Activity and structural analysis of GRL-117C: a novel small molecule CCR5 inhibitor active against R5-tropic HIV-1s

Abstract

CCR5 is a member of the G-protein coupled receptor family that serves as an essential co-receptor for cellular entry of R5-tropic HIV-1, and is a validated target for therapeutics against HIV-1 infections. In the present study, we designed and synthesized a series of novel small CCR5 inhibitors and evaluated their antiviral activity. GRL-117C inhibited the replication of wild-type R5-HIV-1 with a sub-nanomolar IC₅₀ value. These derivatives retained activity against vicriviroc-resistant HIV-1s, but did not show activity against maraviroc (MVC)-resistant HIV-1. Structural modeling indicated that the binding of compounds to CCR5 occurs in the hydrophobic cavity of CCR5 under the second extracellular loop, and amino acids critical for their binding were almost similar with those of MVC, which explains viral cross-resistance with MVC. On the other hand, one derivative, GRL-10018C, less potent against HIV-1, but more potent in inhibiting CC-chemokine binding, occupied the upper region of the binding cavity with its bis-THF moiety, presumably causing greater steric hindrance with CC-chemokines. Recent studies have shown additional unique features of certain CCR5 inhibitors such as immunomodulating properties and HIV-1 latency reversal properties, and thus, continuous efforts in developing new CCR5 inhibitors with unique binding profiles is necessary.

Figure 1

Structures of GRL-CCR5 inhibitors (GRL-117C, GRL-10007C, and GRL-10018C) and APL (aplaviroc), MVC (maraviroc), VVC (vicriviroc), AD101, and CVC (cenicriviroc).

Figure 2

Inhibitory effect on HIV-1 replication in TZM-bl cells. Percent inhibition of (A) MVC, (B) CVC, and (C) GRL-117C on HIV-1 replication is shown. Data are shown as means ± s.d. of three independent experiments.

Figure 3

Inhibition of ¹²⁵I-labeled CC-chemokine binding to CCR5 by CCR5 inhibitors. CCR5⁺ CHO cells were incubated with (A) ¹²⁵I-MIP-1α, (B) ¹²⁵I-MIP-1β, and (C) ¹²⁵I-RANTES (200 ng/ml) in the presence or absence of varying concentrations of CCR5 inhibitors. Data are shown as means ± s.d. of three independent experiments.

Figure 4

Binding pocket of CCR5. A side view of CCR5 with the bound CCR5 inhibitor is shown. (A) MVC, (B) GRL-117C, (C) GRL-10018C, and (D) APL in the binding pocket of CCR5 are illustrated. (Upper) The transmembrane (TM) domains and the second extracellular loop (ECL2) are indicated. (Center) Detailed interactions between a CCR5 inhibitor and CCR5 residues are shown. The bis-THF moiety of GRL-10018C (C) locates upper region of the binding cavity. APL (D) has hydrogen-bond interactions with Y37, S180 and T195 (Bottom) Interactions of each CCR5 inhibitor (MVC, GRL-117C, and GRL-10018C) with Y37, E283, and Y251. Yellow dot: hydrogen-bonding.