Avian adenovirus vector CELO-TK displays anticancer activity in human cancer cells and suppresses established murine melanoma tumors

Abstract

Avian adenovirus CELO is a novel adenovirus vector system with the advantages of efficient production, high virion stability, and the absence of crossreactivity with Ad5-neutralizing antibodies. In this study, we evaluated the anticancer efficacy of a CELO vector encoding the herpes simplex virus type 1 thymidine kinase, a prodrug-activating therapeutic gene. Vectors carrying the gene for HSV-tk or EGFP under the control of the HCMV promoter in place of the ''nonessential'' region of the CELO genome were constructed. Anticancer activity of the CELO-TK vector was studied in vitro, in human and murine tumor cells in cell culture, and in vivo, in established subcutaneous murine B16 melanoma tumors in C57BL/6 mice. The CELO-TK vector mediated delivery of functional HSV-tk to tumor cell lines in cell culture. Comparison of the CELO-TK vector to a first-generation human adenovirus type 5 vector Ad5-TK in cultured H1299 cells showed equal levels of functional activity at increasing multiplicities of infection with CELO-based vector. CELO vectors allowed for transduction and expression of EGFP and HSV-tk genes in subcutaneous melanoma tumors in C57BL/6 mice. Intratumoral injections of CELO-TK followed by ganciclovir administration resulted in suppression of tumor growth and significantly increased the median of survival. The results of the study demonstrated the efficacy of CELO vector as a vehicle for the delivery of prodrug-activating genes such as HSV-tk to tumor cells in vitro and in vivo. Cancer Gene Therapy ( 1 This experimental approach to cancer treatment is currently in a transition from promise to reality with recent approval of an adenovirus (Ad) vector expressing p53 for use in clinics and with many more vectors in late stages of clinical trials.2 At the same time, new generations of cancer gene therapy vectors are being developed that will provide higher levels of efficacy, specificity, and cost-effectiveness.Whereas human Ad type 5 (Ad5) is a common platform for Ad vectors for the in vitro and in vivo delivery of genes, 3,4 non-human adenoviruses (Ads), also referred to as ''xenogeneic'' vectors, are currently emerging as alternative or additional gene delivery vehicles. 5,6 Avian Ad CELO (FAV-1) is a novel non-human Ad vector that has potential advantages for the development of anticancer vectors including: (i) the absence of pre-existing immunity to CELO in the human population, 7 (ii) the absence of immunological crossreactivity between virions of Ad5 and CELO, 8 which allows for in vivo transduction by CELO vectors in the presence of anti-Ad5 neutralizing antibodies, 9 (iii) higher stability of CELO virions as compared to Ad5 virions, 7 (iv) the natural inability of CELO to replicate in non-avian cells, which renders CELO vectors gene delivery vehicles rather than replicative agents in mammalian cells, 7 (v) the ability of CELO vectors to grow in noncomplementing cells resulting in the absence of recombination with the homologous viral DNA sequences in the genome of a complementing cell line, and the a...

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