Hydroxylated metabolites of thalidomide: formation in-vitro and in-vivo in man

Polydopamine-coated thalidomide nanocrystals promote DSS-induced murine colitis recovery through Macrophage M2 polarization together with the synergistic anti-inflammatory and anti-angiogenic effects

High levels of proinflammatory cytokines, macrophage polarization status and immune-mediated angiogenesis play pivotal roles in the pathogenesis of inflammatory bowel disease (IBD). Thalidomide, an anti-inflammatory, immunomodulatory and antiangiogenic agent, is used off-label for treatment of IBD. The therapeutic potential of thalidomide is limited by its poor solubility and side effects associated with its systemic exposure. To address these issues and promote its therapeutic effects on IBD, thalidomide nanocrystals (Thali NCs) were prepared and coated with polydopamine (PDA), a potential macrophage polarization modulator, to form PDA coated Thali NCs (Thali@PDA). Thali@PDA possessed a high drug loading and displayed average particle size of 764.7 ± 50.30 nm. It showed a better anti-colitis effect than bare thalidomide nanocrystals at the same dose of thalidomide. Synergistic effects of polydopamine on anti-inflammatory and anti-angiogenic activities of thalidomide were observed. Furthermore, PDA coating could direct polarization of macrophages towards M2 phenotype, which boosted therapeutic effects of Thali@PDA on IBD. Upon repeated dosing of Thali@PDA for one week, symptoms of IBD in mice were significantly relieved, and histomorphology of the colitis colons were normalized. Key proinflammatory cytokine levels in the inflamed intestines were significantly decreased. Toxicity study also revealed that Thali@PDA is a safe formulation.

The Exploration of Chirality for Improved Druggability within the Human Kinome

Chirality is important in drug discovery because stereoselective drugs can ameliorate therapeutic difficulties including adverse toxicity and poor pharmacokinetic profiles. The human kinome, a major druggable enzyme class has been exploited to treat a wide range of diseases. However, many kinase inhibitors are planar and overlap in chemical space, which leads to selectivity and toxicity issues. By exploring chirality within the kinome, a new iteration of kinase inhibitors is being developed to better utilize the three-dimensional nature of the kinase active site. Exploration into novel chemical space, in turn, will also improve drug solubility and pharmacokinetic profiles. This perspective explores the role of chirality to improve kinome druggability and will serve as a resource for pioneering kinase inhibitor development to address current therapeutic needs.

A validated LC-MS/MS method for the simultaneous determination of thalidomide and its two metabolites in human plasma: Application to a pharmacokinetic assay

An accurate and sensitive LC-MS/MS method for determining thalidomide, 5-hydroxy thalidomide and 5'-hydroxy thalidomide in human plasma was developed and validated using umbelliferone as an internal standard. The analytes were extracted from plasma (100 μL) by liquid-liquid extraction with ethyl acetate and then separated on a BETASIL C₁₈ column (4.6 × 150 mm, 5 μm) with mobile phase composed of methanol-water containing 0.1% formic acid (70:30, v/v) in isocratic mode at a flow rate of 0.5 mL/min. The detection was performed using an API triple quadrupole mass spectrometer in atmospheric pressure chemical ionization mode. The precursor-to-product ion transitions m/z 259.1 → 186.1 for thalidomide, m/z 273.2 → 161.3 for 5-hydroxy thalidomide, m/z 273.2 → 146.1 for 5'-hydroxy thalidomide and m/z 163.1 → 107.1 for umbelliferone (internal standard, IS) were used for quantification. The calibration curves were obtained in the concentrations of 10.0-2000.0 ng/mL for thalidomide, 0.2-50.0 ng/mL for 5-hydroxy thalidomide and 1.0-200.0 ng/mL for 5'-hydroxy thalidomide. The method was validated with respect to linear, within- and between-batch precision and accuracy, extraction recovery, matrix effect and stability. Then it was successfully applied to estimate the concentration of thalidomide, 5-hydroxy thalidomide and 5'-hydroxy thalidomide in plasma samples collected from Crohn's disease patients after a single oral administration of thalidomide 100 mg.

Combining Chimeric Mice with Humanized Liver, Mass Spectrometry, and Physiologically-Based Pharmacokinetic Modeling in Toxicology

Species differences exist in terms of drug oxidation activities, which are mediated mainly by cytochrome P450 (P450) enzymes. To overcome the problem of species extrapolation, transchromosomic mice containing a human P450 3A cluster or chimeric mice transplanted with human hepatocytes have been introduced into the human toxicology research area. In this review, drug metabolism and disposition mediated by humanized livers in chimeric mice are summarized in terms of biliary/urinary excretions of phthalate and bisphenol A and plasma clearances of the human cocktail probe drugs caffeine, warfarin, omeprazole, metoprolol, and midazolam. Simulation of human plasma concentrations of the teratogen thalidomide and its human metabolites is possible with a simplified physiologically based pharmacokinetic model based on data obtained in chimeric mice, in accordance with reported clinical thalidomide concentrations. In addition, in vivo nonspecific hepatic protein binding parameters of metabolically activated ¹⁴C-drug candidate and hepatotoxic medicines in humanized liver mice can be analyzed by accelerator mass spectrometry and are useful for predictions in humans.

