X-ray crystallographic analysis of pokeweed antiviral protein-II after reductive methylation of lysine residues

Pokeweed antiviral protein II (PAP-II) is a naturally occurring protein isolated from early summer leaves of the pokeweed plant (Phytolacca americana). PAP-II belongs to a family of ribosome-inactivating proteins which catalytically deadenylate ribosomal and viral RNA. The chemical modification of PAP-II by reductive methylation of its lysine residues significantly improved the crystal quality for X-ray diffraction studies. Hexagonal crystals of the modified PAP-II, with unit cell parameters a = b = 92.51 A, c = 79.05 A, were obtained using 1.8 M Na/K phosphate as the precipitant. These crystals contained one enzyme molecule per asymmetric unit and diffracted up to 2.4 A, when exposed to a synchroton source.

X-ray crystallographic analysis of the structural basis for the interactions of pokeweed antiviral protein with its active site inhibitor and ribosomal RNA substrate analogs

The pokeweed antiviral protein (PAP) belongs to a family of ribosome-inactivating proteins (RIP), which depurinate ribosomal RNA through their site-specific N-glycosidase activity. We report low temperature, three-dimensional structures of PAP co-crystallized with adenyl-guanosine (ApG) and adenyl-cytosine-cytosine (ApCpC). Crystal structures of 2.0-2.1 A resolution revealed that both ApG or ApCpC nucleotides are cleaved by PAP, leaving only the adenine base clearly visible in the active site pocket of PAP. ApCpC does not resemble any known natural substrate for any ribosome-inactivating proteins and its cleavage by PAP provides unprecedented evidence for a broad spectrum N-glycosidase activity of PAP toward adenine-containing single stranded RNA. We also report the analysis of a 2.1 A crystal structure of PAP complexed with the RIP inhibitor pteoric acid. The pterin ring is strongly bound in the active site, forming four hydrogen bonds with active site residues and one hydrogen bond with the coordinated water molecule. The second 180 degrees rotation conformation of pterin ring can form only three hydrogen bonds in the active site and is less energetically favorable. The benzoate moiety is parallel to the protein surface of PAP and forms only one hydrogen bond with the guanido group of Arg135.

Pokeweed antiviral protein isoforms PAP-I, PAP-II, and PAP-III depurinate RNA of human immunodeficiency virus (HIV)-1

Pokeweed antiviral protein (PAP) is a naturally occurring broad-spectrum antiviral agent with potent anti-human immunodeficiency virus (HIV)-1 activity by an as yet undeciphered molecular mechanism. In the present study, we sought to determine if PAP is capable of recognizing and depurinating viral RNA. Depurination of viral RNA was monitored by directly measuring the amount of the adenine base released from the viral RNA species using quantitative high-performance liquid chromatography. Our findings presented herein provide direct evidence that three different PAP isoforms from Phytolacca americana (PAP-I from spring leaves, PAP-II from early summer leaves, and PAP-III from late summer leaves) cause concentration-dependent depurination of genomic RNA (63 to 400 pmols of adenine released per micrograms of RNA) purified from human immunodeficiency virus type-I (HIV-I), plant virus (tobacco mosaic virus (TMV), and bacteriophage (MS 2). In contrast to the three PAP isoforms, ricin A chain (RTA) failed to cause detectable depurination of viral RNA even at 5 microM, although it was as effective as PAP in inhibiting protein synthesis in cell-free translation assays. PAP-I, PAP-II, and PAP-III (but not RTA) inhibited the replication of HIV-1 in human peripheral blood mononuclear cells with IC(50) values of 17 nM, 25 nM, and 16 nM, respectively. These findings indicate that the highly conserved active site residues responsible for the depurination of rRNA by PAP or RTA are not sufficient for the recognition and depurination of viral RNA. Our study prompts the hypothesis that the potent antiviral activity of PAP may in part be due to its unique ability to extensively depurinate viral RNA, including HIV-1 RNA.

TXU (anti-CD7)-pokeweed antiviral protein as a potent inhibitor of human immunodeficiency virus

We have evaluated the clinical potential of TXU (anti-CD7)-pokeweed antiviral protein (PAP) immunoconjugate (TXU-PAP) as a new biotherapeutic anti-human immunodeficiency virus (anti-HIV) agent by evaluating its anti-HIV type 1 (anti-HIV-1) activity in vitro, as well as in a surrogate human peripheral blood lymphocyte-severe combined immunodeficient (Hu-PBL-SCID) mouse model of human AIDS. The present report documents in a side-by-side comparison the superior in vitro anti-HIV-1 activity of TXU-PAP compared to the activities of zidovudine, 2',3'-didehydro-2',3'-dideoxythymidine, unconjugated PAP, and B53-PAP, an anti-CD4-PAP immunoconjugate. Notably, TXU-PAP elicited potent anti-HIV activity in the Hu-PBL-SCID mouse model of human AIDS without any side effects and at doses that were very well tolerated by cynomolgus monkeys. Furthermore, plasma samples from TXU-PAP-treated cynomolgus monkeys showed potent anti-HIV-1 activity in vitro.

In vivo toxicity, pharmacokinetics, and antileukemic activity of TXU (anti-CD7)-pokeweed antiviral protein immunotoxin

We evaluated the TXU (anti-CD7)-pokeweed antiviral protein (PAP) immunotoxin in both murine and nonhuman primate models. TXU-PAP caused dose-limiting cardiac toxicity in BALB/c mice. In a SCID mouse model of invariably fatal human T-lineage acute lymphoblastic leukemia (ALL), TXU-PAP therapy resulted in a marked improvement of leukemia-free survival without any side effects. Whereas 100% of control mice treated with PBS, unconjugated TXU antibody, or B43-PAP (an immunotoxin that does not react with T-lineage ALL cells) died of disseminated human leukemia within 80 days (median survival, 37 days), 80 +/- 13% of SCID mice treated with 15 microgram of TXU-PAP (median survival, >120 days) and 100% of mice treated with 30 microgram of TXU-PAP (median survival, > 120 days) remained alive and free of leukemia for >120 days. In cynomolgus monkeys, TXU-PAP showed favorable pharmacokinetics with an elimination half-life of 8.1-8.7 h. The monkeys treated with TXU-PAP at dose levels of 0.05 mg/kg/day x 5 days and 0.10 mg/kg/day x 5 days tolerated the therapy very well, without any significant clinical compromise or side effects, and at necropsy, no gross or microscopic lesions were found. This study provides a basis for further evaluation of TXU-PAP as an investigational biotherapeutic agent in the treatment of T-lineage ALL.

