Combination of onconase and dihydroartemisinin synergistically suppresses growth and angiogenesis of non-small-cell lung carcinoma and malignant mesothelioma.

Onconase (Onc) is a cytotoxic ribonuclease derived from leopard frog oocytes or early embryos, and has been applied to the treatment of malignant mesothelioma in clinics. Onc also exhibits effective growth suppression of human non-small-cell lung cancer (NSCLC). Artemisinin (Art) and its derivatives are novel antimalarial drugs that exhibit antitumor and antivirus activities. In this study, we investigated the antitumor effects of combinations of Onc and an Art derivative, dihydroartemisinin (DHA), both in vitro and in vivo Isobologram analyses showed synergistic effects on the proliferation of NSCLC cells under the treatment with Onc and DHA. In vivo experiments also showed that the antitumor effect of Onc was markedly enhanced by DHA in mouse xenograft models. No obvious adverse effect was observed after the treatment. The density of microvasculature in the tumor tissues treated with Onc/DHA combination was lower than those treated with Onc or DHA alone. The above results are consistent with the results of the matrigel plug test for angiogenesis suppression using the Onc/DHA combination. These results imply that the anti-angiogenesis effects may make important contributions to the in vivo antitumor effects of the Onc/DHA combination treatment. The Onc/DHA combination therapy may have the potential to become a novel regimen for NSCLC and mesothelioma.

Genetic delivery of an immunoRNase by an oncolytic adenovirus enhances anticancer activity.

Antibody therapy of solid cancers is well established, but suffers from unsatisfactory tumor penetration of large immunoglobulins or from low serum retention of antibody fragments. Oncolytic viruses are in advanced clinical development showing excellent safety, but suboptimal potency due to limited virus spread within tumors. Here, by developing an immunoRNase-encoding oncolytic adenovirus, we combine viral oncolysis with intratumoral genetic delivery of a small antibody-fusion protein for targeted bystander killing of tumor cells (viro-antibody therapy). Specifically, we explore genetic delivery of a small immunoRNase consisting of an EGFR-binding scFv antibody fragment fused to the RNase Onconase (ONC(EGFR)) that induces tumor cell death by RNA degradation after cellular internalization. Onconase is a frog RNase that combines lack of immunogenicity and excellent safety in patients with high tumor killing potency due to its resistance to the human cytosolic RNase inhibitor. We show that ONC(EGFR) expression by oncolytic adenoviruses is feasible with an optimized, replication-dependent gene expression strategy. Virus-encoded ONC(EGFR) induces potent and EGFR-dependent bystander killing of tumor cells. Importantly, the ONC(EGFR)-encoding oncolytic adenovirus showed dramatically increased cytotoxicity specifically to EGFR-positive tumor cells in vitro and significantly enhanced therapeutic activity in a mouse xenograft tumor model. The latter demonstrates that ONC(EGFR) is expressed at levels sufficient to trigger tumor cell killing in vivo. The established ONC(EGFR)-encoding oncolytic adenovirus represents a novel agent for treatment of EGFR-positive tumors. This viro-antibody therapy platform can be further developed for targeted/personalized cancer therapy by exploiting antibody diversity to target further established or emerging tumor markers or combinations thereof.

[Targeted Delivery of Quantum Dots to HER2-Expressing Tumor Using Recombinant Antibodies].

Targeted delivery of semiconductor quantum dots (Q Ds) to tumors overexpressing HER2 cancer marker has been. demonstrated on immunocompromised mice bearing human breast cancer xenografts. To obtain targeted QDs complexes we applied the approach based on the use of protein adaptor system, RNAase barnase and its inhibitor barstar. Specific binding to target cancer marker was achieved through bivalent fusion protein containing two fragments of4D5scFv recombinant antibody and a fragment of barnase. QDs were conjugated to barstar, and final assembly of targeted complexes was obtained through non-covalent specific interaction of barstar, attached to QD, and barnase, that is part of the recombinant targeting protein. The efficient delivery of QDs to HER2-expressing tumor demonstrates the possibilities and prospects of the approach for targeted delivery of nanoparticles to cancer cells in vivo as the way to improve the efficiency of diagnosis and promote development of therapies based on the use of nanoparticles.

In vitro cytotoxicity of ranpirnase (onconase) in combination with components of R-CHOP regimen against diffuse large B cell lymphoma (DLBCL) cell line.

