ASP-9521 is an effective, specific and orally available AKR1C3 inhibitor (IC50: 11 nM, for human).

AKR1C3:11 nM

ASP-9521 concentration-dependently inhibits conversion of androstenedione (AD) into androstenediol and testosterone (T) by recombinant human or cynomolgus monkey AKR1C3 (IC50: 11/49 nM, human/monkey). ASP-9521 has more than 100-fold selectivity for AKR1C3 over the isoform AKR1C2. In LNCaP-AKR1C3 cells, ASP-9521 suppresses AD-dependent PSA production and cell proliferation.

In CWR22R xenografts, ASP-9521 (3 mg/kg, p.o.) inhibits AD-induced intratumoural T production and this inhibitory effect is maintained for 24 h. ASP-9521 (p.o.) is rapidly eliminated from plasma, while its intratumoural concentration remained high. The bioavailability of ASP-9521 after oral administration (1 mg/kg) is 35 %, 78 % and 58 % in rats, dogs and monkeys, respectively.

LNCaP-AKR1C3 cells stably expressing human AKR1C3 are seeded in 96-well plates at 10000 cells/100 μL/well in RPMI-1640 medium supplemented with heat-inactivated charcoal-dextran-stripped FBS (1 % for the PSA expression assay and T measurement and 5 % for the cell proliferation assay). After 24 h incubation, AD is added to each well with or without ASP-9521 (0.3-100 nM). The cell culture media are collected 24 h after administration of AD to measure T concentration and 6 days after administration of AD to measure cell proliferation using Cell-Titer Glo assay.

ASP-9521 is prepared in 0.5 % methyl cellulose.Mice carrying HEK293 or HEK293-AKR1C3 tumors with similar sizes are selected and randomly divided into 5 groups (N=3 for each group). All groups are treated with ASP-9521 (single oral administration; 3 mg/kg). Plasma (from the central vein) and tumor tissues are collected at 0.25, 0.5, 1, 2 and 4 h after administration of ASP-9521, and ASP-9521 concentrations are determined using the HPLCMS/MS method.