NQO1 and cancer: Dicoumarol effects on cancer cells may also be independent of its inhibitory action on NQO1 and several mechanisms have been proposed: (i) impairment of mitochondrial functionality; (ii) decrease of pregnancy-specific beta-1-glycoprotein 1 (PSG1) levels; (iii) inhibition of heat shock protein 90 (Hsp90); (iv) downregulation of anti-apoptotic proteins; (v) inhibition of heat shock protein 90 (Hsp90); and (vi) inhibition of phosphoinositide-dependent kinase-1 (PDK1).