Permeability changes and effect of chemotherapy in brain adjacent to tumor in an experimental model of metastatic brain tumor from breast cancer.

BACKGROUND: Brain tumor vasculature can be significantly compromised and leakier than that of normal brain blood vessels. Little is known if there are vascular permeability alterations in the brain adjacent to tumor (BAT). Changes in BAT permeability may also lead to increased drug permeation in the BAT, which may exert toxicity on cells of the central nervous system. Herein, we studied permeation changes in BAT using quantitative fluorescent microscopy and autoradiography, while the effect of chemotherapy within the BAT region was determined by staining for activated astrocytes. METHODS: Human metastatic breast cancer cells (MDA-MB-231Br) were injected into left ventricle of female NuNu mice. Metastases were allowed to grow for 28 days, after which animals were injected fluorescent tracers Texas Red (625 Da) or Texas Red dextran (3 kDa) or a chemotherapeutic agent 14C-paclitaxel. The accumulation of tracers and 14C-paclitaxel in BAT were determined by using quantitative fluorescent microscopy and autoradiography respectively. The effect of chemotherapy in BAT was determined by staining for activated astrocytes. RESULTS: The mean permeability of texas Red (625 Da) within BAT region increased 1.0 to 2.5-fold when compared to normal brain, whereas, Texas Red dextran (3 kDa) demonstrated mean permeability increase ranging from 1.0 to 1.8-fold compared to normal brain. The Kin values in the BAT for both Texas Red (625 Da) and Texas Red dextran (3 kDa) were found to be 4.32 ± 0.2 × 105 mL/s/g and 1.6 ± 1.4 × 105 mL/s/g respectively and found to be significantly higher than the normal brain. We also found that there is significant increase in accumulation of 14C-Paclitaxel in BAT compared to the normal brain. We also observed animals treated with chemotherapy (paclitaxel (10 mg/kg), erubilin (1.5 mg/kg) and docetaxel (10 mg/kg)) showed activated astrocytes in BAT. CONCLUSIONS: Our data showed increased permeation of fluorescent tracers and 14C-paclitaxel in the BAT. This increased permeation lead to elevated levels of activated astrocytes in BAT region in the animals treated with chemotherapy.

Liposomal Irinotecan Accumulates in Metastatic Lesions, Crosses the Blood-Tumor Barrier (BTB), and Prolongs Survival in an Experimental Model of Brain Metastases of Triple Negative Breast Cancer.

PURPOSE: The blood-tumor barrier (BTB) limits irinotecan distribution in tumors of the central nervous system. However, given that the BTB has increased passive permeability we hypothesize that liposomal irinotecan would improve local exposure of irinotecan and its active metabolite SN-38 in brain metastases relative to conventional irinotecan due to enhanced-permeation and retention (EPR) effect. METHODS: Female nude mice were intracardially or intracranially implanted with human brain seeking breast cancer cells (brain metastases of breast cancer model). Mice were administered vehicle, non-liposomal irinotecan (50 mg/kg), liposomal irinotecan (10 mg/kg and 50 mg/kg) intravenously starting on day 21. Drug accumulation, tumor burden, and survival were evaluated. RESULTS: Liposomal irinotecan showed prolonged plasma drug exposure with mean residence time (MRT) of 17.7 ± 3.8 h for SN-38, whereas MRT was 3.67 ± 1.2 for non-liposomal irinotecan. Further, liposomal irinotecan accumulated in metastatic lesions and demonstrated prolonged exposure of SN-38 compared to non-liposomal irinotecan. Liposomal irinotecan achieved AUC values of 6883 ± 4149 ng-h/g for SN-38, whereas non-liposomal irinotecan showed significantly lower AUC values of 982 ± 256 ng-h/g for SN-38. Median survival for liposomal irinotecan was 50 days, increased from 37 days (p<0.05) for vehicle. CONCLUSIONS: Liposomal irinotecan accumulates in brain metastases, acts as depot for sustained release of irinotecan and SN-38, which results in prolonged survival in preclinical model of breast cancer brain metastasis.

