Studies on the metabolism and biological activity of the epimers of sulindac

Phosphosulindac (OXT-328) prevents and reverses chemotherapy induced peripheral neuropathy in mice

Background

Chemotherapy-induced peripheral neuropathy (CIPN), a side effect of chemotherapy, is particularly difficult to treat. We explored whether phosphosulindac (PS), a modified NSAID, could treat CIPN.

Methods

CIPN was induced in male C57BL/6 J mice by paclitaxel, vincristine or oxaliplatin. Mechanical allodynia was measured with the von Frey test and cold allodynia with the acetone test. To determine the preventive effect of PS, it was administered 2 days before the induction of CIPN. Mouse Lewis lung carcinoma xenografts were used to determine if PS altered the chemotherapeutic efficacy of paclitaxel. Cultured cell lines were used to evaluate the effect of PS on neuroinflammation.

Results

Treatment with each of the three chemotherapeutic agents used to induce CIPN lowered the mechanical allodynia scores by 56 to 85% depending on the specific agent. PS gel was applied topically 3x/day for 16-22 days to the hind paws of mice with CIPN. This effect was dose-dependent. Unlike vehicle, PS returned mechanical allodynia scores back to pre-CIPN levels. PS had a similar effect on paclitaxel-induced CIPN cold allodynia. Sulindac, a metabolite of PS, had no effect on CIPN. PS significantly prevented CIPN compared to vehicle. Given concomitantly with paclitaxel to mice with lung cancer xenografts, PS relieved CIPN without affecting the anticancer effect of paclitaxel. The enantiomers of PS were equally efficacious against CIPN, suggesting the therapeutic suitability of the racemate PS. There were no apparent side effects of PS. PS suppressed the levels of IL-6, IL-10, CXCL1, and CXCL2 induced by paclitaxel in a neuroblastoma cell line, and macrophage activation to the M1 proinflammatory phenotype.

Conclusion

Topically applied PS demonstrated broad therapeutic and preventive efficacy against CIPN, preserved the anticancer effect of paclitaxel, and was safe. Its anti-CIPN effect appears to be mediated, in part, by suppression of neuroinflammation. These data support further evaluation of topical PS for the control of CIPN.

Effects of acidic non-steroidal anti-inflammatory drugs on human cytochrome P450 4A11 activity: Roles of carboxylic acid and a sulfur atom in potent inhibition by sulindac sulfide

Cytochrome P450 4A11 (CYP4A11) has many endogenous and exogenous compounds containing a carboxyl group in their structure as substrates. If drugs with this characteristic potently attenuate the catalytic function of CYP4A11, drug-drug interactions may occur. Acidic non-steroidal anti-inflammatory drugs (NSAIDs) possess a carboxylic acid in their structure. However, it remains unclear whether these drugs inhibit CYP4A11 activity. The present study examined the inhibitory effects of acidic NSAIDs on CYP4A11 activity using human liver microsomes (HLMs) and recombinant CYP4A11. Sulindac sulfide, ibuprofen, and flurbiprofen effectively decreased the luciferin-4A O-demethylase activity of HLMs and recombinant CYP4A11 (inhibition rates of 30-96% at an inhibitor concentration of 100 μM), while salicylic acid, aspirin, diclofenac, mefenamic acid, indomethacin, etodolac, ketoprofen, loxoprofen, S-naproxen, pranoprofen, zaltoprofen, and oxaprozin exhibited weaker inhibitory activity (inhibition rates up to 23%). Among the drugs tested, sulindac sulfide was the most potent inhibitor of CYP4A11 activity. A kinetic analysis of the inhibition of CYP4A11 by sulindac sulfide revealed mixed-type inhibition for HLMs (Ki = 3.38 μM) and recombinant CYP4A11 (Ki = 4.19 μM). Sulindac sulfide is a pharmacologically active metabolite of sulindac (sulfoxide form), which is also oxidized to sulindac sulfone. To elucidate the role of a sulfur atom of sulindac sulfide in the inhibition of CYP4A11, the inhibitory effects of sulindac sulfide and its oxidized forms on CYP4A11 activity were examined. The potency of inhibition against HLMs was greater in the order of sulindac sulfide, sulindac, and sulindac sulfone; IC50 values were 6.16, 52.7, and 71.6 μM, respectively. The present results indicate that sulindac sulfide is a potent inhibitor of CYP4A11. These results and the molecular modeling of CYP4A11 with sulindac sulfide and its oxidized forms suggest that a sulfur atom of sulindac sulfide as well as its carboxylic acid play important roles in the inhibition of CYP4A11.

