Preclinical Toxicology Studies with Acyclovir: Genetic Toxicity Tests

Preclinical Toxicology Studies with Acyclovir: Genetic ToxicityTests. Clive, D., Turner, N.T., Hozier, J., Batson, A.G. andTucker, W.E., Jr. (1983). Fundam. Appl. Toxicol 3: 587–602.Acyclovir (ACV), an antiviral drug active in the treatment oforal and genital Herpes infections, has been evaluated for mutagenicand carcinogenic potential in a battery of in vitro and in vivoshort-termassays. Negative results were obtained in the following in vitrotests: Ames Salmonella, plate incorporation and preincubationmodification assays; E. coli polA⁺/polA^– DNA repair; yeast(S. cerevisiae D4) gene conversion; Chinese hamster ovary cells(HGPRT, APRT loci and ouabain-resistance marker); L5178 Y mouselymphoma cells (HGPRT locus and ouabain-resistance marker);and C3H/10Tmouse fibroblast neo-plastic transformation assay.All except the last assay were performed in the presence andabsence of an exogenous metabolic activation system. ACV waspositive at high concentrations x exposure times in the absenceof exogenous metabolic activation in the following in vitrosystems and at the indicated concentrations: BALB/c-3T3 neoplastictransformation (50 /µg/mL, 72 h exposure); human lymphocytecytogenetics (250–500 µg/mL, 48 h exposure); andL5178Y mouse lymphoma cells (TK locus, 400–2400 µg/mL,4 h exposure; predominantly small colony mutants of chromosomalorigin produced). No effects were seen in vivo (mouse dominantlethal assay; rat and Chinese hamster bone marrow cytogenetics)at up to maximum tolerated doses (MTD). An unusual clastogeniceffect was seen in Chinese hamsters at 5 times the MTD. Overall,positive effects were seen only at either high concentrations(250 µg/mL in vitro or plasma levels) or prolonged exposure(72 hr in the BALB/ c-3T3 neoplastic transformation assay).These studies support the view that ACV is a chromosomal mutagen,i.e., one which causes multi-locus damage but not single geneeffects. The significance of these results for the genetic riskof ACV to man is discussed.     

Preclinical Toxicology Studies with Acyclovir: Ophthalmic and Cutaneous Tests

Preclinical Toxicology Studies with Acyclovir: Ophthalmic andCutaneous Tests. Tucker, W.E., Jr., Johnston, R.E., Macklin,A.W., Szot, R.J., Elion, G.B., de Miranda, P. and Szczech, G.M.(1983). Fundam. Appl. Toxicol. 3:569–572. Topical formulationsof acyclovir (ACV) were tested in animals to define potentialfor tissue irritation and systemic toxicity. Acyclovir ointments(5 and 10% concentrations in polyethylene glycol vehicle) producedno sign of dermal irritation or systemic toxicity when appliedto shaved abraded and intact skin of guinea pigs for 24 consecutivedays. Solutions (0.9% normal saline vehicle) of ACV did notsensitize guinea pigs when 10 sensitizing doses and a challengedose were injected intradermally. Petrolatum base ophthalmicointments containing 1 and 3% ACV did not produce significantocular irritation when applied to the corneas of New ZealandWhite rabbits 5 times each day for 21 consecutive days. A 6%petrolatum base ointment produced mild conjunctival irritationbut no sign of corneal or iridic toxicity. Mean concentrationsof 2.53 µM ACV were found in aqueous humor 2 hours aftera 1 cm ribbon (21 mg) of 3% ophthalmic ointment was placed inthe eyes of rabbits. A single treatment with a topical ointmentcontaining 5% ACV in polyethylene glycol vehicle produced minimalirritation when placed in the eyes of New Zealand White rabbits.     

Preclinical Toxicology Studies with Acyclovir: Teratologic, Reproductive and Neonatal Tests