Anti-cancer Antibody Trastuzumab-Melanotransferrin Conjugate (BT2111) for the Treatment of Metastatic HER2+ Breast Cancer Tumors in the Brain: an In-Vivo Study.

PURPOSE: The ability of human melanotransferrin (hMTf) to carry a therapeutic concentration of trastuzumab (BTA) in the brain after conjugation (in the form of trastuzumab-melanotransferrin conjugate, BT2111 conjugate) was investigated by measuring the reduction of the number and size of metastatic human HER2+ breast cancer tumors in a preclinical model of brain metastases of breast cancer. METHODS: Human metastatic brain seeking breast cancer cells were injected in NuNu mice (n = 6-12 per group) which then developed experimental brain metastases. Drug uptake was analyzed in relation to metastasis size and blood-tumor barrier permeability. To investigate in-vivo activity against brain metastases, equimolar doses of the conjugate, and relevant controls (hMTf and BTA) in separate groups were administered biweekly after intracardiac injection of the metastatic cancer cells. RESULTS: The trastuzumab-melanotransferrin conjugate (BT2111) reduced the number of preclinical human HER2+ breast cancer metastases in the brain by 68% compared to control groups. Tumors which remained after treatment were 46% smaller than the control groups. In contrast, BTA alone had no effect on reducing number of metastases, and was associated with only a minimal reduction in metastasis size. CONCLUSIONS: The results suggest the novel trastuzumab-melanotransferrin conjugate (BT2111) may have utility in treating brain metastasis and validate hMTf as a potential vector for antibody transport across the Blood Brain Barrier (BBB).

NKTR-102 Efficacy versus irinotecan in a mouse model of brain metastases of breast cancer.

BACKGROUND: Brain metastases are an increasing problem in women with invasive breast cancer. Strategies designed to treat brain metastases of breast cancer, particularly chemotherapeutics such as irinotecan, demonstrate limited efficacy. Conventional irinotecan distributes poorly to brain metastases; therefore, NKTR-102, a PEGylated irinotecan conjugate should enhance irinotecan and its active metabolite SN38 exposure in brain metastases leading to brain tumor cytotoxicity. METHODS: Female nude mice were intracranially or intracardially implanted with human brain seeking breast cancer cells (MDA-MB-231Br) and dosed with irinotecan or NKTR-102 to determine plasma and tumor pharmacokinetics of irinotecan and SN38. Tumor burden and survival were evaluated in mice treated with vehicle, irinotecan (50 mg/kg), or NKTR-102 low and high doses (10 mg/kg, 50 mg/kg respectively). RESULTS: NKTR-102 penetrates the blood-tumor barrier and distributes to brain metastases. NKTR-102 increased and prolonged SN38 exposure (>20 ng/g for 168 h) versus conventional irinotecan (>1 ng/g for 4 h). Treatment with NKTR-102 extended survival time (from 35 days to 74 days) and increased overall survival for NKTR-102 low dose (30 % mice) and NKTR-102 high dose (50 % mice). Tumor burden decreased (37 % with 10 mg/kg NKTR-102 and 96 % with 50 mg/kg) and lesion sizes decreased (33 % with 10 mg/kg NKTR-102 and 83 % with 50 mg/kg NKTR-102) compared to conventional irinotecan treated animals. CONCLUSIONS: Elevated and prolonged tumor SN38 exposure after NKTR-102 administration appears responsible for increased survival in this model of breast cancer brain metastasis. Further, SN38 concentrations observed in this study are clinically achieved with 145 mg/m(2) NKTR-102, such as those used in the BEACON trial, underlining translational relevance of these results.

Deception by obfuscation: Studnicki et al.'s retracted longitudinal cohort study of emergency room utilization following abortion.

