CCR5 inhibitors: emergence, success, and challenges.

INTRODUCTION: The discovery of CC-chemokine receptor 5 (CCR5) as a human immunodeficiency virus type 1 (HIV-1) coreceptor opened a new avenue to exploit CCR5 as a potential target for the intervention of HIV-1's cellular entry. AREAS COVERED: Various small-molecule CCR5 inhibitors were identified in the last decade; however, maraviroc (MVC) is the only CCR5 inhibitor currently used in the clinic. Concerns and challenges that exist for wider clinical use of CCR5 inhibitors are discussed. EXPERT OPINION: Although MVC-containing regimens have been recommended for treatment-naïve patients, MVC appears to have been used as one of drugs for salvage therapy rather than for treating drug-naïve patients. This is apparently due to MVC's twice-daily dosing schedule. Another significant disadvantage is that a costly tropism assay must be performed prior to MVC treatment. The access to inexpensive, sensitive, and rapid tropism tests should be made easily available. Only a few novel CCR5 inhibitors are presently in the pipeline. Development of potent and metabolically-stable novel CCR5 inhibitors allowing once-daily dosing regimens is needed. Development of CXCR4 inhibitors should greatly improve the treatment options available to patients infected with X4- and/or dual-tropic HIV-1 strains in combination with a CCR5 inhibitor.