Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Original Article
  • Published:

Δ24-hyCD adenovirus suppresses glioma growth in vivo by combining oncolysis and chemosensitization


Replication-competent adenoviruses could provide an efficient method for delivering therapeutic genes to tumors. The most promising strategies among adenovirus-based oncolytic systems are designed to exploit free E2F-1 activity in cancer cells, which in the absence of pRb activates transcription and regulates the expression of genes involved in differentiation, proliferation, and apoptosis. We previously developed Δ24, an E1A-mutant, conditionally replicative oncolytic adenovirus. Here, we examine the ability of a second-generation Δ24 (Δ24-hyCD) engineered to express a humanized form of the Saccharomyces cerevisiae cytosine deaminase gene (hyCD). Real-time quantitative PCR, Western blotting, thin-layer chromatography, and radioisotope quantitative enzymatic assays confirmed the production of a catalytically active hyCD enzyme in the setting of an oncolytic infection in vitro; other experiments assessing local production of 5-fluorouracil and a concomitant bystander effect showed improved cytotoxicity. The IC50 dose of 5-fluorocytosine (5-FC) required for a complete cytopathic effect by the Δ24-hyCD virus was fivefold lower than with Δ24 alone in U251MG and U87MG malignant glioma (MG) cell lines. Intratumoral treatment of mice bearing intracranial U87MG xenografts with Δ24-hyCD+5-FC significantly improved survival, confirming that Δ24-hyCD with 5-FC is a more efficient anticancer tool than Δ24 alone. Histopathologically, Δ24-hyCD replication was accompanied by progressively augmented oncolysis and drug-induced necrosis. These findings demonstrate that Δ24-hyCD with concomitant systemic 5-FC is a significant improvement over the earlier Δ24 oncolytic tumor-selective strategy for therapy of experimental gliomas.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Figure 5
Figure 1
Figure 2
Figure 3
Figure 4
Figure 6
Figure 7

Similar content being viewed by others


  1. Central Brain Tumor Registry of the United States. Statistical Report: Primary Brain tumors in the United States, 1992–1997. (2001) Available at (accessed November 21, 2002).

  2. Fueyo J, Gomez-Manzano C, Alemany R, et al. A mutant oncolytic adenovirus targeting the Rb pathway produces anti-glioma effect in vivo. Oncogene. 2000;19:2–12.

    Article  CAS  PubMed  Google Scholar 

  3. Alemany R, Gomez-Manzano C, Balague C, et al. Gene therapy for gliomas: molecular targets, adenoviral vectors, and oncolytic adenoviruses. Exp Cell Res. 1999;252:1–12.

    Article  CAS  PubMed  Google Scholar 

  4. Henson JW, Schnitker BL, Correa KM, et al. The retinoblastoma gene is involved in malignant progression of astrocytomas. Ann Neurol. 1994;36:714–721.

    Article  CAS  PubMed  Google Scholar 

  5. Huang HJ, Yee JK, Shew JY, et al. Suppression of the neoplastic phenotype by replacement of the RB gene in human cancer cells. Science. 1988;242:1563–1566.

    Article  CAS  PubMed  Google Scholar 

  6. Aghi M, Chou TC, Suling K, et al. Multimodal cancer treatment mediated by a replicating oncolytic virus that delivers the oxazaphosphorine/rat cytochrome P450 2B1 and ganciclovir/herpes simplex virus thymidine kinase gene therapies. Cancer Res. 1999;59:3861–3865.

    CAS  PubMed  Google Scholar 

  7. Chase M, Chung RY, Chiocca EA . An oncolytic viral mutant that delivers the CYP2B1 transgene and augments cyclophosphamide chemotherapy. Nat Biotechnol. 1998;16: 444–448.

    Article  CAS  PubMed  Google Scholar 

  8. Boviatsis EJ, Park JS, Sena-Esteves M, et al. Long-term survival of rats harboring brain neoplasms treated with ganciclovir and a herpes simplex virus vector that retains an intact thymidine kinase gene. Cancer Res. 1994;54:5745–5751.

    CAS  PubMed  Google Scholar 

  9. Hermiston T . Gene delivery from replication-selective viruses: arming guided missiles in the war against cancer. J Clin Invest. 2000;105:1169–1172.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  10. Wildner O, Blaese RM, Morris JC, et al. Therapy of colon cancer with oncolytic adenovirus is enhanced by the addition of herpes simplex virus-thymidine kinase. Cancer Res. 1999;59:410–413.

    CAS  PubMed  Google Scholar 

  11. Bischoff JR, Kirn DH, Williams A, et al. An adenovirus mutant that replicates selectively in p53-deficient human tumor cells. Science. 1996;274:373–376.

    Article  CAS  PubMed  Google Scholar 

  12. Freytag SO, Stricker H, Pegg J, et al. Phase I study of replication-competent adenovirus-mediated double-suicide gene therapy in combination with conventional-dose three-dimensional conformal radiation therapy for the treatment of newly diagnosed, intermediate to high-risk prostate cancer. Cancer Res. 2003;63:7497–7506.

