Nanoparticle-Mediated Co-Delivery of Notch-1 Antibodies and ABT-737 as a Potent Treatment Strategy for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) accounts for nearly one-quarter of all breast cancer cases, but effective targeted therapies for this disease remain elusive because TNBC cells lack expression of the three most common receptors seen on other subtypes of breast cancer. Here, we exploit TNBC cells' overexpression of Notch-1 receptors and Bcl-2 anti-apoptotic proteins to provide an effective targeted therapy. Prior studies have shown that the small molecule drug ABT-737, which inhibits Bcl-2 to reinstate apoptotic signaling, is a promising candidate for TNBC therapy. However, ABT-737 is poorly soluble in aqueous conditions, and its orally bioavailable derivative causes severe thrombocytopenia. To enable targeted delivery of ABT-737 to TNBC and enhance its therapeutic efficacy, we encapsulated the drug in poly(lactic-co-glycolic acid) nanoparticles (NPs) that were functionalized with Notch-1 antibodies to produce N1-ABT-NPs. The antibodies in this NP platform enable both TNBC cell-specific binding and suppression of Notch signaling within TNBC cells by locking the Notch-1 receptors in a ligand unresponsive state. This Notch inhibition potentiates the effect of ABT-737 by up-regulating Noxa, resulting in effective killing of TNBC cells. We present the results of in vitro studies that demonstrate N1-ABT-NPs can preferentially bind TNBC cells versus noncancerous breast epithelial cells to effectively regulate Bcl-2 and Notch signaling to induce cell death. Further, we show that N1-ABT-NPs can accumulate in subcutaneous TNBC xenograft tumors in mice following systemic administration to reduce tumor burden and extend animal survival. Together, these findings demonstrate that NP-mediated co-delivery of Notch-1 antibodies and ABT-737 is a potent treatment strategy for TNBC that may improve patient outcomes with further development and implementation.

Layer-by-layer assembled PLGA nanoparticles carrying miR-34a cargo inhibit the proliferation and cell cycle progression of triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) accounts for 15-25% of diagnosed breast cancers, and its lack of a clinically defined therapeutic target has caused patients to suffer from earlier relapse and higher mortality rates than patients with other breast cancer subtypes. MicroRNAs (miRNAs) are small non-coding RNAs that regulate the expression of multiple genes through RNA interference to maintain normal tissue function. The tumor suppressor miR-34a is downregulated in TNBC, and its loss-of-expression correlates with worse disease outcomes. Therefore, delivering miR-34a mimics into TNBC cells is a promising strategy to combat disease progression. To achieve this goal, we synthesized layer-by-layer assembled nanoparticles (LbL NPs) comprised of spherical poly(lactic-co-glycolic acid) cores surrounded by alternating layers of poly-L-lysine (PLL) and miR-34a. TNBC cells internalized these LbL NPs to a greater extent than polyplexes comprised of PLL and miRNA, and confocal microscopy showed that LbL NPs delivered a substantial fraction of miR-34a cargo into the cytosol. This yielded robust suppression of the miR-34a target genes CCND-1, Notch-1, Bcl-2, Survivin, and MDR-1, which reduced TNBC cell proliferation and induced cell cycle arrest. These data validate that miR-34a delivery can impair TNBC cell function and support continued investigation of this platform for treatment of TNBC.

Gold Nanoshell-Linear Tetrapyrrole Conjugates for Near Infrared-Activated Dual Photodynamic and Photothermal Therapies

Photodynamic therapy (PDT) is a treatment in which photoactive compounds delivered to cancerous tissues are excited with light and then transfer the absorbed energy to adjacent tissue oxygen molecules to generate toxic singlet oxygen (¹O₂). As ¹O₂ is produced only where light and photosensitizers (PSs) are combined, PDT holds promise as a minimally invasive, highly selective treatment for certain cancers. The practical application of PDT requires easily synthesized, water-soluble PSs that have low dark toxicities, high ¹O₂ quantum yields, and efficient absorption of 650-850 nm near-infrared (NIR) light, which deeply penetrates tissue. We recently developed a linear tetrapyrrole metal complex, Pd[DMBil1]-PEG₇₅₀, that meets most of these criteria. This complex is remarkably effective as a PS for PDT against triple-negative breast cancer (TNBC) cells but, critically, it does not absorb NIR light, which is necessary to treat deeper tumors. To enable NIR activation, we synthesized a new derivative, Pd[DMBil1]-PEG₅₀₀₀-SH, which bears a thiol functionality that facilitates conjugation to NIR-absorbing gold nanoshells (NSs). Upon excitation with pulsed 800 nm light, NSs emit two-photon-induced photoluminescence spanning 500-700 nm, which can sensitize the attached PSs to initiate PDT. Additionally, NSs produce heat upon 800 nm irradiation, endowing the NS-PS conjugates with an auxiliary photothermal therapeutic (PTT) capability. Here, we demonstrate that NS-PS conjugates are potent mediators of NIR-activated tandem PDT/PTT against TNBC cells in vitro. We show that Pd[DMBil1]-PEG₅₀₀₀-SH retains the photophysical properties of the parent Pd[DMBil1] complex, and that NS-PS generate ¹O₂ under pulsed 800 nm irradiation, confirming activation of the PSs by photoluminescence emitted from NSs. TNBC cells readily internalize NS PS conjugates, which generate reactive oxygen species in the cells upon pulsed NIR irradiation to damage DNA and induce apoptosis. Together, these findings demonstrate that exploiting photoluminescent NSs as carriers of efficient Pd[DMBil1] PSs is an effective strategy to enable NIR light-activated tandem PDT/PTT.

