Indinavir Alters the Pharmacokinetics of Lamivudine Partially <Emphasis Type="Italic">via</Emphasis> Inhibition of Multidrug and Toxin Extrusion Protein 1 (MATE1)

Purpose

Lamivudine, a characterized substrate for human multidrug and toxin extrusion protein 1 (hMATE1) in vitro, was commonly used with indinavir as a therapy against human immunodeficiency virus (HIV). We aimed to investigate whether mouse MATE1 is involved in the disposition of lamivudine in vivo, and whether there is any transporter-mediated interaction between indinavir and lamivudine.

Methods

The role of MATE1 in the disposition of lamivudine was determined using Mate1 wild type (+/+) and knockout (?/?) mice. The inhibitory potencies of indinavir on lamivudine uptake mediated by OCT2 and MATE1 were determined in human embryonic kidney 293 (HEK 293) cells stably expressing these transporters. The role of MATE1 in the interaction between indinavir and lamivudine in vivo was determined using Mate1 (+/+) and Mate1 (?/?) mice.

Results

The plasma concentrations and tissue accumulation of lamivudine were markedly elevated in Mate1 (?/?) mice as compared to those in Mate1 (+/+) mice. Indinavir significantly increased the pharmacokinetic exposure of lamivudine in mice; however, the effect by indinavir was significantly less pronounced in Mate1 (?/?) mice as compared to Mate1(+/+) mice.

Conclusion

MATE1 played an important role in lamivudine pharmacokinetics. Indinavir could cause drug-drug interaction with lamivudine in vivo via inhibition of MATE1 and additional mechanism.

     

Role of the equilibrative and concentrative nucleoside transporters in the intestinal absorption of the nucleoside drug, ribavirin, in wild-type and ent1(-/-) mice

Ribavirin is frontline treatment for hepatitis C virus infection. To determine the role of nucleoside transporters in the intestinal absorption of orally administered ribavirin, we perfused the intestines of Ent1(-/-) and wild-type mice, in situ, with [(3)H] ribavirin (20, 200, and 5000 μM) in the presence and absence of sodium. The decrease in luminal ribavirin concentration over 30 min was measured at 5 min intervals. Blood samples were collected approximately every 10 min. Ribavirin plus phosphorylated metabolite concentrations (hereafter referred to as ribavirin) were determined in tissue, blood, and plasma by HPLC fractionation and scintillation counting. There was no significant difference between wild-type and Ent1(-/-) mice in intestinal loss of ribavirin at any ribavirin concentration studied. Perfusions without sodium drastically reduced the intestinal loss of ribavirin in both wild-type and Ent1(-/-) mice. After 20 μM ribavirin perfusions, Ent1(-/-) intestinal tissue contained 8-fold greater ribavirin than wild-type mice (p < 0.01). Ribavirin concentrations in the wild-type intestinal tissue were 70-fold higher after 200 vs 20 μM perfusions (p < 0.001), indicating saturation of intestinal ribavirin efflux and possibly other processes as well. Ribavirin plasma concentrations were significantly higher in wild-type mice (2.7-fold) vs Ent1(-/-) mice at 30 min after the 20 μM perfusion (p < 0.01). These results suggest that, at lower intestinal concentrations of ribavirin, concentrative and equilibrative nucleoside transporters are important in the intestinal absorption of ribavirin. At higher intestinal concentrations, these transporters are saturated and other processes in the intestine (transport and/or metabolism) play an important role in the absorption of ribavirin.     

Impact of genetic deficiencies of P-glycoprotein and breast cancer resistance protein on pharmacokinetics of aripiprazole and dehydroaripiprazole

Abstract

1.?We investigated how deficiencies in P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) affect the pharmacokinetics of atypical antipsychotics aripiprazole and its active metabolite (dehydroaripiprazole) using normal Friend leukemia virus strain B (FVB) mice, BCRP knockout (Bcrp[?/?]) mice, and P-gp and BCRP triple knockout (Mdr1a/1b[?/?]Bcrp[?/?]) mice.

