Seeing ophthalmologic problems in Parkinson disease: Results of a visual impairment questionnaire.

OBJECTIVE: To determine the prevalence and clinical effect of ophthalmologic symptoms in patients with Parkinson disease (PD), compared with controls, using a standardized questionnaire. METHODS: In this observational, cross-sectional, multicenter study, 848 patients with PD and 250 healthy controls completed the Visual Impairment in Parkinson's Disease Questionnaire (VIPD-Q). The VIPD-Q addressed 4 domains according to structures: (1) ocular surface; (2) intraocular; (3) oculomotor; and (4) optic nerve. The questionnaire also assessed the effect of ophthalmologic symptoms on daily activities. RESULTS: One or more ophthalmologic symptoms were reported by 82% (95% confidence interval [CI], 80-85) of patients, compared with 48% (95% CI, 42-54) of controls (p < 0.001). Patients with PD experienced more ophthalmologic symptoms across all domains than controls (p < 0.001), as reflected by a higher VIPD-Q total score among patients (median 10 [interquartile range (IQR) 13]) than controls (median 2 [IQR 5]; p < 0.001). Ophthalmologic symptoms interfered with daily activities in 68% (95% CI, 65-71) of patients, compared with 35% (95% CI, 29-41) of controls (p < 0.001). CONCLUSION: Patients with PD have a higher prevalence of ophthalmologic symptoms than controls. Moreover, these frequently interfere with daily activities. A screening questionnaire such as the VIPD-Q may help with identifying ophthalmologic symptoms in PD, thereby enabling more timely treatment.

Effectiveness of home-based and remotely supervised aerobic exercise in Parkinson's disease: a double-blind, randomised controlled trial.

BACKGROUND: High-intensity aerobic exercise might attenuate the symptoms of Parkinson's disease, but high-quality evidence is scarce. Moreover, long-term adherence remains challenging. We aimed to evaluate the effectiveness of aerobic exercise-gamified and delivered at home, to promote adherence-on relieving motor symptoms in patients with Parkinson's disease with mild disease severity who were on common treatment regimes. METHODS: In this single-centre, double-blind, randomised controlled trial (Park-in-Shape), we recruited sedentary patients with Parkinson's disease from the outpatient clinic at Radboudumc, Nijmegen, Netherlands. Patients were made aware of the study either by their treating neurologist or via information in the waiting room. Patients could also contact the study team via social media. We included patients aged 30-75 years with a Hoehn and Yahr stage of 2 or lower, who were on stable dopaminergic medication. Patients were randomly assigned (in a 1:1 ratio) to either aerobic exercise done on a stationary home-trainer (aerobic intervention group) or stretching (active control group) by means of a web-based system with minimisation for sex and medication status (treated or untreated) and permuted blocks of varying sizes of more than two (unknown to study personnel). Patients were only aware of the content of their assigned programme. Assessors were unaware of group assignments. Both interventions were home based, requiring 30-45 min training three times per week for 6 months. Both groups received a motivational app and remote supervision. Home trainers were enhanced with virtual reality software and real-life videos providing a so-called exergaming experience (ie, exercise enhanced by gamified elements). The primary outcome was the between-group difference in the Movement Disorders Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) motor section at 6 months, tested during the off state (≥12 h after last dopaminergic medication). The analysis was done on an intention-to-treat basis in patients who completed the follow-up assessment, regardless of whether they completed the assigned intervention. Patients reported adverse events directly to their coach and also after the 6-month visit retrospectively. A between-group difference of 3·5 points or more was deemed a-priori clinically relevant. The study is concluded and registered with the Dutch Trial Registry, NTR4743. FINDINGS: Between Feb 2, 2015, and Oct 27, 2017, 139 patients were assessed for eligibility in person, of whom 130 were randomly assigned to either the aerobic intervention group (n=65) or the active control group (n=65). Data from 125 (96%) patients were available for the primary analysis; five patients were lost to follow-up (four in the intervention group; one in the control group). 20 patients (ten in each group) did not complete their assigned programme. The off-state MDS-UPDRS motor score revealed a between-group difference of 4·2 points (95% CI 1·6-6·9, p=0·0020) in favour of aerobic exercise (mean 1·3 points [SE 1·8] in the intervention group and 5·6 points [SE 1·9] for the control group). 11 patients had potentially related adverse events (seven [11%] in the intervention group, four [6%] in the control group) and seven had unrelated serious adverse events (three in the intervention group [vestibilar disorder, vasovagal collapse, knee injury during gardening that required surgery; 6%], four in the control group [supraventricular tachycardia, hip fracture, fall related injury, severe dyskinesias after suprathreshold dose levodopa in a patient with deep brain stimulation; 7%]). INTERPRETATION: Aerobic exercise can be done at home by patients with Parkinson's disease with mild disease severity and it attenuates off-state motor signs. Future studies should establish long-term effectiveness and possible disease-modifying effects. FUNDING: Netherlands Organization for Health Research and Development.

