P4HB and cancer: On the other hand, the observed ability of E2 and particularly some of its structural analogs to interact with human PDI may also have pharmacological relevance given that some of these compounds can effectively inhibit PDI's catalytic activity in vitro[10], [12], [13], [19] and that PDI has received considerable attention in recent years as a potential therapeutic target in cancer chemotherapy [20], [21] and HIV prevention [22]–[25].