Robert A. McClelland

Iron-chelation therapy with oral deferiprone in patients with thalassemia major

BACKGROUND To determine whether the orally active iron chelator deferiprone (1,2-dimethyl-3-hydroxy-pyridin-4-one) is efficacious in the treatment of iron overload in patients with thalassemia major, we conducted a prospective trial of deferiprone in 21 patients unable or unwilling to use standard chelation therapy with parenteral deferoxamine. METHODS Hepatic iron stores were determined yearly by chemical analysis of liver-biopsy specimens or magnetic-susceptibility measurements. Detailed clinical and laboratory studies were used to monitor safety and compliance. RESULTS The patients received deferiprone therapy for a mean (+/-SE) of 3.1 +/- 0.3 years. Ten patients in whom previous chelation therapy with deferoxamine had been ineffective had initial hepatic iron concentrations of at least 80 mumol per gram of liver, wet weight -- values associated with complications of iron overload. Hepatic iron concentrations decreased in all 10 patients, from 125.3 +/- 11.5 to 60.3 +/- 9.6 mumol per gram (P < 0.005), with values that were less than 80 mumol per gram in 8 of the 10 patients (P < 0.005). In all 11 patients in whom deferoxamine therapy had previously been effective, deferiprone maintained hepatic iron concentrations below 80 mumol of iron per gram. CONCLUSIONS Oral deferiprone induces sustained decreases in body iron to concentrations compatible with the avoidance of complications from iron overload. The risk of agranulocytosis associated with deferiprone may restrict its administration to patients who are unable or unwilling to use deferoxamine.

Preparation, toxicity and mutagenicity of 1-methyl-2-nitrosoimidazole: A toxic 2-nitroimidazole reduction product

1-Methyl-2-nitrosoimidazole (INO), the 2-electron reduction product of 1-methyl-2-nitroimidazole (INO2), was prepared by electrochemical reduction of INO2 to 2-hydroxylamino-1-methyl-imidazole (INHOH), followed by back oxidation with iodine. Although stable in crystalline form, INO reacted in water, phosphate-buffered saline, and mammalian cell growth medium. Half-lives for decay were determined by UV-visible spectroscopy. INO was found to be highly toxic towards Chinese hamster ovary (CHO) cells, concentrations of 10-60 microM producing significant cytotoxicity. The rate of INO decay was found to be increased in the presence of CHO cells. INO was also toxic and mutagenic towards Salmonella typhimurium TA-100. When compared on a molar basis to the parent nitro compound INO2, and the 4- and 6-electron reduction products INHOH and 2-amino-1-methylimidazole (INH2), INO was by far (two orders of magnitude) the most toxic under aerobic conditions. These results suggest that the nitroso reduction product of 2-nitroimidazoles may be the reduced species responsible for hypoxic cell selective toxicity of 2-nitroimidazoles.

Increasing D2 affinity results in the loss of clozapine's atypical antipsychotic action.

Typical antipsychotics (haloperidol) give rise to severe motor side-effects while atypical antipsychotics like clozapine do not. Action at several neurotransmitter receptors have been implicated. To identify the critical mechanisms involved we synthesized an 8-C1 isomer of clozapine which showed an equivalent affinity to clozapine on multiple receptors (5-HT1A, 5-HT2, D1, D4, M1) but differed in having a 10-fold higher affinity at the dopamine D2/3 receptor. When tested in a series of animal models indicative of the typical/atypical distinction (catalepsy, striatal gene-induction, prolactin elevation) isoclozapine lost atypical properties and behaved like a typical antipsychotic. Simultaneous in vivo receptor occupancy studies confirmed that alterations in D2 receptor occupancy were most closely related to loss of atypicality by clozapines isomer isoclozapine. The implications for the design of future antipsychotics is discussed.