2.?While plasma concentrations of aripiprazole and dehydroaripiprazole after oral administration were slightly higher in both Bcrp(?/?) and Mdr1a/1b(?/?)/Bcrp(?/?) mice than in normal FVB mice, the difference was not marked. The increase in absolute bioavailability (F) compared with normal mice (approximately 1.3-fold increase) was comparable between Bcrp(?/?) and Mdr1a/1b(?/?)/Bcrp(?/?) mice. This finding suggests that BCRP may be involved in the intestinal absorption of aripiprazole in mice, albeit with minimal contribution to absorption at best.

3.?In contrast, the brain-to-plasma concentration ratio (K_p,brain) for aripiprazole and dehydroaripiprazole after oral administration was significantly higher in Mdr1a/1b(?/?)/Bcrp(?/?) mice than in normal mice, whereas Bcrp(?/?) mice exhibited K_p,brain values similar to those in normal mice. In addition, the K_p,brain values in Mdr1a/1b(?/?)/Bcrp(?/?) mice were not drastically different from those previously reported in Mdr1a/1b(?/?) mice, suggesting that brain penetration of aripiprazole and dehydroaripiprazole can be affected by P-gp, but with little synergistic effect of BCRP.     

Pharmacokinetics of dietary cancer chemopreventive compound dibenzoylmethane in rats and the impact of nanoemulsion and genetic knockout of Nrf2 on its disposition

The pharmacokinetic disposition of a dietary cancer chemopreventive compound dibenzoylmethane (DBM) was studied in male Sprague‐Dawley rats after intravenous (i.v.) and oral (p.o.) administrations. Following a single i.v. bolus dose, the mean plasma clearance (CL) of DBM was low compared with the hepatic blood flow. DBM displayed a high volume of distribution (Vss). The elimination terminal t_1/2 was long. The mean CL, Vss and AUC_0?∞/dose were similar between the i.v. 10 and 10 mg/kg doses. After single oral doses (10, 50 and 250 mg/kg), the absolute oral bioavailability (F^*) of DBM was 7.4%–13.6%. The increase in AUC was not proportional to the oral doses, suggesting non‐linearity. In silico prediction of oral absorption also demonstrated low DBM absorption in vivo. An oil‐in‐water nanoemulsion containing DBM was formulated to potentially overcome the low F^* due to poor water solubility of DBM, with enhanced oral absorption. Finally, to examine the role of Nrf2 on the pharmacokinetics of DBM, since DBM activates the Nrf2‐dependent detoxification pathways, Nrf2 wild‐type (+/+) mice and Nrf2 knockout (?/?) mice were utilized. There was an increased systemic plasma exposure of DBM in Nrf2 (?/?) mice, suggesting that the Nrf2 genotype could also play a role in the pharmacokinetic disposition of DBM. Taken together, the results show that DBM has low oral bioavailability which could be due in part to poor water solubility and this could be overcome by a nanotechnology‐based drug delivery system and furthermore the Nrf2 genotype could also play a role in the pharmacokinetics of DBM. Copyright © 2010 John Wiley & Sons, Ltd.     

Bio‐distribution and in vivo antioxidant effects of cerium oxide nanoparticles in mice