Preclinical Toxicology Studies with Acyclovin Teratologic, Reproductiveand Neonatal Tests. Moore, H.L., Jr., Szczech, G.M., Rodwell,D.E., Kapp, R.W., Jr., de Miranda, P. and Tucker, W.E., Jr.(1983).Fundam. Appl Toxicol 3:560–568. Five studies weredone to define the potential of Acyclovir (ACV), a new nucleosideanalog for antiviral chemotherapy, to produce adverse effectson reproduction and development in laboratory animals. ACV producedno adverse effects when given by gavage to F₀ generation miceat 50, 150 and 450 mg/kg/day in a two generation reproduction/fertilitystudy. Some mice were evaluated for teratologic effects andothers for postnatal development, including behavior, with negativeresults. ACV was not embryotoxic and did not increase the incidenceof fetal malformations when given by subcutaneous injectionto pregnant rats and rabbits at dose levels of 12, 25 and 50mg/kg/day during the periods of major organogenesis. A comparativeLD₅₀ study revealed that 3-day-old rats were not more sensitiveto acute toxic effects of ACV than more mature rats. Finally,in a comprehensive multidose toxicity study ACV was given subcutaneouslyto neonatal rats at 5, 20 and 80 mg/kg/day for 19 consecutivedays. There was minimal effect on body weight gain in neonatestreated at 20 mg/kg/day and a significant decrease in body weightgain at 80 mg/kg/day. Minimal renal lesions occurred at 80 mg/kg/ day but no other signs of adverse effects on developingorgan systems were observed. Except for decreased body weightgain in neonatal rats treated at 80 mg/kg/day, ACV did not produceadverse effects on mammalian development when tested in a varietyof preclinical toxicology studies.     

Preclinical Toxicology Studies with Acyclovir: Carcinogenicity Bioassays and Chronic Toxicity Tests

Preclinical Toxicology Studies with Acyclovir: CarcinogenicityBioassays and Chronic Toxicity Tests. Tucker, W.E., Jr., Krasny,H.C., de Miranda, P., Goldenthal, E.I., Elion, G.B., Hajian,G. and Szczech, G.M. (1983). Fundam. Appl. Toxicol. 3:579–586.Acyclovir (ACV), a nucleoside analog that is a new herpes-specificantiviral drug, was given by gavage at 50, 150 and 450 mg/kg/dayto Sprague Dawley rats and Swiss mice for most of their lifetimeto assess chronic toxicity and carcinogenicity. Treatment withACV did not shorten the lifespan of either rats or mice. Infact, female mice given 150 and 450 mg/kg/day had significantlylonger mean durations of survival than control female mice whenanalyzed by the life table technique. There were no signs oftoxicosis produced by chronic exposure to ACV in either therats or mice, and there was no drug-related increase in neoplasmsin either species. Four groups of Beagle dogs were initiallygiven daily oral doses of 15, 45 or 150 mg/kg ACV in a 1 yearchronic toxicity study. Dogs treated at 150 mg/ kg/day vomited,had diarrhea, consumed less feed and lost weight within 2 weeks.Dogs treated at 45 mg/kg/day also had minimal signs of gastrointestinaltoxicosis. These dose levels were then decreased to 60 and 30mg/kg/day for the rest of the one year test period. With theexception of occasional and inconsistent emesis and diarrhea,the 60 mg/kg/day dose level was well tolerated. Some mid andhigh dose dogs had sore paws due to erosion of footpads andcracking, splitting and loosening of the nails first becomingevident during the 13th week of the study. Several of thesedogs subsequently lost the keratin from some claws. There wasnail regeneration and healing of footpads as the study progressed,with all claws appearing essentially normal at the end of 1year. Nails and footpads of dogs given 15 mg/kg/day were normalthroughout the study.     

Preclinical Toxicology Studies with Nizatidine, A New H2-Receptor Antagonist: Acute, Subchronic, and Chronic Toxicity Evaluations

Nizatidine (NIZ), a new antiulcer drug, was evaluated for toxicityin acute, subchronic, and chronic tests. Acute toxicity studieswere conducted in rats, mice, dogs, and monkeys. Median lethaldoses (MLD) in rodents were greater than 1600,230, and 1000mg/kg by oral (po), iv, and sc administration, respectively.No deaths occurred in dogs given single doses of 800 mg/kg (po),75 mg/kg (iv), or 225 mg/kg (im) or in monkeys given 1200 mg/kg(po) or 200 mg/kg (iv). Rats survived up to 1.0% dietary NIZ(daily intake ranging from 24 to 800 mg/kg/day) for 1 year.Slight decreases in body weight gain and increases in liverand kidney weights occurred. Slight decreases in erythrocyticparameters at 3 months were not present at 6 or 12 months. Micesurvived up to 1.5% dietary NIZ for 3 months and effects werelimited to slight decreases in body weight gain and increasesin relative liver weight Dogs survived oral doses up to 800mg/kg/day for 3 months but had numerous clinical signs of toxicityand body weight loss. All dogs given oral NIZ doses up to 400mg/kg/day survived except for one high-dose dog that was killedin a moribund condition following convulsions in the 41st weekof treatment Effects in dogs included miosis, body weight loss,increased thrombocyte counts, and decreased hepatic micro-somalenzyme activity and P450 content. The increase in thrombocytecounts was unaccompanied by changes in thrombocyte functionand did not reoccur in a subsequent study. A decrease in plasmatestosterone in two of three surviving male dogs given 400 mg/kg/dayfor 1 year was unaccompanied by effects on the size or morphologyof testes or prostate. Peak plasma levels of NIZ in all speciestested were in excess of human plasma levels after therapeuticdoses. In conclusion, there was no evidence of significant toxicityin organs or tissues including those sites (gastric mucosa,male sex organs, and liver) that have been affected by someagents of this therapeutic Class.     

