Dichloroacetate (DCA) enhances tumor cell death in combination with oncolytic adenovirus armed with MDA-7/IL-24

Distinguishing the Pros and Cons of Metabolic Reprogramming in Oncolytic Virus Immunotherapy

Oncolytic viruses (OVs) represent a class of cancer immunotherapies that rely on hijacking the host cell factory for replicative oncolysis and eliciting immune responses for tumor clearance. An increasing evidence suggests that the metabolic state of tumor cells and immune cells is a putative determinant of the efficacy of cancer immunotherapy. However, how therapeutic intervention with OVs affects metabolic fluxes within the tumor microenvironment (TME) remains poorly understood. Herein, we review the complexities of metabolic reprogramming involving the effects of viruses and their consequences on tumor cells and immune cells. We highlight the inherent drawback of oncolytic virotherapy, namely that treatment with OVs inevitably further exacerbates the depletion of nutrients and the accumulation of metabolic wastes in the TME, leading to a metabolic barrier to antitumor immune responses. We also describe targeted metabolic strategies that can be used to unlock the therapeutic potential of OVs.

Insights into the Mechanisms of Action of MDA-7/IL-24: A Ubiquitous Cancer-Suppressing Protein

Melanoma differentiation associated gene-7/interleukin-24 (MDA-7/IL-24), a secreted protein of the IL-10 family, was first identified more than two decades ago as a novel gene differentially expressed in terminally differentiating human metastatic melanoma cells. MDA-7/IL-24 functions as a potent tumor suppressor exerting a diverse array of functions including the inhibition of tumor growth, invasion, angiogenesis, and metastasis, and induction of potent "bystander" antitumor activity and synergy with conventional cancer therapeutics. MDA-7/IL-24 induces cancer-specific cell death through apoptosis or toxic autophagy, which was initially established in vitro and in preclinical animal models in vivo and later in a Phase I clinical trial in patients with advanced cancers. This review summarizes the history and our current understanding of the molecular/biological mechanisms of MDA-7/IL-24 action rendering it a potent cancer suppressor.

Targeted Metabolic Reprogramming to Improve the Efficacy of Oncolytic Virus Therapy

Oncolytic viruses (OVs) represent a promising new class of cancer therapeutics and cause antitumor effects by two major mechanisms: (1) directly killing cancer cells in a process known as oncolysis, or (2) initiating a powerful antitumor immune response. Interestingly, energy metabolism, within either cancer cells or immune cells, plays a pivotal role in defining the outcome of OV-mediated antitumor effects. Following therapeutic administration, OVs must hijack host cell metabolic pathways to acquire building blocks such as nucleotides, lipids, and amino acids for the process of replication that is necessary for oncolysis. Additionally, OV-stimulated antitumor immune responses are highly dependent on the metabolic state within the tumor microenvironment. Thus, metabolic reprogramming strategies bear the potential to enhance the efficacy of both OV-mediated oncolysis and antitumor immune responses.

Inhibition of Pyruvate Dehydrogenase Kinase Enhances the Antitumor Efficacy of Oncolytic Reovirus

Oncolytic viruses (OV) such as reovirus preferentially infect and kill cancer cells. Thus, the mechanisms that dictate the susceptibility of cancer cells to OV-induced cytotoxicity hold the key to their success in clinics. Here, we investigated whether cancer cell metabolism defines its susceptibility to OV and if OV-induced metabolic perturbations can be therapeutically targeted. Using mass spectrometry-based metabolomics and extracellular flux analysis on a panel of cancer cell lines with varying degrees of susceptibility to reovirus, we found that OV-induced changes in central energy metabolism, pyruvate metabolism, and oxidative stress correlate with their susceptibility to reovirus. In particular, reovirus infection accentuated Warburg-like metabolic perturbations in cell lines relatively resistant to oncolysis. These metabolic changes were facilitated by oxidative stress-induced inhibitory phosphorylation of pyruvate dehydrogenase (PDH) that impaired the routing of pyruvate into the tricarboxylic acid cycle and established a metabolic state unsupportive of OV replication. From the therapeutic perspective, reactivation of PDH in cancer cells that were weakly sensitive for reovirus, either through PDH kinase (PDK) inhibitors dichloroacetate and AZD7545 or short hairpin RNA-specific depletion of PDK1, enhanced the efficacy of reovirus-induced oncolysis in vitro and in vivo. These findings identify targeted metabolic reprogramming as a possible combination strategy to enhance the antitumor effects of OV in clinics. SIGNIFICANCE: This study proposes targeted metabolic reprogramming as a valid combinatorial strategy to enhance the translational efficacy of oncolytic virus-based cancer therapies.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/15/3824/F1.large.jpg.

