Trans-(±)-Kusunokinin Binding to AKR1B1 Inhibits Oxidative Stress and Proteins Involved in Migration in Aggressive Breast Cancer

Synthetic trans-(±)-kusunokinin ((±)KU), a potential anticancer substance, was revealed to have an inhibitory effect on breast cancer. According to the computational modeling prediction, AKR1B1, an oxidative stress and cancer migration protein, could be a target protein of trans-(−)-kusunokinin. In this study, we determined the binding of (±)KU and AKR1B1 on triple-negative breast and non-serous ovarian cancers. We found that (±)KU exhibited a cytotoxic effect that was significantly stronger than zopolrestat (ZP) and epalrestat (EP) (known AKR1B1 inhibitors) on breast and ovarian cancer cells. (±)KU inhibited aldose reductase activity that was stronger than trans-(−)-arctiin ((−)AR) but weaker than ZP and EP. Interestingly, (±)KU stabilized AKR1B1 on SKOV3 and Hs578T cells after being heated at 60 and 75 °C, respectively. (±)KU decreased malondialdehyde (MDA), an oxidative stress marker, on Hs578T cells in a dose-dependent manner and the suppression was stronger than EP. Furthermore, (±)KU downregulated AKR1B1 and its downstream proteins, including PKC-δ, NF-κB, AKT, Nrf2, COX2, Twist2 and N-cadherin and up-regulated E-cadherin. (±)KU showed an inhibitory effect on AKR1B1 and its downstream proteins, similar to siRNA–AKR1B1. Interestingly, the combination of siRNA–AKR1B1 with EP or (±)KU showed a greater effect on the suppression of AKR1B1, N-cadherin, E-cadherin and NF-κB than single treatments. Taken together, we concluded that (±)KU-bound AKR1B1 leads to the attenuation of cellular oxidative stress, as well as the aggressiveness of breast cancer cell migration.