Cyclic Dichalcogenides Extend the Reach of Bioreductive Prodrugs to Harness Thiol/Disulfide Oxidoreductases: Applications to seco-Duocarmycins Targeting the Thioredoxin System

Abstract

Small-molecule prodrug approaches that can activate cancer therapeutics selectively in tumors are urgently needed. Here, we developed the first antitumor prodrugs designed for activation by thiol-manifold oxidoreductases, targeting the thioredoxin (Trx) system. The Trx system is a critical cellular redox axis that is tightly linked to dysregulated redox/metabolic states in cancer, yet it cannot be addressed by current bioreductive prodrugs, which mainly cluster around oxidized nitrogen species. We instead harnessed Trx/TrxR-specific artificial dichalcogenides to gate the bioactivity of 10 “off-to-on” reduction-activated duocarmycin prodrugs. The prodrugs were tested for cell-free and cellular reductase-dependent activity in 177 cell lines, establishing broad trends for redox-based cellular bioactivity of the dichalcogenides. They were well tolerated in vivo in mice, indicating low systemic release of their duocarmycin cargo, and in vivo anti-tumor efficacy trials in mouse models of breast and pancreatic cancer gave promising indications of effective tumoral drug release, presumably by in situ bioreductive activation. This work therefore presents a chemically novel class of bioreductive prodrugs against a previously unaddressed reductase chemotype, validates its ability to access in vivo-compatible small-molecule prodrugs even of potently cumulative toxins, and so introduces carefully tuned dichalcogenides as a platform strategy for specific bioreduction-based release.

Piperazine-Fused Cyclic Disulfides Unlock High-Performance Bioreductive Probes of Thioredoxins and Bifunctional Reagents for Thiol Redox Biology

“…Translating the design principles and cellular specificity of the fluorogenic X-SS66C/T-MF imaging probes to high-performance thioredoxin- or thiol-redox-responsive prodrugs is a natural goal for research that we pursue for selective therapeutics of inflammatory diseases and cancer . The results of screening >170 cell lines and four mouse cancer therapy models with a panel of 10 redox-activated DNA-alkylating prodrugs typified by the duocarmycin P-SS66C–CBI-TMI (Figure b) have been published elsewhere during preparation of this paper, and further research is ongoing.…”

“…The outlook for C-DiThia and T-DiThia as redox-active disulfide motifs is rich. The modular nature of the trigger-cargo system offers that many “cargos”, e.g., diagnostics, therapeutics, or other functional agents, can be released tracelessly. Since the cellular performance, degree of activation, and speed of release are defined by the piperazine-dithiane “trigger”, they are transferrable from any cargo (e.g., reporters) to any other (e.g., drug, resin, or antibody).…”

“…Other properties can be installed or modified by derivatization at the second nitrogen, e.g., biolocalization targeting . The utility of the cis systems for interfacing to Trx biology goes beyond probes for fundamental physiology; we expect that they will be the key for effective therapeutic prodrugs targeting inflammation, autoimmune disorders, and solid cancers since each is closely associated with dysregulation of the central Trx redox node. The trans systems’ speed and target promiscuity instead suit them for fast, traceless, intracellular, or triggered release, with alternative biochemical scope to current cleavable linkers (e.g., ValCit) and so to applications in solid phase synthesis, protein purification, and as stimulus-responsive linkers for antibody-drug conjugates.…”

Back in Person: Frontiers in Medicinal Chemistry 2023

“…These prodrugs (e. g. P-SS66C-CBI-TMI (8, Figure 4)) were tested in vitro and in mouse models of pancreatic and breast cancers where they showed promising results. [24] Matthias Gehringer (University of Tübingen) gave the second presentation of this session on the discovery of a selective covalent chemical probe for the protein kinase S6K2, a barely studied p70 ribosomal protein S6 kinase, which may play an important role in cancer drug resistance. A selective inhibitor targeting this protein would be of great value to study the function of this kinase.…”

Fluorescent Probes for Mammalian Thioredoxin Reductase: Mechanistic Analysis, Construction Strategies, and Future Perspectives

“…Conversely, non-tensile cyclic probes typically remain stable against monothiols attack via reversible thiol–disulfide exchange reactions. Interestingly, alicyclic six-membered disulfides were recently reported as selective substrates of Trx by the Thorn-Seshold group [ 119 , 121 ]. In this sense, 1,2-dithianes may be tuned and harnessed for probe designs, acting as specific triggers for various oxidoreductases.…”