Comparison and evaluation of pesticide monitoring programs using a process-based mixture model

A number of European countries run large-scale pesticide monitoring schemes in watersheds aimed at identifying and evaluating the presence of pesticide residues in the environment. These schemes provide national and regional scale assessments of pesticide concentrations within the context of environmental quality assessment, aiming to ensure some degree of ecological protection. The present study is aimed at evaluating the joint effects of the pesticide mixtures detected in monitoring programs, using a process-based mixture model that was parameterized for Daphnia magna. In total, over 15 000 samples containing over 1 million individual measurements were evaluated for effects. It was found that there are only a small number of places where one can expect to have effects on daphnids, based on measured concentrations. The most polluted samples would cause extinction of a daphnid population within only 30 h. The results show that effects are mostly triggered by a limited number of pesticide residues at locations with high emissions. It was also shown that the analytical detection limits are basically too high to exclude mixture effects. So, despite all the effort that is put into chemical monitoring programs, it remains a challenge to make statements on whether or not the environment is protected. Recommendations are offered for a different setup of monitoring programs to improve this situation. Environ Toxicol Chem 2016;35:3113-3123. © 2016 SETAC.

A universal virus inactivant for decontaminating blood and biopharmaceutical products

Removal of virus infectivity from blood and biopharmaceutical products prepared from blood is an issue of considerable importance. Irrespective of the methods that are chosen it is vital that the biological activity of the product is not impaired. For blood and unfractionated plasma or serum, the problem is even more challenging. Selective inactivation of the genome is the key step in the preparation of killed virus vaccines. Imines have been used for more than 30 years for the preparation of inactivated foot-and-mouth disease virus vaccines without any evidence of survival of virus infectivity. Moreover, the immunogenicity of the virus is unimpaired. Viruses belonging to all the recognised families can be inactivated by imines. The biological properties of several proteins, including the cell growth-promoting factors in calf serum, are not impaired using conditions which ensure the inactivation of > 10(15) infectious units of poliovirus and foot-and-mouth disease virus (FMDV). Moreover, both viruses can be inactivated by imines at 4 degrees C, thus providing a method for removing infectivity from protein preparations which are unstable at higher temperatures. The mechanism by which FMDV is inactivated has been studied. We found that the RNA extracted from the virus after inactivation at 4 degrees C was not degraded and contained no hidden breaks but nevertheless was non-infectious. However, it could be amplified by PCR using primers corresponding to the gene coding for a portion of the viral RNA polymerase, but not from that coding for VP1, one of the structural proteins, showing that alteration of a base or bases had occurred in that region.

Effect of nerve growth factor and thyrotropin releasing hormone on cholinergic neurones in developing rat brain reaggregate cultures lesioned with ethylcholine mustard aziridinium

Foetal rat whole brain reaggregate cultures were prepared in a serum-supplemented (S+) or serum-free medium (S-). Ethylcholine mustard aziridinium (ECMA) was added to the cultures at 9 days in vitro (DIV) at concentrations of 12.5, 25 or 50 microM. Choline acetyltransferase (ChAT) activity was measured at +2, +48 and +96 hr following treatment. In certain experiments the neurotrophic factors, thyrotropin releasing hormone (TRH: 50 micrograms/ml, daily from 9 DIV) or nerve growth factor (NGF: 7S subunit, 5 ng/ml, 0 and +48 hr following ECMA) were added during ECMA treatment. In both types of reaggregate cultured in S+ and S- media there was a 40-80% loss of ChAT activity following ECMA exposure (final concentration = 12.5 microM), presumed to reflect cholinergic cell loss. In both S+ and S- brain reaggregates NGF produced increased ChAT activity with more marked effects in S+ (45-55% increase, +48-96 hr) than in S- medium (20-25% increase, 2-96 hr). No effect on cholinergic muscarinic receptors (specific 3H-QNB binding) was evident after treatment with NGF. TRH had no effect on ChAT activity in the S+ cultures but produced small increases in the S- culture condition (approx 20%, +2-48 hr). Despite a residual "ECMA-resistant" pool of ChAT in the cultures, neither neurotrophic agent was found to cause a reversal of the lesion. In conclusion, the cholinotoxin ECMA appears to produce a cholinergic deficit in both developing S+ and S- reaggregates. This was not reversible by NGF or TRH at the concentrations and under the conditions tested. NGF had marked effects on ChAT activity without affecting muscarinic receptors in untreated developing brain reaggregates cultured in an S+ medium.

Noradrenaline depletion protects cholinergic neurons in rat hippocampus against AF64A-induced damage

The role of the noradrenergic system in the cholinotoxicity of ethylcholine aziridinium ion (AF64A) was studied in rats. Male Sprague-Dawley rats were treated with the noradrenergic neurotoxin DSP-4 (N-(2-chloroethyl)-n-ethyl-2-bromobenzylamine; 50 mg/kg i.p.) in the presence of the serotonin uptake inhibitor fluoxetine, 14 days prior to bilateral intracerebroventricular injection of AF64A (2 nmol/lateral ventricle). In rats in which noradrenaline (NA) was depleted by 94%, the loss of acetylcholine (ACh) in hippocampus induced by AF64A was significantly attenuated (p less than 0.02). However, when there was only a partial depletion of NA (50% reduction), the AF64A-induced loss of ACh was a pronounced as in rats with intact noradrenergic function. These findings indicate that the noradrenergic lesion has to be complete before a protective effect is apparent. Moreover, they imply that noradrenergic input is involved in AF64A-induced cholinergic damage in the hippocampus.

