Site-specific PEGylation of a lysine-deficient TNF-alpha with full bioactivity

Functionalization of Tumor Necrosis Factor-α Using Phage Display Technique and PEGylation Improves Its Antitumor Therapeutic Window

PURPOSE

In this study, the optimization of antitumor therapy with tumor necrosis factor-alpha (TNF-alpha) was attempted.

EXPERIMENTAL DESIGN

Using the phage display technique, we created a lysine-deficient mutant TNF-alpha (mTNF-K90R). This mutant had higher affinities to both TNF receptors, despite reports that certain lysine residues play important roles in trimer formation and receptor binding.

RESULTS

The mTNF-K90R showed an in vivo therapeutic window that was 13-fold higher than that of the wild-type TNF-alpha (wTNF-alpha). This was due to the synergistic effect of its 6-fold stronger in vitro bioactivity and its 2-fold longer plasma half-life derived from its surface negative potential. The reason why the mTNF-K90R showed a higher bioactivity was understood by a molecular modeling analysis of the complex between the wTNF-alpha and TNF receptor-I. The mTNF-K90R, which was site-specifically mono-PEGylated at the NH2 terminus (sp-PEG-mTNF-K90R), had a higher in vitro bioactivity and considerably longer plasma half-life than the wTNF-alpha, whereas the randomly mono-PEGylated wTNF-alpha had 6% of the bioactivity of the wTNF-alpha. With regard to effectiveness and safety, the in vivo antitumor therapeutic window of the sp-PEG-mTNF-K90R was 60-fold wider than that of the wTNF-alpha.

CONCLUSIONS

These results indicated that this functionalized TNF-alpha may be useful not only as an antitumor agent but also as a selective enhancer of vascular permeability in tumors for improving antitumor chemotherapy.

The targeting of anionized polyvinylpyrrolidone to the renal system

We reported that the co-polymer composed of vinylpyrrolidone and maleic acid selectively distributed into the kidneys after i.v. injection. To further optimize the renal drug delivery system, we assessed the renal targeting capability of anionized polyvinylpyrrolidone (PVP) derivatives after intravenous administration in mice. The elimination of anionized PVP derivatives from the blood decreased with increasing anionic groups, and the clearance of carboxylated PVP and sulfonated PVP from the blood was almost similar. But carboxylated PVP efficiently accumulated in the kidney, whereas sulfonated PVP was rapidly excreted in the urine. The renal levels of carboxylated PVP were about five-fold higher than sulfonated PVP. Additionally, carboxylated PVP was effectively taken up by the renal proximal tubular epithelial cells in vivo after i.v. injection. These anionized PVP derivatives did not show any cytotoxicity against renal tubular cells and endothelial cells in vitro. Thus, these carboxylated and sulfonated PVPs may be useful polymeric carriers for drug delivery to the kidney and bladder, respectively.

Optimal construction of non-immune scFv phage display libraries from mouse bone marrow and spleen established to select specific scFvs efficiently binding to antigen

Monoclonal antibodies (MAbs) are widely applied in basic research, medicine, and the pharmaceutical industry. Recently, applications and generations of MAbs have been increasingly attracting attention in many research areas since MAbs could be produced in large quantities with the development of genetic technology and antibody engineering. On the other hand, in recent years, phage display system has been developed for high-throughput isolation and generation of novel MAbs that have high affinity with various antigens. This technology is capable of constructing "Library" containing billions of phage repertoires displaying various antibody fragments, and rapid selection of a specific MAb from this phage library. Additionally, this technology has a great advantage that MAbs can be generated without immunization to animals. However, there are still relatively few reports confirming that useful MAbs can be derived from non-immune antibody libraries. The latter, as undertaken by current methods, seem unable to achieve the high quality required to produce useful MAbs for any desired antigen because cloning of antibody gene from non-immune donors is inefficient. This problem is caused by the fact that their RT-PCR primer sets, PCR conditions, and efficiency of subcloning through construction of antibody gene library cannot encompass all the antibody diversity. In an attempt to overcome some of these earlier problems, here we describe an optimized method to establish a high quality, non-immune library from mouse bone-marrow and spleen, and assess its diversity in terms of content of multiple antibodies for a wide antigenic repertoire. As an example of the application of the methodology, we describe the selection of specific MAbs binding to Luciferase and identify at least 18 different clones. Using this non-immune mouse antibody library, we also obtained MAbs for VEGF, VEGF receptor 2, TNF-alpha, and Pseudomonas Exotoxin, confirming the high quality of the library and its suitability for this application.

