Ranpirnase is a ribonuclease enzyme found in the oocytes of the Northern Leopard Frog (Rana pipiens). Ranpirnase is a member of the pancreatic ribonuclease (RNase A) protein superfamily and degrades RNA substrates with a sequence preference for uracil and guanine nucleotides. Along with amphinase, another leopard frog ribonuclease, ranpirnase has been studied as a potential cancer treatment due to its unusual mechanism of cytotoxicity tested against tumor cells.^[1]

Ranpirnase was originally discovered by scientists at TamirBio, a biotechnology company (formerly Alfacell Corporation), where it was tested in clinical trials under the brand name Onconase. The mechanism of action of ranpirnase tumor-selective cytotoxicity has been attributed to the RNA interference pathway, potentially through cleaving siRNA molecules;^[2] to cleavage of transfer RNA;^[1] and to interference with the NF-κB pathway.^[3] Despite early indications of promise as a mesothelioma treatment,^[4][5][6] and an orphan drug status designation from the United States Food and Drug Administration in 2007,^[7] the Phase III clinical trial for this indication did not demonstrate statistical significance against primary endpoints.^[8]