Role of MDA-7/IL-24 a Multifunction Protein in Human Diseases

Subtraction hybridization identified genes displaying differential expression as metastatic human melanoma cells terminally differentiated and lost tumorigenic properties by treatment with recombinant fibroblast interferon and mezerein. This approach permitted cloning of multiple genes displaying enhanced expression when melanoma cells terminally differentiated, called melanoma differentiation associated (mda) genes. One mda gene, mda-7, has risen to the top of the list based on its relevance to cancer and now inflammation and other pathological states, which based on presence of a secretory sequence, chromosomal location, and an IL-10 signature motif has been named interleukin-24 (MDA-7/IL-24). Discovered in the early 1990s, MDA-7/IL-24 has proven to be a potent, near ubiquitous cancer suppressor gene capable of inducing cancer cell death through apoptosis and toxic autophagy in cancer cells in vitro and in preclinical animal models in vivo. In addition, MDA-7/IL-24 embodied profound anticancer activity in a Phase I/II clinical trial following direct injection with an adenovirus (Ad.mda-7; INGN-241) in tumors in patients with advanced cancers. In multiple independent studies, MDA-7/IL-24 has been implicated in many pathological states involving inflammation and may play a role in inflammatory bowel disease, psoriasis, cardiovascular disease, rheumatoid arthritis, tuberculosis, and viral infection. This review provides an up-to-date review on the multifunctional gene mda-7/IL-24, which may hold potential for the therapy of not only cancer, but also other pathological states.

Mechanism of Action and Applications of Interleukin 24 in Immunotherapy

Interleukin 24 (IL-24) is an important pleiotropic immunoregulatory cytokine, whose gene is located in human chromosome 1q32-33. IL-24's signaling pathways have diverse biological functions related to cell differentiation, proliferation, development, apoptosis, and inflammation, placing it at the center of an active area of research. IL-24 is well known for its apoptotic effect in cancer cells while having no such effect on normal cells. IL-24 can also be secreted by both immune and non-immune cells. Downstream effects of IL-24, after binding to the IL-20 receptor, can occur dependently or independently of the JAK/STAT signal transduction pathway, which is classically involved in cytokine-mediated activities. After exogenous addition of IL-24, apoptosis is induced in tumor cells independently of the JAK/STAT pathway. We have shown that IL-24 binds to Sigma 1 Receptor and this event induces endoplasmic reticulum stress, calcium mobilization, reactive oxygen species generation, p38MAPK activity, and ceramide production. Here we review IL-24's role in autoimmunity, infectious disease response, wound repair, and vascular disease. Detailed understanding of the pleiotropic roles of IL-24 signaling can assist in the selection of more accurate therapeutic approaches, as well as targeting of appropriate cell types in treatment strategy development, and ultimately achieve desired therapeutic effects.

Dichloroacetate and cancer: new home for an orphan drug?

We reviewed the anti-cancer effects of DCA, an orphan drug long used as an investigational treatment for various acquired and congenital disorders of mitochondrial intermediary metabolism. Inhibition by DCA of mitochondrial pyruvate dehydrogenase kinases and subsequent reactivation of the pyruvate dehydrogenase complex and oxidative phosphorylation is the common mechanism accounting for the drug's anti-neoplastic effects. At least two fundamental changes in tumor metabolism are induced by DCA that antagonize tumor growth, metastases and survival: the first is the redirection of glucose metabolism from glycolysis to oxidation (reversal of the Warburg effect), leading to inhibition of proliferation and induction of caspase-mediated apoptosis. These effects have been replicated in both human cancer cell lines and in tumor implants of diverse germ line origin. The second fundamental change is the oxidative removal of lactate, via pyruvate, and the co-incident buffering of hydrogen ions by dehydrogenases located in the mitochondrial matrix. Preclinical studies demonstrate that DCA has additive or synergistic effects when used in combination with standard agents designed to modify tumor oxidative stress, vascular remodeling, DNA integrity or immunity. These findings and limited clinical results suggest that potentially fruitful areas for additional clinical trials include 1) adult and pediatric high grade astrocytomas; 2) BRAF-mutant cancers, such as melanoma, perhaps combined with other pro-oxidants; 3) tumors in which resistance to standard platinum-class drugs alone may be overcome with combination therapy; and 4) tumors of endodermal origin, in which extensive experimental research has demonstrated significant anti-proliferative, pro-apoptotic effects of DCA, leading to improved host survival.

