Abstract P5-04-04: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Das GM, Kulkarni S, Oturkar C, Edge SB, Wilton JH, Wang J, Swetzig WM, Adjei AA, Bies R, Hutson AD, Morrison CD, Kaipparettu BA, Groman A, Kumar S, Capuccino H. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-04-04.

Inhibition of dihydrotestosterone synthesis in prostate cancer by combined frontdoor and backdoor pathway blockade

Androgen deprivation therapy (ADT) is palliative and prostate cancer (CaP) recurs as lethal castration-recurrent/resistant CaP (CRPC). One mechanism that provides CaP resistance to ADT is primary backdoor androgen metabolism, which uses up to four 3α-oxidoreductases to convert 5α-androstane-3α,17β-diol (DIOL) to dihydrotestosterone (DHT). The goal was to determine whether inhibition of 3α-oxidoreductase activity decreased conversion of DIOL to DHT. Protein sequence analysis showed that the four 3α-oxidoreductases have identical catalytic amino acid residues. Mass spectrometry data showed combined treatment using catalytically inactive 3α-oxidoreductase mutants and the 5α-reductase inhibitor, dutasteride, decreased DHT levels in CaP cells better than dutasteride alone. Combined blockade of frontdoor and backdoor pathways of DHT synthesis provides a therapeutic strategy to inhibit CRPC development and growth.

Serum-free complete medium, an alternative medium to mimic androgen deprivation in human prostate cancer cell line models

BACKGROUND

Almost all men who present with advanced prostate cancer (CaP) and some men who fail therapy for clinically localized CaP are treated with androgen deprivation therapy (ADT). CaP cell lines are used to identify and characterize new agents for ADT or investigate mechanisms of ADT resistance. CaP cell lines are maintained in culture medium that contains fetal bovine serum, which contains testosterone (T). Androgen deprivation experiments are performed using media supplemented with androgen-free serum, such as charcoal stripped fetal bovine serum (CS-FBS). However, CS-FBS composition varies from batch-to-batch and variations may impact experimental reproducibility. Serum free media (SFM) may provide a better defined alternative to media supplemented with CS-FBS (CSM).

METHODS

Cell growth of six human CaP cell lines was assessed using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Androgen levels were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

MTT assays showed 5 of 6 CaP cell lines grew after 6 days of culture in androgen- deprived SFM or CSM. LNCaP and VCaP growth was stimulated when cells were cultured in SFM or CSM supplemented with T. LNCaP, C4-2, LAPC-4, and VCaP cell growth was inhibited when cultured in SFM or CSM with T and bicalutamide. LC-MS/MS data showed LAPC-4 cells produced similar DHT levels when cultured in T-supplemented SFM or CSM. Dutasteride impaired T to DHT metabolism in LAPC-4.

CONCLUSIONS

Media composition contributed to growth differences observed between CaP cells cultured in SFM or CSM. However, the differences in media composition did not impair CaP cell response to T-stimulated growth, bicalutamide growth inhibition, metabolism of T, or dutasteride efficiency. SFM can be used as a better defined alternative to CSM for androgen deprivation experiments.

Dietary folate levels alter the kinetics and molecular mechanism of prostate cancer recurrence in the CWR22 model

Folate impacts the genome and epigenome by feeding into one-carbon metabolism to produce critical metabolites, deoxythymidine monophosphate and s-adenosylmethionine. The impact of folate exposure and intervention timing on cancer progression remains controversial. Due to polyamine metabolism's extraordinary biosynthetic flux in prostate cancer (CaP) we demonstrated androgen stimulated CaP is susceptible to dietary folate deficiency. We hypothesized dietary folate levels may also affect castration recurrent CaP. We used the CWR22 human xenograft model which recurs following androgen withdrawal. Engrafted mice were fed a folate depleted or supplemented diet beginning at androgen withdrawal, or prior to xenograft implantation. Both folate depletion and supplementation at the time of withdrawal significantly decreased recurrence incidence. Folate supplementation prior to xenograft implantation increased time to recurrence, suggesting a protective role. By contrast, folate depleted recurrent tumors exhibited transcriptional adaptive responses that maintained high polyamine levels at the expense of increased DNA damage and DNA methylation alterations. Mining of publically available data demonstrated folate related pathways are exceptionally dysregulated in human CaP, which correlated with decreased time to biochemical recurrence. These findings highlight the potential for novel therapeutic interventions that target these metabolic pathways in CaP and provide a rationale to apply such strategies alongside androgen withdrawal.

Characterization of Prostate Cancer in a Functional Eunuch

BACKGROUND

Eunuchs rarely, if ever, develop prostate cancer (CaP). This article reports on a 62-year-old functional eunuch from prepubertal mumps orchitis who developed clinically localized CaP.

METHODS

Serum and CaP and benign prostate tissue androgen levels were measured using a validated liquid chromatography-tandem mass spectrometry assay. The assay measures testosterone; dihydrotestosterone (DHT); the adrenal androgens, androstenedione and dehydroepiandrosterone; and the androgen metabolites, androsterone and androstanedione. Gene and protein expression levels of androgen metabolism enzymes, and androgen receptor and androgen-regulated genes were measured using quantitative reverse-transcription polymerase chain reaction and immunohistochemistry, respectively.

RESULTS

Intracrine androgen metabolism produced tissue DHT when serum and tissue testosterone levels were castrate and undetectable, respectively. Androgen receptor, androgen-regulated, and androgen metabolism enzyme genes were expressed but at lower levels in CaP than benign tissues.

CONCLUSIONS

DHT was synthesized using the primary backdoor androgen metabolism pathway and not using androstenedione or dehydroepiandrosterone via the frontdoor or secondary backdoor pathways.

Sequential use of the androgen synthesis inhibitors ketoconazole and abiraterone acetate in castration-resistant prostate cancer and the predictive value of circulating androgens

PURPOSE

Patients previously treated with ketoconazole were excluded from phase III trials of abiraterone acetate due to potential overlapping mechanism of action. The purpose of this study was to determine the clinical utility of abiraterone and its impact on circulating androgens following ketoconazole.

EXPERIMENTAL DESIGN

Chemotherapy-naïve patients with progressive metastatic castration-resistant prostate cancer (mCRPC) and prior ketoconazole therapy ≥28 days received abiraterone acetate 1,000 mg daily and prednisone 5 mg twice daily. The primary endpoint was the proportion of patients with PSA response, defined as ≥30% PSA decline at 12 weeks. H0 = 0.30 versus H1 = 0.50 (α = 0.05, power = 0.83). Circulating androgen levels were measured using liquid chromatography tandem mass spectrometry.

