Enantiomers of thalidomide: blood distribution and the influence of serum albumin on chiral inversion and hydrolysis

Discovery and Preclinical Pharmacology of NX-2127, an Orally Bioavailable Degrader of Bruton's Tyrosine Kinase with Immunomodulatory Activity for the Treatment of Patients with B Cell Malignancies

Bruton's tyrosine kinase (BTK), a member of the TEC family of kinases, is an essential effector of B-cell receptor (BCR) signaling. Chronic activation of BTK-mediated BCR signaling is a hallmark of many hematological malignancies, which makes it an attractive therapeutic target. Pharmacological inhibition of BTK enzymatic function is now a well-proven strategy for the treatment of patients with these malignancies. We report the discovery and characterization of NX-2127, a BTK degrader with concomitant immunomodulatory activity. By design, NX-2127 mediates the degradation of transcription factors IKZF1 and IKZF3 through molecular glue interactions with the cereblon E3 ubiquitin ligase complex. NX-2127 degrades common BTK resistance mutants, including BTKC481S. NX-2127 is orally bioavailable, exhibits in vivo degradation across species, and demonstrates efficacy in preclinical oncology models. NX-2127 has advanced into first-in-human clinical trials and achieves deep and sustained degradation of BTK following daily oral dosing at 100 mg.

Rapid chiral purity identification of mandelic acid by Raman spectra in the O-H stretching region

Chiral molecules play a very important role in biological systems, and more and more chiral drugs are used in the treatment of diseases. Mandelic acid (MA) is an important chiral starting substance or the key intermediate of some chiral drugs, and the rapid detection of its chiral purity is very important in the synthesis, separation and detection of drugs. In this study, we developed a method for rapid determination of chiral purity of MA by Raman spectroscopy, and measured a series of Raman spectra of different chiral MA. Through the analysis, it is found that the OH stretching vibration peak can be used to identify the components of chiral molecules, and the enantiomeric excess (ee value) obtained is in good agreement with the real value, and the error is about 5%. The experimental detection speed is fast and the efficiency is high. Our work firstly provides a new idea for the purity detection of chiral molecules by the original Raman spectrum.

Rapid Thalidomide Racemization Is Related to Proton Tunneling Reactions via Water Bridges

Quantum mechanical tunneling (QMT) can play an important role in light element-related chemical reactions; however, its influence on racemization is not fully understood. Herein, we demonstrate that the role of QMT is decisive for rapid racemization of the well-known thalidomide molecule in aqueous environments, increasing the reaction rate constants of the most likely racemization pathways by 87-149 times at approximately body temperature and achieving good agreement between theoretical calculations and experimental observations. In addition, the kinetic isotope effect values fit well with those of previous experiments. These results are attributed to enhanced tunneling probability due to the alteration of potential barriers for proton transfer reactions via water bridges. This work highlights the significance of the QMT effect in racemization and its potential impact on drug safety, providing a fundamental perspective for understanding chirality-related issues in biological systems.

Rapid discrimination of enantiomers by ion mobility mass spectrometry and chemical theoretical calculation: Chiral mandelic acid and its derivatives

Because R/S-mandelic acids (MA) and their derivatives are critical starting materials or intermediates in the synthesis of chiral drugs, their chirality discrimination is important. In this study, R/S-MA and its derivatives, including R/S-2-phenylpropionic acid (2-PPA), R/S-methoxyphenylaceticacid (MPA), and R/S-2-hydroxy-4-phenylbutyric acid (HPBA), were accurate simultaneous mobility-discriminated by forming diastereomer complexes for the first time, which were obtained by simply mixing with cyclodextrins (α, β, γ-CD) and transition-metal ions (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺). The mass spectra revealed non-covalent diastereomer complexes formed by CD, enantiomers, and metal ions, and ion-mobility spectrometry (IMS) was performed for 109 pairs of complexes. Significant chiral discrimination was observed in the formed diastereomeric complexes, and their separation peak-to-peak resolution (R_p-p) for the enantiomers depended on the transition metal ion type. In most cases, the R_p-p value gradually increases with CD size, with quaternary complexes having the largest R_p-p value. The greatest chiral distinctions of 2-PPA, MA, MPA, and HPBA were obtained by the diastereomeric complex ions of [(2-PPA)(α)₂+Zn²⁺-H]⁺, [(MA)(α)₂+Zn²⁺-H]⁺, [(MPA)₂(β)+Co²⁺-H]⁺, and [(HPBA)(α)₂+Fe²⁺-H]⁺, with R_p-p values of 1.35, 1.57, 1.70, and 0.71, respectively. Furthermore, the favorable conformation and collisional cross section (CCS) value of the different [CD + R/S-MA + Cu-H]⁺ complexes were measured using chemical theoretical calculations to detail their intermolecular interaction, revealing that [α-CD + R/S-MA + Cu-H]⁺ has two favored gas complexes, and the CCS calculated were consistent with the TIMS observed. In addition, R² > 0.99 was obtained for the relative quantification of the chiral enantiomers. Overall, the proposed method provides a promising strategy for distinguishing the enantiomers of MA and their derivatives, with the advantages of simplicity, speed, and accuracy, without the need for complex chemical derivatization or chromatographic separation.

