Anticonvulsant drugs fail to modulate chemotherapy-induced cytotoxicity and growth inhibition of human malignant glioma cells

Analysis of Factors Affecting 5-ALA Fluorescence Intensity in Visualizing Glial Tumor Cells-Literature Review

Glial tumors are one of the most common lesions of the central nervous system. Despite the implementation of appropriate treatment, the prognosis is not successful. As shown in the literature, maximal tumor resection is a key element in improving therapeutic outcome. One of the methods to achieve it is the use of fluorescent intraoperative navigation with 5-aminolevulinic acid. Unfortunately, often the level of fluorescence emitted is not satisfactory, resulting in difficulties in the course of surgery. This article summarizes currently available knowledge regarding differences in the level of emitted fluorescence. It may depend on both the histological type and the genetic profile of the tumor, which is reflected in the activity and expression of enzymes involved in the intracellular metabolism of fluorescent dyes, such as PBGD, FECH, UROS, and ALAS. The transport of 5-aminolevulinic acid and its metabolites across the blood–brain barrier and cell membranes mediated by transporters, such as ABCB6 and ABCG2, is also important. Accompanying therapies, such as antiepileptic drugs or steroids, also have an impact on light emission by tumor cells. Accurate determination of the factors influencing the fluorescence of 5-aminolevulinic acid-treated cells may contribute to the improvement of fluorescence navigation in patients with highly malignant gliomas.

Therapeutic concentrations of anti-epileptic drugs do not inhibit the activity of the oncolytic adenovirus Delta24-RGD in malignant glioma

BACKGROUND

The oncolytic adenovirus Delta24-RGD is currently being tested in phase I trials for the treatment of glioblastoma (GBM). Literature suggests that frequently prescribed anticonvulsants for these patients, phenytoin (PHE), valproic acid (VPA) and levetiracetam (LEV), may interfere with cellular mechanisms of cancer or oncolytic virus activity. We therefore investigated the direct effects of these drugs on Delta24-RGD infection and oncolytic activity.

METHODS

The anticonvulsants PHE, VPA, and LEV were combined with Delta24-RGD treatment in established glioma cell lines as well as on a panel of patient-derived GBM cultures. Effects on infection efficiency were assessed using luciferase-encoding adenoviral vectors. Oncolytic activity was determined by WST-1 assay and viral progeny production was quantified by dilution titration.

RESULTS

IC50 values of the anti-epileptic drugs on the four glioma cell lines were far above clinically-relevant concentrations. At therapeutic concentrations, the anti-epileptics generally did not alter the infection efficiency of RGD-modified adenovirus, nor affect progeny production or oncolytic activity of Delta24-RGD. The only exception was found in U373 cells, where VPA slightly antagonised the oncolytic effect of Delta24-RGD (from 29% to 55% viability, p<0.01) as well as viral progeny production (60% decrease, p<0.01). Oncolysis by Delta24-RGD was not inhibited by the anti-epileptics in any of the patient-derived glioma cultures (n=6). In fact, in one culture a slight enhancement of viral oncolysis by PHE and LEV was found, from 89.7% viability to 76% and 62.4%, respectively (p<0.01)

CONCLUSIONS

Therapeutic levels of valproic acid, phenytoin and levetiracetam do not negatively interfere with the infection efficiency or oncolytic activity of Delta24-RGD in patient-derived GBM cells. Therefore, there is no indication that the choice of anticonvulsant for seizure control in glioma patients should take treatment with Delta24-RGD into account.

Improved therapeutic effect on malignant glioma with adenoviral suicide gene therapy combined with temozolomide

Malignant gliomas (MGs) are cancers with poor prognosis and limited therapeutic options. Herpes Simplex virus-1 thymidine kinase expressed from adenoviruses with prodrug ganciclovir (TK/GCV) is the best-characterized suicide gene therapy, whereas temozolomide (TMZ) is the first-line chemotherapy for MG. However, the potential of their combination has not been studied thoroughly. The aim of this study was to evaluate the therapeutic response of this combination and to study whether addition of valproic acid (VPA) could benefit the treatment outcome. Efficacies of different treatments were first studied in vitro in BT4C rat MG cells. Therapeutic assessment in vivo was done in an immunocompetent rat MG model for treatment efficacy and toxicity. In vitro, VPA was able to significantly enhance cytotoxicity and increase adenovirus-mediated transduction efficiency up to sevenfold. In vivo, rats receiving TK/GCV+TMZ had notably smaller tumors and enhanced survival (P<0.001) in comparison with control rats. However, VPA was not able to further enhance the treatment response in vivo. Leukocytopenia and thrombocytopenia were the major side effects. We conclude that careful optimization of the treatment schedules and doses of individual therapies are necessary to achieve an optimal therapeutic effect with TK/GCV+TMZ combination. No further in vivo benefit with VPA was observed.

