A Fast Hydrogen Sulfide-Releasing Donor Increases the Tumor Response to Radiotherapy

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Co-assembled Nanocarriers of De Novo Thiol-Activated Hydrogen Sulfide Donors with an RGDFF Pentapeptide for Targeted Therapy of Non-Small-Cell Lung Cancer

Hydrogen sulfide releasing agents (or H₂S donors) have been recognized gasotransmitters with potent cytoprotective and anticancer properties. However, the clinical application of H₂S donors has been hampered by their fast H₂S-release, instability, and lack of tumor targeting, despite the unclear molecular mechanism of H₂S action. Here we rationally designed an amphiphilic pentapeptide (RGDFF) to coassemble with the de novo designed thiol-activated H₂S donors (CL2/3) into nanocarriers for targeted therapy of non-small-cell lung cancer, which has been proved as a one-stone-three-birds strategy. The coassembly approach simply solved the solubility issue of CL2/3 by the introduction of electron-donating groups (phenyl rings) to slow down the H₂S release while dramatically improving their biocompatible interface, circulation time, slow release of H₂S, and tumor targeting. Experimental results confirmed that as-prepared coassembled nanocarriers can significantly induce the intrinsic apoptotic, effectively arrest cell cycle at the G2/M phase, inhibit H₂S-producing enzymes, and lead to mitochondrial dysfunction by increasing intracellular ROS production in H1299 cells. The mouse tumorigenesis experiments further confirmed the in vivo anticancer effects of the coassembled nanocarriers, and such treatment made tumors more sensitive to radiotherapy then improved the prognosis of tumor-bearing mice, which holds great promise for developing a new combined approach for NSCLC.

A nitric oxide and hydrogen sulfide dual-donating nanosystem for highly synergistic gas-radiotherapy against hepatocellular carcinoma

A drug delivery system (DDS) based on gold-capped mesoporous silica nanoparticles (MSN) is fabricated for loading NOSH-aspirin, a nitric oxide (NO) and hydrogen sulfide (H₂S) dual-donating cytotoxic molecule. The liver targeting and tumor microenvironment responsive properties of the nanosystem enable, for the first time, the concurrent delivery of NO and H₂S from a DDS into hepatocellular carcinoma (HCC) cells. Combined gas-radiotherapy (GT-RT) from drug-loaded DDS (NOSH@MSN-Au-Gal) and X-ray irradiation shows highly synergistic anti-cancer activity against both normoxic and hypoxic HCC cells. Further studies revealed that the combined GT-RT not only retains the well-known anticancer mechanism of NO, H₂S, and X-ray individually, but also alleviates HCC hypoxia via NO- and H₂S- involved unique pathways. In mice, the GT-RT greatly slows the growth of both subcutaneous and orthotopic HCC tumors and shows high biocompatibility. The current work is expected to promote the clinical application of combined GT-RT as an effective cancer treatment.

EPR Investigations to Study the Impact of Mito-Metformin on the Mitochondrial Function of Prostate Cancer Cells

Background: Mito-metformin10 (MM10), synthesized by attaching a triphenylphosphonium cationic moiety via a 10-carbon aliphatic side chain to metformin, is a mitochondria-targeted analog of metformin that was recently demonstrated to alter mitochondrial function and proliferation in pancreatic ductal adenocarcinoma. Here, we hypothesized that this compound may decrease the oxygen consumption rate (OCR) in prostate cancer cells, increase the level of mitochondrial ROS, alleviate tumor hypoxia, and radiosensitize tumors. Methods: OCR and mitochondrial superoxide production were assessed by EPR (9 GHz) in vitro in PC-3 and DU-145 prostate cancer cells. Reduced and oxidized glutathione were assessed before and after MM10 exposure. Tumor oxygenation was measured in vivo using 1 GHz EPR oximetry in PC-3 tumor model. Tumors were irradiated at the time of maximal reoxygenation. Results: 24-hours exposure to MM10 significantly decreased the OCR of PC-3 and DU-145 cancer cells. An increase in mitochondrial superoxide levels was observed in PC-3 but not in DU-145 cancer cells, an observation consistent with the differences observed in glutathione levels in both cancer cell lines. In vivo, the tumor oxygenation significantly increased in the PC-3 model (daily injection of 2 mg/kg MM10) 48 and 72 h after initiation of the treatment. Despite the significant effect on tumor hypoxia, MM10 combined to irradiation did not increase the tumor growth delay compared to the irradiation alone. Conclusions: MM10 altered the OCR in prostate cancer cells. The effect of MM10 on the superoxide level was dependent on the antioxidant capacity of cell line. In vivo, MM10 alleviated tumor hypoxia, yet without consequence in terms of response to irradiation.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