Simulation of Human Plasma Concentrations of Thalidomide and Primary 5-Hydroxylated Metabolites Explored with Pharmacokinetic Data in Humanized TK-NOG Mice

Plasma concentrations of thalidomide and primary 5-hydroxylated metabolites including 5,6-dihydroxythalidomide and glutathione (GSH) conjugate(s) were investigated in chimeric mice with highly "humanized" liver cells harboring cytochrome P450 3A5*1. Following oral administration of thalidomide (100 mg/kg), plasma concentrations of GSH conjugate(s) of 5-hydroxythalidomide were higher in humanized mice than in controls. Simulation of human plasma concentrations of thalidomide were achieved with a simplified physiologically based pharmacokinetic model in accordance with reported thalidomide concentrations. The results indicate that the pharmacokinetics in humans of GSH conjugate and/or catechol primary 5-hydroxylated thalidomide contributing in vivo activation can be estimated for the first time.

Identification of phototransformation products of thalidomide and mixture toxicity assessment: an experimental and quantitative structural activity relationships (QSAR) approach

The fate of thalidomide (TD) was investigated after irradiation with a medium-pressure Hg-lamp. The primary elimination of TD was monitored and structures of phototransformation products (PTPs) were assessed by LC-UV-FL-MS/MS. Environmentally relevant properties of TD and its PTPs as well as hydrolysis products (HTPs) were predicted using in silico QSAR models. Mutagenicity of TD and its PTPs was investigated in the Ames microplate format (MPF) aqua assay (Xenometrix, AG). Furthermore, a modified luminescent bacteria test (kinetic luminescent bacteria test (kinetic LBT)), using the luminescent bacteria species Vibrio fischeri, was applied for the initial screening of environmental toxicity. Additionally, toxicity of phthalimide, one of the identified PTPs, was investigated separately in the kinetic LBT. The UV irradiation eliminated TD itself without complete mineralization and led to the formation of several PTPs. TD and its PTPs did not exhibit mutagenic response in the Salmonella typhimurium strains TA 98, and TA 100 with and without metabolic activation. In contrast, QSAR analysis of PTPs and HTPs provided evidence for mutagenicity, genotoxicity and carcinogenicity using additional endpoints in silico software. QSAR analysis of different ecotoxicological endpoints, such as acute toxicity towards V. fischeri, provided positive alerts for several identified PTPs and HTPs. This was partially confirmed by the results of the kinetic LBT, in which a steady increase of acute and chronic toxicity during the UV-treatment procedure was observed for the photolytic mixtures at the highest tested concentration. Moreover, the number of PTPs within the reaction mixture that might be responsible for the toxification of TD during UV-treatment was successfully narrowed down by correlating the formation kinetics of PTPs with QSAR predictions and experimental toxicity data. Beyond that, further analysis of the commercially available PTP phthalimide indicated that transformation of TD into phthalimide was not the cause for the toxification of TD during UV-treatment. These results provide a path for toxicological assessment of complex chemical mixtures and in detail show the toxic potential of TD and its PTPs as well as its HTPs. This deserves further attention as UV irradiation might not always be a green technology, because it might pose a toxicological risk for the environment in general and specifically for water compartments.

Aquatic photochemistry, abiotic and aerobic biodegradability of thalidomide: identification of stable transformation products by LC-UV-MS(n)

Thalidomide (TD), besides being notorious for its teratogenicity, was shown to have immunomodulating and anti-inflammatory activities. This is why recently TD became a promising drug for the treatment of different cancers and inflammatory diseases. Yet nothing is known about the environmental fate of TD, which therefore was assessed experimentally and by in silico prediction programs (quantitative structure activity relationship (QSAR) models) within this study. Photolytic degradation was tested with two different light sources (medium-pressure mercury lamp; xenon lamp) and aerobic biodegradability was investigated with two OECD tests (Closed Bottle test (CBT), Manometric Respirometry test (MRT)). An additional CBT was performed for TD samples after 16 min of UV-photolysis. The primary elimination of TD was monitored and the structures of its photo-, abiotic and biodegradation products were elucidated by HPLC-UV-Fluorescence-MS(n). Furthermore, elimination of dissolved organic carbon was monitored in the photolysis experiment. LC-MS revealed that new photolytic transformation products (TPs) were identified, among them two isomers of TD with the same molecular mass. These TPs were different to the products formed by biodegradation. The experimental findings were compared with the results obtained from the in silico prediction programs where e.g. a good correlation for TD biodegradation in the CBT was confirmed. Moreover, some of the identified TPs were also structurally predicted by the MetaPC software. These results demonstrate that TD and its TPs are not readily biodegradable and not fully mineralized by photochemical treatment. They may therefore pose a risk to the aquatic environment due to the pharmacological activity of TD and unknown properties of its TPs. The applied techniques within this study emphasize the importance of QSAR models as a tool for estimating environmental risk assessments.

In vivo drug interactions of the teratogen thalidomide with midazolam: heterotropic cooperativity of human cytochrome P450 in humanized TK-NOG mice

In vivo drug interactions of the teratogen thalidomide with the model cytochrome P450 (P450) 3A substrate midazolam were investigated in mice with humanized livers. The clearance of midazolam (administered intravenously, 10 mg kg(-1)) in chimeric mice was enhanced by orally co-administered thalidomide (100 mg kg(-1)). A larger area under the curve of the major metabolite 1'-hydroxymidazolam (1.7-fold) was obtained with thalidomide because of the heterotropic cooperativity of human P450 3A enzymes. A larger area under the curve of the minor metabolite 4-hydroxymidazolam (3.5-fold) was seen with daily pretreatment with thalidomide for 3 days, presumably because of human P450 3A induction. These results demonstrate that livers of humanized mice mediate drug interactions of thalidomide and suggest interactions of therapeutic agents during therapies with thalidomide.

