Polyacrylamide-punicic acid conjugate-based micelles for flutamide delivery in PC3 cells of prostate cancer: synthesis, characterisation and cytotoxicity studies

The aim of the present study was to synthesize a novel biopolymeric micelle based on punicic acid (PA) and polyacrylamide (PAM) for carrying chemotherapeutic drugs used in prostate cancer treatment. A polymer composite micelle was prepared by chemical conjugation between PAM and PA. The micelles were prepared by self-assembly via film casting followed by ultrasonication method. The successful production of PAMPA copolymeric micelles was confirmed using FTIR, 1H-NMR, and TEM. Then, flutamide was loaded in the designed nanomicelles and they were characterized. The cell cytotoxicity of the micelles was studied on PC3 cells of prostate cancer. The prepared nanomicelles showed the particle size of 88 nm, PDI of 0.246, zeta potential of -9 mV, drug loading efficiency of 94.5%, drug release of 85.6% until 10 hours in pH 7.4 and CMC of 74.13 μg/ml. The cell viability in blank nanocarriers was about 70% in PC3 cells at concentration of 25 μM. More significant cytotoxic effects were seen for flutamide loaded micelles at this concentration compared to the free drug. The results suggest that the PAMPA co-polymeric nanomicelles can be utilized as an effective carrier to enhance the cytotoxic effects of flutamide in prostate cancer.

Development and evaluation of a harmonized whole body physiologically based pharmacokinetic (PBPK) model for flutamide in rats and its extrapolation to humans

By their definition, inadvertent exposure to endocrine disrupting compounds (EDCs) intervenes with the endocrine signalling system, even at low dose. On the one hand, some EDCs are used as important pharmaceutical drugs that one would not want to dismiss. On the other hand, these pharmaceutical drugs are having off-target effects and increasingly significant exposure to the general population with unwanted health implications. Flutamide, one of the top pharmaceutical products marketed all over the world for the treatment of prostate cancer, is also a pollutant. Its therapeutic action mainly depends on targeting the androgen receptors and inhibiting the androgen action that is essential for growth and survival of prostate tissue. Currently flutamide is of concern with respect to its categorization as an endocrine disruptor. In this work we have developed a physiologically based pharmacokinetic (PBPK) model of flutamide that could serve as a standard tool for its human risk assessment. First we built the model for rat (where many parameters have been measured). The rat PBPK model was extrapolated to human where the re-parameterization involved human-specific physiology, metabolic kinetics derived from in-vitro studies, and the partition coefficient same as the rat model. We have harmonized the model by integrating different sets of in-vitro, in-vivo and physiological data into a PBPK model. Then the model was used to simulate different exposure scenarios and the results were compared against the observed data. Both uncertainty and sensitivity analysis was done. Since this new whole-body PBPK model can predict flutamide concentrations not only in plasma but also in various organs, the model may have clinical applications in efficacy and safety assessment of flutamide. The model can also be used for reverse dosimetry in the context of interpreting the available biomonitoring data to estimate the degree to which the population is currently being exposed, and a tool for the pharmaceutical companies to validate the estimated Permitted Daily Exposure (PDE) for flutamide.

The expression, induction and pharmacological activity of CYP1A2 are post-transcriptionally regulated by microRNA hsa-miR-132-5p

Cytochrome P450 1A2 (CYP1A2) is one of the most abundant and important drug metabolizing enzymes in human liver. However, little is known about the post-transcriptional regulation of CYP1A2, especially the mechanisms involving microRNAs (miRNAs). This study applied a systematic approach to investigate the post-transcriptional regulation of CYP1A2 by miRNAs. Candidate miRNAs targeting the 3'-untranslated region (3'-UTR) of CYP1A2 were screened in silico, resulting in the selection of sixty-two potential miRNAs for further analysis. The levels of two miRNAs, hsa-miR-132-5p and hsa-miR-221-5p, were inversely correlated with the expression of CYP1A2 mRNA transcripts in normal human liver tissue samples represented in The Cancer Genome Atlas (TCGA) dataset. The interactions between these miRNAs and cognate CYP1A2 mRNA sequences were evaluated using luciferase reporter gene studies and electrophoretic mobility shift assays, by which a direct interaction was confirmed involving hsa-miR-132-5p and a cognate binding site present in the CYP1A2 3'-UTR. Experiments by which hsa-miR-132-5p or random miRNA controls were introduced into HepG2, Huh-7 and HepaRG hepatic cell lines showed that only hsa-miR-132-5p suppressed the endogenous and lansoprazole-induced expression of CYP1A2, at biological activity, protein production, and mRNA transcript levels. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and lactate dehydrogenase (LDH) assays showed that hsa-miR-132-5p attenuates CYP1A2-mediated, lansoprazole-enhanced, flutamide-induced hepatic cell toxicity. Results from multilayer experiments demonstrate that hsa-miR-132-5p suppresses the expression of CYP1A2 and that this suppression is able to decrease the extent of an adverse drug-drug interaction involving lansoprazole and flutamide.

Novel ionically crosslinked casein nanoparticles for flutamide delivery: formulation, characterization, and in vivo pharmacokinetics

A novel particulate delivery matrix based on ionically crosslinked casein (CAS) nanoparticles was developed for controlled release of the poorly soluble anticancer drug flutamide (FLT). Nanoparticles were fabricated via oil-in-water emulsification then stabilized by ionic crosslinking of the positively charged CAS molecules below their isoelectric point, with the polyanionic crosslinker sodium tripolyphosphate. With the optimal preparation conditions, the drug loading and incorporation efficiency achieved were 8.73% and 64.55%, respectively. The nanoparticles exhibited a spherical shape with a size below 100 nm and a positive zeta potential (+7.54 to +17.3 mV). FLT was molecularly dispersed inside the nanoparticle protein matrix, as revealed by thermal analysis. The biodegradability of CAS nanoparticles in trypsin solution could be easily modulated by varying the sodium tripolyphosphate crosslinking density. A sustained release of FLT from CAS nanoparticles for up to 4 days was observed, depending on the crosslinking density. After intravenous administration of FLT-CAS nanoparticles into rats, CAS nanoparticles exhibited a longer circulation time and a markedly delayed blood clearance of FLT, with the half-life of FLT extended from 0.88 hours to 14.64 hours, compared with drug cosolvent. The results offer a promising method for tailoring biodegradable, drug-loaded CAS nanoparticles as controlled, long-circulating drug delivery systems of hydrophobic anticancer drugs in aqueous vehicles.

