Aptamer targeting EGFRvIII mutant hampers its constitutive autophosphorylation and affects migration, invasion and proliferation of glioblastoma cells

Aptamers: ushering in new hopes in targeted glioblastoma therapy

Glioblastoma, a formidable brain cancer, has remained a therapeutic challenge due to its aggressive nature and resistance to conventional treatments. Recent data indicate that aptamers, short synthetic DNA or RNA molecules can be used in anti-cancer therapy due to their better tumour penetration, specific binding affinity, longer retention in tumour sites and their ability to cross the blood-brain barrier. With the ability to modify these oligonucleotides through the selection process, and using rational design to modify them, post-SELEX aptamers offer several advantages in glioblastoma treatment, including precise targeting of cancer cells while sparing healthy tissue. This review discusses the pivotal role of aptamers in glioblastoma therapy and diagnosis, emphasising their potential to enhance treatment efficacy and also highlights recent advancements in aptamer-based therapies which can transform the landscape of glioblastoma treatment, offering renewed hope to patients and clinicians alike.

In Vivo Evaluation of 68Ga-Labeled NOTA-EGFRvIII Aptamer in EGFRvIII-Positive Glioblastoma Xenografted Model

EGFRvIII is expressed only in tumor cells and strongly in glioblastoma and is considered a promising target in cancer diagnosis and therapy. Aptamers are synthetic single-stranded oligonucleotides that bind to biochemical target molecules with high binding affinity and specificity. This study examined the potential of the 68Ga-NOTA-EGFRvIII aptamer as a nuclear imaging probe for visualizing EGFRvIII-expressing glioblastoma by positron emission tomography (PET). EGFRvIII aptamer was selected using the SELEX technology, and flow cytometry and fluorescence microscopy verified the high binding affinity to EGFRvIII positive U87MG vIII 4.12 glioma cells but not to EGFRvIII negative U87MG cells. The EGFRvIII aptamer was conjugated with a chelator (1,4,7-triazanonane-1,4,7-triyl)triacetic acid (NOTA) for 68Ga-labeling. The 68Ga-NOTA-EGFRvIII aptamer was prepared using the preconcentration-based labeling method with a high radiolabeling yield at room temperature. Ex vivo biodistribution analyses confirmed the significantly higher tumor uptake of the 68Ga-NOTA-EGFRvIII aptamer in EGFRvIII-expressing xenograft tumors than that in EGFRvIII negative tumors, confirming the specific tumor uptake of the 68Ga-NOTA-EGFRvIII aptamer in vivo. PET imaging studies revealed a high retention rate of the 68Ga-NOTA-EGFRvIII aptamer in U87MG vIII 4.12 tumors but only low uptake levels in U87-MG tumors, suggesting that the 68Ga-NOTA-EGFRvIII aptamer may be used as a PET imaging agent for EGFRvIII-expressing glioblastoma.

Gedunin modulates cellular growth and apoptosis in glioblastoma cell lines

BACKGROUND

Glioblastomas are characterized by aggressive behavior. Surgery, radiotherapy, and alkylating agents, including temozolomide are the most common treatment options for glioblastoma. Often, conventional therapies fail to treat these tumors since they develop drug resistance. There is a need for newer agents to combat this deadly tumor. Natural products such as gedunin have shown efficacy in several human diseases. A comprehensive study of gedunin, an heat shock protein (HSP)90 inhibitor, has not been thoroughly investigated in glioblastoma cell lines with different genetic modifications.

AIMS

A key objective of this study was to determine how gedunin affects the biological and signaling mechanisms in glioblastoma cells, and to determine how those mechanisms affect the proliferation and apoptosis of glioblastoma cells.

METHODS

The viability potentials of gedunin were tested using MTT, cell counts, and wound healing assays. Gedunin's effects on glioma cells were further validated using LDH and colony formation assays. In addition, we investigated the survival and apoptotic molecular signaling targets perturbed by gedunin using Western blot analysis and flow cytometry.

RESULTS

Our results show that there was a reduction in cell viability and inhibition of wound healing in the cells tested. Western blot analysis of the gene expression data revealed genes such as EGFR and mTOR/Akt/NF kappa B to be associated with gedunin sensitivity. Gedunin treatment induced apoptosis by cleaving poly ADP-ribose polymerase, activating caspases, and downregulating BCL-xL. Based on these results, gedunin suppressed cell growth and HSP client proteins, resulting in apoptosis in glioblastoma cell lines.

CONCLUSION

Our data provide in vitro support for the anticancer activity of gedunin in glioma cells by downregulating cancer survival proteins.

Bispecific aptamer-decorated and light-triggered nanoparticles targeting tumor and stromal cells in breast cancer derived organoids: implications for precision phototherapies

BACKGROUND

Based on the established role of cancer-stroma cross-talk in tumor growth, progression and chemoresistance, targeting interactions between tumor cells and their stroma provides new therapeutic approaches. Dual-targeted nanotherapeutics selectively acting on both tumor and stromal cells may overcome the limits of tumor cell-targeting single-ligand nanomedicine due to the complexity of the tumor microenvironment.

METHODS

Gold-core/silica-shell nanoparticles embedding a water-soluble iridium(III) complex as photosensitizer and luminescent probe (Iren-AuSiO2_COOH) were efficiently decorated with amino-terminated EGFR (CL4) and PDGFRβ (Gint4.T) aptamers (Iren-AuSiO2_Aptamer). The targeting specificity, and the synergistic photodynamic and photothermal effects of either single- and dual-aptamer-decorated nanoparticles have been assessed by confocal microscopy and cell viability assays, respectively, on different human cell types including mesenchymal subtype triple-negative breast cancer (MES-TNBC) MDA-MB-231 and BT-549 cell lines (both EGFR and PDGFRβ positive), luminal/HER2-positive breast cancer BT-474 and epidermoid carcinoma A431 cells (only EGFR positive) and adipose-derived mesenchymal stromal/stem cells (MSCs) (only PDGFRβ positive). Cells lacking expression of both receptors were used as negative controls. To take into account the tumor-stroma interplay, fluorescence imaging and cytotoxicity were evaluated in preclinical three-dimensional (3D) stroma-rich breast cancer models.

RESULTS

We show efficient capability of Iren-AuSiO2_Aptamer nanoplatforms to selectively enter into target cells, and kill them, through EGFR and/or PDGFRβ recognition. Importantly, by targeting EGFR+ tumor/PDGFRβ+ stromal cells in the entire tumor bulk, the dual-aptamer-engineered nanoparticles resulted more effective than unconjugated or single-aptamer-conjugated nanoparticles in either 3D spheroids cocultures of tumor cells and MSCs, and in breast cancer organoids derived from pathologically and molecularly well-characterized tumors.

CONCLUSIONS

Our study proposes smart, novel and safe multifunctional nanoplatforms simultaneously addressing cancer-stroma within the tumor microenvironment, which are: (i) actively delivered to the targeted cells through highly specific aptamers; (ii) localized by means of their luminescence, and (iii) activated via minimally invasive light, launching efficient tumor death, thus providing innovative precision therapeutics. Given the unique features, the proposed dual targeted nanoformulations may open a new door to precision cancer treatment.

