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C-Terminal Amidation of Chlorotoxin Does Not Affect Tumour Cell Proliferation and Has No Effect on Toxin Cytotoxicity

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Chlorotoxin (Cltx), a cell-penetrating peptide from the venom of the scorpion Leiurus quinquestriatus has selective activity on a range of neuroectodermal tumours and related cell lines. Although the precise mechanism of Cltx action is not clear, Cltx has been shown to be a useful tumour imaging agent and radiolabelled Cltx has undergone clinical trials for targeted glioma radiotherapy. The native peptide (and synthetic material, TM601) is amidated at its C-terminus (Cltx-CONH2). A recombinant form produced in E. coli is not processed and has a free C-terminal carboxyl group (Cltx-COOH). The amidated form appears to have no effects on proliferation and cytotoxicity, whereas studies on the free carboxyl form are contradictory. Cltx-CONH2 and Cltx-COOH have been used interchangeably over many years and this has resulted in confusion in the literature; the significance of any difference is extremely important one with respect to the use of the toxin in a clinical diagnostic or therapeutic setting. This study was carried out to investigate, in parallel, the effects of Cltx-CONH2 and Cltx-COOH on cell proliferation and cytotoxicity on a variety of representative tumour cell lines (U87MG, MCF-7, PC3 and A549) using cell Titer Glo and cell Tox Green assays, respectively. Neither Cltx-CONH2 nor Cltx-COOH affected cell proliferation or cytotoxicity, indicating that terminal arginine amidation does not play an important role in cytotoxic or cytostatic properties of Cltx.

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ASA acknowledges the support of the Egyptian Ministry of Higher Education through a Scholarship to study at Sheffield Hallam University (Channel Scheme between Suez Canal University, Egypt and Sheffield Hallam University, UK). ASA, KAN and PNS acknowledge support from Biomolecular Research Center, Sheffield Hallam University, UK.

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Correspondence to Kirsti A. Newton or Mohamed A. Abdel-Rahman.

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Ayed, A.S., Omran, M.A.A.A., Nabil, Z.I. et al. C-Terminal Amidation of Chlorotoxin Does Not Affect Tumour Cell Proliferation and Has No Effect on Toxin Cytotoxicity. Int J Pept Res Ther 27, 659–667 (2021).

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