Mini-review: nucleus-targeted ribonucleases as antitumor drugs

Functional Materials for Subcellular Targeting Strategies in Cancer Therapy: Progress and Prospects

Neoadjuvant and adjuvant therapies have made significant progress in cancer treatment. However, tumor adjuvant therapy still faces challenges due to the intrinsic heterogeneity of cancer, genomic instability, and the formation of an immunosuppressive tumor microenvironment. Functional materials possess unique biological properties such as long circulation times, tumor-specific targeting, and immunomodulation. The combination of functional materials with natural substances and nanotechnology has led to the development of smart biomaterials with multiple functions, high biocompatibilities, and negligible immunogenicities, which can be used for precise cancer treatment. Recently, subcellular structure-targeting functional materials have received particular attention in various biomedical applications including the diagnosis, sensing, and imaging of tumors and drug delivery. Subcellular organelle-targeting materials can precisely accumulate therapeutic agents in organelles, considerably reduce the threshold dosages of therapeutic agents, and minimize drug-related side effects. This review provides a systematic and comprehensive overview of the research progress in subcellular organelle-targeted cancer therapy based on functional nanomaterials. Moreover, it explains the challenges and prospects of subcellular organelle-targeting functional materials in precision oncology. The review will serve as an excellent cutting-edge guide for researchers in the field of subcellular organelle-targeted cancer therapy.

Exploring the RNase A scaffold to combine catalytic and antimicrobial activities. Structural characterization of RNase 3/1 chimeras

Design of novel antibiotics to fight antimicrobial resistance is one of the first global health priorities. Novel protein-based strategies come out as alternative therapies. Based on the structure-function knowledge of the RNase A superfamily we have engineered a chimera that combines RNase 1 highest catalytic activity with RNase 3 unique antipathogen properties. A first construct (RNase 3/1-v1) was successfully designed with a catalytic activity 40-fold higher than RNase 3, but alas in detriment of its anti-pathogenic activity. Next, two new versions of the original chimeric protein were created showing improvement in the antimicrobial activity. Both second generation versions (RNases 3/1-v2 and -v3) incorporated a loop characteristic of RNase 3 (L7), associated to antimicrobial activity. Last, removal of an RNase 1 flexible loop (L1) in the third version enhanced its antimicrobial properties and catalytic efficiency. Here we solved the 3D structures of the three chimeras at atomic resolution by X-ray crystallography. Structural analysis outlined the key functional regions. Prediction by molecular docking of the protein chimera in complex with dinucleotides highlighted the contribution of the C-terminal region to shape the substrate binding cavity and determine the base selectivity and catalytic efficiency. Nonetheless, the structures that incorporated the key features related to RNase 3 antimicrobial activity retained the overall RNase 1 active site conformation together with the essential structural elements for binding to the human ribonuclease inhibitor (RNHI), ensuring non-cytotoxicity. Results will guide us in the design of the best RNase pharmacophore for anti-infective therapies.

Alginate-Based Hydrogel as Delivery System for Therapeutic Bacterial RNase

To deliver therapeutic proteins into a living body, it is important to maintain their target activity in the gastrointestinal tract after oral administration. Secreted ribonuclease from Bacillus pumilus (binase) has antitumor and antiviral activity, which makes it a promising therapeutic agent. This globular protein of small molecular weight (12.2 kDa) is considered as a potential agent that induces apoptosis of tumor cells expressing certain oncogenes, including colorectal and duodenum cancer. The most important problem of its usage is the preservation of its structure and target activity, which could be lost during oral administration. Here, we developed alginate microspheres reinforced with divalent cations and analyzed the enzyme release from them. Using methods of scanning electron microscopy, measurements of fluorescence, enzyme catalytic activity, and determination of viability of the duodenum adenocarcinoma tumor cell line, we characterized obtained microspheres and chose calcium as a biogenic ion-strengthening microsphere structure. Among such modified additivities as beta-casein, gelatin, and carbon nanotubes introduced into microspheres, only gelatin showed a pronounced increase in their stability and provided data on the prolonged action of enzyme release from microspheres into tumor cell culture medium during 48 h in an amount of about 70% of the loaded quantity.