Development of Novel DDS Technologies for Pharmacoproteomic-based Drug Discovery and Development

With the success of the Human Genome Project, the focus of life science research has shifted to the functional and structural analyses of proteins, such as proteomics and structural genomics. These novel approaches to the analysis of proteins, including newly identified ones, are expected to help in the identification and development of protein therapies for various diseases. Thus pharmacoproteomic-based drug discovery currently has a very high profile. Nevertheless, the use of bioactive proteins in the clinical setting is not straightforward because in vivo these proteins have low stability and pleiotropic action. To promote pharmacoproteomic-based drug discovery and development, we have attempted to establish a system for creating functional mutant proteins (muteins) with the desired properties and to develop a site-specific bioconjugation system for further improving their therapeutic potency. These innovative protein-drug systems are discussed in this review.

Increased Site 1 Affinity Improves Biopotency of Porcine Growth Hormone

Based on phage display optimization studies with human growth hormone (GH), it is thought that the biopotency of GH cannot be increased. This is proposed to be a result of the affinity of the first receptor for hormone far exceeding that which is required to trap the hormone long enough to allow diffusion of the second receptor to form the ternary complex, which initiates signaling. We report here that despite similar site 1 kinetics to the hGH/hGH receptor interaction, the potency of porcine GH for its receptor can be increased up to 5-fold by substituting hGH residues involved in site 1 binding into pGH. Based on extensive mutations and BIAcore studies, we show that the higher potency and site 1 affinity of hGH for the pGHR is primarily a result of a decreased off-rate associated with residues in the extended loop between helices 1 and 2 that interact with the two key tryptophans Trp104 and Trp169 in the receptor binding hot spot. Our mutagenic analysis has also identified a second determinant (Lys165), which in addition to His169, restricts the ability of non-primate hormones to activate hGH receptor. The increased biopotency of GH that we observe can be explained by a model for GH receptor activation where subunit alignment is critical for effective signaling.

α-Aldehyde Terminally Functional Methacrylic Polymers from Living Radical Polymerization: Application in Protein Conjugation “Pegylation”

Application of proteins and peptides as human therapeutics is expanding rapidly as drug discovery becomes more prevalent. Conjugation of polymers to proteins can circumvent many problems and pegylation of proteins is now emerging as acceptable practice. This paper describes the synthesis of alpha-aldehyde-terminated poly(methoxyPEG)methacrylates from Cu(I) mediated living radical polymerization (Mn = 11 000, 22 000 and 32 000; PDi < 1.15), and their efficient conjugation to lysozyme, as a model protein. This offers an attractive and flexible alternative to linear poly(ethylene glycol) opening up the possibility of using the full power of living radical polymerization.

Creation of Functional Muteins Using Phage Libraries for Pharmacoproteomic-based Drug Discovery and Development of DDS

Tumor necrosis factor-alpha (TNF-alpha) has been expected to be a promising new antitumor agent, but toxic side effects by the systemic administration of TNF-alpha limit its clinical application. In this study, we attempted to improve the therapeutic potency of TNF-alpha by using our protein-drug innovation systems. Among phage libraries displaying various mutant TNF-alphas, we isolated some lysine-deficient super mutant TNF-alphas, typified by mTNF-alpha-K90R, with higher TNF-receptor affinities and stronger bioactivity in vitro, in spite of the importance of lysine residues for trimer formation and receptor binding. mTNF-alpha-K90R showed more than 10 times stronger in vivo antitumor effects and 1.3 times less toxicity than wild-type TNF-alpha (wTNF-alpha). Site-specifically mono-PEGylated mTNF-alpha-K90R (sp-PEG-mTNF-alpha-K90R) at N-terminus showed higher in vitro bioactivity than unmodified wTNF-alpha, whereas randomly mono-PEGylated wTNF-alpha at a lysine residue (ran-PEG-wTNF-alpha) had less than 6% of the bioactivity of wTNF-alpha. The antitumor therapeutic window of sp-PEG-mTNF-alpha-K90R was extended by about 5 times, 60 times and 18 times compared with those of mTNF-alpha-K90R, wTNF-alpha and ran-PEG-wTNF-alpha, respectively. sp-PEG-mTNF-alpha-K90R may, thus, be a potential systemic anti-tumor therapeutic agent. These data suggested that our fusion protein-drug innovation system composed of a creation system of functional mutant proteins based on phage display technique and a site-specific PEGylation system may open up a new avenue to the optimal protein therapy.

