Investigation of the role of macrophages on the cytotoxicity of doxorubicin and doxorubicin-loaded nanoparticles on M5076 cells in vitro

Doxorubicin-loaded PACA nanoparticles have been shown to be more efficient than free drug in mice bearing hepatic metastasis of the M5076 tumour. Due to the high phagocytic activity of Kupffer cells in the liver, it may be th at these cells played a role of drug reservoir after nanoparticle phagocyto sis. Therefore, the objective of this study was to assess the role of macro phages in mediating the cytotoxicity of doxorubicin-loaded nanoparticles on M5076 cells. The growth inhibition of tumour cells was evaluated in two wa ys: firstly, the cells were incubated in a coculture system consisting of s pecial wells with two compartments separated by a porous membrane. M5076 ce lls were seeded into the lower compartment and the macrophages J774.A1 were introduced into the upper part. The macrophages were activated or not by I FN-gamma. The drug preparations were added only in the macrophage insert. S econdly, growth inhibition was also assessed in the conventional way, i.e. in direct contact with the tumour cells to serve as a reference. After dire ct contact, free doxorubicin (Dox) and doxorubicin-loaded nanoparticles (NP -Dox) had the same efficacy against M5076 cell growth. The coculture experi ments led to a 5-fold increase in the IC50 for both Dox and NP-Dox. The act ivation of macrophages by IFN-gamma in coculture significantly decreased th e IC50 values. In conclusion, after phagocytosis of doxorubicin-loaded nano particles, J774.A1 cells were able to release active drug, allowing it to e xert its cytotoxicity against M5076 cells. Drug efficacy was potentiated by the activation of macrophages releasing cytotoxic factors such as NO, whic h resulted in increased tumour cell death. Thereby, the coculture system pe rmitted us to investigate the macrophage-mediated cytotoxicity of colloidal carriers loaded with an anticancer drug, which is of great interest when f urther i.v. administration is envisaged. (C) 2000 Elsevier Science B.V. All rights reserved.