Abstract 385: iRGD mediated delivery of neoantigens to enable immunotherapy in integrin b5-rich tumors

Pancreatic duct adenocarcinomas are known for their abundant desmoplastic stroma that acts as a barrier for drug penetration and reduces treatment efficacy. iRGD is a tumor-penetrating peptide that initially targets αv integrins expressed on tumor vasculature with its RGD motif and then is proteolytically processed to expose a CendR motif (R/KXXR/K) that interacts with neuropilin-1 (NRP-1), leading to extravasation. We investigated the mechanism of iRGD tissue penetration and found that iRGD initially targets Carcinoma Associated Fibroblasts (CAFs) and then spreads to the tumor cells in a time dependent manner. CAF targeting was dependent on integrin β5 expression and CAFs induced upregulation of integrin β5 in the adjacent tumor cells in a TGF- β dependent manner. Drugs conjugated or co-administered with iRGD can penetrate deep into tumor tissue, significantly increasing the efficacy of chemotherapeutic agents in a variety of solid tumors. Our recent data shows that KrasLSL-G12D/+ Trp53LSL-R172H/+ Pdx1-Cre (KPC) mice treated with iRGD co-administered with Gemcitabine increased survival compared to drug alone. In addition, we are using iRGD to deliver neoantigens to breast and pancreatic cancers to enable immunotherapy. These tumors have a low mutational burden and a very immunosuppressive microenvironment, rendering them resistant to such therapies. We have used iRGD, to deliver the ovalbumin 257-264 (OVAI) peptide to triple negative breast tumors, followed by adoptive T cell transfer of OT1 CD8 T cells, in order to elicit an antitumor immune response. Our preliminary data showed tumor regression in 70%, and complete response in 42% of the mice treated with iRGD plus OVA1. We are now working on adapting this strategy to pancreatic cancer.

Citation Format: Tatiana Hurtado de Mendoza, Evangeline S. Mose, Gregory P. Botta, Gary B. Braun, Venkata R. Kotamraju, Randall P. French, Kodai Suzuki, Norio Miyamura, Siming Sun, Jay Patel, Tambet Teesalu, Erkki Ruoslahti, Kazuki N. Sugahara, Andrew M. Lowy. iRGD mediated delivery of neoantigens to enable immunotherapy in integrin b5-rich tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 385.

Tumor-penetrating therapy for β5 integrin-rich pancreas cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterized by marked desmoplasia and drug resistance due, in part, to poor drug delivery to extravascular tumor tissue. Here, we report that carcinoma-associated fibroblasts (CAFs) induce β5 integrin expression in tumor cells in a TGF-β dependent manner, making them an efficient drug delivery target for the tumor-penetrating peptide iRGD. The capacity of iRGD to deliver conjugated and co-injected payloads is markedly suppressed when β5 integrins are knocked out in the tumor cells. Of note, β5 integrin knock-out in tumor cells leads to reduced disease burden and prolonged survival of the mice, demonstrating its contribution to PDAC progression. iRGD significantly potentiates co-injected chemotherapy in KPC mice with high β5 integrin expression and may be a powerful strategy to target an aggressive PDAC subpopulation.

Graphene biointerfaces for optical stimulation of cells

Noninvasive stimulation of cells is crucial for the accurate examination and control of their function both at the cellular and the system levels. To address this need, we present a pioneering optical stimulation platform that does not require genetic modification of cells but instead capitalizes on unique optoelectronic properties of graphene, including its ability to efficiently convert light into electricity. We report the first studies of optical stimulation of cardiomyocytes via graphene-based biointerfaces (G-biointerfaces) in substrate-based and dispersible configurations. The efficiency of stimulation via G-biointerfaces is independent of light wavelength but can be tuned by changing the light intensity. We demonstrate that an all-optical evaluation of use-dependent drug effects in vitro can be enabled using substrate-based G-biointerfaces. Furthermore, using dispersible G-biointerfaces in vivo, we perform optical modulation of the heart activity in zebrafish embryos. Our discovery is expected to empower numerous fundamental and translational biomedical studies.

Antibiotic-loaded nanoparticles targeted to the site of infection enhance antibacterial efficacy

Bacterial resistance to antibiotics has made it necessary to resort to antibiotics that have considerable toxicities. Here, we show that the cyclic 9-amino acid peptide CARGGLKSC (CARG), identified via phage display on Staphylococcus aureus (S. aureus) bacteria and through in vivo screening in mice with S. aureus-induced lung infections, increases the antibacterial activity of CARG-conjugated vancomycin-loaded nanoparticles in S. aureus-infected tissues and reduces the needed overall systemic dose, minimizing side effects. CARG binds specifically to S. aureus bacteria but not Pseudomonas bacteria in vitro, selectively accumulates in S. aureus-infected lungs and skin of mice but not in non-infected tissue and Pseudomonas-infected tissue, and significantly enhances the accumulation of intravenously injected vancomycin-loaded porous silicon nanoparticles bearing the peptide in S. aureus-infected mouse lung tissue. The targeted nanoparticles more effectively suppress staphylococcal infections in vivo relative to equivalent doses of untargeted vancomycin nanoparticles or of free vancomycin. The therapeutic delivery of antibiotic-carrying nanoparticles bearing peptides targeting infected tissue may help combat difficult-to-treat infections.

Identification of a peptide recognizing cerebrovascular changes in mouse models of Alzheimer's disease

Cerebrovascular changes occur in Alzheimer’s disease (AD). Using in vivo phage display, we searched for molecular markers of the neurovascular unit, including endothelial cells and astrocytes, in mouse models of AD. We identified a cyclic peptide, CDAGRKQKC (DAG), that accumulates in the hippocampus of hAPP-J20 mice at different ages. Intravenously injected DAG peptide homes to neurovascular unit endothelial cells and to reactive astrocytes in mouse models of AD. We identified connective tissue growth factor (CTGF), a matricellular protein that is highly expressed in the brain of individuals with AD and in mouse models, as the target of the DAG peptide. We also showed that exogenously delivered DAG homes to the brain in mouse models of glioblastoma, traumatic brain injury, and Parkinson’s disease. DAG may potentially be used as a tool to enhance delivery of therapeutics and imaging agents to sites of vascular changes and astrogliosis in diseases associated with neuroinflammation.

Cerebrovascular changes and astrogliosis occur in Alzheimer’s disease (AD). Using an in vivo phage display technique, the authors identified a peptide that upon systematic administration, can home to brain endothelial cells and astrocytes in mouse models of AD at the early stages of the disease.

