The accumulation of topotecan in 9L glioma and in brain parenchyma with and without dexamethasone administration

Glucocorticoids in the management of peritumoral brain edema: a review of molecular mechanisms

Peritumoral brain edema (PTBE) is mediated by blood-brain barrier breakdown. PTBE results from interstitial vasogenic brain edema due to vascular endothelial growth factor and other inflammatory products of brain tumors. Glucocorticoids (GCs) are the mainstay for treatment of PTBE despite significant systemic side effects. GCs are thought to affect multiple cell types in the edematous brain. Here, we review preclinical studies of GC effects on edematous brain and review mechanisms underlying GC action on tumor cells, endothelial cells, and astrocytes. GCs may reduce tumor cell viability and suppress vascular endothelial growth factor (VEGF) production in tumor cells. Modulation of expression and distribution of tight junction proteins occludin, claudin-5, and ZO-1 in endothelial cells likely plays a central role in GC action on endothelial cells. GCs may also have an effect on astrocyte angiopoietin production and limited effect on astrocyte aquaporin. A better understanding of these molecular mechanisms may lead to the development of novel therapeutics for management of PTBE with a better side effect profile.

Blood-brain barrier, cytotoxic chemotherapies and glioblastoma

INTRODUCTION

Glioblastomas (GBM) are the most common and aggressive primary malignant brain tumors in adults. The blood brain barrier (BBB) is a major limitation reducing efficacy of anti-cancer drugs in the treatment of GBM patients. Areas covered: Virtually all GBM recur after the first-line treatment, at least partly, due to invasive tumor cells protected from chemotherapeutic agents by the intact BBB in the brain adjacent to tumor. The passage through the BBB, taken by antitumor drugs, is poorly and heterogeneously documented in the literature. In this review, we have focused our attention on: (i) the BBB, (ii) the passage of chemotherapeutic agents across the BBB and (iii) the strategies investigated to overcome this barrier. Expert commentary: A better preclinical knowledge of the crossing of the BBB by antitumor drugs will allow optimizing their clinical development, alone or combined with BBB bypassing strategies, towards an increased success rate of clinical trials.

Efficacy of topotecan treatment on antioxidant enzymes and TBA-RS levels in submandibular glands of rabbits: An experimental study

OBJECTIVE:

The aim of this study was to investigate the effects of topotecan (Hycamtin), a topoisomerase I inhibiting anticancer agent, on antioxidant enzymes (SOD, CAT, and GSH-Px) and TBA-RS values of the submandibular glands of the rabbits.

STUDY DESIGN AND SETTING:

The study was conveyed in two groups (Group I, II) and control with a total of 24 rabbits. Eight rabbits in group I received intravenous (i.v.) topotecan (0.25 mg/kg once daily) for 3 days. Eight rabbits in group II received i.v. topotecan (0.5 mg/kg once daily) for 3 days. On the 15th day after administration of topotecan, sub-mandibular glands were removed and levels of the SOD, CAT, and GSH-Px and the TBA-RS in the sub-mandibular glands of the rabbits were examined.

RESULTS:

SOD, CAT, and GSH-Px values were significantly higher in high-dose topotecan group compared to control group ( P < 0.05). SOD and TBA-RS values were significantly higher in high-dose topotecan group compared to low-dose topotecan group ( P < 0.05).

CONCLUSION:

It was concluded that, to prevent the hazardous effects of oxygen free radicals due to topotecan, antioxidant enzymes SOD, CAT, and GSH-Px were increased. The higher levels of the TBA-RS values in group II showed that permanent damage was present because of high-dose topotecan administration in the submandibular glands of the rabbits.

Drug interactions at the blood-brain barrier: fact or fantasy?

