HDAC inhibitor valproic acid enhances tumor cell kill in adenovirus-HSVtk mediated suicide gene therapy in HNSCC xenograft mouse model

Modifying gap junction communication in cancer therapy

AIM

Drug delivery is crucial for therapeutic efficacy and gap junction communication channels (GJIC) facilitate movement within the tumour. Pro-drug activation, a modality of cancer therapy leads to Ganciclovir triphosphate (GCV-TP) incorporation into newly synthesized DNA resulting in cell death. The objective was to enhance, with Histone deacetylase inhibitors (HDACi) and All Trans Retinoic Acid (ATRA), GJIC, crucial for drug delivery, and with combination, abrogate the observed detrimental effect of Dexamethasone (DXM).

METHODS

Cell lines (NT8E, and HeLa) were pre-treated with Valproic Acid (VPA) (1 mM), 4 Phenyl Butyrate (4PB) (2 mM), ATRA (10 μM) and Dexamethasone (1 μM). Protein quantitated with the Bicinchoninic (BCA) assay for cell lysates, membrane and soluble fractions was assessed with Western blotting for Connexins (43, 26 and 32) and E-Cadherin. A qRT-PCR was done for CX 43-GJA1, CX 26-GJB2, CX 32-GJB1 and E-Cadherin, and normalized with Glyceraldehyde Phosphate dehydrogenase (GAPDH). Further, localization of Connexins (CX) and E-Cadherin, GJIC competence, pre-clinical in-vitro studies and the mechanism of cell death were evaluated.

RESULTS

There was no toxicity or change in growth patterns observed with the drugs. In both the cell lines CX 43 localized to the membrane whereas CX 32 and CX 26 were present but not membrane bound. E-Cadherin was present on the membrane in NT8E and completely absent in HeLa cells. Effects of HDACi, DXM and ATRA were seen on the expression of Connexins and E-Cadherin in both the cell lines. NT8E and HeLa cell lines showed enhanced GJIC with 4PB [30 %], VPA [36 %] and ATRA [54 %] with a 60 % increase in cytotoxicity and an abrogation of Dexamethasone inhibition on combination with VPA or ATRA.

CONCLUSION

An enhancement of GJIC function by HDACi and ATRA increased cytotoxicity and could be effective in the presence of Dexamethasone, when combined with ATRA or VPA.

Adenovirus-mediated herpes simplex virus thymidine kinase gene therapy combined with ganciclovir induces hepatoma cell apoptosis

The present study aimed to examine the apoptotic effects of adenovirus (ADV)-mediated herpes simplex virus thymidine kinase (ADV-TK) combined with ganciclovir (GCV) in tissues obtained from patients with hepatocellular carcinoma in order to provide a theoretical basis for the development of this gene therapy program. Apoptosis detection was conducted using the terminal deoxynucleotidyl-transferase-mediated dUTP nick end labelling assay and the apoptosis index was compared between the experimental; and control groups. Furthermore, the protein expression levels of caspase-3, B-cell lymphoma-2 (Bcl-2), Bcl-2-assoicated protein X (Bax) and nuclear factor (NF)-κB were examined in pathological specimens using immunohistochemical staining. The Bax/Bcl-2 ratio and the release of cytochrome c were examined using western blot analysis. Results indicated that combined ADV-TK and GCV treatment significantly increased the number of apoptotic cells compared with the control group (P<0.05). Immunohistological analysis revealed that ADV-TK and GCV treatment significantly increased the number of caspase-3-positive cells, reduced the Bax/Bcl-2 ratio and NF-κB expression levels and promoted the release of cytochrome c compared with the control group (P<0.01). In conclusion, the present results suggest that combined ADV-TK and GCV treatment exerts its effect through the apoptotic signaling pathway.

