2011). Also in our hands, AAV-GDNF-treated rat brain showed clear GDNF staining in the injected area (striatum), lateral GP, SNpc, and SNpr. The site of delivery is one major open question regarding future gene therapy with neurotrophic

factors in PD. When the nigrostriatal DAergic projections are lost, intraputamenal delivery Inhibitors,research,lifescience,medical of therapeutic agents to target the SN will probably require alternative routes of transportation. In this regard, GABAergic projections may play a significant role (Kirik et al. 2000; Ciesielska et al. 2011). It is also noteworthy that efficacy in a rodent model may not guarantee efficacy in humans. In animal models of PD, intrastriatal infusion of a recombinant AAV2-NRTN vector (CERE-120) was effective in behavioral tests, and NRTN immunoreactivity was traced to the striatum, GP, endopeduncular nucleus, SNpc, and SNpr (Kordower et al. 2006; Gasmi et al. 2007a,b; Herzog et al. 2007), suggesting both retrograde and anterograde transport. However, when CERE-120 was delivered into the putamen of PD patients, Inhibitors,research,lifescience,medical NRTN immunoreactivity was find more mainly restricted to the injected area, with a very scanty NRTN signal in the SN of postmortem brains (Bartus et al. 2011). The limited distribution of NRTN protein in the human brain may explain the very modest improvement Inhibitors,research,lifescience,medical in motor scores in the Phase 2 CERE-120 clinical trial (Marks et

al. 2010). It is also consistent with the observation that in postmortem brains, there was very little induction of TH following intraputamenal infusion of CERE-120 (Bartus et al. 2011). In our study, only a scanty CDNF Inhibitors,research,lifescience,medical immunoreactivity could be detected along the anterograde indirect projections from the striatum to SN, and therefore, CDNF evidently would need the direct pathways. It is

tempting to speculate that for an optimal clinical effect, AAV2-CDNF should be administered close to the SN, or to both the striatum and SN. Inhibitors,research,lifescience,medical Only when the CDNF receptor is identified and its location is found, further conclusions of the optimal administration site of CDNF can be made. others In conclusion, AAV2-CDNF was able to induce functional recovery of the rat midbrain neural circuitry to the same extent as AAV2-GDNF. AAV2-CDNF did not produce significant sprouting of neither TH-reactive fibers in the striatum nor increase in TH-positive cells in the SNpc. The modest neuroprotection is most probably due to rather low viral vector titers for both AAV2-CDNF and AAV2-GDNF and in the case of AAV2-CDNF, restricted and mainly intracellular expression of hCDNF protein. However, our results indicate that AAV2-CDNF is an alternative method for sustained delivery of CDNF protein in the brain. In the future, it would be important to find out the level of protection using higher titers, multiple injection sites, other vector serotypes, different promoter, and/or different injection site.