Melanoma differentiation-associated 7 (interleukin 24) inhibits growth and enhances radiosensitivity of glioma cells in vitro and in vivo.

PURPOSE: Despite therapeutic interventions including surgery, chemotherapy, and radiotherapy, glioblastoma multiforme (GBM) has a very poor prognosis and novel therapies are required. EXPERIMENTAL DESIGN: Melanoma differentiation-associated 7 (mda-7) (interleukin 24), when expressed via a recombinant replication-defective adenovirus, adenovirus (Ad).mda-7, has profound antiproliferative and cytotoxic effects in a variety of tumor cells but not in nontransformed cells. The present studies examined the combined impact of Ad.mda-7 and ionizing radiation on the proliferation and survival of GBM cell lines. RESULTS: Ad.mda-7 caused a dose-dependent reduction in the proliferation of glioma cells in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. The antiproliferative effects of Ad.mda-7 were enhanced by radiation in a greater than additive fashion. These effects were not observed in cultures of nontransformed primary astrocytes. Purified MDA-7 protein caused a similar dose-dependent reduction in GBM cell growth that was enhanced after radiation exposure. The enhanced reduction in growth correlated with increased necrosis and DNA degradation. These modifications in cell phenotype correlated with reduced expression of Bcl-(XL) and enhanced expression of BAX. Overexpression of Bcl-(XL) protected cells from the antiproliferative and cytotoxic effects of Ad.mda-7 + radiation. Incubation of cells with N-acetyl cysteine abolished the enhancing effects of radiation. In vitro, Ad.mda-7 and radiation reduced colony formation ability, which was significantly increased when the two treatments were combined. In vivo, Ad.mda-7 enhanced the survival of Fischer 344 rats implanted intracranially with glioma cells. Radiation did not alter survival in control infected animals, whereas it prolonged survival in those infected with Ad.mda-7. CONCLUSIONS: These findings demonstrate that mda-7 reduces the proliferation and enhances the radiosensitivity of GBM cells in vitro and in vivo.

Melanoma differentiation associated gene-7, mda-7/IL-24, selectively induces growth suppression, apoptosis and radiosensitization in malignant gliomas in a p53-independent manner.

Malignant gliomas are extremely aggressive cancers currently lacking effective treatment modalities. Gene therapy represents a promising approach for this disease. A requisite component for improving gene-based therapies of brain cancer includes tumor suppressor genes that exhibit cancer constrained inhibitory activity. Subtraction hybridization identified melanoma differentiation associated gene-7 (mda-7) as a gene associated with melanoma cell growth, differentiation and progression. Ectopic expression of mda-7 by means of a replication-incompetent adenovirus (Ad), Ad.mda-7, induces growth suppression and apoptosis selectively in diverse human cancers, without producing any apparent harmful effect in normal cells. We presently demonstrate that Ad.mda-7 induces growth inhibition and apoptosis in malignant human gliomas expressing both mutant and wild-type p53, and these effects correlate with an elevation in expression of members of the growth arrest and DNA damage (GADD) gene family. In contrast, infection with a recombinant Ad expressing wild-type p53, Ad.wtp53, specifically affects mutant p53 expressing gliomas. When tested in early passage normal and immortal human fetal astrocytes, growth inhibition resulting from infection with Ad.mda-7 or Ad.wtp53 is significantly less than in malignant gliomas and no toxicity is evident in these normal cells. Moreover, infection of gliomas with Ad.mda-7 or treatment with purified GST-MDA-7 protein sensitizes both wild-type and mutant p53 expressing tumor cells to the growth inhibitory and antisurvival effects of ionizing radiation, and this response correlates with increased expression of specific members of the GADD gene family. Since heterogeneity in p53 expression is common in evolving gliomas, the present findings suggest that Ad.mda-7 may, in many instances, prove more beneficial for the gene-based therapy of malignant gliomas than administration of wild-type p53.