In vivo formation of dihydroxylated and glutathione conjugate metabolites derived from thalidomide and 5-Hydroxythalidomide in humanized TK-NOG mice

The formation of dihydroxythalidomide and glutathione (GSH) conjugate(s) of 5-hydroxythalidomide was investigated in chimeric mice modified with "humanized" liver: novel humanized TK-NOG mice were prepared by the introduction of thymidine kinase, followed by induction with ganciclovir, and human liver cells were transplanted. Following oral administration of racemic thalidomide (100 mg/kg), plasma concentrations of 5-hydroxy- and dihydroxythalidomide were higher in humanized mice than in controls. After administration of 5-hydroxythalidomide (10 mg/kg), higher concentrations of dihydroxythalidomide were detected. These results indicate that livers of humanized mice mediate thalidomide oxidation, leading to catechol and/or the GSH conjugate in vivo and suggest that thalidomide activation occurs.

In vivo formation of a glutathione conjugate derived from thalidomide in humanized uPA-NOG mice

Metabolism of the teratogen thalidomide is proposed to be relevant to its toxicological action. We demonstrated the formation of the glutathione (GSH) conjugate of (R)-5-hydroxythalidomide in vivo in chimeric NOD-scid IL2Rg(null) mice with humanized livers (uPA-NOG mice). After an oral administration of racemic thalidomide (270 mg/kg), plasma concentrations of 5-hydroxythalidomide were significantly higher in humanized mice than in control mice. The GSH conjugate of 5-hydroxythalidomide was detected in the plasma. These results indicate that livers of humanized mice mediate thalidomide 5-hydroxylation and further oxidation leading to the GSH conjugate in vivo as well as in vitro and suggest that thalidomide activation occurs.

Human liver microsomal cytochrome P450 3A enzymes involved in thalidomide 5-hydroxylation and formation of a glutathione conjugate

(R)-Thalidomide was oxidized to 5-hydroxythalidomide and 5'-hydroxythalidomide by NADPH-fortified liver microsomes from humans and monkeys. (R)-Thalidomide was hydroxylated more efficiently than (S)-thalidomide. Recombinant human P450s 3A4, 3A5, and 3A7 and monkey P450s 3A8 and 3A5 (coexpressed with NADPH-P450 reductase in bacterial membranes) also catalyzed (R)-thalidomide 5-hydroxylation. Purified human P450s 2C19, 3A4, and 3A5 mediated (R)-thalidomide 5-hydroxylation at similar rates in reconstituted systems. P450 2C19 showed a rather nonsaturable substrate-velocity curve; however, P450s 3A4 and 3A5 showed sigmoidal curves. P450 also oxidized 5-hydroxythalidomide to an epoxide or dihydroxy compound. Liquid chromatography-mass spectrometry analysis revealed the formation of a glutathione conjugate from (R)- and (S)-5-hydroxythalidomide, catalyzed by liver microsomal P450s 3A4 and 3A5 in the presence of glutathione (assigned as a conjugate of 5-hydroxythalidomide formed on the phenyl ring). These results indicate that human P450s 3A4 and 3A5 mediate thalidomide 5-hydroxylation and further oxidation leading to a glutathione conjugate, which may be of relevance in the pharmacological and toxicological actions of thalidomide.

Recent advances in analytical determination of thalidomide and its metabolites

Thalidomide, a racemate, is coming into clinical use as immuno-modulating and anti-inflammatory drug. Thalidomide was approved by the FDA in July 1998 for the treatment of erythema nodusum leprosum associated with leprosy. Recently, thalidomide is proving to be a promising drug in the treatment of a number of cancers and inflammatory diseases, such as multiple myeloma, inflammatory bowel disease (Crohn's disease), HIV and cancer associated cachexia. These effects may chiefly be exerted by S-thalidomide, but the enantiomers are inter-converted in vivo. Thalidomide is given orally, although parenteral administration would be desirable in some clinical situations. Thalidomide has been determined in formulations and, principally in biological fluids by a variety of methods such as high-performance liquid chromatography with ultraviolet detection and liquid chromatography coupled with tandem mass spectrometry. The overview includes the most relevant analytical methodologies used in its determination.

Thalidomide enantiomers: Determination in biological samples by HPLC and vancomycin-CSP

Thalidomide is a racemate with potentially different pharmacokinetics and pharmacodynamics of the component (+)-(R)- and (-)-(S)-thalidomide enantiomers. As part of a project on the adjunctive effects of thalidomide and cytotoxic agents, a method for the chiral separation and quantitation of thalidomide was developed and validated. Thalidomide in relevant serum and tissue homogenate samples was stabilized by buffering with an equal volume of citrate-phosphate buffer (pH 2, 0.2M), and stored at -80 degrees C pending assay. The thalidomide enantiomers, extracted from the samples with diethyl ether, were well separated on a chiral HPLC column of vancomycin stationary phase and a mobile phase of 14% acetonitrile in 20 mM ammonium formate adjusted to pH 5.4; their concentrations were determined with phenacetin as internal standard at 220 nm detection. Over a thalidomide concentration range of 0.1-20 microg/ml, assay precision was 1-5% (CV) for both enantiomers, and calibration curves were linear with all correlation coefficients being >0.99. The estimated limit of quantification for both enantiomers was 0.05 microg/ml with 0.2-0.6 ml serum samples. Thalidomide in rat and human serum, acidified and stored as described above, was found to be chemically and chirally stable over 1 year. The method has been successfully applied to serum samples from human patients undergoing thalidomide treatment for mesothelioma, and to serum, blood and tissue samples from a laboratory rodent model using transplanted 9l gliosarcoma. Enantioselectivity in thalidomide pharmacokinetics has been found, thereby reinforcing the need for considering the relevance of chirality in thalidomide pharmacology.

