Comparison of Tumor Penetration of Podophyllotoxin-Carboxymethylcellulose Conjugates with Various Chemical Compositions in Tumor Spheroid Culture and In Vivo Solid Tumor.

Polymer conjugation is an attractive approach for delivering insoluble and highly toxic drugs to tumors. However, most reports in the literature only disclose the optimal composition without emphasizing rational design or composition optimization to achieve maximized biological effects. In this study, we aimed to demonstrate that composition of a polymer conjugate would determine its physiochemical characteristics, tumor penetration, and, ultimately, the in vivo efficacy. We also aimed to examine whether the tumor spheroid model could generate comparable results with the in vivo tumor model in terms of tumor penetration and efficacy of the various polymer conjugates. We have designed a polymer conjugate delivery system for a chemotherapeutic drug podophyllotoxin (PPT) by covalently conjugating PPT and polyethylene glycol (PEG) with acetylated carboxymethyl cellulose to yield conjugates containing various amounts of PPT and PEG. Depending on the composition, these conjugates self-assembled into nanoparticles (NPs) with different physicochemical properties. Conjugates with an increased PPT content formed particles with an increased diameter. In the present study, we selected three conjugates representing compositions containing high, medium, and low drug content, and compared their particle formation, drug release kinetics, their ability to penetrate tumor spheroid and in vivo s.c. tumor, and finally their antitumor efficacy in spheroid culture and an in vivo s.c. tumor model. We found that the low drug content conjugate formed smaller NPs (20 nm) compared to the high drug content conjugates (30-120 nm), and displayed faster drug release kinetics (5%/day vs 1-3%/day), improved tumor penetration, and enhanced antitumor efficacy in both the spheroid model and s.c. tumor model. In particular, the low drug content conjugate preferentially accumulated in the hypovascular region within the tumor, inducing complete regression of s.c. tumors and the metastasis to the lungs. Our data indicate composition optimization is needed to select the optimal conjugate, and tumor spheroid culture is a robust screening tool to help select the optimal formulation.

Synthesis of a Gemcitabine Prodrug for Remote Loading into Liposomes and Improved Therapeutic Effect.

The chemotherapeutic gemcitabine was actively and stably loaded into lipid nanoparticles through the formation of a prodrug. Gemcitabine was chemically modified to increase the lipophilicity and introduce a weak base moiety for remote loading. Several derivatives were synthesized and screened for their potential to be good liposomal drug candidates for remote loading by studying their solubility, stability, cytotoxicity, and loading efficiency. Two morpholino derivatives of GEM (22 and 23) were chosen as the preferred prodrugs for this purpose as they possessed the best loading efficiencies (100% for drug-to-lipid ratio of 0.36 w/w). This is a considerable improvement over a passive loading strategy where typical loading efficiencies are on the order of ∼10-20% for a drug-to-lipid ratio of ∼0.01. Liposomes loaded with these two prodrugs were studied in an s.c. tumor model in vivo and showed improved therapeutic effect over free GEM (∼2-fold) and saline control (8- to 10-fold). This work demonstrates how chemical modification of a known hydrophilic drug can lead to improved loading, stability, and drug delivery in vivo.

A Simple and Improved Active Loading Method to Efficiently Encapsulate Staurosporine into Lipid-Based Nanoparticles for Enhanced Therapy of Multidrug Resistant Cancer.

PURPOSE: This study was aimed at developing a new active loading method to stably encapsulate staurosporine (STS), a water insoluble drug, into lipid-based nanoparticles (LNPs) for drug targeting to tumors. METHODS: A limited amount of DMSO was included during the active loading process to prevent precipitation and facilitate the loading of insoluble STS into the aqueous core of a LNP. The drug loading kinetics under various conditions was studied and the STS-LNPs were characterized by size, drug-to-lipid ratio, drug release kinetics and in vitro potency. The antitumor efficacy of the STS-LNPs was compared with free STS in a mouse model. RESULTS: The drug loading efficiency reached 100% within 15 min of incubation at a drug-to-lipid ratio of 0.31 (mol) via an ammonium gradient. STS formed nano-aggregates inside the aqueous core of the LNPs and was stably retained upon storage and in the presence of serum. A 3-fold higher dose of the STS-LNPs could be tolerated by BALB/c mice compared with free STS, leading to nearly complete growth inhibition of a multidrug resistant breast tumor, while free STS only exhibited moderate activity. CONCLUSION: This simple and efficient drug loading method produced a stable LNP formulation for STS that was effective for cancer treatment.

