Doxorubicin possesses high affinity for binding to
cardiolipin. We have utilized these properties in preparing stable
liposomes of
doxorubicin and
cardiolipin with a net positive charge.
Doxorubicin liposomes were formed by using 11.2 mumol of
drug, 5.6 mumol of
cardiolipin, 28.5 mumol of
phosphatidylcholine, 19.5 mumol of
cholesterol, and 11.1 mumol of
stearylamine. These
liposomes were sonicated for 90 min at 37 degrees followed by extensive dialysis against
buffer. The pharmacological, toxicological, and
therapeutic effects of
doxorubicin entrapped in
cardiolipin liposomes were compared with those of free
doxorubicin in mice. At a dose of 4 mg/kg i.v., the peak cardiac concentration was achieved in 30 min following free
doxorubicin administration, the value being 8.1 micrograms/g. The peak cardiac concentration with
doxorubicin in
cardiolipin liposomes was obtained at 5 min with a value of 2.8 micrograms/g of tissue. The cardiac concentration X time values for free
doxorubicin for the 24-hr period of observation were 55.1 micrograms X hr/g, whereas it was only 7.8 micrograms X hr/g with the
drug entrapped in
cardiolipin liposomes. Compared to free
drug, the liposomal entrapped
doxorubicin significantly reduced the histopathological lesions in cardiac tissue of mice at a dose of 15 mg/kg as determined by electron microscopy. The nadir of peripheral white blood cell counts in mice with free
drug, 6 mg/kg, was observed on Day 3 which was 50% of control, whereas with liposomal encapsulated
drug it was reduced only 23% on Day 7.
Doxorubicin in
cardiolipin liposomes demonstrated enhanced chemotherapeutic potential against murine ascitic
P388 leukemia with
a 144% increased life span compared to 55% increased life span with free
drug at a dose of 7.5 mg/kg on Days 1, 3, and 7. We conclude that
doxorubicin liposomes developed in these studies possess improved therapeutic action as demonstrated by their ability to reduce the toxicity of the
drug substantially.