IN VITRO PHOTORADIATION - HEMATOPORPHYRIN DERIVATIVE ACCUMULATION, SENSITIZATION AND INTERACTION WITH IONIZING RADIATION

The in vitro uptake and retention of hematoporphyrin derivative, using ('3)H-Hpd, was studied in monolayer CHO cells. Uptake was biphasic with the resulting intracellular Hpd concentrations directly proportional to the external porphyrin levels at all uptake times. Hpd was partially removed from the cells during incubation in porphyrin-free, serum-rich medium. The pattern of porphyrin efflux was biphasic, with a rapid loss occurring at times up to 1 hour followed by a much slower efflux component thereafter. The amount of porphyrin remaining in the cells was proportional to the length of initial porphyrin contact time.; The in vitro Hpd-induced cytotoxicity was also examined. External Hpd concentrations as low as 3.13 (mu)g/ml inhibited both cell growth and DNA synthesis.; Cell survival was studied in CHO cells and related to intracellular Hpd concentration and porphyrin contact time (uptake time). Photoirradiation with red light resulted in a family of survival curves with terminal slopes proportional to cellular porphyrin concentration for cells incubated with Hpd under equivalent conditions. The influence of prolonged Hpd incubation time on the lethal response of cells exposed to red light was determined and compared to the response of cells incubated with Hpd for short times but which contained equivalent porphyrin concentrations. Resultant survival data show an increase in photosensitivity and concommitant decrease in cellular ability to accumulate or repair photodamage with increasing Hpd contact time.; Hpd-sensitized photolysis was studied in this system using a ('51)Cr labeling technique. Cytolysis was proportional to the ceullular porphyrin concentration and incident light fluence. The amount of ('51)Cr released increased with postirradiation incubation time to a level parallel to cell lethality as measured by colony formation, suggesting that cell membrane damage may be largely responsible for cellular inactivation following Hpd photoirradiation.; Survival after (gamma)-irradiation was measured for CHO cells containing various intracellular Hpd concentrations with no significant difference in radiosensitivity between control cells and cells containing Hpd. The interaction between ionizing radiation and Hpd photoinactivation was also investigated. Exposure to (gamma)-radiation and Hpd-sensitized photoradiation resulted in survival curves which indicated that damage and/or expression of damage due to each modality interacted in an independent manner at that level (clonogenicity).