PolyIC GE11 polyplex inhibits EGFR-overexpressing tumors

Synthesis, Radiolabeling, and In Vitro and In Vivo Characterization of Heterobivalent Peptidic Agents for Bispecific EGFR and Integrin αvβ3 Targeting

Radiolabeled heterobivalent peptidic ligands (HBPLs) are a highly promising compound class for the sensitive and specific visualization of tumors as they often exhibit superior properties compared to their monospecific counterparts and are able to concomitantly or complementarily address different receptor types. The combination of two receptor-specific agents targeting the epidermal growth factor receptor (EGFR) and the integrin α_vβ₃ in one HBPL would constitute a synergistic combination of binding motifs as these two receptor types are concurrently overexpressed on several human tumor types and are closely associated with disease progression and metastasis. Here, we designed and synthesized two heterobivalent radioligands consisting of the EGFR-specific peptide GE11 and α_vβ₃-specific cyclic RGD peptides, bearing a (1,4,7-triazacyclononane-4,7-diyl)diacetic acid-1-glutaric acid chelator for efficient radiolabeling and linkers of different lengths between both peptides. Both HBPLs were radiolabeled with ⁶⁸Ga³⁺ in high radiochemical yields, purities of 96-99%, and molar activities of 36-88 GBq/μmol. [⁶⁸Ga]Ga-1 and [⁶⁸Ga]Ga-2 were evaluated for their log _D(7.4) and stability toward degradation by human serum peptidases, showing a high hydrophilicity for both agents of -3.07 ± 0.01 and -3.44 ± 0.08 as well as a high stability toward peptidase degradation in human serum with half-lives of 272 and 237 min, respectively. Further on, the in vitro receptor binding profiles of both HBPLs to the target EGF and integrin α_vβ₃ receptors were assessed on EGFR-positive A431 and α_vβ₃-positive U87MG cells. Finally, we investigated the in vivo pharmacokinetics of HBPL [⁶⁸Ga]Ga-1 by positron emission tomography/computed tomography imaging in A431 tumor-bearing xenograft mice to assess its potential for the receptor-specific visualization of EGFR- and/or α_vβ₃-expressing tumors. In these experiments, [⁶⁸Ga]Ga-1 demonstrated a tumor uptake of 2.79 ± 1.66% ID/g, being higher than in all other organs and tissues apart from kidneys and blood at 2 h p.i. Receptor blocking studies revealed the observed tumor uptake to be solely mediated by integrin α_vβ₃, whereas no contribution of the GE11 peptide sequence to tumor uptake via the EGFR could be determined. Thus, the approach to develop radiolabeled EGFR- and integrin α_vβ₃-bispecific HBPLs is in general feasible although another peptide lead structure than GE11 should be used as the basis for the EGFR-specific part of the agents.

Regulation of Signaling from the Epidermal Growth Factor Family

The epidermal growth factor (EGF) system has allowed chemists, biologists, and clinicians to improve our understanding of cell production and cancer therapy. The discovery of EGF led to the recognition of cell surface receptors capable of controlling the proliferation and survival of cells. The detailed structures of the EGF-like ligand and the responses of their receptors (EGFR-family) has revealed the conformational and aggregation changes whereby ligands activate the intracellular kinase domains. Biophysical analysis has revealed the preformed clustering of different EGFR-family members and the processes which occur on ligand binding. Understanding these receptor activation processes and the consequential cytoplasmic signaling has allowed the development of inhibitors which are revolutionizing cancer therapy. This Review describes the recent progress in our understanding of the activation of the EGFR-family, the effects of signaling from the EGFR-family on cell proliferation, and the targeting of the EGFR-family in cancer treatment.

Toward the Development of GE11-Based Radioligands for Imaging of Epidermal Growth Factor Receptor-Positive Tumors

The epidermal growth factor receptor (EGFR) is closely associated with tumor development and progression and thus an important target structure for imaging and therapy of various tumors. As a result of its important role in malignancies of various origins and the fact that antibody-based compounds targeting the EGFR have significant drawbacks in terms of in vivo pharmacokinetics, several attempts have been made within the last five years to develop peptide-based EGFR-specific radioligands based on the GE11 scaffold. However, none of these approaches have shown convincing results so far, which has been proposed to be attributed to different potential challenges associated with the GE11 lead structure: first, an aggregation of radiolabeled peptides, which might prevent their interaction with their target receptor, or second, a relatively low affinity of monomeric GE11, necessitating its conversion into a multimeric or polymeric form to achieve adequate EGFR-targeting properties. In the present work, we investigated if these aforementioned points are indeed critical and if the EGFR-targeting ability of GE11 can be improved by choosing an appropriate hydrophilic molecular design or a peptide multimer system to obtain a promising radiopeptide for the visualization of EGFR-overexpressing malignancies by positron emission tomography (PET). For this purpose, we developed several monovalent ⁶⁸Ga-labeled GE11-based agents, a peptide homodimer and a homotetramer to overcome the challenges associated with GE11. The developed ligands were successfully labeled with ⁶⁸Ga³⁺ in high radiochemical yields of ≥97% and molar activities of 41-104 GBq/μmol. The resulting radiotracers presented log _D(7.4) values between -2.17 ± 0.21 and -3.79 ± 0.04 as well as a good stability in human serum with serum half-lives of 112 to 217 min for the monovalent radiopeptides and 84 and 62 min for the GE11 homodimer and homotetramer, respectively. In the following in vitro studies, none of the ⁶⁸Ga-labeled radiopeptides demonstrated a considerable EGF receptor-specific uptake in EGFR-positive A431 cells. Moreover, none of the agents was able to displace [¹²⁵I]I-EGF from the EGFR in competitive displacement assays in the same cell line in concentrations of up to 1 mM, whereas the endogenous receptor ligand hEGF demonstrated a high affinity of 15.2 ± 3.3 nM. These results indicate that it is not the aggregation of the GE11 sequence that seems to be the factor limiting the usefulness of the peptide as basis for radiotracer design but the limited affinity of monovalent and small homomultivalent GE11-based radiotracers to the EGFR. This highlights that the development of small-molecule GE11-based radioligands is not promising.