Association of oncolytic adenoviruses with chemotherapies: an overview and future directions

Oncolytic adenoviruses have been used in different preclinical and clinical studies, showing their capacity to kill tumor cells without major adverse events. However, these studies also underline the limitations of this approach. The efficacy of oncolytic adenoviruses is hampered by their limited ability to transduce some tumor types, their lack of selectivity, and their poor dissemination within tumors. In addition, the host immune response may limit oncolytic adenovirus efficacy. Combining oncolytic adenoviruses with chemotherapeutics constitutes an appealing strategy to increase their potency. The first part of this review describes the molecular basis of oncolytic adenoviruses, their use in preclinical studies and clinical trials, their limitations, and strategies to circumvent these limitations. The second part will focus on studies combining oncolytic adenoviruses with chemotherapeutic drugs, including standard chemotherapeutic drugs, molecularly targeted drugs, and other drugs that have been combined with oncolytic adenoviruses. Finally, based on these studies, we describe future directions and general rules that could be followed to identify chemotherapeutic drugs displaying additive/synergistic effects when combined with oncolytic adenoviruses.

Molecular targets and signaling pathways regulated by interleukin (IL)-24 in mediating its antitumor activities

Cancer remains a major health issue in the world and the effectiveness of current therapies is limited resulting in disease recurrence and resistance to therapy. Therefore to overcome disease recurrence and have improved treatment efficacy there is a continued effort to develop and test new anticancer drugs that are natural or synthetic - (conventional chemotherapeutics, small molecule inhibitors) and biologic (antibody, tumor suppressor genes, oligonucleotide) product. In parallel, efforts for identifying molecular targets and signaling pathways to which cancer cells are "addicted" are underway. By inhibiting critical signaling pathways that is crucial for cancer cell survival, it is expected that the cancer cells will undergo a withdrawal symptom akin to "de-addiction" resulting in cell death. Thus, the key for having an improved and greater control on tumor growth and metastasis is to develop a therapeutic that is able to kill tumor cells efficiently by modulating critical signaling pathways on which cancer cells rely for their survival.Currently several small molecule inhibitors targeted towards unique molecular signaling pathways have been developed and tested in the clinic. Few of these inhibitors have shown efficacy while others have failed. Thus, targeting a single molecule or pathway may be insufficient to completely block cancer cell proliferation and survival. It is therefore important to identify and test an anticancer drug that can inhibit multiple signaling pathways in a cancer cell, control growth of both primary and metastatic tumors and is safe.One biologic agent that has the characteristics of serving as a potent anticancer drug is interleukin (IL)-24. IL-24 suppresses multiple signaling pathways in a broad-spectrum of human cancer cells leading to tumor cell death, inhibition of tumor angiogenesis and metastasis. Additionally, combining IL-24 with other therapies demonstrated additive to synergistic antitumor activity. Clinical testing of IL-24 as a gene-based therapeutic for the treatment of solid tumors demonstrated that IL-24 is efficacious and is safe. The unique features of IL-24 support its further development as an anticancer drug for cancer treatment.In this review we summarize the current understanding on the molecular targets and signaling pathways regulated by IL-24 in mediating its anticancer activity.

DCA increases the antitumor effects of capecitabine in a mouse B16 melanoma allograft and a human non-small cell lung cancer A549 xenograft

PURPOSE

Capecitabine is one of the few chemotherapy drugs with high oral availability. Recently, sodium dichloroacetate (DCA) has shown great potential as an anticancer agent. In the present study, we assessed the anticancer effect of DCA in combination with capecitabine for cancers that modestly expressed TP.

METHODS

A mouse B16 melanoma allograft and a human non-small cell lung cancer A549 xenograft were used to assess the effect of DCA and capecitabine combined treatment. Histology and immunohistochemistry were used to detect the apoptosis and proliferation of cancer cells. Real-time PCR and Western blot were carried out to detect the expression of TP and caspases, respectively.

RESULTS

For the first time, we report that DCA increased the antitumor effects of capecitabine in a mouse B16 allograft and a human A549 xenograft by promoting apoptosis of tumor cells. DCA has little effect on the expression of TP.