There is considerable interest in the therapeutic and adverse outcomes of drug interactions at the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB). These include altered efficacy of drugs used in the treatment of CNS disorders, such as AIDS dementia and malignant tumors, and enhanced neurotoxicity of drugs that normally penetrate poorly into the brain. BBB- and BCSFB-mediated interactions are possible because these interfaces are not only passive anatomical barriers, but are also dynamic in that they express a variety of influx and efflux transporters and drug metabolizing enzymes. Based on studies in rodents, it has been widely postulated that efflux transporters play an important role at the human BBB in terms of drug delivery. Furthermore, it is assumed that chemical inhibition of transporters or their genetic ablation in rodents is predictive of the magnitude of interaction to be expected at the human BBB. However, studies in humans challenge this well-established paradigm and claim that such drug interactions will be lesser in magnitude but yet may be clinically significant. This review focuses on current known mechanisms of drug interactions at the blood-brain and blood-CSF barriers and the potential impact of such interactions in humans. We also explore whether such drug interactions can be predicted from preclinical studies. Defining the mechanisms and the impact of drug-drug interactions at the BBB is important for improving efficacy of drugs used in the treatment of CNS disorders while minimizing their toxicity as well as minimizing neurotoxicity of non-CNS drugs.

Topotecan in combination with radiotherapy in unresectable glioblastoma: a phase 2 study

Improving glioblastoma multiforme (GBM) treatment with radio-chemotherapy remains a challenge. Topotecan is an attractive option as it exhibits growth inhibition of human glioma as well as brain penetration. The present study assessed the combination of radiotherapy (60 Gy/30 fractions/40 days) and topotecan (0.9 mg/m(2)/day on days 1-5 on weeks 1, 3 and 5) in 50 adults with histologically proven and untreated GBM. The incidence of non-hematological toxicities was low and grade 3-4 hematological toxicities were reported in 20 patients (mainly lymphopenia and neutropenia). Partial response and stabilization rates were 2% and 32%, respectively, with an overall time to progression of 12 weeks. One-year overall survival (OS) rate was 42%, with a median OS of 40 weeks. Topotecan in combination with radiotherapy was well tolerated. However, while response and stabilization concerned one-third of the patients, the study did not show increased benefits in terms of survival in patients with unresectable GBM.

Topotecan treatment and its toxic effects on hematologic parameters and trace elements

The aim of this study was to investigate the effects of topotecan, a topoisomerase I-inhibiting anticancer agent, on hematologic parameters and serum levels of trace elements. The study was conducted on three groups consisting of 16 and 18 rabbits in the study groups and 15 rabbits in the control group. Rabbits in group I (n = 16) received high-dose topotecan intravenously (i.v.; 0.5 mg/kg once daily), while rabbits in group II (n = 18) received low-dose topotecan i.v. (0.25 mg/kg once daily) for 3 days. The 15 rabbits comprising the control group did not receive topotecan. Serum samples were collected from each rabbit on the first day, before the treatment, and on the 15th day of treatment. Erythrocytes, hemoglobin, white blood cell count, thrombocyte count, and trace elements such as selenium, copper, lead, zinc, and cobalt were analyzed. Hemoglobin levels and erythrocyte counts were lower in both study groups than in the control group. However, thrombocyte and leukocyte counts were similar in all three groups (p > 0.005). Serum trace element levels (copper, lead, zinc, and cobalt) did not differ significantly between groups. However, serum selenium levels were significantly lower in both study groups than the control group (p < 0.001). The results revealed that topotecan treatment causes a decrease in erythrocyte counts and hemoglobin levels due to bone marrow suppression, and these effects must be taken into account during treatment. In addition, selenium supplementation might be helpful in cancer patients receiving topotecan to increase the effect of the chemotherapeutic agent.

Chemotherapy delivery issues in central nervous system malignancy: a reality check

PURPOSE

This review assesses the current state of knowledge regarding preclinical and clinical pharmacology for brain tumor chemotherapy and evaluates relevant brain tumor pharmacology studies before October 2006.

RESULTS

Chemotherapeutic regimens in brain tumor therapy have often emerged from empirical clinical studies with retrospective pharmacologic explanations, rather than prospective trials of rational chemotherapeutic approaches. Brain tumors are largely composed of CNS metastases of systemic cancers. Primary brain tumors, such as glioblastoma multiforme or primary CNS lymphomas, are less common. Few of these tumors have well-defined optimal treatment. Brain tumors are protected from systemic chemotherapy by the blood-brain barrier (BBB) and by intrinsic properties of the tumors. Pharmacologic studies of delivery of conventional chemotherapeutics and novel therapeutics showing actual tumor concentrations and biologic effect are lacking.

