Antitumoral efficacy and neurotoxic profile of adenoviral vectors encoding proapoptotic genes to be used in combination with Flt3L for immunotherapy against glioblastoma

MARIANELA CANDOLFI; AKM GHULAM MUHAMMAD; MARIANA PUNTEL; KURT M KROEGER; CHUNYAN LIU; GABRIELLE E ALZADEH; JONATHAN LERNER; SHARON LEE; DAVID FOULAD; GWENDALYN D KING; KANTSUAKI SATO; PEDRO R LOWENSTEIN; MARIA G CASTRO

Boston, MA, EEUU

Congreso; American Society of Gene Therapy 11 Annual Meeting; 2008

Glioblastoma 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) to be used 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 and Ad-FasL inhibited tumor progression, and significantly improved the survival. However, when we used Ad-TK or Ad-FasL to treat larger tumors (day 9 after implantation), we found that alone; they are ineffective to improve survival. Less than 20% of rats treated with Ad-TK 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 or Ad-FasL with Ad-Flt3L which were injected intratumorally in rats bearing large tumors. Flt3L recruits and activates dendritic cells into the brain, eliciting 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; 70% of long term survivors. The neuropathological analysis of na ve 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 did not significantly alter the structure of the normal brain and induced only a mild, transient 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 expression of proapoptotic cytokines like TRAIL and FasL is very toxic to the normal brain, administration of Ad-TK 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.