RESULTS

Thirty-nine patients were included in the final analysis. Twenty (51%; 95% confidence interval, 36%-66%) patients had ≥30% PSA decline; the null hypothesis was rejected. Sixteen (41%) had ≥50% PSA decline. Median PFS (progression-free survival) was 16 weeks; median radiographic PFS (rPFS) was 36 weeks. Samples for measurement of baseline androgens were available in 37 patients. The PSA response proportion was 59% in 29 patients with DHEA ≥ limit of quantitation (LOQ), compared with 13% in 8 patients with DHEA < LOQ (P = 0.042). Median PFS was 6 and 16 weeks in DHEA < LOQ and DHEA ≥ LOQ patients, respectively (P = 0.017); median rPFS was 14 and 36 weeks in DHEA < LOQ and DHEA ≥ LOQ patients, respectively (P < 0.001).

CONCLUSIONS

Abiraterone demonstrates modest clinical efficacy in mCRPC patients previously treated with ketoconazole. Patients with DHEA ≥ LOQ were more likely to demonstrate PSA responses and longer PFS. Analysis of circulating androgens merits further investigation as a biomarker for response to androgen synthesis inhibitor therapy.

Androgenic biomarker prof|ling in human matrices and cell culture samples using high throughput, electrospray tandem mass spectrometry

BACKGROUND. A high throughput, high pressure liquid chromatographic (HPLC) method with triple quadrupole mass spectral detection (LC/MS/MS) was validated for the measurement of 5 endogenous androgens in human plasma and serum and applied to various in vivo and in vitro study samples to pursue a better understanding of the interrelationship of the androgen axis, intracrine metabolism, and castration-recurrent prostate cancer (CaP).

METHODS

A Shimadzu HPLC system interfaced with a Sciex QTRAP 5500 mass spectrometer with electrospray ionization was used with in line column-switching. Samples were liquid/liquid extracted and chromatographed on a Luna C18(2) column at 60°C with a biphasic gradient using a 15-min run time.

RESULTS

The method was validated for five androgens in human plasma and serum, and applied to four sets of samples. Plasma (n=188) and bone marrow aspirate (n=129) samples from patients with CaP, who received abiraterone acetate plus prednisone for up to 945 days(135 weeks), had undetectable androgens after 8 weeks of treatment. Plasma dehydroepiandrosterone(DHEA) concentrations were higher in African Americans than Caucasian Americans with newly diagnosed CaP. Analysis of prostate tumor tissue homogenates demonstrated reproducible testosterone (T) and dihydrotestosterone (DHT) concentrations with a minimal sample size of 1.0–2.0 mg of tissue. Finally, cell pellet and media samples from the LNCaP C4-2 cell line showed conversion of T to DHT.

CONCLUSION

The proposed LC/MS/MS method was validated for quantitation of five endogenous androgens in human plasma and serum, and effectively profiles androgens in clinical specimens and cell culture samples.

Prostate cancer cells differ in testosterone accumulation, dihydrotestosterone conversion, and androgen receptor signaling response to steroid 5α-reductase inhibitors

BACKGROUND

Blocking 5α-reductase-mediated testosterone conversion to dihydrotestosterone (DHT) with finasteride or dutasteride is the driving hypothesis behind two prostate cancer prevention trials. Factors affecting intracellular androgen levels and the androgen receptor (AR) signaling axis need to be examined systematically in order to fully understand the outcome of interventions using these drugs.

METHODS

The expression of three 5α-reductase isozymes, as determined by immunohistochemistry and qRT-PCR, was studied in five human prostate cancer cell lines. Intracellular testosterone and DHT were analyzed using mass spectrometry. A luciferase reporter assay and AR-regulated genes were used to evaluate the modulation of AR activity.

RESULTS

Prostate cancer cells were capable of accumulating testosterone to a level 15-50 times higher than that in the medium. The profile and expression of 5α-reductase isozymes did not predict the capacity to convert testosterone to DHT. Finasteride and dutasteride were able to depress testosterone uptake in addition to lowering intracellular DHT. The inhibition of AR activity following drug treatment often exceeded the expected response due to reduced availability of DHT. The ability to maintain high intracellular testosterone might compensate for the shortage of DHT.

CONCLUSIONS

The biological effect of finasteride or dutasteride appears to be complex and may depend on the interplay of several factors, which include testosterone turnover, enzymology of DHT production, ability to use testosterone and DHT interchangeably, and propensity of cells for off-target AR inhibitory effect.

Covalently linked tandem lesions in DNA

Reactive oxygen species (ROS) generate a type of DNA damage called tandem lesions, two adjacent nucleotides both modified. A subcategory of tandem lesions consists of adjacent nucleotides linked by a covalent bond. Covalently linked tandem lesions generate highly characteristic liquid chromotography-tandem mass spectrometry (LC-MS/MS) elution profiles. We have used this property to comprehensively survey X-irradiated DNA for covalently linked tandem lesions. A total of 15 tandem lesions were detected in DNA irradiated in deoxygenated aqueous solution, five tandem lesions were detected in DNA that was irradiated in oxygenated solution.

Lack of bioequivalence of ciprofloxacin when administered with calcium-fortified orange juice: a new twist on an old interaction

Fluoroquinolones are known to interact with drugs containing multivalent ions. Current Food and Drug Administration (FDA) labeling states that ciprofloxacin and most other fluoroquinolones are safe to be given with food and dietary calcium but not calcium supplements. Although many of the currently marketed calcium fortified foods have calcium contents that usually exceed those in dietary calcium sources, it is unclear whether they represent a risk for less than optimal absorption of fluoroquinolones, which may result in subsequent clinical failures due to lack of bacterial eradication and antibiotic resistance. The purpose of this three-way, randomized, crossover study was to characterize and compare the bioequivalence of single doses of oral ciprofloxacin in 15 healthy volunteers when administered with water, concurrently with orange juice, and concurrently with calcium-fortified orange juice. Compared to the control arm, the Cmax of ciprofloxacin significantly decreased when it was given with orange juice (23%, p = 0.001) and with calcium-fortified orange juice (41%, p < 0.001). Twenty-four-hour ciprofloxacin AUCs were also decreased for both forms of the orange juice (22% [p < 0.001] and 38% [p < 0.001], respectively). When compared to each other, neither of the orange juice regimens were bioequivalent to each other, with the Cmax and AUC for the fortified form being 22% (p = 0.005) and 21% (p = 0.015) lower than those of the nonfortified form. By FDA standards, although ciprofloxacin is marginally bioequivalent when administered with orange juice, it is not when it is administered with calcium-fortified orange juice. The changes in Cmax and AUC have the potential to significantly decrease clinical efficacy and promote antibiotic resistance. Not warning patients about potential food-drug interactions with fortified foods may be a major unrealized and unstudied inadvertent source of clinical failures and resistance trends with fluoroquinolones.