Effect of selected fluorinated drugs in a “ringing” gel on rheological behaviour and skin permeation

The purpose of the present study was to investigate the influence of different drugs exhibiting different solubility on the viscoelastic properties and on the skin diffusion profile of a ringing gel. In a preliminary rheology study with the placebo gel predominating elastic properties were confirmed and a temperature influence was indicated. Fluconazole, fludrocortisone-acetate, flumethasone-pivalate, flutamide and flufenamic-acid each 1% (w/w) were incorporated into the preparation and oscillatory measurements were performed at temperatures of 25, 28, 32 and 37 degrees C. In all drug containing formulations a high elastic G' value predominated the viscous G'' value. The highest G' value could be obtained with the incorporated flumethasone-pivalate. Additionally in almost all cases the G' values decreased with increasing temperature compared to the placebo gel. Additionally in vitro standard diffusion experiments using Franz-type cells and porcine skin were performed. Following rank order of the cumulative drug release after 48 h was obtained: fluconazole>flufenamic-acid>flumethasone-pivalate>flutamide>fludrocortisone-acetate. Furthermore an excellent chemical stability of all incorporated drugs was confirmed over 10 weeks.

Bioactivation and Hepatotoxicity of Nitroaromatic Drugs

Certain drugs containing a nitroaromatic moiety (e.g., tolcapone, nimesulide, nilutamide, flutamide, nitrofurantoin) have been associated with organ-selective toxicity including rare cases of idiosyncratic liver injury. What they have in common is the potential for multistep nitroreductive bioactivation (6-electron transfer) that produces the potentially hazardous nitroanion radical, nitroso intermediate, and N-hydroxy derivative. These intermediates have been associated with increased oxidant stress and targeting of nucleophilic residues on proteins and nucleic acids. However, other mechanisms including the formation of oxidative metabolites and mitochondrial liability, as well as inherent toxicokinetic properties, also determine the drugs' overall potency. Therefore, structural modification not only of the nitro moiety but also of ring substituents can greatly reduce toxicity. Novel concepts have revealed that, besides the classical microsomal nitroreductases, cytosolic and mitochondrial enzymes including nitric oxide synthase can also bioactivate certain nitroarenes (nilutamide). Furthermore, animal models of silent mitochondrial dysfunction have demonstrated that a mitochondrial oxidant stress posed by certain nitroaromatic drugs (nimesulide) can produce significant mitochondrial injury if superimposed on a genetic mitochondrial abnormality. Finally, there may be mechanisms for all nitroaromatic drugs that do not involve bioactivation of the nitro group, e.g., AHR interactions with flutamide. Taken together, the focus of research on the hepatic toxicity of nitroarene-containing drugs has shifted over the past years from the identification of the reactive intermediates generated during the bioreductive pathway to the underlying biomechanisms of liver injury. Most likely one of the next paradigm shifts will include the identification of determinants of susceptibility to nitroaromatic drug-induced hepatotoxicity.

Detection of a new N-oxidized metabolite of flutamide, N-[4-nitro-3-(trifluoromethyl)phenyl]hydroxylamine, in human liver microsomes and urine of prostate cancer patients

Flutamide (2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide), a nonsteroidal antiandrogen, is used in the treatment of prostate cancer but is occasionally associated with hepatic dysfunction. In the present study, the metabolism of flutamide including the formation of the possible reactive toxic metabolites was investigated using human liver microsomes and 10 isoforms of recombinant human cytochrome P450 (P450). 2-Hydroxyflutamide (OH-flutamide) and 4-nitro-3-(trifluoromethyl)phenylamine (FLU-1) were the main products of flutamide metabolism in human liver microsomes. The formation of OH-flutamide was markedly inhibited by ellipticine, an inhibitor of CYP1A1/1A2, and was mainly catalyzed by the recombinant CYP1A2. FLU-1 was also produced from OH-flutamide, but its metabolic rate was much less than that from flutamide. An inhibitor of carboxylesterase, bis-(p-nitrophenyl)phosphoric acid, completely inhibited the formation of FLU-1 from flutamide in human liver microsomes. A new metabolite, N-[4-nitro-3-(trifluoromethyl)phenyl]hydroxylamine (FLU-1-N-OH), was detected as a product of the reaction of FLU-1 with human liver microsomes and identified by comparison with the synthetic standard. The formation of FLU-1-N-OH was markedly inhibited by the addition of miconazole, an inhibitor of CYP3A4, and was mediated by recombinant CYP3A4. Furthermore, FLU-1-N-OH was detected mostly as the conjugates (glucuronide/sulfate) in the urine of prostate cancer patients collected for 3 h after treatment with flutamide. The formation of FLU-1-N-OH, however, did not differ between patients with and without abnormalities of hepatic functions among a total of 29 patients. The lack of an apparent association of the urinary excretion of FLU-1-N-OH and hepatic disorder may suggest the involvement of an additional unknown factor in the mechanisms of flutamide hepatotoxicity.

