To assess the bioavailability of the liposomal drugs, we used nuclear doxorubicin accumulation as an indicator of drug cytotoxicity [40] . The AUC 0-48 hours of bioavailable doxorubicin (i.e., bound to nuclei) for FD, LD, MP5-2-LD, and SP5-2-LD was 3.7 mg?hr/g, 6.7 mg?hr/g, 7.5 mg?hr/g, and 17.7 mg?hr/g, respectively (Table S2 ). The intra-tumor nuclear doxorubicin concentration in the SP5-2-LD group was 4.8-, 2.6-and 2.4-fold higher than the nuclear doxorubicin concentration in the FD, LD, and MP5-2-LD groups ( Fig. 4B and Table S2 ). Doxorubicin concentration inside tumor tissues and nucleus was not significantly different between the LD and MP5-2-LD groups ( Fig. 4 and Table S2 ).