Feasibility of intracerebrally administering multiple doses of genetically modified neural stem cells to locally produce chemotherapy in glioma patients

Neural stem cells (NSCs) are tumor tropic and can be genetically modified to produce anti-cancer therapies locally in the brain. In a prior first-in-human study we demonstrated that a single dose of intracerebrally administered allogeneic NSCs, which were retrovirally transduced to express cytosine deaminase (CD), tracked to glioma sites and converted oral 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU). The next step in the clinical development of this NSC-based anti-cancer strategy was to assess the feasibility of administering multiple intracerebral doses of CD-expressing NSCs (CD-NSCs) in patients with recurrent high-grade gliomas. CD-NSCs were given every 2 weeks using an indwelling brain catheter, followed each time by a 7-d course of oral 5-FC (and leucovorin in the final patient cohort). Fifteen evaluable patients received a median of 4 (range 2–10) intracerebral CD-NSC doses; doses were escalated from 50 × 106 to 150 × 106 CD-NSCs. Neuropharmacokinetic data confirmed that CD-NSCs continuously produced 5-FU in the brain during the course of 5-FC. There were no clinical signs of immunogenicity, and only three patients developed anti-NSC antibodies. Our results suggest intracerebral administration of serial doses of CD-NSCs is safe and feasible and identified a recommended dose for phase II testing of 150 × 106 CD-NSCs.