Chemical derivatization in combination with supercritical fluid chromatography to improve resolution of stereoisomers

Aim: Quantification of stereoisomers in biological matrices is of pivotal importance for drug development. Supercritical fluid chromatography paired with chiral stationary phases is the gold standard for resolution of enantiomers. However, this technique often proves inadequate for resolution of polar stereoisomers. Materials & methods: A combination of achiral chemical derivatization with supercritical fluid chromatography using chiral stationary columns to improve enantiomeric resolution is described. Results: Separation of four possible stereoisomers of linerixibat was achieved after derivatization with 3N HCl in n-butanol within 12 min (case1). Derivatization with acetic, propionic, butyric, isobutyric, valeric and isovaleric anhydrides significantly improved the separation of stereoisomers (case 2 and 3) within 10 min. The best stereoisomeric resolution was achieved using valeric and isovaleric anhydrides.

Activation of Neurogenesis in Multipotent Stem Cells Cultured In Vitro and in the Spinal Cord Tissue After Severe Injury by Inhibition of Glycogen Synthase Kinase-3

The inhibition of glycogen synthase kinase-3 (GSK-3) can induce neurogenesis, and the associated activation of Wnt/β-catenin signaling via GSK-3 inhibition may represent a means to promote motor function recovery following spinal cord injury (SCI) via increased astrocyte migration, reduced astrocyte apoptosis, and enhanced axonal growth. Herein, we assessed the effects of GSK-3 inhibition in vitro on the neurogenesis of ependymal stem/progenitor cells (epSPCs) resident in the mouse spinal cord and of human embryonic stem cell-derived neural progenitors (hESC-NPs) and human-induced pluripotent stem cell-derived neural progenitors (hiPSC-NPs) and in vivo on spinal cord tissue regeneration and motor activity after SCI. We report that the treatment of epSPCs and human pluripotent stem cell-derived neural progenitors (hPSC-NPs) with the GSK-3 inhibitor Ro3303544 activates β-catenin signaling and increases the expression of the bIII-tubulin neuronal marker; furthermore, the differentiation of Ro3303544-treated cells prompted an increase in the number of terminally differentiated neurons. Administration of a water-soluble, bioavailable form of this GSK-3 inhibitor (Ro3303544-Cl) in a severe SCI mouse model revealed the increased expression of bIII-tubulin in the injury epicenter. Treatment with Ro3303544-Cl increased survival of mature neuron types from the propriospinal tract (vGlut1, Parv) and raphe tract (5-HT), protein kinase C gamma-positive neurons, and GABAergic interneurons (GAD65/67) above the injury epicenter. Moreover, we observed higher numbers of newly born BrdU/DCX-positive neurons in Ro3303544-Cl-treated animal tissues, a reduced area delimited by astrocyte scar borders, and improved motor function. Based on this study, we believe that treating animals with epSPCs or hPSC-NPs in combination with Ro3303544-Cl deserves further investigation towards the development of a possible therapeutic strategy for SCI.

Absolute Configuration of Small Molecules by Co-Crystallization

The most reliable method to determine the absolute configuration of chiral molecules is X-ray crystallography, but small molecules can be difficult to crystallize. We report rapid co-crystallization of tetraaryladamantanes with small molecules as different as n-decane to nicotine to produce crystals for X-ray analysis and the assignment of absolute configuration when the molecules are chiral. A screen of 52 diverse compounds gave inclusion in co-crystals for 88 % of all cases and a high-resolution structure in 77 % of cases. Furthermore, starting from three milligrams of analyte, a combination of NMR spectroscopy and X-ray crystallography produced a full structure in less than three days using an adamantane crystallization chaperone that encapsulates the analyte at room temperature.

Structural basis of thalidomide enantiomer binding to cereblon

Thalidomide possesses two optical isomers which have been reported to exhibit different pharmacological and toxicological activities. However, the precise mechanism by which the two isomers exert their different activities remains poorly understood. Here, we present structural and biochemical studies of (S)- and (R)-enantiomers bound to the primary target of thalidomide, cereblon (CRBN). Our biochemical studies employed deuterium-substituted thalidomides to suppress optical isomer conversion, and established that the (S)-enantiomer exhibited ~10-fold stronger binding to CRBN and inhibition of self-ubiquitylation compared to the (R)-enantiomer. The crystal structures of the thalidomide-binding domain of CRBN bound to each enantiomer show that both enantiomers bind the tri-Trp pocket, although the bound form of the (S)-enantiomer exhibited a more relaxed glutarimide ring conformation. The (S)-enantiomer induced greater teratogenic effects on fins of zebrafish compared to the (R)-enantiomer. This study has established a mechanism by which thalidomide exerts its effects in a stereospecific manner at the atomic level.