[DDS and Me]

With the success of the human genome project, the focus of life science research has shifted to the functional and structural analyses of proteins, such as proteomics and structural genomics. These analyses of proteins including newly identified proteins are expected to contribute to the identification of therapeutically applicable proteins for various diseases. Thus, pharmaco-proteomic-based drug discovery and development for protein therapies, including gene therapy, cell therapy, and vaccine therapy, is attracting current attention. However, there is clinical difficulty in using almost all bioactive proteins, because of their very low stability and pleiotropic actions in vivo. To promote pharmaco-proteomic-based drug discovery and development, we have attempted to develop drug delivery systems (DDSs), such as the protein-drug innovation system and the optimal cell therapeutic system. In this review, we introduce our original DDSs.

The use of PVP as a polymeric carrier to improve the plasma half-life of drugs

To achieve an optimum drug delivery such as targeting or controlled release utilizing bioconjugation with polymeric modifier, the conjugate between drugs and polymeric modifiers must be designed to show desirable pharmacokinetic characteristics in vivo. In this study, we assessed the biopharmaceutical properties of various nonionic water-soluble polymers as polymeric drug carriers. Polyvinylpyrrolidone (PVP) showed the longest mean resident time (MRT) after i.v. injection of all nonionic polymers with the same molecular size. In fact, tumor necrosis factor-alpha (TNF-alpha) bioconjugated with PVP (PVP-TNF-alpha) circulated longer than TNF-alpha bioconjugated with polyethylene glycol (PEG-TNF-alpha) with the same molecular size. Each nonionic polymeric modifier showed a different tissue distribution. Dextran was accumulated in the spleen and liver. Polydimethylacrylamide (PDAAm) tended to distribute in the kidney. However, PVP showed the minimum volume of tissue distribution. These results suggested that PVP is the most suitable polymeric modifier for prolonging the circulation lifetime of a drug and localizing the conjugated drug in blood.

Peptidyl Linkers for Protein Heterodimerization Catalyzed by Microbial Transglutaminase

Specific peptidyl linkers that result in the heterodimerization of functional proteins, which is catalyzed by microbial transglutaminase from Streptomyces mobaraensis (MTG), were generated based on a ribonuclease S-peptide using site-directed mutagenesis. The peptidyl linkers designated as Lys-tag and Gln-tag were designed to possess sole reactive Lys or Gln residue that was amenable for selective Lys-Gln cross-linkage of different proteins. Green fluorescent protein variants, ECFP and EYFP, were employed as model proteins, and those Lys- and Gln-tags were fused to the N-termini of ECFP and EYFP, respectively. As a result, we succeeded in solely obtaining the ECFP-EYFP heterodimer without forming multiply cross-linked byproducts. It was found that the reactivity of peptidyl linkers varied according to the type of amino acid to be replaced. Peptidyl linkers with a basic amino acid (Arg) exhibited the highest reactivity in the cross-linking reaction, suggesting the cationic residue substrate preference of MTG. Kinetic analysis utilizing fluorescent resonance energy transfer (FRET), that is only observed upon the heterodimeric ECFP-EYFP conjugation, revealed that the amino acid replacement contributed to the acceleration of cross-linking reactions by increasing catalytic turnover (k(cat)), rather than substrate binding affinity (K(m)). Finally, using a ribonuclease S-protein, the manipulation of enzymatic protein cross-linking based on specific S-peptide:S-protein interactions was explored. Since newly designed Lys- and Gln-tags retained binding affinities to the S-protein, the heterodimerization was perfectly restrained by wrapping them with the S-protein. The results suggest the possibility of limited protein conjugation by tuning steric hindrance against the MTG. Tailoring enzymatic posttranslational modifications with either engineering peptidyl substrates or by taking specific peptide-protein interactions into consideration may facilitate the development of a new sequential protein conjugation method for the preparation of multifunctional protein.

Design of a pH-Sensitive Polymeric Carrier for Drug Release and Its Application in Cancer Therapy

PURPOSE

In this study, to optimize the polymeric drug delivery system for cancer chemotherapy, we developed a new pH-sensitive polymeric carrier, poly(vinylpyrrolidone-co-dimethylmaleic anhydride) [PVD], that could gradually release native form of drugs with full activity, from the conjugates in response to changes in pH. We examined the usefulness of PVD as a polymeric drug carrier.

EXPERIMENTAL DESIGN

PVD was radically synthesized with vinylpyrrolidone and 2,3-dimethylmaleic anhydride, which is known to be a pH-reversible amino-protecting reagent. Conjugates between PVD and other drugs, such as Adriamycin (ADR), were prepared under the slightly basic conditions (pH 8.5). The drug-release pattern and the antitumor activity of PVD were examined.