Gender-related effects on metoprolol pharmacokinetics and pharmacodynamics in healthy volunteers

OBJECTIVE

To determine whether there are gender-specific differences in the pharmacokinetics and pharmacodynamics of metoprolol enantiomers.

METHODS

Twenty normal volunteers (10 men and 10 women) received 100 mg oral metoprolol tartrate twice daily for a total of nine doses. Pharmacokinetics and pharmacodynamics were studied after the last dose. Subjects also completed a control pharmacodynamic study; the order of drug and control studies was randomized. Measurements of heart rate and systolic blood pressure were obtained during peak submaximal bicycle exercise testing. (R)-Metoprolol and (S)-metoprolol concentrations were determined by stereospecific HPLC. The percentage difference in exercise heart rate and systolic blood pressure (metoprolol versus control), and (R)- and (S)-metoprolol plasma concentrations were comodeled.

RESULTS

Men and women showed stereoselective pharmacokinetics; (S)-metoprolol concentrations were significantly greater than those for (R)-metoprolol for both groups. Women had greater drug exposure than men (higher maximum concentration and area under the plasma concentration-time curve). No differences were observed between genders with respect to elimination half-life. Females had a greater reduction in exercise heart rate and systolic blood pressure; however, the area under the effect curve was significantly greater for heart rate only. Pharmacodynamic data were best fitted by the Hill equation with the effect site in the central compartment. The fitted maximum effect and the concentration at one-half of the maximum effect for heart rate and systolic blood pressure did not differ between men and women (P > .20).

CONCLUSIONS

Gender-related differences exist in the pharmacokinetics of metoprolol enantiomers, resulting in greater drug exposure in female subjects. However, concentration-effect relationships did not differ between men and women. Therefore the observed differences in drug effects were the result of gender-specific differences in metoprolol pharmacokinetics.

Longiberine and O-methyllongiberine, dimeric protoberberine-benzyl tetrahydroisoquinoline alkaloids from Thalictrum longistylum(1)

Two benzyltetrahydroisoquinoline-protoberberine dimers, longiberine (1) and O-methyllongiberine (2), were isolated from the roots of Thalictrum longistylum and represent a new class of dimeric alkaloids. The structure of longiberine (1) was established by spectral and chemical methods. Reductive cleavage of O-ethyllongiberine (4) with Na/liquid NH(3) yielded (+)-(S)-N-methylcoclaurine (5), which determined one-half of the dimer, and 1D and 2D NMR studies arranged the substituents on the protoberberine nucleus. Chemical conversion of thalidezine (6) to 1 via the O-acetyl N,N-didemethyl derivative 9, which was methylenated in the Mannich reaction and N-methylated by the Eschweiler-Clarke procedure, established the second asymmetric center as S and confirmed the ring size and the order of the substituents for 1. Methylation of 1 with diazomethane formed the O-methyl derivative 2, identical with the natural product.

Ciprofloxacin concentrations in lung tissue following a single 400 mg intravenous dose

Intravenous ciprofloxacin is frequently prescribed for the treatment of infections due to nosocomially acquired gram-negative organisms, including those originating in the respiratory tract. In this study, the concentrations of ciprofloxacin in serum and lung tissue were determined by HPLC in patients undergoing lung surgery. A total of 22 patients scheduled for lung surgery received a single 400 mg i.v. dose of ciprofloxacin administered as a 1 h infusion. A specimen of healthy lung tissue was obtained from resected lung from 18 of the patients for analysis of ciprofloxacin concentration during the following time intervals after infusion (one sample/patient): 0-2, 2-4, 4-8 and 8-12 h. Corresponding mean serum and tissue concentrations were 2.37 mg/L and 3.84 mg/kg (0-2 h), 1.18 mg/L and 1.92 mg/kg (2-4 h), 0.69 mg/L and 1.77 mg/kg (4-8 h), and 0.13 mg/L and 0.67 mg/kg (8-12 h). Ciprofloxacin distributed rapidly to lung tissue, as seen by the high concentrations in the lung tissue as early as 2 h after infusion. Concentrations in lung tissue were generally higher than those in serum (tissue:serum ratios ranged from 1.7 to 7.1). The mean tissue concentrations found in this study remained above the MIC for most susceptible organisms.

Assessment of the enzymuria resulting from gentamicin alone and combinations of gentamicin with various beta-lactam antibiotics

OBJECTIVE

To determine the propensity of beta-lactam antimicrobials to ameliorate or potentiate aminoglycoside-induced renal enzymuria.

DESIGN

Two open, randomized, double-blind, parallel-group studies were conducted in young, healthy, male volunteer subjects. Using a common protocol, 24-hour urine collections were analyzed for the renal tubular enzymes alanine aminopeptidase (AAP) and N-acetyl-beta-D-glucosaminidase (NAG), as well as for creatinine. Antimicrobial combinations studied included gentamicin plus placebo and gentamicin plus ticarcillin/clavulanate (protocol 1); and gentamicin plus placebo, gentamicin plus piperacillin, and gentamicin plus ceftazidime (protocol 2). The antimicrobial regimens were administered for 7 days. Eight subjects completed each treatment group.

RESULTS

There were no significant differences between treatment groups with regard to urine creatinine excretion or serum gentamicin concentrations in either protocol. Enzymuria (AAP [p = 0.039] and NAG [p = 0.337]) was decreased in the gentamicin plus ticarcillin/clavulanate treatment compared with that in the gentamicin plus placebo treatment. Increased enzymuria, as indicated by increased urine concentrations of AAP and NAG, was observed in the gentamicin plus ceftazidime treatment (p < 0.05) compared with the other two treatments.

CONCLUSIONS

Based on relative enzymuria, ticarcillin/clavulanate may be renal protective. Piperacillin neither potentiated nor ameliorated aminoglycoside-induced enzymuria. Since acute elevations in AAP and NAG reflect insults to the kidney, these studies suggest that ceftazidime may enhance aminoglycoside-induced renal injury. Piperacillin had no effect on enzymuria and would appear not to enhance or protect against aminoglycoside-induced renal injury.