H2S Protects Against Immobilization-Induced Muscle Atrophy via Reducing Oxidative Stress and Inflammation

Chronic inflammation and oxidative stress are major triggers of the imbalance between protein synthesis and degradation during the pathogenesis of immobilization-induced muscle atrophy. This study aimed to elucidate the effects of hydrogen sulfide (H2S), a gas transmitter with potent anti-inflammatory and antioxidant properties, on immobilization-induced muscle atrophy. Mice were allocated to control and immobilization (IM) groups, which were treated with slow (GYY4137) or rapid (NaHS) H2S releasing donors for 14 days. The results showed that both GYY4137 and NaHS treatment reduced the IM-induced muscle loss, and increased muscle mass. The IM-induced expressions of Muscle RING finger 1 (MuRF1) and atrogin-1, two muscle-specific E3 ubiquitin ligases, were decreased by administration of GYY4137 or NaHS. Both GYY4137 and NaHS treatments alleviated the IM-induced muscle fibrosis, as evidenced by decreases in collagen deposition and levels of tissue fibrosis biomarkers. Moreover, administration of GYY4137 or NaHS alleviated the IM-induced infiltration of CD45 + leukocytes, meanwhile inhibited the expressions of the pro-inflammatory biomarkers in skeletal muscles. It was found that administration of either GYY4137 or NaHS significantly attenuated immobilization-induced oxidative stress as indicated by decreased H2O2 levels and 8-hydroxy-2′-deoxyguanosine (8-OHdG) immunoreactivity, as well as increased total antioxidant capacity (T-AOC), nuclear factor erythroid-2-related factor 2 (NRF2) and NRF2 downstream anti-oxidant targets levels in skeletal muscles. Collectively, the present study demonstrated that treatment with either slow or rapid H2S releasing donors protected mice against immobilization-induced muscle fibrosis and atrophy. The beneficial effects of H2S on immobilization-induced skeletal muscle atrophy might be due to both the anti-inflammatory and anti-oxidant properties of H2S.

Measurement of Mitochondrial (Dys)Function in Cellular Systems Using Electron Paramagnetic Resonance (EPR): Oxygen Consumption Rate and Superoxide Production

The oxygen consumption rate (OCR) and superoxide production are crucial when assessing mitochondrial function and/or dysfunction. EPR spectroscopy allows the measurement of both components either independently or simultaneously in a same cellular or mitochondrial preparation. OCR determination using EPR oximetry is based on the change in EPR linewidth of a paramagnetic oxygen sensing probe (a perdeuterated nitroxide) in the presence of oxygen consuming cells in a closed system. Superoxide production can be monitored by the oxidation of cyclic hydroxylamines into nitroxides. The contribution of superoxide to the nitroxide formation is deduced from experiments in the presence and in the absence of SOD and PEG-SOD as appropriate controls.

Role of hydrogen sulfide donors in cancer development and progression

In recent years, a vast number of potential cancer therapeutic targets have emerged. However, developing efficient and effective drugs for the targets is of major concern. Hydrogen sulfide (H2S), one of the three known gasotransmitters, is involved in the regulation of various cellular activities such as autophagy, apoptosis, migration, and proliferation. Low production of H2S has been identified in numerous cancer types. Treating cancer cells with H2S donors is the common experimental technique used to improve H2S levels; however, the outcome depends on the concentration/dose, time, cell type, and sometimes the drug used. Both natural and synthesized donors are available for this purpose, although their effects vary independently ranging from strong cancer suppressors to promoters. Nonetheless, numerous signaling pathways have been reported to be altered following the treatments with H2S donors which suggest their potential in cancer treatment. This review will analyze the potential of H2S donors in cancer therapy by summarizing key cellular processes and mechanisms involved.