OBJECTIVES: In November 2022, the anti-abortion advocacy group Alliance for Hippocratic Medicine filed a lawsuit against the U.S. Food and Drug Administration challenging the initial 2000 approval of mifepristone and its subsequent approvals, which removed unnecessary restrictions on its use, by disputing the medication's safety record. Such challenges relied on a study examining the incidence of emergency room visits following medication abortion with mifepristone and procedural abortion using Medicaid claims data from 1999-2015. In February 2024 that study was retracted by its publisher. In this paper, we analyzed the methods and presentations of the data used in the study. STUDY DESIGN: We drew upon commonly accepted principles in responsible epidemiologic and scientific research to evaluate the methods and presentations of the data and organized our findings into themes. RESULTS: We found multiple instances of methodological flaws, mischaracterizations, and obfuscations of data in this study, including use of a misleading research question and framing, analytic flaws, inappropriate use of an unvalidated proxy measure for outcomes of interest, and inappropriate and deceptive visualizations of data. In each instance, the resulting effect obfuscated and misrepresented the safety of medication abortion with mifepristone. CONCLUSIONS: The misrepresentation and exaggeration of data promoted and exacerbated misinterpretations about the study's findings, resulting in substantial harm before it was retracted. Recognizing that ongoing judicial proceedings threaten access to conventional reproductive health care in the United States, public health policies must be informed by scientific and medical literature that is comprehensive, methodologically sound, and absent any obfuscations or misrepresentations. IMPLICATIONS: Studnicki et al.'s study of emergency room visits after abortion misrepresented the safety of mifepristone with multiple instances of methodological flaws and obfuscations of data. While the study has now been retracted, it led to irrevocable harm, threatening access to medication abortion, which has an established safety record.

Impact of L-DOPA treatment on regional cerebral blood flow and metabolism in the basal ganglia in a rat model of Parkinson's disease.

Large increases in regional cerebral blood flow (rCBF) have been measured in patients with Parkinson's disease (PD) following the administration of L-DOPA, but the underlying mechanisms have remained unknown. In this study, rats with unilateral 6-hydroxydopamine (6-OHDA) lesions were used to compare patterns of rCBF and regional cerebral glucose utilisation (rCGU) in chronically L-DOPA-treated subjects following a final injection of L-DOPA or saline. The same animal model was used to the leakage of a blood-brain barrier (BBB) tracer molecule at 60 min vs. 24h following the last L-DOPA injection of a chronic treatment. All the parameters under investigation were examined with brain autoradiography following intravenous injections of specific radiotracers in awake animals ([14C]-iodoantipyrine for rCBF, [14C]-2-deoxyglucose for rCGU, and [14C]-α-aminoisobutyric acid for BBB leakage). Significant changes in rCBF and rCGU on the side ipsilateral to the 6-OHDA lesion relative to the non-lesioned side were seen at 60 min ("ON") but not 24h ("OFF") following L-DOPA administration. These changes were not seen in sham-operated rats. In the output nuclei of the basal ganglia (the entopeduncular nucleus and the substantia nigra pars reticulata) both rCBF and rCGU were elevated both in acutely L-DOPA-treated rats and chronically L-DOPA-treated rats displaying dyskinesia, but did not change significantly in chronically L-DOPA-treated non-dyskinetic cases. Acutely and chronically L-DOPA-treated rats with dyskinesia exhibited increases in rCBF "ON L-DOPA" also in the motor cortex, the striatum, and the globus pallidus, but the corresponding changes in rCGU did not show the same direction, magnitude, and/or relative group differences. The uptake of a BBB tracer (studied in the striatum and the substantia nigra reticulata in chronically L-DOPA treated rats) was significantly higher ON vs. OFF L-DOPA. The present results are the first to show that the administration of L-DOPA is followed by transient and robust increases in rCBF in the dopamine-denervated basal ganglia. This effect occurs already upon acute L-DOPA treatment and persists upon repeated drug administration in animals that develop dyskinesia. Increases in rCBF ON L-DOPA are not necessarily accompanied by enhanced glucose utilisation in the affected regions, pointing to altered mechanisms of neurovascular coupling. Finally, our results show that increases in rCBF ON L-DOPA may be accompanied by BBB hyperpermeability in the most affected regions.