Pharmacodynamic modeling of the in vivo interaction between cefotaxime and ofloxacin by using serum ultrafiltrate inhibitory titers

The pharmacokinetics (PK) and pharmacodynamics (PD) of cefotaxime and ofloxacin and of their combination were examined in a three-period randomized crossover study involving 12 healthy adults. The PK of cefotaxime and ofloxacin were modeled. PD was assessed from the predicted concentrations in serum and serum untrafiltrate inhibitory titers for 10 test organisms. An inhibitory sigmoid Emax model based on the probability of bacterial growth was used, where Emax = 1 and EC50 is the concentration resulting in a 50% probability of growth. The total body clearance (CL(T)) and volume of distribution at steady state (V(SS)) for cefotaxime were 0.236 liters/kg/h and 0.207 liters/kg, respectively, for the monotherapy and 0.231 liters/kg/h and 0.208 liters/kg for the combination therapy. Ofloxacin exhibited PK parameters of 0.143 liters/kg/h for CL(T) and 1.20 liters/kg for V(SS) following the monotherapy and of 0.141 liters/kg/h for CL(T) and 1.16 liters/kg for V(SS) following combination therapy. For the combination therapy, an interaction term, theta, defined the type and relative extent of interaction. The range of observed theta values (-0.033 to 0.067) is consistent with an additive PD interaction according to standards similar to those used for the in vitro fractional inhibitory concentration index.

Comparative pharmacokinetics of oral ceftibuten, cefixime, cefaclor, and cefuroxime axetil in healthy volunteers

STUDY OBJECTIVE

To compare the pharmacokinetics of ceftibuten, cefixime, ceturoxime axetil, and cefaclor after oral administration.

DESIGN

Randomized, four-period, crossover study.

SETTING

Hospital-based clinical research center.

SUBJECTS

Healthy adult men and women volunteers.

INTERVENTIONS

Single 400-mg doses of cefixime and ceftibuten, and 500-mg doses of cefuroxime axetil and cefaclor.

MEASUREMENTS AND MAIN RESULTS

Serum concentrations were determined by high-performance liquid chromatography methods. The mean oral clearances of cefixime, cefuroxime axetil, and cefaclor were similar, ranging from 20.4-27.0 L/hour; clearance of ceftibuten was approximately 4-fold less, 5.45 L/hour. The serum half-lives of ceftibuten (2.35 hrs) and cefixime (2.38 hrs) were prolonged compared with those of cefuroxime axetil (1.30 hrs) and cefaclor (0.693 hr). These agents also differed in terms of time to maximum concentration, time to peak plasma level, area under the curve, and apparent volume of distribution, the last reflecting differences in biovailability.

CONCLUSION

Ceftibuten had a relatively high time to maximum concentration and long half-life, resulting in a 3.5-fold higher area under the curve than cefixime, cefuroxime axetil, and cefaclor. These pharmacokinetic data can be used as a basis to compare the four oral cephalosporins; however, comparative susceptibility data must also be considered.

Effect of aging on atenolol pharmacokinetics and pharmacodynamics

A study was conducted to characterize and compare the pharmacodynamics and pharmacokinetics of atenolol in young and elderly men. Six young (mean +/- SD, 25.0 +/- 3.0 years) and six elderly (63.0 +/- 3.2 years) healthy men took atenolol 100 mg orally once daily for 6 days. Heart rate response to submaximal exercise was measured at selected times for 48 hours, and plasma and urine samples were collected over the same time interval. The Sigmoid Emax model was fit to percent reductions in exercise heart rate and atenolol plasma concentrations. The younger men had significantly lower values for area under the steady-state plasma concentration-time curve and higher values for systemic clearance/F and renal clearance. EC50 values showed a trend toward greater sensitivity to the negative chronotropic effects of atenolol among the elderly men. Model-derived percent reductions in heart rate were greater at all concentrations among the elderly men. These data suggest that group differences in atenolol pharmacokinetics were likely a result of age-related decline in renal function, and that the elderly subjects were at least as sensitive as, and maybe even more sensitive than, the younger subjects to the negative chronotropic effects of atenolol.

Structures and biological activities of tobramycin-ticarcillin adducts

Aminoglycosides and penicillins chemically interact when they are combined in vitro or in vivo. The resulting adducts are considered to be biologically inactive. The major adducts formed in he interaction between tobramycin and ticarcillin have been recently isolated in pure form in our laboratory. On the basis of mass, infrared, and proton magnetic resonance spectra, the major adducts appeared 10 be amides formed by an attack of the beta-lactam carbonyl group of ticarcillin by an amino group of tobramycin. All other moieties of ticarcillin were intact except that the beta-lactam ring was opened and was rotated by 120-130 degrees . The minimum inhibitory concentrations (MICs) of the adducts, tobramycin, and ticarcillin were 20.0, 0.25, and 2.0 microg/mL for Staphylococcus aureus and Escherichia coli, and 160.0, 0.5, and 8.0 microg/mL for Pseudomonas aeruginosa. Thus, the major adducts possessed some antimicrobial activity, but not enough to be active in the treatment of infections. As shown by fluorescence polarization immunoassay (FPIA), the adducts demonstrate some cross-reactivity in the assay of tobramycin. However, it was insufficient to cause significant error in the measurement of tobramycin in human serum.

Predictors of trough concentrations of oral ciprofloxacin

Patients enrolled in a fixed-dose clinical trial of oral ciprofloxacin had trough concentrations measured to document absorption and monitor compliance. The objective was to determine whether any demographic characteristics might be important predictors of the concentrations. Stepwise multivariate linear regression revealed no correlation between ciprofloxacin trough concentrations and serum creatinine, estimated creatinine clearance (Clcr), weight, height, body surface area, or gender. However, age exhibited a direct linear relationship with trough concentrations (Y in microgram/ml), Y = 0.020.age--0.541 (p < 0.003). We conclude that for patients with Clcr 30 ml/minute or above, age is a more important predictor of ciprofloxacin trough concentration than renal function. Dosage adjustment should not be arbitrary but should be guided by minimum inhibitory concentration, clinical response, and side effects.

