Tanshinone IIA Increases the Bystander Effect of Herpes Simplex Virus Thymidine Kinase/Ganciclovir Gene Therapy via Enhanced Gap Junctional Intercellular Communication

Abstract

The bystander effect is an intriguing phenomenon by which adjacent cells become sensitized to drug treatment during gene therapy with herpes simplex virus thymidine kinase/ganciclovir (HSV-tk/GCV). This effect is reported to be mediated by gap junctional intercellular communication (GJIC), and therefore, we postulated that upregulation of genes that facilitate GJIC may enhance the HSV-tk/GCV bystander effect. Previous findings have shown Tanshinone IIA (Tan IIA), a chemical substance derived from a Chinese medicine herb, promotes the upregulation of the connexins Cx26 and Cx43 in B16 cells. Because gap junctions are formed by connexins, we hypothesized that Tan IIA might increase GJIC. Our results show that Tan IIA increased GJIC in B16 melanoma cells, leading to more efficient GCV-induced bystander killing in cells stably expressing HSV-tk. Additionally, in vivo experiments demonstrated that tumors in mice with 10% HSV-tk positive B16 cells and 90% wild-type B16 cells became smaller following treatment with the combination of GCV and Tan IIA as compared to GCV or Tan IIA alone. These data demonstrate that Tan IIA can augment the bystander effect of HSV-tk/GCV system through increased gap junction coupling, which adds strength to the promising strategy that develops connexins inducer to potentiate the effects of suicide gene therapy.

Progress and problems with the use of suicide genes for targeted cancer therapy

“…For example, ganciclovir triphosphate (GCV-TP), the final toxic metabolite of herpes simplex virus thymidine kinase/ganciclovir (HSVTK/GCV) system is a charged molecule. The bystander effect induced by this metabolite is entirely dependent on active transport via gap junctional intercellular communication (GJIC) [32]. This can be a drawback for such systems because compared to normal tissue, tumor tissues usually lack highly ordered cell junctions.…”

Genetically engineered theranostic mesenchymal stem cells for the evaluation of the anticancer efficacy of enzyme/prodrug systems

“…The similarity of sensitivity to prodrug and bystander effects for MSC-TK SR39 -Luc and MSC-TK 007 -Luc clones signifies that both suicide genes could effectively convert GCV into its charged cytotoxic form GCV-triphosphate (GCV-TP). Moreover, it indirectly suggests that gap junctions were present in between MSCs and SKOV3 cells because the bystander effect induced by GCV-TP is largely dependent on active transport via gap junctional intercellular communication (GJIC) [29]. In a mechanistic study by Matuskova et al (2010), the formation of gap junctions between MSCs and cancer cells after co-culturing is demonstrated [6].…”

“…It appears that to slow down the growth of a tumor that has surpassed the 200mm 3 volume, administration of more than 1 million MSCs per week is necessary. This is sensible as the efficacy of GCV-TP is entirely dependent on GJIC and in tumors gap junctions in between cancer cells are either highly compromised or in many cases non-existent [29, 33]. Literature search also shows that TK/GCV enzyme/prodrug therapy has been effective when tumors were small (<100mm 3 ) and treated early [34, 35].…”

Connexin32-mediated antitumor effects of suicide gene therapy against hepatocellular carcinoma: In vitro and in vivo anticancer activity

“…The present study evaluated the use of gene therapy to target HCC, using the herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) suicide gene system via its 'bystander effect'. It is not a requirement that all tumor cells are directly targeted, and the occurrence of the bystander effect in HSV-TK/GCV therapy may represent an important therapeutic opportunity (4). There is compelling evidence demonstrating that gap junctional intercellular communication (GJIC) is directly involved (5,6).…”

“…There is compelling evidence demonstrating that gap junctional intercellular communication (GJIC) is directly involved (5,6). Gap junctions are formed by connexins, a family of homologous proteins, which directly link the cytoplasms of adjacent cells to allow the passage of ions (4). Connexins can also act as tumor suppressor genes (7).…”