Telavancin pharmacokinetics in patients with chronic kidney disease receiving haemodialysis

BACKGROUND

Telavancin is a lipoglycopeptide antibiotic with limited pharmacokinetic data to guide drug dosing in patients receiving haemodialysis.

OBJECTIVES

This study characterized telavancin pharmacokinetics in patients receiving haemodialysis.

PATIENTS AND METHODS

This was a Phase IV, prospective, open-label, single-centre, crossover pharmacokinetic study (ClinicalTrials.gov: NCT02392208). Eight subjects with end-stage kidney disease requiring maintenance haemodialysis (mean ± SD: 47 ± 20 years, 69.5 ± 17.1 kg) received 5 mg/kg telavancin IV 3 h before starting a 3.5 hour haemodialysis treatment with a high-permeability haemodialyser (haemodialysis period). After a 14 day washout period, a second 5 mg/kg dose was administered post-haemodialysis (control period). Telavancin plasma concentrations were measured over a 2 day period after each dose and non-compartmental pharmacokinetic analyses were performed.

RESULTS

The geometric mean (GM) of telavancin overall clearance was 11.2 mL/h/kg (intrinsic clearance and dialytic clearance) in the haemodialysis period and 5.9 mL/h/kg (off-haemodialysis clearance) in the control period [GM ratio (GMR) = 1.89; 90% CI: 1.70-2.10; P < 0.01]. The GM t½ was 13.1 h when haemodialysis occurred 3 h post-dosing in the haemodialysis period but extended to 20.9 h with post-haemodialysis dosing in the control period (GMR = 0.63; 90% CI: 0.54-0.73; P < 0.01). The GM of telavancin plasma concentrations removed by haemodialysis was 27.7%. The GMR of peak plasma concentration and volume of distribution of the haemodialysis period and the control period were 0.88 (90% CI: 0.79-0.98; P = 0.08) and 1.17 (90% CI: 1.05-1.30; P = 0.048), respectively.

CONCLUSIONS

Haemodialysis with high-permeability haemodialysers removes telavancin considerably (∼⅓ of body load). Telavancin 5 mg/kg every 48 h post-haemodialysis dosing is recommended, but dose adjustments may be warranted if haemodialysis starts within 3 h of telavancin administration.

Tumor microenvironment-targeted nanoparticles loaded with bortezomib and ROCK inhibitor improve efficacy in multiple myeloma

Drug resistance and dose-limiting toxicities are significant barriers for treatment of multiple myeloma (MM). Bone marrow microenvironment (BMME) plays a major role in drug resistance in MM. Drug delivery with targeted nanoparticles have been shown to improve specificity and efficacy and reduce toxicity. We aim to improve treatments for MM by (1) using nanoparticle delivery to enhance efficacy and reduce toxicity; (2) targeting the tumor-associated endothelium for specific delivery of the cargo to the tumor area, and (3) synchronizing the delivery of chemotherapy (bortezomib; BTZ) and BMME-disrupting agents (ROCK inhibitor) to overcome BMME-induced drug resistance. We find that targeting the BMME with P-selectin glycoprotein ligand-1 (PSGL-1)-targeted BTZ and ROCK inhibitor-loaded liposomes is more effective than free drugs, non-targeted liposomes, and single-agent controls and reduces severe BTZ-associated side effects. These results support the use of PSGL-1-targeted multi-drug and even non-targeted liposomal BTZ formulations for the enhancement of patient outcome in MM.

Single dose oral ranolazine pharmacokinetics in patients receiving maintenance hemodialysis

Purpose: Ranolazine is a novel anti-angina treatment approved in the United States for chronic stable angina. Ranolazine pharmacokinetics have not been studied previously in patients who receive maintenance hemodialysis. This study describes the pharmacokinetics of ranolazine and three major metabolites (CVT-2738, CVT-2512, CVT-2514) in patients receiving thrice weekly hemodialysis.

Methods: Eight participants receiving maintenance hemodialysis completed this prospective, open-label study (study identifier NCT01435174 at Clinicaltrials.gov). Three participants received a single tablet of ranolazine 500 mg (followed by an interim analysis), and five received 2 tablets of ranolazine 500 mg. Blood samples were collected over 65 h to determine the pharmacokinetic characteristics during and between hemodialysis sessions. Non-compartmental analysis was used to determine the individual pharmacokinetic parameters.

