Optimized S‑Trityl‑L‑cysteine-Based Inhibitors of Kinesin Spindle Protein with Potent in Vivo Antitumor Activity in Lung Cancer Xenograft Models

*S Supporting Information ABSTRACT: The mitotic kinesin Eg5 is critical for the assembly of the mitotic spindle and is a promising chemo-therapy target. Previously, we identified S-trityl-L-cysteine as a selective inhibitor of Eg5 and developed triphenylbutanamine analogues with improved potency, favorable drug-like proper-ties, but moderate in vivo activity. We report here their further optimization to produce extremely potent inhibitors of Eg5 (Ki app < 10 nM) with broad-spectrum activity against cancer cell lines comparable to the Phase II drug candidates ispinesib and SB-743921. They have good oral bioavailability and pharmacokinetics and induced complete tumor regression in nude mice explanted with lung cancer patient xenografts. Furthermore, they display fewer liabilities with CYP-metabolizing enzymes and hERG compared with ispinesib and SB-743921, which is important given the likely application of Eg5 inhibitors in combination therapies. We present the case for this preclinical series to be investigated in single and combination chemotherapies, especiall