The clinical utility of imaging methods used to measure hypoxia in cervical cancer

While it is well-established that hypoxia is a major factor that affects clinical outcomes in cervical cancer, widespread usage of clinically available methods to detect and evaluate hypoxia during the course of treatment have not been established. This review compares these methods, summarizes their strengths and weaknesses, and assesses the pathways for their useful employment to alter clinical practice. We conducted a search on PubMed for literature pertaining to imaging hypoxic cervical cancer, and implemented keywords related to oxygen measurement tools to improve the relevance of the search results.Oxygenation level-dependent applications of MRI have demonstrated hypoxia-induced radioresistance, and changes in cervix tumor oxygenation from hyperoxic therapy.The hypoxic areas within tumors can be indirectly identified in dynamic contrast-enhanced images, where they generally display low signal enhancement, and diffusion-weighted images, which demonstrates areas of restricted diffusion (which correlates with hypoxia). Positron emmision tomography, used independently and with other imaging modalities, has demonstrated utility in imaging hypoxia through tracers specific for low oxygen levels, like Cu-ATSM tracers and nitroimidazoles. Detecting hypoxia in the tumors of patients diagnosed with cervical cancer via medical imaging and non-imaging tools like electron paramagnetic resonance oximetry can be utilized clinically, such as for guiding radiation and post-treatment surveillance, for a more personalized approach to treatment. The merits of these methods warrant further investigation via comparative effectiveness research and large clinical trials into their clinical applications.

Hydrogen sulfide and its donors: Novel antitumor and antimetastatic therapies for triple-negative breast cancer

Hydrogen sulfide (H₂S) is considered as a novel second-messenger molecule associated with the modulation of various physiological and pathological processes. In the field of antitumor research, endogenous H₂S induces angiogenesis, accelerates the cell cycle and inhibits apoptosis, which results in promoting oncogenesis eventually. Interestingly, high concentrations of exogenous H₂S liberated from donors suppress the growth of various tumors via inducing cellular acidification and modulating several signaling pathways involved in cell cycle regulation, proliferation, apoptosis and metastasis. The selective release of certain concentrations of H₂S from H₂S donors in the target has been considered as an alternative tumor therapy strategy. Triple-negative breast cancer (TNBC), an aggressive subtype with less than one year median survival time, is known to account for approximately 15–20% of all breast cancers. Due to the lack of approved targeted therapy, the clinical treatment of TNBC is still hindered by metastasis as well as recurrence. Significant efforts have been spent on developing novel treatments of TNBC, and remarkable progress in the control of TNBC by H₂S donors and their derivatives have been made in recent years. This review summarizes various pathways involved in antitumor and anti-metastasis effects of H₂S donors and their derivatives on TNBC, which provides novel insights for TNBC treatment.

H2S mediates apoptosis in response to inflammation through PI3K/Akt/NFκB signaling pathway

OBJECTIVES

Hydrogen sulfide (H₂S) is involved in regulating cell apoptosis and proliferation. However, The effects and mechanism of H₂S on the apoptosis of mammary epithelial cells that suffer from an inflammatory response remain unknown.

RESULTS

An inflammatory cell model was used to explore whether exogenous H₂S regulates lipopolysaccharides (LPS)-induced cell proliferation and apoptosis. We found that H₂S affected cell viability, the inflammatory response and apoptosis in LPS-treated cells in a concentration-dependent manner. Moreover, exogenous H₂S rescued LPS-induced cystathionine γ-lyase (CSE) inhibition and cystathionine β-synthase (CBS) synthesis. Interestingly, in cells undergoing inflammation-induced apoptosis, H₂S activated the PI3K/Akt and NFκB signal pathways both tested concentrations. Akt appeared to be a key crosstalk molecule that played a "bridge" role.

