Control of pharmaceutical properties of soybean trypsin inhibitor by conjugation with dextran. II: Biopharmaceutical and pharmacological properties

Biopharmaceutical and pharmacological properties of the Kunitz-type soybean trypsin inhibitor (STI)-dextran conjugate (STI-D) were studied. Dextran having a molecular weight of approximately 10,000 was covalently attached to the STI molecule by periodate oxidation. The STI-polyethylene glycol (PEG) conjugate (STI-PEG) was also tested for comparison. After iv injection to mice, native STI showed rapid elimination of activity from plasma (t 1/2 = 2 min), and approximately 60% of the dose was excreted in urine within 1 h after injection. On the other hand, STI-D was slowly cleared from plasma and its urinary excretion was restricted. The STI-PEG conjugate showed a pharmacokinetic behavior similar to that of STI-D. Pharmacological activities of native and modified STI were evaluated by two animal experimental models; that is, trypsin-induced shock in mice and acute pancreatitis in rats. In mice, shock induced by iv injection of trypsin was inhibited by the iv pretreatment with native STI, but the effect was observed for only 1 h. The STI-D conjugate showed a superior inhibitory effect on trypsin-induced shock to that of STI alone at the same dose, and this effect continued for 5 h. A similar effect was also observed in mice given an iv injection of STI-PEG. In rats with acute pancreatitis, no significant therapeutic effect was shown by the iv treatment with native STI, as well as saline treatment. On the other hand, the iv treatment with STI-D at the same dose as STI lowered the mortality of the rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunoconjugates of Soybean Bowman-Birk Protease Inhibitor as Targeted Antitumor Polymeric Agents

To enhance the antitumor potential of soybean Bowman-Birk inhibitor (BBI), the conjugate of BBI with an antibody via a macromolecular carrier was prepared. Clinical dextran (D) was used as a biocompatible biodegradable carrier for co-immobilization of BBI and antibody. A model immunoglobulin isolated from sheep serum (slgG), raised against human IgM was utilized to develop the procedure of immunoconjugate synthesis. The molar ratio of the ingredients in the conjugate was the following BBI:D:sIgG=9:1:1. Comparison of the dose response curves for the native sIgG and the BBI-D-sIgG conjugate indicated that sIgG completely retained its specific activity (>90%) after modification with dextran. The determination of the K_i, values for chymotrypsin interaction with the native BBI and the BBI-D-sIgG conjugate indicated high anti-chymotrypsin activity. In the next step, the monoclonal antibody (ICO 25 MAb) against the mucin-like human epithelial membrane antigen was used for conjugation as it is the most universal vector for targeting different agents to human tumors of epithelial origin. The influence of conjugation on the specificity of the Mab reaction with its antigen was studied. The conjugated MAb reacted with tumor cells of different epithelial genesis (breast, lung, gastric, ovarian and uterus tumors), but did not react with tumor cells of non-epithelial origin. It was shown that BBI-D-ICO 25 MAb conjugate has almost the same immunohistochemical activity as non-conjugated MAb. These results demonstrated the feasibility of exploiting the activities of covalently bound BBI and ICO 25 MAb for anticarcinogenic agent targeting.     

刺桐胰蛋白酶抑制剂的高效表达、纯化、亲和介质的制备及其在r-PA纯化中的应用

刺桐胰蛋白酶抑制剂(ETI)是一种丝氨酸蛋白酶抑制剂,能够特异性结合胰蛋白酶及组织型纤溶酶原激活剂,抑制其活性。因此ETI可以作为配体与固定相偶联制备亲和层析介质,用于tPA(组织型纤溶酶原激活剂)及其突变体的纯化。利用基因工程方法构建了ETI的高表达工程菌株,诱导表达后目的蛋白占总蛋白的39.6%,经包涵体变性、复性、纯化,制备了纯度高于96%的ETI样品,收率达到了63.5%。利用纯化的ETI,偶联制备了亲和层析介质,偶联率达到99%。用制备的ETI亲和层析介质纯化瑞替普酶(r-PA),获得的r-PA样品纯度高于95%,生物学活性高于5×105U/mg。本研究为ETI的进一步生产及应用奠定了基础。     

Effect of PEG molecular weight and linking chemistry on the biological activity and thermal stability of PEGylated trypsin