CONCLUSION

In this article, we review drug delivery across the BBB, as well as blood-tumor and -cerebrospinal fluid (CSF) barriers, and mechanisms to increase drug delivery to CNS and CSF tumors. Because of the difficulty in treating CNS tumors, innovative treatments and alternative delivery techniques involving brain/cord capillaries, choroid plexus, and CSF are needed.

Pharmacokinetic considerations in the treatment of CNS tumours

Despite aggressive therapy, the majority of primary and metastatic brain tumour patients have a poor prognosis with brief survival periods. This is because of the different pharmacokinetic parameters of systemically administered chemotherapeutic agents between the brain and the rest of the body. Specifically, before systemically administered drugs can distribute into the CNS, they must cross two membrane barriers, the blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCB). To some extent, these structures function to exclude xenobiotics, such as anticancer drugs, from the brain. An understanding of these unique barriers is essential to predict when and how systemically administered drugs will be transported to the brain. Specifically, factors such as physiological variables (e.g. blood flow), physicochemical properties of the drug (e.g. molecular weight), as well as influx and efflux transporter expression at the BBB and BCB (e.g. adenosine triphosphate-binding cassette transporters) determine what compounds reach the CNS. A large body of preclinical and clinical research exists regarding brain penetration of anticancer agents. In most cases, a surrogate endpoint (i.e. CSF to plasma area under the concentration-time curve [AUC] ratio) is used to describe how effectively agents can be transported into the CNS. Some agents, such as the topoisomerase I inhibitor, topotecan, have high CSF to plasma AUC ratios, making them valid therapeutic options for primary and metastatic brain tumours. In contrast, other agents like the oral tyrosine kinase inhibitor, imatinib, have a low CSF to plasma AUC ratio. Knowledge of these data can have important clinical implications. For example, it is now known that chronic myelogenous leukaemia patients treated with imatinib might need additional CNS prophylaxis. Since most anticancer agents have limited brain penetration, new pharmacological approaches are needed to enhance delivery into the brain. BBB disruption, regional administration of chemotherapy and transporter modulation are all currently being evaluated in an effort to improve therapeutic outcomes. Additionally, since many chemotherapeutic agents are metabolised by the cytochrome P450 3A enzyme system, minimising drug interactions by avoiding concomitant drug therapies that are also metabolised through this system may potentially enhance outcomes. Specifically, the use of non-enzyme-inducing antiepileptic drugs and curtailing nonessential corticosteroid use may have an impact.

Effects of topotecan treatment on nasal, buccal, and lingual mucosa in the rabbit: light and transmission electron microscopic evaluation

Anticancer agents may cause side effects and some of which may be dose dependant. It is important for clinicians to see the effects on tissues histopathologically. The aim of this study was to investigate the effects of topotecan (hycamtin), a topoisomerase I inhibiting anticancer agent, on nasal, buccal, and lingual mucosa of rabbits. The study was carried out in two groups each consisting of 20 rabbits. Rabbits in group I received i.v. topotecan (0.5 mg/kg once daily) for 3 days. Rabbits in group II received i.v. topotecan (0.25 mg/kg once daily) for 3 days. In group I and II, biopsies from the nasal, buccal, and lingual mucosa were taken on the fourth (1 day after the 3-day topotecan treatment) and 15th day (12 days after the 3-day topotecan treatment). Light and transmission electron microscopic (TEM) observations have shown that nasal mucosa was not affected by topotecan administration. Topotecan treatment resulted in the formation of some ulcerative lesions in the lingual mucosa especially on the lower surface of the tongue. On the dorsal surface, the epithelium showed highly edematous and degenerating cells and separations in the stratum granulosum. In the buccal mucosa, effects were similar. In lingual and buccal mucosa, healing was observed on the 15th day. The oral (lingual and buccal) mucosal side effects of topotecan were observed as reversible and not dose dependent. It was concluded that these side effects are not severe, and topotecan may be used safely in cancer treatment.

