Constitutive expression and anticancer potency of a novel immunotoxin onconase-DV3

Biological Activities of Secretory RNases: Focus on Their Oligomerization to Design Antitumor Drugs

Ribonucleases (RNases) are a large number of enzymes gathered into different bacterial or eukaryotic superfamilies. Bovine pancreatic RNase A, bovine seminal BS-RNase, human pancreatic RNase 1, angiogenin (RNase 5), and amphibian onconase belong to the pancreatic type superfamily, while binase and barnase are in the bacterial RNase N1/T1 family. In physiological conditions, most RNases secreted in the extracellular space counteract the undesired effects of extracellular RNAs and become protective against infections. Instead, if they enter the cell, RNases can digest intracellular RNAs, becoming cytotoxic and having advantageous effects against malignant cells. Their biological activities have been investigated either in vitro, toward a number of different cancer cell lines, or in some cases in vivo to test their potential therapeutic use. However, immunogenicity or other undesired effects have sometimes been associated with their action. Nevertheless, the use of RNases in therapy remains an appealing strategy against some still incurable tumors, such as mesothelioma, melanoma, or pancreatic cancer. The RNase inhibitor (RI) present inside almost all cells is the most efficacious sentry to counteract the ribonucleolytic action against intracellular RNAs because it forms a tight, irreversible and enzymatically inactive complex with many monomeric RNases. Therefore, dimerization or multimerization could represent a useful strategy for RNases to exert a remarkable cytotoxic activity by evading the interaction with RI by steric hindrance. Indeed, the majority of the mentioned RNases can hetero-dimerize with antibody derivatives, or even homo-dimerize or multimerize, spontaneously or artificially. This can occur through weak interactions or upon introducing covalent bonds. Immuno-RNases, in particular, are fusion proteins representing promising drugs by combining high target specificity with easy delivery in tumors. The results concerning the biological features of many RNases reported in the literature are described and discussed in this review. Furthermore, the activities displayed by some RNases forming oligomeric complexes, the mechanisms driving toward these supramolecular structures, and the biological rebounds connected are analyzed. These aspects are offered with the perspective to suggest possible efficacious therapeutic applications for RNases oligomeric derivatives that could contemporarily lack, or strongly reduce, immunogenicity and other undesired side-effects.

Critical Issues in the Development of Immunotoxins for Anticancer Therapy

Immunotoxins (ITs) are attractive anticancer modalities aimed at cancer-specific delivery of highly potent cytotoxic protein toxins. An IT consists of a targeting domain (an antibody, cytokine, or another cell-binding protein) chemically conjugated or recombinantly fused to a highly cytotoxic payload (a bacterial and plant toxin or human cytotoxic protein). The mode of action of ITs is killing designated cancer cells through the effector function of toxins in the cytosol after cellular internalization via the targeted cell-specific receptor-mediated endocytosis. Although numerous ITs of diverse structures have been tested in the past decades, only 3 ITs-denileukin diftitox, tagraxofusp, and moxetumomab pasudotox-have been clinically approved for treating hematological cancers. No ITs against solid tumors have been approved for clinical use. In this review, we discuss critical research and development issues associated with ITs that limit their clinical success as well as strategies to overcome these obstacles. The issues include off-target and on-target toxicities, immunogenicity, human cytotoxic proteins, antigen target selection, cytosolic delivery efficacy, solid-tumor targeting, and developability. To realize the therapeutic promise of ITs, novel strategies for safe and effective cytosolic delivery into designated tumors, including solid tumors, are urgently needed.

Targeted delivery of immuno-RNase may improve cancer therapy

Background

Immunotoxins are typical therapeutic drugs that can target cancer cells. They exploit the affinity of specific monoclonal antibodies or ligands to cancer cells to deliver a conjugated protein toxin to target sites, thus, attacking the cancer cells.

Methods

The immuno-RNase, Onc-V3, showed the stability of Onc-V3 in the blood stream. Flow cytometry showed that apoptosis occurred in the HO-8910PM cells when treated with Onc-V3. Under the confocal microscope, the green fluorescent, FITC-Onc-V3, were located in the cytoplasm, suggesting that Onc-V3 had a function in the cytoplasm of cancer cells. Moreover, after staining by DAPI, the blue fluorescent nuclei showed shrinkage and grainy. Wound healing assay showed that high concentrations of Onc-V3 inhibited cell migration and the transwell invasion assay showed that Onc-V3 could inhibit cell invasion to the basement membrane. Western blot results showed significantly decreased PARP, procaspase-9, and procaspase-3 in Onc-V3-induced apoptosis.

Results

These results of the experiments in vitro had shown that the Onc-V3 could be delivered to the cancer cells accurately and it had strong cytotoxicity on high metastatic cancer cells.

Conclusion

The specific toxicity of Onc-V3 on highly metastatic cancer cells can make it a promising anti-cancer drug by using V3 to target delivery of Onconase.