Cancer Cell Membrane-Coated Nanoparticles for Cancer Management

Cancer is a global health problem in need of transformative treatment solutions for improved patient outcomes. Many conventional treatments prove ineffective and produce undesirable side effects because they are incapable of targeting only cancer cells within tumors and metastases post administration. There is a desperate need for targeted therapies that can maximize treatment success and minimize toxicity. Nanoparticles (NPs) with tunable physicochemical properties have potential to meet the need for high precision cancer therapies. At the forefront of nanomedicine is biomimetic nanotechnology, which hides NPs from the immune system and provides superior targeting capabilities by cloaking NPs in cell-derived membranes. Cancer cell membranes expressing "markers of self" and "self-recognition molecules" can be removed from cancer cells and wrapped around a variety of NPs, providing homotypic targeting and circumventing the challenge of synthetically replicating natural cell surfaces. Compared to unwrapped NPs, cancer cell membrane-wrapped NPs (CCNPs) provide reduced accumulation in healthy tissues and higher accumulation in tumors and metastases. The unique biointerfacing capabilities of CCNPs enable their use as targeted nanovehicles for enhanced drug delivery, localized phototherapy, intensified imaging, or more potent immunotherapy. This review summarizes the state-of-the-art in CCNP technology and provides insight to the path forward for clinical implementation.

IR820-loaded PLGA nanoparticles for photothermal therapy of triple-negative breast cancer

Triple-negative breast cancer (TNBC) accounts for 15-25% of breast cancer cases and lacks expression of the three most common receptors seen on other subtypes of breast cancer. This lack of expression makes TNBC unsusceptible to currently available targeted or hormonal therapies, so new treatment strategies are desperately needed. Photothermal therapy (PTT), which utilizes nanoparticles (NPs) embedded in tumors as exogenous energy absorbers to convert externally applied near-infrared (NIR) light into heat to ablate cancer cells, has shown promise as an alternative strategy. However, it typically uses gold-based NPs that will remain in the body for extended period of time with unknown long-term health effects. To enable PTT with biodegradable, polymeric NPs, we encapsulated the NIR-absorbing dye IR820 in poly(lactic-co-glycolic acid) (PLGA) NPs. We characterized the physicochemical properties of these IR820-loaded PLGA NPs and evaluated their performance as PTT agents using both in vitro and in vivo models of TNBC. The results demonstrate that these NPs are potent mediators of PTT that induce cell death primarily through apoptosis to effectively hinder the growth of TNBC tumors. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1702-1712, 2019.

Polyethylenimine-Spherical Nucleic Acid Nanoparticles against Gli1 Reduce the Chemoresistance and Stemness of Glioblastoma Cells