Improved Brain Penetration and Antitumor Efficacy of Temozolomide by Inhibition of ABCB1 and ABCG2.

The anticancer drug temozolomide is the only drug with proven activity against high-grade gliomas and has therefore become a part of the standard treatment of these tumors. P-glycoprotein (P-gp; ABCB1) and breast cancer resistance protein (BCRP; ABCG2) are transport proteins, which are present at the blood-brain barrier and limit the brain uptake of substrate drugs. We have studied the effect of P-gp and BCRP on the pharmacokinetics and pharmacodynamics of temozolomide, making use of a comprehensive set of in vitro transport experiments and in vivo pharmacokinetic and antitumor efficacy experiments using wild-type, Abcg2-/-, Abcb1a/b-/-, and Abcb1a/b;Abcg2-/- mice. We here show that the combined deletion of Abcb1a/b and Abcg2 increases the brain penetration of temozolomide by 1.5-fold compared to wild-type controls (P < .001) without changing the systemic drug exposure. Moreover, the same increase was achieved when temozolomide was given to wild-type mice in combination with the dual P-gp/BCRP inhibitor elacridar (GF120918). The antitumor efficacy of temozolomide against three different intracranial tumor models was significantly enhanced when Abcb1a/b and Abcg2 were genetically deficient or pharmacologically inhibited in recipient mice. These findings call for further clinical testing of temozolomide in combination with elacridar for the treatment of gliomas, as this offers the perspective of further improving the antitumor efficacy of this already active agent.

Standard set of health outcome measures for older persons.

BACKGROUND: The International Consortium for Health Outcomes Measurement (ICHOM) was founded in 2012 to propose consensus-based measurement tools and documentation for different conditions and populations.This article describes how the ICHOM Older Person Working Group followed a consensus-driven modified Delphi technique to develop multiple global outcome measures in older persons. The standard set of outcome measures developed by this group will support the ability of healthcare systems to improve their care pathways and quality of care. An additional benefit will be the opportunity to compare variations in outcomes which encourages and supports learning between different health care systems that drives quality improvement. These outcome measures were not developed for use in research. They are aimed at non researchers in healthcare provision and those who pay for these services. METHODS: A modified Delphi technique utilising a value based healthcare framework was applied by an international panel to arrive at consensus decisions.To inform the panel meetings, information was sought from literature reviews, longitudinal ageing surveys and a focus group. RESULTS: The outcome measures developed and recommended were participation in decision making, autonomy and control, mood and emotional health, loneliness and isolation, pain, activities of daily living, frailty, time spent in hospital, overall survival, carer burden, polypharmacy, falls and place of death mapped to a three tier value based healthcare framework. CONCLUSIONS: The first global health standard set of outcome measures in older persons has been developed to enable health care systems improve the quality of care provided to older persons.

Physical therapy and occupational therapy in Parkinson's disease.

Current medical management is only partially effective in controlling the symptoms of Parkinson's disease. As part of comprehensive multidisciplinary care, physical therapy and occupational therapy aim to support people with Parkinson's disease in dealing with the consequences of their disease in daily activities. In this narrative review, we address the limitations that people with Parkinson's disease may encounter despite optimal medical management, and we clarify both the unique and shared approaches that physical therapists and occupational therapists can apply in treating these limitations.

Large variety in a panel of human colon cancer organoids in response to EZH2 inhibition.

EZH2 inhibitors have gained great interest for their use as anti-cancer therapeutics. However, most research has focused on EZH2 mutant cancers and recently adverse effects of EZH2 inactivation have come to light. To determine whether colorectal cancer cells respond to EZH2 inhibition and to explore which factors influence the degree of response, we treated a panel of 20 organoid lines derived from human colon tumors with different concentrations of the EZH2 inhibitor GSK126. The resulting responses were associated with mutation status, gene expression and responses to other drugs. We found that the response to GSK126 treatment greatly varied between organoid lines. Response associated with the mutation status of ATRX and PAX2, and correlated with BIK expression. It also correlated well with response to Nutlin-3a which inhibits MDM2-p53 interaction thereby activating p53 signaling. Sensitivity to EZH2 ablation depended on the presence of wild type p53, as tumor organoids became resistant when p53 was mutated or knocked down. Our exploratory study provides insight into which genetic factors predict sensitivity to EZH2 inhibition. In addition, we show that the response to EZH2 inhibition requires wild type p53. We conclude that a subset of colorectal cancer patients may benefit from EZH2-targeting therapies.