A Study of Liposomal Formulations to Improve the Delivery of Aquated Cisplatin to a Multidrug Resistant Tumor.

PURPOSE: This study was aimed at exploring the use of liposomes to deliver aquated cisplatin (ACP), a metabolite of CDDP, with increased potency and toxicity. Three liposomal formulations were compared for delivery of ACP to a multidrug resistant tumor. METHODS: Three different liposomes (DMPC, DPPC and DSPC as the main lipid components) were loaded with ACP by the thin-film hydration method. In vitro drug release was assessed over 72 h at 37°C in PBS. The pharmacokinetics of free CDDP and the three ACP liposomes was determined using ICP-AES and their efficacy against EMT6-AR1 multidrug resistant murine breast tumor was compared. RESULTS: The DSPC formulation, composed of a C18 acyl chain lipid, exhibited the slowest drug release (~2%) after 72 h at 37°C, compared to the other two formulations with decreased carbon chain lengths (C16 and C14; 7 and 25% release respectively). The pharmacokinetic profile was improved with all liposomal formulations relative to free CDDP, with clearance reduced by 500-fold for DSPC, 200-fold for DPPC and 130-fold for DMPC. The DSPC formulation displayed the highest drug accumulation in the tumor with 2-fold, 3-fold and 100-fold increases compared to DPPC, DMPC and free CDDP respectively. The DSPC formulation significantly inhibited the EMT6-AR1 tumor growth by ~90%, while the other formulations displayed no statistically significant improved activity compared to saline. CONCLUSION: These results suggest that the DSPC liposomal formulation is a promising formulation for MDR tumor therapy over DMPC and DPPC formulations and free drug.

Carboxymethylcellulose-based and docetaxel-loaded nanoparticles circumvent P-glycoprotein-mediated multidrug resistance.

Taxanes are a class of anticancer agents with a broad spectrum and have been widely used to treat a variety of cancer. However, its long-term use has been hampered by accumulating toxicity and development of drug resistance. The most extensively reported mechanism of resistance is the overexpression of P-glycoprotein (Pgp). We have developed a PEGylated carboxymethylcellulose conjugate of docetaxel (Cellax), which condenses into ∼120 nm nanoparticles. Here we demonstrated that Cellax therapy did not upregulate Pgp expression in MDA-MB-231 and EMT-6 breast tumor cells, whereas a significant increase in Pgp expression was measured with native docetaxel (DTX) treatment. Treatment with DTX led to 4-7-fold higher Pgp mRNA expression and 2-fold higher Pgp protein expression compared with Cellax treatment in the in vitro and in vivo system, respectively. Cellax also exhibited significantly increased efficacy compared with that of DTX in a taxane-resistant breast tumor model. Against the highly Pgp expressing EMT6/AR1 cells, Cellax exhibited a 6.5 times lower IC50 compared with that of native DTX, and in the in vivo model, Cellax exhibited 90% tumor growth inhibition, while native DTX had no significant antitumor activity.

Thermosensitive liposomes for the delivery of gemcitabine and oxaliplatin to tumors.

The majority of ultrafast temperature sensitive liposome (uTSL) formulations reported in the literature deliver the highly membrane permeable drug, doxorubicin (DOX). Here we report on the study of the uTSL formulation, HaT (Heat activated cytoToxic, composed of the phospholipid DPPC and the surfactant Brij78) loaded with the water-soluble, but poorly membrane permeable anticancer drugs, gemcitabine (GEM) and oxaliplatin (OXA). The HaT formulation displayed ultrafast release of these drugs in response to temperature, whereas attempts with LTSL (Lyso-lipid Temperature Sensitive Liposome, composed of DPPC, MSPC, and DSPE-PEG) were unsuccessful. HaT-GEM and HaT-OXA both released >80% of the encapsulated drug within 2 min at 40-42 °C, with <5% drug leakage at 37 °C after 30 min in serum. The pharmacokinetic profile of both drugs was improved by formulating with HaT relative to the free drug, with clearance reduced by 50-fold for GEM and 3-fold for OXA. HaT-GEM and HaT-OXA both displayed improved drug uptake in the heated tumor relative to the unheated tumor (by 9-fold and 3-fold, respectively). In particular, HaT-GEM showed 25-fold improved delivery to the heated tumor relative to free GEM and significantly enhanced antitumor efficacy with complete tumor regression after a single dose of HaT-GEM. These data suggest that uTSL technology can also be used to deliver nonmembrane permeable drugs via an intravascular ultrafast release mechanism to great effect.

