Integration of ancient DNA with transdisciplinary dataset finds strong support for Inca resettlement in the south Peruvian coast.

Ancient DNA (aDNA) analysis provides a powerful means of investigating human migration, social organization, and a plethora of other crucial questions about humanity's past. Recently, specialists have suggested that the ideal research design involving aDNA would include multiple independent lines of evidence. In this paper, we adopt a transdisciplinary approach integrating aDNA with archaeological, biogeochemical, and historical data to investigate six individuals found in two cemeteries that date to the Late Horizon (1400 to 1532 CE) and Colonial (1532 to 1825 CE) periods in the Chincha Valley of southern Peru. Genomic analyses indicate that these individuals are genetically most similar to ancient and present-day populations from the north Peruvian coast located several hundred kilometers away. These genomic data are consistent with 16th century written records as well as ceramic, textile, and isotopic data. These results provide some of the strongest evidence yet of state-sponsored resettlement in the pre-Colonial Andes. This study highlights the power of transdisciplinary research designs when using aDNA data and sets a methodological standard for investigating ancient mobility in complex societies.

Synthesis of l-[4-11 C]Asparagine by Ring-Opening Nucleophilic 11 C-Cyanation Reaction of a Chiral Cyclic Sulfamidate Precursor.

The development of a convenient and rapid method to synthesize radiolabeled, enantiomerically pure amino acids (AAs) as potential positron emission tomography (PET) imaging agents for mapping various biochemical transformations in living organisms remains a challenge. This is especially true for the synthesis of carbon-11-labeled AAs given the short half-life of carbon-11 (11 C, t1/2 =20.4 min). A facile synthetic pathway to prepare enantiomerically pure 11 C-labeled l-asparagine was developed using a partially protected serine as a starting material with a four-step transformation providing a chiral five-membered cyclic sulfamidate as the radiolabeling precursor. Its structure and absolute configuration were confirmed by X-ray crystallography. Utilizing a [11 C]cyanide nucleophilic ring opening reaction followed by selective acidic hydrolysis and deprotection, enantiomerically pure l-[4-11 C]asparagine was synthesized. Further optimization of reaction parameters, including base, metal ion source, solvent, acid component, reaction temperature and reaction time, a reliable two-step method for synthesizing l-[4-11 C]asparagine was presented: within a 45±3 min (n=5, from end-of-bombardment), the desired enantiomerically pure product was synthesized with the initial nucleophilic cyanation yield of 69±4 % (n=5) and overall two-step radiochemical yield of 53±2 % (n=5) based on starting [11 C]HCN, and with radiochemical purity of 96±2 % (n=5).

Dynamic Precision Phenotyping Reveals Mechanism of Crop Tolerance to Root Herbivory.

The western corn rootworm (WCR; Diabrotica virgifera virgifera LeConte) is a major pest of maize (Zea mays) that is well adapted to most crop management strategies. Breeding for tolerance is a promising alternative to combat WCR but is currently constrained by a lack of physiological understanding and phenotyping tools. We developed dynamic precision phenotyping approaches using 11C with positron emission tomography, root autoradiography, and radiometabolite flux analysis to understand maize tolerance to WCR Our results reveal that WCR attack induces specific patterns of lateral root growth that are associated with a shift in auxin biosynthesis from indole-3-pyruvic acid to indole-3-acetonitrile. WCR attack also increases transport of newly synthesized amino acids to the roots, including the accumulation of Gln. Finally, the regrowth zones of WCR-attacked roots show an increase in Gln turnover, which strongly correlates with the induction of indole-3-acetonitrile-dependent auxin biosynthesis. In summary, our findings identify local changes in the auxin biosynthesis flux network as a promising marker for induced WCR tolerance.

Total cyanide mass measurement with micro-ion selective electrode for determination of specific activity of carbon-11 cyanide.

