Validation of HSV1-TK plus ganciclovir in combination with the immune-stimulant Flt3L as a powerful therapeutic target for Glioblastoma multiforme in a preclinical syngeneic rat model

CANDOLFI; KING; MUHAMMAD; PUNTEL; KROEGER; LIU; ALZADEH; LERNER; LEE; FOULAD; SATO; LOWENSTEIN; CASTRO

San Diego, California, USA

Congreso; American Association for Cancer Research; 2008

Abstract #2870Validation of HSV1-TK plus ganciclovir in combination with the immune-stimulant Flt3L as a powerful therapeutic target for Glioblastoma multiforme in a preclinical syngeneic rat modelMarianela CANDOLFI, Gwendalyn King, Akm Muhammad, Mariana Puntel, Kurt Kroeger, Chunyan Liu, Gabrielle Ahlsadeh, Jonathan Lerner, Sharon Lee, David Foulad, Katsuaki Sato, Pedro Lowenstein and Maria CastroCedars Sinai Medical Center, Los Angeles, CA, Laboratory for Dendritic Cell Immunobiology, Research Center for Allergy and Immunology, RIKEN Yokohama Institute, Kanagawa, JapanGlioblastoma Multiforme (GBM) is the most common subtype of primary brain tumor in adults, and its prognosis is dismal. We assessed the efficacy and neurotoxicity of adenoviruses (Ads) expressing proapoptotic transgenes, i.e. HSV1-thymidine kinase (Ad-TK), TNF- (Ad-TNF-), FasL (Ad-FasL) or TRAIL (Ad-TRAIL) for GBM immunotherapy in combination with the immuno-stimulant Flt3L (Ad-Flt3L). TK selectively kills rapidly dividing cells in combination with the prodrug ganciclovir (GCV), while TNF-, FasL or TRAIL kill cells expressing the respective death receptor. Rats bearing intracranial CNS-1 tumors were injected intratumorally with the Ads expressing the proapoptotic transgenes 4 days after tumor implantation. We found that while rats bearing small tumors treated with saline, Ad-TNF- and Ad-TRAIL succumbed due to tumor burden, Ad-TK+GCV and Ad-FasL inhibited tumor progression, and significantly improved the survival of the rats. However, when we used Ad-TK+GCV or Ad-FasL to treat larger tumors (day 9 after implantation), we found that they are ineffective to improve survival. Less than 20% of rats treated with Ad-TK+GCV survived long term and none of the rats treated with Ad-FasL rats survived further than the saline group. Thus, we used the combination of Ad-TK+GCV or Ad-FasL with Ad-Flt3L which were injected intratumorally in rats bearing large tumors. Flt3L recruits and activates dendritic cells into the brain, improving antigen presentation. We found that although Ad-Flt3L poorly improved the survival of Ad-FasL-treated rats, it significantly increased survival when combined with Ad-TK+GCV; >60% of long term survivors. The neuropathological analysis of naïve rat brains injected with these proapoptic viruses demonstrated that expression of FasL and TRAIL caused overt toxicity, leading to profuse infiltration of inflammatory cells, reduction in TH expression in the striatum, local hemorrhages and ventriculomegaly, while administration of Ad-TK+GCV did not significantly alter the structure of the normal brain and induced only a mild, transcient local inflammation. Our results show that the combination therapy, Ad-Flt3L/Ad-TK plus GCV is the most efficient amongst the several proapoptotic approaches tested. Moreover, while intracranial delivery of non-specific proapoptotic cytokines like TRAIL and FasL is very toxic to the normal brain, administration of Ad-TK+GCV does not induce overt neuropathological side effects. Our results warrant further development of this combination therapy for the future implementation of a clinical trial for GBM. Supported by NIH/NINDS R01 NS44556.01, R21-NSO54143.01; UO1 NS052465.01; RO3 TW006273-01 to M.G.C.; RO1 NS 054193.01; RO1 NS 42893.01; U54 NS045309-01, and R21 NS047298-01 to P.R.L; F32 NS058156.01 to M.C.