Objectives

Developed a theranostic approach using 89Zr/177Lu-labeled EphA2 monoclonal antibody (mAb) (clone 230-1).
Demonstrated high tumor retention of [89Zr]Zr-/[177Lu]Lu-EphA2 mAb in HT-1080 (EphA2-expressing human fibrosarcoma) xenografts.
Achieved significant tumor shrinkage and complete remission in some mice (6/18) with [177Lu]Lu-EphA2 mAb treatment without severe toxicity.

Methodology

EphA2 mAb (clone 230-1) was generated by immunizing mice with human EphA2 proteins.
Radiolabeling of EphA2 mAb with 89Zr using DFO chelator and 177Lu using NOTA chelator.
89Zr production via 89Y(p, n)89Zr nuclear reaction using a cyclotron.
Purification of 89Zr using a hydroxamate-based resin.
Radiochemical purity analysis using radio-thin-layer chromatography (radio-TLC) and electrophoresis.
In vitro analysis using HT-1080 WT and EphA2-KO cells, including western blotting and flow cytometry.
In vivo PET imaging with [89Zr]Zr-EphA2 mAb.
Biodistribution studies and blocking studies with [177Lu]Lu-EphA2 mAb.
Radioimmunotherapy experiments with different doses of [177Lu]Lu-EphA2 mAb, non-radiolabeled EphA2 mAb, [177Lu]LuCl3, and saline.
Tumor volume measurement using the elliptical sphere model.
Immunohistochemical staining for EphA2.

[89Zr]Zr-EphA2 mAb PET showed high tumor accumulation (SUVmax: 11.8 ± 4.98 on day 1, 20.1 ± 6.42 on day 5).
[177Lu]Lu-EphA2 mAb biodistribution: high tumor uptake (49.4 ± 10.8 %IA/g at 24h, 101.8 ± 26.3 %IA/g at 72h).
Blocking study: significant tumor uptake reduction (47.2 ± 8.22 vs. 10.7 ± 0.52 %IA/g, P=0.02).
Radioimmunotherapy: substantial tumor growth inhibition and complete remission in 6/18 mice with [177Lu]Lu-EphA2 mAb (3 and 10 MBq).
Estimated absorbed doses in the tumor: 51.7 Gy (3 MBq) and 172.4 Gy (10 MBq).
No sustained weight loss or apparent renal/hematological toxicity in the [177Lu]Lu-EphA2 mAb group.

The study uses a single xenograft model (HT-1080). While the results are promising, further validation in other EphA2-expressing tumor models, ideally including patient-derived xenografts (PDX), is crucial to assess the generalizability of the findings.
The study lacks a comprehensive assessment of potential side effects. Detailed hematological analysis (e.g., complete blood counts over time) and histopathological examination of major organs (especially kidneys and liver) are needed.
While the blocking study demonstrates specificity, the mechanism of [177Lu]LuCl3's partial tumor growth inhibition is unclear and warrants further investigation. Is it due to non-specific radiation exposure, or is there another mechanism at play?
The study does not evaluate the long-term effects of the treatment. A longer follow-up period is needed to assess the durability of the response and potential for delayed toxicity.
The manuscript would benefit from a clearer description of the antibody humanization process, if any. This is important for assessing the clinical translatability of the findings.
The rationale for the selected doses of [177Lu]Lu-EphA2 mAb (3 and 10 MBq) should be better justified. A more systematic dose-response study would strengthen the conclusions.