Emerging biological functions of ribonuclease 1 and angiogenin

Pancreatic-type ribonucleases (ptRNases) are a large family of vertebrate-specific secretory endoribonucleases. These enzymes catalyze the degradation of many RNA substrates and thereby mediate a variety of biological functions. Though the homology of ptRNases has informed biochemical characterization and evolutionary analyses, the understanding of their biological roles is incomplete. Here, we review the functions of two ptRNases: RNase 1 and angiogenin. RNase 1, which is an abundant ptRNase with high catalytic activity, has newly discovered roles in inflammation and blood coagulation. Angiogenin, which promotes neovascularization, is now known to play roles in the progression of cancer and amyotrophic lateral sclerosis, as well as in the cellular stress response. Ongoing work is illuminating the biology of these and other ptRNases.

The Selectivity for Tumor Cells of Nuclear-Directed Cytotoxic RNases Is Mediated by the Nuclear/Cytoplasmic Distribution of p27KIP1

Although single targeted anti-cancer drugs are envisaged as safer treatments because they do not affect normal cells, cancer is a very complex disease to be eradicated with a single targeted drug. Alternatively, multi-targeted drugs may be more effective and the tumor cells may be less prone to develop drug resistance although these drugs may be less specific for cancer cells. We have previously developed a new strategy to endow human pancreatic ribonuclease with antitumor action by introducing in its sequence a non-classical nuclear localization signal. These engineered proteins cleave multiple species of nuclear RNA promoting apoptosis of tumor cells. Interestingly, these enzymes, on ovarian cancer cells, affect the expression of multiple genes implicated in metabolic and signaling pathways that are critic for the development of cancer. Since most of these targeted pathways are not highly relevant for non-proliferating cells, we envisioned the possibility that nuclear directed-ribonucleases were specific for tumor cells. Here, we show that these enzymes are much more cytotoxic for tumor cells in vitro. Although the mechanism of selectivity of NLSPE5 is not fully understood, herein we show that p27^KIP1 displays an important role on the higher resistance of non-tumor cells to these ribonucleases.

A nucleus-directed bombesin derivative for targeted delivery of metallodrugs to cancer cells

We have synthesized a set of bombesin derivatives with the aim of exploring their tumor targeting properties to deliver metal-based chemotherapeutics into cancer cells. Peptide QRLGNQWAVGHLL-NH₂ (BN3) was selected based on its high internalization in gastrin-releasing peptide receptor (GRPR)-overexpressing PC-3 cells. Three metallopeptides were prepared by incorporating the terpyridine Pt(II) complex [PtCl(cptpy)]Cl (1) (cptpy = 4'-(4-carboxyphenyl)-2,2':6,2″-terpyridine) at the N-terminus of BN3 or at the N^Ɛ- or N^α-amino group of an additional Lys residue (1-BN3, Lys-1-BN3 and 1-Lys-BN3, respectively). 1-Lys-BN3 displayed the best cytotoxic activity (IC₅₀: 19.2 ± 1.7 μM) and similar ability to intercalate into DNA than complex 1. Moreover, the polypyridine Ru(II) complex [Ru(bpy)₂)(cmbpy)](PF₆)₂ (2) (bpy = 2,2'-bipyridine; cmbpy = 4-methyl-2,2'-bipyridine-4'-carboxylic acid), with proven activity as photosensitizer, was coupled to BN3 leading to metallopeptide 2-Lys-BN3. Upon photoactivation, 2-Lys-BN3 displayed 2.5-fold higher cytotoxicity against PC-3 cells (IC₅₀: 7.6 ± 1.0 μM) than complex 2. To enhance the accumulation of the drugs into the cell nucleus, the nuclear localization signal (NLS) PKKKRKV was incorporated at the N-terminus of BN3. NLS-BN3 displayed higher cellular internalization along with nuclear biodistribution. Accordingly, metallopeptides 1-NLS-BN3 and 2-NLS-BN3 showed increased cytotoxicity (IC₅₀: 12.0 ± 1.1 μM and 2.3 ± 1.1 μM). Interestingly, the phototoxic index of 2-NLS-BN3 was 8-fold higher than that of complex 2. Next, the selectivity towards cancer cells was explored using 1BR3.G fibroblasts. Higher selectivity indexes were obtained for 1-NLS-BN3 and 2-NLS-BN3 than for the unconjugated complexes. These results prove NLS-BN3 effective for targeted delivery of metallodrugs to GRPR-overexpressing cells and for enhancing the cytotoxic efficacy of metal-based photosensitizers.

