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D R Richardson

Publications and source records attributed to D R Richardson.

At least 55 records · Page 3Linked to original sources
PubMed2000

The 10th International Conference on Oral Iron Chelators in the treatment of beta-thalassemia and other diseases and biomed meeting.

Development of oral iron (Fe) chelation therapy remains an important goal for the treatment of Fe-overload disease and perhaps other conditions. For many years, the major problem with Fe chelation therapy has been that the drug in clinical use. desferrioxamine (DFO), requires long sc. infusions (12-24 h day, 5-6 days per week). In addition, DFO is not orally effective, is highly expensive and does not easily permeate cell membranes to bind intracellular Fe pools. Obviously, the development of an orally effective and economical drug is vital. The recent 10th International Conference on Oral Iron Chelators (ICOC) discussed the latest findings in this challenging field. The conference was particularly focused to discuss recent investigations with the orally effective chelator, deferiprone (also) known as Li, DMHP or 1, 2-dimethylhydroxypyridone).

Administration, Oral↗
PubMed2000

Complexes of gallium(III) and other metal ions and their potential in the treatment of neoplasia.

The metal complexes of a variety of ligands show diverse pharmacological properties. The potential of these compounds as antineoplastic agents is underlined by the success of the clinically used platinum complex cisplatin (cis-[(NH(3))(2)PtCl(2)]). In the current review, specific examples of gallium, copper, ruthenium and titanium complexes are discussed with special relevance to their use in the treatment of cancer. Some of these complexes have demonstrated marked activity in a number of animal models and for some compounds, clinical trials are anticipated or have already begun. Collectively, the results in the literature indicate that the study of metal complexes as antineoplastic agents deserves continued intensive investigation.

Animals↗
PubMed1999

The biologically active iron chelators 2-pyridylcarboxaldehyde isonicotinoylhydrazone, 2-pyridylcarboxaldehyde benzoylhydrazone monohydrate and 2-furaldehyde isonicotinoylhydrazone.

In the crystal structures of the respective title compounds, C12H10N4O, C13H11N3O.H2O and C11H9N3O2, variations in the torsion angles of the aromatic pyridyl and benzoyl groups are observed, and the disposition of the heterocyclic aldehyde is shown to be influenced by the ring size of this group.

Crystallography, X-Ray↗
PubMed1999

The potential of iron chelators of the pyridoxal isonicotinoyl hydrazone class as effective antiproliferative agents III: the effect of the ligands on molecular targets involved in proliferation.

We have identified specific iron (Fe) chelators of the pyridoxal isonicotinoyl hydrazone (PIH) class that are far more effective ligands than desferrioxamine (DFO; Richardson et al, Blood 86:4295, 1995; Richardson and Milnes, Blood 89:3025, 1997). In the present study, we have compared the effect of DFO and one of the most active chelators (2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone; 311) on molecular targets involved in proliferation. This was performed to further understand the mechanisms involved in the antitumor activity of Fe chelators. Ligand 311 was far more active than DFO at increasing Fe release from SK-N-MC neuroepithelioma and BE-2 neuroblastoma cells and preventing Fe uptake from transferrin. Like DFO, 311 increased the RNA-binding activity of the iron-regulatory proteins (IRPs). However, despite the far greater Fe chelation efficacy of 311 compared with DFO, a similar increase in IRP-RNA binding activity occurred after 2 to 4 hours of incubation with either chelator, and the binding activity was not inhibited by cycloheximide. These results suggest that, irrespective of the Fe chelation efficacy of a ligand, an increase IRP-RNA binding activity occurred via a time-dependent step that did not require protein synthesis. Further studies examined the effect of 311 and DFO on the expression of p53-transactivated genes that are crucial for cell cycle control and DNA repair, namely WAF1, GADD45, and mdm-2. Incubation of 3 different cell lines with DFO or 311 caused a pronounced concentration- and time-dependent increase in the expression of WAF1 and GADD45 mRNA, but not mdm-2 mRNA. In accordance with the distinct differences in Fe chelation efficacy and antiproliferative activity of DFO and 311, much higher concentrations of DFO (150 micromol/L) than 311 (2.5 to 5 micromol/L) were required to markedly increase GADD45 and WAF1 mRNA levels. The increase in GADD45 and WAF1 mRNA expression was seen only after 20 hours of incubation with the chelators and was reversible after removal of the ligands. In contrast to the chelators, the Fe(III) complexes of DFO and 311 had no effect on increasing GADD45 and WAF1 mRNA levels, suggesting that Fe chelation was required. Finally, the increase in GADD45 and WAF1 mRNAs appeared to occur by a p53-independent pathway in SK-N-MC and K562 cells, because these cell lines lack functional p53. Our results suggest that GADD45 and WAF1 may play important roles in the cell cycle arrest observed after exposure to these chelators.

