Erbulozole (P.I.N.N.) (R 55 104) encapsulated into cyclodextrins: has it a combined antitumoral and radioprotective potential?

The clinically applicable formulation of the microtubule inhibitor erbulozole (R 55 104), dissolved into an aqueous hydroxypropyl-beta-cyclodextrin solution (designated as R 55 104-CYCLO), exerts a similar effect on growth delay of subcutaneous MO4 fibrosarcomas in mice, with or without 10 Gy gamma-irradiation given locally to the tumors 2 h later, compared to R 55 104 in water. The drug concentration can be reduced from 80 mg/kg to 5 mg/kg without affecting the activity of this particular drug-radiation combination. Furthermore, 80 mg/kg R 55 104-CYCLO show a radioprotective effect when given 2 h before total body irradiation of non-tumor bearing mice. A radiation dose of 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 Gy respectively was given resulting in a LD50(30) of 5.97 Gy for the irradiated mice and 7.65 Gy for the drug-radiation treated animals (Dose Effect Factor = 0.78). Therapeutic implications of both observations are discussed.