Cationized Bowman-Birk protease inhibitor as a targeted cancer chemopreventive agent

Identification and pharmaceutical evaluation of novel frog skin-derived serine proteinase inhibitor peptide-PE-BBI (Pelophylax esculentus Bowman-Birk inhibitor) for the potential treatment of cancer

Amphibian venom-derived peptides have high potential in the field of anticancer drug discovery. We have isolated a novel Bowman-Birk proteinase inhibitor (BBI)-type peptide from the skin secretion of Pelophylax esculentus (PE) named PE-BBI, and evaluated its bio-functions and anti-cancer activity in vitro. PE-BBI is a heptadecapeptide with C-terminal amidation. The mRNA sequence and primary structure of PE-BBI were identified using RT-PCR and LC/MS, respectively. A trypsin inhibitory assay was used to characterize the serine proteinase inhibitory activity of synthetic PE-BBI. PE-BBI’s myotropic activity was analyzed using isolated rat bladder and rat-tail artery smooth muscle tissues, and the anti-cancer ability of PE-BBI using human colorectal cancer cells. PE-BBI’s mechanism of action was investigated using Discovery studio software. PE-BBI showed trypsin inhibitory activity (K_i = 310 ± 72 nM), strong myotropic activity, and cytotoxicity that were specific to cancer cells, and no side effect to normal epithelial cells. The docking stimulation showed that PE-BBI had high affinity to several members of human kallikrein related peptidase (KLK) family. This finding helps to enrich our understanding of BBI peptides’ mode of action. Moreover, the data presented here validates frog secretions as sources of potential novel proteinase inhibitors for cancer treatment.

Fabrication of a Soybean Bowman-Birk Inhibitor (BBI) Nanodelivery Carrier To Improve Bioavailability of Curcumin

Curcumin is a poorly water-soluble drug, and its oral bioavailability is very low. Here, a novel self-assembly nanoparticle delivery carrier has been successfully developed by using soybean Bowman-Birk inhibitor (BBI) to improve the solubility, bioaccessibility, and oral absorption of curcumin. BBI is a unique protein, which can be resistant to the pH range and proteolytic enzymes in the gastrointestinal tract (GIT), bioavailable, and not allergenic. The encapsulation efficiencies (EE) and the loading capacities (LC) of curcumin in the curcumin-loaded BBI nanoparticles (Cur-BBI-NPs, size = 90.09 nm, PDI = 0.103) were 86.17 and 10.31%, respectively. The in vitro bioaccessibility of Cur-BBI-NPs was superior to that of curcumin-loaded sodium caseinate (SC) nanoparticles (Cur-SC-NPs) (as control). Moreover, Cur-BBI-NPs significantly enhanced the bioavailability of curcumin in rats compared with Cur-SC-NPs, and the clathrin-mediated endocytosis pathway probably contributed to the favorable bioavailability of Cur-BBI-NPs, as revealed by the cellular uptake inhibition study.

pLR-HL: A Novel Amphibian Bowman-Birk-type Trypsin Inhibitor from the Skin Secretion of the Broad-folded Frog, Hylarana latouchii

In this study, we report a novel heptadecapeptide (LIGGCWTKSIPPKPCLV) of the pLR/ranacyclin family, named pLR-HL, whose structure was deduced from its biosynthetic precursor-encoding cDNA cloned from the skin secretion-derived cDNA library of the broad-folded frog, Hylarana latouchii, by employing a 'shotgun' cloning technique. It contains a disulphide loop between Cys(5) and Cys(15) which is consistent with Bowman-Birk-type protease inhibitors. The primary structure of pLR-HL deduced from the cDNA sequence was confirmed by fractionating the skin secretion using reverse-phase HPLC and subsequent analysis using MALDI-TOF mass spectrometry and LC/MS/MS fragmentation sequencing. On the basis of the establishment of unequivocal amino acid sequence, a synthetic replicate was synthesized by solid-phase Fmoc chemistry, and it displayed a moderately potent trypsin inhibition with a Ki of 143 nm. The substitution of Lys-8 by Phe (Phe(8) -pLR-HL) resulted in abolition of trypsin inhibition but generation of modest inhibition on chymotrypsin with a Ki of 2.141 μm. Additionally, both the disulphide loops of pLR-HL and Phe(8) -pLR-HL were synthesized and tested. Both of the catalytic loops retained similar inhibitory potencies towards trypsin or chymotrypsin in comparison with the original intact molecules. Thus, the replacement of reactive site residues could alter the specificity of these protease inhibitors, while the canonical reactive loop alone can independently constitute biologically active moiety.

