Imaging and treatment of malignant metastatic tumors by using radiation-sensitive, immunolabeled liquid-core microcapsules

In this study, two types of microcapsules were designed: (1) computed tomography (CT)-detectable anti-αvβ3 (E[c(RGDfK)]₂) microcapsules, containing P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1), for the observation of metastases through αvβ3-antigen- antibody accumulation; and (2) metastasis-targeting microcapsules that upon irradiation release anticancer drugs with high affinity for P-selectin. These microcapsules were tested on C₃He/N mice with MM48 tumors undergoing two radiotherapy sessions. The injected anti-αvβ3 microcapsules accumulated in the vascular endothelium of metastatic tissues and could be detected by CT. These microcapsules released P-selectin in response to the first irradiation, which was also induced in the endothelium of vessels in the case of metastasis. The microcapsules used for radiosensitizing metastases were injected 6 h after the first radiotherapy session. Their accumulation reached a maximum at 3 h after injection. After the second radiotherapy session, the microcapsules released carboplatin, which reduced the number of metastases; however, this reduction was not significant.