P53+/- hemizygous knockout mouse: overview of available data.

The performance of the p53-/- transgenic (knockout) mouse model was evaluated through review of the data from 31 short-term carcinogenicity studies with 21 compounds tested as part of the International Life Sciences Institute's (ILSI) Alternatives to Carcinogenicity Testing (ACT) project, together with data from other studies which used comparable protocols. As expected based on the hypothesis for the model, a significant number (12/16 or 75%) of the genotoxic human and/or rodent carcinogens tested were positive and the positive control, p-cresidine, gave reproducible responses across laboratories (18/19 studies positive in bladder). An immunosuppressive human carcinogen, cyclosporin A, was positive for lymphomas but produced a similar response in wild type mice. Two hormones that are human tumorigens, diethylstilbestrol and 17beta-estradiol, gave positive and equivocal results, respectively, in the pituitary with p53-deficient mice showing a greater incidence of proliferative lesions than wild type. None of the 22 nongenotoxic rodent carcinogens that have been tested produced a positive response but 2 compounds in this category, chloroform and diethylhexylphthalate, were judged equivocal based on effects in liver and kidney respectively. Four genotoxic noncarcinogens and 6 nongenotoxic, noncarcinogens were also negative. In total (excluding compounds with equivocal results), 42 of 48 compounds or 88% gave results that were concordant with expectations. The technical lessons learned from the ILSI ACT-sponsored testing in the p53+/- model are discussed.

Enhanced apoptotic activity of a p53 variant in tumors resistant to wild-type p53 treatment.

TP53 is the most commonly altered tumor-suppressor gene in cancer and is currently being tested in Phase II/III gene replacement trials. Many tumors contain wild-type TP53 sequence with elevated MDM2 protein levels, targeting p53 for degradation. These tumors are more refractory to treatment with exogenous wild-type p53. Here we generate a recombinant adenovirus expressing a p53 variant, rAd-p53 (d 13-19), that is deleted for the amino acid sequence necessary for MDM2 binding (amino acids 13-19). We compared the apoptotic activity of rAd-p53 (d 13-19) with that of a recombinant adenovirus expressing wild-type p53 (rAd-p53) in cell lines that differ in endogenous p53 status. rAd-p53 (d 13-19) caused higher levels of apoptosis in p53 wild-type tumor lines compared with wild-type p53 treatment, as measured by annexin V-FITC staining. In p53-altered tumor lines, rAd-p53 (d 13-19) showed apoptotic activity similar to that seen with wild-type p53 treatment. In normal cells, no increase in cytopathicity was detected with rAd-p53 (d 13-19) compared with wild-type p53 treatment. This variant protein displayed synergy with chemotherapeutic agents to inhibit proliferation of ovarian and breast cell lines. The p53 variant showed greater antitumor activity in an established p53 wild-type tumor compared with treatment with wild-type p53. The p53 variant represents a means of expanding TP53 gene therapy to tumors that are resistant to p53 treatment due to the cellular responses to wild-type p53.

Population pharmacokinetic analysis of pegylated interferon alfa-2b and interferon alfa-2b in patients with chronic hepatitis C.

BACKGROUND: This study quantified pharmacokinetic changes in pegylated and nonpegylated interferon alfa-2b during 48 weeks of treatment and the influences of covariates on the basis of sparsely sampled serum concentrations and activity values. Possible relationships between pharmacokinetic and pharmacodynamic variables were investigated. METHODS: Patients with chronic hepatitis C were enrolled in a clinical trial that compared the efficacy of pegylated interferon alfa-2b with interferon alfa-2b. Single blood samples were obtained from each patient at weeks 4, 12, 24, 36, and 48. Three pharmacostatistical models were developed for 2 immunoassays and 1 bioassay. RESULTS: Apparent clearance values of pegylated interferon alfa-2b and interferon alfa-2b at the end of treatment declined 33.7% and 80.0%, respectively, from their week 4 values. Bioactivity increased 41% to 58% at week 48 for different treatment groups. Changes were greatest in the first weeks of administration and diminished during the subsequent months. Body weight had a modest positive effect on clearance values and activity. Within each dose level, no significant associations were observed between pharmacokinetic variables and any pharmacodynamic variables (hepatitis C virus--RNA responses or changes in neutrophils and platelets). CONCLUSIONS: This analysis confirms earlier observations of progressive pharmacokinetic changes in the patients with hepatitis C during 48 weeks of treatment. The absence of a relationship between toxicity or efficacy variables and interferon concentration or activity (within a dose level) suggests that clinical management of patients (eg, for efficacy or to manage toxicity) should be based on clinically derived dosing guidelines rather than on serum concentration or activity criteria.