Discovery of OICR12694: A Novel, Potent, Selective, and Orally Bioavailable BCL6 BTB Inhibitor.

B cell lymphoma 6 (BCL6), a highly regulated transcriptional repressor, is deregulated in several forms of non-Hodgkin lymphoma (NHL), most notably in diffuse large B-cell lymphoma (DLBCL). The activities of BCL6 are dependent on protein-protein interactions with transcriptional co-repressors. To find new therapeutic interventions addressing the needs of patients with DLBCL, we initiated a program to identify BCL6 inhibitors that interfere with co-repressor binding. A virtual screen hit with binding activity in the high micromolar range was optimized by structure-guided methods, resulting in a novel and highly potent inhibitor series. Further optimization resulted in the lead candidate 58 (OICR12694/JNJ-65234637), a BCL6 inhibitor with low nanomolar DLBCL cell growth inhibition and an excellent oral pharmacokinetic profile. Based on its overall favorable preclinical profile, OICR12694 is a highly potent, orally bioavailable candidate for testing BCL6 inhibition in DLBCL and other neoplasms, particularly in combination with other therapies.

Cabazitaxel-conjugated nanoparticles for docetaxel-resistant and bone metastatic prostate cancer.

Effective treatment of metastatic castration resistant prostate cancer (mCRPC) remains an unmet challenge. Cabazitaxel (CBZ) is approved for mCRPC after docetaxel (DTX) failure, but the improvement in survival is only moderate (∼2 months) and patients suffer from significant side effects. Here, we report the development of a polymer based delivery system for CBZ to improve its safety and efficacy against DTX-resistant mCRPC. CBZ was conjugated to a carboxymethylcellulose-based polymer (Cellax-CBZ), which self-assembled into ∼100 nm particles in saline and exhibited sustained drug release in serum at 10%/day. Cellax-CBZ delivered 157-fold higher CBZ to PC3-RES prostate tumor in mice and could be safely administered at a 25-fold higher dose compared to free CBZ, resulting in superior tumor inhibition in multiple mice models of DTX-resistant CRPC. In a metastatic bone model of CRPC, Cellax-CBZ significantly improves overall survival with a 70% long-term survival rate to day 120, while mice treated with free CBZ had a median survival of 40 days. Cellax-CBZ induced mild and reversible neutropenia in mice but no other tissue damage. Cellax-CBZ showed significant potential for improving therapy of mCRPC over clinically approved CBZ.

Photoacoustic signal characterization of cancer treatment response: Correlation with changes in tumor oxygenation.

Frequency analysis of the photoacoustic radiofrequency signals and oxygen saturation estimates were used to monitor the in-vivo response of a novel, thermosensitive liposome treatment. The liposome encapsulated doxorubicin (HaT-DOX) releasing it rapidly (<20 s) when the tumor was exposed to mild hyperthermia (43 °C). Photoacoustic imaging (VevoLAZR, 750/850 nm, 40 MHz) of EMT-6 breast cancer tumors was performed 30 min pre- and post-treatment and up to 7 days post-treatment (at 2/5/24 h timepoints). HaT-DOX-treatment responders exhibited on average a 22% drop in oxygen saturation 2 h post-treatment and a decrease (45% at 750 nm and 73% at 850 nm) in the slope of the normalized PA frequency spectra. The spectral slope parameter correlated with treatment-induced hemorrhaging which increased the optical absorber effective size via interstitial red blood cell leakage. Combining frequency analysis and oxygen saturation estimates differentiated treatment responders from non-responders/control animals by probing the treatment-induced structural changes of blood vessel.