Molecular Idiosyncratic Toxicology of Drugs in the Human Liver Compared with Animals: Basic Considerations

Drug induced liver injury (DILI) occurs in patients exposed to drugs at recommended doses that leads to idiosyncratic DILI and provides an excellent human model with well described clinical features, liver injury pattern, and diagnostic criteria, based on patients assessed for causality using RUCAM (Roussel Uclaf Causality Assessment Method) as original method of 1993 or its update of 2016. Overall, 81,856 RUCAM based DILI cases have been published until mid of 2020, allowing now for an analysis of mechanistic issues of the disease. From selected DILI cases with verified diagnosis by using RUCAM, direct evidence was provided for the involvement of the innate and adapted immune system as well as genetic HLA (Human Leucocyte Antigen) genotypes. Direct evidence for a role of hepatic immune systems was substantiated by (1) the detection of anti-CYP (Cytochrome P450) isoforms in the plasma of affected patients, in line with the observation that 65% of the drugs most implicated in DILI are metabolized by a range of CYP isoforms, (2) the DIAIH (drug induced autoimmune hepatitis), a subgroup of idiosyncratic DILI, which is characterized by high RUCAM causality gradings and the detection of plasma antibodies such as positive serum anti-nuclear antibodies (ANA) and anti-smooth muscle antibodies (ASMA), rarely also anti-mitochondrial antibodies (AMA), (3) the effective treatment with glucocorticoids in part of an unselected RUCAM based DILI group, and (4) its rare association with the immune-triggered Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) caused by a small group of drugs. Direct evidence of a genetic basis of idiosyncratic DILI was shown by the association of several HLA genotypes for DILI caused by selected drugs. Finally, animal models of idiosyncratic DILI mimicking human immune and genetic features are not available and further search likely will be unsuccessful. In essence and based on cases of DILI with verified diagnosis using RUCAM for causality evaluation, there is now substantial direct evidence that immune mechanisms and genetics can account for idiosyncratic DILI by many but not all implicated drugs, which may help understand the mechanistic background of the disease and contribute to new approaches of therapy and prevention.

Cytochrome P450-mediated herb-drug interaction (HDI) of Polygonum multiflorum Thunb. based on pharmacokinetic studies and in vitro inhibition assays

BACKGROUND

Polygonum multiflorum Thunb. (PM) is well known both in China and other countries of the world for its tonic properties, however, it has lost its former glory due to liver toxicity incidents in recent years.

PURPOSE

The purpose of this study is to determine whether the occurrence of herb-drug interaction (HDI) caused by PM is associated with cytochrome P450 (CYP450) based on pharmacokinetic studies and in vitro inhibition assays. The objective was to provide a reference for the rational and safe use of drugs in clinical practice.

METHODS

In this study, raw PM (R), together with its two processed products which included PM by Chinese Pharmacopoeia (M) and PM by "nine cycles of steaming and sunning (NCSS)" ("9"), were prepared as the main research objects. A method based on fluorescence technology was used to evaluate the inhibition levels of raw and processed PMs, as well as corresponding characteristic compounds on seven recombinant human cytochrome P450s (rhCYP450s). The pharmacokinetics of sulindac (a representative of commonly used nonsteroidal anti-inflammatory drugs) and psoralen (a major compound of Psoralea in combination with PM) in rat plasma were studied when combined with raw and different processed products of PM.

RESULTS

The inhibitory level order of the three extracts on major different subtypes of CYP450 (CYP1A2, CYP2B6, CYP2C8, CYP2C19, CYP2D6, and CYP3A4) was: R > M > "9". However, the inhibition level of R and "9" is higher than that of M on CYP2C9. Further studies showed that trans-THSG and emodin could selectively inhibit CYP3A4 and CYP1A2, respectively. Epicatechin gallate mainly inhibited CYP3A4 and CYP1A2, followed by CYP2C8 and CYP2C9. Genistein mainly inhibited CYP3A4, followed by CYP2C9 and CYP2C8. CYP3A4 and CYP2C9 were also inhibited by daidzein. The inhibitory effects of all the PM extracts were associated with their characteristic compounds. The results of HDI showed that R increased sulindac exposure to rat blood, and R and M increased psoralen exposure to rat blood, which were consistent with corresponding metabolic enzymes. Overall, the in vitro and in vivo results indicated that PM, especially R, would be at high risk to cause toxicity and drug interactions via CYP450 inhibition.

