Douglas W. Oliver

Medicinal chemistry of polycyclic cage compounds in drug discovery research

Saturated polycyclic hydrocarbon structures such as the monocyclic octane, bicylic norbornane and tricyclic adamantane have attracted the attention of several research groups since the 1930s. In the 1950s the synthesis of the so called bird-cage pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione, also known as Cookson’s diketone was reported. This pentacyclic cage diketone is the product of the intramolecular photocyclized Diels Alder adduct of p-bensoquinone and cyclopentadiene. The conversion of this diketone to its monoketone analog formed the basis of a variety of monosubstituted derivatives. Furthermore, acid-based rearrangement reactions of hydroxyl-substituted compounds led to, amongst others, the unique D3-trishomocubane symmetrical compounds, which consists of only five-membered carbon rings. The D3 stereoisomerism of the trishomobubane affords unique chemical challenges with potential medicinal implications. The medicinal chemistry of these cage compounds gained momentum in the 1980s with the discovery of the calcium-channel-modulating effects and antiviral activity thereof. The 1990s and 2000s saw several reports on a variety of pharmacological areas, i.e., dopaminergic, catecholaminergic, and focusing on disorders, in particular that of the central nervous system, such as neurodegeneration (Parkinson’s disease). These polycyclic structures have proved to be very useful in drug discovery research, in particular during the past 25 years.

Polycyclic Cage Structures as Lipophilic Scaffolds for Neuroactive Drugs

Polycyclic cage scaffolds have been successfully used in the development of numerous lead compounds demonstrating activity in the central nervous system (CNS). Several neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, schizophrenia, and stroke, as well as drug abuse, can be modulated with polycyclic cage derivatives. These cage moieties, including adamantane and pentacycloundecane derivatives, improve the pharmacokinetic and pharmacodynamic properties of conjugated parent drugs and serve as an important scaffold in the design of therapeutically active agents for the treatment of neurological disorders. In this Minireview, we focus on the recent developments in the field of polycyclic cage compounds, as well as the relationship between the lipophilic character of these cage‐derived drugs and the ability of such compounds to target and reach the CNS and improve the pharmacodynamic properties of compounds conjugated to it.

Studies on cellular resilience and adaptation following acute and repetitive exposure to ozone in cultured human epithelial (HeLa) cells

Abstract Ozone is used to treat several medical conditions, while the underlying mechanisms of action are sometimes poorly understood. In the current study, we exposed cultured human epithelial (HeLa) cells acutely and repeatedly to ozone and investigated the effects thereof on cell viability. The involvement of anti-apoptotic pathways in observed adaptive responses to ozone were investigated by employing the Akt inhibitor (–)-deguelin. Cells were exposed to an ozone-saturated physiological solution using various dosing regimens, including acute exposure and various repetitive exposures. Cell viability was determined with Trypan Blue or MTT tests, or by a DNA-fragmentation (comet) assay. Acute ozone exposure compromised cell membrane integrity severely, while adaptation to reverse an initial reduction in mitochondrial activity was observed. Repetitive, short-duration exposures followed by a single long-duration exposure to ozone furnished a protective adaptation that was reversed by Akt inhibition. Extracellular and intracellular damage (and adaptation) occurs differentially. While acute ozone may decrease cell viability, multiple preexposures up-regulates cellular plasticity via induction of anti-apoptotic pathways in a treatment regimen-specific manner.

GUANIDINES: FROM MOLECULE TO PRIMATE

Guanidine-like compounds have been investigated since the first observations of their therapeutic potential some 30 years ago in fields of cancer and virology. Guanidine-type compounds that reached clinical status include amongst others the potassium channel opener, pinacidil and the histamine H2-receptor antagonists (e.g. cimetidine). Recent research on guanidines has focused on enzyme systems such as xanthine oxidase and nitric oxide synthase. Our studies demonstrated an in vivo cardioprotection effect of (N-(3,4,-dimethoxy-2-chlorobenzylideneamino)-guanidine: ME10092) in ischaemic reperfusion injury in the rodent. The present investigation in the normal non-human primate, Papio ursinus baboons showed cardiovascular negative chronotropic effects and transient decreases in blood pressure, which correspond to those observed in the in vivo cardioprotection studies in the rodent.

