Mechanism of interaction of Arginase-1 inhibitors

Understanding the impact of different assay conditions

  • Arginase-1 is a target for cancer immunotherapy
  • N-terminal his-tagged Arginase was covalently immobilized on a Ni-NTA chip

  • Binding kinetics of ABH, nor-NOHA and CB-1158 were determined at pH 7.4 and pH 9.5 using SPR, while their potency and stabilizing effects were evaluated in an enzyme activity assay and a thermal shift assay

  • At pH 9.5, ABH is the most potent inhibitor in the activity assay, and has the highest affinity for Arginase-1 as measured by SPR. Moreover, the IC50 of 22 nM and KD of 27 nM are highly comparable
  • At pH 7.4, CB-1158 has the most favorable characteristics in all three assay formats
  • Based on crystal structure analysis of Arginase-1 in complex with ABH at pH 7 and 9, a more symmetrical coordination structure presumably explains the increased potency of ABH at higher pH
Boxplot of the correlation of cobimetinib-response and gene expression (genes on y-axis). The more negative the value (x-axis), the better the correlation between high expression and low IC50. The red dots represent cobimetinib, the blue dots are 160 other compounds.
Binding characteristics of Arginase-1 inhibitors
Inhibition assay Thermal shift assay SPR assay
Inhibitor IC50 (nM) ΔTm (°C) ka (M-1 s-1) kd (s-1) KD (nM) τ (s)
pH 9.5 ABH 22 3.5 5.1 × 103 1.4 × 10-4 27 7200
nor-NOHA 109 4.7 3.6 × 104 6.2 × 10-3 173 160
CB-1158 132 5.6 1.3 × 103 9.2 × 10-5 72 11000
pH 7.4 ABH 184 4.5 3.6 × 104 9.9 × 10-3 797 100
nor-NOHA 59 4.8 3.6 × 104 1.9 × 10-2 1497 54
CB-1158 8.6 8.1 4.8 × 103 1.8 × 10-4 38 5500