CONCLUSIONS

H₂S regulates LPS-induced inflammation and apoptosis by activating the PI3K/Akt/NFκB signaling pathway. Hence, NaHS may be clinically useful for preventing or treating mastitis.

Breaking the Depth Dependence by Nanotechnology-Enhanced X-Ray-Excited Deep Cancer Theranostics

The advancements in nanotechnology have created multifunctional nanomaterials aimed at enhancing diagnostic accuracy and treatment efficacy for cancer. However, the ability to target deep-seated tumors remains one of the most critical challenges for certain nanomedicine applications. To this end, X-ray-excited theranostic techniques provide a means of overcoming the limits of light penetration and tissue attenuation. Herein, a comprehensive overview of the recent advances in nanotechnology-enhanced X-ray-excited imaging and therapeutic methodologies is presented, with an emphasis on the design of multifunctional nanomaterials for contrast-enhanced computed tomography (CT) imaging, X-ray-excited optical luminescence (XEOL) imaging, and X-ray-excited multimodal synchronous/synergistic therapy. The latter is based on the concurrent use of radiotherapy with chemotherapy, gas therapy, photodynamic therapy, or immunotherapy. Moreover, the featured biomedical applications of X-ray-excited deep theranostics are discussed to highlight the advantages of X-ray in high-sensitivity detection and efficient elimination of malignant tumors. Finally, key issues and technical challenges associated with this deep theranostic technology are identified, with the intention of advancing its translation into the clinic.

Impact of myo-inositol trispyrophosphate (ITPP) on tumour oxygenation and response to irradiation in rodent tumour models

Tumour hypoxia is a well-established factor of resistance in radiation therapy (RT). Myo-inositol trispyrophosphate (ITPP) is an allosteric effector that reduces the oxygen-binding affinity of haemoglobin and facilitates the release of oxygen by red blood cells. We investigated herein the oxygenation effect of ITPP in six tumour models and its radiosensitizing effect in two of these models. The evolution of tumour pO₂ upon ITPP administration was monitored on six models using 1.2 GHz Electron Paramagnetic Resonance (EPR) oximetry. The effect of ITPP on tumour perfusion was assessed by Hoechst staining and the oxygen consumption rate (OCR) in vitro was measured using 9.5 GHz EPR. The therapeutic effect of ITPP with and without RT was evaluated on rhabdomyosarcoma and 9L-glioma rat models. ITPP enhanced tumour oxygenation in six models. The administration of 2 g/kg ITPP once daily for 2 days led to a tumour reoxygenation for at least 4 days. ITPP reduced the OCR in six cell lines but had no effect on tumour perfusion when tested on 9L-gliomas. ITPP plus RT did not improve the outcome in rhabdomyosarcomas. In 9L-gliomas, some of tumours receiving the combined treatment were cured while other tumours did not benefit from the treatment. ITPP increased oxygenation in six tumour models. A decrease in OCR could contribute to the decrease in tumour hypoxia. The association of RT with ITPP was beneficial for a few 9L-gliomas but was absent in the rhabdomyosarcomas.

Transcutaneous oxygen measurement in humans using a paramagnetic skin adhesive film

PURPOSE

Transcutaneous oxygen tension (TcpO₂ ) provides information about blood perfusion in the tissue immediately below the skin. These data are valuable in assessing wound healing problems, diagnosing peripheral vascular/arterial insufficiency, and predicting disease progression or the response to therapy. Currently, TcpO₂ is primarily measured using electrochemical skin sensors, which consume oxygen and are prone to calibration errors. The goal of the present study was to develop a reliable method for TcpO₂ measurement in human subjects.