The biochemical and functional food properties of the bowman-birk inhibitor

The Bowman-Birk inhibitor (BBI) is a small water-soluble protein present in soybean and almost all monocotyledonous and dicotyledonous seeds. The molecular size of BBI ranges from 1,513 Da to about 20,000 Da. BBI is to seeds what alpha(1)-antitrypsin is to humans. Soy-based food products rich in BBI include soybean grits, soymilk, oilcake, soybean isolate, and soybean protein concentrate. BBI is stable within the pH range encountered in most foods, can withstand boiling water temperature for 10 min, resistant to the pH range and proteolytic enzymes of the gastrointestinal tract, bioavailable, and not allergenic. BBI reduces the proteolytic activities of trypsin, chymotrypsin, elastase, cathepsin G, and chymase, serine protease-dependent matrix metalloproteinases, urokinase protein activator, mitogen activated protein kinase, and PI3 kinase, and upregulates connexin 43 (Cx43) expression. Several studies have demonstrated the efficacy of BBI against tumor cells in vitro, animal models, and human phase IIa clinical trials. FDA considers BBI as a drug. In 1999, FDA allowed a health claim on food labels stating that a daily diet containing 25 grams of soy protein, also low in saturated fat and cholesterol, may reduce the risk of heart disease [corrected] This review highlights the biochemical and functional food properties of the Bowman-Birk inhibitor.

Effects of spermine-conjugated Bowman-Birk inhibitor (spermine-BBI) on carcinogenesis and cholesterol biosynthesis in mice

PURPOSE

The goals of the studies reported here were to evaluate the effects of the soybean-derived protease inhibitor known as the Bowman-Birk inhibitor (BBI) and its spermine-conjugate (spermine-BBI) on the prevention of lung tumorigenesis and the reduction of heart disease parameters.

METHODS

Both spermine-BBI and purified BBI (pBBI), at a dose of 20 mg/kg body weight, were administered as intraperitoneal injections to animals treated with the chemical carcinogen 3-methylcholanthrene (MCA) to determine their effects on chemically induced lung tumorigenesis in A/J mice. In addition, the effects of spermine-BBI and pBBI on the aortic cholesterol content and the percent ester in the mice were determined.

RESULTS

The characteristics of the animals in the various treatment groups were comparable in terms of behavioral phenomena, weight gain, and lack of deaths during the experimental period. Thus, there was no detectable toxicity in spermine-BBI-treated mice. Both spermine-BBI and pBBI had a significant suppressive effect on MCA-induced lung tumors, with spermine-BBI being more effective than pBBI. Spermine-BBI was considerably more effective than pBBI at affecting heart-disease-related parameters. The amount of esterified cholesterol present in the aortas of mice treated with spermine-BBI was 9% lower than that of the controls. Both pBBI and spermine-BBI reduced total cholesterol levels in the blood, with pBBI reducing the cholesterol level by 15.5% and spermine-BBI by 33.3%.

CONCLUSIONS

Spermine-BBI can prevent lung carcinogenesis without detectable toxic effects; therefore, it is concluded that lung targeting by the cationization of polypeptides can be achieved without apparent toxicity. The increase in retention of spermine-BBI compared to pBBI in liver tissue may make a difference for the heart disease parameters evaluated. Although spermine-BBI is capable of reducing the total cholesterol and ester levels in mice, pBBI did not have as great an effect on these parameters. Because the liver is the major site for the production of cholesterol, the localization of spermine-BBI in liver tissue may account for the greater effect of spermine-BBI on blood cholesterol levels. Spermine-BBI was administered to animals for only the first 2 months of the 4-month assay period before animal sacrifice, so the results suggest that the effects of spermine-BBI on the parameters related to heart disease are long-lasting, as are the effects of both pBBI and spermine-BBI on lung tumorigenesis.

Development of tobacco smoke-induced lung tumors in mice fed Bowman-Birk protease inhibitor concentrate (BBIC)

Male strain A/J mice were exposed, 6h a day, 5 days a week for 5 months to a mixture of 89% cigarette sidestream and 11% cigarette mainstream smoke and then allowed to recover for another 4 months in air. The animals were fed Bowman-Birk protease inhibitor concentrate (BBIC) at a concentration of 1% in AIN-93G diet either during smoke exposure, following smoke exposure or during the entire 9 months. At the end of the experiment, the incidence and multiplicity of lung tumors were determined. In a positive control experiment, strain A/J mice were injected with 3-methylcholanthrene (MCA) and fed a diet containing 1% BBIC; these animals were killed 5 months later. It was found that in the animals treated with MCA, BBIC decreased lung tumor multiplicities, whereas in the smoke exposed mice, BBIC did not modulate lung tumor development.