In this research, we aim to directly measure the specific activity (SA) of the carbon-11 cyanide ([(11)C]CN¯) produced by our in-house built automated [(11)C]HCN production system and to identify the major sources of (12)C-cyanide ((12)CN¯). The [(11)C]CN¯ is produced from [(11)C]CO2, which is generated by the (14)N(p,α)(11)C nuclear reaction using a cyclotron. Direct measurement of cyanide concentrations was accomplished using a relatively inexpensive, and easy to use ion selective electrode (ISE) which offered an appropriate range of sensitivity for detecting mass. Multiple components of the [(11)C]HCN production system were isolated in order to determine their relative contributions to (12)CN¯ mass. It was determined that the system gases were responsible for approximately 30% of the mass, and that the molecular sieve/nickel furnace unit contributed approximately 70% of the mass. Beam on target (33µA for 1 and 10min) did not contribute significantly to the mass. Additionally, we compared the SA of our [(11)C]HCN precursor determined using the ISE to the SA of our current [(11)C]CN¯ derived radiotracers determined by HPLC to assure there was no significant difference between the two methods. These results are the first reported use of an ion selective electrode to determine the SA of no-carrier-added cyanide ion, and clearly show that it is a valuable, inexpensive and readily available tool suitable for this purpose.

Evidence that formulations of the selective MAO-B inhibitor, selegiline, which bypass first-pass metabolism, also inhibit MAO-A in the human brain.

Selegiline (L-deprenyl) is a selective, irreversible inhibitor of monoamine oxidase B (MAO-B) at the conventional dose (10 mg/day oral) that is used in the treatment of Parkinson's disease. However, controlled studies have demonstrated antidepressant activity for high doses of oral selegiline and for transdermal selegiline suggesting that when plasma levels of selegiline are elevated, brain MAO-A might also be inhibited. Zydis selegiline (Zelapar) is an orally disintegrating formulation of selegiline, which is absorbed through the buccal mucosa producing higher plasma levels of selegiline and reduced amphetamine metabolites compared with equal doses of conventional selegiline. Although there is indirect evidence that Zydis selegiline at high doses loses its selectivity for MAO-B, there is no direct evidence that it also inhibits brain MAO-A in humans. We measured brain MAO-A in 18 healthy men after a 28-day treatment with Zydis selegiline (2.5, 5.0, or 10 mg/day) and in 3 subjects receiving the selegiline transdermal system (Emsam patch, 6 mg/day) using positron emission tomography and the MAO-A radiotracer [(11)C]clorgyline. We also measured dopamine transporter (DAT) availability in three subjects from the 10 mg group. The 10 mg Zydis selegiline dose significantly inhibited MAO-A (36.9±19.7%, range 11-70%, p<0.007)) but not DAT; and while Emsam also inhibited MAO-A (33.2±28.9 (range 9-68%) the difference did not reach significance (p=0.10)) presumably because of the small sample size. Our results provide the first direct evidence of brain MAO-A inhibition in humans by formulations of selegiline, which are currently postulated but not verified to target brain MAO-A in addition to MAO-B.

Investigation of SN2 [11C]cyanation for base-sensitive substrates: an improved radiosynthesis of L-[5-11C]-glutamine.

Carbon-11 (ß(+) emitter, t1/2 = 20.4 min) radiolabeled L-glutamine is a potentially useful molecular imaging agent that can be utilized with positron emission tomography for both human oncological diagnosis and plant imaging research. Based upon a previously reported [(11)C]cyanide end-capping labeling method, a systematic investigation of nucleophilic cyanation reactions and acidic hydrolysis reaction parameters, including base, metal ion source, phase transfer catalyst, solvent, reaction temperature and reaction time, was conducted. The result was a milder, more reliable, two-step method which provides L-[5-(11)C]-glutamine with a radiochemical yield of 63.8 ± 8.7% (range from 51 to 74%, n = 10) with >90% radiochemical purity and >90 % enantiomeric purity. The total synthesis time was 40-50 min from the end of bombardment. In addition, an Fmoc derivatization method was developed to measure the specific activity of this radiotracer.

Therapeutic doses of buspirone block D3 receptors in the living primate brain.

