To further confirm SP5-2 could increase the therapeutic index for lung cancer, we linked the SP5-2 peptide to another anticancer drug, liposomal vinorelbine (SP5-2-LV) and tested its efficacy against lung cancer xenografts. SCID mice bearing sizematched CL1-5-derived xenografts were given i.v. injections of SP5-2-LV, liposomal vinorelbine (LV), or equivalent volumes of PBS at a total vinorelbine dose of 24 mg/kg (2 mg/kg twice a week for twelve injections). The tumor-bearing mice treated with SP5-2-LV (Fig. 3E , group a) had significantly smaller tumors than the LV and PBS groups (P,0.01) (Fig. 3E, group b and c) . The tumor size in the LV group was 6.75-fold larger than the SP5-2-LV group. The average tumor size in the control PBS group was 25-fold larger than the SP5-2-LV group (Fig. 3E ). To assess side effects of the treatments, the mice were weighed twice a week. The body weight of mice increased by 5.7% (1.37 g) in the SP5-2-LV group and by 2.4% (0.58 g) in the LV group at the end of the treatment period (data not shown).