Combined therapy of colon carcinomas with an oncolytic adenovirus and valproic acid

The anti-tumor potential of oncolytic adenoviruses (CRAds) has been demonstrated in preclinical and clinical studies. While these agents failed to eradicate tumors when used as a monotherapy, they may be more effective if combined with conventional treatments such as radiotherapy or chemotherapy. This study seeks to evaluate the combination of a CRAd bearing a ∆24 deletion in E1A with valproic acid (VPA), a histone deacetylase inhibitor, for the treatment of human colon carcinomas. This combination led to a strong inhibition of cell growth both in vitro and in vivo compared to treatment with CRAd or VPA alone. This effect did not stem from a better CRAd replication and production in the presence of VPA. Inhibition of cell proliferation and cell death were induced by the combined treatment. Moreover, whereas cells treated only with CRAd displayed a polyploidy (> 4N population), this phenotype was increased in cells treated with both CRAd and VPA. In addition, the increase in polyploidy triggered by combined treatment with CRAd and VPA was associated with the enhancement of H2AX phosphorylation (γH2AX), a hallmark of DNA damage, but also with a decrease of several DNA repair proteins. Finally, viral replication (or E1A expression) was shown to play a key role in the observed effects since no enhancement of polyploidy nor increase in γH2AX were found following cell treatment with a replication-deficient Ad and VPA. Taken together, our results suggest that CRAd and VPA could be used in combination for the treatment of colon carcinomas.

Histone deacetylase inhibitor trichostatin A enhances the antitumor effect of the oncolytic adenovirus H101 on esophageal squamous cell carcinoma in vitro and in vivo

Replication-selective oncolytic virotherapy provides a novel modality to treat cancer by inducing cell death in tumor cells but not in normal cells. However, the utilization of oncolytic viruses as a stand-alone treatment is problematic due to their poor transduction efficiency in vivo. H101 was the first oncolytic adenovirus (Ads) to be approved by the Chinese FDA, and exhibits modest antitumor effects when applied as a single agent. The multiple histone deacetylase inhibitor trichostatin A (TSA) has been demonstrated to potently enhance the spread and replication of oncolytic Ads in several infection-resistant types of cancer. The present study aimed to investigate the antitumor effects of H101 in combination with TSA on esophageal squamous cell carcinoma (ESCC) in vitro and in vivo, and determine the mechanisms underlying these effects. H101 and TSA in combination increased the survival of mice harboring human ESCC cell line-tumor xenografts, as compared with mice treated with these agents individually. Therefore, TSA may enhance the antitumor effects of H101 in ESCC.

Histone deacetylase inhibitors in oral squamous cell carcinoma treatment

Introduction: The involvement of the histone deacetylases (HDACs) family in tumor development and progression is well demonstrated. HDAC inhibitors (HDACis) constitute a novel, heterogeneous family of highly selective anticancer agents that inhibit HDACs and present significant antitumor activity in several human malignancies, including oral squamous cell carcinoma (OSCC). Areas covered: This review summarizes the current research on the anticancer activity of HDACis against OSCC. The review also presents the molecular mechanisms of HDACis action and the existing studies evaluating their utilization in combined therapies of OSCC. Expert opinion: The currently available data support evidence that HDACis may provide new therapeutic options against OSCC, decreasing treatment side effects and allowing a more conservative therapeutic approach. Future research should be focused on in vivo and clinical evaluation of their utilization as combined therapies or monotherapies. Before HDACis can be brought into clinical practice as treatment options for OSCC, further evaluation is needed to determine their optimal dosage, the appropriate duration of treatment and whether they should be used in combination or as stand-alone therapeutics.

Genetic alterations in head and neck squamous cell carcinoma: The next-gen sequencing era

Head and neck squamous cell carcinoma is the sixth most common cancer in the world with approximately 650000 new cases diagnosed annually. Next-generation molecular techniques and results from phase 2 of the Cancer Genome Atlas becoming available have drastically improved our current knowledge on the genetics basis of head and neck squamous cell carcinoma. New insights and new perspectives on the mutational landscape implicated in head and neck squamous cell carcinoma provide improved tools for prognostication. More importantly, depend on the patient’s tumor subtypes and prognosis, deescalated or more aggressive therapy maybe chosen to achieve greater potency while minimizing the toxicity of therapy. This paper aims to review our current knowledge on the genetic mutations and altered molecular pathways in head and neck squamous cell carcinoma. Some of the most common mutations in head and neck squamous cell carcinoma reported by the cancer genome atlas including TP53, NOTCH1, Rb, CDKN2A, Ras, PIK3CA and EGFR are described here. Additionally, the emerging role of epigenetics and the role of human papilloma virus in head and neck squamous cell carcinoma are also discussed in this review. The molecular pathways, clinical applications, actionable molecular targets and potential therapeutic strategies are highlighted and discussed in details.