Dopamine D3 receptor (D3R) antagonists may be effective medications for multiple substance use disorders (SUDs). However, no selective D3R antagonists are currently available for clinical testing. Buspirone, originally characterized as a 5-HT1A partial agonist and used as an anxiolytic, also binds to D3R and D4R with high affinity, with lower affinity to D2R, and interferes with cocaine reward. Here we used PET with [11C]PHNO (D3R-preferring radioligand), [11C]raclopride (D2R/D3R radioligand) and [11C]NNC-112 (D1R radioligand) to measure occupancy of oral and parenteral buspirone in the primate brain. Intramuscular buspirone (0.19 and 0.5 mg/kg) blocked both [11C]PHNO and [11C]raclopride binding to striatum, exhibiting high occupancy (50-85%) at 15 min and rapid wash-out over 2-6 h. In contrast, oral buspirone (3 mg/kg) significantly blocked [11C]PHNO binding in D3-rich regions (globus pallidum and midbrain) at 3 h, but had minimal effects on [11C]raclopride binding (28-37% at 1 h and 10% at 3 h). Buspirone did not block [11C]NNC-112. Our findings provide evidence that i.m. buspirone blocks D3R and D2R, whereas oral buspirone is more selective towards D3R blockade in vivo, consistent with extensive first pass metabolism and supporting the hypothesis that its metabolites (5- and 6'-hydroxybuspirone) merit evaluation for treating SUDs. They also indicate that for oral buspirone to achieve greater than 80% sustained D3R occupancy, as might be needed to treat addiction, higher doses (at least three-fold) than those used to treat anxiety (maximal 60 mg) will be required. Nonetheless, based on previous clinical studies, these doses would be safe and well tolerated.

Whole-body pharmacokinetics of HDAC inhibitor drugs, butyric acid, valproic acid and 4-phenylbutyric acid measured with carbon-11 labeled analogs by PET.

The fatty acids, n-butyric acid (BA), 4-phenylbutyric acid (PBA) and valproic acid (VPA, 2-propylpentanoic acid) have been used for many years in the treatment of a variety of CNS and peripheral organ diseases including cancer. New information that these drugs alter epigenetic processes through their inhibition of histone deacetylases (HDACs) has renewed interest in their biodistribution and pharmacokinetics and the relationship of these properties to their therapeutic and side effect profiles. In order to determine the pharmacokinetics and biodistribution of these drugs in primates, we synthesized their carbon-11 labeled analogues and performed dynamic positron emission tomography (PET) in six female baboons over 90 min. The carbon-11 labeled carboxylic acids were prepared by using (11)CO2 and the appropriate Grignard reagents. [(11)C]BA was metabolized rapidly (only 20% of the total carbon-11 in plasma was parent compound at 5 min post injection) whereas for VPA and PBA 98% and 85% of the radioactivity were the unmetabolized compound at 30 min after their administration respectively. The brain uptake of all three carboxylic acids was very low (<0.006%ID/cc, BA>VPA>PBA), which is consistent with the need for very high doses for therapeutic efficacy. Most of the radioactivity was excreted through the kidneys and accumulated in the bladder. However, the organ biodistribution between the drugs differed. [(11)C]BA showed relatively high uptake in spleen and pancreas whereas [(11)C]PBA showed high uptake in liver and heart. Notably, [(11)C]VPA showed exceptionally high heart uptake possibly due to its involvement in lipid metabolism. The unique biodistribution of each of these drugs may be of relevance in understanding their therapeutic and side effect profile including their teratogenic effects.

Acute alcohol intoxication decreases glucose metabolism but increases acetate uptake in the human brain.

Alcohol intoxication results in marked reductions in brain glucose metabolism, which we hypothesized reflect not just its GABAergic enhancing effects but also the metabolism of acetate as an alternative brain energy source. To test this hypothesis we separately assessed the effects of alcohol intoxication on brain glucose and acetate metabolism using Positron Emission Tomography (PET). We found that alcohol intoxication significantly decreased whole brain glucose metabolism (measured with FDG) with the largest decrements in cerebellum and occipital cortex and the smallest in the thalamus. In contrast, alcohol intoxication caused a significant increase in [1-(11)C]acetate brain uptake (measured as standard uptake value, SUV), with the largest increases occurring in the cerebellum and the smallest in the thalamus. In heavy alcohol drinkers [1-(11)C]acetate brain uptake during alcohol challenge tended to be higher than in occasional drinkers (p<0.06) and the increases in [1-(11)C]acetate uptake in cerebellum with alcohol were positively associated with the reported amount of alcohol consumed (r=0.66, p<0.01). Our findings corroborate a reduction of brain glucose metabolism during intoxication and document an increase in brain acetate uptake. The opposite changes observed between regional brain metabolic decrements and regional increases in [1-(11)C]acetate uptake support the hypothesis that during alcohol intoxication the brain may rely on acetate as an alternative brain energy source and provides preliminary evidence that heavy alcohol exposures may facilitate the use of acetate as an energy substrate. These findings raise the question of the potential therapeutic benefits that increasing plasma acetate concentration (i.e. ketogenic diets) may have in alcoholics undergoing alcohol detoxification.