Correction: Photoacoustic Imaging of Cancer Treatment Response: Early Detection of Therapeutic Effect from Thermosensitive Liposomes.

[This corrects the article DOI: 10.1371/journal.pone.0165345.].

Photoacoustic Imaging of Cancer Treatment Response: Early Detection of Therapeutic Effect from Thermosensitive Liposomes.

Imaging methods capable of indicating the potential for success of an individualized treatment course, during or immediately following the treatment, could improve therapeutic outcomes. Temperature Sensitive Liposomes (TSLs) provide an effective way to deliver chemotherapeutics to a localized tumoral area heated to mild-hyperthermia (HT). The high drug levels reached in the tumor vasculature lead to increased tumor regression via the cascade of events during and immediately following treatment. For a TSL carrying doxorubicin (DOX) these include the rapid and intense exposure of endothelial cells to high drug concentrations, hemorrhage, blood coagulation and vascular shutdown. In this study, ultrasound-guided photoacoustic imaging was used to probe the changes to tumors following treatment with the TSL, HaT-DOX (Heat activated cytoToxic). Levels of oxygen saturation (sO2) were studied in a longitudinal manner, from 30 min pre-treatment to 7 days post-treatment. The efficacious treatments of HT-HaT-DOX were shown to induce a significant drop in sO2 (>10%) as early as 30 min post-treatment that led to tumor regression (in 90% of cases); HT-Saline and non-efficacious HT-HaT-DOX (10% of cases) treatments did not show any significant change in sO2 at these timepoints. The changes in sO2 were further corroborated with histological data, using the vascular and perfusion markers CD31 and FITC-lectin. These results allowed us to further surmise a plausible mechanism of the cellular events taking place in the TSL treated tumor regions over the first 24 hours post-treatment. The potential for using photoacoustic imaging to measure tumor sO2 as a surrogate prognostic marker for predicting therapeutic outcome with a TSL treatment is demonstrated.

A highly tumor-targeted nanoparticle of podophyllotoxin penetrated tumor core and regressed multidrug resistant tumors.

Podophyllotoxin (PPT) exhibited significant activity against P-glycoprotein mediated multidrug resistant (MDR) tumor cell lines; however, due to its poor solubility and high toxicity, PPT cannot be dosed systemically, preventing its clinical use for MDR cancer. We developed a nanoparticle dosage form of PPT by covalently conjugating PPT and polyethylene glycol (PEG) with acetylated carboxymethyl cellulose (CMC-Ac) using one-pot esterification chemistry. The polymer conjugates self-assembled into nanoparticles (NPs) of variable sizes (20-120 nm) depending on the PPT-to-PEG molar ratio (2-20). The conjugate with a low PPT/PEG molar ratio of 2 yielded NPs with a mean diameter of 20 nm and released PPT at ∼5%/day in serum, while conjugates with increased PPT/PEG ratios (5 and 20) produced bigger particles (30 nm and 120 nm respectively) that displayed slower drug release (∼2.5%/day and ∼1%/day respectively). The 20 nm particles exhibited 2- to 5-fold enhanced cell killing potency and 5- to 20-fold increased tumor delivery compared to the larger NPs. The biodistribution of the 20 nm PPT-NPs was highly selective to the tumor with 8-fold higher accumulation than all other examined tissues, while the larger PPT-NPs (30 and 120 nm) exhibited increased liver uptake. Within the tumor, >90% of the 20 nm PPT-NPs penetrated to the hypovascular core, while the larger particles were largely restricted in the hypervascular periphery. The 20 nm PPT-NPs displayed significantly improved efficacy against MDR tumors in mice compared to the larger PPT-NPs, native PPT and the standard taxane chemotherapies, with minimal toxicity.

Docetaxel-carboxymethylcellulose nanoparticles target cells via a SPARC and albumin dependent mechanism.

