In vitro and in vivo activities of an oncolytic adenoviral vector designed to express GM-CSF

Abstract

Oncolytic adenoviruses are being tested as biological cancer therapeutics. Ar6pAE2fF (E2F vector) contains the E2F-1 promoter to regulate the expression of the E1a gene in cells with a disregulated retinoblastoma pathway. Ar6pAE2fmGmF (E2F-GM vector) includes the murine granulocyte-macrophage colony-stimulating factor (GM-CSF) transgene to enhance anti-tumor activity. Both vectors selectively killed human tumor cells in vitro. The E2F-GM vector expressed biologically active murine GM-CSF in vitro and GM-CSF was detected for several days in serum and tumor extracts following injections of established human xenograft tumors. In vivo, both vectors showed significant dose-dependent anti-tumor responses. The E2F-GM vector elicited greater efficacy compared to the E2F vector, demonstrating that GM-CSF enhanced the anti-tumor activity, even in immunodeficient nude mice. Histological analysis showed that both vectors induced necrosis and mononuclear cell infiltration, but only the E2F-GM vector resulted in eosinophil infiltration. Vector replication in vivo was demonstrated. The data showed that intratumoral injection of a GM-CSF-armed oncolytic vector induced potent anti-tumor responses in xenograft tumor models, likely as the result of both oncolytic vector activity and the induction of GM-CSF-mediated inflammation and innate immunity.

An oncolytic adenovirus expressing granulocyte macrophage colony-stimulating factor shows improved specificity and efficacy for treating human solid tumors

“…Biological activity of GM-CSF was measured in TF-1 cells as described previously. 23 In vivo antitumor efficacy studies Antitumor efficacy studies were performed using tumor xenografts. Xenograft models were established in 6-to 8-week-old female nude mice subcutaneously injecting 2 Â 10 6 of SCC9 or Hep3B cells in Matrigel (injection volume of 0.2 ml).…”

Therapy of cancer by cytokines mediated by gene therapy approach

“…Bristol et al has used oncolytic adenoviruses to express granulocyte-macrophage colony-stimulating factor (GM-CSF). They found that oncolytic adenovirus with GM-CSF elicited greater efficacy compared to oncolytic adenovirus in an animal model with HCC tumor [35]. Genes coding for inducer of apoptosis such as tumor necrosis factor-related apoptosisinducing ligand (TRAIL), second mitochondria-derived activator of caspases (Smac), and Mda7/IL-24 have been incorporated into oncolytic adenovirus.…”

Comparison of the E3 and L3 regions for arming oncolytic adenoviruses to achieve a high level of tumor-specific transgene expression

“…9 Potential anticancer transgenes include tumor suppressor genes, for example, p53; 10 immunomodulatory genes, for example, granulocyte macrophage colony-stimulating factor (GM-CSF) 11,12 and interleukin-24; 13 pro-drug-converting enzymes, for example, thymidine kinase 14 and cytosine deaminase 15 and proapoptotic genes, for example, tumor necrosis factor-a 16 and TRAIL. 17 Several strategies for arming the vectors and for controlling transgene expression have been used, with the most recent attempts utilizing adenoviral promoters and transcriptional control elements to regulate the expression of inserted transgenes.…”

“…15,18 This tumor-specific transgene expression improves the safety of the vector. Several insertion sites, such as the E3A region 11,18,22 and E3B region, 15,18 were identified on the basis of detailed knowledge of transcription in adenoviruses. More recently, a novel transposonbased mechanism has been described that identified other potential insertion sites, even though the exact transcriptional regions had not been previously identified.…”

“…In addition, the effect, if any, of the insertion position of the transgene in the genome on the growth and cytotoxic properties of the vectors was evaluated. Included in this comparison were vectors in which the transgene was inserted in place of the early expressing E3 gp19K region 11 and the late expressing E3 14.K region, as well as the late expressing L3 transcriptional unit. In the latter case, a bipartite splice acceptor 21 was used to link transgene expression to the L3 transcriptional unit to achieve high level of tumor-specific transgene expression.…”