ABSTRACT
Norbormide [5-(α-hydroxy-α-2-pyridylbenzyl)-7-(α-2-pyridylbenzylidene)-5-norbornene-2,3-dicarboximide] (NRB), an existing but infrequently used rodenticide, is known to be uniquely toxic to rats but relatively harmless to other rodents and mammals. However, one major drawback of NRB as a viable rodenticide relates to an evolutionary aversion developed by the rat leading to sub-lethal dosing due to either its unpleasant 'taste' or rapid onset of effects. A series of NRB-derived prodrugs were prepared in an effort to 'mask' this acute response. Their synthesis and biological evaluation (in vitro vasoconstrictory activity, in vitro hydrolytic and enzymatic stability and lethality/palatability in vivo) is described. Prodrug 2 displayed the most promising profile with respect to a delay in the onset of symptoms and was subsequently demonstrated to be significantly more palatable to rats. Moreover, prodrug 25 was found to be largely accepted by rats in a choice trial, resulting in high mortality.
Subject(s)
Imides/chemistry , Norbornanes/chemistry , Prodrugs/chemistry , Animals , Aorta/drug effects , Aorta/physiology , Hydrolysis , Imides/chemical synthesis , Imides/toxicity , Liver/metabolism , Male , Muscle Contraction/drug effects , Norbornanes/toxicity , Prodrugs/chemical synthesis , Prodrugs/toxicity , Rats , Rats, Sprague-Dawley , Rats, WistarABSTRACT
Norbormide [5-(α-hydroxy-α-2-pyridylbenzyl)-7-(α-2-pyridylbenzylidene)-5-norbornene-2,3-dicarboximide] (NRB), an existing but infrequently used rodenticide, is known to be uniquely toxic to rats but relatively harmless to other rodents and mammals. However, one major drawback of NRB as a viable rodenticide relates to an evolutionary aversion developed by the rat leading to sub-lethal dosing due to either its unpleasant 'taste' or rapid onset of effects. A series of NRB prodrugs were prepared in an effort to 'mask' this acute response. Their synthesis and biological evaluation (in vitro vasoconstrictory activity, in vitro hydrolytic and enzymatic stability and lethality/palatability in vivo) is described. Compound 19 displayed the most promising profile with respect to a delay in the onset of symptoms and was subsequently demonstrated to be significantly more palatable to rats.
Subject(s)
Drug Design , Imides/chemical synthesis , Norbornanes/chemical synthesis , Prodrugs/chemical synthesis , Rodenticides/chemical synthesis , Animals , Enzymes/metabolism , Hydrogen-Ion Concentration , Hydrolysis , Imides/metabolism , Imides/toxicity , Liver/enzymology , Liver/metabolism , Norbornanes/metabolism , Norbornanes/toxicity , Prodrugs/metabolism , Prodrugs/toxicity , Rats , Rodenticides/metabolism , Rodenticides/toxicity , Vasoconstriction/drug effectsABSTRACT
We used primary peripheral blood T cells, a population that exists in G(0) and can be stimulated to enter the cell cycle synchronously, to define more precisely the effects of nicotine on pathways that control cell cycle entry and progression. Our data show that nicotine decreased the ability of T cells to transit through the G(0)/G(1) boundary (acquire competence) and respond to progression signals. These effects were due to nuclear factor of activated T cells c2 (NFATc2)-dependent repression of cyclin-dependent kinase 4 (CDK4) expression. Growth arrest at the G(0)/G(1) boundary was further enforced by inhibition of cyclin D2 expression and by increased expression and stabilization of p27Kip1. Intriguingly, T cells from habitual users of tobacco products and from NFATc2-deficient mice constitutively expressed CDK4 and were resistant to the antiproliferative effects of nicotine. These results indicate that nicotine impairs T cell cycle entry through NFATc2-dependent mechanisms and suggest that, in the face of chronic nicotine exposure, selection may favor cells that can evade these effects. We postulate that cross talk between nicotinic acetylcholine receptors and growth factor receptor-activated pathways offers a novel mechanism by which nicotine may directly impinge on cell cycle progression. This offers insight into possible reasons that underlie the unique effects of nicotine on distinct cell types and identifies new targets that may be useful control tobacco-related diseases.
Subject(s)
Cell Cycle/drug effects , DNA-Binding Proteins/metabolism , Nicotine/pharmacology , Nuclear Proteins/metabolism , T-Lymphocytes/drug effects , Transcription Factors/metabolism , Animals , Calcium/metabolism , Cells, Cultured , Cyclin-Dependent Kinase 4 , Cyclin-Dependent Kinases/genetics , Cyclin-Dependent Kinases/metabolism , Cytokines/pharmacology , DNA-Binding Proteins/physiology , Humans , Mice , NFATC Transcription Factors , Nuclear Proteins/physiology , Phenotype , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/metabolism , RNA, Messenger/drug effects , RNA, Messenger/metabolism , T-Lymphocytes/cytology , Nicotiana/chemistry , Transcription Factors/physiologyABSTRACT
We evaluated real-time changes in extracellular acidification rates of human U937 and K562 leukemic cells treated with camptothecin or taxol. U937 cells treated with camptothecin or taxol for 30-60 min showed a continuous, irreversible decrease in extracellular acidification rate that was sensitive to amiloride. In contrast, U937 cells exposed to sodium azide showed an immediate, steep decrease in extracellular acidification rate that was reversible upon azide withdrawal. K562 cells required a >20-fold higher dose of camptothecin to promote similar changes in the extracellular acidification rate, with a corresponding resistance in their susceptibility to camptothecin- or taxol-induced apoptosis. The data show that irreversible commitment to apoptosis is associated with rapid metabolic changes that are reflected by decreased extracellular acidification rate and regulated by the Na(+)/H(+) antiporter. Moreover, detection of extracellular acidification rate changes was not restricted to a particular cell type or apoptosis pathway, making this a potentially useful tool to screen compounds for pro-apoptotic activity.