Cellax, a polymer-docetaxel (DTX) conjugate that self-assembled into 120 nm particles, displayed significant enhancements in safety and efficacy over native DTX across a number of primary and metastatic tumor models. Despite these exciting preclinical data, the underlying mechanism of delivery of Cellax remains elusive. Herein, we demonstrated that serum albumin efficiently adsorbed onto the Cellax particles with a 4-fold increased avidity compared to native DTX, and the uptake of Cellax by cells was primarily driven by an albumin and SPARC (secreted protein acidic and rich in cysteine, an albumin binder) dependent internalization mechanism. In the SPARC-positive cells, a >2-fold increase in cellular internalization of Cellax was observed in the presence of albumin. In the SPARC-negative cells, no difference in Cellax internalization was observed in the presence or absence of albumin. Evaluation of the internalization mechanism using endocytotic inhibitors revealed that Cellax was internalized predominantly via a clathrin-mediated endocytotic mechanism. Upon internalization, it was demonstrated that Cellax was entrapped within the endo-lysosomal and autophagosomal compartments. Analysis of the tumor SPARC level with tumor growth inhibition of Cellax in a panel of tumor models revealed a positive and linear correlation (R(2) > 0.9). Thus, this albumin and SPARC-dependent pathway for Cellax delivery to tumors was confirmed both in vitro and in vivo.

Targeting of metastasis-promoting tumor-associated fibroblasts and modulation of pancreatic tumor-associated stroma with a carboxymethylcellulose-docetaxel nanoparticle.

Pancreatic ductal adenocarcinomas are characterized by the desmoplastic reaction, a dense fibrous stroma that has been shown to be supportive of tumor cell growth, invasion, and metastasis, and has been associated with resistance to chemotherapy and reduced patient survival. Here, we investigated targeted depletion of stroma for pancreatic cancer therapy via taxane nanoparticles. Cellax-DTX polymer is a conjugate of docetaxel (DTX), polyethylene glycol (PEG), and acetylated carboxymethylcellulose, a construct which condenses into well-defined 120nm particles in an aqueous solution, and is suitable for intravenous injection. We examined Cellax-DTX treatment effects in highly stromal primary patient-derived pancreatic cancer xenografts and in a metastatic PAN02 mouse model of pancreatic cancer, focusing on specific cellular interactions in the stroma, pancreatic tumor growth and metastasis. Greater than 90% of Cellax-DTX particles accumulate in smooth muscle actin (SMA) positive cancer-associated fibroblasts which results in long-term depletion of this stromal cell population, an effect not observed with Nab-paclitaxel (Nab-PTX). The reduction in stromal density leads to a >10-fold increase in tumor perfusion, reduced tumor weight and a reduction in metastasis. Consentingly, Cellax-DTX treatment increased survival when compared to treatment with gemcitabine or Nab-PTX in a metastatic PAN02 mouse model. Cellax-DTX nanoparticles interact with the tumor-associated stroma, selectively interacting with and depleting SMA positive cells and macrophage, effects of which are associated with significant changes in tumor progression and metastasis.

Docetaxel-carboxymethylcellulose nanoparticles display enhanced anti-tumor activity in murine models of castration-resistant prostate cancer.

Docetaxel (DTX) remains the only effective drug for prolonging survival and improving quality of life of metastatic castration resistant prostate cancer (mCRPC) patients. Despite some clinical successes with DTX-based therapies, advent of cumulative toxicity and development of drug resistance limit its long-term clinical application. The integration of nanotechnology for drug delivery can be exploited to overcome the major intrinsic limitations of DTX therapy for mCRPC. We evaluated whether reformulation of DTX by facile conjugation to carboxymethylcellulose nanoparticles (Cellax) can improve the efficacy and safety of the drug in s.c. and bone metastatic models of CRPC. A single dose of the nanoparticles completely regressed s.c. PC3 tumor xenografts in mice. In addition, Cellax elicited fewer side effects compared to native DTX. Importantly, Cellax did not increase the expression of drug resistance molecules in androgen-independent PC3 prostate cancer cells in comparison with DTX. Lastly, in a bone metastatic model of CRPC, Cellax treatment afforded a 2- to 3-fold improvement in survival and enhancements in quality-of-life of the animals over DTX and saline controls. These results demonstrate the potential of Cellax in improving the treatment of mCRPC.

