Site-specific PEGylation endows a mammalian ribonuclease with antitumor activity

EGFR-targeting RNase A-cetuximab antibody-drug conjugate induces ROS-mediated apoptosis to overcome drug resistance in KRAS mutant cancer cells

Antibody-drug conjugates (ADCs) are an emerging strategy in cancer therapy, enhancing precision and efficacy by linking targeted antibodies to potent cytotoxic agents. This study introduces a novel ADC that combines ribonuclease A (RNase A) with cetuximab (Cet), an anti-EGFR monoclonal antibody, through a polyethylene glycol (PEG) linker (RN-PEG-Cet), aimed to induce apoptosis in KRAS mutant colorectal cancer (CRC) via a ROS-mediated pathway. RN-PEG-Cet was successfully synthesized and characterized for its physicochemical properties, retaining full enzymatic activity in RNA degradation and high binding affinity to EGFR. In KRAS mutant SW-480 cells, RN-PEG-Cet significantly reduced cell viability at lower doses, with an IC50 of 11.7 µg/mL at 72 h. Compared to free Cet, RN-PEG-Cet demonstrated a ~ 2-fold increase in apoptosis and a ~ 3.5-fold increase in ROS production. The conjugate also disrupted the Nrf2/Keap1 pathway, with a significant upregulation of Keap1 (FC = 3.7, p ≤ 0.01) and downregulation of Nrf2 (FC = 3.3, p < 0.01), highlighting its role in impairing antioxidant defenses and promoting ROS-mediated cytotoxicity. These findings emphasize the potential of RN-PEG-Cet as a novel therapeutic approach for KRAS mutant CRC, offering superior apoptosis induction and targeted cytotoxicity compared to conventional therapies. This ADC could represent a new strategy for improving CRC treatment outcomes by effectively overcoming resistance mechanisms.

Strengths and Challenges of Secretory Ribonucleases as AntiTumor Agents

Approaches to develop effective drugs to kill cancer cells are mainly focused either on the improvement of the currently used chemotherapeutics or on the development of targeted therapies aimed at the selective destruction of cancer cells by steering specific molecules and/or enhancing the immune response. The former strategy is limited by its genotoxicity and severe side effects, while the second one is not always effective due to tumor cell heterogeneity and variability of targets in cancer cells. Between these two strategies, several approaches target different types of RNA in tumor cells. RNA degradation alters gene expression at different levels inducing cell death. However, unlike DNA targeting, it is a pleotropic but a non-genotoxic process. Among the ways to destroy RNA, we find the use of ribonucleases with antitumor properties. In the last few years, there has been a significant progress in the understanding of the mechanism by which these enzymes kill cancer cells and in the development of more effective variants. All the approaches seek to maintain the requirements of the ribonucleases to be specifically cytotoxic for tumor cells. These requirements start with the competence of the enzymes to interact with the cell membrane, a process that is critical for their internalization and selectivity for tumor cells and continue with the downstream effects mainly relying on changes in the RNA molecular profile, which are not only due to the ribonucleolytic activity of these enzymes. Although the great improvements achieved in the antitumor activity by designing new ribonuclease variants, some drawbacks still need to be addressed. In the present review, we will focus on the known mechanisms used by ribonucleases to kill cancer cells and on recent strategies to solve the shortcomings that they show as antitumor agents, mainly their pharmacokinetics.

Surveillance of Tumour Development: The Relationship Between Tumour-Associated RNAs and Ribonucleases

Tumour progression is accompanied by rapid cell proliferation, loss of differentiation, the reprogramming of energy metabolism, loss of adhesion, escape of immune surveillance, induction of angiogenesis, and metastasis. Both coding and regulatory RNAs expressed by tumour cells and circulating in the blood are involved in all stages of tumour progression. Among the important tumour-associated RNAs are intracellular coding RNAs that determine the routes of metabolic pathways, cell cycle control, angiogenesis, adhesion, apoptosis and pathways responsible for transformation, and intracellular and extracellular non-coding RNAs involved in regulation of the expression of their proto-oncogenic and oncosuppressing mRNAs. Considering the diversity/variability of biological functions of RNAs, it becomes evident that extracellular RNAs represent important regulators of cell-to-cell communication and intracellular cascades that maintain cell proliferation and differentiation. In connection with the elucidation of such an important role for RNA, a surge in interest in RNA-degrading enzymes has increased. Natural ribonucleases (RNases) participate in various cellular processes including miRNA biogenesis, RNA decay and degradation that has determined their principal role in the sustention of RNA homeostasis in cells. Findings were obtained on the contribution of some endogenous ribonucleases in the maintenance of normal cell RNA homeostasis, which thus prevents cell transformation. These findings directed attention to exogenous ribonucleases as tools to compensate for the malfunction of endogenous ones. Recently a number of proteins with ribonuclease activity were discovered whose intracellular function remains unknown. Thus, the comprehensive investigation of physiological roles of RNases is still required. In this review we focused on the control mechanisms of cell transformation by endogenous ribonucleases, and the possibility of replacing malfunctioning enzymes with exogenous ones.

