Biotinylation of an acetylenic tricyclic bis(cyanoenone) lowers its potency as an NRF2 activator while creating a novel activity against BACH1.

The transcription factor BACH1 regulates the expression of a variety of genes including genes involved in oxidative stress responses, inflammation, cell motility, cancer cell invasion and cancer metabolism. Based on this, BACH1 has become a promising therapeutic target in cancer (as anti-metastatic target) and also in chronic conditions linked to oxidative stress and inflammation, where BACH1 inhibitors share a therapeutic space with activators of transcription factor NRF2. However, while there is a growing number of NRF2 activators, there are only a few described BACH1 inhibitors/degraders. The synthetic acetylenic tricyclic bis(cyanoenone),(±)-(4bS,8aR,10aS)-10a-ethynyl-4b,8,8-trimethyl-3,7-dioxo-3.4b,7,8,8a,9,10, 10a-octahydrophenanthrene-2,6-dicarbonitrile, TBE31 is a potent activator of NRF2 without any BACH1 activity. Herein we found that biotinylation of TBE31 greatly reduces its potency as NRF2 activator (50-75-fold less active) while acquiring a novel activity as a BACH1 degrader (100-200-fold more active). We demonstrate that TBE56, the biotinylated TBE31, interacts and promotes the degradation of BACH1 via a mechanism involving the E3 ligase FBXO22. TBE56 is a potent and sustained BACH1 degrader (50-fold more potent than hemin) and accordingly a powerful HMOX1 inducer. TBE56 degrades BACH1 in lung and breast cancer cells, impairing breast cancer cell migration and invasion in a BACH1-dependent manner, while TBE31 has no significant effect. Altogether, our study identifies that the biotinylation of TBE31 provides novel activities with potential therapeutic value, providing a rationale for further characterisation of this and related compounds.

The synthetic triterpenoids CDDO-TFEA and CDDO-Me, but not CDDO, promote nuclear exclusion of BACH1 impairing its activity.

The transcription factor BACH1 is a potential therapeutic target for a variety of chronic conditions linked to oxidative stress and inflammation, as well as cancer metastasis. However, only a few BACH1 degraders/inhibitors have been described. BACH1 is a transcriptional repressor of heme oxygenase 1 (HMOX1), which is positively regulated by transcription factor NRF2 and is highly inducible by derivatives of the synthetic oleanane triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO). Most of the therapeutic activities of these compounds are due to their anti-inflammatory and antioxidant properties, which are widely attributed to their ability to activate NRF2. However, with such a broad range of action, these compounds have other molecular targets that have not been fully identified and could also be of importance for their therapeutic profile. Herein we identified BACH1 as a target of two CDDO-derivatives (CDDO-Me and CDDO-TFEA), but not of CDDO. While both CDDO and CDDO-derivatives activate NRF2 similarly, only CDDO-Me and CDDO-TFEA inhibit BACH1, which explains the much higher potency of these CDDO-derivatives as HMOX1 inducers compared with unmodified CDDO. Notably, we demonstrate that CDDO-Me and CDDO-TFEA inhibit BACH1 via a novel mechanism that reduces BACH1 nuclear levels while accumulating its cytoplasmic form. In an in vitro model, both CDDO-derivatives impaired lung cancer cell invasion in a BACH1-dependent and NRF2-independent manner, while CDDO was inactive. Altogether, our study identifies CDDO-Me and CDDO-TFEA as dual KEAP1/BACH1 inhibitors, providing a rationale for further therapeutic uses of these drugs.