In vivo cation exchange in quantum dots for tumor-specific imaging

In vivo tumor imaging with nanoprobes suffers from poor tumor specificity. Here, we introduce a nanosystem, which allows selective background quenching to gain exceptionally tumor-specific signals. The system uses near-infrared quantum dots and a membrane-impermeable etchant, which serves as a cation donor. The etchant rapidly quenches the quantum dots through cation exchange (ionic etching), and facilitates renal clearance of metal ions released from the quantum dots. The quantum dots are intravenously delivered into orthotopic breast and pancreas tumors in mice by using the tumor-penetrating iRGD peptide. Subsequent etching quenches excess quantum dots, leaving a highly tumor-specific signal provided by the intact quantum dots remaining in the extravascular tumor cells and fibroblasts. No toxicity is noted. The system also facilitates the detection of peritoneal tumors with high specificity upon intraperitoneal tumor targeting and selective etching of excess untargeted quantum dots. In vivo cation exchange may be a promising strategy to enhance specificity of tumor imaging.

The imaging of tumors in vivo using nanoprobes has been challenging due to the lack of sufficient tumor specificity. Here, the authors develop a tumor-specific quantum dot system that permits in vivo cation exchange to achieve selective background quenching and high tumor-specific imaging.

Ratiometric in vivo auditioning of targeted silver nanoparticles

Attaching affinity ligands to nanoparticles (NPs) increases selectivity for targeting cells and tissues, and can result in improved sensitivity and reduced off-target toxicity in diagnostic and therapeutic systems. The decision over key features - NP size, shape, coating strategies and targeting ligands for clinical translation is often hampered by a lack of quantitative in vivo NP homing assays. Sensitive, internally controlled assays are needed which allow for quantitative comparisons (auditions) among various formulations of targeted NPs. We recently reported the development of peptide-functionalized, isotopically-barcoded silver NPs (AgNPs) for ultrasensitive studies centered on measuring relative ratios of NP internalization into cultured cells. Here we evaluated the application of this technology for NP homing studies in live mice using peptides with previously described tissue tropism; one peptide that favors vascular beds of the normal lungs (RPARPAR; receptor neuropilin-1, or NRP-1) and another that is selective for central nervous system vessels (CAGALCY). Equimolar mixtures of the peptide-targeted Ag107-NPs and Ag109 control particles were mixed and injected intravenously. Distribution profiles of Ag107 and Ag109 in tissue extracts were determined simultaneously through inductively coupled plasma mass spectrometry (ICP-MS). Compared to non-targeted particles up to ∼9-fold increased lung accumulation was seen for RPARPAR-OH AgNPs (but not for AgNPs functionalized with RPARPAR-NH₂, which does not bind to NRP-1). Similarly, AgNPs functionalized with the brain-homing CAGALCY peptide were overrepresented in brain extracts. Spatial distribution (mapping) analysis by laser ablation ICP-MS (LA-ICP-MS) was used to determine the ratio Ag107/Ag109 in tissue cryosections. The mapping demonstrated preferential accumulation of the RPARPAR-AgNPs in the perivascular areas around pulmonary veins, and CAGALCY AgNPs accumulated in discrete areas of the brain (e.g. in the vessels of cerebellar fibrillary tracts). Based on these results, the internally controlled ratiometric AgNP system is suitable for quantitative studies of the effect of targeting ligands on NP biodistribution, at average tissue concentration and distribution at the microscopic level. The platform might be particularly relevant for target sites with high local variability in uptake, such as tumors.

Composite Porous Silicon-Silver Nanoparticles as Theranostic Antibacterial Agents

A theranostic nanoparticle with biochemically triggered antibacterial activity is demonstrated. Metallic silver is deposited onto porous silicon nanoparticles (pSiNPs) by galvanic displacement. When aqueous diaminesilver ([Ag(NH₃)₂]⁺) is used as a silver source, the pSiNPs template the crystalline silver as small (mean diameter 13 nm) and well-dispersed nanoparticles embedded within and on the larger (100 nm) pSiNPs. The silver nanoparticles (AgNPs) quench intrinsic photoluminescence (PL) from the porous silicon (pSi) matrix. When exposed to an aqueous oxidant, the AgNPs are preferentially etched, Ag⁺ is released into solution, and PL from the pSi carrier is recovered. The released Ag⁺ results in 90% killing of (Gram-negative) Pseudomonas aeruginosa and (Gram-positive) Staphylococcus aureus within 3 h. When conjugated with the TAT peptide (sequence RKKRRQRRR), the silver-deposited porous silicon (pSi-Ag) nanocomposite shows distinct targeting toward S. aureus bacteria in vitro. Intravenously injected TAT-conjugated pSi-Ag nanoparticles accumulate in the liver, spleen, and lungs of mice, and the in vivo release of Ag⁺ and recovery of PL from pSi are demonstrated by the subsequent intraperitoneal administration of a hexacyanoferrate solution. The released Ag⁺ leads to a significant bacterial count reduction in liver tissue relative to the control. The data demonstrate the feasibility of the targeted and triggered delivery of antibacterial Ag⁺ ion in vivo, using a self-reporting and nontoxic nanocarrier.

Nanostructured Antagonist of Extrasynaptic NMDA Receptors

Glutamatergic cytotoxicity mediated by overactivation of N-methyl-d-aspartate receptors (NMDARs) is implicated in numerous neurological disorders. To be therapeutically viable, NMDAR antagonists must preserve physiological role of synaptic NMDARs (sNMDARs) in synaptic transmission and block only excessive pathological activation of NMDARs. Here we present a novel NMDAR antagonist that satisfies this two-fold requirement by exploiting spatial differences in NMDAR subcellular locations. Specifically, we designed a hybrid nanodrug (AuM) to be larger than the synaptic cleft by attaching memantine, NMDAR antagonist, via polymer linkers to a gold nanoparticle. We show that AuM efficiently and selectively inhibited extrasynaptic NMDARs (eNMDARs), while having no effect on sNMDARs and synaptic transmission. AuM exhibited neuroprotective properties both in vitro and ex vivo during such neurotoxic insults as NMDAR-mediated cytotoxicity in cerebrocortical cell culture and oxygen-glucose deprivation in acute hippocampal slices. Furthermore, AuM prevented dendritic spine loss triggered by Aβ oligomers in organotypic hippocampal slices and was more effective than free memantine. Using a novel rational design strategy, we demonstrate a proof of concept for a new class of neuroprotective drugs that might be beneficial for treatment of several neurological disorders.

