Advances in aptamer-based drug delivery vehicles for cancer therapy

Aptamer-functionalized triptolide with release controllability as a promising targeted therapy against triple-negative breast cancer

Targeted delivery and precise release of toxins is a prospective strategy for the treatment of triple-negative breast cancer (TNBC), yet the flexibility to incorporate both properties simultaneously remains tremendously challenging in the X-drug conjugate fields. As critical components in conjugates, linkers could flourish in achieving optimal functionalities. Here, we pioneered a pH-hypersensitive tumor-targeting aptamer AS1411-triptolide conjugate (AS-TP) to achieve smart release of the toxin and targeted therapy against TNBC. The multifunctional acetal ester linker in the AS-TP site-specifically blocked triptolide toxicity, quantitatively sustained aptamer targeting, and ensured the circulating stability. Furthermore, the aptamer modification endowed triptolide with favorable water solubility and bioavailability and facilitated endocytosis of conjugated triptolide by TNBC cells in a nucleolin-dependent manner. The integrated superiorities of AS-TP promoted the preferential intra-tumor triptolide accumulation in xenografted TNBC mice and triggered the in-situ triptolide release in the weakly acidic tumor microenvironment, manifesting striking anti-TNBC efficacy and virtually eliminated toxic effects beyond clinical drugs. This study illustrated the therapeutic potential of AS-TP against TNBC and proposed a promising concept for the development of nucleic acid-based targeted anticancer drugs.

Diselenide-Bridged Mesoporous Silica-Based Nanoplatform with a Triple ROS-Scavenging Effect for Intracerebral Hemorrhage Treatment

Oxidative stress (OS) is a major mediator of secondary brain injury following intracerebral hemorrhage (ICH). Thus, antioxidant therapy is emerging as an attractive strategy to combat ICH. To achieve both reactive oxygen species (ROS) scavenging ability and on-demand drug release ability, we constructed a novel polydopamine (PDA)-coated diselenide-bridged mesoporous silica nanoparticle (DSeMSN) drug delivery system (PDA-DSeMSN). Edaravone (Eda) was blocked in the pores of DSeMSN by covering the pores with PDA as a gatekeeper. The drug maintained nearly "zero release" before reaching the lesion site, while in the ROS-enriched circumstances, the PDA shell went through degradation and the doped diselenide bonds broke up, triggering the disintegration of nanoparticles and leading to Eda release. Interestingly, the ROS-degradable property of the PDA shell and diselenide bond endowed the system with enhanced ROS-eliminating capacity. The synergistic effect of ROS-responsive drug delivery and ROS-scavenging PDA-DSeMSN showed efficient antioxidative and mitochondria protective performance without apparent toxicity in vitro. Importantly, PDA-DSeMSN@Eda through intravenous administration specifically accumulated in perihematomal sites and demonstrated robust neuroprotection in an ICH mouse model through antioxidative and antiapoptotic effects with high biological safety. Thus, the PDA-DSeMSN platform holds tremendous potential as an excellent carrier for on-demand delivery of drugs and provides a new and effective strategy for the clinical treatment of ICH.

Antidote-controlled DNA aptamer modulates human factor IXa activity

Thrombosis leads to elevated mortality rates and substantial medical expenses worldwide. Human factor IXa (HFIXa) protease is pivotal in tissue factor (TF)-mediated thrombin generation, and represents a promising target for anticoagulant therapy. We herein isolated novel DNA aptamers that specifically bind to HFIXa through systematic evolution of ligands by exponential enrichment (SELEX) method. We identified two distinct aptamers, seq 5 and seq 11, which demonstrated high binding affinity to HFIXa (Kd = 74.07 ± 2.53 nM, and 4.93 ± 0.15 nM, respectively). Computer software was used for conformational simulation and kinetic analysis of DNA aptamers and HFIXa binding. These aptamers dose-dependently prolonged activated partial thromboplastin time (aPTT) in plasma. We further rationally optimized the aptamers by truncation and site-directed mutation, and generated the truncated forms (Seq 5-1t, Seq 11-1t) and truncated-mutated forms (Seq 5-2tm, Seq 11-2tm). They also showed good anticoagulant effects. The rationally and structurally designed antidotes (seq 5-2b and seq 11-2b) were competitively bound to the DNA aptamers and effectively reversed the anticoagulant effect. This strategy provides DNA aptamer drug-antidote pair with effective anticoagulation and rapid reversal, developing advanced therapies by safe, regulatable aptamer drug-antidote pair.

