Intercellular Communication Mediates the Bystander Effect During Herpes Simplex Thymidine Kinase/Ganciclovir-Based Gene Therapy of Human Gastrointestinal Tumor Cells

Abstract

A bystander effect is described when nontransduced or genetically unmodified cells are killed during death of genetically modified tumor cells transduced with a suicide gene. The "bystander effect" greatly enhances the efficacy of the herpes simplex virus-thymidine kinase/ganciclovir (HSV-TK/GCV) gene therapy approach for cancer. The mechanism of the bystander effect is controversial. In this study, we examined the role of intercellular gap junction communication (GJIC) for the bystander effect in human gastrointestinal tumor cells. Our results show that the extent of the bystander effect varied amongst the tumor cell lines; pancreatic cancer cells BXPC-3 exhibited excellent bystander effects in vitro and in vivo studies whereas other gastrointestinal tumor cell lines such as pancreatic cancer cells MIAPACA-2, and colon cancer cells HT-29 showed poor bystander effects. Bystander effects were only found in the presence of cell-to-cell contact. The extent of the bystander effect was independent of the level of HSV-TK activity in the transduced tumor cells and was correlated with GJIC as demonstrated by an in vitro dye-transfer assay. Expression of the mRNA levels of gap junction protein connexin 43 was 8- to 26-fold or greater and connexin 26 gene expression was 2- to 229-fold greater in BXPC-3 cells compared to HT-29, MIAPACA-2, and PANC3 cells. Our results suggest that intercellular communication is essential for the bystander effect. The correlation between GJIC and the extent of the bystander effect suggest a role for GJIC in mediating the bystander effect. Analysis of tumors for GJIC or expression of gap junction proteins may identify the subset of patients suitable for gene therapy with the HSV-TK/GCV approach.

Herpes simplex virus thymidine kinase/ganciclovir system in multicellular tumor spheroids

“…22 Three-dimensional organization of cancer cells as MCS is based upon cells in close proximity to one another with a higher number of cell-to-cell interactions than monolayer cultures. 23 Then, it seemed logical to expect a higher bystander effect in MCS with respect to monolayer cultures.…”

Intratracheal injection of manganese superoxide dismutase (MnSOD) plasmid/liposomes protects normal lung but not orthotopic tumors from irradiation

“…[7][8][9] However, in the literature of gene therapy models, 'bystander effects' reported have usually been in the transmission of killing of adjacent tissues by transgeneexpressing cells. [7][8][9][10][11][12][13][14][15][16][17] Delivery of MnSOD-PL complex by IT injection did not facilitate expression of the MnSOD transgene as measured by nested RT-PCR in orthotopic 3LL-LacZ carinal tumors when it was uniformly detected in the normal lung tissue. This may have been due to lack of penetration of the PL complex into the tumor, or to the route of IT administration which distributed the PLs to the upper airway and bronchoalveolar cells that were not in direct contact with central areas of tumor.…”

Targeting of suicide gene delivery in pancreatic cancer cells via FGF receptors

“…17 Pancreatic cancer cells are susceptible to transduction of adenoviral -mediated delivery of the HSV-TK gene. 10,13,16,20 In addition, PDACs overexpress the two Ig -like variants of the FGFR -1 and FGFR -2 21,22 and multiple FGFs. 23 We therefore sought to determine whether an adenoviral -based gene delivery system targeting FGF receptors may be of potential benefit in PDAC, by studying six human pancreatic cancer cell lines and by characterizing FGFR expression in PDAC samples.…”