Preclinical Toxicology Studies with the Lipid-Regulating Agent Gemcadiol

Preclinical Toxicology Studies with the Lipid-Regulating AgentGemcadiol. FITZGERALD, J. E., PETRERE, J. A., MCGUIRE, E. J.,AND DE LA IGLESIA, F. A. (1986). Fundam. Appl. Toxicol. 6,520–531.Gemcadiol is a medium-length diol moiety with lipid-regulatingproperties in animals and man. The compound was not toxic whensingle doses were administered to rodents with the lethal dosegreater than 7000 mg/kg in rats and mice. Rats treated for 13or 52 weeks with 30 to 300 mg/kg had reversible food intakesuppression and weight gain inhibition, decreased blood cholesterol,slight anemia, and generally dose-related but reversible decreasesin glucose, and increases in alkaline phosphatase and bloodurea nitrogen. Liver weights were increased, and there was accompanyinghypertrophy and increased cytoplasmic eosinophilia of hepatocyteswith associated peroxisome proliferation. Rats treated for 52weeks also had mild renal tubular dilatation. Dogs given 25to 300 mg/kg of gemcadiol for up to 52 weeks tolerated the compoundbetter than rats. Effects related to compound administrationwere elevated serum alanine aminotransferase activity in femaleanimals only, and microscopic cytoplasmic vacuolation and hyalinebody formation in both sexes. Monkeys given 25 to 300 mg/kggemcadiol for 13 weeks had slightly decreased serum cholesteroland slightly increased serum creatine phosphokinase. Teratologystudies in rats or rabbits indicated no teratogenic response.Gemcadiol affects principally the liver, and the hepatic alterationsseen in rats and dogs may reflect compensatory manifestationsof altered metabolism related to the lipid-regulating activityof the compound.     

Acute,Subchronic, and Mutagenicity Studies with Norbornene Fluoroalcohol

The object of this study was to evaluate the toxicity of norbornene fluoroalcohol (NBFOH), which is used as an intermediate in the production of fluorinated monomers and polymers. NBFOH was evaluated for acute oral, dermal, and inhalation toxicity, dermal sensitization using the Local Lymph Node Assay (LLNA), mutagenesis by the Ames assay, and subchronic toxicity in a 4-week inhalation rat study. NBFOH demonstrated slight acute toxicity in oral, dermal, and inhalation studies. Approximate lethal doses of 3400 and > 5000 mg/kg for the oral and dermal routes, respectively, and an approximate lethal concentration of 4300 mg/m³ were determined. NBFOH demonstrated moderate skin irritation, was a severe eye irritant, produced dermal sensitization, but did not cause bacterial mutagenicity either in the presence or absence of S9 activation. Male and female rats were exposed nose only to airborne NBFOH at levels of 0, 410, 1400, and 1500 mg/m³, 6 h/day, 5 days/week for 4 weeks with clinical and histopathology specimens collected 1 day after the final exposure. Due to the vapor pressure of NBFOH, the 1500 mg/m³ atmosphere was 27% aerosol and 73% vapor; the 1400 mg/m³ atmosphere was 5% aerosol and 95% vapor, and the 410 mg/m³ level was only vapor. No test substance–related mortality or clinical signs of toxicity were observed over the course of the study, and male rats demonstrated significant weight loss and decreased food consumption at 1400 mg/m³. Male rats from the 1500 mg/m³ group demonstrated an 11% increase in prothrombin time that was significantly higher than the control value. Examination of fluoride in the urine did not demonstrate a concentration–response relationship, with minimal elevations observed in male rats at all exposure levels and sporadic increases in females. Both male and female rats exposed to 1400 mg/m³ or greater had squamous metaplasia of the laryngeal mucosa and degeneration of the nasal olfactory and respiratory mucosa. Based on the above findings, NBFOH demonstrates the potential to produce allergic contact dermatitis, and subchronic inhalation studies indicate a no-observed-adverse-effect-level (NOAEL) of 410 mg/m³.     

