UT-155 is a selective and potent antagonist of the androgen receptor (AR) with a binding affinity (Ki) of 267 nM for the AR ligand-binding domain (AR-LBD).

AR-LBD:267 nM (Ki)

UT-155 binds to the AR-LBD (Ki: 267 nM) and potently inhibits R1881-induced wildtype AR transactivation with 6-10-fold higher potency than enzalutamide. While UT-155 antagonizes both wildtype and mutant ARs comparably, enzalutamide's efficacy is halved against the W742L mutant AR. In LNCaP cells, UT-155 inhibits PSA and FKBP5 gene expression induced by 0.1 nM R1881 at concentrations between 10 and 100 nM, demonstrating 5-10 times better efficacy than enzalutamide.

Consistent with its anti-proliferative effects in vitro, UT-155 significantly inhibits the growth of 22RV1 xenografts by 53%, while enzalutamide has no effect. In UT-155-treated animals, tumor weights, PSA levels, and expression of AR and AR-SV are significantly reduced.