Pharmacokinetic features, immunogenicity, and toxicity of B43(anti-CD19)-pokeweed antiviral protein immunotoxin in cynomolgus monkeys

We studied the pharmacokinetic features, immunogenicity, and toxicity of B43-pokeweed antiviral protein (PAP) immunotoxin in 13 cynomolgus monkeys. The disposition of B43-PAP in two monkeys, when administered as a single i.v. bolus dose, was characterized by a slow clearance (1-2 ml/h/kg) with a very discrete peripheral distribution. B43-PAP was retained and distributed largely in the blood as the sole compartment with no significant equilibration with the extravascular compartment. The circulating B43-PAP immunotoxin detected in monkey plasma samples by ELISA and protein immunoblotting was both immunoreactive with, and active against, human leukemic cells in vitro. In systemic immunogenicity and toxicity studies, which involved 11 cynomolgus monkeys, each monkey received a total of seven i.v. doses of B43-PAP at a specific dose level of the dose escalation schedule. B43-PAP-treated monkeys mounted a dose-dependent humoral immune response against both the mouse IgG and PAP moieties of the immunotoxin. When administered i.v. either on an every-day or every-other-day schedule, B43-PAP was very well tolerated, with no significant clinical or laboratory signs of toxicity at total dose levels ranging from 0.007 to 0.7 mg/kg. A transient episode of a mild capillary leak with a grade 2 hypoalbuminemia and 2+ proteinuria was observed at total dose levels equal to or higher than 0.35 mg/kg. At total dose levels of 3.5 and 7.0 mg/kg, B43-PAP caused dose-limiting renal toxicity due to severe renal tubular necrosis. The present study completes the preclinical evaluation of B43-PAP and provides the basis for its clinical evaluation in children with therapy-refractory B-lineage acute lymphoblastic leukemia.

Treatment of human B-cell precursor leukemia in SCID mice using a combination of the investigational biotherapeutic agent B43-PAP with cytosine arabinoside

Combined immunochemotherapy regimens using the investigational biotherapeutic agent B43(anti-CD19)-poke-weed antiviral protein (PAP) immunotoxin may offer an effective treatment for refractory B-cell precursor leukemias. The purpose of the present study was to explore and identify effective combinations of B43-PAP with standard chemotherapeutic drugs, including the anthracyclin doxorubicin, the epipodophyllotoxin etoposide, the nitrosurea carmustine, and the antimetabolite cytosine arabinoside. Here, we report that the B43-PAP plus cytosine arabinoside combination has potent antileukemic activity against human B-cell precursor leukemia in SCID mice and leads to 100% long-term event-free survival from an otherwise invariably fatal leukemia. Surprisingly, none of the other treatment protocols tested, including combinations of B43-PAP with carmustine, doxorubicin, or etoposide, proved more effective than B43-PAP alone.

Toxicity profile of the investigational new biotherapeutic agent, B43 (anti-CD19)-pokeweed antiviral protein immunotoxin

The investigational biotherapeutic agent, B43(anti-CD19)-pokeweed antiviral protein (PAP) immunotoxin, has shown substantial anti-leukemic activity in SCID mouse models of human B-lineage leukemia and lymphoma. In this report, we describe the results of a comprehensive preclinical toxicity study which determined the toxicity profile of B43-PAP in BALB/c mice. Administration of unconjugated B43 monoclonal antibody was not associated with any toxicity, whereas B43-PAP caused dose-limiting and cardiac and renal toxicities which were fatal. In addition, B43-PAP also caused multifocal skeletal myofiber necrosis, which was associated with abnormal gait and lethargy. Notably, parenteral administrations of methylprednisolone, pentoxyphylline, or dopamine were able to markedly reduce B43-PAP related toxicity. This study provides a basis for further evaluation of the toxicity of B43-PAP in monkeys and humans.

In vitro and in vivo antileukemic activity of B43-pokeweed antiviral protein against radiation-resistant human B-cell precursor leukemia cells

B-cell precursor (BCP) leukemia is the most common form of childhood cancer and represents one of the most radiation-resistant forms of human malignancy. In this study, we examined the antileukemic efficacy of the B43 (anti-CD19)-pokeweed antiviral protein (B43-PAP) immunotoxin against radiation-resistant BCP leukemia cells. B43-PAP caused apoptosis of radiation-resistant primary BCP leukemia cells, killed greater than 99% of radiation-resistant primary leukemic progenitor cells from BCP leukemia patients, and conferred extended survival to severe combined immunodeficiency (SCID) mice xenografted with radiation-resistant human BCP leukemia. Furthermore, the combination of B43-PAP and total body irradiation (TBI) was more effective than TBI alone in two SCID mouse bone marrow transplantation models of radiation-resistant human BCP leukemia. Thus, B43-PAP may prove useful in the treatment of radiation-resistant BCP leukemia.

Favorable pharmacodynamic features and superior anti-leukemic activity of B43 (anti-CD19) immunotoxins containing two pokeweed antiviral protein molecules covalently linked to each monoclonal antibody molecule

Standard immunotoxin production procedures using whole IgG as the MoAb moiety yield a heterogeneous mixture of 180 kDa, 210 kDa, and 240 kDa immunotoxin species with 1 to 1, 1 to 2, and 1 to 3 MoAb to toxin ratios. This heterogeneity makes it impossible to precisely deliver a predetermined immunotoxin dose to target cells and impairs the accuracy of pharmacologic studies. In this report, we describe the preparation and characterization of B43(anti-CD19)-pokeweed antiviral protein (PAP) immunotoxins containing either one or two 30 kDa PAP toxin molecules covalently linked to each 150 kDa B43 monoclonal antibody molecule. Compared to the 180 kDa immunotoxin, the 210 kDa immunotoxin displayed greater in vitro chemical stability, resulted in higher systemic exposure levels in vivo, and was a more effective anti-leukemic agent in a SCID mouse model of human B-lineage acute lymphoblastic leukemia. Taken together, the results of this study recommend the clinical evaluation of 210 kDa B43-PAP as a potentially more effective immunotoxin against relapsed B-lineage ALL.

Extended-release felodipine in patients with mild to moderate hypertension. Felodipine ER Dose-Response Study Group

Two hundred eighty-six patients with mild to moderate hypertension who had untreated diastolic blood pressure while seated of 95 to 115 mm Hg were randomized to receive placebo or once-daily doses of 2.5, 5, or 10 mg of the dihydropyridine calcium channel blocker felodipine extended release (ER). Blood pressure was measured 24 hours after dosing (at trough). Mean reductions in diastolic blood pressure after 8 weeks of double-blind treatment were significantly greater in each of the ER felodipine treatment groups (2.5, 5, and 10 mg ER felodipine: -7.8, -9.5, and -11.3 mm Hg, respectively) than in the placebo group (-5.3 mm Hg). The effect was dose dependent for both diastolic and systolic blood pressure. Moreover, much of the peak antihypertensive effect was still present at trough, confirming the 24-hour efficacy of the drug. Felodipine was well tolerated.

