Recombinant expression, different downstream processing of the disulfide-rich anti-tumor peptide Ranpirnase and its effect on the growth of human glioma cell line SHG-44

Cell-free protein synthesis system: A new frontier for sustainable biotechnology-based products

Cell-free protein synthesis (CFPS) system is an innovative technology with a wide range of potential applications that could challenge current thinking and provide solutions to environmental and health issues. CFPS system has been demonstrated to be a successful way of producing biomolecules in a variety of applications, including the biomedical industry. Although there are still obstacles to overcome, its ease of use, versatility, and capacity for integration with other technologies open the door for it to continue serving as a vital instrument in synthetic biology research and industry. In this review, we mainly focus on the cell-free based platform for various product productions. Moreover, the challenges in the bio-therapeutic aspect using cell-free systems and their future prospective for the improvement and sustainability of the cell free systems.

The crystal structure of the domain-swapped dimer of onconase highlights some catalytic and antitumor activity features of the enzyme

Onconase (ONC) is a monomeric amphibian "pancreatic-type" RNase endowed with remarkable anticancer activity. ONC spontaneously forms traces of a dimer (ONC-D) in solution, while larger amounts can be formed when ONC is lyophilized from mildly acidic solutions. Here, we report the crystal structure of ONC-D and analyze its catalytic and antitumor activities in comparison to ONC. ONC-D forms via the three-dimensional swapping of the N-terminal α-helix between two monomers, but it displays a significantly different quaternary structure from that previously modeled [Fagagnini A et al., 2017, Biochem J 474, 3767-81], and based on the crystal structure of the RNase A N-terminal swapped dimer. ONC-D presents a variable quaternary assembly deriving from a variable open interface, while it retains a catalytic activity that is similar to that of ONC. Notably, ONC-D displays antitumor activity against two human melanoma cell lines, although it exerts a slightly lower cytostatic effect than the monomer. The inhibition of melanoma cell proliferation by ONC or ONC-D is associated with the reduction of the expression of the anti-apoptotic B cell lymphoma 2 (Bcl2), as well as of the total expression and phosphorylation of the Signal Transducer and Activator of Transcription (STAT)-3. Phosphorylation is inhibited in both STAT3 Tyr705 and Ser727 key-residues, as well as in its upstream tyrosine-kinase Src. Consequently, both ONC species should exert their anti-cancer action by inhibiting the pro-tumor pleiotropic STAT3 effects deriving either by its phospho-tyrosine activation or by its non-canonical signaling pathways. Both ONC species, indeed, increase the portion of A375 cells undergoing apoptotic cell death. This study expands the variety of RNase domain-swapped dimeric structures, underlining the unpredictability of the open interface arrangement upon domain swapping. Structural data also offer valuable insights to analyze the differences in the measured ONC or ONC-D biological activities.

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.

Onconase dimerization through 3D domain swapping: structural investigations and increase in the apoptotic effect in cancer cells

Onconase® (ONC), a protein extracted from the oocytes of the Rana pipiens frog, is a monomeric member of the secretory 'pancreatic-type' RNase superfamily. Interestingly, ONC is the only monomeric ribonuclease endowed with a high cytotoxic activity. In contrast with other monomeric RNases, ONC displays a high cytotoxic activity. In this work, we found that ONC spontaneously forms dimeric traces and that the dimer amount increases about four times after lyophilization from acetic acid solutions. Differently from RNase A (bovine pancreatic ribonuclease) and the bovine seminal ribonuclease, which produce N- and C-terminal domain-swapped conformers, ONC forms only one dimer, here named ONC-D. Cross-linking with divinylsulfone reveals that this dimer forms through the three-dimensional domain swapping of its N-termini, being the C-terminus blocked by a disulfide bond. Also, a homology model is proposed for ONC-D, starting from the well-known structure of RNase A N-swapped dimer and taking into account the results obtained from spectroscopic and stability analyses. Finally, we show that ONC is more cytotoxic and exerts a higher apoptotic effect in its dimeric rather than in its monomeric form, either when administered alone or when accompanied by the chemotherapeutic drug gemcitabine. These results suggest new promising implications in cancer treatment.

Anti-gliomas Effect of Chlorotoxin-Conjugated Onconase at High Dose

Malignant gliomas are rarely curable malignant tumors in the central nervous system. Chlorotoxin (CTX) is a peptide derived from scorpion venom, which can selectively target malignant gliomas. Onconase (Onc) is a small cytotoxic ribonuclease derived from frogspawn that exhibits cytotoxicity against some tumor cells. In the present study, we found that CTX-conjugated Onc (CTX-Onc) shows better anti-tumor effect than the physical mixture of CTX and Onc (CTX + Onc) on the nude mice carrying subcutaneous glioblastoma cell-derived tumor. However, CTX-Onc does not show dose-dependent anti-tumor effect. In addition, apoptosis in tumor tissue does not show significant difference between the treatment groups. Our results confirmed that CTX-Onc has better anti-tumor effect than CTX + Onc and suggest that it can be potentially used for glioma therapy.

