AS-99 is a first-in-class, potent, and selective ASH1L histone methyltransferase inhibitor (IC50= 0.79 μM, Kd= 0.89 μM) with anti-leukemic activity, blocking cell proliferation, inducing apoptosis and differentiation, downregulating MLL fusion target genes, and reducing the leukemia burden in vivo[1].

ASH1L histone methyltransferase:0.79 µM

AS-99 is tested against 20 histone methyltransferases, including NSD1, NSD2, NSD3, and SETD2. No significant inhibition is observed at 50 μM of AS-99 on any of the tested histone methyltransferases, indicating over 100-fold selectivity toward ASH1L[1]. AS-99 affects the growth of MLL leukemia cells (MV4;11, MOLM13, KOPN8, RS4;11) with GI50 values ranging from 1.8 μM to 3.6 μM[1]. AS-99 (1-8 μM; 7 days) also induces apoptosis in MLL leukemia cells, but not in K562 cells, as assessed by Annexin V positive cell quantification[1]. AS-99 suppresses MLL fusion-driven transcriptional programs[1].

AS-99 (30 mg/kg; i.p.; q.d., treated for 14 consecutive days) reduces leukemia burden in mice[1].AS-99 is used for in vivo studies in mice, which reveals favorable exposure in plasma upon i.v. and i.p. administration (AUC = 9701 hr* ng/mL and 10,699 hr* ng/mL, respectively), suitable half-life (~5-6 h) and Cmax >10 μM[1].