CONCLUSION

This study not only elucidates the scientific connotation of "efficiency enhancement and toxicity reduction" of PM by NCSS from the perspective of metabolic inhibition but also contributes to HDI prediction and appropriate clinical medication of PM.

A novel sulindac derivative protects against oxidative damage by a cyclooxygenase-independent mechanism

Oxidative damage is believed to play a major role in the etiology of many age-related diseases and the normal aging process. We previously reported that sulindac, a cyclooxygenase (COX) inhibitor and FDA approved anti-inflammatory drug, has chemoprotective activity in cells and intact organs by initiating a pharmacological preconditioning response, similar to ischemic preconditioning (IPC). The mechanism is independent of its COX inhibitory activity as suggested by studies on the protection of the heart against oxidative damage from ischemia/reperfusion and retinal pigmented endothelial (RPE) cells against chemical oxidative and UV damage . Unfortunately, sulindac is not recommended for long-term use due to toxicities resulting from its COX inhibitory activity. To develop a safer and more efficacious derivative of sulindac, we screened a library of indenes and identified a lead compound, MCI-100, that lacked significant COX inhibitory activity but displayed greater potency than sulindac to protect RPE cells against oxidative damage. MCI-100 also protected the intact rat heart against ischemia/reperfusion damage following oral administration. The chemoprotective activity of MCI-100 involves a preconditioning response similar to sulindac, which is supported by RNA sequencing data showing common genes that are induced or repressed by sulindac or MCI-100 treatment. Both sulindac and MCI-100 protection against oxidative damage may involve modulation of Wnt/β-catenin signaling resulting in proliferation while inhibiting TGFb signaling leading to apoptosis. In summary MCI-100, is more active than sulindac in protecting cells against oxidative damage, but without significant NSAID activity, and could have therapeutic potential in treatment of diseases that involve oxidative damage. Significance Statement In this study, we describe a novel sulindac derivative, MCI-100, that lacks significant COX inhibitory activity, but is appreciably more potent than sulindac in protecting retinal pigmented epithelial (RPE) cells against oxidative damage. Oral administration of MCI-100 markedly protected the rat heart against ischemia/reperfusion damage. MCI-100 has potential therapeutic value as a drug candidate for age-related diseases by protecting cells against oxidative damage and preventing organ failure.

Synthesis of Enantiopure Sulfoxides by Concurrent Photocatalytic Oxidation and Biocatalytic Reduction

The concurrent operation of chemical and biocatalytic reactions in one pot is still a challenging task, and, in particular for chemical photocatalysts, examples besides simple cofactor recycling systems are rare. However, especially due to the complementary chemistry that the two fields of catalysis promote, their combination in one pot has the potential to unlock intriguing, unprecedented overall reactivities. Herein we demonstrate a concurrent biocatalytic reduction and photocatalytic oxidation process. Specifically, the enantioselective biocatalytic sulfoxide reduction using (S)-selective methionine sulfoxide reductases was coupled to an unselective light-dependent sulfoxidation. Protochlorophyllide was established as a new green photocatalyst for the sulfoxidation. Overall, a cyclic deracemization process to produce nonracemic sulfoxides was achieved and the target compounds were obtained with excellent conversions (up to 91 %) and superb optical purity (>99 % ee).

Synthesis of Enantiopure Sulfoxides by Concurrent Photocatalytic Oxidation and Biocatalytic Reduction

The concurrent operation of chemical and biocatalytic reactions in one pot is still a challenging task, and, in particular for chemical photocatalysts, examples besides simple cofactor recycling systems are rare. However, especially due to the complementary chemistry that the two fields of catalysis promote, their combination in one pot has the potential to unlock intriguing, unprecedented overall reactivities. Herein we demonstrate a concurrent biocatalytic reduction and photocatalytic oxidation process. Specifically, the enantioselective biocatalytic sulfoxide reduction using (S)-selective methionine sulfoxide reductases was coupled to an unselective light-dependent sulfoxidation. Protochlorophyllide was established as a new green photocatalyst for the sulfoxidation. Overall, a cyclic deracemization process to produce nonracemic sulfoxides was achieved and the target compounds were obtained with excellent conversions (up to 91 %) and superb optical purity (>99 % ee).