Challenges for the application of EGFR-targeting peptide GE11 in tumor diagnosis and treatment

Abnormal regulation of cell signaling pathways on cell survival, proliferation and migration contributes to the development of malignant tumors. Among them, epidermal growth factor receptor (EGFR) is one of the most important biomarkers in many types of malignant solid tumors. Its over-expression and mutation status can be served as a biomarker to identify patients who can be benifit from EGFR tyrosine kinase inhibitors and anti-EGFR monocloncal antibody (mAb) therapy. For decades, researches on EGFR targeted ligands were actively carried out to identify potent candidates for cancer therapy. An ideal EGFR ligand can competitively inhibit the binding of endogenous growth factor, such as epidermal growth factor (EGF) and transforming growth factor-α(TGF-α) to EGFR, thus block EGFR signaling pathway and downregulate EGFR expression. Alternatively, conjugation of EGFR ligands on drug delivery systems (DDS) can facilitate targeting delivery of therapeutics or diagnostic agents to EGFR over-expression tumors via EGFR-mediated endocytosis. GE11 peptide is one of the potent EGFR ligand screened from a phage display peptide library. It is a dodecapeptide that can specifically binds to EGFR with high affinity and selectivity. GE11 has been widely used in the diagnosis and targeted delivery of drugs for radiotherapy, genetherapy and chemotherpy against EGFR positive tumors. In this review, the critical factors affecting the in vivo and in vitro targeting performance of GE11 peptide, including ligand-receptor intermolecular force, linker bond properties and physiochemical properties of carrier materials, are detailedly interpreted. This review provides a valuable vision for the rational design and optimization of GE11-based active targeting strategies for cancer treatment, and it will promote the translation studies of GE11 from lab research to clinical application.

Targeting nucleic acid-based therapeutics to tumors: Challenges and strategies for polyplexes

The current medical reality of cancer gene therapy is reflected by more than ten approved products on the global market, including oncolytic and other viral vectors and CAR T-cells as ex vivo gene-modified cell therapeutics. The development of synthetic antitumoral nucleic acid therapeutics has been proceeding at a lower but steady pace, fueled by a plethora of alternative nucleic acid platforms (from various antisense oligonucleotides, siRNA, microRNA, lncRNA, sgRNA, to larger mRNA and DNA) and several classes of physical and chemical delivery technologies. This review summarizes the challenges and strategies for tumor-targeted nucleic acid delivery. Focusing primarily on polyplexes (polycation complexes) as nanocarriers, delivery options across multiple barriers into tumor cells are illustrated.

In silico studies of interactions of peptide-conjugated cholesterol metabolites and betulinic acid with EGFR, LDR, and N-terminal fragment of CCKA receptors

In this work, we designed three new ligands by conjugating cholesterol metabolites 3-hydroxy-5-cholestenoic acid (3-HC) and 3-oxo-4-cholestenoic acid (3-OC) and the natural tri-terpenoid betulinic acid with the tumor-targeting peptide YHWYGYTPQNVI. Molecular interactions with the unconjugated peptide and the conjugates were examined with three receptors that are commonly overexpressed in pancreatic adenocarcinoma cells using ligand docking and molecular dynamics. This study demonstrated the utility of the designed conjugates as a valuable scaffold for potentially targeting EGFR and LDLR receptors. Our results indicate that the conjugates showed strong binding affinities and formation of stable complexes with EGFR, while the unconjugated peptide, BT-peptide conjugate, an 3-HC-peptide conjugate showed the formation of fairly stable complexes with LDLR receptor. For EGFR, two receptor kinase domains were explored. Interactions with the N-terminal domain of CCKA-R were relatively weaker. For LDLR, binding occurred in the beta-propeller region. For the N-terminal fragment of CCKA-R, the conjugates induced significant conformational changes in the receptor. The molecular dynamic simulations for 100 ns demonstrate that BT-peptide conjugates and the unconjugated peptide had the highest binding and formed the most stable complexes with EGFR. RMSD and trajectory analyses indicate that these molecules transit to a dynamically stable configuration in most cases within 60 ns. NMA analysis indicated that amongst the conjugates that showed relatively higher interactions with the respective receptors, the highest potential for deformability was seen for the N-terminal-47 amino acid region of the CCKA-R receptor with and the lowest for the LDLR-receptor. Thus, the newly designed compounds may be evaluated in the future toward developing drug delivery materials for targeting tumor cells overexpressing LDLR or EGFR.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Optimizing synthetic nucleic acid and protein nanocarriers: The chemical evolution approach

Optimizing synthetic nanocarriers is like searching for a needle in a haystack. How to find the most suitable carrier for intracellular delivery of a specified macromolecular nanoagent for a given disease target location? Here, we review different synthetic 'chemical evolution' strategies that have been pursued. Libraries of nanocarriers have been generated either by unbiased combinatorial chemistry or by variation and novel combination of known functional delivery elements. As in natural evolution, definition of nanocarriers as sequences, as barcode or design principle, may fuel chemical evolution. Screening in appropriate test system may not only provide delivery candidates, but also a refined understanding of cellular delivery including novel, unpredictable mechanisms. Combined with rational design and computational algorithms, candidates can be further optimized in subsequent evolution cycles into nanocarriers with improved safety and efficacy. Optimization of nanocarriers differs for various cargos, as illustrated for plasmid DNA, siRNA, mRNA, proteins, or genome-editing nucleases.

Nucleic Acid-Based Approaches for Tumor Therapy

Within the last decade, the introduction of checkpoint inhibitors proposed to boost the patients' anti-tumor immune response has proven the efficacy of immunotherapeutic approaches for tumor therapy. Furthermore, especially in the context of the development of biocompatible, cell type targeting nano-carriers, nucleic acid-based drugs aimed to initiate and to enhance anti-tumor responses have come of age. This review intends to provide a comprehensive overview of the current state of the therapeutic use of nucleic acids for cancer treatment on various levels, comprising (i) mRNA and DNA-based vaccines to be expressed by antigen presenting cells evoking sustained anti-tumor T cell responses, (ii) molecular adjuvants, (iii) strategies to inhibit/reprogram tumor-induced regulatory immune cells e.g., by RNA interference (RNAi), (iv) genetically tailored T cells and natural killer cells to directly recognize tumor antigens, and (v) killing of tumor cells, and reprograming of constituents of the tumor microenvironment by gene transfer and RNAi. Aside from further improvements of individual nucleic acid-based drugs, the major perspective for successful cancer therapy will be combination treatments employing conventional regimens as well as immunotherapeutics like checkpoint inhibitors and nucleic acid-based drugs, each acting on several levels to adequately counter-act tumor immune evasion.

