Oncolytic adenovirus-mediated shRNA against Apollon inhibits tumor cell growth and enhances antitumor effect of 5-fluorouracil

Abstract

Apollon, a membrane-associated inhibitor of apoptosis protein, protects cells against apoptosis and is upregulated in certain tumor cells. In this study, the effects of Apollon protein knockdown by RNA interference on the growth of human HeLa, HT-1080 and MCF-7 cells in vitro and in vivo were investigated. An oncolytic adenovirus (ZD55) containing the RNA polymerase III-dependent U6 promoter to express short hairpin RNA (shRNA) directed against Apollon (ZD55-siApollon) was constructed. Our data show that ZD55-siApollon successfully exerts a gene knockdown effect and causes the inhibition of tumor cell growth both in culture and in athymic mice in vivo. Cell cycle analysis, 4 0 ,6-diamidino-2-phenylindole staining and western blot analysis reveal that ZD55-siApollon-mediated suppression of Apollon induces apoptosis. Intratumoral injection of ZD55-siApollon significantly inhibits tumor growth in HT-1080 xenograft mice. Furthermore, ZD55-siApollon enhances the antitumor effect of 5-fluorouracil, a chemotherapeutic agent. In conclusion, these results suggest that the depletion of Apollon by oncolytic adenovirus-shRNA delivery system provides a promising method for cancer therapy.

Apollon gene silencing induces apoptosis in breast cancer cells through p53 stabilisation and caspase-3 activation

“…It has been reported that Apollon is upregulated in some brain tumour cell lines that are resistant to certain DNA-damaging agents (Chen et al, 1999), and also that its overexpression is associated with poor prognosis in childhood acute myeloid leukaemia (Sung et al, 2007). These findings, together with preliminary evidence concerning the possibility of sensitising tumour cells to apoptosis induced by some anticancer drugs through antisense oligonucleotide-or small interfering RNA (siRNA)-mediated downregulation of Apollon (Chen et al, 1999;Qiu et al, 2004;Chu et al, 2008), has led researchers to consider the gene as a possible new therapeutic target.…”

“…However, considering that in our study, a total decline of breast cancer cell growth was not observed despite an almost complete abrogation of the Apollon expression, targeting Apollon alone could be insufficient for the effective treatment of tumours overexpressing it. As earlier evidence points to the possibility of improving the activity of specific anticancer drugs through Apollon knockdown (Chen et al, 1999;Chu et al, 2008), such a chemosensitising effect could be exploited for the design of more effective therapies with Apollon inhibitors combined with anticancer drugs to be used in the clinic, after a preclinical validation of the most appropriate ways of combining the different agents in chemoresistant tumour models. However, as the presence of wild-type p53 and 'normal' caspase-3 expression seem to be the major determinants of the antiproliferative effects consequent to Apollon downregulation, the possible induction of toxicity in normal tissues should be verified carefully in animal models.…”

“…An alternative possibility is that increased caspase-3 activity could be the result of caspase-8 activation after Apollon knockdown. In this context, it has been reported recently that apoptosis induction after transduction of HT-1080 human fibrosarcoma cells with an oncolytic adenovirus, expressing a short hairpin RNA against Apollon, was mediated by the proteolytic activation of caspase-8 and caspase-3 (Chu et al, 2008).…”

VEGI-armed oncolytic adenovirus inhibits tumor neovascularization and directly induces mitochondria-mediated cancer cell apoptosis

“…We constructed an E1B-attenuated oncolytic adenovirus, ZD55-VEGI-251, by inserting a VEGI-251 expression cassette into an engineered ZD55-gene system, which has been shown to be a potent antitumor strategy in our previous studies [16][17][18]25]. As anticipated, on ZD55-VEGI-251 infection, VEGI-251 is immediately expressed and released to the extracellular environment of the host cells to exert its function as an antiangiogenic cytokine.…”

“…Previous researches demonstrated that an oncolytic adenoviral system, the engineered ZD55-gene system, could be used as a potent antitumor strategy [16][17][18][19]. In this study, considering that angiogenesis plays a central role in tumor growth, we investigated the therapeutic potential of a combination of the antiangiogenic ability of VEGI-251 and the oncolytic activity of the ZD55-gene system.…”