Patient-centred physical therapy is (cost-) effective in increasing physical activity and reducing frailty in older adults with mobility problems: a randomized controlled trial with 6 months follow-up.

BACKGROUND: Despite the well-known health benefits of physical activity, it is a great challenge to stay physically active for frail-older adults with mobility limitations. The aim of this study was to test the (cost-) effectiveness of a patient-centred physical therapy strategy (Coach2Move) in which individualized treatment (motivational interviewing, physical examination, individualized goal setting, coaching and advice on self management, and physical training) is combined to increase physical activity level and physical fitness and, thereby, to decrease the level of frailty. METHODS: A randomized controlled trial was performed in 13 physical therapy practices with measurements at 3 and 6 months. Eligible patients were aged 70 years or over and had mobility problems (i.e. difficulties with walking, moving, getting up and changing position from bed or chair to standing, or stair climbing). The primary outcome was physical activity (total and moderate intensity) in minutes per day. Secondary outcomes were as follows: frailty, walking speed and distance, mobility, and quality of life. Data were analysed using linear mixed models for repeated measurements. Healthcare costs and quality-adjusted life years (QALYs) were computed and combined using net monetary benefit (NMB) for different willingness to pay thresholds. Data on costs, QALYs, and NMBs were analysed using linear mixed models. RESULTS: One hundred and thirty patients participated in this study. At 6 months, the between-group difference was significant for moderate-intensity physical activity in favour of the Coach2Move group [mean difference: 17.9 min per day; 95% confidence interval (CI) 4.0 to 34.9; P = 0.012]. The between-group difference for total physical activity was 14.1 min per day (95% CI -6.6 to 34.9; P = 0.182). Frailty decreased more in the Coach2Move group compared with usual care [mean difference: -0.03 (95% CI: -0.06 to -0.00; P = 0.027)]. Compared with usual treatment, the Coach2Move strategy resulted in cost savings (€849.8; 95% CI: 1607 to 90; P = 0.028), an improvement in QALYs, (0.02; 95% CI: 0.00 to 0.03; P = 0.03), and a higher NMB at every willingness to pay threshold. CONCLUSIONS: Older adults with mobility problems are able to safely increase physical activity in their own environment and reduce frailty. This study emphasizes both the potential cost-effectiveness of a patient-centred approach in the frail elderly and the importance of physical activity promotion in older adults with mobility limitations.

Nonpharmacological treatments for patients with Parkinson's disease.

Since 2013, a number of studies have enhanced the literature and have guided clinicians on viable treatment interventions outside of pharmacotherapy and surgery. Thirty-three randomized controlled trials and one large observational study on exercise and physiotherapy were published in this period. Four randomized controlled trials focused on dance interventions, eight on treatment of cognition and behavior, two on occupational therapy, and two on speech and language therapy (the latter two specifically addressed dysphagia). Three randomized controlled trials focused on multidisciplinary care models, one study on telemedicine, and four studies on alternative interventions, including music therapy and mindfulness. These studies attest to the marked interest in these therapeutic approaches and the increasing evidence base that places nonpharmacological treatments firmly within the integrated repertoire of treatment options in Parkinson's disease.

Prolonged Ezh2 Depletion in Glioblastoma Causes a Robust Switch in Cell Fate Resulting in Tumor Progression.

EZH2 is frequently overexpressed in glioblastoma (GBM), suggesting an oncogenic function that could be a target for therapeutic intervention. However, reduced EZH2 activity can also promote tumorigenesis, leading to concerns about the use of EZH2 inhibitors. Here, we provide further insight about the effects of prolonged Ezh2 inhibition in glioblastoma using preclinical mouse models and primary tumor-derived human GBM cell lines. Using doxycycline-inducible shRNAs that mimic the effects of a selective EZH2 inhibitor, we demonstrate that prolonged Ezh2 depletion causes a robust switch in cell fate, including significantly enhanced proliferation, DNA damage repair, and activation of part of the pluripotency network, resulting in altered tumor cell identity and tumor progression. Short-term Ezh2 depletion significantly improved survival without the tumor progression observed upon prolonged Ezh2 depletion, suggesting that precise dosing regiments are very important. These results could be of high clinical relevance with regard to how glioblastomas should be treated with epigenetic therapies.

