Vladimir Torchilin

Center for Pharmaceutical Biotechnology and Nanomedicine, Northeastern University, Boston, MA 02115, USA

Nanopreparations of various anti-cancer drugs are causing great interest from pharmaceutical scientists. Both, non-targeted and targeted nanopreparations are under development, including combination nanopreparations containing more than one active ingredient or, more than one specific ligand. Some of those will be discussed here.

Resveratrol (RES), a natural polyphenol with pleiotropic health benefits, has proven chemopreventive effects in all the stages of cancer including initiation, promotion and progression. However, the poor physico-chemical properties of RES severely limit its use as a free drug. To counter its drawbacks as a free drug, for glioblastoma (GBM) treatment, RES was loaded into PEGylated liposomes (RES-L). Since transferrin receptors (TfRs) are up-regulated in GBM, the liposome surface was modified with transferrin moieties (Tf-RES-L) to make them cancer cell-specific. The RES-L were stable, had a good drug-loading capacity, prolonged drug-release in vitro and were easily scalable. As shown by flow cytometry and confocal microscopy with U-87 MG cells, the Tf-RES-Ls were significantly more cytotoxic and induced higher levels of apoptosis accompanied by activation of caspases 3/7 in GBM cells compared to free RES or RES-L. In a subcutaneous xenograft mouse model of GBM, a tumor growth inhibition study and a modified survival study showed that Tf-RES-Ls were more effective than other treatments in their ability to inhibit tumor growth and improve survival in mice.

Among many approaches for active tumor-targeting, arginine-rich cell penetrating peptides (such as octaarginine, R8) and ligands specific to target over-expressed receptors on cancer-cell surfaces, are popular. We have prepared doxorubicin(DOX)-loaded liposomes, surface-modified with, R8 and transferrin (Tf) (Dual DOX-L), to improve targeting of A2780 ovarian carcinoma cells via the over-expressed transferrin receptors (TfRs) with the subsequent R8-mediated intracellular DOX delivery. Flow cytometry analysis with fluorescently-labelled DualL showed 2-fold higher cancer-cell association than other treatments after 4 h treatment. Blocking entry pathways of R8 (macropinocytosis) and Tf (receptor-mediated endocytosis, RME) resulted in a decreased cancer-cell association of DualL. Confocal microscopy confirmed involvement of both entry pathways and cytoplasmic liposome accumulation with nuclear DOX delivery for Dual DOX-L. Dual DOX-L exhibited enhanced cytotoxicity in vitro and was most effective in controlling tumor growth in vivo in an A2780 ovarian xenograft model compared to other treatments.
Other combination preparation include those combining pro-apoptotic drugs and drugs targeting cancer cell energy metabolism as well as nanopreparation with theranostic properties, i.e. combining therapeutic and diagnostic agents in a single nanoparticle.