Integration-deficient lentiviral vectors delivering neurotrophic factors for gene therapy of Parkinson’s disease

Parkinson’s disease (PD) results from the loss of nigral dopaminergic neurons and subsequent depletion of striatal dopamine. Direct injection of neurotrophic factors has shown encouraging protection in animal models of PD. However, clinical delivery of protein requires administration by implanted mini-pumps, with associated surgical risks. Hence, a novel integration-deficient lentiviral vector (IDLV) system, with an improved biosafety profile, was introduced.

Initial experiments examined whether transduction efficiency of IDLVs was comparable with that of the standard integration-proficient lentiviral vectors (IPLVs) through enhanced green fluorescent protein (eGFP) expression. Both data from transduced rat primary ventral mesencephalic cell cultures and 6-OHDA-lesioned rats display higher transduction efficiency of IPLVs in some cases, which may be related to cell proliferation.

IDLVs were further used to deliver insulin-like growth factor 1 (Igf-1) to ascertain the therapeutic effect of this factor, which upon delivery as a protein has recently demonstrated impressive neuroprotection against 6-hydroxydopamine (6-OHDA)-induced toxicity. IDLV-mediated IGF-1 neuroprotection were investigated in comparison with those of the well-characterised glial cell line-derived neurotrophic factor (GDNF). Significant improvements in cell survival of neuronal cultures transduced with either IDLV-Igf-1 or IDLV-Gdnf support the hypothesis that Igf-1-expressing IDLVs could be neuroprotective in vitro.

Animal experiments were then performed to test whether vector-mediated therapeutic effects of IGF-1 and GDNF could be transferred in in vivo. Whilst hGDNF overexpression improved dopaminergic cell survival and behaviour of injected 6-OHDA-lesioned rats, there was no neuroprotection following Igf-1 transduction. A long-term investigation of GDNF-induced neuroprotection in 6-OHDA-lesioned rats further confirms the long-lasting efficacy of hGDNF-expressing vectors, regardless of vector integration proficiency.

Overall, these findings provide evidence for the therapeutic efficacy of IDLVs in PD and support their use in the CNS as a safer delivery system. The data also suggest vector delivery of Igf-1 may not be worthy of further consideration for the treatment of PD.