Mericitabine and ritonavir-boosted danoprevir with or without ribavirin in treatment-naive HCV genotype 1 patients: INFORM-SVR study

BACKGROUND & AIMS

Safety and tolerability of peginterferon-based hepatitis C virus (HCV) infection therapy remains suboptimal, even when direct-acting antiviral agents are added. This study assessed the efficacy, safety and tolerability of mericitabine combined with ritonavir-boosted danoprevir (danoprevir/r) ± ribavirin for up to 24 weeks in treatment-naïve HCV genotype (G)1 infected patients.

METHODS

Patients received twice daily mericitabine (1000 mg) and danoprevir/r (100 mg/100 mg) plus either ribavirin (1000/1200 mg/day; Arm A) or placebo (Arm B) for 12 or 24 weeks. Patients with HCV RNA <43 IU/ml between Weeks 2 and 8 and HCV RNA <15 IU/ml at Week 10 were rerandomized (1:1) at Week 12 to discontinue/continue assigned regimens until Week 24. Because of unacceptable relapse rates in both 12-week arms and in ribavirin-free Arm B, treatment was extended to 24 weeks and patients in Arm B received peginterferon alfa-2a/ribavirin. The primary outcome was sustained virological response 24 weeks after end of treatment (SVR24).

RESULTS

In Arm A, the SVR24 rate in patients receiving 24 weeks of therapy was 37.9% (25/66); 63.6% (14/22) in G1b and 25.0% (11/44) in G1a patients. Virologic breakthrough and relapse were associated with danoprevir-resistant virus in most cases. The mericitabine-resistance mutation (NS5BS282T) was detected in two patients bearing dual resistant virus NS3 R155K/NS5B S282T and dual resistance mutation L159F/L320F in one patient. Treatment was safe and well tolerated.

CONCLUSIONS

Mericitabine, danoprevir/r plus ribavirin for 24 weeks were safe and well tolerated. However, SVR rates were poor, achieving rates of only 25.0% in G1a and 63.6% in G1b patients.

Evaluation of pharmacokinetics, user handling, and tolerability of peginterferon alfa-2a (40 kDa) delivered via a disposable autoinjector device

BACKGROUND

Peginterferon alfa-2a (40 kDa) is currently administered using a prefilled syringe. The peginterferon alfa-2a disposable autoinjector is a new safety-engineered device designed to facilitate injection and reduce the risk of needlestick injuries. The analysis of two open-label Phase I trials evaluated the pharmacokinetics, successful administration, and tolerability of peginterferon alfa-2a when using the autoinjector. The studies were performed to support the filing and registration of the autoinjector device.

METHODS

In trial 1, 50 healthy adult subjects received one 180 μg dose of peginterferon alfa-2a via the autoinjector. Serial blood samples were collected predose, up to 336 hours following drug administration, and at follow-up (28 ± 3 days post-dosing) for noncompartmental pharmacokinetic analysis. Trial 2 randomized 60 adult patients with chronic hepatitis C to 180 μg peginterferon alfa-2a once weekly by the autoinjector or prefilled syringe for 3 weeks followed by the alternative device (prefilled syringe or autoinjector, respectively) for 3 weeks. Patients also received ribavirin. Administration by the devices was evaluated under direct observation by a study staff member and by patient subjective assessment.

RESULTS

In trial 1, following a single dose of peginterferon alfa-2a, the maximum plasma concentration was 16.1 ± 5.3 ng/mL (mean ± standard deviation), and area under the concentration time curve (0-168 hours) was 1996 ± 613 ng · hour/mL, similar to that reported using a vial/syringe or prefilled syringe. In trial 2, few patients showed handling difficulties with either device. Generally, patients were observed to be more satisfied and confident, followed instructions better, and successfully initiated injection with the autoinjector versus the prefilled syringe. Patients reported the autoinjector to be more convenient and easier to use. No pain or discomfort was experienced using the autoinjector. The autoinjector safety profile was consistent with that known for peginterferon alfa-2a/ribavirin.

