Addition of low-dose tumor necrosis factor-alpha to systemic treatment with STEALTH liposomal doxorubicin (Doxil) improved anti-tumor activity in osteosarcoma-bearing rats

Abstract

Improved efficacy of Doxil (STEALTH liposomal doxorubicin) compared to free doxorubicin has been demonstrated in the treatment of several tumor types. We have shown that addition of low-dose tumor necrosis factor (TNF) to systemic Doxil administration dramatically improved tumor response in the highly vascularized rat soft tissue sarcoma BN175. Whether a similar enhanced efficacy can be achieved in less vascularized tumors is uncertain. We therefore examined the effect of systemic administration of Doxil in combination with low-dose TNF in intermediate vascularized osteosarcoma-bearing rats (ROS-1). Small fragments of the osteosarcoma were implanted s.c. in the lower limb. Treatment was started when the tumors reached an average diameter of 1 cm. Rats were treated with five i.v. injections at 4-day intervals with Doxil or doxorubicin and TNF. Systemic treatment with Doxil resulted in a better tumor growth delay than free doxorubicin, but with progressive diseases in all animals. The 3.5-fold augmented accumulation of Doxil compared to free doxorubicin presumably explains the enhanced tumor regression. Addition of low-dose TNF augmented the anti-tumor activity of Doxil, although no increased drug uptake was found compared to Doxil alone. In vitro studies showed that ROS-1 is sensitive to TNF, but systemic treatment with TNF alone did not result in a tumor growth delay. Furthermore, we demonstrated that treatment with Doxil alone or with TNF resulted in massive coagulative necrosis of tumor tissue. In conclusion, combination therapy of Doxil and low-dose TNF seems attractive for the treatment of highly vascularized tumors, but also of intermediate vascularized tumors like the osteosarcoma.