A doxorubicin prodrug activated by the staudinger reaction

Much effort has been devoted to prodrug systems that effect drug release at the tumor through enzymatic action. To widen the scope of prodrug therapy, the use of the selective Staudinger reaction as prodrug activator, instead of relying on enzymatic action, was investigated. Doxorubicin was conjugated to a p-azidobenzyl trigger that is cleaved after reacting with the chemical activator, triphenylphosphine. The prodrug activation was confirmed in water, cell growth medium, and serum, using HPLC and LCMS. Next, this approach was tested in a cell proliferation assay with A431 human vulvar skin squamous carcinoma cells. The doxorubicin prodrug was shown to exhibit a 176-fold higher IC50 of 15.1 microM vs 0.086 microM for the parent drug, doxorubicin. Addition of triphenylphosphine (5 x 60 microM in 72 h) to the prodrug in cell culture effected the complete recovery of the activity of the parent drug as evidenced by an IC50 value of 0.074 microM. Furthermore, high levels of triphenylphosphine were tolerated well by the cells. The demonstrated usefulness of the Staudinger reaction in cell culture and its in vivo potential opens up new avenues for prodrug therapy.