Glioblastoma (GBM) is the most common and lethal primary brain tumor in adults, with nearly 100% of patients ultimately succumbing to the disease. Median patient survival is 15 months, and no standard of care currently exists for recurrent cases. Glioma stem cells (GSCs), a rare and highly aggressive subpopulation of cells within these tumors, have recently emerged as drivers of tumor initiation and recurrence, and a growing body of evidence suggests that they must be completely eradicated to prevent relapse. Toward this goal, we have developed polyethylenimine-wrapped spherical nucleic acid nanoparticles (PEI-SNAs) targeting Gli1, a transcription factor within the Hedgehog signaling pathway that is crucial for the maintenance of GSCs. Here, we demonstrate that Gli1 PEI-SNAs bind scavenger receptors on GBM cells to undergo endocytosis in a caveolae/lipid raft/dynamin-dependent manner. They further achieve ∼30% silencing of tumor-promoting Hedgehog pathway genes and downstream target genes that promote the aggressive, chemoresistant phenotype of GBM. This produces a 30% decrease in proliferation that correlates with a robust onset of GBM cell senescence as well as an ∼60% decrease in metabolic activity with or without cotreatment with temozolomide (TMZ), the frontline chemotherapy for GBM. Most importantly, Gli1 PEI-SNAs impair the self-renewal capacity of GBM cells as indicated by a 30-40% reduction in the expression of stemness genes and further impair the formation of stem-like neurospheres. They also substantially improve neurosphere chemosensitivity as demonstrated by a 2-fold increase in the fraction of cells undergoing apoptosis in response to low doses of TMZ. These results underscore the potential for siRNA therapeutics targeting Gli1 to reduce GBM resistance to therapy and warrant further development of PEI-SNAs and Gli1-targeted therapies to alleviate drug resistance and recurrence for GBM patients.

Layer-by-layer assembled gold nanoshells for the intracellular delivery of miR-34a

INTRODUCTION

MicroRNAs (miRNAs) are short noncoding RNAs whose ability to regulate the expression of multiple genes makes them potentially exciting tools to treat disease. Unfortunately, miRNAs cannot passively enter cells due to their hydrophilicity and negative charge. Here, we report the development of layer-by-layer assembled nanoshells (LbL-NS) as vehicles for efficient intracellular miRNA delivery. Specifically, we developed LbL-NS to deliver the tumor suppressor miR-34a into triple-negative breast cancer (TNBC) cells, and demonstrate that these constructs can safely and effectively regulate the expression of SIRT1 and Bcl-2, two known targets of miR-34a, to decrease cell proliferation.

METHODS

LbL-NS were made by coating negatively charged nanoshells with alternating layers of positive poly-L-lysine (PLL) and negative miRNA, with the outer layer consisting of PLL to facilitate cellular entry and protect the miRNA. Electron microscopy, spectrophotometry, dynamic light scattering, and miRNA release studies were used to characterize LbL-NS. The particles' ability to enter MDA-MB-231 TNBC cells, inhibit SIRT1 and Bcl-2 expression, and thereby reduce cell proliferation was examined by confocal microscopy, Western blotting, and EdU assays, respectively.

RESULTS

Each successive coating reversed the nanoparticles' charge and increased their hydrodynamic diameter, resulting in a final diameter of 208±4 nm and a zeta potential of 53±5 mV. The LbL-NS released ~30% of their miR-34a cargo over 5 days in 1X PBS. Excitingly, LbL-NS carrying miR-34a suppressed SIRT1 and Bcl-2 by 46±3% and 35±3%, respectively, and decreased cell proliferation by 33%. LbL-NS carrying scrambled miRNA did not yield these effects.

CONCLUSION

LbL-NS can efficiently deliver miR-34a to TNBC cells to suppress cancer cell growth, warranting their further investigation as tools for miRNA replacement therapy.

Advances in targeted nanotherapeutics: From bioconjugation to biomimicry

Since the emergence of cancer nanomedicine, researchers have had intense interest in developing nanoparticles (NPs) that can specifically target diseased sites while avoiding healthy tissue to mitigate the off-target effects seen with conventional treatments like chemotherapy. Initial endeavors focused on the bioconjugation of targeting agents to NPs, and more recently, researchers have begun to develop biomimetic NP platforms that can avoid immune recognition to maximally accumulate in tumors. In this review, we describe the advantages and limitations of each of these targeting strategies. First, we review developments in bioconjugation strategies, where NPs are coated with biomolecules such as antibodies, aptamers, peptides, and small molecules to enable cell-specific binding. While bioconjugated NPs offer many exciting features and have improved pharmacokinetics and biodistribution relative to unmodified NPs, they are still recognized by the body as "foreign", resulting in their clearance by the mononuclear phagocytic system (MPS). To overcome this limitation, researchers have recently begun to investigate biomimetic approaches that can hide NPs from immune recognition and reduce clearance by the MPS. These biomimetic NPs fall into two distinct categories: synthetic NPs that present naturally occurring structures, and NPs that are completely disguised by natural structures. Overall, bioconjugated and biomimetic NPs have substantial potential to improve upon conventional treatments by reducing off-target effects through site-specific delivery, and they show great promise for future standards of care. Here, we provide a summary of each strategy, discuss considerations for their design moving forward, and highlight their potential clinical impact on cancer therapy.