Epilepsy meets cancer: when, why, and what to do about it?

The lifetime risk of having epileptic seizures is profoundly increased in patients with cancer: about 20% of all patients with systemic cancer may develop brain metastases. These patients and those with primary brain tumours have a lifetime risk of epilepsy of 20-80%. Moreover, exposure to chemotherapy or radiotherapy to the brain, cancer-related metabolic disturbances, stroke, and infection can provoke seizures. The management of epilepsy in patients with cancer includes diagnosis and treatment of the underlying cerebral pathological changes, secondary prophylaxis with antiepileptic drugs, and limiting of the effect of epilepsy and its treatment on the efficacy and tolerability of anticancer treatments, cognitive function, and quality of life. Because of the concern of drug-drug interactions, the pharmacological approach to epilepsy requires a multidisciplinary approach, specifically in a setting of rapidly increasing choices of agents both to treat cancer and cancer-associated epilepsy.

Valproic acid sensitizes human glioma cells for temozolomide and γ-radiation

Temozolomide (TMZ) is given in addition to radiotherapy in glioma patients, but its interaction with the commonly prescribed antiepileptic drug valproic acid (VPA) is largely unknown. Induction of DNA demethylation by VPA could potentially induce expression of the O(6)-methylguanine-DNA-methyltransferase (MGMT) protein, causing resistance to TMZ and thereby antagonizing its effect. Therefore, this study investigates the interaction between VPA, TMZ, and γ-radiation. Two glioma cell lines were used that differ in TMZ sensitivity caused by the absence (D384) or presence (T98) of the MGMT protein. VPA was administered before (24/48 h) or after (24 h) single doses of γ-radiation; or, after 24 h, VPA treatment was accompanied by a single dose of TMZ for another 24 h. For trimodal treatment the combination of VPA and TMZ was followed by single doses of γ-radiation. In both cell lines VPA caused enhancement of the radiation response after preincubation (DMF(0.2) 1.4 and 1.5) but not after postirradiation (DMF(0.2) 1.1 and 1.0). The combination of VPA and TMZ caused enhanced cytotoxicity (DMF(0.2) 1.7) in both the TMZ-sensitive cell line (D384) and the TMZ-resistant cell line (T98). The combination of VPA and TMZ caused a significant radiation enhancement (DMF(0.2) 1.9 and 1.6) that was slightly more effective than that of VPA alone. VPA does not antagonize the cytotoxic effects of TMZ. Preincubation with VPA enhances the effect of both γ-radiation and TMZ, in both a TMZ-sensitive and a TMZ-resistant human glioma cell line. VPA combined with TMZ may lead to further enhancement of the radiation response.

Prolonged survival with valproic acid use in the EORTC/NCIC temozolomide trial for glioblastoma

OBJECTIVE

This analysis was performed to assess whether antiepileptic drugs (AEDs) modulate the effectiveness of temozolomide radiochemotherapy in patients with newly diagnosed glioblastoma.

METHODS

The European Organization for Research and Treatment of Cancer (EORTC) 26981-22981/National Cancer Institute of Canada (NCIC) CE.3 clinical trial database of radiotherapy (RT) with or without temozolomide (TMZ) for newly diagnosed glioblastoma was examined to assess the impact of the interaction between AED use and chemoradiotherapy on survival. Data were adjusted for known prognostic factors.

RESULTS

When treatment began, 175 patients (30.5%) were AED-free, 277 (48.3%) were taking any enzyme-inducing AED (EIAED) and 135 (23.4%) were taking any non-EIAED. Patients receiving valproic acid (VPA) only had more grade 3/4 thrombopenia and leukopenia than patients without an AED or patients taking an EIAED only. The overall survival (OS) of patients who were receiving an AED at baseline vs not receiving any AED was similar. Patients receiving VPA alone (97 [16.9%]) appeared to derive more survival benefit from TMZ/RT (hazard ratio [HR] 0.39, 95% confidence interval [CI] 0.24-0.63) than patients receiving an EIAED only (252 [44%]) (HR 0.69, 95% CI 0.53-0.90) or patients not receiving any AED (HR 0.67, 95% CI 0.49-0.93).

