Interestingly, costunolide conversely inhibited the expression of Nrf2 in the background of a pronounced pro-oxidant effect in glioblastoma cells [51], and lactone 4 was shown to down-regulate the expression of thioredoxin reductase 1 (TrxR1) [83], which may indicate the ability of STLs to modulate the complex system of negative feedback loops involved in the anti-oxidant response in glioblastoma cells [105]. Here, TXNRD1 is linked to glioblastoma.