Design of potent, non-toxic antimicrobial agents based upon the naturally occurring frog skin peptides, ascaphin-8 and peptide XT-7.
The frog skin peptides, ascaphin-8 (GFKDLLKGAAKALVKTVLF.NH(2)) and XT-7 (GLLGPLLKIAAKVGSNLL.NH(2)), show broad-spectrum antimicrobial activity but their therapeutic potential is limited by toxicity against mammalian cells. Circular dichroism spectra demonstrate that the peptides adopt an amphipathic alpha-helical conformation in a membrane-mimetic solvent. This study has investigated the cytolytic properties of analogs containing selected amino acid substitutions that increase cationicity while maintaining amphipathicity. Substitutions at Ala(10), Val(14), and Leu(18) in ascaphin-8 by either L-Lys or D-Lys produced peptides that retained antimicrobial activity against the bacteria Escherichia coli and Staphylococcus aureus and the opportunistic yeast pathogen, Candida albicans but showed appreciably reduced toxicities (>10-fold) against human erythrocytes, HepG2 hepatoma-derived cells, and L929 fibroblasts. The improved therapeutic index of the L-Lys(18) and D-Lys(18) analogs correlated with a decrease in % helicity and in effective hydrophobicity. Substitution of Gly(4) by L-Lys in XT-7 produced an analog with high potency against micro-organisms (MIC < or = 25 microM) but low cytolytic activity against erythrocytes (LD(50) > 500 microM) and this increase in therapeutic index also correlated with decreased helicity and hydrophobicity. Analogs of XT-7 with increased cationicity, containing multiple substitutions by L-Lys, not only displayed increased antimicrobial potencies, particularly against Candida albicans (MIC < or = 6 microM), but also increased hemolytic activities.
Department of Biochemistry, Faculty of Medicine and Health Sciences, United Arab Emirates University, 17666 Al-Ain, UAE. jmc2016@qatar-med.cornell.edu
J Michael
JM
Conlon
Sehamuddin
S
Galadari
Haider
H
Raza
Eric
E
Condamine
D019943:Amino Acid Substitution; D029845:Amphibian Proteins / Q000737:chemistry* / Q000627:therapeutic use; D000818:Animals; D000890:Anti-Infective Agents / Q000737:chemistry* / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000627:therapeutic use; D002176:Candida albicans / Q000187:drug effects; D045744:Cell Line, Tumor; D015195:Drug Design; D004912:Erythrocytes / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D008826:Microbial Sensitivity Tests; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D011898:Ranidae; D012867:Skin / Q000737:chemistry; D013211:Staphylococcus aureus / Q000187:drug effects; D013329:Structure-Activity Relationship
D029845:Amphibian Proteins; D000890:Anti-Infective Agents; D023181:Antimicrobial Cationic Peptides; D010455:Peptides