Aptamers in neuro-oncology: An emerging therapeutic modality

Despite recent advances in the understanding of brain tumor pathophysiology, challenges associated with tumor location and characteristics have prevented significant improvement in neuro-oncology therapies. Aptamers are short, single-stranded DNA or RNA oligonucleotides that fold into sequence-specific, 3-dimensional shapes that, like protein antibodies, interact with targeted ligands with high affinity and specificity. Aptamer technology has recently been applied to neuro-oncology as a potential approach to innovative therapy. Preclinical research has demonstrated the ability of aptamers to overcome some obstacles that have traditionally rendered neuro-oncology therapies ineffective. Potential aptamer advantages include their small size, ability in some cases to penetrate the blood-brain barrier, inherent lack of immunogenicity, and applicability for discovering novel biomarkers. Herein, we review recent reports of aptamer applications in neuro-oncology including aptamers found by cell- and in vivo- Systematic Evolution of Ligands by Exponential Enrichment approaches, aptamer-targeted therapeutic delivery modalities, and aptamers in diagnostics and imaging. We further identify crucial future directions for the field that will be important to advance aptamer-based drugs or tools to clinical application in neuro-oncology.

Molecular Targeted Therapies in Glioblastoma Multiforme: A Systematic Overview of Global Trends and Findings

This systematic review assesses current molecular targeted therapies for glioblastoma multiforme (GBM), a challenging condition with limited treatment options. Using PRISMA methodology, 166 eligible studies, involving 2526 patients (61.49% male, 38.51% female, with a male-to-female ratio of 1.59/1), were analyzed. In laboratory studies, 52.52% primarily used human glioblastoma cell cultures (HCC), and 43.17% employed animal samples (mainly mice). Clinical participants ranged from 18 to 100 years, with 60.2% using combined therapies and 39.8% monotherapies. Mechanistic categories included Protein Kinase Phosphorylation (41.6%), Cell Cycle-Related Mechanisms (18.1%), Microenvironmental Targets (19.9%), Immunological Targets (4.2%), and Other Mechanisms (16.3%). Key molecular targets included Epidermal Growth Factor Receptor (EGFR) (10.8%), Mammalian Target of Rapamycin (mTOR) (7.2%), Vascular Endothelial Growth Factor (VEGF) (6.6%), and Mitogen-Activated Protein Kinase (MEK) (5.4%). This review provides a comprehensive assessment of molecular therapies for GBM, highlighting their varied efficacy in clinical and laboratory settings, ultimately impacting overall and progression-free survival in GBM management.

Unravelling the Glioblastoma Tumour Microenvironment: Can Aptamer Targeted Delivery Become Successful in Treating Brain Cancers?

The key challenges to treating glioblastoma multiforme (GBM) are the heterogeneous and complex nature of the GBM tumour microenvironment (TME) and difficulty of drug delivery across the blood-brain barrier (BBB). The TME is composed of various neuronal and immune cells, as well as non-cellular components, including metabolic products, cellular interactions, and chemical compositions, all of which play a critical role in GBM development and therapeutic resistance. In this review, we aim to unravel the complexity of the GBM TME, evaluate current therapeutics targeting this microenvironment, and lastly identify potential targets and therapeutic delivery vehicles for the treatment of GBM. Specifically, we explore the potential of aptamer-targeted delivery as a successful approach to treating brain cancers. Aptamers have emerged as promising therapeutic drug delivery vehicles with the potential to cross the BBB and deliver payloads to GBM and brain metastases. By targeting specific ligands within the TME, aptamers could potentially improve treatment outcomes and overcome the challenges associated with larger therapies such as antibodies.

Tissue Inhibitor of Metalloproteinases-1 Overexpression Mediates Chemoresistance in Triple-Negative Breast Cancer Cells

Triple-negative breast cancer (TNBC) is among the most aggressive breast cancer subtypes. Despite being initially responsive to chemotherapy, patients develop drug-resistant and metastatic tumors. Tissue inhibitor of metalloproteinases-1 (TIMP-1) is a secreted protein with a tumor suppressor function due to its anti-proteolytic activity. Nevertheless, evidence indicates that TIMP-1 binds to the CD63 receptor and activates noncanonical oncogenic signaling in several cancers, but its role in mediating TNBC chemoresistance is still largely unexplored. Here, we show that mesenchymal-like TNBC cells express TIMP-1, whose levels are further increased in cells generated to be resistant to cisplatin (Cis-Pt-R) and doxorubicin (Dox-R). Moreover, public dataset analyses indicate that high TIMP-1 levels are associated with a worse prognosis in TNBC subjected to chemotherapy. Knock-down of TIMP-1 in both Cis-Pt-R and Dox-R cells reverses their resistance by inhibiting AKT activation. Consistently, TNBC cells exposed to recombinant TIMP-1 or TIMP-1-enriched media from chemoresistant cells, acquire resistance to both cisplatin and doxorubicin. Importantly, released TIMP-1 reassociates with plasma membrane by binding to CD63 and, in the absence of CD63 expression, TIMP-1-mediated chemoresistance is blocked. Thus, our results identify TIMP-1 as a new biomarker of TNBC chemoresistance and lay the groundwork for evaluating whether blockade of TIMP-1 signal is a viable treatment strategy.

Systematic Review of Molecular Targeted Therapies for Adult-Type Diffuse Glioma: An Analysis of Clinical and Laboratory Studies

Gliomas are the most common brain tumor in adults, and molecularly targeted therapies to treat gliomas are becoming a frequent topic of investigation. The current state of molecular targeted therapy research for adult-type diffuse gliomas has yet to be characterized, particularly following the 2021 WHO guideline changes for classifying gliomas using molecular subtypes. This systematic review sought to characterize the current state of molecular target therapy research for adult-type diffuse glioma to better inform scientific progress and guide next steps in this field of study. A systematic review was conducted in accordance with PRISMA guidelines. Studies meeting inclusion criteria were queried for study design, subject (patients, human cell lines, mice, etc.), type of tumor studied, molecular target, respective molecular pathway, and details pertaining to the molecular targeted therapy-namely the modality, dose, and duration of treatment. A total of 350 studies met the inclusion criteria. A total of 52 of these were clinical studies, 190 were laboratory studies investigating existing molecular therapies, and 108 were laboratory studies investigating new molecular targets. Further, a total of 119 ongoing clinical trials are also underway, per a detailed query on clinicaltrials.gov. GBM was the predominant tumor studied in both ongoing and published clinical studies as well as in laboratory analyses. A few studies mentioned IDH-mutant astrocytomas or oligodendrogliomas. The most common molecular targets in published clinical studies and clinical trials were protein kinase pathways, followed by microenvironmental targets, immunotherapy, and cell cycle/apoptosis pathways. The most common molecular targets in laboratory studies were also protein kinase pathways; however, cell cycle/apoptosis pathways were the next most frequent target, followed by microenvironmental targets, then immunotherapy pathways, with the wnt/β-catenin pathway arising in the cohort of novel targets. In this systematic review, we examined the current evidence on molecular targeted therapy for adult-type diffuse glioma and discussed its implications for clinical practice and future research. Ultimately, published research falls broadly into three categories-clinical studies, laboratory testing of existing therapies, and laboratory identification of novel targets-and heavily centers on GBM rather than IDH-mutant astrocytoma or oligodendroglioma. Ongoing clinical trials are numerous in this area of research as well and follow a similar pattern in tumor type and targeted pathways as published clinical studies. The most common molecular targets in all study types were protein kinase pathways. Microenvironmental targets were more numerous in clinical studies, whereas cell cycle/apoptosis were more numerous in laboratory studies. Immunotherapy pathways are on the rise in all study types, and the wnt/β-catenin pathway is increasingly identified as a novel target.

