Connexin 43 Gene Therapy Delivered by Polymer-Modified Salmonella in Murine Tumor Models

Salmonella-Mediated Cytolethal Distending Toxin Transfer Inhibits Tumor Growth

The Salmonella enterica serovar Choleraesuis (S.C.) has potential as an antitumor agent because of its tumor-targeting characteristics. S.C. can also be used for specific delivery of therapeutic agents and continuous release during replication. Previously, we successfully used S.C. as a vector to transfer a therapeutic gene and oncolytic virus, which suggested that modified S.C. is suitable for incorporating other antitumor agents into a single system. Cytolethal distending toxin B (CdtB) produced by Campylobacter jejuni can induce tumor cell apoptosis. Here we coated CdtB with poly(allylamine hydrochloride) (PAH) to yield PAH-CdtB. Treatment of cells with PAH-coated CdtB induced apoptosis, demonstrating that the compound retained antitumor activity. Furthermore, S.C. coated with PAH-CdtB (CdtB-S.C.) maintained tumor-targeting activity and had an enhanced antitumor effect. Measurement of the cytotoxic effect of CdtB-S.C. in vitro in a tumor cell line showed increased apoptosis whereas treatment of tumor-bearing mice with CdtB-S.C. reduced tumor growth and prolonged survival. Taken together, our results provide evidence that Salmonella carrying CdtB could have application for the treatment of tumors.

Salmonella mediated the hemagglutinating virus of Japan-envelope transfer suppresses tumor growth

Salmonella can target to tumor microenvironments after systemic treatment. The hemagglutinating virus of Japan-envelope (HVJ-E) induced apoptosis in tumor cells without toxicity in normal cells. Current HVJ-E therapeutic strategies, aimed at using HVJ-E for intratumor treatment, have shown great promise in animal models but have achieved only limited systemic treatment. The purpose of this study was to investigate the modulation of the anti-tumor efficiency of HVJ-E by coating the particles with poly (allylamine hydrochloride) (PAH), designated as P-HVJ-E. Treatment with P-HVJ-E resulted in decreased hemagglutinating activity and maintained tumor cell-selective apoptosis and anti-tumor immunity. The use of Salmonella as a coating for P-HVJ-E (PHS) enhanced the antitumor activity and maintained the tumor-targeting activity. Treatment with PHS resulted in delayed tumor growth in tumor-bearing mice. Furthermore, a Western blot assay of the tumors revealed that HVJ-E targeted to the tumor after systemic treatment with PHS. These results indicate that Salmonella coating viral particles may provide a new approach for tumor therapy.

Salmonella inhibits tumor angiogenesis by downregulation of vascular endothelial growth factor

Salmonella is a Gram-negative, facultative anaerobe that is a common cause of host intestinal infections. Salmonella grows under aerobic and anaerobic conditions, and it has been proven capable of inhibiting tumor growth. However, the molecular mechanism by which Salmonella inhibits tumor growth is still unclear. Angiogenesis plays an important role in the development and progression of tumors. We investigated the antitumor effect of Salmonella in a syngeneic murine tumor model. Hypoxia-inducible factor-1 (HIF-1)α plays a significant role in tumor angiogenesis. We examined the molecular mechanism by which Salmonella regulated vascular endothelial growth factor (VEGF), which is an important angiogenic factor. The expression of VEGF in tumor cells was decreased by treatment with Salmonella. The conditioned medium from Salmonella-treated cells inhibited the proliferation of endothelial cells. Salmonella inhibited the expression of HIF-1α as well as downregulated its upstream signal mediator protein kinase B (AKT). Salmonella significantly inhibited tumor growth in vivo, and immunohistochemical studies of the tumors revealed decreased intratumoral microvessel density. These results suggest that Salmonella therapy, which exerts anti-angiogenic activities, represents a promising strategy for the treatment of tumors.

Salmonella overcomes tumor immune tolerance by inhibition of tumor indoleamine 2, 3-dioxygenase 1 expression

Over the past decades, Salmonella has been proven capable of inhibiting tumor growth. It can specifically target tumors and due to its facultative anaerobic property, can be more penetrative than other drug therapies. However, the molecular mechanism by which Salmonella inhibits tumor growth is still incompletely known. The antitumor therapeutic effect mediated by Salmonella is associated with an inflammatory immune response at the tumor site and a T cell-dependent immune response. Many tumors have been proven to have a high expression of indoleamine 2, 3-dioxygenase 1 (IDO), which is a rate-limiting enzyme that catalyzes tryptophan to kynurenine, thus causing immune tolerance within the tumor microenvironment. With decreased expression of IDO, increased immune response can be observed, which might be helpful when developing cancer immunotherapy. The expression of IDO was decreased after tumor cells were infected with Salmonella. In addition, Western blot analysis showed that the expression levels of phospho-protein kinase B (P-AKT), phospho-mammalian targets of rapamycin (P-mTOR), and phospho-p70 ribosomal s6 kinase (P-p70s6K) in tumor cells were decreased after Salmonella infection. In conclusion, our results indicate that Salmonella inhibits IDO expression and plays a crucial role in anti-tumor therapy, which might be a promising strategy combined with other cancer treatments.

Connexin 43 suppresses tumor angiogenesis by down-regulation of vascular endothelial growth factor via hypoxic-induced factor-1α

Previous work showed that connexin 43 (Cx43) reduced the expression of hypoxic-induced factor-1α (HIF-1α) in astrocytes. HIF-1α is a master transcription factor for angiogenesis in tumor. Angiogenesis is essential for tumor progression. Here, we investigated the role of Cx43 in vascular endothelial growth factor (VEGF) production and angiogenesis in murine tumor. In the study, mouse B16F10 and 4T1 cells were overexpressed or knockdown with Cx43. The expression profiles as well as activity of the treated cells were examined. Furthermore, reduced Cx43 expression in B16F10 and 4T1 cells causes increased expression of VEGF and enhanced the proliferation of endothelial cells. On the contrary, the expression of VEGF and the proliferation of endothelial were increased in the conditioned medium of Cx43-knockdown tumor cells. We subcutaneously transplanted Cx43-overexpressing B16F10 cells into mice to evaluate the roles of Cx43 in the tumor angiogenesis. Both tumor size and the number of vessels growing in the tumor were markedly decreased compare with control group. Our findings suggest that Cx43 inhibited tumor growth by reducing angiogenesis.

Salmonella as an innovative therapeutic antitumor agent

Lack of specificity of the therapeutic agent is a primary limitation in the treatment of a tumor. The use of preferentially replicating bacteria as therapeutic agents is an innovative approach to tumor treatment. This is based on the observation that certain obligate or facultative anaerobic bacteria are capable of multiplying selectively in tumors and inhibiting their growth. Bacteria have been employed as antitumor agents that are capable of preferentially amplifying within tumors and inhibiting their growth. Moreover, bacteria-derived factors have an immune-stimulation effect. Therefore, bacteria are able to transfer therapeutic genes into the tumor cells using their infective ability. Herein, we introduce the application of bacteria for tumor therapy and focus on Salmonella, which have been widely used for tumor therapy. Salmonella have mainly been applied as gene-delivery vectors, antitumor immune activators and tumor cell death inducers. This study will not only evaluate the therapeutic efficacy of Salmonella for the treatment of tumor but will also elucidate the mechanisms underlying the antitumor activities mediated by Salmonella, which involve host immune responses and cellular molecular responses.