Factors affecting delivery of antiviral drugs to the brain

Although the CNS is in part protected from peripheral insults by the blood-brain barrier and the blood-cerebrospinal fluid barrier, a number of human viruses gain access to the brain, replicate within this organ, or sustain latent infection. The efficacy of antiviral drugs towards the cerebral viral load is often limited as both blood-brain interfaces impede their cerebral distribution. For polar compounds, the major factor restricting their entry lies in the tight junctions that occlude the paracellular pathway across these barriers. For compounds with more favourable lipid solubility properties, CNS penetration will be function of a number of physicochemical factors that include the degree of lipophilicity, size and ability to bind to protein or red blood cells, as well as other factors inherent to the vascular and choroidal systems, such as the local cerebral blood flow and the surface area available for exchange. In addition, influx and efflux transport systems, or metabolic processes active in both capillary endothelial cells and choroid plexus epithelial cells, can greatly change the bioavailability of a drug in one or several compartments of the CNS. The relative importance of these various factors with respect to the CNS delivery of the different classes of antiviral drugs is illustrated and discussed.

Open-label simultaneous radio-chemotherapy of glioblastoma multiforme with topotecan in adults

BACKGROUND

Due to its radioresistance, the prognosis of glioblastoma multiforme (GBM) remains poor. Therefore, we investigated the impact of simultaneous radio-chemotherapy with topotecan (Hycamtin) on clinical outcome, tolerability and quality of life.

PATIENTS AND METHODS

In this multicenter trial, 60 patients (19 females, 41 males) with histologically proven (5x biopsy, 31x subtotal resection, 24x total resection) GBM were included. Radio-Chemotherapy was performed with daily doses of 2.0 Gy (total, 60 Gy), and 0.5 mg (absolute dose) of topotecan intravenously 1 h prior to irradiation. Toxicity was assessed using common toxicity criteria (CTC). General condition and quality of life were assessed at baseline, at the end of therapy, and 6 weeks post-therapy. Local control and length of survival were compared with an historical control group of 67 patients only treated with postoperative radiotherapy following stereotactic biopsy (15x), subtotal resection (39x), or total resection (13x).

RESULTS

57 patients completed the therapy. Median radiation dose was 60 Gy (range 16-76 Gy). Median cumulative topotecan dose was 15 mg (range 7.5-18.5 mg). CTC toxicity grade 3 was observed in six patients and grade 4 toxicity in two patients (three events). Two patients died of septic disease. Mean Karnofsky index was 87% at baseline, 81% at the end of therapy, and 80% at 6 weeks post-therapy. Median survival time was 15 months, significantly longer than the 11 months seen in the control group (P < 0.002). Extent of tumour resection or patient age did not have a significant effect on survival.

CONCLUSION

This multimodal approach is well tolerated, and quality of life remains preserved. The relatively long median survival time is promising but a further randomised double blind placebo controlled parallel designed clinical trial should be performed to confirm these results.

Efficacy of topotecan treatment on an experimental model of transient evoked otoacoustic emissions

OBJECTIVE

The aim of this study was to investigate the effects of topotecan (Hycamtin), a topoisomerase I inhibiting anticancer agent, on Transient Evoked Otoacoustic Emissions (TEOAEs) of the rabbits. We planned to investigate whether this test might provide a method for monitoring early ototoxic influence of drug administration to the cochlea.

METHODS

The study was conveyed in two groups each consisting of five rabbits with a total of ten ears. Rabbits in group I received i.v. topotecan (0.5 mg/kg once daily) for 3 days. Rabbits in group II received i.v. topotecan (0.25 mg/kg once daily) for 3 days. Cochlear function was serially monitored using transient evoked otoacoustic emissions before administration (BA) and on the 4th and 15th days after administration of topotecan. TEOAEs were analysed in terms of mean stimulus, stability and emission amplitude at 1.0-4.0 kHz.

RESULTS

For group I and II, intergroup and intragroup differences were not statistically significant in the mean stimulus, stability and emission amplitudes at 1.0-4.0 kHz.

CONCLUSIONS

We evaluated the potential role of TEOAEs in early identification of cochlear dysfunction induced by topotecan. It was concluded that topotecan did not have ototoxic effects on the cochlea in the early period of administration. TEOAEs may be useful to monitor the cochlear function and to detect the late stage of ototoxicity especially in the presence of potentially toxic factors for the prevention of permanent damage.

Central nervous system involvement in adult acute lymphocytic leukemia

With effective CNS prophylaxis, most adults with ALL may remain free of CNS leukemia. Several combinations of IT chemotherapy, high-dose systemic chemotherapy, and cranial irradiation have been used with varying results. Excellent prophylaxis can be achieved without cranial irradiation, and in view of the potential acute and long-term toxicity of radiation, these methods may be preferable. A prophylactic approach tailored to the risk of CNS leukemia was shown to be valuable in childhood ALL and in at least one adult study. Further studies should focus on defining risk groups for CNS leukemia and designing effective prophylaxis for each group. More research is needed to define the intensity and duration of treatment and the role of cranial irradiation in the treatment of isolated CNS relapses.