TfR Aptamer-Functionalized MSNs for Enhancing Targeted Cellular Uptake and Therapy of Cancer Cells

Mesoporous silica nanoparticles (MSNs), as novel nanocarriers for drug delivery in cancer treatment, have attracted widespread concern because of their rich pore structure, large pore capacity, ease of modification, and biocompatibility. However, the limitation of nontargeting and low uptake efficiency hindered their further application. Considering the overexpression of the transferrin receptor (TfR) on most cancer cell membranes, herein, we propose a strategy to effectively enhance the cellular internalization of MSNs by arming them with the TfR aptamer. Cellular fluorescent imaging and flow cytometry analysis demonstrated that TfR aptamer-functionalized MSNs exhibited superior cellular internalization compared to unmodified or random sequence-modified MSNs toward three different cancer cell lines, including MCF-7, HeLa, and A549. Furthermore, TfR aptamer-functionalized MSNs displayed enhanced drug delivery efficiency compared with MSNs at equivalent doses and incubation times. These results suggested that TfR aptamer-functionalized MSNs have the potential for enhanced delivery of therapeutic agents into TfR-positive cancer cells to improve therapeutic efficacy.

Editorial to the IJMS Special Issue "Aptamer-Mediated Cancer Theranostics"

Aptamers have emerged as a new generation of bioaffinity probes with enhanced target binding specificity and selectivity [...].

Advances in aptamer-mediated targeted delivery system for cancer treatment

Aptamers with high affinity and specificity for certain targets have rapidly become a novel class of targeted ligands applicated in drug delivery. Based on the excellent characteristics of aptamers, different aptamer-mediated drug delivery systems have been developed, including aptamer-drug conjugate (ApDC), aptamer-siRNA, and aptamer-functionalized nanoparticle systems for the effective treatment of cancer, which can reduce potential toxicity and improve therapeutic efficacy. In this review, we summarize the recent progress of aptamer-mediated delivery systems in cancer therapy, and discuss the application prospects and existing problems of innovative approaches based on aptamer therapy. Overall, this review aims to better understand the current aptamer-based targeted delivery applications through in-depth analysis to improve efficacy and develop new therapeutic methods which can ultimately improve treatment outcomes for cancer patients.

Recent advances in aptamer-based therapeutic strategies for targeting cancer stem cells

Cancer stem cells (CSCs) are believed to be the main cause of chemotherapy resistance and tumor relapse. Various therapeutic strategies to eliminate CSCs have been developed recently. Aptamers, also called "chemical antibodies", can specifically bind with their molecular targets through special tertiary structures. The advantages of aptamers, such as lower immunogenicity and smaller size, make them superior to conventional antibodies. Therefore, aptamers have been used widely as targeting ligands for CSC-targeted therapeutic strategies in different tumor types. To date, various therapeutic cargoes have been conjugated to aptamers to kill CSCs, such as chemotherapy drugs, small interfering RNAs, and microRNAs. Aptamer-based targeted therapies for CSCs have made great progress in recent years, especially the development of multifunctional aptamer-based therapeutic strategies. Besides, cell-systematic evolution of ligands by exponential enrichment has been applied to screen new aptamers that might have a higher binding ability for CSCs. In this review, we focus on recent advances and introduce some new modalities of aptamer-drug conjugates against CSCs. Some considerations of the advantages and limitations of different aptamer-based targeted therapies for CSCs are also discussed.

Nanostructures as Photothermal Agents in Tumor Treatment

Traditional methods of tumor treatment such as surgical resection, chemotherapy, and radiation therapy have certain limitations, and their treatment effects are not always satisfactory. As a new tumor treatment method, photothermal therapy based on nanostructures has attracted the attention of researchers due to its characteristics of minimally invasive, low side effects, and inhibition of cancer metastasis. In recent years, there has been a variety of inorganic or organic nanostructures used in the field of photothermal tumor treatment, and they have shown great application prospects. In this paper, the advantages and disadvantages of a variety of nanomaterials/nanostructures as photothermal agents (PTAs) for photothermal therapy as well as their research progress are reviewed. For the sake of clarity, the recently reported nanomaterials/nanostructures for photothermal therapy of tumor are classified into five main categories, i.e., carbon nanostructures, noble metal nanostructures, transition metal sulfides, organic polymer, and other nanostructures. In addition, future perspectives or challenges in the related field are discussed.