Toxicity of cationic CPPs

Read Also

Because of their highly cationic nature, one could fear that some CPPs could be as toxic as other cationic polymers such as poly-L-Lysine or poly-ethylene imine (PEI) (for a review, [77]). Moreover the cationic Tat peptide has been shown to mediate some neurotoxicity (for a review, see [78] and [79, 80]). Therefore several groups evaluated their in vitro and in vivo cellular toxicity. When the minimal membrane-translocating Tat domain was discovered [6], no toxicity has been found in very extreme conditions on HeLa cells (24 h incubation at 100 micromolar concentration). This absence of toxicity has been also shown in other studies. For example, Toro et al. confirmed that the short Tat peptide was not toxic for lymphocytes at dose up to 300 mM [81]. Using different cationic peptides (namely Tat, Antp, Rev and VP22), no toxicity was observed in Hela or Jurkat cells with up to 20-30 mM concentrations [82]. SiRNA transfected in vivo with a poly-Arginine peptide did not induce any cellular toxicity at a ratio of negative/positive charges of 40 [83]. Frequent injections in mice of a fusion protein corrected the metabolic disorder and immune defects with no apparent toxicity [81]. Incubation of primary or immortalized human keratocytes with the Antennapepdia or Tat peptide resulted in no evidence of toxicity with dosage up to 200 mM and 400 mM, respectively. Similar results were obtained with a human trabecular meshwork cell line, primary human foreskin fibroblasts, Vero, and HeLa cells. In the same work, toxicity was evaluated in vivo by applying peptides to the cornea 4 times daily for 7 days. At concentrations 1000 times the IC50 values, the Antennapedia peptide showed no toxicity, whereas Tat caused some mild eyelid swelling [84]. Park et al. described the equivalent cell translocation potency of a short protamine derivative rich in arginine residues which was equivalent to that of the Tat peptide combined with the absence of toxicity [85]. Cardozo et al. showed that concentrations of up to 100 mM of Tat(48-57) were essentially harmless in all cells tested, whereas Antp(43-58) was significantly more toxic [86]. In addition, it is noteworthy that peptide concentrations used in toxicity tests are in their very large majority far above the concentrations used for delivering various drugs into cells (which range from 1 to 10 mM).