CONCLUSION

These results indicate that peginterferon alfa-2a can be successfully and safely delivered via the autoinjector and that the device is easy to handle.

The effects of enfuvirtide therapy on body composition and metabolic parameters over 48 weeks in the TORO body imaging substudy

OBJECTIVE

The aim of the study was to compare the metabolic and morphological effects of enfuvirtide plus an optimized background (OB) regimen vs. OB alone (control group) in treatment-experienced patients in the T-20 vs. Optimized Regimen Only (TORO) studies.

METHODS

Body composition and metabolic changes were investigated in patients over 48 weeks, based on fasting chemistries, body weight, and other anthropometric measurements. Dual-energy X-ray absorptiometry (DEXA) and computed tomography (CT) scans were performed in a patient subgroup (n=155) at baseline and at weeks 24 and 48.

RESULTS

At week 48, mean changes from baseline were similar between treatment groups for glucose, insulin, C-peptide, total cholesterol, low-density lipoprotein (LDL) cholesterol, very low density lipoprotein (VLDL) cholesterol, high-density lipoprotein (HDL) cholesterol and triglyceride levels. The enfuvirtide group experienced a significant increase in body weight [mean change from baseline +0.99 kg; 95% confidence interval (CI) +0.54, +1.44] and, in those who had body scans, there was a significant increase in truncal fat (by DEXA: median change +419.4 g; 95% CI+71.3, +767.5) and total fat [visceral adipose tissue (VAT)+subcutaneous adipose tissue (SAT) by single-slice abdominal CT scan: median change +25.5 cm(2) ; 95% CI+8.9, +42.0] over 48 weeks; significant increases in these parameters were not seen in the control group. There was no significant change in truncal:peripheral fat ratio in either the enfuvirtide or the control group.

CONCLUSION

The addition of enfuvirtide to an OB regimen does not appear to have unfavourable effects on fat distribution or metabolic parameters.

Efficacy and safety of pamapimod in patients with active rheumatoid arthritis receiving stable methotrexate therapy

OBJECTIVE

To determine the efficacy and safety of pamapimod in adult patients with active rheumatoid arthritis (RA) who had an inadequate clinical response to methotrexate (MTX).

METHODS

Patients receiving stable doses of MTX were randomised to one of six dose groups and received 12 weeks of double-blind pamapimod (up to 300 mg once daily) or matching placebo. The primary efficacy measure was the proportion of patients with > or =20% improvement in RA based on the American College of Rheumatology criteria (ACR20) at 12 weeks. Secondary measures were ACR50, Disease Activity Score (DAS)/European League Against Rheumatism (EULAR) responses and the individual ACR core set of parameters. Safety measures included adverse events (AEs), laboratory testing and immunology assessments.

RESULTS

On a background of MTX, the percentage of patients with an ACR20 response at week 12 in the pamapimod groups (31% to 43%) was not significantly different from placebo (34%). Secondary efficacy end points showed a similar pattern. AEs were typically mild and included infections, gastrointestinal disturbances, dizziness and rashes; AEs resulting in discontinuation of study drug were primarily attributed to infections.

CONCLUSION

In patients with active RA receiving stable doses of MTX, pamapimod showed non-significant improvement in efficacy outcomes compared to placebo.