The effect of isradipine on theophylline pharmacokinetics in healthy volunteers

The effects of isradipine 2.5 mg and 5 mg on the disposition of theophylline were investigated in a placebo-controlled, randomized, three-way, crossover trial. Eleven healthy, nonsmoking men each received a treatment of placebo, and isradipine 2.5 mg and 5 mg every 12 hours for 6 consecutive days. On the morning of day 6, 2 hours after the isradipine dose, theophylline (solution) 5.0 mg/kg was administered orally, and blood samples were collected over 24 hours. A 2-week washout period separated treatment sequences. Plasma samples were analyzed for theophylline using high-performance liquid chromatography. Using a two-way analysis of variance, no significant changes in apparent theophylline clearance were observed between placebo, and isradipine 2.5 and 5 mg (0.815 +/- 0.164, 0.870 +/- 0.212, and 0.827 +/- 0.164 ml/min/kg, respectively; p = 0.136). Similarly, no significant change in volume of distribution was noted. These findings suggest that isradipine at recommended dosages does not impair theophylline metabolism.

Renal tubular enzyme effects of clarithromycin in comparison with gentamicin and placebo in volunteers

This study assessed the potential nephrotoxicity of clarithromycin in comparison with gentamicin and placebo. Increased urinary excretion of alanine aminopeptidase (AAP) and N-acetyl-beta-D-glucosaminidase (NAG) served as markers of renal tubular injury. The study utilised a multiple-dose, double-blind, randomised, parallel group design. 14 healthy male subjects received 1 of 3 treatment regimens: (a) clarithromycin 500 mg orally every 12h for 13 doses and intravenous placebo every 8h (n = 5); (b) oral placebo every 12h and intravenous placebo every 8h (n = 4); and (c) intravenous gentamicin 1.7 mg/kg every 8h for 19 doses and oral placebo every 12h (n = 5). 24h urine collections were obtained daily for determinations of AAP and NAG activities. Gentamicin produced statistically significant increases (p less than 0.0001) in AAP and NAG excretion, with increases as early as the first and second day of dosing. Clarithromycin, when compared with placebo, did not produce significant elevations in AAP or NAG activity. On the basis of these data, it is unlikely that usual doses of clarithromycin have significant potential for causing nephrotoxicity.

Cerebrospinal fluid penetration of cefpirome in patients with non-inflamed meninges

Twenty patients (mean age 52 +/- 12 years, mean weight 75 +/- 15 kg) scheduled for elective myelogram or spinal anaesthesia were enrolled to determine the cerebrospinal fluid (CSF) penetration of a new expanded spectrum cephalosporin antibiotic, cefpirome (HR-810). A single 2 g intravenous dose of cefpirome was administered as a bolus between 1 and 8 h before lumbar puncture. Blood samples were collected at 15 pre-determined times and a single CSF sample was obtained at the time of lumbar puncture. Serum and CSF cefpirome concentrations were determined by high performance liquid chromatography. The mean maximal serum concentration of cefpirome was 264 +/- 76 mg/L. A mean steady-state volume of distribution of 20 +/- 4 L, clearance of 7.4 +/- 1.3 L/h, and half-life of 2.5 +/- 0.5 h were determined. Mean CSF concentrations were 0.50 +/- 0.11 mg/L at 1-2 h post dose (n = 4), 0.57 +/- 0.13 mg/L at 2-4 h post dose (n = 4), 0.76 +/- 0.34 mg/L at 4-6 h post dose (n = 7), and 0.83 +/- 0.29 mg/L at 6-8.3 h post dose (n = 5). Blood:brain barrier permeability to cefpirome may not be a limiting factor as CSF concentrations were rapidly attained. Further studies are required to determine the mechanism of cefpirome transport between plasma and CSF.

Compatibility of ciprofloxacin injection with selected drugs and solutions

The compatibility of ciprofloxacin injection with selected antimicrobials and aminophylline was studied. Ciprofloxacin, amikacin sulfate, aminophylline, clindamycin phosphate, gentamicin sulfate, and tobramycin sulfate were mixed separately in minibags containing 0.9% sodium chloride injection or 5% dextrose injection; admixtures were stored for up to 48 hours at either 4 degrees C or 25 degrees C. Ciprofloxacin was also combined separately with each of the other drugs and solutions and stored under the same conditions. In addition, ciprofloxacin was combined with metronidazole in ready-to-use mini-bags of the latter drug and stored at 25 degrees C. Drug concentrations were measured by fluorescence polarization immunoassay or high-performance liquid chromatography. All admixtures were also examined visually. Stability was defined as retention of at least 90% of the original drug concentration with no visual evidence of incompatibility. With one exception, drugs in all single-drug admixtures were stable for 48 hours. The drug concentration eight hours after amikacin was mixed in 0.9% sodium chloride and refrigerated was 89% of the original concentration. When ciprofloxacin was combined with gentamicin, metronidazole, or tobramycin, all of the involved drugs were stable for 48 hours. Compatibility of ciprofloxacin-amikacin admixtures depended on the fluid and storage temperature; all such admixtures were stable for at least eight hours. A precipitate formed immediately whenever ciprofloxacin was mixed with clindamycin and within four hours after ciprofloxacin was mixed with aminophylline. Ciprofloxacin injection was compatible with gentamicin, metronidazole, and tobramycin and incompatible with aminophylline and clindamycin. The compatibility of ciprofloxacin-amikacin admixtures depended on the i.v. solution and storage temperature.

Effects of ranitidine and sucralfate on ketoconazole bioavailability

Ketoconazole is an oral imidazole antifungal agent useful in the treatment of opportunistic fungal infections. Gastrointestinal absorption of this agent is variable and dependent on the presence of gastric acid. This study compared the effects of concomitant sucralfate administration with ranitidine administration on the pharmacokinetic disposition of a 400-mg ketoconazole dose. Six healthy male volunteers were randomized to receive 400 mg of ketoconazole alone, 1.0 g of sucralfate concomitantly with a 400-mg ketoconazole dose, or ranitidine, administered 2 h prior to a 400-mg ketoconazole dose to titrate to a gastric pH of 6. All subjects received all three regimens in crossover fashion. Gastric pH was measured continuously for 4 h after ketoconazole administration in all subjects by using a Heidelberg radiotelemetry pH capsule. Relative ketoconazole bioavailability was compared between treatments. With sucralfate, five of six subjects demonstrated a decrease in the peak drug concentration in serum as well as an increase in the time to peak concentration, indicating a delay in ketoconazole absorption. The mean area under the concentration-time curve from 0 to 12 h for ketoconazole following gastric alkalinization was significantly different from that of either ketoconazole alone or ketoconazole with sucralfate (P less than 0.01). Continuous gastric pH monitoring allowed correlation between the decrease in ketoconazole bioavailability observed with ranitidine and the increase in gastric pH. The apparent decrease in ketoconazole bioavailability observed with sucralfate appears to be caused by an alternative mechanism since a change in gastric pH was not observed. On the basis of these findings, separating the administration of ketoconazole and sucralfate should be considered to decrease the potential for interaction of sucralfate on ketoconazole bioavailability.