Molecular dynamics simulation and docking analysis of NF-κB protein binding with sulindac acid

It is of interest to document the Molecular Dynamics Simulation and docking analysis of NF-κB target with sulindac sodium in combating COVID-19 for further consideration. Sulindac is a nonsteroidal anti-inflammatory drug (NSAID) of the arylalkanoic acid class that is marketed by Merck under the brand name Clinoril. We show the binding features of sulindac sodium with NF-κB that can be useful in drug repurposing in COVID-19 therapy.

Phosphorus-Alloying as a Powerful Method for Designing Highly Active and Durable Metal Nanoparticle Catalysts for the Deoxygenation of Sulfoxides: Ligand and Ensemble Effects of Phosphorus

The modification of metal nanoparticles (NPs) by incorporating additional metals is a key technique for developing novel catalysts. However, the effects of incorporating nonmetals into metal NPs have not been widely explored, particularly in the field of organic synthesis. In this study, we demonstrate that phosphorus (P)-alloying significantly increases the activity of precious metal NPs for the deoxygenation of sulfoxides into sulfides. In particular, ruthenium phosphide NPs exhibit an excellent catalytic activity and high durability against sulfur-poisoning, outperforming conventional catalysts. Various sulfoxides, including drug intermediates, were deoxygenated to sulfides with excellent yields. Detailed investigations into the structure-activity relationship revealed that P-alloying plays a dual role: it establishes a ligand effect on the electron transfer from Ru to P, facilitating the production of active hydrogen species, and has an ensemble effect on the formation of the Ru-P bond, preventing strong coordination with sulfide products. These effects combine to increase the catalytic performance of ruthenium phosphide NPs. These results demonstrate that P-alloying is an efficient method to improve the metal NP catalysis for diverse organic synthesis.

Mechanism of idiosyncratic drug induced liver injury (DILI): unresolved basic issues

Clinical features of idiosyncratic drug induced liver injury (DILI) are well described in cases that have been assessed for causality using the Roussel Uclaf Causality Assessment Method (RUCAM), but our understanding of the mechanistic steps leading to injury is fragmentary. The difficulties describing mechanistic events can be traced back to the lack of an animal model of experimental idiosyncratic DILI that can mimic the genetic requirements of human idiosyncratic DILI. However, immune tolerance plays a dominant role in the immune response of the liver, and impairment of immune tolerance with immune checkpoint inhibitors increases DILI in both humans and animals. This may provide one method to study the individual steps involved. In general. the human DILI liver is a secret keeper providing little insight into what occurs in the diseased organ. Sufficient evidence exists that most idiosyncratic cases are mediated by the adaptive immune system, which depends on stimulation of the innate immune system, but the triggering factors are unknown. It is attractive to hypothesize that the gut microbiome plays a role; however, it is very difficult to study. Similarly, exosomes are likely to play an important role in communication between hepatic cells and the immune system, but there is a lack of data on blood exosomes in affected patients. Reactive metabolites are likely to play an important role. This is supported by the current analysis, which revealed an association between metabolism by cytochrome P450 and drugs most commonly involved in causing idiosyncratic DILI with causality verified by RUCAM. Circumstantial evidence suggests that reactive oxygen species (ROS) generated by cytochrome P450 could be responsible for the initial steps of injury, but details are unknown. In conclusion, most of the mechanistic steps leading to idiosyncratic DILI remain unclear.

On the role of the vinylsulfoxide side chain of dirchromone towards its bioactivities

Analogs of dirchromone were prepared to shed light on the pivotal role of its peculiar vinylsulfoxide side chain towards its cytotoxic and antimicrobial properties, especially dependant upon the presence and oxidation state of sulfur. The reaction of dirchromone with cysteamine revealed a surprising Michael acceptor behavior with elimination of the methylsulfinyl moiety and redox transformation of the sulfur atom that could be involved in the mode of action of dirchromone within cells.

