This research was supported by grants from the Finnish Cancer Organizations, Jane &#38; Aatos Erkko Foundation, and Sigrid Juselius Foundation (to P.L. and V.L.J.), the Swiss National Science Foundation (Advanced Postdoc.Mobility grant no: P300PB_164732, to S.K.), the Orion Research Foundation (to S.K.), the Maud Kuistila Memorial Foundation (to S.K.), and the Academy of Finland (TERVA 2017, grant no: 314 498). The Biomedicum Imaging Unit (Helsinki) is acknowledged for providing the microscopy imaging core facility.

<ol>
	<li>Daneman, R., Prat, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+blood-brain+barrier.">The blood-brain barrier.</a> Cold Spring Harbor Perspectives in Biology. 7 (1), a020412 (2015).</li><li>Quail, D. F., Joyce, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Microenvironmental+Landscape+of+Brain+Tumors.">The Microenvironmental Landscape of Brain Tumors.</a> Cancer Cell. 31 (3), 326-341 (2017).</li><li>Wang, Z., Sun, H., Yakisich, J. 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The authors have nothing to disclose.

The rise of the interpatient tumor variability concept rejuvenated the research on personalized cancer medicine21. This variability is also a hallmark of central nervous system neoplasms. Due to the unpredictability of the tumor, response to chemotherapy adds to the sheltering effect of the BBB for drug delivery, and altogether constitutes major challenges in patient care22. In order to develop more effective therapies, it is often necessary to screen large libraries of new molecules. To evaluate the antitumor efficacy and ability of the new therapeutic leads to reach the tumor site, the best option is the preclinical study on patient-derived cells implanted in vivo into murine patient avatars. Due to practical (financial, time, human, and facility resources) and ethical reasons (the 3Rs principle when using laboratory animals), the development of such a large-scale in vivo screening platform is often not possible, and therefore, the cell-based assays remain a model of choice23. The principal reason for selecting established cell lines and avoiding primary cells is to facilitate the reproducibility and reduce the use of laboratory animals, which are the main source for the isolation and establishment of primary murine cultures. The methods presenting here, firmly complying with the 3Rs, could efficiently discard nanoparticles from a further preclinical investigation on the criterium of their inability to cross the model BBTB. As a proof-of-principle, we describe here findings obtained during the development and validation of the BBTB. We were able to confirm in vitro findings in vivo, for instance when measuring the passive diffusion of a 376 Da sodium-fluorescein.&#160;
The protocol outlined in this paper describes the preparation of endothelial cells cocultured with astrocytes to form a blood-brain tumor-barrier-like interface in an in vitro setup. Once a physical contact between these two cell types is established, the endothelial cell layer exhibits similarities with the BBB (e.g., a cell surface expression of tight junction proteins and relatively low permeability). Interestingly, the murine BBTB mimic seemed to provide particularly similar Na-Fl permeability values to those obtained with the in vivo mouse BBB permeability measurements24. Therefore, the performance of the BBTB mimics will be directly linked to the choice of the cells used to form the barrier. The bEND3 endothelial cells originate from the brain and are known to be successful in forming barriers when cocultured with astrocytes25. However, we have been using the immortalized HIFko astrocytes26 to generate the BBTB mimic. Due to their lack of hypoxia-inducible factor, these astrocytes do not produce VEGF-A, which is quintessential in the BBTB mimic&#8217;s stabilization described here. Astrocytes have been identified as modulators of the BBB permeability, for instance through the release of VEGF-A in response to neuroinflammation27. Activation of the vascular endothelial growth factor receptors (VEGFRs) is a key regulator of the endothelial/vascular permeability both in vitro28 and in vivo29. Therefore, VEGF-A supplements in the medium activate the VEGFR2 on the endothelial cells, which induces the phosphorylation of adherens junction proteins such as VE-cadherin30. The loss of endothelial cell-cell contacts generates highly permeable blood vessels. Similarly, both the strong mitogenic property and unknown composition of the fetal bovine sera used in the cell culture assays cause major issues in the barrier stabilization and assay reproducibility.
Human umbilical vein endothelial cells (HUVECs) are sometimes used to form BBB in vitro31; however, they significantly differ from the brain microvascular endothelial cells, such as the hCMEC/D3 cell line32, in terms of gene expression and barrier-forming properties. However, the relatively higher permeability values obtained with the HuAR2T cells grown alone compared to the bEND3 were greatly reduced by coculturing them with human primary astrocytes. Although the endothelial cells are required to form the cellular wall, it is clear that the astrocytes have an equally important role to play for the BBTB formation and stabilization.
When patient-derived glioma spheres were added to this equation, the mouse BBTB mimic recapitulated some of the features of murine xenografts, such as the drug diffusion through the brain vasculature and the tumor cell targeting. The BBTB mimics discussed here were, for instance, successful in mirroring the in vivo behavior when we screened several nanoparticles with different diameters. To illustrate the parallelism between the in vitro and in vivo models, we used the previously described mesoporous silicate nanoparticles33 with cell-penetrating properties34 conjugated to the tumor-targeting peptide CooP on their surface20. The CooP-targeting peptide homes to invasive tumor cells through the specific binding to the mammary-derived growth inhibitor (MDGI). Several cancers, including gliomas, are overexpressing MDGI compared to the normal tissue35, which makes the CooP a very efficient tumor-targeting moiety capable of increasing the delivery of a payload20. The nanoparticles used here have been previously shown to diffuse into the brain parenchyma (27547955), and when functionalized with Taxol, these nano-cargos have been successful in reducing glioma growth in preclinical models36. The addition of polyethylene glycol (PEG) residues at the surface of the nanoparticles also maintained their static charge to positive values (around + 4 mV), allowing better interaction with the neurovascular unit37 and also increasing their stability in circulation. In the presented data, 3 kDa of PEG was conjugated to NP110s, while NP350s were coated with 10 kDa of PEG. However, increased-molecular-weight PEG also resulted in a significant increase in the nanoparticle diameter, hence their physical capabilities to cross the BBB. Therefore, we checked whether the physical dimensions of the particles prevented their passage through the BBTB and whether these observations could be mirrored in vivo.
In accordance with the previously published observations, we observed that NP110s extravasated through both the BBTB in vitro and the BBB of mice bearing intracranial tumors, while NP350s retained on the luminal side of the BBTB mimic and in the blood vessels of the mice. These similar results strongly suggest that the BBTB model predicted the in vivo ability of nanoparticles to cross the BBB and reach the brain.&#160;
The relevance of cellular models of the BBB is frequently discussed, even for the central delivery of nanoparticles38. We show here that primary astrocytes and endothelial cells, both considered as the most relevant in vitro tools, can be replaced by immortalized and/or commercially available cells, ensuring greater scalability and reproducibility. The next generation of the in vitro BBB mimics could be developed by incorporating the microfluidic devices, allowing beautifully formed neurovascular units that structurally resemble the actual BBB12,14. However, such models are currently unsuitable for the high-throughput screening of molecules delivered to gliomas, due to technical limitations in the follow-up of the delivery14. It is indeed difficult to capture the physiological complexity of the BBB in a dish, and the possible lack of some receptors/proteins, known to be expressed by the BBB, could compromise the interpretation of the results. Another argument concerns the great variability in gene expression between in vivo and in vitro conditions, as well as from one cell line to another, especially considering endothelial cells. However, it could also be argued that the neurovascular unit is not a uniform entity within the brain39. Scientific research in biology has reached a humane era where the animal welfare, ethical responsibility, and the cost of using animal lives are always considered before designing an experiment. Therefore, to support the replacement of animals, an increasing number of recent studies show that the awareness of the limitations of the models and careful selection of the cellular models to establish the barrier&#8212;with an emphasis on the astrocytes&#8212;warrant a match between results obtained in a dish and in animal models40. With the methodology described here, we get one step closer to reducing the number of experimental animals used for screening purposes of BBB transcytosis for potential therapeutics.

