EPZ015666

EPZ015666 (GSK3235025) is an orally available inhibitor of PRMT5 with an IC₅₀ of 22 nM. IC50 & Target: IC50: 22 nM (PRMT5)^[1] In Vitro: Treatment of MCL cell lines with EPZ015666 (GSK3235025) leads to inhibition of SmD3 methylation and cell death, with IC₅₀ values in the nanomolar range^[1]. EPZ015666 (GSK3235025), a potent peptide-competitive and SAM-cooperative inhibitor with >10,000-fold specificity against PRMT5 relative to other methyltransferases^[2]. In Vivo: EPZ015666 (GSK3235025) is orally bioavailable and amenable to in vivo studies. We performed 21-d efficacy studies in severe combined immunodeficiency (SCID) mice bearing subcutaneous Z-138 and Maver-1 xenografts, with twice-daily (BID) oral dosing on four dose groups: 25, 50, 100 and 200 mg per kilogram of body weight (mg/kg). After 21 d of continuous dosing, animals are euthanized, and blood and tissues are analyzed to determine the relationship between methyl-mark pharmacodynamics and tumor-growth inhibition (TGI). EPZ015666 (GSK3235025) showed dose-dependent exposure and TGI after 21 d in both MCL models. Tumors in all EPZ015666 (GSK3235025) dose groups measured on day 21 showed statistically significant differences in weight, volume and tumor growth compared to vehicle-treated tumors. Dosing at 200 mg/kg BID induced tumor stasis in Z-138 cells, with >93% TGI after 21 d, whereas Maver-1 cells showed >70% TGI. Additionally, a third MCL xenograft is tested using the Granta-519 cell line, a fast-growing model that reached endpoint on day 18 and showed dose-dependent efficacy with 45% TGI in the 200 mg/kg group. EPZ015666 (GSK3235025) is well tolerated in all three models, with minimal bodyweight loss in the 200 mg/kg dose group and no other clinical observations^[1].