Antibacterial and immunostimulatory properties of chemotactic N-formyl peptide conjugates of ampicillin and amoxicillin.

N-Formyl dipeptide conjugates of ampicillin and amoxicillin related to the chemotactic peptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine were synthesized and assessed for antibacterial activity and affinity for the chemotactic peptide receptor of differentiated human promyelocytic leukemia (HL-60) cells. The conjugates and parent beta-lactam antibiotics showed similar antibacterial activities against Escherichia coli and Staphylococcus aureus. The affinity of each conjugate for the chemotactic peptide receptor was determined in a competitive binding assay, using 3H-labeled N-formyl-L-methionyl-L-leucyl-L-phenylalanine. All conjugates bound to the receptor, but with affinities ranging from 1/3 to 1/100 that of the tritiated substrate. There was good correlation between receptor affinity and stimulation of chemotaxis. The peptide-antibiotic conjugates also stimulated the oxidative metabolism of the HL-60 cells by inducing the production of superoxide and hydrogen peroxide as determined by Luminol- and Lucigenin-enhanced chemiluminescence. These conjugates, based on N-formyl-L-methionyl-L-leucyl-L-phenylalanine, thus combine both potent antibacterial and immunostimulatory properties within the same molecule.