Targeted silver nanoparticles for ratiometric cell phenotyping

Affinity targeting is used to deliver nanoparticles to cells and tissues. For efficient targeting, it is critical to consider the expression and accessibility of the relevant receptors in the target cells. Here, we describe isotopically barcoded silver nanoparticles (AgNPs) as a tool for auditing affinity ligand receptors in cells. Tumor penetrating peptide RPARPAR (receptor: NRP-1) and tumor homing peptide GKRK (receptor: p32) were used as affinity ligands on the AgNPs. The binding and uptake of the peptide-functionalized AgNPs by cultured PPC-1 prostate cancer and M21 melanoma cells was dependent on the cell surface expression of the cognate peptide receptors. Barcoded peptide-functionalized AgNPs were synthesized from silver and palladium isotopes. The cells were incubated with a cocktail of the barcoded nanoparticles [RPARPAR (R), GKRK (K), and control], and cellular binding and internalization of each type of nanoparticle was assessed by inductively coupled plasma mass spectrometry. The results of isotopic analysis were in agreement with data obtained using optical methods. Using ratiometric measurements, we were able to classify the PPC-1 cell line as mainly NRP-1-positive, with 75 ± 5% R-AgNP uptake, and the M21 cell line as only p32-positive, with 89 ± 9% K-AgNP uptake. The isotopically barcoded multiplexed AgNPs are useful as an in vitro ratiometric phenotyping tool and have potential uses in functional evaluation of the expression of accessible homing peptide receptors in vivo.

Urokinase-controlled tumor penetrating peptide

Tumor penetrating peptides contain a cryptic (R/K)XX(R/K) CendR element that must be C-terminally exposed to trigger neuropilin-1 (NRP-1) binding, cellular internalization and malignant tissue penetration. The specific proteases that are involved in processing of tumor penetrating peptides identified using phage display are not known. Here we design de novo a tumor-penetrating peptide based on consensus cleavage motif of urokinase-type plasminogen activator (uPA). We expressed the peptide, uCendR (RPARSGR↓SAGGSVA, ↓ shows cleavage site), on phage or coated it onto silver nanoparticles and showed that it is cleaved by uPA, and that the cleavage triggers binding to recombinant NRP-1 and to NPR-1-expressing cells. Upon systemic administration to mice bearing uPA-overexpressing breast tumors, FAM-labeled uCendR peptide and uCendR-coated nanoparticles preferentially accumulated in tumor tissue. We also show that uCendR phage internalization into cultured cancer cells and its penetration in explants of murine tumors and clinical tumor explants can be potentiated by combining the uCendR peptide with tumor-homing module, CRGDC. Our work demonstrates the feasibility of designing tumor-penetrating peptides that are activated by a specific tumor protease. As upregulation of protease expression is one of the hallmarks of cancer, and numerous tumor proteases have substrate specificities compatible with proteolytic unmasking of cryptic CendR motifs, the strategy described here may provide a generic approach for designing proteolytically-actuated peptides for tumor-penetrative payload delivery.

New p32/gC1qR Ligands for Targeted Tumor Drug Delivery

Cell surface p32, the target of LyP-1 homing peptide, is upregulated in tumors and atherosclerotic plaques and has been widely used as a receptor for systemic delivery of payloads. Here, we identified an improved LyP-1-mimicking peptide (TT1, CKRGARSTC). We used this peptide in a fluorescence polarization-based high-throughput screening of a 50,000-compound chemical library and identified a panel of compounds that bind p32 with low micromolar affinity. Among the hits identified in the screen, two compounds were shown to specifically bind to p32 in multiple assays. One of these compounds was chosen for an in vivo study. Nanoparticles surface-functionalized with this compound specifically adhered to surfaces coated with recombinant p32 and, when injected intravenously, homed to p32-expressing breast tumors in mice. This compound provides a lead for the development of p32-targeted affinity ligands that circumvent some of the limitations of peptide-based probes in guided drug delivery.

Paclitaxel-Loaded Polymersomes for Enhanced Intraperitoneal Chemotherapy

Peritoneal carcinomatosis is present in more than 60% of gastric cancer, 40% of ovarian cancer, and 35% of colon cancer patients. It is the second most common cause of cancer-related mortality, with a median survival of 1 to 3 months. Cytoreductive surgery combined with intraperitoneal chemotherapy is the current clinical treatment, but achieving curative drug accumulation and penetration in peritoneal carcinomatosis lesions remains an unresolved challenge. Here, we used flexible and pH-sensitive polymersomes for payload delivery to peritoneal gastric (MKN-45P) and colon (CT26) carcinoma in mice. Polymersomes were loaded with paclitaxel and in vitro drug release was studied as a function of pH and time. Paclitaxel-loaded polymersomes remained stable in aqueous solution at neutral pH for up to 4 months. In cell viability assay on cultured cancer cell lines (MKN-45P, SKOV3, CT26), paclitaxel-loaded polymersomes were more toxic than free drug or albumin-bound paclitaxel (Abraxane). Intraperitoneally administered fluorescent polymersomes accumulated in malignant lesions, and immunofluorescence revealed an intense signal inside tumors with no detectable signal in control organs. A dual targeting of tumors was observed: direct (circulation-independent) penetration, and systemic, blood vessel-associated accumulation. Finally, we evaluated preclinical antitumor efficacy of paclitaxel-polymersomes in the treatment of MKN-45P disseminated gastric carcinoma using a total dose of 7 mg/kg. Experimental therapy with paclitaxel-polymersomes improved the therapeutic index of drug over free paclitaxel and Abraxane, as evaluated by intraperitoneal tumor burden and number of metastatic nodules. Our findings underline the potential utility of the polymersome platform for delivery of drugs and imaging agents to peritoneal carcinomatosis lesions. Mol Cancer Ther; 15(4); 670-9. ©2016 AACR.

Tumor-Targeted Multimodal Optical Imaging with Versatile Cadmium-Free Quantum Dots

The rapid development of fluorescence imaging technologies requires concurrent improvements in the performance of fluorescent probes. Quantum dots have been extensively used as an imaging probe in various research areas because of their inherent advantages based on unique optical and electronic properties. However, their clinical translation has been limited by the potential toxicity especially from cadmium. Here, a versatile bioimaging probe is developed by using highly luminescent cadmium-free CuInSe2/ZnS core/shell quantum dots conjugated with CGKRK (Cys-Gly-Lys-Arg-Lys) tumor-targeting peptides. This probe exhibits excellent photostability, reasonably long circulation time, minimal toxicity, and strong tumor-specific homing property. The most important feature of this probe is that it shows distinctive versatility in tumor-targeted multimodal imaging including near-infrared, time-gated, and two-photon imaging in different tumor models. In a glioblastoma mouse model, the targeted probe clearly denotes tumor boundaries and positively labels a population of diffusely infiltrating tumor cells, suggesting its utility in precise tumor detection during surgery. This work lays a foundation for potential clinical translation of the probe.