The neurovascular unit is composed of neurons, astrocytes, and the BBB, formed by intricate connections between pericytes, astrocytes, endothelial cells, and the associated basement membrane forming the brain microvasculature1. This tight cellular wall formed by continuous, nonfenestrated vessels finely regulates the movement of ions and molecules (including hormones, nutrients, or drugs) but also of circulating cells1. The notably low transcytosis through the BBB of high-molecular-weight molecules, such as therapeutic antibodies, drug conjugates, or nanocompounds, dramatically restricts the advances in the drug discovery for neurological diseases, including malignant gliomas2. Indeed, orally or intravenously delivered chemotherapies reach the brain parenchyma often at inadequately low concentrations to induce an antitumor effect or are simply unable to cross the BBTB to reach the neoplastic cells3. Several preclinical and clinical studies have not dealt with the issue of BBTB penetration but have attempted to disrupt the BBTB transiently, for instance by using focused ultrasounds4,5, or to circumvent it by the direct in situ delivery of drugs6. However, none of these techniques were able to counteract the inevitable tumor expansion or relapse. Therefore, when developing novel antiglioma therapies, the diffusion through the BBTB should be considered as one of the critical aspects for the successful delivery of the therapeutic agents7.
Due to the very complex nature of the cell interactions within the BBTB, in vivo studies in laboratory animals seem to be the obvious choice when studying the passage of molecules from blood to brain. However, high-scale in vivo methods are relatively complex to establish and, therefore, do not allow the high-throughput screening of molecules in a reasonable time at a reasonable cost. Even more importantly, animal testing has to follow the 3R ethical guideline defined as i) refine, ii) reduce, and, of relevance to the current context, iii) replace by alternative protocols (e.g., in vitro/in silico methods). Therefore, recreating the BBTB in vitro appears as an interesting and attractive possibility, but it also constitutes a complex task challenged by various limitations. Many attempts to recreate this complex compartment with cultured primary cells or cell lines from canine, porcine, murine, and even human origin have been published (as reviewed by Rahman et al.8 and Helms et al.9). These models include three-dimensional microfluidic systems10, BBB-on-a-chip11,12, and multitudes of variants based on the classical co-cultures in inserts systems. Nevertheless, current microfluidic and chip systems are either not suitable for rapid, high-throughput drug-validation studies13,14 or are currently incompatible with studies of drug delivery to brain tumors. In addition, the review of 155 published models using primary cells, inducible pluripotent stem cells (iPSC), or commercial cell lines all co-cultured on inserts showed a trend for interstudy discrepancy in their measurements and/or conclusions8. This lack of interlaboratory reproducibility could be correlated with i) nonnormalized culture conditions, for instance with the optional coating with basement membrane matrix proteins in the cell culture vessel, ii) an increased number of subculture and usage of serum-containing media, both major drivers of genetic and phenotypic modifications of the cell lines15, or iii) the difficulty to reproducibly recreate the right equilibrium between the astroglial and endothelial components in a dish. Although the use of immortalized cells or commercial cell lines to establish an in vitro BBB model lacks some of the properties compared to similar models that only use primary cells, in the described method we show that the right combination of cells exhibits a very comparable performance to published studies in other models of reference16,17. Eventually, the lack of a robust and reproducible model to study the passage of therapeutic compounds targeting brain tumors through the BBTB motivated us to develop the methods described here.
Since the goal was to use the model to predict the in vivo delivery of nanoparticles in preclinical animal models, we first validated the BBTB model by utilizing inserts containing murine endothelial cells in contact with murine astrocytes. In addition to this, we also optimized the model to use certain human cell lines. Once stabilized, the cell barriers are transferred to cultures with patient-derived glioblastoma spheres or commercial glioma cell lines. Thereafter, the transcytosis of nanoparticles and tumor cell targeting can be visualized by confocal microscopy and quantified by collecting samples over time. Importantly, results obtained using the BBTB mimics could reliably predict the behavior of the nanoparticles in vivo, supporting the use of the BBTB mimic prior the preclinical validation.