Cerium oxide nanoparticles have oxygen defects in their lattice structure that enables them to act as a regenerative free radical scavenger in a physiological environment. We performed a comprehensive in vivo analysis of the biological distribution and antioxidant capabilities of nanoceria administered to mice perorally (PO), intravenously (IV), or intraperitoneally (IP) by dosing animals weekly for 2 or 5 weeks with 0.5 mg kg^?1 nanoceria. Next, we examined if nanoceria administration would decrease ROS production in mice treated with carbon tetrachloride (CCl₄). Our results showed that the most extensive and cumulative nano‐deposition was via IV and IP administered while PO administration showed mice excreted greater than 95% of their nanoceria within 24 h. Organ deposition for IV and IP mice was greatest in the spleen followed by the liver, lungs, and kidneys. Elimination for all administration routes was through feces. Nanoceria administration showed no overt toxicity, however, WBC counts were elevated with IV and IP administration. Our in vivo studies show that nanoceria administration to mice with induced liver toxicity (by CCl₄) showed similar findings to mice treated with N‐acetyl cystine (NAC), a common therapeutic to reduce oxidative stress. Taken together, our studies show that nanoceria remains deposited in tissues and may decrease ROS, thereby suggesting that cerium oxide nanoparticles may be a useful antioxidant treatment for oxidative stress. © 2011 Wiley Periodicals, Inc. Environ Toxicol 2013.     

Evaluation of the tissue distribution,excretion, and cytochrome P450 induction studies of a potential antitumor agent,TM-2, in animals using LC-MS/MS

1.?TM-2 is a promising novel semi-synthetic taxane derivative with greater antitumor activity especially against resistant tumors and lower toxicity compared with docetaxel. Information on distribution and excretion of the pharmaceutical in animals, as well as biochemical information relevant to potential drug interactions should normally be evaluated prior to human clinical trials.

2.?The present study investigated the tissue distribution and excretion of TM-2 in animals following intravenous administration for further advancement of the molecule. The potential inductive effect of TM-2 on cytochrome P450 iso-enzymes CYP 3A1 in rats was also evaluated.

3.?The tissue distribution study in mice showed that TM-2 was rapidly dispersed in the various tissues and peak concentration levels were achieved within 0.083–1?h. The highest concentration was detected in pancreas, followed by lung, kidney, spleen, heart and liver. TM-2 was mainly excreted in the feces via the bile (0.14% of the dose) and urinary excretion was minimal (0.007%). TM-2 increased CYP3A1 enzyme activities with time and dose dependence in rat liver microsome.

4.?This important data serve as a useful resource to support further research of TM-2 and allow intelligent assessment of toxicology and in vivo activity testing performed in animals.     

Quantification of ENT1 and ENT2 Proteins at the Placental Barrier and Contribution of These Transporters to Ribavirin Uptake

The aims of this study are to quantify the protein levels of nucleoside transporters in placental microvillous membranes (MVMs) and to clarify the contributions of these transporters to ribavirin uptake at the placental barrier. Placental MVMs of human and rat expressed equilibrative nucleoside transporter (ENT) 1 protein, whereas the expression of ENT2 protein was obscure. Maternal-to-fetal transfer of [³H]ribavirin in rats was much higher than that of [¹⁴C]sucrose. The uptake of [³H]ribavirin by rat placental trophoblast TR-TBT 18 d-1 cells, which functionally express both ENT1 and ENT2 proteins, was saturable, and was significantly inhibited by 0.1 μM nitrobenzylthioinosine, which selectively abolishes ENT1-mediated uptake. Dipyridamole at 10 μM is capable of inhibiting ENT2 as well as ENT1, but a degree of inhibition by 10 μM dipyridamole on [³H]ribavirin uptake was not much different from that by 0.1 μM nitrobenzylthioinosine (ENT1-specific inhibitor). Therefore, ENT2 may contribute little to [³H]ribavirin uptake by these cells. Rat ENT1 cRNA-injected oocytes showed increased [³H]ribavirin uptake compared with water-injected oocytes, while rat ENT2 cRNA-injected oocytes did not. In conclusion, ENT1 protein expressed in placental MVMs appears to play a predominant role in the uptake of ribavirin.     