Theoretical Investigations of the Chiral Transition of α-Amino Acid Confined in Various Sized Armchair Boron-Nitride Nanotubes

We computationally study the chiral transition process of the α-Ala molecule under confined different sizes of armchair SWBNNTs to explore the confinement effect. We find that the influence of a confinement environment (in armchair SWBNNTs) on the α-Ala molecule would lead to different reaction pathways. Meanwhile, the preferred reaction pathway is also different in various sizes of armchair SWBNNTs, and their energy barriers for the rate-limiting step decrease rapidly with the decreasing of the diameters of the nanotubes. It is obvious that significant decrease of the chiral transition energy barrier occurs compared with the isolated α-Ala molecule chirality conversion mechanism, by ∼15.6 kcal mol^-1, highlighting the improvement in the activity the enantiomers of α-Ala molecule. We concluded that the confinement environment has a significant impact at the nanoscale on the enantiomer transformation process of the chiral molecule.

Study on the determination and chiral inversion of R-salbutamol in human plasma and urine by liquid chromatography-tandem mass spectrometry

The chiral inversion has been a concerned issue during the research and development of a chiral drug. In this study, a sensitive chiral liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for determination of salbutamol enantiomers in human plasma and urine. The chiral inversion mechanism of R-salbutamol was fully investigated for the first time by studying the effects of physicochemical factors, including pH, temperature and time. A fitted model to predict the chiral inversion ratio of R-salbutamol was proposed using a Box-Behnken design. All the samples were separated on an Astec Chirobiotic T column and detected by a tandem mass spectrometer in multiple reaction monitoring mode. Lower limit of quantification of 0.100ng/mL was achieved under the optimized conditions. The method was fully validated and successfully applied to the clinical pharmacokinetic study of R-salbutamol in healthy volunteers. Chiral inversion of R-salbutamol to S-salbutamol has been detected in urine samples. The results indicated that pH and temperature were two dominant factors that caused the chiral inversion of R-salbutamol, which should be taken into consideration during the analysis of chiral drugs. The chiral inversion of R-salbutamol determined in this study was confirmed resulted from the gastric acid in stomach rather than caused by the analysis conditions. Moreover, the calculated results of the fitted model matched very well with the enantioselective pharmacokinetic study of R-salbutamol, and the individual difference of the chiral inversion ratio of R-salbutamol was related to the individual gastric environment. On the basis of the results, this study provides important and concrete information not only for the chiral analysis but also for the metabolism research of chiral drugs.

Environmental-confinement-induced stability enhancement of chiral molecules

We computationally study the transition process of a chiral difluorobenzo[c]phenanthrene (DFBcPh) molecule within non-polar fullerene C(260) to explore the confinement effect. We find blue-shifts in the infrared and Raman spectra of the molecule inside the fullerene relative to those of isolated systems. Six types of spectrum features of the molecule appear in the 0-60 cm(-1) band. Interestingly, the energy barrier of the chiral transformation of the molecule is elevated by 15.88 kcal mol(-1) upon the confinement by the fullerene, indicating improvement in the stability of the enantiomers. The protection by C(260) lowers the highest occupied molecular orbital energy level and lifts the lowest unoccupied molecular orbital energy level of the chiral molecule such that the chiral molecule is further chemically stabilized. We concluded that the confinement environment has an impact at the nanoscale on the enantiomer transformation process of the chiral molecule.

Clearance of drugs for multiple myeloma therapy during in vitro high-cutoff hemodialysis

Current chemotherapy for multiple myeloma is based on bortezomib (BOR), dexamethasone (DEX), and thalidomide (THA). The purpose of the present study was to examine their clearance during high-cutoff (HCO) hemodialysis and to accordingly apply the results to the dialytic removal of protein-bound substances in general. During in vitro hemodialysis with human blood (blood, dialysate, and ultrafiltration flow rates 250, 500 and 5 mL/min, respectively) comparing a highly permeable HCO dialyzer (Theralite, 2.1 m(2) ) to a high-flux dialyzer (PFX; 2.1 m(2) ), ultrafiltered volume was replaced by saline containing 30 g/L urea. After recirculation for equilibration, BOR was injected, and arterial and venous samples were drawn after 10, 11, and 12 min to measure the plasma clearance (K) of both urea and BOR. The same procedure was performed with THA and DEX. By mathematical simulation, the influence of varying plasma albumin concentrations (CHSA ) on the protein-bound drug fraction (PBF) and K was assessed. Plasma K values of HCO and PFX for THA, BOR, and DEX were about 40% (80 ± 7 vs. 65 ± 6 mL/min; P < 0.05), 70% (40 ± 8 vs. 33 ± 4 mL/min; P < 0.05), and 65% (47 ± 11 vs. 38 ± 7 mL/min; P < 0.05), respectively-lower (P < 0.0001) compared with urea (125 ± 7 vs. 122 ± 5 mL/min). K was highest (P < 0.0001) for THA. K was negatively correlated with CHSA (THA, r(2)  = 0.58, P < 0.001; BOR, r(2)  = 0.24, P < 0.05; DEX, r(2)  = 0.22, P < 0.05). CHSA continually decreased (P < 0.05) over time only with HCO, resulting in lower calculated PBF. Compared with BOR and DEX (minimum 72 and 56%, respectively), the PBF of THA (37%) was significantly lower (P < 0.001). A mathematical simulation based on the K values of urea and the drugs reliably estimated PBF (r(2)  = 0.886, P < 0.001). Drugs for multiple myeloma therapy are significantly removed with both HCO and PFX, with important implications for the dosing and timing of administration, particularly in patients with cast nephropathy receiving extended dialysis. If the Kurea of a dialyzer and the PBF of any given drug are known, Kdrug can be reliably estimated by mathematical simulation.