Aptamers against cancer drug resistance: Small fighters switching tactics in the face of defeat

Discovering novel cancer therapies has attracted extreme interest in the last decade. In this regard, multidrug resistance (MDR) to chemotherapies is the primary challenge in cancer treatment. Cancerous cells are growingly become resistant to existing chemotherapeutics by employing diverse mechanisms, highlighting the significance of discovering approaches to overcome MDR. One promising strategy is utilizing aptamers as unique tools to target elements or signalings incorporated in resistance mechanisms or develop active targeted drug delivery systems or chimeras enabling the precise delivery of novel agents to inhibit the conventionally undruggable resistance elements. Further, due to their advantages over their proteinaceous counterparts, particularly antibodies, including improved targeting action, enhanced thermal stability, easier production, and superior tumor penetration, aptamers are emerging and have frequently been considered for developing cancer therapeutics. Here, we highlighted significant chemoresistance pathways and thoroughly discussed using aptamers as prospective tools to surmount cancer MDR.

NF-κB in neurodegenerative diseases: Recent evidence from human genetics

The transcription factor NF-κB is commonly known to drive inflammation and cancer progression, but is also a crucial regulator of a broad range of cellular processes within the mammalian nervous system. In the present review, we provide an overview on the role of NF-κB in the nervous system particularly including its constitutive activity within cortical and hippocampal regions, neuroprotection as well as learning and memory. Our discussion further emphasizes the increasing role of human genetics in neurodegenerative disorders, namely, germline mutations leading to defects in NF-κB-signaling. In particular, we propose that loss of function mutations upstream of NF-κB such as ADAM17, SHARPIN, HOIL, or OTULIN affect NF-κB-activity in Alzheimer’s disease (AD) patients, in turn driving anatomical defects such as shrinkage of entorhinal cortex and the limbic system in early AD. Similarly, E3 type ubiquitin ligase PARKIN is positively involved in NF-κB signaling. PARKIN loss of function mutations are most frequently observed in Parkinson’s disease patients. In contrast to AD, relying on germline mutations of week alleles and a disease development over decades, somatic mutations affecting NF-κB activation are commonly observed in cells derived from glioblastoma multiforme (GBM), the most common malignant primary brain tumor. Here, our present review particularly sheds light on the mutual exclusion of either the deletion of NFKBIA or amplification of epidermal growth factor receptor (EGFR) in GBM, both resulting in constitutive NF-κB-activity driving tumorigenesis. We also discuss emerging roles of long non-coding RNAs such as HOTAIR in suppressing phosphorylation of IκBα in the context of GBM. In summary, the recent progress in the genetic analysis of patients, particularly those suffering from AD, harbors the potential to open up new vistas for research and therapy based on TNFα/NF-κB pathway and neuroprotection.

Cell-specific aptamers as potential drugs in therapeutic applications: A review of current progress

Cell-specific aptamers are a promising emerging player in the field of disease therapy. This paper reviews the multidimensional research progress made in terms of their classification, modification, and application. Based on the target location of cell-specific aptamers, it is defined and classified cell-specific aptamers into three groups including aptamers for cell surface markers, aptamers for intracellular components, and aptamers for extracellular components. Moreover, the modification methods of aptamers to achieve improved stability and affinity are concluded. In addition, recent advances in the application of cell-specific aptamers are discussed, mainly focusing on the increasing research attraction of cell state improving helpers and cell recruitment mediators in the improvement of cellular microenvironments to achieve successful disease therapy. This review also highlights 11 types of clinical aptamer drugs. Finally, the challenges and future directions of potential clinical applications are presented. In summary, we believe that cell-specific aptamers are promising drugs in disease therapy.

Synthesis and functionalization of casein nanoparticles with aptamers for triple-negative breast cancer targeting

This work shows the synthesis of a drug delivery system made of casein nanoparticles able to host hydrophobic molecules and be functionalized with aptamers targeting the epidermal growth factor receptor.

Profiling Cancer Cells by Cell-SELEX: Use of Aptamers for Discovery of Actionable Biomarkers and Therapeutic Applications Thereof

The identification of tumor cell-specific surface markers is a key step towards personalized cancer medicine, allowing early assessment and accurate diagnosis, and development of efficacious targeted therapies. Despite significant efforts, currently the spectrum of cell membrane targets associated with approved treatments is still limited, causing an inability to treat a large number of cancers. What mainly limits the number of ideal clinical biomarkers is the high complexity and heterogeneity of several human cancers and still-limited methods for molecular profiling of specific cancer types. Thanks to the simplicity, versatility and effectiveness of its application, cell-SELEX (Systematic Evolution of Ligands by Exponential Enrichment) technology is a valid complement to the present strategies for biomarkers' discovery. We and other researchers worldwide are attempting to apply cell-SELEX to the generation of oligonucleotide aptamers as tools for both identifying new cancer biomarkers and targeting them by innovative therapeutic strategies. In this review, we discuss the potential of cell-SELEX for increasing the currently limited repertoire of actionable cancer cell-surface biomarkers and focus on the use of the selected aptamers as components of innovative conjugates and nano-formulations for cancer therapy.

Optimizing cisplatin delivery to triple-negative breast cancer through novel EGFR aptamer-conjugated polymeric nanovectors

BACKGROUND

Management of triple-negative breast cancer (TNBC) is still challenging because of its aggressive clinical behavior and limited targeted treatment options. Cisplatin represents a promising chemotherapeutic compound in neoadjuvant approaches and in the metastatic setting, but its use is limited by scarce bioavailability, severe systemic side effects and drug resistance. Novel site-directed aptamer-based nanotherapeutics have the potential to overcome obstacles of chemotherapy. In this study we investigated the tumor targeting and the anti-tumorigenic effectiveness of novel cisplatin-loaded and aptamer-decorated nanosystems in TNBC.

METHODS

Nanotechnological procedures were applied to entrap cisplatin at high efficacy into polymeric nanoparticles (PNPs) that were conjugated on their surface with the epidermal growth factor receptor (EGFR) selective and cell-internalizing CL4 aptamer to improve targeted therapy. Internalization into TNBC MDA-MB-231 and BT-549 cells of aptamer-decorated PNPs, loaded with BODIPY505-515, was monitored by confocal microscopy using EGFR-depleted cells as negative control. Tumor targeting and biodistribution was evaluated by fluorescence reflectance imaging upon intravenously injection of Cyanine7-labeled nanovectors in nude mice bearing subcutaneous MDA-MB-231 tumors. Cytotoxicity of cisplatin-loaded PNPs toward TNBC cells was evaluated by MTT assay and the antitumor effect was assessed by tumor growth experiments in vivo and ex vivo analyses.

RESULTS

We demonstrate specific, high and rapid uptake into EGFR-positive TNBC cells of CL4-conjugated fluorescent PNPs which, when loaded with cisplatin, resulted considerably more cytotoxic than the free drug and nanovectors either unconjugated or conjugated with a scrambled aptamer. Importantly, animal studies showed that the CL4-equipped PNPs achieve significantly higher tumor targeting efficiency and enhanced therapeutic effects, without any signs of systemic toxicity, compared with free cisplatin and untargeted PNPs.