Pokeweed antiviral protein inactivates pokeweed ribosomes; implications for the antiviral mechanism

Pokeweed antiviral protein (PAP) and other ribosome-inactivating proteins (RIPs) had previously been thought to be incapable of attacking conspecific ribosomes, thus having no effect on endogenous processes. This assertion conflicts with a model for PAP's in vivo antiviral mechanism in which PAP (a cell wall protein) selectively enters virus-infected cells and disrupts protein synthesis, thus causing local suicide and preventing virus replication. We show here that pokeweed (Phytolacca americana) ribosomes, as well as endod (Phytolacca dodecandra) ribosomes, are indeed highly sensitive to inactivation by conspecific RIPs. Ribosomes isolated from RIP-free pokeweed and endod suspension culture cells were found to be highly active in vitro, as measured by poly(U)-directed polyphenylalanine synthesis. Phytolacca ribosomes challenged with conspecific RIPs generated dose-response curves (IC50 of 1 nM PAP or dodecandrin) very similar to those from wheat germ ribosomes. To determine if Phytolacca cells produce a cytosolic 'anti-RIP' protective element, ribosomes were combined with Phytolacca postribosomal supernatant factors from culture cells, then challenged with conspecific RIPs. Resulting IC50 values of 3-7 nM PAP, PAP-II, PAP-S or dodecandrin indicate that supernatants from these Phytolacca cells lack a ribosomal protective element. This research demonstrates that PAP inactivates pokeweed ribosomes (and is therefore potentially toxic to pokeweed cells) and supports the local suicide model for PAP's in vivo antiviral mechanism. The importance of spatial separation between PAP and ribosomes of cells producing this RIP is emphasized, particularly if crop plants are transformed with the PAP gene to confer antiviral protection.

The 2.5 A structure of pokeweed antiviral protein

The pokeweed antiviral protein (PAP), isolated from the leaves of Phytolacca americana, is one of a family of plant and bacterial ribosome-inhibiting proteins (RIPs) which act as specific N-glycosidases on rRNA. Here we report the three-dimensional structure of PAP determined to 2.5 A resolution by X-ray crystallography. After 14 rounds of refinement, the R factor is 0.17 for 5.0 to 2.5 A data. The protein is homologous with the A chain of ricin and exhibits a very similar folding pattern. The positions of key active site residues are also similar. We also report the 2.8 A structure of PAP complexed with a substrate analog, formycin 5'-monophosphate. As seen previously in ricin, the formycin ring is stacked between invariant tyrosines 72 and 123. Arg179 bonds to N-3 which is thought to be important in catalysis.

Effects of the intermolecular toxin-monoclonal antibody linkage on the in vivo stability, immunogenicity and anti-leukemic activity of B43 (anti-CD19) pokeweed antiviral protein immunotoxin

We have successfully constructed highly potent and selective anti-CD19 PAP immunotoxins using each of the three crosslinking agents, SPDP, LC-SPDP, or SMPT, to generate an intermolecular bridge between the B43 MoAb and PAP toxin moieties. These immunotoxins were selectively immunoreactive with and cytotoxic against CD19+ B-lineage ALL cells. In this report, we compared (a) in vivo chemical, immunological, and biological stability, (b) in vivo immunogenicity, and (c) in vivo anti-leukemic activity of various B43-PAP immunotoxin constructs. Our data recommend the use of SPDP and SMPT rather than LC-SPDP for generation of B43(anti-CD19)-PAP immunotoxins as clinical anti-leukemic agents. To our knowledge, this is the first comparative analysis of the in vivo pharmacokinetic features, immunogenicity, and anti-leukemic activity of anti-CD19 PAP immunotoxins that were prepared with different heterobifunctional crosslinking agents.

Anti-human immunodeficiency virus type 1 activity of an anti-CD4 immunoconjugate containing pokeweed antiviral protein

The ability of an alpha CD4-pokeweed antiviral protein (PAP) immunoconjugate to inhibit replication of human immunodeficiency virus type 1 (HIV-1) was evaluated in vitro with 22 clinical HIV-1 strains obtained from four seropositive asymptomatic individuals, three patients with AIDS-related complex, and four patients with AIDS. Fifteen isolates were from zidovudine-untreated individuals, whereas seven isolates were obtained after 24 to 104 weeks of therapy with zidovudine, alone or alternating with zalcitabine. Mean zidovudine 50% inhibitory concentrations (IC50s) were 126 nM (range, 1 to 607 nM) for isolates from zidovudine-untreated individuals and 2,498 nM (range, 14 to 6,497 nM) for strains from patients treated with antiretroviral agents. Mean alpha CD4-PAP IC50s were 48 x 10(-3) nM (range, 0.02 x 10(-3) to 212 x 10(-3) nM) for isolates from zidovudine-untreated individuals, and 16 x 10(-3) nM (range, 2 x 10(-3) to 28 x 10(-3) nM) for isolates from treated patients. Overall, higher concentrations of alpha CD4-PAP were necessary to inhibit HIV-1 strains from untreated individuals at more advanced stages of disease. Seventeen isolates were susceptible to zidovudine (mean IC50, 117 nM), and five were resistant to zidovudine (mean IC50, 3,724 nM). Mean alpha CD4-PAP IC50s were 43 x 10(-3) nM for zidovudine-susceptible isolates and 19 x 10(-3) nM for isolates resistant to zidovudine. All HIV-1 strains had IC50s greater than 0.5 nM for unconjugated PAP, the alpha CD19-PAP immunoconjugate, and monoclonal antibody alpha CD4. At concentrations as high as 5,000 nM, alphaCD4-PAP did not inhibit colony formation by normal bone marrow progenitor cells(BFU-E, CFU-GM , and CFU-GEMM) or myeloid cell lines (KG-1 and HL-60) and did not decrease cell viabilities of T-cell (Jurkat) or B-cell (FL-112 and Raji) precursor lines. Overall, alphaCD4-PAP demonstrated more potent anti-HIV-1 activity than zidovudine and inhibited replication of zidovudine-susceptible and zidovudine-resistant viruses at concentrations that were not toxic to lymphohematopoietic cell populations.

