77. Efficient Transduction and Therapy of Malignant Glioma by Lentiviral Vectors Pseudotyped with LCMV Glycoproteins

Abstract

Malignant gliomas, the most frequent primary brain tumors, still have a dismal prognosis despite advances in neurosurgery, radiation, and chemotherapy. Gene therapy using viral vectors represents an attractive alternative to conventional cancer therapies. In particular, retroviral vectors have been regarded as potent candidates as they transduce only dividing cells, thereby achieving specificity for tumor cells. However, clinical trials have failed, because in a given treatment window, only the minority of tumor cells is dividing and therefore susceptible to retroviral infection. To overcome this problem we used lentiviral vectors, which can transduce dividing as well as quiescent cells, for gene therapy of malignant glioma. In a previous study we established lentiviral vectors pseudotyped with lymphocytic choriomeningitis (LCMV) glycoproteins (GP) and demonstrated efficient transduction of human malignant glioma cells in culture. In the current investigation, we compared the transduction efficacy of LCMV GP- and vesicular stomatitis virus glycoprotein (VSV G)-pseudotyped lentiviral vectors for malignant glioma cells and normal brain cells in vitro and in vivo (Miletic et al., Human Gene Therapy 2004). LCMV pseudotypes transduced predominantly astrocytes, whereas VSV-G pseudotypes infected neurons as well as astrocytes in vitro and in the hippocampus and striatum of Fischer rats. LCMV pseudotypes showed an efficient transduction of solid glioma parts of 9L tumors (69.3 |[plusmn]| 10.6%) and a very specific transduction of infiltrating tumor cells (71.5 |[plusmn]| 10.6%). In contrast, VSV-G pseudotyped lentiviral vectors transduced only a few tumor cells in solid (6.8 |[plusmn]| 1.9%) and infiltrating (2.2 |[plusmn]| 1.9%) tumor parts and infected mostly normal brain cells in infiltrating tumor areas (42.9 |[plusmn]| 11.4%). To investigate the therapeutic impact of LCMV pseudotypes, we used the suicide gene HSV-tk fused to eGFP as therapeutic construct. We could demonstrate a high transduction efficiency of 9L tumors (Fig. 1A; Methionin-PET) using [18F]FHBG-PET to detect HSV-tk expression (Fig. 1B) and by fluorescence microscopy of histological brain sections (Fig. 1C). The Kaplan-Meier survival plot (Fig. 1D) revealed over 90% of long time survivors (100 days) in the therapeutic group (n=13). In conclusion, lentiviral vectors pseudotyped with LCMV glycoproteins represent an attractive option for gene therapy of malignant glioma.