Non-specific effects of the putative cholinergic neurotoxin ethylcholine mustard aziridinium ion in the rat brain examined by autoradiography, immunocytochemistry and gel electrophoresis

Autoradiographic localisation of [3H]-ethylcholine mustard aziridinium ion (ECMA) after microinjection into the rat striatum has revealed intracellular sequestration of the toxin by glial and endothelial cells; fewer neuronal cells were labelled. Intrastriatal injection of 200 pmol ECMA caused severe cavitation of the tissue, extensive gliosis and permanent damage to myelinated structures, as revealed by immunocytochemical detection of glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP). These non-specific effects are in addition to ECMA's irreversible action on the choline carrier associated with cholinergic neurons, and only marginally protected by concomitant administration of the reversible choline transport inhibitor hemicholinium-3. They may instead be attributed to the powerful alkylating action that ECMA has on tissue proteins, as shown by fluorography of synaptosomal proteins treated with [3H]ECMA and separated by SDS-PAGE.

The neurotoxicity of ethylcholine mustard aziridinium (ECMA) in rat brain reaggregate cultures

The cholinergic neurotoxin ECMA causes a biphasic loss of choline acetyltransferase activity in foetal rat whole brain reaggregate cultures. Initial direct inhibition is followed by longer-term loss of cholinergic neurones. Final muscarinic receptor binding, neurofilament protein and Na+, K+-ATPase concentrations suggest that the lesion is specific for cholinergic neurones at 12.5 microM ECMA, but is more generalised at 50 microM ECMA.

Biochemical and histological modifications of the rat retina induced by the cholinergic neurotoxin AF64A

Intraocular injections of ethylcholine mustard aziridinium ion (AF64A) in the rat depressed retinal choline acetyltransferase (ChAT) activity in a dose-dependent manner without any significant change in the content of amino acid neurotransmitters GABA, glycine, aspartate and glutamate. ChAT reduction was already detected 24 h after the injection and persisted for at least one month. In vitro AF64A also inhibited retinal ChAT activity. No changes in muscarinic receptor sites were detected. The histological study showed light cells, characterized by cytoplasmic swelling in the innermost part of the inner nuclear layer and in the ganglion cell layer. We suggest that these light cells are the cholinergic retinal neurons affected by the toxin. In addition, dark cells in the inner nuclear layer, large empty spaces in the outer nuclear layer, inflammatory infiltrate and vascular alterations were also observed in treated retinas. Choline uptake systems in photoreceptors and in endothelial cells or cholinergic perivascular nerve endings may explain the lesions observed in the outer nuclear layer and the vascular alterations.

The toxic effects of ethylcholine mustard aziridinium ion on cholinergic cells in the chicken retina

The chicken retina has been used to examine the toxicity of a highly reactive chemical analog of choline, ethylcholine mustard aziridinium ion (ECMA). Following a single intravitreal injection, retinas were analyzed biochemically for CAT and AChE activities, and GABA, glycine, and dopamine levels. Retinas were also examined using histofluorescence for dopamine histochemistry, for AChE, and immunohistochemistry with antibodies to CAT, tyrosine hydroxylase, GABA, 5-HT, Leu-enkephalin, and somatostatin. A dose of 50 nmol ECMA caused a prolonged 70% depletion of CAT activity and a 40% depletion of AChE activity. The other biochemical parameters were unchanged. This result corresponds to the morphological finding that 2 populations of cholinergic cells were destroyed and that the AChE activity associated with their terminal arbors was lost. A third population of cholinergic cells, located towards the middle of the inner nuclear layer, was resistant to the toxic effects of ECMA. The other cell types, except for somatostatin-immunoreactive cells and photoreceptors, which showed transient effects, were unaffected. ECMA therefore appears to be a highly specific toxin for cholinergic cells in the retina.

Aziridine biotransformation by microsomes and lethality to hepatocytes isolated from rat

To clarify the relationship of aziridine biotransformation to their cytotoxic activities, the metabolism of optical isomers of typical cytotoxic and non-cytotoxic aziridines was studied in isolated hepatocytes, rat liver microsomes, mitochondria and L-1210 mouse leukemia cells. Cytotoxic 1-methyl-2-beta-naphthylaziridine (NAZ) gave nitrosomethane as one of the bioactivation products in isolated hepatocytes and simultaneously induced a marked decrease in cellular ATP followed by cell lethality. NAZ itself did not directly affect the respiratory function of mitochondria in isolated hepatocytes or in buffer solution, however, it inhibited the mitochondrial activity in the presence of microsomes in the buffer solution. Nitroso-t-butane or nitrosomethane dimer, used as a substitute for extremely labile nitrosomethane, strongly inhibited the respiration of mitochondria. On the other hand, optical isomers of 2-aziridinecarboxylic acid (AZC) which did not give nitrosomethane in isolated hepatocytes or microsomes also did not show cytotoxicity. Thus, the cytotoxicity of NAZ seems to be induced by bioactivation via cellular oxidases with the nitrosomethane generated being a major toxic component. This may occur with most of the cytotoxic aziridine derivatives.