Transport of thalidomide by the human intestinal caco-2 monolayers

Studies in patients have indicated that the oral absorption of thalidomide is considerably variable at high doses (>200 mg/day). The aim of this study was to investigate the transport of racemic thalidomide using human colon cancer cell line (Caco-2) monolayers, which have been widely used to investigate drug permeability. A typical 21-day protocol was used to prepare Caco-2 monolayers. Thalidomide was determined by a validated high performance liquid chromatography method with ultraviolet detection. The integrity of Caco-2 monolayer was confirmed when the transepithelial electrical resistance (TEER) exceeded 300 Ohmz . cm2, and the leakage of 14C-manitol was <1% per hour. Uptake of thalidomide by Caco-2 cells was very limited (up to 2.1%). The transport of thalidomide appeared to be linear up to 1 hr. Our study indicated that the permeability coefficients (Papp) of thalidomide at 2.5-300 microM from the apical (AP) to basolateral (BL) and from BL to AP side was 2-6 x 10(-5) cm/sec, with a marked decrease in Papp values from AP to BL at increased thalidomide concentration. The transport of thalidomide was sodium-, temperature- and pH-dependent, as replacement of extracellular sodium chloride or reducing temperature and apical pH can result in significant decreases in the Papp values. Additional data indicated that transport of thalidomide is energy-dependent, as it was significantly (P < 0.05) inhibited by the ATP inhibitors, sodium azide and 2,4-dinitrophenol. In addition, DL-glutamic acid, cytidine, diprodomole, papaverine, quinidine, and cyclophosphamide significantly (P < 0.05) inhibited the transport of thalidomide, while the P-glycoprotein inhibitor verapamil and other nucleosides and nucleotides such as thymidine and guanine had no effect. These results indicated that thalidomide was rapidly transported by Caco-2 monolayers, and this might involve a saturable energy-dependent transporter.

Thalidomide does not interact with P-glycoprotein

BACKGROUND

There is growing clinical interest in thalidomide for the treatment of various disorders due to its anti-inflammatory, immunomodulatory, and anti-angiogenic properties. In numerous clinical trials thalidomide is used as an adjunct to standard therapy. Therefore, clinicians should be aware of all possible drug-drug interactions that might occur with this drug. P-glycoprotein (P-gp), a drug efflux transporter that is expressed in many tissues, is the cause of several drug-drug interactions. P-gp induction or inhibition can lead to ineffective therapy or side-effects. In this study, we investigated thalidomide's potential to cause drug-drug interactions on the level of P-gp.

METHODS

LS180 cells were incubated with thalidomide for 72 h in order to determine P-gp induction using real-time RT-PCR. A human leukaemia cell line over-expressing MDR1 (CCRF-CEM/MDR1) was used to measure uptake of rhodamine 123, a P-gp substrate, in the presence of thalidomide. Dose-dependent and bi-directional transport of thalidomide through Caco-2 cell monolayers was performed to assess site-directed permeability. Transport rates were determined using HPLC including chiral separation of the thalidomide enantiomers.

RESULTS

Thalidomide did not induce P-gp expression in LS180 cells. The uptake of rhodamine 123 in CCRF cells over-expressing MDR1 was not influenced by co-incubation with thalidomide. The transport through Caco-2 monolayers was linear and the permeability was similar for both directions. No differences between the thalidomide enantiomers were observed.

CONCLUSIONS

Our study indicates that thalidomide is neither a substrate, nor an inhibitor or an inducer of P-gp. Therefore, P-gp-related drug-drug interactions with thalidomide are not likely.

Drug bioactivation, covalent binding to target proteins and toxicity relevance

A number of therapeutic drugs with different structures and mechanisms of action have been reported to undergo metabolic activation by Phase I or Phase II drug-metabolizing enzymes. The bioactivation gives rise to reactive metabolites/intermediates, which readily confer covalent binding to various target proteins by nucleophilic substitution and/or Schiff's base mechanism. These drugs include analgesics (e.g., acetaminophen), antibacterial agents (e.g., sulfonamides and macrolide antibiotics), anticancer drugs (e.g., irinotecan), antiepileptic drugs (e.g., carbamazepine), anti-HIV agents (e.g., ritonavir), antipsychotics (e.g., clozapine), cardiovascular drugs (e.g., procainamide and hydralazine), immunosupressants (e.g., cyclosporine A), inhalational anesthetics (e.g., halothane), nonsteroidal anti-inflammatory drugs (NSAIDSs) (e.g., diclofenac), and steroids and their receptor modulators (e.g., estrogens and tamoxifen). Some herbal and dietary constituents are also bioactivated to reactive metabolites capable of binding covalently and inactivating cytochrome P450s (CYPs). A number of important target proteins of drugs have been identified by mass spectrometric techniques and proteomic approaches. The covalent binding and formation of drug-protein adducts are generally considered to be related to drug toxicity, and selective protein covalent binding by drug metabolites may lead to selective organ toxicity. However, the mechanisms involved in the protein adduct-induced toxicity are largely undefined, although it has been suggested that drug-protein adducts may cause toxicity either through impairing physiological functions of the modified proteins or through immune-mediated mechanisms. In addition, mechanism-based inhibition of CYPs may result in toxic drug-drug interactions. The clinical consequences of drug bioactivation and covalent binding to proteins are unpredictable, depending on many factors that are associated with the administered drugs and patients. Further studies using proteomic and genomic approaches with high throughput capacity are needed to identify the protein targets of reactive drug metabolites, and to elucidate the structure-activity relationships of drug's covalent binding to proteins and their clinical outcomes.

