31P-NMR spectroscopy demonstrates decreased ATP levels in vivo as an early response to photodynamic therapy.

31P-Nuclear magnetic resonance was used to monitor in situ phosphorus containing compounds in mammary tumors after photodynamic therapy, consisting of administration of hematoporphyrin derivative followed by photoradiation of the lesion. A rapid decrease in ATP along with an increase in Pi resonance intensities was observed. The beta-ATP/Pi ratio decreased by 1 hour, dropping in 2 to 8 hours to 0 to 20 percent of that found prior to photoradiation. Disrupted cells and pycnotic nuclei were observed 48 to 72 hours after photoradiation to a depth of approximately 5 mm. Together with previous studies in vitro, reduction in tumor ATP levels appears to be an early biochemical response to photodynamic therapy.