Adherence to enfuvirtide and its impact on treatment efficacy

High adherence rates to antiretroviral (ARV) therapy are associated with increased durability of viral suppression and decreased rates of drug resistance. The requirement of twice-daily subcutaneous self-administration of enfuvirtide (ENF) has raised concerns about adherence. This study assesses adherence to ENF and an optimized background (OB) of ARVs and its impact on virological and immunological responses during the TORO trials. Eighty-eight percent of patients in the OB arm reported > or = 85% adherence versus 87% of patients in the ENF + OB arm. Higher overall adherence was associated with improved virological and immunological response in both treatment arms at 48 weeks. In patients with > or = 85% adherence, 33% of patients in the ENF + OB arm achieved HIV-1 RNA < 400 copies/ml, versus 13% in the OB arm (p < 0.0001). Similarly, patients with > or = 85% adherence in the ENF + OB arm achieved a mean increase in CD4 cell count of 104 cells/mm(3) compared with 58 cells/mm(3) for patients in the OB arm (p < 0.001). None of the demographic factors explored (age, gender, race) or baseline characteristics (CD4 count, viral load, or baseline sensitivity score) was significant in predicting adherence to ENF when analyzed by multiple regression. Importantly, a history of intravenous drug use (IDU) was not associated with a significant decrease in adherence (mean adherence for IDU 96% versus mean adherence for non-IDU 96%; p = 0.825). Adherence was high in patients receiving the self-injectable ARV enfuvirtide. In addition, the inclusion of ENF did not negatively impact adherence to the ARV regimen as a whole.

Safety and efficacy of enfuvirtide for 48 weeks as part of an optimized antiretroviral regimen in pediatric human immunodeficiency virus 1-infected patients

BACKGROUND

Enfuvirtide is the only entry inhibitor approved for the treatment of human immunodeficiency virus (HIV)-1 infection. It is approved for use in adults and dosage recommendations exist for children aged 6 years or older.

METHODS

T20-310 was a multicenter, open-label, nonrandomized, noncomparative study of the safety and efficacy of 2.0 mg/kg (maximum 90 mg) twice-daily subcutaneous enfuvirtide for 48 weeks in 52 treatment-experienced, HIV-1-infected pediatric patients (3-16 years) receiving optimized background therapy.

RESULTS

Enfuvirtide was generally well tolerated, and no new patterns of adverse events compared with adults were observed. Mild-to-moderate injection-site reactions were the most common adverse event. Of those participants on treatment for 48 weeks, the median change from baseline in HIV-1 RNA was -1.17 log10 copies/mL (n = 32), and there was a median CD4 change of +106 (n = 25) cells/mm3 and +4.7 CD4%. Seventeen (32.7%) patients achieved a viral load decrease of > or =1 log10 copies/mL and 11 (21.2%) achieved HIV-1 RNA <400 copies/mL. Virologic and immunologic treatment responses were substantially better for children (<11 years) than adolescents. Steady-state mean enfuvirtide C(trough) levels were stable during 24 weeks with no differences between children and adolescents.

CONCLUSIONS

Enfuvirtide is an effective treatment for HIV-1 infection in children and adolescents receiving optimized background therapy and has a favorable safety profile. Efficacy in adolescents was inferior; probably related to unique adherence challenges. The long-term safety and efficacy of enfuvirtide in pediatric patients is comparable to that observed in adults.

Population pharmacokinetics of enfuvirtide in HIV-1-infected pediatric patients over 48 weeks of treatment

The objective of this study was to characterize the population pharmacokinetics of enfuvirtide in HIV-1-infected children and adolescents. HIV-infected patients received combination antiretroviral therapy, including enfuvirtide 2.0 mg/kg subcutaneously, twice daily. Serial and trough blood samples were collected up to 48 weeks. NONMEM was used for population pharmacokinetic analysis. Enfuvirtide exposure was calculated from individual parameter estimates derived from the final model. A total of 218 samples from 43 patients were included in the analysis. Enfuvirtide plasma concentration-time data were described by a 1-compartment model with first-order absorption and elimination. The addition of each subject's actual body weight as a covariate affected CL/F but not V/F or K(a). The population CL/F, V/F, and K(a) for a 33-kg reference patient was 1.31 L/h, 2.31 L, and 0.105 h(-1), respectively. The final model was CL/F (L/h) = 1.31 . (body weight/33 [kg])(0.721). Age did not affect enfuvirtide exposure. These results confirm the appropriateness of body weight-based pediatric enfuvirtide dosing.