Thalidomide Pharmacokinetics and Metabolite Formation in Mice, Rabbits, and Multiple Myeloma Patients

PURPOSE

Thalidomide has a variety of biological effects that vary considerably according to the species tested. We sought to establish whether differences in pharmacokinetics could form a basis for the species-specific effects of thalidomide.

EXPERIMENTAL DESIGN

Mice and rabbits were administered thalidomide (2 mg/kg) p.o. or i.v., and plasma concentrations of thalidomide were measured after drug administration using high performance liquid chromotography. Plasma samples from five multiple myeloma patients over 24 hours after their first dose of thalidomide (200 mg) were similarly analyzed and all data were fitted to a one-compartment model. Metabolites of thalidomide in plasma were identified simultaneously using liquid chromatography-mass spectrometry.

RESULTS

Plasma concentration-time profiles for the individual patients were very similar to each other, but widely different pharmacokinetic properties were found between patients compared with those in mice or rabbits. Area under the concentration curve values for mice, rabbits, and multiple myeloma patients were 4, 8, and 81 micromol/L. hour, respectively, and corresponding elimination half-lives were 0.5, 2.2, and 7.3 hours, respectively. Large differences were also observed between the metabolite profiles from the three species. Hydrolysis products were detected for all species, and the proportion of hydroxylated metabolites was higher in mice than in rabbits and undetectable in patients.

CONCLUSIONS

Our results show major interspecies differences in the pharmacokinetics of thalidomide that are related to the altered degree of metabolism. We suggest that the interspecies differences in biological effects of thalidomide may be attributable, at least in part, to the differences in its metabolism and hence pharmacokinetics.

Metabolism of Thalidomide in Liver Microsomes of Mice, Rabbits, and Humans

Thalidomide is increasingly important in clinical treatment, not only of various inflammatory conditions but also in multiple myeloma and other malignancies. Moreover, the metabolism of thalidomide varies considerably among different species, indicating a need to understand its mechanistic basis. Our previous in vivo studies showed the plasma half-life of thalidomide to be much shorter in mice than in humans, with rabbits showing intermediate values. We were unable to detect hydroxylated thalidomide metabolites in humans and suggested that interspecies differences in thalidomide hydroxylation might account for the differences in plasma half-life. We sought here to establish whether these species differences in the formation of hydroxylated thalidomide metabolites could be discerned from in vitro studies. Liver microsomes of mice, rabbit, and human donors were incubated with thalidomide and analyzed using liquid chromatography-mass spectrometry. Hydrolysis products were detected for all three species, and the rates of formation were similar to those for spontaneous hydrolysis, except in rabbits where phthaloylisoglutamine formation increased linearly with microsomal enzyme concentration. Multiple hydroxylation products were detected, including three dihydroxylated metabolites not observed in vivo. Thalidomide-5-O-glucuronide, detected in vivo, was absent in vitro. The amount of 5-hydroxythalidomide formed was high in mice, lower in rabbits, and barely detectable in humans. We conclude that major interspecies differences in hepatic metabolism of thalidomide relate closely to the rate of in vivo metabolite formation. The very low rate of in vitro and in vivo hydroxylation in humans strongly suggests that thalidomide hydroxylation is not a requirement for clinical anticancer activity.

Clinical Pharmacokinetics of Thalidomide

Thalidomide is a racemic glutamic acid derivative approved in the US for erythema nodosum leprosum, a complication of leprosy. In addition, its use in various inflammatory and oncologic conditions is being investigated. Thalidomide interconverts between the (R)- and (S)-enantiomers in plasma, with protein binding of 55% and 65%, respectively. More than 90% of the absorbed drug is excreted in the urine and faeces within 48 hours. Thalidomide is minimally metabolised by the liver, but is spontaneously hydrolysed into numerous renally excreted products. After a single oral dose of thalidomide 200 mg (as the US-approved capsule formulation) in healthy volunteers, absorption is slow and extensive, resulting in a peak concentration (C(max)) of 1-2 mg/L at 3-4 hours after administration, absorption lag time of 30 minutes, total exposure (AUC( infinity )) of 18 mg. h/L, apparent elimination half-life of 6 hours and apparent systemic clearance of 10 L/h. Thalidomide pharmacokinetics are best described by a one-compartment model with first-order absorption and elimination. Because of the low solubility of the drug in the gastrointestinal tract, thalidomide exhibits absorption rate-limited pharmacokinetics (the 'flip-flop' phenomenon), with its elimination rate being faster than its absorption rate. The apparent elimination half-life of 6 hours therefore represents absorption, not elimination. The 'true' apparent volume of distribution was estimated to be 16L by use of the faster elimination-rate half-life. Multiple doses of thalidomide 200 mg/day over 21 days cause no change in the pharmacokinetics, with a steady-state C(max) (C(ss)(max)) of 1.2 mg/L. Simulation of 400 and 800 mg/day also shows no accumulation, with C(ss)(max) of 3.5 and 6.0 mg/L, respectively. Multiple-dose studies in cancer patients show pharmacokinetics comparable with those in healthy populations at similar dosages. Thalidomide exhibits a dose-proportional increase in AUC at doses from 50 to 400 mg. Because of the low solubility of thalidomide, C(max) is less than proportional to dose, and t(max) is prolonged with increasing dose. Age, sex and smoking have no effect on the pharmacokinetics of thalidomide, and the effect of food is minimal. Thalidomide does not alter the pharmacokinetics of oral contraceptives, and is also unlikely to interact with warfarin and grapefruit juice. Since thalidomide is mainly hydrolysed and passively excreted, its pharmacokinetics are not expected to change in patients with impaired liver or kidney function.