Modulation of the blood-tumor barrier to enhance drug delivery and efficacy for brain metastases.

The blood-brain barrier is the selectively permeable vasculature of the brain vital for maintaining homeostasis and neurological function. Low permeability is beneficial in the presence of toxins and pathogens in the blood. However, in the presence of metastatic brain tumors, it is a challenge for drug delivery. Although the blood-tumor barrier is slightly leaky, it still is not permissive enough to allow the accumulation of therapeutic drug concentrations in brain metastases. Herein, we discuss the differences between primary brain tumors and metastatic brain tumors vasculature, effects of therapeutics on the blood-tumor barrier, and characteristics to be manipulated for more effective drug delivery.

Nicotine and cotinine increases the brain penetration of saquinavir in rat.

Endothelial tight junctions and efflux transporters of the blood-brain barrier (BBB) significantly limit brain accumulation of many drugs, including protease inhibitors such as saquinavir. The cholinergic agonist nicotine is one of the most commonly used drugs in the world and the incidence is even higher in the human immune deficiency virus population (∼ 70%). We examined the ability of nicotine and its primary metabolite cotinine to modify brain uptake of saquinavir in rats. Both nicotine and cotinine at pharmacological concentrations matching those in smokers, increased brain saquinavir uptake by two fold. Co-perfusion with nicotinic receptor antagonists and passive permeability markers showed that the effect was not caused by receptor activation or BBB permeability disruption. Transport inhibition studies demonstrated that brain saquinavir uptake is limited by multiple efflux transporters, P-glycoprotein (P-gp), breast cancer resistance protein and multidrug resistance-associated protein. In situ perfusion and in vitro experiments using a classical P-gp substrate rhodamine 123 linked the effect of nicotine to inhibition of BBB P-gp transport. The effect was confirmed in vivo in chronic 14 day nicotine administration animals. These data suggest nicotine increases antiretroviral drug exposure to brain and may represent a significant in vivo drug-drug interaction at the BBB. Although this may slightly benefit CNS antiretroviral efficacy, it may also expose the brain to potential serious neurotoxicity.

Inhibition of VEGF and Angiopoietin-2 to Reduce Brain Metastases of Breast Cancer Burden.

For metastases in the central nervous system, angiogenesis enhances metastatic potential and promotes progression. Primary factors which drive vessel growth are vascular endothelial growth factor (VEGF) and angiopoietin-2. Preclinical models show inhibition of either factor reduces metastases spread and inhibits growth. This work sets out to answer two questions in a preclinical mouse model. First, whether the combined inhibition of VEGF and angiopoietin-2, reduces passive permeability and limits drug uptake into brain metastases; and second, whether this inhibition reduces metastases burden in brain. We observed combinatorial inhibition of VEGF and angiopoietin-2, decreased (p < 0.05) angiogenesis and vascular branching in an aortic ring assay and decreased (p < 0.05) endothelial wound closure times. Using a brain metastases of breast cancer model (induced by intracardiac injections of brain seeking MDA-MB-231Br cells or 4T1Br cells), we observed, similar to VEGF, angiopoetin-2 expression correlates to increased angiogenesis (p < 0.05) and increased lesion permeability. To determine efficacy, animals were administered bevacizumab plus L1-10 (angiopoietin inhibitor) twice per week until neurological symptoms developed. Lesion permeability significantly decreased by ∼50% (p < 0.05) compared to untreated lesions, but remained ∼25% greater (p < 0.0%) than brain. In subsequent experiments, animals were administered similar regimens but sacrificed on day 32. The number of metastatic lesions developed was significantly (p < 0.001) reduced in the bevacizumab group (56%) and combination group (86%). Lesions' size was reduced in bevacizumab treated lesions (∼67%) and bevacizumab and L1-10 treated lesions (∼78%) developing area < 0.5 mm2. In summary, combinatorial inhibition of VEGF and angiopoietin reduces lesion permeability and brain metastatic burden.

