SCID mice bearing NSCLC xenografts (,500 mm 3 ), were injected in the tail vein with various formulations of liposomal doxorubicin (SP5-2-LD, MP5-2-LD, and LD) and free doxorubicin at a dose of 2 mg/kg. At selected time points, three mice in each group were anaesthetized and sacrificed. Blood samples were collected through submaxillary punctures, and plasma samples were prepared. After perfusion, xenograft tumors and mouse organs were removed and homogenized. Procedures for isolating tumor cell nuclei and extracting nuclear doxorubicin were carried out according to previous reports [40, 49] . Total doxorubicin concentration was measured using a method described by Mayer et al. [49] . Total doxorubicin was quantified using spectrofluorometry at l ex 485/20 nm and l em 645/40 nm (Synergy HT Multi-Detection Microplate Reader, BioTek Instruments, Winooski, VT 05404 USA).