Neuropilin-1 and heparan sulfate proteoglycans cooperate in cellular uptake of nanoparticles functionalized by cationic cell-penetrating peptides

Cell-penetrating peptides (CPPs) have been widely used to deliver nanomaterials and other types of macromolecules into mammalian cells for therapeutic and diagnostic use. Cationic CPPs that bind to heparan sulfate (HS) proteoglycans on the cell surface induce potent endocytosis; however, the role of other surface receptors in this process is unclear. We describe the convergence of an HS-dependent pathway with the C-end rule (CendR) mechanism that enables peptide ligation with neuropilin-1 (NRP1), a cell surface receptor known to be involved in angiogenesis and vascular permeability. NRP1 binds peptides carrying a positive residue at the carboxyl terminus, a feature that is compatible with cationic CPPs, either intact or after proteolytic processing. We used CPP and CendR peptides, as well as HS- and NRP1-binding motifs from semaphorins, to explore the commonalities and differences of the HS and NRP1 pathways. We show that the CendR-NRP1 interaction determines the ability of CPPs to induce vascular permeability. We also show at the ultrastructural level, using a novel cell entry synchronization method, that both the HS and NRP1 pathways can initiate a macropinocytosis-like process and visualize these CPP-cargo complexes going through various endosomal compartments. Our results provide new insights into how CPPs exploit multiple surface receptor pathways for intracellular delivery.

Quantitative multiplexed simulated-cell identification by SERS in microfluidic devices

A reliable identification of cells on the basis of their surface markers is of great interest for diagnostic and therapeutic applications. We present a multiplexed labeling and detection strategy that is applied to four microparticle populations, each mimicking cellular or bacterial samples with varying surface concentrations of up to four epitopes, using four distinct biotags that are meant to be used in conjunction with surface enhanced Raman spectroscopy (SERS) instead of fluorescence, together with microfluidics. Four populations of 6 μm polystyrene beads were incubated with different mixtures, "cocktails" of four SERS biotags (SBTs), simulating the approach that one would follow when seeking to identify multiple biomarkers encountered in biological applications. Populations were flowed in a microfluidic flow-focusing device and the SERS signal from individual beads was acquired during continuous flow. The spectrally rich SERS spectra enabled us to separate confidently the populations by utilizing principal component analysis (PCA). Also, using classical least squares (CLS), we were able to calculate the contributions of each SBT to the overall signal in each of the populations, and showed that the relative SBT contributions are consistent with the nominal percentage of each marker originally designed into that bead population, by functionalizing it with a given SBT cocktail. Our results demonstrate the multiplexing capability of SBTs in potential applications such as immunophenotyping.

Biotags Based on Surface-Enhanced Raman Can Be as Bright as Fluorescence Tags

Surface enhanced Raman spectroscopy (SERS) is a powerful analytical technique that has been proposed as a substitute for fluorescence for biological imaging and detection but is not yet commercially utilized. The reason lies primarily in the lower intensity and poor reproducibility of most metal nanoparticle-based tags as compared to their fluorescence-based counterparts. Here, using a technique that scrupulously preserves the same number of dye molecules in both the SERS and fluorescence measurements, we show that SERS-based biotags (SBTs) with highly reproducible optical properties can be nanoengineered such that their brightness is at least equal to that of fluorescence-based tags.

Abstract NG03: A novel endocytic and intercellular transport pathway for drug delivery across blood vessels and into nutrient-deprived tumor cells

A major limiting factor in the development of cancer therapy, especially for solid tumors, is the delivery of therapeutic agents into target cells in vivo to reach the site of action. Major barriers to the efficient delivery of drugs, especially macromolecules and nanomaterials, include the vascular walls, extravascular tissue, and membrane of cells and intracellular organelles. Peptides with high affinity to signature surface receptors displayed on tumor vasculature have been attractive carriers of therapeutic and diagnostic agents into tumors. Major efforts have been devoted to complexing these peptides with drug carriers of various physical and chemical properties, while little is known about either the cellular machinery that mediates the intake of these agents, or the underlying regulatory mechanism for delivery efficiency. We tackle this problem by characterizing the cell entry and tissue penetration process of a novel class of tumor-penetrating peptides. These peptides contain a carboxy (C)-terminal, basic sequence R/KXXR/K motif (C-end Rule or CendR motif). Peptides with this motif (CendR peptides) bind to neuropilin-1 (NRP1) on the cell surface and initiate an endocytic process into cells. Neuropilins (NRPs) are trans-membrane receptors involved in axon guidance and vascular development, and their expression is often upregulated on tumor vasculature and tumor cells. Many growth factors and other signalling molecules bind to NRPs through the CendR motif. To achieve a tumor-specific homing in vivo, the CendR motif is rendered cryptic in the middle of the peptide. Tumor-homing CendR peptides recognize different primary receptors to achieve the initial homing to the target tissues. The notable example is iRGD (CRGD(K/R)GP(D/E)C; the terminal Cys residues form a disulfide bond; CendR motif underlined), which use the RGD motif to first recognize αv integrins highly expressed on tumor endothelium. The peptide is then proteolytically cleaved to expose the CendR motif at the C-terminus. The activated CendR peptides thus bind to NRP1, which initiate an active penetration process across the blood vessels and throughout the extravascular tumor tissue. This tumor homing and penetration effect has been shown in a wide range of tumor types, and displays a good compatibility with various drug types. Most interestingly, the cargo does not need to be chemically conjugated to the peptide; co-injection with iRGD can also enhance the transport of diverse therapeutic payloads from the circulation into the tumor parenchyma (bystander activity), leading to an improved antitumor efficacy.