Brain distribution of ribavirin after intranasal administration

Ribavirin has proved to be effective in vitro against several RNA viruses responsible for encephalitis in humans and animals. However, the in vivo efficacy towards the cerebral viral load seems to be limited by the blood–brain barrier. Since the nose-to-brain pathway has been indicated for delivering drugs to the brain, we investigated here the distribution of ribavirin in the central nervous system (CNS) after intranasal administration. We first tested in vitro ribavirin diffusion from an aqueous solution across a biological membrane, using Franz cells and rabbit nasal mucosa. About 35% of ribavirin permeated in 4 h across the mucosa, after reaching steady-state flux in less than 30 min. In the first in vivo experiment, ribavirin aqueous solution was administered intranasally to Sprague Dawley rats (10 mg/kg). Animals were sacrificed at 10, 20 or 30 min after administration to collect brain areas (cerebellum, olfactory bulb, cerebral cortex, basal ganglia and hippocampus) and biological fluids (cerebrospinal fluid and plasma). Ribavirin, quantified by LC–MS/MS spectrometry, was detected at each time point in all compartments with the highest concentration in olfactory bulb and decreasing in rostro-caudal direction. Two subsequent in vivo experiments compared the nasal route (ribavirin solution) with the intravenous one and the nasal administration of ribavirin solution with ribavirin powder (10 mg/kg). It was found that 20 min after administration, ribavirin concentration in olfactory bulb was similar after intravenous or nasal administration of the ribavirin solution, whereas the powder led to significantly higher levels. Ribavirin was also present in deeper compartments, such as basal ganglia and hippocampus.Even if the mechanisms involved in ribavirin nose-to-brain transport are not clear, these results suggest a rapid extracellular diffusive flux from the nasal epithelium to the olfactory bulb and different CNS areas.     

Hepatitis C virus: quasispecies dynamics,virus persistance and antiviral therapy

Hepatitis C virus (HCV) has been the subject of intense research and clinical investigation due to its worldwide prevalence and major role in chronic liver disease. HCV circulates in vivo as a complex population of different, but closely related, viral variants, commonly referred to as a quasispecies. The introduction of IFN-α plus ribavirin combination therapy was an important breakthrough in the treatment of chronic HCV infection. Nevertheless, the rate of sustained virological response is still unsatisfactory. Viral persistence, a hallmark of HCV, may result from a dynamic control of the host response by the action of non-structural protein 3 of virus. There is a clear need for a search for new antiviral compounds against HCV and for a therapy that efficiently, and with fewer side effects, can attack the virus, modulates the immune response system and reduces the frequency of relapse. As a safe and effective vaccine against HCV remains to be achieved, the development of new antiviral agents, particularly against non-structural proteins of the virus, will be very important for the control of HCV infection.     

Role for α6 nicotinic receptors in l-dopa-induced dyskinesias in parkinsonian mice

l-Dopa-induced dyskinesias are a serious side effect that develops in most Parkinson's disease patients on dopamine replacement therapy. Few treatment options are available to manage dyskinesias; however, recent studies show that nicotine reduces these abnormal involuntary movements (AIMs) in parkinsonian animals by acting at nicotinic acetylcholine receptors (nAChRs). Identification of the nAChR subtypes that mediate this reduction in AIMs is important as it will help in the development of nAChR subtype selective drugs for their treatment. Here we investigate the role of α6β2* nAChRs, a subtype selectively present in the nigrostriatal pathway, using α6 nAChR subunit null mutant (α6(?/?)) mice. Wildtype and α6(?/?) mice were lesioned by unilateral injection of 6-hydroxydopamine (3 μg/μl) into the medial forebrain bundle. They were then given l-dopa (3 mg/kg) plus benserazide (15 mg/kg) 2–3 wk later. l-dopa-induced AIMs developed to a similar extent in α6(?/?) and wildtype mice. However, AIMs in α6(?/?) mice declined to ～50% of that in wildtype mice with continued l-dopa treatment. Nicotine treatment also decreased AIMs by ～50% in wildtype mice, although not in α6(?/?) mice. There were no effects on parkinsonism under any experimental condition. To conclude, the similar declines in l-dopa-induced AIMs in nicotine-treated wildtype mice and in α6(?/?) mice treated with and without nicotine indicate an essential role for α6β2* nAChRs in the maintenance of l-dopa-induced AIMs. These findings suggest that α6β2* nAChR drugs have potential for reducing l-dopa-induced dyskinesias in Parkinson's disease.     

