Oncolytic adenoviruses are alternative promising therapies for the treatment of gliomas. Nevertheless, the effective treatment of gliomas with oncolytic adenovirus has been hampered by the relative low persistence of the vectors, difficulty in systemic delivery and side toxicity due to undesired targeting of normal cells and to the immune system response. One strategy to improve the efficacy of oncolytic adenoviruses is to combine them with chemotherapeutic drugs. We have generated an adenovirus, termed ICOVIR, that encompasses three elements: enhanced tropism trough integrin infection (RGD-4C modification of the fiber HI loop), tumor selectivity (Delta-24 mutation in the Rb-binding CR2 region of E1A), and decrease of E1A-mediated toxicity (insertion of two E2F1 promoter sequences preceded by an insulator upstream of the E1A coding sequence in substitution of the native E1A promoter) to provide the construct with both cell-specific gene expression and strong viral replication capability in cancer cells. In this regard, ICOVIR-5 probed to be a highly selective vector in gliomas at the same time that retained a robust cell killing potential and a negligible toxicity in vitro and which is more important in vivo. To test the hypothesis that ICOVIR-5 infection favors the effect of temozolomide (TMZ) and RAD001, we first examine in vitro the effect of ICOVIR-5 alone or in combination with TMZ or RAD001 in U87-MG and U251-MG glioma cell lines by MTT. Our data showed that both drugs were more efficient in combination with ICOVIR-5 that when administer alone. In addition, ICOVIR-5 replication properties were not affected by the addition either drug. Of interest, individually systemic administration of ICOVIR-5 resulted in improved survival and generation of long-term survivors (animal living more than 100 days after treatment). Importantly, the combination of the drugs with ICOVIR-5 resulted in a significant increased in the median survival (P<0.001) and in 40% of long time survivors. examination of the brains by IHC showed E1A and hexon staining meaning the ability of the virus to infect and efficiently replicate in combination with the drugs. Of importance, all the regimens showed very low hepatotoxicity as probed by the low expression levels of E1A in liver and serum levels of AST and ALT similar to the physiological values. We believe that the combination of ICOVIR and chemotherapy allows for multi-compartmental treatment. The antiangiogenic, cytostatic and immunosuppressant effect of the drugs facilitates the local spread of the virus within the tumour and into the surrounding brain areas that may contain invading cells from the glioma at the same time that generate a wider window of time for the virus to elicit an oncolytic effect. In summary, ICOVIR-5 in combination with TMZ and RAD001 constitutes a promising strategy for the treatment of gliomas.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]