In vivo RNAi screen for BMI1 targets identifies TGF-ß/BMP-ER stress pathways as key regulators of neural- and malignant glioma-stem cell homeostasis.

In mouse and human neural progenitor and glioblastoma "stem-like" cells, we identified key targets of the Polycomb-group protein BMI1 by combining ChIP-seq with in vivo RNAi screening. We discovered that Bmi1 is important in the cellular response to the transforming growth factor-ß/bone morphogenetic protein (TGF-ß/BMP) and endoplasmic reticulum (ER) stress pathways, in part converging on the Atf3 transcriptional repressor. We show that Atf3 is a tumor-suppressor gene inactivated in human glioblastoma multiforme together with Cbx7 and a few other candidates. Acting downstream of the ER stress and BMP pathways, ATF3 binds to cell-type-specific accessible chromatin preloaded with AP1 and participates in the inhibition of critical oncogenic networks. Our data support the feasibility of combining ChIP-seq and RNAi screens in solid tumors and highlight multiple p16(INK4a)/p19(ARF)-independent functions for Bmi1 in development and cancer.

Restricted brain penetration of the tyrosine kinase inhibitor erlotinib due to the drug transporters P-gp and BCRP.

PURPOSE: Erlotinib (Tarceva®, OSI-774) is a small molecule inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase. As high-grade gliomas frequently show amplification, overexpression and/or mutation of EGFR, this drug has been tested in several clinical trials with glioblastoma patients, but unfortunately, with little success. As erlotinib is a known substrate of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) we have investigated the effect of these ABC-transporters on the brain penetration of erlotinib. STUDY DESIGN: Erlotinib (50 mg/kg) was given by i.p. administration to wild-type (WT), Mdr1ab(-/-) (single P-gp knockout), Bcrp1(-/-) (single Bcrp1 knockout) and Mdr1ab(-/-)Bcrp1(-/-) (compound P-gp and Bcrp1 knockout) mice. Drug levels in plasma and tissues were determined by reversed-phase high-performance liquid chromatography. RESULTS: Relative to Mdr1ab(-/-)Bcrp1(-/-) mice that are deficient for both drug transporters, the area under the concentration time curve in brain tissue (AUC)(brain) of erlotinib decreased significantly by 1.6-fold in Mdr1ab(-/-) mice where Bcrp1 is present (49.6 ± 3.95 versus 31.1 ± 1.7, µg/g*h; P < 0.01). In Bcrp1(-/-) mice, were P-gp is present, a more pronounced 3.8-fold decrease to 13.0 ± 0.70, µg/g*h (P < 0.01) was observed, which is close to the 4.5-fold decrease in the AUC(brain) of erlotinib found in WT mice where both drug transporters are present (11.0 ± 1.35, P < 0.01). The plasma clearance of erlotinib was similar in mice deficient for P-gp and/or Bcrp1 compared with wild-type mice. In all other tissues the differences between the genotypes were negligible. CONCLUSIONS: Both P-gp and Bcrp1 reduce the brain penetration of erlotinib. Although P-gp appears to be the most effective factor limiting the brain penetration of erlotinib, the highest brain accumulation was observed when Bcrp1 was also absent. Strategies to inhibit P-gp/BCRP in patients to improve delivery of (novel molecular-targeted) substrate agents, such as erlotinib, to the brain may be required for treatment of intracranial malignancies.

Rapid and robust transgenic high-grade glioma mouse models for therapy intervention studies.

PURPOSE: To develop a transgenic mouse model of glioma that can be conveniently used for testing therapy intervention strategies. High-grade glioma is a devastating and uniformly fatal disease for which better therapy is urgently needed. Typical for high-grade glioma is that glioma cells infiltrate extensively into surrounding pivotal brain structures, thereby rendering current treatments largely ineffective. Evaluation of novel therapies requires the availability of appropriate glioma mouse models. EXPERIMENTAL DESIGN: High-grade gliomas were induced by stereotactic intracranial injection of lentiviral GFAP-Cre or CMV-Cre vectors into compound LoxP-conditional mice, resulting in K-Ras(v12) expression and loss of p16(Ink4a)/p19(Arf) with or without concomitant loss of p53 or Pten. RESULTS: Tumors reproduced many of the features that are characteristic for human high-grade gliomas, including invasiveness and blood-brain barrier functionality. Especially, CMV-Cre injection into p53;Ink4a/Arf;K-Ras(v12) mice resulted in high-grade glioma with a short tumor latency (2-3 weeks) and full penetrance. Early detection and follow-up was accomplished by noninvasive bioluminescence imaging, and the practical utility for therapy intervention was shown in a study with temozolomide. CONCLUSION: We have developed a realistic high-grade glioma model that can be used with almost the same convenience as traditional xenograft models, thus allowing its implementation at the forefront of preclinical evaluation of new treatments.