Ranpirnase (onconase; ONC) is an endoribonuclease obtained from the frog Rana pipiens. This enzyme exhibits anticancer properties mediated by degradation of cellular RNA and induction of apoptosis. In this study we assessed cytotoxicity of ONC in combination with currently used anticancer drugs on a human diffuse large B-cell lymphoma (DLBCL)-derived cell line (Toledo). Cytotoxic activity was measured by the exclusion of propidium iodide assay while apoptosis was assessed using the annexin-V binding method. Additionally, flow cytometry was used to assess the decline of mitochondrial potential and to determine activation of caspases 3, 8 and 9. It was observed that in vitro treatment with ONC in combination with rituximab, mafosfamide, vincristine, doxorubicin, and dexamethasone (drugs corresponding with elements of R-CHOP regimen) resulted in increased cytotoxicity. As a result ONC showed marked cytotoxicity against Toledo cells. Importantly, in combination of ONC with drugs imitating the R-CHOP regimen, this effect was significantly intensified. The main mechanism responsible for this event was induction of apoptosis along a mitochondrial dependent pathway. In conclusion, these data indicate that further preclinical and eventually clinical studies assessing activity of ONC+R-CHOP treatment are warranted.

Eosinophil ribonucleases and their cutaneous lesion-forming activity.

Eosinophil granule proteins are deposited in cutaneous lesions in many human diseases, but how these proteins contribute to pathophysiology is obscure. We injected eosinophil cationic protein (ECP or RNase 3), eosinophil-derived neurotoxin (EDN or RNase 2), eosinophil peroxidase (EPO), and major basic protein-1 (MBP1) intradermally into guinea pig and rabbit skin. ECP and EDN each induced distinct skin lesions at >or=2.5 microM that began at 2 days, peaking at approximately 7 days and persisting up to 6 wk. These lesions were ulcerated (ECP) or crusted (EDN) with marked cellular infiltration. EPO and MBP1 (10 microM) each produced perceptible induration and erythema with moderate cellular infiltration resolving within 2 wk. ECP and EDN localized to dermal cells within 2 days, whereas EPO and MBP1 remained extracellular. Overall, cellular localization and RNase activity of ECP and EDN were critical for lesion formation; differential glycosylation, net cationic charge, or RNase activity alone did not account for lesion formation. Ulcerated lesions from patients with the hypereosinophilic syndrome showed ECP and EDN deposition comparable to that in guinea pig skin. In conclusion, ECP and EDN disrupt skin integrity and cause inflammation. Their presence in ulcerative skin lesions may explain certain findings in human eosinophil-associated diseases.

In vitro transcribed mRNA for expression of designer nucleases: Advantages as a novel therapeutic for the management of chronic HBV infection.

Chronic infection with the hepatitis B virus (HBV) remains a significant worldwide medical problem. While diseases caused by HIV infection, tuberculosis and malaria are on the decline, new cases of chronic hepatitis B are on the rise. Because often fatal complications of cirrhosis and hepatocellular carcinoma are associated with chronic hepatitis B, the need for a cure is as urgent as ever. Currently licensed therapeutics fail to eradicate the virus and this is attributable to persistence of the viral replication intermediate comprising covalently closed circular DNA (cccDNA). Elimination or inactivation of the viral cccDNA is thus a goal of research aimed at hepatitis B cure. The ability to engineer nucleases that are capable of specific cleavage of a DNA sequence now provides the means to disable cccDNA permanently. The scientific literature is replete with many examples of using designer zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and RNA-guided endonucleases (RGENs) to inactivate HBV. However, important concerns about safety, dose control and efficient delivery need to be addressed before the technology is employed in a clinical setting. Use of in vitro transcribed mRNA to express therapeutic gene editors goes some way to overcoming these concerns. The labile nature of RNA limits off-target effects and enables dose control. Compatibility with hepatotropic non-viral vectors is convenient for the large scale preparation that will be required for advancing gene editing as a mode of curing chronic hepatitis B.

Inflammatory responses improve with milk ribonuclease-enriched lactoferrin supplementation in postmenopausal women.

