To further test whether SP5-2 would optimize the therapeutic index in lung cancer treatment, SP5-2-LD was used to treat a different type of lung cancer xenograft (H460-derived tumor). SCID mice bearing size-matched, H460-derived xenografts were treated with SP5-2-LD, LD, FD, or equivalent volumes of PBS, through i.v. injection at a total doxorubicin dosage of 8 mg/kg (1 mg/kg twice a week for eight injections). The final tumor size in the SP5-2-LD group was significantly smaller than those in the LD, FD and PBS groups (P,0.05). Mice in the LD, FD and PBS groups had tumors with sizes 2.0-, 8.6-and 10.0-fold larger than that in the SP5-52-LD group (Fig. 3C) . Free doxorubicin at this concentration reduced the tumor size by only 14% compared with PBS groups. Not only was tumor growth markedly suppressed in the SP5-2-LD group (Fig. 3C) , the body weight of the mice in this group increased by 10.3% (2.38 g) at the end of the treatment period. In contrast the LD-treated mice had a smaller increase in body weight of 2.4% (0.59 g) (Fig. 3D) .