Quantitative Fluorescence Microscopy Measures Vascular Pore Size in Primary and Metastatic Brain Tumors.

Tumors residing in the central nervous system (CNS) compromise the blood-brain barrier (BBB) via increased vascular permeability, with the magnitude of changes dependent on the tumor type and location. Current studies determine penetrability of a cancer therapeutic by administering progressively larger molecules until cutoff is observed where little to no tumor accumulation occurs. However, decades-old experimental work and mathematical modeling document methods to calculate both the size of the vascular opening (pore) with solute permeability values. In this study, we updated this classic mathematical modeling approach with quantitative fluorescence microscopy in two preclinical tumor models, allowing simultaneous administration of multiple sized tracers to determine vascular permeability at a resolution of nearly one micron. We observed that three molecules ranging from 100 Da to 70 kDa permeated into a preclinical glioblastoma model at rates proportional to their diffusion in water. This suggests the solutes freely diffused from blood to glioma across vascular pores without steric restriction, which calculates to a pore size of >140 nm in diameter. In contrast, the calculated pore size of a brain metastasis of breast cancer was approximately 10-fold smaller than glioma vasculature. This difference explains why antibodies are effective against glioblastoma but generally fail in brain metastases of breast cancer. On the basis of our observations, we hypothesize that trastuzumab most likely fails in the treatment of brain metastases of breast cancer because of poor CNS penetration, while the similar sized antibody bevacizumab is effective in the same tumor type not because it penetrates the CNS degree better, but because it scavenges VEGF in the vascular compartment, which reduces edema and permeation. Cancer Res; 77(2); 238-46. ©2016 AACR.

A mouse Model of Focal Vascular Injury Induces Astrocyte Reactivity, Tau Oligomers, and Aberrant Behavior.

Neuropsychiatric symptom development has become more prevalent with 270,000 blast exposures occurring in the past 10 years in the United States. How blast injury leads to neuropsychiatric symptomology is currently unknown. Preclinical models of blast-induced traumatic brain injury have been used to demonstrate blood-brain barrier disruption, degenerative pathophysiology, and behavioral deficits. Vascular injury is a primary effect of neurotrauma that can trigger secondary injury cascades and neurodegeneration. Here we present data from a novel scaled and clinically relevant mouse blast model that was specifically developed to assess the outcome of vascular injury. We look at the biochemical effects and behavioral changes associated with blast injury in young-adult male BALB/c mice. We report that blast exposure causes focal vascular injury in the Somatosensory Barrel Field cortex, which leads to perivascular astrocyte reactivity, as well as acute aberrant behavior. Biochemical analysis revealed that mild blast exposure also invokes tauopathy, neuroinflammation, and oxidative stress. Overall, we propose our model to be used to evaluate focal blood-brain barrier disruption and to discover novel therapies for human neuropsychiatric symptoms.

Semi-automated rapid quantification of brain vessel density utilizing fluorescent microscopy.

BACKGROUND: Measurement of vascular density has significant value in characterizing healthy and diseased tissue, particularly in brain where vascular density varies among regions. Further, an understanding of brain vessel size helps distinguish between capillaries and larger vessels like arterioles and venules. Unfortunately, few cutting edge methodologies are available to laboratories to rapidly quantify vessel density. NEW METHOD: We developed a rapid microscopic method, which quantifies the numbers and diameters of blood vessels in brain. Utilizing this method we characterized vascular density of five brain regions in both mice and rats, in two tumor models, using three tracers. RESULTS: We observed the number of sections/mm(2) in various brain regions: genu of corpus callosum 161±7, hippocampus 266±18, superior colliculus 300±24, frontal cortex 391±55, and inferior colliculus 692±18 (n=5 animals). Regional brain data were not significantly different between species (p>0.05) or when using different tracers (70kDa and 2000kDa Texas Red; p>0.05). Vascular density decreased (62-79%) in preclinical brain metastases but increased (62%) a rat glioma model. COMPARISON WITH EXISTING METHODS: Our values were similar (p>0.05) to published literature. We applied this method to brain-tumors and observed brain metastases of breast cancer to have a ∼2.5-fold reduction (p>0.05) in vessels/mm(2) compared to normal cortical regions. In contrast, vascular density in a glioma model was significantly higher (sections/mm(2) 736±84; p<0.05). CONCLUSIONS: In summary, we present a vascular density counting method that is rapid, sensitive, and uses fluorescence microscopy without antibodies.

