EO-9 bladder instillations: Formulation selection based on stability characteristics and in vitro simulation studies

A bladder instillation of EO-9 (EOquin™) is currently used in phase II clinical trials for the treatment of superficial bladder cancer. Three alternative formulations were developed to improve its pharmaceutical properties and clinical acceptability. Freeze-dried products composed of EO-9, 2-hydroxypropyl-β-cyclodextrin (HPβCD), tri(hydroxymethyl) aminomethane (Tris), and sodium bicarbonate (NaHCO3) were tested. Selection of one formulation for further development was based on stability studies. These studies comprised stability of the freeze-dried products, stability after reconstitution and dilution and stability during bladder instillation in an experimental set-up. The stability study of the freeze-dried products showed that the formulation composed of EO-9/HPβCD/Tris (4/600/1 mg/vial) was most stable. After reconstitution and dilution all products were stable for at least 8 h. The product composed of EO9/HPβCD/NaHCO3 (4/600/20 mg/vial) was the least stable product both as freeze-dried formulation and after reconstitution and dilution. The bladder instillation simulation experiment showed that all products were stable when mixed with urine of pH 8 and unstable in urine of pH 4 and 6. The degradation products formed in urine were EO-5a and EO-9-Cl.Based on these results, the product composed of EO-9/HPβCD/Tris (4/600/1 mg/vial) was selected for further pharmaceutical development.