In vivo anti-leukemic efficacy of anti-CD7-pokeweed antiviral protein immunotoxin against human T-lineage acute lymphoblastic leukemia/lymphoma in mice with severe combined immunodeficiency

Mice with severe combined immunodeficiency (SCID) were injected with 1 x 10(7) MOLT-3 human T-lineage acute lymphoblastic leukemia cells to provide a model for the evaluation of anti-CD7-pokeweed antiviral protein (PAP) immunotoxin directed against the human CD7 antigen. Of control SCID mice (treated with phosphate-buffered saline, PBS) challenged intravenously with 1 x 10(7) MOLT-3 cells, 5/5 died at 29 to 35 days after inoculation, with a median event-free survival of 33 days. Similarly, 6/6 anti-CD19-PAP treated control SCID mice died of MOLT-3 leukemia at a median of 36 days. In contrast, treatment with anti-CD7-PAP (15 micrograms total dose in 5 micrograms intraperitoneal injections on days 1-3) significantly improved event-free survival of SCID mice challenged with 1 x 10(7) MOLT-3 cells. Of nine SCID mice treated with anti-CD7-PAP, four died at 54-149 days and five remained alive for > 172 days without clinical evidence of leukemia (median event-free survival > 172 days). When long-term survivors among the anti-CD7-PAP treated SCID mice were electively killed at 173 days to assess their leukemia burden, histopathologic examination and polymerase chain reaction provided evidence of disseminated leukemia in some of these mice. Intriguingly, marked differences in morphology, tissue distribution, and histologic pattern of organ invasion existed between leukemic blasts killing 100% of PBS-treated control mice at a median of 33 days and 'therapy-refractory' leukemic blasts detected in anti-CD7-PAP-treated long-term survivors. This novel SCID mouse model of disseminated human T-lineage ALL provides a unique in vivo system to investigate the therapeutic potential of new treatment strategies and to study possible mechanisms of in vivo immunotoxin resistance.

Effective immunochemotherapy of CALLA+C mu+ human pre-B acute lymphoblastic leukemia in mice with severe combined immunodeficiency using B43 (anti-CD19) pokeweed antiviral protein immunotoxin plus cyclophosphamide

A highly aggressive human CALLA+C mu+ pre-B acute lymphoblastic leukemia (ALL) cell line (NALM-6-UM1) causes disseminated and invariably fatal leukemia in CB.17 mice with severe combined immunodeficiency (SCID). We used this SCID mouse model of human pre-B ALL to evaluate and compare, in a total of 434 SCID mice, the antileukemic efficacy of B43 (anti-CD19)-pokeweed antiviral protein (PAP) immunotoxin and cyclophosphamide (CPA) as individual reagents and as combined immunochemotherapeutic regimens. B43-PAP plus CPA was superior to either the immunotoxin or drug alone, and combined immunochemotherapy markedly improved the event-free survival (EFS) of SCID mice challenged with NALM-6-UM1 pre-B ALL cells. Notably, 90% to 100% of SCID mice challenged with 1 x 10(6) leukemia cells and then treated with B43-PAP plus CPA combined immunochemotherapy regimens became long-term survivors, a result not achieved with B43-PAP alone or CPA alone. The advantage was particularly evident in mice inoculated with 5 x 10(6) leukemia cells. While neither 15 micrograms B43-PAP (median survival, 58 days) nor 1 mg CPA (median survival, 49 days) resulted in long-term EFS of SCID mice challenged with 5 x 10(6) NALM-6-UM1 pre-B ALL cells, the probability of EFS at 6 months was 50% +/- 16% for SCID mice treated with 15 micrograms B43-PAP plus 1 mg CPA (median survival, greater than 180 days) (P less than .0001). The probability of long-term EFS was only 14% +/- 7% for mice treated with 30 micrograms B43-PAP and 0% +/- 0% for mice treated with 1 mg CPA, but 40% +/- 16% for mice treated with 30 micrograms B43-PAP plus 1 mg CPA (P less than .0001). Similarly, the probability of EFS at 6 months was 40% +/- 16% for mice treated with 2 mg CPA alone, 70% +/- 15% for mice treated with 2 mg CPA plus 15 micrograms B43-PAP, and 70% +/- 15% for mice treated with 2 mg CPA plus 30 micrograms B43-PAP. Ten SCID mice in the B43-PAP plus CPA combined immunochemotherapy arms surviving long term after the inoculation of 5 x 10(6) NALM-6-UM1 pre-B ALL cells were electively killed at 174 to 181 days to assess their leukemia burden. We found no evidence of leukemia in any of the bone marrow specimens by two-color immunofluorescence and multiparameter flow cytometry.(ABSTRACT TRUNCATED AT 400 WORDS)

In vivo efficacy of B43 (anti-CD19)-pokeweed antiviral protein immunotoxin against BCL-1 murine B-cell leukemia

We show that a highly aggressive subclone of murine BCL-1 B-lineage leukemia expresses a single 2.4-kb transcript hybridizing to the human CD19 cDNA probe and reacts strongly with the anti-human CD19 monoclonal antibodies (MoAb) B43, B4, Leu-12, and J3-119. In contrast to their strong reactivity with anti-human CD19 MoAb, BCL-1 cells show no reactivity with MoAb directed against human CD22, CD72, HLA-DR, IgD, or IgM. Western blot analysis of BCL-1 whole cell lysates with the anti-human CD19 MoAb J3-119 showed a single 69-Kd protein band, which was not detected by the negative control MoAb G19.4 (anti-CD3). In contrast to BCL-1 cells, normal BALB/c splenocytes or mouse splenocyte/myeloma hybridoma cell lines did not (1) express any transcripts that hybridized to the human CD19 cDNA probe, (2) react with B43/anti-CD19 MoAb, or (3) express the 69-Kd protein that reacts with the anti-human CD19 MoAb J3-119. Murine BCL-1 B-cell leukemia thus provides a unique model of disseminated B-lineage leukemia to evaluate the antileukemic efficacy of anti-CD19 immunotoxins. This model was subsequently used to evaluate the in vivo homing ability, pharmacokinetics, and antileukemic efficacy of B43 MoAb conjugated to the plant hemitoxin pokeweed antiviral protein (PAP). B43-PAP immunotoxin (1) showed strong and antigen-specific reactivity with BCL-1 cells, (2) promptly penetrated the spleens of leukemic mice, (3) rapidly reduced the BCL-1 leukemia burden of leukemic mice and, most importantly, (4) improved survival. Finally, B43-PAP immunotoxin was more effective against BCL-1 leukemia than 700 cGy (LD100/30) total body irradiation (TBI) followed by syngeneic bone marrow transplantation (BMT).

In vivo efficacy of B43 (anti-CD19)-pokeweed antiviral protein immunotoxin against human pre-B cell acute lymphoblastic leukemia in mice with severe combined immunodeficiency