Role of ribavirin in HCV treatment response: now and in the future

Importance of the field: Ribavirin is a broad spectrum antiviral agent that is used with pegylated IFN (Peg-IFN) for HCV treatment. Ribavirin does not significantly reduce HCV viral load when used alone but increases rates of sustained virologic response (SVR) when combined with Peg-IFN. HCV genotype 1 infected patients require higher doses of ribavirin administered for a longer duration of time versus HCV genotypes 2 and 3 patients who respond effectively to Peg-IFN with lower doses of ribavirin and shorter duration of therapy. Higher serum concentrations of ribavirin are associated with higher response rates but also higher rates of hemolytic anemia which is a dose limiting side effect. Alternatives to current therapy are under clinical evaluation.

Areas covered in this review: Systematic literature review of ribavirin use in HCV patients from 1995 to 2009 was conducted.

What the reader will gain: To review the efficacy and safety of ribavirin in current HCV treatment and in new therapies in Phase III clinical trials.

Take home message: Ribavirin is a drug which is essential to produce higher SVR rates both with Peg-IFN and HCV protease inhibitors currently in Phase III clinical trials. Thus, ribavirin is and will remain an important drug to achieving higher SVR rates in HCV infected persons.     

Paritaprevir/ritonavir/ombitasvir and dasabuvir for the treatment of chronic hepatitis C virus infection

Introduction: The use of direct-acting antiviral (DAA) agents against chronic hepatitis C virus (HCV) infections can result in the successful treatment of nearly all patients. Effective antiviral treatments can prevent the progression to cirrhosis and hepatocellular malignancy, and decrease liver-related morbidity and mortality.

Areas covered: Paritaprevir–ritonavir–ombitasvir and dasabuvir (PrOD), with or without ribavirin, is an all-oral regimen approved for the treatment of HCV genotype 1 infections, including patients with compensated cirrhosis. Phase 2 and 3 clinical trials demonstrated the safety and efficacy of this regimen in HCV genotype 1-infected patients who are treatment-naïve and those who have failed peginterferon/ribavirin therapy. Additional studies evaluated the use of PrOD with or without ribavirin among special populations, including patients co-infected with human immunodeficiency virus-1 and HCV, liver transplant recipients with HCV recurrence, and patients with severe renal impairment. Additionally, the combination of paritaprevir-ritonavir-ombitasvir plus ribavirin is found to be highly efficacious, and is now approved in the US, for the treatment of HCV genotype 4 infections.

Expert opinion: The availability and use of interferon-free DAA combination regimens has resulted in a major paradigm shift in the treatment of HCV. PrOD, with or without ribavirin, is an effective, safe and tolerable treatment option.     

Taribavirin for the treatment of chronic hepatitis C

Background: The current standard therapy for chronic hepatitis C virus (HCV), combination therapy with pegylated interferon and ribavirin, is plagued by a number of side effects, most notably anemia. This anemia is typically managed with a reduction of ribavirin dosing, which may lead to reduced efficacy. Taribavirin, an oral prodrug of ribavirin, which has been shown to induce a lesser degree of anemia, is being investigated for the treatment of chronic HCV. Objective: To summarize the clinical trials involving taribavirin and its potential role in the treatment of chronic HCV. Methods: Information was obtained via searches for data related to taribavirin, as well as other current and investigational therapies for chronic HCV. Press releases discussing otherwise unpublished trial outcomes were obtained from the website of Valeant Pharmaceuticals, the producer of Viramidine^® (taribavirin). Conclusion: Taribavirin may increase adherence to therapy for chronic HCV by reducing the need for dose reduction due to anemia. A recent Phase II trial investigating early and sustained virological response showed no statistically significant differences between ribavirin 1000/1200 mg and taribavirin at 800-, 1200-, or 1600-mg dosing, while illustrating a lesser degree of anemia in 800- and 1200-mg dosing of taribavirin. Ongoing studies will continue to examine the efficacy of combination therapy with taribavirin in the place of ribavirin.     