CONCLUSIONS

VPA may be preferred over an EIAED in patients with glioblastoma who require an AED during TMZ-based chemoradiotherapy. Future studies are needed to determine whether VPA increases TMZ bioavailability or acts as an inhibitor of histone deacetylases and thereby sensitizes for radiochemotherapy in vivo.

Correlation of enzyme-inducing anticonvulsant use with outcome of patients with glioblastoma

BACKGROUND

Clinical trials involving patients with glioblastoma (GBM) distinguish cohorts who are treated with enzyme-inducing anticonvulsants (EIAC). Such anticonvulsants induce hepatic P450 microsomal enzymes, which accelerate the metabolism of certain chemotherapy and molecular targeted agents. However, the resultant effect of such induction on patient outcome has received limited study.

METHODS

We performed a correlative analysis of baseline EIAC use with outcome, using a cross-sectional database of 620 patients with newly diagnosed GBM treated prospectively on North Central Cancer Treatment Group trials.

RESULTS

At registration, 72% were receiving treatment with EIAC; 2% were receiving non-EIACs, and the 26% were not receiving anticonvulsants (26%). Surprisingly, in the multivariable Cox model, overall survival (OS) and progression-free survival (PFS) showed a positive correlation with EIAC use (hazard ratio [HR] = 0.75, p = 0.0028 and HR = 0.80, p = 0.022), even after adjustment for the known prognostic factors of age, performance status, extent of resection, steroid use, and baseline neurocognitive function. Specifically, the median OS was longer in EIAC compared with non-EIAC patients (12.3 vs 10.7 months, p = 0.0002). Similarly, PFS was longer in EIAC patients (5.6 vs 4.8 months, p = 0.003). No differences in median OS or PFS were observed when comparing patients with or without a history of seizures at baseline.

CONCLUSIONS

Paradoxically, enzyme-inducing anticonvulsant (EIAC) use correlated with superior outcome of patients with glioblastoma. These results suggest that in comparative clinical trials testing agents metabolized by P450 microsomal enzymes, treatment arms may need stratification for the proportion of patients receiving EIAC.

Carbamazepine induces mitotic arrest in mammalian Vero cells

We reported recently that the anticonvulsant drug carbamazepine, at supratherapeutic concentrations, exerts antiproliferative effects in mammalian Vero cells, but the underlying mechanism has not been elucidated. This motivates us to examine rigorously whether growth arrest was associated with structural changes in cellular organization during mitosis. In the present work, we found that exposure of the cells to carbamazepine led to an increase in mitotic index, mainly due to the sustained block at the metaphase/anaphase boundary, with the consequent inhibition of cell proliferation. Indirect immunofluorescence, using antibodies directed against spindle apparatus proteins, revealed that mitotic arrest was associated with formation of monopolar spindles, caused by impairment of centrosome separation. The final consequence of the spindle defects induced by carbamazepine, depended on the duration of cell cycle arrest. Following the time course of accumulation of metaphase and apoptotic cells during carbamazepine treatments, we observed a causative relationship between mitotic arrest and induction of cell death. Conversely, cells released from the block of metaphase by removal of the drug, continued to progress through mitosis and resume normal proliferation. Our results show that carbamazepine shares a common antiproliferative mechanism with spindle-targeted drugs and contribute to a better understanding of the cytostatic activity previously described in Vero cells. Additional studies are in progress to extend these initial findings that define a novel mode of action of carbamazepine in cultured mammalian cells.