Gut microbiota in reductive drug metabolism

Gut bacteria are predominant microorganisms in the gut microbiota and have been recognized to mediate a variety of biotransformations of xenobiotic compounds in the gut. This review is focused on one of the gut bacterial xenobiotic metabolisms, reduction. Xenobiotics undergo different types of reductive metabolisms depending on chemically distinct groups: azo (-NN-), nitro (-NO₂), alkene (-CC-), ketone (-CO), N-oxide (-NO), and sulfoxide (-SO). In this review, we have provided select examples of drugs in six chemically distinct groups that are known or suspected to be subjected to the reduction by gut bacteria. For some drugs, responsible enzymes in specific gut bacteria have been identified and characterized, but for many drugs, only circumstantial evidence is available that indicates gut bacteria-mediated reductive metabolism. The physiological roles of even known gut bacterial enzymes have not been well defined.

Population Pharmacokinetics of Sulindac and Genetic Polymorphisms of FMO3 and AOX1 in Women with Preterm Labor

PURPOSE

This prospective study aimed to evaluate the effects of genetic polymorphisms in sulindac-related metabolizing enzyme genes including FMO3 and AOX1 on the population pharmacokinetics of sulindac in 58 pregnant women with preterm labor.

METHODS

Plasma samples were collected at 1.5, 4, and 10 h after first oral administration of sulindac. Plasma concentrations of sulindac and its active metabolite (sulindac sulfide) were determined, and pharmacokinetic analysis was performed with NONMEM 7.3.

RESULTS

The mean maternal and gestational ages at the time of dosing were 32.5 ± 4.4 (range, 20-41) years and 27.4 ± 4.4 (range, 16.4-33.4) weeks, respectively. In the population pharmacokinetic analysis, one depot compartment model of sulindac with absorption lag time best described the data. The metabolism of sulindac and sulindac sulfide was described using Michaelis-Menten kinetics. In stepwise modeling, gestational age impacted volume of distribution (Vc), and FMO3 rs2266782 was shown by the Michaelis constant to affect conversion of sulindac sulfide to sulindac (K_M32); these were retained in the final model.

CONCLUSIONS

Genetic polymorphisms of FMO3 and AOX1 could affect the pharmacokinetics of sulindac in women who undergo preterm labor. The results of this study could help clinicians develop individualized treatment plans for administering sulindac.

Pharmacological modulation of oncogenic Ras by natural products and their derivatives: Renewed hope in the discovery of novel anti-Ras drugs

Oncogenic rat sarcoma (Ras) is linked to the most fatal cancers such as those of the pancreas, colon, and lung. Decades of research to discover an efficacious drug that can block oncogenic Ras signaling have yielded disappointing results; thus, Ras was considered "undruggable" until recently. Inhibitors that directly target Ras by binding to previously undiscovered pockets have been recently identified. Some of these molecules are either isolated from natural products or derived from natural compounds. In this review, we described the potential of these compounds and other inhibitors of Ras signaling in drugging Ras. We highlighted the modes of action of these compounds in suppressing signaling pathways activated by oncogenic Ras, such as mitogen-activated protein kinase (MAPK) signaling and the phosphoinositide-3-kinase (PI3K) pathways. The anti-Ras strategy of these compounds can be categorized into four main types: inhibition of Ras-effector interaction, interference of Ras membrane association, prevention of Ras-guanosine triphosphate (GTP) formation, and downregulation of Ras proteins. Another promising strategy that must be validated experimentally is enhancement of the intrinsic Ras-guanosine triphosphatase (GTPase) activity by small chemical entities. Among the inhibitors of Ras signaling that were reported thus far, salirasib and TLN-4601 have been tested for their clinical efficacy. Although both compounds passed phase I trials, they failed in their respective phase II trials. Therefore, new compounds of natural origin with relevant clinical activity against Ras-driven malignancies are urgently needed. Apart from salirasib and TLN-4601, some other compounds with a proven inhibitory effect on Ras signaling include derivatives of salirasib, sulindac, polyamine, andrographolide, lipstatin, levoglucosenone, rasfonin, and quercetin.