Inhibition of homologous recombination with vorinostat synergistically enhances ganciclovir cytotoxicity

The nucleoside analog ganciclovir (GCV) elicits cytotoxicity in tumor cells via a novel mechanism in which drug incorporation into DNA produces minimal disruption of replication, but numerous DNA double strand breaks occur during the second S-phase after drug exposure. We propose that homologous recombination (HR), a major repair pathway for DNA double strand breaks, can prevent GCV-induced DNA damage, and that inhibition of HR will enhance cytotoxicity with GCV. Survival after GCV treatment in cells expressing a herpes simplex virus thymidine kinase was strongly dependent on HR (>14-fold decrease in IC50 in HR-deficient vs. HR-proficient CHO cells). In a homologous recombination reporter assay, the histone deacetylase inhibitor, suberoylanilide hydroxamic acid (SAHA; vorinostat), decreased HR repair events up to 85%. SAHA plus GCV produced synergistic cytotoxicity in U251tk human glioblastoma cells. Elucidation of the synergistic mechanism demonstrated that SAHA produced a concentration-dependent decrease in the HR proteins Rad51 and CtIP. GCV alone produced numerous Rad51 foci, demonstrating activation of HR. However, the addition of SAHA blocked GCV-induced Rad51 foci formation completely and increased γH2AX, a marker of DNA double strand breaks. SAHA plus GCV also produced synergistic cytotoxicity in HR-proficient CHO cells, but the combination was antagonistic or additive in HR-deficient CHO cells. Collectively, these data demonstrate that HR promotes survival with GCV and compromise of HR by SAHA results in synergistic cytotoxicity, revealing a new mechanism for enhancing anticancer activity with GCV.

Enhanced antitumor efficacy of telomerase-specific oncolytic adenovirus with valproic acid against human cancer cells

Replication-selective oncolytic viruses are being developed for human cancer therapy. We previously developed an attenuated adenovirus (OBP-301, Telomelysin), in which the human telomerase reverse transcriptase promoter element drives expression of E1A and E1B genes linked with an internal ribosome entry site. OBP-301 can replicate in, and causes selective lysis of, human cancer cells. Valproic acid (VPA), which is an effective antiepileptic drug, is known to inhibit the histone deacetylase activities. We determined whether the antitumor effect of OBP-301 could be enhanced by VPA in human lung cancer cells. In an in vitro cell viability assay, OBP-301 infection killed four human lung cancer cell lines, H1299, H1299-R5 (a subline of H1299 with a low level of the coxsackievirus and adenovirus receptor (CAR) expression), H460, and A549, more efficiently in the presence of VPA than in its absence. VPA treatment increased CAR expression in all the four lung cancer cells. Consistent with their CAR upregulation, the infection efficiency of adenoviruses in the presence of VPA was significantly higher than that in its absence. The molecular mechanism of this combined effect could be explained by an increase in adenovirus infectivity via VPA-mediated upregulation of CAR. These results suggest that treatment with OBP-301 in combination with VPA is a promising strategy for human lung cancer.

Oncolytic virotherapy with modified adenoviruses and novel therapeutic targets

INTRODUCTION

Numerous oncolytic viral mutants derived from a variety of strains have antitumor efficacy with limited or no toxicity to normal tissue. While all modes of administration were determined to be safe in patients with solid cancers refractory to current standard of care, this therapeutic approach requires further improvements to achieve definite efficacy.

AREAS COVERED

We review the most promising clinical developments with several oncolytic viruses. The focus is on preclinical and clinical findings with replication-selective adenoviral mutants including ONYX-015, H101 and Ad5ΔCR mutants that, to date, are the most studied oncolytic viruses. Cellular pathways reported to play a role in virus-induced cell killing are reviewed as potential targets for the development of more effective combinatorial therapies.

