The carcinoma-specific epithelial glycoprotein-2 promoter controls efficient and selective gene expression in an adenoviral context

Targeted expression of suicide gene by tissue-specific promoter and microRNA regulation for cancer gene therapy

In order to realise the full potential of cancer suicide gene therapy that allows the precise expression of suicide gene in cancer cells, we used a tissue specific Epithelial cell adhesion molecule (EpCAM) promoter (EGP-2) that directs transgene Herpes simplex virus–thymidine kinase (HSV-TK) expression preferentially in EpCAM over expressing cancer cells. EpCAM levels are considerably higher in retinoblastoma (RB), a childhood eye cancer with limited expression in normal cells. Use of miRNA regulation, adjacent to the use of the tissue-specific promoter, would provide the second layer of control to the transgene expression only in the tumor cells while sparing the normal cells. To test this hypothesis we cloned let-7b miRNA targets in the 3’UTR region of HSV-TK suicide gene driven by EpCAM promoter because let-7 family miRNAs, including let-7b, were found to be down regulated in the RB tumors and cell lines. We used EpCAM over expressing and let-7 down regulated RB cell lines Y79, WERI-Rb1 (EpCAM ^+ve/let-7b^{down-regulated}), EpCAM down regulated, let-7 over expressing normal retinal Müller glial cell line MIO-M1(EpCAM ^−ve/let-7b^up-regulated), and EpCAM up regulated, let-7b up-regulated normal thyroid cell line N-Thy-Ori-3.1(EpCAM ^+ve/let-7b^up-regulated) in the study. The cell proliferation was measured by MTT assay, apoptosis was measured by probing cleaved Caspase3, EpCAM and TK expression were quantified by Western blot. Our results showed that the EGP2-promoter HSV-TK (EGP2-TK) construct with 2 or 4 copies of let-7b miRNA targets expressed TK gene only in Y79, WERI-Rb-1, while the TK gene did not express in MIO-M1. In summary, we have developed a tissue-specific, miRNA-regulated dual control vector, which selectively expresses the suicide gene in EpCAM over expressing cells.

EpCAM in carcinogenesis: the good, the bad or the ugly

The epithelial cell adhesion molecule (EpCAM) is a membrane glycoprotein that is highly expressed on most carcinomas and therefore of potential use as a diagnostic and prognostic marker for a variety of carcinomas. Interestingly, EpCAM is explored as target in antibody-based therapies. Recently, EpCAM has been identified as an additional marker of cancer-initiating cells. In this review, we describe the controversial biological role of EpCAM with the focus on carcinogenesis: as an adhesion molecule, EpCAM mediates homophilic adhesion interactions, which in turn might prevent metastasis. On the other hand, EpCAM abrogates E-cadherin mediated cell-cell adhesion thereby promoting metastasis. Also, upon cleavage of EpCAM, the intracellular domain functions as a part of a transcriptional complex inducing c-myc and cyclin A and E. In line with these seemingly controversial roles, EpCAM overexpression has been associated with both decreased and increased survival of patients. Similarly, either induction or downregulation of EpCAM expression lowers the oncogenic potential depending on the cell type. As epigenetic dysregulation underlies aberrant EpCAM expression, we propose epigenetic editing as a novel approach to investigate the biological role of EpCAM, expanding the options for EpCAM as a therapeutic target in cancer.

Selective killing of Smad4-negative tumor cells via a designed repressor strategy

Smad4 is a key tumor suppressor that is frequently deleted or inactive in pancreatic and colon tumors. In this report, we describe an approach for attaining selective killing of Smad4-deficient tumor cells. Using a vector system involving a designed repressor with zinc finger binding domains and the herpes simplex virus thymidine kinase (HSV-TK) "suicide gene," we demonstrate Smad4-responsive regulation of HSV-TK expression and consequent altered susceptibility to the prodrug ganciclovir (GCV). In pancreatic tumor cell lines stably transfected with the vector system, a robust differential of HSV-TK expression and GCV toxicity was attained depending on the presence or absence of cotransfected Smad4. In matched colon tumor cell lines lacking Smad4 or expressing physiological levels of Smad4, an adenoviral version of the vector system attained a significant degree of preferential killing of Smad4-negative tumor cells in response to GCV. These findings demonstrate the possibility of achieving selective killing of pancreatic and colon cells depending on their Smad4 status.

Engineering zinc finger protein transcription factors to downregulate the epithelial glycoprotein-2 promoter as a novel anti-cancer treatment

Zinc finger protein transcription factors (ZFP-TFs) are emerging as powerful novel tools for the treatment of many different diseases. ZFPs are DNA-binding motifs and consist of modular zinc finger domains. Each domain can be engineered to recognize a specific DNA triplet, and stitching six domains together results in the recognition of a gene-specific sequence. Inhibition of gene expression can be achieved by fusing a repressor domain to these DNA-binding motifs. In this study, we engineered ZFP-TFs to downregulate the activity of the epithelial glycoprotein-2 (EGP-2) promoter. The protein EGP-2 is overexpressed in a wide variety of cancer types and EGP-2 downregulation has been shown to result in a decreased oncogenic potential of tumor cells. Therefore, downregulation of EGP-2 expression by ZFP-TFs provides a novel anti-cancer therapeutic. Using a straightforward strategy, we engineered a 3-ZFP that could bind a 9 bp sequence within the EGP-2 promoter. After the addition of a repressor domain, this 3-ZFP-TF could efficiently downregulate EGP-2 promoter activity by 60%. To demonstrate the flexibility of this technology, we coupled an activation domain to the engineered ZFP, resulting in a nearly 200% increase in EGP-2 promoter activity. To inhibit the endogenous EGP-2 promoter, we engineered 6-ZFP-TFs. Although none of the constructed ZFP-TFs could convincingly modulate the endogenous promoter, efficient and specific inhibition of the exogenous promoter was observed. Overall, ZFP-TFs are versatile bi-directional modulators of gene expression and downregulation of EGP-2 promoter activity using ZFP-TFs can ultimately result in a novel anti-cancer treatment.