Dose-dependent transitions in mechanisms of toxicity: case studies

Experience with dose response and mechanisms of toxicity has shown that multiple mechanisms may exist for a single agent along the continuum of the full dose-response curve. It is highly likely that critical, limiting steps in any given mechanistic pathway may become overwhelmed with increasing exposures, signaling the emergence of new modalities of toxic tissue injury at these higher doses. Therefore, dose-dependent transitions in principal mechanisms of toxicity may occur, and could have significant impact on the interpretation of reference data sets for risk assessment. To illustrate the existence of dose-dependent transitions in mechanisms of toxicity, a group of academic, government, and industry scientists, formed under the leadership of the ILSI Health and Environmental Sciences Institute (HESI), developed a series of case studies. These case studies included acetaminophen, butadiene, ethylene glycol, formaldehyde, manganese, methylene chloride, peroxisome proliferator-activated receptor (PPAR), progesterone/hydroxyflutamide, propylene oxide, vinyl acetate, vinyl chloride, vinylidene chloride, and zinc. The case studies formed the basis for technical discourse at two scientific workshops in 2003.

Effect of the multidrug resistance protein on the transport of the antiandrogen flutamide

Prostate cancer is the most common noncutaneous malignancy of American men. Although it can be initially treated with androgen deprivation therapy, tumors that relapse become resistant to future hormonal manipulation. We previously found that the multidrug resistance protein (MRP), MRP1, is overexpressed in advanced stage and grade human prostate cancer and is negatively regulated by p53. In this study, we sought to determine whether the cellular accumulation of the antiandrogen flutamide, a drug commonly used in the treatment of prostate cancer, is affected by MRP1 expression. There were significant differences between the wild-type and MRP1-overexpressing cells in efflux and accumulation of flutamide and hydroxyflutamide, its active metabolite. In contrast, transport of dihydrotestosterone was not affected by MRP1. Treating the cells with leukotriene D4, a known MRP1 substrate, or VX-710, an MRP1 modulator, restored flutamide and hydroxyflutamide accumulation. Finally, intracellular glutathione depletion with buthionine sulfoximine or energy depletion using 2-deoxy-D-glucose/sodium azide restored flutamide accumulation to that of parental cells while incubating the cells at 4 degrees C abolished MRP1-mediated transport. In summary, these studies indicate that flutamide and hydroxyflutamide but not dihydrotestosterone are transported by MRP1 and that these findings may contribute to our understanding of resistance to hormone refractory prostate cancer.

Hydroxypropyl-beta-cyclodextrin-flutamide inclusion complex. II. Oral and intravenous pharmacokinetics of flutamide in the rat

PURPOSE

The objective of this work was to determine the pharmacokinetics of flutamide (FLT) and its active metabolite, 2-hydroxy-flutamide (FLT-2-OH) in rats, following formulation in hydroxypropyl-Beta-cyclodextrin (FLT-HPBetaCyD).

METHODS

The pharmacokinetics of FLT-HPBetaCyD, FLT-suspension (FLT-SUSP), and FLT-solution (FLT-COSOLV) were compared after oral (p.o.) and intravenous (i.v.) administration, respectively. In a non-crossover design, male Sprague-Dawley rats received each formulation as a single oral dose [15 mg (54 micro mol) FLT/kg] by oral gavage, or single i.v. dose [1.6 mg (5.8 micro mol) FLT/kg] via an indwelling jugular vein catheter. FLT and its metabolite, FLT-2-OH, were determined in plasma and urine aliquots by an HPLC method.

RESULTS

In a preliminary in vitro experiment, using the dialysis bag dissolution method, 80% of a test dose of FLT was released from lyophilized FLT-HPBetaCyD into simulated gastric juice within 2 h, compared to less than 5% release from commercial FLT powder (FLT-SUSP). Following oral FLT-HPBetaCyD, the mean area under the plasma concentration curve (AUC(0- infinity)) for FLT, was 1580 +/- 228 ng x h/mL, with the maximum plasma concentration (Cmax; 1297 +/- 127 ng/mL) at 0.5 h (Tmax) after administration. The AUC(0- infinity) and C(max) were significantly higher than after FLT-SUSP (AUC(0- infinity) 748 +/- 206 ng x h/mL; C(max) 230 +/- 111 ng/mL and T(max) 2.33 +/- 0.29 h, respectively). After i.v. FLT-HPBetaCyD, the FLT AUC(0- infinity) was 1355 +/- 162 ng x h/mL, compared to 1421 +/- 283 ng x h/mL for FLT-COSOLV. FLT C(max) were 714 +/- 144 mL/h and 735 +/- 88 mL/h, respectively. The respective volumes of distribution (V(z)) were 369 +/- 191 mL and 242 +/- 25 mL. The plasma concentration-time profile and pharmacokinetic parameters of FLT after FLT-HPBetaCyD and FLT-COSOLV did not differ significantly. The pharmacokinetic parameters for FLT-2-OH were formulation independent after i.v. dosing, but AUC(0- infinity); C(max) and T(max), values were substantially greater with the FLT-HPBetaCyD in the oral study (40269 +/- 5875 ng x h/mL, 4062 +/- 502 ng/mL, and 3.50 +/- 0.41 h, respectively).

CONCLUSIONS

FLT from FLT-HPBetaCyD was released rapidly into solution in vitro and in vivo. FLT-HPBetaCyD improved oral bioavailability relative to FLT-SUSP. Intravenous pharmacokinetic profiles for both FLT and FLT-2-OH were identical following either FLT-HPBetaCyD or FLT-COSOLV, indicating that the FLT-HPBetaCyD formulation behaved as a true solution.

Treatment with flutamide decreases cortisol clearance: implications for therapy in congenital adrenal hyperplasia

BACKGROUND

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is characterized by a defect in cortisol and often aldosterone secretion, and adrenal hyperandrogenism. Current treatment is to provide adequate glucocorticoid and mineralocorticoid substitution to prevent adrenal crises and to suppress excess adrenocortical androgen secretion. Anti-androgen therapy with flutamide is an option that allows control of hyperandrogenism without recourse to supraphysiological doses of glucocorticoid.

METHODS

We examined the pharmacokinetic parameters of hydrocortisone administered i.v. as a bolus at a dose of 15 mg/m2 in a 17.3 year-old female patient with classic CAH before and four weeks after institution of flutamide treatment by determining serum cortisol concentrations at 10 min intervals for 6 h following the i.v. bolus of hydrocortisone.

