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.

Targeting CCR5 as a Component of an HIV-1 Therapeutic Strategy

“…Given that CCR5 can be utilized by HIV-1 to enter and infect immune cells, extracellular methods of inhibiting the interaction of gp120 with CCR5 have been developed ( Table 1 ). Targeting and preventing this interaction has been mainly done with the use of small molecule inhibitors, which generally work by inducing conformational changes to CCR5 thereby preventing fusion of the HIV-1 envelope with the cellular membrane ( 108 ). In contrast to many therapeutics targeting viral proteins, these inhibitors target the various components of the transmembrane CCR5 receptor protein on host cells.…”

“…In the early 2000s, several drugs were designed as orally available small molecule CCR5 inhibitors but did not complete stage 3 clinical trials. One of the earliest small molecules, Aplaviroc, was discontinued due to evidence of hepatoxicity in four patients ( 108 ). Another CCR5 antagonist, Vicriviroc, showed efficacy in reducing viral loads of treated patients by about one log over 24 weeks, but in vivo resistance developed in one patient ( Table 1 ).…”

“…Despite promising clinical trial results, mutations in the highly variable V2 and V3 loop region of viral gp120 have been reported, which result in a recovered CCR5 receptor usage even with the presence of Maraviroc at the binding site ( 101 ). Finally, potential changes in viral tropism to utilize CXCR4 as a co-receptor have been of concern, but diagnostic limitations make it difficult to discern novel Maraviroc resistance within the host from the emergence of a pre-existing CXCR4-tropic strain ( 108 , 109 ). For these reasons, current clinical use trends towards a treatment experienced cohort where ART strategies have failed.…”

“…Other more recent small molecule inhibitors in development include GRL-117C, which demonstrated inhibition of R5-utilizing HIV-1 ( 108 ). Interestingly, this study also implicated CCR5 inhibitors in additional benefits for treatment of HIV-1 infection including immunomodulation and even latency reversal.…”

“…Preliminary studies have shown that contrary to natural antibodies, Leronlimab is able to bind the N-terminal domain of EL2 on the CCR5 receptor, the same binding site used by gp120 ( Figure 2 ). This loop is thought to be a well conserved area of CCR5 encoding genes ( 108 ). Another CCR5 antibody HGS004 directed at the same area of CCR5 has also show in vitro and in vivo efficacy in infected patients.…”