Suberoylanilide hydroxamic acid (SAHA) has potent anti-glioma properties in vitro, ex vivo and in vivo

Current treatment modalities for malignant gliomas do not allow long-term survival. Here, we identify suberoylanilide hydroxamic acid (SAHA), an inhibitor of histone deacetylases (HDAC), as an effective experimental anti-glioma agent. Administration of SAHA to various glioma cell lines obtained from human, rat and mouse inhibited tumour cell growth in a range of 1-10 microm. This anti-glioma property is associated with up-regulation of the cell cycle control protein p21/WAF, as well as the induction of apoptosis. A novel tumour invasion model using slice cultures of rat brain corroborated the anti-glioma properties of SAHA in the organotypic brain environment. In this model, glioma invasion compromised adjacent brain parenchyma, and this tumour-associated cytotoxicity could be inhibited by SAHA. In addition, a 10-fold dose escalation experiment did not challenge the viability of cultured brain slices. In vivo, a single intratumoural injection of SAHA 7 days after orthotopic implantation of glioma cells in syngeneic rats doubled their survival time. These observations identify chromatin-modifying enzymes as possible and promising targets for the pharmacotherapy of malignant gliomas.

NCIC-CTG phase II study of gemcitabine in patients with malignant glioma (IND.94)

PURPOSE

We conducted a phase II multicentre study of gemcitabine in patients with anaplastic astrocytoma and glioblastoma multiforme at first relapse.

PATIENTS AND METHODS

Patients with anaplastic astrocytoma or glioblastoma multiforme receiving a stable dose of steroids and ECOG performance status < or = 3 were eligible for this study at the time of first relapse. One adjuvant chemotherapy regimen was permissible. Patients received gemcitabine 1000 mg/m2 i.v. weekly x 3, repeated on a four-weekly cycle.

RESULTS

Of 20 patients enrolled, 15 were evaluable for response, 19 for non-hematological toxicity and 18 for hematological toxicity. Seven patients had anaplastic astrocytoma (AA) and twelve glioblastoma multiforme (GBM). Age ranged from 28-71 years (median 50). Fifteen patients discontinued therapy due to disease progression. The median number of cycles administered was 1 (range 1-11); only two patients received more than three cycles. Hematologic toxicity was acceptable and no grade 4 toxicity was seen. One patient developed Pneumocystis pneumonia and eventual pulmonary embolism; one died of gastric hemorrhage related to steroid therapy. No objective responses were seen. Nine patients had stable disease (median duration 2.7 months, range 0.9-11.2).

CONCLUSIONS

Gemcitabine given in this dose and schedule seems well tolerated but is not active in patients with recurrent high-grade gliomas.

Resistance to methotrexate in SKOV-3 cell lines after chronic exposure to carbamazepine is associated with a decreased expression of folate receptor

The detrimental effect of chronic administration of carbamazepine (CBZ) on serum and erythrocyte folates of patients has been extensively analyzed. However, at present, no data have been reported on the effect of CBZ on the intracellular content and activity of antimetabolite cytotoxic agents that can be used together with CBZ in the treatment of cancer patients. To investigate this issue, we chronically exposed in vitro the human ovarian cancer cell line SKOV-3 (grown under physiological folate concentrations) to CBZ, thus selecting SKOV-CBZ clones (SKOV-CBZ-50-2, SKOV-CBZ-50-5 and SKOV-CBZ-100-2) able to grow in the continuous presence of the antiepileptic drug. All of the SKOV-CBZ clones were more resistant to methotrexate (MTX) than the parental cells. MTX resistance index, as determined by the ratio between MTX concentrations inhibiting cell growth by 50% (MTX IC(50)) in SKOV-CBZ clones and in the parental cells, ranged between 3- and 5-fold. This resistance was related to a reduced intracellular content of MTX. No alteration activity of the cellular enzymes directly involved in MTX cytotoxicity (dihydrofolate reductase, thymidylate synthase [TS] and folylpolyglutamate synthetase) was observed. SKOV-CBZ clones were cross-resistant to the TS inhibitors tomudex and CB3717, but not to the TS inhibitor 5-fluoro-deoxy uridine and other antineoplastic drugs (cisplatin, doxorubicin, vincristine and taxol), whose cellular uptake is derived from transmembrane transport mechanisms different from folate receptor alpha (FRalpha) or reduced folate carrier (RFC). FRalpha mRNA and protein levels were significantly lower in SKOV-CBZ clones than in the parental cells. The reduced level of FRalpha in SKOV-CBZ clones was associated with a decreased binding capacity of folic acid. No variation of mRNA RFC expression in the SKOV-CBZ clones as compared to the parental cells was observed. Thus, after chronic exposure to CBZ, SKOV-CBZ clones develop resistance towards MTX due to defective MTX uptake.