Toxicology and Toxicokinetics of Acute and Subchronic Administration of Histamine Dihydrochloride in Rats

Abstract

Histamine dihydrochloride is currently being evaluated as an adjuvant to immunotherapy regimens in neoplastic and infectious diseases. The no-observed-effect-level (NOEL), no-observable-adverse-effect-level (NOAEL), and pharmacokinetics of subcutaneously administered histamine dihydrochloride were determined via 5 and 28 day repeated dose studies in Sprague-Dawley rats. In the five day study, male rats received 0 (vehicle), 5, 30, 500, or 1000 mg/kg BID. Acute tissue damage was observed at one or more injection sites in the two highest dose groups after 24 h. At five days, animals in these groups displayed indications of pathological inflammation at the injection sites. In the 28 day study, male and female rats received 0 (vehicle), 0.5, 5, or 100 mg/kg BID. The most significant treatment-related pathological findings were signs of inflammation at the injection sites for animals in the 100 mg/kg BID group. Hematology and clinical chemistry changes in the highest dose groups in both studies were consistent with inflammation and anemia but were found to be reversible following a 14-day recovery. Plasma histamine levels were quantified from male and female animals receiving 0.5, 5, and 100 mg/kg injections on Day 1 and 28 of the twenty-eight day study. C_max was achieved within 0.25 h and was dose-proportional. The elimination half-life and t_max were longer at the 100 mg/kg dose than the lower doses. No marked differences between genders or between Day 1 and 28 were found. Based on these findings, the NOEL and NOAEL were established at 0.5 mg/kg BID and 5 mg/kg BID, respectively. When converted to human equivalent dose, the NOAEL is 0.81 mg/kg which is 54 times the intended human dose. These studies support a wide safety margin for histamine dihydrochloride.     

Subchronic, Developmental, and Genetic Toxicology Studies with the Ethane Sulfonate Metabolite of Alachlor

The ethane sulfonate (ESA) metabolite of the herbicide alachloris formed in soil by microbial action. The present studies wereconducted to assess the toxicity of ESA and provide a base setof data for risk assessment. ESA did not induce chromosomaleffects in a mouse bone marrow micronucleus assay followingacute administration. Administration of ESA to rats in drinkingwater at concentrations of 200, 2000, and 10,000 ppm for 91days elicited biologically significant indications of toxicityonly at the high-dose level (1002 mg/kg/day). The observed responsesincluded decreases in body weights and food consumption as wellas effects on clinical chemistry values. Many of the changesappeared to be due to decreased palatability of the drinkingwater. There were no ESA-induced gross pathology findings, organweight changes, or microscopic lesions. ESA did not produceany adverse effects in pregnant rats or their offspring evenat 1000 mg/kg/day, the highest dose tested. These findings showthat the subchronic and developmental toxicity of ESA are low.Furthermore, comparison of results from studies with alachlorand its metabolite shows that the toxicity of ESA is substantiallylower. Margins of exposure for ESA range from 133,824 to 2,573,529even using worst-case estimates of exposure, indicating thatthe metabolite poses little risk of producing adverse effectsat the very low levels occasionally encountered. These resultsand accompanying analyses support the conclusion that ESA isnot of toxicological concern.     

Nonclinical Toxicology Studies with Zidovudine: Genetic Toxicity Tests and Carcinogenicity Bioassays in Mice and Rats