OBJECTIVE AND DESIGN: A 6-month, randomized clinical study was conducted to evaluate the effect of a ribonuclease-enriched lactoferrin (R-ELF) supplement on the circulating cytokine levels and bone health of postmenopausal women. SUBJECTS: Thirty-eight healthy postmenopausal women, aged 45-60 years, were randomized into placebo and R-ELF groups. TREATMENT: The R-ELF group was supplemented with R-ELF (2 × 125 mg/day) and calcium (100% RDA), while the placebo group received only the calcium supplement. METHODS: Serum levels of receptor activator for NF-κB ligand (RANKL), C-reactive protein (CRP) and various pro- and anti-inflammatory cytokines were determined by ELISA. RESULTS: Pro-inflammatory cytokines IL-6 and TNF-α decreased significantly (-44 and -10%, respectively) while anti-inflammatory IL-10 increased (140%) due to R-ELF supplementation at the end of study. RANKL and CRP were modestly reduced (-50%) relative to their placebo levels, although RANKL elevated initially. CONCLUSIONS: R-ELF supplementation showed beneficial effects towards improvement of inflammatory status in postmenopausal women.

Antiviral Ranpirnase TMR-001 Inhibits Rabies Virus Release and Cell-to-Cell Infection In Vitro.

Currently, no rabies virus-specific antiviral drugs are available. Ranpirnase has strong antitumor and antiviral properties associated with its ribonuclease activity. TMR-001, a proprietary bulk drug substance solution of ranpirnase, was evaluated against rabies virus in three cell types: mouse neuroblastoma, BSR (baby hamster kidney cells), and bat primary fibroblast cells. When TMR-001 was added to cell monolayers 24 h preinfection, rabies virus release was inhibited for all cell types at three time points postinfection. TMR-001 treatment simultaneous with infection and 24 h postinfection effectively inhibited rabies virus release in the supernatant and cell-to-cell spread with 50% inhibitory concentrations of 0.2-2 nM and 20-600 nM, respectively. TMR-001 was administered at 0.1 mg/kg via intraperitoneal, intramuscular, or intravenous routes to Syrian hamsters beginning 24 h before a lethal rabies virus challenge and continuing once per day for up to 10 days. TMR-001 at this dose, formulation, and route of delivery did not prevent rabies virus transit from the periphery to the central nervous system in this model (n = 32). Further aspects of local controlled delivery of other active formulations or dose concentrations of TMR-001 or ribonuclease analogues should be investigated for this class of drugs as a rabies antiviral therapeutic.

Local controlled delivery of anti-neoplastic RNAse to the brain.

PURPOSE: Antineoplastic RNAse proteins, also known as Amphibinases, have been shown effective against various solid tumors but were found selectively neurotoxic to Purkinje cells in the cerebellum. This work describes the use of a waxy biodegradable poly(ricinoleic-co-sebacic acid) for the local controlled delivery of cytotoxic amphibinases in the parietal lobe of the brain in an attempt to overcome cerebellar neuronal toxicity while affecting glioma cells. METHODS: Amphibinase analogues were encapsulated in poly(ricinoleic-co-sebacic acid) formulations using mix-melt technology and loaded onto surgical foam. In-vitro release was monitored by BCA colorimetry and by RNAse specific bioactivity. The implants were inserted into rat brains bearing 9L glioma to assess toxicity and efficacy. RESULTS: The various formulations showed extended linear release for several weeks with minimal burst effect. Best in-vivo efficacy was obtained with ACC7201 containing implants, resulting in the extension of the median survival from 13 to 18 days with 13% long-term survivors. CONCLUSION: Antineoplastic proteins were released from a p(SA-RA) polyanhydride implants in a controlled manner, providing efficacy against 9L glioma, while evading neurotoxicity in the cerebellum. The controlled release of Amphibinases forms the potential for a new therapy against brain tumors.

Esterification Delivers a Functional Enzyme into a Human Cell.

A major hurdle in chemical biology is the delivery of native proteins into the cytosol of mammalian cells. Herein, we report that esterification of the carboxyl groups of an enzyme with a diazo compound enables not only its passage into the cytosol but also the retention of its catalytic activity there. This scenario is demonstrated with human ribonuclease 1, which manifests ribonucleolytic activity that can be cytotoxic. After internalization, the nascent esters are hydrolyzed in situ by endogenous esterases, making the process traceless. This strategy provides unprecedented opportunities for the delivery of functional enzymes into human cells.

Mechanisms of enhanced tumoricidal efficacy of multiple small dosages of ranpirnase, the novel cytotoxic ribonuclease, on lung cancer.