cis- and trans-1,2-diphenylaziridines: induction of xenobiotic-metabolizing enzymes in rat liver and mutagenicity in Salmonella typhimurium

trans-Stilbene imine (trans-1,2-diphenylaziridine) is the nitrogen analog of trans-stilbene oxide, a potent inducer of several microsomal and cytosolic xenobiotic-metabolizing enzymes. Although the acute toxicity of cis- and trans-stilbene imines prevents their application at the usual dose for trans-stilbene oxide (400 mg/kg/day), it is apparent that the imines nevertheless potently induce several xenobiotic-metabolizing enzymes in rat liver. The IP administration of trans-stilbene imine resulted in statistically significant increases in the activities of aminopyrine N-demethylase, microsomal epoxide hydrolase, glutathione transferase (toward 1-chloro-2,4-dinitrobenzene, 1,2-dichloro-4-nitrobenzene and delta 5-androstene-3,17-dione) and UDP-glucuronosyltransferase (toward testosterone). cis-Stilbene imine was less potent in inducing these activities. Although trans-stilbene imine (total dose = 400 mg/kg) was more potent than trans-stilbene oxide (total dose = 1200 mg/kg) in inducing the activities of glutathione transferase (toward 1-chloro-2,4-dinitrobenzene) and UDP-glucuronosyltransferase (toward testosterone), both compounds belong to the class of substances which are more potent inducers of conjugating (phase II) enzymes. Because of their structural similarity with K-region arene imines which are potent mutagens, cis-stilbene imine and trans-stilbene imine were investigated for mutagenicity (reversion of his- strains of Salmonella typhimurium). cis-Stilbene imine and trans-stilbene imine were direct mutagens in the strain TA100. This result, and the finding that acenaphthene 1,2-imine efficiently reverts various strains of Salmonella typhimurium, demonstrates that not only K-region arene imines, but also other aziridines substituted at the two carbons with aromatic moieties, are mutagenic.

Cholinergic neurotoxicity induced by ethylcholine aziridinium (AF64A) in neuron-enriched cultures

The sequence of events in neuronal changes induced by the cholinotoxin ethylcholine aziridinium (AF64A) was studied. Neuron-enriched cultures derived from 8-day-embryonic chick cerebra were treated with AF64A at concentrations of 10(-5), 10(-4) and 10(-3) M. Choline acetyltransferase (ChAT) was used as an index of cholinergic neurons. Changes in cell morphology, the immunocytochemical and biochemical presence of ChAT, and DNA and protein content were assessed. Neuron-enriched cultures exposed to AF64A showed a dose-dependent response; after 24 h of exposure to 10(-3) M toxin all cells were dead, whereas a concentration of 10(-5) M did not alter culture morphology or DNA and protein contents. Despite the lack of cytological changes and the presence of ChAT immunoreactivity, biochemically assessed ChAT activity was reduced 36% in 10(-5) M treated cultures. Thus, the implicated decrease in acetylcholine synthesis in these cells cannot entirely account for the neuronal degeneration. Simultaneous exposure of cultures to both AF64A and 10 times higher concentrations of choline chloride delayed or diminished the neurotoxic changes. The protective effect of high choline concentrations was interpreted as evidence of competition between choline and AF64A for the high affinity choline transport system and as constituents in the cell membrane. Examination of the temporal sequence of cytotoxic changes in 10(-4) M exposed cultures revealed that disruption of neuronal aggregates and fragmentation of neurites occurred between 4 and 8 hours of exposure. After 24 h, some neurons survived but with attenuated arbors; in contrast, astrocytes appeared intact, suggesting that glial cells are more resistant than neurons to the toxic effects of AF64A. These findings suggest this culture model may be useful to further elucidate the mechanisms of AF64A drug action and study differentiation of cultured neuronal populations in the absence of cholinergic cells.

Specific toxic effects of ethylcholine nitrogen mustard on cholinergic neurons of the nucleus basalis of Meynert

The putative cholinergic neurotoxin, ethylcholine aziridinium ion (AF64A), was injected unilaterally into the nucleus basalis of Meynert (nbM) in order to determine whether it would produce specific damage to the cholinergic cell bodies of this nucleus. Injections of small amounts of AF64A (0.01 nmol in 1 microliter) or of its vehicle had little effect on the appearance of the nbM or on the levels of choline acetyltransferase (ChAT) in the cortex. Injections of larger amounts of AF64A (0.02 and 0.05 nmol in 1 microliter and 0.02 nmol in 10 microliters) produced a loss of diffuse acetylcholinesterase staining in the nbM and a loss of large positively staining neurons. Furthermore, these injections produced a significant reduction of ChAT activity in the central portion of the cortex. However, non-cholinergic neurons in the area of the nbM were not affected by these AF64A injections. In addition, cortical uptake of monoamines was not affected by these lesions. Further increases in the amount of AF64A injected (0.1 nmol in 1 microliter and 0.035 nmol in 10 microliters) caused damage at the site of the injection which was not limited to the cholinergic elements of the nbM. These results suggest that AF64A can be used to produce specific lesions of cholinergic neurons, and therefore may be useful in developing animal models of human disorders involving cholinergic hypofunction, such as senile dementia of the Alzheimer type. However, there is a narrow dose range for producing these specific effects.