RESULTS

At pH 8.5, the release of the drugs from the conjugate was not observed. In contrast, PVD could release fully active drugs in the native form in response to the change in pH near neutrality, and gradually released drugs at neutral pH (7.0) and slightly acidic pH (6.0). The drug-release pattern in serum was almost similar to that observed during these physiological conditions. The PVD-conjugated ADR showed superior antitumor activity against sarcoma-180 solid tumor in mice, and it had less toxic side effects than free ADR. This enhancement in the antitumor therapeutic window may be due to not only the improvement of plasma half-lives and tumor accumulation of ADR, but also its controlled and sustained release from the conjugates in vivo.

CONCLUSIONS

These results indicate that PVD is an effective polymeric carrier for optimizing cancer therapy.

A site-specific polymeric drug carrier for renal disease treatment

A well-designed polymeric carrier for site-specific drug delivery in the treatment of renal disease has been reported recently. Approximately 80% of the water-soluble polymer poly(vinylpyrrolidone-co-dimethyl maleic anhydride selectively accumulated in the kidney of mice 24 h after intravenous injection. The detailed mechanism of such selective accumulation is not clear but an energy-dependent process, other than endocytosis, might be involved in the uptake of the polymer. This study is the first to report active targeting using a synthetic polymeric drug carrier.

Optimal site-specific PEGylation of mutant TNF-α improves its antitumor potency

Recently, we created a lysine-deficient mutant tumor necrosis factor-alpha [mTNF-alpha-Lys(-)] with full bioactivity in vitro compared with wild-type TNF-alpha (wTNF-alpha), and site-specific PEGylation of mTNF-alpha-Lys(-) was found to selectively enhance its in vivo antitumor activity. In this study, we attempted to optimize this PEGylation of mTNF-alpha-Lys(-) to further improve its therapeutic potency. mTNF-alpha-Lys(-) was site-specifically modified at its N-terminus with linear polyethylene glycol (LPEG) or branched PEG (BPEG). While randomly mono-PEGylated wTNF-alpha (ran-LPEG5K-wTNF-alpha) with 5 kDa of LPEG (LPEG5K) had about only 4% in vitro bioactivity of wTNF-alpha, mono-PEGylated mTNF-alpha-Lys(-) [sp-PEG-mTNF-alpha-Lys(-)] with LPEG5K, LPEG20K, BPEG10K, and BPEG40K had 82%, 58%, 93%, and 65% bioactivities of mTNF-alpha-Lys(-), respectively. sp-LPEG-mTNF-alpha-Lys(-) and sp-BPEG10K-mTNF-alpha-Lys(-) had much superior antitumor activity to those of both unmodified TNF-alphas and ran-LPEG5K-wTNF-alpha, though sp-BPEG40K-mTNF-alpha-Lys(-) did not show in vivo antitumor activity. Thus, the molecular shape and weight of PEG may strongly influence the in vivo antitumor activity of sp-PEG-mTNF-alpha-Lys(-).

Poly(vinylpyrrolidone-co-dimethyl maleic acid) as a novel renal targeting carrier

Poly(vinylpyrrolidone-co-dimethyl maleic acid) (PVD) was found to have high renal-targeting capability and safety as a drug carrier. To optimize the renal drug delivery system using PVD, the relationship between the molecular weight of PVD and its renal accumulation were evaluated in mice by their intravenous injection. It was found that the molecular size of 6-8 kDa was associated with the highest renal accumulation. The specific bioactivity of PVD-conjugated superoxide dismutase (SOD) relative to that of unmodified SOD gradually decreased with an increase in the degree of modification to SOD with PVD6K. The conjugated SOD (L-PVD-SOD) with the molecular size of 73 kDa, which had comparable specific bioactivity with native SOD, showed longer plasma half-life than native SOD. About sixfold more L-PVD-SOD was distributed to the kidneys than native SOD 3 h after intravenous injection, whereas extensive PVD modification did not enhance the renal accumulation of SOD. This L-PVD-SOD effectively accelerated recovery from mercuric chloride-induced acute renal failure in vivo. These results suggest that L-PVD-SOD may be the optimal derivative as a potential therapeutic agent to various renal diseases.