<table border="0" cellpadding="0" cellspacing="0" style="width:1761px;" width="1761">
	<tbody>
		<tr height="21">
			<td colspan="4" height="21" style="height:21px;width:1761px;">Cells</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">bEND3</td>
			<td style="width:239px;">ATCC</td>
			<td style="width:273px;">CRL-2299</td>
			<td style="width:961px;">Cultured in: DMEM (1g/L glucose) supplemented with 10% FBS, 5 mL L-glutamine and 5 mL penicillin/streptomycin</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">HIFko immortalized mouse astrocytes</td>
			<td style="width:239px;">Isolated in Dr. Gabriele Bergers Lab</td>
			<td style="width:273px;">https://doi.org/10.1016/S1535-6108(03)00194-6</td>
			<td style="width:961px;">Cultured in: BME-1 supplemented with 5% FBS, 5 mL 1 M HEPES, 5 mL 100 mM sodium pyruvate, 3 g D-glucose and 5 mL penicillin/streptomycin</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">HuAR2T</td>
			<td style="width:239px;">Isolated in Dr. Dagmar Wirth Lab</td>
			<td style="width:273px;">https://doi.org/10.1089/ten.tea.2009.0184</td>
			<td style="width:961px;">Cultured in: EBM-2 with SupplementMix</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">normal human primary astrocytes</td>
			<td style="width:239px;">Lonza</td>
			<td style="width:273px;">CC-2565</td>
			<td style="width:961px;">Cultured in: ABM with SingleQuots</td>
		</tr>
		<tr height="21">
			<td colspan="4" height="21" style="height:21px;width:1761px;">Material and reagents</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">100x17mm Dish, Nunclon Delta</td>
			<td style="width:239px;">ThermoFisher Scientific</td>
			<td>150350</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">10 mL serological pipet</td>
			<td style="width:239px;">ThermoFisher Scientific</td>
			<td style="width:273px;">170361</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">15mL Conical Sterile Polypropylene Centrifuge Tubes</td>
			<td style="width:239px;">ThermoFisher Scientific</td>
			<td style="width:273px;">339650</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">ABM Basal Medium, 500 mL</td>
			<td style="width:239px;">Lonza</td>
			<td style="width:273px;">CC-3187</td>
			<td>For primary human astrocytes. ABM+: contains all the additives from the supplement mix. ABM-:all the additives except for rhEGF and FBS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Accutase Cell Detachment Solution</td>
			<td style="width:239px;">Corning</td>
			<td style="width:273px;">25-058-CI</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">AGM SingleQuots Supplements and Growth Factors</td>
			<td style="width:239px;">Lonza</td>
			<td>CC-4123</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">B27 supplement</td>
			<td style="width:239px;">Gibco</td>
			<td>17504-044</td>
			<td>for both GBM + and - medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Basal Medium Eagle</td>
			<td style="width:239px;">ThermoFisher Scientific</td>
			<td style="width:273px;">21010046</td>
			<td>BME-1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Corning Costar TC-Treated 6-Well Plates</td>
			<td style="width:239px;">Sigma-Aldrich</td>
			<td style="width:273px;">CLS3506</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">Corning Transwell polyester membrane cell culture inserts</td>
			<td style="width:239px;">Sigma-Aldrich</td>
			<td style="width:273px;">CLS3452&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">D-glucose</td>
			<td style="width:239px;">Sigma-Aldrich</td>
			<td style="width:273px;">G8270</td>
			<td>dissolve in 50 mL of BME-1 and sterile filter before adding to the medium</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">Dulbecco&#39;s Modified Eagle&#39;s Medium/Nutrient F-12 Ham</td>
			<td style="width:239px;">Gibco</td>
			<td>21331-020</td>
			<td>Specific to the culture of the patient-derived spheres isolated in our lab, may vary for other glioma cell lines</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EBM-2 growth Medium SupplementMix</td>
			<td style="width:239px;">PromoCell</td>
			<td style="width:273px;">c-39216</td>
			<td>EBM+: contains all the additives from the supplement mix. EBM-:all the additives except for VEGF-A and FBS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Endothelial Basal Medium 2 (EBM-2)</td>
			<td style="width:239px;">PromoCell</td>
			<td style="width:273px;">c-22211</td>
			<td>EBM+: contains all the additives from the supplement mix. EBM-:all the additives except for VEGF-A and FBS</td>
		</tr>
		<tr height="62">
			<td height="62" style="height:62px;width:288px;">Fetal Bovine Serum (FBS), qualified, heat inactivated, E.U.-approved, South America Origin</td>
			<td style="width:239px;">ThermoFisher Scientific</td>
			<td style="width:273px;">10500056</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Fluorescein sodium salt</td>
			<td style="width:239px;">Sigma-Aldrich</td>
			<td style="width:273px;">F6377</td>
			<td style="width:961px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Greiner CELLSTAR 96 well plates</td>
			<td style="width:239px;">Sigma-Aldrich</td>
			<td style="width:273px;">Greiner 655090</td>
			<td>black polystyrene wells flat bottom (with micro-clear bottom)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">Menzel-Gl&#228;ser 0.9 cm round borosilicate Cover Slips</td>
			<td style="width:239px;">Thermo Scientific</td>
			<td style="width:273px;">10313573</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">PBS tablets</td>
			<td style="width:239px;">Medicago</td>
			<td>09-9400-100</td>
			<td>one tablet per liter of dH2O, then sterilize the solution by autoclaving</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Poly-D-lysine hydrobromide</td>
			<td style="width:239px;">Sigma-Aldrich</td>
			<td>P6407&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Recombinant Human EGF</td>
			<td style="width:239px;">Peprotech</td>
			<td style="width:273px;">GMP100-15</td>
			<td>for GBM+ medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Recombinant Human FGF-basic (154 a.a.)</td>
			<td style="width:239px;">Peprotech</td>
			<td style="width:273px;">100-18B</td>
			<td>for GBM+ medium</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Immunofluorescence</td>
			<td style="width:239px;"></td>
			<td style="width:273px;"></td>
			<td style="width:961px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Paraformaldehyde</td>
			<td style="width:239px;">Sigma-Aldrich</td>
			<td style="width:273px;">158127</td>
			<td></td>
		</tr>
		<tr height="18">
			<td height="18" style="height:18px;width:288px;">24 x 60 mm microscope slide cover glass</td>
			<td style="width:239px;">ORSAtec</td>
			<td style="width:273px;">0224601-D</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:23px;width:288px;">AlexaFluor 488 and 594 secondary antibodies</td>
			<td style="width:239px;">ThermoFisher Scientific</td>
			<td style="width:273px;"></td>
			<td>dilution: 1/500</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Anti-Claudin-5 antibody</td>
			<td style="width:239px;">Abcam</td>
			<td style="width:273px;">ab15106</td>
			<td>dilution: 1/150</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Anti-GFAP antibody clone GF5</td>
			<td style="width:239px;">Abcam</td>
			<td style="width:273px;">ab10062</td>
			<td>dilution: 1/150</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">Anti-Mouse CD31&#160;antibody Clone MEC 13.3</td>
			<td style="width:239px;">BD Biosciences</td>
			<td style="width:273px;">550274</td>
			<td>dilution 1/800</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Anti-SV40 T-antigen antibody</td>
			<td style="width:239px;">Abcam</td>
			<td style="width:273px;">ab16879</td>
			<td>dilution: 1/150</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Anti-Zonula Occludens-1</td>
			<td style="width:239px;">Abcam</td>
			<td style="width:273px;">ab96587</td>
			<td>dilution: 1/200</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">DAPI</td>
			<td style="width:239px;">TOCRIS</td>
			<td style="width:273px;">5748</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">Fluoromount Aqueous Mounting Medium&#160;</td>
			<td style="width:239px;">Sigma-Aldrich</td>
			<td style="width:273px;">F4680</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">LysoTracker Red DND-99</td>
			<td style="width:239px;">ThermoFisher Scientific</td>
			<td style="width:273px;">L7528</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Animal procedures</td>
			<td style="width:239px;"></td>
			<td style="width:273px;"></td>
			<td style="width:961px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">10 cm curved dissecting scissors</td>
			<td style="width:239px;">World Precision Instruments</td>
			<td style="width:273px;">14394</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">BD Microlance 25-gauge needles</td>
			<td style="width:239px;">Becton Dickinson</td>
			<td style="width:273px;">300600</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Fine Forceps (12.5 cm)</td>
			<td style="width:239px;">World Precision Instruments</td>
			<td style="width:273px;">503283</td>
			<td>for tissue dissociation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Intramedic Polyethylene tubing PE20</td>
			<td style="width:239px;">Becton Dickinson</td>
			<td style="width:273px;">427406</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Ketaminol vet 50 mg/mL</td>
			<td style="width:239px;">Intervet</td>
			<td style="width:273px;">Vnr511485</td>
			<td>Ketamine</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Mains Powered microdrill</td>
			<td style="width:239px;">World Precision Instruments</td>
			<td style="width:273px;">503599</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">Menzel-Gl&#228;ser 0.5 cm round borosilicate Cover Slips</td>
			<td style="width:239px;">Thermo Scientific</td>
			<td style="width:273px;">11888372</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Micro Bulldog clamp</td>
			<td style="width:239px;">World Precision Instruments</td>
			<td style="width:273px;">14119</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">Physiological saline solution</td>
			<td style="width:239px;">Mustela</td>
			<td style="width:273px;">Sterile single dose vials 20 x 5 mL / 40 x 5 mL - Medical device class</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Rochester-Oschner forceps</td>
			<td style="width:239px;">World Precision Instruments</td>
			<td style="width:273px;">501709</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Rompun vet 20 mg/mL</td>
			<td style="width:239px;">Intervet</td>
			<td style="width:273px;">Vnr148999</td>
			<td>Xylazine</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Stereotaxic adapter</td>
			<td style="width:239px;">World Precision Instruments</td>
			<td style="width:273px;">502063</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Sugi Sponge Points</td>
			<td style="width:239px;">Kettenbach</td>
			<td style="width:273px;">31603</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Equipment</td>
			<td style="width:239px;"></td>
			<td style="width:273px;"></td>
			<td style="width:961px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">Axio Zoom.V16 fluorescence stereo zoom microscope&#160;</td>
			<td style="width:239px;">Carl Zeiss</td>
			<td style="width:273px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">FLUOstar Omega microplate reader</td>
			<td style="width:239px;">BMG Labtech</td>
			<td style="width:273px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">ORCA-Flash 4.0 digital sCMOS camera</td>
			<td style="width:239px;">Hamamatsu Photonics</td>
			<td style="width:273px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Universal 320 tabletop centrifuge&#160;</td>
			<td style="width:239px;">Hettich</td>
			<td style="width:273px;">Cat. No. 1401</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">ZEISS LSM 880 with Airyscan confocal microscope</td>
			<td style="width:239px;">Carl Zeiss</td>
			<td style="width:273px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