Spherical Nucleic Acid Architecture Can Improve the Efficacy of Polycation-Mediated siRNA Delivery

Clinical translation of small interfering RNA (siRNA) nanocarriers is hindered by limited knowledge regarding the parameters that regulate interactions between nanocarriers and biological systems. To address this, we investigated the influence of polycation-based nanocarrier architecture on intracellular siRNA delivery. We compared the cellular interactions of two polycation-based siRNA carriers that have similar size and surface charge but different siRNA orientation: (1) polyethylenimine-coated spherical nucleic acids (PEI-SNAs), in which polyethylenimine is wrapped around a spherical nucleic acid core containing radially oriented siRNA and (2) randomly assembled polyethylenimine-siRNA polyplexes that lack controlled architecture. We found that PEI-SNAs undergo enhanced and more rapid cellular uptake than polyplexes, suggesting a prominent role for architecture in cellular uptake. Confocal microscopy studies demonstrated that while PEI-SNAs and polyplexes exhibit similar intracellular stability, PEI-SNAs undergo decreased accumulation within lysosomes, identifying another advantage conferred by their architecture. Indeed, these advantageous cellular interactions enhanced the gene silencing potency of PEI-SNAs by 10-fold relative to polyplexes. Finally, cytocompatibility studies showed that PEI-SNAs exhibit decreased toxicity per PEI content relative to polyplexes, allowing the use of more polycation. Our studies provide critical insight into design considerations for engineering siRNA carriers and warrant future investigation of how nanocarrier architecture influences cellular-, organ-, and organism-level interactions.

Photochemotherapeutic Properties of a Linear Tetrapyrrole Palladium(II) Complex displaying an Exceptionally High Phototoxicity Index

Photodynamic therapy (PDT) represents a minimally invasive and highly localized treatment strategy to ablate tumors with few side effects. In PDT, photosensitizers embedded within tumors are activated by light and undergo intersystem crossing, followed by energy transfer to molecular oxygen, resulting in the production of toxic singlet oxygen (¹O₂). Previously, we reported a robust, linear tetrapyrrole palladium(II) complex, Pd[DMBil1], characterized by its facile and modular synthesis, broad absorption profile, and efficient ¹O₂ quantum yield of Φ_Δ = 0.8 in organic media. However, the insolubility of this porphyrinoid derivative in aqueous solution prevents its use under biologically relevant conditions. In this work, we report the synthesis of Pd[DMBil1]-PEG₇₅₀, a water-soluble dimethylbiladiene derivative that is appended with a poly(ethylene) glycol (PEG) functionality. Characterization of this complex shows that this PEGylated biladiene architecture maintains the attractive photophysical properties of the parent complex under biologically relevant conditions. More specifically, the absorption profile of Pd[DMBil1]-PEG₇₅₀ closely matches that of Pd[DMBil1] and obeys the Beer-Lambert Law, suggesting that the complex does not aggregate under biologically relevant conditions. Additionally, the emission spectrum of Pd[DMBil1]-PEG₇₅₀ retains the fluorescence and phosphorescence features characteristic of Pd[DMBil1]. Importantly, the PEGylated photosensitizer generates ¹O₂ with Φ_Δ = 0.57, which is well within the range to warrant interrogation as a potential PDT agent for treatment of cancer cells. The Pd[DMBil1]-PEG₇₅₀ is biologically compatible, as it is taken up by MDA-MB-231 triple negative breast cancer (TNBC) cells and has an effective dose (ED₅₀) of only 0.354 μM when exposed to λ_ex > 500 nm light for 30 min. Impressively, the lethal dose (LD₅₀) of Pd[DMBil1]-PEG₇₅₀ without light exposure was measured to be 1.87 mM, leading to a remarkably high phototoxicity index of ∼5300, which is vastly superior to existing photosensitizers that form the basis for clinical PDT treatments. Finally, through flow cytometry experiments, we show that PDT with Pd[DMBil1]-PEG₇₅₀ induces primarily apoptotic cell death in MDA-MB-231 cells. Overall these results demonstrate that Pd[DMBil1]-PEG₇₅₀ is an easily prepared, biologically compatible, and well-tolerated photochemotherapeutic agent that can efficiently drive the photoinduced apoptotic death of TNBC cells.

