Genetically engineered stem cells may have an

Genetically engineered stem cells may have an advantage for gene therapy due to their inherent migration to tumor sites (Kang et al., 2012a; Kang et al., 2012b; Kang et al., 2012d). In this study, we employed HB1.F3 human neural stem cells (hNSCs) obtained from 15week fetal telencephalon and immortalized using a retroviral vector encoding v-myc, and cloned (Yi et al., 2011b). hNSCs have been shown to effectively migrate to the target tumor site, drawn to various chemokines and growth factors such as stem cell factor (SCF), hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), and c-kit that are secreted by proliferative by tumor cells (Aboody et al., 2008). We used two NDEPT paradigms in our breast cancer studies: 1) HB1.F3.CD expressing Escherichia coli CD and 2) HB1.F3.CD.IFN-β additionally expressing human IFN-β (Yi et al., 2011a). We previously showed that HB1.F3.CD or HB1.F3.CE (carboxylesterase) cells significantly inhibit the growth of SKOV-3 human ovarian cancer cells in the presence of the prodrug 5-FC or camptothecin-11 (CPT-11), respectively (Kim et al., 2010). Of translational significance, HB1.F3.CD NSCs plus 5-FC is currently in first-in-human phase I clinical trials for recurrent cetrimonium bromide tumors (Aboody et al., 2011). In the current study, CD and IFN-β genes were fused and transduced into HB1.F3 cells for stable expression, to examine the potential cytotoxic effect of the therapeutic products 5-FU (in the presence of 5-FC) and IFN-β on breast cancer cells. Interferons (IFNs) are cytotoxic cytokines that are released by lymphocytes of host cells responding to viral infection and activate immune cells by up-regulating antigen presentation (Yoshiji et al., 2005). IFNs are mainly divided two groups: type І IFN and type II IFN (Sottini et al., 2009). IFN-alpha (IFN-α), IFN-beta (IFN-β), and IFN-omega (IFN-ω) belong to type І IFN class, and IFN-gamma (IFN-γ) belongs to type II IFN (Uze and Monneron, 2007). In humans, IFN-α, IFN-ω and especially IFN-β expression strongly inhibit tumor cell growth and induce apoptosis by Jak-Stat1 intracellular signaling pathways, including immunomodulatory and anti-angiogenic effects, in vitro and in vivo (Matsuzuka et al., 2009). These functions of the type І IFN family are mediated by a common cell surface receptor known as type І IFN receptor (Pestka et al., 2004; Rosewicz et al., 2004). Despite the strong anti-proliferative effect of IFN-β on cancer cell growth, the underlying mechanism has not been successfully elucidated in vivo because of its exceptionally short half-life (Oie et al., 2006). We therefore investigated whether CD.IFN-β expressing hNSCs could migrate to breast cancer cells and exert a more potent therapeutic effect in the presence of 5-FC in a co-culture system in vitro and a mouse mammary fat pad xenograft model in vivo.
Materials and methods
Results
Discussion Conventional cancer therapies (radiotherapy, hormone therapy, and chemotherapy) for breast cancer have many undesirable side effects (McArthur et al., 2011; Piccart, 2003). Gene therapy delivered by a packaging line or viruses with activated ‘suicide’ genes appears to selectively treat cancers, however the packaging line stayed at or near injection sites and virus only reached neighboring tumor cells. The inability of virus to deliver therapeutic genes to invading and distant tumor sites greatly limits its effectiveness. The enzyme/prodrug distribution and efficacy of gene delivery mediators, i.e., adenovirus and lentivirus, is also questionable (Pastorakova et al., 2006). A tumor specific delivery system is critical for enhancing the selective effectiveness of well-known prodrugs for de novo various tumors. NSCs overcome these limitations of current gene therapy systems by targeting invasive and distant tumor foci and expressing the ‘suicide’ genes locally. To minimize systemic toxicities, NDEPT has received much attention for cancer-targeted therapy (Kim et al., 2010; Nawa et al., 2008). These gene therapies use viral vectors as vehicles to transport prodrug activating or ‘suicide’ genes, which convert a non-toxic prodrug to a toxic agent (Anderson, 2000). This leads to a bystander effect, where not only the suicide gene transduced vehicle cells, but also the untransfected neighboring target cells are eradicated (Kang et al., 2012d). Typical enzyme/prodrug therapy systems are CD/5-FC, CE/CPT-11, and thymidine kinase (TK)/ganciclovir (GCV) (Kang et al., 2012c; Shah, 2012). In previous studies, the antitumor effects of CD/5-FC and CE/CPT-11 were demonstrated in animal models of disseminated neuroblastoma (Kim et al., 2010), intracranial medulloblastoma (Kim et al., 2006a), and glioma (Kang et al., 2012b; Longley et al., 2003).