Bone marrow toxicity of cyclophosphazenes is related to their structure and the treatment schedule

For three aziridinyl-substituted inorganic heterocycles belonging to the cyclophosphazene group, the tendency for cumulative bone marrow toxicity was studied in mice. In a one-day regimen, one of these drugs, gem-N3P3Az4Pyr2 (Az = aziridinyl, Pyr = pyrrolidinyl) (AZX), led to an increased death rate after a repeated injection, the number of bone marrow stem cells (CFUgm) being decreased 5 weeks after the second injection of this drug. In a four-day regimen two drugs, (NPAz2)2 NSOAz (Soaz) and AZX, led to an increased death rate after the second treatment course. In surviving animals leucocyte and thrombocyte counts were significantly lower in the second than in the first course. CFUgm counts were decreased for both drugs. For the third drug, trans-N3P3(Az)2(NHMe)4 (AZP), no evidence of cumulative bone marrow toxicity was demonstrated. It is suggested that whereas cytostatic activity of these compounds seems to be comparable, their tendency to cause cumulative marrow toxicity may vary.

Mutagenicity of N-substituted phenanthrene 9,10-imines in Salmonella typhimurium and Chinese hamster V79 cells

We previously showed that some (nonsubstituted) aziridines derived from polycyclic aromatic hydrocarbons (arene imines) elicit various mutagenic and genotoxic effects in bacteria and mammalian cells and that these arene imines are active at much lower concentrations than the corresponding epoxide analogues. In the present study, N-substituted derivatives of phenanthrene 9,10-imine were investigated. All 10 derivatives studied showed direct mutagenicity in Salmonella typhimurium TA100. Some of the compounds additionally exhibited weak effects in the strains TA98 and TA1537. Most N-substituted derivatives were weaker mutagens than unsubstituted phenanthrene 9,10-imine but stronger mutagens than phenanthrene 9,10-oxide. Bulky substituents reduced the mutagenicity more than did small substituents. In addition, the derivatives with electron-withdrawing substituents (with the exception of N-chlorophenanthrene 9,10-imine) were weaker mutagens than those with electron-donating substituents. Phenanthrene 9,10-imine and five N-substituted derivatives were investigated to determine whether they induce gene mutations at the hgprt locus in V79 cells. Four compounds, including the parent aziridine, were positive in the V79 test. The other two compounds were negative. The mutagenic potencies in the V79 cell system did not correlate well with those obtained with the Salmonella system. Overall, the study shows that in addition to unsubstituted arene imines, N-substituted derivatives are mutagenic. This finding is of interest, as metabolic pathways leading from aromatic compounds to N-substituted arene imines are conceivable.

Regional differences in ethylcholine mustard aziridinium ion (AF64A)-induced deficits in presynaptic cholinergic markers for the rat central nervous system

Several highly selective biochemical markers were used to assess the persistent central cholinergic dysfunction which accompanies administration of the cholinergic neurotoxin ethylcholine mustard aziridinium ion (AF64A). Rats received a single bilateral intracerebroventricular injection of AF64A (3 nmol/3 microliter/side) or vehicle and measurements were carried out in the cerebral cortices, hippocampi and corpora striata at 7 and 21 days postinjection. The drug binding sites of muscarinic cholinergic receptors, as revealed by high-affinity binding of (-)-[3H]quinuclidinyl benzilate (a classical muscarinic antagonist), [3H]pirenzepine (a selective antagonist of the putative M1 muscarinic receptor subclass) and (+)-[3H]cis-methyldioxolane (a potent muscarinic agonist), were not significantly affected by AF64A treatment. As reported previously, activity of the cholinergic synthetic enzyme choline acetyltransferase was reduced markedly (60-65%) in the hippocampi of AF64A-treated rats. A similar reduction was noted in high-affinity binding of [3H]hemicholinium-3 (a putative radioligand for sodium-dependent high-affinity choline uptake sites on cholinergic nerve terminals) in hippocampal membranes (59-65%). However, in the cerebral cortex, these presynaptic cholinergic markers were differentially altered by AF64A pretreatment (choline acetyltransferase, unchanged; [3H]hemicholinium-3 binding, reduced by 59-65%). These results indicate that a single intracerebroventricular injection of AF64A promotes biochemical and possibly functional deficits in presynaptic cholinergic nerve terminals distal from the injection site while having minimal influences upon muscarinic cholinergic receptor populations.

