Enhancing effect of ubenimex (bestatin) on proliferation and differentiation of hematopoietic progenitor cells, and the suppressive effect on proliferation of leukemic cell lines via peptidase regulation

The effects of bestatin on humoral response to sheep erythrocytes in non-treated and cyclophosphamide-immunocompromised mice

The effects of bestatin on humoral immune response to sheep erythrocytes (SRBC) and restoration of the response impaired by a single cyclophosphamide dose (350 mg/kg) were tested on mice. Bestatin (at doses of 10, 1, and 0.1 mg/kg) was administered intraperitoneally (i.p.) 5 or 10 times. The pharmacological immunosuppression was induced by a single i.p. injection of cyclophosphamide (350 mg/kg) administered 24 h before the first bestatin dose. The mice were immunized i.p. with SRBC 24 h after the last dose of bestatin. It was found that multiple administration of bestatin at all three doses potentiated the humoral response to SRBC in non-treated mice, resulting in an increased number of plaque-forming cells (PFC) and 2-mercaptoethanol (2-ME)-resistant anti-SRBC antibodies. However, five times administration of bestatin at the doses under investigation caused further decreases in total anti-SRBC hemagglutinins. A single injection of cyclophosphamide (350 mg/kg) suppressed humoral response of mice to the antigen. Administration of bestatin after pharmacological immunosuppression partially prevented the suppressive action of cyclophosphamide in the in vivo model of the humoral immune response to SRBC. The protective action of bestatin was both dose- and schedule-dependent. Ten times' exposure to a bestatin dose of 0.1 mg/kg after a high cyclophosphamide dose partially reduced the suppressive effect of this drug on humoral response of SRBC-immunized mice, increasing PFC on days 4 and 7 after immunization, which coincided with restored ability of the lymphocytes to produce the 2-ME-resistant hemagglutinins on day 7 and the total anti-SRBC hemagglutinins on day 14 after priming.

Heterologous expression and purification of Vibrio proteolyticus (Aeromonas proteolytica) aminopeptidase: a rapid protocol

Metalloaminopeptidases (mAPs) are enzymes that are involved in HIV infectivity, tumor growth and metastasis, angiogenesis, and bacterial infection. Investigation of structure-function relationships in mAPs is a prerequisite to rational design of anti-mAP chemotherapeutics. The most intensively studied member of the biomedically important dinuclear mAPs is the prototypical secreted Vibrio proteolyticus di-zinc aminopeptidase (VpAP). The wild-type enzyme is readily purified from the supernatant of cultures of V. proteolyticus, but recombinant variants require expression in Escherichia coli. A greatly improved system for the purification of recombinant VpAP is described. A VpAP-(His)(6) polypeptide, containing an N-terminal propeptide, and a C-terminal (His)(6) adduct, was purified by metal ion affinity chromatography from the supernatant of cultures of E. coli. This single step replaced the sequence of (NH(4))(2)SO(4) fractionation, and anion-exchange and hydrophobic interaction chromatographic separations of earlier methods. Traditionally, recombinant VpAP proenzyme has been treated with proteinase K and with heat (70 degrees C), to remove the N- and C-terminal regions, and yield the mature active enzyme. This method is unsuitable for VpAP variants that are unstable towards these treatments. In the new method, the hitherto noted, but not fully appreciated, ability of VpAP to autocatalyze the hydrolysis of the N-terminal propeptide and C-terminal regions was exploited; extensive dialysis of the highly purified VpAP-(His)(6) full-length polypeptide yielded the mature active protein without recourse to proteinase K or heat treatment. Purification of variants that have previously defied isolation as mature forms of the protein was thus carried out.

