Structure-based design of the approved drug zafirlukast identifies HLC40 as a potent WDR5 WIN-site inhibitor with antitumor efficacy.

WD40 repeat-containing protein 5 (WDR5) plays a critical role in chromatin-related processes, and its overexpression is associated with poor prognosis in multiple cancers, making it an attractive therapeutic target. Screening of an approved drug library identified zafirlukast (ZAF), an anti-asthmatic agent, as a binder to the WIN site of WDR5, inhibiting the histone methyltransferase activity of the MLL1 complex with an IC50 of 22.96 μM. Structure-based optimization yielded the candidate HLC40, which not only abolished its original CysLT1 receptor antagonism (IC50 > 5 μM) but also exhibited a 30-fold enhancement in MLL1 histone methyltransferase (HMT) inhibitory activity (IC50 = 0.82 μM). Consistent with these findings, HLC40 exhibited potent antiproliferation efficacy (IC50 = 7-8 μM) in AML cells and demonstrated significant efficacy in the MV4-11 xenograft model (TGI = 49.1% @ 30 mg/kg). Collectively, these results highlight that HLC40 is a promising WDR5-targeting candidate with high therapeutic potential for hematologic malignancies.