Arene imines, a new class of exceptionally potent mutagens in bacterial and mammalian cells

K-region aziridines of polycyclic aromatic hydrocarbons reverted Salmonella typhimurium his- (TA100, TA98) and Escherichia coli trp- strains (WP2 uvrA), without requiring activation by mammalian enzymes. The number of revertants induced per nmol in S. typhimurium TA 100, the most responsive strain, variea from 6 to 10,000 for the seven monoaziridines and the two bisaziridines tested. Interestingly, the mutagenic potencies (y) of the monoaziridines were closely related (r = 0.984) with those of the corresponding epoxide analogues (x) by the equation y = 19.6 X0.97, i.e., the aziridines were about 20-fold stronger mutagens than were the epoxides. One of the aziridines, benzo(a)pyrene (BP)-4,5-imine, was investigated in several additional mutagenicity test systems: toxicity in DNA repair-deficient (rec-) and -proficient (rec+) Bacillus subtilis strains; induction of 6-thioguanine resistance in V79 Chinese hamster cells; and induction of sister chromatid exchanges in cultured human fibroblasts. In all systems, BP-4,5-imine was much more active than the epoxide analogue, BP-4,5-oxide. The difference in activity was particularly large in the two test systems with mammalian target cells in which several hundredfold higher concentrations of the epoxide had to be used in order to elicit equipotent effects. Even r-7,t-8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydro-BP, which is one of the most potent mutagens known for V79 cells, was less active in the mammalian cells than was BP-4,5-imine. One reason that arene imines are such potent mutagens may be that they are poorly detoxified. Addition of highly purified microsomal epoxide hydrolase, which strongly reduced the mutagenicity of BP-4,5-oxide and benz(a)anthracene-5,6-oxide in S. typhimurium, had no effect on the mutagenicity of the corresponding aziridines. Furthermore, while benz(a)anthracene-5,6-oxide was inactivated by highly purified cytosolic epoxide hydrolase, benz(a)anthracene-5,6-imine was not inactivated. It is noteworthy that the arene imines are isomeric with and structurally closely related to aromatic amines. Some aziridines derived from nonaromatic structures (ethylene imines) have been reported as metabolites of xenobiotics; others are used as chemotherapeutics. At present, however, the results are mainly of theoretical interest in that a new type of arene derivatives with exceptionally potent, probably ultimate, mutagenicity was discovered and may be exploited for the study of mechanisms of chemical carcinogenesis.

Phase II evaluation of diaziquone (CI-904, AZQ) in the treatment of human malignant glioma

Diaziquone, a new alkylating agent which crosses the blood brain barrier, has shown a 20% response rate in phase II studies in heavily pretreated patients. We have treated 23 patients at our institution as part of a multicentric phase II European trial of diaziquone. All had histologically proven malignant glioma unequivocally progressing on CT scan. Prior therapy had consisted of surgical excision (13 patients), cobalt radiotherapy to CNS (13 patients), and chemotherapy with nitrosourea derivatives (11 patients). Six patients had no prior therapy. Median age was 42 years (range 22-69) and performance status was 3+ or better. They were treated with monthly courses of diaziquone 5.5 mg/m2 I.V. (10 min.) X 5 days. Dosage adjustments were made according to leucocyte and platelet nadirs. Thrombocytopenia was the dose limiting toxicity. Very mild gastrointestinal toxicity was observed. One patient developed hemolytic anemia. One complete response (clinical and CT scan), 7 partial clinical responses (3: greater than 50%, 4: 25-50%), and 1 disease stabilization (less than 25%) were documented. The longest response has now lasted over 26 months. These preliminary results show that chemotherapy with diaziquone can achieve a response rate as high as 35% in malignant glioma even in patients previously treated with a chemotherapy regimen including a nitrosourea (four of the seven objective responses were seen in such patients). Diaziquone is well tolerated and deserves further study in the management of malignant glioma.

Induction of DNA strand breaks and cross-links by 2,5-diaziridinyl-3,6-bis(carboethoxyamino)-1,4-benzoquinone in Chinese hamster ovary cells

The DNA-damaging effects of 2,5-diaziridinyl-3,6-bis(carboethoxyamino)-1,4-benzoquinone (AZQ) in Chinese hamster ovary cells were investigated. As determined by alkaline elution, DNA strand breaks were observed in cells treated with 50 microM AZQ for 2 hr. The single-strand break frequency was 31.3 +/- 5.3 (S.D.) rad equivalents. Strand breaks could also be detected at lower drug concentration if proteinase K treatment was included before DNA elution. In comparison, DNA cross-links were apparent in cells treated with as low as 6.25 microM AZQ. The cross-linking frequencies were 39.7, 124.3, 230.3, and 625.1 rad-equivalents for 6.25, 12.5, 25, and 50 microM AZQ, respectively. Both DNA-DNA and DNA-protein cross-links in AZQ-treated cells were revealed by the proteinase K assay. The DNA strand breaks induced by AZQ were rapidly rejoined within 1 hr after drug removal. DNA interstrand cross-links increased within the first 6 hr of postincubation and then slightly decreased by 12 hr, and most of the cross-links disappeared after cells were allowed to recover for 24 hr. DNA-protein cross-links were immediately formed during the drug treatment period and were gradually decreased after drug removal.

