PRE-CLINICAL SAFETY AND EFFICACY STUDIES OF NEURAL STEM CELL MEDIATED CARBOXYLESTERASE/IRINOTECAN ENZYME/PRODRUG GENE THERAPY FOR RECURRENT GLIOMA LEADING TO FIRST-IN-HUMAN PHASE I CLINICAL TRIAL

Human neural stem cells (NSCs) are inherently tumor-tropic, localizing to invasive brain tumor foci following intracerebral administration in preclinical models of primary and secondary brain tumors, thus overcoming obstacles limiting current therapeutic modalities. These NSCs can be engineered to express numerous anti-cancer agents, making them attractive drug delivery vehicles. By concentrating therapy selectively at the tumor sites, toxicity to normal tissues and associated side effects are minimized, improving quality of life. A first-in-human pilot safety/feasibility clinical trial for recurrent glioma patients using a clonal, allogeneic NSC line (HB1.F3.CD21) for cytosine deaminase/5-fluorocytosine (5-FC) enzyme/prodrug gene therapy demonstrated safety, proof of concept for brain tumor localized NSC-mediated conversion of prodrug to active chemotherapeutic agent, non-tumorigenicity, and non-immunogenicity with a single round of treatment (Portnow et al, 2016). HB1.F3.CD21 NSCs were further engineered to secrete a modified human carboxylesterase (hCE1m6) that converts irinotecan (IRN) to the potent topoisomerase-1 inhibitor SN-38. Presented are the preclinical in vitro and in vivo pharmacokinetic studies optimizing dose and scheduling of hCE1m6-NSCs and a clinically equivalent bolus dose of IRN. Efficacy studies in orthotopic glioma models with multiple treatment cycles demonstrated a highly significant increase in the long-term survival distribution in mice treated with hCE1m6-NSCs + IRN as compared to IRN alone (Holm-Bonferroni adjusted p-value <0.0001). Results of IND-enabling safety/toxicity studies showed no significant increase in toxicity, as determined by daily clinical observations, blood chemistries, CBCs, and histopathology, in mice treated with hCE1m6-NSCs + IRN as compared to IRN alone. These results led to FDA approval for a recently initiated first-in-human phase I dose escalation, multiple treatment cycle study of intracranially administered carboxylesterase expressing NSCs in combination with intravenous irinotecan for the treatment of recurrent high grade gliomas (IND 16265; clincialtrial.gov ID NCT02192359).