Combined use of ciprofloxacin and sucralfate

The effect of sucralfate on the bioavailability of ciprofloxacin hydrochloride was assessed in 12 healthy male volunteers. The study was a four-period crossover design where subjects were randomized to one of four treatment sequences at entry. Treatments A, B, and C included sucralfate 2 g q12h for five doses. For treatment A, the fifth dose sucralfate was administered concurrently with ciprofloxacin 750 mg. For treatment B, 750 mg of ciprofloxacin was administered two hours before the fifth dose of sucralfate. Treatment C consisted of ciprofloxacin 750 mg six hours before the fifth dose of sucralfate. A 750-mg dose of ciprofloxacin was administered alone for treatment D. Blood and urine samples were collected at predetermined time intervals for 24 hours. Ciprofloxacin concentrations were determined by HPLC. The area under the concentration versus time curve from zero to infinity and the urinary recovery of ciprofloxacin were used for determining relative bioavailability. Concurrent administration of ciprofloxacin and sucralfate (treatment A) resulted in a significant decrease (p less than 0.05) in ciprofloxacin absorption. The relative bioavailabilities for treatments A, B, and C were 0.0429 +/- 0.0202, 0.829 + 0.21, and 0.965 + 0.32, respectively, relative to ciprofloxacin alone. In normal volunteers, ciprofloxacin may be administered between two and six hours before sucralfate, allowing sufficient time for ciprofloxacin absorption prior to the sucralfate dose and thereby minimizing the chance of a significant interaction. In patients with decreased gastric emptying the interaction may be more difficult to avoid.

Lidocaine absorption and metabolism after oropharyngeal application in young and young-elderly adults

The purpose of this study was to evaluate the effect of age on lidocaine absorption and metabolism after application to the oropharynx and vocal cords in a manner similar to preparation for flexible fiberoptic bronchoscopy. Five healthy volunteers were studied in each of two age groups: from 25 to 37 and 60 to 68 years of age. Each volunteer had a total of lidocaine 300 mg administered as a gargle, gel, or directly to the vocal cords. Blood samples and expectorant were collected to determine concentrations of lidocaine and its metabolites, monoethylglycinxylidide (MEGX) and glycinxylidide (GX). No differences in peak plasma lidocaine concentrations, 2.09 +/- 1.28 mumol/L (1 microgram/mL = 4.27 mumol/L) in young subjects, and 2.35 +/- 0.85 mumol/L in young-elderly subjects, or lidocaine AUC were seen between the two age groups. Lidocaine recovered in expectorant ranged from 96 to 168 mg. This study suggests that, over the age range studied, increased age does not impair lidocaine absorption from the oropharynx or lidocaine metabolism when topical lidocaine is used during flexible fiberoptic bronchoscopy.

Effect of fluconazole on the disposition of phenytoin

In a randomized, placebo-controlled, parallel study, phenytoin was given in the presence and absence of fluconazole. Twenty healthy male subjects received phenytoin, 200 mg orally, on study days 1 to 3 and 18 to 20 and 250 mg intravenously on study days 4 and 21. Ten subjects received fluconazole, 200 mg orally, and 10 received placebo daily on study days 8 to 21. Serial blood samples were collected during a 24-hour period after the intravenous phenytoin dose. Fluconazole trough concentrations were determined on days 14, 18, and 21. Serum phenytoin area under the concentration-time curve from 0 to 24 hours increased 75% and minimum plasma drug concentration increased 128% after administration of fluconazole, 200 mg/day, for 14 days. These values were significantly greater than the 5% increase in area under the concentration-time curve from 0 to 24 hours and 11.6% increase in minimum plasma drug concentration in the placebo group. Fluconazole trough concentrations remained unchanged during the coadministration of phenytoin. The increased phenytoin concentrations in the presence of fluconazole suggest that fluconazole inhibits phenytoin metabolism. Serum concentration monitoring with a reduction in phenytoin dosage is clinically warranted in patients receiving phenytoin and concomitant fluconazole therapy.

Comparative evaluation of the pharmacokinetics of N-methylthiotetrazole following administration of cefoperazone, cefotetan, and cefmetazole

The comparative pharmacokinetics and in vivo production of N-methylthiotetrazole (NMTT) were evaluated following administration of cefoperazone, cefotetan, and cefmetazole. In a randomized-crossover manner, 11 healthy male volunteers received single 2-g intravenous doses of each agent and serial blood and urine samples were collected. Concentrations of NMTT and the parent compound in plasma, urine, and the reconstituted antibiotic solution were determined by high-pressure liquid chromatography. The amounts of NMTT administered were 6.06 +/- 0.46, 14.4 +/- 0.87, and 17.4 +/- 1.06 mg for cefoperazone, cefotetan, and cefmetazole, respectively (P less than 0.05). The mean NMTT plasma concentration-time profiles following administration of each cephalosporin were markedly different. Six hours after dosing, NMTT concentrations in plasma following cefoperazone administration were higher than those following administration of cefmetazole and cefotetan. Urinary recoveries of NMTT averaged 137.0 +/- 37.1, 38.3 +/- 6.98, and 25.2 +/- 5.95 mg following administration of cefoperazone, cefotetan, and cefmetazole, respectively (P less than 0.01). The apparent amount of NMTT produced in vivo, calculated by subtracting the amount of NMTT administered from the amount of NMTT excreted in urine, was significantly lower following cefmetazole administration than after administration of cefoperazone and cefotetan (P less than 0.01). The discrepancy between in vitro NMTT production (cefmetazole greater than cefotetan greater than cefoperazone) and the amount of NMTT formed in vivo and excreted unchanged (cefoperazone greater than cefotetan greater than cefmetazole) suggests that in vivo production of NMTT is dependent on the disposition of the parent cephalosporin. These results further suggest that cephalosporins which undergo extensive biliary excretion, such as cefoperazone, are associated with the greatest amount of in vivo NMTT release, whereas cephalosporins which are primarily renally excreted, such as cefmetazole, are associated with the lowest in vivo production of NMTT.

