E1B Attenuated Adenoviruses in Genetic Therapy for Cancer

Ganly, Ian (1998) E1B Attenuated Adenoviruses in Genetic Therapy for Cancer. PhD thesis, University of Glasgow.

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The E1B deleted adenovirus, Onyx-015, has been shown to selectively replicate in and lyse cells with nonfunctional p53 (Bischoff et a1,1996). This virus may be therapeutically useful in the treatment of a wide range of tumours since p53 abnormalities are very common in human cancer. The aims of this thesis were to develop an immunocompetent mouse model to study the role of the immune system in this form of therapy, to further examine the mechanism of selectivity of Onyx-015 for cells with non-functional p53, and lastly to determine whether or not Onyx-015 could increase the cytotoxicity to DNA damaging agents in functional and non-functional p53 cells. We have shown that human adenoviruses will infect rodent cell lines but with variable infectivity. In tissues with high infectivity, productive virus infection only occurs in mouse epidermal cells but is 25 to 50 fold less efficient compared to the human ovarian adenocarcinoma cell line A2780Cp70. The efficiency of replication in mouse epidermal cells is dependent on the expression of the early gene E1A and this correlated with the expression of the nuclear factor ϕAP3 , a transcriptional repressor of the E1A promotor. Replication is shown to be 20 fold greater in squamous (well differentiated ) epidermal cell lines in which there is a high expression of E1A and low ϕAP3 expression compared to clonally related spindle (poorly differentiated) epidermal cell lines. Using mouse epidermal cell lines of known p53 status and function, the selective replication of Onyx-015 for cells with non-functional p53 is in general agreement with that reported in human cell lines. However, some cell lines with wild type p53 function do allow replication of Onyx-015 and we postulate that this is determined by 2 factors, the expression of E1A and the ability for Onyx-015 to repress p21 levels. Using the squamous epidermal cell line PDVc57, in-vivo studies in both nude mouse and syngeneic mouse tumour xenograft models showed decreased tumour growth with intratumoural virus injection compared to diluent injected tumours. However, viral replication is markedly reduced in the syngeneic host suggesting limitation of viral replication by the immune system. Using the paired cell lines A2780 (functional p53) and the cisplatin resistant variant A2780Cp70 (non-functional p53) we have shown that replication is dependent on S-phase entry of the host infected cell and this correlated with E2F induction. In the cell line A2780, S phase entry and viral replication is limited due to virus induced p53 mediated apoptosis. We suggest that this is mediated by E1A induction of p19ARF. In contrast, A2780Cp70 allows a productive virus infection since apoptosis does not occur due to the absence of functional p53 and high expression of the anti-apoptotic factor E1B19kDa. We have shown that in the cell line with nonfunctional p53 (A2780Cp70), cytotoxicity to both cisplatin and radiation is increased by preinfecting cells with Onyx-015. In the cell line with functional p53 (A2780), preinfection with Onyx-015 for 72 hours also resulted in increased cytotoxicity to both cisplain and radiation. In contrast, preinfection of A2780 for 24 hours followed by cisplatin resulted in an antagonistic interaction leading to reduced drug sensitivity. It is suggested that this was due to p21 induction causing a reduction in the S-phase cell population. Further in vivo and clinical studies investigating the role of the immune system in this form of therapy and in the use of combination therapies are therefore warranted.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Allan Balmain
Keywords: Oncology, Virology, Genetics
Date of Award: 1998
Depositing User: Enlighten Team
Unique ID: glathesis:1998-74696
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 17:07
Last Modified: 27 Sep 2019 17:07
URI: https://theses.gla.ac.uk/id/eprint/74696

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