Results: Ranolazine off-hemodialysis elimination phase half-lives were 3.6 and 3.9 h for 500 mg and 1000 mg doses, respectively. The time to maximum concentration ranged from 2 to 18 hours and the average maximum concentration was 0.65 ± 0.27 mcg/mL and 1.18 ± 0.48 mcg/mL for ranolazine 500 mg and 1000 mg dose, respectively. The mean hemodialysis percent reduction ratio for the ranolazine 500 mg dose was 52.3 ± 8.1% and for the ranolazine 1000 mg dose was 69.2 ± 37.6%.

Conclusions: Data on ranolazine dosing in patients receiving maintenance hemodialysis is almost non-existent. Given the extent of pharmacokinetic variability observed with the 500 mg and 1000 mg oral doses of ranolazine, neither can be recommended as a starting dose in patients receiving maintenance hemodialysis. Guided by the information gained form this study about the extent of hemodialytic drug clearance, further multi-dose clinical trials of ranolazine are needed to optimize therapeutic outcomes in this patient population.

Pazopanib plus cetuximab in recurrent or metastatic head and neck squamous cell carcinoma: an open-label, phase 1b and expansion study

BACKGROUND

Angiogenesis is a hallmark of head and neck squamous cell carcinoma (HNSCC), and a mechanism of resistance to EGFR inhibition. We investigated the safety and potential activity of pazopanib, an angiogenesis inhibitor, plus cetuximab, an EGFR inhibitor, in patients with recurrent or metastatic HNSCC.

METHODS

We did an open-label, single-centre, dose-escalation phase 1b trial using a standard 3 + 3 design, followed by an expansion cohort phase. Eligible participants were patients with histologically or cytologically confirmed recurrent or metastatic HNSCC, aged at least 18 years, had measurable disease as per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1, and an Eastern Cooperative Oncology Group performance status of 0-1. During dose escalation, pazopanib oral suspension was administered daily in 8-week cycles at doses of 200 mg/day, 400 mg/day, 600 mg/day, or 800 mg/day, with cetuximab given intravenously once per week (400 mg/m² first dose and 250 mg/m² in consecutive cycles). The primary endpoint was to determine the maximum tolerated dose or recommended phase 2 dose of pazopanib in combination with cetuximab. Analyses were done per protocol. This trial is registered with ClinicalTrials.gov, number NCT01716416, and it is ongoing but closed to accrual.

FINDINGS

Between June 5, 2013, and April 4, 2017, we enrolled 22 patients into the phase 1b, dose-escalation phase of the trial. A maximum tolerated dose of pazopanib in combination with cetuximab was not reached. Single dose-limiting toxic events (all grade 3) during dose escalation occurred with pazopanib 400 mg/day (neutropenia with infection), 600 mg/day (proteinuria), and 800 mg/day (fatigue). The established recommended phase 2 dose for the combination was 800 mg/day of pazopanib during cycles of 8 weeks each, plus cetuximab 400 mg/m² on day 1 of cycle 1, then cetuximab 250 mg/m² weekly. A further nine patients were enrolled into the expansion cohort and treated with the established recommended phase 2 dose. The most common (grade 3-4) adverse events for all patients were hypertension (ten [32%] of 31), lymphocyte count decrease (seven [23%]), and dysphagia (seven [23%]). There were no treatment-related deaths. 11 (35%; 95% CI 19·2-54·6) of 31 patients achieved an overall response, as assessed by the investigator; two (6%) had a complete response and nine (29%) a partial response. Tumour responses were also observed in six (55%) of 11 patients with platinum-naive and cetuximab-naive disease, three (25%) of 12 patients with cetuximab-resistant disease, and five (28%) of 18 patients with platinum-resistant disease.

INTERPRETATION

Pazopanib oral suspension at a dose of 800 mg/day was feasible to administer in combination with standard weekly cetuximab for patients with recurrent or metastatic HNSCC. Encouraging preliminary antitumour activity was observed with this combination therapy and warrants further validation in randomised trials.

FUNDING

GlaxoSmithKline and Novartis.