RNases Disrupt the Adaptive Potential of Malignant Cells: Perspectives for Therapy

Exogenous RNases are selectively toxic to tumor cells. The reasons for this selectivity are not quite clear and should be searched for in the properties that distinguish malignant from normal cells. During onco-transformation, cells acquire properties allowing them to adapt to the altered microenvironment, such as resistance to hypoxia, changes in intracellular pH, disruption of ion transport, reduced adhesion and increased mobility, and production of specific exosomes. These adaptation mechanisms distinguish malignant cells from normal ones and give them a competitive advantage, ensuring survival and spread in the organism. Here, we analyze if the directed cytotoxic effect of exogenous RNases is linked to the disruption of the adaptive potential of tumor cells and how it can be used in anticancer therapy.

Construction of Highly Stable Cytotoxic Nuclear-Directed Ribonucleases

Ribonucleases are proteins whose use is promising in anticancer therapy. We have previously constructed different human pancreatic ribonuclease variants that are selectively cytotoxic for tumor cells by introducing a nuclear localization signal into their sequence. However, these modifications produced an important decrease in their stability compromising their behavior in vivo. Here, we show that we can significantly increase the thermal stability of these cytotoxic proteins by introducing additional disulfide bonds by site-directed mutagenesis. One of these variants increases its thermal stability by around 17 °C, without affecting its catalytic activity while maintaining the cytotoxic activity against tumor cells. We also show that the most stable variant is significantly more resistant to proteolysis when incubated with proteinase K or with human sera, suggesting that its half-live could be increased in vivo once administered.

Targeting and delivery of therapeutic enzymes

Biotechnology has revolutionized therapeutics for the treatment of a wide range of diseases. Recent advances in protein engineering and material science have made the targeted delivery of enzyme therapeutics using nanocarriers (NCs) a new model of treatment. Several NCs have been approved for clinical use in drug delivery. Despite their advantages, few NCs have been approved to deliver enzyme cargo in a targeted manner. This review details the current arsenal of platforms developed to deliver enzyme therapeutics as well as the advantages and challenges of using enzymes as drugs, with examples from the literature, and discusses the benefits and liabilities of a given approach. We conclude by providing a perspective on how this field may evolve over the near and long-term.

Association between the ERCC2 Asp312Asn polymorphism and risk of cancer

Cancer is the leading cause of death in economically developed countries and the second leading cause of death in developing countries. The relationship between genetic polymorphisms and the risk of cancers has been widely researched. Excision repair cross-complementing group 2 (ERCC2) gene plays important roles in the nucleotide excision repair pathway. There is contrasting evidence on the association between the ERCC2 Asp312Asn polymorphism and the risk of cancer. We conducted a comprehensive meta-analysis in order to assess the correlation between these factors. We searched the PubMed, EMBASE, Science Direct, Web of Science, and CNKI databases for studies published from January 1, 2005 to January 1, 2016. Finally, 86 articles with 38,848 cases and 48,928 controls were included in the analysis. The overall analysis suggested a significant association between the ERCC2 Asp312Asn polymorphism and cancer risk. Furthermore, control source, ethnicity, genotyping method, and cancer type were used for subgroup analysis. The result of a trial sequential analysis indicated that the cumulative evidence is adequate; hence, further trials were unnecessary in the overall analysis for homozygote comparison. In summary, our results suggested that ERCC2 Asp312Asn polymorphism is associated with increased cancer risk. A significantly increased cancer risk was observed in Asian populations, but not in Caucasian populations. Furthermore, the ERCC2 Asp312Asn polymorphism is associated with bladder, esophageal, and gastric cancers, but not with breast, head and neck, lung, prostate, and skin cancers, and non-Hodgkin lymphoma. Further multi-center, well-designed studies are required to validate our results.