Antineoplastic Agents↗
PubMed1999

Crystal and molecular structure of 2-hydroxy-1-naphthaldehyde isonicotinoyl hydrazone (NIH) and its iron(III) complex: an iron chelator with anti-tumour activity.

Previous studies have demonstrated that 2-hydroxy-1-naphthaldehyde isonicotinoyl hydrazone (NIH) and several other aroylhydrazone chelators possess anti-neoplastic activity due to their ability to bind intracellular iron. In this study we have examined the structure and properties of NIH and its FeIII complex in order to obtain further insight into its anti-tumour activity. Two tridentate NIH ligands deprotonate upon coordination to FeIII in a meridional fashion to form a distorted octahedral, high-spin complex. Solution electrochemistry of [Fe(NIH-H)2]+ shows that the trivalent oxidation state is dominant over a wide potential range and that the FeII analogue is not a stable form of this complex. The fact that [Fe(NIH-H)2]+ cannot cycle between the FeII and FeIII states suggests that the production of toxic free-radical species, e.g. OH. or O2.-, is not part of this ligand's cytotoxic action. This suggestion is supported by cell culture experiments demonstrating that the addition of FeIII to NIH prevents its anti-proliferative effect. The chemistry of this chelator and its FeIII complex are discussed in the context of understanding its anti-tumour activity.

Antineoplastic Agents↗
PubMed1999

Activation of an iron uptake mechanism from transferrin in hepatocytes by small-molecular-weight iron complexes: implications for the pathogenesis of iron-overload disease.

The liver is one of the principal sites of iron overload in diseases such as hemochromatosis and beta thalassemia. Hence, much effort has been invested in examining the mechanisms of Fe uptake by hepatocytes. In the present study we have examined the effect of small molecular weight (M(r)) Fe complexes on Fe uptake from iron 59-labeled transferrin (Tf) and 59Fe-labeled citrate by primary cultures of hepatocytes. This was important to assess because Fe-citrate and saturated diferric Tf coexist in the serum of patients with untreated Fe overload. Preincubation of hepatocytes with the low-M(r) Fe complex ferric ammonium citrate (FAC; 25 microg/mL; (Fe) = 4.4 microg/mL) followed by incubation with 59Fe-Tf or 59Fe-citrate ((Fe) = 0.25 to 25 micromol/L) resulted in the marked stimulation of 59Fe uptake. For example, at a physiologically relevant Tf-Fe concentration of 25 micromol/L, there was an 8-fold increase in 59Fe uptake by cells incubated with FAC compared to control cells. In contrast, at Tf-Fe concentrations of 0.25 to 2.5 micromol/L, 59Fe uptake in FAC-treated cells was only 1-fold to 3-fold greater than that in the corresponding controls. These data suggest that the FAC-activated Fe uptake process predominates at physiologically relevant Tf concentrations above the saturation of the Tf receptor (TfR). This is the first study to demonstrate that preincubation of hepatocytes with Iow-M(r)Fe complexes can markedly increase Fe uptake from diferric Tf. In conclusion, these results may help to explain the loading of hepatocytes with Fe that occurs in Fe-overload disease despite marked down-regulation of the TfR.

Animals↗
PubMed1999

Role of ceruloplasmin and ascorbate in cellular iron release.

