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 αβ 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-HSA. ApoXHb-HSA engendered no aggregates in the physiological solutions. Moreover, apoXHb-HSA was reconstituted with zinc(II)-protoporphyrin IX (ZnP), generating ZnXHb-HSA, a potent photosensitizer for photodynamic therapy (PDT). The photophysical properties of ZnXHb-HSA were identical to those of zinc-substituted XHb (ZnXHb). Cellular uptake behavior was evaluated using various cancer cell lines. ZnXHb-HSA released ZnP around the cells, and the free ZnP penetrated cell membranes. In contrast, protein units were not observed within the cells. ZnXHb-HSA showed no cytotoxicity under dark conditions and demonstrated superior PDT activity in comparison to naked ZnXHb. ZnXHb-HSA acts as an innovative porphyrin carrier for enhanced PDT.