Chloroquine enhanced the anticancer capacity of VNP20009 by inhibiting autophagy

In Situ Synthesis of an Immune-Checkpoint Blocker from Engineered Bacteria Elicits a Potent Antitumor Response

Immune-checkpoint blockade (ICB) reinvigorates T cells from exhaustion and potentiates T-cell responses to tumors. However, most patients do not respond to ICB therapy, and only a limited response can be achieved in a "cold" tumor with few infiltrated lymphocytes. Synthetic biology can be used to engineer bacteria as controllable bioreactors to synthesize biotherapeutics in situ. We engineered attenuated Salmonella VNP20009 with synthetic gene circuits to produce PD-1 and Tim-3 scFv to block immunosuppressive receptors on exhausted T cells to reinvigorate their antitumor response. Secreted PD-1 and Tim-3 scFv bound PD-1+ Tim-3+ T cells through their targeting receptors in vitro and potentiated the T-cell secretion of IFN-γ. Engineered bacteria colonized the hypoxic core of the tumor and synthesized PD-1 and Tim-3 scFv in situ, reviving CD4+ T cells and CD8+ T cells to execute an antitumor response. The bacteria also triggered a strong innate immune response, which stimulated the expansion of IFN-γ+ CD4+ T cells within the tumors to induce direct and indirect antitumor immunity.

Engineered oncolytic bacteria HCS1 exerts high immune stimulation and safety profiles for cancer therapy

Background and rationale: Attenuated Salmonella typhimurium VNP20009 has been used to treat tumor-bearing mice and entered phase I clinical trials. However, its mild anticancer effect in clinical trials may be related to insufficient bacterial colonization and notable adverse effects with increasing dosages. Guanosine 5'-diphosphate-3'-diphosphate (ppGpp) synthesis-deficient Salmonella is an attenuated strain with good biosafety and anticancer efficacy that has been widely investigated in various solid cancers in preclinical studies. Integration of the advantages of these two strains may provide a new solution for oncolytic bacterial therapy. Methods: We incorporated the features of ΔppGpp into VNP20009 and obtained the HCS1 strain by deleting relA and spoT, and then assessed its cytotoxicity in vitro and antitumor activities in vivo. Results: In vitro experiments revealed that the invasiveness and cytotoxicity of HCS1 to cancer cells were significantly lower than those of the VNP20009. Additionally, tumor-bearing mice showed robust cancer suppression when treated with different doses of HCS1 intravenously, and the survival time and cured mice were dramatically increased. Furthermore, HCS1 can increase the levels of pro-inflammatory cytokines in tumor tissues and relieve the immunosuppression in the tumor microenvironments. It can also recruit abundant immune cells into tumor tissues, thereby increasing immune activation responses. Conclusion: The newly engineered Salmonella HCS1 strain manifests high prospects for cancer therapeutics and is a promising option for future clinical cancer immunotherapy.

Tryptophanase Expressed by Salmonella Halts Breast Cancer Cell Growth In Vitro and Inhibits Production of Immunosuppressive Kynurenine

Tryptophan is an essential amino acid required for tumor cell growth and is also the precursor to kynurenine, an immunosuppressive molecule that plays a role in limiting anticancer immunity. Tryptophanase (TNase) is an enzyme expressed by different bacterial species that converts tryptophan into indole, pyruvate and ammonia, but is absent in the Salmonella strain VNP20009 that has been used as a therapeutic delivery vector. We cloned the Escherichia coli TNase operon tnaCAB into the VNP20009 (VNP20009-tnaCAB), and were able to detect linear production of indole over time, using Kovács reagent. In order to conduct further experiments using the whole bacteria, we added the antibiotic gentamicin to stop bacterial replication. Using a fixed number of bacteria, we found that there was no significant effect of gentamicin on stationary phase VNP20009-tnaCAB upon their ability to convert tryptophan to indole over time. We developed a procedure to extract indole from media while retaining tryptophan, and were able to measure tryptophan spectrophotometrically after exposure to gentamicin-inactivated whole bacterial cells. Using the tryptophan concentration equivalent to that present in DMEM cell culture media, a fixed number of bacteria were able to deplete 93.9% of the tryptophan in the culture media in 4 h. In VNP20009-tnaCAB depleted tissue culture media, MDA-MB-468 triple negative breast cancer cells were unable to divide, while those treated with media exposed only to VNP20009 continued cell division. Re-addition of tryptophan to conditioned culture media restored tumor cell growth. Treatment of tumor cells with molar equivalents of the TNase products indole, pyruvate and ammonia only caused a slight increase in tumor cell growth. Using an ELISA assay, we confirmed that TNase depletion of tryptophan also limits the production of immunosuppressive kynurenine in IFNγ-stimulated MDA-MB-468 cancer cells. Our results demonstrate that Salmonella VNP20009 expressing TNase has improved potential to stop tumor cell growth and reverse immunosuppression.