Development of a liquid chromatography/tandem mass spectrometry assay for the determination of bestatin in rat plasma and its application to a pharmacokinetic study

Bestatin is a low molecular weight aminopeptidase inhibitor originally isolated from culture filtrates of Streptomyces olivoreticuli. We have developed a sensitive, specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the quantitative determination of bestatin in rat plasma using granisetron as the internal standard. The analyte and internal standard were isolated from 50 microL plasma samples by solid phase extraction (SPE). Reverse-phase HPLC separation was accomplished on a Lichrospher C18 column (4.6 mm x 50 mm, 5 microm) with a mobile phase composed of methanol-water-formic acid (70:30:0.5, v/v/v) at a flow rate of 0.8 mL/min. The method had a chromatographic total run time of 3 min. A Varian 1200L electrospray tandem mass spectrometer equipped with an electrospray ionization source was operated in selected reaction monitoring (SRM) mode with the precursor-to-product ion transitions m/z 309.2-->120.0 (bestatin) and 313.4-->138.0 (granisetron) used for quantitation. The method was sensitive with a lower limit of quantitation (LLOQ) of 5 ng/mL, with good linearity (r2 >or= 0.999) over the linear range of 5-2000 ng/mL. All the validation data, such as accuracy, precision, and inter-day repeatability, were within the required limits. The method was successfully applied to pharmacokinetic study of bestatin in rats.

Aminopeptidase-N/CD13 (EC 3.4.11.2) inhibitors: chemistry, biological evaluations, and therapeutic prospects

Aminopeptidase N (APN)/CD13 (EC 3.4.11.2) is a transmembrane protease present in a wide variety of human tissues and cell types (endothelial, epithelial, fibroblast, leukocyte). APN/CD13 expression is dysregulated in inflammatory diseases and in cancers (solid and hematologic tumors). APN/CD13 serves as a receptor for coronaviruses. Natural and synthetic inhibitors of APN activity have been characterized. These inhibitors have revealed that APN is able to modulate bioactive peptide responses (pain management, vasopressin release) and to influence immune functions and major biological events (cell proliferation, secretion, invasion, angiogenesis). Therefore, inhibition of APN/CD13 may lead to the development of anti-cancer and anti-inflammatory drugs. This review provides an update on the biological and pharmacological profiles of known natural and synthetic APN inhibitors. Current status on their potential use as therapeutic agents is discussed with regard to toxicity and specificity.

Aminopeptidase inhibitors bestatin and actinonin inhibit cell proliferation of myeloma cells predominantly by intracellular interactions

The antiproliferative effects of bestatin and actinonin on U937 and K562 cells have been compared with their inhibitory activity on cell surface aminopeptidases. The results strongly suggest that the inhibition of cell surface aminopeptidases cannot be the main reason for the inhibition of cell proliferation. This was confirmed by studying the effect of buthionine sulfoximine (BSO), MK-571 (3-([[3-(2-[7-chloro-2-quinolinyl]-ethenyl)-phenyl]-[(3-dimethyl-amino-3-oxopropyl)-thio]-methyl]thio)propanoic acid) and verapamil on the inhibition of cell proliferation by bestatin and actinonin. BSO and MK-571, which inhibit the efflux of drugs mediated by multidrug resistance-associated protein (MRP), increased the action of both inhibitors, indicating that the latter enter the cells and that their export is mediated by MRP in both cell lines. Verapamil significantly increased the inhibitory activity of bestatin on K562 cells, indicating that the intracellular concentration of bestatin can be mediated also by P-glycoprotein.

CD13/N-aminopeptidase is involved in the development of dendritic cells and macrophages from cord blood CD34+ cells

