A Novel, Conditionally Replicative Adenovirus for the Treatment of Breast Cancer That Allows Controlled Replication of E1a-Deleted Adenoviral Vectors

Abstract

The efficiency of gene therapy strategies against cancer is limited by the poor distribution of the vectors in the malignant tissues. To solve this problem, a new generation of tumor-specific, conditionally replicative adenoviruses is being developed. To direct the replication of the virus to breast cancer, we have considered one characteristic present in a great proportion of these cancers, which is the expression of estrogen receptors (ERs). On the basis of the wild-type adenovirus type 5, we have constructed a conditionally replicative adenovirus (Ad5ERE2) in which the E1a and E4 promoters have been replaced by a portion of the pS2 promoter containing two estrogen-responsive elements (EREs). This promoter induces transcriptional activation of the E1a and E4 units in response to estrogens in cells that express the ERs. Ad5ERE2 is able to kill ER(+) human breast cancer cell lines as efficiently as the wild-type virus, but has decreased capacity to affect ER(-) cells. By complementation of the E1a protein in trans, Ad5ERE2 allows restricted replication of a conventional E1a-deleted adenoviral vector. When a virus expressing the proapoptotic gene Bc1-xs (Clarke et al., Proc. Natl. Acad. Sci. U.S.A. 1995;92:11024-11028) is used in combination with Ad5ERE2, the ability of both viruses to induce cell death is dramatically increased, and the effect can be modulated by addition of the antiestrogen tamoxifen.

Adenoviruses with Tcf binding sites in multiple early promoters show enhanced selectivity for tumour cells with constitutive activation of the wnt signalling pathway

“…This contrasts with the approach used to produce prostate, hepatocellular cancer and breast cancer targeting viruses, which retain the complete E1A enhancer, but place exogenous promoters between it and the E1A start site. 1,3,4 To remove the E1A enhancer in vCF11, it was necessary to transfer the viral packaging signal to the right ITR. In addition, half of the ITR was replaced by Tcf sites.…”

“…Expression of essential viral genes from tumour-specific promoters results in tumour-specific viral replication. [1][2][3][4] In principle, viruses of this type can replicate and spread throughout the tumour mass until all of the tumour cells are killed. Replicating adenoviruses with defects in early genes which can be complemented by p53 and Rb defects in tumour cells have also been described.…”

Evaluation of a new dual-specificity promoter for selective induction of apoptosis in breast cancer cells

“…29 This vector was used in combination with Ad5ERE2, an adenovirus that preferentially replicates in ER + cells, because both E1A and E4 transcription units are controlled by a promoter that contains EREs. 15 In addition, we are currently investigating the use of dual -specificity promoters similar to the one described here to direct the expression of E1A and E4 genes in the context of a conditionally replicative adenovirus. We propose the development of similar strategies to obtain new artificial promoters and viruses specifically designed to target each particular type of cancer.…”

“…15 This is a luciferase reporter plasmid that contains a promoter composed of a portion of the pS2 promoter ( À 90/ + 10 bp ), with two EREs that confer its estrogen responsiveness. 33 The new construct was named pBERE /HRE.…”

“…15 In this case, we placed both the E1 a and E4 transcription units of adenovirus under the control of a promoter that contained estrogen response elements (EREs). These sequences are recognized by the estrogen receptors ( ERs ), which are intracellular receptors that act as transcription factors to activate the expression of genes in the presence of estrogens.…”