Tariquidar sensitizes multiple myeloma cells to proteasome inhibitors via reduction of hypoxia-induced P-gp-mediated drug resistance

Multiple myeloma (MM) presents a poor prognosis and high lethality of patients due to development of drug resistance. P-glycoprotein (P-gp), a drug-efflux transporter, is upregulated in MM patients post-chemotherapy and is involved in the development of drug resistance since many anti-myeloma drugs (including proteasome inhibitors) are P-gp substrates. Hypoxia develops in the bone marrow niche during MM progression and has long been linked to chemoresistance. Additionally, hypoxia-inducible transcription factor (HIF-1α) was demonstrated to directly regulate P-gp expression. We found that in MM patients P-gp expression positively correlated with the hypoxic marker, HIF-1α. Hypoxia increased P-gp protein expression and its efflux capabilities in MM cells in vitro using flow cytometry. We reported herein that hypoxia-mediated resistance to carfilzomib and bortezomib in MM cells is due to P-gp activity and was reversed by tariquidar, a P-gp inhibitor. These results suggest combining proteasome inhibitors with P-gp inhibition for future clinical studies.

The role of P-glycoprotein in drug resistance in multiple myeloma

Multiple myeloma (MM) is a malignant neoplastic cancer of the plasma cells that involves the bone marrow. The majority of patients with MM initially respond to chemotherapy, but they eventually become resistant to later drug therapy. One of the reasons for drug resistance in patients with MM is efflux transporters. P-glycoprotein (P-gp) is the most studied of the multidrug resistance proteins, and is up-regulated in response to many chemotherapeutic drugs. This up-regulation of P-gp causes a decrease in the intracellular accumulation of these drugs, limiting their therapeutic efficacy. In this review, we focus on the role of P-gp in drugs used for patients with MM. P-gp has been found to be an important factor with regard to drug resistance in many of the drug classes used in the treatment of MM (proteasome inhibitors, anthracyclines, alkylating agents and immunomodulators are examples). Thus, our further understanding of its mechanism and inhibitory effects will help us decrease drug resistance in patients with MM.

Longitudinal hemodiafilter performance in modeled continuous renal replacement therapy

BACKGROUND/AIMS

With advanced anticoagulation, many institutions operate continuous renal replacement therapy (CRRT) circuits longer than manufacturers' recommendations. This extended use may change hemodiafilter performance and clearance properties. However, hemodiafilter performance over time has not been assessed. We investigated solute clearance over time in modeled CRRT.

METHODS

In vitro continuous hemofiltration (CH) and continuous hemodialysis (CD) were operated for 48 h using AN69 polyacrylonitrile, cellulose triacetate, F70 polysulfone, and Optiflux F160NR polysulfone hemodiafilters with citrated bovine blood. Urea, creatinine, gentamicin, vancomycin, and albumin clearances were assessed in CH (ultrafiltration rates = 1 and 3 l/h). Clearances of urea, creatinine, gentamicin, and albumin, were assessed in CD with dialysate flow rate of 2 l/h.

RESULTS

Solute CH clearances were significantly higher at 3 l/h. Only creatinine and gentamicin clearances were affected by time. Creatinine CD clearance significantly declined at 48 h for all hemodiafilters, especially polysulfone hemodiafilters.

CONCLUSIONS

CRRT duration affects solute transmembrane clearance. Clinicians should consider hemodiafilter age when assessing hemodialysis dose or drug clearance.

Single-dose daptomycin pharmacokinetics in chronic haemodialysis patients

BACKGROUND

Daptomycin has concentration-dependent antibacterial activity against Gram-positive bacteria. Its use is increasing in haemodialysis units. The manufacturer recommends a 4-6-mg/kg dose administered every 48 hrs for patients receiving haemodialysis. However, there are no published data about daptomycin pharmacokinetics and clearance during haemodialysis. The recommended dosing regimen would conflict with asymmetric thrice-weekly haemodialysis, which yields two ~44-hr and one ~68-hr interdialytic periods. This is the first study to evaluate daptomycin pharmacokinetics in haemodialysis patients, assess the extent of daptomycin dialytic removal and model serum concentrations at 44 and 68 hrs.

METHODS

Six otherwise healthy subjects on chronic haemodialysis (55.3 +/- 16.1 years old, three females, 66.2 +/- 14.2 kg) received a single 6-mg/kg dose of daptomycin post-haemodialysis infused over 30 minutes. Serial blood samples were collected for ~44 hrs (pre-next haemodialysis) and throughout the subsequent haemodialysis session with a high permeability haemodialyser. Individual pharmacokinetic parameters determined by compartmental analysis were used to model trough serum concentrations at 44 and 68 hrs with 6-, 8- and 10-mg/kg post-haemodialysis doses.

