Abstract
The use of polyethylene glycolated (PEGylated) liposomal doxorubicin (LIPO-DOX®) for clinical chemotherapy of cancers is well known. While LIPO-DOX® can accumulate DOX in tumor tissues due to the enhanced permeability and retention (EPR) effect, further conjugation of specific tumor targeting ligand to the doxorubicin (DOX) encapsulated liposome may be a very useful strategy to improve the tumor uptake and antitumor efficacy. On the other hand, 188Re encapsulated liposomes may have potential applications in radiotherapy and diagnostic imaging. Methods: In this study, Arg-Gly-Asp (RGD) peptides with a high affinity for αvβ3 integrin were conjugated to the PEGylated liposomes, where two types of RGD, c(RGDyK) and E[c(RGDyK)]2 were used. 188Re-BMEDA and DOX were subsequently encapsulated into the liposomes. The resulted liposomes are referred to c(RGDyK)-PL-DOX-188Re and E[c(RGDyK)]2-PL-DOX-188Re. 188Re-BMEDA was also encapsulated into LIPO-DOX to produce the liposome referred to LIPO-DOX-188Re. U-87 MG cells were used for in vitro bioactivity test for the three liposomes. For animal trial, the main works included investigation of biodistribution, pharmacokinetics and imaging of c(RGDyK)-PL-DOX-188Re and E[c(RGDyK)]2-PL-DOX-188Re in comparison with non RGD conjugated liposome, LIPO-DOX-188Re using female athymic nude mice bearing subcutaneous U-87 MG glioblastoma tumors. Results: The cellular uptake of DOX for c(RGDyK)-PL-DOX and E[c(RGDyK)]2-PL-DOX in the U-87 MG cells were about seven-fold and six-fold higher than that for LIPO-DOX, respectively. The biodistribution studies indicated that the three liposomal formulations showed very close activity accumulation in the tumor, but tumor-to-blood ratio for LIPO-DOX-188Re being lower than that for c(RGDyK)-PL-DOX-188Re or E[c(RGDyK)]2-PL-DOX-188Re. The spleen uptake of LIPO-DOX-188Re was significantly higher than that of c(RGDyK)-PL-DOX-188Re and E[c(RGDyK)]2-PL-DOX-188Re at all time points examined. Pharmacokinetic studies revealed that the elimination half-life (T1/2) and mean residence time (MRT) of c(RGDyK)-PL-DOX-188Re (T1/2 = 25.94 h, MRT = 12.1 h) and E[c(RGDyK)]2-PL-DOX-188Re (T1/2 = 26.79 h, MRT = 11.57 h) in blood were longer than that of LIPO-DOX-188Re (T1/2 = 13.29 h, MRT = 11 h), respectively. The coronal microSPECT/CT images of c(RGDyK)-PL-DOX-188Re and E[c(RGDyK)]2-PL- DOX-188Re showed their significant accumulations in the tumor at 16 and 24 h postinjection. In contrast, the coronal microSPECT/CT image of LIPO-DOX-188Re became almost invisible in the tumor at 16 and 24 h postinjection. Conclusion: The results suggest that the use of RGD conjugation to the 188Re and DOX encapsulated liposome is beneficial to pronouncedly reduce the accumulation in the spleen and simultaneously enhance slightly higher specific tumor accumulation. Further studies such as tumor inhibitory activities and mice survival prolongation in tumor-bearing mice are necessary to confirm therapeutic efficacy for LIPO-DOX-188Re, c(RGDyK)-PL-DOX-188Re and E[c(RGDyK)]2-PL-DOX-188Re.