Role of the aryl hydrocarbon receptor and Cyp1b1 in the antiestrogenic activity of 2,3,7,8-tetrachlorodibenzo-<Emphasis Type="Italic">p</Emphasis>-dioxin

The role of aryl hydrocarbon receptor (AhR) and cytochrome P450 (Cyp) 1 family in the antiestrogenic activity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was investigated in vivo. Immature (21 days old) AhR, Cyp1a2, or Cyp1b1 knockout (–/–) mice were treated intraperitoneally with estradiol (E2, 20 ng/mouse per day, for 14 consecutive days) and/or TCDD (200 ng/mouse per day, on days 7, 9, 11, and 13). Uterine wet weight and uterine peroxidase activity (UPA) were measured as markers of estrogen responsiveness. UPA was a better marker of estrogen responsiveness than the uterine wet weight. In AhR wild-type (+/+) mice, UPA (208.1±81.6 units/g tissue) was increased by the administration of E2 (to 297.2±178.7 units/g). The administration of TCDD significantly (p<0.01) decreased the UPA (10.5±3.4 units/g) compared with that in the control mice. Co-administration of TCDD with E2 also significantly (p<0.05) decreased the UPA (18.8±19.9 units/g) compared with that in E2-treated mice. In AhR(–/–) mice, UPA (162.9±146.7 units/g) was significantly (p<0.01) increased by the administration of E2 (486.8±108.2 units/g). In contrast to the results in AhR(+/+) mice, UPA was not affected by the administration of TCDD (51.8±70.6 units/g) compared with control, and co-administration of TCDD with E2 (545.8±189.4 units/g) compared with that in E2-treated mice. In Cyp1a2/1b1(+/+) mice, UPA was significantly (p<0.05) increased by the administration of E2 (70.0±36.4 units/g). Co-administration of TCDD with E2 significantly (p<0.05) decreased the UPA (29.6±22.2 units/g) compared with that in E2-treated mice. In Cyp1a2(–/–) mice, co-administration of TCDD with E2 significantly (p<0.01) decreased the UPA (6.8±5.1 units/g) compared with that in E2-treated mice. In Cyp1b1(–/–) mice, UPA (5.5±8.1 units/g) was significantly (p<0.05) increased by the administration of E2 (56.6±34.1 units/g). In contrast to the results in Cyp1a2/1b1(+/+) mice or Cyp1a2(–/–) mice, UPA was not affected by the co-administration of TCDD and E2 (52.6±30.1 units/g) compared with that in E2-treated mice. This is the first demonstration that Cyp1b1 as well as AhR is involved in the antiestrogenic effects of TCDD.     

Clinical trial: extended treatment duration of peginterferon-alpha2b plus ribavirin for 72 and 96 weeks in hepatitis C genotype 1-infected late responders

