mda-7/IL-24 Induces Cell Death in Neuroblastoma through a Novel Mechanism Involving AIF and ATM

Advanced stages of neuroblastoma, the most common extracranial malignant solid tumor of the central nervous system in infants and children, are refractive to therapy. Ectopic expression of melanoma differentiation-associated gene-7/interleukin- 24 (mda-7/IL-24) promotes broad-spectrum antitumor activity in vitro, in vivo in preclinical animal models, and in a phase I clinical trial in patients with advanced cancers without harming normal cells. mda-7/IL-24 exerts cancer-specific toxicity (apoptosis or toxic autophagy) by promoting endoplasmic reticulum stress and modulating multiple signal transduction pathways regulating cancer cell growth, invasion, metastasis, survival, and angiogenesis. To enhance cancerselective expression and targeted anticancer activity of mda7/IL-24, we created a tropism-modified cancer terminator virus (Ad. 5/3-CTV), which selectively replicates in cancer cells producing robust expression of mda-7/IL-24. We now show that Ad. 5/3-CTV induces profound neuroblastoma antiprolifera-tive activity and apoptosis in a caspase-3/9-independent manner, both in vitro and in vivo in a tumor xenograft model. Ad. 5/3-CTV promotes these effects through a unique pathway involving apoptosis-inducing factor (AIF) translocation into the nucleus. Inhibiting AIF rescued neuroblastoma cells from Ad. 5/3-CTV-induced cell death, whereas pan-caspase inhibition failed to promote survival. Ad. 5/3-CTV infection of neuroblastoma cells increased ATM phosphorylation instigating nuclear translocation and increased gamma-H2AX, triggering nuclear translocation and intensified expression of AIF. These results were validated further using two ATM small-molecule inhibitors that attenuated PARP cleavage by inhibiting gamma-H2AX, which in turn inhibited AIF changes in Ad. 5/3-CTV-infected neuroblastoma cells. Taken together, we elucidate a novel pathway for mda-7/IL-24-induced caspase-independent apoptosis in neuroblastoma cells mediated throughmodulation of AIF, ATM, and gamma-H2AX. (C) 2016 AACR.