Development of EGFR-targeted evodiamine nanoparticles for the treatment of colorectal cancer

Invasion and metastasis of colorectal cancer (CRC) are leading causes of death of CRC patients. Previous findings demonstrate that evodiamine (Evo), an indolequinone alkaloid, is effective in combating CRC; however, its poor aqueous solubility and low oral bioavailability limit its application in the prevention of invasion and metastasis of CRC. It is known that selectively targeting cancer-specific receptors highly expressed on the surface of cancer cells by nanocarriers loaded with cytotoxic drugs is a viable strategy in nanobiotechnology to enhance cancer cell killing and minimize side effects. In this study, we report the development of a new class of nanotherapeutics: EGFR-targeting Evo-encapsulated poly(amino acid) nanoparticles (GE11-Evo-NPs). These nanoparticles exhibited good aqueous solubility, slow release, and active targeting capability. Their inhibitory effect on human colon cancer cells and therapeutic efficacy against invasion and metastasis of CRC in nude mice were systematically investigated. Mechanisms of the GE11-Evo-NPs against EGFR mediated invasion and metastasis of CRC were also explored. Compared with free Evo, the GE11-Evo-NPs showed significantly increased cytotoxicity to colon cancer cells and potently inhibited CRC LoVo cell adhesion, invasion, and migration. The expression of EGFR, VEGF, and MMP proteins was dramatically down-regulated, which may partially account for their inhibition of invasion and metastasis of CRC. Moreover, in vivo studies show that the GE11-Evo-NPs exhibited much greater potency than other control groups in inhibiting CRC invasion and metastasis, tumor volume, and growth in nude mice, leading to a significantly prolonged tumor-bearing survival duration (P < 0.01).

Peptide-Targeted Polyplexes for Aerosol-Mediated Gene Delivery to CD49f-Overexpressing Tumor Lesions in Lung

Peptide ligands can enhance delivery of nucleic acid-loaded nanoparticles to tumors by promoting their cell binding and internalization. Lung tumor lesions accessible from the alveolar side can be transfected, in principle, using gene vectors delivered as an aerosol. The cell surface marker CD49f (Integrin α6) is frequently upregulated in metastasizing, highly aggressive tumors. In this study, we utilize a CD49f binding peptide coupled to linear polyethylenimine (LPEI) promoting gene delivery into CD49f-overexpressing tumor cells in vitro and into lung lesions in vivo. We have synthesized a molecular conjugate based on LPEI covalently attached to the CD49f binding peptide CYESIKVAVS via a polyethylene glycol (PEG) spacer. Particles formed with plasmid DNA were small (<200 nm) and could be aerosolized without causing major aggregation or particle loss. In vitro, CD49f targeting significantly improved plasmid uptake and reporter gene expression on both human and murine tumor cell lines. For evaluation in vivo, localization and morphology of 4T1 murine triple-negative breast cancer tumor lesions in the lung of syngeneic BALB/c mice were identified by MRI. Polyplexes applied via intratracheal aerosolization were well tolerated and resulted in measurable transgene activity of the reporter gene firefly luciferase in tumor areas by bioluminescence imaging (BLI). Transfectability of tumors correlated with their accessibility for the aerosol. With CD49f-targeted polyplexes, luciferase activity was considerably increased and was restricted to the tumor area.

Synthesis, Microtubule-Binding Affinity, and Antiproliferative Activity of New Epothilone Analogs and of an EGFR-Targeted Epothilone-Peptide Conjugate

A new simplified, epoxide-free epothilone analog was prepared incorporating an N-(2-hydroxyethyl)-benzimidazole side chain, which binds to microtubules with high affinity and inhibits cancer cell growth in vitro with nM potency. Building on this scaffold, a disulfide-linked conjugate with the purported EGFR-binding (EGFR, epidermal growth factor receptor) peptide GE11 was then prepared. The conjugate retained significant microtubule-binding affinity, in spite of the size of the peptide attached to the benzimidazole side chain. The antiproliferative activity of the conjugate was significantly lower than for the parent scaffold and, surprisingly, was independent of the EGFR expression status of cells. Our data indicate that the disulfide-based conjugation with the GE11 peptide is not a viable approach for effective tumor-targeting of highly potent epothilones and probably not for other cytotoxics.

Dual-targeted NIS polyplexes-a theranostic strategy toward tumors with heterogeneous receptor expression

Tumor heterogeneity, within and between tumors, may have severe implications for tumor therapy, especially for targeted gene therapy, where single-targeted approaches often result in limited efficacy and therapy resistance. Polymer-formulated nonviral vectors provide a potent delivery platform for cancer therapy. To improve applicability for future clinical use in a broad range of patients and cancer types, a dual-targeting approach was performed. Synthetic LPEI-PEG_2kDa-based polymer backbones were coupled to two tumor-specific peptide ligands GE11 (EGFR-targeting) and cMBP (cMET-targeting). The dual-targeting approach was used to deliver the theranostic sodium iodide symporter (NIS) gene to hepatocellular cancer. NIS as auspicious theranostic gene allows noninvasive imaging of functional NIS gene expression and effective anticancer radioiodide therapy. Enhanced tumor-specific transduction efficiency of dual-targeted polyplexes compared to single-targeted polyplexes was demonstrated in vitro using tumor cell lines with different EGFR and cMET expression and in vivo by ¹²⁴I-PET-imaging. Therapeutic efficacy of the bispecific concept was mirrored by significantly reduced tumor growth and perfusion, which was associated with prolonged animal survival. In conclusion, the dual-targeting approach highlights the benefits of a bifunctional strategy for a future clinical translation of the bioimaging-based NIS-mediated radiotherapy allowing efficient targeting of heterogeneic tumors with variable receptor expression levels.

