Theranostic role of ⁸⁹Zr- and ¹⁷⁷Lu-labeled aflibercept in breast cancer

Triple-negative breast cancer (TNBC) has a poor prognosis due to the absence of effective therapeutic targets. Vascular endothelial growth factor (VEGF) family are expressed in 30–60% of TNBC, therefore providing potential therapeutic targets for TNBC. Aflibercept (Abe), a humanized recombinant fusion protein specifically bound to VEGF-A, B and placental growth factor (PIGF), has proven to be effective in the treatment in some cancers. Therefore, ⁸⁹Zr/¹⁷⁷Lu-labeled Abe was investigated for its theranostic role in TNBC.

Abe was radiolabeled with ⁸⁹Zr and ¹⁷⁷Lu via the conjugation of chelators. Flow cytometry and cell immunofluorescent staining were performed to evaluate the binding affinity of Abe. Sequential PET imaging and fluorescent imaging were conducted in TNBC tumor bearing mice following the injection of ⁸⁹Zr-labeled Abe and Cy5.5-labeled Abe. Treatment study was performed after the administration of ¹⁷⁷Lu-labeled Abe. Tumor volume and survival were monitored and SPECT imaging and biodistribution studies were conducted. Safety evaluation was performed including body weight, blood cell measurement, and hematoxylin–eosin (H&E) staining of major organs. Expression of VEGF and CD31 was tested by immunohistochemical staining. Dosimetry was estimated using the OLINDA software.

FITC-labeled Abe showed a strong binding affinity to VEGF in TNBC 4T1 cells and HUVECs by flow cytometry and cell immunofluorescence. Tumor uptake of ⁸⁹Zr-labeled Abe peaked at 120 h (SUVmax = 3.2 ± 0.64) and persisted before 168 h (SUVmax = 2.54 ± 0.42). The fluorescence intensity of the Cy5.5-labeled Abe group surpassed that of the Cy5.5-labeled IgG group, implying that Cy5.5-labeled Abe is a viable candidate monitoring in vivo tumor targeting and localization. ¹⁷⁷Lu-labeled Abe (11.1 MBq) served well as the therapeutic component to suppress tumor growth with standardized tumor volume at 16 days, significantly smaller than PBS group (about 815.66 ± 3.58% vs 3646.52 ± 11.10%, n = 5, P < 0.01). Moreover, SPECT images confirmed high contrast between tumors and normal organs, indicating selective tumor uptake of ¹⁷⁷Lu-labeled Abe. No discernible abnormalities in blood cells, and no evident histopathological abnormality observed in liver, spleen, and kidney. Immunohistochemical staining showed that ¹⁷⁷Lu-labeled Abe effectively inhibited the expression of VEGF and CD31 of tumor, suggesting that angiogenesis may be suppressed by ¹⁷⁷Lu-labeled Abe. The whole-body effective dose for an adult human was estimated to be 0.16 mSv/MBq.

⁸⁹Zr/¹⁷⁷Lu-labeled Abe could be a TNBC-specific marker with diagnostic value and provide insights into targeted therapy in the treatment of TNBC. Further clinical evaluation and translation may be of high significance for TNBC.