Alkaline Elution Studies of Hematoporphyrin‐derivative Photosensitized Dna Damage and Repair in Chinese Hamster Ovary Cells

Abstract

We have used alkaline elution to study DNA damage produced by the photosensitizer hematoporphyrin derivative (HPD) in cultured Chinese hamster cells. Dosimetry was performed by measuring fluence and calculating photon absorption by intracellular HPD. HPD photosensitization causes DNA strand breakage. These breaks are repaired by the cell, although their fractional rate of repair is smaller than that for X‐ray induced strand breaks at equivalent levels of strand breakage. The combined DNA polymerase inhibitors cytosine arabinoside and hydroxyurea suppress the repair of HPD‐photosensitized breaks more strongly than they suppress repair of X‐ray induced breaks. Addition of novobiocin to the aforementioned inhibitors causes almost total suppression of photosensitized break repair. A nucleotide excision repair system with inhibitor susceptibility similar to that of the system which removes pyrimidine dimers thus does not act upon HPD‐photosensitized damage. The repair rate and inhibitor sensitivity findings together suggest biologically important differences in the chemical nature of X‐ray induced and HPD‐photosensitized strand breaks. In addition to strand breaks, HPD photosensitization produces covalent DNA‐protein crosslinks, some of which persist through at least 90 min incubation, but which are repaired within 180 min.

Haematoporphyrin Derivative Photosensitization and γ-radiation Damage Interaction in Chinese Hamster Ovary Fibroblasts

“…In the same report, however, mutations at the hypoxanthine-guanine phosphoribosyltransferase locus were not photodynamically induced. In addition, haematoporphyrin-and HPDphotoinduced DNA-protein crosslinks have been observed (Dubbelman et al 1982, Blazek andHariharan 1984).…”

Porphyrin Photosensitization and Phototherapy

“…I will add only a few references. Blazek and Hariharan (1984) studied HPD sensitized photodamage of DNA in Chinese hamster ovary cells by the alkaline elution technique. They found DNA strand breaks in agreement with earlier published work, and in addition, covalent DNAprotein crosslinks.…”

Computational Study of Oxidation of Guanine by Singlet Oxygen (1Δg) and Formation of Guanine:Lysine Cross‐Links

“…Numerous experimental studies have been carried out to explore the formation of DNA–protein cross‐links with isolated nucleobases and single‐ and double‐stranded DNA under different oxidative environments . Various oxidizing agents such as hydroxyl radicals, sulfate radicals, carbonate radicals, organic carcinogens such as aldehydes, transition‐metal ions such as Ni II , Cr VI , Fe II , Fe III , Ir IV , and ionizing radiation, UV‐, and visible light with photosensitizers are also found to induce DPC formation . The spectrum of the DPC products depends on the nature of the oxidizing agent .…”