Thermosensitive
liposomes grafted with
cholesterol-conjugated poly(N-(2-hydroxypropyl)
methacrylamide mono/dilactate) (chol-pHPMAlac) have been developed for heat-induced release of
doxorubicin (DOX). These
liposomes release DOX completely during mild
hyperthermia, but their interaction with blood cells and
cancer cells has not been studied. Following
intravenous administration,
liposomes may interact with
plasma proteins and various types of cells (e.g., endothelial cells, platelets, and macrophages), which would reduce their disposition in the
tumor stroma. Interaction between
liposomes and platelets may further cause platelet activation and
thrombosis, which could lead to vascular occlusion and thromboembolic complications. The aim was to investigate DOX release kinetics in the presence of serum, stability, in vitro uptake by and toxicity to
cancer cells and somatic cells, and platelet activating potential of the chol-pHPMAlac
liposomes. DOX release was determined spectrofluorometrically.
Liposome stability was determined in
buffer and serum by dynamic light scattering and nanoparticle tracking analysis. Association with/uptake by and toxicity of empty
liposomes to AML-12, HepG2 (both hepatocyte-derived
cancer cells), RAW 264.7 (macrophages), and HUVEC (endothelial) cells was assayed in vitro. Platelet activation was determined by analysis of
P-selectin expression and
fibrinogen binding. DOPE:
EPC liposomes (diameter = 135 nm) grafted with 5% chol-pHPMAlac (cloud point (CP) = 16 °C; Mn = 8.5 kDa) released less than 10% DOX at 37 °C in 30 min, whereas complete release took place at 47 °C or higher within 10 min. The size of these
liposomes remained stable in
buffer and serum during 24 h at 37 °C. Fluorescently labeled but DOX-lacking chol-pHPMAlac-
liposomes exhibited poor association with/uptake by all cells under investigation, were not cytotoxic, and did not activate platelets in both buffered
solution and whole blood. In conclusion, thermosensitive chol-pHPMAlac-grafted
liposomes rapidly release DOX during mild
hyperthermia. The
liposomes are stable in a physiological milieu, are not taken up by cells that are encountered in an in vivo setting, and are non-antagonistic towards platelets. Chol-pHPMAlac-grafted
liposomes are therefore good candidates for DOX delivery to
tumors and temperature-triggered release in
tumor stroma.