Data Mining FAERS to Analyze Molecular Targets of Drugs Highly Associated with Stevens-Johnson Syndrome

Drug features that are associated with Stevens-Johnson syndrome (SJS) have not been fully characterized. A molecular target analysis of the drugs associated with SJS in the FDA Adverse Event Reporting System (FAERS) may contribute to mechanistic insights into SJS pathophysiology. The publicly available version of FAERS was analyzed to identify disproportionality among the molecular targets, metabolizing enzymes, and transporters for drugs associated with SJS. The FAERS in-house version was also analyzed for an internal comparison of the drugs most highly associated with SJS. Cyclooxygenases 1 and 2, carbonic anhydrase 2, and sodium channel 2 alpha were identified as disproportionately associated with SJS. Cytochrome P450 (CYPs) 3A4 and 2C9 are disproportionately represented as metabolizing enzymes of the drugs associated with SJS adverse event reports. Multidrug resistance protein 1 (MRP-1), organic anion transporter 1 (OAT1), and PEPT2 were also identified and are highly associated with the transport of these drugs. A detailed review of the molecular targets identifies important roles for these targets in immune response. The association with CYP metabolizing enzymes suggests that reactive metabolites and oxidative stress may have a contributory role. Drug transporters may enhance intracellular tissue concentrations and also have vital physiologic roles that impact keratinocyte proliferation and survival. Data mining FAERS may be used to hypothesize mechanisms for adverse drug events by identifying molecular targets that are highly associated with drug-induced adverse events. The information gained may contribute to systems biology disease models.

Design, synthesis and evaluation of novel anti-HCV molecules that deliver intracellularly three highly potent NS5A inhibitors

The design and synthesis of new non-symmetrical NS5A inhibitors with sulfur containing amino acids is reported along with their ability to block HCV replication in an HCV 1b replicon system. These compounds display EC50 values in the picomolar range with a large therapeutic index (>10(6)). Moreover, cellular pharmacology studies show that our preferred compounds intracellularly deliver three potent NS5A inhibitors.

Chemoprevention in gastrointestinal physiology and disease. Anti-inflammatory approaches for colorectal cancer chemoprevention

Colorectal cancer (CRC) is one of the most common human malignancies and a leading cause of cancer-related deaths in developed countries. Identifying effective preventive strategies aimed at inhibiting the development and progression of CRC is critical for reducing the incidence and mortality of this malignancy. The prevention of carcinogenesis by anti-inflammatory agents including nonsteroidal anti-inflammatory drugs (NSAIDs), selective cyclooxygenase-2 (COX-2) inhibitors, and natural products is an area of considerable interest and research. Numerous anti-inflammatory agents have been identified as potential CRC chemopreventive agents but vary in their mechanism of action. This review will discuss the molecular mechanisms being studied for the CRC chemopreventive activity of NSAIDs (i.e., aspirin, sulindac, and ibuprofen), COX-2 inhibitors (i.e., celecoxib), natural products (i.e., curcumin, resveratrol, EGCG, genistein, and baicalein), and metformin. A deeper understanding of how these anti-inflammatory agents inhibit CRC will provide insight into the development of potentially safer and more effective chemopreventive drugs.

The discovery of methionine sulfoxide reductase enzymes: An historical account and future perspectives

L-Methionine (L-Met) is the only sulphur-containing proteinogenic amino acid together with cysteine. Its importance is highlighted by it being the initiator amino acid for protein synthesis in all known living organisms. L-Met, free or inserted into proteins, is sensitive to oxidation of its sulfide moiety, with formation of L-Met sulfoxide. The sulfoxide could not be inserted into proteins, and the oxidation of L-Met in proteins often leads to the loss of biological activity of the affected molecule. Key discoveries revealed the existence, in rats, of a metabolic pathway for the reduction of free L-Met sulfoxide and, later, in Escherichia coli, of the enzymatic reduction of L-Met sulfoxide inserted in proteins. Upon oxidation, the sulphur atom becomes a new stereogenic center, and two stable diastereoisomers of L-Met sulfoxide exist. A fundamental discovery revealed the existence of two unrelated families of enzymes, MsrA and MsrB, whose members display opposite stereospecificity of reduction for the two sulfoxides. The importance of Msrs is additionally emphasized by the discovery that one of the only 25 selenoproteins expressed in humans is a Msr. The milestones on the road that led to the discovery and characterization of this group of antioxidant enzymes are recounted in this review.