The farnesyl protein transferase inhibitor SCH66336 synergizes with taxanes in vitro and enhances their antitumor activity in vivo.

PURPOSE: SCH66336 is an orally active, farnesyl protein transferase inhibitor. SCH66336 inhibits ras farnesylation in tumor cells and suppresses tumor growth in human xenograft and transgenic mouse cancer models in vivo. The taxanes, paclitaxel (Taxol) and docetaxel (Taxotere) block cell mitosis by enhancing polymerization of tubulin monomers into stabilized microtubule bundles, resulting in apoptosis. We hypothesized that anticancer combination therapy with SCH66336 and taxanes would be more efficacious than single drug therapy. METHODS: We tested the efficacy of SCH66336 and taxanes when used in combination against tumor cell proliferation in vitro, against NCI-H460 human lung tumor xenografts in nude mice, and against mammary tumors in wap-ras transgenic mice. RESULTS: SCH66336 synergized with paclitaxel in 10 out of 11 tumor cells lines originating from breast, colon, lung, ovary, prostate, and pancreas. SCH66336 also synergized with docetaxel in four out of five cell lines tested. In the NCI-H460 lung cancer xenograft model, oral SCH66336 (20 mg/kg twice daily for 14 days) and intraperitoneal paclitaxel (5 mg/kg once daily for 4 days) caused a tumor growth inhibition of 56% by day 7 and 65% by day 14 compared to paclitaxel alone. Male transgenic mice of the wap-ras/F substrain [FVB/N-TgN(WapHRAS)69LlnYSJL] spontaneously develop mammary tumors at 6 9 weeks of age which have been previously shown to be resistant to paclitaxel. Paclitaxel resistance was confirmed in the present study, while SCH66336 inhibited growth of these tumors. Most importantly, SCH66336 was able to sensitize wap-ras/F mammary tumors to paclitaxel chemotherapy. CONCLUSION: Clinical investigation of combination therapy using SCH66336 and taxanes in cancer patients is warranted. Further, SCH66336 may be useful for sensitizing paclitaxel-resistant tumors to taxane treatment.

Population pharmacokinetic and pharmacodynamic analysis of ribavirin in patients with chronic hepatitis C.

The population pharmacokinetics of ribavirin were assessed in patients with chronic hepatitis C virus (HCV) infection treated with interferon alpha-2b and ribavirin in four clinical efficacy studies. The authors collected 3450 ribavirin serum concentrations from 1105 patients at different treatment weeks for inclusion in the analysis. Population factors included gender, age, body weight, serum creatinine, creatinine clearance, and previous interferon treatment history. Ribavirin apparent clearance (CL/F) was calculated from individual patients' daily doses divided by concentration values, and the influence of these factors was assessed by multiple regression. Body weight, gender, age, and serum creatinine affected CL/F. Population mean CL/F estimates were 17.9 L/h (female) and 21.5 L/h (male) assuming an age of 40 years and body weight of 70 kg. Ribavirin apparent clearance increased as a function of body weight and decreased at ages greater than 40 years. Serum creatinine had little influence on CL/F, which may reflect the relatively normal renal function of these patients. Total CL/F variability was approximately 28%. The four covariates in the model explained 27% of this variability, and were thus of limited clinical significance because of the substantial residual variability not accounted for by the model. In assessing the relationship between pharmacokinetics and pharmacodynamics, the week 4 hemoglobin nadir value was negatively associated with week 4 ribavirin concentrations. The percentage of reduction from baseline was positively associated with ribavirin concentrations, although these data were highly variable. Loss of HCV-RNA at 24 weeks after completion of treatment was considered a response to interferon and ribavirin treatment in a logistic regression analysis of clinical and pharmacokinetic variables and treatment response in the interferon-naive patients. Hepatitis C virus genotype, pretreatment HCV-RNA titer, duration of treatment period, week 4 ribavirin concentration, and patient age affected the likelihood of response. Higher ribavirin concentrations at treatment week 4 were associated with a higher response rate. Variables that have predictive value for treatment outcome in patients treated with interferon and ribavirin are similar to those previously reported for interferon monotherapy.

