NOVEL BI-CISTRONIC HIGH-CAPACITY HELPER-DEPENDENT ADENOVIRAL VECTOR CO-EXPRESSING FLT3L AND TK (+GCV) INDUCES INTRACRANIAL GBM REGRESSION AND ANTI-GBM IMMUNOLOGICAL MEMORY

MUHAMMAD; KROEGER; PUNTEL; CANDOLFI; YAGIZ; LIU; GOZO; BAKER; FOULAD; XIONG; PALMER; NG; LOWENSTEIN; CASTRO

Dallas, Texas, USA

Congreso; Society for Neuro-Oncology; 2008

239. NOVEL BI-CISTRONIC HIGH-CAPACITY HELPER-DEPENDENT ADENOVIRALVECTOR CO-EXPRESSING FLT3L AND TK (+GCV) INDUCES INTRACRANIAL GBMREGRESSION AND ANTI-GBM IMMUNOLOGICAL MEMORYA.K.M. Ghulam Muhammad, MBBS, PhD; Kurt Kroeger; Mariana Puntel; Marianela Candolfi, VMD,PhD; Kader Yagiz, PhD; Chunyan Liu; Alireza Salem; Maricel Gozo; Greg Baker; David Foulad; WeiXiong; Dona Palmer; Philip Ng; Pedro Lowenstein; Maria Castro INTRODUCTION: The combined immunotherapy/conditional cytotoxic approach involving intratumoraldelivery of first generation adenoviral vectors (Ad) encoding the conditional cytotoxic gene, herpessimplex virus type 1-thimidine kinase (TK) and the immune stimulatory, Fms-like Tyrosine Kinase 3ligand (Flt3L) generates anti-GBM immune response and memory resulting in significantly improvedsurvival in several intracranial, syngeneic, rodent GBM models. We have now engineered a novel, bicistronichigh-capacity (HC-Ad) vector capable of inducible expression of Flt3L using the TetOnregulatory system and constitutive expression of TK. METHODS: Lewis rats bearing large, syngeneic,intracranial GBMs were treated with the HC-Ad-TetON-Flt3L/TK and efficacy, neuropathology, biodistributionand systemic side effects were assessed at short-term (5 days), medium-term (1 month) andlong-term (6 month) time points. RESULTS: Over 80% of the treated rats survived long term. Real-timequantitative PCR (qPCR) revealed that HC-Ad vector genomes were restricted to the brain injection site.Using ELISA, the levels of Flt3L in the serum could be detected at 5 days only. At the 6 months timepoint, Nissl staining showed absence of residual tumor. Immunocytochemistry with antibodies againstmyelin basic protein or tyrosine hydroxylase showed absence of demyelination or striatal damage,respectively; CD68+ macrophages/activated microglia, CD8+ T cells, and MHC II immunopositive cellswere observed at the site of tumor regression. Long term survivors survived a second tumor implanted inthe contra-lateral hemisphere, indicating that this therapeutic modality induces long-term anti-GBMimmunological memory. CONCLUSION: Our results indicate that tumor regression in response to HCAd-mediated gene therapy does not lead to overt adverse neuropathological side effects to the normalsurrounding brain parenchyma and no "off target" leakage of the therapeutic HC-Ad vector. Thus, thehigh therapeutic efficacy and safety profile of the bi-cistronic HC-Ad vector makes it an excellentcandidate to be tested as an adjuvant therapy for human GBM in Phase I clinical trials.