HIF1α-siRNA and gemcitabine combination-based GE-11 peptide antibody-targeted nanomedicine for enhanced therapeutic efficacy in pancreatic cancers

Pancreatic cancer is one of the deadliest cancers across the world with an average 5-year survival rate of less than <6%. In this study, gemcitabine (GEM) and HIF1α-siRNA loaded GE-11 peptide conjugated liposome was successfully prepared and evaluated for its antitumor efficacy in pancreatic cancer cells. The GE11 increased the targeting specificity of liposome carrier and increased the intracellular concentrations in the cancer cells. Furthermore, synergistic combination of GEM and HIF1a-siRNA exhibited remarkable improvement in the declining of cancer cell proliferations. siRNA could effectively decrease the expression of HIF1a gene in the cancer cells. Importantly, GE-11 peptide-conjugated GEM/siRNA-loaded liposomes (GE-GML/siRNA) increased the total amount of apoptosis cells with higher proportion of cells in late apoptosis phase. GE-GML induced remarkable apoptosis of cancer cells and induced chromatin condensation and nuclear fragmentation which are considered to be typical features of apoptosis and cell death. GE-GML/siRNA showed a significant reduction in the tumour burden suggesting the superior anticancer efficacy of this formulation. GE-GML/siRNA showed four-fold reduction in tumour compared to control and two-fold reduction compared to GE-GML, respectively. Overall, present work lays foundation for the combination of GEM and HIF1a-siRNA loaded in a targeted nanocarrier system as a unique therapeutic option in pancreatic cancer treatment.

Exploring pitfalls of 64Cu-labeled EGFR-targeting peptide GE11 as a potential PET tracer

The epidermal growth factor receptor (EGFR) represents an important molecular target for both radiotracer-based diagnostic imaging and radionuclide therapy of various cancer entities. For the delivery of radionuclides to the tumor, peptides hold great potential as a transport vehicle. With respect to EGFR, the peptide YHWYGYTPQNVI (GE11) has been reported to bind the receptor with high specificity and affinity. In the present study, GE11 with β-alanine (β-Ala-GE11) was conjugated to the chelating agent p-SCN-Bn-NOTA and radiolabeled with ⁶⁴Cu for the first radio pharmacological evaluation as a potential probe for positron emission tomography (PET)-based cancer imaging. For better water solubility, an ethylene glycol-based linker was introduced between the peptide's N terminus and the radionuclide chelator. The stability of the ⁶⁴Cu-labeled peptide conjugate and its binding to EGFR-expressing tumor cells was investigated in vitro and in vivo, and then compared with the ⁶⁴Cu-labeled EGFR-targeting antibody conjugate NOTA-cetuximab. The GE11 peptide conjugate [⁶⁴Cu]Cu-NOTA-linker-β-Ala-GE11 ([⁶⁴Cu]Cu-1) was stable in a buffer solution for at least 24 h but only 50% of the original compound was detected after 24 h of incubation in human serum. Stability could be improved by amidation of the peptide's C terminus (β-Ala-GE11-NH₂ (2)). Binding assays with both conjugates, [⁶⁴Cu]Cu-1 and [⁶⁴Cu]Cu-2, using the EGFR-expressing tumor cell lines A431 and FaDu showed no specific binding. A pilot small animal PET investigation in FaDu tumor-bearing mice revealed only low tumor uptake (standard uptake value (SUV) < 0.2) for both conjugates. The best tumor-to-muscle ratio determined was 3.75 for [⁶⁴Cu]Cu-1, at 1 h post injection. In conclusion, the GE11 conjugates in its present form are not suitable for further biological investigations, since they presumably form aggregates.

Epidermal growth factor receptor targeted methotrexate and small interfering RNA co-delivery

BACKGROUND

Developing new drug delivery carriers addressing chemoresistance is still full of challenges and opportunities. As the rapid development of small interfering RNA (siRNA) provides promising therapeutic perspectives, nanocarriers for drug and siRNA co-delivery present new alternatives for cancer therapy.

METHODS

A co-delivery nanosystem for methotrexate (MTX) or gamma-glutamylated derivatives (gE₂ -MTX and gE₅ -MTX) and antitumoral EG5 siRNA has been developed utilizing the sequence defined cationic lipo-oligomers 454, 1021 and 1027. Based on a lipo-oligomer-MTX-siRNA core, an epidermal growth factor receptor (EGFR) targeted delivery system was established via post modification with the GE11 targeting peptide.

RESULTS

Almost 100% MTX derivative incorporation was achieved in gE₂ -MTX or gE₅ -MTX siRNA/454 polyplexes, whereas the particle sizes (100-150 nm) and siRNA binding abilities were well maintained. Our co-delivery system greatly increased the MTX sensitivity of MTX resistant KB cells. Enhanced cellular internalization of GE11 siRNA/454 polyplexes incorporating either gE₂ -MTX or gE₅ -MTX was observed and attributed to GE11-mediated targeting of EGFR overexpressing KB cells. GE11 modified gE₂ -MTX or gE₅ -MTX EG5 siRNA polyplexes illustrated the highest anti-tumoral activities compared to free MTX or nontargeted polyplexes. The His-containing gE₂ -MTX or gE₅ -MTX siRNA/1027 polyplexes showed increased tumor cell killing compared to the His-free analogous 1021 polyplexes.

CONCLUSIONS

A new strategy for co-delivering negatively charged MTX and cytotoxic siRNA has been developed by utilizing sequence defined cationic lipo-oligomers. Mediated by the combined effect of antifolate MTX, antimitotic EG5 siRNA and EGFR targeting by GE11, superior tumor cell killing was obtained with GE11 gE₂ -MTX or gE₅ -MTX EG5 siRNA/454 polyplexes.