The process of iron (Fe) release from cells plays an important role in health and disease, although the mechanisms responsible remain unclear. In this study we have examined the process of Fe efflux from HepG2 cells, including the possible roles of Cp and ascorbate in this process. Recently, it has been suggested that Cp plays no role in Fe release but can increase Fe uptake by Fe-deficient HepG2 cells (Mukhopadhyay et al. Science 1998;279:714-7). However, this latter study used a nonphysiologically relevant Fe complex (iron 59-NTA) to label cells with 59Fe at a nonphysiologic temperature (25 degrees C) and Cp concentration (<100 microg/mL). Because of these problems, the experiments have been repeated by maintaining physiologic conditions and labeling cells with the physiologic Fe donor diferric Tf. When cells were labeled at 37 degrees C with 59Fe-Tf in the presence of a physiologically relevant Cp concentration (300 microg/mL), this latter protein had no effect on the uptake of 59Fe in control cells or in cells depleted of Fe by using desferrioxamine. In addition, when Fe-replete or Fe-depleted cells were incubated with 59Fe-NTA at 25 degrees C or 37 degrees C, Cp had no effect on 59Fe uptake compared with the control. When the effect of Cp (10-500 microg/mL) on 59Fe release was examined in cells prelabeled with 59Fe-Tf, a concentration-dependent increase in 59Fe efflux was observed, whereas BSA had no effect. However, in contrast to membrane-permeable Fe chelators that caused a marked increase in Fe release, the effect of Cp on Fe efflux was less impressive. To further investigate the mechanism of 59Fe mobilization, we compared 59Fe efflux among HepG2 cells, SK-Mel-28 melanoma cells, and SK-N-MC neuroblastoma cells. These studies demonstrated that 59Fe release was dependent on the incubation time with 59Fe-Tf, the cell line, and the reincubation temperature. Although 59Fe mobilization from cells was markedly temperature dependent, a range of metabolic inhibitors did not affect 59Fe release. Additional experiments showed that physiologic concentrations of ascorbate reduced 59Fe efflux, whereas glutathione had no effect. This study provides further evidence that Cp is involved in Fe mobilization but does not appear to affect Fe uptake from Tf or NTA.

Antimetabolites↗
PubMed1999

Development of novel aroylhydrazone ligands for iron chelation therapy: 2-pyridylcarboxaldehyde isonicotinoyl hydrazone analogs.

Previous studies have demonstrated that aroylhydrazone iron (Fe) chelators of the pyridoxal isonicotinoyl hydrazone (PIH) class have high Fe chelation efficacy both in vitro and in vivo. Depending on their design, these drugs may have potential as agents for the treatment of Fe overload disease or cancer. Considering the high potential of this class of ligands, we have synthesized seven novel aroylhydrazones in an attempt to identify Fe chelators more efficient than desferrioxamine (DFO) and more soluble than those of the PIH class. These compounds belong to a new series of tridentate chelators known as the 2-pyridylcarboxaldehyde isonicotinoyl hydrazones (PCIH). In this study we have examined the Fe chelation efficacy and antiproliferative activity of these chelators including their effects on the expression of genes (WAF1 and GADD45) known to be important in mediating cell cycle arrest at G1/S. From seven chelators synthesized, three ligands, namely 2-pyridylcarbox-aldehyde benzoyl hydrazone (PCBH), 2-pyridylcarboxaldehyde m-bromobenzoyl hydrazone (PCBBH), and 2-pyridylcarboxaldehyde 2-thiophenecarboxyl hydrazone (PCTH), showed greater Fe chelation activity than DFO and comparable or greater efficiency than PIH. These ligands were highly effective at both mobilizing 59Fe from cells and preventing 59Fe uptake from 59Fe-transferrin and caused a marked increase in the RNA-binding activity of the iron-regulatory proteins (IRP). Our studies have also demonstrated that compared with the cytotoxic Fe chelator, 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311), these ligands have far less effect on cellular growth and 3H-thymidine, 3H-leucine, or 3H-uridine incorporation. In addition, in contrast to 311, which markedly increased WAF1 and GADD45 mRNA expression, PCBH and PCTH did not have any effect, whereas PCBBH increased the expression of GADD45 mRNA. Collectively, these results demonstrate the potential of several of these ligands as agents for the management of Fe overload disease.

Biological Transport, Active↗
PubMed1999

The effect of intracellular iron concentration and nitrogen monoxide on Nramp2 expression and non-transferrin-bound iron uptake.

