Polymerized Apoferritin: A promising carrier for efficient compartmentalized and deep-layer delivery of calcium donors in tumor Ca overload therapy.

Calcium overload is an emerging tumor treatment strategy that induces cell death by disrupting the homeostasis of calcium ions (Ca) in tumor cells. In this study, we have engineered a novel polymerized apoferritin carrier, utilizing reversible boronate ester bonds to interconnect the dihydrocaffeic acid modified ε-polylysine (ε-PLL-CAT) and 3-formylphenylboronic acid (3-FPBA) modified on the surface of individual apoferritin. This carrier is further compartmentalized with calcium phosphate and the calcium ion extrusion inhibitor curcumin. We have confirmed that during in vivo circulation, polymerized apoferritin can effectively reduce the interception and interference of the nanocage by masking the long unstructured loop on the surface of the apoferritin nanocage. Upon encountering the acidic tumor microenvironment, the reversible boronate ester bonds gradually degrade, triggering the progressive disassembly of the polymerized protein cage. This process culminates in the release of a high concentration of intracellular calcium ions within tumor cells, thereby significantly enhancing the efficacy of calcium overload therapy for breast cancer. Moreover, these dispersed nanocages can trigger a domino effect in neighboring tumor cells, facilitating deep-layer delivery. This process is mediated by calcium ion-dependent lysosomal exocytosis and transcytosis, which has been shown to be highly beneficial for inducing calcium overload. In summary, the strategy presented in this study not only improves the in vivo biodistribution of apoferritin nanocages for drug delivery, but also considerably broadens their potential applications in calcium overload therapy for tumors.