Selective Enhancer of Tumor Vascular Permeability for Optimization of Cancer Chemotherapy

Clinical approach using tumor necrosis factor-alpha (TNF-alpha) as selective destruction against tumor endothelial cells and selective enhancer of tumor vascular permeability for effective accumulation of antitumor chemotherapeutic agents has attracted attention. However, the clinical application of TNF-alpha as a systemic antitumor agent has been limited because of toxic side-effects. To systemically use TNF-alpha as an antitumor agent and the selective enhancer of tumor vascular permeability, we assessed the usefulness of PEGylated TNF-alpha (PEG-TNF-alpha). PEG-TNF-alpha at a dose of 1000 JRU showed marked hemorrhagic necrosis in S-180 tumors without side-effects due to selective destruction of tumor vasculature, whereas wild-type TNF-alpha at a dose of 10,000 JRU showed a little hemorrhagic necrosis with severe side-effects. PEG-TNF-alpha induced the enhancement of tumor vascular permeability. The permeability was increased at 1 h, after an i.v. injection of PEG-TNF-alpha and returned to the basal level at 2 h. In addition, high molecular weight of PEG (molecular weight; 500K) accumulated in tumor tissue as well as low molecular weight of PEG (molecular weight; 12K). On the other hand, PEG-TNF-alpha didn't affect the permeability of normal tissue and inflammation site. This data suggested that PEG-TNF-alpha was useful agent as selective enhancer of tumor vascular permeability with safe.

Development of Novel Drug Delivery System (DDS) Technologies for Proteomic-Based Drug Development

With the success of human genome projects, the focus of life science research has shifted to the functional and structural analyses of proteins, such as disease proteomics. These structural and functional analyses of expressed proteins in the cells and/or tissues are expected to contribute to the identification of therapeutically applicable proteins for various diseases. Thus, pharmaco-proteomic based drug development for protein therapies is most noticed currently. However, there is a clinical difficulty to use almost bioactive proteins, because of their very low stability and pleiotropic actions in vivo. To promote pharmaco-proteomic based drug development for protein therapies to various diseases, we have attempted to establish a system for creating functional mutant proteins (muteins) with desired properties, and to develop a site-specific polymer-conjugation system for further improving the therapeutic potency of proteins. In this review, we are introducing our original protein-drug innovation systems mentioned above.

Effective accumulation of poly(vinylpyrrolidone-co-vinyl laurate) into the spleen

To optimize polymer-conjugated drugs as a polymeric drug delivery system, it is essential to design polymeric carriers with tissue-specific targeting capacity. Previously, we showed that polyvinylpyrrolidone (PVP) was the most suitable polymeric carrier for prolonging the blood-residency of drugs, and was one of the best parent polymers to design the polymeric carriers with targeting capacity. In this study, we synthesized some hydrophobic PVP derivatives, poly(vinylpyrrolidone-co-styrene) [poly(VP-co-S)] and poly(vinylpyrrolidone-co-vinyl laurate) [poly(VP-co-VL)], and assessed their biopharmaceutical properties after intravenous administration in mice. The elimination of hydrophobic PVP derivatives from blood was the same as PVP, and the plasma half-lives of poly(VP-co-S) were almost similar to that of poly(VP-co-VL). Poly(VP-co-VL) efficiently accumulated in the spleen, whereas poly(VP-co-S) effectively accumulated in the liver. The level of poly(VP-co-VL) in the spleen was about 20 times higher than PVP and poly(VP-co-S). These hydrophobic PVP derivatives did not show any cytotoxicity against endothelial cells in vitro. Thus, poly(VP-co-VL) may be a useful polymeric carrier for drug delivery to the spleen. This study will provide useful information to design optimal polymeric carriers with targeting capacity to the spleen and liver.

Combination effects of complement regulatory proteins and anti-complement polymer

We previously reported the development of a "cytomedicine" that consists of cells trapped in alginate-poly-L-lysine-alginate (APA) microcapsules and agarose microbeads. The functional cells that are entrapped in semipermeable polymer are completely isolated from cellular immune system. However, the ability of cytomedicine to isolate cells from the humoral immune system, which plays an essential role in xenograft rejection, is low. Therefore, the goal of the present study was to develop a novel cytomedicine that could protect the entrapped cells from injury of the complement system. We investigated the applicability of the complement regulatory protein (CRP), Crry, to cytomedicine. Crry-transfected cells entrapped within agarose microbeads resisted injury by complement to a degree, while entrapment of Crry transfected cells within agarose microbeads containing polyvinyl sulfate (PVS), a novel cytomedical device with anti-complement activity, clearly protected against complement attack. These data indicate that the combination of a CRP and a cytomedical device with anti-complement activity is a superior device for cytomedical therapy.