Characterization of passive permeability at the blood-tumor barrier in five preclinical models of brain metastases of breast cancer.

The blood-brain barrier (BBB) is compromised in brain metastases, allowing for enhanced drug permeation into brain. The extent and heterogeneity of BBB permeability in metastatic lesions is important when considering the administration of chemotherapeutics. Since permeability characteristics have been described in limited experimental models of brain metastases, we sought to define these changes in five brain-tropic breast cancer cell lines: MDA-MB-231BR (triple negative), MDA-MB-231BR-HER2, JIMT-1-BR3, 4T1-BR5 (murine), and SUM190 (inflammatory HER2 expressing). Permeability was assessed using quantitative autoradiography and fluorescence microscopy by co-administration of the tracers (14)C-aminoisobutyric acid (AIB) and Texas red conjugated dextran prior to euthanasia. Each experimental brain metastases model produced variably increased permeability to both tracers; additionally, the magnitude of heterogeneity was different among each model with the highest ranges observed in the SUM190 (up to 45-fold increase in AIB) and MDA-MB-231BR-HER2 (up to 33-fold in AIB) models while the lowest range was observed in the JIMT-1-BR3 (up to 5.5-fold in AIB) model. There was no strong correlation observed between lesion size and permeability in any of these preclinical models of brain metastases. Interestingly, the experimental models resulting in smaller mean metastases size resulted in shorter median survival while models producing larger lesions had longer median survival. These findings strengthen the evidence of heterogeneity in brain metastases of breast cancer by utilizing five unique experimental models and simultaneously emphasize the challenges of chemotherapeutic approaches to treat brain metastases.

Alterations in Pericyte Subpopulations Are Associated with Elevated Blood-Tumor Barrier Permeability in Experimental Brain Metastasis of Breast Cancer.

PURPOSE: The blood-brain barrier (BBB) is modified to a blood-tumor barrier (BTB) as a brain metastasis develops from breast or other cancers. We (i) quantified the permeability of experimental brain metastases, (ii) determined the composition of the BTB, and (iii) identified which elements of the BTB distinguished metastases of lower permeability from those with higher permeability. EXPERIMENTAL DESIGN: A SUM190-BR3 experimental inflammatory breast cancer brain metastasis subline was established. Experimental brain metastases from this model system and two previously reported models (triple-negative MDA-231-BR6, HER2+ JIMT-1-BR3) were serially sectioned; low- and high-permeability lesions were identified with systemic 3-kDa Texas Red dextran dye. Adjoining sections were used for quantitative immunofluorescence to known BBB and neuroinflammatory components. One-sample comparisons against a hypothesized value of one were performed with the Wilcoxon signed-rank test. RESULTS: When uninvolved brain was compared with any brain metastasis, alterations in endothelial, pericytic, astrocytic, and microglial components were observed. When metastases with relatively low and high permeability were compared, increased expression of a desmin+ subpopulation of pericytes was associated with higher permeability (231-BR6 P = 0.0002; JIMT-1-BR3 P = 0.004; SUM190-BR3 P = 0.008); desmin+ pericytes were also identified in human craniotomy specimens. Trends of reduced CD13+ pericytes (231-BR6 P = 0.014; JIMT-1-BR3 P = 0.002, SUM190-BR3, NS) and laminin α2 (231-BR6 P = 0.001; JIMT-1-BR3 P = 0.049; SUM190-BR3 P = 0.023) were also observed with increased permeability. CONCLUSIONS: We provide the first account of the composition of the BTB in experimental brain metastasis. Desmin+ pericytes and laminin α2 are potential targets for the development of novel approaches to increase chemotherapeutic efficacy. Clin Cancer Res; 22(21); 5287-99. ©2016 AACR.