Safety of enfuvirtide in combination with an optimized background of antiretrovirals in treatment-experienced HIV-1-infected adults over 48 weeks

BACKGROUND

Antiretroviral tolerability is a critical factor contributing to treatment outcome. The T-20 Versus Optimized Background Regimen Only (TORO) studies assessed the safety and efficacy of enfuvirtide in treatment-experienced HIV-1-infected patients.

METHODS

A total of 997 patients were randomized at a 2:1 ratio to an optimized background antiretroviral regimen plus enfuvirtide (n = 663) or an optimized background regimen alone (control group; n = 334). Control patients could switch to enfuvirtide on virologic failure.

RESULTS

In total, 26.5% of patients randomized to enfuvirtide and 36.6% to the control group discontinued study treatment before week 48; the percentage of patients withdrawn for safety reasons (including adverse events [AEs], deaths, and laboratory abnormalities) was 14.0% in the enfuvirtide group and 11.6% in the control group. Injection site reactions (ISRs) occurred in 98% of enfuvirtide patients and led to treatment discontinuation in 4.4%. Treatment-related (defined as possibly, probably, or remotely) AE rates per 100 patient-years were lower with enfuvirtide (96.2) than in the control group (149.9); diarrhea, nausea, and fatigue, the most frequently reported AEs, were significantly less frequent with enfuvirtide than in the control group. Pneumonia was significantly more frequent in patients treated with enfuvirtide (6.7 vs. 0.6 events per 100 patient-years), although the incidence was within expected ranges for this population. Lymphadenopathy was also higher in enfuvirtide-treated patients (7.1 vs. 1.2 events per 100 patient-years) for control patients.

CONCLUSION

The addition of enfuvirtide to an optimized background regimen does not exacerbate AEs commonly associated with antiretrovirals. ISRs limited treatment in <5% of patients.

Aspects of the ecology of the Asian tapeworm, Bothriocephalus acheilognathi Yamaguti, 1934 in yellowfish in the Vaal Dam, South Africa

Seasonal surveys were conducted at the Vaal Dam between April 2000 and January 2001. Twenty smallmouth yellowfish (Labeobarbus aeneus) and 20 largemouth yellowfish (Labeobarbus kimberleyensis) were collected with the aid of gill nets. Surface water quality variables were included. The cestodes were identified as either Bothriocephalus acheilognathi Yamaguti, 1934 or "other cestode spp.". The majority (99.8 %) of the cestodes found in both yellowfish species were identified as B. acheilognathi (Asian tapeworm). The prevalence, mean intensity and abundance of B. acheilognathi in both yellowfish species were calculated. Ecological parameters including species specificity, seasonality, gender specificity and relationships between fish size and the Asian tapeworm prevalence were also included. In this study, B. acheilognathi preferred L. kimberleyensis over L. aeneus although a low intensity was observed in smallmouth yellowfish. Furthermore, the infection (in terms of prevalence, abundance and mean intensity) in largemouth yellowfish was markedly higher. Seasonal patterns observed in the Asian tapeworm's infection of smallmouth yellowfish are attributed to breeding and subsequent feeding patterns of this fish species with relatively high infections recorded in winter and spring. For L. kimberleyensis no explanation can be given regarding the seasonal patterns observed for the mean intensity and abundance of B. acheilognathi. The maximum and minimum mean intensity and abundance values in largemouth yellowfish were recorded in autumn and spring, respectively. In addition, the prevalence of B. acheilognathi was consistently high in all four seasons.

Pharmacokinetics of enfuvirtide in pediatric human immunodeficiency virus 1-infected patients receiving combination therapy

BACKGROUND

Enfuvirtide is the first of a new class of antiretroviral agents, the fusion inhibitors.

OBJECTIVES

The primary objective of this analysis was to evaluate the pharmacokinetics of 2.0 mg/kg enfuvirtide in human immunodeficiency virus 1 (HIV-1)-infected children and adolescents when administered in combination with at least 3 other antiretrovirals.