Current status of thalidomide and its role in the treatment of metastatic prostate cancer

Following the discovery of its anti-angiogenic properties and despite its tragic history, thalidomide has re-surfaced in the field of oncology. Concurrent with its evaluation in various clinical trials for cancer, thalidomide's mechanism of action is sought and new analogues with improved efficacy and pharmacological profile are emerging. This review is a critical evaluation of thalidomide metabolism, molecular targets, anti-angiogenic activity and clinical efficacy with an emphasis on metastatic prostate cancer.

Antimyeloma efficacy of thalidomide in the SCID-hu model

To determine the mechanism of thalidomide's antimyeloma efficacy, we studied the drug's activity in our severe combined immunodeficiency-human (SCID-hu) host system for primary human myeloma. In this model, tumor cells interact with the human microenvironment to produce typical myeloma manifestations in the hosts, including stimulation of neoangiogenesis. Because mice are not able to metabolize thalidomide efficiently, SCID-hu mice received implants of fetal human liver fragments under the renal capsule in addition to subcutaneous implants of the fetal human bone. Myeloma cell growth in these mice was similar to their growth in hosts without liver implant, as assessed by change in levels of circulating human immunoglobulins and by histologic examinations. Thalidomide given daily by peritoneal injection significantly inhibited myeloma growth in 7 of 8 experiments, each with myeloma cells from a different patient, in hosts implanted with human liver. In contrast, thalidomide exerted an antimyeloma effect only in 1 of 10 mice without liver implants. Microvessel density in the untreated controls was higher than in thalidomide-responsive hosts but not different from nonresponsive ones. Expression of vascular endothelial growth factor by myeloma cells and by other cells in the human bone, determined immunohistochemically, was not affected by thalidomide treatment in any experiment. Our study suggests that thalidomide metabolism is required for its antimyeloma efficacy. Although response to thalidomide was strongly associated with decreased microvessel density, we were unable to conclude whether reduced microvessel density is a primary result of thalidomide's antiangiogenic activity or is secondary to a lessened tumor burden.

Thalidomide in cancer treatment: a potential role in the elderly?

There is increased interest in the treatment of cancer with thalidomide because of its antiangiogenic, immunomodulating and sedative effects. In animal models, the antitumour activity of thalidomide is dependent on the species, route of administration and coadministration of other drugs. For example, thalidomide has shown antitumour effects as a single agent in rabbits, but not in mice. In addition, the antitumour effects of the conventional cytotoxic drug cyclophosphamide and the tumour necrosis factor inducer 5,6-dimethylxanthenone-4-acetic acid (DMXAA) were found to be potentiated by thalidomide in mice bearing colon 38 adenocarcinoma tumours. Further studies have revealed that thalidomide upregulates intratumoral production of tumour necrosis factor-alpha 10-fold over that induced by DMXAA alone. Coadministration of thalidomide also significantly reduced the plasma clearance of DMXAA and cyclophosphamide. All these effects of thalidomide may contribute to the enhanced antitumour activity. Recent clinical trials of thalidomide have indicated that it has minimal anticancer activity for most patients with solid tumours when used as a single agent, although it was well tolerated. However, improved responses have been reported in patients with multiple myeloma. Palliative effects of thalidomide on cancer-related symptoms have also been observed, especially for geriatric patients with prostate cancer. Thalidomide also eliminates the dose-limiting gastrointestinal toxic effects of irinotecan. There is preliminary evidence indicating that the clearance of thalidomide may be reduced in the elderly. The exact role of thalidomide in the treatment of cancer and cancer cachexia in the elderly remains to be elucidated. However, it may have some value as part of a multimodality anticancer therapy, rather than as a single agent.

Effects of putative hydroxylated thalidomide metabolites on blood vessel density in the chorioallantoic membrane (CAM) assay and on tumor and endothelial cell proliferation

