The tumors in mice that received SP5-2-LD ( Fig. 3A group a) were significantly smaller than those in the MP5-2-LD, LD, FD, and PBS groups (P,0.01) ( Fig. 3A group b-e). The tumor sizes in the LD and MP5-2-LD groups were 2.1 and 2.6 times larger than those in the SP5-2-LD group, respectively. The tumor sizes in the FD and control PBS groups were 7.0 and 8.3 times larger than that in the SP5-2-LD group, respectively (Fig. 3A) . Interestingly, the greater therapeutic efficacy of SP5-2-LD was lost when the WTY motif in the peptide had been changed to GGG in MP5-2-LD. Free doxorubicin exhibited little therapeutic efficacy at this concentration, as the tumor size in this group was only 16% smaller than that in the PBS group (Fig. 3A) .