Sister-chromatid exchanges and chromosomal aberrations in lymphocytes of male albino rats treated with an alkylating agent, apholate (NSC 26, 812; ENT 26, 316)

A lymphocyte culture system was used to study the frequency of chromosomal aberrations and SCEs at various time intervals after an intraperitoneal injection of apholate (0.5 mg/kg b.w.) in male albino rats. Treatment with apholate increased the frequency of chromosomal aberrations significantly (P less than 0.001). The majority of chromosomal aberrations were single chromatid breaks, although other aberrations were also present. The distribution of chromatid breaks was non-random and the large chromosomes were affected to a greater extent. SCEs frequency in lymphocytes of apholate-treated rats was more than 5-fold higher in comparison to controls. The highest number of chromosomal aberrations and SCEs/rat was recorded at 48 h post-treatment, after which there was a gradual decline in both SCE and chromosomal aberration frequency. The results indicate that apholate is a mutagenic compound and it may also be carcinogenic.

Effect of the chemosterilant bisazir on the eggs of Earias fabia stoll

Bisazir-induced inhibition of nucleic acids and protein, and enhancement of free amino acids in the eggs of treated Earias fabia (Lepidoptera; Noctuidae) is reported. The degree of alterations in various crosses followed: T male X T female greater than UT male X T female greater than T male X UT female, which was also reflected in the weight loss of eggs. The alterations have been attributed to the abnormalities in the developing embryos due to genic imbalance in the spermatozoa, nurse cells and oocytes, ultimately leading to embryonic death.

DNA strand scission and cross-linking by diaziridinylbenzoquinone (diaziquone) in human cells and relation to cell killing

The effects of 3,6-diaziridinyl-2,5-bis(carboethoxyamino)-1,4-benzoquinone (diaziquone; AZQ) on various cell types were studied in relation to two chemical reactivities that this drug would be expected to have intracellularly. AZQ can undergo a reduction-oxidation cycle of the quinone function; this could generate free radicals which could produce DNA damage, especially DNA strand scission. The second reactivity, based on the two aziridine groups, could produce alkylation reactions that could produce DNA cross-links. DNA strand breakage and cross-linking were measured by alkaline elution and were compared with cell killing assayed by colony survival. Among the cell strains studied (human IMR-90, VA-13, and HT-29 and mouse L1210), marked differences were found in the magnitudes of DNA strand breakage and interstrand cross-linking produced by AZQ. Most striking, IMR-90 cells exhibited substantial strand breakage and little or no interstrand cross-linking, whereas the reverse was true for HT-29 cells. Cell killing correlated well with interstrand cross-linking but did not correlate with strand scission in these cell lines. It is concluded that AZQ produces DNA strand breaks and interstrand cross-links by different mechanisms which vary independently among different cell lines.

Photosensitive interaction of RSU 1069 with DNA

RSU 1069 is a 2-nitroimidazole radiosensitizer with an aziridine-containing side chain. In light (360 nm) the absorbance maximum of the nitro group at 325 nm disappears, which is accompanied by expulsion of the nitro group as the nitrite ion. We suggest an intramolecular cyclization of the aziridine side chain and the C2 of the imidazole ring as a possible explanation. This photosensitive effect was used to determine separately the damage to DNA induced by the reduced nitro group and the alkylating property of the aziridine. The aziridine-induced DNA damage is maximized in the dark when the nitro group is either absent (electrolytically reduced prior to the addition of DNA) or non functional (unreduced). In the light, damage is reduced. Typical DNA damage includes helix disruption leading to single strand breaks and the release of thymidine. Alkaline filter elution studies show evidence only for strand breakage and none for cross-linking indicating the drug is capable of mono-functional alkylation only.

Treatment of human glioma and medulloblastoma tumor lines in athymic mice with diaziquone and diaziquone-based drug combinations

We used diaziquone (NSC 182986) alone and in combination with other antineoplastic drugs to treat six human glioma and one human medulloblastoma tumor lines growing s.c. in athymic mice. Pharmacokinetic studies of diaziquone in the plasma of athymic mice indicated rapid clearance with a half-life of approximately 11.5 min. Diaziquone produced significant growth delays in at least one experiment using each of seven different tumor lines, and it produced consistent and significant delays in five of the seven. There was no obvious difference between a single dose and a dose administered once daily for 5 days, and tumor regressions to a volume smaller than that at treatment were uncommon in any of the single-drug experiments. Using our most extensively characterized human glioma line, D-54 MG, we found striking enhancement of the therapeutic effect by using nontoxic combinations of either diaziquone and carmustine (1,3-bis(2-chloroethyl)-1-nitrosourea, NSC 409962) or diaziquone and procarbazine (NSC 77213). These combinations produced significant increases in the median growth delay, significant increases in the number of tumor regressions, and some instances in which no palpable tumors were present 100 days after treatment. In contrast, in experiments using diaziquone -based chemotherapy combinations with either cyclophosphamide, cis-platinum, or vincristine, there was only slight enhancement of the therapeutic effect. These results, using human glioma and medulloblastoma tumor lines in athymic mice, suggest a broad range of activity of diaziquone against primary nervous system tumors and enhancement of its therapeutic effect with either 1,3-bis(2-chloroethyl)-1-nitrosourea or procarbazine. If Phase II and Phase III clinical trials corroborate these findings, the value of the nude mouse system for the evaluation of new therapeutic approaches to brain neoplasms would be further confirmed.