High-grade glioma mouse models and their applicability for preclinical testing.

High-grade gliomas (WHO grade III anaplastic astrocytoma and grade IV glioblastoma multiforme) are the most common primary tumors in the central nervous system in adults. Unfortunately, despite great efforts in finding better therapies, high-grade glioma remains among the most devastating and deadliest of all human cancers. During recent years, genetic and molecular alterations that underlie this disease have been identified and advanced our basic knowledge about gliomagenesis. Moreover, understanding the molecular biology has also led to the development of genetically engineered mouse models that resemble many of the features of human gliomas. Ideally, such "patient-like" models should be instrumental for preclinical testing of novel therapeutics, but thus far they have not yet been widely implemented for this purpose. This review will discuss the advantages and shortcomings of the established high-grade glioma mouse models with emphasis on their potential applicability for preclinical testing of novel drugs and treatment regimens.

Tumor microvasculature supports proliferation and expansion of glioma-propagating cells.

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor. The identification of 'cancer stem cells' (CSC) has shed new light on the potential mechanism of therapy resistance of these tumors. Because these cells appear to be more resistant to conventional treatments, they are thought to drive tumor regrowth after therapy. Therefore, novel therapeutic approaches that target these cells are needed. Tumor cells interact with their microenvironment. It has been reported that close contact between CSCs and tumor microvascular endothelium in GBM is important for CSCs to preserve their undifferentiated state and self-renewal ability. However, our understanding of this interaction is still rudimentary. This is in part due to a lack of suitable in vitro models that accurately represent the in vivo situation. Therefore, we set up a co-culture system consisting of primary brain tumor microvascular endothelial cells (tMVECs) and glioma propagating cells (GPCs) derived from biopsies of GBM patients. We found that tMVECs support the growth of GPCs resulting in higher proliferation rates comparing to GPCs cultured alone. This effect was dependent on direct contact between the 2 cell types. In contrast to GPCs, the FCS-cultured cell line U87 was stimulated by culturing on tMVEC-derived ECM alone, suggesting that both cell types interact different with their microenvironment. Together, these results demonstrate the feasibility and utility of our system to model the interaction of GPCs with their microenvironment. Identification of molecules that mediate this interaction could provide novel targets for directed therapy for GBM.

Effect of the ATP-binding cassette drug transporters ABCB1, ABCG2, and ABCC2 on erlotinib hydrochloride (Tarceva) disposition in in vitro and in vivo pharmacokinetic studies employing Bcrp1-/-/Mdr1a/1b-/- (triple-knockout) and wild-type mice.

UNLABELLED: We tested whether erlotinib hydrochloride (Tarceva, OSI-774), an orally active epidermal growth factor receptor tyrosine kinase inhibitor, is a substrate for the ATP-binding cassette drug transporters P-glycoprotein (P-gp; MDR1, ABCB1), breast cancer resistance protein (BCRP; ABCG2), and multidrug resistance protein 2 (MRP2; ABCC2) in vitro and whether P-gp and BCRP affect the oral pharmacokinetics of erlotinib hydrochloride in vivo. In vitro cell survival, drug transport, accumulation, and efflux of erlotinib were done using Madin-Darby canine kidney II [MDCKII; wild-type (WT), MDR1, Bcrp1, and MRP2] and LLCPK (WT and MDR1) cells and monolayers as well as the IGROV1 and the derived human BCRP-overexpressing T8 cell lines. In vivo, the pharmacokinetics of erlotinib after p.o. and i.p. administration was studied in Bcrp1/Mdr1a/1b(-/-) (triple-knockout) and WT mice. In vitro, erlotinib was actively transported by P-gp and BCRP/Bcrp1. No active transport of erlotinib by MRP2 was observed. In vivo, systemic exposure (P = 0.01) as well as bioavailability of erlotinib after oral administration (5 mg/kg) were statistically significantly increased in Bcrp1/Mdr1a/1b(-/-) knockout mice (60.4%) compared with WT mice (40.0%; P = 0.02). CONCLUSION: Erlotinib is transported efficiently by P-gp and BCRP/Bcrp1 in vitro. In vivo, absence of P-gp and Bcrp1 significantly affected the oral bioavailability of erlotinib. Possible clinical consequences for drug-drug and drug-herb interactions in patients in the gut between P-gp/BCRP-inhibiting substrates and oral erlotinib need to be addressed.