Zidovudine (ZDV), an antiviral drug active in the treatmentof acquired immunodeficiency syndrome (recommended human dose,100 mg every 4 hr while awake), was evaluated for mutagenicand carcinogenic potential in a battery of short-term in vitroand in vivo assays and in lifetime studies in mice and rats.In L5178Y mouse lymphoma cells (tk^+/– locus), a weak positiveresult was obtained only at the highest concentrations tested(4000 to 5000 µg/ml) in the absence of metabolic activation.In the presence of metabolic activation, the drug was weaklymutagenic at concentrations of 1000 µg/ml and higher.Following 24 hr treatment in the absence of metabolic activation,ZDV was moderately mutagenic at concentrations up to 600 µg/ml;dose-related structural chromosomal alterations were seen atconcentrations of 3 µg/ml and higher in cultured humanlymphocytes. Such effects were not noted at the two lowest concentrationstested, 0.3 and 1 µg/ml, and BALB/c-3T3 cells were transformedat concentrations of 0.5 µg/ml and higher. No effectswere seen in the Ames Salmonella plate incorporation and preincubationmodification assays (possibly due to bacteriocidal activityof ZDV at low concentrations) at concentrations ranging from0.01 to 10 µg/plate or in a single-dose intravenous bonemarrow cytogenetic assay in CD rats. In multidose micronucleusstudies, increases in micronucleated erythrocytes were seenin mice at doses of 100 to 1000 mg/kg/day. Similar results wereseen in rats and mice after 4 or 7 days of dosing at 500 mg/kg/day.In carcinogenicity bioassays, adjusted doses of 20, 30, or 40mg/kg/day and 80, 220, and 300 mg/kg/day were given to CD-1mice and CD rats, respectively, for up to 22 months in miceand 24 months in rats. ZDV caused a macrocytic, normochromicanemia in both species. No evidence of carcinogenicity was seenin male mice or rats. In female mice, five malignant and twobenign vaginal epithelial neoplasms occurred in animals given40 mg/kg/day. A single benign vaginal epithelial tumor was seenin a mouse given 30 mg/kg/day. In rats, two malignant vaginalepithelial neoplasms were seen in animals given 300 mg/kg/day.In a 7-day study in mice, ZDV was shown to be devoid of estrogenicactivity. In an oral pharmacokinetics study, the AUC was 17and 144 µg/ml hr in female mice and rats given 40 or 300mg/kg of ZDV, respectively. In contrast, the average steady-stateconcentration in humans at the recommended daily dose is 0.62µg/ml. Twenty-four hour urine concentrations were 1245and 4417 µg/ml in female mice and rats given 40 or 300mg/kg of ZDV, respectively. These values were approximately26-and 136-fold higher than the human urine concentration atthe recommended daily dose. In a one- to three-day study withintravenously administered sodium fluoroscein in rats and mice,retrograde flow of urine into the vagina was demonstrated. Ina subsequent lifetime carcinogenicity bioassay in mice in whichZDV was given intravaginally at concentrations of 5 or 20 mgZDV/ml in saline, 13 vaginal squamous cell carcinomas were seenat the highest concentration tested. It was concluded that thevaginal tumors seen in the oral carcinogenicity studies werethe result of chronic local exposure of the vaginal epitheliumto high urine concentrations of ZDV.     

Toxicity of Cyclohexanone Oxime: II. Acute Dermal and Subchronic Oral Studies

Toxicity of Cyclohexanone Oxime. II. Acute Dermal and SubchronicOral Studies, GAD, S. C., DERELANKO, M. J., POWERS, W. J., MULDER,S., GAVIGAN, F., AND BABICH, P. C. (1985). Fundam. Appl. Toxicol.5, 128–136. Derrnal exposure of rabbits to cyclohexanoneoxime (CHO) for 24 hr at 0, 0.8, 2, and 5 g/kg caused dose-relatedreticulocytosis on the day after dosing as well as a decreasein hemoglobin in the 5-g/kg females 7 days postdosing. Gavageof rats 5 days a week for 13 weeks at levels of 0, 0.25, 2.5,and 25 mg/kg resulted in a dose-related decrease in erythrocytenumber, hemoglobin, and hematocrit, with an accompanying increasein circulating reticulocytes and nucleated erythrocytes, inboth sexes. Also seen were corneal opacities and an increasedincidence of Howell-Jolly bodies. Results suggested an increasederythropoiesis in the spleen and bone marrow. The data fromsatellite groups terminated at 30 and 60 days revealed no effectat the lower test level, but results from the end of the studyshowed a clear cumulative dose response down to the 0.25-mg/kglevel. Males were affected earlier and at lower doses than females.These results, along with those of a subacute study with a recoveryperiod, suggest that CHO induces an oxidative attack on erythrocyteswhich appears reversible upon cessation of exposure.     

Acute, Distribution, and Subchronic Toxicological Studies of Succinate Tartrates

The estimated single-dose oral toxicity (50% lethality) of succinatetartrates (ST) was 2–3 g/kg in rats. ST produced minimalto moderate dermal irritation but no evidence of systemic toxicityin a standard acute percutaneous toxicity test in rabbits. STwas not an eye irritant in a standard rabbit low-volume eyeirritation test ST was not genotoxic in a series of six genotoxicitytests. A 14-day oral gavage study in rats at a dose range of0.05–1.0 g ST/kg/day produced only gastric irritation.The no-observed-effect level (NOEL) for gastric irritation was0.1 g/kg for males and 0.05 g/kg for females. A 28-day percutaneoustoxicity study in rabbits produced minimal to moderate dermalirritation and no adverse systemic effects at a high dose of450 mg ST/kg/day. Single-dose absorption, distribution, andelimination (ADE) studies in male rats showed that 10–15%of an oral dose and 1–3% of a dermal dose were absorbed.Approximately 98% of the orally administered ST was eliminatedas ¹⁴C in urine, feces, or expired CO₂ after 72 hr. Approximately80% of the dermally absorbed ¹⁴C dose was eliminated in urine,feces, or expired CO₂ after 72 hr. In conclusion, no adverseeffects were noted in acute toxicity, genotoxicity, or subchronictoxicity studies conducted with ST.     