Spherical Nucleic Acid Nanoparticles: Therapeutic Potential

Spherical nucleic acids (SNAs) are highly oriented, well organized, polyvalent structures of nucleic acids conjugated to hollow or solid core nanoparticles. Because they can transfect many tissue and cell types without toxicity, induce minimum immune response, and penetrate various biological barriers (such as the skin, blood-brain barrier, and blood-tumor barrier), they have become versatile tools for the delivery of nucleic acids, drugs, and proteins for various therapeutic purposes. This article describes the unique structures and properties of SNAs and discusses how these properties enable their application in gene regulation, immunomodulation, and drug and protein delivery. It also summarizes current efforts towards clinical translation of SNAs and provides an expert opinion on remaining challenges to be addressed in the path forward to the clinic.

Evaluating the Mechanisms of Light-Triggered siRNA Release from Nanoshells for Temporal Control Over Gene Regulation

The ability to regulate intracellular gene expression with exogenous nucleic acids such as small interfering RNAs (siRNAs) has substantial potential to improve the study and treatment of disease. However, most transfection agents and nanoparticle-based carriers that are used for the intracellular delivery of nucleic acids cannot distinguish between diseased and healthy cells, which may cause them to yield unintended widespread gene regulation. An ideal delivery system would only silence targeted proteins in diseased tissue in response to an external stimulus. To enable spatiotemporal control over gene silencing, researchers have begun to develop nucleic acid-nanoparticle conjugates that keep their nucleic acid cargo inactive until it is released from the nanoparticle on-demand by externally applied near-infrared laser light. This strategy can overcome several limitations of other nucleic acid delivery systems, but the mechanisms by which these platforms operate remain ill understood. Here, we perform a detailed investigation of the mechanisms by which silica core/gold shell nanoshells (NSs) release conjugated siRNA upon excitation with either pulsed or continuous wave (CW) near-infrared (NIR) light, with the goal of providing insight into how these nanoconjugates can enable on-demand gene regulation. We demonstrate that siRNA release from NSs upon pulsed laser irradiation is a temperature-independent process that is substantially more efficient than siRNA release triggered by CW irradiation. Contrary to literature, which suggests that only pulsed irradiation releases siRNA duplexes, we found that both modes of irradiation release a mixture of siRNA duplexes and single-stranded oligonucleotides, but that pulsed irradiation results in a higher percentage of released duplexes. To demonstrate that the siRNA released from NSs upon pulsed irradiation remains functional, we evaluated the use of NSs coated with green fluorescent protein (GFP)-targeted siRNA (siGFP-NS) for on-demand knockdown of GFP in cells. We found that GFP-expressing cells treated with siGFP-NS and irradiated with a pulsed laser experienced a 33% decrease in GFP expression compared to cells treated with no laser. Further, we observed that light-triggered gene silencing mediated by siGFP-NS is more potent than using commercial transfection agents to deliver siRNA into cells. This work provides unprecedented insight into the mechanisms by which plasmonic NSs release siRNA upon light irradiation and demonstrates the importance of thoroughly characterizing photoresponsive nanosystems for applications in triggered gene regulation.

Investigating the role of Hedgehog/GLI1 signaling in glioblastoma cell response to temozolomide

Resistance to chemotherapy substantially hinders successful glioblastoma (GBM) treatment, contributing to an almost 100% mortality rate. Resistance to the frontline chemotherapy, temozolomide (TMZ), arises from numerous signaling pathways that are deregulated in GBM, including Hedgehog (Hh) signaling. Here, we investigate suppression of Hh signaling as an adjuvant to TMZ using U87-MG and T98G cell lines as in vitro models of GBM. We found that silencing GLI1 with siRNA reduces cell metabolic activity by up to 30% in combination with TMZ and reduces multidrug efflux activity by 2.5-fold. Additionally, pharmacological GLI inhibition modulates nuclear p53 levels and decreases MGMT expression in combination with TMZ. While we surprisingly found that silencing GLI1 does not induce apoptosis in the absence of TMZ co-treatment, we discovered silencing GLI1 without TMZ co-treatment induces senescence as evidenced by a significant 2.3-fold increase in senescence associated β-galactosidase staining, and this occurs in a loss of PTEN-dependent manner. Finally, we show that GLI inhibition increases apoptosis in glioma stem-like cells by up to 6.8-fold in combination with TMZ, and this reduces the size and number of neurospheres grown from glioma stem-like cells. In aggregate, our data warrant the continued investigation of Hh pathway inhibitors as adjuvants to TMZ chemotherapy and highlight the importance of identifying signaling pathways that determine whether co-treatment will be successful.

