Enhancement of cytotoxicity of antimicrobial peptide magainin II in tumor cells by bombesin-targeted delivery.
OBJECTIVE
To investigate whether the conjugation of magainin II (MG2), an antimicrobial peptides (AMPs), to the tumor-homing peptide bombesin could enhance its cytotoxicity in tumor cells.


METHODS
A magainin II-bombesin conjugate (MG2B) was constructed by attaching magainin II (MG2) to bombesin at its N-terminus. The peptides were synthesized using Fmoc-chemistry. The in vitro cytotoxicity of the peptide in cancer cells was quantitatively determined using the CCK-8 cell counting kit. Moreover, the in vivo antitumor effect of the peptide was determined in tumor xenograft models.


RESULTS
The IC(50) of MG2B for cancer cells (10-15 μmol/L) was at least 10 times lower than the IC(50) of unconjugated MG2 (125 μmol/L). Moreover, the binding affinity of MG2B for cancer cells was higher than that of unconjugated MG2. In contrast, conjugation to a bombesin analog lacking the receptor-binding domain failed to increase the cytotoxicity of MG2, suggesting that bombesin conjugation enhances the cytotoxicity of MG2 in cancer cells through improved binding. Indeed, MG2B selectively induced cell death in cancer cells in vitro with the IC(50) ranging from 10 to 15 μmol/L, which was about 6-10 times lower than the IC(50) for normal cells. MG2B (20 mg/kg per day, intratumorally injected for 5 d) also exhibited antitumor effects in mice bearing MCF-7 tumor grafts. The mean weights of tumor grafts in MG2B- and PBS-treated mice were 0.21±0.05 g and 0.59±0.12 g, respectively.


CONCLUSIONS
The results suggest that conjugation of AMPs to bombesin might be an alternative approach for targeted cancer therapy.
Key Lab of Transplant Engineering and Immunology, Ministry of Health, West China Hospital, Sichuan University, Chengdu 610041, China.
Shan
S
Liu
Hao
H
Yang
Lin
L
Wan
Hua-wei
HW
Cai
Sheng-fu
SF
Li
You-ping
YP
Li
Jing-qiu
JQ
Cheng
Xiao-feng
XF
Lu
D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000008:administration & dosage* / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D001839:Bombesin / Q000737:chemistry* / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D016503:Drug Delivery Systems; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000188:drug therapy*; D018004:Receptors, Bombesin / Q000378:metabolism
D023181:Antimicrobial Cationic Peptides; D000970:Antineoplastic Agents; D018004:Receptors, Bombesin; D020169:Caspases; D001839:Bombesin