predicting in vivo payloads delivery using a blood-brain tumor-barrier in a dish

Highly selective by nature, the blood-brain barrier (BBB) is essential for the brain homeostasis in physiological conditions. However, in the context of brain tumors, the molecular selectivity of BBB also shields the neoplastic cells by blocking the delivery of peripherally administered chemotherapies. The development of novel drugs (including nanoparticles) targeting malignant brain tumors ideally requires the use of preclinical animal models to study the drug&#8217;s transcytosis and antitumor efficacy. In order to comply with the 3R principle (refine, reduce, and replace) to reduce the number of laboratory animals in experimental setup and perform the high-throughput screening of a large library of antitumor agents, we developed a reproducible in vitro human and murine mimic of the blood-brain tumor-barrier (BBTB) using three-layered cultures of endothelial cells, astrocytes, and patient-derived glioblastoma spheres. For higher scalability and reproducibility, commercial cell lines or immortalized cells have been used in tailored conditions to allow the formation of a barrier resembling the actual BBB. Here we describe a protocol to obtain a BBTB mimic by culturing endothelial cells in contact with astrocytes at specific cell densities on inserts. This BBTB mimic can be used, for instance, for the quantification and confocal imaging of the nanoparticle passage through the endothelial and astrocytic barriers, in addition to the evaluation of the tumor cell targeting within the same assay. Moreover, we show that the obtained data can be used to predict the behavior of nanoparticles in preclinical animal models. In a broader perspective, this in vitro model could be adapted to other neurodegenerative diseases for the determination of the passage of new therapeutic molecules through the BBB and/or be supplemented with brain organoids to directly evaluate the efficacy of drugs.