Enzyme-Linked Immunosorbent Assay to Quantify Targeting Molecules on Nanoparticles

Molecular targeting presents a promising means of improving the specificity of cancer therapeutics, increasing accumulation at the cancer site and limiting off-target effects. These targeting schemes can be applied to nanoparticle-based treatments to further enhance their anticancer efficacy. Here, we describe methods to conjugate antibodies to silica-gold nanoshells and to quantify the resulting antibody content on the nanoparticles using a solution-based enzyme-linked immunosorbent assay (ELISA). Although we will be using anti-EGFR (epidermal growth factor receptor) antibodies conjugated to gold-silica nanoshells as a model system, this method is adaptable to quantify a range of targeting antibodies and proteins on various types of nanoparticles.

Frizzled7 Antibody-Functionalized Nanoshells Enable Multivalent Binding for Wnt Signaling Inhibition in Triple Negative Breast Cancer Cells

Antibodies that antagonize cell signaling pathways specific to their targeted receptor are invaluable tools to study and treat malignancies, but their utility is limited by high production costs and treatment dosages. Researchers have shown that antibodies conjugated to nanoparticles display increased affinity for their target relative to freely delivered antibodies due to multivalency, and this study investigates how this multivalency can enable antibody-nanoparticle conjugates to inhibit oncogenic cell signaling more effectively than freely delivered antibodies. This effect was evaluated using triple negative breast cancer (TNBC) cells that are characterized by hyperactive Wnt signaling mediated through overexpressed Frizzled7 (FZD7) transmembrane receptors. Through analysis of the expression of β-catenin and Axin2, two downstream targets in the Wnt pathway, the results demonstrate that FZD7 antibody-nanoshell conjugates (FZD7-NS) are drastically more effective at inhibiting Wnt signaling in TNBC cells than freely delivered FZD7 antibodies. Additionally, cells treated with FZD7-NS, but not cells treated with freely delivered FZD7 antibodies, have decreased viability, indicating the therapeutic potential of this technology. The results demonstrate that antibody-functionalized nanoparticles can exploit multivalency for improved signal cascade interference over free antibodies, and this may ultimately permit lower antibody dosages to be administered to study signaling pathways or to manage diseases.

Gold nanoparticle-mediated photothermal therapy: applications and opportunities for multimodal cancer treatment

Photothermal therapy (PTT), in which nanoparticles embedded within tumors generate heat in response to exogenously applied laser light, has been well documented as an independent strategy for highly selective cancer treatment. Gold-based nanoparticles are the main mediators of PTT because they offer: (1) biocompatibility, (2) small diameters that enable tumor penetration upon systemic delivery, (3) simple gold-thiol bioconjugation chemistry for the attachment of desired molecules, (4) efficient light-to-heat conversion, and (5) the ability to be tuned to absorb near-infrared light, which penetrates tissue more deeply than other wavelengths of light. In addition to acting as a standalone therapy, gold nanoparticle-mediated PTT has recently been evaluated in combination with other therapies, such as chemotherapy, gene regulation, and immunotherapy, for enhanced anti-tumor effects. When delivered independently, the therapeutic success of molecular agents is hindered by premature degradation, insufficient tumor delivery, and off-target toxicity. PTT can overcome these limitations by enhancing tumor- or cell-specific delivery of these agents or by sensitizing cancer cells to these additional therapies. All together, these benefits can enhance the therapeutic success of both PTT and the secondary treatment while lowering the required doses of the individual agents, leading to fewer off-target effects. Given the benefits of combining gold nanoparticle-mediated PTT with other treatment strategies, many exciting opportunities for multimodal cancer treatment are emerging that will ultimately lead to improved patient outcomes. WIREs Nanomed Nanobiotechnol 2017, 9:e1449. doi: 10.1002/wnan.1449 For further resources related to this article, please visit the WIREs website.

Antibody-nanoparticle conjugates to enhance the sensitivity of ELISA-based detection methods