CONCLUSIONS

Our study proposes novel and safe drug-loaded targeted nanosystems for EGFR-positive TNBC with excellent potential for the application in cancer diagnosis and therapy.

Assessing the capacity for mental manipulation in patients with statically-determined mild cognitive impairment using digital technology

Aims: Prior research employing a standard backward digit span test has been successful in operationally defining neurocognitive constructs associated with the Fuster’s model of executive attention. The current research sought to test if similar behavior could be obtained using a cross-modal mental manipulation test. Methods: Memory clinic patients were studied. Using Jak-Bondi criteria, 24 patients were classified with mild cognitive impairment (MCI), and 33 memory clinic patients did not meet criteria for MCI (i.e. non-MCI). All patients were assessed with the digital version of the WRAML-2 Symbolic Working Memory Test-Part 1, a cross-modal mental manipulation task where patients hear digits, but respond by touching digits from lowest to highest on an answer key. Only 4 and 5-span trials were analyzed. Using an iPad, all test stimuli were played; and, all responses were obtained with a touch key. Only correct trials were analyzed. Average time to complete trials and latency for each digit was recorded. Results: Groups did not differ when average time to complete 4-span trials was calculated. MCI patients displayed slower latency, or required more time to re-order the 1st and 3rd digits. Regression analyses, primarily involving initial and latter response latencies, were associated with better, but different underlying neuropsychological abilities. Almost no 5-span analyses were significant. Conclusions: This cross-modal test paradigm found no difference for total average time. MCI patients generated slower 1st and 3rd response latency, suggesting differences in time allocation to achieve correct serial order recall. Moreover, different neuropsychological abilities were associated with different time-based test components. These data extend prior findings using a standard backward digit span test. Differences in time epochs are consistent with constructs underlying the model of executive attention and help explain mental manipulation deficits in MCI. These latency measures could constitute neurocognitive biomarkers that track emergent disease.

Aptamers and antibodies: rivals or allies in cancer targeted therapy?

The goal of an efficacious cancer therapy is to specifically target diseased cells at high accuracy while sparing normal, healthy cells. Over the past three decades, immunotherapy, based on the use of monoclonal antibodies (mAbs) directed against tumor-associated antigens, to inhibit their oncogenic function, or against immune checkpoints, to modulate specific T cell responses against cancer, has proven to be an important strategy for cancer therapy. Nevertheless, the number of mAbs approved for clinical use is still limited because of significant drawbacks to their applicability. Oligonucleotide aptamers, similarly to antibodies, form high-affinity bonds with their specific protein targets, thus representing an effective tool for active cancer targeting. Compared to antibodies, aptamers’ use as therapeutic agents benefits from their low size, low/no immunogenicity, simple synthesis and design flexibility for improving efficacy and stability. This review intends to highlight recently emerged applications of aptamers as recognition elements, from biomarker discovery to targeted drug delivery and targeted treatment, showing aptamers’ potential to work in conjunction with antibodies for attacking cancer from multiple flanks.

Aptamer-Based In Vivo Therapeutic Targeting of Glioblastoma

Glioblastoma (GBM) is the most aggressive, infiltrative, and lethal brain tumor in humans. Despite the extensive advancement in the knowledge about tumor progression and treatment over the last few years, the prognosis of GBM is still very poor due to the difficulty of targeting drugs or anticancer molecules to GBM cells. The major challenge in improving GBM treatment implicates the development of a targeted drug delivery system, capable of crossing the blood–brain barrier (BBB) and specifically targeting GBM cells. Aptamers possess many characteristics that make them ideal novel therapeutic agents for the treatment of GBM. They are short single-stranded nucleic acids (RNA or ssDNA) able to bind to a molecular target with high affinity and specificity. Several GBM-targeting aptamers have been developed for imaging, tumor cell isolation from biopsies, and drug/anticancer molecule delivery to the tumor cells. Due to their properties (low immunogenicity, long stability, and toxicity), a large number of aptamers have been selected against GBM biomarkers and tested in GBM cell lines, while only a few of them have also been tested in in vivo models of GBM. Herein, we specifically focus on aptamers tested in GBM in vivo models that can be considered as new diagnostic and/or therapeutic tools for GBM patients’ treatment.

Aptamer targeted therapy potentiates immune checkpoint blockade in triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) is a uniquely aggressive cancer with high rates of relapse due to resistance to chemotherapy. TNBC expresses higher levels of programmed cell death-ligand 1 (PD-L1) compared to other breast cancers, providing the rationale for the recently approved immunotherapy with anti-PD-L1 monoclonal antibodies (mAbs). A huge effort is dedicated to identify actionable biomarkers allowing for combination therapies with immune-checkpoint blockade. Platelet-derived growth factor receptor β (PDGFRβ) is highly expressed in invasive TNBC, both on tumor cells and tumor microenvironment. We recently proved that tumor growth and lung metastases are impaired in mouse models of human TNBC by a high efficacious PDGFRβ aptamer. Hence, we aimed at investigating the effectiveness of a novel combination treatment with the PDGFRβ aptamer and anti-PD-L1 mAbs in TNBC.

METHODS

The targeting ability of the anti-human PDGFRβ aptamer toward the murine receptor was verified by streptavidin-biotin assays and confocal microscopy, and its inhibitory function by transwell migration assays. The anti-proliferative effects of the PDGFRβ aptamer/anti-PD-L1 mAbs combination was assessed in human MDA-MB-231 and murine 4 T1 TNBC cells, both grown as monolayer or co-cultured with lymphocytes. Tumor cell lysis and cytokines secretion by lymphocytes were analyzed by LDH quantification and ELISA, respectively. Orthotopic 4 T1 xenografts in syngeneic mice were used for dissecting the effect of aptamer/mAb combination on tumor growth, metastasis and lymphocytes infiltration. Ex vivo analyses through immunohistochemistry, RT-qPCR and immunoblotting were performed.

RESULTS

We show that the PDGFRβ aptamer potentiates the anti-proliferative activity of anti-PD-L1 mAbs on both human and murine TNBC cells, according to its human/mouse cross-reactivity. Further, by binding to activated human and mouse lymphocytes, the aptamer enhances the anti-PD-L1 mAb-induced cytotoxicity of lymphocytes against tumor cells. Importantly, the aptamer heightens the antibody efficacy in inhibiting tumor growth and lung metastases in mice. It acts on both tumor cells, inhibiting Akt and ERK1/2 signaling pathways, and immune populations, increasing intratumoral CD8 + T cells and reducing FOXP3 + Treg cells.

CONCLUSION

Co-treatment of PDGFRβ aptamer with anti-PD-L1 mAbs is a viable strategy, thus providing for the first time an evidence of the efficacy of PDGFRβ/PD-L1 co-targeting combination therapy in TNBC.