RESULTS

The haemodialysis session in this trial yielded mean urea and daptomycin reduction ratios of 79.6 +/- 5.8% and 57.6 +/- 9.2%, respectively. Daptomycin half-life was 19.4 +/- 6.5 and 3.8 +/- 1.1 hrs 'off' and 'on haemodialysis', respectively, with minimal rebound 1 hr post-haemodialysis. All modelled trough concentrations at 44 and 68 hrs at all doses exceed typical minimum inhibitory concentration (MIC(90)) values for Staphylococcus aureus and Enterococcus faecalis.

CONCLUSIONS

Daptomycin serum concentrations declined by ~50% after a 4-hr haemodialysis session with a high permeability haemodialyser. A 6-mg/kg i.v. post-haemodialysis thrice-weekly dose should result in sufficient pre-haemodialysis daptomycin serum concentrations even after a 68-hr interdialytic period.

Etanercept clearance during an in vitro model of continuous venovenous hemofiltration

BACKGROUND/AIMS

Etanercept is a tumor necrosis factor-alpha antagonist used in inflammation-mediated conditions. Continuous venovenous hemofiltration (CVVH) has also been used in patients with inflammatory conditions. This study evaluated etanercept clearance using an in vitro CVVH model.

METHODS

Etanercept clearance was assessed in vitro in bovine blood at 1-3 mg/l final serum concentration, and urea control at 750 mg/l. CVVH was performed using polyacrylonitrile, polysulfone, and polymethylmethacrylate filters at 3 l/h ultrafiltrate and 200 ml/min blood flow rates. Transmembrane clearance was estimated using sieving coefficient calculations, and adsorptive removal rate was approximated using a mass balance calculation.

RESULTS

Urea sieving coefficient remained constant (1.04 +/- 0.01). Ultrafiltrate etanercept concentrations were undetectable (sieving coefficient < 0.02) and transmembrane and adsorptive clearances were negligible.

CONCLUSION

Etanercept is not cleared appreciably by transmembrane or adsorptive mechanisms in CVVH using polyacrylonitrile, polysulfone, or polymethylmethacrylate hemofilters.

Intradialytic administration of daptomycin in end stage renal disease patients on hemodialysis

BACKGROUND AND OBJECTIVES

Infusion of intravenous antibiotics after hemodialysis (HD) may delay initiation of treatment for the next HD shift. Intradialytic administration of drugs such as vancomycin during the final hour of HD obviates these delays. Daptomycin has potent activity against Gram-positive bacteria, but the manufacturer recommends that the dose be infused after HD ends. This study determined the pharmacokinetics of intradialytically dosed daptomycin in patients with ESRD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This prospective crossover study compared single-dose daptomycin (6 mg/kg, 30-min intravenous infusion) pharmacokinetics administered after HD versus during the last part of HD with high-permeability (HP) and low-permeability (LP) dialyzers to seven patients who had ESRD and were on thrice-weekly HD. Serial blood samples were collected to determine daptomycin serum concentrations and protein binding. Statistical analysis was done using linear mixed model analysis.

RESULTS

The maximum serum concentration observed with a 6 mg/kg post-HD dose was 61.1 +/- 7.6 microg/ml with a mean protein binding of 89.2%. Intradialytic daptomycin administration resulted in reduced maximum serum concentration and area under the curve values that were approximately 12 to 20% lower when administered during HD with LP dialyzers and approximately 35% lower with HP dialyzers.

CONCLUSIONS

Intradialytic daptomycin administration during the last 30 min of HD is feasible, provided that larger dosages are used to compensate for intradialytic drug loss. On the basis of our findings, intradialytic doses of approximately 7 mg/kg (LP) or approximately 9 mg/kg (HP) theoretically should be bioequivalent to 6 mg/kg infused after HD. The calculated dosages are mathematically driven and must be validated in prospective clinical trials.

Enaminones: Exploring Additional Therapeutic Activities

Enaminones, enamines of beta-dicarbonyl compounds, have been known for many years. Their early use has been relegated to serving as synthetic intermediates in organic synthesis and of late, in pharmaceutical development. Recently, the therapeutic potential of these entities has been realized. This review provides the background and current research in this area with emphasis of these agents as potential anticonvulsants, their proposed mechanisms of action, and as potential modulators of multidrug resistance (MDR).

