Enhancing mda-7/IL-24 therapy in renal carcinoma cells by inhibiting multiple protective signaling pathways using sorafenib and by Ad.5/3 gene delivery

We have determined whether an adenovirus that comprises the tail and shaft domains of a serotype 5 virus and the knob domain of a serotype 3 virus expressing MDA-7/IL-24, Ad. 5/3-mda-7, more effectively infects and kills renal carcinoma cells (RCCs) compared to a serotype 5 virus, Ad. 5-mda-7. RCCs are a tumor cell type that generally does not express the receptor for the type 5 adenovirus; the coxsakie and adenovirus receptor (CAR). Ad. 5/3-mda-7 infected RCCs to a much greater degree than Ad. 5-mda-7. MDA-7/IL-24 protein secreted from Ad. 5/3-mda-7-infected RCCs induced MDA-7/IL-24 expression and promoted apoptosis in uninfected "bystander" RCCs. MDA-7/IL-24 killed both infected and bystander RCCs via CD95 activation. Knockdown of intracellular MDA-7/IL-24 in uninfected RCCs blocked the lethal effects of conditioned media. Infection of RCC tumors in one flank, with Ad. 5/3-mda-7, suppressed growth of infected tumors and reduced the growth rate of uninfected tumors implanted on the opposite flank. The toxicity of the serotype 5/3 recombinant adenovirus to express MDA-7/IL-24 was enhanced by combined molecular or small molecule inhibition of MEK1/2 and PI3K; inhibition of mTOR, PI3K and MEK1/2; or use of the multi-kinase inhibitor sorafenib. In RCCs, combined inhibition of cytoprotective cell signaling pathways enhanced the MDA-7/IL-24-induction of CD95 activation, with greater mitochondrial dysfunction due to loss of MCL-1 and BCL-X-L expression and tumor cell death. Treatment of RCC tumors in vivo with sorafenib also enhanced Ad. 5/3-mda-7 toxicity and prolonged animal survival. Future combinations of these approaches hold promise for developing a more effective therapy for kidney cancer.