The chemistry and biology of platinum complexes with the 1,2-diaminocyclohexane carrier ligand (review)

Dach-Pt compounds have been intensively studied because of their potential. efficacy against cisplatin-resistant tumors and their reduced nephrotoxicity and myelotoxicity compared to cisplatin and carboplatin. Because the dach carrier ligand can be H-3-labeled, the biotransformations of dach-Pt compounds have been studied in detail. Some of these biotransformation studies have provided new information about the likely cellular biotransformation pathways of Pt complexes in general. For example, biotransformation studies with 1,2-diaminocyclohexanedichloroplatinum(II) [Pt(dach)Cl-2] and 1,2-diaminocyclohexanemalonatoplatinum(II) [Pt(dach)(mal)] have shown that displacement of leaving ligands by HCO3- and PO4= are likely to represent important activation pathways for platinum(II) complexes in vivo and that the intracellular t(1/2) is much more rapid [15' for Pt(dach)Cl-2 and 30' for Pt(dach)(mal)] than predicted by previous in vitro experiments. Biotransformation studies with 1,2-diaminocyclohexanetetrachloroplatinum(IV) (ormaplatin) have suggested that Pt(II)-assisted Pt(IV) ligand exchange reactions can occur in vivo with platinum(IV) complexes. This is important for our understanding of platinum(IV) biotransformations because the specificity of Pt(II)-assisted Pt(IV) ligand exchange reactions is different than that for Pt(II) ligand exchange reactions. Finally, plasma biotransformation studies with ormaplatin in vivo have shown that ultrafilterable, active biotransformation products are cleared from the circulation much more rapidly than the ultrafilterable, inactive biotransformation products. This has lead to the suggestion that pharmacokinetic parameters based on the active biotransformation products are likely to be much more useful than pharmacokinetic parameters based on ultrafilterable platinum for predicting the efficacy and/or toxicity of platinum compound with chloro leaving ligands such as ormaplatin and cisplatin. Since dach-Pt compounds can overcome cisplatin resistance in some cancer cell lines but not in others, it is important to understand the mechanism(s) which determine(s) the carrier ligand specificity of resistance. A great deal has been learned about how dach-Pt compounds interact with DNA. The dach carier ligand constrains the N-Pt-N bond angle and can exist as 3 isomers with a total of 4 different non-planar conformations. These constraints do not appear to affect the rate or sequence specificity of Pt-DNA monoadduct formation, but do appear to alter the rate of monoadduct to diadduct conversions. The dach carrier ligand may also have significant effects on the conformation of DNA in the region of Pt-DNA adducts, although the biological consequences of these effects are not clear. Much less is known about the effects of the dach carrier ligand on the interactions of Pt compounds with proteins. Because Pt compounds primarily interact with nonadjacent amino acids on the surface of proteins, these interactions are not likely to be significantly affected by the conformation of dach-Pt compounds. However, the hydrophobicity of the dach carrier ligand may allow it to react with amino acid side chains in hydrophobic pockets that are inaccessible to cisplatin. At the cellular level, the dach carrier ligand appears to affect Pt accumulation in Pt resistant mouse L1210 cells, but has little effect on either Pt uptake or efflux in Pt-resistant human ovarian and colon carcinoma cell lines. While enhanced repair also appears to contribute to resistance in many eel lines, there is little or no difference in the repair of dach-Pt and cis-diammine-Pt adducts in any of the cell lines tested to date. Current data suggest that replicative bypass makes a significant contribution to platinum resistance and, in many cell lines, is the only process to predict the carrier ligand specificity of resistance. These data suggest that further elucidation of this process should add significantly to our understanding of platinum resistance and the role of platinum complexes with the dach carrier ligand in chemotherapy.

Force transducer-based movement detection in fear conditioning in mice: a comparative analysis

Fear conditioning (FC) allows the dissociation of hippocampal and nonhippocampal behavioral function in rodents, and has become a diagnostic tool in transgenic mouse research employed to investigate mutation-induced changes in brain function. Although the procedural details of the paradigm have been established, quantification of the behavioral output, freezing, remains problematic in mice. Observation-based techniques are time-consuming and may be subject to bias, while movement detection with photocells is imprecise. Here we describe an alternative method for movement detection, based on an electronic force transducer system that allows the quantification of acceleration forces generated by a moving subject. We compare the behavior of two inbred strains of mice (C57BL/6 and DBA/2) whose performance is known to differ in hippocampal tasks, including FC. The comparison is made using multiple techniques: the force transducer approach, and three observation-based methods, a computer-aided event-recording approach, a traditional time-sampling paper/pencil method, and a subjective impression-based scoring system. In addition, we investigate the correlation structures of behavioral elements quantified by event recording, using principal component analyses; we conclude that fear may manifest in multiple forms and in a stimulus- and genotype-dependent manner. We suggest that the force transducer system provides precise quantification of movements in an automated manner and will allow high-throughput screening for mutation and drug effects in mice. However, we also argue that fear responses can be complex, and freezing behavior may not be the only measure of fear or fear-associated memory.

