Potential antitumor therapeutic application of Grimontia hollisae thermostable direct hemolysin mutants

We report on the preparation of a new type of immunotoxin by conjugation of an epidermal growth factor receptor (EGFR)-binding peptide and an R46E mutation of thermostable direct hemolysin from Grimontia hollisae, (Gh-TDH(R)(46E)/EB). The hybrid immunotoxin was purified to homogeneity and showed a single band with slight slower mobility than that of Gh-TDH(R)(46E). Cytotoxicity assay of Gh-TDH(R)(46E)/EB on EGFR highly, moderately, low, and non-expressed cells, A431, MDA-MB-231, HeLa, and HEK293 cells, respectively, showed apparent cytotoxicity on A431 and MDA-MB-231 cells but not on HeLa or HEK293 cells. In contrast, no cytotoxicity was observed for these cells treated with either Gh-TDH(R)(46E) or EB alone, indicating enhanced cytotoxic efficacy of Gh-TDH(R)(46E) by the EGFR binding moiety. Further antitumor activity assay of Gh-TDH(R)(46E)/EB in a xenograft model of athymic nude mice showed obvious shrinkage of tumor size and degeneration, necrosis, and lesions of tumor tissues compared to the normal tissues. Therefore, the combination of Gh-TDH(R)(46E) with target affinity agents opens new possibilities for pharmacological treatment of cancers and potentiates the anticancer drug's effect.