    CAS  PubMed  Google Scholar 

  13. Rogulski K, Wing MS, Paielli DL, et al. Double suicide gene therapy augments the antitumor activity of a replication-competent lytic adenovirus through enhanced cytotoxicity and radiosensitization. Hum Gene Ther. 2000;11:67–76.

    Article  CAS  PubMed  Google Scholar 

  14. Bernt KM, Steinwaerder DS, Ni S, et al. Enzyme-activated prodrug therapy enhances tumor-specific replication of adenovirus vectors. Cancer Res. 2002;62:6089–6098.

    CAS  PubMed  Google Scholar 

  15. Ueda K, Iwahashi M, Nakamori M, et al. Carcinoembryonic antigen-specific suicide gene therapy of cytosine deaminase/5-fluorocytosine enhanced by the Cre/loxP system in the orthotopic gastric carcinoma model. Cancer Res. 2001;61:6158–6161.

    CAS  PubMed  Google Scholar 

  16. Miller CR, Williams CR, Buchsbaum DJ, et al. Intratumoral 5-fluorouracil produced by cytosine deaminase/5-fluorocytosine gene therapy is effective for experimental human glioblastomas. Cancer Res. 2002;62:773–780.

    CAS  PubMed  Google Scholar 

  17. Erbs P, Exinger F, Jund R . Characterization of the Saccharomyces cerevisiae FCY1 gene encoding cytosine deaminase and its homologue FCA1 of Candida albicans. Curr Genet. 1997;31:1–6.

    Article  CAS  PubMed  Google Scholar 

  18. Hamstra DA, Rice DJ, Fahmy S, et al. Enzyme/prodrug therapy for head and neck cancer using a catalytically superior cytosine deaminase. Hum Gene Ther. 1999;10:1993–2003.

    Article  CAS  PubMed  Google Scholar 

  19. Whyte P, Williamson NM, Harlow E, et al. Cellular targets for transformation by the adenovirus E1A proteins. Cell. 1989;56:67–75.

    Article  CAS  PubMed  Google Scholar 

  20. Blanquicett C, Gillespie GY, Nabors LB, et al. Induction of thymidine phosphorylase in both irradiated and shielded, contralateral human U87MG glioma xenografts: Implications for a dual modality treatment using capecitabine and irradiation. Mol Cancer Ther. 2002;1:1139–1145.

    CAS  PubMed  Google Scholar 

  21. Rubery ED, Newton AA . A simple paper chromatographic method for separation of methylated adenines and cytosine from the major bases found in nucleic acids. Anal Biochem. 1971;42:149–154.

    Article  CAS  PubMed  Google Scholar 

  22. Lal S, Lacroix M, Tofilon P, et al. An implantable guide-screw system for brain tumor studies in small animals. J Neurosurg. 2000;92:326–333.

    Article  CAS  PubMed  Google Scholar 

  23. Kievit E, Bershad E, Ng E, et al. Superiority of yeast over bacterial cytosine deaminase for enzyme/prodrug gene therapy in colon cancer xenografts. Cancer Res. 1999;59:1417–1421.

    CAS  PubMed  Google Scholar 

  24. Roth JA, Cristiano RJ . Gene therapy for cancer: what have we done and where are we going? J Natl Cancer Inst. 1997;89:21–39.

    Article  CAS  PubMed  Google Scholar 

  25. Ueki K, Ono Y, Henson JW, et al. CDKN2/p16 or RB alterations occur in the majority of glioblastomas and are inversely correlated. Cancer Res. 1996;56:150–153.

    CAS  PubMed  Google Scholar 

  26. Suzuki K, Fueyo J, Krasnykh V, et al. A conditionally replicative adenovirus with enhanced infectivity shows improved oncolytic potency. Clin Cancer Res. 2001;7:120–126.

    CAS  PubMed  Google Scholar 

  27. Fueyo J, Alemany R, Gomez-Manzano C, et al. Preclinical characterization of the antiglioma activity of a tropism-enhanced adenovirus targeted to the retinoblastoma pathway. J Natl Cancer Inst. 2003;95:652–660.

    Article  CAS  PubMed  Google Scholar 

Download references


We wish to thank Joann Aaron (Department of Neuro-Oncology) and Christine Wogan (Department of Scientific Publications) at MD Anderson Cancer Center for editorial services. We also acknowledge the technical assistance of the animal core facility staff at the MD Anderson Brain Tumor Center. This work was supported in part by grants from the Anthony Bullock III Foundation, the Jonsson Family Foundation and the Golfers Against Cancer organization.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Charles Conrad.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Conrad, C., Miller, C., Ji, Y. et al. Δ24-hyCD adenovirus suppresses glioma growth in vivo by combining oncolysis and chemosensitization. Cancer Gene Ther 12, 284–294 (2005).

Download citation

  • Received:

  • Published:

  • Issue Date:

  • DOI:


This article is cited by


Quick links