hematoporphyrin

Hematoporphyrin is a porphyrin-based compound derived from heme. In medical contexts, the term hematoporphyrin derivative (HpD) refers to a heterogeneous mixture of porphyrin compounds produced by oxidation of hematoporphyrin. HpD and its purified forms are used as photosensitizers in photodynamic therapy (PDT) and for fluorescence-guided diagnostics. The most widely known commercial preparation is porfimer sodium (Photofrin), marketed as a hematoporphyrin derivative.

Chemically, HpD comprises monomeric and oligomeric porphyrin units that absorb light in the blue–near-UV and red regions, with a strong Soret band near 400 nm and additional absorption around 630 nm. Upon illumination with light in the red region, the excited photosensitizer transfers energy to molecular oxygen to generate reactive oxygen species, notably singlet oxygen, which damages cellular membranes, mitochondria, and other structures, leading to tumor cell death and vascular injury.

Clinically, HpD-based PDT involves intravenous administration of the photosensitizer followed by light exposure of the tumor site after a delay (commonly 24–72 hours). The treatment is used for localized or accessible tumors and in some diagnostic applications. Photosensitivity is a major adverse effect, requiring avoidance of bright light for days to weeks after administration.

Development: In the 1970s, Dougherty and colleagues demonstrated PDT using HpD, leading to FDA approval of Photofrin in 1995 for certain cancers. Second-generation photosensitizers have since been developed to improve selectivity and reduce prolonged photosensitivity.