MDR1 haplotypes significantly minimize intracellular uptake and transcellular P‐gp substrate transport in recombinant LLC‐PK1 cells

To date, research on the effect of single nucleotide polymorphisms (SNPs) on P-glycoprotein (P-gp) expression and functionality has rendered inconsistent results. This study systematically evaluates the impact of MDR1 haplotypes (1236/2677, 1236/3435, 2677/3435, 1236/2677/3435) on P-gp functionality compared to individual SNPs (1236, 2677, and 3435) in validated stable recombinant epithelial cells. Recombinant LLC-PK1 cells expressing MDR1wt or its variants were developed and validated for this purpose. Intracellular accumulation and time-dependant efflux of a P-gp substrate, Rhodamine 123 (R123, 5 microM) were evaluated in control and recombinant cells. Additionally, the transepithelial transport of R123 (1 microM) and Vinca alkaloids (5 microM) was evaluated. Except for MDR1(2677T) and MDR1(1236T/2677T/3435T), cells expressing MDR1 variants displayed intermediate R123 intracellular accumulation (1.5-2-fold higher) and lower effluxed R123 (10-20% vs. 52%) compared to those expressing MDR1wt. Efflux ratios across MDR1wt expressing cells were significantly larger for R123 (3.95+/-1.1), Vinblastine (3.75+/-0.26), and Vincristine (2.8+/-0.29). Recombinant cells expressing MDR1 variants displayed 0%-22.7% P-gp activity (approximately 80%-100% efflux loss). Results suggest that MDR1 polymorphisms at the 1236, 2677, and/or 3435 positions significantly minimize P-gp functionality in vitro, the extent of which appears to be substrate dependant.

Recent developments in drug targets and delivery of anti-HIV drugs

With almost 40 million people infected with human immunodeficiency virus (HIV), it is one of the most devastating diseases with no cure in sight. Over the past two decades, significant progress has been made to identify and validate drug targets for HIV. However, most of the 20 FDA approved drugs are targeted to two enzymes; reverse transcriptase and protease. Other drug targets derived from HIV and host factors are being validated, and novel compounds are being developed to overcome drug resistance. Recent data indicate that low and residual virus found in tissues of the lymphoid and central nervous system (CNS) is likely due to insufficient drug levels. Thus, improvement in the delivery of anti-HIV drugs to these tissues with limited drug penetration or accumulation, is equally important to maximally suppress viral replication. Novel lipid associated drugs (i.e. indinavir) targeted to the lymphoid tissue have been shown to overcome limited drug exposure in the lymph nodes and to further reduce residual virus in tissue. This review discusses viral and cellular targets that could interrupt viral replication, as well as novel and proven strategies to enhance the delivery of anti-HIV drugs to the lymphoid, CNS, and cells where low viral replication and limited drug levels exist.

Tight junction modulation and its relationship to drug delivery

In order for therapeutic agents to exert their pharmacological effects, they have to cross the biological membranes into the systemic circulation and reach the site of action. Drugs cross the membranes by one of two pathways; paracellular or transcellular. Most drugs are transported transcellularly depending on their physiocochemical properties, however the paracellular route is usually the main route of absorption for hydrophilic drugs (proteins, peptides, etc.). The paracellular pathway is governed by the tight junctions (TJs). The modulation of the TJs by absorption enhancers for paracellular drug transport enhancement and hence drug delivery improvement has been hampered for so many years by lack of comprehensive understanding of the structure and function of the TJs. The TJs are a multiple unit structure composed of multiprotein complex that affiliates with the underlying apical actomyosin ring. TJ proteins identified include transmembrane proteins; occludin and claudin, and cytoplasmic plaque proteins; ZO-1, ZO-2, ZO-3, cingulin, and 7H6. Among the new absorption enhancers that evolved in the past few years is Zonula Occludens toxin, Zot. In vivo and in vitro studies have shown that Zot and its biologically active fragment DeltaG could be effectively used to increase the transport/absorption of paracellular markers and low bioavailable drugs across the intestinal epithelium. Above all, the transient opening of the TJs by Zot suggests that it could be used as a novel approach for the safe drug delivery of therapeutic agents.

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.

