Antibody Targeting of Long-Circulating Lipidic Nanoparticles Does Not Increase Tumor Localization but Does Increase Internalization in Animal Models

Abstract

We describe evidence for a novel mechanism of monoclonal antibody (MAb)-directed nanoparticle (immunoliposome) targeting to solid tumors in vivo. Long-circulating immunoliposomes targeted to HER2 (ErbB2, Neu) were prepared by the conjugation of anti-HER2 MAb fragments (Fab ¶ or single chain Fv) to liposome-grafted polyethylene glycol chains. MAb fragment conjugation did not affect the biodistribution or long-circulating properties of i.v.-administered liposomes. However, antibody-directed targeting also did not increase the tumor localization of immunoliposomes, as both targeted and nontargeted liposomes achieved similarly high levels (7-8% injected dose/g tumor tissue) of tumor tissue accumulation in HER2-overexpressing breast cancer xenografts (BT-474). Studies using colloidal gold-labeled liposomes showed the accumulation of anti-HER2 immunoliposomes within cancer cells, whereas matched nontargeted liposomes were located predominantly in extracellular stroma or within macrophages. A similar pattern of stromal accumulation without cancer cell internalization was observed for anti-HER2 immunoliposomes in non-HER2-overexpressing breast cancer xenografts (MCF-7). Flow cytometry of disaggregated tumors posttreatment with either liposomes or immunoliposomes showed up to 6-fold greater intracellular uptake in cancer cells due to targeting. Thus, in contrast to nontargeted liposomes, anti-HER2 immunoliposomes achieved intracellular drug delivery via MAb-mediated endocytosis, and this, rather than increased uptake in tumor tissue, was correlated with superior antitumor activity. Immunoliposomes capable of selective internalization in cancer cells in vivo may provide new opportunities for drug delivery.

Antitumor activity of an epithelial cell adhesion molecule–targeted nanovesicular drug delivery system

“…However, with increasing time, both SIL-Dox and SL-Dox accumulated in the liver and spleen (Table 3). This reflects the ultimate clearance of both targeted and nontargeted liposomes by the reticuloendothelial system, as the PEG-containing phospholipids may gradually be metabolized, and is in good agreement with the findings of others (39,40).…”

“…The EpCAM-targeted immunoliposomes described here, with their long circulation half-lives, achieved double the uptake of nontargeted liposomes into tumors 24 h after injection, although both types of liposomes showed similar biodistribution patterns for the other major organs. Other investigators have reported that the tumor localization was similar for either targeted or nontargeted liposomes (18,40). Given that both types of liposomes reach solid tumors by the passive targeting mechanism, the reason for the increased tumor localization of the EpCAM-targeted liposomes versus the nontargeted liposomes may be due to both the high affinity of the scFv fragment, for the antigen, its rapid internalization, and its stability, as a high percentage of scFv remains intact after coupling and during 48 h in the body (30).…”

PLGA-Based Nanoparticles as Cancer Drug Delivery Systems

“…The improved cellular internalization rather than an increased tumor accumulation is responsible of the anti-tumoral efficacy of actively targeted nanocarriers. This is the foundation of the design of delivery systems targeted to endocytosis-prone surface receptors (Kirpotin et al, 2006;Danhier et al, 2010). The aptitude of the nanocarrier to be internalized after binding to target cell is so an significant criterion in the selection of proper targeting ligands (Cho et al, 2008;Danhier et al, 2010).…”

Immunoliposomes: A Multipurpose Strategy in Breast Cancer Targeted Therapy

“… Finally, the antibody attached to the liposome can be used either as a whole protein or fragmented. Several approaches have been developed using the single-chain antibody variable region (scFv) (Mamot, Drummond et al, 2003;Hu, Chen et al, 2006), the complete variable region (Fab) (Kirpotin, Drummond et al, 2006) or the whole antibody (Barrajón-Catalán, Menéndez-Gutiérrez et al, 2010). It must be considered that, scFv and Fab (Figure 1) are less immunogenic than the whole antibody, however these fragments are not easy to obtain.…”