To decipher the molecular machinery of CendR-mediated cell entry, we performed a genome-wide RNAi screening to identify important genes for the cellular uptake of a prototypic CendR peptide displayed on silver-based nanoparticles. Silver-based platform is advantageous here since it allows the exclusive tracing of the internalized particles while the extracellular ones are effectively removed by a mild etching procedure. The genome screen and subsequent validation studies demonstrated that NRP1-mediated endocytosis of CendR peptides is a novel cell entry mechanism distinct from known endocytic pathways. CendR endocytosis depends little on critical genes of the other pathways, and is resistance to the treatment of the established endocytic inhibitors. CendR cargo also exhibits little colocalization with structural components of classic endocytic vesicles (e.g. clathrin-coated pits and caveolae) over time. Ultrastructurally, CendR endocytosis resembles macropinocytosis. But they are mechanistically different, especially in the receptor (NRP1) dependence of CendR endocytosis.

The uniqueness of CendR pathway also lies in the regulatory mechanism of its activity. The genome screen surprisingly showed that nutrient-sensing networks, such as mTOR signaling, rank the highest among the canonical pathways regulating the activity of CendR endocytosis. Nutrient deprivation was shown to enhance the penetration of CendR cargo into cells in vitro, live tumor slices ex vivo and tumor tissue in vivo. Moreover, we developed assays to observe the intercellular transport of CendR cargo, which is also stimulated by nutrient deprivation.

We are carrying on subsequent studies to elucidate the structural and molecular basis of CendR transport pathway. A methodology has been developed to synchronize the peptide entry, and ultrastructural imaging pinpoints a step-wise roadmap for the subcellular transport of CendR cargo. We have also performed magnetic isolation of intracellular vesicles containing CendR cargo, and identified signature molecules associated with these vesicles based on proteomic analysis. Moreover, we are able to observe the engulfment of bystander cargo in vitro, and molecular and ultrastructural characterization is undergoing to elucidate this intriguing cellular process. Using zebrafish and mouse models, we are monitoring the vascular penetration in vivo and characterizing the dynamic profile. Meanwhile, we are continuing to decode how mTOR regulates the activity of CendR endocytosis. A transcription factor, Sp1, has been found to serve as a link between mTOR and cell surface NRP1 level. Overall, we have discovered a novel pathway for peptide-functionalized payloads to enter tumor cells and tissue after receptor engagement. The ultrastructural studies of CendR endocytic structures supports the notion that CendR peptides activate a bulk transport system sweeping along bystander compounds, such as drugs and imaging agents present within tumor vessels. The platform to monitor the intercellular transfer of CendR cargo in vitro, together with the in vivo models, enables us to further optimize the transport efficiency of therapeutic agents across the vascular barriers. Particularly, the nutrient regulation of CendR transport pathway is of great significance by linking cancer metabolism with drug delivery. Due to dysfunctional angiogenesis, the nutrient conditions vary significantly in solid tumors. Some regions (e.g. hypoxia) are well known to undergo molecular changes and thus adapt to the nutrient-deprived environment. As a bulk transport pathway, our results suggest a role for CendR pathway in nutrient transport. Moreover, our studies point out a new direction to apply CendR-enhanced drug delivery into nutrient-deprived pathological tissues. These results shed new light in the fields of cell biology, cancer metabolism and drug delivery, while they also highlight the importance to bridge drug delivery with mechanistic studies.

Citation Format: Hongbo Pang, Gary B. Braun, Tomas Friman, Pedro Aza-Blanc, Manuel E. Ruidiaz, Kazuki N. Sugahara, Tambet Teesalu, Erkki Ruoslahti. A novel endocytic and intercellular transport pathway for drug delivery across blood vessels and into nutrient-deprived tumor cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr NG03. doi:10.1158/1538-7445.AM2015-NG03

Abstract 5526: Deciphering the basis of CendR-mediated penetration into tumors

Cell-penetrating peptides (CPPs) have proven their usefulness in overcoming barriers (such as the cell membrane) of drug delivery into tumor cells. We recently discovered a novel class of cell-penetrating peptides that also have tumor-penetrating properties. These so-called, CendR peptides,bind to neuropilin-1 (NRP1) and initiate an active endocytic process into tumor cells. Subsequent studies showed that CendR-initiated endocytosis is a receptor-dependent macropinocytosis process, and that its activity is stimulated by mTOR inhibition and nutrient deprivation. In vivo, CendR peptides penetrate across tumor vessels deeply into the extravascular tumor tissue, and show ability to improve the tumor accumulation and antitumor efficacy of coupled, and even co-administrated, drugs. Further understanding of the CendR-mediated cell and tissue penetration is of value to cell biology and cancer therapy.

Here, we report ultrastructural studies to unveil the subcellular transport route for CendR peptide. After synchronized cell entry, transmission electron microscopy (TEM) imaging shows that CendR cargo is transported from early endosomes to late endosomes and lysosomes. We have also identified some of the genes important for this transport. Moreover, magnetic isolation of intracellular vesicles containing CendR cargo and proteomics analysis identified signature molecules associated with these vesicles. Studies with TAT peptide comprised of D-amino acids (D-TAT), included in these studies as a non-CendR CPP, indicate that D-TAT also penetrates into tumor cells through a variation of macropinocytosis independent of NRP1. The uniqueness of CendR pathway lies in the linkage of CendR endocytosis to mTOR and cellular nutrient status. We provide evidence that a transcription factor, Sp1, serves as a link between mTOR and CendR endocytosis by regulating the NRP1 level on the cell surface. Additionally, we have shown the intercellular transport of CendR cargo that affords tissue penetration and is also stimulated by nutrient deprivation. Here we identify genes critical to the export and re-entry of CendR cargo during intercellular transport. These results shed light into the mechanism of action of CPPs, and endocytosis in general. They also have implications in cancer metabolism and drug delivery.

Citation Format: Hongbo Pang, Gary B. Braun, Tomas Friman, Erkki Ruoslahti. Deciphering the basis of CendR-mediated penetration into tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5526. doi:10.1158/1538-7445.AM2015-5526

Rapid identification by surface-enhanced Raman spectroscopy of cancer cells at low concentrations flowing in a microfluidic channel

Reliable identification and collection of cells from bodily fluids is of growing interest for monitoring patient response to therapy and for early detection of disease or its recurrence. We describe a detection platform that combines microfluidics with surface-enhanced Raman spectroscopy (SERS) for the identification of individual mammalian cells continuously flowing in a microfluidics channel. A mixture of cancerous and noncancerous prostate cells was incubated with SERS biotags (SBTs) developed and synthesized by us, then injected into a flow-focused microfluidic channel, which forces the cells into a single file. The spectrally rich SBTs are based on a silver nanoparticle dimer core labeled with a Raman-active small reporter molecule paired with an affinity biomolecule, providing a unique barcode whose presence in a composite SERS spectrum can be deconvoluted. Individual cancer cells passing through the focused laser beam were correctly identified among a proportionally larger number of other cells by their Raman signatures. We examine two deconvolution strategies: principal component analysis and classical least-squares. The deconvolution strategies are used to unmix the overall spectrum to determine the relative contributions between two SBT barcodes, where one SBT barcode indicates neuropilin-1 overexpression, while a second SBT barcode is more universal and indicates unspecific binding to a cell's membrane. Highly reliable results were obtained for all of the cell mixture ratios tested, the lowest being 1 in 100 cells.