Simulation of the Impact of Atropisomer Interconversion on Plasma Exposure of Atropisomers of an Endothelin Receptor Antagonist

BMS-207940, a potent endothelin receptor antagonist, exists as rapidly interconverting atropisomers. The plasma interconversion t(1/2) is approximately 2.5 hours at 400 microg/mL under room temperature and decreases to < 0.1 hours at 20 microg/mL, making it extremely difficult to conduct pharmacokinetic studies of individual atropisomers. The pharmacokinetics of the 50/50 racemate of BMS-207940 in humans were reasonably described by a one-compartmental model with an apparent terminal elimination t(1/2) of 15 hours. Given the above rates, simulations were conducted based on a one-compartmental model to explore the possible range of individual rates of atropisomer elimination and potential difference in plasma exposure to the two atropisomers. Simulations demonstrated that the elimination rates of the individual atropisomers are bounded between 0 and 0.046 h(-1) and between 0.046 and 0.092 h(-1), respectively. The estimation of the upper bounds for atropisomer elimination rate constants is robust and relatively insensitive to the rate of atropisomer interconversion compared to the rate of racemate elimination. Simulations of the administration of a single atropisomer or the 50/50 racemate, based on all the possible scenarios of individual atropisomer elimination, showed little difference in plasma exposure to the two atropisomers. Potential differences in plasma exposure to the two atropisomers depend, to a larger extent, on the ratio of the rate of atropisomer interconversion versus racemate elimination and, to a lesser extent, on the conformation of atropisomers administered. When atropisomer interconversion is 10-fold or more rapid than racemate elimination, the largest possible difference in plasma exposure between the two atropisomers is below 20%, regardless of the route and conformation of the atropisomer(s) administered.

Human Pharmacokinetics and Interconversion of Enantiomers of MK-0767, a Dual PPARα/γ Agonist

MK-0767, a dual peroxisome proliferator-activated receptor (PPAR) alpha/gamma agonist, has been studied as a potential treatment of type 2 diabetes and dyslipidemia. The pharmacokinetics and interconversion of (+)-(R)-MK-0767 and (-)-(S)-MK-0767 were evaluated following oral administration of each single enantiomer and the racemate to healthy subjects. The results demonstrate that, consistent with in vitro experiments, chiral inversion occurs rapidly in vivo, and interconversion equilibrium favors (+)-(R). After all treatments, a stable ratio (R/S) of 2 to 2.5 was achieved within 8 hours in most individuals, congruent with model-based estimates of interconversion half-life. In addition, the pharmacokinetics of each enantiomer were generally similar regardless of treatment. Modeling and simulation of enantiomer disposition suggest that the observed predominance of (+)-(R)-MK-0767 in plasma may result from differential volumes of distribution between (-)-(S) and (+)-(R), preferential conversion from (-)-(S) to (+)-(R), or a combination of these, but not faster clearance of (-)-(S) compared to (+)-(R).

Enantiomerization mechanism of thalidomide and the role of water and hydroxide ions

The significance of the molecular chirality of drugs has been widely recognized due to the thalidomide tragedy. Most of the new drugs reaching the market today are single enantiomers, rather than racemic mixtures. However, many optically pure drugs, including thalidomide, undergo enantiomerization in vivo, thus negating the single enantiomers' benefits or inducing unexpected effects. A detailed atomic level understanding of chiral conversion, which is still largely lacking, is thus critical for drug development. Herein, we use first-principle density function theory (DFT) to explore the mechanism of enantiomerization of thalidomide. We have identified the two most plausible interconversion pathways for isolated thalidomide: 1) proton transfer from the chiral carbon center to an adjacent carbonyl oxygen atom, followed by isomerization and rotation of the glutarimide ring (before the proton hops back to the chiral carbon atom); and 2) a pathway that is the same as "1", but with the isomerization of the glutarimide ring occurring ahead of the initial proton transfer reaction. There are two remarkable energy barriers, 73.29 and 23.59 kcal mol(-1), corresponding to the proton transfer and the rotation of the glutarimide ring, respectively. Furthermore, we found that water effectively catalyzes the interconversion by facilitating the proton transfer with the highest energy barrier falling to approximately 30 kcal mol(-1), which, to our knowledge, is the first time that this important role of water in chiral conversion has been demonstrated. Finally, we show that the hydroxide ion can further lower the enantiomerization energy barrier to approximately 24 kcal mol(-1) by facilitating proton abstraction, which agrees well with recent experimental data under basic conditions. Our current findings highlight the importance of water and hydroxide ions in the enantiomerization of thalidomide and also provide new insights into the mechanism of enantiomerization at an atomic level.

Racemates revisited: heterochiral assemblies and the example of DL-thalidomide

The existence of racemic compounds, comprised of pairs of opposite enantiomers as discrete molecular entities, has been accepted for over a century. However, their ability to remain as associated dimers when in solution is uncertain, if not generally doubted. In this article, data has been assembled to provide evidence for the presence of intact dimeric heterochiral assemblies in solution and presents DL-thalidomide as a probable example of this phenomenon.