RESULTS

Treatment with flutamide resulted in a decrease in cortisol clearance from 420 ml/l to 305 ml/l (27% reduction), and a decrease in volume of distribution from 51.61 to 451 (12.9% reduction). The half-life of cortisol increased from 85.3 min to 102.1 min.

CONCLUSIONS

Flutamide treatment decreases cortisol clearance, thereby prolonging its half-life. These findings indicate that a reduction in the daily dose of glucocorticoid replacement may need to be considered when flutamide is added to the treatment regimen of patients receiving hydrocortisone.

Determination of 2-hydroxyflutamide in human plasma by high-performance liquid chromatography and its application to pharmacokinetic studies

Flutamide is a potent antiandrogen used for the treatment of prostatic cancer. Flutamide undergoes extensive first-pass metabolism to the pharmacologically active metabolite 2-hydroxyflutamide. A simple, sensitive, precise, accurate and specific HPLC method, using carbamazepine as the internal standard, for the determination of 2-hydroxyflutamide in human plasma was developed and validated. After addition of the internal standard, the analytes were isolated from human plasma by liquid-liquid extraction. The method was linear in the 25 to 1,000 ng/ml concentration range (r>0.999). Recovery for 2-hydroxyflutamide was greater than 91.4% and for internal standard was 93.6%. The limit of quantitation was 25 ng/ml. Inter-batch precision, expressed as the relative standard deviation (RSD), ranged from 4.3 to 7.9%, and accuracy was better than 93.9%. Analysis of 2-hydroxyflutamide concentrations in plasma samples from 16 healthy volunteers following oral administration of 250 mg of flutamide provided the following pharmacokinetic data (mean+/-SD): Cmax, 776 +/- 400 ng/ml; AUC(0-infinity), 5,368 +/- 2,689 ng h/ml; AUC(0-t) 5,005 +/- 2,605 ng h/ml; Tmax 2.6 +/- 1.6 h; elimination half-life, 5.2 +/- 2.0 h.

Comparative study of the clinical efficacy of two dosing regimens of flutamide

PURPOSE

We performed a randomized trial to compare the efficacy and toxicity of a new dose of flutamide (500 mg QD) with the currently recommended dose (250 mg q8h) in the treatment of advanced prostate cancer. The primary endpoints were percent of patients having normalization of prostate specific antigen (PSA), time to normalization, and percent change from baseline. Secondary endpoints were quality of life and toxicity.

PATIENTS

Altogether, 440 men aged 46 to 94 years (mean 71 years) with confirmed stage M(1) disease, documented PSA rise >0.2 ng/mL, ECOG status 0 to 2, no second neoplasm, no liver function tests > or = 1.5-fold normal values, and no previous treatment for metastatic disease were entered in the trial.

RESULTS

The PSA normalized by week 12 in 71% of the patients receiving 500-mg dose and 75% of those receiving the standard dose. The percent change in PSA was 89% and 96%, respectively. The treatment groups were not significantly different with respect to the incidence of adverse events: 71% v 68% in the 500-mg and 250-mg arms, respectively (P = 0.337).

CONCLUSIONS

When combined with castration, 500 mg of flutamide appears to be equally effective in lowering serum PSA and is not significantly more toxic than conventional dosing. The use of 500 mg QD instead of the standard 250 mg q8h would result in a cost savings of 30%.

New topical antiandrogenic formulations can stimulate hair growth in human bald scalp grafted onto mice

The purpose of this study was to test the ability of topical formulations of finasteride and flutamide to re-enlarge hair follicles in male-pattern baldness. This was evaluated by an experimental model of human scalp skin graft transplanted onto SCID mice. A comparison was made between formulations containing finasteride and flutamide, and a vehicle formulation in terms of the mean hairs per graft, length, diameter of the shafts, and structures of the growth stages of the hair. Flutamide and finasteride had a significantly higher effect (P<0.05) than the placebo in all the tested parameters, but flutamide demonstrated more hair per graft and longer hair shafts than finasteride (P<0.05). The number of hairs per graft for flutamide and finasteride groups were 1.22+/-0. 47 and 0.88+/-0.95 hairs/0.5 mm2 graft, respectively, versus 0. 35+/-0.6 hairs/graft for vehicle-treated graft. Similarly, hair lengths for flutamide and finasteride were 5.82+/-0.50 and 4.50+/-0. 32 mm, respectively, versus 2.83+/-0.18 mm for the vehicle-treated grafts. An in vitro diffusion study of flutamide gel using hairless mouse skin demonstrated the beneficial effect of the vehicle composition in comparison with a hydroalcoholic solution or a gel containing no penetration enhancer. It is therefore suggested that this topical composition containing flutamide or finasteride may effectively result in regression of male-pattern baldness.

Dissolution rate limited bioavailability of flutamide, and in vitro - in vivo correlation

Flutamide is due to its properties as a practically water-insoluble, high-dose drug substance a typical representative of a drug with particle size limited dissolution rate and bioavailability. An in vitro dissolution test method comprising of standard paddle stirrer, round-bottomed vessel of 4 l capacity, and 0.1 N hydrochloric acid with 0.5% of sodium lauryl sulphate as dissolution medium, was developed. The dissolution method was shown discriminatory and predictive regarding bioavailability of conventional 250 mg flutamide tablets with different in vitro dissolution rates. Relative bioavailability of flutamide from the tablets, determined as AUC of the active metabolite 2-hydroxyflutamide in healthy male subjects, could be correlated with drug amount dissolved during 45 min in the in vitro test. Also bioavailability data from four different biostudies could be compared utilising the calculated ratios R(AUC) and R(Diss.) for the test and reference formulations in the individual studies. It is suggested that the concept of R(AUC) and R(Diss.) can also be applied to other orally administered, poorly soluble, high-dose drug substances with dissolution rate limited bioavailability.

Pharmacokinetics of 2-hydroxyflutamide, a major metabolite of flutamide, in normal and CCl4-poisoned rats

AIM

To study the pharmacokinetics of 2-hydroxyflutamide (HF), a major active metabolite of flutamide (Flu), in normal and CCl4-poisoned rats.

