Gene therapy is a promising treatment option for cancer. However, its utility may be limited due to expression in off-target cells. Cancer-specific promoters such as telomerase reverse transcriptase (TERT), survivin, and chemokine receptor 4 (CXCR4) have enhanced activity in a variety of human and murine cancers, however, little has been published regarding these promoters in dogs. Given the utility of canine cancer models, the activity of these promoters along with adenoviral E2F enhanced E1a promoter (EEE) was evaluated in a variety of canine tumors, both from the endogenous gene and from exogenously administered constructs. Endogenous expression levels were measured for cTERT, cSurvivin, and cCXCR4 and were low for all three, with some non-malignant and some tumor cell lines and tissues expressing the gene. Expression levels from exogenously supplied promoters were measured by both the number of cells expressing the construct and the intensity of expression in individual cells. Exogenously supplied promoters were active in more cells in all tumor lines than in normal cells, with the EEE promoter being most active, followed by cTERT. The intensity of expression varied more with cell type than with specific promoters. Ultimately, no single promoter was identified that would result in reliable expression, regardless of the tumor type. Thus, these findings imply that identification of a pan-cancer promoter may be difficult. In addition, this data raises the concern that endogenous expression analysis may not accurately predict exogenous promoter activity.
A variety of novel therapeutic approaches to cancer have been proposed in the past several decades. One of the most compelling is the use of gene therapy to treat tumors. Restricting the expression of these genes to tumor avoids toxicity in normal cells and the concurrent side effects that this activity engenders. Promoter sequences can be used as a tool for transcriptional targeting, by restricting the expression of the therapeutic genes, or, in the case of oncolytic virotherapy, the replication of the viral agent. Several tumor-upregulated promoters have been identified in a wide variety of human tumors. Given the recognition of the validity of canine tumors as comparative models of human disease, it is critical to determine the activities of these promoters in the canine system. To achieve this goal, endogenous cSurvivin, cTERT, and cCXCR4 promoter activity was evaluated in a panel of canine normal and tumor cell lines/tissues and primary tumors by RT-Q-PCR. These three promoters, along with an E2F modified Canine Adenovirus 2 E1a promoter (E2F-E1a), were also assessed for their activity when supplied exogenously to tumor cells in an in vitro GFP reporter transfection assay. Endogenous expression of cTERT showed negligible differences between normal canine cells/tissues and tumor cell/tissues. cSurvivin showed elevated endogenous activity in non-hematopoietic tumor cells and moderately elevated activity in some normal tissues and hematopoietic tumors. cCXCR4 activity was elevated exclusively in a T-lymphoma cell line and a primary T-cell lymphoma. Exogenous expression in most cancer cell lines showed enhanced activity with most of the promoters tested. The percentage of cells expressing GFP was elevated in tumor compared to normal with all four tested promoters, when normalized to CMV-GFP expression. However, the relative fluorescence intensity varied significantly between cell lines, while the fluorescence intensity varied less between promoters within a specific cell line. Exogenous expression results did not correlate well with endogenous expression in tumor cells, but they did correlate well in normal cells. This disparity implies that promoter selection for transcriptional targeting of tumors should account for both endogenous and exogenous expression patterns. Additionally, these findings indicate that identification of a pan-cancer promoter is complex and that expression targeting may need to rely on selecting patient-specific promoters to drive the activity of therapeutic genes. Citation Format: Abdul Mohin Sajib, Maninder Sandey, Samantha Morici, Bradley Schuler, Payal Agarwal, Bruce Smith. Identification of promoters for targeted gene expression in tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4778.
transplanted in NSG mice. After in vitro or in vivo expansion of the transduced CRCs cetuximab treatment was applied. After an initial shrinking of the tumor mass in mice we observed ACDR in 3 out of 10 mice transplanted with NCI-H508 cells transduced with SFFV-LV and in none of the controls. Genomic DNA from resistant cells is being used for insertion site (IS) analysis to identify common IS, ACDR gene candidates. IS obtained from SIN-LV groups will be used to filter LV integration biases, whereas IS from SFFV-LV transduced cells but not treated with cetuximab will be used to filter mutations that provide a proliferative advantage unrelated to cetuximab treatment. We will validate the most promising candidates by LV-mediated overexpression and knockdown techniques. This approach could pave the way to perform insertional mutagenesis-based forward genetics studies on primary human samples.
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