Molecular determinants of blood-brain barrier permeation.

The blood-brain barrier (BBB) is a microvascular unit which selectively regulates the permeability of drugs to the brain. With the rise in CNS drug targets and diseases, there is a need to be able to accurately predict a priori which compounds in a company database should be pursued for favorable properties. In this review, we will explore the different computational tools available today, as well as underpin these to the experimental methods used to determine BBB permeability. These include in vitro models and the in vivo models that yield the dataset we use to generate predictive models. Understanding of how these models were experimentally derived determines our accurate and predicted use for determining a balance between activity and BBB distribution.

A novel preclinical method to quantitatively evaluate early-stage metastatic events at the murine blood-brain barrier.

The observation that approximately 15% of women with disseminated breast cancer will develop symptomatic brain metastases combined with treatment guidelines discouraging single-agent chemotherapeutic strategies facilitates the desire for novel strategies aimed at outright brain metastasis prevention. Effective and robust preclinical methods to evaluate early-stage metastatic processes, brain metastases burden, and overall mean survival are lacking. Here, we develop a novel method to quantitate early metastatic events (arresting and extravasation) in addition to traditional end time-point parameters such as tumor burden and survival in an experimental mouse model of brain metastases of breast cancer. Using this method, a reduced number of viable brain-seeking metastatic cells (from 3,331 ± 263 cells/brain to 1,079 ± 495 cells/brain) were arrested in brain one week postinjection after TGFß knockdown. Treatment with a TGFß receptor inhibitor, galunisertib, reduced the number of arrested cells in brain to 808 ± 82 cells/brain. Furthermore, we observed a reduction in the percentage of extravasated cells (from 63% to 30%) compared with cells remaining intralumenal when TGFß is knocked down or inhibited with galunisertib (40%). The observed reduction of extravasated metastatic cells in brain translated to smaller and fewer brain metastases and resulted in prolonged mean survival (from 36 days to 62 days). This method opens up potentially new avenues of metastases prevention research by providing critical data important to early brain metastasis of breast cancer events.

Novel treatment strategies for brain tumors and metastases.

This review summarizes patent applications in the past 5 years for the management of brain tumors and metastases. Most of the recent patents discuss one of the following strategies: the development of new drug entities that specifically target the brain cells, the blood-brain barrier and the tumor cells, tailor-designing a novel carrier system that is able to perform multitasks and multifunction as a drug carrier, targeting vehicle and even as a diagnostic tool, direct conjugation of a US FDA approved drug with a targeting moiety, diagnostic moiety or PK modifying moiety, or the use of innovative nontraditional approaches such as genetic engineering, stem cells and vaccinations. Until now, there has been no optimal strategy to deliver therapeutic agents to the CNS for the treatment of brain tumors and metastases. Intensive research efforts are actively ongoing to take brain tumor targeting, and novel and targeted CNS delivery systems to potential clinical application.

Quantitative fluorescence microscopy provides high resolution imaging of passive diffusion and P-gp mediated efflux at the in vivo blood-brain barrier.

