Selective Killing of AFP-Positive Hepatocellular Carcinoma Cells by Adeno-Associated Virus Transfer of the Herpes Simplex Virus Thymidine Kinase Gene

Abstract

The use of viral thymidine kinase (TK) gene coupled with the administration of ganciclovir to render cancer cell death has been studied extensively. Many of these experiments utilized retrovirus to transfer the TK gene under the control of a nonspecific promoter. Because nonspecific expression of the viral TK gene may cause death of proliferating cells, other than cancer cells, we explored the use of a liver-specific promoter and a tumor-specific AFP enhancer to achieve regulated viral TK gene expression for treatment of hepatocellular carcinoma. We also used the adeno-associated virus (AAV) as vector for the delivery of the TK gene because this virus is not associated with any pathological consequences in humans. Because it can infect nondividing S-phase cells, AAV can transfer genes into noncycling tumor cells. A recombinant AAV virus was constructed to include the selectable marker neoR gene and the herpes simplex virus (HSV)-TK gene driven by the human AFP enhancer and the albumin promoter. The liver-predominant expression pattern of the TK gene was observed when this construct was tested in transgenic mice. When human hepatocellular carcinoma cell lines displaying different levels of AFP and albumin and nonhepatocyte tumor cell lines were infected with the recombinant AAV virus, ganciclovir treatment caused only AFP and albumin-positive hepatocellular carcinoma cells death, but not nonhepatocyte tumor cells or AFP and albumin-negative hepatic tumor cells. Moreover, the dose required to kill the cancer cells was inversely proportional to the level of AFP expression in the cells.

Tumor-specific transcriptional targeting of suicide gene therapy

“…It has been demonstrated that gene expression of highly efficient gene therapy vectors can be targeted to tumors using cell-type or tissue-type specific promoter elements. [6][7][8][9][10][11][12] Most of these tumor-specific promoters, however, are relatively weak resulting in insufficient transgene expression levels. Several studies have reported that a CEA promoter driving a prodrug gene could mediate selective gene expression in CEA-producing tumors.…”

Reversal of drug resistance of hepatocellular carcinoma cells by adenoviral delivery of anti-MDR1 ribozymes

“…29 In addition, adenoassociated viruses were used that express HSV-TK from an AFP or albumin promoter and were shown to selectively inhibit growth of HCC cells in vitro as well as in vivo. 30,31 Even interleukin 2 expressing adenoviral vectors containing the AFP promoter were capable of selective growth retardation of human HCC xenografts in SCID mice. 32 Adenoviral vectors are highly efficient for in vivo gene transfer into a variety of tissues and tumors.…”

Tissue-specific expression of a suicide gene for selective killing of neuroblastoma cells using a promoter region of the NCX gene

“…This strategy has been evidenced by osteocalcin 8 and thyroglobulin 9 promoters for osteosarcoma and thyroid tumors, respectively. Another approach is to use the regulatory sequences of oncofetal protein such as -fetoprotein and carcinoembryonic antigen to express foreign genes in hepatic tumors 10,11 and tumors of the digestive tract, 12,13 respectively. Although the gene expression with the cell typespecific promoters is strictly regulated, the promoter activity could not be as strong as that with the promoters of oncofetal protein genes.…”