P4HB and neoplasm: Bepristats demonstrated more potent inhibitory activity in the insulin turbidimetric assay compared with quercetin-3-rutinoside (rutin), a glycosylated flavonoid quercetin shown to block PDI activity and inhibit thrombus formation in vivo22, 37; PACMA-31, an irreversible inhibitor of PDI that binds the catalytic cysteines and impairs tumour growth in a murine model of ovarian cancer9; and bacitracin, a dodecapeptide that has been used for decades as the standard PDI inhibitor38 (Fig. 1e).