Expression of CD13/N-aminopeptidase may reflect cell activation and growth. We examined its role regarding cell growth in cultures of cord blood CD34+ cells with stem cell factor/Flt-3 ligand/granulocyte-macrophage colony-stimulating factor/tumor necrosis factor-. Indeed, 82% ± 6% of cells from culture day 5 were CD13hi, 25% ± 8% of which were still Lin−. About 50% of CD13hiLin− cells, which comprise progenitors of dendritic cells (DC), monocytes/macrophages and granulocytes, and 30% of CD13loLin− cells were CD34+. Sorted CD34+CD13hiLin− cells, cultured further for 7 days with the same cytokines, expanded 31-fold and CD34-CD13hiLin− cells 7-fold, but CD34+CD13loLin− and CD34−CD13loLin− cells did not grow. Thus, cell growth correlated with CD13 expression, all the more so that cells were CD34+. Actinonin, the most potent N-aminopeptidase inhibitor, was used to engage CD13 on sorted CD13hiLin− cells and on culture day-7 bulk cells. In both cases, this resulted in reversible cell growth arrest, with 30% to 60% fewer cells in the G2/S-M phase than in controls. Interestingly, similar effects were noted with CD13 monoclonal antibody TÜK1, which does not inhibit N-aminopeptidase activity, but not with N-aminopeptidase-blocking antibodies WM15 and F23. All cycling cells appeared susceptible to actinonin, which induced cell apoptosis at the same time as Bcl-2 was downregulated and caspase-3 activity increased, but finally percentages and yields of DC and macrophage precursors were affected more than those of granulocytic cells. Thus, through engagement of N-aminopeptidase enzymatic site but possibly also of an independent determinant, CD13 plays a role in the growth of DC/macrophage progenitors and precursors.

Requirement for surface aminopeptidase activities during development of CD8+ fetal thymocytes

The role of surface aminopeptidases (APs), enzymes that cleave amino-terminal residues from polypeptide chains, in the development of fetal thymocytes was studied using a murine fetal thymic organ culture (FTOC) model. FTOC AP activity was demonstrable for various amino acid-p-nitroanilide substrates, and specific inhibitors of AP (amastatin and bestatin) inhibited enzymatic activity. AP activity decreased from Day 4 to Day 7 in FTOC. Inhibition of AP activity during thymic development by FTOC in the presence of bestatin caused a significant selective decrease in the percentage of CD8+ cells (both CD4+CD8+ and CD4-CD8+). Bestatin did not downregulate expression of CD8 by a mature CD8+ T cell clone. These data suggest that APs are involved in the development of thymocytes expressing CD8.

Ubenimex activates the E-cadherin-mediated adhesion of a breast cancer cell line YMB-S

It has been reported that ubenimex, a biological response modifier, has a direct anti-tumor effect. To clarify the mechanism involved, we examined the effects of ubenimex on the growth and adhesive property of a breast cancer cell line YMB-S. The cells proliferate in a floating manner without aggregation in normal complete medium. Ubenimex induced cell-cell and cell-surface adhesion of the cells accompanied with growth suppression. E-Cadherin localized at cell-cell contact sites of adhered cells, and anti-E-cadherin antibody inhibited the adhesion. Both Western blot analysis and binding assay disclosed that there was no apparent difference between E-cadherin levels of the cells before and after the treatment with ubenimex. These results indicate that ubenimex inhibits the proliferation of YMB-S cells and augments cell-to-cell adhesion through the induction of E-cadherin-mediated adhesion resulting from the functional activation of pre-expressed but inefficient E-cadherin.

Successful treatment of a 93-year-old patient with hypoplastic acute monocytic leukemia using macrophage colony-stimulating factor

A 93-year-old patient with hypoplastic acute monocytic leukemia (AMoL) achieved a complete remission after macrophage colony-stimulating factor (M-CSF) therapy. Initially, the patient was treated with a low dose of cytarabine, but this treatment proved ineffective. M-CSF was administered for 14 days by drip intravenous infusion, 800 x 10(4) units per day. After a gradual decrease in the number of leukemic cells, a rapid increase in neutrophils was observed in the peripheral blood, and a bone marrow examination 22 days after discontinuation of M-CSF medication revealed a complete remission. These findings suggest that M-CSF may be useful in treating some elderly patients who have hypoplastic AMoL.

