Cytotoxic activity of the amphibian ribonucleases onconase and r-amphinase on tumor cells from B cell lymphoproliferative disorders.

Although major advancements in antitumor treatment have been observed, several B cell-derived malignancies still remain incurable. A promising approach that involves targeting RNA either by the use of specific antisense oligonucleotides or cytostatic/cytotoxic ribonucleases (RNases) is being promoted. Two amphibian RNases, onconase (ONC; ranpirnase) and, more recently, r-amphinase (r-Amph), have already been tested, but thus far, mostly on solid tumors.

Ribonucleases as potential modalities in anticancer therapy.

Antitumor ribonucleases are small (10-28 kDa) basic proteins. They were found among members of both, ribonuclease A and T1 superfamilies. Their cytotoxic properties are conferred by enzymatic activity, i.

The cytotoxic ribonuclease onconase targets RNA interference (siRNA).

Onconase (Onc), a ribonuclease from oocytes of Northern Leopard frogs (Rana pipiens) is cytostatic and cytotoxic to a variety of tumor lines in vitro, inhibits growth of tumors in animal in vivo models and enhances sensitivity of tumor cells to a number of other cytotoxic agents with diverse mechanism of action. In Phase III clinical trials Onc demonstrated significant efficacy in patients with malignant mesothelioma that failed prior chemotherapy. We previously postulated that the antitumor activity of Onc and the observed synergisms with other antitumor modalities at least in part may be mediated by targeting RNA interference (RNAi).

Cytostatic and cytotoxic properties of Amphinase: a novel cytotoxic ribonuclease from Rana pipiens oocytes.

Onconase (Onc), is a novel amphibian cytotoxic ribonuclease with antitumor activity, and is currently in a confirmatory phase III clinical trial for the treatment of malignant mesothelioma. It was recently reported that Rana pipiens oocytes contain still another ribonuclease, named Amphinase (Amph). Amph shows 38-40% amino acid sequence identity with onconase, presents as four variants varying between themselves from 87-99% in amino acid sequence identity and has a molecular mass approximately 13,000.

The interdependence between catalytic activity, conformational stability, and cytotoxicity of onconase.

Onconase (ONC) is a cytotoxic ribonuclease of the pancreatic ribonuclease A superfamily isolated from oocytes or early embryos of the Northern leopard frog (Rana pipiens). It shows anticancer activity and currently is in Phase IIIb clinical trial for unresectable malignant mesothelioma. We generated several variants of ONC possessing mutations in selected structural regions of the molecule that have altered ribonucleolytic activity and/or conformational stability.

Enzymatic and structural characterisation of amphinase, a novel cytotoxic ribonuclease from Rana pipiens oocytes.

Besides Onconase (ONC) and its V11/N20/R103-variant, oocytes of the Northern Leopard frog (Rana pipiens) contain another homologue of ribonuclease A, which we named Amphinase (Amph). Four variants (Amph-1-4) were isolated and sequenced, each 114 amino acid residues in length and N-glycosylated at two positions. Sequence identities (a) among the variants and (b) versus ONC are 86.

Cytotoxic ribonucleases and RNA interference (RNAi).

Several cytotoxic ribonucleases (CRs), homologs of the pancreatic RNase A, have been isolated from amphibian oocytes or embryos. Of them, onconase (Onc), the CR that shows antitumor properties and is in phase III clinical trials, was the most extensively researched. Degradation of tRNA by Onc internalized into cells that leads to inhibition of protein synthesis is considered the mechanism of its cytotoxicity.

Entry into cells and selective degradation of tRNAs by a cytotoxic member of the RNase A family.

Onconase (P-30 protein), an enzyme in the ribonuclease A superfamily, exerts cytostatic, cytotoxic, and antiviral activity when added to the medium of growing mammalian cells. We find that onconase enters living mammalian cells and selectively cleaves tRNA with no detectable degradation of rRNA. The RNA specificity of onconase in vitro using reticulocyte lysate and purified RNA substrates indicates that proteins associated with rRNA protect the rRNA from the onconase ribonucleolytic action contributing to the cellular tRNA selectivity of onconase.