Penetrative and prolonged liposome-based convection-enhanced delivery system for glioblastoma treatment

Abstract

Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary brain tumor in humans. Although the incidence rate of GBM is low, the median survival without treatment is only about 5 months, and 15 months with the standard radiotherapy and chemotherapy. Due to this aggressiveness, there have been many attempts to treat GBM in new ways such as drug delivery through blood vessels. However, the blood-brain barrier (BBB), impedes the deep penetration of drugs in the brain tissue, thus reducing the therapeutic efficacy. A convention-enhanced delivery (CED) method, which is a delivery technique to infuse drugs directly into tissue using a catheter with continuous positive pressure, was recently developed to solve the delivery issues in the brain. However, although the CED improves the drug penetration, the interstitial and cerebrospinal fluids of brain clear out the infused drugs by the drainage pathway to the cervical lymph nodes. Here, we optimized a liposomal formulation to simultaneously improve penetration and retention of infused drugs using the CED method in the brain tissue. We prepared various liposomal formulations with different surface chemistries (fluidity, charge and PEGylation), which were loaded with fluorescent dyes. Then, we incubated liposomes with the U87MG glioblastoma cell line in vitro. The fluorescence intensity analysis data indicates that liposomes which have positive charge showed the better location inside the cells. The effects of fluidity do not affects the cellular uptake. Next, we injected liposomes directly into the brain and tumor tissue via the CED and examined their time-dependent distribution using confocal fluorescent microscopy. Interestingly, different from the in vitro results, liposomal formulations containing both positively charged and PEGylated lipids remained relatively long in the brain tissue rather than positive-only liposomes. Furthermore, PEGylated liposomes which have same structure of Doxil but lack of doxorubicin seemed to clear rapidly in the brain and tumor tissue. We examined this hypothesis by observing the cervical lymph node. The PEGylated liposomes accumulated more in the cervical lymph nodes than other liposomes even before 2 hours of injection. We believe that both positive and PEGylated lipids on the liposomal surface can determine the retentions in the brain tissue. These results suggest that optimized liposomal formulation can further enhance the therapeutic effect of drugs administered via the CED for glioblastoma treatment.