Rana catesbeiana ribonuclease induces cell apoptosis via the caspase-9/-3 signaling pathway in human glioblastoma DBTRG, GBM8901 and GBM8401 cell lines

Human glioblastoma multiforme is one of the most aggressive malignant brain tumor types, and the mean survival time of patients with a brain tumor is <2 years when traditional therapies are administered. Thus, numerous studies have focused on the development of novel treatments for brain tumors. Frog ribonucleases, such as Onconase and Rana catesbeiana ribonuclease (RC-RNase), exert antitumor effects on various tumor cells, including cervical cancer, breast cancer, hepatoma, leukemia, pancreatic cancer and prostate cancer cells. In addition, frog Onconase has been applied as a treatment in clinical trials. However, the antitumor effects of frog ribonucleases on brain tumors are unclear. Previous studies have indicated that RC-RNase demonstrates a decreased cytotoxic effect in normal cells compared with Onconase. Therefore, the present study investigated the ability of RC-RNase to exert antitumor activities on human glioblastoma. It was found that RC-RNase inhibits the growth of the human glioblastoma DBTRG, GBM8901 and GBM8401 cells. In addition, the present study revealed that RC-RNase induces caspase-9/-3 activity and triggers the apoptotic cell death pathway in human glioblastoma cells. Notably, it was also demonstrated that RC-RNase effectively inhibits the growth of human glioblastoma tumors in a nude mouse model. Overall, the present study indicates that RC-RNase may be a potential agent for the treatment of human glioblastoma.

Chlorotoxin-conjugated onconase as a potential anti-glioma drug

Gliomas are rarely curable malignant brain tumors arising from normal glial cells. The scorpion-derived small peptide, chlorotoxin (CTX), can selectively bind malignant gliomas. In the present study, a CTX-conjugated onconase (Onc), a small cytotoxic ribonuclease, was prepared as a potential anti-glioma drug. In this conjugate, recombinant CTX was covalently linked with recombinant Onc by reversible disulfide linkage. The chemically conjugated CTX-Onc showed much higher cytotoxicity to the cultured glioma U251 and SHG-44 cells than the physical mixture of CTX and Onc (CTX + Onc). In the nude mouse models bearing subcutaneous U251 or SHG-44 tumors, the CTX-Onc conjugate also showed improved anti-tumor effects than the CTX + Onc control. These results suggested that the reversible chemical-conjugated CTX promoted the tumor targeting of Onc, and thus the present CTX-Onc conjugate could be further developed as a potential targeted anti-glioma drug.

Onconase induces autophagy sensitizing pancreatic cancer cells to gemcitabine and activates Akt/mTOR pathway in a ROS-dependent manner

Onconase® (ONC) is a member of the RNase super-family that is secreted in oocytes and early embryos of Rana pipiens. Over the last years, research interest about this small and basic frog RNase, also called ranpirnase, constantly increased because of its high cytotoxicity and anticancer properties. Onconase is currently used in clinical trials for cancer therapy; however, the precise mechanisms determining cytotoxicity in cancer cells have not yet been fully investigated. In the present manuscript, we evaluate the antitumoral property of onconase in pancreatic adenocarcinoma cells and in non-tumorigenic cells as a control. We demonstrate that ONC stimulates a strong antiproliferative and proapoptotic effect in cancer cells by reporting for the first time that ONC triggers Beclin1-mediated autophagic cancer cell death. In addition, ONC inhibits the expression of mitochondrial uncoupling protein 2 (UCP2) and of manganese-dependent superoxide dismutase (MnSOD) triggering mitochondrial superoxide ion production. ONC-induced reactive oxygen species (ROS) are responsible for Akt/mTOR pathway stimulation determining the sensitivity of cancer cells to mTOR inhibitors and lessening autophagic stimulation. This indicates ROS/Akt/mTOR axis as a strategy adopted by cancer cells to reduce ONC-mediated cytotoxic autophagy stimulation. In addition, we demonstrate that ONC can sensitize pancreatic cancer cells to the standard chemotherapeutic agent gemcitabine allowing a reduction of drug concentration when used in combination settings, thus suggesting a lowering of chemotherapy-related side effects. Altogether, our results shed more light on the mechanisms lying at the basis of ONC antiproliferative effect in cancer cells and support its potential use to develop new anticancer strategies.