Confocal imaging of the murine BBTB mimic shows the expression and cellular localization of the tight junction proteins zonula occludens-1 (ZO-1) and claudin-5 in bEND3. Contacts between the endothelial cells and astrocytes clearly induced the relocation of the ZO-1 and claudin-5 to the endothelial cell-cell contacts compared to the bEND3 monocultures (Figure 1D). Using immunofluorescence staining to visualize the GFAP-expressing astrocytes at the brain-side of the membrane, it is possible to observe and study the astrocytic processes and end-feet contacting the endothelial cells through the membrane (Figure 1E). The astrocyte-endothelial cell contacts are known to promote and stabilize the tightening of the cellular barrier and are associated with lower permeability values of the BBB19. In accordance with that, we observed a substantial decrease in the permeability of the mouse BBTB mimic for the Na-Fl from 27.63 (&#177; 3.45) x 10-6 cm/s in case of monocultures to 6.74 (&#177; 3.01) x 10-6 cm/s when co-cultured with the hypoxia-inducible factor knock out (HIFko) astrocytes (Table 1). The immortalized HuAR2T form highly permeable cellular barriers (104.92 &#177; 27.1 x 10-6 cm/s, Table 1). Similar to the murine model, we measured significantly lower permeability of the BBTB to Na-Fl, namely 47.4 (&#177; 14.32) x 10-6 cm/s, when the HuAR2T cells were co-cultured with the human primary astrocytes (Table 1).
In both murine and human BBTB mimics, the presence of the patient-derived glioblastoma spheres induced a slight increase in the permeability values compared to the endothelial cell-astrocyte co-cultures alone (Table 1). This phenomenon is observed with several but not all of the patient glioma sphere models. This may be due to the VEGF-A that is secreted by some of these patient-derived cells.
To compare the permeability values of the in vitro BBTB mimics with the in vivo BBB, we imaged the real-time diffusion of the Na-Fl through a cranial window implanted in nude mice. Using a fluorescence stereomicroscope, Na-Fl diffusion from the blood vessel capillaries deriving from the main pial blood vessels was recorded before, during, and after systemic injection of the probe (Figure 2C). Measurements of the differential fluorescence values from the circulating blood and brain cortical parenchyma over time allowed us to calculate the approximate permeability values of the nude mouse&#8217;s BBB for Na-Fl (5.57 &#177; 2.19 x 10-6 cm/s, Table 1).
To illustrate how this BBTB mimic can be used for visualization of the passage of compounds from to the blood side to the brain side, we compared the transcytosis of &#248; 110 nm (NP110) and &#248; 350 nm (NP350) nanoparticles targeting patient-derived glioblastoma spheres. Results obtained in vitro were then compared to the in vivo transcytosis. In the presented example, nanoparticles were surface-coated with the tumor-targeting peptide CooP20 and loaded with the fluorescent dye (FITC) to facilitate the visualization. We labeled the cells using the lysosomal dye and counterstained with DAPI 24 h after the addition of the FITC nanoparticles on the blood-side of the BBTB mimic and acquired confocal micrographs at different levels (e.g., the blood side, the membrane, the brain side, and the patient glioblastoma spheres) (Figure 3A). The NP110-associated fluorescent signal colocalized with the lysosomes in the endothelial cells, astrocytes, and tumor cells. In addition, NP110s were detected in-between the endothelial cells and astrocytes, passing through the membrane pores of the insert (Figure 3A).
The passage of NP110s was quantified by measuring the fluorescence from samples collected from both the blood and brain side. These permeability values were compared to those determined for the nanoparticles of&#160;&#248; 350 nm (NP350). The results show that only NP110 was able to cross the BBTB mimics (Figure 3B). NP350 remained on the blood-side of the BBTB mimic, which resulted in lower permeability values for these nanoparticles.
To highlight the relevance of the BBTB mimics compared to the in vivo models, nude mice were intravenously injected with NP110 or NP350 nanoparticles coated with the tumor-targeting peptide CooP and conjugated with red fluorescent dye (TRITC) for the detection. Tissues collected at several time points revealed that after 8 h, BBB-permeable nanoparticles have extravasated into the brain parenchyma, while the nonpermeable ones that stayed in the circulation were mainly cleared from the systemic circulation in vivo. Therefore, we collected the brains and quantified the number of nanoparticles per square millimeter 8 h postinjection. In accordance with the in vitro findings, NP110, but not NP350, successfully extravasated into the brain parenchyma (Figure 3C). High-magnification imaging of the nanoparticle location in the brain showed that NP110 was homogeneously distributed in the brain parenchyma outside the blood capillaries and successfully homed to the implanted glioblastoma cells (Figure 3D). Despite exhibiting the same tumor targeting moiety (CooP), NP350 was unable to extravasate into the brain parenchyma and was only detected within the luminal side of brain blood vessels (Figure 3E), similar to the results obtained in vitro.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59384/59384fig1.jpg" /> 
