Ja Hye Myung

Dendrimer‐Mediated Multivalent Binding for the Enhanced Capture of Tumor Cells

Multivalent binding, the simultaneous binding of multiple ligands to multiple receptors, has played a central role in a number of pathological processes, including the attachment of viral, parasitic, mycoplasmal, and bacterial pathogens.[1] These biological activities have been extensively investigated to promote targeting of specific cell types, [2] and biological multivalent inhibitors have yielded significant increases in binding avidities by 1–9 orders of magnitude.[3] In particular, nano-scale poly(amidoamine) (PAMAM) dendrimers have been reported to be an excellent mediator for facilitated multivalent effect due to their capability to pre-organize/orient ligands and easy deformability of the polymer chains.[2a]

Enhanced Tumor Cell Isolation by a Biomimetic Combination of E-selectin and anti-EpCAM: Implications for the Effective Separation of Circulating Tumor Cells (CTCs)

The selective detection of circulating tumor cells (CTCs) is of significant clinical importance for the clinical diagnosis and prognosis of cancer metastasis. However, largely because of the extremely low number of CTCs (as low as 1 in 10(9) hematologic cells) in the blood of patients, effective detection and separation of the rare cells remain a tremendous challenge. Cell rolling is known to play a key role in physiological processes such as the recruitment of leukocytes to sites of inflammation and selectin-mediated CTC metastasis. Furthermore, because CTCs typically express the epithelial-cell adhesion molecule (EpCAM) on the surface whereas normal hematologic cells do not, substrates with immobilized antibody against EpCAM may specifically interact with CTCs. In this article, we created biomimetic surfaces functionalized with P- and E-selectin and anti-EpCAM that induce different responses in HL-60 (used as a model of leukocytes in this study) and MCF-7 (a model of CTCs) cells. HL-60 and MCF-7 cells showed different degrees of interaction with P-/E-selectin and anti-EpCAM at a shear stress of 0.32 dyn/cm(2). HL-60 cells exhibited rolling on P-selectin-immobilized substrates at a velocity of 2.26 +/- 0.28 microm/s whereas MCF-7 cells had no interaction with the surface. Both cell lines, however, had interactions with E-selectin, and the rolling velocity of MCF-7 cells (4.24 +/- 0.31 microm/s) was faster than that of HL-60 cells (2.12 +/- 0.15 microm/s). However, only MCF-7 cells interacted with anti-EpCAM-coated surfaces, forming stationary binding under flow. More importantly, the combination of the rolling (E-selectin) and stationary binding (anti-EpCAM) resulted in substantially enhanced separation capacity and capture efficiency (more than 3-fold enhancement), as compared to a surface functionalized solely with anti-EpCAM that has been commonly used for CTC capture. Our results indicate that cell-specific detection and separation may be achieved through mimicking the biological processes of combined dynamic cell rolling and stationary binding, which will likely lead to a CTC detection device with significantly enhanced specificity and sensitivity without a complex fabrication process.

Direct Measurements on CD24-Mediated Rolling of Human Breast Cancer MCF-7 Cells on E-Selectin

Tumor cell rolling on the endothelium plays a key role in the initial steps of cancer metastasis, i.e., extravasation of circulating tumor cells (CTCs). Identification of the ligands that induce the rolling of cells is thus critical to understanding how cancers metastasize. We have previously demonstrated that MCF-7 cells, human breast cancer cells, exhibit the rolling response selectively on E-selectin-immobilized surfaces. However, the ligand that induces rolling of MCF-7 cells on E-selectin has not yet been identified, as these cells lack commonly known E-selectin ligands. Here we report, for the first time to our knowledge, a set of quantitative and direct evidence demonstrating that CD24 expressed on MCF-7 cell membranes is responsible for rolling of the cells on E-selectin. The binding kinetics between CD24 and E-selectin was directly measured using surface plasmon resonance (SPR), which revealed that CD24 has a binding affinity against E-selectin (K(D) = 3.4 ± 0.7 nM). The involvement of CD24 in MCF-7 cell rolling was confirmed by the rolling behavior that was completely blocked when cells were treated with anti-CD24. A simulated study by flowing microspheres coated with CD24 onto E-selectin-immobilized surfaces further revealed that the binding is Ca(2+)-dependent. Additionally, we have found that actin filaments are involved in the CD24-mediated cell rolling, as observed by the decreased rolling velocities of the MCF-7 cells upon treatment with cytochalasin D (an inhibitor of actin-filament dynamics) and the stationary binding of CD24-coated microspheres (the lack of actins) on the E-selectin-immobilized slides. Given that CD24 is known to be directly related to enhanced invasiveness of cancer cells, our results imply that CD24-based cell rolling on E-selectin mediates, at least partially, cancer cell extravasation, resulting in metastasis.

