P-glycoprotein expression and antiepileptic drug resistance

PaxlovidTM Information From FDA and Guidance for AES Members

This American Epilepsy Society (AES) official statement provides information and preliminary guidance to Society members related to the U.S. Food & Drug Administration (FDA) December 22, 2021 Emergency Use Authorization for Paxlovid™ for the oral treatment of mild to moderate COVID-19 in adults and children (≥12 years and weighing ≥40 kg). Paxlovid is likely to be widely prescribed, and important considerations for patients on antiseizure medications (ASMs) include key contraindications and potential toxicity or dose adjustments while taking Paxlovid. This statement highlights concerns and provides information about their pharmacologic basis. Of particular concern, concomitant use of Paxlovid with the ASMs carbamazepine, phenobarbital, phenytoin, and primidone is contraindicated, because they are strong inducers of the CYP3A4 isozyme that metabolizes Paxlovid and thereby could cause loss of virologic response and development of resistance. Alternate oral or intravenous COVID-19 treatments should be considered. A second concern is that Paxlovid may increase the plasma concentrations of many ASMs, because it inhibits the CYP3A4 isozyme. ASMs that are metabolized, at least in part, by CYP3A4 include cannabidiol, carbamazepine, clobazam, clonazepam, diazepam, ethosuximide, everolimus, felbamate, lacosamide, midazolam, oxcarbazepine, perampanel, stiripentol, tiagabine, and zonisamide. Patients receiving these medications may warrant closer monitoring while being treated with Paxlovid.

Silencing GnT-V reduces oxaliplatin chemosensitivity in human colorectal cancer cells through N-glycan alteration of organic cation transporter member 2

Organic cation transporter member 2 (OCT2) is an N-glycosylated transporter that has been shown to be closely associated with the transport of antitumor drugs. Oxaliplatin, a platinum-based drug, is used for the chemotherapy of colorectal cancer (CRC). However, oxaliplatin resistance is a major challenge in the treatment of advanced CRC. The aim of the present study was to better understand the mechanism underlying the chemosensitivity of CRC cells to oxaliplatin. The present study describes a potential novel strategy for enhancing oxaliplatin sensitivity involving the glycosylation of this drug transporter, specifically the modification of β-1,6-N-acetylglucosamine (GlcNAc) residues by N-acetylglucosaminyltransferase V (GnT-V). The results revealed that the downregulation of GnT-V inhibited the oxaliplatin chemosensitivity of CW-2 cells. Furthermore, the knockdown of GnT-V caused a marked reduction in the presence of β-1,6-GlcNAc structures on OCT2 and decreased the localization of OCT2 in the cytomembrane, which were associated with a reduced uptake of oxaliplatin in wild-type and oxaliplatin-resistant CW-2 cells. Overall, the study provides novel insights into the molecular mechanism by which GnT-V regulates the chemosensitivity to oxaliplatin, which involves the modulation of the drug transporter OCT2 by N-glycosylation in CRC cells.

5-(3,4,5-trimethoxybenzoyl)-4-methyl-2-(p-tolyl) imidazol (BZML) targets tubulin and DNA to induce anticancer activity and overcome multidrug resistance in colorectal cancer cells

Colorectal cancer (CRC) is one of the most common malignancies, and multidrug resistance (MDR) reduces the efficiency of anticancer drugs. Therefore, the development of novel anticancer drugs that are highly active against CRC with MDR is urgently needed. Our previous study showed that 5-(3,4,5-trimethoxybenzoyl)-4-methyl-2-(p-tolyl) imidazol (BZML) is not a P-glycoprotein (P-gp) substrate and has a potent anticancer effect against paclitaxel -sensitive or -resistant non-small-cell lung cancer (NSCLC) in vitro and in vivo. In the present study, we found that BZML exhibited strong anticancer activity not only in sensitive CRC cells (SW480 and HCT-116 cells) but also in intrinsically drug-resistant CRC cells (Caco2 cells). In addition, by targeting the colchicine binding site, BZML inhibited tubulin polymerization, which induced G2/M phase arrest, and it caused DNA damage by directly targeting DNA or producing ROS. Further, BZML induced apoptosis through the time-dependent ROS-mediated mitochondrial apoptotic pathway in the CRC cells. Additionally, BZML inhibited P-gp-mediated drug efflux and enhanced the inhibition of the cell growth that had been induced by paclitaxel or doxorubicin in Caco2 cells. In summary, BZML is a multi-targeted anticancer drug that targets tubulin and DNA, and the mechanisms underlying its potent anticancer activity involve disrupting microtubule assembly, causing DNA damage, inducing cell cycle arrest and eventually activating the ROS-mediated mitochondrial apoptotic pathway in SW480, HCT-116 and Caco2 cells. Therefore, the novel compound BZML is a promising anticancer drug that has tremendous potential for CRC treatment, especially for the treatment of drug-resistant CRC.