METHODS

Normal and CCl4-poisoned rats were given i.g. HF 25 mg.kg-1. HF concentrations of plasma were determined by HPLC with YWG C 18 column, Flu was used as an internal standard. The mobile phase was composed of methanol: water = 3:2 (vol), and absorbance was measured at lambda 295 nm.

RESULTS

HF elimination was inhibited in CCl4-poisoned rats compared with normal rats. K decreased from (0.11 +/- 0.05) to (0.05 +/- 0.01) h-1 (P < 0.01), T1/2 was prolonged from (6.8 +/- 1.9) to (14 +/- 4) h (P < 0.01), Cl decreased from (0.18 +/- 0.06) to (0.12 +/- 0.02) L.kg-1.h-1 (P < 0.05), AUC increased from (149 +/- 47) to (226 +/- 54) mg.L-1.h (P < 0.05).

CONCLUSION

This HPLC assay was sensitive and precise, and the elimination of HF was inhibited due to CCl4 poisoning.

Correlation between proliferation, apoptosis, and angiogenesis in prostate carcinoma and their relation to androgen ablation

BACKGROUND

Proliferation, apoptosis, and angiogenesis are essential for carcinogenesis. Little is known regarding the relation between proliferation, apoptosis, and angiogenesis in untreated prostate carcinoma as well as alterations associated with androgen ablation.

METHODS

Eighty patients who underwent radical prostatectomy for clinically localized prostate carcinoma were recruited for the study. The study population included 2 groups: 35 patients receiving 3-month neoadjuvant hormonal treatment using a combination of luteinizing hormone-releasing hormone analogue and the antiandrogen flutamide (NHT group) and 45 patients without prior treatment (non-NHT group). The authors measured the Ki-67 labeling index (Ki-67 LI) by MIB-1 immunohistochemistry, the apoptotic index (AI) by the terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labeling technique, and intratumoral microvessel density (IMVD) by CD31 immunohistochemistry on serial sections of formalin fixed, paraffin embedded tissues. Correlations among these parameters were examined in both groups.

RESULTS

A significant decrease in the Ki-67 LI coupled with a significant increase in AI was found in the NHT group compared with the non-NHT group, whereas IMVDs in both groups were not significantly different. AI was related to IMVD inversely in the non-NHT group (correlation coefficient [r] = -0.327; P = 0.03); in contrast, AI was related to IMVD positively in the non-NHT group (r = 0.579; P < 0.001). The Ki-67 LI was related to AI significantly in the non-NHT group but not in the NHT group. There was no correlation between Ki-67 LI and IMVD in either group.

CONCLUSIONS

Correlations between proliferation, apoptosis, and angiogenesis in prostate carcinoma are altered significantly in association with androgen ablation. The results indicate that spontaneous apoptosis is suppressed by neovascularization, whereas hormone-induced apoptosis is enhanced in hypervascular tumors.

Pharmacokinetics of flutamide in patients with renal insufficiency

AIMS

The aim of this study was to determine the pharmacokinetic parameters of flutamide, a nonsteroidal antiandrogenic compound, and its pharmacologically active metabolite, hydroxyflutamide, in renal insufficiency. Haemodialysis (HD) clearance of flutamide and hydroxyflutamide was also determined.

METHODS

Pharmacokinetic parameters were assessed for flutamide and hydroxyflutamide in 26 male subjects with normal renal function (creatinine clearance by 24 h urine collection, CLcr, greater than 80 ml min(-1) 1.73 m(-2); n=6) or reduced renal function; CLcr=50-80 (n=7), 30-49 (n=3), 5-29 (n=4), and <5 ml min(-1) 1.73 m(-2)-HD (n=6), following a single, oral 250 mg flutamide dose. Subjects undergoing HD received a second 250 mg dose of flutamide 4 h prior to HD; blood and dialysate were collected during HD to determine dialysability of flutamide and hydroxyflutamide.

RESULTS

Cmax, tmax, AUC, t1/2, and renal clearance of flutamide and hydroxyflutamide did not differ between groups. Less than 1% of the dose appeared in dialysate as hydroxyflutamide. No serious adverse events were observed.

CONCLUSIONS

Renal function did not affect flutamide nor hydroxyflutamide disposition. HD did not alter hydroxyflutamide pharmacokinetics. Dosing adjustments for renal impairment or HD are not indicated for flutamide.

Clinical pharmacokinetics of the antiandrogens and their efficacy in prostate cancer

Prostatic cancer is the second most common cause of cancer death in males. Treatment by radical prostatectomy and radiotherapy is useful in the early stages of the disease. Whenever metastases occur, patients are usually treated by surgical (orchidectomy) or medical [gonadotropin releasing hormone (GnRH) analogue] castration. This form of treatment is, however, associated with unwanted adverse effects, such as flushing, loss of libido and potency and all patients ultimately escape therapy after a delay of 1 to 2 years. For this reason antiandrogens have been developed as another means of endocrine ablation therapy. Antiandrogens fall in 2 groups of which the first group, the steroidal antiandrogens such as cyproterone acetate (CPA), have a direct blocking effect at the cellular level but also inhibit testosterone production by their additional gestagenic properties blocking gonadotropin secretion. Except in preventing the flare-up associated with the start of GnRH analogue therapy and in reducing flushing, no evidence exist of any superiority for CPA over classical therapy in terms of adverse effects and survival. The second group, the nonsteroidal or 'pure' antiandrogens, only block androgens at the cellular level without any central effects. In contrast with other forms of castration, patients on pure antiandrogens as monotherapy preserve their sexual function and potency, at the expense of a slightly inferior androgen blockade and gynecomastia. These latter effects are explained by a compensatory rise in androgens as a result of the blockade at the central level, which weakens the androgen blockade, and by peripheral aromatisation of the increased androgens to oestrogens. In addition, some evidence exist that pure antiandrogens improve survival if combined with other forms of castration as they also inhibit the adrenal androgens, the so-called maximal androgen blockade (MAB). If patients escape control under MAB, a trial of stopping the antiandrogen must always be considered, as some tumours have 'learned' to be activated by these drugs. At the moment it is not yet clear if antiandrogens are of any benefit in downstaging the extent of disease before prostatectomy and/or radiotherapy. Of the currently known pure antiandrogens, bicalutamide offers some advantages over flutamide as it possesses a much longer half-life, allowing a once daily regimen, and has advantages over nilutamide in terms of fewer adverse effects.