P-glycoprotein and breast cancer resistance protein: two dominant transporters working together in limiting the brain penetration of topotecan.

PURPOSE: The brain is a pharmacologic sanctuary site, due to the presence of the blood-brain barrier (BBB). Whereas the effect of P-glycoprotein (P-gp) at the BBB is well established, the role of breast cancer resistance protein (BCRP) that is also expressed at the BBB is not. EXPERIMENTAL DESIGN: We have studied the effect of BCRP by administering topotecan to wild-type (WT), single Mdr1a/b(-/-) and Bcrp1(-/-), and compound Mdr1a/b(-/-)Bcrp1(-/-) knockout mice. Drug levels in plasma and tissues were determined by high-performance liquid chromatography. RESULTS: The area under the plasma and tissue concentration-time curve (AUC) of topotecan in brains of Mdr1a/b(-/-) and Bcrp1(-/-) mice was only 1.5-fold higher compared with WT mice, but in Mdr1a/b(-/-)Bcrp1(-/-) mice, where both transporters are absent, the AUC increased by 12-fold. The AUC in plasma was approximately 0.75-, 2.4-, and 3.7-fold higher in Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) mice, respectively, resulting in 2.0-fold (P < 0.01), 0.65-fold (P, not significant), and 3.2-fold (P < 0.01), respectively, higher brain-to-plasma AUC ratios. Results using Mrp4(-/-) mice showed that this transporter had no effect on the brain penetration of topotecan. The P-gp/BCRP inhibitor elacridar fully inhibited P-gp-mediated transport of topotecan, whereas inhibition of Bcrp1-mediated transport by elacridar was minimal. CONCLUSIONS: Our results using Mdr1a/b(-/-)Bcrp1(-/-) mice clearly show the effect of Bcrp1 at the BBB and also show how two drug transporters act in concert to limit the brain penetration of topotecan. We expect that this finding will also apply to other drugs that are substrates of both P-gp and BCRP. Consequently, to improve the brain penetration of such compounds for targeting intracranial malignancies in patients, it will be essential to use potent inhibitors of both drug transporters.

Determination of topotecan in human and mouse plasma and in mouse tissue homogenates by reversed-phase high-performance liquid chromatography.

A sensitive and selective reversed-phase high-performance liquid chromatographic (HPLC) assay has been developed and validated for quantification of total topotecan in human and mouse plasma and in mouse tissue samples. Isocratic separation was achieved on a Zorbax SB-C(18) column and topotecan was monitored fluorimetrically. Two ranges of calibrations curves were used to determine lower levels of topotecan more accurately. Acceptable accuracy and precision was achieved for all matrices. Topotecan was stable upon repeated freeze-thawing for three cycles or storage for 24 h at ambient temperatures in spiked plasma samples and tissue homogenates, except in heart homogenates. In an additional validation experiment in which (14)C-labeled topotecan was administered to mice, the levels of unchanged topotecan were about 80-90% of the total radioactivity in tissue homogenates collected 10 min after drug administration and virtually similar as in plasma samples. However, results in tissue homogenates obtained 4 h post-drug administration indicated substantial metabolism of topotecan. This assay is suitable for studying the pharmacokinetics and tissue distribution of topotecan in mice. Our results demonstrate the importance of including all tissues of interest for pharmacokinetic studies in the validation procedure.

Blood-brain barrier and chemotherapeutic treatment of brain tumors.

The blood-brain barrier (BBB) is of pivotal importance to maintain homeostasis of the CNS, as it closely regulates the composition of the interstitial fluid in the brain. Unfortunately, malignancies that grow within the CNS may evade chemotherapeutic drugs using the same barrier, making this disease refractory to most chemotherapy regimens. This review will outline the impact of the BBB in brain cancer and discuss the efforts that have been made to enhance the drug exposure of brain tumors. Although this review will focus on the role of the BBB in primary brain cancer (malignant glioma), its impact on brain metastases will also be briefly discussed.