Accurate antigen detection is imperative for clinicians to diagnose disease, assess treatment success, and predict patient prognosis. The most common technique used for the detection of disease-associated biomarkers is the enzyme linked immunosorbent assay (ELISA). In an ELISA, primary antibodies are incubated with biological samples containing the biomarker of interest. Then, detectible secondary antibodies conjugated with horseradish peroxidase (HRP) bind the primary antibodies. Upon addition of a color-changing substrate, the samples provide a colorimetric signal that directly correlates to the targeted biomarker concentration. While ELISAs are effective for analyzing samples with high biomarker content, they lack the sensitivity required to analyze samples with low antigen levels. We hypothesized that the sensitivity of ELISAs could be enhanced by replacing freely delivered primary antibodies with antibody-nanoparticle conjugates that provide excess binding sites for detectible secondary antibodies, ultimately leading to increased signal. Here, we investigated the use of nanoshells (NS) decorated with antibodies specific to epidermal growth factor receptor (EGFR) as a model system (EGFR-NS). We incubated one healthy and two breast cancer cell lines, each expressing different levels of EGFR, with EGFR-NS, untargeted NS, or unconjugated EGFR antibodies, as well as detectable secondary antibodies. We found that EGFR-NS consistently increased signal intensity relative to unconjugated EGFR antibodies, with a substantial 13-fold enhancement from cells expressing high levels of EGFR. Additionally, 40x more unconjugated antibodies were required to detect EGFR compared to those conjugated to NS. Our results demonstrate that antibody-nanoparticle conjugates lower the detection limit of traditional ELISAs and support further investigation of this strategy with other antibodies and nanoparticles. Owing to their enhanced sensitivity, we anticipate that nanoparticle-modified ELISAs can be used to detect low levels of biomarkers found in various diseases, such as cancers, tuberculosis, and rheumatoid arthritis, and may ultimately enable earlier diagnosis, better prognostication, and improved treatment monitoring.

Using Gold Nanoparticles To Disrupt the Tumor Microenvironment: An Emerging Therapeutic Strategy

Gold nanoparticles have received much attention recently as carriers for anticancer drugs and therapeutic oligonucleotides, but little research has investigated their potential to act as stand-alone therapeutics. Previous studies interrogating their short- and long-term systemic toxicity have found that although gold nanoparticles accumulate within and clear slowly from the liver and spleen, they do not appear to exert toxic effects in these organs. Interestingly, gold nanoparticles innately exhibit the ability to modulate the tumor microenvironment specifically by interfering with crosstalk between tumor cells and stromal cells. In this issue of ACS Nano, Mukherjee and colleagues demonstrate that bare gold nanoparticles can disturb crosstalk between pancreatic stellate cells and pancreatic cancer cells by modulating the cellular secretome to reduce the growth of desmoplastic tissue and inhibit tumor growth. In this Perspective, we highlight opportunities for anticancer targeting within the tumor microenvironment and discuss gold nanoparticles as potential mediators of microenvironment-targeted therapy.

Nanoshell-mediated photothermal therapy can enhance chemotherapy in inflammatory breast cancer cells

Nanoshell-mediated photothermal therapy (PTT) is currently being investigated as a standalone therapy for the treatment of cancer. The cellular effects of PTT include loss of membrane integrity, so we hypothesized that nanoshell-mediated PTT could potentiate the cytotoxicity of chemotherapy by improving drug accumulation in cancer cells. In this work, we validated our hypothesis using doxorubicin as a model drug and SUM149 inflammatory breast cancer cells as a model cancer subtype. In initial studies, SUM149 cells were exposed to nano-shells and near-infrared light and then stained with ethidium homodimer-1, which is excluded from cells with an intact plasma membrane. The results confirmed that nanoshell-mediated PTT could increase membrane permeability in SUM149 cells. In complementary experiments, SUM149 cells treated with nanoshells, near-infrared light, or a combination of the two to yield low-dose PTT were exposed to fluorescent rhodamine 123. Analyzing rhodamine 123 fluorescence in cells via flow cytometry confirmed that increased membrane permeability caused by PTT could enhance drug accumulation in cells. This was validated using fluorescence microscopy to assess intracellular distribution of doxorubicin. In succeeding experiments, SUM149 cells were exposed to subtherapeutic levels of doxorubicin, low-dose PTT, or a combination of the two treatments to determine whether the additional drug uptake induced by PTT is sufficient to enhance cell death. Analysis revealed minimal loss of viability relative to controls in cells exposed to subtherapeutic levels of doxorubicin, 15% loss of viability in cells exposed to low-dose PTT, and 35% loss of viability in cells exposed to combination therapy. These data indicate that nanoshell-mediated PTT is a viable strategy to potentiate the effects of chemotherapy and warrant further investigation of this approach using other drugs and cancer subtypes.

miR-182 integrates apoptosis, growth, and differentiation programs in glioblastoma

Glioblastoma multiforme (GBM) is a lethal, therapy-resistant brain cancer consisting of numerous tumor cell subpopulations, including stem-like glioma-initiating cells (GICs), which contribute to tumor recurrence following initial response to therapy. Here, we identified miR-182 as a regulator of apoptosis, growth, and differentiation programs whose expression level is correlated with GBM patient survival. Repression of Bcl2-like12 (Bcl2L12), c-Met, and hypoxia-inducible factor 2α (HIF2A) is of central importance to miR-182 anti-tumor activity, as it results in enhanced therapy susceptibility, decreased GIC sphere size, expansion, and stemness in vitro. To evaluate the tumor-suppressive function of miR-182 in vivo, we synthesized miR-182-based spherical nucleic acids (182-SNAs); i.e., gold nanoparticles covalently functionalized with mature miR-182 duplexes. Intravenously administered 182-SNAs penetrated the blood-brain/blood-tumor barriers (BBB/BTB) in orthotopic GBM xenografts and selectively disseminated throughout extravascular glioma parenchyma, causing reduced tumor burden and increased animal survival. Our results indicate that harnessing the anti-tumor activities of miR-182 via safe and robust delivery of 182-SNAs represents a novel strategy for therapeutic intervention in GBM.

