Evaluation of the effects of photodynamic therapy with phosphorus 31 magnetic resonance spectroscopy

Magnetic resonance spectroscopy in situ was used to study changes in phosph orus 31 metabolism after photodynamic therapy (PDT) of transplanted HeLa ce ll tumours. Tumours were irradiated 2 h after administration of ATX-S10 (8- formyloximethylidene-7-hydroxy-3-ethenyl-2,7,12,18, tetramethyl-porphyrin-1 3,17-bispropionil aspartate), a new photosensitizer and chlorin derivative. Nuclear magnetic resonance spectra were measured prior to illumination and 1, 3, 7, 14, 21 and 28 days after PDT on each mouse. A drastic decrease in adenosine triphosphate (ATP) and a concomitant increase in inorganic phosp hate (Pi) were evident on the first day after PDT in all cases. The beta-AT P/total phosphate (P) ratio was 0.64 +/- 0.29% (average +/- s.d.) in comple te response, 0.67 +/- 0.30% in recurrence and 2.45 +/- 0.93% in partial res ponse. Comparison of this ratio to the histological findings revealed that the beta-ATP/total P ratio reflects the HeLa cell tumours which survived PD T. In other words, partial response on the one hand was distinguished from complete response and recurrence on the other with this ratio 1 day after P DT (P < 0.05). In addition, the ratio of phosphomonoester (PME) to Pi rose beyond 1.0 when macroscopic recurrence occurred, while it stayed under 1.0 in complete response. This finding suggests that the recurrence of HeLa cel l tumours can be detected by the PME/Pi ratio.