The apomorphine-induced contralateral rotation test was used to demonstrate therapeutic efficacy. In the negative control group administered with the 951-THLs targeted with the non-specific IgG2a, the drug-induced rotation increased in all animals [30]. On the contrary, in the rats injected with the 951-THLs targeted with the TfRMAb, there was an 82% reduction in the apomorphine-induced contralateral

rotations [30]. The therapeutic effect of the TH gene replacement was correlated with the levels of TH Inhibitors,research,lifescience,medical determined by enzyme activity (Table 2) or Src inhibitor immunocytochemistry (Figure 4). The latter was performed in coronal sections of brain and showed complete normalization of the immunoreactive TH in the striatum of 6-OHDA lesioned rats 3 days after a single injection of the gene therapy (Figures 4(a)–4(c)). In contrast, lesioned control animals treated with

the THLs targeted with the non-specific IgG2a isotype control antibody show Inhibitors,research,lifescience,medical a marked reduction in striatal immunoreactive TH (Figures 4(d)–4(f)). Inhibitors,research,lifescience,medical The levels of the TH enzyme activity were also normalized in the ipsilateral striatum (Table 2). Additional studies were performed in the 6-OHDA PD rat model with THLs carrying the TH gene under the widely read SV40 promoter, that is, clone 877 (Table 2) [22]. Similar data were obtained in both the restoration of the TH expression pattern in brain and in the reduction of the apomorphine-induced contralateral rotation [22]. The only difference

between the studies Inhibitors,research,lifescience,medical performed with the TH expression plasmid driven by the SV40 promoter, Inhibitors,research,lifescience,medical or the Gfap promoter, was a 10-fold increase in the levels of TH activity in liver of animals injected with the SV40-TH construct, which is not seen with the Gfap-TH plasmid (Table 2 and Figure 2). The stability of the TH is associated with the availability of the biopterin cofactor, and the expression of from the TH enzyme is found in regions of the brain that express GTP cyclohydrolase 1 (GTPCH) [42–44]. The GTPCH is also expressed in peripheral tissues, like liver [45], which supports the increased expression in liver TH activity when the TH transgene is driven by the SV40 promoter (Table 2) [22]. The gene therapy in this PD model with either SV40- or Gfap-TH plasmids produced normalization of the expression pattern of TH and without expression of supranormal levels of TH activity (Table 2) [22, 30]. This observation parallels findings observed in TH transgenic mice, which showed only a minor increase in either immunoreactive TH or TH activity in striatum despite a 50-fold increase in the level of TH mRNA in the substantia nigra [46].