Anionic liposomes are often Caspase activation rejected from further by the blood vessels; therefore, neutral charged liposomes are optimal for drug delivery. Both the EGFR-IL and hIgG-IL used in this study were slightly anionic, but not to an extent that would affect the efficiency of drug delivery to the tumor. Thus, the properties of these liposomes were in accordance with other studies applying liposomes for targeting purpose in vitro and in vivo [23]. When comparing brain Inhibitors,research,lifescience,medical tumor cryosections gray scale intensities for EGFR-IL and hIgG-IL, an increase of 3.39 fold versus 1,95-fold change could be

observed above the background fluorescence of the tumor tissue. This clearly demonstrated a preferential accumulation of the EGFR-immunoliposomes within the tumor tissue. Both α-hEGFR-IL and hIgG-IL occurred inside the tumor blood vessels. Additionally, Inhibitors,research,lifescience,medical both the α-hEGFR-IL and the hIgG-IL were accumulating in the tumor interstitium, which is likely due to the EPR-effect where liposomes regardless of conjugation

will accumulate gradually over Inhibitors,research,lifescience,medical time [14, 17, 24]. The liposomes trapped in the tumor interstitium by this EPR-effect have substantially increased cellular binding when liposomes were conjugated with anti-EGFR antibody. The EGFR labeling in vivo using the Cetuximab antibody demonstrated good affinity for the EGFR-expressing U87mg cells, which supports prior Inhibitors,research,lifescience,medical findings demonstrating a preferential accumulation of α-hEGFR-IL and even increased tumor growth inhibition compared with naked liposomes in a subcutaneous xenograft model [18]. As part of the current study, it was observed that blood vessels of the U87mg xenograft tumor grown in a cranial microenvironment have significantly smaller pore cutoff-size than xenograft tumors grown in a subcutaneous microenvironment (unpublished observation), which is explainable by the influence of cells denoting

the neurovascular unit [14]. Enhanced permeability of macromolecules Inhibitors,research,lifescience,medical seen in solid tumor is well documented [14, 25, 26]. Here, we show that the EPR effect is present in the U87mg intracranial xenograft model by means of the accumulation and retention of endogenous mouse albumin and liposomes in the tumor interstitium. Albumin accumulation in the U87mg intracranial tumors in mice also exhibited a significantly higher accumulation when examined in another human GBM cell line (HGL21) used for intracranial xenograft Rutecarpine formation [25]. The tumor blood vessels generated when using U87mg for intracranial xenografts are small (100nm) compared with many other cell lines (500nm) [14]. In our study, U87mg intracranial xenografts also displayed high vascularization, but the center of the tumor was less vascularized compared with the tumor periphery. This was not unexpected, since necrosis of tumors is often seen due to their rapid growth. 5.