Pharmacokinetics of flutamide and its metabolite 2-hydroxyflutamide in normal and hepatic injury rats

AIM

To develop a new HPLC assay to study the pharmacokinetics of flutamide (Flu) and its active metabolite 2-hydroxyflutamide (HF) in rats.

METHODS

Normal or hepatic injury rats were given i.g. Flu 50 mg.kg-1. Reverse phase HPLC was developed with a mu-Bondapak C 18 column. Internal standard was methyltestosterone. The mobile phase was a mixture of methanol:acetonitrile:water:diethyl ether = 40:20:35:1 (vol). Absorbance was measured at lambda 234 nm.

RESULTS

The pharmacokinetic parameters of Flu were as follows: in normal rats, K = 0.62 +/- 0.16 h-1, Cl = 6.0 +/- 1.0 L.kg-1.h-1, AUC = 8.6 +/- 1.3 mg.L-1.h, Cmax = 2.4 +/- 0.7 mg.L-1; in hepatic injury rats, K = 0.16 +/- 0.03 h-1, Cl = 0.63 +/- 0.29 L.kg-1.h-1, AUC = 100 +/- 44 mg.L-1.h, Cmax = 6.7 +/- 2.8 mg.L-1. The pharmacokinetic parameters of HF were as follows: in normal rats, K(m) = 0.07 +/- 0.01 h-1, AUC = 219 +/- 22 mg.L-1.h, Cmax = 8.6 +/- 0.6 mg.L-1; in hepatic injury rats, K(m) = 0.05 +/- 0.01 h-1, AUC = 170 +/- 42 mg.L-1.h, Cmax = 3.8 +/- 0.8 mg.L-1. There were significant differences between the parameters of normal and hepatic injury rats (P < 0.01) except AUC of HF (P > 0.05).

CONCLUSION

This HPLC assay was sensitive and precise, and the elimination of Flu and HF was inhibited significantly due to hepatic injury.

Bioequivalence evaluation of two flutamide preparations in healthy female subjects

In the present study two different preparations containing 250 mg flutamide (3'-trifluoromethyl-4'-nitro-2-methyl-propionylanilide, CAS 13311-84-7) were compared in 20 female subjects. The trial was performed in a randomized two-way cross-over design. Each subject received one tablet with 250 mg flutamide in each period. The two treatment periods were separated by a wash-out phase of 7 days. Blood samples were obtained just before dosing and 18 times during the subsequent 36 h. The plasma concentrations of flutamide, 2-hydroxyflutamide and trifluoromethylnitroaniline were determined by HPLC with UV-detection. Due to the low plasma levels of the parent drug flutamide, the data of the pharmacologically active metabolite 2-hydroxyflutamide (CAS 52806-53-8) were used for bioequivalence assessment. The following mean values were obtained after administration of the test and reference preparation respectively: Flutamide: AUC0-36 = 95.82 ng.h/ml vs 93.33 ng.h/ml, Cmax = 44.78 ng/ml vs 38.73 ng/ml, tmax = 1.71 h vs 1.66 h, 2-hydroxyflutamide: AUC0-infinity = 6090.73 ng.h/ml vs 6068.83 ng. h/ml, Cmax = 772.74 ng/ml vs 779.84 ng/ml, tmax = 2.21 h vs 2.17 h, t1/2 = 8.21 h vs 8.32 h, trifluoromethylnitroaniline: AUC0-infinity = 1771.87 ng.h/ml vs 1701.44 ng.h/ml, Cmax = 173.36 ng/ml vs 171.32 ng/ml, tmax = 2.74 h vs 2.63 h, t1/2 = 10.75 h vs 9.83 h. The two preparations proved to be bioequivalent.

[Phase I study of flutamide, a nonsteroidal antiandrogen, in patients with prostatic cancer]

A phase I study of orally administered flutamide (a pure anti-androgen) was performed in 26 patients with prostatic cancer. No side effects were observed in 11 patients receiving single doses of either 125, 250, 375 or 500 mg. However, in the daily dosing schedule of 375, 750, 1125 and 1,500 mg/day doses, where medication was taken in three divided doses, discomfort in the stomach, nausea, vomiting and anorexia were experienced in one of the four patients receiving the highest dose of 1,500 mg. Nine patients receiving the other doses did not complain of toxic symptoms. Laboratory values did not change in the three patients receiving the lowest 375 mg/day dose, but elevation of transaminase was observed in five of the nine patients given higher doses. This elevation was observed in all the three patients receiving 1,500 mg/day dose. Among the serum hormone levels, significant increases of luteinizing hormone were observed. As for efficacy, objective responses were observed in two of the three patients in each of the four daily dosing groups. Improvement of pain, voiding obstruction symptoms, and performance status were also observed. Flutamide was found to be absorbed rapidly and to exist as a hydroxylated form (hydroxy-flutamide) in the plasma. The half-life of hydroxy-flutamide was similar in the single and daily administration, but the peak concentration and area under the concentration versus time curve in the daily administration became greater than those in the single administration. In conclusion, flutamide should be examined for efficacy and safety using doses of 375 to 1,125 mg/day in the phase II study.