CONCLUSIONS

Our finding suggests that DCA in combination with capecitabine might be potential as a new therapeutic regimen against some cancers.

Chapter One---Cancer terminator viruses and approaches for enhancing therapeutic outcomes

No single or combinatorial therapeutic approach has proven effective in decreasing morbidity or engendering a cure of metastatic cancer. In principle, conditionally replication-competent adenoviruses that induce tumor oncolysis through cancer-specific replication hold promise for cancer therapy. However, a single-agent approach may not be adequate to completely eradicate cancer in a patient because most cancers arise from abnormalities in multiple genetic and signal transduction pathways and targeting disseminated metastases is difficult to achieve. Based on these considerations, a novel class of cancer destroying adenoviruses have been produced, cancer terminator viruses (CTVs), in which cancer-specific replication is controlled by the progression-elevated gene-3 promoter and replicating viruses produce a second transgene encoding an apoptosis-inducing and immunomodulatory cytokine, either melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24) or interferon-γ. This review focuses on these viruses and ways to improve their delivery systemically and enhance their therapeutic efficacy.

Complete eradication of hepatomas using an oncolytic adenovirus containing AFP promoter controlling E1A and an E1B deletion to drive IL-24 expression

Interleukin (IL)-24, a promising therapeutic gene, has been widely used for Cancer Targeting Gene-Viro-Therapy (CTGVT). In this study, IL-24 was inserted into an oncolytic adenovirus in which the E1A gene is driven by an enhanced, short α-fetoprotein (AFP) promoter and the E1B gene is completely deleted to form Ad.enAFP-E1A-ΔE1B-IL-24. This construct has a potent antitumor effect on liver cancer cell lines in vitro, but little or no effect on normal cell lines, such as L-02 and QSG-7701. In vivo, the complete elimination of Huh-7 liver cancer in nude mice with Ad.enAFP-E1A-ΔE1B-IL-24 intratumor injection was observed. The design of Ad.enAFP-E1A-ΔE1B-IL-24 and its potent antitumor effect on liver cancer have not been published previously. The mechanism of the potent antitumor effect of Ad.enAFP-E1A-ΔE1B-IL-24 is due to the upregulation of GADD34 and intrinsic and extrinsic apoptotic signaling.

Mitochondrial remodeling in cancer metabolism and survival: potential for new therapies

Mitochondria are semi-autonomous organelles that play essential roles in cellular metabolism and programmed cell death pathways. Genomic, functional and structural mitochondrial alterations have been associated with cancer. Some of those alterations may provide a selective advantage to cells, allowing them to survive and grow under stresses created by oncogenesis. Due to the specific alterations that occur in cancer cell mitochondria, these organelles may provide promising targets for cancer therapy. The development of drugs that specifically target metabolic and mitochondrial alterations in tumor cells has become a matter of interest in recent years, with several molecules undergoing clinical trials. This review focuses on the most relevant mitochondrial alterations found in tumor cells, their contribution to cancer progression and survival, and potential usefulness for stratification and therapy.

Conditionally replicating adenoviruses carrying mda-7/IL-24 for cancer therapy

BACKGROUND

Melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) suppresses growth and induces apoptosis in a broad range of human cancers without significant cytotoxicity to normal cells. Conditionally replicating adenoviruses (CRAds) not only have the ability to destroy cancer cells but may also be potential vectors for the expression of therapeutic genes.

METHODS

This review provides an overview of specifications for a novel anti-tumor approach CRAds carrying IL-24, and discusses recent progress in this field.

RESULTS

Studies in multiple laboratories report that CRAds carrying IL-24 selectively induced apoptosis in some cancer cells, and enhanced selective toxicity to cancer cells when combined with chemotherapeutic agents.

CONCLUSION

CRAds carrying IL-24 may prove a novel and effective approach for the treatment of cancers.

Dichloroacetate Induces Different Rates of Cell Death in Cancer and Noncancer Cell Lines in Vitro

Aims and Background

The pyruvate mimetic dichloroacetate (DCA) has been shown to induce cell death in cancer cells. A number of studies in vitro and in vivo have suggested this molecule may serve as an anticancer agent, but some cells are resistant. Here we wanted to examine the effects of DCA on cancerous and noncancerous cells grown in culture for a prolonged period of exposure and at increasing concentrations.

