Targeting Lysosomal Thiols for Immunogenic Cancer Cell Death

The number and stability of lysosomes (LYs) are different in cancer and healthy cells that makes them a possible target for cancer specific therapy. However, no LY-targeting drug is clinically approved yet. We describe in this paper a new therapeutic approach based on alkylation of lysosomal thiols in cancer cells by reversible thiol binder 11. The treatment with 11 increases the level of lysosomal reactive oxygen species leading to their destabilization, disruption and immunogenic cancer cell death. These effects are not observed in healthy cells. In murine sarcoma Nemeth-Kellner (NK)/Ly-RB model, 11 exhibits the spectacular therapeutic effect: it extends the lifespan of the treated mice from 21 to 85 days and cures 40 % of mice. The survived mice develop antibodies against tumor NK/Ly-RB cells. Their repeated challenge with the NK/Ly-RB cells results in 100 % mice survival compared to 0 % survival in the control group of naïve mice. Ex vivo data indicate that neutrophils in spleen of the cured animals are also involved in targeting cancer cells and produce neutrophil extracellular traps. In summary, 11 induces the direct antitumor effect supported by humoral immune responses, as well as priming neutrophil's reaction against tumors.

Cyanine- and Rhodamine-Derived Alkynes for the Selective Targeting of Cancerous Mitochondria through Radical Thiol-Yne Coupling in Live Cells

Despite their long history and their synthetic potential underlined by various recent advances, radical thiol-yne coupling reactions have so far only rarely been exploited for the functionalization of biomolecules, and no examples yet exist for their application in live cells - although natural thiols show widespread occurrence therein. By taking advantage of the particular cellular conditions of mitochondria in cancer cells, we have demonstrated that radical thiol-yne coupling represents a powerful reaction principle for the selective targeting of these organelles. Within our studies, fluorescently labeled reactive alkyne probes were investigated, for which the fluorescent moiety was chosen to enable both mitochondria accumulation as well as highly sensitive detection. After preliminary studies under cell-free conditions, the most promising alkyne-dye conjugates were evaluated in various cellular experiments comprising analysis by flow cytometry and microscopy. All in all, these results pave the way for improved future therapeutic strategies relying on live-cell compatibility and selectivity among cellular compartments.

Anticancer Aminoferrocene Derivatives Inducing Production of Mitochondrial Reactive Oxygen Species

Elevated levels of reactive oxygen species (ROS) and deficient mitochondria are two weak points of cancer cells. Their simultaneous targeting is a valid therapeutic strategy to design highly potent anticancer drugs. The remaining challenge is to limit the drug effects to cancer cells without affecting normal ones. We have previously developed three aminoferrocene (AF)-based derivatives, which are activated in the presence of elevated levels of ROS present in cancer cells with formation of electron-rich compounds able to generate ROS and reduce mitochondrial membrane potential (MMP). All of them exhibit important drawbacks including either low efficacy or high unspecific toxicity that prevents their application in vivo up to date. Herein we describe unusual AF-derivatives lacking these drawbacks. These compounds act via an alternative mechanism: they are chemically stable in the presence of ROS, generate mitochondrial ROS in cancer cells, but not normal cells and exhibit anticancer effect in vivo.