The effect of delta G on the transport and oral absorption of macromolecules

Delta G (DeltaG) is the biologically active fragment of Zonula Occludens Toxin (Zot), an absorption enhancer, that reversibly opens the tight junctions of epithelial and endothelial cells in the small intestine and brain. This study evaluates the possible use of DeltaG in enhancing the oral bioavailability of macromolecules using large paracellular markers as model agents. The transport of [(14)C]Inulin and [(14)C]PEG4000 was evaluated across Caco-2 cells with DeltaG (0, 100, 180 microg/ml). The apparent permeability coefficients (P(app)) were calculated. The in vitro toxicity of DeltaG (180 microg/ml) was assessed. Sprague Dawley rats were dosed intraduodenally (ID) with the following treatments: [(14)C]Inulin or [(14)C]PEG4000 (30 microci/kg) w/o DeltaG (720 microg/kg)/protease inhibitors (PI). Blood was collected and plasma was analyzed for radioactivity. DeltaG (180 microg/ml) increased [(14)C]Inulin and [(14)C]PEG4000 P(app) by 82.6 and 24.4%, respectively, without any toxicity. After ID administration with DeltaG/PI, C(max) and AUC were significantly (p < 0.05) increased for both Inulin and PEG4000. However, Inulin displayed greater enhancement ratios in vitro and in vivo. This study suggests that DeltaG may be used to enhance the oral bioavailability of macromolecules (e.g., proteins) after coadministration through modulation of paracellular transport.

The impact of DeltaG on the oral bioavailability of low bioavailable therapeutic agents

Low oral bioavailability continues to drive research toward identifying novel approaches to enhance drug delivery. Over the past few years, emphasis on the use of absorption enhancers has been overwhelming despite their major adverse effects. Zonula occludens toxin (Zot) was recently established as a safe and effective absorption enhancer, reversibly opening the tight junctions for hydrophilic markers and hydrophobic drugs across the small intestine and the blood brain barrier. DeltaG, the biologically active fragment of Zot, was isolated and shown to increase the in vitro transport and in vivo absorption of paracellular markers. The objective of this study was to examine the effect of DeltaG on the oral bioavailability of low bioavailable therapeutic agents. Jugular vein cannulated Sprague-Dawley rats were randomly assigned to receive the following treatments intraduodenally (ID): [(3)H]cyclosporin A, [(3)H]ritonavir, [(3)H]saquinavir, or [(3)H]acyclovir at (120 microCi/kg) alone, with protease inhibitors (PIs), or with DeltaG (720 microg/kg)/PI. Serial blood samples were collected, and plasma was analyzed for radioactivity. After ID administration with DeltaG/PI, C(max) significantly (p < 0.05) increased over a range of 197 to 5700%, whereas area under the plasma concentration time curve displayed significant increases extending over a range of 123.8 to 4990.3% for the investigated drugs. DeltaG significantly increased the in vivo oral absorption of some low bioavailable drugs in the presence of PI. This study suggests that DeltaG-mediated tight junction modulation, combined with metabolic protection, may be used to enhance the low oral bioavailability of certain drugs when administered concurrently.

DM27, an enaminone, modifies thein vitro transport of antiviral therapeutic agents

OBJECTIVE

For most antiviral drugs, low or variable bioavailability is attributed to poor absorption, susceptibility to efflux, or first pass metabolism. Enaminones are beta dicarbonyl compounds, which display P-glycoprotein (P-gp) substrate properties with high efflux ratios. This study investigates the influence of DM27, an enaminone, on the in vitro transport of antiviral agents and the possibility of using DM27 as a P-gp inhibitor to prevent the efflux of certain antiretroviral agents.

METHODS

The transport of [3H]amprenavir, [3H]saquinavir, [3H]ritonavir, [14C]zidovudine (AZT) and [3H]acyclovir was evaluated across Caco-2 cells with DM27 (10(-10)-10(-4) M). In addition, the effect of DM27 (10(-6) M) on the transport of transcellular and paracellular markers was tested to evaluate its influence on these transport pathways. The apparent permeability coefficient (Papp) for each drug or marker was calculated with/without DM27 and toxicity evaluation for DM27 was performed using the MTS assay.

RESULTS

The mean Papp for the investigated antiviral agents significantly increased by 22%-51% after DM27 incubation without any toxicity to the Caco-2 cells. In addition, DM27 did not influence the transcellular or paracellular transport of propranolol and mannitol, respectively.

CONCLUSIONS

DM27, an enaminone, increased the transport of antiretroviral drugs and acyclovir in a nontoxic manner without affecting the paracellular or transcellular transport of these drugs. This study suggests that DM27 may be used as a P-gp efflux inhibitor to enhance the oral bioavailability of antiviral drugs and that drug-drug interactions will most probably be encountered upon co-administration of P-gp substrate drugs with enaminones.