Human Cancer Antigen Globo H Is a Cell-Surface Ligand for Human Ribonuclease 1

Pancreatic-type ribonucleases are secretory enzymes that catalyze the cleavage of RNA. Recent efforts have endowed the homologues from cow (RNase A) and human (RNase 1) with toxicity for cancer cells, leading to a clinical trial. The basis for the selective toxicity of ribonuclease variants for cancerous versus noncancerous cells has, however, been unclear. A screen for RNase A ligands in an array of mammalian cell-surface glycans revealed strong affinity for a hexasaccharide, Globo H, that is a tumor-associated antigen and the basis for a vaccine in clinical trials. The affinity of RNase A and RNase 1 for immobilized Globo H is in the low micromolar-high nanomolar range. Moreover, reducing the display of Globo H on the surface of human breast adenocarcinoma cells with a small-molecule inhibitor of biosynthesis or a monoclonal antibody antagonist decreases the toxicity of an RNase 1 variant. Finally, heteronuclear single quantum coherence (HSQC) NMR spectroscopy showed that RNase 1 interacts with Globo H by using residues that are distal from the enzymic active site. The discovery that a systemic human ribonuclease binds to a moiety displayed on human cancer cells links two clinical paradigms and suggests a mechanism for innate resistance to cancer.

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.

Human ribonuclease with a pendant poly(ethylene glycol) inhibits tumor growth in mice

Human pancreatic ribonuclease (RNase 1) is a small secretory protein that catalyzes the cleavage of RNA. This highly cationic enzyme can enter human cells spontaneously but is removed rapidly from circulation by glomerular filtration. Here, this shortcoming is addressed by attaching a poly(ethylene glycol) (PEG) moiety to RNase 1. The pendant has no effect on ribonucleolytic activity but does increase persistence in circulation. The RNase 1-PEG conjugates inhibit the growth of tumors in a xenograft mouse model of human lung cancer. Both retention in circulation and tumor growth inhibition correlate with the size of the pendant PEG. A weekly dose of the 60-kDa conjugate at 1 µmol/kg inhibited nearly all tumor growth without affecting body weight. Its molecular efficacy is ∼5000-fold greater than that of erlotinib, which is a small molecule in clinical use for the treatment of lung cancer. These data demonstrate that the addition of a PEG moiety can enhance the in vivo efficacy of human proteins that act within cells and highlight a simple means of converting an endogenous human enzyme into a cytotoxin with potential clinical utility.

Ribonuclease binase inhibits primary tumor growth and metastases via apoptosis induction in tumor cells

Exogenous ribonucleases are known to inhibit tumor growth via apoptosis induction in tumor cells, allowing to consider them as promising anticancer drugs for clinical application. In this work the antitumor potential of binase was evaluated in vivo and the mechanism of cytotoxic effect of binase on tumor cells was comprehensively studied in vitro. We investigated tumoricidal activity of binase using three murine tumor models of Lewis lung carcinoma (LLC), lymphosarcoma RLS 40 and melanoma B-16. We show for the first time that intraperitoneal injection of binase at a dose range 0.1-5 mg/kg results in retardation of primary tumor growth up to 45% in LLC and RLS 40 and inhibits metastasis up to 50% in LLC and RLS 40 and up to 70% in B-16 melanoma. Binase does not exhibit overall toxic effect and displays a general systemic and immunomodulatory effects. Treatment of RLS 40-bearing animals with binase together with polychemotherapy revealed that binase decreases the hepatotoxicity of polychemotherapy while maintaining its antitumor effect. It was demonstrated that the cytotoxic effect of binase is realized via the induction of the intrinsic and extrinsic apoptotic pathways. Activation of intrinsic apoptotic pathway is manifested by a drop of mitochondrial potential, increase in calcium concentration and inhibition of respiratory activity. Subsequent synthesis of TNF-α in the cells under the action of binase triggers extrinsic apoptotic pathway through the binding of TNF with cell-death receptors and activation of caspase 8. Thus binase is a potential anticancer therapeutics inducing apoptosis in cancer cells.

Rational design and evaluation of mammalian ribonuclease cytotoxins

Mammalian pancreatic-type ribonucleases (ptRNases) comprise an enzyme family that is remarkably well suited for therapeutic exploitation. ptRNases are robust and prodigious catalysts of RNA cleavage that can naturally access the cytosol. Instilling cytotoxic activity requires endowing them with the ability to evade a cytosolic inhibitor protein while retaining other key attributes. These efforts have informed our understanding of ptRNase-based cytotoxins, as well as the action of protein-based drugs with cytosolic targets. Here, we address the most pressing problems encountered in the design of cytotoxic ptRNases, along with potential solutions. In addition, we describe assays that can be used to evaluate a successful design in vitro, in cellulo, and in vivo. The emerging information validates the continuing development of ptRNases as chemotherapeutic agents.