Angiogenesis, in particular anti-angiogenesis, is an area of particular therapeutic interest in cancer treatment. Several anti-angiogenic agents are in the final stages of clinical trials. One of these agents, thalidomide, best known for its teratogenic potential, is showing promise against several tumor types. Thalidomide has been shown previously to require bio-activation to exert its anti-angiogenic effect in isolated blood vessels and endothelial cells. In this work, we confirmed these findings using the in utero chicken embryo chorioallantoic membrane (CAM) system. In particular, the anti-angiogenic effect of thalidomide is significantly enhanced by activation by human but not by rat liver microsomes. We also showed in the CAM assay that hydroxylation of thalidomide at either the 1'- or 5-position retained anti-angiogenic activity whereas its hydroxylation at the 4-position led to an inactive compound. We further demonstrated that thalidomide shows weak anti-proliferative activity against MDA-MB-231 human breast cancer cells in culture. Thalidomide showed slightly more anti-proliferative activity, however, against the SH-SY5Y human neuroblastoma and human umbilical vein endothelial cell (HUVEC) types. Furthermore, incubation of thalidomide with human liver microsomes added no additional anti-proliferative effect in these cell types versus thalidomide given alone. Finally, we report that none of the thalidomide metabolites tested had any anti-proliferative effect against the breast or neuroblastoma cells, but do possess appreciable anti-proliferative activity against the endothelial cells. In summary, this work suggests that hydroxylated thalidomide analogs based on putative metabolites of the drug possess significant anti-angiogenic activity and that exploring further derivatives of these as potential anti-angiogenic agents warrants further merit.

5'-OH-thalidomide, a metabolite of thalidomide, inhibits angiogenesis

Despite its known teratogenic effects, thalidomide has been used to treat a variety of diseases ranging from alleviation of autoimmune disorders to prevention of metastasis of cancers. The exact method of action of thalidomide and its derivatives is still under investigation. Thalidomide undergoes very little metabolism by the cytochrome P 450 system in vitro, but at least two hydroxylated metabolites have been found in humans. The two metabolites are 5-hydroxythalidomide, formed by hydroxylation of the phthalimide ring, possibly via arene oxides, and 5'-hydroxythalidomide, formed by hydroxylation of the glutarimide ring, leading to diastereomeric products. These two metabolites, along with another minor metabolite of thalidomide, were tested in a rat aortic ring assay, a human saphenous vein model, and a tube formation assay to assess the metabolite's ability to inhibit angiogenesis. Of the metabolites tested, only 5'-OH-thalidomide showed biologic activity in the rat aortic ring assay, and none of the metabolites showed activity in the human model. The studies with thalidomide and thalidomide metabolites underline the difficulty and complexity of trying to isolate and evaluate a single biologically active agent. These studies, however, do suggest that at least one metabolite, 5'-OH-thalidomide, has moderate antiangiogenic activity at high concentrations. Unfortunately, because of the lack of observed activity of 5'-OH-thalidomide in the human saphenous vein assay, it remains unclear whether there is species specificity for the activity of this metabolite.

Pharmacokinetics and pharmacodynamics of thalidomide in HIV patients treated for oral aphthous ulcers: ACTG protocol 251. AIDS Clinical Trials Group

Thalidomide has increasing clinical benefits, including the healing of aphthous ulcers in patients with HIV. Unfortunately, pharmacological information addressing the pharmacokinetics (PK) of this compound in HIV patients is limited. Concern exists as to whether thalidomide may alter its own metabolism owing to in vitro data previously reported. Furthermore, no information is available defining the relationship between drug exposure and clinical response. This study evaluated the PK and pharmacodynamics (PD) of thalidomide in patients enrolled in AIDS Clinical Trials Group Protocol 251. Study patients had HIV infection and oral aphthous ulcers of at least 2 weeks'duration. Pharmacologic studies were completed in those subjects randomized to receive active thalidomide at a dose of 200 mg daily for the 4-week study period. PK studies involving serial sampling were carried out in 7 subjects following multiple dosing during study weeks 1 and 4. In addition, trough measurements were done in 20 subjects during each of the 4 study weeks to explore the relationship between time-averaged trough values and extent of clinical response. All samples were analyzed using a validated HPLC method, and parameters were determined using noncompartmental PK analysis. Thalidomide oral clearance averaged 0.14 +/- 0.08 and 0.12 +/- 0.05 l/h/kg on weeks 1 and 4 (p = 0.72), while the terminal elimination half-life averaged 5.7 +/- 1.5 and 7.3 +/- 1.7 hours (p = 0.12). The median time-averaged trough value for subjects deemed complete responders was 0.60, while the median value for noncomplete responders was 0.54. Adjusting for baseline CD4 count and initial index ulcer area, no significant effects were observed of increased thalidomide levels on response. In summary, this study provides steady-state PK data in HIV patients managed with thalidomide and suggests negligible effect of chronic dosing on drug clearance (comparing results from weeks 1 and 4). Furthermore, variable trough measurements between patients do not directly influence the effectiveness of thalidomide for oral aphthous ulcers.

Investigation of the stereoselective in vitro biotransformation of thalidomide using a dual cyclodextrin system in capillary electrophoresis

A previously developed capillary electrophoresis method for the simultaneous separation and enantioseparation of thalidomide (TD) and its hydroxylated metabolites was extended to one additional biotransformation product. The dual chiral selector system using native beta-cyclodextrin (beta-CD) and the negatively charged sulfobutyl ether-beta-CD (SBE-beta-CD) was slightly modified up to a concentration of 12 mg/mL running buffer of each CD. The carrier mode in which these buffer additives transport the neutral compounds to the detector as well as the use of a polyacrylamide-coated capillary were necessary to achieve reproducible enantioseparations of all eight analytes. The optimized method was applied to the analysis of the in vitro biotransformation of TD by rat liver microsomes. The S-enantiomer undergoes metabolism preferentially by hydroxylation in the phthalimide ring, whereas R-(+)-TD is mainly transformed to diastereomeric 5'-hydroxythalidomide (5'-OH-TD) pairs. The chiral capillary electrophoresis of incubation samples of TD enantiomers in combination with X-ray diffraction data allowed us to determine the absolute configuration of all metabolites and furthermore to follow the enantio- and stereoselective effects of metabolism in detail.

