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  • Title: Photosensitization and split-dose recovery in cultured human urinary bladder carcinoma cells containing nonexchangeable hematoporphyrin derivative.
    Author: Bellnier DA, Lin CW.
    Journal: Cancer Res; 1985 Jun; 45(6):2507-11. PubMed ID: 3986790.
    Abstract:
    The photosensitization and survival recovery of cultured EJ human urinary bladder carcinoma cells containing nonexchangeable hematoporphyrin derivative (HPD) were studied. Cultures were incubated at 37 degrees C in growth medium supplemented with HPD (50 micrograms/ml) and 5% fetal bovine serum for 12 h followed by incubation in HPD-free medium containing 5% fetal bovine serum for 9 or 18 h. The levels of porphyrin remaining in the cells (termed the "nonexchangeable" intracellular porphyrin component) were not significantly different at these times, and as a result sensitivities to broad-band red light (greater than 580 nm) were also identical. Shouldered survival curves were obtained in each case, indicating the ability to accumulate sublethal photodamage. Recovery from photosensitized damage using a split-dose technique was examined. Single, attached, asynchronously growing cells containing nonexchangeable HPD (12 h HPD uptake plus 9 h in porphyrin-free medium) were exposed to red light (1.2 kJ/sq m) and, after various intervals at 37 degrees C in the dark, a second dose of 1.2 kJ/sq m. Survival rapidly increased and reached a maximum at about 9 h between light doses. Analysis of dose-response curves revealed a partial reappearance of the curve shoulder (Dq = 0.22 kJ/sq m) and a markedly reduced curve slope (D0 = 0.82 kJ/sq m) for fractionated irradiations with a 9-h interval in comparison with graded, single light exposures (Dq = 0.48 kJ/sq m; D0 = 0.41 kJ/sq m). These observations suggest that the cells developed an increased tolerance to photosensitized damage after prior HPD-light treatment. No significant change in intracellular HPD levels between irradiations was detected, indicating that the increased survival was not due to a loss of sensitizer from inside the cells. These results demonstrate that EJ cells accumulate and recover from HPD-sensitized photodamage; analogous to the accumulation and recovery from sublethal damage (Elkind recovery) in other mammalian cultures treated with ionizing radiation.
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