S-trityl-L-Cysteine

S-trityl-L-Cysteine is a non-natural amino acid and an inhibitor of Eg5, also known as KSP and Kif11, a mitotic kinesin necessary for mitotic spindle formation.¹ S-trityl-L-Cysteine inhibits the ATPase activity of Eg5 in basal and microtubule-stimulated states (IC₅₀s = 1,000 and 140 nM, respectively).² It is selective for Eg5 over nine other human kinesins in an enzyme-coupled assay.¹ It reversibly inhibits Eg5-driven microtubule sliding velocity with an IC₅₀ value of 500 nM using X. laevis recombinant Eg5. It induces cell cycle arrest in HeLa cells (IC₅₀ = 700 nM), reversibly halting the cell cycle in the mitotic phase by inhibiting the separation of duplicated chromosomes and preventing bipolar spindle formation. S-trityl-L-Cysteine inhibits the growth of cancer cells in vitro when tested against the National Cancer Institute (NCI) 60 human cancer cell line panel (average GI₅₀ = 1.3 µM) and in mouse xenograft models.¹

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1. Skoufias, D.A., DeBonis, S., Saoudi, Y., et al. S-Trityl-L-cysteine is a reversible, tight binding inhibitor of the human kinesin Eg5 that specifically blocks mitotic progression. The Journal of Biological Chemisty 281(26), 17559-17569 (2006).

2. DeBonis, S., Skoufias, D.A., Lebeau, L., et al. In vitro screening for inhibitors of the human mitotic kinesin Eg5 with antimitotic and antitumor activities. Mol. Cancer Ther. 3(9), 1079-1090 (2004).