I-138 (0.5 μM; 4 hours) eliminates HAP-1 USP1 WT and knockout cells' USP1 autodeubiquitination[1]. I-138 (0.5 μM; 4 hours) induces monoubiquitination of FANCD2 and PCNA in MDA-MB-436 cells[1].I-138 (0.01-10 μM; 10 days) dose-dependently inhibits the viability of MDA-MB-436 cells without affecting HCC1954 cells[1].

I-138 (50 mg/kg/day; oral administration; for 41 days) exhibits USP1 inhibition and moderate antitumor activity in mice carrying MDA-MB-436 tumors. However, the combination of I-138 and the PARP inhibitor Niraparib is more effective in inhibiting BRCA1/2 mutant tumors in vivo[1].