A highly aggressive subclone of the human CALLA+C mu+ pre-B acute lymphoblastic leukemia (ALL) cell line NALM-6 (designated NALM-6-UM1) caused disseminated and fatal leukemia in CB.17 mice with severe combined immunodeficiency (SCID). An intravenous challenge with 1 x 10(6) (NALM-6-UM1 cells caused 15 of 27 (56%) SCID mice to become paraplegic at 31 +/- 2 days (median = 33 days) and 27 of 27 (100%) mice to die of disseminated leukemia at 38 +/- 1 days (median = 39 days). We used this SCID mouse model of aggressive human pre-B ALL to evaluate the in vivo antileukemic efficacy of B43 (anti-CD19)-pokeweed antiviral protein (PAP) immunotoxin. A 3-day treatment with nontoxic doses of B43-PAP markedly reduced the incidence of paraplegia and improved event-free survival (EFS) in SCID mice challenged with 1 x 10(6) NALM-6-UM1 pre-B ALL cells, as reflected by significantly higher cumulative proportions of mice free of paraplegia or alive at 1 to 7 months, as compared with phosphate-buffered saline (PBS) treated control mice. The Kaplan-Meier estimates and standard errors of the probability of developing paraplegia after inoculation of 1 x 10(6) NALM-6-UM1 cells was 64% +/- 10% for PBS-treated mice (median time to paraplegia = 37 days) (N = 27), 18% +/- 8% for mice treated with 15 micrograms B43-PAP (5 micrograms/mouse/d x 3 days) (N = 23) and 5% +/- 5% for mice treated with 30 micrograms B43-PAP (10 micrograms/mouse/d x 3 days) (N = 21). While 27 of 27 PBS-treated control SCID mice died of leukemia at 38 +/- 1 days (range = 24 to 54 days), only 16 of 44 B43-PAP-treated mice developed leukemia at 74 +/- 12 days (range = 30 to 182 days), consistent with greater than or equal to 6 logs kill of clonogenic NALM-6-UM1 cells in 64% of SCID mice. The Kaplan-Meier estimates and standard errors of the probability of long-term EFS after inoculation of 1 x 10(6) NALM-6-UM1 cells were 65% +/- 10% for mice treated with 15 micrograms B43-PAP and 60% +/- 11% for mice treated with 30 micrograms B43-PAP with a median survival time of greater than 7 months for both groups. In contrast, neither unconjugated B43 monoclonal antibody nor the anti-T-cell immunotoxin G17.2 (anti-CD4)-PAP decreased the incidence of paraplegia or improved EFS.(ABSTRACT TRUNCATED AT 400 WORDS)

Pokeweed antiviral protein: ribosome inactivation and therapeutic applications

Pokeweed antiviral protein (PAP) is a ribosome-inactivating protein (RIP) that inactivates ribosomes by the removal of a single adenine from ribosomal RNA. The studies summarized in our review concern the nature and application of this novel therapeutic agent. We describe how researchers continue to elucidate the structure and biologic activity of RIPs. Pokeweed antiviral protein is among the RIPs that have been conjugated to selective monoclonal antibodies for the treatment of several human cancers and viral diseases. Clinical trials using PAP immunotoxins for the treatment of leukemia have been particularly encouraging.

Production of a pokeweed antiviral protein (PAP)-containing immunotoxin, B43-PAP, directed against the CD19 human B lineage lymphoid differentiation antigen in highly purified form for human clinical trials

We describe a standardized method for the preparation and purification of a potent immunotoxin against B-lineage leukemia/lymphoma cells, constructed with the ribosome inhibitory single chain plant toxin pokeweed antiviral protein (PAP) and a murine IgG1 monoclonal antibody (MoAb) specific for the human B lineage differentiation antigen CD19 for human clinical trials. PAP was prepared from spring leaves of Phytolacca americana plants by ammonium sulfate precipitation and purified to homogeneity by successive steps of ion exchange chromatography. B43 MoAb was produced in vitro by hollow fiber technology and purified to homogeneity by affinity chromatography. PAP toxin and B43 MoAb were modified via their free amino groups prior to their intermolecular conjugation. 2-iminothiolane was used to introduce reactive sulfhydryl groups into PAP and N-succinimidyl 3-(2-pyridyldithio) propionate was used to introduce 2-pyridyl disulfide bonds into B43 MoAb. Modified PAP was reacted with modified B43 MoAb resulting in a sulfhydryl-disulfide exchange reaction and yielding disulfide linked PAP-B43 MoAb conjugates, which we refer to as B43-PAP immunotoxin. B43-PAP immunotoxin was subjected to preparative gel filtration chromatography and cation exchange chromatography to obtain a highly purified, sterile, and pyrogen-free immunotoxin preparation with less than 5% free antibody contamination and less than 0.5% free PAP contamination. The final product displayed a high affinity for and a very potent anti-leukemic activity against B lineage leukemia cells. With slight modifications, the procedures detailed in this report should be generally applicable to preparation of other PAP-MoAb conjugates for treatment of cancer or AIDS.

Depurination of plant ribosomes by pokeweed antiviral protein

Mammalian ribosomes have been shown to be enzymatically modified by ribosomal inactivating protein (RIPs) via specific depurination of rRNA. Here we report that ribosomes isolated from wheat germ contain intact and undepurinated rRNA and are depurinated by pokeweed antiviral protein (PAP). Pokeweed ribosomes isolated under the same conditions are depurinated. Total RNA isolated from pokeweed in the presence of strong denaturants was found to pbe partially depurinated. We conclude that wheat germ ribosomes are resistant to the endogenous RIP, tritin, but are sensitive to PAP and that pokeweed ribosomes can be depurinated by the N-glycosidase activity of endogenous PAP during isolation.

Poliovirus-mediated entry of pokeweed antiviral protein

Infection of HeLa cells with poliovirus results in cell permeabilization to pokeweed antiviral protein. Cell permeabilization was dependent on the integrity of virus capsid proteins and directly proportional to the multiplicity of infection. This study demonstrates that virus adsorption is sufficient for the entry of pokeweed antiviral protein into poliovirus-infected cells.

Tolerability of long term therapy with enalapril maleate in patients resistant to other therapies and intolerant to captopril

Patients with severe hypertension and/or congestive heart failure (n = 281) who were unresponsive to other therapies and intolerant to captopril received enalapril treatment (mean dose 19.5 mg/day) under study conditions as part of a Compassionate Use Program. Many of these patients had serious concurrent disorders known to predispose them to a greater risk of adverse experiences and death. The mean duration of enalapril treatment was 29 weeks, with a range of 1 day to approximately 3.5 years. Enalapril was generally well tolerated, and the estimated long term probability of patients terminating enalapril therapy because of adverse effects was low. 20 patients had discontinued captopril treatment because of low white blood cell counts; during subsequent enalapril treatment these reactions resolved in 14 patients, persisted in 2 patients, and could not be evaluated in 4 patients. Captopril-related proteinuria improved or resolved in 9 and persisted in 2 of 15 patients, taste disturbances resolved in 35 and persisted in 2 of 38 patients; and rash resolved in all but 7 of 178 patients during enalapril treatment. 18 patients (6%) discontinued enalapril treatment because of lack of efficacy; 6 of these 18 patients died due to a progression of heart failure, and another 11 patients died for other reasons. The deaths were considered unrelated to therapy with enalapril. Adverse reactions were the reason for discontinuation of enalapril treatment in 53 patients (19%). The most common adverse experiences that resulted in discontinuation of enalapril were: impairment of renal function (5%), hypotension (2%) and rash (2%). No neutropenia, proteinuria, or new taste disturbances were recorded as reasons for discontinuation.(ABSTRACT TRUNCATED AT 250 WORDS)