Clotting activity of polyphosphate-functionalized silica nanoparticles

We present a silica nanoparticle (SNP) functionalized with polyphosphate (polyP) that accelerates the natural clotting process of the body. SNPs initiate the contact pathway of the blood-clotting system; short-chain polyP accelerates the common pathway by the rapid formation of thrombin, which enhances the overall blood-clotting system, both by accelerating fibrin generation and by facilitating the regulatory anticoagulation mechanisms essential for hemostasis. Analysis of the clotting properties of bare SNPs, bare polyP, and polyP-functionalized SNPs in plasma demonstrated that the attachment of polyP to SNPs to form polyP-SNPs creates a substantially enhanced synergistic effect that lowers clotting time and increases thrombin production at low concentrations. PolyP-SNP even retains its clotting function at ambient temperature. The polyP-SNP system has the potential to significantly improve trauma-treatment protocols and outcomes in hospital and prehospital settings.

Targeted intracellular delivery of proteins with spatial and temporal control

While a host of methods exist to deliver genetic materials or small molecules to cells, very few are available for protein delivery to the cytosol. We describe a modular, light-activated nanocarrier that transports proteins into cells by receptor-mediated endocytosis and delivers the cargo to the cytosol by light triggered endosomal escape. The platform is based on hollow gold nanoshells (HGN) with polyhistidine tagged proteins attached through an avidity-enhanced, nickel chelation linking layer; here, we used green fluorescent protein (GFP) as a model deliverable cargo. Endosomal uptake of the GFP loaded nanocarrier was mediated by a C-end Rule (CendR) internalizing peptide fused to the GFP. Focused femtosecond pulsed-laser excitation triggered protein release from the nanocarrier and endosome disruption, and the released protein was capable of targeting the nucleoli, a model intracellular organelle. We further demonstrate the generality of the approach by loading and releasing Sox2 and p53. This method for targeting of individual cells, with resolution similar to microinjection, provides spatial and temporal control over protein delivery.

Tumor-penetrating iRGD peptide inhibits metastasis

Tumor-specific tissue-penetrating peptides deliver drugs into extravascular tumor tissue by increasing tumor vascular permeability through interaction with neuropilin (NRP). Here, we report that a prototypic tumor-penetrating peptide iRGD (amino acid sequence: CRGDKGPDC) potently inhibits spontaneous metastasis in mice. The antimetastatic effect was mediated by the NRP-binding RXXK peptide motif (CendR motif), and not by the integrin-binding RGD motif. iRGD inhibited migration of tumor cells and caused chemorepulsion in vitro in a CendR- and NRP-1-dependent manner. The peptide induced dramatic collapse of cellular processes and partial cell detachment, resulting in the repellent activity. These effects were prominently displayed when the cells were seeded on fibronectin, suggesting a role of CendR in functional regulation of integrins. The antimetastatic activity of iRGD may provide a significant additional benefit when this peptide is used for drug delivery to tumors.

An endocytosis pathway initiated through neuropilin-1 and regulated by nutrient availability

Neuropilins (NRPs) are trans-membrane receptors involved in axon guidance and vascular development. Many growth factors and other signalling molecules bind to NRPs through a carboxy (C)-terminal, basic sequence motif (C-end Rule or CendR motif). Peptides with this motif (CendR peptides) are taken up into cells by endocytosis. Tumour-homing CendR peptides penetrate through tumour tissue and have shown utility in enhancing drug delivery into tumours. Here we show, using RNAi screening and subsequent validation studies, that NRP1-mediated endocytosis of CendR peptides is distinct from known endocytic pathways. Ultrastructurally, CendR endocytosis resembles macropinocytosis, but is mechanistically different. We also show that nutrient-sensing networks such as mTOR signalling regulate CendR endocytosis and subsequent intercellular transport of CendR cargo, both of which are stimulated by nutrient depletion. As CendR is a bulk transport pathway, our results suggest a role for it in nutrient transport; CendR-enhanced drug delivery then makes use of this natural pathway.

Abstract 4504: Urokinase plasminogen activator-dependent tumor penetrating peptide

Activity of tumor penetrating peptides depends on C-end Rule (CendR) peptide motif (R/KXXR/K) that must be C-terminally exposed for tissue and cell penetration. We describe here a cryptic CendR peptide (uCendR; amino acid sequence: RPARSGR↓SAGGSVA) that is proteolytically activated by urokinase-type plasminogen activator (uPA), a protease overexpressed in human tumors. uPA cleavage unmasks the cryptic CendR element of uCendR peptide and triggers its binding and internalization to the neuropilin-expressing cultured cancer cells. Intradermally injected post-cleavage mimic of uCendR peptide (RPARSGR) increases permeability of skin microvessels to tracer compounds. Phage and silver nanoparticles functionalized with uCendR peptide in combination with angiogenic integrin-recruitment motif (CRGDC) home to tumor blood vessels, extravasate, and trigger vascular exit of co-injected tracer compounds. This study shows that modular tumor penetrating peptides that are specifically activated by a tumor derived protease can be developed for tumor-targeted drug delivery.

Citation Format: Tambet Teesalu, Kazuki N. Sugahara, Gary B. Braun, Venkata Ramana Kotamraju, Erkki Ruoslahti. Urokinase plasminogen activator-dependent tumor penetrating peptide. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4504. doi:10.1158/1538-7445.AM2014-4504

Abstract 5406: The CendR pathway: A novel cell penetration and transcytosis pathway regulated by nutrient availability

Transport of molecules across the vascular wall, through tissue, and into target cells plays an important role in various physiological and pathological processes. We previously described a novel class of tumor-targeting peptides (CendR peptides) that penetrate into cells and tumor tissue through an as yet incompletely characterized transport pathway initiated by peptide binding to neuropilin-1 (NRP1). This pathway has shown promise in enhancing drug delivery into tumors. Here we perform a genome-wide RNAi screen to identify components responsible for cell penetration of CendR peptides. We show that the binding of CendR peptides to NRP1 initiates a novel endocytic process that depends on a subset of genes and a transport route distinct from those of known endocytic pathways. Strikingly, we found the internalization of CendR peptides to be controlled by nutrient-sensing and cell growth-regulatory pathways. Nutrient deprivation stimulated the cell penetration and intercellular transport of CendR peptides, both in vitro and in vivo. These data suggest a physiological role for CendR pathway in nutrient sensing and transport. The ability to activate this pathway with peptides provides immediate applications to drug delivery.