Metabolic activation of the nitroaromatic antiandrogen flutamide by rat and human cytochromes P-450, including forms belonging to the 3A and 1A subfamilies

The in vitro metabolic activation of flutamide, a nitroaromatic antiandrogen which produces hepatitis in a few recipients, was first studied with male rat liver microsomes. There was no electron spin resonance evidence for the reduction of flutamide by reduced nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P-450 reductase into a nitro anion free radical. In contrast, flutamide was oxidatively transformed by cytochrome P-450 into reactive metabolite(s) that covalently bound to microsomal proteins. Covalent binding required oxygen and NADPH, and was decreased by the nucleophile glutathione and by the cytochrome P-450 inhibitors SKF 525-A, piperonyl butoxide and troleandomycin (an inhibitor of the cytochrome P-450 3A subfamily). Covalent binding was increased markedly by pretreatment with dexamethasone (an inducer of the cytochrome P-450 3A subfamily) and moderately by pretreatment with beta-naphthoflavone (an inducer of the 1A family). Covalent binding was immunoinhibited markedly by anticytochrome P-450 3A immunoglobulin G and moderately by anticytochrome P-450 1A immunoglobulin G. Covalent binding was much lower with liver microsomes from female rats (not expressing P-450 3A2). Covalent binding of flutamide also occurred with human liver microsomes (where it was inhibited by troleandomycin), and with yeast microsomes expressing human liver cytochromes P-450 1A1, 1A2 or 3A4. We concluded that flutamide was oxidatively transformed into chemically reactive metabolite(s) by rat and human cytochromes P-450, including forms belonging to the 3A and 1A subfamilies.

A rationale for the use of non-steroidal anti-androgens in the management of prostate cancer

Flutamide is a non-steroidal anti-androgen which has been used to treat prostate cancer. Results to date indicate that flutamide is as effective as other conventional therapy. It has only moderate activity in patients in whom conventional hormonal therapy has previously failed, but appears to be beneficial when combined with an LHRH agonist.

Flutamide. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in advanced prostatic cancer

Flutamide, a nonsteroidal antiandrogenic drug devoid of hormonal agonist activity, is used in the treatment of advanced prostate cancer. In previously untreated patients, flutamide 750 mg daily given alone is of comparable efficacy to diethylstilbestrol (stilboestrol) 1 or 3 mg daily and estramustine 560 or 840 mg daily, but has the potential advantages of fewer cardiovascular effects and maintenance of some sexual potency. Its greatest therapeutic potential is as a component of combination androgen blockade, where administration with an agonist analogue of gonadotrophin-releasing hormone (GnRH) [luteinising hormone-releasing hormone (LH-RH)] in both initial uncontrolled and randomised studies increased survival time relative to GnRH agonist monotherapy or orchidectomy. Subsequent multicentre trials, however, have been unable to confirm an improvement in survival time. Thus, while there seems to be little doubt that flutamide prevents the initial disease flare caused by GnRH agonists, an improvement in remission rate and survival remains contentious. Flutamide is generally well tolerated and is suitable monotherapy in patients with previously untreated advanced prostatic cancer who wish to preserve sexual potency. However, full assessment of the role of combination androgen blockade awaits publication of the final results of ongoing multicentre trials.

Steady-state hydroxyflutamide plasma levels after the administration of two dosage forms of flutamide

A bioavailability study of randomized cross-over design was carried out in eight volunteers who were given a 48-h flutamide treatment consisting of 250-mg tablets three times daily or 400-mg sustained-release tablets twice daily, followed 3 weeks later by the alternative dosage form. Just before the last dose and 15 times during the subsequent 24 h, blood samples were obtained for the determination of plasma hydroxyflutamide (the active metabolite of flutamide) levels by high-performance liquid chromatography. No statistically significant differences between the two dosage forms were found for the lag time, rate of initial increase in concentration, peak plasma concentration, mean hydroxyflutamide concentration within one dosing interval or 24-h AUC value. One subject presented mild and transient nausea during both treatment periods. After the first treatment period (250-mg tablets), an increase in serum bilirubin was observed in another volunteer, who was withdrawn from the study. It may be concluded that both dosage forms were bioequivalent.

Flutamide: an antiandrogen for advanced prostate cancer

Flutamide is a nonsteroidal pure antiandrogen that acts by inhibiting the uptake and/or binding of dihydrotestosterone to the target cell receptor, thus interfering with androgen action. Flutamide is well absorbed orally and extensively metabolized; its active metabolite, 2-hydroxyflutamide, is formed rapidly and excreted almost entirely by the kidneys. Clinical studies in prostate cancer patients have demonstrated efficacy with flutamide monotherapy in patients who had received no prior treatment, in untreated patients with combined androgen blockade concomitantly with a luteinizing hormone-releasing hormone (LHRH)-agonist, and in relapsed patients. A randomized, placebo-controlled trial demonstrated a 26 percent increase in median survival for patients treated with leuprolide plus flutamide compared with leuprolide plus placebo. When given as monotherapy and in combination with an LHRH-agonist, flutamide is well tolerated. The usual adverse effects are gynecomastia and mild diarrhea when given as a single agent. In combination with an LHRH-agonist, hot flashes, loss of libido, impotence, mild nausea and vomiting, gynecomastia, and diarrhea are commonly reported. However, only diarrhea occurred more frequently in patients treated with leuprolide plus flutamide than in those treated with leuprolide plus placebo. Flutamide is indicated in combination with an LHRH-agonist (e.g., leuprolide) as initial therapy in metastatic (stage D2) prostate cancer. The usual dose is 250 mg po tid given at eight-hour intervals and started concurrently with the LHRH-agonist. Formulary addition is recommended.

