Kuslima Shogen

Phase II Trial of a Single Weekly Intravenous Dose of Ranpirnase in Patients With Unresectable Malignant Mesothelioma

PURPOSE A multicenter phase II trial of ranpirnase (Onconase; Alfacell Corp, Bloomfield, NJ) as a single agent was conducted to further assess the safety and clinical efficacy of this novel antitumor ribonuclease. Patients with unresectable and histologically confirmed malignant mesothelioma (MM) were eligible. PATIENTS AND METHODS One hundred five patients with Eastern Cooperative Oncology Group performance status 0 to 2 were enrolled onto the study. Thirty-seven percent of patients had not responded to prior chemotherapy. The primary end point of the study was survival. Tumor responses and time to progression were also assessed. The Cancer and Leukemia Group B (CALGB) prognostic group criteria were used to define a treatment target group (TTG). Both the intent-to-treat (ITT) and the TTG populations were analyzed for survival. RESULTS Median survival times of 6 months for the ITT and 8.3 months for the TTG populations were observed. The 1- and 2-year survival rates were 34.3% and 21.6% for ITT, respectively, and 42% and 26.8% for TTG, respectively. Among the 81 patients assessable for tumor response, four had partial responses, two had minor regressions, and thirty-five experienced stabilization of previously progressive disease. Patients with responses and stable disease demonstrated markedly prolonged survival. Ranpirnase was well tolerated in the majority of patients, and there were no drug-related deaths. CONCLUSION Ranpirnase demonstrated activity and a tolerable toxicity profile in patients with unresectable MM. The prognostic value of the CALGB groups was confirmed.

Inhibition of HIV-1 Production and Selective Degradation of Viral RNA by an Amphibian Ribonuclease

Ribonucleases appear to have physiologic roles in host defense against cancer, viruses, and other parasites. Previously it was shown that select ribonucleases added to cells concurrently with virions blocked human immunodeficiency virus, type I (HIV-1) infection of H9 cells. We now report that a ribonuclease homologous to RNase A, named onconase, inhibits virus replication in chronically HIV-1-infected human cells without killing the virally infected cell. Examining the mechanism of this inhibition shows that onconase enters the infected cells and degrades HIV-1 RNA without degrading ribosomal RNA or the three different cellular messenger RNAs analyzed. The homologous human pancreatic RNase lacks anti-viral activity. Comparing recombinant forms of onconase and a onconase-human RNase chimera shows that the N-terminal 9 amino acids and the pyroglutamyl residue of onconase are required for full anti-viral activity. Thus extracellular ribonucleases can enter cells, metabolize select RNAs, and inhibit HIV virion production within viable replicating cells.

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). In the present study we observed that the silencing of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene in human lung adenocarcinoma A549 cells by siRNA was effectively prevented by Onc. While transfection of cells with GAPDH siRNA reduced expression of this protein by nearly 70%, the expression was restored in the cells exposed to 0.8 µM Onc for 48 or 72 h. The data thus provide evidence that one of the targets of Onc is siRNA, likely within the RNA-induced silencing complex (RISC). In light of the findings that microRNAs are involved in tumor pathogenesis as well as in enhancing cell resistance to anticancer therapy the present data may provide explanation for both, the antitumor Onc activity and its propensity to enhance effectiveness of cytotoxic drugs.

Tumoricidal effects of onconase on various tumors.

The effects of Onconase (Onc) on the tumor growth in vitro and in vivo were examined. Because elevated tumor interstitial fluid pressure (TIFP) is one of the major causes of inadequate drug delivery into solid tumors, we tested if Onc could lower TIFP in solid tumors.

Remarkable enhancement of cytotoxicity of onconase and cepharanthine when used in combination on various tumor cell lines

Onconase (Onc), a ribonuclease from oocytes or early embryos of Northern Leopard frog (Rana pipiens), is cytostatic and cytotoxic to a variety of tumor lines in vitro, inhibits growth of tumors in animal in vivo models and is currently in Phase IIIb clinical trials for malignant mesothelioma where it displays antitumor activity with minor overall toxicity to the patient. One of the characteristic features of Onc is a synergism with a variety of other antitumor modalities. Cepharanthine (Cep), a biscoclaurine alkaloid from Stephania cepharantha Hayata, is widely used in Japan to treat variety of ailments. It also shows low toxicity to patients. The aim of the present study was to assess the interaction of these two drugs on different tumor cell lines. When human promyelocytic leukemia HL-60, histiomonocytic lymphoma U937, multiple myeloma RPMI-8228, prostate carcinoma DU 145 and prostate adenocarcinoma LNCaP cells were exposed to relatively low concentrations of Onc or Cep their growth rates were somewhat suppressed but the cells were still able to proliferate. Cell growth, however, was totally abolished in each of these cell lines when treated with Onc and Cep combined. The frequency of apoptosis was also many-fold higher in cultures treated with a combination of Onc and Cep than in respective cultures treated with Onc or Cep alone. The mechanism of the observed synergism is unclear but it may be associated with the Onc activity in targeting microRNAs and/or NFkappaB and Cep activity also targeting NFkappaB. The data suggest that the combination of these two drugs, that individually express a low toxic profile, may have strong antitumor potential.

