Discovery of New Catalytic Topoisomerase II Inhibitors for Anticancer Therapeutics.

Poison inhibitors of DNA topoisomerase II (TOP2) are clinically used drugs that cause cancer cell death by inducing DNA damage, which mechanism of action is also associated with serious side effects such as secondary malignancy and cardiotoxicity. In contrast, TOP2 catalytic inhibitors induce limited DNA damage, have low cytotoxicity, and are effective in suppressing cancer cell proliferation. They have been sought after to be prospective anticancer therapies. Herein the discovery of new TOP2 catalytic inhibitors is described. A new druggable pocket of TOP2 protein at its DNA binding domain was used as a docking site to virtually screen ~6 million molecules from the ZINC15 library. The lead compound, T60, was characterized to be a catalytic TOP2 inhibitor that binds TOP2 protein and disrupts TOP2 from interacting with DNA, resulting in no DNA cleavage. It has low cytotoxicity, but strongly inhibits cancer cell proliferation and xenograft growth. T60 also inhibits androgen receptor activity and prostate cancer cell growth. These results indicate that T60 is a promising candidate compound that can be further developed into new anticancer drugs.

Acetylation Regulates Thioredoxin Reductase Oligomerization and Activity.

AIMS: Thioredoxin reductase 1 (TrxR1) is a cancer target and essential selenoprotein that defends the cell against reactive oxygen species and regulates cellular signaling and redox pathways. Previous cell-based studies correlated TrxR1 acetylation with modulated cellular reduction activity, yet the function of specific acetylation sites on TrxR1 remains unknown. INNOVATION: We produced site-specifically acetylated TrxR1 variants that also contain selenocysteine (Sec). We demonstrated efficient high-fidelity protein synthesis with 22 different amino acids by simultaneous UAG codon reassignment to Nɛ-acetyl-lysine and UGA codon recoding to Sec. RESULTS: We characterized TrxR1 variants acetylated at physiologically relevant sites and found that single acetylation sites increased TrxR1 activity, enhancing the apparent catalytic rate up to 2.7-fold. The activity increase in acetylated TrxR1 (acTrxR1) is reversible and is reduced following deacetylation with histone deacetylase. CONCLUSION: Here we present a novel mechanism through which acetylation increases TrxR1 activity by destabilizing low-activity TrxR1 multimers, increasing the population of active dimeric TrxR1. Antioxid. Redox Signal. 29, 377-388.

Strictosidine Synthase Triggered Enantioselective Synthesis of N-Substituted (S)-3,14,18,19-Tetrahydroangustines as Novel Topoisomerase I Inhibitors.

Monoterpenoid indole alkaloids (MIAs) comprise an important class of molecules for drug discovery, and they have variant carbon skeletons with prominent bioactivities. For instance, in spite of limitations to their use, camptothecins are the only clinically approved topoisomerase I (Top1) inhibitors. The enzyme strictosidine synthase, which is key for MIA biosynthesis, was applied to the enantioselective preparation of three N-substituted (S)-3,14,18,19-tetrahydroangustine (THA) derivatives. These non-camptothecin MIAs were shown to have moderate in vitro HepG2 cytotoxicity and Top1 inhibition activities. The (S)-configured MIAs had stronger cytotoxicity and Top1 inhibition than their chemically synthesized (R)-enantiomers, which aligned with the results of molecular dynamics simulations. A series of N-substituted (S)-THAs were then chemoenzymatically synthesized to investigate structure-activity relationships. The most active analogue observed was the N-(2-Cl benzoyl)-substituted derivative (7i). Insight into the binding mode of 7i and a Top1-DNA covalent complex was investigated by molecular dynamics simulations, which will facilitate future efforts to optimize the Top1 inhibitory activities of non-camptothecin MIAs.