Citation Format: Hong-Bo Pang, Gary B. Braun, Tomas Friman, Pedro Aza-Blanc, Manuel E. Ruidiaz, Kazuki N. Sugahara, Tambet Teesalu, Erkki Ruoslahti. The CendR pathway: A novel cell penetration and transcytosis pathway regulated by nutrient availability. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5406. doi:10.1158/1538-7445.AM2014-5406

Etchable plasmonic nanoparticle probes to image and quantify cellular internalization

There is considerable interest in using nanoparticles as labels or to deliver drugs and other bioactive compounds to cells in vitro and in vivo. Fluorescent imaging, commonly used to study internalization and subcellular localization of nanoparticles, does not allow unequivocal distinction between cell surface-bound and internalized particles, as there is no methodology to turn particles 'off'. We have developed a simple technique to rapidly remove silver nanoparticles outside living cells, leaving only the internalized pool for imaging or quantification. The silver nanoparticle (AgNP) etching is based on the sensitivity of Ag to a hexacyanoferrate-thiosulphate redox-based destain solution. In demonstration of the technique we present a class of multicoloured plasmonic nanoprobes comprising dye-labelled AgNPs that are exceptionally bright and photostable, carry peptides as model targeting ligands, can be etched rapidly and with minimal toxicity in mice, and that show tumour uptake in vivo.

Modular plasmonic nanocarriers for efficient and targeted delivery of cancer-therapeutic siRNA

We have combined a versatile and powerful route to deliver nucleic acids with peptide-based cell-specific targeting. siRNA targeting the polo-like kinase gene is in clinical trials for cancer treatment, and here we deliver this RNA selectively to cancer cells displaying the neuropilin-1 epitope using gold nanoshells. Release of the siRNA from the nanoparticles results from irradiation with a pulsed near-infrared laser, which also provides efficient endosomal escape within the cell. As a result, our approach requires 10-fold less material than standard nucleic acid transduction materials and is significantly more efficient than other particle-based methods. We also describe a particle-nucleic acid design that does not rely on modified RNA, thereby making the preparation of these materials more efficient and much less expensive. These improvements, when combined with control over when and where the siRNA is released, could provide the basis for diverse cell biological studies.

A free cysteine prolongs the half-life of a homing peptide and improves its tumor-penetrating activity

The accessibility of extravascular tumor tissue to drugs is critical for therapeutic efficacy. We previously described a tumor-targeting peptide (iRGD) that elicits active transport of drugs and macromolecules (covalently coupled or co-administered) across the vascular wall into tumor tissue. Short peptides (iRGD is a 9-amino acid cyclic peptide) generally have a plasma half-life measured in minutes. Since short half-life limits the window of activity obtained with a bolus injection of iRGD, we explored to extend the half-life of the peptide. We show here that addition of a cysteine residue prolongs the plasma half-life of iRGD and increases the accumulation of the peptide in tumors. This modification prolongs the activity of iRGD in inducing macromolecular extravasation and leads to greater drug accumulation in tumors than is obtained with the unmodified peptide. This effect is mediated by covalent binding of iRGD to plasma albumin through a disulfide bond. Our study provides a simple strategy to improve peptide pharmacokinetics and activity. Applied to RGD, it provides a means to increase the entry of therapeutic agents into tumors.

Application of a proapoptotic peptide to intratumorally spreading cancer therapy

Bit1 is a proapoptotic mitochondrial protein associated with anoikis. Upon cell detachment, Bit1 is released into the cytoplasm and triggers caspase-independent cell death. Bit1 consists of 179 amino acids; for the C-terminal, two thirds of the molecule functions as a peptidyl-tRNA hydrolase, whereas the N-terminus contains a mitochondrial localization signal. Here, we localize the cell death domain (CDD) to the N-terminal 62 amino acids of Bit1 by transfecting cells with truncated Bit1 cDNA constructs. CDD was more potent in killing cells than the full-length Bit1 protein when equivalent amounts of cDNA were transfected. To develop Bit1 CDD into a cancer therapeutic, we engineered a recombinant protein consisting of the CDD fused to iRGD, which is a tumor-specific peptide with unique tumor-penetrating and cell-internalizing properties. iRGD-CDD internalized into cultured tumor cells through a neuropilin-1-activated pathway and triggered cell death. Importantly, iRGD-CDD spread extensively within the tumor when injected intratumorally into orthotopically implanted breast tumors in mice. Repeated treatment with iRGD-CDD strongly inhibited tumor growth, resulting in an average reduction of 77% in tumor volume and eradication of some tumors. The caspase independence of Bit1-induced cell death makes CDD a potentially attractive anticancer agent, because tumor resistance to the main mechanisms of apoptosis is circumvented. Using iRGD to facilitate the spreading of a therapeutic agent throughout the tumor mass may be a useful adjunct to local therapy for tumors that are surgically inoperable or difficult to treat systemically.

Robust SERS enhancement factor statistics using rotational correlation spectroscopy

We characterize the distribution of surface-enhanced Raman spectroscopy (SERS) enhancement factors observed in individual hot spots of single Ag "nanocapsules", encapsulated Ag nanoparticle dimers formed via controlled nanoparticle linking, polymer encapsulation, and small molecule infusion. The enhancement factors are calculated for over 1000 individual nanocapsules by comparing Raman scattering intensities of 4-mercaptobenzoic acid (MBA) measured from single SERS hot spots to intensities measured from high-concentration solutions of MBA. Correlation spectroscopy measurements of the rotational diffusion identify nanocapsules with signals dominated by single hot spots via their strong polarization response. Averaging over the entire surface of the nanocapsules, the distribution of enhancement factors is found to range from 10(6) to 10(8), with a mean of 6 × 10(6). Averaging only over nanoparticle junctions (where most SERS signals are expected) increases this average value to 10(8), with a range from 2 × 10(7) to 2 × 10(9). This significant statistical sampling shows that very high SERS enhancement factors can be obtained on a consistent basis using nanoparticle linking.