Searching for New Leads To Treat Epilepsy: Target-Based Virtual Screening for the Discovery of Anticonvulsant Agents

The purpose of this investigation is to contribute to the development of new anticonvulsant drugs to treat patients with refractory epilepsy. We applied a virtual screening protocol that involved the search into molecular databases of new compounds and known drugs to find small molecules that interact with the open conformation of the Nav1.2 pore. As the 3D structure of human Nav1.2 is not available, we first assembled 3D models of the target, in closed and open conformations. After the virtual screening, the resulting candidates were submitted to a second virtual filter, to find compounds with better chances of being effective for the treatment of P-glycoprotein (P-gp) mediated resistant epilepsy. Again, we built a model of the 3D structure of human P-gp, and we validated the docking methodology selected to propose the best candidates, which were experimentally tested on Nav1.2 channels by patch clamp techniques and in vivo by the maximal electroshock seizure (MES) test. Patch clamp studies allowed us to corroborate that our candidates, drugs used for the treatment of other pathologies like Ciprofloxacin, Losartan, and Valsartan, exhibit inhibitory effects on Nav1.2 channel activity. Additionally, a compound synthesized in our lab, N, N'-diphenethylsulfamide, interacts with the target and also triggers significant Na1.2 channel inhibitory action. Finally, in vivo studies confirmed the anticonvulsant action of Valsartan, Ciprofloxacin, and N, N'-diphenethylsulfamide.

Polymorphisms in ABCB1 and EPHX1 genes influence drug effectiveness in refractory epilepsy: a retrospective study

Aim: Thirty percent of epileptic patients are refractory to treatment. We investigated the association between the number of seizures in refractory epileptic patients and potential interactions between their antiepileptic medications (AEDs) and single nucleotide polymorphisms in genes ABCB1, CYP2C9 and EPHX1. Methods: Thirty-three adult patients were included and tested for genetic variations using the Neuropharmagen® test. Retrospective data on AED therapy and number of seizures during the 12 months before inclusion were extracted from clinical records. Results: Patients displaying potential single nucleotide polymorphisms × AED interactions had a median of 14.5 seizures during the previous 12 months (IQR 5.5–105.0), compared to a median of 7.0 seizures (IQR 4.0–12.0) in patients without these interactions (univariate p = 0.051, adjusted p = 0.034). Conclusion: Refractory patients carrying genetic variations potentially affecting their AED medication experienced a significantly higher number of seizures. Thus, genotyping could help to better control epilepsy in some refractory patients.

Analysis of the Variables Influencing Valproic Acid Concentration in the Serum and Cerebrospinal Fluid of Chinese Patients After Craniotomy

BACKGROUND

Valproic acid (VPA) has been widely used in Chinese patients after craniotomy. Many studies have focused on the influencing factors of VPA serum concentration, but conclusions are sometimes paradoxical. Furthermore, the concentration of VPA in the cerebrospinal fluid (CSF) has been rarely reported. In the present study, VPA CSF concentrations were measured, and the potential factors influencing serum concentration and CSF distribution of VPA were investigated. In addition, the functional relationship between serum and CSF concentration was explored.

METHODS

Subjects were patients who underwent craniotomy and were administrated with VPA and had a lumbar puncture. Serum and CSF VPA concentrations were measured by use of the Abbott i1000 system. CYP2C9 (430 C>T, 1075 A>C, 1076 T>C, 1080 C>G), UGT1A6 (541 A>G, 552 A>C), UGT2B7 (211 G>T, 802 C>T), and ABCB1 (1236 C>T, 2677 G>T/A, 3435 C>T) genotypes were determined by direct sequencing. Information, such as age, gender, and height, was collected, and their effect on serum and CSF VPA concentrations was investigated by univariate analysis and multiple linear regression analysis.

RESULTS

First, the concomitant use of carbapenems (β' = -0.422) and UGT1A6 (552 AA → AC) (β' = -0.249) had a significant negative correlation with the weight-adjusted VPA serum concentration (C:W ratio), whereas CYP2C9 (1075 AA → AC) (β' = 0.186) and gender (female compared with male) (β' = 0.322) showed a positive correlation with VPA serum C:W ratio. The coefficient of determination (R) was only 0.348. Second, the relationship between the serum concentration and the CSF square root of the concentration (R = 0.705) had a better linear fit. Third, serum VPA concentration (β' = 0.810), concomitant use of glycerol fructose (β' = 0.160), and age (≥65 compared with <65) (β' = 0.118) showed a positive correlation (R = 0.748) with the variability of square root of the concentration of the CSF.