METHODS

We have developed a novel TcpO₂ oximetry method based on electron paramagnetic resonance (EPR) principles with an oxygen-sensing skin adhesive film, named the superficial perfusion oxygen tension (SPOT) chip. The SPOT chip is a 3-mm diameter, 60-μm thick circular film composed of a stable paramagnetic oxygen sensor. The chip is covered with an oxygen-barrier material on one side and secured on the skin by a medical adhesive transfer tape to ensure that only the oxygen that diffuses through the skin surface is measured. The method quantifies TcpO₂ through the linewidth of the EPR spectrum.

RESULTS

Repeated measurements using a cohort of 10 healthy human subjects showed that the TcpO₂ measurements were robust, reliable, and reproducible. The TcpO₂ values ranged from 7.8 ± 0.8 to 22.0 ± 1.0 mmHg in the volar forearm skin (N = 29) and 8.1 ± 0.3 to 23.4 ± 1.3 mmHg in the foot (N = 86).

CONCLUSIONS

The results demonstrated that the SPOT chip can measure TcpO₂ reliably and repeatedly under ambient conditions. The SPOT chip method could potentially be used to monitor TcpO₂ in the clinic.

The dichotomous role of H2S in cancer cell biology? Déjà vu all over again

Nitric oxide (NO) a gaseous free radical is one of the ten smallest molecules found in nature, while hydrogen sulfide (H2S) is a gas that bears the pungent smell of rotten eggs. Both are toxic yet they are gasotransmitters of physiological relevance. There appears to be an uncanny resemblance between the general actions of these two gasotransmitters in health and disease. The role of NO and H2S in cancer has been quite perplexing, as both tumor promotion and inflammatory activities as well as anti-tumor and antiinflammatory properties have been described. These paradoxes have been explained for both gasotransmitters in terms of each having a dual or biphasic effect that is dependent on the local flux of each gas. In this review/commentary, I have discussed the major roles of NO and H2S in carcinogenesis, evaluating their dual nature, focusing on the enzymes that contribute to this paradox and evaluate the pros and cons of inhibiting or inducing each of these enzymes.

Hydrogen sulphide donors selectively potentiate a green tea polyphenol EGCG-induced apoptosis of multiple myeloma cells

Hydrogen sulphide (H₂S) is a colourless gas with the odour of rotten eggs and has recently been recognized as a signal mediator in physiological activities related with the regulation of homeostasis, the vascular system and the inflammatory system. Here we show that H₂S donors, including sodium hydrogen sulphide (NaHS), GYY 4137 and diallyltrisulfide (DATS), synergistically enhanced the anti-cancer effect of a green tea polyphenol (−)-epigallocatechin-3-O-gallate (EGCG) against multiple myeloma cells without affecting normal cells. NaHS significantly potentiated the anti-cancer effect of EGCG and prolonged survival in a mouse xenograft model. In this mechanism, H₂S enhanced apoptotic cell death through cyclic guanosine monophosphate (cGMP)/acid sphingomyelinase pathway induced by EGCG. Moreover, NaHS reduced the enzyme activity of cyclic nucleotide phosphodiesterase that is known as cGMP negative regulator. In conclusion, we identified H₂S as a gasotransmitter that potentiates EGCG-induced cancer cell death.

Magnetic Nanoliposomes as in Situ Microbubble Bombers for Multimodality Image-Guided Cancer Theranostics

Nanosized drug delivery systems have offered promising approaches for cancer theranostics. However, few are effective to simultaneously maximize tumor-specific uptake, imaging, and therapy in a single nanoplatform. Here, we report a simple yet stimuli-responsive anethole dithiolethione (ADT)-loaded magnetic nanoliposome (AML) delivery system, which consists of ADT, hydrogen sulfide (H₂S) pro-drug, doped in the lipid bilayer, and superparamagnetic nanoparticles encapsulated inside. HepG2 cells could be effectively bombed after 6 h co-incubation with AMLs. For in vivo applications, after preferentially targeting the tumor tissue when spatiotemporally navigated by an external magnetic field, the nanoscaled AMLs can intratumorally convert to microsized H₂S bubbles. This dynamic process can be monitored by magnetic resonance and ultrasound dual modal imaging. Importantly, the intratumoral generated H₂S bubbles imaged by real-time ultrasound imaging first can bomb to ablate the tumor tissue when exposed to higher acoustic intensity; then as gasotransmitters, intratumoral generated high-concentration H₂S molecules can diffuse into the inner tumor regions to further have a synergetic antitumor effect. After 7-day follow-up observation, AMLs with magnetic field treatments have indicated extremely significantly higher inhibitions of tumor growth. Therefore, such elaborately designed intratumoral conversion of nanostructures to microstructures has exhibited an improved anticancer efficacy, which may be promising for multimodal image-guided accurate cancer therapy.