Performance deficits of mGluR8 knockout mice in learning tasks: the effects of null mutation and the background genotype

mGluR8 is a G-protein coupled metabotropic glutamate receptor expressed in the mammalian brain. Members of the mGluR family have been shown to be modulators of neural plasticity and learning and memory. Here we analyze the consequences of a null mutation at the mGluR8 gene locus generated using homologous recombination in embryonic stem cells by comparing the learning performance of the mutants with that of wild type controls in the Morris water maze (MWM) and the context and cue dependent fear conditioning (CFC). Our results revealed robust performance deficits associated with the genetic background, the ICR outbred strain, in both mGluR8 null mutant and the wild type control mice. Mice of this strain origin suffered from impaired vision as compared to CD1 or C57BL/6 mice, a significant impediment in MWM, a visuo-spatial learning task. The CFC task, being less dependent on visual cues, allowed us to reveal subtle performance deficits in the mGluR8 mutants: novelty induced hyperactivity and temporally delayed and blunted responding to shocks and temporally delayed responding to contextual stimuli were detected. The role of mGluR8 as a presynaptic autoreceptor and its contribution to cognitive processes are hypothesized and the utility of gene targeting as compared to pharmacological methods is discussed.

Altered performance characteristics in cognitive tasks: comparison of the albino ICR and CD1 mouse strains

With the advent of recombinant DNA technology the mouse has become a favored model organism in brain research. Numerous mouse strains are available to use as a host for carrying genetic alteration induced by targeted or random mutagenesis. Most strains differ in their genetic makeup and phenotypical characteristics. The choice of the host strain thus can be crucial for the analysis of functional effects of the induced mutation. In the present paper we analyze the behavior of two related outbred albino strains of mice, ICR and CD1, that are often used in transgenic research. Using two frequently employed learning tasks, the Morris water maze (MWM) and the context-dependent fear conditioning (CFC) as well as other behavioral tests, we demonstrate significant performance differences between the strains. ICR suffers from a severe visual impairment making this strain difficult to use in several behavioral paradigms that require good visual perception, e.g. the MWM. CD1 does not suffer from grossly impaired vision but, similarly to the ICR strain, CD1 mice exhibit decreased freezing in all phases of CFC. Although the strains are able to learn, such deficits can render them significantly impaired dependent on the performance demands of the cognitive test employed. Our findings underscore the need for careful examination of the characteristics of the host strain, the choice of which must be made in accordance with the expected functional alterations induced by the mutation.

Cellular and molecular pharmacology of oxaliplatin

Oxaliplatin, a diaminocyclohexane-containing platinum, has a spectrum of activity and mechanisms of action and resistance that appear to be different from those of other platinum-containing compounds, notably cisplatin. The first part of this review describes the differences between oxaliplatin and cisplatin in terms of their spectrum of activity and adduct formation and then goes on to discuss molecular and cellular experimental data that potentially explain them. Particular emphasis is placed on the differential role of DNA repair mechanisms. In addition, the anticancer effects of oxaliplatin are optimized when it is administered in combination with other anticancer agents, such as 5-fluorouracil, gemcitabine, cisplatin, or carboplatin; topoisomerase I inhibitors; and taxanes. In vitro and preclinical combination data that could optimize oxaliplatin-based chemotherapy are also reviewed.

Ectopic G-protein expression in dopamine and serotonin neurons blocks cocaine sensitization in Drosophila melanogaster

Sensitization to repeated doses of psychostimulants is thought to be an important component underlying the addictive process in humans [1] [2] [3] [4]. In all vertebrate animal models, including humans [5], and even in fruit flies, sensitization is observed after repeated exposure to volatilized crack cocaine [6]. In vertebrates, sensitization is thought to be initiated by processes occurring in brain regions that contain dopamine cell bodies [2] [7]. Here, we show that modulated cell signaling in the Drosophila dopamine and serotonin neurons plays an essential role in cocaine sensitization. Targeted expression of either a stimulatory (Galpha(s)) or inhibitory (Galpha(i)) Galpha subunit, or tetanus toxin light chain (TNT) in dopamine and serotonin neurons of living flies blocked behavioral sensitization to repeated cocaine exposures. These flies showed alterations in their initial cocaine responsiveness that correlated with compensatory adaptations of postsynaptic receptor sensitivity. Finally, repeated drug stimulation of a nerve cord preparation that is postsynaptic to the brain amine cells failed to induce sensitization, further showing the importance of presynaptic modulation in sensitization.

Requirement of circadian genes for cocaine sensitization in Drosophila

The circadian clock consists of a feedback loop in which clock genes are rhythmically expressed, giving rise to cycling levels of RNA and proteins. Four of the five circadian genes identified to date influence responsiveness to freebase cocaine in the fruit fly, Drosophila melanogaster. Sensitization to repeated cocaine exposures, a phenomenon also seen in humans and animal models and associated with enhanced drug craving, is eliminated in flies mutant for period, clock, cycle, and doubletime, but not in flies lacking the gene timeless. Flies that do not sensitize owing to lack of these genes do not show the induction of tyrosine decarboxylase normally seen after cocaine exposure. These findings indicate unexpected roles for these genes in regulating cocaine sensitization and indicate that they function as regulators of tyrosine decarboxylase.