Blockade of the brain histamine H3 receptor by JNJ-39220675: preclinical PET studies with [¹¹C]GSK189254 in anesthetized baboon.

RATIONALE: The preclinical characterization of a series of aryloxypyridine amides has identified JNJ-39220675 ((4-cyclobutyl-1,4-diazepan-1-yl)(6-(4-fluorophenoxy)pyridin-3-yl)methanone) as a high-affinity histamine H(3) receptor antagonist and a candidate for further drug development particularly in the treatment of alcohol-related behaviors. OBJECTIVE: This study measured brain histamine H(3) receptor blockade by JNJ-39220675 (1 mg/kg) in the female baboon. METHODS: Positron emission tomography imaging and [(11)C]GSK189254, a reversible high-affinity radiotracer with specificity for the histamine H(3) receptor, was used to measure histamine H(3) receptor availability at baseline and after i.v. and oral administration of JNJ-39220675 (1 mg/kg) in the anesthetized baboon. Histamine H(3) receptor availability was estimated as the total distribution volume (V (T)) in brain regions. The sensitivity of [(11)C]GSK189254 binding to injected mass and carryover effects was determined. RESULTS: JNJ-39220675 produces robust (ca. 90 %) blockade of [(11)C]GSK189254 binding after i.v. and oral administration. After oral administration of JNJ-39220675 (1 mg/kg), the fractional receptor occupancy was >0.9 at 90 min with a slight increase from 90 to 240 min. Similar to prior studies in humans, V (T) was highly sensitive to the mass of GSK189254 with ED(50) estimated to be 0.16 µg/kg. CONCLUSIONS: The robust blockade of binding of [(11)C]GSK189254 by JNJ-39220675 demonstrates that this compound readily penetrates the blood-brain barrier and occupies the histamine H(3) receptor after oral administration at low plasma concentrations (∼1 ng/cc) supporting further drug development for alcohol addiction and other disorders. This study corroborates prior reports of the high sensitivity of [(11)C]GSK189254 to injected mass at doses >0.1 µg/kg.

Characterisation of [¹¹C]PR04.MZ in Papio anubis baboon: a selective high-affinity radioligand for quantitative imaging of the dopamine transporter.

N-(4-fluorobut-2-yn-1-yl)-2ß-carbomethoxy-3ß-(4'-tolyl)nortropane (PR04.MZ, 1) is a PET radioligand for the non-invasive exploration of the function of the cerebral dopamine transporter (DAT). A reliable automated process for routine production of the carbon-11 labelled analogue [(11)C]PR04.MZ ([(11)C]-1) has been developed using GMP compliant equipment. An adult female Papio anubis baboon was studied using a test-retest protocol with [(11)C]-1 in order to assess test-retest reliability, metabolism and CNS distribution profile of the tracer in non-human primates. Blood sampling was performed throughout the studies for determination of the free fraction in plasma (f(P)), plasma input functions and metabolic degradation of the radiotracer [(11)C]-1. Time-activity curves were derived for the putamen, the caudate nucleus, the ventral striatum, the midbrain and the cerebellum. Distribution volumes (V(T)) and non-displaceable binding potentials (BP(ND)) for various brain regions and the blood were obtained from kinetic modelling. [(11)C]-1 shows promising results as a selective marker of the presynaptic dopamine transporter. With the reliable visualisation of the extra-striatal dopaminergic neurons and no indication on labelled metabolites, the tracer provides excellent potential for translation into man.

Polymer-supported organotin reagent for prosthetic group labeling of biological macromolecules with radioiodine.

In this study, we investigated the use of poly-mer-bound precursor for generating a radiolabeled prosthetic group to be used for conjugate labeling of biological macromolecules. For the approach, a trialkyltin chloride in which the tin was bound to a hydrophilic PEG-based resin support via one of the alkyl groups was synthesized. This resin was then used to prepare a resin-bound trialkyltin benzoic acid, which in some cases was further derivatized on-resin by converting it to a succinimidyl ester. Exposure of the resin-bound compounds to electrophilic radioiodine (¹²5I) in either an aqueous or methanol solvent liberated either free radiolabeled [¹²5I]iodobenzoic acid or its succinimidyl ester without co-release of the resin-bound precursors. Radiochemical yield was between 35% and 75%, depending on the solvent system and precursor. As example applications for the released compounds, the amine-reactive N-succinimidyl-[¹²5I]iodobenzoate prosthetic group was used for conjugate radiolabeling of a peptide, tomato plant systemin, and two proteins, albumin and IgG antibody. These results demonstrate that resin-bound organotin precursors in which the compound to be labeled is tethered to the support via the tin group to be substituted can be used to produce radioiodine-labeled aromatic prosthetic groups in good specific activity without the need for HPLC purification. This solid-phase approach is potentially adaptable to kit-formulation for performing conjugate radiolabeling of biological macromolecules.