PEGylated proteins are routinely used as therapeutics, but systematic studies of the effect of PEG molecular weight and linking chemistry on the biological activity and particularly the thermal stability of the conjugated protein are rarely made. Here, activated monomethoxypolyethylene glycol (mPEG)s (Mw 1100, 2000 and 5000 g/mol) were prepared using succinic anhydride (SA), cyanuric chloride (CC) or tosyl chloride (TC) and used to synthesise a library of trypsin conjugates. The enzyme activity (K_M, V_max and K_cat) of native trypsin and the mPEG-modified trypsin conjugates was compared using N-benzoyl-l-arginine p-nitroanilide (BAPNA) as a substrate, and their thermal stability determined using both BAPNA and N--benzoyl-l-arginine ethyl ester hydrochloride (BAEE) as substrates to measure amidase and esterase activity respectively. The effect of conjugate chemistry on trypsin autolysis was also examined at 40 °C. PEG-trypsin conjugates containing the higher molecular weight of mPEG (5000 g/mol) were more stable than free trypsin, and the conjugate containing CC-mPEG 5000 g/mol had the best thermal stability.     

1-Deoxyglycitolation of protein amino groups and their regeneration by periodate oxidation*

Reductive alkylation of lysyl e-amino groups with sugars (1-deoxyglycitolation) using pyridine borane as the reducing agent has been recently described [Wong, W.S.D., Osuga, D.T. & Feeney, R.E. (1984) Anal. Biochem. 139 , 58–67]. The regeneration of the lysines has now been achieved by oxidation with e10 mM periodate. In experiments with glycitolated bovine serum albumin, reactions using 5, 20, and 80 mM periodate were essentially complete in the first 10 min. Oxidations of methionine to the sulfoxide were evident even at this lower concentration of periodate, while higher concentrations and prolonged reaction times only caused unnecessary destruction of amino acids. The removal was shown to occur in a wide pH range with little variation in the recovery of the lysines. The degree of glycitolation, or the nature of the attached carbohydrate residues, had no effect on the yield of products. Reductive 1-deoxygalactitolation of e55% of the lysyl e-amino groups of lysozyme caused no loss in enzymatic activity; when 5 mM periodate was used to remove the 1-deoxy-galactitol moiety, e95% of the amino groups were regenerated, concomitant with destruction of e16% of the activity. On reductive 1-deoxygalactitolation of the amino groups of turkey ovomucoid, 65% of the lysyl e-amino groups were modified with 70% loss of the inhibitory activity against trypsin. On treatment with 5 mM periodate, e80% of the amino groups were regained with a similar recovery of the inhibitory activity.     

Covalent linkage of carboxypeptidase G2 to soluble dextrans--I. Properties of conjugates and effects on plasma persistence in mice

The covalent attachment of the therapeutic enzyme carboxypeptidase G2 to soluble dextrans of varying molecular weight resulted in a 5-15-fold increase in plasma persistence in normal and tumour-bearing mice. The molecular weight of the dextran used markedly affected the number of dextran molecules present in the conjugate, resulting in a molecular weight distribution between 6 and 12 X 10(5) daltons. The isoelectric point of the conjugates varied between 4.1 and 4.8 compared to native enzyme 7.8. Conjugates were resistant to proteolysis by trypsin and chymotrypsin, but showed little difference in their affinity for substrate.     

The role of aromatic amino acid oxidation, protein unfolding, and aggregation in the hypobromous acid-induced inactivation of trypsin inhibitor and lysozyme

Hypobromous acid (HOBr) generated by activated eosinophils has been implicated in tissue injury observed in asthma, allergic reactions, and some infections. Proteins are major targets for this oxidant, but the mechanisms by which HOBr induces loss of function are not well-established. In this study, we have examined the effect of HOBr on protein structure (as assessed by amino acid loss, side chain oxidation, fragmentation, aggregation, and unfolding) and activity of a model protease inhibitor, soybean trypsin inhibitor (STI), and the protective enzyme lysozyme. Exposure of both proteins to low oxidant concentrations (< or = 5-fold molar excess) results in loss of function. In each case, loss of activity is associated with the selective oxidation of His, Trp, and Tyr residues, which results in protein unfolding (with lysozyme) and protein aggregation (with STI). Reaction with these residues accounts for 25 and 50% of the HOBr with STI (25-fold excess) and lysozyme (4-fold excess), respectively. These processes are believed to lead to changes in the structure of the proteins, which disrupts substrate binding. With both proteins, the oxidation of other residues, including Met, does not appear to play a major role. Bromamines, formed by reaction with amine groups, are major products, which account for 45 and 35% of the HOBr with STI (25-fold excess) and lysozyme (4-fold excess), respectively. Decomposition of these species correlates with secondary oxidation reactions, and with lysozyme, a time-dependent loss in activity. Overall, 70% of the HOBr can be accounted for with STI and 95% with lysozyme.     