Modification of methyliminodiacetato-trans-R,R-1,2-diamminocyclohexane platinum(II) pharmacology using a platinum-specific monoclonal antibody

Platinum complexes are extremely active chemotherapeutic agents. A murine monoclonal antibody designated 1C1 was developed that binds to the third-generation platinum complex methyliminodiacetato-trans-R,R-1,2-diamminocyclohexane platinum(II) (MIDP). Competitive enzyme-linked immunosorbent assay (ELISA) shows that antibody 1C1 binds preferentially to the 1,2-diamminocyclohexane (DACH) side-chain of the platinum complex, although non-DACH-containing platinum complexes can compete for binding at high concentrations. When tested against MCF-7 breast carcinoma cells, the 1C1-MIDP complex caused 50% growth inhibition at 0.63 micrograms Pt/ml, whereas MIDP alone caused 50% growth inhibition at a concentration of 0.16 micrograms Pt/ml. Pharmacokinetic studies in rats using [3H]-MIDP showed that the drug was cleared triphasically from plasma, with elimination-phase half-lives (t1/2) of 1.2, 10.2, and 243 min for alpha, beta, and gamma phases, respectively. The MIDP-1C1 complex was cleared with longer half-lives of 5, 26, and 291 min, respectively. The overall clearance rate from plasma of the MIDP-1C1 complex was 10-fold lower than that of MIDP alone (0.37 vs 3.01 ml/kg x min). Tissue concentrations of [3H]-MIDP 3 h after administration showed that 1C1 antibody prevented MIDP distribution to most organs and dramatically reduced [3H] concentration in the intestine, liver, kidney, heart, and skeletal muscles. Studies are under way to determine the relative therapeutic activity of the 1C1 antibody-MIDP complex and assess whether the 1C1 antibody may be useful for antibody-directed delivery of platinum complexes to tumors.

Biochemical changes in humans upon exposure to nitrogen dioxide while at rest

The biological response to controlled exposures of nitrogen dioxide (NO2) was studied in 19 human subjects exposed to 0.2 ppm NO2 for 2 hr and compared to 15 control subjects exposed to filtered air for 2 hr. Seven biochemical blood parameters, including glutathione, red blood cell glutathione reductase, 2,3-diphosphoglycerate, methemoglobin, vitamin E, complement C2, and IgA were measured prior to exposure, immediately after exposure, and 22 hr following exposure. The only variable that showed significant change due to NO2 exposure was glutathione. Glutathione is known to protect the erythrocyte from oxidative stress. The increase in glutathione observed upon exposure to NO2 may be a protective reaction of the erythrocyte to meet the oxidative stress.

Biochemical effects of sulfuric acid mist inhalation by human subjects while at rest

This study evaluated the effect of sulfuric acid aerosol exposure for 2 consecutive days on seven human biochemical blood parameters. A total of 20 human subjects were exposed to 100 micrograms/m3 (0.033 microM) sulfuric acid aerosol (0.5 microns mean mass diameter) for 4 hr/day for 2 consecutive days. A total of 17 human subjects were exposed to 4 hr of ambient air on both exposure days. The chemical blood parameters were measured pre- and post-exposure, and 20 hr after the second exposure: serum glutathione, red blood cell glutathione reductase, red blood cell glucose-6-phosphate dehydrogenase, lysozyme, serum glutamic oxaloacetic acid transaminase, serum vitamin E, and 2, 3-diphosphoglycerate. The results indicate no significant response in any of the seven biochemical blood parameters measured. At this level, repeated exposure did not over-burden the upper airway defenses against acid aerosol.

Biochemical changes in humans upon exposure to sulfuric acid aerosol and exercise

This study evaluated the effect of a single exposure to sulfuric acid aerosol on six human biochemical blood parameters. A total of 18 human subjects were exposed to ambient air for 4 hr on the first day of exposure and to 100 microgram/m3 (0.033 microM) sulfuric acid aerosol (0.5 micrometer mean mass diameter) for 4 hr on the second day. A total of 17 human subjects were exposed for 4 hr to ambient air on both exposure days. On each exposure day, at 30 min and 90 min after exposure was initiated, all subjects engaged in a 15-min exercise period (walking 4 mph on a treadmill inclined at 10 degrees). Six biochemical blood parameters were measured before and after exposure: glutathione, lysozyme, glutathione reductase, serum glutamic oxaloacetic acid transaminase, serum vitamin E, and 2, 3-diphosphoglyceric acid. The results indicate no significant effect of one 4-hr exposure of humns to 100 microgram/m3 sulfuric acid aerosol. One significant post-exposure effect did occur--an increase in glutathione reductase--for both the control and acid-exposed group. It is concluded that at the levels studied, sulfuric acid aerosol is neutralized in the upper airways; consequently, no cellular damage is measurable.