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
link to the publication describing these findings (Grobben et al, 2020)
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