Derivation and initial characterization of a mouse mammary tumor cell line carrying the polyomavirus middle T antigen: utility in the development of novel cancer therapeutics.

Here we describe the derivation of novel cell lines from spontaneous mammary tumors that arose in mouse mammary tumor virus-polyomavirus (MMTV-PyV) Middle T (MidT) transgenic mice. Clonal cell lines from four mixed cell populations were tested for adenovirus transducibility and sensitivity to p53 tumor suppressor gene therapy mediated by SCH58500, a replication-deficient adenovirus that expresses human p53. The MidT2-1 cell line was selected for further characterization in vitro and in vivo. This cell line carried the PyV MidT antigen, had wild-type p53 DNA, and was sensitive to suppression of proliferation by MMAC/PTEN tumor suppressor gene therapy. MidT2-1 cells gave rise to highly aggressive tumors in syngeneic FVB mice in both the mammary fat pad and the peritoneal cavity. The histopathology of MidT2-1 tumors closely resembled the histopathology of the primary transgenic tumors. Tumor growth in vivo was inhibited by p53 gene therapy or by MMAC gene therapy. In addition, combination therapy with a number of anticancer agents had synergistic or additive efficacy in vitro. In particular, MMAC gene therapy synergized with SCH58500 or paclitaxel. In the i.p. MidT2-1 tumor model p53 gene therapy enhanced the survival benefits of paclitaxel/cisplatin chemotherapy. Combination therapy has become a mainstay in cancer treatment. In this report, we use a novel transgenic mouse tumor cell line to suggest new combinations that might be explored in clinical cancer care. These include gene therapy using the tumor suppressors MMAC and p53, chemotherapy using farnesyl transferase inhibitors, the microtubule stabilizing taxanes, and the DNA synthesis disruptors gemcitabine and cisplatin. The precise biological mechanisms by which these therapies induce their antitumor effects are not fully elucidated. However, the work presented here suggests that many of these therapeutic approaches have synergistic antitumor activity when used in combination.

Population pharmacokinetics of temozolomide in cancer patients.

PURPOSE: To evaluate covariate effects on the pharmacokinetics of temozolomide in cancer patients, and to explore the dose-pharmacokinetics-toxicity relationship of temozolomide. METHODS: Non-linear mixed-effects modeling approach was used to analyze the data from 445 patients enrolled in eleven Phase I and Phase II clinical trials. All patients in the phase I trials had advanced cancer. Patients in the phase II trials had anaplastic astrocytoma (AA), glioblastoma multiforme (GBM) or malignant melanoma (MM). A sparse sampling scheme was prospectively developed using Phase I data and was successfully implemented in Phase II trials. Population factors included age, gender, height (HT), weight (WT), body surface area (BSA), serum creatinine (Sr.Cr.), estimated creatinine clearance, serum chemistry data as indices of hepatic function and disease, smoking status, and selected concomitant medications. Descriptive statistics were used to summarize the toxicity and temozolomide dose and exposure relationship. RESULTS: The pharmacokinetics of temozolomide follows a one-compartment model with first order absorption and elimination. Temozolomide clearance (CL) increased with BSA for both genders. The population mean clearance for GBM or AA patients was 11.2 L/hr for male with BSA equal to 2.0 m2, and 8.8 L/hr for female with BSA equal to 1.7 m2. The mean clearance for MM patients was slightly higher. The inter-subject variability in clearance was 15%, and the residual variability was 26%. Other factors investigated in this analysis had little effect on clearance. The overall incidence of neutropenia and thrombocytopenia were 5-8%. Temozolomide dose and AUC did not predict nadir neutrophil and platelet counts due to large variability in counts. CONCLUSIONS: The current dose regimen is administered according to BSA which is the most important factor influencing temozolomide clearance. No further dose adjustment is required.

