Effects of valency on thermodynamic parameters of specific membrane interactions

The effect of internalizing human single chain antibody fragment on liposome targeting to epithelioid and sarcomatoid mesothelioma

Immunoliposomes (ILs) anchored with internalizing human antibodies capable of targeting all subtypes of mesothelioma can be useful for targeted imaging and therapy of this malignant disease. The objectives of this study were to evaluate both the in vitro and in vivo tumor targeted internalization of novel internalizing human single chain antibody (scFv) anchored ILs on both epithelioid (M28) and sarcomatoid (VAMT-1) subtypes of human mesothelioma. ILs were prepared by post-insertion of mesothelioma-targeting human scFv (M1) onto preformed liposomes and radiolabeled with (111)In ((111)In-IL-M1), along with control non-targeted liposomes ((111)In-CL). Incubation of (111)In-IL-M1 with M28, VAMT-1, and a control non-tumorigenic cell line (BPH-1) at 37 °C for 24 h revealed efficient binding and rapid internalization of ILs into both subtypes of tumor cells but not into the BPH-1 cells; internalization accounted for approximately 81-94% of total cell accumulation in mesothelioma cells compared to 37-55% in control cells. In tumor-bearing mice intravenous (i.v.) injection of (111)In-IL-M1 led to remarkable tumor accumulation: 4% and 4.7% injected dose per gram (% ID/g) for M28 and VAMT-1 tumors, respectively, 48 h after injection. Furthermore, tumor uptake of (111)In-IL-M1 in live xenograft animal models was verified by single photon emission computed tomography (SPECT/CT). In contrast, i.v. injection of (111)In-CL in tumor-bearing mice revealed very low uptake in both subtypes of mesothelioma, 48 h after injection. In conclusion, M1 scFv-anchored ILs showed selective tumor targeting and rapid internalization into both epithelioid and sarcomatoid subtypes of human mesothelioma, demonstrating its potential as a promising vector for enhanced tumor drug targeting.

The role of multivalency in antibody mediated liposome targeting

We have investigated the role of multivalency in immunoliposome binding to cells displaying different amounts of surface antigen using liposomes with increasing numbers of palmitoyl anti-H2Kk antibodies incorporated into the bilayer. RDM-4 lymphoma cells were treated with proteinase k to generate a series of cells with various amounts of H2Kk antigen. Percent binding of immunoliposomes was related to the number of antigens displayed by the RDM-4 cell. Increasing liposome binding was observed with increasing number of antibody molecules per liposome. However, the ratio of binding of the high-antigen-density cells to that of the low-antigen-density cells was higher with immunoliposomes of lower antibody density than the ones with higher antibody density. This result suggests that for better discrimination between cells differing in antigen density, liposomes with lower numbers of antibody molecules per liposome may be more useful as a discriminatory tool for cells with a low level antigen expression than liposomes with greater antibody densities.