NLP-1: A DNA INTERCALATING HYPOXIC CELL RADIOSENSITIZER AND CYTOTOXIN

The 2-nitroimidazole linked phenanthridine, NLP-1 (5-[3-(2-nitro-1-imidazoyl)-propyl]-phenanthridinium bromide), was synthesized with the rationale of targeting the nitroimidazole to DNA via the phenanthridine ring. The drug is soluble in aqueous solution (greater than 25 mM) and stable at room temperature. It binds to DNA with a binding constant 1/30 that of ethidium bromide. At a concentration of 0.5 mM, NLP-1 is 8 times more toxic to hypoxic than aerobic cells at 37 degrees C. This concentration is 40 times less than the concentration of misonidazole, a non-intercalating 2-nitroimidazole, required for the same degree of hypoxic cell toxicity. The toxicity of NLP-1 is reduced at least 10-fold at 0 degrees C. Its ability to radiosensitize hypoxic cells is similar to misonidazole at 0 degrees C. Thus the putative targeting of the 2-nitroimidazole, NLP-1, to DNA, via its phenanthridine group, enhances its hypoxic toxicity, but not its radiosensitizing ability under the present test conditions. NLP-1 represents a lead compound for intercalating 2-nitroimidazoles with selective toxicity for hypoxic cells.

Direct observation of β-fluoro-substituted 4-methoxyphenethyl cations by laser flash photolysis

4-Methoxyphenethyl cations bearing β-fluorine substituents [4-MeOC6H4C+R1R2 with R1= H, R2= CH2F (3), R1= H, R2= CHF2(4), R1= H, R2= CF3(5), R1R2= CF3(6)] are observed as transient intermediates following 248 nm laser photolysis of chloride or bromide precursors ArC(–X)R1R2 in 2,2,2-trifluoroethanol (TFE) and TFE–water mixtures. Corresponding phenethyl radicals are also observed; successive fluoro-substitution has remarkably little effect on the Absorbance(cation): Absorbance-(radical) ratio. Rate constants ks for the decay of the cations have been directly measured, and compared with those of non-fluorinated analogues. In TFE–water mixtures the reactivity order is ArCH+CHF2 > ArCH+CH2F > ArCH+CF3 > ArCH+CH3(1) > ArC+(CH3)2(2) > ArC+(CF3)2, but the differences are small, there being little more than a two-order of magnitude decrease across the series. This remarkably small effect of fluorine had previously been observed in an examination of azide:solvent partitioning ratios kaz:ks. Rate constants kaz have also been obtained in this work, and, with the exception of 2 which reacts somewhat more slowly, these are constant, with values consistent with the azide : cation combination occurring at the diffusion limit for these cations, as had been assumed in the previous work. The small, complex effects of fluoro substitution on the reactivities of these cations have been explained by a model which has, as a key component, an effect of electron withdrawing substituents of forcing the positive charge away from the benzylic carbon to the oxygen of the 4-methoxy group. Evidence for a significant perturbation of the π electron density is available in the present work, in that the absorption maxima of the α-CF3and bis-α-CF3 cations 5 and 6 are shifted 20 nm and 50 nm, respectively, to lower wavelengths than the corresponding α-methyl derivatives 1 and 2. Studies of 6 in 100% aqueous solution reveal a second, slower, transformation following the decay of the cation. Product studies have previously indicated that a fraction of the hydration of this cation occurs at the 4-position of the aromatic ring, producing a quinone methide and products arising from such a species. An unobserved hemiacetal is an intermediate in this sequence. From spectral and kinetic considerations the second process observed with flash photolysis has been identified as representing the breakdown of the hemiacetal to the quinone methide. A complete rate–pH profile for this reaction has been obtained, from which a pKa of 11.0 has been determined for the ionization of the hemiacetal.

Reduction potentials in relation to physiological activities of benzenoid and heterocyclic nitroso compounds: Comparison with the nitro precursors

Abstract Reduction potentials were determine for various physiologically active benzenoid and heterocyclic nitroso compounds, namely, substituted nitrosobenzenes, 1-nitrosopyrene, and 1-methyl-2-nitrosoimidazole. The values, favorable for biological activity, ranging from 0.2 to −0.2 V, increased in acidic medium. These potentials were appreciably higher than those for the corresponding nitro parents. In most cases, the nitroso form was more biologically active than the nitro counterpart. Catalytic electron transfer processes may play a role in vivo , along with other actions, in the observed responses from the nitroso category.