Unique distribution of aromatase in the human brain: in vivo studies with PET and [N-methyl-11C]vorozole.

Aromatase catalyzes the last step in estrogen biosynthesis. Brain aromatase is involved in diverse neurophysiological and behavioral functions including sexual behavior, aggression, cognition, and neuroprotection. Using positron emission tomography (PET) with the radiolabeled aromatase inhibitor [N-methyl-(11)C]vorozole, we characterized the tracer distribution and kinetics in the living human brain. Six young, healthy subjects, three men and three women, were administered the radiotracer alone on two separate occasions. Women were scanned in distinct phases of the menstrual cycle. Specificity was confirmed by pretreatment with a pharmacological (2.5 mg) dose of the aromatase inhibitor letrozole. PET data were acquired over a 90-min period and regions of interest placed over selected brain regions. Brain and plasma time activity curves, corrected for metabolites, were used to derive kinetic parameters. Distribution volume (V(T)) values in both men and women followed the following rank order: thalamus > amygdala = preoptic area > medulla (inferior olive) > accumbens, pons, occipital and temporal cortex, putamen, cerebellum, and white matter. Pretreatment with letrozole reduced V(T) in all regions, though the size of the reduction was region-dependent, ranging from ∼70% blocking in thalamus andpreoptic area to ∼10% in cerebellum. The high levels of aromatase in thalamus and medulla (inferior olive) appear to be unique to humans. These studies set the stage for the noninvasive assessment of aromatase involvement in various physiological and pathological processes affecting the human brain.

Histone deacetylase inhibitor, MS-275, exhibits poor brain penetration: PK studies of [C]MS-275 using Positron Emission Tomography.

MS-275 (Entinostat) is a histone deacetylase (HDAC) inhibitor currently in clinical trials for the treatment of several types of cancer. Recent reports have noted that MS-275 can cross the blood brain barrier (BBB) and cause region specific changes in rodent brain histone acetylation. To characterize the pharmacokinetics and distribution of MS-275 in the brain using positron emission tomography (PET), we labeled the carbamate carbon of MS-275 with carbon-11. Using PET, we determined that [(11)C]MS-275 has low uptake in brain tissue when administered intravenously to non-human primates. In rodent studies, we observed that pharmacokinetics and brain accumulation of [(11)C]MS-275 were not changed by the co-administration of large doses of unlabeled MS-275. These results, which both highlight the poor brain penetration of MS-275, clearly suggest its limitation as a therapeutic agent for the central nervous system (CNS). Moreover, our study demonstrates the effectiveness of PET at providing brain pharmacokinetic data for HDAC inhibitors. These data are important not only for the development of new compounds for peripheral cancer treatment (where CNS exclusion is often advantageous), but also for the treatment of neurological disorders (where CNS penetration is critical).

Evaluation of [(11)C]metergoline as a PET radiotracer for 5HTR in nonhuman primates.

Metergoline, a serotonin receptor antagonist, was labeled with carbon-11 in order to evaluate its pharmacokinetics and distribution in non-human primates using positron emission tomography. [(11)C]Metergoline had moderate brain uptake and exhibited heterogeneous specific binding, which was blocked by pretreatment with metergoline and altanserin throughout the cortex. Non-specific binding and insensitivity to changes in synaptic serotonin limit its potential as a PET radiotracer. However, the characterization of [(11)C]metergoline pharmacokinetics and binding in the brain and peripheral organs using PET improves our understanding of metergoline drug pharmacology.

Radiosynthesis and bioimaging of the tuberculosis chemotherapeutics isoniazid, rifampicin and pyrazinamide in baboons.