Inhibition of norfloxacin absorption by antacids

The effect of antacids on the systemic absorption of oral norfloxacin was evaluated in 12 healthy volunteers. Subjects were given each treatment in a balanced sequence at 7-day intervals. Treatments included 400 mg of norfloxacin alone, 400 mg of norfloxacin 5 min after aluminum-magnesium hydroxide (Maalox), Maalox 2 h after 400 mg of norfloxacin, and 400 mg of norfloxacin 5 min after calcium carbonate (Titralac). Blood and urine samples were collected at predetermined time intervals for 24 and 48 h, respectively. Norfloxacin concentrations in plasma and urine were determined by high-pressure liquid chromatography. The area under the plasma concentration-versus-time curve from time zero to infinity and urinary recovery were used to compare the relative bioavailability of norfloxacin with antacids with that of norfloxacin alone. Norfloxacin bioavailability was markedly reduced when subjects received antacid pretreatment. When norfloxacin was given 5 min after Maalox and Titralac, the bioavailabilities were 9.02 and 37.5%, respectively, relative to that for 400 mg of norfloxacin alone. When Maalox was given 2 h after norfloxacin, maximal concentrations of norfloxacin in plasma occurred between 1 and 1.5 h postdose, and absorption was reduced to a lesser extent, with a relative bioavailability of 81.31%. Norfloxacin concentrations in urine were also reduced as a result of antacid administration. Antacids containing aluminum and magnesium salts and calcium carbonate should be avoided by patients taking norfloxacin.

The effect of verapamil on the pharmacokinetic disposition of theophylline in cigarette smokers

In a randomized cross-over study the effect of verapamil on the pharmacokinetics of theophylline was evaluated in eight cigarette smoking male volunteers. Theophylline was administered as an intravenous infusion of aminophylline, 6 mg/kg based on ideal body weight, over 30 minutes in the control phase. In the treatment phase, aminophylline was administered after a four day regimen of oral verapamil 80 mg every 8 hours. Serial blood samples were collected over a 24 hour period following aminophylline administration. Theophylline serum concentrations were determined by a fluorescence polarization immunoassay, the Abbott TDxR. Theophylline clearance decreased by 11.5%, from a mean (+/-SD) of 1.39 +/- 0.38 mL/min/kg in the control phase to 1.23 +/- 0.21 mL/min/kg with the co-administration of verapamil (P = 0.104). Theophylline elimination rate constant decreased by approximately 9.4% from 0.171 +/- 0.032 to 0.155 + 0.023 hr-1 during the treatment phase (P = 0.085). The area under the curve (AUCo alpha) and volume of distribution at steady-state (Vss) for theophylline were also not statistically different between the two study phases. These results are inconsistent with those of other investigators and the relevance of a potential theophylline-verapamil drug interaction remains unclear.

The influence of intravenous cimetidine dosage regimens on the disposition of theophylline

The influence of the method of cimetidine administration on theophylline disposition was studied in nine healthy, cigarette smoking male volunteers. The treatment phases consisted of: A) theophylline alone, B) theophylline plus intermittent cimetidine therapy (300 mg IV every 6 hr), and C) theophylline in combination with continuous infusion cimetidine (50 mg/hr). Theophylline (4.8 mg/kg) was administered intravenously as aminophylline over 30 minutes during each treatment phase. During study phases B and C subjects received 48 hours of cimetidine therapy beginning 24 hours prior to theophylline dosing. Blood samples for determination of theophylline concentrations were collected serially over 24 hours. Serum theophylline concentrations were determined in duplicate using fluorescence polarization immunoassay (Abbott Diagnostic TDx). The average age of the subjects was 27.4 +/- 4.7 years, and the individual smoking histories ranged from 0.5 to 1.5 packs per day (average 0.89 +/- 0.33). The mean (+/- SD) body weight was 79.1 +/- 8.2 kg and all subjects were within 20% of their ideal body weight. Theophylline pharmacokinetic parameters were determined using noncompartmental analysis. ANOVA for repeated measures and Tukey's multiple comparison test were used for statistical analysis. The mean (+/- SD) theophylline clearance for each of the treatment groups was: 1.4 +/- 0.4, 1.2 +/- 0.3, and 1.2 +/- 0.2 ml/min/kg for phases A, B and C, respectively. Cimetidine decreased the clearance of theophylline, however, theophylline clearance was not statistically different between regimens B and C. Thus, the method of cimetidine administration (intermittent versus continuous infusion) did not influence the magnitude of the drug-drug interaction.

Comparison of N-methylthiotetrazole dispositions in healthy volunteers following single intravenous doses of moxalactam, cefoperazone, and cefotetan

The N-methylthiotetrazole side chain (NMTT) that is present on several cephalosporins has been implicated in the development of antibiotic-associated hypoprothrombinemia. A randomized three-way crossover trial was conducted to compare the release of the NMTT side chain from three NMTT-containing antibiotics. Single 2-g doses of moxalactam, cefoperazone, and cefotetan were given, followed by serial blood and urine sampling. The concentrations of the parent compound and the NMTT side chain in plasma, urine, and the reconstituted antibiotic solution were determined by high-pressure liquid chromatography. Peak NMTT concentrations ranged from 0.42 to 16.50 micrograms/ml and were significantly higher after moxalactam administration than after cefoperazone or cefotetan administration (P less than 0.01). The NMTT trough concentrations (12.5 h) ranged from nondetectable to 2.47 micrograms/ml and tended to be greater following cefoperazone administration. The amounts of NMTT administered (e.g., the amount in the reconstituted antibiotic solution) were 25.8 +/- 1.4, 15.2 +/- 0.9, and 22.1 +/- 3.0 mg following moxalactam, cefoperazone, and cefotetan administration, respectively (P less than 0.01). In contrast, urinary recoveries of NMTT were 57.4 +/- 26.2, 73.6 +/- 44.3, and 29.7 +/- 22.9 mg following moxalactam, cefoperazone, and cefotetan, respectively. The amount of NMTT formed in vivo and excreted unchanged, as assessed by subtracting in vitro NMTT formation from NMTT urinary recovery, was significantly higher after cefoperazone than after moxalactam or cefotetan administration (P less than 0.05). The discrepancy between in vitro NMTT production (moxalactam > cefotetan > cefoperazone) and the amount of NMTT formed in vivo and excreted unchanged (cefoperazone > moxalactam > cefotetan) demonstrated that the in vivo production of NMTT is dependent on the disposition of the parent cephalosporin.

