N-(4-hydroxyphenyl) retinamide induced astrocytic differentiation and increased sensitivity to interferon-gamma for apoptosis in three human glioblastoma cell lines (A172, LN18, and SNB19)
Authors: Rajiv Janardhanan, Naren Banik, Swapan Ray
Journal: Clinical Cancer Research (2007)

B40   The incidence of glioblastoma, which is the most prevalent and deadliest brain tumor, is dramatically increasing over the years. Glioblastoma is composed of heterogeneous cell populations that grow aggressively due to their ability to maintain abnormally high potentials for cell proliferation and vascularization. The conventional therapeutic measures to combat glioblastoma are mostly ineffective necessitating the need for development of innovative and new therapeutic strategies. Because glioblastoma cells avoid terminal differentiation and apoptotic death, one treatment strategy would be to use a combination of two therapeutic agents for induction of both differentiation and death in glioblastoma cells. Also, an effective combination therapy should be capable of controlling the growth of different glioblastoma cell types. Retinoids, natural and synthetic, are well known for their capability of inducing cell differentiation. However, several retinoids at high doses cause severe organ toxicity and are not highly recommended as therapeutic agents. On the other hand, N-(4-hydroxyphenyl) retinamide (4-HPR) is a synthetic retinoid that at low concentration is non-toxic and known to inhibit cell proliferation and induce differentiation in many cancer cells. Interferon-gamma (IFN-γ) is a famous cytotoxic cytokine, which is capable of initiating the apoptotic death with activation of proteolytic cascades in several types of solid tumors including glioblastoma. In the present study, we have tested the efficacy of the combination of 4-HPR and IFN-γ for induction of terminal differentiation and apoptotic death in three human glioblastoma cell lines (A172, LN18, and SNB19). Cells were treated first with 0.5 µM 4-HPR for 3 days and then in combination with IFN-γ (200 units/ml) for 2 days. Results indicated that treatment with 4-HPR alone induced terminal astrocytic differentiation as evidenced by characteristic changes in the cell morphology and biochemical features such as increase in expression of glial fibrillary acidic protein (GFAP, a marker for astrocytic differentiation) and decreases in expression of the catalytic subunit of human telomerase reverse transcriptase (hTERT, a factor for sustained proliferation of cancer cells), survivin (an important member of the inhibitor-of-apoptosis proteins), and anti-apoptotic Bcl-2 protein; but 4-HPR alone did not induce any notable amount of apoptosis. While treatment with IFN-γ alone induced apoptosis to some extents, the combination of 4-HPR and IFN-γ highly increased the amounts of apoptosis in all three glioblastoma cell lines. Apoptosis occurred with the activation of both receptor-mediated and mitochondria-mediated caspase cascades. Our results showed that combination therapy decreased the expression of the survival factors (hTERT, survivin, and Bcl-2) to make different glioblastoma cell lines highly sensitive to IFN-γ for induction of apoptosis with activation of proteolytic cascades involving caspase-8, caspase-9, and caspase-3. Hence, the combination of 4-HPR and IFN-γ can be considered as an effective therapeutic strategy for controlling the malignant growth of different glioblastoma cell populations.