Targeting Cancer with PCPA-Drug Conjugates: LSD1 Inhibition-Triggered Release of 4-Hydroxytamoxifen

Nitroreductase-Mediated Release of Inhibitors of Lysine-Specific Demethylase 1 (LSD1) from Prodrugs in Transfected Acute Myeloid Leukaemia Cells

Lysine-specific demethylase 1 (LSD1) has evolved as a promising therapeutic target for cancer treatment, especially in acute myeloid leukaemia (AML). To approach the challenge of site-specific LSD1 inhibition, we developed an enzyme-prodrug system with the bacterial nitroreductase NfsB (NTR) that was expressed in the virally transfected AML cell line THP1-NTR+ . The cellular activity of the NTR was proven with a new luminescent NTR probe. We synthesised a diverse set of nitroaromatic prodrugs that by design do not affect LSD1 and are reduced by the NTR to release an active LSD1 inhibitor. The emerging side products were differentially analysed using negative controls, thereby revealing cytotoxic effects. The 2-nitroimidazolyl prodrug of a potent LSD1 inhibitor emerged as one of the best prodrug candidates with a pronounced selectivity window between wild-type and transfected THP1 cells. Our prodrugs are selectively activated and release the LSD1 inhibitor locally, proving their suitability for future targeting approaches.

Drug Design Concepts for LSD1-Selective Inhibitors

Lysine-specific demethylase 1 (LSD1) is one of the flavin-dependent oxidases and is involved in many cellular processes by controlling the methylation of histone H3. Recently, it has been reported that LSD1 is associated with several diseases such as cancer, metabolic disorders, and psychiatric diseases. Thus, LSD1 is an attractive molecular target for the treatment of these diseases, and its inhibitors are predicted as therapeutic agents. Although a variety of LSD1 inhibitors have been reported to date, many of them show insufficient activities and selectivity toward LSD1. Meanwhile, we identified several LSD1-selective inhibitors using target-guided synthesis strategies based on our original ideas. Our LSD1 inhibitors show not only potent LSD1-selective inhibitory activities, but also unique bioactivities both in vitro and in vivo. This account highlights our drug design concepts for and identification of LSD1-selective inhibitors.

Selective Activation of a Prodrug by Thioredoxin Reductase Providing a Strategy to Target Cancer Cells

Elevated reactive oxygen species and antioxidant defense systems have been recognized as one of the hallmarks of cancer cells. As a major regulator of the cellular redox homeostasis, the selenoprotein thioredoxin reductase (TrxR) is increasingly considered as a promising target for anticancer drug development. The current approach to inhibit TrxR predominantly relies on the modification of the selenocysteine residue in the C-terminal active site of the enzyme, in which it is hard to avoid the off-target effects. By conjugating the anticancer drug gemcitabine with a 1,2-dithiolane scaffold, an unprecedented prodrug strategy is disclosed that achieves a specific release of gemcitabine by TrxR in cells. As overexpression of TrxR is frequently found in different types of tumors, the TrxR-dependent prodrugs are promising for further development as cancer chemotherapeutic agents.