The application of tumor targeting ligands for the treatment of cancer holds the promise of enhanced efficacy and reduced toxicity. L-SP5 ((L)(SVSVGMKPSPRP)) is a peptide that recognizes tumor neovasculature but not normal blood vessels (Lee et al., Cancer Res. 2007, 67, 10958-65). The current report presents the design and application of D-SP5 ((D)(PRPSPKMGVSVS)), a novel retro-inverso analogue of L-SP5. Peptides D-SP5 and parental L-SP5 are shown to compete for the same target sites of a yet unknown cellular target and possess a dual-targeting bioactivity for both activated endothelial cells (HUVEC) and several tumor cell lines. Cellular uptake experiments showed superior in vitro targeting abilities of D-SP5 compared with L-SP5, such as enhanced internalization into stimulated HUVEC or KB, U87, and SGC tumor cells. A radioligand receptor binding assay revealed a higher cell affinity of D-SP5 in all tested cell lines, with K-d values for D-SP5 about 2-fold lower than for L-SP5. An up to 3-fold higher maximum binding capacity (B-max) to cells of D-SP5 was noted. Fluorescein-labeled D-SP5 upon intravenous administration displayed strong association with tumor endothelium. D-SP5-conjugated PEG-DSPE micelles displayed enhanced tumor homing (evidenced by near infrared in vivo imaging). When loaded with doxorubicin, D-SP5 micelles could markedly suppress tumor growth with higher efficacy than L-SP5 micelles both in vitro and in vivo in KB tumor xenografts. In summary, the data demonstrate that D-SP5 displays higher binding affinities toward tumor endothelium as well as tumor cells and enhanced tumor targeting capability in vitro and in vivo.
[1]Fudan Univ, Sch Pharm, Minist Educ, Key Lab Smart Drug Delivery, Shanghai 201203, Peoples R China;
[2]Fudan Univ, Sch Pharm, Dept Pharmaceut, PLA, Shanghai 201203, Peoples R China;
[3]Fudan Univ, Sch Pharm, Dept Radiopharm, Shanghai 201203, Peoples R China
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