The influence of enaminones on the transport and oral bioavailability of P-glycoprotein substrate therapeutic agents

OBJECTIVE

The enaminones have shown high P-gp affinity and may act as P-gp modulators. This study investigated the potential inhibition of the enaminones on paclitaxel efflux in vitro compared to cyclosporin A, a known P-gp inhibitor, and the effectiveness of select enaminones on paclitaxel oral absorption in rats.

METHODS

Caco-2 transport of [14C]paclitaxel was evaluated in presence of various enaminones at 10(-5)M. Concentration-effect (10(-10)M to 10(-4)M) profiles for the enaminones, DM27 and/or DM40, with paclitaxel and cyclosporin A were determined. Male Sprague-Dawley (250-275 g) rats were orally administered either [14C]paclitaxel (30 microCi/kg) or [14C]paclitaxel/DM27 (7 mg/kg) and blood samples were collected. Paclitaxel brain concentrations were measured.

RESULTS

Papp(A-B) of [14C]paclitaxel, with DM27 and DM40 at 10(-5)M, was significantly (P < 0.05) higher versus control. DM27 produced a 360% and a 139% increase in Papp(A-B)Paclitaxel and Papp(A-B)Cyclosporin, respectively. DM40 displayed a 131% increase in Papp(A-B)Paclitaxel whereas cyclosporin A produced a 213% increase in Papp(A-B)Paclitaxel. Rats in the DM27 group displayed large Vdss/F values (23.35 liters/kg versus 14.62 liters/kg) and lower AUC (5.47 microg/ml min versus 8.74 microg/ml min) versus control. However, significantly higher levels (2.25-fold) of paclitaxel were observed in the brains of the DM27 group.

CONCLUSION

This study presents the enaminones as promising P-gp inhibitors with comparable potency to other P-gp inhibitors. Furthermore, the enaminones may improve conventional therapy when used in combination with P-gp substrate drugs.

Effect of the biologically active fragment of zonula occludens toxin, delta G, on the intestinal paracellular transport and oral absorption of mannitol

OBJECTIVE

Many therapeutically active agents experience low bioavailability upon oral administration due to low permeability, low solubility, interaction with efflux transporters or first pass metabolism. In general, absorption enhancers are agents that can modulate the paracellular permeability of drugs, thus, potentially increasing oral bioavailability. The objective of this study was to examine the effect of the active fragment of Zonula occludens toxin (Zot), deltaG, on the transport of a paracellular marker, mannitol, using in vitro (Caco-2 cell monolayers) and in vivo (intraduodenal administration in rats) experimental methods.

METHODS

The transport of [14C]mannitol with deltaG (0, 50, 80, or 100 microg/ml) was determined across Caco-2 cells. Male Sprague-Dawley rats were assigned to receive one of the following treatments: [14C] mannitol (40 microCi/kg), [14C]mannitol/deltaG (417 microg/kg), or [14C] mannitol/deltaG/Protease inhibitors (PI).

RESULTS

The mean (+/-S.E.M.) apparent mannitol permeability coefficients (P(app)) observed after incubation with 0, 50, 80, and 100 microg/ml deltaG were 3.5 (+/-0.4), 4.17 (+/-0.27), 4.33 (+/-0.61), and 9.94 (+/-0.24)x10(-6) cm/s. After oral administration, C(max) (3.8 x 10(-4) vs. 4.4 x 10(-4) mM) and AUC(0-6 h) (0.096 vs. 0.088 mM min), obtained for [14C]mannitol and [14C]mannitol/deltaG, respectively, were not statistically different. However, both C(max) (7.6 x 10(-4) mM) and AUC(0-6 h) (0.25 mM min) were significantly higher for the [14C]mannitol/deltaG/PI treatment.

CONCLUSIONS

The 12 kDa fragment of Zot, deltaG, enhanced the in vitro transport and oral absorption of the paracellular marker, mannitol, in the presence of protease inhibitors (PI).