Enalapril and hydrochlorothiazide as antihypertensive agents in the elderly

This randomized, double blind study compared the antihypertensive effects of enalapril to hydrochlorothiazide (HCTZ) in the elderly. One hundred seventy-four patients with diastolic blood pressures (DBP) of 90-120 mm Hg or isolated systolic hypertension (ISH) (systolic BP greater than 160 mm Hg and diastolic BP less than 90 mm Hg) were studied. After four weeks of placebo, patients received either enalapril 10 mg or HCTZ 12.5 mg once daily. If the BP was uncontrolled (DBP greater than 85 mm Hg or SBP greater than 140 mm Hg) after 4 weeks, the dose was doubled. At 8 weeks, if necessary, the other drug could be added at the lower dose, then doubled 4 weeks later. Two-thirds of the patients had essential hypertension (EH), the rest ISH; 68% were male and 80% Caucasian. The baseline BPs were 167/94 mm Hg in both groups, at 8 weeks the mean BPs were 148/85 mm Hg in both groups (p less than or equal to 0.01), and at the end of the study the BPs with enalapril were 144/83 mm Hg and with HCTZ they were 145/83 mm Hg (p less than or equal to 0.01). The Caucasians showed greater BP falls on enalapril than HCTZ after 4 weeks (p less than or equal to 0.05). The SBP falls for the ISH (-22 mm Hg) and EH (-23 mm Hg) groups were similar at the end of the study. Both drugs were generally well tolerated. Laboratory adverse experiences (AEs) were 9% more common in the HCTZ patients (n.s.). Enalapril and HCTZ both seem to be effective antihypertensive agents in the elderly.

Safety profiles of the angiotensin converting enzyme inhibitors captopril and enalapril

The safety profiles of the angiotensin converting enzyme inhibitors, captopril and enalapril, are the focus of this review. Adverse effects are reviewed as those associated with sulfhydryl compounds and as those considered class-specific adverse effects of angiotensin converting enzyme inhibitors. Specifically discussed are the incidences of the adverse effects of rash, taste disturbance, neutropenia, and proteinuria, which are characteristic of compounds containing sulfhydryl moieties, such as captopril. It is concluded from the review of these safety data that enalapril is well tolerated, has few class-specific adverse effects, and may offer a potential advantage over captopril by having fewer sulfhydryl-related adverse effects.

[Worldwide experience with enalapril]

Up to now, the experiments carried out throughout the world with enalapril have been most encouraging. The drug gives good, even excellent responses in 54 to 66 % of patients with essential hypertension, and it is at least as effective as diuretics and beta-blockers. Compared with those of diuretics, the effects of enalapril confirm that the best responders are those patients who are most dependent on the renin-angiotensin system. When a diuretic is administered concomitantly with enalapril, almost all patients respond and the therapeutic effect is well maintained in long term. Blocadren or alpha-methyldopa can be added to hydrochlorothiazide, thus providing additional benefits to patients with severe hypertension. Enalapril reduces the undesirable metabolic effects of hydrochlorothiazide, particularly hypokalaemia. Altogether, enalapril and captopril have similar effectiveness, but enalapril is better tolerated and does not seem to produce the side-effects encountered with captopril, notably skin rashes and ageusia. As expected, enalapril and other angiotensin-converting enzyme inhibitors may be associated with azotaemia in patients with bilateral renovascular hypertension.

The effect of renal function on enalapril kinetics

Enalapril maleate (MK-421), a nonmercapto-containing angiotensin converting enzyme (ACE) inhibitor, is converted in vivo to enalaprilat (MK-422), the active diacid. We evaluated serum profiles and urinary excretion of oral enalapril maleate in patients with renal disease (group I, creatinine clearance less than 3 ml/min, patients undergoing dialysis, n = 10; group II, creatinine clearance 10 to 79 ml/min, n = 9) compared with healthy subjects (group III, creatinine clearance greater than 80 ml/min, n = 10). Group I received a 10 mg dose during a day while not receiving dialysis and a 10 mg dose 1 hour before dialysis 2 weeks later. Groups II and III received a single 10 mg dose. Blood samples and urine were collected for 48 hours. Impaired renal function resulted in elevated serum and plasma concentrations of enalapril maleate and decreased excretion rates and urinary recovery of enalapril maleate and enalaprilat. The data suggest an apparent increase in the extent of metabolism of enalapril maleate to enalaprilat or an increase in nonrenal elimination of unchanged enalapril maleate in renal disease compared with normal health. Enalaprilat was dialyzable.

Enalapril: a review of human pharmacology

Enalapril, an orally-active, long-acting, nonsulphydryl angiotensin-converting enzyme (ACE) inhibitor, is extensively hydrolysed in vivo to enalaprilat, its bioactive form. Bioactivation probably occurs in the liver. Metabolism beyond activation to enalaprilat is not observed in man. Administration with food does not affect the bioavailability of enalapril; excretion of enalapril and enalaprilat is primarily renal. Peak serum enalaprilat concentrations are reached 4 hours post-dose, and the profile is polyphasic with a prolonged terminal half-life (greater than 30 hours) due to the binding of enalaprilat to ACE. Steady-state is achieved by the fourth daily dose, with no evidence of accumulation. The effective accumulation half-life following multiple dosing is 11 hours. Higher serum concentrations and delayed urinary excretion occur in patients with severe renal insufficiency. Enalapril reduces blood pressure in hypertensive patients by decreasing systemic vascular resistance. The blood pressure reduction is not accompanied by an increase in heart rate. Furthermore, cardiac output is slightly increased and cardiovascular reflexes are not impaired. Once- and twice-daily dosage regimens reduce blood pressure to a similar extent. Enalapril increases renal blood flow and decreases renal vascular resistance. Enalapril also augments the glomerular filtration rate in patients with a glomerular filtration rate less than 80 ml/min. Enalapril reduces left ventricular mass, and does not affect cardiac function or myocardial perfusion during exercise. There is no rebound hypertension after enalapril therapy is stopped. Enalapril does not produce hypokalaemia, hyperglycaemia, hyperuricaemia or hypercholesterolaemia. When combined with hydrochlorothiazide, enalapril attenuates the undesirable diuretic-induced metabolic changes. Therapeutic doses of enalapril do not affect serum prolactin and plasma cortisol in healthy volunteers or T3, rT3, T4 and TSH in hypertensive patients. Enalapril has natriuretic and uricosuric properties. The antihypertensive effect of enalapril is potentiated by hydrochlorothiazide, timolol and methyldopa, but unaffected by indomethacin and sulindac. No interactions occur between enalapril and frusemide, hydrochlorothiazide, digoxin and warfarin. The bioavailability of enalapril is slightly reduced when propranolol is coadministered, but this does not appear to be of any clinical significance. Enalapril increases cardiac output and stroke volume and decreases pulmonary capillary wedge pressure in patients with congestive heart failure refractory to conventional treatment with digitalis and diuretics.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of food on the bioavailability of enalapril

In a randomized, two-period crossover study in 12 normal volunteers, serum and urine concentrations of the angiotensin-converting enzyme inhibitor enalapril and its active metabolite enalaprilat were determined following administration of a single 40-mg tablet of enalapril maleate administered both in the fasting state and with a standard breakfast. A 7-d interval separated the two treatment periods. Area under the serum concentration-time curves for enalaprilat and urinary recoveries for enalaprilat and total drug did not differ significantly between the fed and fasted conditions. The mean observed maximum serum concentration of enalaprilat was slightly higher for the fasting treatment, but the time to peak concentration was almost identical for the two treatments. Enalapril maleate is unlike the prototype angiotensin-converting enzyme inhibitor captopril in that a standard meal does not appear to influence absorption of this new drug.

