Doctor of Philosophy (PhD)


Veterinary Medical Sciences - Pathobiological Sciences

Document Type



Oncolytic herpes simplex virus type-1 (HSV-1) has shown great potential as an effective agent for cancer therapy ¨C oncolytic virotherapy. To enhance oncolytic capabilities of previously reported agents, new oncolytic and fusogenic HSV-1 OncSyn and OncdSyn viruses were constructed based on wild type HSV-1 (F) strain. To provide for safety and tumor selectivity, the viruses carried a large deletion including one of the two ¦Ã134.5 genes. The ¦Ã134.5 gene, a major neurovirulence factor, was replaced by a gene cassette constitutively expressing the red fluorescent protein. Homologous recombination was utilized to transfer the fusogenic gBsyn3 mutation to the viral genome to produce the OncSyn virus. The syncytial mutation gKsyn1 was introduced into the OncSyn genome cloned into a bacterial artificial chromosome using double-red mutagenesis in E. coli to produce the OncdSyn virus carrying both syncytial mutations gBsyn3 and gKsyn1. Both viruses caused extensive virus-induced cell fusion (syncytia) and were able to infect and replicate in mammary cancer cells. A xenograft mouse model system using MDA-MB-435S-luc human breast cancer cells constitutively expressing the luciferase gene implanted within the interscapular region of animals was utilized to test the ability of the OncSyn virus to inactivate breast tumor cells in vivo. A single round of intratumoral virus injections resulted in a drastic reduction of tumor sizes (p ¡Ü 0.0001) and dimunition of chemiluminscence emitted by the cancer cells (p ¡Ü 0.0002). Systematic necropsy and pathological evaluation of the primary tumors revealed that the single round of injections resulted in extensive necrosis of tumor cells (p ¡Ü 0.0001). Both effects were enhanced by a second round of virus injections. The oncolytic potential of both OncSyn and OncdSyn viruses was tested in a highly metastatic syngeneic mouse model system utilizing 4T1 murine mammary cancer cells. Intratumoral injections of both OncSyn and OncdSyn resulted in significant reduction of tumor sizes (p < 0.05) compared to controls. Virus treated mice but not controls showed a marked reduction of metastatic foci in lungs and internal organs. These results show that the attenuated, but highly fusogenic and oncolytic HSV-1(F) virus strains OncSyn and OncdSyn may effectively treat breast tumors in vivo.



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Committee Chair

Konstantin G. Kousoulas