Docetaxel conjugate nanoparticles that target α-smooth muscle actin-expressing stromal cells suppress breast cancer metastasis.

Docetaxel-conjugate nanoparticles, known as Cellax, were synthesized by covalently conjugating docetaxel and polyethylene glycol to acetylated carboxymethylcellulose via ester linkages, yielding a polymeric conjugate that self-assembled into 120 nm particles suitable for intravenous administration. In 4T1 and MDA-MB-231 orthotopic breast tumor models, Cellax therapy reduced α-smooth muscle actin (α-SMA) content by 82% and 70%, respectively, whereas native docetaxel and nab-paclitaxel (albumin-paclitaxel nanoparticle, Abraxane) exerted no significant antistromal activity. In Cellax-treated mice, tumor perfusion was increased by approximately 70-fold (FITC-lectin binding), tumor vascular permeability was enhanced by more than 30% (dynamic contrast-enhanced magnetic resonance imaging), tumor matrix was decreased by 2.5-fold (immunohistochemistry), and tumor interstitial fluid pressure was suppressed by approximately 3-fold after Cellax therapy compared with the control, native docetaxel, and nab-paclitaxel groups. The antistromal effect of Cellax treatment corresponded to a significantly enhanced antimetastatic effect: lung nodules were reduced by 7- to 24-fold by Cellax treatment, whereas native docetaxel and nab-paclitaxel treatments were ineffective. Studies of the 4T1 tumor showed that more than 85% of the Cellax nanoparticles were delivered to the α-SMA+ stroma. Significant tumor stromal depletion occurred within 16 hours (∼50% depletion) postinjection, and the α-SMA+ stroma population was almost undetectable (∼3%) by 1 week. The 4T1 tumor epithelial cell population was not significantly reduced in the week after Cellax injection. These data suggest that Cellax targets tumor stroma and performs more efficaciously than docetaxel and nab-paclitaxel.

Tumor-targeted drug delivery using MR-contrasted docetaxel - carboxymethylcellulose nanoparticles.

A carboxymethylcellulose-based polymer conjugate with nanoparticle forming properties (Cellax) has been shown to enhance the pharmacokinetics, specificity of biodistribution, anti-tumor efficacy and safety of docetaxel (DTX) in comparison to the Taxotere™ formulation. We examined Cellax and Taxotere efficacy in four tumor models (EMT-6, B16F10, PC3, and MDA-MB-231), and observed variances in efficacy. To explore whether differences in tumor uptake of Cellax were responsible for these effects, we incorporated superparamagnetic iron oxide nanoparticles (SPIONs) into Cellax particles to enable magnetic resonance (MR) imaging (Cellax-MR). In the EMT-6 tumor model, Cellax-MR nanoparticles exhibited peak tumor accumulation 3-24 h post intravenous injection, and 3 days post-treatment, significant MR contrast was still detected. The amount of Cellax-MR deposited in the EMT-6 tumors was quantifiable as a hypointense volume fraction, a value positively correlated with drug content as determined by LC/MS analysis (R(2) = 0.97). In the four tumor models, Cellax-MR uptake was linearly associated with anti-tumor efficacy (R(2) > 0.9), and was correlated with blood vessel density (R(2) > 0.9). We have affirmed that nanoparticle uptake is variable in tumor physiology, and that this efficacy-predictive parameter can be non-invasively estimated in real-time using a theranostic variant of Cellax.

A docetaxel-carboxymethylcellulose nanoparticle outperforms the approved taxane nanoformulation, Abraxane, in mouse tumor models with significant control of metastases.

Cellax is a PEGylated carboxymethylcellulose conjugate of docetaxel (DTX) which condenses into a 120-nm nanoparticle, and was compared against the approved clinical taxane nanoformulation (Abraxane®) in mouse models. Cellax increased the systemic exposure of taxanes by 37× compared to Abraxane, and improved the delivery specificity: Cellax uptake was selective to the tumor, liver and spleen, with a 203× increase in tumor accumulation compared to Abraxane. The concentration of released DTX in Cellax treated tumors was well above the IC50 for at least 10 d, while paclitaxel released from Abraxane was undetectable after 24h. In s.c. PC3 (prostate) and B16F10 (melanoma) models, Cellax exhibited enhanced efficacy and was better tolerated compared to Abraxane. In an orthotopic 4T1 breast tumor model, Cellax reduced the incidence of lung metastasis to 40% with no metastasic incidence in other tissues. Mice treated with Abraxane displayed increased lung metastasic incidence (>85%) with metastases detected in the bone, liver, spleen and kidney. These results confirm that Cellax is a more effective drug delivery strategy compared to the approved taxane nanomedicine.