Mesoporous multifunctional upconversion luminescent and magnetic "nanorattle" materials for targeted chemotherapy

Nanorattles consisting of hydrophilic, rare-earth-doped NaYF(4) shells each containing a loose magnetic nanoparticle were fabricated through an ion-exchange process. The inner magnetic Fe(3)O(4) nanoparticles are coated with a SiO(2) layer to avoid iron leaching in acidic biological environments. This multifunctional mesoporous nanostructure with both upconversion luminescent and magnetic properties has excellent water dispersibility and a high drug-loading capacity. The material emits visible luminescence upon NIR excitation and can be directed by an external magnetic field to a specific target, making it an attractive system for a variety of biological applications. Measurements on cells incubated with the nanorattles show them to have low cytotoxicity and excellent cell imaging properties. In vivo experiments yield highly encouraging tumor shrinkage with the antitumor drug doxorubicin (DOX) and significantly enhanced tumor targeting in the presence of an applied magnetic field.

Abstract C33: N-terminal fragment of Bit1 apoptotic protein induces autophagy in tumor cells

Bit1 is a proapoptotic mitochondrial protein associated with anoikis, cell death resulting from the loss of cell attachment to extracellular matrix. Upon cell detachment, Bit1 is released into the cytoplasm, where it complexes with the Groucho family protein amino-terminal enhancer of split, and triggers cell death through a caspase-independent pathway. Bit1 consists of 179 amino acids; the N-terminal 62 amino acid mitochondrial localization domain, a transmembrane domain, and the C-terminal peptidyl-tRNA hydrolase domain. In the present study, we localized the Bit1 cell death domain (BCDD) to the N-terminal 62 amino acids of Bit1 by introducing truncated Bit1 proteins into the cytoplasm with cDNAtransfection and protein transduction. BCDD was more potent than the full-length Bit1 protein, when equivalent amounts of cDNA was transfected. Treatment of cultured prostate and breast cancer cells with recombinant proteins in which BCDD was fused with two cell-internalizing peptides, one of which is tumor specific, also caused cell death. Bit1 and BCDD shared the characteristics previously attributed to Bit1-induced cell death. In addition, we found that the cells exhibited the signs of autophagy. These results define the cell death domain in Bit1 and reveal autophagy as the main mechanism of Bit1-induced cell death. Tumor-targeted exogenous BCDD may have potential as an anticancer agent.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C33.

Fabrication of Ag@SiO(2)@Y(2)O(3):Er nanostructures for bioimaging: tuning of the upconversion fluorescence with silver nanoparticles

We demonstrated that the nanostructures comprising silver cores and dense layers of Y(2)O(3):Er separated by a silica shell are an excellent model system to study the interaction between upconversion materials and metals in nanoscale. This architecture allows for versatile control of the Y(2)O(3):Er-metal interaction through control of the silica dielectric spacer thickness and the metal-core size. Finally, the nanoparticles are potentially interesting as fluorescent labels in, for instance (single particle), imaging experiments or bioassays which require low background or tissue penetrating wavelengths.

Single-order, subwavelength resonant nanograting as a uniformly hot substrate for surface-enhanced Raman spectroscopy

The surface-enhanced Raman spectroscopy (SERS) activity and the optical reflectance of a subwavelength gold nanograting fabricated entirely using top down technologies on silicon wafers are presented. The grating consists of 120 nm gold cladding on top of parallel silica nanowires constituting the grating's lines, with gaps between nanowires <10 nm wide at their narrowest point. The grating produces inordinately intense SERS and shows very strong polarization dependence. Reflectance measurements for the optimized grating indicate that (when p-polarization is used and at least one of the incident electric field components lies across the grating lines) the reflectance drops to <1% at resonance, indicating that essentially all of the radiant energy falling on the surface is coupled into the grating. The SERS intensity and the reflectance at resonance anticorrelate predicatively, suggesting that reflectance measurements can provide a nondestructive, wafer-level test of SERS efficacy. The SERS performance of the gratings is very uniform and reproducible. Extensive measurements on samples cut from both the same wafer and from different wafers, produce a SERS intensity distribution function that is similar to that obtained for ordinary Raman measurements carried out at multiple locations on a polished (100) silicon wafer.

Cell-targeted self-assembled DNA nanostructures

We present two strategies for attaching self-assembled DNA arrays to the surfaces of cells. Our first approach uses biotin-streptavidin interactions to bind DNA architectures to biotinylated cells. The second approach takes advantage of specific antibody-cell surface interactions, conjugated arrays and the subsequent binding to native epidermal growth factor receptors expressed on cancer cells. DNA array-cell surface interactions were visualized by fluorescence, confocal microscopy, and scanning electron microscopy. This novel application of DNA nanoarrays provides strategies to specifically label cell surfaces with micrometer-sized patches, bind cells onto a designed functionalized DNA scaffold, engineer cell/cell networks into microtissues, and deliver materials to cell surfaces.

Laser-Activated Gene Silencing via Gold Nanoshell-siRNA Conjugates

The temporal and spatial control over the delivery of materials such as siRNA into cells remains a significant technical challenge. We demonstrate the pulsed near-infrared (NIR) laser-dependent release of siRNA from coated 40 nm gold nanoshells. Tat-lipid coating mediates the cellular uptake of the nanomaterial at picomolar concentration, while spatiotemporal silencing of a reporter gene (green fluorescence protein) was studied using photomasking. The NIR laser-induced release of siRNA from the nanoshells is found to be power- and time-dependent, through surface-linker bond cleavage, while the escape of the siRNA from endosomes occurs above a critical pulse energy attributed to local heating and cavitation. NIR laser-controlled drug release from functional nanomaterials should facilitate more sophisticated developmental biology and therapeutic studies.

A feasible approach to all-electronic digital labeling and readout for cell identification

We present two critical innovations that enable a unique, purely electronic approach to microfluidic whole-cell analysis, focusing on the problem of cell identification and sorting. We used fully-scalable lithographic techniques to microfabricate digital barcodes, providing a means for low-cost, large volume production. We have demonstrated molecular functionalization of the barcodes, using biotin-streptavidin, as well as human CD4 antibody, and we have successfully linked the barcodes to polystyrene beads using the biotin-streptavidin complex. This functionalization allows unique barcodes to be attached to specific cell types, based on phenotype. We have also implemented an electronic barcode readout scheme, using a radio frequency microsensor integrated in an elastomeric microfluidic channel, that can read individual barcodes at rates in excess of 1000 labels s(-1). The barcodes are biologically compatible, and coupled with the electronic sensing technology, provide a route to compact, inexpensive, disposable cell identification, sorting and purification.