Combination therapy with the farnesyl protein transferase inhibitor SCH66336 and SCH58500 (p53 adenovirus) in preclinical cancer models.

SCH66336 is a p.o.-active, farnesyl protein transferase inhibitor. SCH66336 inhibits farnesylation of RAS and other proteins in tumor cells and suppresses tumor growth in human xenograft and transgenic mouse cancer models in vivo. SCH58500 is a replication-deficient, recombinant adenovirus, which expresses the human p53 tumor suppressor. In preclinical models, SCH58500 has therapeutic efficacy against a wide range of human tumor types containing nonfunctional p53 and enhanced activity in combination with many chemotherapeutic drugs. Here we report that combination therapy with SCH66336 and SCH58500 has synergistic or additive antiproliferative effects on a panel of tumor cells lines in vitro. The efficacy of the three-drug combination of SCH66336, SCH58500, and paclitaxel was also examined in vitro. Each two-drug interaction displayed such marked synergy, the addition of a third drug to the statistical model could only yield additivity. Greater combined efficacy for SCH66336 and SCH58500 was also observed in vivo in the DU-145 human prostate and wap-ras/F transgenic mouse cancer models.

Adenovirus-mediated p53 gene therapy and paclitaxel have synergistic efficacy in models of human head and neck, ovarian, prostate, and breast cancer.

Synergy (or antagonism) between two chemical agents is an in vitro empirical phenomenon, in which the observed effect of the combination is more (or less) than what would be predicted from the effects of each agent working alone. Although mathematical synergy is not directly provable in the clinical setting, it does predict a favorable outcome when the two therapeutics are combined in vivo and strongly suggests the presence of in vivo synergy. In contrast, overt antagonism warns of future problems. Sophisticated three-dimensional statistical modeling was used to evaluate the presence of synergistic, additive, or antagonistic efficacy between adenovirus (Ad)-mediated p53 gene therapy (p53 Ad) and paclitaxel (Taxol) in a panel of human tumor cell lines. Cells were either pretreated with paclitaxel 24 h before p53 Ad or treated with both agents simultaneously. Cell proliferation was measured 3 days later. Paclitaxel had synergistic or additive efficacy with p53 gene therapy. In no case was the interaction antagonistic. Cell cycle analysis demonstrated that p53 Ad arrested cells in G0/G1 prior to apoptotic cell death, whereas paclitaxel arrested cells in G2-M prior to apoptotic cell death. When combined, the relative concentration of each agent determined the dominant cellular response. These results are consistent with the previously reported cell cycle effects of p53 or paclitaxel, respectively; however, these data fail to explain the observed drug synergy. We found that low concentrations of paclitaxel (1-14 nM) increased the number of cells transduced by recombinant Ad 3-35% in a dose-dependent manner, which is one possible mechanism for the observed synergy. Of particular note, the concentrations of paclitaxel responsible for increased Ad transduction were lower than the concentrations required for microtubule condensation. The efficacy of combination therapy was also evaluated in vivo. In the p53null SK-OV-3 xenograft model of ovarian cancer, a dosing schedule of p53 Ad that, by itself, had a relatively minimal effect on tumor burden (16%) caused a much greater decrease in tumor burden (55%) when combined with paclitaxel. Greater combined efficacy was also observed in the p53mut DU-145 prostate, p53mut MDA-MB-468 breast, and p53mut MDA-MB-231 breast cancer xenograft models in vivo. In summary, p53 Ad for cancer shows enhanced efficacy when combined with paclitaxel. This combination is recommended for clinical cancer trials.

Analysis of 24-hour blood pressure data.