The Role of RNA and DNA Aptamers in Glioblastoma Diagnosis and Therapy: A Systematic Review of the Literature

Glioblastoma (GBM) is the most lethal primary brain tumor of the central nervous system in adults. Despite advances in surgical and medical neuro-oncology, the median survival is about 15 months. For this reason, initial diagnosis, prognosis, and targeted therapy of GBM represent very attractive areas of study. Aptamers are short three-dimensional structures of single-stranded nucleic acids (RNA or DNA), identified by an in vitro process, named systematic evolution of ligands by exponential enrichment (SELEX), starting from a partially random oligonucleotide library. They bind to a molecular target with high affinity and specificity and can be easily modified to optimize binding affinity and selectivity. Thanks to their properties (low immunogenicity and toxicity, long stability, and low production variability), a large number of aptamers have been selected against GBM biomarkers and provide specific imaging agents and therapeutics to improve the diagnosis and treatment of GBM. However, the use of aptamers in GBM diagnosis and treatment still represents an underdeveloped topic, mainly due to limited literature in the research world. On these bases, we performed a systematic review aimed at summarizing current knowledge on the new promising DNA and RNA aptamer-based molecules for GBM diagnosis and treatment. Thirty-eight studies from 2000 were included and investigated. Seventeen involved the use of aptamers for GBM diagnosis and 21 for GBM therapy. Our findings showed that a number of DNA and RNA aptamers are promising diagnostic and therapeutic tools for GBM management.

Novel Aptamers Selected on Living Cells for Specific Recognition of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a high heterogeneous group of tumors with a distinctly aggressive nature and high rates of relapse. So far, the lack of any known targetable proteins has not allowed a specific anti-tumor treatment. Therefore, the identification of novel agents for specific TNBC targeting and treatment is desperately needed. Here, by integrating cell-SELEX (Systematic Evolution of Ligands by EXponential enrichment) for the specific recognition of TNBC cells with high-throughput sequencing technology, we identified a panel of 2′-fluoropyrimidine-RNA aptamers binding to TNBC cells and their cisplatin- and doxorubicin-resistant derivatives at low nanomolar affinity. These aptamers distinguish TNBC cells from both non-malignant and non-TNBC breast cancer cells and are able to differentiate TNBC histological specimens. Importantly, they inhibit TNBC cell capacity of growing in vitro as mammospheres, indicating they could also act as anti-tumor agents. Therefore, our newly identified aptamers are a valuable tool for selectively dealing with TNBC.

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Six 2′FPy-RNA aptamers were obtained by TNBC Cell-SELEX/NGS

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They distinguish TNBC cells from non-malignant and non-TNBC breast cancer cells

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They differentiate TNBC histological specimens by aptamer-based staining

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They inhibit TNBC cell lines capacity of growing in vitro as mammospheres

Post-SELEX Optimization and Characterization of a Prostate Cancer Cell-Specific Aptamer for Diagnosis

The RNA aptamer A4 binds specifically to tumor prostate cells. A4 was modified (mA4) by adding deoxyribonucleotides to its ends to remove the reactive 2' hydroxyl groups of RNA's sugar at the ends of the aptamer and to make it more stable to widespread RNase contamination in laboratories. Thus, mA4 would be more suitable to use in the clinical settings of prostate cancer (PCa). We aimed to characterize this optimized oligonucleotide to verify its potential as a diagnostic tool. The sequences and structures of A4 and mA4 were compared through in silico approaches to corroborate their similarity. Then, the degradation of mA4 was measured in appropriate media and human plasma for in vitro tests. In addition, the binding abilities of A4 to prostate cells were contrasted with those of mA4. The effects of mA4 were assessed on the viability, proliferation, and migration of human prostate cell lines RWPE-1 and PC-3 in three-dimensional (3D) cell cultures. mA4 showed configurational motifs similar to those of A4, displayed a half-life in plasma substantially higher than A4, and exhibited a comparable binding capacity to that of A4 and unaltered viability, proliferation, and migration of prostatic cells. Therefore, mA4 maintains the crucial 3D structures of A4 that would allow binding to its target, as suggested by in silico and binding analyses. mA4 may be a good PCa reporter as it does not change cellular parameters of prostate cells when incubated with it. Its additional deoxyribonucleotides make mA4 inherently more chemically stable than A4, avoiding its degradation and favoring its storage and handling for clinical applications. These characteristics support the potential of mA4 to be used in diagnostic systems for PCa.

Ipilimumab and Its Derived EGFR Aptamer-Based Conjugate Induce Efficient NK Cell Activation against Cancer Cells

The immune checkpoint CTLA-4 (cytotoxic T-lymphocyte-antigen 4), which inhibits the co-stimulatory CD28 signal on T cells, has been recently found expressed on other cell populations, such as tumor and natural killer (NK) cells. We tested for the first time the effects of ipilimumab, the human anti-CTLA4 mAb in clinical use, on these cells and found that it inhibits the growth of tumor cells expressing CTLA-4 also in the absence of lymphocytes, and efficiently activates NK cells, thus suggesting an important unexplored role of NK cells in ipilimumab-modulated immune responses. Interestingly, the epidermal growth factor receptor (EGFR) has been shown to play a key role in tumor cell escape from immune surveillance, and in cytotoxic T lymphocyte inhibition. Thus, we tested combinatorial treatments of ipilimumab with an anti-EGFR aptamer endowed with anti-tumor activity, and constructed for the first time a novel bispecific immunoconjugate, made up of these two compounds. The novel immunoconjugate binds to the target cells, induces the activation of lymphocytes, including NK cells, and inhibits the growth of tumor target cells more efficiently than the parental compounds, by strongly enhancing the cytotoxic activity of both human peripheral blood mononuclear cells and NK cells against tumor cells.

Pyrene-Modified DNA Aptamers with High Affinity to Wild-Type EGFR and EGFRvIII

Nucleic acid aptamers have been proven to be a useful tool in many applications. Particularly, aptamers to epidermal growth factor receptor (EGFR) have been successfully used for the recognition of EGFR-expressing cells, the inhibition of EGFR-dependent pathways, and targeted drug delivery into EGFR-positive cells. Several aptamers are able to discriminate wild-type EGFR from its mutant form, EGFRvIII. Aptamers to EGFR have hairpin-like secondary structures with several possible folding variations. Here, an aptamer, previously selected to EGFRvIII, was chosen as a lead compound for extensive post-SELEX maturation. The aptamer was 1.5-fold truncated, the ends of the hairpin stem were appended with GC-pairs to increase thermal stability, and single pyrene modification was introduced into the aptamer to increase affinity to the target protein. Pyrene modification was selected from extensive computer docking studies of a library of thousands of chemicals to EGFR near the EGF-binding interface. The resulting aptamers bound extracellular domains of both variants of EGFR: EGFRwt and EGFRvIII with subnanomolar apparent dissociation constants. Compared with the initial aptamer, affinity to EGFRwt was increased up to 7.5-fold, whereas affinity to EGFRvIII was increased up to 4-fold.

Novel Human Bispecific Aptamer-Antibody Conjugates for Efficient Cancer Cell Killing

Monoclonal antibodies have been approved by the Food and Drug Administration for the treatment of various human cancers. More recently, oligonucleotide aptamers have risen increasing attention for cancer therapy thanks to their low size (efficient tumor penetration) and lack of immunogenicity, even though the short half-life and lack of effector functions still hinder their clinical applications. Here, we demonstrate, for the first time, that two novel bispecific conjugates, consisting of an anti-epidermal growth factor receptor (EGFR) aptamer linked either with an anti-epidermal growth factor receptor 2 (ErbB2) compact antibody or with an immunomodulatory (anti-PD-L1) antibody, were easily and rapidly obtained. These novel aptamer-antibody conjugates retain the targeting ability of both the parental moieties and acquire a more potent cancer cell killing activity by combining their inhibitory properties. Furthermore, the conjugation of the anti-EGFR aptamer with the immunomodulatory antibody allowed for the efficient redirection and activation of T cells against cancer cells, thus dramatically enhancing the cytotoxicity of the two conjugated partners. We think that these bispecific antibody-aptamer conjugates could have optimal biological features for therapeutic applications, such as increased specificity for tumor cells expressing both targets and improved pharmacokinetic and pharmacodynamic properties due to the combined advantages of the aptamer and antibody.