SPECT monitoring of improved cerebral blood flow during long-term treatment of elderly patients with nootropic drugs

PURPOSE In normal aging persons, oxygen and glucose consumption progressively decreases with reduced cerebral blood flow (CBF), which could be responsible for age-related changes in cognitive functions. A data processing model with the use of Tc-99m SPECT of the human brain has been developed and found to be sensitive for monitoring the effects of drugs that increase CBF. In this study, the effect of two vasodilator drugs (the combination of pentifylline and nicotinic acid versus piracetam) was compared with the effect of placebo on CBF. MATERIALS AND METHODS Thirty elderly volunteers had three different procedures using the Peelproc method to spatially standardize and compare CBF patterns by SPECT before and after drug intervention. The 30 patients were divided into five groups of six persons each who were randomly assigned in a 1:1 ratio to the treatment sequences consisting of three phases: the combination of pentifylline and nicotinic acid (C), piracetam (N), and placebo (P), or C-N-P; P-N-C; P-C-N; N-C-P; C-P-N; or N-P-C. Phases 1 to 3 each consisted of a baseline recording of parameters (day 0), treatment for 60 days (days 1 to 60), and recording of parameters after treatment (day 61). RESULTS In elderly human volunteers (ages, 52 to 70 years), after 2 months of oral treatment with a combination of pentifylline and nicotinic acid (800 mg pentifylline, 200 mg nicotinic acid daily), SPECT results for the Peel-proc program indicated a statistically significant improvement in CBF of the total brain, with a more pronounced improvement in the cerebellum and frontal regions, where a definite shift from abnormal to normal blood flow was detected. Spontaneous communication from most of the volunteers suggested that they experienced an improvement in memory and general well-being from the combination treatment. After 2 months of oral treatment with piracetam (2.4 g daily) in elderly human volunteers, SPECT results indicated a regional improvement in CBF, particularly in the cerebellum. However, no beneficial effects with this drug were spontaneously reported. CONCLUSION The in vivo method to quantitatively monitor the progress of long-term drug therapy on CBF described here could be useful to assess and even direct changes in therapy.

Nitric Oxide Synthase Inhibition by Pentacycloundecane Conjugates of Aminoguanidine and Tryptamine

This paper describes the synthesis and in‐vitro activity of pentacycloundecane‐conjugated aminoguanidine and tryptamine analogues on nitric oxide synthase (NOS) using rat brain homogenate. Both aminoguanidine and tryptamine‐derived NOS inhibitors show selectivity towards the inducible and neuronal isoforms of the NOS enzyme, but are weak inhibitors and complete inhibition of the enzyme occurs only at high millimolar concentrations. In view of the increased NOS inactivation observed with alkyl substitution of these structures, the present study aimed to evaluate the effect of the pentacycloundecane cage moiety as an alkyl substituent on the in vitro NOS inhibition of aminoguanidine and tryptamine compounds. Comparison of the IC50 values of aminoguanidine (IC50 = 2.306×10–3 M) and 8‐imino‐N‐guanidino‐pentacyclo‐undecane 2 (IC50 = 8.803×10–5 M) revealed a more than 26‐fold increase in potency. The ability of tryptamine to inhibit NOS activity was also markedly improved by the various pentacycloundecane substituents. The compounds, 3‐hydroxy‐4‐[3‐(2‐aminoethyl)indole]‐azahexacyclo[5.4.1.02,6.03,10.05,9.08,11]dodecane 4 and 8‐[3‐(2‐aminoethyl) indole]‐pentacyclo[5.4.02,6.03,10.05,9]undecane 7 showed the best activity of the tryptamine analogues with a more than 3‐fold increase in nitric oxide synthase inhibition. The results confirmed that the pentacycloundecane structure substantially enhanced the NOS inhibitory potency as observed for the six new NOS inhibitors.

Dopamine receptor binding of 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-1, 2,3,6-tetrahydropyridine (HPTP), an intermediate metabolite of haloperidol

The neuroleptic agent haloperidol (HP) is biotransformed to metabolites such as 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-1,2,3,6- tetrahydropyridine (HPTP) and 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]pyridinium (HPP+). In this study, radioligand binding studies were performed using [3H]SCH23390 as a dopamine D1 receptor ligand and [3H]spiperone as a D2 ligand. Ki values for D1 receptors were 35.8 microM and 54.9 microM for HP and HPTP, respectively. Corresponding values for D2 receptors were 39.1 nM and 329.8 nM. These results indicate similar low affinities in the micromolar range for both HP and HPTP at the dopamine D1 receptor, a much higher affinity of both HP and HPTP for the D2 receptor than for the D1 receptor, and that HPTP binds to D2 receptors with a 9-fold lower affinity than HP. The data are consistent with observations in mice that HPTP is a much less potent acute neuroleptic agent than HP.

