P2′ Benzene Carboxylic Acid Moiety Is Associated with Decrease in Cellular Uptake: Evaluation of Novel Nonpeptidic HIV-1 Protease Inhibitors Containing P2 bis-Tetrahydrofuran Moiety

GRL007 and GRL008, two structurally related nonpeptidic human immunodeficiency virus type 1 (HIV-1) protease inhibitors (PIs) containing 3(R),3a(S),6a(R)-bis-tetrahydrofuranylurethane (bis-THF) as the P2 moiety and a sulfonamide isostere consisting of benzene carboxylic acid and benzene carboxamide as the P2′ moiety, respectively, were evaluated for their antiviral activity and interactions with wild-type protease (PR^WT). Both GRL007 (K_i of 12.7 pM with PR^WT) and GRL008 (K_i of 8.9 pM) inhibited PR^WT with high potency in vitro. X-ray crystallographic analysis of PR^WT in complex with GRL007 or GRL008 showed that the bis-THF moiety of both compounds has three direct polar contacts with the backbone amide nitrogen atoms of Asp29 and Asp30 of PR^WT. The P2′ moiety of both compounds showed one direct contact with the backbone of Asp30′ and a bridging polar contact with Gly48′ through a water molecule. Cell-based antiviral assays showed that GRL007 was inactive (50% effective concentration EC₅₀] of >1 μM) while GRL008 was highly active (EC₅₀ of 0.04 μM) against wild-type HIV-1. High-performance liquid chromatography (HPLC)/mass spectrometry-based cellular uptake assays showed 8.1- and 84-fold higher intracellular concentrations of GRL008 than GRL007 in human MT-2 and MT-4 cell extracts, respectively. Thus, GRL007, in spite of its favorable enzyme-inhibitory activity and protease binding profile, exhibited a lack of antiviral activity in cell-based assays, most likely due to its compromised cellular uptake associated with its P2′ benzene carboxylic acid moiety. The anti-HIV-1 potency, favorable toxicity, and binding profile of GRL008 suggest that further optimization of the P2′ moiety may improve its antiretroviral features.