CONCLUSIONS

In Chinese patients, after craniotomy, female patients with 1 or more of CYP2C9 (1075 AC) and UGT1A6 (552 AA) genotypes required a lower VPA dosage compared with male patient. There was a better-fitted linear relationship between VPA serum and the square root of CSF concentrations. CSF VPA concentrations were relatively stable, with only age and the use of glycerol fructose having a small influence.

Influence of the dual combination of silymarin and (-)-epigallocatechin gallate, natural dietary flavonoids, on the pharmacokinetics of oxcarbazepine in rats

Considering the potential of flavonoids in reversing the P-glycoprotein (P-gp)-mediated multidrug resistance, this work aimed to assess the combined effects of silymarin and (-)-epigallocatechin gallate (EPG) on the pharmacokinetics of the P-gp substrates oxcarbazepine (OXC) and licarbazepine (LIC). Rats were pre-treated intraperitoneally with silymarin (25 mg/kg), EPG (25 mg/kg), silymarin/EPG (12.5/12.5 mg/kg; 6.25/18.75 mg/kg; 18.75/6.25 mg/kg) or verapamil (25 mg/kg, reference P-gp inhibitor) before the intraperitoneal administration of OXC (50 mg/kg). Pre-treatment with dual silymarin/EPG combinations originated peak plasma concentrations of OXC and LIC (pharmacologically active metabolite of OXC) similar to those achieved in the presence of verapamil (positive control). Moreover, the effects promoted by silymarin/EPG combinations on the magnitude of systemic drug exposure to OXC and LIC were also reflected in the corresponding drug levels attained in the brain (biophase). These findings evidence the synergistic effect of silymarin and EPG in enhancing the degree of systemic exposure to OXC and LIC in rats, which occurred in a comparable extent to that observed with verapamil. Hence, our findings support the combination of flavonoid-type P-gp inhibitors and P-gp substrate antiepileptic drugs as a potential therapeutic strategy for the management of pharmacoresistant epilepsy.

Pregnane X Receptor Not Nuclear Factor-kappa B Up-regulates P-glycoprotein Expression in the Brain of Chronic Epileptic Rats Induced by Kainic Acid

Drug-resistance epilepsy (DRE) is attributed to the brain P-glycoprotein (P-gp) overexpression. We previously reported that nuclear factor-kappa B (NF-κB) played a critical role in regulating P-gp expression at the brain of the acute seizure rats. This study was extended further to investigate the interaction effect of NF-κB and pregnane X receptor (PXR) on P-gp expression at the brain of chronic epileptic rats treated with carbamazepine (CBZ). The chronic epileptic models were induced by the micro-injection of kainic acid (KA) into rats' hippocampus. Subsequently, the successful models were treated with different intervention agents of CBZ; PMA(a non-specific PXR activity inhibitor) or PDTC(a specific NF-κB activity inhibitor) respectively. The expression levels of P-gp and its encoded gene mdr1a/b were significantly up-regulated on the brain of KA-induced chronic epilepsy rats or the epilepsy rats treated with CBZ for 1 week, meanwhile with a high expression of PXR. The treatment of PMA dramatically reduced both PXR and P-gp expressions at the protein and mRNA levels in the chronic epilepsy brain. By compared to the epilepsy model group, the P-gp expression was not markedly attenuated by the inhibition of NF-κB activity with PDTC treatment, nevertheless with a decrease of NF-κB expression in this intervention group. Higher levels of proinflammatory cytokines(IL-1β, IL-6, TNF-α) were found both in the brain tissue and the serum in the epilepsy rats of each group. There was a declined trend of the pro-inflammatory cytokines expression of the PDTC treatment group but with no statistical significance. This study demonstrates for the first time that P-gp up-regulation is due to increase PXR expression in the chronic phase of epilepsy, differently from that NF-κB signaling may induce the P-gp expression in the acute seizure phase. Our results offer insights into the mechanism underlying the development of DRE using or not using CBZ treatment.