Methods

Six cancer cell lines (A549, SK-HEP-1, HCT116, UPCI:SCC070, HeLa and MES-SA) and three noncancerous lines (RPE, GM03349B and HEK293) were exposed to 0.5 mM DCA for seven days and cell counts were taken every day to determine viability and cell cycle progression. The same cell lines were also exposed to higher doses of DCA up to 10 mM and viability was scored.

Results

Five cancer cell lines showed high levels of cell death early in the trial, but three of the lines showed a second delayed increase in cell death at later stages. HCT116 cells were unaffected by 0.5 mM DCA. GM03349B and RPE cells also died when treated with DCA. At high concentrations, all cell lines exhibited high rates of death. No specific cell cycle arrest of the cells was observed.

Conclusion

We found that there is considerable difference in the way cancer cells are affected by DCA. Some have populations that are highly resistant to treatment, while others have stronger rates of death only after prolonged exposure. We also found noncancerous cells are not all resistant to DCA, a significant finding that has not previously been observed in other in vitro DCA trials.

In vitro effects of an in silico-modelled 17β-estradiol derivative in combination with dichloroacetic acid on MCF-7 and MCF-12A cells

OBJECTIVES

  To investigate anti-proliferative properties of a novel in silico-modelled 17β-oestradiol derivative (C9), in combination with dichloroacetic acid (DCA), on MCF-7 and MCF-12A cells.

MATERIALS AND METHODS

  xCELLigence system was employed to determine optimal seeding number for cells, and crystal violet assay was used to assess cell number and to determine IC(50) value (24 h) for combination treatment. Light and fluorescent microscopy techniques were used to morphologically detect types of cell death. Flow cytometry was used to analyse cell cycle and apoptosis.

RESULTS

  Optimal seeding number for 96-well plates was determined to be 5000-10 000 cells/well for both MCF-7 and MCF-12A cells. IC(50) for MCF-7 cells of the combination treatment after 24 h was 130 nm of C9 in conjunction with 7.5 mm of DCA (P < 0.05). In contrast, the same concentration inhibited cell population growth by only 29.3% for MCF-12As after 24-h treatment (P < 0.05). Morphological studies revealed lower cell density of both types of combination-treated cells. Flow cytometric analyses demonstrated increase in sub-G(1) phase in combination-treated MCF-7 cells.

CONCLUSIONS

  These results demonstrate that the novel 17β-oestradiol derivative C9, in combination with DCA is a potent anti-proliferation treatment, with properties of selectivity towards tumourigenic cells. Thus, this warrants further studies as a potential combination chemotherapeutic agent for further cancer cell lines.

Role of SLC5A8, a plasma membrane transporter and a tumor suppressor, in the antitumor activity of dichloroacetate

There has been growing interest among the public and scientists in dichloroacetate as a potential anticancer drug. Credible evidence exists for the antitumor activity of this compound, but high concentrations are needed for significant therapeutic effect. Unfortunately, these high concentrations produce detrimental side effects involving nervous system, thereby precluding its use for cancer treatment. The mechanistic basis of the compound’s antitumor activity is its ability to activate pyruvate dehydrogenase complex through inhibition of pyruvate dehydrogenase kinase. Since the compound inhibits the kinase at micromolar concentrations, it is not known why therapeutically prohibitive high doses are needed for suppression of tumor growth. We hypothesized that lack of effective mechanisms for the entry of dichloroacetate into tumor cells may underlie this phenomenon. Here we show that SLC5A8 transports dichloroacetate very effectively with high affinity. This transporter is expressed in normal cells, but the expression is silenced in tumor cells via epigenetic mechanisms. The lack of the transporter makes tumor cells resistant to the antitumor activity of dichloroacetate. However, if the transporter is expressed in tumor cells ectopically, the cells become sensitive to the drug at low concentrations. This is evident in breast cancer cells, colon cancer cells, and prostate cancer cells. Normal cells, which constitutively express the transporter, are however not affected by the compound, indicating the tumor cell-selective therapeutic activity. The mechanism of the antitumor activity of the compound is still its ability to inhibit pyruvate dehydrogenase kinase and force mitochondrial oxidation of pyruvate. Since the silencing of SLC5A8 in tumors involves DNA methylation and its expression can be induced by treatment with DNA methylation inhibitors, our findings suggest that combining dichloroacetate with a DNA methylation inhibitor would offer a means to reduce the doses of dichloroacetate to avoid detrimental effects associated with high doses but without compromising antitumor activity.