FIGURE 1.

Colony survival of trastuzumab-sensitive BT474 (1.50 ± 0.10 × 10⁶ HER2 copies per cell) breast cancer cells after 6 h of incubation at 37°C with free ²²⁵Ac-DOTA, tumor-responsive liposomes loaded with ²²⁵Ac-DOTA, and radiolabeled trastuzumab (²²⁵Ac-DOTA-SCN-Ab) at extracellular pH of 7.4 (A and C) or 6.0 (B and D), as lowest expected acidic value of tumor interstitial pH_e. Radiolabeled trastuzumab’s specific activity was 2.9 MBq/mg at highest radioactivity concentration. Cold conditions of liposomes and antibody are indicated at zero radioactivity concentration. Error bars correspond to SD of repeated measurements (4–6 samples per radioactivity concentration).