Quantitative fluorescent microscopy is an emerging technology that has provided significant insight into cellular dye accumulation, organelle function, and tissue physiology. However, historically dyes have only been used to qualitatively or semi-quantitatively (fold change) determine changes in blood-brain barrier (BBB) integrity. Herein, we present a novel method to calculate the blood to brain transfer rates of the dyes rhodamine 123 and Texas red across the in situ BBB. We observed that rhodamine 123 is subject to p-glycoprotein mediated efflux at the rat BBB and can be increased nearly 20-fold with p-glycoprotein inhibition. However, Texas Red appears to not be subject to MRP2 mediated efflux at the rat BBB, agreeing with literature reports suggesting MRP2 may lack functionality at the normal rat BBB. Lastly, we present data demonstrating that once dyes have crossed the BBB, diffusion of the dye molecule is not as instantaneous as has been previously suggested. We propose that future work can now be completed to (1) match BBB transfer coefficients to interstitial diffusion constants and (2) use dyes with specific affinities to cellular organelles or that have specific properties (e.g., subject to efflux transporters) to more fully understand BBB physiology.

Paclitaxel-hyaluronic nanoconjugates prolong overall survival in a preclinical brain metastases of breast cancer model.

Brain (central nervous system; CNS) metastases pose a life-threatening problem for women with advanced metastatic breast cancer. It has recently been shown that the vasculature within preclinical brain metastasis model markedly restricts paclitaxel delivery in approximately 90% of CNS lesions. Therefore to improve efficacy, we have developed an ultra-small hyaluronic acid (HA) paclitaxel nanoconjugate (∼5 kDa) that can passively diffuse across the leaky blood-tumor barrier and then be taken up into cancer cells (MDA-MB-231Br) via CD44 receptor-mediated endocytocis. Using CD44 receptor-mediated endocytosis as an uptake mechanism, HA-paclitaxel was able to bypass p-glycoprotein-mediated efflux on the surface of the cancer cells. In vitro cytoxicity of the conjugate and free paclitaxel were similar in that they (i) both caused cell-cycle arrest in the G2-M phase, (ii) showed similar degrees of apoptosis induction (cleaved caspase), and (iii) had similar IC50 values when compared with paclitaxel in MTT assay. A preclinical model of brain metastases of breast cancer using intracardiac injections of Luc-2 transfected MDA-MB-231Br cells was used to evaluate in vivo efficacy of the nanoconjugate. The animals administered with HA-paclitaxel nanoconjugate had significantly longer overall survival compared with the control and the paclitaxel-treated group (P < 0.05). This study suggests that the small molecular weight HA-paclitaxel nanoconjugates can improve standard chemotherapeutic drug efficacy in a preclinical model of brain metastases of breast cancer.

P-glycoprotein mediated efflux limits substrate and drug uptake in a preclinical brain metastases of breast cancer model.

The blood-brain barrier (BBB) is a specialized vascular interface that restricts the entry of many compounds into brain. This is accomplished through the sealing of vascular endothelial cells together with tight junction proteins to prevent paracellular diffusion. In addition, the BBB has a high degree of expression of numerous efflux transporters which actively extrude compounds back into blood. However, when a metastatic lesion develops in brain the vasculature is typically compromised with increases in passive permeability (blood-tumor barrier; BTB). What is not well documented is to what degree active efflux retains function at the BTB despite the changes observed in passive permeability. In addition, there have been previous reports documenting both increased and decreased expression of P-glycoprotein (P-gp) in lesion vasculature. Herein, we simultaneously administer a passive diffusion marker ((14)C-AIB) and a tracer subject to P-gp efflux (rhodamine 123) into a murine preclinical model of brain metastases of breast cancer. We observed that the metastatic lesions had similar expression (p > 0.05; n = 756-1214 vessels evaluated) at the BBB and the BTB. Moreover, tissue distribution of R123 was not significantly (p > 0.05) different between normal brain and the metastatic lesion. It is possible that the similar expression of P-gp on the BBB and the BTB contribute to this phenomenon. Additionally we observed P-gp expression at the metastatic cancer cells adjacent to the vasculature which may also contribute to reduced R123 uptake into the lesion. The data suggest that despite the disrupted integrity of the BTB, efflux mechanisms appear to be intact, and may be functionally comparable to the normal BBB. The BTB is a significant hurdle to delivering drugs to brain metastasis.