Chloroquine Inhibition of Autophagy Enhanced the Anticancer Effects of Listeria monocytogenes in Melanoma

Listeria monocytogenes has been shown to exhibit antitumor effects. However, the mechanism remains unclear. Autophagy is a cellular catabolic process that mediates the degradation of unfolded proteins and damaged organelles in the cytosol, which is a double-edged sword in tumorigenesis and treatment outcome. Tumor cells display lower levels of basal autophagic activity than normal cells. This study examined the role and molecular mechanism of autophagy in the antitumor effects induced by LM, as well as the combined antitumor effect of LM and the autophagy inhibitor chloroquine (CQ). We investigated LM-induced autophagy in B16F10 melanoma cells by real-time PCR, immunofluorescence, Western blotting, and transmission electron microscopy and found that autophagic markers were increased following the infection of tumor cells with LM. The autophagy pathway in B16F10 cells was blocked with the pharmacological autophagy inhibitor chloroquine, which led to a significant increase in intracellular bacterial multiplication in tumor cells. The combination of CQ and LM enhanced LM-mediated cancer cell death and apoptosis compared with LM infection alone. Furthermore, the combination of LM and CQ significantly inhibited tumor growth and prolonged the survival time of mice in vivo, which was associated with the increased colonization and accumulation of LM and induced more cell apoptosis in primary tumors. The data indicated that the inhibition of autophagy by CQ enhanced LM-mediated antitumor activity in vitro and in vivo and provided a novel strategy to improving the anticancer efficacy of bacterial treatment.

Direct and indirect antiparasitic effects of chloroquine against the virulent RH strain of Toxoplasma gondii: An experimental study

BACKGROUND

Toxoplasmosis is a deleterious parasitic disease with harmful impact on both humans and animals. The present study was carried out to evaluate the antiparasitic effect of chloroquine (CQ), spiramycin (SP), and combination of both against the highly virulent RH HXGPRT (-) strain of Toxoplasma gondii (T. gondii) and to explore the mechanisms underlying such effect.

METHODS

We counted the tachyzoites in the peritoneal fluid and liver smears of mice and performed scanning and transmission electron microscopy and immunofluorescence staining of tachyzoites. Moreover, relative caspase 3 gene expression was measured by real time polymerase chain reaction of liver tissues and immunoassay of anti-apoptotic markers [B cell lymphoma-2 (Bcl-2) and X-chromosome linked inhibitor of apoptosis (XIAP)] and interferon gamma (IFN-γ) was done in liver tissues by ELISA. In addition, we estimated serum levels of aspartate transaminase (AST) and alanine transaminase (ALT) and performed histopathological examination of liver sections for scoring of inflammation.

RESULTS

We found that both CQ and CQ/SP combination significantly reduced parasitic load in the peritoneal fluid and liver smears, induced apical disruption of tachyzoites, triggered host cell apoptosis through elevation of relative caspase 3 gene expression and suppression of both Bcl-2 and XIAP. Also, they upregulated IFN-γ level, reduced serum AST and ALT, and ameliorated liver inflammation.

CONCLUSIONS

Either of CQ and CQ/SP combination was more effective than SP alone against T. gondii with the CQ/SP combination being more efficient. Therefore, adding CQ to other anti-Toxoplasma therapeutic regimens may be considered in future research.

