Cystathionine-beta-synthase inhibition for colon cancer: Enhancement of the efficacy of aminooxyacetic acid via the prodrug approach

Upregulation of Cystathionine-β-Synthase in Colonic Epithelia Reprograms Metabolism and Promotes Carcinogenesis

The trans-sulfuration enzyme cystathionine-β-synthase (CBS) and its product hydrogen sulfide (H2S) are aberrantly upregulated in colorectal cancers, where they contribute to tumor growth and progression by both autocrine and paracrine mechanisms. However, it is unknown whether the CBS/H2S axis plays a role in colorectal carcinogenesis. Here, we report upregulation of CBS in human biopsies of precancerous adenomatous polyps and show that forced upregulation of CBS in an adenoma-like colonic epithelial cell line is sufficient to induce metabolic and gene expression profiles characteristic of colorectal cancer cells. Differentially expressed metabolites (65 increased and 20 decreased) clustered into the glycolytic pathway, nucleotide sugars, intermediates of the pentose phosphate pathway, and lipogenesis, including primarily phospholipids, sphingolipids, and bile acids. CBS upregulation induced broad changes in the NCM356 cell transcriptome with over 350 differentially expressed genes. These genes overlapped significantly with gene sets related to glycolysis, hypoxia, and a colon cancer cell phenotype, including genes regulated by NF-κB, KRAS, p53, and Wnt signaling, genes downregulated after E-cadherin knockdown, and genes related to increased extracellular matrix, cell adhesion, and epithelial-to-mesenchymal transition. The CBS-induced switch to an anabolic metabolism was associated with increased NCM356 cell bioenergetics, proliferation, invasion through Matrigel, resistance to anoikis, and CBS-dependent tumorigenesis in immunocompromised mice. Genetic ablation of CBS in CBS heterozygous mice (CBS^+/- ) reduced the number of mutagen-induced aberrant colonic crypt foci. Taken together, these results establish that activation of the CBS/H2S axis promotes colon carcinogenesis. Cancer Res; 77(21); 5741-54. ©2017 AACR.

Consensus Molecular Subtypes of Colorectal Cancer and their Clinical Implications

The colorectal cancer (CRC) Subtyping Consortium has unified six independent molecular classification systems, based on gene expression data, into a single consensus system with four distinct groups, known as the Consensus Molecular Subtypes (CMS); clinical implications are discussed in this review. This article is based on a literature review relevant to the CMS of CRC indexed in PubMed (US National Library of Medicine) as well as the authors' own published data. The CMS were determined and correlated with epigenomic, transcriptomic, microenvironmental, genetic, prognostic and clinical characteristics. The CMS1 subtype is immunogenic and hypermutated. CMS2 tumors are activated by the WNT-β-catenin pathway and have the highest overall survival. CMS3 feature a metabolic cancer phenotype and CMS4 cancers have the worst survival and have a strong stromal gene signature. The Consensus Molecular Subtypes of CRC may better inform clinicians of prognosis, therapeutic response, and potential novel therapeutic strategies.

Vascular biology of hydrogen sulfide

Hydrogen sulfide (H2S) is a ubiquitous signaling molecule with important functions in many mammalian organs and systems. Observations in the 1990s ascribed physiological actions to H2S in the nervous system, proposing that this gasotransmitter acts as a neuromodulator. Soon after that, the vasodilating properties of H2S were demonstrated. In the past decade, H2S was shown to exert a multitude of physiological effects in the vessel wall. H2S is produced by vascular cells and exhibits antioxidant, antiapoptotic, anti-inflammatory, and vasoactive properties. In this concise review, we have focused on the impact of H2S on vascular structure and function with an emphasis on angiogenesis, vascular tone, vascular permeability and atherosclerosis. H2S reduces arterial blood pressure, limits atheromatous plaque formation, and promotes vascularization of ischemic tissues. Although the beneficial properties of H2S are well established, mechanistic insights into the molecular pathways implicated in disease prevention and treatment remain largely unexplored. Unraveling the targets and downstream effectors of H2S in the vessel wall in the context of disease will aid in translation of preclinical observations. In addition, acute regulation of H2S production is still poorly understood and additional work delineating the pathways regulating the enzymes that produce H2S will allow pharmacological manipulation of this pathway. As the field continues to grow, we expect that H2S-related compounds will find their way into clinical trials for diseases affecting the blood vessels.