Recent studies have demonstrated that the protein product (natural resistance associated macrophage protein 2, Nramp2) encoded by the gene Nramp2 acts as an Fe transporter involved in the uptake of Fe from transferrin (Tf) and low Mr Fe complexes. Interestingly, there are two splice variants of Nramp2, one with a putative iron-responsive element (IRE) in its 3' untranslated region (UTR) and another without. Due to the importance of Nramp2 in Fe transport, and the presence of an IRE in its 3'-UTR, we have examined the effect of Fe-deprivation, Fe-loading, and nitrogen monoxide on the expression of Nramp2 mRNA. These results were compared to the expression of transferrin receptor (TfR) mRNA which also has IREs in its 3'-UTR and is regulated by Fe and NO via the binding of iron-regulatory proteins (IRPs) to its IREs. Our experiments show that the IRE in Nramp2 mRNA does bind the IRPs in lysates from a mouse fibroblast cell line (LMTK-). Moreover, reverse transcription-PCR (RT-PCR) demonstrated that both the IRE and non-IRE-containing transcripts were present within these cells. However, there was no change in Nramp2 mRNA expression in LMTK- cells after a 20-h incubation with either the Fe chelator, desferrioxamine (DFO), the Fe donor, ferric ammonium citrate (FAC), or the NO generator, S-nitroso-N-acetylpenicillamine (SNAP). In contrast, these agents caused a marked change in the RNA-binding activity of the IRPs and the expression of TfR mRNA. In addition, both FAC and DFO caused an appropriate change in [59Fe] uptake from [59Fe]Tf, viz., an increase in Fe uptake after exposure to DFO and a decrease after treatment with FAC. As Nramp2 can transport Fe from non-Tf-bound Fe, the effect of preincubation with DFO and FAC was also examined on Fe uptake from [59Fe]nitrilotriacetate and [59Fe]citrate. However, in contrast to the results found for [59Fe]Tf, incubation with DFO and FAC did not result in appropriate regulation of Fe uptake from [59Fe]nitrilotriacetate or [59Fe]citrate. These data demonstrate that non-Tf-bound Fe uptake was not under control of the IRP-IRE system in these cells. Collectively, the results indicate that in LMTK-fibroblasts Nramp2 mRNA expression was not regulated like TfR mRNA.

3' Untranslated Regions↗
PubMed1999

How accurate are our assumptions about our students' background knowledge?

Teachers establish prerequisites that students must meet before they are permitted to enter their courses. It is expected that having these prerequisites will provide students with the knowledge and skills they will need to successfully learn the course content. Also, the material that the students are expected to have previously learned need not be included in a course. We wanted to determine how accurate instructors' understanding of their students background knowledge actually was. To do this, we wrote a set of multiple-choice questions that could be used to test students' knowledge of concepts deemed to be essential for learning respiratory physiology. Instructors then selected 10 of these questions to be used as a prerequisite knowledge test. The instructors also predicted the performance they expected from the students on each of the questions they had selected. The resulting tests were administered in the first week of each of seven courses. The results of this study demonstrate that instructors are poor judges of what beginning students know. Instructors tended to both underestimate and overestimate students' knowledge by large margins on individual questions. Although on the average they tended to underestimate students' factual knowledge, they overestimated the students' abilities to apply this knowledge. Hence, the validity of decisions that instructors make, predicated on the basis of their students having the prerequisite knowledge that they expect, is open to question.

Educational Measurement↗
PubMed1998

Development of iron chelators to treat iron overload disease and their use as experimental tools to probe intracellular iron metabolism.

The development of an orally effective iron (Fe) chelator for the treatment of Fe overload diseases such as beta-thalassemia has been a difficult challenge. Even though the drug in current clinical use, desferrioxamine (DFO), is efficient and remarkably free of toxicity, it suffers from not being orally effective and requiring long subcutaneous infusion to mobilize sufficient quantities of Fe. In addition, DFO is very expensive, which precludes it from treating most of the world's thalassemic population. Therefore, the development of an economical and orally effective Fe chelator is of great importance. Despite the screening of a wide range of structurally diverse ligands from both natural and synthetic sources, few compounds have been promising enough to proceed to clinical trials. In the current review, the properties of an ideal chelator are discussed, followed by a description of the most successful ligands that have been identified. Apart from the use of Fe chelators as therapeutic agents, some of these compounds have also been useful as experimental probes to investigate cellular Fe metabolism. We describe here the most important of these studies.

Deferoxamine↗
PubMed1998

Pyridoxal isonicotinoyl hydrazone and its analogs: potential orally effective iron-chelating agents for the treatment of iron overload disease.