METHODS

Twenty-five HIV-1-infected pediatric patients (5-16 years of age) enrolled in an ongoing phase I/II study were included in this analysis. Patients received enfuvirtide 2.0 mg/kg sc twice daily (bid) for at least 7 days. Blood samples were collected on day 7, and plasma concentrations of enfuvirtide and its metabolite were measured by a validated liquid chromatography-tandem mass spectrometry method. Pharmacokinetics measures [Cmax, tmax, Ctrough, and area under the concentration time curve time 0 to 12 hours (AUC12 hours)] were calculated from plasma concentration-time data by standard noncompartmental methods.

RESULTS

There was no significant difference between children and adolescents for enfuvirtide Cmax (6.43 versus 5.88 microg/mL), Ctrough (2.87 versus 2.98 microg/mL) and AUC12 hours (56.1 versus 52.7 hours . microg/mL). Similarly no significant differences were found when the pharmacokinetic measures were compared based on sexual maturity stages. A post hoc regression analysis based on AUC12 hours showed that body weight-adjusted dosing of enfuvirtide provides drug exposure that is independent of age group, body weight and body surface area.

CONCLUSIONS

Body weight-adjusted dosing of enfuvirtide, at a dose of 2.0 mg/kg sc bid, in HIV-1-infected pediatric patients at least 5 years of age, provides drug exposure comparable with that previously observed in HIV-1-infected adults after 90 mg sc bid dosing. Drug exposure in children and adolescents is independent of age group, body weight, body surface area and sexual maturity stage.

Low-level resistance to the cephalosporin 3'-quinolone ester Ro 23-9424 in Escherichia coli

Four spontaneous, single-step mutants of Escherichia coli K-12 resistant to low levels of the cephalosporin 3'-quinolone ester Ro 23-9424 were isolated at a frequency of 10(-10) to 10(-11) mutants per CFU plated. The mutants were cross-resistant to both cephalosporin (cefotaxime) and quinolone (fleroxacin) components. Accordingly, they had altered porins and replicative DNA biosynthesis resistant to fleroxacin. There was no increase in beta-lactamase activity when tested with nitrocephin, and the penicillin-binding protein profiles were normal.

Porins and lipopolysaccharide of Escherichia coli ATCC 25922 and isogenic rough mutants

The lipopolysaccharide and porin profile of Escherichia coli ATCC 25922, a smooth strain commonly used in antibiotic susceptibility testing, and five isogenic rough mutants was examined. The lipopolysaccharide of the parent strain had the characteristic ladder pattern on polyacrylamide gels, while that of the mutants appeared similar to chemotypes Ra and Rc of Salmonella typhimurium with some changes in chemical composition. Of the porins, OmpC appeared markedly reduced in the parent strain while OmpF appeared markedly reduced in the mutants. In addition, a new outer-membrane protein of size intermediate to that of OmpC and OmpF was detected in all mutants. Neither parent nor mutants were susceptible to the LPS core-specific P1 phage or the porin-specific PA2 and K20 phages.

Mechanisms of action of cephalosporin 3'-quinolone esters, carbamates, and tertiary amines in Escherichia coli

Cephalosporin 3'-quinolone esters, carbamates, and tertiary amines are potent antibiotics whose antibacterial activities reflect the action of both the beta-lactam and the quinolone components. The biological properties of representative compounds from each class were compared in Escherichia coli. All compounds bound to the essential PBP 3, inhibited DNA gyrase, and caused filamentation in growing cells. To distinguish between cephalosporin- and quinolone-induced filaments, nucleoid segregation was also examined, as quinolones disrupt nucleoid segregation while the beta-lactams do not (N. H. Georgopapadakou and A. Bertasso, Antimicrob. Agents Chemother. 35:2645-2648, 1991). The cephalosporin quinolone esters Ro 23-9424 and Ro 24-6392, at concentrations causing filamentation in E. coli ATCC 25922, did not affect nucleoid segregation after 1 h of incubation (cephalosporin response) but did not affect it after 2 h (quinolone response), indicating the release of free quinolone. Accordingly, only the quinolone response was produced in a strain possessing TEM-3, an expanded-spectrum beta-lactamase. The cephalosporin carbamate Ro 24-4383 and the tertiary amine Ro 24-8138 produced a quinolone response in E. coli ATCC 25922, though they produced a cephalosporin response in a quinolone-resistant strain. Carbamate and tertiary amine linkages are chemically more stable than the ester linkage, and both cephalosporin 3'-quinolone carbamates and tertiary amines are more potent inhibitors of DNA gyrase than are the corresponding esters. The results suggest that, while intact cephalosporin 3'-quinolone esters act as cephalosporins, carbamates and amines may possess both cephalosporin and quinolone activity in the intact molecule.