Indacrinone: natriuretic and uricosuric effects of various ratios of its enantiomers in healthy men

Indacrinone is an investigational loop-acting diuretic. To evaluate the natriuretic and uricosuric effects of varying ratios of its enantiomers, 10 healthy men, on a controlled Na+ (100 mEq) and K+ (80 mEq) diet, participated in a double-blind, randomized, balanced incomplete block, multiple-dose (one week) study of a fixed daily dose (10 mg) of (-) enantiomer combined with increasing doses (40, 90 and 140 mg) of (+) enantiomer versus 50 mg hydrochlorothiazide and placebo. On day 1, mean 24-h urinary Na+ increased (p less than 0.01) comparably (approximately 285 mEq) after each enantiomer combination and hydrochlorothiazide; however, the enantiomer combinations had marked uricosuric and hypouricemic effects that were enhanced with increased (+) enantiomer doses. By day 7, while enantiomer combinations and hydrochlorothiazide demonstrated comparable natriuretic activity, mean serum uric acid levels (mg/dl), in comparison to placebo, were increased (p less than 0.05) with hydrochlorothiazide but progressively decreased with increases in (+) enantiomer. Thus varying the ratio [(+, uricosuric): (-, natriuretic)] of the enantiomers of indacrinone caused natriuresis similar to hydrochlorothiazide, but had an opposite effect on serum uric acid.

Enalapril worldwide experience

Overall, the worldwide experience on enalapril to date is very encouraging. The drug produces good to excellent responses in 54 to 66 percent of patients with essential hypertension and is at least as effective as either diuretics or beta blockers. The effects of enalapril compared with those of diuretics confirm that patients more dependent upon the renin-angiotensin system respond better. When hydrochlorothiazide is administered concomitantly with enalapril, almost all patients respond, with good long-term maintenance. In patients with severe hypertension, Blocadren or Aldomet may be added in addition to hydrochlorothiazide and will produce additional benefit. Enalapril attenuates the adverse metabolic effects of hydrochlorothiazide, particularly hypokalemia. Overall, although the efficacy of enalapril and that of captopril are similar, enalapril is better tolerated and does not appear to be associated with any significant occurrence of captopril-type side effects, particularly the skin rash and loss of taste. As expected, enalapril and other converting inhibitors may be associated with azotemia in patients with bilateral renovascular hypertension.

Initial evaluation of the non-sulfhydryl-containing converting enzyme inhibitor MK-521 in hypertensive humans

MK-521 is a new orally active, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor. Single doses of 2.5, 5.0, 10.0, and 20.0 mg were administered to nine hypertensive patients alternating with placebo. All doses of MK-521 caused profound suppression of ACE activity for more than 24 h and decreased standing diastolic blood pressure for more than 12 h without changes in pulse rate. Although there was no further reduction in blood pressure with doses above 5.0 mg, the duration of action was prolonged for more than 24 h with the higher doses. Serum MK-521 concentrations increased with dosage, and ACE was inhibited maximally at concentrations above 10 ng/ml. In this initial study, MK-521 was well tolerated and proved to be a potent and long-acting antihypertensive agent.

Purification and characterization of three elongation factors, EF-1 alpha, EF-1 beta gamma, and EF-2, from wheat germ

Three elongation factors, EF-1 alpha, EF-1 beta gamma and EF-2, have been isolated from wheat germ. EF-1 alpha and EF-2 are single polypeptides with molecular weights of approximately 52,000 and 102,000, respectively. The most highly purified preparations of EF-1 beta gamma contain four polypeptides with molecular weights of approximately 48,000, 46,000 and 36,000, 34,000. EF-1 alpha supports poly(U)-directed binding of Phe-tRNA to wheat germ ribosomes and catalyzes the hydrolysis of GTP in the presence of ribosomes, poly(U), and Phe-tRNA. EF-2 catalyzes the hydrolysis of GTP in the presence of ribosomes alone and is ADP-ribosylated by diphtheria toxin to the extent of 0.95 mol of ADP-ribose/mol of EF-2. EF-1 beta gamma decreases the amount of EF-1 alpha required for polyphenylalanine synthesis about 20-fold. EF-1 beta gamma enhances the ability to EF-1 alpha to support the binding of Phe-tRNA to the ribosomes and enhances the GTPase activity of EF-1 alpha. Wheat germ EF-1 alpha, EF-1 beta gamma, and EF-2 support polyphenylalanine synthesis on rabbit reticulocyte ribosomes as well as on yeast ribosomes.

Antihypertensive efficacy of once daily MK-521, a new nonsulfhydryl angiotensin-converting enzyme inhibitor

The effects of the new nonsulfhydryl-containing oral converting-enzyme inhibitor MK-521 on blood pressure, heart rate, angiotensin-converting enzyme activity, plasma renin activity and plasma aldosterone concentration were assessed in 10 hypertensive patients. After a 2-week no-treatment period, patients received placebo and then 14 days each: MK-521 20 mg once daily, hydrochlorothiazide 50 mg once daily and the latter 2 in combination. During the last day of each treatment, the mean (+/- standard deviation) time-averaged (1- to 12-hour) standing diastolic blood pressure decreased from 106 +/- 8 (placebo) to 95 +/- 10 mm Hg with MK-521, 95 +/- 13 mm Hg with hydrochlorothiazide (p less than 0.05 vs placebo) and 88 +/- 11 mm Hg with the combination (p less than 0.05 vs all other treatments). The antihypertensive effect of MK-521 was maintained 24 hours after dosing. Heart rate did not change significantly after MK-521 treatment. MK-521 caused a marked suppression of converting enzyme activity for over 24 hours; plasma renin activity increased significantly after each active treatment and MK-521 significantly decreased the hydrochlorothiazide-induced elevation of plasma aldosterone concentration. In this short-term trial, MK-521 was well tolerated.