Embryopathic effects of thalidomide and its hydrolysis products in rabbit embryo culture: evidence for a prostaglandin H synthase (PHS)-dependent, reactive oxygen species (ROS)-mediated mechanism

Thalidomide (TD) causes birth defects in humans and rabbits via several potential mechanisms, including bioactivation by embryonic prostaglandin H synthase (PHS) enzymes to a reactive intermediate that enhances reactive oxygen species (ROS) formation. We show herein that TD in rabbit embryo culture produces relevant embryopathies, including decreases in head/brain development by 28% and limb bud growth by 71% (P<0.05). Two TD hydrolysis products, 2-phthalimidoglutaramic acid (PGMA) and 2-phthalimidoglutaric acid (PGA), were similarly embryopathic, attenuating otic vesicle (ear) and limb bud formation by up to 36 and 77%, respectively (P<0.05). TD, PGMA, and PGA all increased embryonic DNA oxidation measured as 8-oxoguanine (8-oxoG) by up to 2-fold (P<0.05). Co- or pretreatment with the PHS inhibitors eicosatetraynoic acid (ETYA) or acetylsalicylic acid (ASA), or the free-radical spin trap phenylbutylnitrone (PBN), completely blocked embryonic 8-oxoG formation and/or embryopathies initiated by TD, PGMA, and PGA. This is the first demonstration of limb bud embryopathies initiated by TD, as well as its hydrolysis products, in a mammalian embryo culture model of a species susceptible to TD in vivo, indicating that all likely contribute to TD teratogenicity in vivo, in part through PHS-dependent, ROS-mediated mechanisms.

Enantiomeric fraction as an indicator of pharmaceutical biotransformation during wastewater treatment and in the environment--a review

Enantioselective analysis of some pharmaceuticals during wastewater treatment has the potential to reveal significant insights regarding the effectiveness of biotransformation processes. Furthermore, enantioselective analysis of chiral pharmaceuticals in the aquatic environment may provide a useful historical record revealing the dominant source of (treated or untreated) wastewater contamination. This review of the recent scientific literature has identified only a handful of studies that have directly investigated these promising applications. However, a range of enantioselective analytical techniques are likely to be adaptable from those which have been developed within the pharmaceutical industry. These include direct enantioseparations of enantiomers on chiral stationary phases as well as indirect separations by achiral stationary phases after chiral derivatization to form pairs of physically distinguishable diastereomers. Further investigations of the patterns of enantiomeric fractionation of pharmaceuticals in wastewater and environmental samples will provide an increasingly solid understanding of the relationship between biotransformation processes and the often overlooked parameter of enantiomeric fraction.

Stereodynamics of tetramezine

The antidepressant drug tetramezine [1,2-bis-(3,3-dimethyldiaziridin-1-yl)ethane] consists of two bridged diaziridine moieties with four stereogenic nitrogen centers, which are stereolabile and, therefore, are prone to interconversion. The adjacent substituents at the nitrogen atoms of the diaziridines moieties exist only in an antiperiplanar conformation, which results in a coupled interconversion. Therefore, three stereoisomers exist (meso form and two enantiomeric forms), which epimerize when the diaziridine moieties are regarded as stereogenic units due to the coupled interconversion. Here, we have investigated the epimerization between the meso and enantiomeric forms by dynamic gas chromatography. Temperature-dependent measurements were performed, and reaction rate constants were determined using the unified equation of chromatography implemented in the software DCXplorer. The activation barriers of the epimerization were found to be ΔG(≠) = 100.7 kJ mol(-1) at 25°C and ΔG(≠) = 104.5 kJ mol(-1) at 37°C, respectively. The activation enthalpy and entropy were determined to be ΔH(≠) = 70.3 ± 0.4 kJ mol(-1) and ΔS(≠) = -102 ± 2 J mol(-1) K(-1) .

Supramolecular dynamics of thalidomide and its derivatives in water-sediment system

The contamination of drug residues, including chiral ones, is not acceptable in earth's ecosystem. The dynamicity of enantiomers of thalidomide and its derivatives (3-methyl thalidomide, 3-ethyl thalidomide, and 3-butyl thalidomide) was ascertained at supramolecular level in water-sediment system using solid phase extraction (SPE) and stereoselective HPLC. Enantiomeric separation of these drugs was carried out on Ceramosphere RU-2 (25 cm x 0.46 cm, particle size 50 microm) chiral column using pure ethanol (1.0 ml/min) as eluent at 230 nm detection. Retention times, capacity, separation, and resolution factors of the enantiomers of these drugs were in the range of 20.0-36.0, 2.08-3.93, 1.35-1.57, and 1.0-2.0 min, respectively. Percentage recoveries of the enantiomers in SPE were in the range of 90.0 to 95.0 in water-sediment system. Langmuir and Freundlich model were best fitted for dynamic equilibrium concentrations at different experimental parameters. Thalidomide and its derivatives follow first-order kinetics at dynamic equilibrium. The rate constants of chiral interconversions were 0.390 and 0.385 days(-1) for S- and R-enantiomers, respectively. The uptake of thalidomide by sediment is quite good and of endothermic nature indicating good self-purification capacity of the nature for such toxic species.