Effects of Bestatin on hematopoiesis in long-term human bone marrow cultures

The effects of Bestatin (Ubenimex, UBX) on normal hematopoiesis were investigated using long-term bone marrow cultures (LTBMC) to determine whether it might enhance hematopoiesis over a long period, as well as induce the release of cytokines. LTBMC were inoculated with 0.1 or 1.0 microgram/ml of UBX at the onset of culture and was added at each weekly medium change. The cellularity and the content of the progenitors in nonadherent layer were examined each week for 5 weeks; those from the adherent layer were examined at week 5. The number of the nucleated mature cells and that of the myeloid progenitors from the nonadherent layer increased significantly (approximately two-fold) following treatment with UBX vs controls. The total number of colonies and the number of myeloid progenitors, but not that of erythroid progenitors, from the adherent layer increased significantly (about 1.5-fold) following treatment with 1.0 microgram/ml UBX. The level of interleukin-6 (IL-6) in the culture supernatants was significantly increased one day after the addition of 1.0 microgram/ml UBX. Findings indicate that UBX stimulated both the production of mature cells and myeloid progenitors on normal hematopoiesis in LTBMC. This was mediated by an indirect action via IL-6 production.

Expression of aminopeptidase N on human choriocarcinoma cells and cell growth suppression by the inhibition of aminopeptidase N activity

We previously found that an aminopeptidase inhibitor, ubenimex (bestatin), had a growth-suppressive effect on choriocarcinoma cell lines in vitro. To clarify the mechanism of this action, we investigated the expression of aminopeptidase N (AP-N/CD13) on choriocarcinoma cells and other human tumor cells. Two choriocarcinoma cell lines, NaUCC-4 and BeWo, had higher AP-N activity than other cell lines (358.8 and 340.2 nmol/h/10(6) cells, respectively), as did human myeloid leukemia cell line, HL-60 (373.8 nmol/h/10(6) cells). These choriocarcinoma and leukemia cell lines with abundant AP-N activity showed much higher sensitivity to bestatin (IC50 = 0.5, 2.1 and 1.0 micrograms/ml, respectively) than the other cell lines. By immunoblotting and immunocytochemical staining, AP-N was detected as an approximately 165-kDa protein and localized on the cell membrane in choriocarcinoma cells. We also examined the effects of two other aminopeptidase inhibitors and three anti-CD13 monoclonal antibodies (MAbs) (WM15, MCS2 and MY7) on the growth of NaUCC-4 cells. Cell growth was markedly suppressed by the AP-N inhibitor actinonin as well as bestatin, but not by the AP-B inhibitor arphamenine. Of the three MAbs, only WM15, which is able to inhibit AP-N activity, suppressed cell growth in a dose-dependent manner. These results indicate that AP-N inhibitors show a growth-suppressive effect, presumably through inhibition of the enzymatic activity of AP-N on tumor cells, and suggest that AP-N may play important roles in the growth of certain tumors, such as choriocarcinoma and leukemia.

Modulation of CD13 expression during retinoic acid-induced differentiation of HL60 cells

CD13/aminopeptidase-N, an enzyme expressed by myeloid cells, may be important in the regulation and signalling pathways that control myeloid growth and differentiation. In this study we have used the myeloid leukaemic cell line HL60, and its ability to differentiate when induced by all-trans-retinoic acid (ATRA), to study the regulation of CD13 molecules, and its associated aminopeptidase-N enzyme activity during the myeloid differentiation pathway. In addition, the effect of the growth factor granulocyte-macrophage colony stimulating factor (GM-CSF) on CD13 expression, by undifferentiated and differentiated HL60 cells, has been investigated. Our results show that CD13 expression, and its enzyme activity, is downregulated during differentiation of HL60 induced by ATRA, but not when using GM-CSF.