The front-line tuberculosis (TB) chemotherapeutics isoniazid (INH), rifampicin (RIF), and pyrazinamide (PZA) have been labeled with carbon-11 and the biodistribution of each labeled drug has been determined in baboons using positron emission tomography (PET). Each radiosynthesis and formulation has been accomplished in 1 h, using [(11)C]CH(3)I to label RIF and [(11)C]HCN to label INH and PZA. Following iv administration, INH, PZA, RIF, and/or their radiolabeled metabolites clear rapidly from many tissues; however, INH, PZA, and/or their radiolabeled metabolites accumulate in the bladder while RIF and/or its radiolabeled metabolites accumulates in the liver and gall bladder, consistent with the known routes of excretion of the drugs. In addition, the biodistribution data demonstrate that the ability of the three drugs and their radiolabeled metabolites to cross the blood-brain barrier decreases in the order PZA > INH > RIF, although in all cases the estimated drug concentrations are greater than the minimum inhibitory concentration (MIC) values for inhibiting bacterial growth of Mycobacterium tuberculosis (MTB). The pharmacokinetic (PK) and drug distribution data have important implications for treatment of disseminated TB in the brain and pave the way for imaging the distribution of the pathogen in vivo.

Reversible inhibitors of monoamine oxidase-A (RIMAs): robust, reversible inhibition of human brain MAO-A by CX157.

Reversible inhibitors of monoamine oxidase-A (RIMA) inhibit the breakdown of three major neurotransmitters, serotonin, norepinephrine and dopamine, offering a multi-neurotransmitter strategy for the treatment of depression. CX157 (3-fluoro-7-(2,2,2-trifluoroethoxy)phenoxathiin-10,10-dioxide) is a RIMA, which is currently in development for the treatment of major depressive disorder. We examined the degree and reversibility of the inhibition of brain monoamine oxidase-A (MAO-A) and plasma CX157 levels at different times after oral dosing to establish a dosing paradigm for future clinical efficacy studies, and to determine whether plasma CX157 levels reflect the degree of brain MAO-A inhibition. Brain MAO-A levels were measured with positron emission tomography (PET) imaging and [(11)C]clorgyline in 15 normal men after oral dosing of CX157 (20-80 mg). PET imaging was conducted after single and repeated doses of CX157 over a 24-h time course. We found that 60 and 80 mg doses of CX157 produced a robust dose-related inhibition (47-72%) of [(11)C]clorgyline binding to brain MAO-A at 2 h after administration and that brain MAO-A recovered completely by 24 h post drug. Plasma CX157 concentration was highly correlated with the inhibition of brain MAO-A (EC(50): 19.3 ng/ml). Thus, CX157 is the first agent in the RIMA class with documented reversible inhibition of human brain MAO-A, supporting its classification as a RIMA, and the first RIMA with observed plasma levels that can serve as a biomarker for the degree of brain MAO-A inhibition. These data were used to establish the dosing regimen for a current clinical efficacy trial with CX157.

Salvinorin A and derivatives: protection from metabolism does not prolong short-term, whole-brain residence.

Salvinorin A (SA) is a potent kappa opioid agonist with a brief duration of action. Consistent with this, our previous positron emission tomography (PET) studies of carbon-11 labeled SA showed that brain levels decrease rapidly after intravenous administration. SA is rapidly metabolized, giving the much less potent salvinorin B (SB), which is presumed to be responsible in part for SA's brief duration of action. To test this, we labeled the metabolically stable methyl ester of SA and SB with carbon-11 and compared their pharmacokinetics by PET imaging after intravenous administration to baboons. Labeling of salvinorin B ethoxymethyl ether (EOM-SB), a derivative with greater potency and resistance to metabolism, provided an additional test of the role of metabolism in brain efflux. Plasma analysis confirmed that SB and EOM-SB exhibited greater metabolic stability than SA. However, the three compounds exhibited very similar pharmacokinetics in brain, entering and exiting rapidly. This suggests that metabolism is not solely responsible for the brief brain residence time of SA. We determined that whole-brain concentrations of EOM-SB declined more slowly than SA after intraperitoneal administration in rodents. This is likely due to a combination in EOM-SB's increased metabolic stability and its decreased plasma protein affinity. Our results suggest that protecting salvinorin A derivatives from metabolism will prolong duration of action, but only when administered by routes giving slow absorption.

Effects of modafinil on dopamine and dopamine transporters in the male human brain: clinical implications.

