STAT3 inhibition reduces toxicity of oncolytic VSV and provides a potentially synergistic combination therapy for hepatocellular carcinoma

Positive allosteric γ-aminobutyric acid type A receptor modulation prevents lipotoxicity-induced injury in hepatocytes in vitro

AIM

To determine if a novel positive allosteric modulator of the γ-aminobutyric acid type A (GABA_A ) receptor, the thioacrylamide-derivative HK4, which does not penetrate the blood-brain barrier, protects human hepatocytes against lipotoxicity-induced injury.

MATERIALS AND METHODS

Allosteric modulation of the GABA_A receptor by HK4 was determined by patch clamp in HEK-293 cells, calcium influx in INS-1E cells and by using the specific GABA_A channel blockers picrotoxin and tert-butylbicyclophosphorothionate (TBPS) in HepG2 cells. Apoptosis was analysed using caspase 3/7, terminal deoxynucleotidyl transferase-dUTP nick end labelling (TUNEL) and array assays in HepG2 cells and/or human primary hepatocytes. Phosphorylation of STAT3 and the NF-κB subunit p65, protein disulphide isomerase (PDI) and poly-ADP-ribose polymerase-1 (PARP-1) was detected by Western blotting.

RESULTS

Patch clamping, calcium influx measurements and apoptosis assays with the non-competitive GABA_A channel blockers picrotoxin and TBPS proved HK4 as a selective positive allosteric modulator of the GABA_A receptor. In HepG2 cells, which expressed the main GABA_A receptor subunits, HK4 prevented palmitate-induced apoptosis. This protective effect was mediated by downregulation of caspase 3/7 activity and was additionally verified by TUNEL assay. HK4 effectively prevented palmitate-induced apoptosis in human primary hepatocytes. HK4 reduced STAT3 and NF-κB phosphorylation, reduced cleaved PARP-1 expression and upregulated the endoplasmic reticulum (ER) chaperone PDI.

CONCLUSIONS

HK4 reduced lipotoxic-induced apoptosis by preventing inflammation, DNA damage and ER stress. We propose that the effect of HK4 is mediated by STAT3 and NF-κB. It is suggested that thioacrylamide compounds represent an innovative pharmacological tool to treat or prevent non-alcoholic steatohepatitis as first-in-class drugs.

Therapeutic Efficacy of Oncolytic Viruses in Fighting Cancer: Recent Advances and Perspective

Immunotherapy is at the cutting edge of modern cancer treatment. Innovative medicines have been developed with varying degrees of success that target all aspects of tumor biology: tumors, niches, and the immune system. Oncolytic viruses (OVs) are a novel and potentially immunotherapeutic approach for cancer treatment. OVs reproduce exclusively in cancer cells, causing the tumor mass to lyse. OVs can also activate the immune system in addition to their primary activity. Tumors create an immunosuppressive environment by suppressing the immune system’s ability to respond to tumor cells. By injecting OVs into the tumor, the immune system is stimulated, allowing it to generate a robust and long-lasting response against the tumor. The essential biological properties of oncolytic viruses, as well as the underlying mechanisms that enable their usage as prospective anticancer medicines, are outlined in this review. We also discuss the increased efficacy of virotherapy when combined with other cancer medications.

Improving antitumor efficacy via combinatorial regimens of oncolytic virotherapy

As a promising therapeutic strategy, oncolytic virotherapy has shown potent anticancer efficacy in numerous pre-clinical and clinical trials. Oncolytic viruses have the capacity for conditional-replication within carcinoma cells leading to cell death via multiple mechanisms, including direct lysis of neoplasms, induction of immunogenic cell death, and elicitation of innate and adaptive immunity. In addition, these viruses can be engineered to express cytokines or chemokines to alter tumor microenvironments. Combination of oncolytic virotherapy with other antitumor therapeutic modalities, such as chemotherapy and radiation therapy as well as cancer immunotherapy can be used to target a wider range of tumors and promote therapeutic efficacy. In this review, we outline the basic biological characteristics of oncolytic viruses and the underlying mechanisms that support their use as promising antitumor drugs. We also describe the enhanced efficacy attributed to virotherapy combined with other drugs for the treatment of cancer.

The mechanisms of sorafenib resistance in hepatocellular carcinoma: theoretical basis and therapeutic aspects

Sorafenib is a multikinase inhibitor capable of facilitating apoptosis, mitigating angiogenesis and suppressing tumor cell proliferation. In late-stage hepatocellular carcinoma (HCC), sorafenib is currently an effective first-line therapy. Unfortunately, the development of drug resistance to sorafenib is becoming increasingly common. This study aims to identify factors contributing to resistance and ways to mitigate resistance. Recent studies have shown that epigenetics, transport processes, regulated cell death, and the tumor microenvironment are involved in the development of sorafenib resistance in HCC and subsequent HCC progression. This study summarizes discoveries achieved recently in terms of the principles of sorafenib resistance and outlines approaches suitable for improving therapeutic outcomes for HCC patients.