Evaluation of hyaluronic acid-protein conjugates for polymer masked-unmasked protein therapy

Bioresponsive polymers may effectively be utilized to enhance the circulation time and stability of biologically active proteins and peptides, while reducing their immunogenicity and toxicity. Recently, dextrin-epidermal growth factor (EGF) conjugates, which make use of the Polymer-masked UnMasked Protein Therapy (PUMPT) concept, have been developed and shown potential as modulators of impaired wound healing. This study investigated the potential of PUMPT using hyaluronic acid (HA) conjugates to mask activity and enhance protein stability, while allowing restoration of biological activity following triggered degradation. HA fragments (Mw ～90,000g/mol), obtained by acid hydrolysis of Rooster comb HA, were conjugated to trypsin as a model enzyme or to EGF as a model growth factor. Conjugates contained 2.45 and 0.98% (w/w) trypsin or EGF, respectively, and contained <5% free protein. HA conjugation did not significantly alter trypsin's activity. However, incubation of the conjugate with physiological concentrations of HAase increased its activity to ～145% (p<0.001) that of the free enzyme. In contrast, when HA-EGF conjugates were tested in vitro, no effect on cell proliferation was seen, even in the presence of HAase. HA conjugates did not display typical masking/unmasking behavior, HA-trypsin conjugates exhibited ～52% greater stability in the presence of elastase, compared to free trypsin, demonstrating the potential of HA conjugates for further development as modulators of tissue repair.     

Growth inhibition of human melanoma tumor cells by the combination of sodium phenylacetate (NaPA) and substituted dextrans and one NaPA-dextran conjugate

We have studied the cytostatic effects of sodium phenylacetate (NaPA) in association with several substituted dextrans on human tumor melanoma 1205LU cells. We show that NaPA alone inhibits the growth of these cells (IC50 = 3.9 mM) while a weak inhibitory effect appears at a concentration of 37 microM (10 microg/ml) for a dextran methyl carboxylate benzylamide (LS17-DMCB). The precursors of LS17-DMCB [T40 Dextran and carboxymethyl dextran (LS17-DMC)] did not affect the growth of 1205LU cells. To potentiate the inhibitory activity of NaPA at low concentrations (below 5.6 mM), we have tested NaPA and LS17-DMCB in physical mixture (association) or linked together covalently (this conjugate is termed 'LS17-NaPaC'). We have observed an increase of the 1205LU cell growth inhibition effect with NaPA in association (IC50 1.8 mM). For a concentration of 5 mM of NaPA (free in the case of association or linked in the case of conjugate), the association with dextran derivative exhibits a 4.6-fold higher efficacy than with NaPA alone (9 versus 41% surviving fraction), while the conjugate is 1.3-fold smaller (52% growth inhibition). By performing isobologram analysis of the IC50 data, we have shown a synergistic effect for a particular molar ratio of NaPA and LS17-DMCB (NaPA:LS17-DMCB = 0.35).     

Development and in vitro evaluation of a drug delivery system protecting from trypsinic degradation