Elucidating the fundamental mechanisms of cell death triggered by photothermal therapy

Photothermal therapy (PTT) utilizes nanoparticles embedded within tumors as exogenous energy absorbers to convert laser light energy into heat to ablate cancer cells. While PTT is a promising alternative to conventional cancer therapy, under certain irradiation conditions, it can produce cellular necrosis, and this necrosis may lead to pro-inflammatory responses that are detrimental to treatment success. Recent studies have shown that PTT can be modulated to induce apoptosis rather than necrosis, which is appealing since apoptosis discourages an inflammatory response. In this issue of ACS Nano, del Pino, Pardo, de la Fuente, and colleagues reveal the intracellular signaling cascades involved in the apoptotic response to PTT using cells harboring photothermal transducing nanoprisms. In this Perspective, we present an overview of nanoparticle-mediated PTT and discuss photothermally induced apoptosis as a potential therapeutic pathway.

Spherical nucleic acid nanoparticle conjugates as an RNAi-based therapy for glioblastoma

Glioblastoma multiforme (GBM) is a neurologically debilitating disease that culminates in death 14 to 16 months after diagnosis. An incomplete understanding of how cataloged genetic aberrations promote therapy resistance, combined with ineffective drug delivery to the central nervous system, has rendered GBM incurable. Functional genomics efforts have implicated several oncogenes in GBM pathogenesis but have rarely led to the implementation of targeted therapies. This is partly because many "undruggable" oncogenes cannot be targeted by small molecules or antibodies. We preclinically evaluate an RNA interference (RNAi)-based nanomedicine platform, based on spherical nucleic acid (SNA) nanoparticle conjugates, to neutralize oncogene expression in GBM. SNAs consist of gold nanoparticles covalently functionalized with densely packed, highly oriented small interfering RNA duplexes. In the absence of auxiliary transfection strategies or chemical modifications, SNAs efficiently entered primary and transformed glial cells in vitro. In vivo, the SNAs penetrated the blood-brain barrier and blood-tumor barrier to disseminate throughout xenogeneic glioma explants. SNAs targeting the oncoprotein Bcl2Like12 (Bcl2L12)--an effector caspase and p53 inhibitor overexpressed in GBM relative to normal brain and low-grade astrocytomas--were effective in knocking down endogenous Bcl2L12 mRNA and protein levels, and sensitized glioma cells toward therapy-induced apoptosis by enhancing effector caspase and p53 activity. Further, systemically delivered SNAs reduced Bcl2L12 expression in intracerebral GBM, increased intratumoral apoptosis, and reduced tumor burden and progression in xenografted mice, without adverse side effects. Thus, silencing antiapoptotic signaling using SNAs represents a new approach for systemic RNAi therapy for GBM and possibly other lethal malignancies.

Vascular-targeted photothermal therapy of an orthotopic murine glioma model

AIM

To develop nanoshells for vascular-targeted photothermal therapy of glioma.

MATERIALS & METHODS

The ability of nanoshells conjugated to VEGF and/or poly(ethylene glycol) (PEG) to thermally ablate VEGF receptor-2-positive endothelial cells upon near-infrared laser irradiation was evaluated in vitro. Subsequent in vivo studies evaluated therapy in mice bearing intracerebral glioma tumors by exposing tumors to near-infrared light after systemically delivering saline, PEG-coated nanoshells, or VEGF-coated nanoshells. The treatment effect was monitored with intravital microscopy and histology.

RESULTS

VEGF-coated but not PEG-coated nanoshells bound VEGF receptor-2-positive cells in vitro to enable targeted photothermal ablation. In vivo, VEGF targeting doubled the proportion of nanoshells bound to tumor vessels and vasculature was disrupted following laser exposure. Vessels were not disrupted in mice that received saline. The normal brain was unharmed in all treatment and control mice.

CONCLUSION

Nanoshell therapy can induce vascular disruption in glioma.