Background  The benefits of prolonging peginterferon and ribavirin after 48 weeks of treatment to maximize sustained virological responses (SVR) in hepatitis C virus (HCV) genotype 1-infected patients remain to be understood.
Aim  To investigate whether extended treatment longer than 72 weeks may be superior to 72-week treatment.
Methods  A total of 120 treatment-naïve or retreated patients with HCV genotype 1 were treated with peginterferon-alpha-2b (1.5 μg/kg/week) plus weight-based ribavirin. We had 34 late responders, in whom HCV RNA first became undetectable at week 12–48, and randomized them into three groups receiving standard-dose peginterferon-alpha-2b plus low-dose ribavirin (200 mg/day) for extended 24 weeks (group A), receiving low-dose peginterferon-alpha-2b (0.75 μg/kg/week) plus low-dose ribavirin for extended 48 weeks (group B) or no extended treatment (group C), and evaluated the outcome according to their virological response.
Results  Multivariate analysis showed that the treatment for 96 weeks was identified as a significant, independent factor associated with SVR in HCV genotype 1-infected late responders in comparison with group A [odds ratio (OR), 10.002; P  =   0.080] and group C (OR, 17.748; P  =   0.025).
Conclusion  Extending the treatment duration from 48 weeks to 96 weeks improves SVR rates in genotype 1-infected patients with late virological response to peginterferon-alpha-2b and ribavirin.     

Impact of ribavirin plasma level on sustained virological response in patients treated with pegylated interferon and ribavirin for chronic hepatitis C

Background  The main goal of therapy in hepatitis C virus (HCV) infection is to achieve a sustained virological response (SVR). However, the impact of the pharmacological properties of ribavirin on the SVR has not been fully investigated.
Aim  To evaluate, through a prospective study, the association between ribavirin plasma level and SVR response in HCV patients treated with pegylated interferon (PEG-IFN) and ribavirin.
Patients and methods  Patients treated with PEG-IFN and ribavirin had plasmatic ribavirin dosage at weeks 4 and 12. SVR was evaluated 6 months after the end of treatment.
Results  At week 4, a strong correlation was found between HCV-RNA and C _min of ribavirin plasma level ( r  = −0.376, P  = 0.002) and AUC _0→12h of ribavirin plasma level ( r  = −0.277, P  = 0.018). At week 12, a strong correlation was found between HCV-RNA and C _min of ribavirin plasma level ( r  = −0.384, P  < 0.0001) and AUC _0→12h of ribavirin plasma level ( r  = −0.257, P  = 0.002). In genotype 1 patients, AUC _0→12h ribavirin and C _min were significantly correlated with negative HCV-RNA at week 12 and SVR. In the multiple logistic regression model, the only factor independently associated with SVR in genotype 1 patients was negative HCV-RNA at week 12.
Conclusion  C_min of ribavirin at weeks 4 and 12 was significantly higher in sustained virological responders compared with relapser or nonresponder patients. However, in genotype 1 patients, plasma ribavirin level at weeks 4 and 2 was not associated with SVR.     

The impact of pharmacologic and genetic knockout of P-glycoprotein on nelfinavir levels in the brain and other tissues in mice

Insufficient concentrations of protease inhibitors such as nelfinavir may reduce the effectiveness of HIV dementia treatment. The efflux transporter mdr1 product P-glycoprotein (P-gp) has been demonstrated to play a role in limiting nelfinavir brain levels. The goal of this study was to compare the effect of GF120918 (10 mg/kg, IV), a P-gp inhibitor, on intravenous nelfinavir (10 mg/kg) in vivo disposition and tissue penetration in P-gp-competent mdr1a/1b (+/+) mice versus P-gp double knockout mdr1a/1b (-/-) mice. Intravenous administration with the P-gp inhibitor GF120918 to mdr1a/1b (+/+) mice increased nelfinavir concentrations over a range of 2.3- to 27-fold, whereas nelfinavir distribution in mdr1a/1b (-/-) mice was 2- to 16-fold higher than that in their wild counterparts. Nelfinavir levels after GF120918 coadministration were higher in the heart, liver, and kidneys than those detected with mdr1a/1b knockout mice. In contrast, mdr1a/1b knockout mice exhibited higher nelfinavir levels in the brain (16.1-fold vs. 8.9-fold increase) and spleen (4.1-fold vs. 2.3-fold increase) compared to pharmacological inhibition with GF120918 in wild mice. Most notably, GF120918 provided tissue-specific effects in mdr1a/1b knockout mice with enhanced (p < 0.05) drug accumulation in the brain ( approximately 21-fold) and heart (3.3-fold). Our results suggest mdr1a/1b-independant mechanisms may also contribute to nelfinavir tissue distribution in mice.     