Blood pressure is not constant over the course of a 24-h period, but exhibits a predictable and characteristic rise and decline during the day. Although the general shape of this pattern is similar from patient to patient, the knowledge of an individual's blood pressure at one or two points on this curve is of no predictive value in estimating the remainder of the curve. Since critical events are associated with both the maximum and minimum blood pressures that an individual experiences, a characterization of this curve can be very important. The development of antihypertensive agents historically presumed that the reduction in blood pressure associated with therapy would be, if not constant, at least adequate throughout the entire period. However, with the advent of less frequent dosing, the importance of assuring that blood pressure was adequately controlled over the 24-h period became important. This created interest in two basic types of comparisons. One is the comparison of dosing regimens, e.g., comparing a once-a-day regimen with a twice-a-day regimen. The second is a comparison of two therapies with the same regimen; for example, two doses designed to be administered twice a day. The shape of the curves in the first case is inherently different, whereas they have a similar configuration in the second. Many techniques have been attempted, but few recommended for these types of comparisons. Examples include time series, the use of composite indices, univariate statistical procedures, multivariate procedures, and mathematical characterization of the curves with subsequent comparison of model parameters. This presentation will provide a background and overview of several of these methodologies and their relative utility.

Characterization of AUCs from sparsely sampled populations in toxicology studies.

PURPOSE: The objective of this work was to develop and validate blood sampling schemes for accurate AUC determination from a few samples (sparse sampling). This will enable AUC determination directly in toxicology studies, without the need to utilize a large number of animals. METHODS: Sparse sampling schemes were developed using plasma concentration-time (Cp-t) data in rats from toxicokinetic (TK) studies with the antiepileptic felbamate (F) and the antihistamine loratadine (L); Cp-t data at 13-16 time-points (N = 4 or 5 rats/time-point) were available for F, L and its active circulating metabolite descarboethoxyloratadine (DCL). AUCs were determined using the full profile and from 5 investigator designated time-points termed "critical" time-points. Using the bootstrap (re-sampling) technique, 1000 AUCs were computed by sampling (N = 2 rats/point, with replacement) from the 4 or 5 rats at each "critical" point. The data were subsequently modeled using PCNONLIN, and the parameters (ka, ke, and Vd) were perturbed by different degrees to simulate pharmacokinetic (PK) changes that may occur during a toxicology study due to enzyme induction/inhibition, etc. Finally Monte Carlo simulations were performed with random noise (10 to 40%) applied to Cp-t and/or PK parameters to examine its impact on AUCs from sparse sampling. RESULTS: The 5 time-points with 2 rats/point accurately and precisely estimated the AUC for F, L and DCL; the deviation from the full profile was approximately 10%, with a precision (%CV) of approximately 15%. Further, altered kinetics and random noise had minimal impact on AUCs from sparse sampling. CONCLUSIONS: Sparse sampling can accurately estimate AUCs and can be implemented in rodent toxicology studies to significantly reduce the number of animals for TK evaluations. The same principle is applicable to sparse sampling designs in other species used in safety assessments.

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 zidovudine (ZDV) was > 750 mg/kg after iv dosing and > 3000 mg/kg after po administration (recommended human dose is 100 mg every 4 hr while awake). Because of the short half-life in rats (0.8 hr), dogs (1.0 hr), and monkeys (0.8 hr), the daily dose of ZDV in most studies was given in two equal portions approximately 6 hr apart. Intravenous administration of ZDV was well tolerated in beagle dogs at dose levels up to 42.5 mg/kg bid for 2 weeks and in CD rats at dose levels up to 75 mg/kg bid for 4 weeks. In a 2-week dose range-finding study in beagle dogs, cytostatic effects were noted at po dose levels of 62.5 to 250 mg/kg bid in certain tissues with rapid cell replication rates. In contrast, in 3- to 12-month oral toxicity studies in CD rats and cynomolgus monkeys, the principal toxicologic finding was reversible macrocytic normochromic anemia which occurred at 225-250 mg/kg bid in rats and 17.5-150 mg/kg bid in monkeys. In the 12-month rat study, RBC was decreased at 25 and 75 mg/kg bid. In the 12-month monkey study WBC was slightly decreased at 150 mg/kg bid.

