An approach toward characterizing the fraction of all oxidation events that attack a particular site within cells during PDT

This paper considers the the fraction PDT-induced oxidizing radicals that react with a specific oxidizable target within a cell rather than with all possible oxidizable sites. There are many oxidizable sites within the cell, each with a different efficiency of oxidation (Y_ox_j) and a different in vivo concentration (C_iv_j). One measures the efficiency of oxidation of a single ith chemical species in vitro (Y_it_i), then measures the oxidation of the same species in vivo (Y_iv_i). The concentration of this ith species in vivo must be measured (C_iv_i). A convenient test chemical species is chosen, such as a photobleachable fluorophore. Then the in vivo yield is approximately: Y_iv_i = (C_iv_i * Y_it_i) / sum_all_j(C_iv_j * Y_iv_j) (Eq.1). Rearranging to solve for the total oxidation: sum_all_j(C_iv_j * Y_iv_j) = (C_iv_i * Y_it_i) Y_iv_I (Eq.2). Once the sum_all_j() in Eq. 2 is specified, one can measure the in vitro oxidation efficiency and the in vivo concentration of any ith species and use Eq. 1 to predict the fraction of PDT-generated singlet oxygen that will attack that ith species in vivo. Of course, the above is only a first approximation toward a complex problem but is a beginning. This paper illustrates the experimental specification of the Y_ox_j for NADPH oxidation in a cuvette using the photosensitizer Photofrin.