Breast Cancer Resistance Protein and Multidrug Resistance Protein 2 Regulate the Disposition of Acacetin Glucuronides

Purpose

To determine the mechanism responsible for acacetin glucuronide transport and the bioavailability of acacetin.

Methods

Area under the curve (AUC), clearance (CL), half-life (T_1/2) and other pharmacokinetic parameters were determined by the pharmacokinetic model. The excretion of acacetin glucuronides was evaluated by the mouse intestinal perfusion model and the Caco-2 cell model.

Results

In pharmacokinetic studies, the bioavailability of acacetin in FVB mice was 1.3%. Acacetin was mostly exposed as acacetin glucuronides in plasma. AUC of acacetin-7-glucuronide (Aca-7-Glu) was 2-fold and 6-fold higher in Bcrp1 (?/?) mice and Mrp2 (?/?) mice, respectively. AUC of acacetin-5-glucuronide (Aca-5-Glu) was 2-fold higher in Bcrp1 (?/?) mice. In mouse intestinal perfusion, the excretion of Aca-7-Glu was decreased by 1-fold and 2-fold in Bcrp1 (?/?) and Mrp2 (?/?) mice, respectively. In Caco-2 cells, the efflux rates of Aca-7-Glu and Aca-5-Glu were significantly decreased by breast cancer resistance protein (BCRP) inhibitor Ko143 and multidrug resistance protein 2 (MRP2) inhibitor LTC4. The use of these inhibitors markedly increased the intracellular acacetin glucuronide content.

Conclusions

BCRP and MRP2 regulated the in vivo disposition of acacetin glucuronides. The coupling of glucuronidation and efflux transport was probably the primary reason for the low bioavailability of acacetin.

     

Progress towards improving antiviral therapy for hepatitis C with hepatitis C virus polymerase inhibitors. Part I: Nucleoside analogues

Background: With an increasing worldwide burden of liver failure and liver cancer from chronic hepatitis C virus (HCV) infection, discovery and development efforts for new antiviral medicines for HCV are expanding rapidly. Two HCV protease inhibitors (PIs), telaprevir (VX950) and boceprevir (SCH503034), are now furthest along in clinical development, with Phase II data suggesting a potential treatment advance with triple combination regimens comprising a protease inhibitor, pegylated interferon and ribavirin. However, the current data suggest that such regimens will fail to produce sustained virologic responses in ≥ 30 – 40% of patients, and tolerance of interferon/ribavirin treatment regimens is often problematic; hence, there is a need for continued development of new anti-HCV agents to further optimize treatment efficacy and safety. The HCV polymerase (HCV Pol) is an attractive target for antiviral therapy because the gene sequences encoding HCV Pol are relatively conserved across the six main HCV genotypes and the emergence of viral resistance is expected to be relatively slow for pharmaceutical agents, such as nucleoside analogues, that are targeted to the active (catalytic) site of HCV Pol. Methods: This review (Part I) of HCV Pol inhibitors focuses on the scientific rationale and recent development progress for nucleoside-type HCV Pol inhibitors; a subsequent review (Part II) will assess progress with non-nucleosidic HCV Pol inhibitors. Results/conclusions: Early clinical data for several nucleosides targeted to HCV Pol indicate marked antiviral effects and a likelihood of relatively slow HCV resistance, consistent with the profile of nucleosidic inhibitors of HIV and hepatitis B virus infection and supporting potentially important roles for nucleoside agents in optimizing combination therapies for HCV infection. Optimally effective future anti-HCV therapies are likely to be based on multi-class treatment regimens combining polymerase and PIs, together with pegylated interferon and ribavirin or pharmaceutical agents from other mechanistic classes.