KRH-3955 hydrochloride is a CXCR4 antagonist with oral bioavailability. It effectively inhibits the binding of SDF-1alpha to CXCR4, exhibiting an IC 50 of 0.61 nM. Additionally, KRH-3955 hydrochloride displays high potency and selectivity as an inhibitor of X4 HIV-1, with an EC 50 ranging from 0.3 to 1.0 nM.