Preclinical evaluation of the pharmacokinetics, brain uptake and metabolism of E121, an antiepileptic enaminone ester, in rats

The present study describes the brain uptake, pharmacokinetics and metabolism of an anticonvulsant enaminone ester E121, which belongs to a new and active series of compounds with potential in vivo anticonvulsant activity in rodent models, in rats. A single dose of E121 was administered i.p. to male Sprague Dawley rats at 10 mg E121/kg body weight. Cohorts of animals (n=3) were killed at varying times over 0-24 h to collect plasma and brain samples. Urinary excretion of E121 was studied in a separate group of five rats at the same dose. A validated HPLC method was used to quantify E121 and its metabolites in plasma, brain and urine. LC-MS/MS was used to characterize the metabolites. The plasma and brain Cmax of 11.0+/-3.0 mg/l and 10.4+/-1.4 mg/kg, respectively, were observed for E121 at 15 min post dose and they declined in a mono-exponential fashion. The plasma Cl/F and t1/2 were 0.57 l/h/kg and 0.75 h, respectively. The brain uptake ratio of E121 was 0.9. Mass spectral analysis of urine showed two major metabolites (m/z 280) and one minor metabolite (m/z 236) that were consistent with initial hydrolysis of the compound to the acid followed by further decarboxylation and appears to be the major route of elimination of E121. The rapid and moderate brain uptake of E121 correlates well with its potential anticonvulsant activity (ED50 3.0 mg/kg p.o. in rats). The brain uptake, pharmacokinetic and metabolic profile of E121 supports the need to further evaluate this compound for its potential as an antiepileptic.

Synthesis and anticonvulsant activity of enaminones. Part 7. Synthesis and anticonvulsant evaluation of ethyl 4-[(substituted phenyl)amino]-6-methyl-2-oxocyclohex-3-ene-1-carboxylates and their corresponding 5-methylcyclohex-2-enone derivatives

Further investigation of the potential anticonvulsant activity of the enaminones was attempted to discern the possible role of metabolites as the active/co-active entities of the esters of the enaminones. A series of 5-methyl-2-cyclohexene enaminones, the hypothesised metabolites corresponding to a sequence of active and inactive esters were synthesised and evaluated for anticonvulsant activity. With two exceptions, ethyl 4-[(4-cyanophenyl)amino]-6-methyl-2-oxocyclohex-3-ene-1-carboxylate (1k), and 3-[N-(4-cyanophenyl)amino]-5-methyl-2-cyclohexenone (3g), and ethyl 4-(phenylamino)-6-methyl-2-cyclohexenone (1n), and 3-N-(phenylamino)-5-methyl-2-cyclohexenone (3j), anticonvulsant screening data were parallel, with the ester and their putative decarboxylated analogue displaying similar activity. The most active analogue evaluated in this series, ethyl 4-[(4-chlorophenyl)amino]-6-methyl-2-oxocyclohex-3-ene-1-carboxylate (1e), which displayed an ED(50) of 16.7 mg kg(-1) and a TD(50) of 110.7 mg kg(-1) (protective index, PI = TD(50)/ED(50) = 6.6) in the maximal electroshock seizure (MES) test in mice and an ED(50) of 3.0 mg kg(-1) and a TD(50) >250 mg kg(-1) (PI > 83.3) in rats in the same evaluation, making this compound the most potent enaminone emanating from our laboratories. Pharmacokinetic evaluation of compound 1e in rats using LC/MS analysis unequivocally provides evidence that this compound is converted into the decarboxylated analogue 3a in the brain and the urine.

Enhanced permeability of molecular weight markers and poorly bioavailable compounds across Caco-2 cell monolayers using the absorption enhancer, zonula occludens toxin

PURPOSE

Zonula occludens toxin (Zot), a protein elaborated from Vibrio cholerae, has been shown to be capable of reversibly opening tight junctions. The objective of this work was to determine the stability of Zot and to examine the permeability of a series of molecular weight hydrophilic markers and therapeutic agents in the presence of Zot.

METHOD

The transport of molecular weight markers (i.e., PEG 4000, FITC-dextran 10.000 and inulin) and therapeutic agents (i.e., acyclcovir, cyclopsorin, paclitaxel. doxorubicin) was evaluated with Zot (0, 2, and 4 microg/mL) using Caco-2 cell monolayers.

RESULTS

Zot was found to be stable over a 10-day period. Significantly higher (p < 0.05) permeability of the molecular weight markers, in lin, and PEG4000 were observed with Zot (4 microg/mL). The transport of each therapeutic marker was significantly increased with paclitaxel displaying a >3-fold enhancement in Papp values with Zot (4 microg/mL). A 30% decrease in transepithelial electrical resistance values wa observed, which returned to baseline 30 min after Zot was removed.

CONCLUSIONS

Considering the problems of poor oral bioavailability, it is concluded that Zot is a promising drug delivery technology to be used to enhance drug transport across the intestinal mucosa. Future applications are targeted at assessing its usefulness in oral drug delivery using in vivo systems.