Purpose: We used two ligand-modified liposomal drugs to selectively deliver two different chemotherapeutics to tumor cells (TC) and tumor vasculature endothelial (TV) cells, and examined the therapeutic effect of altering the order of treatment administration, and the effect of the temporal spacing of the treatments on the accumulation of a second dose of liposomes and therapeutic activity.
Methods: Studies were completed in an orthotopic mouse model of human epidermal growth factor receptor 2 (HER2)-positive breast cancer, utilizing liposomal doxorubicin, targeted to TC via αHER2 Fab' fragments, and liposomal vincristine, targeted to CD13 on TV cells via NGR peptides.
Results and discussion: Combination treatment with TV-targeted plus TC-targeted therapies was therapeutically superior to either single agent; switching the order of administration of the combination did not alter treatment efficacy. The tumor accumulation of a second dose of liposomes was increased if administered at 4 days after pre-treatment with TV-targeted therapy. Using a treatment schedule exploiting this increase, the dose of simultaneously administered combination therapy was halved without compromising therapeutic effect.
Conclusion: Proof-of-concept studies revealed the therapeutic potential of a dual-targeted two drug approach against HER2-positive breast cancer, and may be applicable to the treatment of other solid tumors.