Phase I evaluation of SOAz (1,3,3,5,5 pentakis(aziridino)-1 lambda 6, 2,4,6,3 lambda 5, 5 lambda 5 thiatriaza-diphosphorine-1-oxide) in a weekly schedule

Eleven patients with advanced cancer were treated with SOAz, the first aziridino substituted inorganic heterocyclic compound to undergo phase I clinical trials. The agent was administered as a rapid i.v. infusion once a week in a dose of 50, 75 or 100 mg/m2. Severe myelotoxicity, which was prolonged and delayed in onset, precluded continuing treatment for more than three courses in 9 of 11 patients. In two patients thrombocytopenia showed no signs of recovery 9 and 11 weeks after the last infusion. Two minor responses were noted and there was one therapy-related death. Because of severe myelotoxicity, which is cumulative and may be irreversible, this treatment schedule seems unsuitable for phase II studies.

Acute toxicity study of 1,3,3,5,5-pentaziridino-1-thia-2,4,6-triaza-3,5-diphosp horine-1-oxide (a new antitumor agent with an inorganic ring) in mice, rats and dogs

In order to study the safety of 1,3,3,5,5-pentaziridino-1-thia-2,4,6-triaza-3,5-diphospho rine-1-oxide (SOAz), a new antitumor agent, acute toxicity studies by intravenous administration were performed in ddY mice, Wistar rats and beagle dogs. The LD50 values in rodents were 325 mg kg-1 for male mice, 450 mg kg-1 for female mice, 100 mg kg-1 for male rats and 82 mg kg-1 for female rats. In dogs, the LD50 values were 12 mg kg-1 for males and 18 mg/kg-1 for females. The dosed animals showed diarrhoea and decreased movement in the three species, and emaciation and loss of body weight in mice and rats. Dogs also showed signs of pneumonia. Histopathological examination revealed bone marrow suppression, atrophy of lymphoid organs and testes, and damage to the digestive tract mucosa in the three species. The main causes of death from single-dose administration were bone marrow aplasia and atrophy of lymphoid tissue in all species, together with gastro-intestinal ulceration in rats and dogs, and infection in mice and dogs.

Decreased cytotoxicity of aziridinylbenzoquinone caused by polyamine depletion in 9L rat brain tumor cells in vitro

The in vitro cytotoxicity of aziridinylbenzoquinone (AZQ) used either alone or after induced intracellular polyamine depletion in 9L rat brain tumor cells was studied using a colony-forming efficiency assay. Used alone, AZQ was cytotoxic to 9L cells; however, depletion of intracellular putrescine and spermidine levels by treatment with 1 mM alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, for 72 hr decreased significantly the cytotoxicity of AZQ. Dose modification factors were 1.9 and 1.8 at 10 and 1% survival levels, respectively. Decreased cytotoxicity could be almost completely prevented by addition of putrescine to polyamine-depleted cells 24 hr before AZQ treatment. Although AZQ alone was cytotoxic against 9L cells, metabolic activation by the S-9 rat liver microsomal fraction increased greatly the observed cytotoxicity. However, even with microsomal activation, pretreatment of cells with 1 mM alpha-difluoromethylornithine for 48 hr produced a significant decrease in AZQ cytotoxicity; dose modification factors were 2.4 and 2.2 at 10 and 1% survival levels, respectively. Addition of putrescine to polyamine-depleted cells 24 hr before AZQ treatment prevented the decrease in cytotoxicity. Pretreatment of 9L cells for 48 hr with 40 microM methylglyoxal bis(guanylhydrazone), a polyamine biosynthesis inhibitor that competitively inhibits S-adenosylmethionine decarboxylase, caused a decrease in the cytotoxicity of AZQ administered without microsomal activation. The dose modification factor was 1.6 at both 10 and 1% survival levels.

Phase II and pharmacokinetic study of aziridinylbenzoquinone [2,5-diaziridinyl-3,6-bis(carboethoxyamino)-1,4-benzoquinone, diaziquone, NSC 182986] in high-grade gliomas

2,5-Diaziridinyl-3,6-bis(carboethoxyamino)-1,4-benzoquinone (AZQ; Diaziquone, NSC 182986) is a rationally designed antitumor drug possessing sufficient lipid solubility to allow penetration into the central nervous system. Thirty-one patients with high-grade glioma and progressive disease following radiation, with or without previous chemotherapy, have been treated with 144 cycles of drug, consisting of 20 mg/sq m given as an i.v. infusion on Days 1 and 8 of a 28-day cycle. Responses were measured by serial computer tomography scanning. Of the 28 evaluable patients, 6 (21%) had limited improvement (10 to 40% reduction in tumor size) on computer tomography scan, 10 (36%) had disease stabilization, and 12 (43%) had progressive disease. The drug was well tolerated clinically, with little acute toxicity. The major toxicity was myelosuppression, which appeared cumulative, using this dose regimen. AZQ was measurable in both tumor tissue and tumor cyst fluid in patients on therapy. Plasma samples taken during the period of infusion confirm that 50% or more of the total AZQ exposure occurs during the infusion period. AZQ behaves as intended by design and demonstrates activity in this poor-prognosis group of patients.