Detection of mRNAs of GA733 genes by RT-PCR in exfoliated cells of pleural and peritoneal effusions and its clinical values

OBJECTIVE

To evaluate the diagnostic values of the detection of mRNAs of GA733 gene family in exfoliated cells of pleural and peritoneal effusions.

METHODS

Sixty specimens of pleural and peritoneal fluids from 60 patients were collected. GA733-1 and GA733-2 mRNA in the exfoliated cells were detected by qualitative RT-PCR, and their diagnostic values were assessed. Patients Sixty patients with pleural or peritoneal effusions, from May 2003 and August 2004, aged 23-85 (average 56.5 years).

RESULTS

GA733-1 and GA733-2 mRNA were positive in 5 (13.9%) and 27 (75.0%) of 36 malignant specimens, and in 1 and 7 of 11 cause-unknown specimens, respectively, but both of them were negative in all 13 benign specimens, and the difference of GA733-2 mRNA positive rates among the three groups was significant (P<0.005), but that of GA733-1 mRNA was not (P>0.05). GA733-1 and GA733-2 mRNA were positive in 4 (15.4%) and 22 (84.6%) of 26 cytological positive specimens, and in 1 and 6 of 6 suspicious specimens, and in 1 (3.5%) and 6 (21.4%) of 28 negative specimens, respectively and the difference of GA733-2 mRNA positive rates among the three groups was significant (P<0.005), but that of GA733-1 mRNA was not (P>0.05). Sensitivity, specificity and accuracy of detection for GA733-2 mRNA for diagnosis of malignant effusions were 75.0%, 100% and 81.6%, respectively.

CONCLUSIONS

The detection of GA733-2 mRNA by qualitative RT-PCR is sensitive and highly specific for the diagnosis of malignant pleural and peritoneal effusions, while the diagnostic value of GA733-1 mRNA needs to be further investigated.

Highly efficient and carcinoma-specific adenoviral replication restricted by the EGP-2 promoter

Although some successes have been reported using adenoviral vectors for the treatment of cancer, adenoviral cancer gene therapy is still hampered by the lack of sufficient tumor cell killing. To increase the efficiency, adenoviruses have been modified to replicate specifically in tumor tissues by using tumor specific promoters controlling genes essential for adenoviral replication. However, many conditionally replicating adenoviral vectors replicate in one tumor type only, which limits their application. The epithelial glycoprotein-2 (EGP-2) promoter is active in a broad variety of carcinomas, the most common type of cancer. We utilized this promoter to restrict adenoviral replication. In this report we demonstrate that the potency of the replication-competent adenovirus AdEGP-2-E1 to specifically lyse EGP-2 positive cells is comparable to wild-type adenovirus (AdWT). In addition, we show that in vivo AdEGP-2-E1 replicates as efficient as AdWT in EGP-2 positive tumor cells. On the contrary, in EGP-2 negative cell lines as well as in primary human liver samples, the replication was attenuated up to 4-log in comparison to wild-type virus. This report clearly shows the potency of the EGP-2 promoter to mediate highly efficient and specific adenoviral replication for carcinoma gene therapy.

Saporin as a novel suicide gene in anticancer gene therapy

We used a non-viral gene delivery approach to explore the potential of the plant saporin (SAP) gene as an alternative to the currently employed suicide genes in cancer therapy. Plasmids expressing cytosolic SAP were generated by placing the region encoding the mature plant ribosome-inactivating protein under the control of cytomegalovirus (CMV) or simian virus 40 (SV40) promoters. Their ability to inhibit protein synthesis was first tested in cultured tumor cells co-transfected with a luciferase reporter gene. In particular, SAP expression driven by CMV promoter (pCI-SAP) demonstrated that only 10 ng of plasmid per 1.6 x 10(4) B16 cells drastically reduced luciferase activity to 18% of that in control cells. Direct intratumoral injection of pCI-SAP complexed with either lipofectamine or N-(2,3-dioleoyloxy-1-propyl) trimethylammonium methyl sulfate (DOTAP) in B16 melanoma-bearing mice resulted in a noteworthy attenuation of tumor growth. This antitumor effect was increased in mice that received repeated intratumoral injections. A SAP catalytic inactive mutant (SAP-KQ) failed to exert any antitumor effect demonstrating that this was specifically owing to the SAP N-glycosidase activity. Our overall data strongly suggest that the gene encoding SAP, owing to its rapid and effective action and its independence from the proliferative state of target cells might become a suitable candidate suicide gene for oncologic applications.