Quinolone accumulation in Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus

The accumulation of quinolones by Escherichia coli JF568, Pseudomonas aeruginosa PAO1, and Staphylococcus aureus ATCC 29213 was measured by a modified fluorometric assay (J. S. Chapman and N. H. Georgopapadakou, Antimicrob. Agents Chemother. 33:27-29, 1989). The quinolones examined were fleroxacin, pefloxacin, norfloxacin, difloxacin, A56620, ciprofloxacin, ofloxacin, and Ro 09-1168. In all three organisms, uptake was complete in less than 5 min and was proportional to extracellular quinolone concentrations between 2 and 50 micrograms/ml, which is consistent with simple diffusion. Washing cells with quinolone-free buffer decreased accumulation by up to 70% in E. coli and P. aeruginosa but not in S. aureus. Similarly, incubation with the uncouplers 2,4-dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone increased accumulation up to fourfold in E. coli and P. aeruginosa, though not in S. aureus, suggesting endogenous, energy-dependent efflux. High quinolone hydrophobicity was generally associated with decreased accumulation in E. coli and P. aeruginosa (except in the case of pefloxacin) but was associated with increased accumulation in S. aureus (except in the case of difloxacin). Ciprofloxacin had the highest accumulation in E. coli and P. aeruginosa, while pefloxacin had the highest accumulation in S. aureus.

Effects of squalene epoxidase inhibitors on Candida albicans

The relationship between sterol biosynthesis inhibition, membrane integrity, and cell growth inhibition in Candida albicans was examined for five squalene epoxidase inhibitors. The compounds were the thiocarbamates tolnaftate and tolciclate and the allylamines naftifine, terbinafine, and SDZ 87-469. All compounds inhibited sterol biosynthesis, with the concentrations that caused a 50% decrease in the total sterol-to-squalene ratio ranging from less than or equal to 0.01 microM for terbinafine and SDZ 87-469 to 500 microM for tolnaftate. At 100 microM, the compounds also caused up to a 30% release of intracellular [14C]aminoisobutyric acid. With terbinafine and SD2 87-469, aminoisobutyric acid release further increased in cells grown at concentrations that inhibited ergosterol biosynthesis. It is suggested that inhibition of ergosterol synthesis may render the C. albicans membrane susceptible to further damage, including direct damage from squalene epoxidase inhibitors.

Effects of quinolones on nucleoid segregation in Escherichia coli

The effects of quinolone antibiotics on nucleoid segregation in growing Escherichia coli were examined by using fleroxacin (Ro 23-6240, AM 833) as a prototype compound. At levels that were close to its MIC and induced growth arrest and filamentation, fleroxacin caused large nucleoids to appear in midcell, suggesting inhibition of nucleoid segregation. With increasing fleroxacin concentrations, nucleoids became progressively smaller, suggesting inhibition of DNA replication. Removal of fleroxacin restored normal cell and nucleoid morphology in filaments with large nucleoids but not in filaments with small nucleoids. The results are consistent with inhibition of chromosome decatenation at low quinolone concentrations (bacteriostatic effect) and DNA supercoiling at high concentrations (bactericidal effect).