We have been developing a delivery system based on a novel polymer conjugate protecting perorally administered (poly)peptide drugs from trypsinic degradation. The trypsin inhibitor antipain was, therefore, covalently attached to the mucoadhesive polymer chitosan. The protective effect of resulting chitosan–antipain conjugates was quantified by an enzyme assay. In contrast to the unmodified polymer, chitosan–antipain conjugates exhibited a significant inhibitory effect towards enzymatic activity of trypsin (EC 3.4.21.4). Moreover, the mucoadhesive force of chitosan was not influenced by the slight modification. Based on a chitosan–antipain conjugate, a drug delivery system was generated using insulin as model drug. Tablets containing 5% polymer conjugate demonstrated after incubation with trypsin (180 spectrophotometric BAEE units/ml) for 1.5 h in lateral parts of the swelled dosage form a 13.3±2.3% (mean±S.D., n=3) minor proteolysis of matrix embedded insulin compared to tablets lacking the polymer conjugate. In the inner part of the swelled dosage form containing the conjugate proteolysis was completely inhibited, whereas in control tablets 11.3±9.5% (mean±S.D., n=3) insulin was degraded. Furthermore, a controlled drug release over a period of 6 h was guaranteed by the delivery system. According to these results, the novel chitosan–antipain conjugates shielding from luminal enzymatic attack may be a useful tool for the peroral administration of mainly trypsinic degraded peptide and protein drugs.     

In vitro characteristics and in vivo plasma disposition of cisplatin conjugated with oxidized and dicarboxymethylated dextrans.

In vitro release behavior and cytotoxic activity, and in vivo plasma disposition of newly synthesized macromolecular derivatives of cisplatin (CDDP) were investigated and compared with CDDP. The derivatives included oxidized dextran conjugate of CDDP (OX-Dex/CDDP) and dicarboxymethylated dextran conjugate of CDDP (DCM-Dex/CDDP). In vitro release of platinum complex from dextran conjugated CDDP was determined by an equilibrium dialysis method. These dextran conjugates showed sustained release of the platinum complex. In vitro release half-life for DCM-Dex/CDDP was significantly longer (4.5 times) than that for OX-Dex/CDDP. In vitro cytotoxic activity of CDDP and dextran conjugated CDDP against colon 26, mouse colon cancer cell line, was measured using the MTT assay method. OX-Dex/CDDP showed a similar cytotoxic activity to CDDP. However, both cytotoxic activities were markedly decreased when preincubated with the medium containing serum. On the other hand, DCM-Dex/CDDP retained residual cytotoxic activity at a significantly higher level than OX-Dex/CDDP after preincubation with the medium containing serum, although it showed the lowest cytotoxic activity. This indicated longer maintenance of the in vitro antitumor activity of DCM-Dex/CDDP in serum compared with OX-Dex/CDDP. Plasma disposition of CDDP and dextran conjugated CDDP was determined by intravenous administration to rats. Although the total platinum plasma concentration-time profile for OX-Dex/CDDP was similar to that for CDDP, its markedly higher profile was achieved when DCM-Dex/CDDP was administered. The values of the total platinum AUC and MRT, where AUC is the area under the platinum concentration-time curve and MRT is the mean residence time, for DCM-Dex/CDDP were 11.2 times and 4.8 times significantly higher than with OX-Dex/CDDP in plasma, respectively. DCM-Dex/CDDP also showed a significantly lower total clearance compared with OX-Dex/CDDP. These results from the in vivo experiments revealed that retention of DCM-Dex/CDDP in blood circulation was much greater than that for OX-Dex/CDDP. DCM-Dex/CDDP thus has potential as a macromolecular derivative of CDDP for passive tumor targeting.     

HYDROLYSIS OF SOYBEAN TRYPSIN INHIBITOR BY THE γ SUBUNIT OF 7SNGF AND EGF-BP: Demonstration of Proteolytic Activity

Although soybean trypsin inhibitor (STI) does not inhibit the esterase activity of either epidermal growth factor binding protein (EGF-BP) or the γ subunit of 7SNGF, it does behave as a substrate for proteolysis. Cleavage of the active site peptide bond of STI does occur when incubated in the presence of either EGF-BP or the γ subunit of 7SNGF. The hydrolysis is pH dependent with maximum proteolysis at pH 6.0–7.0. The newly formed C-terminal arginine residue in modified STI can be released by carboxypeptidase B digestion. Both enzymes are inhibited by low concentrations (2–4μg/ml) of the microbial protease inhibitors leupeptin and antipain. These inhibitors are specific for trypsin-like proteases. Since both enzymes can be found as part of high molecular weight complexes with growth factors these results confirm the hypothesis that they are involved during a postranslational modification event.     

Immunogenic and tolerogenic properties of monomethoxypoly(ethylene glycol) conjugated proteins.