High performance liquid chromatographic determination of thalidomide in patients affected by hepatocellular carcinoma

The present study developed a validate and precise reversed-phase high performance liquid chromatography (HPLC) method for the determination of thalidomide (T) in plasma, to quantify T in patients affected by hepatocellular carcinoma. Twelve male subjects aging from 62 to 82 years and weighting 66-88kg, were orally administered with single dose of T (200mg/BW). Two ml of stabilizer-solution (CH3OH/CH3CN, 1/1 (v/v)+CH3COOH 2%) were added to 1ml of human plasma and stoked to -80 degrees C until analyses. This moisture (1.38microl) was added with 20microl of CF3COOH and 100microl of phthalimide (IS) 1.75microg/ml, vortexed and centrifuged. Surnatant (800microl) was dried under vacuum at room temperature, added with 50microl of appropriate solution and injected onto HPLC. T and IS were detected at UV wavelength of 220nm with a run time of 10min. Mobile phase was 10mM pH 5.5NH4+CH3COO-/CH3CN, 75/25 (v/v) buffer at flow rate of 1.5ml/min. Inter-day and intra-day variation coefficient was <10% with an error of accuracy <10%. The present detection method was able to quantify T to every withdrawal time period (LOD 0.05microg/ml). The IS used in the present study had the same wavelength maximum absorption of T, differently from early UV detection methods reported in literature where phenacetin was used. Pharmacokinetic parameters belonging from the present study are not significantly different from those calculated in previously studies performed in human health subjects and patients affected by other pathology.

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.

Drug disposition in three dimensions: an update on stereoselectivity in pharmacokinetics

Many marketed drugs are chiral and are administered as the racemate, a 50:50 combination of two enantiomers. Pharmacodynamic and pharmacokinetic differences between enantiomers are well documented. Because of enantioselectivity in pharmacokinetics, results of in vitro pharmacodynamic studies involving enantiomers may differ from those in vivo where pharmacokinetic processes will proceed. With respect to pharmacokinetics, disparate plasma concentration vs time curves of enantiomers may result from the pharmacokinetic processes proceeding at different rates for the two enantiomers. At their foundation, pharmacokinetic processes may be enantioselective at the levels of drug absorption, distribution, metabolism and excretion. In some circumstances, one enantiomer can be chemically or biochemically inverted to its antipode in a unidirectional or bidirectional manner. Genetic consideration such as polymorphic drug metabolism and gender, and patient factors such as age, disease state and concomitant drug intake can all play a role in determining the relative plasma concentrations of the enantiomers of a racemic drug. The use of a nonstereoselective assay method for a racemic compound can lead to difficulties in interpretation of data from, for example, bioequivalence or dose/concentration vs effect assessments. In this review data from a number of representative studies involving pharmacokinetics of chiral drugs are presented and discussed.

Inhibitory effects of benzoate on chiral inversion and clearance of N(G)-nitro-arginine in conscious rats

N(G)-nitro-arginine (NNA) is known to exhibit stereoselective pharmacokinetics in which N(G)-nitro-d-arginine (d-NNA) has a faster clearance rate than N(G)-nitro-l-arginine (l-NNA) in anesthetized rats, and d-NNA undergoes unidirectional chiral inversion. It was postulated that chiral inversion of d-NNA was performed in a two-step pathway by d-amino acid oxidase (DAAO) followed by an unidentified transaminase. Such chiral inversion contributes (at least partially) to the pharmacokinetic stereoselectivity of NNA. This study used the selective inhibitor of DAAO, sodium benzoate, to test the above hypothesis. An i.v. bolus injection of d-NNA (32 mg/kg) and l-NNA (16 mg/kg) in conscious rats exhibited biphasic disposition with different pharmacokinetic parameters in a stereospecific manner (approximately 5-10-fold differences). Unidirectional chiral inversion of d-NNA but not l-NNA was found from these animals. In addition to its similar inhibitory effects on the d-NNA conversion and DAAO activity in kidney homogenates, sodium benzoate completely blocked chiral inversion of d-NNA and led to a smaller stereospecific difference, reflected by a nearly 50% reduction of d-NNA clearance and a 2-fold increase in t(1/2) and area under the curve of d-NNA in benzoate-pretreated rats. The results suggest that DAAO plays an essential role in chiral inversion of d-NNA and chiral inversion contributes mostly to the pharmacokinetic stereospecificity of NNA.

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.

Thalidomide in multiple myeloma

Multiple myeloma is an incurable bone marrow cancer, the treatment of which is notoriously difficult. Only modest advances have been achieved using complex polychemotherapeutic regimens, transplant strategies and supportive therapy. In 1999, when new drugs for myeloma were urgently needed, thalidomide was introduced and opened up a completely new line of therapy for the disease. Although the mechanism of action is not yet completely understood, thalidomide has demonstrated efficacy in patients with refractory, relapsed myeloma, even in late-stage cases. This article reviews the current knowledge of thalidomide in myeloma treatment, focusing especially on the possible mechanisms of action, clinical results and adverse events of this drug.

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.