Escherichia coli resistant to cephalosporins and quinolones is still susceptible to the cephalosporin-quinolone ester Ro 23-9424

Ro 23-9424 is a broad-spectrum antibacterial agent consisting of a cephalosporin (desacetylcefotaxime) linked through an ester bond to a fluoroquinolone (fleroxacin). Its activity against mutants of Escherichia coli TE18 resistant to both antibacterial components was examined. E. coli TE18 overproduces the AmpC beta-lactamase and is resistant to several cephalosporins, including desacetylcefotaxime (MIC, 50 micrograms/ml), although it is still susceptible to Ro 23-9424 (MIC, 0.2 microgram/ml). Thirty-five spontaneous, two-step mutants of E. coli TE18 which were resistant to fleroxacin (MIC, 50 micrograms/ml) were isolated. In the mutants, replicative DNA biosynthesis (permeabilized cells) was resistant to fleroxacin, and some mutants had porin abnormalities. However, all remained susceptible to Ro 23-9424 (MIC, 0.5 microgram/ml). Examination of beta-lactamase activity in the parent strain revealed that it hydrolyzes desacetylcefotaxime more rapidly than it does Ro 23-9424. Thus, Ro 23-9424 may be less susceptible to the gram-negative, chromosomal beta-lactamases that hydrolyze several broad-spectrum cephalosporins and may be effective in cases in which neither of its two components is active.

Mode of action of the dual-action cephalosporin Ro 23-9424

Ro 23-9424 is a broad-spectrum antibacterial agent composed of a cephalosporin and a quinolone moiety. Its biological properties were compared with those of its two components and structurally related cephalosporins and quinolones. Like ceftriaxone and cefotaxime but unlike its decomposition product, desacetyl cefotaxime, Ro 23-9424 bound at less than or equal to 2 micrograms/ml to the essential penicillin-binding proteins 1b and 3 of Escherichia coli and 1, 2, and 3 of Staphylococcus aureus. In E. coli, Ro 23-9424 produced filaments exclusively and decreased cell growth; cefotaxime produced both filaments and lysis. Like its decomposition product fleroxacin but unlike quinolone esters, Ro 23-9424 also inhibited replicative DNA biosynthesis in E. coli. In an E. coli strain lacking OmpF, growth continued after addition of Ro 23-9424, decreased after addition of cefotaxime, and stopped immediately after addition of fleroxacin. The results, together with the chemical stability of Ro 23-9424 (half-life, approximately 3 h at pH 7.4 and 37 degrees C), suggest that in E. coli the compound acts initially as a cephalosporin with intrinsic activity comparable to that of cefotaxime but with poorer penetration. Subsequent to the decomposition of Ro 23-9424 to fleroxacin and desacetyl cefotaxime, quinolone activity appears. The in vitro antibacterial activity reflects both mechanisms of action.

Fleroxacin resistance in Escherichia coli

Spontaneous fleroxacin-resistant mutants of Escherichia coli K-12 were isolated at a frequency of 10(-10) to 10(-11) mutants per CFU plated. All mutants exhibited quinolone-resistant replicative DNA biosynthesis, and 4 of 11 mutants also had decreased amounts of OmpF or OmpC porin. None of the mutants had changes solely in porin proteins.

Effect of nutritional and enzymatic methionine deprivation upon human normal and malignant cells in tissue culture

Human embryonic lung fibroblasts (F-136-35-56) capable of growing in medium containing DL-homocysteine instead of L-methionine and human acute lymphoblastic leukemia cells (CCRF-HSB-2) with absolute methionine requirement exhibited dose-dependent growth inhibition when semipurified L-methionine-degrading enzyme (L-methioninase, EC 4.4.1.11) was added to the tissue cultures. When D-homocystine was added to the cultures together with L-methioninase (0.1 units/ml, which completely degraded the available L-methionine in tissue culture), the F-136-35-56 cells continued to grow whereas the CCRF-HSB-2 cells were completely inhibited. In mixed cultures of the two cell lines with added L-methioninase + D-homocystine or L-methioninase + L-homocysteine thiolactone, the normal fibroblasts grew and synthesized DNA vigorously, whereas the lymphocytic malignant cells lost their viability completely and died within 3 to 4 days.