Effect of ONCONASE +/- tamoxifen on ASPC-1 human pancreatic tumors in nude mice.

To evaluate changes in tumor physiological parameters after treatment with ONCONASE (ONC), we used laser Doppler flowmetery for tumor blood flow (TBF) in legs of nude mice bearing AsPC-1 human pancreatic carcinoma. Tumor interstitial fluid pressure (TIFP) was measured using the wick-in-needle technique, while intratumoral pO2 utilized O2 sensitive needle electrodes. TBF was significantly increased by an i.p. injection of ONC, then returned to the untreated levels at 150 min post-treatment. Single and multiple intraperitoneal injections of ONC significantly reduced TIFP (post-treatment at 1-7 days). ONC significantly improved tumor oxygenation evidenced by an increase in median pO2 from 4.2 mm Hg to 8.2 mm Hg. Since ONC had a synergistic interaction with tamoxifen (TAMX) on the cytotoxic clonogenicity of AsPC-1 tumor cells in vitro, we evaluated the antitumoral effects in vivo by ONC +/- TAMX, using nude mice bearing AsPC-1 pancreatic tumor cells of ascite (intraperitoneally implanted) or solid (subcutaneously implanted to legs) tumors. ONC alone effectively retarded the tumor growth, but TAMX alone did not. ONC + TAMX was synergistically effective in inhibiting tumor growth.

ONCONASE® and Its Therapeutic Potential

Early work by Shogen and Yoon1 demonstrated an anti-tumor activity in extracts of Northern leopard frog (Rana pipiens) embryos. More than a decade later, in 1987, the main active component of those extracts was isolated and purified by Alfacell M. It turned out to be a small (approximately 12 Kd) basic protein of maternal origin (present also in large amounts in unfertilized oocytes). Its complete amino acid sequence was determined in our laboratory and was found to be unique.2 Surprisingly, the sequence was similar to those of pancreatic ribonuclease A (RNase A, EC 3.1.27.5) and other members of the RNase A superfamily. All 3 catalytic residues of RNase A were conserved as were some of the other residues forming the active site and/or the hydrophobic core.2,3 Thus, the protein seemed to be fully equipped to exert ribonucleolytic activity, and indeed was found capable of degrading highly polymerized RNA from yeast and wheat germ, although the reaction rates were distinctly lower that those of other pancreatic-type ribonucleases.2 It was also cytostatic and cytotoxic to several cancer cell lines in vitro including human submaxillary carcinoma A-253,2,4 and significantly increased the survival of mice bearing M109 Madison Carcinoma5. As we discuss later in this article, the protein also posses strong anti viral activity. We provisionally named the molecule P-30 Protein and later changed the name to Onconase (ONC). In addition to ONC, extracts of Rana pipiens oocytes, contain its natural variant, different by 3 amino acid residues6 and at least 4 variants of a novel cytotoxic ribonuclease, amphinase, recently discovered and sequenced in our laboratory.7 In this article, we discuss the structure and function of ONC as well as therapeutic potential of this enzyme with particular emphasis on its anti viral activity.

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 Onc; presents as four variants varying between themselves from 87 to 99 % in amino acid sequence identity and has a molecular mass ~ 13,000. In the present study we describe the effects of Amph on growth of several tumor cell lines. All four variants demonstrated cytostatic and cytotoxic activity against human promyelocytic HL-60-, Jurkat T-cell- and U-937 monocytic leukemia cells. The pattern of Amph activity to certain extent resembled that of Onc. Thus, cell proliferation was suppressed at 0.5 – 10.0 µg/ml (40 – 80 nM) Amph concentration with distinct accumulation of cells in G1 phase of the cell cycle. In addition, the cells were undergoing apoptosis, which manifested by DNA fragmentation (presence of “sub-G1” cells, TUNEL-positivity), caspases and serine proteases activation as well as activation of transglutaminase. The cytotostatic and cytotoxic effects of Amph required its ribonuclease activity: the enzymatically inactive Amph-2 having histidine at the active site alkylated was ineffective. The effectiveness and cell cycle specificity was generally similar for all four Amph variants and at the equimolar concentrations was somewhat more pronounced than that of Onc. The observed cytostatic and cytotoxic activity of Amph against tumor cell lines suggests that similar to Onc this cytotoxic ribonuclease may have antitumor activity and find an application in clinical oncology.