Onconase and Amphinase, the Antitumor Ribonucleases from Rana pipiens Oocytes

Abstract

Rana pipiens oocytes contain two homologues of pancreatic ribonuclease A that are cytostatic and cytotoxic to human cancer cells. Extensively studied Onconase is in advanced Phase IIIb clinical trials against malignant mesothelioma, while Amphinase is a novel enzyme in pre-clinical development. Onconase is the smallest (104 amino acid residues) member of the ribonuclease A superfamily while Amphinase (114 residues) is the largest among amphibian ribonucleases. Both enzymes share the characteristic frog ribonucleases C-terminal disulfide bond but another signature of this group, the N-terminal pyroglutamate, an integral part of Onconase active site is not conserved in Amphinase. Although Onconase and Amphinase are weak catalysts their enzymatic activities are required for cytostatic and cytotoxic activity. While it was postulated that tRNA is the primary substrate of Onconase in vivo there is also extensive indirect evidence that suggests other RNA species, in particular micro RNAs, may actually be the critical target of these ribonucleases. The cytostatic effects of Onconase and Amphinase are manifested as cell arrest in the G(1) cell cycle phase. Apoptosis then follows involving activation of endonucleases(s), caspases, serine proteases and transglutaminase. Onconase was shown to be strongly synergistic when combined with numerous other antitumor modalities. Onconase and Amphinase are highly cationic molecules and their preferential toxicity towards cancer cells (having distinctly higher negative charge compared to normal cells) may depend on increased binding efficiency to the cell surface by electrostatic interactions.

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

“…Binase is a purine-specific RNase of T1 family and a typical representative of the microbial RNases. 5,15,17 Earlier the cytotoxic activity of a number of microbial RNases, including binase, was shown in vitro on different types of tumor cells, 1,5,[9][10][11][28][29][30] but no studies have been performed in vivo.…”

Ranpirnase (Frog RNase) Targeted with a Humanized, Internalizing, Anti–Trop-2 Antibody Has Potent Cytotoxicity against Diverse Epithelial Cancer Cells

“…1) and its more basic variant, amphinase (2), are potential antitumor agents (3). The extensively studied Rap (4) has recently completed a randomized phase IIIb clinical trial, which compared the effectiveness of Rap plus doxorubicin with that of doxorubicin alone in patients with unresectable malignant mesothelioma, with the interim analysis showing that the MST for the combination was 12 months, whereas that of the monotherapy was 10 months (5).…”

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

“…Rana catesbeiana ribonuclease (RC-RNase) and Onconase are cytotoxic ribonucleases that are purified from frog oocyte (7,8). Onconase, which is derived from Rana pipiens, and RC-RNase, which is derived from Rana catesbeiana, each belong to the RNase A superfamily (9,10).…”