PURPOSE: The effect of multiple small dosages of the cytotoxic RNase, ranpirnase (ONCONASE, ONC), on lung cancer was studied. The possible mechanisms for the enhanced tumoricidal efficacy of multiple small dosages of ONC were also investigated. METHODS: Hematoxylin and eosin staining, TUNEL labeling, and caspase-3-antibody labeling were used for in vivo analysis of apoptosis. A growth-delay assay was applied to detect the therapeutic potential of small and multiple dosages of ONC in vivo. ONC-induced changes in blood flow in A549 tumors and the kidney were measured non-invasively by dynamic contrast enhanced magnetic resonance imaging (DCE-MRI). RESULTS: In cell culture studies, ONC significantly inhibited tumor growth of A549 human NSCLC cells without damaging non-cancerous cells (HLF-1 human lung fibroblast). Multiple small dosages of ONC significantly prolonged tumor growth delay of A549 tumors, with increased apoptosis in vivo from 0.5 +/- 0.3 to 70.1 +/- 1.1% (by TUNEL labeling, N = 3, P < 0.05). Interestingly, multiple small doses of ONC were more effective than a single large dose for the inhibition of tumor growth with reduced side effect. Using non-invasive DCE-MRI methods, we found that the mean of the K (trans) median values increased to 49.3 +/- 7.5% from the pre-ONC values by ONC (N = 4 mice, P < 0.05). A subsequent T (1) map of the kidney showed that T (1) values were temporarily decreased for up to 2 days (however, fully recovered approximately 4 days post-treatment). CONCLUSIONS: Multiple small dosages of ONC significantly inhibited tumor growth of A549 NSCLC cells in vivo, with markedly increased apoptosis. This investigation suggests important potential clinical uses of ONC for the treatment of NSCLC cancer patients.

Antitumor efficacy of the cytotoxic RNase, ranpirnase, on A549 human lung cancer xenografts of nude mice.

BACKGROUND: The cytotoxic RNase, ranpirnase (ONCONASE, ONC), may have promising therapeutic implication as an alternative for cisplatin for the treatment of lung cancer, due to inhibition of protein synthesis by t-RNA cleavage. MATERIALS AND METHODS: A549 and NCI-H1975 human NSCLC cell lines were cultured in the presence and absence of ONC. Cytotoxicity was monitored using a clonogenic assay. Using an inverted phase and fluorescence microscope, we studied whether apoptosis was induced by ONC in gefitinib-induced apoptosis-resistant A549 tumor cells. The therapeutic effectiveness of ONC was studied via single and multiple administrations on A549 human non-small cell lung cancer (NSCLC), including tumors previously untreatable by cisplatin. ONC-induced changes in ATP levels were also monitored by non-localized phosphorus MR spectroscopy. RESULTS: ONC significantly inhibited the cell growth of A549 tumors. Apoptosis was significantly induced by ONC in a dose-dependent manner. In animal studies, multiple small doses of ONC were more effective than one large single dose for the inhibition of tumor growth with reduced side-effects, probably due to the normalization of leaky tumor vessels. ONC in combination with cisplatin significantly reduced tumor growth of A549 tumors. In large tumors, including those unsuccessfully treated with cisplatin, ONC showed inhibition of tumor growth, while a second treatment of cisplatin did not. During monitoring by non-localized phosphorus MR spectroscopy, ATP levels decreased, likely due to ONC-induced inhibition of oxygen consumption (QO2). CONCLUSION: ONC significantly inhibited tumor growth of A549 NSCLC cells in both in vitro and in vivo studies. This investigation suggests important potential clinical uses of ONC for the treatment of NSCLC cancer patients.

Hyaluronic acid modification of RNase A and its intracellular delivery using lipid-like nanoparticles.

Developing safe and effective nanosystems to deliver active and therapeutic proteins to targeted cells and organs is an important tool for many biomedical applications. We present here a simple and efficient strategy for this purpose: delivering hyaluronic acid (HA)-modified RNase A (RNase A-HA) in nanocomplex with cationic lipid-like molecules (lipidoids) to cancer cells, resulting in targeted inhibition of cancer proliferation. The chemical conjugation of RNase A with HA both increased the supramolecular interaction with carrier lipidoids, promoting protein encapsulation efficacy, and facilitated cancer cell targeting via interaction with overexpressed CD44. Through confocal laser scanning microscopy and flow cytometry analysis, we demonstrated that protein/lipidoid nanoparticles could facilely enter cells with high CD44 expression, and inhibit cell proliferation in a dose-dependent manner.

miRNases: Novel peptide-oligonucleotide bioconjugates that silence miR-21 in lymphosarcoma cells.

