In vitro activity: Reparixin L-lysine salt, the L-lysine salt form of reparixin, is a novel, potent small molecular weight allosteric inhibitor of chemokine receptor 1/2 (CXCR1/2) activation. It is the first drug candidate currently under clinical investigation in the prevention of ischemia/reperfusion injury in organ transplantation. Reparixin binding mode to CXCR1 has been studied and used for a computer-assisted design program of dual allosteric CXCR1 and CXCR2 inhibitors. Structural and biochemical data are consistent with a noncompetitive allosteric mode of interaction between CXCR1 and Repertaxin, which, by locking CXCR1 in an inactive conformation, prevents signaling. Repertaxin is an effective inhibitor of polymorphonuclear cell recruitment in vivo and protects organs against reperfusion injury. Targeting the Repertaxin interaction site of CXCR1 represents a general strategy to modulate the activity of chemoattractant receptors.

Kinase Assay: Reparixin L-lysine salt, the L-lysine salt form of reparixin, is a novel, potent small molecular weight allosteric inhibitor of chemokine receptor 1/2 (CXCR1/2) activation. Reparixin is a potent functional inhibitor of CXCL8-induced biological activities on human PMNs with a marked selectivity (around 400-fold) for CXCR1, as shown in specific experiments on CXCR1/L1.2 and CXCR2/L1.2 transfected cells and on human PMNs. The efficacy of Reparixin is significantly lower in L1.2 cells expressing Ile43Val CXCR1 mutant (IC50 values of 5.6 nM and 80 nM for CXCR1 wt and CXCR1 Ile43Val, respectively).

Cell Assay: L1.2 Cell suspension (1.5-3×106 cells/mL) is incubated at 37°C for 15 min in the presence of vehicle or of Reparixin (1 nM-1 μM) and next seeded in triplicates in the upper compartment of the chemotactic chamber. Different agonists are seeded in the lower compartment of the chamber at the following concentrations: 1 nM CXCL8, 0.03 nM fMLP, 10 nM CXCL1, 2.5 nM CCL2, 30 nM C5a. The chemotactic chamber is incubated at 37°C in air with 5% CO2 for 45 min (human PMNs) or 2 h (monocytes). At the end of incubation, the filter is removed, fixed, and stained and five oil immersion fields at high magnification (100×) are counted for each migration well after sample coding. L1.2 migration is evaluated using 5 μm pore size Transwell filters.