Nonclinical toxicology studies with zidovudine: genetic toxicity tests and carcinogenicity bioassays in mice and rats.

Zidovudine (ZDV), an antiviral drug active in the treatment of acquired immunodeficiency syndrome (recommended human dose, 100 mg every 4 hr while awake), was evaluated for mutagenic and carcinogenic potential in a battery of short-term in vitro and in vivo assays and in lifetime studies in mice and rats. In L5178Y mouse lymphoma cells (tk+/- locus), a weak positive result was obtained only at the highest concentrations tested (4000 to 5000 micrograms/ml) in the absence of metabolic activation. In the presence of metabolic activation, the drug was weakly mutagenic at concentrations of 1000 micrograms/ml and higher. Following 24 hr treatment in the absence of metabolic activation, ZDV was moderately mutagenic at concentrations up to 600 micrograms/ml; dose-related structural chromosomal alterations were seen at concentrations of 3 micrograms/ml and higher in cultured human lymphocytes. Such effects were not noted at the two lowest concentrations tested, 0.3 and 1 microgram/ml, and BALB/c-3T3 cells were transformed at concentrations of 0.5 microgram/ml and higher. No effects were seen in the Ames Salmonella plate incorporation and preincubation modification assays (possibly due to bacteriocidal activity of ZDV at low concentrations) at concentrations ranging from 0.01 to 10 micrograms/plate or in a single-dose intravenous bone marrow cytogenetic assay in CD rats. In multidose micronucleus studies, increases in micronucleated erythrocytes were seen in mice at doses of 100 to 1000 mg/kg/day. Similar results were seen 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 40 mg/kg/day and 80, 220, and 300 mg/kg/day were given to CD-1 mice and CD rats, respectively, for up to 22 months in mice and 24 months in rats. ZDV caused a macrocytic, normochromic anemia in both species. No evidence of carcinogenicity was seen in male mice or rats. In female mice, five malignant and two benign vaginal epithelial neoplasms occurred in animals given 40 mg/kg/day. A single benign vaginal epithelial tumor was seen in a mouse given 30 mg/kg/day. In rats, two malignant vaginal epithelial neoplasms were seen in animals given 300 mg/kg/day. In a 7-day study in mice, ZDV was shown to be devoid of estrogenic activity. In an oral pharmacokinetics study, the AUC was 17 and 140 micrograms/ml.hr in female mice and rats given 40 or 300 mg/kg of ZDV, respectively. In contrast, the average steady-state concentration in humans at the recommended daily dose is 0.62 microgram/ml. Twenty-four hour urine concentrations were 1245 and 4417 micrograms/ml in female mice and rats given 40 or 300 mg/kg of ZDV, respectively. These values were approximately 26- and 136-fold higher than the human urine concentration at the recommended daily dose. In a one- to three-day study with intravenously administered sodium fluoroscein in rats and mice, retrograde flow of urine into the vagina was demonstrated. In a subsequent lifetime carcinogenicity bioassay in mice in which ZDV was given intravaginally at concentrations of 5 or 20 mg ZDV/ml in saline, 13 vaginal squamous cell carcinomas were seen at the highest concentration tested. It was concluded that the vaginal tumors seen in the oral carcinogenicity studies were the result of chronic local exposure of the vaginal epithelium to high urine concentrations of ZDV.

Accuracy and precision for analytical results.

Unknown amounts of drug from plasma samples are determined from inverse prediction of a calibration line. A statistician's criteria for accuracy and three methods for computing precision are given.

Membrane permeation characteristics of 5'-modified thymidine analogs.