Transfer of Dyes and Drugs into Cells Using EGFR-Targeted Nanosyringes

Selective targeting of drug loaded nanovectors to specific epitopes highly expressed on the surface of cancer cells is a goal for nanotechnologists. We have modified our previously described PEGylated-hydrophilic carbon clusters (PEG-HCCs) so that the epidermal growth factor receptor (EGFR) binding peptide, GE11, is attached using click chemistry at the end of each PEG. The resulting nanosyringe, Pep_EGFR-PEG-HCC, can be loaded with a wide range of hydrophobic drugs and dyes. We show that, both in vitro and in vivo, this payload can be delivered to cancer cells expressing EGFR. We can observe the activation of EGFR and track the normal physiological internalization and recycling/signaling pathways of this tyrosine kinase following binding of Pep_EGFR-PEG-HCC. We also demonstrate the competitive binding of the nanosyringe to EGFR with its normal activator, EGF, as well as observing the colocalization of the nanosyringe with clathrin, the coated pit integral protein. The internalization of the drug/dye loaded nanosyringe can be inhibited by using anti-EGFR antibodies, the drug erlotinib, or Pitstop-1, the clathrin coated pit formation specific inhibitor. To further demonstrate the specificity of the drug loaded nanovectors, we demonstrated that, in both flank and intracranial xenograft mouse models, dye delivery is highly specific to tumors and no other tissues. Finally, using nanosyringes loaded with esterase sensitive fluorescein diacetate, we demonstrated that the drug payloads can be in vivo delivered to the cytosol of cancer cells within the mouse brain.

GE11 Peptide as an Active Targeting Agent in Antitumor Therapy: A Minireview

A lot of solid tumors are characterized by uncontrolled signal transduction triggered by receptors related to cellular growth. The targeting of these cell receptors with antitumor drugs is essential to improve chemotherapy efficacy. This can be achieved by conjugation of an active targeting agent to the polymer portion of a colloidal drug delivery system loaded with an antitumor drug. The goal of this minireview is to report and discuss some recent results in epidermal growth factor receptor targeting by the GE11 peptide combined with colloidal drug delivery systems as smart carriers for antitumor drugs. The minireview chapters will focus on explaining and discussing: (i) Epidermal growth factor receptor (EGFR) structures and functions; (ii) GE11 structure and biologic activity; (iii) examples of GE11 conjugation and GE11-conjugated drug delivery systems. The rationale is to contribute in gathering information on the topic of active targeting to tumors. A case study is introduced, involving research on tumor cell targeting by the GE11 peptide combined with polymer nanoparticles.

Solid-phase supported design of carriers for therapeutic nucleic acid delivery

Nucleic acid molecules are important therapeutic agents in the field of antisense oligonucleotide, RNA interference, and gene therapies. Since nucleic acids are not able to cross cell membranes and enter efficiently into cells on their own, the development of efficient, safe, and precise delivery systems is the crucial challenge for development of nucleic acid therapeutics. For the delivery of nucleic acids to their intracellular site of action, either the cytosol or the nucleus, several extracellular and intracellular barriers have to be overcome. Multifunctional carriers may handle the different special requirements of each barrier. The complexity of such macromolecules however poses a new hurdle in medical translation, which is the chemical production in reproducible and well-defined form. Solid-phase assisted synthesis (SPS) presents a solution for this challenge. The current review provides an overview on the design and SPS of precise sequence-defined synthetic carriers for nucleic acid cargos.

Peptide ligand-modified nanomedicines for targeting cells at the tumor microenvironment

Since their initial discovery more than 30years ago, tumor-homing peptides have become an increasingly useful tool for targeted delivery of therapeutic and diagnostic agents into tumors. Today, it is well accepted that cells at the tumor microenvironment (TME) contribute in many ways to cancer development and progression. Tumor-homing peptide-decorated nanomedicines can interact specifically with surface receptors expressed on cells in the TME, improve cellular uptake of nanomedicines by target cells, and impair tumor growth and progression. Moreover, peptide ligand-modified nanomedicines can potentially accumulate in the target tissue at higher concentrations than would small conjugates, thus increasing overall target tissue exposure to the therapeutic agent, enhance therapeutic efficacy and reduce side effects. This review describes the most studied peptide ligands aimed at targeting cells in the TME, discusses major obstacles and principles in the design of ligands for drug targeting and provides an overview of homing peptides in ligand-targeted nanomedicines that are currently in development for cancer therapy and diagnosis.

EGFR Targeting and Shielding of pDNA Lipopolyplexes via Bivalent Attachment of a Sequence-Defined PEG Agent

For successful nonviral gene delivery, cationic polymers are promising DNA carrier, which need to comprise several functionalities. The current work focuses on the postincorporation of epidermal growth factor receptor (EGFR) targeted PEGylation agents onto lipopolyplexes for pDNA delivery. T-shaped lipo-oligomers are previously found to be effective sequence-defined carriers for pDNA and siRNA. Here, the bis-oleoyl-oligoaminoethanamide 454 containing tyrosine trimer-cysteine ends is applied for complex formation with pDNA coding for luciferase or sodium iodide symporter (NIS). In a second step, the lipopolyplexes are modified via disulfide formation with sequence-defined monovalent or bivalent PEGylation agents containing one or two 3-nitro-2-pyridinesulfenyl (NPys)-activated cysteines, respectively. For targeting, the polyethylene glycol (PEG) agents comprise the EGFR targeting peptide GE11. In comparison of all transfection complexes, 454 lipopolyplexes modified with the bidentate PEG-GE11 agent show the best, EGFR-dependent uptake as well as luciferase and NIS gene expression into receptor-positive tumor cells.

Tumor-targeting peptides from combinatorial libraries

Cancer is one of the major and leading causes of death worldwide. Two of the greatest challenges in fighting cancer are early detection and effective treatments with no or minimum side effects. Widespread use of targeted therapies and molecular imaging in clinics requires high affinity, tumor-specific agents as effective targeting vehicles to deliver therapeutics and imaging probes to the primary or metastatic tumor sites. Combinatorial libraries such as phage-display and one-bead one-compound (OBOC) peptide libraries are powerful approaches in discovering tumor-targeting peptides. This review gives an overview of different combinatorial library technologies that have been used for the discovery of tumor-targeting peptides. Examples of tumor-targeting peptides identified from each combinatorial library method will be discussed. Published tumor-targeting peptide ligands and their applications will also be summarized by the combinatorial library methods and their corresponding binding receptors.