H2S-induced S-sulfhydration of lactate dehydrogenase a (LDHA) stimulates cellular bioenergetics in HCT116 colon cancer cells

Cystathionine-β-synthase (CBS) is upregulated and hydrogen sulfide (H₂S) production is increased in colon cancer cells. The functional consequence of this response is stimulation of cellular bioenergetics and tumor growth and proliferation. Lactate dehydrogenase A (LDHA) is also upregulated in various colon cancer cells and has been previously implicated in tumor cell bioenergetics and proliferation. In the present study, we sought to determine the potential interaction between the H₂S pathway and LDH activity in the control of bioenergetics and proliferation of colon cancer, using the colon cancer line HCT116. Low concentrations of GYY4137 (a slow-releasing H₂S donor) enhanced mitochondrial function (oxygen consumption, ATP production, and spare respiratory capacity) and glycolysis in HCT116 cells. SiRNA-mediated transient silencing of LDHA attenuated the GYY4137-induced stimulation of mitochondrial respiration, but not of glycolysis. H₂S induced the S-sulfhydration of Cys163 in recombinant LDHA, and stimulated LDHA activity. The H₂S-induced stimulation of LDHA activity was absent in C163A LDHA. As shown in HCT116 cell whole extracts, in addition to LDHA activation, GYY4137 also stimulated LDHB activity, although to a smaller extent. Total cellular lactate and pyruvate measurements showed that in HCT116 cells LDHA catalyzes the conversion of pyruvate to lactate. Total cellular lactate levels were increased by GYY4137 in wild-type cells (but not in cells with LDHA silencing). LDHA silencing sensitized HCT116 cells to glucose oxidase (GOx)-induced oxidative stress; this was further exacerbated with GYY4137 treatment. Treatment with low concentrations of GYY4137 (0.3mM) or GOx (0.01U/ml) significantly increased the proliferation rate of HCT116 cells; the effect of GOx, but not the effect of GYY4137 was attenuated by LDHA silencing. The current report points to the involvement of LDHA in the stimulatory effect of H₂S on mitochondrial respiration in colon cancer cells and characterizes some of the functional interactions between LDHA and H₂S-stimulated bioenergetics under resting conditions, as well as during oxidative stress.

Cystathionine-gamma-lyase deficient mice are protected against the development of multiorgan failure and exhibit reduced inflammatory response during burn

Considering the role of H₂S in critical illness, the aim of this study was to compare the outcome of burn in wild-type mice and in mice deficient in CSE, one of the principal mammalian H₂S-generating enzymes. Animals were subjected to scald burn. Outcome variables included indices of organ injury, clinical chemistry parameters and plasma levels of inflammatory mediators. Plasma levels of H₂S significantly increased in response to burn in wild-type mice, but remained unchanged in CSE^-/- mice. Expression of the three H₂S-producing enzymes (CSE, CBS and 3-MST) in the lung and liver, and the capacity of tissue homogenates to produce H₂S, however, was not affected by burn. In CSE deficient mice there was a significant amelioration of burn-induced accumulation of myeloperoxidase levels in heart, lung, liver and kidney and significantly lower degree of malon dialdehyde accumulation in the heart, lung and kidney than in wild-type mice. CSE deficient mice, compared to wild-type mice, showed a significant attenuation of the burn-induced elevation in circulating alkaline aminotransferase and blood urea nitrogen and creatinine levels, indicative of protective effects of CSE deficiency against burn-induced hepatic, and renal functional impairment. Multiple burn-induced inflammatory mediators (TNF-α, IL-1β, IL-4, IL-6, IL-10 and IL-12) were significantly lower in the plasma of CSE^-/- animals after burn than in the plasma of wild-type controls subjected to burns. In conclusion, CSE deficiency improves organ function and attenuates the inflammatory response in a murine model of burn.

Development of a stretch-induced neurotrauma model for medium-throughput screening in vitro: identification of rifampicin as a neuroprotectant

BACKGROUND AND PURPOSE

We hypothesized that an in vitro, stretch-based model of neural injury may be useful to identify compounds that decrease the cellular damage in neurotrauma.

EXPERIMENTAL APPROACH

We screened three neural cell lines (B35, RN33B and SH-SY5Y) subjected to two differentiation methods and selected all-trans-retinoic acid-differentiated B35 rat neuroblastoma cells subjected to rapid stretch injury, coupled with a subthreshold concentration of H₂ O₂ , for the screen. The model induced marked alterations in gene expression and proteomic signature of the cells and culminated in delayed cell death (LDH release) and mitochondrial dysfunction [reduced 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) conversion]. Follow-up studies utilized human stem cell-derived neurons subjected to rapid stretch injury.

