Prostate cancers generally become androgen-independent and resistant to hormone therapy with progression. To understand the underlying mechanisms and facilitate the development of novel treatments for androgen-independent prostate cancer, we have investigated plasma membrane-associated sialidase (NEU3), the key enzyme for ganglioside hydrolysis participating in transmembrane signaling. We have discovered NEU3 to be upregulated in human prostate cancer compared with non-cancerous tissue, correlating with the Gleason score. NEU3 silencing with siRNA in prostate cancer PC-3 and LNCaP cells resulted in increased expression of differentiation markers and in cell apoptosis, but decrease in Bcl-2 as well as a progression-related transcription factor, early growth response gene (EGR-1). In androgen-sensitive LNCaP cells, forced overexpression of NEU3 significantly induced expression of EGR-1, androgen receptor (AR) and PSA both with and without androgen, the cells becoming sensitive to androgen. The NEU3-mediated induction was abrogated by inhibitors for PI-3 kinase and MAP kinase and more specifically by their silencing in the absence of androgen, being confirmed by increased phosphorylation of AKT and ERK1/2 in NEU3 overexpressing cells. NEU3 siRNA introduction caused reduction of cell growth of an androgen-independent PC-3 cells in culture and of transplanted tumors in nude mice. These data suggest that NEU3 regulates tumor progression through AR signaling, and thus be a potential tool for diagnosis and therapy of androgen-independent prostate cancer.

High-risk human papillomavirus (hr-HPV) E6 and E7 oncogenes are associated with resistance to radiotherapy in cervical cancer. Efforts have been taken to employ HPV E2, a crucial negative transcriptional modulator of HPV E6 and E7 oncogenes, and also an apoptosis-inducing agent, for therapeutic intervention. Despite being conceptually attractive, the potency and feasibility of current hr-HPV E2-based therapies remain limited. Here, we designed a novel recombinant adenovirus, named M5, with a 27-bp deletion in E1A conserved region-2 by which to realize tumor-specific replication, and a total HPV type 16 (HPV16) E2 gene complementary DNA inserted into the E3 coding region. In this design, M5 exploited the adenovirus E3 promoters to express HPV16 E2 gene in a viral replication-dependent manner and preferentially silenced the hr-HPV E6 and E7 oncogenes in HPV-positive cervical cancer cells. In vitro and in vivo assays confirmed that M5 exhibited potent antitumoral efficacy. Moreover, the effects of combined treatment with M5 and radiation treatment resulted in synergistically enhanced potency (Po0.01). The increase in killing efficacy of M5 was also found in HPV-negative cervical cancer cells, for which the pro-apoptotic activity of HPV16 E2 was thus responsible. Our results indicated that the use of M5 that locally delivers HPV16 E2 to cancers has broad therapeutic windows and that the combination therapy with radiation for cervical cancer will be the more effective way of improving survival.

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