Pharmacology and pharmacokinetics of flutamide

Flutamide is rapidly metabolized by hydroxylation of the side chain to SCH 16423 (alpha, alpha, alpha-trifluoro-2-methyl-4'-nitro-m-lactotoluidide), the major metabolic product in all species studied, which is biologically active in vivo and in vitro studies. Flutamide exhibits its antiandrogenic activity by inhibiting androgen uptake and/or inhibition of nuclear binding of the androgens in the target tissues. At daily doses from 1 to 50 mg/kg body weight, flutamide reduced seminal vesicle and ventral prostate weights of intact male rats without affecting sexual potency. In addition, flutamide reduced the rate of DNA synthesis in the prostate of rats to a greater degree than other steroidal antiandrogens. The antiandrogenic activity was corroborated by the inhibition of androgen-induced prostate hypertrophy in orchiectomized rats through the use of testosterone, testosterone propionate, dihydrotestosterone, androstenedione, and dehydroepiandrosterone. Flutamide, given orally, reduced prostatic size in aged dogs with benign prostate hyperplasia after six weeks and one year. The baboon prostate was also reduced in size when flutamide was administered three times a week for four weeks.

Flutamide. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in advanced prostatic cancer

Flutamide is a non-steroidal antiandrogenic drug devoid of hormonal agonist activity. Flutamide appears to be a specific antiandrogen only at androgen-dependent accessory genital organs. Its pharmacological activity is due substantially to the principal metabolite, 2-hydroxyflutamide. In comparative trials involving small numbers of patients with previously untreated advanced prostatic cancer, flutamide 750mg daily is comparable with stilboestrol 1 or 3mg daily and with estramustine 560 or 840mg daily. Treatment of newly diagnosed advanced prostatic cancer with flutamide plus a luteinising hormone releasing hormone (LHRH) agonist has produced very promising results, and appears to prolong survival relative to that achieved with leuprolide alone. However, these results require confirmation in suitably designed prospective studies. In previously treated patients refractory to castration, flutamide 750mg daily appears comparable in efficacy to estramustine phosphate 600 mg/m2 daily. Apart from a high incidence (34 to 100%) of gynaecomastia flutamide monotherapy is usually well tolerated, and has the advantage of preserving libido and sexual potency in at least 80% of patients. Gynaecomastia is infrequent, however, when flutamide is used in conjunction with surgical castration or an LHRH agonist. Thus, flutamide is a suitable alternative to other systemic treatment in patients with advanced prostatic cancer who wish to preserve sexual potency. In combination with an LHRH agonist flutamide may become a first-line agent for previously untreated patients with cancer of the prostate.

Single and multiple dose pharmacokinetic evaluation of flutamide in normal geriatric volunteers

Single dose and steady-state pharmacokinetics of flutamide (F) and its active plasma metabolite, hydroxyflutamide (HF) were studied in twelve healthy geriatric volunteers administered 250 mg flutamide capsules on day 1 and 250 mg flutamide capsules three times a day on days 2 through 9. After oral administration, F was rapidly absorbed and metabolized. It was present in the plasma in small and variable concentrations, which precluded quantitative assessment of pharmacokinetic parameters for individual subjects. Steady-state plasma concentrations were reached on or before Day 6. The mean steady state Cmax (Day 9), 112.7 ng/ml, occurred at 1.3 hr. Pharmacokinetic analysis of mean data at steady-state gave a distribution and elimination half-life of 0.8 hr and 7.8 hours, respectively. The plasma levels for HF were much higher and less variable than F. The mean Cmax for HF averaged 894 ng/ml at 2.7 hours after a single dose and 1719 ng/ml (Day 9) at 1.9 hr after multiple doses. The distribution and elimination half-lives of HF at steady-state were 1.9 and 9.6 hours, respectively. The steady-state HF plasma concentrations were also achieved on or before Day 6 and were approximately twice those obtained after a single dose. From this study, it has been demonstrated that the pharmacokinetics of F and HF do not change appreciably upon multiple dosing of 250 mg F capsule given three times a day.

The pharmacokinetics of flutamide and its major metabolites after a single oral dose and during chronic treatment

Flutamide is a nonsteroidal antiandrogen used in the treatment of prostatic carcinoma. We have investigated the disposition of flutamide and its two major metabolites in ten urological in-patients without significant liver or renal disease. After oral administration flutamide is absorbed from the gastrointestinal tract with a tmax of about 2 h. Flutamide undergoes extensive first-pass metabolism, and its major metabolites are 2-hydroxyflutamide and the hydrolysis product 3-trifluoromethyl-4-nitroaniline. After the oral administration of a single dose of 250 mg or 500 mg maximum flutamide plasma concentrations of 0.02 and 0.1 micrograms.ml-1 respectively were observed. Maximum plasma concentrations of 2-hydroxyflutamide for the same flutamide doses were 1.3 and 2.4 micrograms.ml-1 (mean of n = 2 or n = 3). Steady-state concentrations of the biologically active metabolite 2-hydroxyflutamide (0.94 +/- 0.23 micrograms.ml-1, mean +/- SD, n = 5) were found at 2-4 days after the administration of 250 mg every 8 h. The area under the plasma concentration time curve for 2-hydroxyflutamide averaged 11.4 (10.6 and 12.1) and 24.3 (21.5-29.4, n = 3) micrograms.ml-1.h for 250 mg and 500 mg flutamide orally. 2-Hydroxyflutamide and 3-trifluoromethyl-4-nitroaniline were eliminated monoexponentially with half-times of 4.3-21.9 and 4.3-17.2 h (n = 5) respectively.

Plasma levels of hydroxy-flutamide in patients with prostatic cancer receiving the combined hormonal therapy: an LHRH agonist and flutamide

The present study describes a method for the measurement of the plasma levels of hydroxy-flutamide (Flu-OH), the biologically active and main circulating metabolite of flutamide. We have observed that two to four hours after oral administration of 250 mg of flutamide to healthy young men, as well as to patients with prostate cancer, the plasma concentration of Flu-OH reaches a peak at approximately 1.7 microM. The plasma concentration of Flu-OH measured at months 6, 12, and 18 of treatment shows a minimal basal level of 3.4 microM with a maximal increase at 6.8 to 8.5 microM at 2 to 4 hours. Since the serum levels of testosterone in these patients are approximately 1 nM, the levels of the active antiandrogen are at a 5000- to 10000-fold excess. However, due to the low affinity of the antiandrogen for the androgen receptor, it is extremely important to maintain this concentration of the antiandrogen in plasma constant.