Differential detection of tumor cells using a combination of cell rolling, multivalent binding, and multiple antibodies.

Effective quantification and in situ identification of circulating tumor cells (CTCs) in blood are still elusive because of the extreme rarity and heterogeneity of the cells. In our previous studies, we developed a novel platform that captures tumor cells at significantly improved efficiency in vitro using a unique biomimetic combination of two physiological processes: E-selectin-induced cell rolling and poly(amidoamine) (PAMAM) dendrimer-mediated strong multivalent binding. Herein, we have engineered a novel multifunctional surface, on the basis of the biomimetic cell capture, through optimized incorporation of multiple antibodies directed to cancer cell-specific surface markers, such as epithelial cell adhesion molecule (EpCAM), human epidermal growth factor receptor-2 (HER-2), and prostate specific antigen (PSA). The surfaces were tested using a series of tumor cells, MDA-PCa-2b, MCF-7, and MDA-MB-361, both in mixture in vitro and after being spiked into human blood. Our multifunctional surface demonstrated highly efficient capture of tumor cells in human blood, achieving up to 82% capture efficiency (∼10-fold enhancement than a surface with the antibodies alone) and up to 90% purity. Furthermore, the multipatterned antibodies allowed differential capturing of the tumor cells. These results support that our multifunctional surface has great potential as an effective platform that accommodates virtually any antibodies, which will likely lead to clinically significant, differential detection of CTCs that are rare and highly heterogeneous.

Microfluidic devices to enrich and isolate circulating tumor cells

Given the potential clinical impact of circulating tumor cells (CTCs) in blood as a clinical biomarker for the diagnosis and prognosis of various cancers, a myriad of detection methods for CTCs have been recently introduced. Among those, a series of microfluidic devices are particularly promising as they uniquely offer micro-scale analytical systems that are highlighted by low consumption of samples and reagents, high flexibility to accommodate other cutting-edge technologies, precise and well-defined flow behaviors, and automation capability, presenting significant advantages over conventional larger scale systems. In this review, we highlight the advantages of microfluidic devices and their potential for translation into CTC detection methods, categorized by miniaturization of bench-top analytical instruments, integration capability with nanotechnologies, and in situ or sequential analysis of captured CTCs. This review provides a comprehensive overview of recent advances in CTC detection achieved through application of microfluidic devices and the challenges that these promising technologies must overcome to be clinically impactful.

Channel Surface Patterning of Alternating Biomimetic Protein Combinations for Enhanced Microfluidic Tumor Cell Isolation

Here, we report a new method for multicomponent protein patterning in a microchannel and also a technique for improving immunoaffinity-based circulating tumor cell (CTC) capture by patterning regions of alternating adhesive proteins using the new method. The first of two proteins, antiepithelial cell adhesion molecule (anti-EpCAM), provides the specificity for CTC capture. The second, E-selectin, increases CTC capture under shear. Patterning regions with and without E-selectin allows captured leukocytes, which also bind E-selectin and are unwanted impurities in CTC isolation, to roll a short distance and detach from the capture surface. This reduces leukocyte capture by up to 82%. The patterning is combined with a leukocyte elution step in which a calcium chelating buffer effectively deactivates E-selectin so that leukocytes may be rinsed away 60% more efficiently than with a buffer containing calcium. The alternating patterning of this biomimetic protein combination, used in conjunction with the elution step, reduces capture of leukocytes while maintaining a high tumor cell capture efficiency that is up to 1.9 times higher than the tumor cell capture efficiency of a surface with only anti-EpCAM. The new patterning technique described here does not require mask alignment and can be used to spatially control the immobilization of any two proteins or protein mixtures inside a sealed microfluidic channel.

Recent advances in nanotechnology-based detection and separation of circulating tumor cells

Although circulating tumor cells (CTCs) in blood have been widely investigated as a potential biomarker for diagnosis and prognosis of metastatic cancer, their inherent rarity and heterogeneity bring tremendous challenges to develop a CTC detection method with clinically significant specificity and sensitivity. With advances in nanotechnology, a series of new methods that are highly promising have emerged to enable or enhance detection and separation of CTCs from blood. In this review, we systematically categorize nanomaterials, such as gold nanoparticles, magnetic nanoparticles, quantum dots, graphenes/graphene oxides, and dendrimers and stimuli-responsive polymers, used in the newly developed CTC detection methods. This will provide a comprehensive overview of recent advances in the CTC detection achieved through application of nanotechnology as well as the challenges that these existing technologies must overcome to be directly impactful on human health.

