A thermosensitive liposome prepared with a Cu²⁺ gradient demonstrates improved pharmacokinetics, drug delivery and antitumor efficacy.

Here we report the development of an enhanced thermosensitive formulation composed of DPPC and Brij78, loaded with doxorubicin (DOX) using a Cu²⁺ gradient and post-inserted with an additional amount of Brij78. This optimal formulation (HaT-II: Hyperthermia-activated cytoToxic) displayed significantly improved stability in serum at 37 °C, and enhanced drug release rates at 41-42 °C, compared to LTSL (lyso-lipid temperature sensitive liposomes, DPPC/MSPC/DSPE-PEG₂₀₀₀=86/10/4, pH gradient drug loading). HaT-II released 100% DOX within 15-40s at 40-42 °C, with only 5% drug leakage at 37 °C after 30 min in serum, while LTSL lost 30% of its drug content at 37 °C and exhibited ~2-fold decreased release rate constants at 41-42 °C under the same conditions. The pharmacokinetics of DOX was significantly improved in non-heated HaT-II treated healthy mice with 2.5-fold increased area under the curve and 2-fold prolonged circulation half life compared to LTSL. This led to 2-fold improved drug delivery to the heated tumor by HaT-II (~20% injected dose/g tissue), relative to LTSL and significantly enhanced antitumor efficacy with complete inhibition of tumor growth after a single dose of HaT-II. Finally, HaT-II exhibited little toxicity in mice, inducing no body weight loss and no abnormality in the blood chemistry (10 mg DOX/kg).