Comparative study of five antiepileptic drugs on a translational cognitive measure in the rat: relationship to antiepileptic property.

RATIONALE: Antiepileptic drugs (AEDs) have been available for many years; yet, new members of this class continue to be identified and developed due to the limitations of existing drugs, which include a propensity for cognitive impairment. However, there is little preclinical information about the cognitive effects they produce, which clinically include deficits in attention and slowing of reaction time. OBJECTIVES: The purpose of this study was to profile two first-generation AEDs, phenytoin and valproate, and three second-generation AEDs, levetiracetam, pregabalin and lacosamide. Initially, each drug was examined across a range of well characterised preclinical seizure tests, and then each drug was evaluated in the five-choice serial reaction time test (5-CSRTT) based on efficacious doses from the seizure tests. MATERIALS AND METHODS: Each AED was tested for anti-seizure efficacy in either (1) the maximal electroshock seizure test, (2) s.c. PTZ seizure test, (3) amygdala-kindled seizures and (4) the genetic absence epilepsy rat of Strasbourg model of absence seizures. On completion of these studies, each drug was tested in rats trained to asymptotic performance in the 5-CSRTT (0.5 s SD, 5 s ITI, 100 trials). Male rats were used in all studies. RESULTS: Each AED was active in at least one of the seizure tests, although only valproate was active in each test. In the 5-CSRT test, all drugs with the exception of levetiracetam, significantly slowed reaction time and increased omissions. Variable effects were seen on accuracy. The effect on omissions was reversed by increasing stimulus duration from 0.5 to 5 s, supporting a drug-induced attention deficit. Levetiracetam had no negative effect on performance; indeed, reaction time was slightly increased (i.e. faster). CONCLUSIONS: These results highlight somewhat similar effects of phenytoin, valproate, pregabalin and lacosamide on attention and reaction time, and comparison to efficacious doses from the seizure tests support the view that there may be a better separation with the newer AEDs. Levetiracetam had no detrimental effect in the 5-CSRTT, which may be consistent with clinical experience where the drug is considered to be well tolerated amongst the AED class.

The anti-epileptic drug lacosamide (Vimpat) has anxiolytic property in rodents.

Lacosamide ((R)-2-acetamido-N-benzyl-3-methoxypropionamide; formerly harkoseride, SPM 927; Vimpat), has been recently approved by US and European regulatory authorities for use as add-on therapy for partial-onset seizures in adults. Because a number of anti-epileptic drugs are used to treat conditions beyond epilepsy, including anxiety, in the present study we investigated the anxiolytic potential of lacosamide in a conditioned emotional response (CER) model in rat, and the mouse marble burying assay. In each test lacosamide produced a significant effect consistent with anxiolysis, i.e. lacosamide increased suppression ratio in the CER test, and reduced the number of marbles buried in the marble burying assay. The doses necessary for an anxiolytic effect were higher than those necessary for efficacy in seizure tests conducted in the same species. For example in the mouse, the lacosamide oral ED(50) in the maximal electroshock seizure (MES) and 6 Hz tests was 5.3 and 9.6 mg/kg respectively, and the minimal effective dose in the marble burying assay was 30 mg/kg. In both seizure and anxiety tests, the (S)-enantiomer of lacosamide was inactive suggesting a similar mechanism of action, possibly use-dependent inhibition of sodium channel function (Errington et al., 2008). Efficacy in the CER model was equivalent to diazepam and pregabalin (Lyrica). In tests of side-effects, lacosamide had no effect on choice accuracy in the delayed match to position task of working memory, although at the 30 mg/kg dose, response rates and response latencies were significantly affected. In sum, the present results identify for the first time, an anxiolytic potential of lacosamide.