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 ±â€ŠSD: 47 ±â€Š20 years, 69.5 ±â€Š17.1 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.

Palbociclib and cetuximab in platinum-resistant and in cetuximab-resistant human papillomavirus-unrelated head and neck cancer: a multicentre, multigroup, phase 2 trial.

BACKGROUND: Most head and neck squamous-cell carcinomas (HNSCCs) are driven by p16INK4A inactivation and cyclin D1 overexpression that results in hyperactivation of cyclin-dependent kinase 4 and 6 (CDK4/6), rather than by the human papillomavirus (HPV). Deregulated cyclin D1 expression also causes resistance to EGFR inhibitors. We previously reported that palbociclib (a selective CDK4/6 inhibitor) given with cetuximab (an EGFR inhibitor) was safe. The aim of this study was to establish the proportion of patients achieving an objective response with palbociclib and cetuximab in recurrent or metastatic HNSCC. METHODS: We did a multicentre, multigroup, phase 2 trial to evaluate the activity of palbociclib and cetuximab in platinum-resistant (group 1) and cetuximab-resistant (group 2) HPV-unrelated HNSCC. The study was done across eight university sites in the USA. Eligibility required measurable disease (according to Response Evaluation Criteria in Solid Tumors, version 1·1 [RECIST 1·1]), Eastern Cooperative Oncology Group (ECOG) performance status of 0-2, age of 18 years or older, and disease progression on platinum but cetuximab-naive (group 1) or disease progression on cetuximab (group 2). All patients received palbociclib orally (125 mg/day, on days 1-21) and intravenous cetuximab (400 mg/m2 on cycle one, day 1, then 250 mg/m2 once per week) in 28-day cycles. The primary endpoint was objective response (complete responses and partial responses per RECIST 1·1). Analyses were done per protocol. This trial was registered with ClinicalTrials.gov, NCT02101034, and is ongoing, but both groups are closed to accrual. FINDINGS: Between Oct 19, 2015, and Nov 7, 2018, 62 patients were enrolled onto the trial: 30 patients were enrolled in group 1 and 32 in group 2. Median follow-up was 5·4 months (IQR 4·4-12·1) for group 1 and 5·5 months (4·3-8·3) for group 2. In group 1, of 28 evaluable patients, an objective response was achieved by 11 (39%; 95% CI 22-59). In group 2, of 27 evaluable patients, an objective response was achieved by five (19%; 6-38) in group 2. The most common grade 3-4 palbociclib-related adverse event was neutropenia (in 21 [34%] of 62 patients). No treatment-related deaths occurred. INTERPRETATION: In patients with platinum-resistant or cetuximab-resistant HPV-unrelated HNSCC, palbociclib and cetuximab results in promising activity outcomes. Further studies of CDK4/6 inhibitors are warranted in HPV-unrelated HNSCC. FUNDING: Pfizer.

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.

Daptomycin pharmacokinetics and pharmacodynamics in a pooled sample of patients receiving thrice-weekly hemodialysis.

While the pharmacokinetic (PK) properties of daptomycin in hemodialysis (HD) patients have been evaluated previously by three groups, resultant dosing recommendations have varied. To address this clinical conundrum, this study combined concentration-time data from these PK evaluations and derived uniform dosing recommendations among patients on HD receiving daptomycin. A two-compartment model with separate HD and non-HD clearance terms was fit to the PK data from these studies by using BigNPAG. Embedded with PK parameters from the population PK analysis, 5,000-subject Monte Carlo simulations (MCS) were performed to identify HD dosing schemes that provided efficacy (cumulative and daily area under the concentration-time curve [AUC] values) and toxicity (trough concentrations of ≥ 24.3 mg/liter) profiles comparable to those from simulations employing the daptomycin PK model derived from the Staphylococcus aureus bacteremia-infective endocarditis (SAB-IE) study. Separate HD dosing schemes were sought for the two weekly interdialytic periods (48 and 72 h). For the 48-h interdialytic period, intra- and post-HD dosing provided the most isometric cumulative and daily AUCs. For the 72-h interdialytic period, all HD dosing schemes provided noncumulative AUC values from 48 to 72 h (AUC(48-72)) that were <50% of the SAB-IE AUC(48-72) values. Increasing the parent dose by 50% intra- or post-HD provided comparable AUC(48-72) values, while maintaining acceptable trough concentration (C(min)) values. When efficacy and toxicity profiles were evaluated for each individual study, higher probabilities for C(min) reaching ≥ 24.3 mg/liter were observed in one of the three studies. Given the high probability of C(min) being ≥ 24.3 mg/liter in one of the three studies, more intensive creatine phosphokinase (CPK) monitoring may be warranted in HD patients receiving daptomycin.