MiR-466b-1-3p regulates P-glycoprotein expression in rat cerebral microvascular endothelial cells

Epilepsy is one of the most common neurological disorders, and approximately one-third of epilepsy cases are resistant to treatment with anti-epileptic drug (AED). P-glycoprotein (P-gp) is a multi-drug transporter that is thought to play a pivotal role in multiple drug resistance (MDR) in epilepsy. The regulatory mechanism of P-gp remains largely unknown; however, recent studies have demonstrated that microRNAs (miRNAs) may regulate the chemo-resistance mediated by P-gp. This study investigated the effect of specific miRNAs that regulate P-gp expression in rat cerebral microvascular endothelial cells (RCMECs). Primary cultures of RCMECs were treated with phenobarbital (PB) at various concentrations to induce P-gp overexpression. MiRNA microarrays were used to investigate the expression profiles of miRNAs in the resistant RCMECs induced by PB and corresponding non-resistant cells. Our data demonstrated decreased miR-466b-1-3p expression in the resistant cells compared with the non-resistant cells. Moreover, the recombinant RNA of 466b-1-3p (mimic) and the artificial antisense RNA of miR-466b-1-3p (inhibitor) were constructed and transfected into resistant RCMECs. The expression and function of P-gp were measured by Western blotting, quantitative real-time polymerase chain reaction (qRT-PCR) and flow cytometry using rhodamine efflux. The mRNA and protein levels of P-gp increased as the concentration of PB increased, whereas miR-466b-1-3p levels decreased with increasing PB concentrations (P<0.05). The miR-466b-1-3p mimic down-regulated P-gp expression, whereas the miR-466b-1-3p inhibitor up-regulated P-gp expression (P<0.05). These findings demonstrate that miR-466b-1-3p may regulate PB-induced P-gp expression in RCMECs.

Inhibition of mTOR Pathway by Rapamycin Decreases P-glycoprotein Expression and Spontaneous Seizures in Pharmacoresistant Epilepsy

The mammalian target of rapamycin (mTOR) has been demonstrated to mediate multidrug resistance in various tumors by inducing P-glycoprotein (P-gp) overexpression. Here, we investigated the correlation between the mTOR pathway and P-gp expression in pharmacoresistant epilepsy. Temporal cortex specimens were obtained from patients with refractory mesial temporal lobe epilepsy (mTLE) and age-matched controls who underwent surgeries at West China Hospital of Sichuan University between June 2014 and May 2015. We established a rat model of epilepsy kindled by coriaria lactone (CL) and screened pharmacoresistant rats (non-responders) using phenytoin. Non-responders were treated for 4 weeks with vehicle only or with the mTOR pathway inhibitor rapamycin at doses of 1, 3, and 6 mg/kg. Western blotting and immunohistochemistry were used to detect the expression of phospho-S6 (P-S6) and P-gp at different time points (1 h, 8 h, 1 day, 3 days, 1 weeks, 2 weeks, and 4 weeks) after the onset of treatment. Overexpression of P-S6 and P-gp was detected in both refractory mTLE patients and non-responder rats. Rapamycin showed an inhibitory effect on P-S6 and P-gp expression 1 week after treatment in rats. In addition, the expression levels of P-S6 and P-gp in the 6 mg/kg group were significantly lower than those in the 1 mg/kg or the 3 mg/kg group at the same time points (all P < 0.05). Moreover, rapamycin decreased the duration and number of CL-induced seizures, as well as the stage of non-responders (all P < 0.05). The current study indicates that the mTOR signaling pathway plays a critical role in P-gp expression in drug-resistant epilepsy. Inhibition of the mTOR pathway by rapamycin may be a potential therapeutic approach for pharmacoresistant epilepsy.

ABC transporters P-gp and Bcrp do not limit the brain uptake of the novel antipsychotic and anticonvulsant drug cannabidiol in mice

Cannabidiol (CBD) is currently being investigated as a novel therapeutic for the treatment of CNS disorders like schizophrenia and epilepsy. ABC transporters such as P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) mediate pharmacoresistance in these disorders. P-gp and Bcrp are expressed at the blood brain barrier (BBB) and reduce the brain uptake of substrate drugs including various antipsychotics and anticonvulsants. It is therefore important to assess whether CBD is prone to treatment resistance mediated by P-gp and Bcrp. Moreover, it has become common practice in the drug development of CNS agents to screen against ABC transporters to help isolate lead compounds with optimal pharmacokinetic properties. The current study aimed to assess whether P-gp and Bcrp impacts the brain transport of CBD by comparing CBD tissue concentrations in wild-type (WT) mice versus mice devoid of ABC transporter genes. P-gp knockout (Abcb1a/b (-∕-)), Bcrp knockout (Abcg2 (-∕-)), combined P-gp/Bcrp knockout (Abcb1a/b (-∕-) Abcg2 (-∕-)) and WT mice were injected with CBD, before brain and plasma samples were collected at various time-points. CBD results were compared with the positive control risperidone and 9-hydroxy risperidone, antipsychotic drugs that are established ABC transporter substrates. Brain and plasma concentrations of CBD were not greater in P-gp, Bcrp or P-gp/Bcrp knockout mice than WT mice. In comparison, the brain/plasma concentration ratios of risperidone and 9-hydroxy risperidone were profoundly higher in P-gp knockout mice than WT mice. These results suggest that CBD is not a substrate of P-gp or Bcrp and may be free from the complication of reduced brain uptake by these transporters. Such findings provide favorable evidence for the therapeutic development of CBD in the treatment of various CNS disorders.