Appraisal of ozone as biologically active molecule and experimental tool in biomedical sciences

Ozone (O3) (CAS 10028-15-6) is a major air industrial pollutant and is well known for its very strong oxidative actions which affords the molecule its useful antimicrobial and deodorizing properties, but also its potential toxic effects. Knowledge of the activity and safety of ozone is important if its potential for use as a biologically active agent is to be realized, especially in view of the numerous unsubstantiated medicinal claims that are being made. To investigate ozone-induced oxidative stress as a model for investigating the neurobiology and treatment of certain central nervous system disorders, an experimental ozone inhalation model was developed to administer ozone to intact test animals following acute or chronic exposure. The model was successfully utilized to investigate the effect of dose and duration of exposure to ozone and its resultant effect on oxidative stress markers, depressive-like behaviours and response to antidepressant treatment. These studies demonstrate that the model not only is useful for studying the biological activity of ozone, but also for studying disorders of the brain associated with increased oxidative stress as well as the effects of altered redox status on drug treatment and response.

Non-human primate SPECT model for determining cerebral perfusion effects of cerebrovasoactive drugs acting via multiple modes of pharmacological action

Increasing clinical and experimental evidence implicate cerebral hypoperfusion during increased ageing and points to chronic cerebrovascular ischemia as a vital component of the neuropathological progression of dementia. In vivo cerebral perfusion animal models can greatly contribute to the evaluation of drugs and to the screening of drug interactions. This study describes a baboon Papio ursinus model under anaesthesia, for in vivo cerebral blood flow (CBF) determinations, using Single Photon Emission Computed Tomography (SPECT) following the split-dose method with 99mTc-hexamethylpropylene amine oxime (99mTc-HMPAO). Perfusion studies with acetazolamide as intervention clearly showed that the non-human primate model under aneasthesia is sufficiently sensitive to serve in the evaluation of other cerebrovasoactive drugs for induced perfusion changes with significant increases of the R-value (+40%) for comparative measurement when compared to the control value (2.53+/-0.15 vs. 1.79+/-0.13). These findings stimulated investigations of several drugs, i.e. pentifylline (phosphodiesterase inhibitor); nimodipine (calcium channel blocker); sumatriptan (serotonin receptor agonist) and nicotinic acid (vasodilator) for CBF effects. Increases in the cerebral perfusion in some cases more than +30% for nimodipine (2.51+/-0.14 vs. 1.79+/-0.13), acetazolamide and +29% for the combination of pentifylline and nicotinic acid (2.31+/-0.19 vs. 1.79+/-0.13) were observed. Drug interaction studies revealed an attenuation of increased CBF due to nimodipine, with sumatriptan (-25%) and acetazolamide (+22%) in combination with nimodipine. Drug interactions with clinical implications may result during simultaneous use of cerebrovasoactive drugs in managing patients with cerebrovascular disorders. This study further showed that the CBF non-human primate model under anaesthesia is useful for the investigation of vasoactive drugs acting via various pharmacological modes of action.

Structure and conformation of the sodium chloride salt of N-t-Boc-Phenylalanyl-Proline (Boc-Phe-Pro·NaCl) and the dihydrate of N-t-Boc-Tyrosyl-Proline (Boc-Tyr-Pro·2H2O)

The structure and conformation of the salt of N-t-Boc-Phenylalanyl-Proline (Boc-Phe-Pro·NaCl) (C19H26N2O5NaCl) (compound 2) and the dihydrate of N-t-Boc-Tyrosyl-Proline (Boc-Tyr-Pro·2H2O) (C19H30O8N2) (compound 1) have been investigated with X-ray crystallographic and spectroscopic methods. Boc-Phe-Pro·NaCl crystallizeds in an extended trans conformation in the space groupP21 with cell dimensionsa=7.961 (3),b=10.045(2), andc=13.495(4). One intermolecular hydrogen bond and one intramolecular hydrogen bond was observed for the dipeptide salt. Boc-Tyr-Pro·2H2O crystallized in an extended trans conformation in the space group P21 with cell dimensionsa=7.964(1),b=10.011(1), andc=13.853(2). Six intermolecular hydrogen bonds were observed for Boc-Tyr-Pro·2H2O. The conformation of both dipeptides reflect collagen-type of proline-compounds. The puckering mode of the pyrrolidine ring of the proline residues can be described as an approximate C2 half-chair symmetry having an A conformation with the Cγ atom located exo and Cβ atom located endo relative to the carboxamide group, i.e., γ/β T.Cis-trans isomerism was observed in the NMR spectra of both dipeptides with a predominance for the extended side chain for the phenylalanyl and tyrosyl residues, respectively.