Thalidomide: a remarkable comeback

The thalidomide product is a racemic mixture of the L- and D-enantiomeric forms of a synthetic glutamic acid derivative that contains a phthalimide ring and a glutarimide ring. Initially marketed as a sedative, it was withdrawan from the world market after it was found to be associated with severe birth defects. Recently, the compound has generated renewed interest because of its immunomodulatory and anti-angiogenic properties. The nature of its immunologic effects is under active investigation. It is orally bioavailable and can be administered in once daily dosing. Its primary route of metabolism is spontaneous hydrolysis. In controlled clinical trials, thalidomide has proven effective in the treatment of erythema nodosum leprosum, oral and oesophageal aphthous ulceration associated with advanced HIV infection and oral ulceration associated with Behcet's syndrome. Promising results have been obtained in preliminary studies of other immunologic and neoplastic disorders, but controlled clinical studies are still lacking for these entities. Adverse effects include teratogenicity, peripheral neuropathy and sedation. In the US, thalidomide can be prescribed only through a restricted drug distribution program.

Simultaneous separation and enantioseparation of thalidomide and its hydroxylated metabolites using high-performance liquid chromatography in common-size columns, capillary liquid chromatography and nonaqueous capillary electrochromatography

The separation of thalidomide (TD) and its hydroxylated metabolites including their simultaneous enantioseparation was studied using three different polysaccharide-type chiral stationary phases (CSPs) in combination with polar organic mobile phases. Three different techniques, high-performance liquid chromatography in common-size columns, capillary LC and nonaqueous capillary electrochromatography were compared in terms of separation. As this study illustrates, polar organic mobile phases represent a valuable extension for less polar and polar aqueous-organic mobile phases in combination with polysaccharide CSPs. Chiralpak AD consisting of 25% of amylose-tris(3,5-dimethylphenylcarbamate) coated on wide-pore aminopropylsilanized silica gel exhibited higher resolving ability compared to the similar cellulose derivative (Chiralcel OD) as well as to cellulose-tris(4-methylbenzoate) (Chiralcel OJ) CSPs for this particular set of chiral analytes. Baseline separation and simultaneous enantioseparation of all three compounds could be achieved under optimized separation conditions.

Enantiomer separation of drugs by capillary electromigration techniques

The review summarizes the most recent developments in the field of enantioseparation of chiral drugs using capillary electromigration techniques. The basic principles of enantioseparations in CE are discussed. Recent developments in sample introduction, separation and detection in capillary electrophoresis and capillary electrochromatography are summarized. The applications are arbitrarily divided into the following three groups: (a) racemates and artificial mixtures of enantiomers, (b) drug forms and (c) chiral drugs and their metabolites in biological fluids. Among the various techniques involved the relatively new developments such as CEC in aqueous and nonaqueous buffers, on-line CE-MS coupling, etc. are emphasized.

Metabolism of thalidomide in human microsomes, cloned human cytochrome P-450 isozymes, and Hansen's disease patients

Previous in vitro studies in rat microsomal preparations suggested that thalidomide is metabolized by the cytochrome P450 system (CYP). In this study, we examined the extent of thalidomide metabolism by preparations of pooled human microsomes, microsomes containing cloned human CYP isozymes (CYPIA2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4), and Hansen's disease patients. Results indicated that thalidomide was a poor substrate for CYP isozymes. Alteration of incubation buffer, pH, incubation time, and microsome and thalidomide concentrations did not increase the production of any metabolites. Thalidomide also did not inhibit metabolism of CYP-specific substrates and therefore any interactions with other drugs that are metabolized by the same enzyme system are unlikely. Hansen's patients were given a single oral dose of thalidomide (400 mg), and their blood and urine were collected at time points up to 72 hours, processed, and analyzed by tandem mass spectrometry. Although thalidomide was present in the plasma and urine, no metabolites were found in the plasma and very low amounts of the 5-OH thalidomide metabolite were present in the urine. These results suggest that thalidomide does not undergo significant metabolism by human CYP and that clinically important interactions between thalidomide and drugs that are also metabolized by this enzyme system are unlikely. The major route of thalidomide breakdown in humans and animals is through spontaneous hydrolysis with subsequent elimination in the urine.

Enantioseparation of thalidomide and its hydroxylated metabolites using capillary electrophoresis with various cyclodextrins and their combinations as chiral buffer additives

The separation of thalidomide (TD) and its hydroxylated metabolites including their simultaneous enantioseparation was studied in capillary electrophoresis (CE) using four different randomly substituted charged cyclodextrin (CD) derivatives, the combinations of some of them with each other, and beta-CD. TD, as well as two metabolites recently found in incubations of human liver microsomes and human blood, 5-hydroxythalidomide (5-OH-TD) and one of the diastereomeric 5'-hydroxythalidomides (5'-OH-TD), are neutral compounds. Therefore, they were resolved using charged chiral selectors in CE. Two different separation modes (normal polarity and carrier mode) and two different capillaries (fused-silica and polyacrylamide-coated) were tested. Based on the behavior of the individual CDs, their designed combinations were selected in order to improve the separation selectivity and enantioselectivity. Under optimized conditions all three chiral compounds and their enantiomers were resolved simultaneously.