Inhibition of enoxacin absorption by antacids or ranitidine

Ten normal volunteers participated in a randomized, five-way crossover study to determine the effect of concurrent enoxacin and antacid or ranitidine administration on enoxacin absorption. The bioavailability of a single oral 400-mg enoxacin dose was significantly decreased, by 73 and 49%, when Maalox TC was administered 0.5 and 2 h before enoxacin, respectively. Enoxacin bioavailability was not significantly altered when the antacid was given 8 h before or 2 h after enoxacin administration. Ranitidine, administered intravenously 2 h before enoxacin, also significantly decreased enoxacin bioavailability, by 40%. The correlation between the proximity of antacid administration and the magnitude of the decrease in enoxacin bioavailability supports complexation as the mechanism of the antacid-enoxacin interaction. However, reduction of enoxacin bioavailability by ranitidine suggests that elevated gastric pH may also play a role in the antacid-enoxacin drug-drug interaction.

Large surface area activated charcoal and the inhibition of aspirin absorption

Activated charcoal's adsorptive capacity, and therefore potential efficacy, is generally related to its surface area. In our study, the efficacy of two activated charcoal preparations, Actidose-Aqua 1,500 m2/g and Super Char, 3,000 m2/g, were compared on the basis of their ability to inhibit aspirin absorption. Twelve healthy male subjects fasted for eight hours before and four hours after a 20 mg/kg oral dose of aspirin. One hour after aspirin dosing, each subject received either no charcoal, 25 g Actidose-Aqua, or 25 g Super Char in a randomized crossover design. Each aspirin dose was separated from the previous dose by at least seven days. Total urine volumes were collected over 12-hour intervals, beginning 12 hours before the aspirin dose and continuing for 72 hours after dosing. Urine salicylate concentration was measured with a colorimetric assay. The fraction of aspirin dose recovered in the urine was 0.96 +/- 0.13, 0.78 +/- 0.18, and 0.50 +/- 0.20 for the control, Actidose-Aqua, and Super Char treatment phases, respectively. In vitro, Super Char was found to bind more salicylic acid than Actidose-Aqua at pH 8.1. We conclude that both activated charcoal preparations significantly reduced the gastrointestinal absorption of aspirin (P less than .05) and that Super Char was significantly more effective than Actidose-Aqua in reducing the gastrointestinal absorption of aspirin (P less than .01).

Sucralfate reduces the gastrointestinal absorption of norfloxacin

The effect of sucralfate on the bioavailability of norfloxacin after single 400-mg doses of norfloxacin was evaluated in eight healthy males. Subjects received each of the following treatments in random sequence: (i), norfloxacin, 400 mg alone; (ii) sucralfate, 1 g, concurrently with norfloxacin, 400 mg; and (iii) sucralfate, 1 g, followed by norfloxacin, 400 mg, 2 h later. One day before administration of treatments 2 and 3, 1 g of sucralfate was given at 7 a.m., 11 a.m., 5 p.m., and 10 p.m. Blood samples were collected immediately before the norfloxacin dose and at 0.25, 0.5, 0.75, 1.0, 1.5, 2, 3, 4, 6, 8, 12, and 24 h postdose. Urine was collected in divided intervals: from 0 to 12, from 12 to 24, and from 24 to 48 h. Norfloxacin concentrations in plasma and urine were determined by high-performance liquid chromatography. Mean area under the plasma concentration-versus-time curve extrapolated to infinity decreased significantly (P less than 0.001) after norfloxacin was given with and 2 h after sucralfate. The relative bioavailabilities were 1.8% when norfloxacin was taken with sucralfate and 56.6% when it was taken 2 h after sucralfate. After norfloxacin was given alone, the mean norfloxacin concentrations in urine collected during intervals of 0 to 12, 12 to 24, and 24 to 28 h were 118.9 +/- 72.3, 18.8 +/- 12.5, and 2.4 +/- 2.2 micrograms/ml, respectively. After norfloxacin was given with sucralfate, however, the mean norfloxacin concentrations in urine collected during the same time intervals were 6.8 +/- 4.7, 1.8 +/- 1.4, and 0 +/- 0 microgram/ml, respectively. Because of low pH and relatively high magnesium concentration in urine, susceptibilities of bacteria in urine are 8- to 32-fold lower than in broth. This fact, in combination with the reduced bioavailability of norfloxacin in the presence of sucralfate or antacids, is likely to result in treatment failure. The effect of sucralfate given after norfloxacin was not examined, nor was the effect of sucralfate given more than 2 h before norfloxacin. Administration or norfloxacin with sucralfate should therefore by avoided.

Kinetics and action of N-methylthiotetrazole in volunteers and patients. Population-based clinical comparisons of antibiotics with and without this moiety

Normal volunteers and patients were studied to determine the relative importance of NMTT and patient risk factors in the production of hypoprothrombinemia. The normal volunteers demonstrated in vivo NMTT production, but the order of magnitude (cefoperazone, moxalactam, and cefotetan in descending order) was different from the usual order of clinical risk. In patients, there was not a NMTT-concentration-versus-effect relationship. Patients who were vitamin K deficient were more sensitive to lower NMTT concentrations than those with normal vitamin K status. In surveillance studies, NMTT-containing antibiotics were nor more frequently associated with hypoprothrombinemia or bleeding than antibiotics that lack this moiety.

PD 113,618 and PD 118,309, new pactamycin analogs

Two antibiotics were isolated from culture broths of a Streptomyces sp. and identified as 8"-hydroxypactamycin and 7-deoxypactamycin. The latter antibiotic was shown to be identical to cranomycin. An additional compound, 8"-hydroxypactamycate, was also isolated.

PD 116,152, a new phenazine antitumor antibiotic. Structure and antitumor activity

A new, highly substituted phenazine with antitumor activity was isolated from the culture broth of a Streptomyces sp. This compound, whose structure was determined by spectroscopic methods and verified by X-ray diffraction analysis, was found to be methyl 6-formyl-4,7,9-trihydroxy-8-methyl-1-phenazinecarboxylate.

PD 118,576: a new antitumor macrolide antibiotic

The isolation and properties of PD 118,576, a new cytotoxic antibiotic obtained from the culture broth of a Streptomyces sp., are described. The structure of this compound was established by spectral analyses of the parent compound and its tri-O-acetyl derivative. PD 118,576 proved to be related to the bafilomycins and therefore is a new member of this recently discovered family of macrolide antibiotics.