The tumor-suppressive activity of melanoma differentiation associated gene-7 (mda-7) also known as interleukin-24 (IL-24) has been demonstrated in a broad spectrum of human cancer cells in vitro and in vivo. However the tumor suppressive effect of mda-7 in human ovarian cancer cells has not been extensively studied. Therefore, the purpose of this study was to determine the efficacy of adenovirus-based mda-7 (Ad-mda7) gene therapy in the treatment of ovarian cancer in vitro and in vivo. In vitro, treatment of human ovarian cancer cells (MDAH 2774, and OVCA 420) with Ad-mda7 resulted in significant (P <0.5) growth suppression leading to cell-cycle arrest in the G2/M phase and apoptosis. In contrast cells treated with PBS or Ad-luc (vector control) showed no significant growth inhibitory effects. Lack of Ad-mda7-mediated growth inhibitory effects was also observed in normal fibroblast (MRC-9) cells indicating tumor-selective activity. Studies addressing the molecular mechanism for Ad-mda7-induced apoptosis revealed activation of PKR, pJNK and p38MAPK in both MDAH 2774 and OVCA 420 tumor cells but not in normal MRC-9 cells. Associated with increased expressions of PKR, p38MAPK and pJNK were increased in caspase-9, caspase-3 and PARP cleavage in Ad-mda7 treated tumor cells but not in PBS or Ad-luc treated cells. These results showed Ad-mda7 inhibits ovarian tumor cell proliferation and induced apoptosis in a p53 independent manner as MDAH 2774 cells are mutant for p53 while OVCA 420 are wild-type for p53. To further test whether Ad-mda7 can inhibit ovarian tumors in vivo, a subcutaneous xenograft model was used. Subcutaneous tumors were established in nude mice by injecting MDAH 2774 cells. Treatment was initiated when the tumors were palpable. Tumors were injected intratumorally with PBS, Ad-luc or Ad-mda7 (1x1010 vp/dose) for a total of ten doses on alternate days and tumor growth measured. Treatment with Ad-mda7 resulted in a significant (P < 0.5) tumor growth suppression compared to growth of tumors treated with PBS and Ad-luc. That the inhibition was due to MDA-7 was demonstrated by detecting MDA-7 protein in the Ad-mda7 treated tumor specimens. Similar results were also obtained when tested in an intraperitoneal (i.p.) model of ovarian cancer using MDAH 2774 cells. Animals with i.p. MDAH 2774 tumors were treated with Ad-luc or Ad-mda7 encapsulated in nanoparticles daily and animal survival monitored. Animals treated with Ad-mda7 encapsulated in nanoparticles showed increased survival than animals treated with Ad-luc encapsulated in nanoparticles. Our results demonstrate for the first time the growth inhibitory effects of Ad-mda7 in ovarian cancer both in vitro and in vivo. These findings constitute a step in translating promising preclinical data to the clinic for treatment of human ovarian cancer.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]