Figure 1: Description of the blood-brain tumor-barrier (BBTB) model. (A) Schematic representation of the locations of different cell types. (B) Illustration of the insert placement on the 6-well plate cover and the seeding technique for the astrocytes on the brain side of the insert&#8217;s membrane. (C) Illustration of the 6-well plate placement allowing the astrocyte adhesion. (D) Immunofluorescence micrographs of the tight junction proteins zonula occludens-1 (ZO-1, upper row, red) and claudin-5 (lower row, green). The protein expression is compared to the murine brain microvascular endothelial cells (bEND3) cultured on the blood side of the BBTB alone as a monoculture (left column) or with murine immortalized HIFko astrocytes (right column). Cell nuclei are counterstained with DAPI (blue). (E) Immunofluorescence micrograph showing the glial fibrillary acidic protein (GFAP, red) in HIFko astrocytes cultured at the brain side of the BBTB. The high-magnification image shows astrocyte processes and end-feet (arrows) contacting the endothelial cells through the membrane pores (right panel). The identity of the HIFko astrocytes was verified by immunofluorescence staining of the simian virus 40 large T antigen (SV40 large T, green) used for the immortalization of the cells. Endothelial cells express neither the GFAP nor the SV40 large T and, therefore, can be partially observed through the transparent, opposite side of the membrane as DAPI-only stained cells (dashed lines). Cell nuclei are counterstained with DAPI (blue). <a href="https://www.jove.com/files/ftp_upload/59384/59384fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/59384/59384fig2.jpg" /> 
Figure 2: Intravital live determination of the mouse BBB permeability. (A) Preparation of the implantable caudal vein catheter. (1) Tools and equipment are the following: (a) a PE20 polyethylene tube (b) two 25 G needles (c) Rochester-Ochsner forceps, and (d) a small bulldog clamp. (2) A 25 G needle is removed by several torsions using the forceps and (3) carefully inserted in the tube. (4) The other side of the tube is connected to another 25 G needle. (B) Guidance for the catheter implantation and positioning to infuse the sodium-fluorescein solution through the tail vein of a mouse. The circled area indicates the area where a drop of cyanoacrylate glue is placed to secure the catheter. The bulldog clamp is used to handle the catheter and removed once the catheter is secured. (C) Representative imaging and quantification method to determine the sodium-fluorescein permeability values. Prior to the sodium-fluorescein infusion (left column), the autofluorescence/blank is measured within a region of interest (ROI) placed on the brain (top panel, white rectangle) and blood vessel areas (bottom panel, red rectangle). During the sodium-fluorescein infusion (right column), the fluorescence intensity is measured in both ROIs, allowing the calculation of the BBB permeability. <a href="https://www.jove.com/files/ftp_upload/59384/59384fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/59384/59384fig3.jpg" /> 
Figure 3: Prediction of the intracerebral transcytosis of nanoparticles through BBB in vivo using the in vitro BBTB model. (A) Graphic representation of the BBTB assay with representative confocal images obtained at the indicated different levels of the murine BBTB model. Nanoparticles of 110 nm in diameter (NP110) and conjugated to FITC (green) were added to the blood side of the BBTB Cells were labelled with the lysosomal probe (LT-99, red). &#160;(1) Endothelial cells, (2) Endothelial transcytosis of the nanoparticles through the pores of the membrane (white dashed line), (3) astrocytes, and (4) patient glioblastoma spheres are identified on the graphic and corresponding confocal micrographs (right). Lysosomal encapsulation of the nanoparticles (arrows) suggests active transcytosis through the endothelial and astrocyte layers of the BBTB. (B) Quantification of the indicated nanoparticle permeability through the BBTB in vitro (n = 6). (C) Quantification of the indicated nanoparticle density in the brain tissue sections, 8 h after the caudal vein infusion of the nude mice (n = 3). (D) Confocal micrographs showing the distribution of the &#248; 110 nm nanoparticles (NP110, red) in murine brain tissue sections labeled with an anti-mouse CD31 antibody (green). The arrow highlights the nanoparticle transcytosis (left panel). Nanoparticles accumulated around the brain tumor cells (tumor, right panel) owing to the CooP-targeting peptide presented on their surface. No significant homing is observed in the brain tissue (Brain). (E) Confocal micrographs show the distribution of the &#248; 350 nm nanoparticles (NP350, red) in murine brain tissue sections labeled with an anti-mouse CD31 antibody (green). Arrowheads point to the NP350s that were retained in the blood vessel lumen and were unable to cross the BBB, probably due to their larger diameter compared to the NP110s. Cell nuclei are counterstained with DAPI (blue). ** P &#60; 0.01. P-values were calculated using a two-tailed, nonparametric Mann-Whitney U test. The error bars represent the standard deviation. <a href="https://www.jove.com/files/ftp_upload/59384/59384fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>murine BBTB mimic</td>
			<td>bEND3</td>
			<td>bEND3+HIFko As</td>
			<td>bEND3+GB</td>
			<td>bEND3+HIFko As+GB</td>
			<td>In vivo</td>
		</tr>
		<tr>
			<td>Permeability (10-6 cm/s)</td>
			<td>27.63</td>
			<td>6.74</td>
			<td>26.8</td>
			<td>10.83</td>
			<td>5.57</td>
		</tr>
		<tr>
			<td>SD (10-6 cm/s)</td>
			<td>3.45</td>
			<td>3.01</td>
			<td>7.99</td>
			<td>2.65</td>
			<td>2.19</td>
		</tr>
		<tr>
			<td>human BBTB mimic</td>
			<td>HuAR2T</td>
			<td>HuAR2T+hIAs</td>
			<td>HuAR2T+GB</td>
			<td>HuAR2T+hIAs+GB</td>
			<td></td>
		</tr>
		<tr>
			<td>Permeability (10-6 cm/s)</td>
			<td>104.92</td>
			<td>47.4</td>
			<td>89.08</td>
			<td>48.24</td>
			<td></td>
		</tr>
		<tr>
			<td>SD (10-6 cm/s)</td>
			<td>27.1</td>
			<td>14.32</td>
			<td>10.21</td>
			<td>13.07</td>
			<td></td>
		</tr>
	</tbody>
</table>
Table 1: Values of the sodium-fluorescein (Na-Fl) permeability (in centimeters per second) determined in vitro in the indicated co-culture systems and in vivo in NMRI nude mice. Data from a representative experiment (n = 3 mice).