Targeted and effective glioblastoma therapy via aptamer-modified tetrahedral framework nucleic acid-paclitaxel nanoconjugates that can pass the blood brain barrier

Targeted DNA nanoparticles have been identified as one of the most promising nanocarriers in anti-glioma drug delivery. We established a multifunctional nanosystem for targeted glioma therapy. Tetrahedral framework nucleic acid (tFNA), entering U87MG cells and bEnd.3 cells, was chosen to deliver two aptamers, GMT8 and Gint4.T, and paclitaxel. GMT8 and Gint4.T, which specifically bind with U87MG cells and with PDGFRβ, were linked with tFNA, to form Gint4.T-tFNA-GMT8 (GTG). GTG was efficiently internalized by U87MG and bEnd.3 cells and penetrated an in-vitro blood-brain-barrier model. GTG loaded with paclitaxel (GPC) had potentiated anti-glioma efficacy. It inhibited the proliferation, migration, and invasion of U87MG cells, and enhanced apoptosis induction in these cells. The expression of apoptosis-related proteins was significantly changed after treatment with GPC, confirming apoptosis induction. Our study demonstrated that the combination of GTG and paclitaxel has great potential for glioma treatment and tFNA shows great promise for use in drug delivery.

Proneural-Mesenchymal Transition: Phenotypic Plasticity to Acquire Multitherapy Resistance in Glioblastoma

Glioblastoma (GBM) is an extremely aggressive tumor of the central nervous system, with a prognosis of 12–15 months and just 3–5% of survival over 5 years. This is mainly because most patients suffer recurrence after treatment that currently consists in maximal resection followed by radio- and chemotherapy with temozolomide. The recurrent tumor shows a more aggressive behavior due to a phenotypic shift toward the mesenchymal subtype. Proneural-mesenchymal transition (PMT) may represent for GBM the equivalent of epithelial–mesenchymal transition associated with other aggressive cancers. In this review we frame this process in the high degree of phenotypic inter- and intra-tumor heterogeneity of GBM, which exists in different subtypes, each one characterized by further phenotypic variability in its stem-cell compartment. Under the selective pressure of different treatment agents PMT is induced. The mechanisms involved, as well as the significance of such event in the acquisition of a multitherapy resistance phenotype, are taken in consideration for future perspectives in new anti-GBM therapeutic options.

The protean world of non-coding RNAs in glioblastoma

Non-coding ribonucleic acids (ncRNAs) are a diverse group of RNA molecules that are mostly not translated into proteins following transcription. We review the role of ncRNAs in the pathobiology of glioblastoma (GBM), and their potential applications for GBM therapy. Significant advances in our understanding of the protean manifestations of ncRNAs have been made, allowing us to better decipher the molecular complexity of GBM. A large number of regulatory ncRNAs appear to have a greater influence on the molecular pathology of GBM than thought previously. Importantly, also, a range of therapeutic approaches are emerging whereby ncRNA-based systems may be used to molecularly target GBM. The most successful of these is RNA interference, and some of these strategies are being evaluated in ongoing clinical trials. However, a number of limitations exist in the clinical translation of ncRNA-based therapeutic systems, such as delivery mechanisms and cytotoxicity; concerted research endeavors are currently underway in an attempt to overcome these. Ongoing and future studies will determine the potential practical role for ncRNA-based therapeutic systems in the clinical management of GBM. These applications may be especially promising, given that current treatment options are limited and prognosis remains poor for this challenging malignancy.

TNBC Challenge: Oligonucleotide Aptamers for New Imaging and Therapy Modalities

Compared to other breast cancers, triple-negative breast cancer (TNBC) usually affects younger patients, is larger in size, of higher grade and is biologically more aggressive. To date, conventional cytotoxic chemotherapy remains the only available treatment for TNBC because it lacks expression of the estrogen receptor (ER), progesterone receptor (PR) and epidermal growth factor receptor 2 (HER2), and no alternative targetable molecules have been identified so far. The high biological and clinical heterogeneity adds a further challenge to TNBC management and requires the identification of new biomarkers to improve detection by imaging, thus allowing the specific treatment of each individual TNBC subtype. The Systematic Evolution of Ligands by EXponential enrichment (SELEX) technique holds great promise to the search for novel targetable biomarkers, and aptamer-based molecular approaches have the potential to overcome obstacles of current imaging and therapy modalities. In this review, we highlight recent advances in oligonucleotide aptamers used as imaging and/or therapeutic agents in TNBC, discussing the potential options to discover, image and hit new actionable targets in TNBC.

Targeted imaging and inhibition of triple-negative breast cancer metastases by a PDGFRβ aptamer

While the overall mortality for breast cancer has recently declined, management of triple-negative breast cancer (TNBC) is still challenging because of its aggressive clinical behavior and the lack of targeted therapies. Genomic profiling studies highlighted the high level of heterogeneity of this cancer, which comprises different subtypes with unique phenotypes and response to treatment. Platelet-derived growth factor receptor β (PDGFRβ) is an established mesenchymal/stem cell-specific marker in human glioblastoma and, as recently suggested, it may uniquely mark breast cancer cells with stem-like characteristics and/or that have undergone epithelial-mesenchymal transition.

Methods: Immunohistochemical analysis for PDGFRβ expression was performed on a human TNBC tissue microarray. Functional assays were conducted on mesenchymal-like TNBC cells to investigate the effect of a previously validated PDGFRβ aptamer on invasive cell growth in three-dimensional culture conditions, migration, invasion and tube formation. The aptamer was labeled with a near-infrared (NIR) dye and its binding specificity to PDGFRβ was assessed both in vitro (confocal microscopy and flow cytometry analyses) and in vivo (fluorescence molecular tomography in mice bearing TNBC xenografts). A mouse model of TNBC lung metastases formation was established and NIR-labeled PDGFRβ aptamer was used to detect lung metastases in mice untreated or intravenously injected with unlabeled aptamer.

Results: Here, we present novel data showing that tumor cell expression of PDGFRβ identifies a subgroup of mesenchymal tumors with invasive and stem-like phenotype, and propose a previously unappreciated role for PDGFRβ in driving TNBC cell invasiveness and metastases formation. We show that the PDGFRβ aptamer blocked invasive growth and migration/invasion of mesenchymal TNBC cell lines and prevented TNBC lung metastases formation. Further, upon NIR-labeling, the aptamer specifically bound to TNBC xenografts and detected lung metastases.

Conclusions: We propose PDGFRβ as a reliable biomarker of a subgroup of mesenchymal TNBCs with invasive and stem-like phenotype as well as the use of the PDGFRβ aptamer as a high efficacious tool for imaging and suppression of TNBC lung metastases. This study will allow for the significant expansion of the current repertoire of strategies for managing patients with more aggressive TNBC.