At present, the only iron (Fe) chelator in clinical use for the treatment of Fe overload disease is the tris-hydroxamate deferoxamine (DFO). However, DFO suffers from a number of disadvantages, including the need for subcutaneous infusion (12 to 24 hours a day, 5 or 6 times per week), its poor intestinal absorption, and high cost. Therefore, there is an urgent need for an efficient, economical, and orally effective Fe chelator. Pyridoxal isonicotinoyl hydrazone (PIH) is a tridentate Fe-chelating agent that shows high Fe chelation efficacy both in vitro in cell culture models and also in vivo in rats and mice. In addition, this chelator is relatively nontoxic, economical to synthesize, and orally effective, and it shows high selectivity and affinity for Fe. However, over the last 10 years the development of PIH and its analogs has largely been ignored because of justifiable interest in other ligands such as 1,2-dimethyl-3-hydroxypyrid-4-one (L1). Unfortunately, recent clinical trials have shown that significant complications occur with L1 therapy, and it is controversial whether this chelator is effective at reducing hepatic Fe levels in patients. Because of the current lack of a clinically useful Fe chelator to replace DFO, PIH and its analogs appear to be potential candidate compounds that warrant further investigation. In this review we will discuss the studies that have been performed to characterize these chelators at the chemical and biologic levels as effective agents for treating Fe overload. The evidence from the literature suggests that these ligands deserve further careful investigation as potential orally effective Fe chelators.

Animals↗
PubMed1998

Sequence and analysis of the 60 kb conjugative, bacteriocin-producing plasmid pMRC01 from Lactococcus lactis DPC3147.

The complete sequence of pMRC01, a large conjugative plasmid from Lactococcus lactis ssp. lactis DPC3147, has been determined. Using a shotgun sequencing approach, the 60,232 bp plasmid sequence was obtained by the assembly of 1056 underlying sequences (sevenfold average redundancy). Sixty-four open reading frames (ORFs) were identified. Analysis of the gene organization of pMRC01 suggests that the plasmid can be divided into three functional domains, with each approximately 20 kb region separated by insertion sequence (IS) elements. The three regions are (i) the conjugative transfer region, including a 16-gene Tra (transfer) operon; (ii) the bacteriocin production region, including an operon responsible for the synthesis of the novel bacteriocin lacticin 3147; and (iii) the phage resistance and plasmid replication region of the plasmid. The complete sequence of pMRC01 provides important information about these industrially relevant phenotypes and gives insight into the structure, function and evolution of large gram-positive conjugative plasmids in general. The completely sequenced pMRC01 plasmid should also provide a useful framework for the design of novel plasmids to be incorporated into starter strain improvement programmes for the dairy industry.

Bacteriocins↗
PubMed1998

Absence of detectable pharmacological effects after oral administration of isoxsuprine.

Isoxsuprine is reported to be a peripheral vasodilator used in human and veterinary medicine to treat ischaemic vascular disease. In horses, it is generally administered orally to treat navicular disease and other lower limb problems. To define the scope and duration of its pharmacological responses after oral administration, 6 horses were dosed with isoxsuprine HCl (1.2 mg/kg bwt) q. 12 h for 8 days and then tested to assess the duration and extent of pharmacological actions. There was no significant difference between isoxsuprine and control treatment values for heart rate, spontaneous activity, sweat production, anal muscle tone, core and skin temperatures, and cutaneous blood flow. The lack of pharmacological effect following oral administration was in sharp contrast to the marked response following i.v. dosing reported in earlier experiments.

Administration, Oral↗
PubMed1998

Analogues of pyridoxal isonicotinoyl hydrazone (PIH) as potential iron chelators for the treatment of neoplasia.

Cancer cells have a high requirement for iron (Fe) as it plays a crucial role in a variety of metabolic processes including energy production and DNA synthesis. Studies in vitro and in vivo have demonstrated that the Fe chelator in current clinical use, desferrioxamine (DFO), can effectively inhibit the growth of some neoplasms, including leukemia and neuroblastoma. Unfortunately, DFO suffers from a number of serious disadvantages, including its high cost, the need for prolonged subcutaneous infusion (12-24 h/day, 5-6 nights/week), and its poor intestinal absorption precluding oral administration. Hence, the development of more effective Fe chelators is necessary. The Fe chelator, pyridoxal isonicotinoyl hydrazone (PIH), was initially identified as a ligand that showed high activity at mobilizing Fe from cells. More recently, a range of PIH analogues have been examined for their anti-proliferative effect, with several classes of these compounds showing high activity at inhibiting tumor growth in vitro. In fact, some of these hydrazones, particularly those derived from 2-hydroxy-1-naphthylaldehyde, showed comparable activity to the cytotoxic drugs cis-platin and bleomycin. In this review the role of Fe in cellular proliferation will be examined followed by a description of the most recent studies using the PIH analogues as effective anti-proliferative agents. Further studies in vivo with these Fe chelators are essential to determine their potential as chemotherapeutic agents.

Animals↗