Comparison of Anticancer Activities and Biosafety Between Salmonella enterica Serovar Typhimurium ΔppGpp and VNP20009 in a Murine Cancer Model

Salmonella Typhimurium defective in guanosine 5′-diphosphate-3′-diphosphate (ppGpp) synthesis (ΔppGpp) is an attenuated strain with good biosafety and excellent anticancer efficacy. It has been widely applied in preclinical studies of anticancer therapy for various types of solid cancer. VNP20009 is another genetically modified auxotrophic strain with 108-kb deletion, purI⁻, msbB⁻, and many single nucleotide polymorphisms (SNPs); it has shown promising therapeutic efficacy in various preclinical tumor models and entered phase I clinical trials. Here, the invasion activities and virulence of ΔppGpp were obviously lower than those of the VNP20009 strain when tested with cancer cells in vitro. In addition, the MC38 tumor-bearing mice showed comparable cancer suppression when treated with ΔppGpp or VNP20009 intravenously. However, the ΔppGpp-treated mice showed 16.7% of complete cancer eradication and prolonged survival in mice, whereas VNP20009 showed higher toxicity to animals, even with equal tumor size individually. Moreover, we found decreased levels of inflammatory cytokines in circulation but strengthened immune boost in tumor microenvironments of ΔppGpp-treated mice. Therefore, the engineered ΔppGpp has high potential for cancer therapeutics, and it is a promising option for future clinical cancer therapy.

Evidence and speculation: the response of Salmonella confronted by autophagy in macrophages

Bacteria of the Salmonella genus cause diseases ranging from self-limited gastroenteritis to typhoid fever. Macrophages are immune cells that engulf and restrict Salmonella. These cells will carry Salmonella into the circulatory system and provoke a systemic infection. Therefore, the interaction between macrophages and intracellular Salmonella is vital for its pathogenicity. As one of the immune responses of macrophages, autophagy, along with the fusion of autophagosomes with lysosomes, occupies an important position in eliminating Salmonella. However, Salmonella that can overcome cellular defensive responses and infect neighboring cells must derive strategies to escape autophagy. This review introduces novel findings on Salmonella and macrophage autophagy as a mechanism against infection and explores the strategies used by Salmonella to escape autophagy.

Chloroquine ameliorates carbon tetrachloride-induced acute liver injury in mice via the concomitant inhibition of inflammation and induction of apoptosis

This is the first study to investigate the hepatoprotective effect of CQ on acute liver injury caused by carbon tetrachloride (CCl₄) in a murine model and the underlying molecular mechanisms. Ninety-six mice were randomly divided into the control (n = 8), CQ (n = 8), CCl₄ (n = 40), and CCl₄ + CQ (n = 40) treatment groups. In the CCl₄ group, mice were intraperitoneally (i.p) injected with 0.3% CCl₄ (10 mL/kg, dissolved in olive oil); in the CCl₄ + CQ group, mice were i.p injected with CQ at 50 mg/kg at 2, 24, and 48 h before CCl₄ administration. The mice in the control and CQ groups were administered with an equal vehicle or CQ (50 mg/kg). Mice were killed at 2, 6, 12, 24, 48 h post CCl₄ treatment and their livers were harvested for analysis. The results showed that CQ pre-treatment markedly inhibited CCl₄-induced acute liver injury, which was evidenced by decreased serum transaminase, aspartate transaminase and lower histological scores of liver injury. CQ pretreatment downregulated the CCl₄-induced hepatic tissue expression of high-mobility group box 1 (HMGB1) and the levels of serum HMGB1 as well as IL-6 and TNF-α. Furthermore, CQ pre-treatment inhibited autophagy, downregulated NF-kB expression, upregulated p53 expression, increased the ratio of Bax/Bcl-2, and increased the activation of caspase-3 in hepatic tissue. This is the first study to demonstrate that CQ ameliorates CCl₄-induced acute liver injury via the inhibition of HMGB1-mediated inflammatory responses and the stimulation of pro-apoptotic pathways to modulate the apoptotic and inflammatory responses associated with progress of liver damage.