Oligonucleotide aptamers against tyrosine kinase receptors: Prospect for anticancer applications

Transmembrane receptor tyrosine kinases (RTKs) play crucial roles in cancer cell proliferation, survival, migration and differentiation. Area of intense research is searching for effective anticancer therapies targeting these receptors and, to date, several monoclonal antibodies and small-molecule tyrosine kinase inhibitors have entered the clinic. However, some of these drugs show limited efficacy and give rise to acquired resistance. Emerging highly selective compounds for anticancer therapy are oligonucleotide aptamers that interact with their targets by recognizing a specific three-dimensional structure. Because of their nucleic acid nature, the rational design of advanced strategies to manipulate aptamers for both diagnostic and therapeutic applications is greatly simplified over antibodies. In this manuscript, we will provide a comprehensive overview of oligonucleotide aptamers as next generation strategies to efficiently target RTKs in human cancers.

Effects of Aptamer to U87-EGFRvIII Cells on the Proliferation, Radiosensitivity, and Radiotherapy of Glioblastoma Cells

Glioblastoma multiforme (GBM) is the most prevalent and lethal malignant intracranial tumor in the brain, with very poor prognosis and survival. The epidermal growth factor receptor variant III (EGFRvIII) contributes to increased oncogenicity that does not occur through binding EGFR ligands and instead occurs through constitutive activation, which enhances glioma tumorigenicity and resistance to targeted therapy. Aptamers are nucleic acids with high affinity and specificity to targets selected by systematic evolution of ligands by exponential enrichment (SELEX), and are usually developed as antagonists of disease-associated factors. Herein, we generated a DNA aptamer U2, targeting U87-EGFRvIII cells, and demonstrated that U2 alters the U87-EGFRvIII cell growth, radiosensitivity, and radiotherapy of glioblastoma cells. We detected U2 and U87-EGFRvIII cells by flow cytometry and confocal microscopy to explore the binding ability of U2 to U87-EGFRvIII cells. Then, we found that aptamer U2 inhibits the proliferation, migration, invasion, and downstream signaling of U87-EGFRvIII cells. Moreover, the U2 aptamer can increase the radiosensitivity of U87-EGFRvIII in vitro and has a better antitumor effect on 188Re-U2 in vivo. Therefore, the results revealed the promising potential of the U2 aptamer to be a new type of drug candidate and aptamer-targeted drug delivery system for glioblastoma therapy.

CD109 is identified as a potential nasopharyngeal carcinoma biomarker using aptamer selected by cell-SELEX

Nasopharyngeal carcinoma (NPC) is one of the most prevailing cancers in southern China and southern Asia. Because of the nonspecific symptoms and lack of effective biomarker, most patients are diagnosed at advanced stages, resulting in poor 5-year survival rate. To identify a novel NPC biomarker facilitating early detection and effective therapy of NPC, a two-step strategy consisting of cancer cell-Systematic Evolution of Ligands by EXponential enrichment (cell-SELEX) procedure and aptamer-based purification approach was developed. Using cell-SELEX procedure, four aptamers (S3, S5, S12 and S27) differentiating the molecular differences between NPC cells and NP cells were successfully screened. Then, using aptamer-based protein purification, membrane protein CD109 was identified as the target of aptamer S3. CD109 protein was further identified to be over-expressed in NPC cell lines and clinic tissues, but not or low in NP cell line and clinic NP tissues, detected by western blot and immunohistochemistry experiments. Our study demonstrated that CD109 identified by cell-SELEX and aptamer-based purification strategy might be used as a potential NPC biomarker for early diagnosis and targeted therapy.

Aptamers and Glioblastoma: Their Potential Use for Imaging and Therapeutic Applications

Glioblastoma is a highly aggressive primary brain tumour, renowned for its infiltrative growth and varied genetic profiles. The current treatment options are insufficient, and their off-target effects greatly reduce patient quality of life. The major challenge in improving glioblastoma diagnosis and treatment involves the development of a targeted imaging and drug delivery platform, capable of circumventing the blood brain barrier and specifically targeting glioblastoma tumours. The unique properties of aptamers demonstrate their capability of bridging the gap to the development of successful diagnosis and treatment options, where antibodies have previously failed. Aptamers possess many characteristics that make them an ideal novel imaging and therapeutic agent for the treatment of glioblastoma and other brain malignancies, and are likely to provide patients with a better standard of care and improved quality of life. Their target sensitivity, selective nature, ease of modification and low immunogenicity make them an ideal drug-delivery platform. This review article summarises the aptamers previously generated against glioblastoma cells or its identified biomarkers, and their potential application in diagnosis and therapeutic targeting of glioblastoma tumours.

Emerging cancer-specific therapeutic aptamers

PURPOSE OF REVIEW

We will describe recently discovered smart aptamers with tumor specificity, with an emphasis on targeted delivery of novel therapeutic molecules, cancer-specific biomarkers, and immunotherapy.

RECENT FINDINGS

The development of cancer-specific aptamers has facilitated targeted delivery of potent therapeutic molecules to cancer cells without harming nontumoral cells. This specificity also makes it possible to discover novel cancer biomarkers. Furthermore, alternative immune-checkpoint blockade aptamers have been developed for combinational immunotherapy.

SUMMARY

Aptamers selected against cancer cells show cancer specificity, which has great potential for targeting. First, functionalizing targeted aptamers with therapeutic molecule payloads (e.g., small activating RNAs, antimitotic drugs, therapeutic antibodies, and peptides) facilitates successful delivery into cancer cells. This approach greatly improves the therapeutic index by minimizing side-effects in nontumoral cells. Second, cancer-specific proteins have been identified as cancer biomarkers through in-vitro and in-vivo selection, aptamer pull-down assays, and mass spectrometry. These newly discovered biomarkers improve therapeutic intervention and diagnostic specificity. In addition, the development of alternative immune-checkpoint blockade aptamers is suggested for use in combinational immunotherapeutic with current immune blockade regimens, to reduce the resistance and exhaustion of T cells in clinical trials. VIDEO ABSTRACT: http://links.lww.com/COON/A21.

Inhibition of Bone Marrow-Derived Mesenchymal Stem Cells Homing Towards Triple-Negative Breast Cancer Microenvironment Using an Anti-PDGFRβ Aptamer

Bone marrow-derived mesenchymal stem cells (BM-MSCs) are shown to participate in tumor progression by establishing a favorable tumor microenvironment (TME) that promote metastasis through a cytokine networks. However, the mechanism of homing and recruitment of BM-MSCs into tumors and their potential role in malignant tissue progression is poorly understood and controversial. Here we show that BM-MSCs increase aggressiveness of triple-negative breast cancer (TNBC) cell lines evaluated as capability to migrate, invade and acquire stemness markers. Importantly, we demonstrate that the treatment of BM-MSCs with a nuclease-resistant RNA aptamer against platelet-derived growth factor receptor β (PDGFRβ) causes the inhibition of receptor-dependent signaling pathways thus drastically hampering BM-MSC recruitment towards TNBC cell lines and BM-MSCs trans-differentiation into carcinoma-associated fibroblast (CAF)-like cells. Moreover, in vivo molecular imaging analysis demonstrated the aptamer ability to prevent BM-MSCs homing to TNBC xenografts. Collectively, our results indicate the anti-PDGFRβ aptamer as a novel therapeutic tool to interfere with BM-MSCs attraction to TNBC providing the rationale to further explore the aptamer in more complex pre-clinical settings.

