The effect of fractionation of light treatment on necrosis and vascular function of normal skin following photodynamic therapy

Abstract

Summary Sparing of normal tissue, mouse tail skin, by fractionation of light treatment in photodynamic therapy has been demonstrated in BDF1 mice injected with 2mg tetrasodium-meso-tetra(4-sulphophenyl) porphine dodecahydrate i.v. When the time between 2 fractions of 67.5 Jcm-2 and 90Jcm-2 was increased to 2 and 4 days respectively the incidence of necrosis fell to that expected after a single fraction. Blood flow in the tail skin 5 days after the second light fraction, as measured by the clearance of an intradermally injected solution of 133xenon in 0.9% saline, returned to control values when the time between 2 fractions was 2 days with 67.51Jcm-2 fractions, and 3 days with 90Jcm-2 fractions. al., 1987) and chloroaluminium phthalocyanine (Ben Hur et al., 1985).Evidence that environmental conditions may modulate the expression of this sublethal damage initially came from studies on the effect of temperature on the shapes of cell survival curves following PDT. Moan et al. (1979a) noted that following exposure to HP, irradiation of NHIK cells in vitro at 4°C resulted in more efficient inactivation than irradiation at 37°C and there was no shoulder on the cell survival curve. Subsequently, Gomer et al. (1985) demonstrated an inhibition of repair of 'potentially lethal damage' when Chinese hamster lung fibroblasts that had received prolonged exposure to HPD, were held post-irradiation at 4°C or in the presence of the metabolic inhibitor caffeine.Attempts to measure repair of sub-lethal damage by splitdose experiments in vitro have been reported by Moan et al. (1979a), who found that for NHIK cells exposed to light in the presence of HP, a given total light dose was more efficient when it was fractionated than when given in a single exposure. Subsequently however, Christensen et al. (1985) used the same cell line to demonstrate that relative survival after two doses was a complex function of the interval between doses and that 'sparing' occurred with a 3 h interval. Bellnier & Lin (1985) found that survival of EJ human urinary bladder carcinoma cells rapidly increased with interval between two light fractions, reaching a maximum at 9 h.The aim of the present study was to determine whether or not fractionation of light treatment resulted in sparing of tissue in vivo, using as a model normal mouse tail skin. (Sacchini et al., 1987). Tissue injury was assessed using two endpoints:1. the incidence of tail necrosis, as described by Moore et al. (1986); and 2. blood flow in the mouse tail skin 5 days after a second light fraction as measured by the clearance of 133xenon injected intradermally. There is evidence that impairment of vascular function is an important mechanism resulting in damage to both malignant and normal tissues. A previous study found an initial impairment in blood flow following PDT but this returned to normal by day 5 at low light doses. However, at light doses greater than the threshold for skin necrosis, there was increasing impairment of blood flow on day 5 (Benstead & Moore, 1988). Material...

Vascular function and tissue injury in murine skin following hyperthermia and photodynamic therapy, alone and in combination

“…Qualitatively, these effects closely resembled those previously described and illustrated for the tail system, using the combination of light and the photosensitiser TPPS4 (Benstead & Moore, 1989). Following hyperthermia for 40 minutes at 43°C, significant increases in absolute area of the compartment compared to age-matched controls, occurred at one or more time intervals in epidermis, dermis, and hypodermis, but not in bone or tendon ( Figure 3; data for dermis and tendon not shown).…”

“…Large changes in probability of necrosis did occur over the subsequent period (7 to 28 days) during which time however, "'Xe clearance varied little (TI being shorter than in controls; Figs 2, 5). This non-association of clearance time of "'Xe and probability of necrosis, using the lipophilic sensitiser HPD is in seeming contrast with our earlier results using the hydrophilic sensitiser TPPS4 (Benstead & Moore, 1988b). The possibility must be considered that the effects on a given vasculature of light in combination with different photosensitisers, may vary.…”

“…As regards vascular function, in a previous study using this tail model and the photosensitiser TPPS4, clearance inhibition was directly associated with the probability of skin necrosis when light dose was delivered as two fractions separated by increasing intervals of days (Benstead & Moore, 1988b). In that study therefore, improvement in "'Xe clearance was associated with 'recovery' processes that led to tissue sparing.…”

“…The possibility must be considered that the effects on a given vasculature of light in combination with different photosensitisers, may vary. Thus the peak degree of oedema induced by tolerance TPPS4 plus light was only 60% that induced with HPD (Table 1 in Benstead and Moore (1989), Figure 3, this paper). Also, 5 days after PDT with TPPS4 the absolute number of capillaries per tail circumference was 60% greater than in controls, whereas with HPD there was no significant increase in the number of small vessels relative to agematched controls ( Figure 5 in Benstead & Moore (1989), Figure 4, this paper).…”

“…Vascular histology Quantitative analysis of vascular histology in tails exposed to PDT or hyperthermia, was carried out by methods described in detail elsewhere (Benstead & Moore, 1989). Briefly, groups of 6 mice received either: (1) A 'tolerance' dose of hyperthermia given with the tails clamped (i.e.…”