Cu-releasing nanoparticles induce the catalytic transamination of amino acids and GSSG under tumor microenvironment conditions

Catalytic cancer therapy is emerging as a powerful tool to target cancer cells by exploiting specific characteristics of the tumor microenvironment (TME). To this end, the catalytic activity of nanoparticles, enzymes and homogeneous catalysts is recruited to induce reactions that are damaging to cancer cells. Thus, the pro-drug activation approach uses chemical constructs that become toxic species inside the tumor, typically following removal of a protecting group. In contrast, TME-based catalytic strategies do not rely on the introduction of foreign species and instead use molecules that are already present in the TME. So far, only four processes have been explored in relation to cancer therapy, two oxidation reactions (glucose and glutathione), generation of reactive oxygen species (ROS) and production of oxygen to alleviate tumor hypoxia. This is surprising, since the rich chemical environment in tumor cells could in principle provide many other therapeutic opportunities. In particular, amino groups seem a suitable target, given the abundance of proteins and peptides in biological environments. Here we show that catalytic CuFe nanoparticles are able to foster transamination reactions between different amino acids and pyruvate, another key molecule that abounds in the TME. Transamination would then reduce the available aminoacid pool, which is likely to affect cell homeostasis and to effectively hinder tumor proliferation. After internalization of Cu-containing nanoparticles in U251-MG cells, we observed a significant decrease in glutamine and alanine levels up to 48 hours after treatment. In addition, we have found that not only simple amino acids, but also di- and tri-peptides undergo catalytic transamination when exposed to the Cu cations released by our nanoparticles, thus extending the range of the effects to other molecules such as GSSG. Mechanistic calculations for GSSG transamination revealed the formation of an imine between the oxo-group of pyruvate and the free -NH2 group of GSSG, followed by the coordination of the imine to Cu(II). Our results demonstrate that transamination reactions can be catalyzed in cellulo by Cu-releasing nanoparticles, adding a new reaction to the existing toolbox of catalytic therapies.