An overview of the clinical pharmacology of enalapril

Enalapril maleate is a prodrug which when administered orally is hydrolysed to release the active converting enzyme inhibitor enalaprilat. Enalapril maleate is 60% absorbed and 40% bioavailable as enalaprilat. Both compounds undergo renal excretion without further metabolism. The functional half-life for accumulation of enalaprilat is 11 h, and this is increased in the presence of a reduction in renal function. Inhibition of converting enzyme inhibition is associated with reductions in plasma angiotensin II and plasma aldosterone, and with increases in plasma renin activity and plasma angiotensin I. Acute and chronic effects have been reviewed. When given with hydrochlorothiazide, enalapril attenuates the secondary aldosteronism and ameliorates the hypokalaemia from diuretics. Both acutely and chronically in patients with essential hypertension, enalapril reduced blood pressure with a rather flat dose-response curve. No evidence of a triphasic response such as seen with captopril has been demonstrated with enalapril, and blood pressure returns smoothly to pretreatment levels when the drug is abruptly discontinued. Once- or twice-daily dosing gives similar results. The antihypertensive effects of enalapril are potentiated by hydrochlorothiazide. Haemodynamically, blood pressure reduction is associated with a reduced peripheral vascular resistance and an increase in cardiac output and stroke volume with little change in heart rate. Renal vascular resistance decreases, and renal blood flow may increase without an increase in glomerular filtration in patients with normal renal function. In patients with essential hypertension and glomerular filtration rates below 80 ml/min/m2, both renal blood flow and glomerular filtration rates may increase.

Comparative antihypertensive effects of enalapril maleate and hydrochlorothiazide, alone and in combination

Enalapril maleate is an investigational oral prodrug whose hydrolyzed diacid metabolite is a potent angiotensin-converting enzyme inhibitor. Fourteen patients with mild to moderate hypertension were evaluated after receiving placebo, and two weeks of treatment with each of the following: enalapril maleate (20 mg b.i.d.), hydrochlorothiazide (25 mg b.i.d.), and the two in combination. In comparison to placebo, the magnitudes of the blood pressure reduction after enalapril and hydrochlorothiazide alone were comparable. The reduction in blood pressure following enalapril was evident throughout the 12-hour dosing interval. The combination of enalapril and hydrochlorothiazide resulted in a marked further reduction in blood pressure that was greater than that predicted from the responses to the individual drugs (P less than 0.05). Biochemical parameters confirmed inhibition of angiotensin-converting enzyme during enalapril treatment; serum angiotensin-converting enzyme activity proved an excellent monitor of compliance. Enalapril was generally well tolerated. Adverse effects included symptomatic hypotension in three patients when enalapril was first added to hydrochlorothiazide and hyperesthesia of the oral mucosa without a loss of taste in one patient on enalapril. Enalapril maleate alone and especially in combination with hydrochlorothiazide appears to be an effective, well-tolerated converting enzyme inhibitor with at least a 12-hour duration of action.

Inhibition of herpes simplex virus DNA synthesis by pokeweed antiviral protein

Pokeweed antiviral protein at a concentration of 3 microM inhibited both the synthesis and release of infectious herpes simplex virus type 1 in cell culture by 90 and 99%, respectively. Addition of pokeweed antiviral protein to Vero cell monolayers before virus infection was 10 to 15% more effective in reducing virus yields than was the simultaneous addition of the antiviral protein with virus inoculum. Viral DNA synthesis was inhibited by 90% in cells which had been exposed to the antiviral protein, whereas cellular DNA synthesis was unaffected. No significant inhibition in the synthesis of the majority of viral infected-cell polypeptides was observed early postinfection (7 h), with the exception of infected cell polypeptides 4 and 41, whose syntheses were reduced by 38 and 25%, respectively. At 9 to 21 h postinfection, however, the synthesis of individual infected cell polypeptides was reduced by 48 to greater than 99%.

Chemical modifications of pokeweed antiviral protein: effects upon ribosome inactivation, antiviral activity and cytotoxicity

Pokeweed antiviral protein (PAP) is a protein known to inactivate eukaryotic ribosomes by an unknown enzymatic action and inhibit the production of mammalian viruses in tissue culture. This protein was subjected to a variety of chemical modifications to determine their effects upon ribosomal inactivation, antiviral action, and cytotoxicity. It was found that modifications of a number of different amino acid residues had similar effects upon all 3 activities. Also the inactivation of PAP with diethylpyrocarbonate was not due to its reaction with a histidine residue but to a modification of an unidentified amino acid residue.

Effects of enalapril, a new converting enzyme inhibitor, in hypertension

The new angiotensin converting enzyme inhibitor enalapril maleate was given in single oral doses of 2.5, 5, and 10 mg to 11 hospitalized patients with uncomplicated essential hypertension who were on a 150-mEq sodium diet. All doses of enalapril induced reduction of mean seated diastolic blood pressure (SDBP). The magnitude of the initial SDBP reduction was not dose related, but the duration of effect was longer (greater than 12 hr) after the 5 and 10 mg. After dosing, mean plasma angiotensin converting enzyme activity (ACE) and aldosterone concentration (PAC) fell, while plasma renin activity (PRA) rose. Serum concentrations of the active diacid from of enalapril increased linearly with dosage; ACE was inhibited maximally at concentrations above 10 ng/ml. During repeated dosing in the outpatient trial there was attenuation of the antihypertensive effect (12 to 24 hr after dosing) in eight of 10 patients. Despite dose increases only two patients achieved SDBP control (less than or equal to 90 mm Hg). In the five patients in whom 50 mg/day hydrochlorothiazide was added near the end of the trail mean SDBP was further reduced. Enalapril was well tolerated. Further studies of the drug, especially in combination with diuretic, are needed.

A comparative pilot study of enalapril, a new converting enzyme inhibitor, and hydrochlorothiazide in essential hypertension

Eight patients with essential hypertension completed a double-blind, randomly allocated crossover comparison of either 5 or 10 mg enalapril maleate, 50 mg hydrochlorothiazide, or their combination administered once daily during sequential two-week periods. Blood pressure, pulse rate, plasma renin activity, angiotensin-converting enzyme activity, plasma aldosterone concentration, and urinary electrolytes were monitored for 24 hours after placebo and on days 1 and 14 of each treatment period. After two weeks of each treatment, only the combination of enalapril and hydrochlorothiazide significantly lowered the mean seated diastolic blood pressure (SDBP). Likewise, SDBP control (less than or equal to 90 mm Hg) was achieved only after combination therapy; six of the eight patients were controlled by the combination for up to 24 hours. The initial SDBP response to combination therapy differed with the sequence of drug addition; however, by day 14 the responses were comparable, regardless of whether hydrochlorothiazide or enalapril was first given. Mean converting enzyme activity was suppressed by enalapril in all patients, though it did not always correlate with changes in SDBP or plasma aldosterone. Mean plasma renin activity increased, but the increase was significant only on the combination. There were no serious adverse effects.