CONTEXT: Modafinil, a wake-promoting drug used to treat narcolepsy, is increasingly being used as a cognitive enhancer. Although initially launched as distinct from stimulants that increase extracellular dopamine by targeting dopamine transporters, recent preclinical studies suggest otherwise. OBJECTIVE: To measure the acute effects of modafinil at doses used therapeutically (200 mg and 400 mg given orally) on extracellular dopamine and on dopamine transporters in the male human brain. DESIGN, SETTING, AND PARTICIPANTS: Positron emission tomography with [(11)C]raclopride (D(2)/D(3) radioligand sensitive to changes in endogenous dopamine) and [(11)C]cocaine (dopamine transporter radioligand) was used to measure the effects of modafinil on extracellular dopamine and on dopamine transporters in 10 healthy male participants. The study took place over an 8-month period (2007-2008) at Brookhaven National Laboratory. MAIN OUTCOME MEASURES: Primary outcomes were changes in dopamine D(2)/D(3) receptor and dopamine transporter availability (measured by changes in binding potential) after modafinil when compared with after placebo. RESULTS: Modafinil decreased mean (SD) [(11)C]raclopride binding potential in caudate (6.1% [6.5%]; 95% confidence interval [CI], 1.5% to 10.8%; P = .02), putamen (6.7% [4.9%]; 95% CI, 3.2% to 10.3%; P = .002), and nucleus accumbens (19.4% [20%]; 95% CI, 5% to 35%; P = .02), reflecting increases in extracellular dopamine. Modafinil also decreased [(11)C]cocaine binding potential in caudate (53.8% [13.8%]; 95% CI, 43.9% to 63.6%; P < .001), putamen (47.2% [11.4%]; 95% CI, 39.1% to 55.4%; P < .001), and nucleus accumbens (39.3% [10%]; 95% CI, 30% to 49%; P = .001), reflecting occupancy of dopamine transporters. CONCLUSIONS: In this pilot study, modafinil blocked dopamine transporters and increased dopamine in the human brain (including the nucleus accumbens). Because drugs that increase dopamine in the nucleus accumbens have the potential for abuse, and considering the increasing use of modafinil, these results highlight the need for heightened awareness for potential abuse of and dependence on modafinil in vulnerable populations.

Evaluation of 6-([(18)F]fluoroacetamido)-1-hexanoicanilide for PET imaging of histone deacetylase in the baboon brain.

INTRODUCTION: Histone deacetylases (HDACs) are enzymes involved in epigenetic modifications that shift the balance toward chromatin condensation and silencing of gene expression. Here, we evaluate the utility of 6-([(18)F]fluoroacetamido)-1-hexanoicanilide ([(18)F]FAHA) for positron emission tomography imaging of HDAC activity in the baboon brain. For this purpose, we assessed its in vivo biodistribution, sensitivity to HDAC inhibition, metabolic stability and the distribution of the putative metabolite [(18)F]fluoroacetate ([(18)F]FAC). METHODS: [(18)F]FAHA and its metabolite [(18)F]FAC were prepared, and their in vivo biodistribution and pharmacokinetics were determined in baboons. [(18)F]FAHA metabolism and its sensitivity to HDAC inhibition using suberanilohydroxamic acid (SAHA) were assessed in arterial plasma and by in vitro incubation studies. The chemical form of F-18 in rodent brain was assessed by ex vivo studies. Distribution volumes for [(18)F]FAHA in the brain were derived. RESULTS: [(18)F]FAHA was rapidly metabolized to [(18)F]FAC, and both labeled compounds entered the brain. [(18)F]FAHA exhibited regional differences in brain uptake and kinetics. In contrast, [(18)F]FAC showed little variation in regional brain uptake and kinetics. A kinetic analysis that takes into account the uptake of peripherally produced [(18)F]FAC indicated that SAHA inhibited binding of [(18)F]FAHA in the baboon brain dose-dependently. In vitro studies demonstrated SAHA-sensitive metabolism of [(18)F]FAHA to [(18)F]FAC within the cell and diffusion of [(18)F]FAC out of the cell. All radioactivity in brain homogenate from rodents was [(18)F]FAC at 7 min postinjection of [(18)F]FAHA. CONCLUSION: The rapid metabolism of [(18)F]FAHA to [(18)F]FAC in the periphery complicates the quantitative analysis of HDAC in the brain. However, dose-dependent blocking studies with SAHA and kinetic modeling indicated that a specific interaction of [(18)F]FAHA in the brain was observed. Validating the nature of this interaction as HDAC specific will require additional studies.