EGFR/EGFRvIII Dual-Targeting Peptide-Mediated Drug Delivery for Enhanced Glioma Therapy

Tumor-homing peptides have been widely used to mediate active targeted drug delivery. l-AE is a reported targeting peptide demonstrating high binding affinity to epidermal growth factor receptor (EGFR) and mutation variant III (EGFRvIII) overexpressed on neovasculature, vasculogenic mimicry, tumor cells, and tumor stem cells. To improve its proteolytic stability, a d-peptide ligand (termed d-AE, the enantiomer of l-AE) was developed. d-AE was confirmed to bind receptors EGFR and EGFRvIII with targeting capability comparable to l-AE. In vivo biodistribution demonstrated the superiority of d-AE in prolonged circulation and enhanced intratumoral accumulation. Furthermore, stabilized peptide modification endowed micelles higher transcytosis efficiency and penetrating capability on blood-brain tumor barrier/U87 tumor spheroids coculture model. When paclitaxel (PTX) was loaded, d-AE-micelle/PTX demonstrated excellent antitumor effect in comparison to Taxol, micelle/PTX, and l-AE-micelle/PTX. These findings indicated that the multitargeted drug delivery system enabled by d-AE ligand provides a promising way for glioma therapy.

Selection of Nucleic Acid Aptamers Targeting Tumor Cell-Surface Protein Biomarkers

Aptamers are nucleic acids referred to as chemical antibodies as they bind to their specific targets with high affinity and selectivity. They are selected via an iterative process known as ‘selective evolution of ligands by exponential enrichment’ (SELEX). Aptamers have been developed against numerous cancer targets and among them, many tumor cell-membrane protein biomarkers. The identification of aptamers targeting cell-surface proteins has mainly been performed by two different strategies: protein- and cell-based SELEX, when the targets used for selection were proteins and cells, respectively. This review aims to update the literature on aptamers targeting tumor cell surface protein biomarkers, highlighting potentials, pitfalls of protein- and cell-based selection processes and applications of such selected molecules. Aptamers as promising agents for diagnosis and therapeutic approaches in oncology are documented, as well as aptamers in clinical development.

Aptamer Functionalization of Nanosystems for Glioblastoma Targeting through the Blood-Brain Barrier

Polymeric nanoparticles (PNPs) may efficiently deliver in vivo therapeutics to tumors when conjugated to specific targeting agents. Gint4.T aptamer specifically recognizes platelet-derived growth factor receptor β and can cross the blood-brain barrier (BBB). We synthesized Gint4.T-conjugated PNPs able of high uptake into U87MG glioblastoma (GBM) cells and with astonishing EC₅₀ value (38 pM) when loaded with a PI3K-mTOR inhibitor. We also demonstrated in vivo BBB passage and tumor accumulation in a GBM orthotopic model.

Aptamer-mediated impairment of EGFR-integrin αvβ3 complex inhibits vasculogenic mimicry and growth of triple-negative breast cancers

Current treatment options for triple-negative breast cancers (TNBCs) is limited by the absence of well-defined biomarkers, excluding a targeted therapy. Notably, epidermal growth factor receptor (EGFR) is overexpressed in a great proportion of TNBCs and is a negative prognostic factor. In clinical trials, however, existing EGFR inhibitors showed disappointing outcome. Oligonucleotide aptamers are a valid alternative to antibodies for diagnostic and therapeutic uses. Here, we prove that, when applied to aggressive TNBC cell lines with unique stem-like plasticity, the anti-EGFR CL4 aptamer, but not erlotinib or cetuximab, prevents the vasculogenic mimicry (VM) capability of the cells and destroys previously formed channels in three-dimensional culture. Notably, we found that CL4 impairs the matrix-induced integrin αvβ3 interaction with EGFR and integrin αvβ3-dependent cell adhesion. Consistently, the aptamer strongly inhibits VM and tumor growth in a xenograft TNBC model. These data suggest that in TNBC cells, EGFR may cooperate with integrin αvβ3 to regulate integrin binding to extracellular ligands required for VM, and EGFR-targeting by CL4 aptamer may counteract this event. Overall, we demonstrate a novel mechanism of action for CL4 related with integrin αvβ3-EGFR interaction, that may help to develop new oligonucleotide-based strategy addressing unmet need for TNBCs therapy.

Combination of a STAT3 Inhibitor and an mTOR Inhibitor Against a Temozolomide-resistant Glioblastoma Cell Line

BACKGROUND

Temozolomide-resistant (TMZ-R) glioblastoma is very difficult to treat, and a novel approach to overcome resistance is needed.

MATERIALS AND METHODS

The efficacy of a combination treatment of STAT3 inhibitor, STX-0119, with rapamycin was investigated against our established TMZ-resistant U87 cell line.

RESULTS

The growth-inhibitory effect of the combination treatment was significant against the TMZ-R U87 cell line (IC₅₀: 78 μM for STX-0119, 30.5 μM for rapamycin and 11.3 μM for combination of the two). Western blotting analysis demonstrated that the inhibitory effect of STX-0119 on S6 and 4E-BP1 activation through regulation of YKL-40 expression occurred in addition to the inhibitory effect of rapamycin against the mTOR pathway.

CONCLUSION

These results suggest that the STAT3 pathway is associated with the mTOR downstream pathway mediated by YKL-40 protein, and the combination therapy of the STAT3 inhibitor and rapamycin could be worth developing as a novel therapeutic approach against TMZ-resistant relapsed gliomas.

F25P preproinsulin abrogates the secretion of pro-growth factors from EGFRvIII cells and suppresses tumor growth in an EGFRvIII/wt heterogenic model

Extensive heterogeneity is a defining hallmark of glioblastoma multiforme (GBM) at the cellular and molecular levels. EGFRvIII, the most common EGFR mutant, is expressed in 24-67% of cases and strongly indicates a poor survival prognosis. By co-expressing EGFRvIII and EGFRwt, we established an EGFRvIII/wt heterogenic model. Using this approach, we confirmed that a mixture of EGFRvIII and EGFRwt at a certain ratio could clearly enhance tumor growth in vitro and in vivo compared with EGFRwt cells, thereby indicating that EGFRvIII cells promote tumor growth. Furthermore, we demonstrated that the EGFRvIII cells could support the growth of EGFRwt cells by secreting growth factors, thus acting as the principal source for maintaining tumor survival. F25P preproinsulin effectively reduced the concentrations of EGF, VEGF, and MMP-9 in the blood of tumor-bearing mice by competitively inhibiting the endoplasmic reticulum signal peptidase and increased the overall survival in orthotopic models. Taken together, our results provided an effective therapy of F25P preproinsulin in the EGFRvIII/wt heterogenic model.

Aptamers: A promising chemical antibody for cancer therapy

Aptamers, also known as chemical antibodies, are single-stranded nucleic acid oligonucleotides which bind to their targets with high specificity and affinity. They are typically selected by repetitive in vitro process termed systematic evolution of ligands by exponential enrichment (SELEX). Owing to their excellent properties compared to conventional antibodies, notably their smaller physical size and lower immunogenicity and toxicity, aptamers have recently emerged as a new class of agents to deliver therapeutic drugs to cancer cells by targeting specific cancer-associated hallmarks. Aptamers can also be structurally modified to make them more flexible in order to conjugate other agents such as nano-materials and therapeutic RNA agents, thus extending their applications for cancer therapy. This review presents the current knowledge on the practical applications of aptamers in the treatment of a variety of cancers.