STUDY OF THE ACCUMULATIVE FUNCTION OF TUMOUR CELLS AFTER THE INJECTION OF HAEMATOPORPHYRIN DERIVATIVES UNDER LOW-INTENSITY LASER ENERGY IRRADIATION

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The use of photodynamic therapy (PDT) using a photosensitizer such as haematoprphyrin and its derivatives (HpD) followed by application of low-intensity visible red laser energy in therapy for early-stage tumour destruction is well documented. The effect of the application of low intensity laser irradiation of a different wavelength, in low level laser therapy (LLLT) on the uptake or excretion of HpD into and from the tumour cells and tissue has not been investigated. The present study investigates the effect on tumour HpD uptake and excretion at from 30 minutes to 6 hours post HpD injection following the application of an infrared (890 nm) GaAs diode laser at two dosages (0.03067 J/cm² and 0.3067 J/cm²) immediately after; immediately and at 30 min after; 30 min before; and one day and 30 min before HpD injection compared with HpD injected but unirradiated control rats, all previously inoculated with Walker’s N256 sarcoma. The degree of fluorescence in the tumour was assessed using microspectrofluorometry, thus giving a direct indication of the amount of HpD compound present in the tumour. Previous reports on LLLT and its mechanisms suggested that there would be a higher absorption or uptake rate in the LLLT groups compared with controls. Contrary to these expectations, post HpD injection low intensity laser irradiated tumours showed slightly lower HpD uptake compared with the controls, and faster excretion, although the differences were not very statistically significant. Those tumours irradiated before HpD injection, on the other hand, showed dramatically and very highly statistically significantly decreased HpD uptake at 30 min postinjection, then a very slight tendency towards increased uptake until 3 hours postinjection, followed by increased excretion. In the LLLT groups there was no statistically significant difference between the two different doses. It is proposed that LLLT retards the uptake of HpD in the tumour cells by direct or indirect action on the microvasculature specifically on the permeability of the blood vessel walls and the celt membranes. The authors suggest that LLLT, at least at the wavelength and parameters used in the present study, should not be used as an adjunctive therapy before or after HpD injection for PDT in treatment of early-stage tumours.