Fine-Tuning of Type I Interferon Response by STAT3

Type I interferon (IFN-I) is induced during innate immune response and is required for initiating antiviral activity, growth inhibition, and immunomodulation. STAT1, STAT2, and STAT3 are activated in response to IFN-I stimulation. STAT1, STAT2, and IRF9 form ISGF3 complex which transactivates downstream IFN-stimulated genes and mediates antiviral response. However, the role of STAT3 remains to be characterized. Here, we review the multiple actions of STAT3 on suppressing IFN-I responses, including blocking IFN-I signaling, downregulating the expression of ISGF3 components, and antagonizing the transcriptional activity of ISGF3. Finally, we discuss the evolution of the suppressive activity of STAT3 and the therapeutic potential of STAT3 inhibitors in host defense against viral infections and IFN-I-associated diseases.

Oncolytic Viruses and Immune Checkpoint Inhibition: The Best of Both Worlds

Cancer immunotherapy and the emergence of immune checkpoint inhibitors have markedly changed the treatment paradigm for many cancers. They function to disrupt cancer cell evasion of the immune response and activate sustained anti-tumor immunity. Oncolytic viruses have also emerged as an additional therapeutic agent for cancer treatment. These viruses are designed to target and kill tumor cells while leaving the normal cells unharmed. As part of this process, oncolytic virus infection stimulates anti-cancer immune responses that augment the efficacy of checkpoint inhibition. These viruses have the capability of transforming a “cold” tumor microenvironment with few immune effector cells into a “hot” environment with increased immune cell and cytokine infiltration. For this reason, there are multiple ongoing clinical trials that combine oncolytic virotherapy and immune checkpoint inhibitors. This review will detail the key oncolytic viruses in preclinical and clinical studies and highlight the results of their testing with checkpoint inhibitors.

Enhanced Safety and Efficacy of Oncolytic VSV Therapy by Combination with T Cell Receptor Transgenic T Cells as Carriers

Vesicular stomatitis virus (VSV) represents an attractive oncolytic virotherapy platform because of its potent tumor cell-killing and immune-stimulating properties; yet the clinical translation of VSV faces numerous challenges, such as inefficient systemic delivery and severe side effects such as neurotoxicity. We hypothesized that we could overcome these limitations and simultaneously enhance the therapy, by combining VSV with adoptively transferred T cell receptor (TCR) transgenic T cells as carrier cells. We show that CD8⁺ T central memory cells (CD8⁺ T cm) can be efficiently loaded with VSV, they support intracellular virus production, and they can efficiently transfer VSV to tumor cells without compromising their own viability or antitumor reactivity. Loading VSV onto CD8⁺ T cm not only improves the safety compared with systemic administration of naked virus, but this approach also allows for an effective delivery of virus to its tumor target, resulting in an effective combination therapy in NSG mice bearing subcutaneous human acute myeloid leukemia (AML) tumors. We conclude that the combination of potent tumor debulking provided by the oncolytic VSV with the added effector functions afforded by the cytotoxic immune carrier cells results in a potent and safer immunotherapeutic, which can be further developed for clinical translation.

Phosphatase of regenerating liver maintains cellular magnesium homeostasis

Phosphatase of regenerating liver (PRL) is highly expressed in malignant cancers and promotes cancer progression. Recent studies have suggested its functional relationship with Mg2+, but the importance and molecular details of this relationship remain unknown. Here, we report that PRL expression is regulated by Mg2+ and PRL protects cells from apoptosis under Mg2+-depleted conditions. When cultured cells were subjected to Mg2+ depletion, endogenous PRL protein levels increased significantly. siRNA-mediated knockdown of endogenous PRL did not significantly affect cell proliferation under normal culture conditions, but it increased cell death after Mg2+ depletion. Imaging analyses with a fluorescent probe for Mg2+ showed that PRL knockdown severely reduced intracellular Mg2+ levels, indicating a role for PRL in maintaining intracellular Mg2+. We also examined the mechanism of augmented expression of PRL proteins and found that PRL mRNA transcription was stimulated by Mg2+ depletion. A series of analyses revealed the activation and the crucial importance of signal transducer and activator of transcription 1 in this process. Collectively, these results implicate PRL in maintaining cellular Mg2+ homeostasis.

Recent advances in vesicular stomatitis virus-based oncolytic virotherapy: a 5-year update

Oncolytic virus (OV) therapy is an anti-cancer approach that uses viruses that preferentially infect, replicate in and kill cancer cells. Vesicular stomatitis virus (VSV, a rhabdovirus) is an OV that is currently being tested in the USA in several phase I clinical trials against different malignancies. Several factors make VSV a promising OV: lack of pre-existing human immunity against VSV, a small and easy to manipulate genome, cytoplasmic replication without risk of host cell transformation, independence of cell cycle and rapid growth to high titres in a broad range of cell lines facilitating large-scale virus production. While significant advances have been made in VSV-based OV therapy, room for improvement remains. Here we review recent studies (published in the last 5 years) that address 'old' and 'new' challenges of VSV-based OV therapy. These studies focused on improving VSV safety, oncoselectivity and oncotoxicity; breaking resistance of some cancers to VSV; preventing premature clearance of VSV; and stimulating tumour-specific immunity. Many of these approaches were based on combining VSV with other therapeutics. This review also discusses another rhabdovirus closely related to VSV, Maraba virus, which is currently being tested in Canada in phase I/II clinical trials.