Determination of thalidomide by high performance liquid chromatography: Plasma pharmacokinetic studies in the rat

A sensitive and simple high performance liquid chromatography (HPLC) method was developed and validated for the determination of thalidomide in rat plasma. Chromatography was accomplished with a reversed-phase Hypersil C18 column. Mobile phase consisted of acetonitrile-10 mM ammonium acetate buffer (pH 5.50) (28:72, v/v), at a flow rate of 0.8 ml/min. Thalidomide was monitored by ultraviolet detector at 220 nm and it gave a linear response as a function of concentration over 0.02-50 microM. The limit of quantitation in rat plasma was 0.50 ng (0.02 microM plasma concentration) with an aliquot of 20 microl. Results from a 3-day validation study indicated that this method allows for simple and rapid quantitation of thalidomide with excellent accuracy and reliability. Using this validated assay, the effect of coadministered irinotecan (CPT-11) on the plasma pharmacokinetics of thalidomide in rats was determined. Coadministration of CPT-11 (intravenously, 60 mg/kg) increased the maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC(0-10h)) of thalidomide by 32.29 and 11.66%, respectively, as compared to the control, but none of the effect of CPT-11 was of statistical significance (P > 0.05). Concomitant CPT-11 also caused a 10.04% decrease in plasma clearance (CL) and 14.51% decrease in volume of distribution (V(d)) (P > 0.05). These results suggest that coadministered CPT-11 did not significantly alter the plasma pharmacokinetics of thalidomide in rats. Further studies are warranted to explore the pharmacokinetic and pharmacodynamic interactions between CPT-11 and thalidomide.

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.

Identification of 3-(Acylamino)azepan-2-ones as Stable Broad-Spectrum Chemokine Inhibitors Resistant to Metabolism in Vivo

3-(acylamino)glutarimides, a class of broad spectrum chemokine inhibitors, are rapidly hydrolyzed in serum, despite being stable in aqueous solution. Synthesis and high-performance liquid chromatography analysis of the proposed N-acyl-glutamate and -glutamine metabolites establish the enzyme-catalyzed breakdown pathways. In vitro assays suggest that despite their short half-life in vivo, the parent acylamino-glutarimides, not the ring-opened hydrolysis products, are the source of the antiinflammatory activity. Identification of this metabolic pathway has led to the development of 3-(acylamino)azepan-2-ones that are also broad spectrum chemokine inhibitors and act as stable, orally available powerful antiinflammatory agents in vivo with doses of 1 mg/kg.

Atropisomeric property of 1-(2,6-difluorobenzyl)-3-[(2R)-amino-2-phenethyl]-5-(2-fluoro-3-methoxyphenyl)-6-methyluracil

1-(2,6-Difluorobenzyl)-3-[(2R)-amino-2-phenethyl]-5-(2-fluoro-3-methoxyphenyl)-6-methyluracil (6), a potent and orally active antagonist of the human gonadotropin-releasing hormone receptor, exists as a pair of atropisomers in solution, which was detected by NMR spectroscopy, and separable by HPLC. In addition to a (R)-configured benzylamine, there is a second stereogenic element due to the presence of a chiral axis between the substituted 5-phenyl group and the uracil core. The rate constant of the interconversion (k = 5.07 x 10(-5) s(-1)) of these two atropisomers was determined by proton NMR analysis of a diastereoisomer-enriched sample in aqueous solution at 25 degrees C, and the corresponding Gibbs free energy DeltaG(#) of rotation barrier (97.4 kJ mol(-1)) was calculated using the Eyring equation. The diastereoisomer half-life at physiological temperature (37 degrees C) in aqueous media was estimated to be about 46 min.

Renal d-Amino Acid Oxidase Mediates Chiral Inversion ofNG-Nitro-d-arginine

N(G)-nitro-d-arginine (d-NNA), i.v. injected into rats, produced a pressor response, and was presumed to act via chiral inversion into N(G)-nitro-l-arginine (l-NNA), an inhibitor of nitric oxide synthase. We examined the possible role of renal d-amino acid oxidase (DAAO) in the chiral inversion of d-NNA to l-NNA. In pentobarbital-anesthetized rats, l-NNA was detected via capillary electrochromatography in the blood immediately after i.v. injection of d-NNA. The time course of appearance of l-NNA paralleled the increase in blood pressure elicited by d-NNA. Unilateral renal ligation partially, and bilateral ligation completely, blocked the pressor response as well as the conversion of d-NNA to l-NNA. Furthermore, injection into conscious rats of sodium benzoate, a selective DAAO inhibitor, completely blocked the pressor response to naive d-NNA, but not pressor response to d-NNA preincubated with homogenates of the kidney. Homogenates of the kidneys, liver (lesser degree), and brain (much lesser degree) converted d-NNA to l-NNA, and the chiral inversion was blocked by the addition of benzoate. Moreover, d-NNA chiral inversion correlates with the activity of DAAO. Our results reveal a novel pathway of chiral inversion of d-amino acids where the renal DAAO plays an essential role that accounts for the biological activity of d-NNA.