EXPERT OPINION

The most promising clinical outcomes for metastatic cancers have been reported for oncolytic vaccinia and herpes virus mutants expressing the cytokine GMCSF. However, highly efficacious and selective adenoviral mutants have been developed that interact synergistically with cytotoxic drugs in model systems. We anticipate that by delineating the cellular targets for synergistic cancer cell killing in response to adenoviral mutants and drugs such as apoptosis and autophagy signaling, greatly improved anticancer therapies will result in the near future.

Valproic acid enhances anti-tumor effect of mesenchymal stem cell mediated HSV-TK gene therapy in intracranial glioma

Suicide gene therapy of glioma based on herpes simplex virus type I thymidine kinase (HSV-TK) and prodrug ganciclovir (GCV) suffers from the lack of efficacy in clinical trials, which is mostly due to low transduction efficacy and absence of bystander effect in tumor cells. Recently, stem cells as cellular delivery vehicles of prodrug converting gene has emerged as a new treatment strategy for malignant glioma. In this study, we evaluated the anti-glioma effect of suicide gene therapy using human bone marrow mesenchymal stem cells expressing HSV-TK (MSCs-TK) combined with valproic acid (VPA), which can upregulate the gap junction proteins and may enhance the bystander effect of suicide gene therapy. Expression of HSV-TK in MSCs was confirmed by RT-PCR analysis and the sensitivity of MSCs-TK to GCV was assessed. A bystander effect was observed in co-cultures of MSCs-TK and U87 glioma cells by GCV in a dose-dependent manner. VPA induced the expression of the gap junction proteins connexin (Cx) 43 and 26 in glioma cell and thereby enhanced the bystander effect in co-culture experiment. The enhanced bystander effect was inhibited by the gap junction inhibitor 18-β-glycyrrhetinic acid (18-GA). Moreover, the combined treatment with VPA and MSCs-TK synergistically enhanced apoptosis in glioma cells by caspase activation. In vivo efficacy experiments showed that combination treatment of MSCs-TK and VPA significantly inhibited tumor growth and prolonged the survival of glioma-bearing mice compared with single-treatment groups. In addition, TUNEL staining also demonstrated a significant increase in the number of apoptotic cells in the combination treated group compared with single-treatment groups. Taken together, these results provide the rational for designing novel experimental protocols to increase bystander killing effect against intracranial gliomas using MSCs-TK and VPA.

Antiglioma effects of combined use of a baculovirual vector expressing wild-type p53 and sodium butyrate

BACKGROUND

Combination therapy is usually desirable for successful cancer treatment, especially in cancers that are resistant to single forms of therapy.

METHODS

To achieve an optimal therapeutic effect against glioblastoma, we tested a strategy that combines baculovirus-mediated transfer of the p53 tumor suppressor gene with the use of sodium butyrate, a histone deacetylase inhibitor. This strategy was designed based on the findings that the transduction efficiency of baculovirus in mammalian cells can be markedly enhanced by the addition of histone deacetylase inhibitors and that these inhibitors are effective in inducing cell cycle arrest, differentiation, or apoptosis in tumor cells.

RESULTS

We observed a synergistic effect of the combination of the two treatments in provoking apoptosis in glioblastoma cells with mutant p53. In a mouse glioma xenograft model, the tumor inhibitory effect of baculovirus-expressed p53 was significantly enhanced by co-administration of sodium butyrate.

CONCLUSIONS

These findings suggest a new approach to treat glioblastoma using baculovirus-mediated gene transfer in combination with administration of histone deacetylase inhibitor.

The current state of head and neck cancer gene therapy

The incidence of head and neck cancer continues to increase worldwide, with tobacco exposure and human papillomavirus type 16 infections being the major etiological factors. Current therapeutic options are ineffective in approximately half of the individuals afflicted with this malignancy. Developments in the identification of molecules that sustain head and neck squamous cell carcinoma (HNSCC) growth and survival have made molecular targeting by gene therapy approaches a feasible therapeutic strategy. Although gene therapy was originally designed to correct single gene defects, it has now evolved to encompass all forms of therapeutic interventions involving engineered cells and nucleic acids that modify the overall pattern of gene expression within target tissues. Several preclinical studies and clinical trials have tested the efficacy of targeting specific molecules in patients with HNSCC, using genetic therapy approaches. This review discusses promising preclinical and clinical approaches and new directions for HNSCC gene therapy.