Acute and Subchronic Inhalation Studies on Trifluoroiodomethane Vapor in Fischer 344 Rats

Trifluoroiodomethane (CF₃I) is being considered as a replacementcompound for halon fire suppressants. Its structure is similarto that of Halon 1301 (CF₃Br), but it has very low ozone depletionpotential compared to CF₃Br. As part of the process of developingenvironmental and health effects criteria, acute, 2-week, and13- week nose-only inhalation toxicity studies were conductedin Fischer 344 rats. In the acute study, three groups of 30male rats each were exposed to 0 (control), 0.5, or 1.0% (v/v)CF₃I for 4 hr and euthanized immediately following exposure,3 days postexposure, or 14 days postexposure. There were nodeaths and no clinical signs of toxicity throughout the study.Histopathologic examination of select tissues showed no lesionsof pathologic significance. In the 2-week study, four groupsof 5 male rats each were exposed for 2 hr/day, 5 days/week to0, 3, 6, or 12% CF₃I No deaths were observed, though lethargyand slight incoordination were noted in rats of the 6 and 12%groups at the conclusion of each daily exposure. Mean body weightgains were depressed in rats of the 6 and 12% groups. Serumthyroglobulin and reverse T₃ (rT₃) values were increased atall exposure levels. At necropsy, no gross lesions or differencesin absolute or relative organ weights were noted. Histopathologicexamination of the thyroid and parathyroid glands indicatedno morphological abnormalities in the CF₃I-exposed rats. Inthe 13-week study, four groups of 15 male and 15 female ratswere exposed to 0, 2, 4, or 8% CF₃I 2 hr/day, 5 days/week for13 weeks. Rats exposed to 4 or 8% CF₃I had lower mean body weightsthan the controls. Deaths observed in the 2 and 8% groups wereattributed to accidents resulting from the restraint systememployed. Hematologic alterations were minimal and consideredinsignificant. Increases in the frequency of micronucleatedbone marrow polychromatic erythrocytes were observed in ratsof all three CF₃I groups. Serum chemistry alterations observedin rats of all CF₃I exposure groups included decreases in T₃and increases in thyroglobulin, rT₃, T₄, and TSH. Relative organweight increases (8% CF₃I group) occurred in the brain, liver,and thyroid glands; decreases were observed in the thymus andtestes. A decrease in relative thymus weights and an increasein relative thyroid weights were observed also in rats of the2 and 4% groups. Histopathological findings included a mildinflammation in the nasal turbinates of rats exposed to 4 or8% CF₃I, mild atrophy and degeneration of the testes (4 and8% CF₃I groups), and a mild increase in thyroid follicular colloidcontent in rats of all CF₃I exposure groups. Though NOAELs wereobserved for select target organs (e.g., nasal turbinates, testes),NOAELs were not apparent in all target organs examined (e.g.,thyroid glands, bone marrow).     

Preclinical Studies on Human Insulin. I. Acute and Subacute Toxicity Studies

Abstract: Human insulin (prepared from porcine insulin) and porcine insulin were tested for acute toxicity by subcutaneous administration to unfasted mice and rats and fasted mice. The animals were observed for signs of reaction and post mortem examination was performed. LD50 values were calculated when possible. The LD50 values in the unfasted animals were several times higher than in the fasted mice, but similar for the two insulin preparations. The deaths and the signs observed were most probably caused by hypoglycaemia. No dose-related macroscopic organ changes were found. In a 28 day toxicity study rats were given human or porcine insulin subcutaneously at dosages of 2, 20 or 200 U/kg/day. The criteria examined included mortality, body-weight change, food consumption and utilization, haematology, blood chemistry, urinalysis, opthalmoscopy, organ weights, gross- and histopathology. A few deaths occurred because of hypoglycaemia. In surviving rats from dosage groups 20 and 200 U/kg/day of either insulin preparation higher plasma glucose levels than in the control were observed 24 hours after dosing. Higher food intake and body-weight gains, lower plasma protein concentrations and higher urinary volumes with associated low specific gravity were observed in animals given either human or porcine insulin at 200 U/kg/day. No other adverse effects were registered, and no overt difference was found between the effect of human and porcine insulin.     

