ES 936 is a potent and selective NQO1 inhibitor, inhibiting more than 95% of NQO1 activity within 30 minutes at a concentration of 100 nM, with a cell line-dependent inhibition duration resulting in a small number of DNA strand breaks.

Streptonigrin cytotoxicity in HCT116 cells (with ES936 pretreatment):11 ± 0.6 nM, Streptonigrin cytotoxicity in HCT116 cells (without ES936 pretreatment):6.7 ± 1 nM, Cell proliferation (reflecting cytotoxicity) in MDA468 NQ-16 cells:732 ± 49 nM, Streptonigrin cytotoxicity in MDA468 NQ-16 cells (without ES936 pretreatment):2.2 ± 0.06 nM, Cell proliferation in HCT116 cells:569 ± 48 nM, Streptonigrin cytotoxicity in MDA468 NQ-16 cells (with ES936 pretreatment):13 ± 0.4 nM 

ES 936 exhibited relatively low cytotoxicity toward MDA468 NQ-16 (high NQO1 activity) and HCT116 (low NQO1 activity) cells, with IC₅₀ values of 732 ± 49 nM and 569 ± 48 nM, respectively. These concentrations are approximately 8–20 times higher than those required for effective NQO1 inhibition, indicating weak intrinsic growth-inhibitory activity.[1] In co-treatment experiments, ES 936 pretreatment significantly increased the IC₅₀ of streptonigrin, from 2.2 ± 0.06 nM to 13 ± 0.4 nM in MDA468 NQ-16 cells (approximately 6-fold), and from 6.7 ± 1 nM to 11 ± 0.6 nM in HCT116 cells (approximately 2-fold). These results indicate that ES 936 reduces the bioactivation and cytotoxicity of streptonigrin by inhibiting NQO1 activity.[1]