Bacteria-Driven Hypoxia Targeting for Combined Biotherapy and Photothermal Therapy

The facultative anaerobe Salmonella strain VNP20009 selectively colonizes into tumors following systemic injection due to its preference for the hypoxia in the tumor cores. However, the phase 1 clinical trial of VNP20009 has been terminated mainly due to its weak antitumor effects and exhibition of dose-dependent toxicity. Here, we leveraged the advantages of VNP20009 biotherapy together with polydopamine-mediated photothermal therapy in order to enhance the antitumor efficacy toward malignant melanoma. VNP20009 was coated with polydopamine via oxidation and self-polymerization, which was then injected into tumor-bearing mice via the tail vein. Polydopamine-coated VNP20009 targeted hypoxic areas of the solid tumors, and near-infrared laser irradiation of the tumors induced heating due to polydopamine. This combined approach eliminated the tumors without relapse or metastasis with only one injection and laser irradiation. More importantly, we found both VNP and pDA potentiate the therapeutic ability of each other, resulting in a superior anticancer effect.

The Salmonella effectors SseF and SseG inhibit Rab1A-mediated autophagy to facilitate intracellular bacterial survival and replication

In mammalian cells, autophagy plays crucial roles in restricting further spread of invading bacterial pathogens. Previous studies have established that the Salmonella virulence factors SseF and SseG are required for intracellular bacterial survival and replication. However, the underlying mechanism by which these two effectors facilitate bacterial infection remains elusive. Here, we report that SseF and SseG secreted by Salmonella Typhimurium (S. Typhimurium) inhibit autophagy in host cells and thereby establish a replicative niche for the bacteria in the cytosol. Mechanistically, SseF and SseG impaired autophagy initiation by directly interacting with the small GTPase Rab1A in the host cell. This interaction abolished Rab1A activation by disrupting the interaction with its guanine nucleotide exchange factor (GEF), the TRAPPIII (transport protein particle III) complex. This disruption of Rab1A signaling blocked the recruitment and activation of Unc-51-like autophagy-activating kinase 1 (ULK1) and decreased phosphatidylinositol 3-phosphate biogenesis, which ultimately impeded autophagosome formation. Furthermore, SseF- or SseG-deficient bacterial strains exhibited reduced survival and growth in both mammalian cell lines and mouse infection models, and Rab1A depletion could rescue these defects. These results reveal that virulence factor-dependent inactivation of the small GTPase Rab1A represents a previously unrecognized strategy of S Typhimurium to evade autophagy and the host defense system.

Antiproliferative activity of di-2-pyridylhydrazone dithiocarbamate acetate partly involved in p53 mediated apoptosis and autophagy

Cancer cells have higher demand of iron and copper ions for growth, disturbing the metal's homeostasis can inhibit proliferation of cancer cell. Dithiocarbamates possessing excellent metal chelating ability and antitumor activity are considered as candidates in chelation therapy, however, their antitumor molecular mechanisms remain to be elucidated. In the present study, a dithiocarbamate derivative, di-2-pyridylhydrazone dithiocarbamate s-acetic acid (DpdtaA) was prepared to address the issue whether the molecular mechanism behind biological behavior showed by dithiocarbamate was p53 mediated. The proliferation inhibition assay showed that DpdtaA exhibited excellent antiproliferative effect for hepatocellular carcinoma (IC50= 3.0±0.4 µM for HepG2, 6.1±0.6 µM for Bel-7402 cell). However, in the presence of copper ion, the antiproliferative activity of DpdtaA significantly attenuated (~3-fold for HepG2) due to formation of copper chelate. The ROS assay revealed that the antiproliferative activity of DpdtaA correlated with ROS generation. Western blotting demonstrated that DpdtaA could upregulate p53 via down-regulating the Mdm2, accordingly leading to changes of bcl family proteins, indicating that a p53-dependent intrinsic apoptosis was partly involved. Simulation from molecular docking hinted that DpdtaA could disrupt interaction between p53 and Mdm2, indicating the disruption might also contribute to the upregulation of p53. The alternations in lysosome membrane permeability and acidic vacuoles as well as LC3-II upregulation indicated that autophagy was involved. The copper addition led to significantly attenuate biological activity of DpdtaA, with few dithiocarbamates, but the mechanism in apoptosis induction was not altered except for weaker ability.