Oral Toxicity of Carbon Tetrachioride: Acute, Subacute, and Subchronic Studies in Rats

Oral Toxicity of Carbon Tetrachloide: Acute, Subacute, and SubchronicStudies in Rats. BRUCKNER, J. V., MACKENZIE, W. F., MURALIDHARA,S., LUTHRA, R., KYLE, G. M., AND ACOSTA, D. (1986). Fundam.Appl. Toxicol. 6, 16–34. This investigation was conductedto characterize the acute, subacute, and subchronic toxic potencyof ingested carbon tetrachloride (CCl₄) In the first acute andsubacute toxicity study, male Sprague-Dawley rats of 300–350g were gavaged with 0, 20, 40, or 80 mg CCl₄/kg once daily for5 consecutive days, rested for 2 days, and dosed once dailyfor 4 additional days. Rats of 200–250 g were gavagedwith 0, 20, 80, or 160 mg CCl₄/kg according to the same dosageregimen in the second acute and subacute study. In the firstand second studies one group of rats at each dosage level wassacrificed for clinical chemistry and histopathological evaluationat 24 hr, 4 days, and 11 days after initiation of dosing. Single20- and 40-mg/kg doses had no apparent toxic effect at 24 hr,although 80 mg/kg caused mild hepatic centrilobular vacuolizationand significant increases in some serum enzyme levels. In general,there was progressively severe hepatic injury at each dosagelevel over the 11-day period. CCl₄ was more hepatotoxic to the200–250-g rats than to the 300–350-g rats. In thesubchronic study, rats initially 200–250 g were gavaged5 times weekly for 12 weeks with 0, 1, 10, or 33 mg CCl4/kgBody weight and clinical chemistry indices were monitored duringthe 12 weeks of dosing and 2 weeks after cessation of dosing,A dose of 1 mg/kg had no apparent adverse effect; 10 mg/kg producedslight, but statistically significant increases in sorbitoldehydrogenase activity and mild hepatic centrilobular vacuolization;33 mg/kg caused marked hepatotoxicity. Serum enzyme levels remainedelevated during the 12-week dosing period, but returned towardnormal within 13 days of cessation of CCl₄ exposure. Microscopicexamination of livers of the 33-mg/kg rats revealed cirrhosis,characterized by bile duct proliferation, fibrosis, lobulardistortion, parenchymal regeneration, hyperplastic nodules,and single-cell necrosis. The fibrosis was not reversed withinthe 13-day recovery period.     

Acute, Subchronic, and Chronic Toxicity Studies with Felbamate, 2-Phenyl-1,3-propanediol Dicarbamate

Felbamate, 2-phenyl-1,3-propanediol dicarbamate, is a novelanticonvulsant that is effective against both chemically andelectrically induced seizures in laboratory animals. Acute,subchronic, and chronic studies were conducted in mice, rats,and dogs to establish a preclinical safety profile for thisdrug. Clinical signs following single intraperitoneal dosesincluded hypoactivity, tremors, decreased muscle tone, ataxia,prostration, and labored breathing. Death was observed afterintraperitoneal but not oral administration. A consistent drug-relatedeffect noted in al multiple-dose studies with this compoundwas decreased body weight and food consumption. The only otherconsistent change noted in multiple-dose studies with felbamatewas an increase in liver weight (relative and absolute) in therat and dog which was accompanied in some cases by increasesin serum enzyme levels. No histopathological changes were observedin the liver that could explain these elevated serum enzymelevels. Based on the results of these studies it was concludedthat long-term administration of felbamate in himan clinicaltrials was warranted.     

Capecitabine: Preclinical Pharmacology Studies

Capecitabine (N⁴-pentyloxycarbonyl-5-deoxy-5-fluorocytidine) is a novel fluoropyrimidine carbamate, which was designed to besequentially converted to 5-fluorouracil (5-FU) by three enzymes located inthe liver and in tumors; the final step is the conversion of5-deoxy-5-fluorouridine (5-DFUR) to 5-FU by thymidine phosphorylase (dThdPase) in tumors. In human cancer xenograft models, capecitabine given orally yielded substantially higher concentrations of 5-FU within tumors than in plasma ornormal tissue (muscle). The tumor 5-FU levels were also much higherthan those achieved by intravenous administration of 5-FU at equitoxic doses.Capecitabine and its intermediates are not cytotoxic by themselves,but become effective after their conversion to 5-FU. This tumor selectivedelivery of 5-FU ensured greater efficacy and a more favorable safety profilethan with other fluoropyrimidines. In 24 human cancer xenograft modelsstudied, capecitabine was more effective at a wider dose range andhad a broader spectrum of antitumor activity than 5-FU, UFT or itsintermediate metabolite 5-DFUR. The susceptibility of the xenografts tocapecitabine correlated with tumor dThdPase levels. Moreover, theconversion of 5-DFUR to 5-FU by dThdPase in tumor was insufficient in axenograft model refractory to capecitabine. In addition, the efficacy ofcapecitabine was enhanced by dThdPase up-regulators, such astaxanes and cyclophosphamide. The efficacy of capecitabine may, therefore, beoptimized by selecting the most appropriate patient population based on dThdPasestatus and/or by combining it with dThdPase up-regulators. Capecitabinehas additional characteristics not found with 5-FU, such as potentantimetastatic and anticachectic actions in mouse tumor models.With this profile, capecitabine may have substantial potential in cancer treatment.     