Structural analysis of sulindac as an inhibitor of aldose reductase and AKR1B10

Aldose reductase (AR, AKR1B1) and AKR1B10 are enzymes implicated in important pathologies (diabetes and cancer) and therefore they have been proposed as suitable targets for drug development. Sulindac is the metabolic precursor of the potent non-steroidal anti-inflammatory drug (NSAID) sulindac sulfide, which suppresses prostaglandin production by inhibition of cyclooxygenases (COX). In addition, sulindac has been found to be one of the NSAIDs with higher antitumoral activity, presumably through COX inhibition. However, sulindac anticancer activity could be partially mediated through COX-independent mechanisms, including the participation of AR and AKR1B10. Previously, it had been shown that sulindac and sulindac sulfone were good AR inhibitors and the structure of the ternary complex with NADP(+) and sulindac was described (PDB ID 3U2C). In this work, we determined the three-dimensional structure of AKR1B10 with sulindac and established structure-activity relationships (SAR) of sulindac and their derivatives with AR and AKR1B10. The difference in the IC50 values for sulindac between AR (0.36 μM) and AKR1B10 (2.7 μM) might be explained by the different positioning and stacking interaction given by Phe122/Phe123, and by the presence of two buried and ordered water molecules in AKR1B10 but not in AR. Moreover, SAR analysis shows that the substitution of the sulfinyl group is structurally allowed in sulindac derivatives. Hence, sulindac and its derivatives emerge as lead compounds for the design of more potent and selective AR and AKR1B10 inhibitors.

Pharmacological protection of retinal pigmented epithelial cells by sulindac involves PPAR-α

The retinal pigmented epithelial (RPE) layer is one of the major ocular tissues affected by oxidative stress and is known to play an important role in the etiology of age-related macular degeneration (AMD), the major cause of blinding in the elderly. In the present study, sulindac, a nonsteroidal antiinflammatory drug (NSAID), was tested for protection against oxidative stress-induced damage in an established RPE cell line (ARPE-19). Besides its established antiinflammatory activity, sulindac has previously been shown to protect cardiac tissue against ischemia/reperfusion damage, although the exact mechanism was not elucidated. As shown here, sulindac can also protect RPE cells from chemical oxidative damage or UV light by initiating a protective mechanism similar to what is observed in ischemic preconditioning (IPC) response. The mechanism of protection appears to be triggered by reactive oxygen species (ROS) and involves known IPC signaling components such as PKG and PKC epsilon in addition to the mitochondrial ATP-sensitive K(+) channel. Sulindac induced iNOS and Hsp70, late-phase IPC markers in the RPE cells. A unique feature of the sulindac protective response is that it involves activation of the peroxisome proliferator-activated receptor alpha (PPAR-α). We have also used low-passage human fetal RPE and polarized primary fetal RPE cells to validate the basic observation that sulindac can protect retinal cells against oxidative stress. These findings indicate a mechanism for preventing oxidative stress in RPE cells and suggest that sulindac could be used therapeutically for slowing the progression of AMD.

Deconstructing breast cancer cell biology and the mechanisms of multidrug resistance

Cancer complexity constantly challenges the way that clinicians manage breast cancer therapy. Tumor heterogeneity and intratumoral stroma characteristics allow cells with different phenotypes and deregulated apoptotic, proliferative and migration abilities to co-exist contributing to a disappointing therapeutic response. While new approaches are being associated with conventional chemotherapy, such as hormonal therapy or target monoclonal antibodies, recurrence and metastasization are still observed. Membrane transporters are the cell's first line of contact with anticancer drugs having a major role in multidrug resistance events. This structural-based activity enables the cell to be drug-resistant by decreasing drug intracellular concentration through an efflux-transport mechanism, mainly associated with overexpression of ATP-binding cassette (ABC) proteins. This review focuses on some of the important structural and biological properties of the malignant cell and tumor microenvironment, addressing the role of the membrane ABC transporters in therapeutic outcomes, and highlighting related molecular pathways that may represent meaningful target therapies.

Population pharmacokinetic model for cancer chemoprevention with sulindac in healthy subjects

Sulindac is a prescription-based non-steroidal anti-inflammatory drug (NSAID) that continues to be actively investigated as a candidate cancer chemoprevention agent. To further current understanding of sulindac bioavailability, metabolism, and disposition, we developed a population pharmacokinetic model for the parent compound and its active metabolites, sulindac sulfide, and exisulind. This analysis was based on data from 24 healthy subjects who participated in a bioequivalence study comparing two formulations of sulindac. The complex disposition of sulindac and its metabolites was described by a seven-compartment model featuring enterohepatic recirculation and is the first reported population pharmacokinetic model for sulindac. The derived model was used to explore effects of clinical variables on sulindac pharmacokinetics and revealed that body weight, creatinine clearance, and gender were significantly correlated with pharmacokinetic parameters. Moreover, the model quantifies the relative bioavailability of the sulindac formulations and illustrates the utility of population pharmacokinetics in bioequivalence assessment. This novel population pharmacokinetic model provides new insights regarding the factors that may affect the pharmacokinetics of sulindac and the exisulind and sulindac sulfide metabolites in generally healthy subjects, which have implications for future chemoprevention trial design for this widely available agent.