KEY RESULTS

From screening of a composite library of 3500 drugs, five drugs (when applied in a post-treatment regimen relative to stretch injury) improved both LDH and MTT responses. The effects of rifampicin were investigated in further detail. Rifampicin reduced cell necrosis and apoptosis and improved cellular bioenergetics. In a second model (stretch injury in human stem cell-derived neurons), rifampicin pretreatment attenuated LDH release, protected against the loss of neurite length and maintained neuron-specific class III β-tubulin immunoreactivity.

CONCLUSIONS AND IMPLICATIONS

We conclude that the current model is suitable for medium-throughput screening to identify compounds with neuroprotective potential. Rifampicin, when applied either in pre- or post-treatment, improves the viability of neurons subjected to stretch injury and protects against neurite loss. Rifampicin may be a candidate for repurposing for the therapy of traumatic brain injury.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Screening of a composite library of clinically used drugs and well-characterized pharmacological compounds for cystathionine β-synthase inhibition identifies benserazide as a drug potentially suitable for repurposing for the experimental therapy of colon cancer

Cystathionine-β-synthase (CBS) has been recently identified as a drug target for several forms of cancer. Currently no potent and selective CBS inhibitors are available. Using a composite collection of 8871 clinically used drugs and well-annotated pharmacological compounds (including the LOPAC library, the FDA Approved Drug Library, the NIH Clinical Collection, the New Prestwick Chemical Library, the US Drug Collection, the International Drug Collection, the ‘Killer Plates’ collection and a small custom collection of PLP-dependent enzyme inhibitors), we conducted an in vitro screen in order to identify inhibitors for CBS using a primary 7-azido-4-methylcoumarin (AzMc) screen to detect CBS-derived hydrogen sulfide (H₂S) production. Initial hits were subjected to counterscreens using the methylene blue assay (a secondary assay to measure H₂S production) and were assessed for their ability to quench the H₂S signal produced by the H₂S donor compound GYY4137. Four compounds, hexachlorophene, tannic acid, aurintricarboxylic acid and benserazide showed concentration-dependent CBS inhibitory actions without scavenging H₂S released from GYY4137, identifying them as direct CBS inhibitors. Hexachlorophene (IC₅₀: ∼60 μM), tannic acid (IC₅₀: ∼40 μM) and benserazide (IC₅₀: ∼30 μM) were less potent CBS inhibitors than the two reference compounds AOAA (IC₅₀: ∼3 μM) and NSC67078 (IC₅₀: ∼1 μM), while aurintricarboxylic acid (IC₅₀: ∼3 μM) was equipotent with AOAA. The second reference compound NSC67078 not only inhibited the CBS-induced AzMC fluorescence signal (IC₅₀: ∼1 μM), but also inhibited with the GYY4137-induced AzMC fluorescence signal with (IC₅₀ of ∼6 μM) indicative of scavenging/non-specific effects. Hexachlorophene (IC₅₀: ∼6 μM), tannic acid (IC₅₀: ∼20 μM), benserazide (IC₅₀: ∼20 μM), and NSC67078 (IC₅₀: ∼0.3 μM) inhibited HCT116 colon cancer cells proliferation with greater potency than AOAA (IC₅₀: ∼300 μM). In contrast, although a CBS inhibitor in the cell-free assay, aurintricarboxylic acid failed to inhibit HCT116 proliferation at lower concentrations, and stimulated cell proliferation at 300 μM. Copper-containing compounds present in the libraries, were also found to be potent inhibitors of recombinant CBS; however this activity was due to the CBS inhibitory effect of copper ions themselves. However, copper ions, up to 300 μM, did not inhibit HCT116 cell proliferation. Benserazide was only a weak inhibitor of the activity of the other H₂S-generating enzymes CSE and 3-MST activity (16% and 35% inhibition at 100 μM, respectively) in vitro. Benserazide suppressed HCT116 mitochondrial function and inhibited proliferation of the high CBS-expressing colon cancer cell line HT29, but not the low CBS-expressing line, LoVo. The major benserazide metabolite 2,3,4-trihydroxybenzylhydrazine also inhibited CBS activity and suppressed HCT116 cell proliferation in vitro. In an in vivo study of nude mice bearing human colon cancer cell xenografts, benserazide (50 mg/kg/day s.q.) prevented tumor growth. In silico docking simulations showed that benserazide binds in the active site of the enzyme and reacts with the PLP cofactor by forming reversible but kinetically stable Schiff base-like adducts with the formyl moiety of pyridoxal. We conclude that benserazide inhibits CBS activity and suppresses colon cancer cell proliferation and bioenergetics in vitro, and tumor growth in vivo. Further pharmacokinetic, pharmacodynamic and preclinical animal studies are necessary to evaluate the potential of repurposing benserazide for the treatment of colorectal cancers.