Responses to photodynamic therapy in a murine tumor model-³¹p nmr and water proton relaxation studies

In this study we report the tumor responses to photodynamic therapy (PDT) as measured by in vivo ³¹P NMR and water relaxation measurements on a murine tumor model. We evaluate the PDT responses to two new photosensitizers by monitoring the tumor volumes post PDT for one tumor and by in vivo ³¹P NMR for the other. Both photosensitizers are structurally well defined, pure compounds, unlike Photofrin II (PF II), which is a complex chemical mixture of a variety of porphyrin species. Dramatic increases in inorganic phosphate (P_i) were noticed following PDT treatment. The tumor water relaxation time measurements also suggest corresponding increases in T₁values of water after PDT treatment. From a combined study of relaxation times, ³¹P NMR, and tumor volumes, we conclude that the relaxation measurements can serve as a useful and sensitive method of monitoring PDT.