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Predicting In Vivo Payloads Delivery using a Blood-brain Tumor-barrier in a Dish

Drug targeting to central nervous system tumors is a major challenge. Here we describe a protocol to produce an in vitro mimic of the blood-brain tumor-barrier using murine and/or human cells and discuss their relevance for the predictability of central nervous system tumor targeting in vivo.

Highly selective by nature, the blood-brain barrier (BBB) is essential for the brain homeostasis in physiological conditions. However, in the context of ...

predicting-vivo-payloads-delivery-using-blood-brain-tumor-barrier

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Cancer Research

9.0K Views.  University of Helsinki. Drug targeting to central nervous system tumors is a major challenge. Here we describe a protocol to produce an in vitro mimic of the blood-brain tumor-barrier using murine and/or human cells and discuss their relevance for the predictability of central nervous system tumor targeting in vivo.

Video: Predicting In Vivo Payloads Delivery using a Blood-brain Tumor-barrier in a Dish

In Vivo EPR Assessment of pH, pO2, Redox Status, and Concentrations of Phosphate and Glutathione in the Tumor Microenvironment

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In Vivo EPR Assessment of pH, pO2, Redox Status, and Concentrations of Phosphate and Glutathione in the Tumor Microenvironment

Low-field (L-band, 1.2 GHz) electron paramagnetic resonance using soluble nitroxyl and trityl probes is demonstrated for assessment of physiologically important parameters in the tumor microenvironment in mouse models of breast cancer.

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Fluorescence Molecular Tomography for In Vivo Imaging of Glioblastoma Xenografts

Tumorigenicity is the capability of cancer cells to form a tumor mass. A widely used approach to determine if the cells are tumorigenic is by injecting immunodeficient mice subcutaneously with cancer cells and measuring the tumor mass after it becomes visible and palpable. Orthotopic injections of cancer cells aim to introduce the xenograft in the microenvironment that most closely resembles the tissue of origin of the tumor being studied. Brain cancer research requires intracranial injection of cancer cells to allow the tumor formation and analysis in the unique microenvironment of the brain. The in vivo imaging of intracranial xenografts monitors instantaneously the tumor mass of orthotopically engrafted mice. Here we report the use of fluorescence molecular tomography (FMT) of brain tumor xenografts. The cancer cells are first transduced with near infrared fluorescent proteins and then injected in the brain of immunocompromised mice. The animals are then scanned to obtain quantitative information about the tumor mass over an extended period of time. Cell pre-labeling allows for cost effective, reproducible, and reliable quantification of the tumor burden within each mouse. We eliminated the need for injecting imaging substrates, and thus reduced the stress on the animals. A limitation of this approach is represented by the inability to detect very small masses; however, it has better resolution for larger masses than other techniques. It can be applied to evaluate the efficacy of a drug treatment or genetic alterations of glioma cell lines and patient-derived samples.

Fluorescence Molecular Tomography for In Vivo Imaging of Glioblastoma Xenografts

Orthotopic intracranial injection of tumor cells has been used in cancer research to study brain tumor biology, progression, evolution, and therapeutic response. Here we present fluorescence molecular tomography of tumor xenografts, which provides real-time intravital imaging and quantification of a tumor mass in preclinical glioblastoma models.

