430 nm after the reaction with FeCl3. SDS-PAGE and SE-HPLC demonstrated a pure and homogeneous immunoconjugate. DFO-T-DM1 and DFO-trastuzumab were labeled to high efficiency (>97%) with 89Zr at a specific activity of 0.55 MBq/μg in a 2 M Na2CO3/0.5 M HEPES buffer, pH 7.0, at RT for 60–90 min. The labeling efficiency was measured by instant thin layer-silica gel chromatography (ITLC-SG) and SE-HPLC. HER2 immunoreactivity was measured in a saturation binding assay using SK-BR-3 human BC cells. 89Zr-DFO-T-DM1 exhibited high affinity HER2 binding (Kd = 3.7 ± 0.4 nM) that was not significantly different than 89Zr-DFO-trastuzumab (4.4 ± 0.5 nM; P = 0.06). The optimal time for tumor imaging with 89Zr-DFO-T-DM1 was 96 h post-injection in NOD-scid mice with s.c. HER2 overexpressing (HER2 3+) BT-474 human BC xenografts. Tumor uptake was dependent on the level of HER2 expression in mice with s.c. BT-474 (HER2 3+), MDA-MB-231/H2N (HER2 2+), MDA-MB-231 (HER2 0–1+), or MDA-MB-468 (HER2 0) human BC xenografts injected with 89Zr-DFO-T-DM1 (10 μg, 5.2 MBq). All tumors were visualized by microPET/CT, but the tumor intensity was greatest for BT-474 and MDA-MB-231/H2N xenografts. The tumor uptake of 89Zr-DFO-T-DM1 was 4.1-fold significantly higher than 89Zr-DFO-trastuzumab in mice with s.c. BT-474 (HER2 3+) xenografts (43.5 ± 4.3%ID/g vs 10.6 ± 5.4%ID/g, respectively; P < 0.001). Tumor uptake of 89Zr-DFO-T-DM1 in MDA-MB-231/H2N xenografts (HER2 2+) was 3.7-fold significantly higher than 89Zr-DFO-trastuzumab (10.1 ± 3.6%ID/g vs 2.7 ± 0.5%ID/g; P < 0.001). The higher tumor uptake of 89Zr-DFO-T-DM1 compared to 89Zr-DFO-trastuzumab was not due to a higher HER2 binding affinity or to differences in the residence time in the blood or tumor size. We conclude that 89Zr-DFO-T-DM1 is a useful probe to assess the delivery of T-DM1 to HER2-positive BC. PET with 89Zr-DFO-trastuzumab has been studied clinically to predict response to T-DM1, but our results suggest that 89Zr-DFO-T-DM1 may be more accurate due to the differences in the tumor uptake observed in the preclinical BC xenograft mouse models.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.000 |
| Bibliometrics | 0.001 | 0.003 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.002 |
| Insufficient payload (model declined to judge) | 0.001 | 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".