Evaluating the influence of common antibiotics on the efficacy of a recombinant immunotoxin in tissue culture

Abstract

Objective: Recombinant immunotoxins (RITs) are antibody-toxin fusion proteins that can selectively eliminate populations of cells expressing specific surface receptors. They are in evaluation as therapeutic agents for cancer. RITs based on Pseudomonas exotoxin A (PE) are in use clinically for the treatment of hairy cell leukemia, and under trial for the treatment of other cancers. In an effort to improve the efficacy of PE-based RITs, we evaluated the potential of combination therapy with several common antibiotics (tetracycline, chloramphenicol, streptomycin, linezolid, fusidic acid, and kanamycin) on human cell lines HEK293, OVCAR8, and CA46. Antibiotics were selected based on their potential to inhibit mitochondrial protein synthesis and disrupt energy metabolism in cancer cells.

Results: Tetracycline, chloramphenicol, linezolid, and fusidic acid alone killed cultured human cells at high concentrations. At high but nontoxic concentrations of each antibiotic, only chloramphenicol treatment of the Burkitt's lymphoma cell line CA46 showed enhanced cytotoxicity when paired with an anti-transferrin receptor/PE RIT. This result, however, could not be replicated in additional Burkitt's lymphoma cell lines Ramos and Raji. Although the six antibiotics we tested are not promising candidates for RIT combination therapy, we suggest that fusidic acid could be considered independently as a potential cancer therapeutic.

Keywords: Antibiotics; Combination therapy; Cytotoxicity; HB21-LR; Mitochondrial translation; Pseudomonas exotoxin A; Recombinant immunotoxins; Translation inhibition.

Fig. 1

Responses of human cell lines to antibiotic combination treatment. Cytotoxicity assays were performed evaluating human cell lines HEK293, CA46, and OVCAR8 in response to the recombinant immunotoxin HB21-LR in the presence and absence of various antibiotics. EC₅₀ values of each treatment condition are plotted. Error bars indicate standard error of the mean. All values are the average of at least three separate experiments. The P value shown is from a two-tailed, paired T test and reflects a significant difference between EC₅₀ values of an antibiotic-treated and untreated control. Cell lines HEK293 (a), OVCAR8 (b), and CA46 (c) were evaluated in combination with antibiotics chloramphenicol, tetracycline, fusidic acid, kanamycin, linezolid, and streptomycin. Cell lines Ramos (d) and Raji (d) were evaluated in combination with chloramphenicol