An immunogenic and tolerogenic characterisation of monomethoxypoly(ethylene glycol) conjugated proteins was carried out using, as immunogen models, an anti-malaria chimera monoclonal antibody (PfChMab) and a macrophage colony stimulating factor (M-CSF). Two conjugates of PfChMab were prepared by polymer derivatisation of 19 and 33% protein amino groups and one conjugate of M-CSF was obtained by modification of 24% amino groups. In mice M-CSF was found to elicit rapidly high IgG and IgM levels whereas the monomethoxypoly(ethylene glycol) derivatised M-CSF stimulated a significantly lower immunoresponse. Native PfChMab was found to induce a delayed immunoresponse with high IgM levels but low production of IgG. Furthermore, similar immunogenic profiles were obtained with the native and modified protein forms. The pre-administration of polymer conjugated M-CSF to mice subsequently treated with the native protein was found to suppress up to 75% of anti-native M-CSF IgG, while IgM production was not affected. On the other hand the pre-administration of monomethoxypoly(ethylene glycol) derivatised PfChMab was found to reduce significantly the generation of anti-native PfChMab IgM. Such suppression depended on the degree of modification: the conjugate with the higher number of polymer chains was more effective in suppressing the immunoresponse.     

新型顺铂给药系统的制备及其生物活性评价

以生物发酵法获得的γ-聚谷氨酸经酸降解后得到小分子γ-聚谷氨酸(γ-PGA),柠檬酸(CA)通过酯化反应修饰其侧链羧基制备γ-聚谷氨酸-柠檬酸(γ-PGA-CA),再将顺铂(CDDP)与γ-PGA-CA上的羧基相结合制备得载药复合物γ-PGA-CA-CDDP,凝胶色谱法测定分子量,OPDA法测定载药量及有效结合率,透析法结合HPLC研究其对顺铂的缓释效果,MTT法检测复合物的体外抗肿瘤活性,采用新鲜兔血检测载体材料及复合物的溶血性。实验结果表明:成功获得γ-PGA-CA及γ-PGA-CA-CDDP,该复合物相对分子质量约为66k,有效结合率达65%,载药率达16%～20%,48 h时顺铂的累计释放率达到50%,MTT检测显示该复合物对肿瘤细胞具有良好的抑制效果,相对于游离顺铂具有较低的毒性,且无溶血性。因此,γ-PGA-CA可作为药物载体,γ-PGA-CA-CDDP具有潜在的临床应用价值。     

阿霉素与胃癌单克隆抗体交联物的体内外抗肿瘤作用

以氧化葡聚糖法制备了阿霉素(ADM)与胃癌单克隆抗体(MoAb)3H11的交联物3H11-DEX-ADM,ADM与3H11克分子比为73:1。经ELISA法测定,交联物的抗体活性保留86%。体外细胞毒试验显示,3H11-DEX-ADM对胃癌细胞BGC823的杀伤作用比游离ADM明显增强,其IC₅₀分别为1.0μg/ml及3.75μg/ml。在荷瘤裸鼠治疗实验中3H11-DEX-ADM能显著抑制肿瘤生长,抑制率为51.5%(P<0.05),明显高于ADM组及其非特异性抗体交联物(NI gG-DEX-ADM)组,后者的抑制率分别为21%及24%。表明3H11-DEX-ADM对肿瘤具有选择杀伤作用。将3H11-DEX-ADM与丝裂霉素C(MMC)-3H11交联物(3H11-HSA-MMC)联合应用,细胞素实验未能显示协同或相加作用;游离ADM与MMC联合亦呈相似结果。     

小鼠胰腺对梯度胆囊收缩素的应答

目的 分析胆囊收缩素（CCK）对胰腺及胰腺癌发生的影响,并探讨绿茶成分表没食子儿茶素没食子酸酯（EGCG）的抗癌作用。方法 将生长期小鼠随机分为4组,分别给予含大豆胰蛋白酶抑制剂（STI）0 g/L(11只)、2 g/L(11只)、4 g/L(10只)和8 g/L(11只)的饮水,2周后处死小鼠,记录胰腺湿质量。采用酶联免疫吸附试验（ELISA）检测血浆CCK水平;测定胰腺组织中蛋白质、DNA、胰蛋白酶和脂肪酶含量;免疫组织化学染色检测胰腺组织增殖细胞核抗原（PCNA）阳性细胞百分比。采用胰腺内包埋化学致癌物二甲基苯并蒽（DMBA）法建立癌发生模型。将15只小鼠随机均分为正常对照组、DMBA包埋组、DMBA+2 g/L STI组、DMBA+8 g/L STI组、DMBA+8 g/L STI+EGCG组,6周后处死小鼠,取胰腺进行组织学分析。结果 2 g/L STI组CCK水平高于0 g/L STI组,8 g/L STI组高于0、2和4 g/L STI组（P<0.05）。2、4 g/L STI组胰腺湿质量高于0 g/L STI组,8 g/L STI组高于0、2 g/L STI组（P...     