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In Vivo Inhibition of MicroRNA to Decrease Tumor Growth in Mice

MicroRNAs (miRNAs) are important regulators of gene expression through their ability to destabilize mRNA and inhibit translation of target mRNAs. An ever-increasing number of studies have identified miRNAs as potential biomarkers for cancer diagnosis and prognosis, and also as therapeutic targets, adding an extra dimension to cancer evaluation and treatment. In the context of thyroid cancer, tumorigenesis results not only from mutations in important genes, but also from the overexpression of many miRNAs. Accordingly, the role of miRNAs in the control of thyroid gene expression is evolving as an important mechanism in cancer. Herein, we present a protocol to examine the effects of miRNA-inhibitor delivery as a therapeutic modality in thyroid cancer using human tumor xenograft and orthotopic mouse models. After engineering stable thyroid tumoral cells expressing GFP and luciferase, cells are injected into nude mice to develop tumors, which can be followed by bioluminescence. The in vivo inhibition of a miRNA can reduce tumor growth and upregulate miRNA gene targets. This method can be used to assess the importance of a determined miRNA in vivo, in addition to identifying new therapeutic targets.

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In Vivo Targeting of Xenografted Human Cancer Cells with Functionalized Fluorescent Silica Nanoparticles in Zebrafish

Developing nanoparticles capable of detecting, targeting, and destroying cancer cells is of great interest in the field of nanomedicine. In vivo animal models are required for bridging the nanotechnology to its biomedical application. The mouse represents the traditional animal model for preclinical testing; however, mice are relatively expensive to keep and have long experimental cycles due to the limited progeny from each mother. The zebrafish has emerged as a powerful model system for developmental and biomedical research, including cancer research. In particular, due to its optical transparency and rapid development, zebrafish embryos are well suited for real-time in vivo monitoring of the behavior of cancer cells and their interactions with their microenvironment. This method was developed to sequentially introduce human cancer cells and functionalized nanoparticles in transparent Casper zebrafish embryos and monitor in vivo recognition and targeting of the cancer cells by nanoparticles in real time. This optimized protocol shows that fluorescently labeled nanoparticles, which are functionalized with folate groups, can specifically recognize and target metastatic human cervical epithelial cancer cells labeled with a different fluorochrome. The recognition and targeting process can occur as early as 30 min postinjection of the nanoparticles tested. The whole experiment only requires the breeding of a few pairs of adult fish and takes less than 4 days to complete. Moreover, zebrafish embryos lack a functional adaptive immune system, allowing the engraftment of a wide range of human cancer cells. Hence, the utility of the protocol described here enables the testing of nanoparticles on various types of human cancer cells, facilitating the selection of optimal nanoparticles in each specific cancer context for future testing in mammals and the clinic.

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Breast cancer is a devastating malignancy, accounting for 40,000 female deaths and 30% of new female cancer diagnoses in the United States in 2019 alone. The leading cause of breast cancer related deaths is the metastatic burden. Therefore, preclinical models for breast cancer need to analyze metastatic burden to be clinically relevant. The 4T1 breast cancer model provides a spontaneously-metastasizing, quantifiable mouse model for stage IV human breast cancer. However, most 4T1 protocols quantify the metastatic burden by manually counting stained colonies on tissue culture plates. While this is sufficient for tissues with lower metastatic burden, human error in manual counting causes inconsistent and variable results when plates are confluent and difficult to count. This method offers a computer-based solution to human counting error. Here, we evaluate the protocol using the lung, a highly metastatic tissue in the 4T1 model. Images of methylene blue-stained plates are acquired and uploaded for analysis in Fiji-ImageJ. Fiji-ImageJ then determines the percentage of the selected area of the image that is blue, representing the percentage of the plate with metastatic burden. This computer-based approach offers more consistent and expeditious results than manual counting or histopathological evaluation for highly metastatic tissues. The consistency of Fiji-ImageJ results depends on the quality of the image. Slight variations in results between images can occur, thus it is recommended that multiple images are taken and results averaged. Despite its minimal limitations, this method is an improvement to quantifying metastatic burden in the lung by offering consistent and rapid results.

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An understanding of drug resistance and the development of novel strategies to sensitize highly resistant cancers rely on the availability of suitable preclinical models that can accurately predict patient responses. One of the disadvantages of existing preclinical models is the inability to contextually preserve the human tumor microenvironment (TME) and accurately represent intratumoral heterogeneity, thus limiting the clinical translation of data. By contrast, by representing the culture of live fragments of human tumors, the patient-derived explant (PDE) platform allows drug responses to be examined in a three-dimensional (3D) context that mirrors the pathological and architectural features of the original tumors as closely as possible. Previous reports with PDEs have documented the ability of the platform to distinguish chemosensitive from chemoresistant tumors, and it has been shown that this segregation is predictive of patient responses to the same chemotherapies. Simultaneously, PDEs allow the opportunity to interrogate molecular, genetic, and histological features of tumors that predict drug responses, thereby identifying biomarkers for patient stratification as well as novel interventional approaches to sensitize resistant tumors. This paper reports PDE methodology in detail, from collection of patient samples through to endpoint analysis. It provides a detailed description of explant derivation and culture methods, highlighting bespoke conditions for particular tumors, where appropriate. For endpoint analysis, there is a focus on multiplexed immunofluorescence and multispectral imaging for the spatial profiling of key biomarkers within both tumoral and stromal regions. By combining these methods, it is possible to generate quantitative and qualitative drug response data that can be related to various clinicopathological parameters and thus potentially be used for biomarker identification.

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Here we present a flow cytometry-based method for visualization and quantification of multiple senescence-associated markers in single cells.

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In Vivo Gene Delivery into Mouse Mammary Epithelial Cells Through Mammary Intraductal Injection

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