AZD-5991 is a potent and selective Mcl-1 inhibitor (IC50: 0.7 nM in FRET assay; Kd: 0.17 nM in SPR assay).

MCL1:0.17 nM (kd), MCL1:0.7 nM

AZD-5991 is selective for Mcl-1 (IC50: 0.72?nM, Ki: 200?pM) vs. Bcl-2 (IC50: 20?μM, Ki: 6.8?μM), Bcl-xL (IC50: 36?μM, Ki: 18?μM), Bcl-w (IC50: 49?μM, Ki: 25?μM), and Bfl-1 (IC50: 24?μM, Ki: 12?μM). MOLP-8, MV4-11, and NCI-H23 cells are treated with AZD5991 (EC50: 0.033, 0.024, 0.19?μM, respectively). AZD5991 binds directly to Mcl-1 and induces rapid apoptosis in cancer cells by activating the Bak-dependent mitochondrial apoptotic pathway. AZD5991 reduces the levels of Mcl-1 protein in AZD5991-sensitive but not in AZD5991-resistant MM cell lines.

A single intravenous (i.v.) dose of AZD5991 leads to a dose-dependent antitumor effect ranging from tumor growth inhibition (TGI) to tumor regression (TR). Ten days after treatment, AZD5991 shows 52% and 93% TGI at 10 and 30?mg/kg, respectively. At the same time point, AZD5991 at 60?mg/kg leads to 99% TR with no detectable tumors in 6 out of 7 mice, while complete TR is seen in 7 out of 7 mice in the 100?mg/kg dose group. AZD5991 also shows a dose-dependent duration of response with tumors in the 100?mg/kg group growing back later than those in the 60?mg/kg group. The magnitude of in vivo tumor efficacy is correlated with activation of caspase-3 in the tumor and concentration of AZD5991 in plasma. Treatment with AZD5991 was well tolerated at all dose levels with no significant bodyweight loss. A single dose of AZD5991 36 days after the first dose causes tumor regression in 4 out of 4 mice. In mice dosed with AZD5991 at 100?mg/kg on day 0 and day 1, tumors grow back later than those dosed with a single dose of AZD5991 at the same dose level.