EGF receptor targeted lipo-oligocation polyplexes for antitumoral siRNA and miRNA delivery

Antitumoral siRNA and miRNA delivery was demonstrated by epidermal growth factor receptor (EGFR) targeted oligoaminoamide polyplexes. For this purpose, the T-shaped lipo-oligomer 454 was used to complex RNA into a core polyplex, which was subsequently functionalized with the targeting peptide ligand GE11 via a polyethylene glycol (PEG) linker. To this end, free cysteines on the surface of 454 polyplex were coupled with a maleimide-PEG-GE11 reagent (Mal-GE11). Resulting particles with sizes of 120-150 nm showed receptor-mediated uptake into EGFR-positive T24 bladder cancer cells, MDA-MB 231 breast cancer cells and Huh7 liver cancer cells. Furthermore, these formulations led to ligand-dependent gene silencing. RNA interference (RNAi) triggered antitumoral effects were observed for two different therapeutic RNAs, a miRNA-200c mimic or EG5 siRNA. Using polyplexes modified with a ratio of 0.8 molar equivalents of Mal-GE11, treatment of T24 or MDA-MB 231 cancer cells with miR-200c led to the expected decreased proliferation and migration, changes in cell cycle and enhanced sensitivity towards doxorubicin. Delivery of EG5 siRNA into Huh7 cells resulted in antitumoral activity with G2/M arrest, triggered by loss of mitotic spindle separation and formation of mono-astral spindles. These findings demonstrate the potential of GE11 ligand-containing RNAi polyplexes for cancer treatment.

Targeting polyIC to EGFR over-expressing cells using a dsRNA binding protein domain tethered to EGF

Selective delivery of drugs to tumor cells can increase potency and reduce toxicity. In this study, we describe a novel recombinant chimeric protein, dsRBEC, which can bind polyIC and deliver it selectively into EGFR over-expressing tumor cells. dsRBEC, comprises the dsRNA binding domain (dsRBD) of human PKR (hPKR), which serves as the polyIC binding moiety, fused to human EGF (hEGF), the targeting moiety. dsRBEC shows high affinity towards EGFR and triggers ligand-induced endocytosis of the receptor, thus leading to the selective internalization of polyIC into EGFR over-expressing tumor cells. The targeted delivery of polyIC by dsRBEC induced cellular apoptosis and the secretion of IFN-β and other pro-inflammatory cytokines. dsRBEC-delivered polyIC is much more potent than naked polyIC and is expected to reduce the toxicity caused by systemic delivery of polyIC.

EGFR targeted thermosensitive liposomes: A novel multifunctional platform for simultaneous tumor targeted and stimulus responsive drug delivery

The epidermal growth factor receptor (EGFR) is a promising target for anti-cancer therapy. The aim of this study was to design thermosensitive liposomes (TSL), functionalized with anti-EGFR ligands for targeted delivery and localized triggered release of chemotherapy. For targeting, EGFR specific peptide (GE11) and Fab' fragments of cetuximab were used and the effect of ligand density on in vitro tumor targeting was investigated. Ligand conjugation did not significantly change the physicochemical characteristics of liposomes. Fab'-decorated TSL (Fab'-TSL) can specifically and more efficiently bind to the EGFR overexpressed cancer cells as compared to GE11 modified TSL. Calcein labeled Fab'-TSL showed adequate stability at 37°C in serum (<4% calcein released after 1h) and a temperature dependent release at above 40°C. FACS analysis and live cell imaging showed efficient and EGFR mediated cellular association as well as dramatic intracellular cargo release upon hyperthermia. Fab'-conjugation and hyperthermia induced enhanced tumor cell cytotoxicity of doxorubicin loaded TSL. The relative cytotoxicity of Fab'-TSL was also correlated to EGFR density on the tumor cells. These results suggest that Fab'-TSL showed great potential for combinational targeted and triggered release drug delivery.

Aminoflavone-loaded EGFR-targeted unimolecular micelle nanoparticles exhibit anti-cancer effects in triple negative breast cancer

Triple negative breast cancer (TNBC) is an aggressive subtype of breast cancer for which there is no available targeted therapy. TNBC cases contribute disproportionately to breast cancer-related mortality, thus the need for novel and effective therapeutic methods is urgent. We have previously shown that a National Cancer Institute (NCI) investigational drug aminoflavone (AF) exhibits strong growth inhibitory effects in TNBC cells. However, in vivo pulmonary toxicity resulted in withdrawal or termination of several human clinical trials for AF. Herein we report the in vivo efficacy of a nanoformulation of AF that enhances the therapeutic index of AF in TNBC. We engineered a unique unimolecular micelle nanoparticle (NP) loaded with AF and conjugated with GE11, a 12 amino acid peptide targeting epidermal growth factor receptor (EGFR), since EGFR amplification is frequently observed in TNBC tumors. These unimolecular micelles possessed excellent stability and preferentially released drug payload at endosomal pH levels rather than blood pH levels. Use of the GE11 targeting peptide resulted in enhanced cellular uptake and strong growth inhibitory effects in TNBC cells. Further, AF-loaded, GE11-conjugated (targeted) unimolecular micelle NPs significantly inhibit orthotopic TNBC tumor growth in a xenograft model, compared to treatment with AF-loaded, GE11-lacking (non-targeted) unimolecular micelle NPs or free AF. Interestingly, the animals treated with AF-loaded, targeted NPs had the highest plasma and tumor level of AF among different treatment groups yet exhibited no increase in plasma aspartate aminotransferase (AST) activity level or observable tissue damage at the time of sacrifice. Together, these results highlight AF-loaded, EGFR-targeted unimolecular micelle NPs as an effective therapeutic option for EGFR-overexpressing TNBC.