弹性蛋白酶化学修饰的研究

本文用溴化氰活化的右旋糖酐对弹性蛋白酶进行共价修饰,以改变其若干性质,使之更有利于应用。结果表明,修饰酶不仅完全保留了天然酶的活性,而且在耐热性、耐酸性、抗胃蛋白酶水解能力上,都明显地优于天然酶。修饰酶较天然酶稳定,有较高的应用价值。     

四环素-阿霉素复合物的制备及性质研究

目的:介绍四环素-阿霉素复合物(ADM-D ex-TC)的制备方法,探讨复合物作为靶向性抗癌药物的性质。方法:以多醛基葡聚糖(Po lya ldehyde D ex tran,PAD)作为载体通过共价键将阿霉素(A driam ycin,ADM)、四环素(T etracycline,TC)连接其上制备四环素-阿霉素复合物(ADM-D ex-TC),M TT试验测定骨肉瘤细胞株HO S8603对不同浓度复合物的敏感性,羟基磷灰石吸附试验检验复合物的亲骨特性。结果:成功合成四环素阿霉素复合物,其中四环素与阿霉素的摩尔比为1:16。M TT试验证明复合物具有抗骨肉瘤活性,羟基磷灰石吸附试验证明复合物有亲骨活性。结论:成功合成四环素阿霉素复合物,该复合物同时具有亲骨活性和抗瘤活性。     

氧化葡聚糖的制备及表征

目的合成可用作药物制剂辅料的氧化葡聚糖。方法以葡聚糖40为反应起始物、高碘酸钾为氧化剂,在适宜条件下制备氧化葡聚糖,以红外分光光度计、紫外分光光度计、旋光仪测定其结构和光学性质,以凝胶渗透色谱法测定其分子量,以盐酸羟胺法测定氧化度。结果经氧化,葡聚糖分子上的部分羟基变成了醛基;生成物的最大紫外吸收波长为238nm;比旋光度为181;分子量(Mw)为4106;氧化度为131.68%。结论所制备的氧化葡聚糖具有准确可靠的质量控制指标,可以作为药物制剂辅料,用于前体药物及缓释药物制剂的制备。     

Polycarbophil-cysteine conjugates as platforms for oral polypeptide delivery systems

The purpose of the present study was to evaluate the potential of polycarbophil-cysteine conjugates as carrier systems for orally administered peptide and protein drugs. Mediated by a carbodiimide, cysteine was covalently attached to polycarbophil. The properties of resulting conjugates, displaying 35-50 microM thiol groups per gram of polymer, to bind polypeptides and to inhibit pancreatic proteases was evaluated in vitro. Results demonstrated that only some polypeptides are immobilized to the polycarbophil-cysteine conjugate. Due to the covalent attachment of cysteine to polycarbophil, the inhibitory effect of the polymer toward carboxypeptidase A (EC 3.4. 17.1) and carboxypeptidase B (EC 3.4.17.2) could be significantly (p < 0.05) improved. As the zinc binding affinity of polycarbophil could be improved by the covalent attachment of cysteine, the raised inhibitory effect seems to be based on the complexation of this divalent cation from the enzyme structure. Whereas the covalent attachment of cysteine on polycarbophil had no influence on the enzymatic activity of trypsin (EC 3.4.21.4) and elastase (EC 3.4.21. 36), the inhibitory effect of the polymer-cysteine conjugate toward chymotrypsin (EC 3.4.21.1) was significantly (p < 0.05) higher than that of the unmodified polymer. Because of these inhibitory features, polycarbophil-cysteine conjugates seem to be a promising tool in protecting orally administered therapeutic polypeptides, which are not bound to the polymer, from presystemic metabolism in the intestine.