The membrane permeation characteristics of 5'-deoxythymidine (5'-ddThd) and 5'-azido-5'-deoxythymidine (5'-N3-5'-ddThd) were investigated in human erythrocytes, with an inhibitor-stop assay, at 20 degrees. Uptake of both nucleoside analogs occurred without metabolism, was nonconcentrative, and was partially inhibited by nucleosides or inhibitors of nucleoside transport at micromolar permeant concentrations. At higher permeant concentrations (greater than 1.0 mM), the influx rate of each analog was linearly dependent on concentration and insensitive to inhibition by nucleosides, inhibitors of nucleoside transport, and nucleobases. Kinetic analyses using nonlinear regression revealed that a saturable component of 5'-ddThd influx (Km = 200 microM) was competitively inhibited by thymidine (dThd) (Ki = 86 microM) or 5-iodo-2'-deoxyuridine (Ki = 84 microM). Similarly, a saturable component of 5'-N3-5'-ddThd influx (Km = 220 microM) was competitively inhibited by 2-chloroadenosine (Ki = 18 microM). The Ki values for these nucleoside inhibitors were similar to their reported Km values as permeants of the nucleoside transporter. Both 5'-ddThd and 5'-N3-5'-ddThd competitively inhibited the influx of dThd (Km = 60 microM), with similar Ki values (150 and 200 microM, respectively). We conclude that these two 5'-modified dThd analogs enter human erythrocytes both by nonfacilitated diffusion and by the nucleoside transporter. The absence of the 5'-hydroxyl group of dThd (5'-ddThd) resulted in a large increase in the octanol/buffer partition coefficient, in an ability to permeate human erythrocytes by nonfacilitated diffusion, and in a 3-fold diminished binding to the nucleoside transporter. The 5'-azido group (5'-N3-5'-ddThd) resulted in an additional 1.4-fold increase in the octanol/buffer partition coefficient and in a 2-fold increase in the rate of nonfacilitated diffusion.

Preclinical toxicology studies with acyclovir: carcinogenicity bioassays and chronic toxicity tests.

Acyclovir (ACV), a nucleoside analog that is a new herpes-specific antiviral drug, was given by gavage at 50, 150 and 450 mg/kg/day to Sprague Dawley rats and Swiss mice for most of their lifetime to assess chronic toxicity and carcinogenicity. Treatment with ACV did not shorten the lifespan of either rats or mice. In fact, female mice given 150 and 450 mg/kg/day had significantly longer mean durations of survival than control female mice when analyzed by the life table technique. There were no signs of toxicosis produced by chronic exposure to ACV in either the rats or mice, and there was no drug-related increase in neoplasms in either species. Four groups of Beagle dogs were initially given daily oral doses of 15, 45 or 150 mg/kg ACV in a 1 year chronic 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 gastrointestinal toxicosis. These dose levels were then decreased to 60 and 30 mg/kg/day for the rest of the one year test period. With the exception of occasional and inconsistent emesis and diarrhea, the 60 mg/kg/day dose level was well tolerated. Some mid and high dose dogs had sore paws due to erosion of footpads and cracking, splitting and loosening of the nails first becoming evident during the 13th week of the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Statistical issues in the design and analysis of carcinogenicity bioassays.

A general outline of the statistical issues in the design and analysis of carcinogenicity bioassays is given in this paper. Design issues, such as assignment of animals to treatment groups, dual control groups, duration of study, and the number of animals per group are discussed. Information needed by the biostatistician are listed to facilitate the recording of data by the pathologist. Issues in the analysis of tumor incidence data are given. Use of historical control data is encouraged and discussed.

Trimethoprim and sulfadiazine: experimental infection of Beagles.

The purpose in the present study was to determine whether the commercial combination of trimethoprim (TMP) and sulfadiazine (SDZ) tribrissen (TRI) was more effective than either of the components for treating experimentally induced infection of Streptococcus zooepidemicus. Two dose levels of each were given subcutaneously for treatment, and their effectiveness was compared with that of sulfadimethoxine (SDM) in terms of (i) clinical manifestations, (ii) hematologic changes, (iii) blood culture examinations, and (iv) tissue culture examinations. According to these four measurements, the combination TMP/SDZ was more effective than either of the components. This effect was observed at the two dosages of TRI (30 and 15 mg/kg). The higher dosage, however, was more effective as demonstrated by three of the measurements. Alone, TMP and SDZ were not effective, but SDM treatment was effective in this model.