Nonclinical Toxicology Studies with Zidovudine: Reproductive Toxicity Studies in Rats and Rabbits

Zidovudine (ZDV) was evaluated for adverse effects on reproductionand fetal development in animal test species. Standard preclinicaltests for reproduction and fertility, developmental toxicity,and postnatal toxicity were conducted in CD (Sprague-Dawley)rats and a developmental toxicity study was conducted in NewZealand white rabbits. In an additional study, reproductiveoutcome was characterized in female rats given ZDV before, during,or after mating and drug levels in the plasma and milk of lactatingrats were determined. Finally, drug exposure data includingobserved peak plasma concentrations (C_max) and area under theconcentration-time curve (AUC) were evaluated for pregnant ratsand rabbits. In a reproduction/fertility study in CD rats, toxicityto the early rat embryo, manifested as an increase in earlyresorptions and a decrease in litter size, was noted followingdosage of the parental animals with 75 or 225 mg ZDV/kg bid.A dose of 25 mg/kg bid was a no-effect level in rats. At thetime of mating, male rats had been dosed for 85 days, and femaleshad been dosed for 26 days. To further evaluate the effectsof ZDV on reproduction, dosing of male rats was continued to149 days when they were mated a second time to virgin, untreatedfemales. All reproductive parameters were normal in the untreatedfemales from this second mating, indicating that the embryotoxiceffect of the drug was not likely mediated by a genotoxic orother effect in the male. A separate study in female CD ratsgiven 225 mg/kg bid for various periods pre- or postconceptionsuggests that the toxic effect of ZDV is primarily to the earlyrodent embryo. Early embryo death did not occur in rats or rabbitsin standard developmental (teratology) studies; however, pregnantNew Zealand white rabbits given 250 mg/kg bid during gestationDays 6–18 showed reduced weight gain, anemia, and an increasein late fetal deaths. No other evidence of developmental toxicitywas noted in either species, and ZDV was not teratogenic inrats or rabbits given up to 250 mg/kg bid during the periodof major organogenesis. At this dose, C_max, values in rats andrabbits were approximately 234 and 150 times higher, respectively,than the mean steady-state serum concentration in adults followingchronic oral administration of 250 mg every 4 hr. In both thereproduction/fertility study and a periand postnatal study inrats, liveborn offspring showed no adverse effects on survival,growth, or developmental measurements.     

Nonclinical Toxicology Studies with Zidovudine: Acute, Subacute, and Chronic Toxicity in Rodents, Dogs, and Monkeys

In single dose acute toxicity studies in CD-1 mice and CD rats,the median lethal dose (MLD) for zidovudlne (ZDV) was >750mg/kg after iv dosing and >3000 mg/kg after po administration(recommended human dose is 100 mg every 4 hr while awake). Becauseof the short half-life in rats (0.8 hr), dogs (1.0 hr), andmonkeys (0.8 hr), the daily dose of ZDV in most studies wasgiven in two equal portions approximately 6 hr apart. Intravenousadministration of ZDV was well tolerated in beagle dogs at doselevels up to 42.5 mg/kg bid for 2 weeks and in CD rats at doselevels up to 75 mg/kg bid for 4 weeks. In a 2-week dose range-findingstudy in beagle dogs, cytostatic effects were noted at po doselevels of 62.5 to 250 mg/kg bid in certain tissues with rapidcell replication rates. In contrast, in 3-to 12-month oral toxicitystudies in CD rats and cynomolgus monkeys, the principal toxicologicfinding was reversible macrocytic normochromic anemia whichoccurred at 225–250 mg/kg bid in rats and 17.5–150mg/kg bid in monkeys. In the 12-month rat study, RBC was decreasedat 25 and 75 mg/kg bid. In the 12-month monkey study WBC wasslightly decreased at 150 mg/kg bid.