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. Zinc‐substituted hemoglobin wrapped covalently with human serum albumins (ZnXHb‐HSA3) is a stable porphyrin carrier in physiological conditions. HSA binding did not affect the photophysical property of ZnXHb.The ZnXHb‐HSA3 transport only zinc‐protoporphyrin IX without cellular uptake of protein unit and achieved enhanced photodynamic therapy compared to ZnXHb.