MicroRNAs (miRNAs) are active regulators in malignant growth and constitute potential targets for anticancer therapy. Consequently, considerable effort has focused on identifying effective ways to modulate aberrant miRNA expression. Here we introduce and assess a novel type of chemically engineered biomaterial capable of cleaving specific miRNA sequences, i.e. miRNA-specific artificial ribonucleases (hereafter 'miRNase'). The miRNase template presented here consists of the catalytic peptide Acetyl-[(LeuArg)2Gly]2 covalently attached to a miRNA-targeting oligonucleotide, which can be linear or hairpin. The peptide C-terminus is conjugated to an aminohexyl linker located at either the 3'- or 5'-end of the oligonucleotide. The cleavage efficacy, structural aspects of cleavage and biological relevance of a set of these designed miRNases was assayed with respect to highly oncogenic miR-21. Several miRNases demonstrated effective site-selective cleavage of miR-21 exclusively at G-X bonds. One of the most efficient miRNase was shown to specifically inhibit miR-21 in lymphosarcoma cells and lead to a reduction in their proliferative activity. This report provides the first experimental evidence that metallo-independent peptide-oligonucleotide chemical ribonucleases are able to effectively and selectively down-regulate oncogenic miRNA in tumour cells, thus suggesting their potential in development of novel therapeutics aimed at overcoming overexpression of disease-related miRNAs.

[Antiviral activity of Bacillus intermedius RNAase in guinea-pigs and rabbits infected with outdoor rabies virus].

Single injection of Bacillus intermedius RNAase in a dose of 5 mg/kg could protect 40 and 50-70% of the outdoor rabies virus-preinfected guinea-pigs and rabbits, respectively. In the control group there were 100 and 75-100% deaths of the RNAase-untreated guinea-pigs and rabbits, respectively. Animal protection was observed only when RNAase was injected into the site of viral administration. The intramuscular injection of RNAase, other than the site of viral administration failed to protect the infected animals. The efficacy (75%) of RNAase injected into the rabbits was similar 1 and 24 hours after animal infection.

Boronic Acid for the Traceless Delivery of Proteins into Cells.

The use of exogenous proteins as intracellular probes and therapeutic agents is in its infancy. A major hurdle has been the delivery of native proteins to an intracellular site of action. Herein, we report on a compact delivery vehicle that employs the intrinsic affinity of boronic acids for the carbohydrates that coat the surface of mammalian cells. In the vehicle, benzoxaborole is linked to protein amino groups via a "trimethyl lock." Immolation of this linker is triggered by cellular esterases, releasing native protein. Efficacy is demonstrated by enhanced delivery of green fluorescent protein and a cytotoxic ribonuclease into mammalian cells. This versatile strategy provides new opportunities in chemical biology and pharmacology.

Preventive Activity against Influenza (H1N1) Virus by Intranasally Delivered RNA-Hydrolyzing Antibody in Respiratory Epithelial Cells of Mice.

The antiviral effect of a catalytic RNA-hydrolyzing antibody, 3D8 scFv, for intranasal administration against avian influenza virus (H1N1) was described. The recombinant 3D8 scFv protein prevented BALB/c mice against H1N1 influenza virus infection by degradation of the viral RNA genome through its intrinsic RNA-hydrolyzing activity. Intranasal administration of 3D8 scFv (50 µg/day) for five days prior to infection demonstrated an antiviral activity (70% survival) against H1N1 infection. The antiviral ability of 3D8 scFv to penetrate into epithelial cells from bronchial cavity via the respiratory mucosal layer was confirmed by immunohistochemistry, qRT-PCR, and histopathological examination. The antiviral activity of 3D8 scFv against H1N1 virus infection was not due to host immune cytokines or chemokines, but rather to direct antiviral RNA-hydrolyzing activity of 3D8 scFv against the viral RNA genome. Taken together, our results suggest that the RNase activity of 3D8 scFv, coupled with its ability to penetrate epithelial cells through the respiratory mucosal layer, directly prevents H1N1 virus infection in a mouse model system.