Chemopreventive agents: protease inhibitors

Certain protease inhibitors, called the anticarcinogenic protease inhibitors in this review, are capable of preventing carcinogenesis in a wide variety of in vivo and in vitro model systems. The anticarcinogenic protease inhibitors are extremely potent agents with the ability to prevent cancer, with some unique characteristics as anticarcinogenic agents. The anticarcinogenic protease inhibitors have the ability to irreversibly suppress the carcinogenic process. They do not have to be continuously present to suppress carcinogenesis. They can be effective when applied in both in vivo and in vitro carcinogenesis assay systems at long time periods after carcinogen exposure, and are effective as anticarcinogenic agents at extremely low molar concentrations. While several different types of protease inhibitors can prevent the carcinogenic process, the most potent of the anticarcinogenic protease inhibitors on a molar basis are those with the ability to inhibit chymotrypsin or chymotrypsin-like proteases. The soybean-derived protease inhibitor, Bowman-Birk inhibitor (BBI), is a potent chymotrypsin inhibitor that has been extensively studied for its ability to prevent carcinogenesis in many different model systems. Much of this review is focused on the characteristics of BBI as the anticarcinogenic protease inhibitor, as this is the protease inhibitor that has risen to the human trial stage as a human cancer chemopreventive agent. Part of this review hypothesizes that the Bowman-Birk family of protease inhibitors plays a role in plants similar to that of alpha1-antichymotrypsin in people. Both BBI and alpha1-antichymotrypsin are potent inhibitors of chymotrypsin and chymotrypsin-like enzymes, are highly anti-inflammatory, and are thought to play important roles in the defense of their respective organisms. It is believed that BBI will be shown to play a major role in the prevention and/or treatment of several different diseases, in addition to cancer.

Water-soluble fatty acid derivatives as acylating agents for reversible lipidization of polypeptides

A novel method allowing the conjugation of a fatty acid to a peptide or protein in aqueous buffer is described in this paper. L-Cysteinyl 2-pyridyl disulfide (CPD) (III), which was obtained by reacting L-cysteine (I) with 2,2-dithiopyridine (II), was reacted with the N-hydroxysuccinimide ester of palmitic acid (IV) to yield a water-soluble derivative of palmitic acid, termed Pal-CPD (V). Pal-CPD (V) could be reacted with a sulfhydryl-containing peptide or protein in aqueous buffer to yield the palmitic acid-derivatized conjugate (VI). The palmitic acid-derivatized Bowman-Birk protease inhibitor (BBI), synthesized using this conjugation method, was demonstrated to have 140-fold higher uptake into Caco-2 cell monolayers compared to native-BBI. The biological activity of the conjugate, as assessed using an in vitro transformation assay, was retained.

Disposition of positively charged Bowman-Birk protease inhibitor conjugates in mice: influence of protein conjugate charge density and size on lung targeting

The influence of conjugate charge density and size on the targeting of cationic Bowman-Birk inhibitor (BBI) conjugates to the lungs was studied in mice. The biodistribution of BBI, either as the native protein or in the conjugated form (conjugated to a dicationic, tetracationic, or polycationic carrier), indicated that by increasing the charge density of BBI conjugates, the lung accumulation of the conjugates administered intravenously (i.v.) can be increased. The order of lung accumulation in these studies was as follows: polycationic- > tetracationic- > dicationic-conjugated BBI > BBI. The influence of conjugate size on lung accumulation was studied in three experiments. First, the biodistribution of poly(D-lysine) carriers of equal charge density but different molecular weight demonstrated that lung accumulation of polycationic carriers increases with an increase in carrier size. Second, the biodistributions of BBI, tyramine-derivatized poly(D-lysine)3 kDa, and poly(D-lysine)3 kDa conjugated to BBI indicated that an increase in conjugate size alone is not sufficient to promote the lung accumulation of cationic BBI conjugates. Finally, the biodistribution poly(D-lysine) complexed with heparin showed that targeting of a conjugate to the lungs can be abolished by neutralizing the charge on the carrier. Collectively, data in this paper demonstrate that the carrier-mediated targeting of BBI to the lungs is dependent on (a) cationization of BBI, (b) the conjugate positive charge density, and (c) the size of the cationic conjugate if the charge density is maintained. Also, the data show the size of the conjugate alone does not make a significant impact on lung accumulation.

Carbamylation decreases the cytotoxicity but not the drug-carrier properties of polylysines

The charge density of Poly(D-lysine) was reduced by the carbamylation of the lysyl residues with potassium cyanate. A decrease in the charge density of poly(D-lysine) by 25% and 50% reduced the cytotoxicity of the ligand to cultured L929 cells by a 5-, and a 20 to 25-fold level, respectively, as estimated by using either the viability or the protein assay. The uptake of cyanate-modified poly(D-lysine) ligands in cultured L929 cells was not reduced, while the uptake of poly(D-lysine)/Heparin complex was reduced by 80%, as compared to that of unmodified poly(D-lysine). The in vivo biodistribution of cyanate-modified poly(D-lysine) ligands in the lungs and the liver of mice was not altered in comparison to that of unmodified poly(D-lysine), whereas the poly(D-lysine)/Heparin complex was only accumulated in the liver but not in the lungs. The data in this paper indicate that a 50% decrease in the positive charge density of poly(D-lysine) reduces the toxicity, but not the carrier potential of this polycationic ligand.