Zinc-Substituted Hemoglobin-Albumin Cluster as a Porphyrin-Carrier for Enhanced Photodynamic Therapy

Apohemoprotein is focused on the field of theranostics, serving as a porphyrin carrier. Hemoglobin (Hb) consists of α₂β₂ tetramer with iron(II)-protoporphyrin IX (heme) bound to each globin. However, heme-removed Hb (apoHb) causes dissociation at αβ interfaces and aggregation under physiological conditions. We synthesized a stable apoHb derivative comprising intramolecular-crosslinked apoHb (apoXHb) and human serum albumin (HSA), apoXHb-HSA₃. ApoXHb-HSA₃ engendered no aggregates in the physiological solutions. Moreover, apoXHb-HSA₃ was reconstituted with zinc(II)-protoporphyrin IX (ZnP), generating ZnXHb-HSA₃, a potent photosensitizer for photodynamic therapy (PDT). The photophysical properties of ZnXHb-HSA₃ were identical to those of zinc-substituted XHb (ZnXHb). Cellular uptake behavior was evaluated using various cancer cell lines. ZnXHb-HSA₃ released ZnP around the cells, and the free ZnP penetrated cell membranes. In contrast, protein units were not observed within the cells. ZnXHb-HSA₃ showed no cytotoxicity under dark conditions and demonstrated superior PDT activity in comparison to naked ZnXHb. ZnXHb-HSA₃ acts as an innovative porphyrin carrier for enhanced PDT.