Metabolism and toxicity of thioacetamide and thioacetamide S-oxide in rat hepatocytes

The hepatotoxicity of thioacetamide (TA) has been known since 1948. In rats, single doses cause centrolobular necrosis accompanied by increases in plasma transaminases and bilirubin. To elicit these effects, TA requires oxidative bioactivation, leading first to its S-oxide (TASO) and then to its chemically reactive S,S-dioxide (TASO(2)), which ultimately modifies amine-lipids and proteins. To generate a suite of liver proteins adducted by TA metabolites for proteomic analysis and to reduce the need for both animals and labeled compounds, we treated isolated hepatocytes directly with TA. Surprisingly, TA was not toxic at concentrations up to 50 mM for 40 h. On the other hand, TASO was highly toxic to isolated hepatocytes as indicated by LDH release, cellular morphology, and vital staining with Hoechst 33342/propidium iodide. TASO toxicity was partially blocked by the CYP2E1 inhibitors diallyl sulfide and 4-methylpyrazole and was strongly inhibited by TA. Significantly, we found that hepatocytes produce TA from TASO relatively efficiently by back-reduction. The covalent binding of [(14)C]-TASO is inhibited by unlabeled TA, which acts as a "cold-trap" for [(14)C]-TA and prevents its reoxidation to [(14)C]-TASO. This in turn increases the net consumption of [(14)C]-TASO despite the fact that its oxidation to TASO(2) is inhibited. The potent inhibition of TASO oxidation by TA, coupled with the back-reduction of TASO and its futile redox cycling with TA, may help explain phenomena previously interpreted as "saturation toxicokinetics" in the in vivo metabolism and toxicity of TA and TASO. The improved understanding of the metabolism and covalent binding of TA and TASO facilitates the use of hepatocytes to prepare protein adducts for target protein identification.

Differential involvement of mitochondrial dysfunction, cytochrome P450 activity, and active transport in the toxicity of structurally related NSAIDs

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used in the treatment of pain and inflammation. However, this group of drugs is associated with serious adverse drug reactions. Previously, we studied the mechanisms underlying toxicity of the NSAID diclofenac using Saccharomycescerevisiae as model system. We identified the involvement of several mitochondrial proteins, a transporter and cytochrome P450 activity in diclofenac toxicity. In this study, we investigated if these processes are also involved in the toxicity of other NSAIDs. We divided the NSAIDs into three classes based on their toxicity mechanisms. Class I consists of diclofenac, indomethacin and ketoprofen. Mitochondrial respiration and reactive oxygen species (ROS) play a major role in the toxicity of this class. Metabolism by cytochrome P450s further increases their toxicity, while ABC-transporters decrease the toxicity. Mitochondria and oxidative metabolism also contribute to toxicity of class II drugs ibuprofen and naproxen, but another cellular target dominates their toxicity. Interestingly, ibuprofen was the only NSAID that was unable to induce upregulation of the multidrug resistance response. The class III NSAIDs sulindac, ketorolac and zomepirac were relatively non-toxic in yeast. In conclusion, we demonstrate the use of yeast to investigate the mechanisms underlying the toxicity of structurally related drugs.

Selective reduction of methylsulfinyl-containing compounds by mammalian MsrA suggests a strategy for improved drug efficacy

Identification of pathways of drug metabolism provides critical information regarding efficacy and safety of these compounds. Particularly challenging cases involve stereospecific processes. We found that broad classes of compounds containing methylsulfinyl groups are reduced to methylsulfides specifically by methionine sulfoxide reductase A, which acts on the S-stereomers of methionine sulfoxides, whereas the R-stereomers of these compounds could not be efficiently reduced by any methionine sulfoxide reductase in mammals. The findings of efficient reduction of S-methylsulfinyls and deficiency in the reduction of R-methylsulfinyls by methionine sulfoxide reductases suggest strategies for improved efficacy and decreased toxicity of drugs and natural compounds containing methylsulfinyls through targeted use of their enantiomers.