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.

Daptomycin pharmacokinetics in critically ill patients receiving continuous venovenous hemodialysis.

OBJECTIVE: To investigate daptomycin pharmacokinetics in critically ill patients receiving continuous venovenous hemodialysis to develop dosing recommendations. DESIGN: Prospective, open-label pharmacokinetic study. SETTING: : Intensive care units located within a teaching medical center. PATIENTS: Eight adults with known/suspected Gram-positive infections receiving continuous venovenous hemodialysis and daptomycin. INTERVENTIONS: Daptomycin at 8 mg/kg intravenously over 30 mins. Serial blood and effluent samples were collected over the next 48 hrs. Daptomycin protein binding was determined by equilibrium dialysis. Daptomycin continuous venovenous hemodialysis transmembrane clearance was determined by dividing daptomycin effluent by serum concentrations and multiplying by mean effluent production rate for each subject. Equations describing a two-compartment, open-pharmacokinetic model were fitted to each subject's daptomycin concentration-time data and pharmacokinetic parameters were determined by standard methods. Serum concentration-time profiles were simulated for two daptomycin regimens (8 mg/kg every 48 hrs and 4 mg/kg every 24 hrs). MEASUREMENTS AND MAIN RESULTS: A total of 7.7 ± 0.6 mg/kg (mean ± sd) of daptomycin was administered, resulting in an observed peak concentration of 81.2 ± 19.0 µg/mL. Daptomycin steady-state volume of distribution (0.23 ± 0.14 L/kg) and free fraction (17.5% ± 5.0%) were increased in critically ill subjects receiving continuous venovenous hemodialysis compared with previous values reported in healthy volunteers. Daptomycin transmembrane clearance (6.3 ± 2.9 mL/min) accounted for more than half of total clearance (11.3 ± 4.7 mL/min). Simulations demonstrated 8 mg/kg daptomycin every 48 hrs would result in higher peak (88.8 ± 20.0 µg/mL vs. 53.0 ± 12.3 µg/mL) and lower trough concentrations (7.2 ± 5.2 µg/mL vs. 12.3 ± 5.1 µg/mL) than 4 mg/kg every 24 hrs. CONCLUSIONS: Daptomycin at 8 mg/kg every 48 hrs in critically ill patients receiving continuous venovenous hemodialysis resulted in good drug exposure, achieved high peak concentrations to maximize daptomycin's concentration-dependent activity, and resulted in trough concentration that would minimize the risk of myopathy. CLINICALTRIALS.GOV IDENTIFIER: NCT00663403.

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.

Combining drug and immune therapy: a potential solution to drug resistance and challenges of HIV vaccines?

According to the World Health Organization's 2007 estimates, close to 33 million people worldwide are living with HIV/AIDS. Over the past two decades, significant progress has been made in understanding HIV pathogenesis and disease progression, which has allowed the identification of a multitude of drug and vaccine targets. Although currently available drug therapies have greatly increased the time from HIV infection to development of AIDS, drug resistance is an inevitable consequence that limits the duration of successful treatment. Consequently, a preventative vaccine remains the top priority; however, no vaccine trial performed to date has shown efficacy in human trials. Therefore, we must use all of our current resources in new creative therapies and strive to develop new methods to reduce persistent viral levels until an effective preventative vaccine is developed. One possible strategy is to use therapeutic vaccination or immune modulators to augment the immune response while antiretroviral chemotherapy limits viral replication. This combination approach is being utilized with success in the treatment of Hepatitis B infections and several trials have been completed and others are ongoing to determine the potential of combination immunological and chemical therapies for HIV infection. We will review the progress to date of anti-HIV drugs, preventative vaccines, and therapeutic vaccines and discuss the future strategies of combination drug and vaccine therapeutic strategies in the fight against HIV.

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 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.