⁶⁴Cu-Labeled Folate-Conjugated Shell Cross-Linked Nanoparticles for Tumor Imaging and Radiotherapy: Synthesis, Radiolabeling, and Biologic Evaluation

Fluorescence micrographs of KB cells incubated for 4 h at 37°C (A and B) and 4°C (C and D) with FTSC and folate-conjugated SCKs (10 μg FTSC-SCK-folate per 33-mm culture dish, plated with 3 × 10⁵ cells per dish 24 h before assay). Incubation at 4°C led to surface uptake of FTSC-SCK-folate onto KB cells (C), whereas fluorescent endocytotic vesicles are visible inside the cells after 4 h of incubation at 37°C (A). At both incubation temperatures, excess folic acid (1 mmol/L) competitively inhibited FTSC-SCK-folate cell uptake (B and D).

Dependence of tumor uptake on tumor size 4 h after injection of ⁶⁴Cu-labeled folated (A) and nonfolated (B) SCKs in KB xenograft-bearing mice. Data are presented as %ID/g. Within each experimental group, small tumors exhibited enhanced nanoparticle uptake. Coadministration of excess folic acid led to competitive block of ⁶⁴Cu-TETA-SCK-folate tumor uptake (A, dashed line), whereas it had no noticeable effect on ⁶⁴Cu-TETA-SCK tumor uptake (B, dashed line).

Dual-tracer autoradiographs demonstrate regional concentration of ⁶⁴Cu-labeled folated (A) or nonfolated (B) SCKs in mice bearing 0.3- to 0.6-g KB xenografts. Tumors were resected and sectioned into 1-mm slices 1 h after ¹⁸F-FDG administration and 24 h after administration of ⁶⁴Cu-radiolabeled SCKs. Images of ¹⁸F-FDG distribution were collected shortly after tumor resection, whereas distribution of ⁶⁴Cu-labeled SCKs in the same slices was imaged with a 20-h delay. Both tumors exhibit scattered necrotic regions (no radiotracer uptake).