Selective presynaptic cholinergic neurotoxicity following intrahippocampal AF64A injection in rats

Compound AF64A, ethylcholine mustard aziridinium ion (0.4-8 nmol) was stereotaxically administered into rat dorsal hippocampus, and neurochemical changes were determined 5 days later. AF64A treatment, over an almost 10-fold dose range, resulted in a significant (up to 70%) decline in choline acetyltransferase activity. In the same tissue samples, Na+-dependent choline transport activity was also lowered, with most decreases ranging between 10 and 50% of controls; however, there was no significant correlation (r = 0.39) between these two parameters. Acetylcholinesterase activity was not affected by AF64A treatment when assayed by either histochemical or enzymatic methods. AF64A reduced acetylcholine levels by 43%, but did not alter norepinephrine content or serotonin uptake. These results demonstrate that AF64A can induce a specific, long-term reduction of cholinergic presynaptic biochemical markers in rat hippocampus. Thus, AF64A can serve as a useful new tool to study the cholinergic system and as an important agent to help develop animal models representing disorders of central cholinergic hypofunction.

Selective inhibition of peripheral cholinergic transmission in the cat produced by AF64A

The neuropharmacologic effects of ethylcholine aziridinium ion, AF64A, were studied in cats, using various physiological techniques, to ascertain its synaptic site of action and to determine whether it may act as a cholinergic specific neurotoxin in vivo. Nictitating membrane contractions elicited by preganglionic nerve stimulation (1-16 Hz) were diminished in a dose-dependent manner after injection of AF64A into the carotid artery. Contractions due to injection of l-norepinephrine, tetramethylammonium or acetylcholine were not changed. Postganglionic action potentials from the superior cervical ganglion evoked by preganglionic stimulation were also abolished by AF64A, whereas the postganglionic firing produced by tetramethylammonium was unchanged. Neither the nictitating membrane nor ganglionic responses on the contralateral side of the animal were affected by AF64A treatment. In the same animals, twitch tension in the tongue produced by stimulation of the ipsilateral hypoglossal nerve (1-16 Hz) was gradually reduced and in most experiments completely blocked by AF64A. Repetitive stimulation of either the autonomic or somatic nerves at high frequencies (greater than 10 Hz) magnified and accelerated the onset of neurotoxic effects of AF64A. The suppression of ganglionic and neuromuscular transmission by AF64A was irreversible during the course of the experiments (12-18 hr). From these results, we can conclude that AF64A produces in the peripheral nervous system a longlasting inhibition of cholinergic transmission, without interfering with adrenergic transmission. Moreover, because AF64A did not block the postganglionic responses elicited by cholinergic nicotinic and muscarinic agonists, the inhibitory effects of AF64A must be mediated by a presynaptic action on cholinergic nerve terminals.

Effect of 1,3,3,5,5-pentaziridino-1-thia-2,4,6-triaza-3,5-diphosphorine-1-oxide, a new antitumor agent with inorganic ring, on various experimental tumors

1,3,3,5,5-Pentaziridino-1-thia-2,4,6-triaza-3,5-diphosphorine-1-oxide (SOAz), a new antitumor agent, was evaluated for antitumor activity against various mouse- and rat-tumor systems. The optimal treatment regimens of SOAz (i.p.) gave 262% and 134% increase in life span (ILS) in mice with P388 leukemia and L1210 leukemia implanted intraperitoneally, respectively, and 239% ILS in rats with Yoshida sarcoma of which 86% survived for 60 d after intraperitoneal tumor implantation. The compound showed a definite activity against Lewis lung carcinoma implanted intravenously. The compound also exhibited 80-100% inhibition of tumor local growth in all of four experimental tumor systems used in the present study. In contrast to cyclophosphamide, SOAz was active against B16 melanoma and Meth A, and demonstrated high activity against a subline of L1210 leukemia resistant to cyclophosphamide.

Factors influencing the severity and progress of ethylenimine-induced papillary necrosis

The severity of the renal papillary necrosis produced in rats by ethylenimine is dependent both on dose and urinary concentration within the medulla. When this is reduced by diuresis, the severity of the lesion is effectively reduced. Increasing urinary concentration has a reverse effect, but of less magnitude. When the concentrating power of the renal medulla is impaired by a single dose of ethylenimine, insufficient to cause necrosis of the whole papilla, further doses of ethylenimine do not cause progressive damage to the papilla.

Testicular damage and change in serum LDH isozyme pattern induced by multiple sub-lethal doses of apholate in albino rats

Treatment with apholate caused degenerative changes in the testes of albino rats. No histological changes were observed in Leydig cells. LDH-X activity was present in the serum of treated rats and absent in controls. Electrophoresis indicates that the activity band present in serum was similar to the activity band found in testes. A colorimetric method for assaying LDH-X activity is reported.

Interaction of endosulfan and metepa in rats

Repeated administration of endosulfan or metepa or their mixture did not induce any significant histological changes in the organs examined in male rats. Similarly, the activity of different enzymes assayed here showed no significant alterations. The level of endosulfan did not differ significantly in presence or absence of metepa in the samples of blood, brain, fatty tissue, kidney, liver and testis. The observations do not suggest any kind of additive or antagonistic effects or potentiation of each compound in presence of the other, at the doses and duration studied in male rats.