Ultrasound-assisted efficient targeting of doxorubicin to the tumor microenvironment by lyso-thermosensitive liposomes of varying phase transition temperatures.

Premature drug release is the primary hindrance to the effective function of the lyso-thermosensitive liposomes (LTSLs) of doxorubicin (Dox), known as ThermoDox® for the treatment of cancer. Herein, we have optimized LTSLs by using a combination of phospholipids (PLs) with high transition temperatures (Tm) to improve the therapeutic outcome in an assisted ultrasound approach. For this, several Dox LTSLs were prepared using the remote loading method at varying molar ratios (0 to 90 %) of DPPC (Tm 41 °C) and HSPC (Tm 54.5 °C), as well as a constant molar ratio of MSPC (10 %), DSPE-mPEG2000 (4 %). The treatment efficacy was explored by using ultrasound as external hyperthermia (HT) (40-42℃) in mice bearing C26 murine colon carcinoma. All the formulations had an average diameter of around 110 nm, PDI ≤ 0.15, zeta potential of around -12 mV, and Dox encapsulation of >90 %. The cytotoxicity results indicated a higher IC50 value of Dox-LTSLs compared to the ThermoDox® (F0: DPPC:MSPC:DSPE-mPEG2000, 90:10:4), attributed to the faster Dox release in F0 formulation devoid of HSPC. Among various formulations, F25 (DPPC: MSPC: DSPE-mPEG2000: HSPC, 65:10:4:25) showed the highest cellular uptake at 42℃ and significantly improved the antitumor and survival efficacy in mice bearing C26 colon carcinoma in combination with ultrasonic HT compared to F0. Collectively, results demonstrated that optimizing the rigidity of the liposomal bilayers through the combinatorial selection of PLs of different transition temperatures could improve the plasma stability of the liposome, and hence ameliorate the outcome of therapy in assistance with an effective HT approach.