Study On The Effect Of Acylation On The Anti-melanoma Activity Of Antimicrobial Peptide Camel

Melanoma is a form of skin cancer.Compared with other tumors,the success rate of melanoma treatment is relatively low due to the drug resistance and tumor metastasis.Therefore,development of new anti-melanoma drugs remains a huge challenge.Antimicrobial peptides(AMPs)is a type of cationic defense peptide with multiple functions,such as antimicrobial activity,antitumor activity and immunomodulatory activity.Because of the special membrane-lytic mechanism,AMPs gains more and more attentions.Camel is a chimeric antimicrobial peptide that derived from the active fragment of melittin and cecropin A.In our previous study,we constructed a novel gene delivery vectors by the conjugation of fatty acid to the N-terminus of camel.We found that the fatty acid could induce camel to form nanostructure.In addition,due to the little studies on effects of nanostructure on the activity of AMPs,we studied the effects of fatty acids with different carbon length(C4,C8,C12,C16)on the self-assembly and anti-melanoma activity.The result demonstrated that C12-camel and C16-camel could self-assemble into nanostructure and form ?-helical structure in saline solution.However,camel,C4-camel and C8-camel could not self-assemble.We found C12-camel could self-assemble into spherical nanoparticle,while C16-camel could self-assemble into nanofiber because the strong hydrophobicity of palmitic acid inhibited the electrostatic repulsion of camel.After the formation of nanostructure,the enzymatic stability of C12-camel and C16-camel were improved,while camel,C4-camel and C8-camel were quickly degraded by trypsin.Although all of fatty acids with different carbon length could enhance the anti-melanoma activity of camel,C16-camel reached the same antitumor level as other peptides needed longer treatment time.This may be that the stable nanostructure hampers the action of C16-camel with tumor cell membrane.The result derived from the antimicrobial experiments,where C16-camellost the antimicrobial activity because it could not reach to the inner cell membrane of bacteria,also demonstrate that large and stable nanofiber would affect the action of C16-camel with cell membrane.Although our results indicated that camel and its analogs could induce the apoptosis of melanoma cells,membrane damage still was the major action mechanism of these peptides.Our results demonstrated that self-assembly could not change the antitumor mechanism of C12-camel and C16-camel.Next,we evaluated the effect of self-assembly on the in vivo antitumor activity of C12-camel and C16-camel.Our results indicated that camel,C12-camel and C16-camel could significantly inhibit the tumor growth after intraperitoneal administration or intratumoral administration.Although a plenty of studies demonstrated that nanoparticles would improve the antitumor efficiency of drugs,the self-assembly could not significantly enhanced the antitumor activity of C12-camel and C16-camel compared with camel.We assumed that this is because the major antitumor mechanism was membrane damage,which can not only directly kill melanoma cells,but also indirectly kill tumor cells by immune cells that induced by cell necrosis.In summary,our results indicated that C12-camel and C16-camel could self-assemble into nanostructure in saline solution.Although fatty acids could enhance the antitumor activity of camel,but not change the major antitumor mechanism of camel based on the membrane damage.In addition,the nanostructure could not significantly enhance the in vivo antitumor activity of C12-camel and C16-camel.Nevertheless,our study provides valuable lessons for the antitumor.