1-Methyl-2-nitrosoimidazole: Cytotoxic and glutathione depleting capabilities☆

We tested 1-methyl-2-nitrosoimidazole (INO), the two electron reduction product of 1-methyl-2-nitroimidazole (INO2) for its in vitro cytotoxicity and glutathione (GSH) depleting capabilities. The half life of INO was shown to be dependent on cell concentration above 10(5) cells/ml, decreasing with increasing cell concentration up to 2 X 10(6) cells/ml. For a 10-fold decrease in cell concentration, from 10(6) to 10(5) cells/ml, the toxicity curve shifted 10-fold towards lower concentrations. At 10(6) cells/ml, INO depleted GSH, in the range of concentrations where toxicity was observed, down to a plateau of 15% of the control level at a concentration of 100 microM INO. Oxidized glutathione (GSSG) levels were not elevated significantly above control cultures at this concentration. INO2, 1000 microM, did not deplete GSH under similar exposure conditions while 2-hydroxylamino-1-methylimidazole (INHOH) depleted GSH minimally at this same concentration. The nitroso intermediate may play a central role in the toxicity and GSH depleting capabilities of 2-nitroimidazoles in mammalian cells.

Flash photolysis study of a Friedel–Crafts alkylation. Reaction of the photogenerated 9-fluorenyl cation with aromatic compounds

A combination of flash photolysis and product analysis is employed to investigate the reaction of aromatic compounds (ArH) with the 9-fluorenyl cation (Fl+) photogenerated from 9-fluorenol in 1,1,1,3,3,3-hexafluoroisopropyl alcohol (HFIP). The availability of the photochemical route to Fl+ means that the reaction of a benzylic-type cation with ArH can be directly followed by flash photolysis. An additional feature with electron-rich ArH is that the cyclohexadienyl cation is observed to grow as Fl+ decays. Thus both cationic intermediates of a Friedel–Crafts alkylation are observed in the same experiment. The formation of the cyclohexadienyl cation is demonstrated to be reversible, or at least quasi-reversible, with the kinetic analysis furnishing absolute rate constants for the formation of this cation, as well as for its loss of H+ and Fl+. Values of kH:kD for benzene: [2H6]benzene and toluene: [2H8]toluene are ∼ 1.5 and demonstrate that Fl+ addition is at least partly reversible with these compounds as well. The Hammett ρ+ value obtained for a series of the less electron-rich ArH is –8, indicative of a transition state with considerable cyclohexadienyl cation character. Anisole shows a negative deviation from the Hammett correlation line, explained by the addition of Fl+ to ArH becoming encounter-controlled. This behaviour is dramatically illustrated in a comparison of data for Fl+ and Br2. For the less electron-rich ArH, rate constants for the two electrophiles are parallel. However, from m-xylene through pentamethylbenzene, the rate with Fl+ is unchanged, while the rate with Br2 increases over 1000-fold. The concept of encounter control with Fl+ is strongly supported by the absolute rate constants, which for the the electron-rich ArH are all in the range 1–2 × 109 dm3 mol–1 s–1, a magnitude typical of diffusion-controlled reactions. The electron-rich ArH also show no intermolecular selectivity since their reactions are encounter-controlled, but have a high intramolecular selectivity. It is suggested that a factor influencing the latter is the reversibility of formation of the cyclohexadienyl cation from the encounter complex.

Locus of Control in Underachieving and Achieving Gifted Students.

This study examined locus of control in underachieving and achieving gifted grade 6, 7, 8 and 9 students. It was found that general locus of control measures did not differentiate between the two groups of students. However, underachievers and achievers both scored significantly higher on positive internal locus of control than on negative internal control. There were no gender or grade effects. This result needs to be replicated by further research since it was unexpected.

Laser flash photolysis observation of the 1-p-methoxyphenylvlnyl cation by photoprotonation of p-methoxyphenylacetylene. Comparison with the 1-p-methoxyphenethyl cation.

Abstract Photolysis of p-methoxyphenylacetylene in trifluoroethanol results in the transient 1-p-methoxyphenylvinyl cation 7 which has been detected by laser flash photolysis (λ = 248 nm). This cation shows remarkably similar behavior to the 1-p-methoxyphenethyl cation 4: λmax - 335 nm (7) and 340 nm (4) and rate constants for decay - 1.3 x 106 s−1 (7) and 3.9 x 105 s−1 (4).