Assessing Tumor Oxygenation for Predicting Outcome in Radiation Oncology: A Review of Studies Correlating Tumor Hypoxic Status and Outcome in the Preclinical and Clinical Settings

Tumor hypoxia is recognized as a limiting factor for the efficacy of radiotherapy, because it enhances tumor radioresistance. It is strongly suggested that assessing tumor oxygenation could help to predict the outcome of cancer patients undergoing radiation therapy. Strategies have also been developed to alleviate tumor hypoxia in order to radiosensitize tumors. In addition, oxygen mapping is critically needed for intensity modulated radiation therapy (IMRT), in which the most hypoxic regions require higher radiation doses and the most oxygenated regions require lower radiation doses. However, the assessment of tumor oxygenation is not yet included in day-to-day clinical practice. This is due to the lack of a method for the quantitative and non-invasive mapping of tumor oxygenation. To fully integrate tumor hypoxia parameters into effective improvements of the individually tailored radiation therapy protocols in cancer patients, methods allowing non-invasively repeated, safe, and robust mapping of changes in tissue oxygenation are required. In this review, non-invasive methods dedicated to assessing tumor oxygenation with the ultimate goal of predicting outcome in radiation oncology are presented, including positron emission tomography used with nitroimidazole tracers, magnetic resonance methods using endogenous contrasts (R₁ and R2*-based methods), and electron paramagnetic resonance oximetry; the goal is to highlight results of studies establishing correlations between tumor hypoxic status and patients’ outcome in the preclinical and clinical settings.

Contribution of Harold M. Swartz to In Vivo EPR and EPR Dosimetry

In 2015, we are celebrating half a century of research in the application of Electron Paramagnetic Resonance (EPR) as a biodosimetry tool to evaluate the dose received by irradiated people. During the EPR Biodose 2015 meeting, a special session was organized to acknowledge the pioneering contribution of Harold M. (Hal) Swartz in the field. The article summarizes his main contribution in physiology and medicine. Four emerging themes have been pursued continuously along his career since its beginning: (1) radiation biology; (2) oxygen and oxidation; (3) measuring physiology in vivo; and (4) application of these measurements in clinical medicine. The common feature among all these different subjects has been the use of magnetic resonance techniques, especially EPR. In this article, you will find an impressionist portrait of Hal Swartz with the description of the 'making of' this pioneer, a time-line perspective on his career with the creation of three National Institutes of Health-funded EPR centers, a topic-oriented perspective on his career with a description of his major contributions to Science, his role as a mentor and his influence on his academic children, his active role as founder of scientific societies and organizer of scientific meetings, and the well-deserved international recognition received so far.

Hydrogen sulfide-releasing anti-inflammatory drugs for chemoprevention and treatment of cancer

For many years it has been recognized that inhibition of cyclooxygenase enzymes is effective in reducing the incidence of many types of cancer, but the adverse effects of these drug, particularly in the gastrointestinal and cardiovascular systems, limits their utility. Recently developed hydrogen sulfide-releasing anti-inflammatory drugs may be a promising option for cancer chemoprevention. In this paper we review evidence suggesting that these novel compounds are effective in a range of animal models of various types of cancer, while exhibiting greatly reduced toxicity relative to currently marketed non-steroidal anti-inflammatory drugs. Some of the possible mechanisms of action of hydrogen sulfide-releasing anti-inflammatory drugs are also discussed.