Epidermal growth factor receptor-targeted peptide conjugated phospholipid micelles for doxorubicin delivery

Specific targeting of tumor cells to achieve higher drug levels in tumor tissue and to overcome side effects is the major goal in cancer chemotherapy. In this study, we used a tumor targeting peptide, GE11, to conjugate onto the surface of doxorubicin encapsulated phospholipid micelles. The GE11 peptide triggered specific binding to epidermal growth factor receptor (EGFR), leading to enhanced cellular uptake and cytotoxicity in vitro and highly accumulation in the tumors in vivo. The results indicated that GE11 conjugated phospholipid micelles should have potential applications in cancer therapy.

Quantitative analysis of ligand-EGFR interactions: a platform for screening targeting molecules

Epidermal growth factor receptor (EGFR) is often constitutively stimulated in many cancers owing to the binding of ligands such as epidermal growth factor (EGF). Therefore, it is necessary to investigate the interaction between EGFR and its targeting biomolecules. The main aim of this study was to estimate the binding affinity and adhesion force of two targeting molecules, anti-EGFR monoclonal antibody (mAb LA1) and the peptide GE11 (YHWYGYTPQNVI), with respect to EGFR and to compare these values with those obtained for the ligand, EGF. Surface plasmon resonance (SPR) was used to determine the equilibrium dissociation constant (KD) for evaluating the binding affinity. Atomic force microscopy (AFM) was performed to estimate the adhesion force. In the case of EGFR, the KD of EGF, GE11, and mAb LA1 were 1.77 × 10-7, 4.59 × 10-4 and 2.07 × 10-9, respectively, indicating that the binding affinity of mAb LA1 to EGFR was higher than that of EGF, while the binding affinity of GE11 to EGFR was the lowest among the three molecules. The adhesion force between EGFR and mAb LA1 was 210.99 pN, which is higher than that observed for EGF (209.41 pN), while the adhesion force between GE11 and EGFR was the lowest (59.51 pN). These results suggest that mAb LA1 binds to EGFR with higher binding affinity than EGF and GE11. Moreover, the adhesion force between mAb LA1 and EGFR was greater than that observed for EGF and GE11. The SPR and AFM experiments confirmed the interaction between the receptor and targeting molecules. The results of this study might aid the screening of ligands for receptor targeting and drug delivery.

Detection and imaging of aggressive cancer cells using an epidermal growth factor receptor (EGFR)-targeted filamentous plant virus-based nanoparticle

Molecular imaging approaches and targeted drug delivery hold promise for earlier detection of diseases and treatment with higher efficacy while reducing side effects, therefore increasing survival rates and quality of life. Virus-based nanoparticles are a promising platform because their scaffold can be manipulated both genetically and chemically to simultaneously display targeting ligands while carrying payloads for diagnosis or therapeutic intervention. Here, we displayed a 12-amino-acid peptide ligand, GE11 (YHWYGYTPQNVI), on nanoscale filaments formed by the plant virus potato virus X (PVX). Bioconjugation was used to produce fluorescently labeled PVX-GE11 filaments targeted toward the epidermal growth factor receptor (EGFR). Cell detection and imaging was demonstrated using human skin epidermoid carcinoma, colorectal adenocarcinoma, and triple negative breast cancer cell lines (A-431, HT-29, MDA-MB-231), all of which upregulate EGFR to various degrees. Nonspecific uptake in ductal breast carcinoma (BT-474) cells was not observed. Furthermore, co-culture experiments with EGFR(+) cancer cells and macrophages indicate successful targeting and partitioning toward the cancer cells. This study lays a foundation for the development of EGFR-targeted filaments delivering contrast agents for imaging and diagnosis, and/or toxic payloads for targeted drug delivery.

Identifying erlotinib-sensitive non-small cell lung carcinoma tumors in mice using [(11)C]erlotinib PET

Background

Non-small cell lung carcinoma (NSCLC) represents approximately 80% of lung cancer cases, and over 60% of these tumors express the epidermal growth factor receptor (EGFR). Activating mutations in the tyrosine kinase (TK) domain of the EGFR are detected in 10% to 30% of NSCLC patients, and evidence of their presence is a prerequisite for initiation of first-line therapy with selective TK inhibitors (TKIs), such as gefitinib and erlotinib. To date, the selection of candidate patients for first-line treatment with EGFR TKIs requires an invasive tumor biopsy to affirm the mutational status of the receptor. This study was designed to evaluate whether positron emission tomography (PET) of NSCLC tumor-bearing mice using [¹¹C]erlotinib could distinguish erlotinib-sensitive from erlotinib-insensitive or erlotinib-resistant tumors.

Methods

Four human NSCLC cell lines were employed, expressing either of the following forms of the EGFR: (i) the wild-type receptor (QG56 cells), (ii) a mutant with an exon 19 in-frame deletion (HCC827 cells), (iii) a mutant with the exon 21 L858R point mutation (NCI-H3255 cells), and (iv) a double mutant harboring the L858R and T790M mutations (NCI-H1975 cells). Sensitivity of each cell line to the anti-proliferative effect of erlotinib was determined in vitro. In vivo PET imaging studies following i.v. injection of [¹¹C]erlotinib were carried out in nude mice bearing subcutaneous (s.c.) xenografts of the four cell lines.

Results

Cells harboring activating mutations in the EGFR TK domain (HCC827 and NCI-H3255) were approximately 1,000- and 100-fold more sensitive to erlotinib treatment in vitro, respectively, compared to the other two cell lines. [¹¹C]Erlotinib PET scans could differentiate erlotinib-sensitive tumors from insensitive (QG56) or resistant (NCI-H1975) tumors already at 12 min after injection. Nonetheless, the uptake in HCC827 tumors was significantly higher than that in NCI-H3255, possibly reflecting differences in ATP and erlotinib affinities between the EGFR mutants.

Conclusions

[¹¹C]Erlotinib imaging in mice differentiates erlotinib-sensitive NSCLC tumors from erlotinib-insensitive or erlotinib-resistant ones.

