Spontaneous and controllable activation of suicide gene expression driven by the stress-inducible Grp78 promoter resulting in eradication of sizable human tumors

Department of Biochemistry and Molecular Biology, University of Southern California Keck School of Medicine, 1441 Eastlake Avenue, Los Angeles, CA 90089-9176, USA.
Human Gene Therapy (Impact Factor: 3.62). 07/2004; 15(6):553-61. DOI: 10.1089/104303404323142006
Source: PubMed

ABSTRACT GRP78 is a stress-inducible chaperone protein with antiapoptotic properties that is overexpressed in transformed cells and cells under glucose starvation, acidosis, and hypoxic conditions that persist in poorly vascularized tumors. Previously we demonstrated that the Grp78 promoter is able to eradicate tumors using murine cells in immunocompetent models by driving expression of the HSV-tk suicide gene. Here, through the use of positron emission tomography (PET) imaging, we provide direct evidence of spontaneous in vivo activation of the HSV-tk suicide gene driven by the Grp78 promoter in growing tumors and its activation by photodynamic therapy (PDT) in a controlled manner. In this report, we evaluated whether this promoter can be applied to human cancer therapy. We observed that the Grp78 promoter, in the context of a retroviral vector, was highly activated by stress and PDT in three different types of human breast carcinomas independent of estrogen receptor and p53. Complete regression of sizable human tumors was observed after prodrug ganciclovir treatment of the xenografts in immunodeficient mice. In addition, the Grp78 promoter-driven suicide gene is strongly expressed in a variety of human tumors, including human osteosarcoma. In contrast, the activity of the murine leukemia virus (MuLV) long-terminal repeat (LTR) promoter varied greatly in different human breast carcinoma cell lines, and in some cases, stress resulted in partial suppression of the LTR promoter activity. In transgenic mouse models, the Grp78 promoter-driven transgene is largely quiescent in major adult organs but highly active in cancer cells and cancer-associated macrophages, which can diffuse to tumor necrotic sites devoid of vascular supply and facilitate cell-based therapy. Thus, transcriptional control through the use of the Grp78 promoter offers multiple novel approaches for human cancer gene therapy.

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    • "Its expression also varies with developmental stages and tissue specificity. A low basal level is identified in most adult tissues whereas it is highly induced in cancer [5] [6]. GRP78 expression is induced under such conditions as hypoxia and nutrient deprivation, partially explaining its high level in tumour cells [7]. "
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    • "The first direct evidence for the involvement of GRP78 in cancer progression came from the demonstration that GRP78 knockdown in fibrosarcoma cells using antisense prevented tumor formation in nude mice [125]. It was further shown that a suicide transgene driven by the GRP78 promoter in breast cancer cells completely blocked tumor growth in mice [126]. More recently, it was demonstrated that GRP78 heterozygous mice develop normally but are resistant to transgene-induced mammary tumor growth [127]. "
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    • "The D2/LacZ transgenic mouse lines (D2D, D2P and D2L) were generated by the same procedure as previously described (Dong et al. 2004). Itpr1 heterozygous mutant mice opt/+ were purchased from Jackson Laboratory, in the B6C3Fe genetic background. "
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