Surface aminopeptidase activity of rat natural killer cells. I. Biochemical and biological properties

Aminopeptidase (AP) activity on rat natural killer (NK) cells was found to have the following characteristics: (1) the activity was surface associated and not secreted, as determined by extracellular location of product and by the cessation of hydrolysis of substrate upon removal of the cells from the medium. (2) The activity was linear with respect to time and cell number. (3) The enzymatic activity on splenocytes and on the NK leukemia cell line CRNK-16, but not on IL-2 activated NK (A-NK) cells, was sensitive to trypsin treatment. (4) The AP activity on intact cells had a broad pH dependency with optimal activity at slightly alkaline pH but lower activity at acidic pH. (5) There was a preference for neutral substrates and essentially no activity towards acidic substrates. (6) Enzymatic activity was inhibited in the presence of the AP inhibitors bestatin and amastatin, and in the presence of the chelator, 1,10 phenanthroline, indicating the involvement of a metalloprotease. (7) Culture of A-NK cells with bestatin resulted in a decrease in cytotoxicity against YAC-1 and P815 targets. Amastatin treatment caused only a slight decrease in cytotoxicity against YAC-1 targets, but a significant decrease in cytotoxicity against P815 targets. (8) Treatment of A-NK cultures with specific inhibitors of APases caused an increase in expression of CD2 (an increase from 20-80% with bestatin and an increase from 25-35% in the presence of amastatin). These results provide the first evidence for the existence of APases on the surface of NK cells and suggest a role for these enzymes in the regulation of cytotoxic activity and of CD2 surface expression.

Inhibitory effect of the oral immune response modifier, bestatin, on cell-mediated and cell-free HIV infection in vitro

The antiviral effect of the immunomodulating anti-cancer agent, bestatin, was examined in vitro by exposing MT-4 lymphocytes to HIV in the presence of 10-fold dilutions of drug (range 100 micrograms-100 pg/ml). The reduction in infectivity was measured by p24 ELISA and compared to the effect of established anti-HIV drugs-azidothymidine (AZT) and dextran sulfate. The results indicate that low doses of bestatin (1 microgram/ml) can completely inhibit viral infection resulting either from inoculation with free virus or coculture with infected lymphocytes. Unlike AZT or dextran sulfate, bestatin prevents HIV infection without interfering with the rate of cell growth. No appreciable decrease in HIV production was observed when chronically infected virus-producing T cell lines ie, H9, MOLT-4, HPB-ALL, 8E5 and MT-2 were treated with bestatin. Bestatin appears to act in the early stages of viral penetration, possibly through inhibition of lymphocyte-associated aminopeptidases.

Ubenimex in the treatment of acute nonlymphocytic leukemia in adults

A multi-institutional randomized study for the evaluation of ubenimex (Bestatin) in the treatment of adult acute nonlymphocytic leukemia was performed. One hundred and ninety-five patients were registered from February 1988 to December 1990. Patients who had reached complete remission by one or two courses of remission induction chemotherapy were divided into the ubenimex group or the control group by randomization. Patients of the ubenimex group started to receive 30 mg ubenimex orally once a day when maintenance therapy began and continued as long as possible. Remission duration and survival were analyzed based on the data as of August 31, 1991. Remission duration of the ubenimex group was superior to that of the control group (generalized Wilcoxon test: p = 0.0338). Fifty percent remission duration was 508 days in the ubenimex group and 386 days in the control group. There has been no statistical difference in survival between the two groups as yet.

The significance of aminopeptidases and haematopoietic cell differentiation

Aminopeptidases are a group of enzymes found on the cell surface and in the cytoplasmic compartments of many peripheral blood cell types and their progenitors. Their functional roles include the hydrolysis of several biologically active peptides and growth factors and some have proved to be of diagnostic and prognostic value in leukaemia. These enzymes may also be found in serum as a consequence of non-haematopoietic related diseases and so have been used as indicators of liver damage.

Haematopoietic cells in the bone marrow go through a process of growth and differentiation before being released into the peripheral circulation where they fulfill many functional roles. The enzyme activities of some aminopeptidases have been shown to modulate the growth of these cells. In addition, the activities of these enzymes themselves can be regulated by haematopoietic growth factors. However, the mechanisms that regulate their expression and activity are not fully understood. In this report the current literature has been reviewed for evidence of expression, regulation and clinical significance.