Regulating cell stress responses by nitric oxide to enhance calcium overload-mediated tumor therapy

Amino acid (AA)-based nanoparticles (NPs) hold promise in cancer therapy due to their excellent biocompatibility and the various therapeutic functions derived from AA monomers. Here, we developed a universal one-step method to synthesize AA-based NPs. We then constructed L-Arginine (L-Arg)/calcium phosphate (CaP) NPs to enhance cancer therapy through synergistic calcium overload to induce apoptosis and immunogenic cell death. The engineered L-Arg/CaP NPs rapidly degraded and released a large amount of exogenous calcium ions (Ca²⁺) in the acidic tumor microenvironment (TME). Notably, L-Arg-derived NO synergistically enhanced calcium overload through two distinct mechanisms: (1) induction of S-nitrosylation of the ryanodine receptor (RyR) on the endoplasmic reticulum (ER) to facilitate endogenous Ca²⁺ release, and (2) significant downregulation of plasma membrane Ca²⁺-ATPase (PMCA) expression to inhibit Ca²⁺ efflux. This unique three-level regulatory mechanism involving external Ca²⁺ supply, internal Ca²⁺ release, and efflux inhibition created a cascading amplification of intracellular Ca²⁺ concentration. Importantly, it overcame the limitations of tumor cell stress adaptation in conventional single-ion therapy, thereby establishing a new therapeutic paradigm. In vitro and in vivo studies confirmed that L-Arg/CaP NPs induce tumor suppression with excellent biosafety, indicating the potential for an innovative strategy integrating calcium overload and gas therapy for cancer treatment.