THEINTEGRATION OFPHARMACOKINETICS ANDPHARMACODYNAMICS: Understanding Dose-Response

Pharmacokinetic (PK) and pharmacodynamic (PD) studies have proven to be powerful and instructive tools, particularly in elucidating important aspects of human pharmacology. Nevertheless, they remain imperfect tools in that they only allow researchers to indirectly extrapolate, through computational modeling, the dynamic processes of drug action. Furthermore, neither tool alone provides a complete nor necessarily relevant picture of drug action. This review explores the utility and applications of PK and PD in the study of drugs, provides examples of lessons learned from their application to studies of human pharmacology, points out some of their limitations, and advances the thesis that these tools ideally should be employed together in an integrated approach. As we continue to apply these tools across the continuum of age and disease, they provide a powerful means to enhance our understanding of drug action, drug interactions, and intrinsic host factors that influence pharmacologic response.

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.

Chiral inversion of the second generation IMiD CC-4047 (ACTIMID ) in human plasma and phosphate-buffered saline

CC-4047 is a racemic second-generation immunomodulatory drug currently in clinical development for various oncologic indications. It has potent effects on key cytokines including tumor necrosis factor-alpha, interleukin (IL-10), and interferon (IFN-gamma). The S-isomer of CC-4047 has been reported to be the more potent enantiomer of the racemate. In this article we report on the rapid racemization of the S-isomer of CC-4047 in human plasma and phosphate-buffered saline. These results support the further development of the racemate instead of the S-isomer.

Thalidomide: a review of approved and investigational uses

BACKGROUND

Thalidomide is best known as a major teratogen that caused birth defects in up to 12,000 children in the 1960s. More recently, this agent has been approved by the US Food and Drug Administration for the treatment of erythema nodosum leprosum (ENL) through a restricted-use program. Its immunomodulatory, anti-inflammatory, and antiangiogenic properties are currently under study in a number of clinical conditions.

OBJECTIVE

This article reviews the pharmacology of thalidomide; its approved and off-label uses in dermatologic, oncologic, and gastrointestinal conditions; and adverse events associated with its use.

METHODS

Relevant articles were identified through searches of MEDLINE (1966-June 2002), International Pharmaceutical Abstracts (1970-June 2002), and EMBASE (1990-June 2002). Search terms included but were not limited to thalidomide, pharmacokinetics, pharmacology, therapeutic use, and teratogenicity, as well as terms for specific disease states and adverse events. Further publications were identified from the reference lists of the reviewed articles. Abstracts of recent symposia were obtained from the American Society of Clinical Oncology Web site.

RESULTS

Thalidomide is thought to exert its therapeutic effect through the modulation of cytokines, particularly tumor necrosis factor-alpha. In addition to its approved indication for ENL, thalidomide has been studied in various other conditions, including graft-versus-host disease, discoid lupus erythematosus, sarcoidosis, relapsed/refractory multiple myeloma, Waldenstrom's macroglobulinemia, myelodysplastic syndromes, acute myeloid leukemia, myelofibrosis with myeloid metaplasia, renal cell carcinoma, malignant gliomas, prostate cancer, Kaposi's sarcoma, colorectal carcinoma, oral aphthous ulcers, Behçet's disease, Crohn's disease, and HIV/AIDS-associated wasting. Adverse events most frequently associated with its use include somnolence, constipation, rash, peripheral neuropathy, and thromboembolism.

CONCLUSIONS

Use of thalidomide is limited by toxicity, limited efficacy data, and restricted access. Evidence of its efficacy in conditions other than ENL awaits the results of controlled clinical trials.

Stereoselective metabolism of pentoxifylline in vitro and in vivo in humans

Pentoxifylline increases erythrocyte flexibility, reduces blood viscosity, and inhibits platelet aggregation and is thus used in the treatment of peripheral vascular disease. It is transformed into at least seven phase I metabolites, of which two, M1 and M5, are active. The reduction of the keto group of pentoxifylline to a secondary alcohol in M1 takes place chiefly in erythrocytes, is rapidly reversible, and creates a chiral center. The aims of this study were: to develop HPLC methods to separate the enantiomers of M1, to investigate the kinetics of the reversible biotransformation of pentoxifylline to (R)- and (S)-M1 in hemolysed erythrocyte suspension, and to quantify the formation of the enantiomers of M1 (as well as M4 and M5) after intravenous and oral administration of pentoxifylline to human volunteers. (R)- and (S)-M1 could be separated preparatively on a cellobiohydrolase column, while determination in blood or plasma was by HPLC after chiral derivatization with diacetyl-L-tartaric acid anhydride. The metabolism of pentoxifylline to (R)-M1 in suspensions of hemolysed erythrocytes followed simple Michaelis-Menten kinetics (K(m) = 11 mM), while that to (S)-M1 was best described by a two-enzyme model (K(m) = 1.1 and 132 mM). Studies with inhibitors indicated that the enzymes were of the carbonyl reductase type. At a therapeutic blood concentration of pentoxifylline, the calculated rate of formation of (S)-M1 is 15 times higher than that of the (R)-enantiomer. Back-conversion of M1 to pentoxifylline was 3-4 times faster for the (S)- than for the (R)-enantiomer. In vivo, the R:S plasma concentration ratio of M1 ranged from 0.010-0.025 after intravenous infusion of 300 or 600 mg of pentoxifylline, and from 0.019-0.037 after oral administration of 600 mg. The biotransformation of pentoxifylline to M1 was thus highly stereoselective in favor of the (S)-enantiomer both in vitro and in vivo.

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.