Antitumor activity and tumor localization of liposomal glucocorticoids in B16 melanoma-bearing mice

Prednisolone disodium phosphate (PLP) encapsulated in long-circulating liposomes (LCL) (LCL-PLP) inhibited tumor growth by 80–90% after a single dose of 20 mg/kg, whereas PLP in the free form was completely ineffective at the same single dose. To generalize our findings with LCL-PLP, the antitumor activity and side effects of LCL containing synthetic glucocorticoids (LCL-GC) other than PLP were investigated. In addition to PLP, budesonide disodium phosphate, dexamethasone disodium phosphate, and methylprednisolone disodium phosphate were selected based on the difference in their potency to activate the human glucocorticoid receptor. The present study shows that the tumor localization of each GC is governed by the transport capacity of the LCL composed of dipalmitoylphosphatidylcholine, cholesterol, and polyethylene glycol 2000-distearoylphosphatidylethanolamine in a molar ratio of 1.85:1.0:0.15. The antitumor potency of the LCL-GC strongly depends on the potency of the type of GC encapsulated. LCL-encapsulated budesonide disodium phosphate (LCL-BUP) had the highest antitumor activity which is likely due to the much higher potency of BUP encapsulated in LCL versus the other three GC types. The high potency of LCL-BUP confers the risk for occurrence of strong side effects. However, at the dose of 3 mg/kg, LCL-BUP was highly efficacious without the occurrence of adverse effects.