eEF-2 Phosphorylation Down-Regulates P-Glycoprotein Over-Expression in Rat Brain Microvessel Endothelial Cells

Objective

We investigated whether glutamate, NMDA receptors, and eukaryote elongation factor-2 kinase (eEF-2K)/eEF-2 regulate P-glycoprotein expression, and the effects of the eEF-2K inhibitor NH125 on the expression of P-glycoprotein in rat brain microvessel endothelial cells (RBMECs).

Methods

Cortex was obtained from newborn Wistar rat brains. After surface vessels and meninges were removed, the pellet containing microvessels was resuspended and incubated at 37°C in culture medium. Cell viability was assessed by the MTT assay. RBMECs were identified by immunohistochemistry with anti-vWF. P-glycoprotein, phospho-eEF-2, and eEF-2 expression were determined by western blot analysis. Mdr1a gene expression was analyzed by RT-PCR.

Results

Mdr1a mRNA, P-glycoprotein and phospho-eEF-2 expression increased in L-glutamate stimulated RBMECs. P-glycoprotein and phospho-eEF-2 expression were down-regulated after NH125 treatment in L-glutamate stimulated RBMECs.

Conclusions

eEF-2K/eEF-2 should have played an important role in the regulation of P-glycoprotein expression in RBMECs. eEF-2K inhibitor NH125 could serve as an efficacious anti-multidrug resistant agent.

In vivo P-glycoprotein function before and after epilepsy surgery

Objectives:

To study the functional activity of the multidrug efflux transporter P-glycoprotein (Pgp) at the blood-brain barrier of patients with temporal lobe epilepsy using (R)-[¹¹C]verapamil (VPM)-PET before and after temporal lobe surgery to assess whether postoperative changes in seizure frequency and antiepileptic drug load are associated with changes in Pgp function.

Methods:

Seven patients with drug-resistant temporal lobe epilepsy underwent VPM-PET scans pre- and postsurgery. Patients were followed up for a median of 6 years (range 4–7) after surgery. Pgp immunoreactivity in surgically resected hippocampal specimens was determined with immunohistochemistry.

Results:

Optimal surgical outcome, defined as seizure freedom and withdrawal of antiepileptic drugs, was associated with higher temporal lobe Pgp function before surgery, higher Pgp-positive staining in surgically resected hippocampal specimens, and reduction in global Pgp function postoperatively, compared with nonoptimal surgery outcome.

Conclusions:

The data from our pilot study suggest that Pgp overactivity in epilepsy is dynamic, and complete seizure control and elimination of antiepileptic medication is associated with reversal of overactivity, although these findings will require confirmation in a larger patient cohort.

Efficacy of verapamil as an adjunctive treatment in children with drug-resistant epilepsy: a pilot study

PURPOSE

Verapamil, a voltage-gated calcium channel blocker, has been occasionally reported to have some effect on reducing seizure frequency in drug-resistant epilepsy or status epilepticus. We aimed to investigate the efficacy of verapamil as add-on treatment in children with drug-resistant epilepsy.

METHODS

Seven children with drug-resistant structural-metabolic, unknown or genetic (e.g., Dravet syndrome [DS]) epilepsy received verapamil as an add-on drug to baseline antiepileptic therapy. Verapamil was slowly introduced at the dosage of 1mg/kg/day and titrated up to 1.5mg/kg/day. After completing the titration period, patients entered a 14-month maintenance period and were followed up at 3, 8, and 14 months. Heart monitoring was performed at baseline and at each follow-up. The primary outcome measure was the response of seizures to verapamil.

RESULTS

Three subjects with genetically determined DS showed a partial (reduction of 50-99%) response for all types of seizures. A patient with DS without known mutation showed a partial control of all types of seizures in the first 13 months; then seizures worsened and verapamil was suspended. Two patients with structural epilepsy and one with Lennox-Gastaut syndrome showed no improvement. Any side effects were recorded.

CONCLUSIONS

Add-on treatment with verapamil seems to have some effect in controlling seizures in patients with genetically determined DS. Our observations justify further research on the relationship between calcium channels, calcium channel blockers, and channelopathies.