Current Pharmaceutical Biotechnology - Volume 9, Issue 3, 2008

As the annual number of newly diagnosed cases of cancer is about 10 million worldwide, combat of cancer is one of the most outstanding challenges of recent medicine. The considerable undesired side effects of chemotherapy and/or radiotherapy caused by their little selectivity call for a specific targeting of the affected tissue. Exploiting the target specificity of antibodies, which selectively bind to tumor-associated an Read More

The eosinophil-derived neurotoxin (EDN, also known as eosinophil protein-X) is best-known as one of the four major proteins found in the large specific granules of human eosinophilic leukocytes. Although it was named for its discovery and initial characterization as a neurotoxin, it is also expressed constitutively in human liver tissue and its expression can be induced in macrophages by proinflammatory stimuli. EDN and it Read More

The eosinophil cationic protein (ECP) is a secretory ribonuclease, which is found in the eosinophilic leukocyte and involved in the innate immune system. Its cytotoxic activity is effective against a wide range of pathogens, suggesting a relatively non-specific mechanism of action. We review here the specific antipathogen activities that have been characterized for ECP. Although eosinophils and ECP are primarily associated wit Read More

Ribotoxins constitute a family of toxic extracellular fungal RNases that exert a highly specific activity on a conserved region of the larger molecule of rRNA, known as the sarcin-ricin loop. This cleavage of a single phosphodiester bond inactivates the ribosome and leads to protein synthesis inhibition and cell death. In addition to this ribonucleolytic activity, ribotoxins can cross lipid membranes in the absence of any known pr Read More

By virtue of their RNA degrading catalytic activity, ribonucleases are potentially cytotoxic. For the application of these enzymes as therapeutics, however, they have to overcome several obstacles whose interplay is not yet fully understood. Ribonucleases with a basic pI are not only able to interact with the (negatively charged) cellular membrane but they are also distinctively selective for tumor cells. After the (endocytotic) Read More

In addition to their ribonucleolytic activity, several ribonucleases (RNases) play important roles in other specific biological activities, such as dendritic cell activation, certain pollen-induced allergies, blood vessel formation and defense against parasitic or microbial infections. Among these diverse actions, cytotoxic activity, which relies in most cases on ribonucleolytic activity, has attracted a considerable attention because o Read More

The cytotoxic properties of naturally occurring or engineered RNases correlate well with their efficiency of cellular internalization and digestion level of cellular RNA. Cationized RNases are considered to adsorb to the anionic cellular surface by Coulombic interactions, and then become efficiently internalized into cells by an endocytosis-like pathway. The design of cytotoxic RNases by chemical modification of surface carboxylic resi Read More

Onconase® (ONC) is an amphibian member of the bovine pancreatic ribonuclease (RNase A) superfamily that exhibits innate antitumoral activity. ONC has been granted both orphan-drug and fast-track status by the U.S. Food and Drug Administration for the treatment of malignant mesothelioma, and is poised to become the first chemotherapeutic agent based on a ribonuclease. Investigations into the mechanism o Read More

After a short introduction with some examples of cytotoxic ribonucleases, the importance of natural or artificial dimerization (oligomerization) as a way for a ribonuclease to acquire novel functional properties has been pointed out. In particular, the role of the three dimensional domain swapping mechanism in bovine pancreatic ribonuclease A oligomerization, as well as its impact for the acquisition of novel biological fun Read More

Immunotoxins are chimeric molecules that specifically target tumor cells, as they are made up of toxins linked to an antibody directed to a specific, cell-surface tumor-associated-antigen (TAA). When the immune moiety is internalized by the tumor cell, it will carry the conjugated toxin into the cell, so that the cell will be selectively killed in a way postulated more than a hundred years ago by Paul Ehrlich, the first author to use th Read More

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 resi Read More

Onconase, a member of the pancreatic ribonuclease A superfamily, is currently in Phase III clinical trials for treatment of unresectable malignant mesothelioma. The anticancer effect of onconase may relate to its intracellular target, a non-coding RNA. Some non- coding RNAs are aberrantly expressed in cancer cells. This discovery is creating new interest in drugs that target RNA. Conjugating onconase to agents that recogniz Read More

Ribonucleases (RNases) of the superfamily A exhibit potent antineoplastic activity yet do not mediate appreciable immunogenicity or non-specific toxicity in both animal models and cancer patients. Ranpirnase (Onconase®), the first ribonuclease being evaluated as a therapeutic in humans, has progressed to phase III clinical trials in patients with unresectable mesothelioma. Conjugation of RNases to internalizing tumor-targe Read More