Graphene nanoribbons elicit cell specific uptake and delivery via activation of epidermal growth factor receptor enhanced by human papillomavirus E5 protein

Ligands such as peptides, antibodies or other epitopes bind and activate specific cell receptors, and are employed for targeted cellular delivery of pharmaceuticals such as drugs, genes and imaging agents. Herein, we show that oxidized graphene nanoribbons, non-covalently functionalized with PEG-DSPE (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N[amino(polyethyleneglycol)]) (O-GNR-PEG-DSPE) activate epidermal growth factor receptors (EGFRs). This activation generates a predominantly dynamin-dependent macropinocytosis-like response, and results in significant O-GNR-PEG-DSPE uptake into cells with high EGFR expression. Cells with an integrated human papillomavirus (HPV) genome also show increased uptake due to the modulation of the activated EGFR by the viral protein E5. We demonstrate that this cell specific uptake of O-GNR-PEG-DSPE can be exploited to achieve significantly enhanced drug efficacies even in drug resistant cells. These results have implications for the development of active targeting and delivery agents without ligand functionalization for use in the diagnosis and treatment of pathologies that overexpress EGFR or mediated by HPV.

Effects of surface displayed targeting ligand GE11 on liposome distribution and extravasation in tumor

Targeting ligands displayed on liposome surface had been used to mediate specific interactions and drug delivery to target cells. However, they also affect liposome distribution in vivo, as well as the tissue extravasation processes after IV injection. In this study, we incorporated an EGFR targeting peptide GE11 on liposome surfaces in addition to PEG at different densities and evaluated their targeting properties and antitumor effects. We found that the densities of surface ligand and PEG were critical to target cell binding in vitro as well as pharmacokinetic profiles in vivo. The inclusion of GE11-PEG-DSPE and PEG-DSPE at 2% and 4% mol ratios in the liposome formulation mediated a rapid accumulation of liposomes within 1 h after IV injection in the tumor tissues surrounding neovascular structures. This is in addition to the EPR effect that was most prominently described for surface PEG modified liposomes. Therefore, despite the fact that the distribution of liposomes into interior tumor tissues was still limited by diffusion, GE11 targeted doxorubicin loaded liposomes showed significantly better antitumor activity in tumor bearing mice as a result of the fast active-targeting efficiency. We anticipate these understandings can benefit further optimization of targeted drug delivery systems for improving efficacy in vivo.

Adenoviral vectors coated with PAMAM dendrimer conjugates allow CAR independent virus uptake and targeting to the EGF receptor

Adenovirus type 5 (Ad) is an efficient gene vector with high gene transduction potential, but its efficiency depends on its native cell receptors coxsackie- and adenovirus receptor (CAR) for cell attachment and α(v)β(3/5) integrins for internalization. To enable transduction of CAR negative cancer cell lines, we have coated the negatively charged Ad by noncovalent charge interaction with cationic PAMAM (polyamidoamine) dendrimers. The specificity for tumor cell infection was increased by targeting the coated Ad to the epidermal growth factor receptor using the peptide ligand GE11, which was coupled to the PAMAM dendrimer via a 2 kDa PEG spacer. Particles were examined by measuring surface charge and size, the degree of coating was determined by transmission electron microscopy. The net positive charge of PAMAM coated Ad enhanced cellular binding and uptake leading to increased transduction efficiency, especially in low to medium CAR expressing cancer cell lines using enhanced green fluorescent protein or luciferase as transgene. While PAMAM coated Ad allowed for efficient internalization, coating with linear polyethylenimine induced excessive particle aggregation, elevated cellular toxicity and lowered transduction efficiency. PAMAM coating of Ad enabled successful transduction of cells in vitro even in the presence of neutralizing antibodies. Taken together, this study clearly proves noncovalent, charge-based coating of Ad vectors with ligand-equipped dendrimers as a viable strategy for efficient transduction of cells otherwise refractory to Ad infection.

Tuning nanoparticle uptake: live-cell imaging reveals two distinct endocytosis mechanisms mediated by natural and artificial EGFR targeting ligand

Therapeutic nanoparticles can be directed to cancer cells by incorporating selective targeting ligands. Here, we investigate the epidermal growth factor receptor (EGFR)-mediated endocytosis of gene carriers (polyplexes) either targeted with natural EGF or GE11, a short synthetic EGFR-binding peptide. Highly sensitive live-cell fluorescence microcopy with single particle resolution unraveled the existence of two different uptake mechanisms; EGF triggers accelerated nanoparticle endocytosis due to its dual active role in receptor binding and signaling activation. For GE11, an alternative EGFR signaling independent, actin-driven pathway is presented.

Targeting the Immune System to Fight Cancer Using Chemical Receptor Homing Vectors Carrying Polyinosine/Cytosine (PolyIC)

Cancer researchers have been looking for ways to harness the immune system and to reinstate immune surveillance, to kill cancer cells without collateral damage. Here we scan current approaches to targeting the immune system against cancer, and emphasize our own approach. We are using chemical vectors attached to a specific ligand, to introduce synthetic dsRNA, polyinosine/cytosine (polyIC), into tumors. The ligand binds to a receptor protein that is overexpressed on the surface of the tumor cells. Upon ligand binding, the receptor complex is internalized, introducing the polyIC into the cell. In this fashion a large amount of synthetic dsRNA can be internalized, leading to the activation of dsRNA-binding proteins, such as dsRNA dependent protein kinase (PKR), Toll-like receptor 3 (TLR3), retinoic acid-inducible gene I (RIG-1), and melanoma differentiation-associated gene 5 (MDA5). The simultaneous activation of these signaling proteins leads to the rapid demise of the targeted cell and to cytokine secretion. The cytokines lead to a strong bystander effect and to the recruitment of immune cells that converge upon the targeted cells. The bystander effects lead to the destruction of neighboring tumor cells not targeted themselves by the vector. Normal cells, being more robust than tumor cells, survive. This strategy has several advantages: (1) recruitment of the immune system is localized to the tumor. (2) The response is rapid, leading to fast tumor eradication. (3) The bystander effects lead to the eradication of tumor cells not harboring the target. (4) The multiplicity of pro-death signaling pathways elicited by PolyIC minimizes the likelihood of the emergence of resistance. In this chapter we focus on EGFR as the targeted receptor, which is overexpressed in many tumors. In principle, the strategy can be extended to other tumors that overexpress a protein that can be internalized by a ligand, which can be a small molecule, a single chain antibody, or an affibody.