Rock the nucleus: significantly enhanced nuclear membrane permeability and gene transfection by plasmonic nanobubble induced nanomechanical transduction

Nanomechanical transduction increases permeability of the nuclear membrane and facilitates nuclear uptake of macromolecules that would otherwise not enter the nucleus.

β-hydroxyisovaleryl-shikonin induces human cervical cancer cell apoptosis via PI3K/AKT/mTOR signaling

The present study aimed to investigate the inhibitory ability of β-hydroxyisovaleryl-shikonin (β-HIVS) on the proliferation of human cervical cancer HeLa cells and to identify the mechanism of this effect. The HeLa cells were treated with β-HIVS and the inhibition of cell growth was detected by an MTT assay. Flow cytometry was performed to analyze the apoptosis rate and cell cycle distribution of HeLa cells. Reverse transcription-polymerase chain reaction and western blot analysis were used to examine the expression of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway proteins. The results revealed that β-HIVS inhibited HeLa cell proliferation in a dose- and time-dependent manner. With the administration of increasing concentrations of β-HIVS, the apoptotic rate of HeLa cells was also increased. The cell cycle was slightly arrested at the S phase, with ~6% of cells in this phase, subsequent to treatment with 10 µM β-HIVS. In addition, β-HIVS markedly reduced the expression levels of PI3K, AKT, mTOR and 70-kDa ribosomal protein S6 kinase in HeLa cells. β-HIVS promoted cervical cancer cell apoptosis by inhibiting the PI3K/AKT/mTOR signaling pathway and suppressing downstream gene expression. The present study is expected to lead to the development of molecular targeted therapy for this signaling pathway as a novel method of cervical cancer treatment.

Bovine seminal ribonuclease triggers Beclin1-mediated autophagic cell death in pancreatic cancer cells

Among the large number of variants belonging to the pancreatic-type secretory ribonuclease (RNase) superfamily, bovine pancreatic ribonuclease (RNase A) is the proto-type and bovine seminal RNase (BS-RNase) represents the unique natively dimeric member. In the present manuscript, we evaluate the anti-tumoral property of these RNases in pancreatic adenocarcinoma cell lines and in nontumorigenic cells as normal control. We demonstrate that BS-RNase stimulates a strong anti-proliferative and pro-apoptotic effect in cancer cells, while RNase A is largely ineffective. Notably, we reveal for the first time that BS-RNase triggers Beclin1-mediated autophagic cancer cell death, providing evidences that high proliferation rate of cancer cells may render them more susceptible to autophagy by BS-RNase treatment. Notably, to improve the autophagic response of cancer cells to BS-RNase we used two different strategies: the more basic (as compared to WT enzyme) G38K mutant of BS-RNase, known to interact more strongly than wt with the acidic membrane of cancer cells, or BS-RNase oligomerization (tetramerization or formation of larger oligomers). Both mutant BS-RNase and BS-RNase oligomers potentiated autophagic cell death as compared to WT native dimer of BS-RNase, while the various RNase A oligomers remained completely ineffective. Altogether, our results shed more light on the mechanisms lying at the basis of BS-RNase antiproliferative effect in cancer cells, and support its potential use to develop new anti-cancer strategies.

Structural and functional relationships of natural and artificial dimeric bovine ribonucleases: new scaffolds for potential antitumor drugs

Protein aggregation via 3D domain swapping is a complex mechanism which can lead to the acquisition of new biological, benign or also malignant functions, such as amyloid deposits. In this context, RNase A represents a fascinating model system, since by dislocating different polypeptide chain regions, it forms many diverse oligomers. No other protein displays such a large number of different quaternary structures. Here we report a comparative structural analysis between natural and artificial RNase A dimers and bovine seminal ribonuclease, a natively dimeric RNase with antitumor activity, with the aim to design RNase A derivatives with improved pharmacological potential.