The blood-brain barrier and oncology: new insights into function and modulation

The efficacy of chemotherapy for malignant primary or metastatic brain tumours is still poor. This is at least partly due to the presence of the blood-brain barrier (BBB). The functionality of the BBB can be explained by physicochemical features and efflux pump mechanisms. An overview of the literature is presented with emphasis on oncology. The BBB consists of capillary endothelial cells that lack fenestrations and are connected together with continuous tight junctions, with a high electrical resistance. Permeability of tight junctions can be increased in vitro by contraction of the cytoskeleton, caused by bradykinin agonists. Different efflux pumps are present in the BBB. Examples are P-glycoprotein (P-gp), organic anion transporters, (OAT) and multidrug-resistance-associated proteins (MRP)(1 and 3). These pumps act as a multi-specific efflux pump for various chemotherapeutic drugs. Experiments have shown that P-gp can be inhibited by different non-chemotherapeutic substrates such as cyclosporin A. The functionality in vivo of P-gp can be measured with positron emission tomography and [(11)C]-verapamil or with single photon emission computer tomography and(99m)Tc-sestamibi. MRP(1)and MRP(3)act as organic anion transporters that in vitro act as efflux pumps for substances that are conjugated or co-transported with glutathione and glucuronide, respectively. Methotrexate has been recently demonstrated to be transported by MRP(1)and MRP(3). Results of studies which demonstrate the clinical relevance and applicability of BBB modulators are eagerly awaited.

Cytotoxic chemotherapy: advances in delivery, pharmacology, and testing

Adjuvant treatment of malignant gliomas, the most common types of primary brain tumors, with intravenous (iv) chemotherapy has not significantly improved survival for patients with these forms of cancer. A major factor in the failure of iv chemotherapy is the blood-brain barrier (BBB), a physiologic impediment to the delivery of cytotoxic chemotherapeutic drugs to the central nervous system (CNS). Intra-arterial and intrathecal infusion, blood-brain barrier disruption, high-dose chemotherapy, intratumoral administration, and convection-enhanced delivery are methods developed to overcome the BBB. Although some of these methods may increase the local concentration-time profile, improvement in clinical outcomes has yet to be definitively established. New methods for assessment of drug delivery to the brain tumor will assume increasing importance in the study of new cytotoxic chemotherapeutic drugs for these types of cancer. Pharmacokinetic studies are critical components of these clinical trials and allow assessment of drug delivery to the CNS and brain tumor. Additionally, pharmacokinetic studies will remain an important component of early clinical trials, particularly for identifying significant drug interactions involving the various supporting medications that are typically used in this patient population.

A North Central Cancer Treatment Group phase II trial of topotecan in relapsed gliomas

Current systemic treatment options for patients with relapsed gliomas are limited. The topoisomerase I inhibitor topotecan has demonstrated broad antitumor activity in both preclinical studies as well as a number of phase I and II trials in humans. Studies in primates have shown good cerebrospinal fluid levels of topotecan following systemic administration. We therefore performed this phase II trial in patients who developed evidence of progressive glioma after definitive radiation therapy. Patients were treated with 1.5 mg/m2 intravenously daily for 5 consecutive days repeated every three weeks. For patients who had received prior nitrosourea-containing chemotherapy, the starting dose was 1.25 mg/m2. Thirty-three patients were entered on this study. All patients were eligible and evaluable for both response and toxicity. Seven patients experienced grade 4 leukopenia with 2 of these patients dying of infection-related complications. Six of these seven patients were not taking anticonvulsants during treatment. Nine patients developed grade 3-4 thrombocytopenia, seven of whom were not taking anticonvulsants. Nonhematologic side effects were infrequent and manageable. One patient experienced a partial response to this treatment for an overall response rate of 3% (95% binomial confidence interval 0.3%-20.4%). The median time to progression was 14.9 weeks and median survival 19.9 weeks. Topotecan at this dose and schedule showed no substantial activity in relapsed gliomas.