A fusogenic peptide from a sea urchin fertilization protein promotes intracellular delivery of biomacromolecules by facilitating endosomal escape.

The low efficiency of endosomal escape has been considered a bottleneck for the cytosolic delivery of biomacromolecules such as proteins and DNA. Although fusogenic peptides (FPs) such as HA2 have been employed to improve the intracellular delivery of biomacromolecules, the FPs studied thus far are not adequately efficient in enabling endosomal escape; therefore, novel FPs with higher activity are required. In this context, we focused on FPs derived from a sea urchin fertilization protein, bindin, which is involved in gamete recognition (B18, residues 103-120 and B55, residues 83-137 of mature bindin). We show that enhanced green fluorescent protein (EGFP)-fused B55 peptide binds to plasma membranes more strongly than EGFP-B18 and promotes the intracellular delivery of dextrans, which were co-administered using the trans method in a pH-dependent manner without affecting cell viability and proliferation, whereas conventional EGFP-HA2 did not affect dextran internalization. Furthermore, EGFP-B55 promoted the intracellular delivery of biomacromolecules such as antibodies, ribonuclease and plasmidic DNA using the trans method. Because the promotion of intracellular delivery by EGFP-B55 was suppressed by endocytosis inhibitors, EGFP-B55 is considered to have facilitated the endosomal escape of co-administered cargos. These results suggested that an FP that promotes the intracellular delivery of a variety of biomacromolecules with no detectable cytotoxicity should be useful for the cytosolic delivery of membrane-impermeable molecules for biomedical and biotechnological applications.

Ribonuclease treatment of tick-borne encephalitis.

Clinical trials of the pancreatic ribonuclease (RNAse) in treatment of patients with tick-borne encephalitis were carried out. Two hundred forty-six patients were treated with RNAse and 261 were given antiencephalitic gamma globulin. Administration of 30 mg of RNAse every four hours over a period of five to six days provided stable high concentrations of the enzyme in blood that exceeded normal values by two to three times. An increase of RNAse activity in cerebrospinal fluid also took place. The comparison of RNAse and gamma globulin demonstrated a considerable advantage of the former: under RNAse treatment the temperature normalized on the average of twice as quickly, and a rapid regression occurred in meningeal symptoms and cerebrospinal fluid pleocytosis. In patients treated with RNAse, no adverse reactions or aftereffects were observed. On the grounds of the reported results, RNAse was accepted officially as a new, highly efficient antiviral drug for the treatment of tick-borne encephalitis.

Polymer-conjugated bovine pancreatic and seminal ribonucleases inhibit growth of human tumors in nude mice.

The hydrophilic poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) was used for RNase A or BS-RNase modification to prevent their degradation in bloodstream or fast elimination. Two PHPMA chains (classic and star-like) were synthesized and their conjugates with both enzymes were tested on the CD-1 nude mice bearing various human tumors. These RNase conjugates injected intravenously or intraperitoneally into the mice bearing melanoma, neuroblastoma or ovarian tumor caused significant reduction of transplanted tumors following ten daily doses of 2.5 and/or 1 mg/kg, respectively, while free RNase A or BS-RNase injected in doses of 10 mg/kg exerted only negligible antitumor activity. Histological examination confirmed potent cytotoxic effect of RNase A conjugates in ovarian tumor. Despite the antitumor activity observed in vivo, the in vitro cytotoxic activity of RNase A conjugates was not pronounced and did not differ from that caused by the free RNase A. The in vitro experiments with 125I-labeled preparations demonstrated that polymer conjugates were internalized by tumor cells very poorly in contrast to the dose-dependent internalization of the wild enzyme preparation. Surprisingly, mice injected with EL-4 leukemic cells, which were preincubated for 4 h with BS-RNase conjugates, exerted significantly prolonged survival compared with the control non-treated mice. It may be supposed that both BS-RNase and RNase A conjugates with PHPMA act after administration in vivo by a mechanism different from that or those occurring under in vitro conditions because in vivo they exert an antitumor action, whereas in vitro, they are ineffective. The experiments proved that RNase A, when conjugated to PHPMA, produced identical aspermatogenic and antitumor effects as BS-RNase conjugated to this polymer and that this preparation may be regarded as a potential anticancer drug.