Effective Capture of Circulating Tumor Cells from a Transgenic Mouse Lung Cancer Model Using Dendrimer Surfaces Immobilized with Anti-EGFR

The lack of an effective detection method for lung circulating tumor cells (CTCs) presents a substantial challenge to elucidate the value of CTCs as a diagnostic or prognostic indicator in lung cancer, particularly in nonsmall cell lung cancer (NSCLC). In this study, we prepared a capture surface exploiting strong multivalent binding mediated by poly(amidoamine) (PAMAM) dendrimers to capture CTCs originating from lung cancers. Given that 85% of the tumor cells from NSCLC patients overexpress epidermal growth factor receptor (EGFR), anti-EGFR was chosen as a capture agent. Following in vitro confirmation using the murine lung cancer cell lines (ED-1 and ED1-SC), cyclin E-overexpressing (CEO) transgenic mice were employed as an in vivo lung tumor model to assess specificity and sensitivity of the capture surface. The numbers of CTCs in blood from the CEO transgenic mice were significantly higher than those from the healthy controls (on average 75.3 ± 14.9 vs 4.4 ± 1.2 CTCs/100 μL of blood, p < 0.005), indicating the high sensitivity and specificity of our surface. Furthermore, we found that the capture surface also offers a simple, effective method for monitoring treatment responses, as observed by the significant decrease in the CTC numbers from the CEO mice upon a treatment using a novel anti-miR-31 locked nucleic acid (LNA), compared to a vehicle treatment and a control-LNA treatment (p < 0.05). This in vivo evaluation study confirms that our capture surface is highly efficient in detecting in vivo CTCs and thus has translational potential as a diagnostic and prognostic tool for lung cancer.

Rheologically biomimetic cell suspensions for decreased cell settling in microfluidic devices.

Many microfluidic devices operate with cells suspended in buffer solutions. Researchers who work with large cell types in such devices often run into problems with gravitational cell settling in the injection equipment and in the device itself. A method for reducing this problematic settling is discussed in this paper using tumor cell lines as an example. Microfluidic circulating tumor cell (CTC) isolation devices (MCIDs) are benchmarked using buffer solutions spiked with in-vitro tumor cell lines prior to validation with clinical samples (i.e. whole blood). However, buffer solutions have different rheological properties than whole blood. Here we describe the use of alginate in PBS buffer solutions to mimic blood rheology and reduce cell settling during preliminary validation experiments. Because alginate increases the viscosity of a solution, it helps to maintain cells in suspension. We report that vertical equipment configurations are important to further mitigate the effects of cell settling for MDA-MB-468 carcinoma cells. We also report that alginate does not disrupt the specific binding interactions that are the basis of carcinoma cell capture in MCIDs. These results indicate that vertical equipment configurations and the addition of alginates can be used to reduce cell settling in buffer based MCID testing and other applications involving large cells suspended in buffer solution.

Next-Generation CDK2/9 Inhibitors and Anaphase Catastrophe in Lung Cancer

Background The first generation CDK2/7/9 inhibitor seliciclib (CYC202) causes multipolar anaphase and apoptosis in lung cancer cells with supernumerary centrosomes (known as anaphase catastrophe). We investigated a new and potent CDK2/9 inhibitor, CCT68127 (Cyclacel). Methods CCT68127 was studied in lung cancer cells (three murine and five human) and control murine pulmonary epithelial and human immortalized bronchial epithelial cells. Robotic CCT68127 cell-based proliferation screens were used. Cells undergoing multipolar anaphase and inhibited centrosome clustering were scored. Reverse phase protein arrays (RPPAs) assessed CCT68127 effects on signaling pathways. The function of PEA15, a growth regulator highlighted by RPPAs, was analyzed. Syngeneic murine lung cancer xenografts (n = 4/group) determined CCT68127 effects on tumorigenicity and circulating tumor cell levels. All statistical tests were two-sided. Results CCT68127 inhibited growth up to 88.5% (SD = 6.4%, P < .003) at 1 μM, induced apoptosis up to 42.6% (SD = 5.5%, P < .001) at 2 μM, and caused G1 or G2/M arrest in lung cancer cells with minimal effects on control cells (growth inhibition at 1 μM: 10.6%, SD = 3.6%, P = .32; apoptosis at 2 μM: 8.2%, SD = 1.0%, P = .22). A robotic screen found that lung cancer cells with KRAS mutation were particularly sensitive to CCT68127 ( P = .02 for IC 50 ). CCT68127 inhibited supernumerary centrosome clustering and caused anaphase catastrophe by 14.1% (SD = 3.6%, P < .009 at 1 μM). CCT68127 reduced PEA15 phosphorylation by 70% (SD = 3.0%, P = .003). The gain of PEA15 expression antagonized and its loss enhanced CCT68127-mediated growth inhibition. CCT68127 reduced lung cancer growth in vivo ( P < .001) and circulating tumor cells ( P = .004). Findings were confirmed with another CDK2/9 inhibitor, CYC065. Conclusions Next-generation CDK2/9 inhibition elicits marked antineoplastic effects in lung cancer via anaphase catastrophe and reduced PEA15 phosphorylation.