[A patient operated for occlusion of the superior mesenteric artery]

A 40-year-old woman presented with fever, dysarthria, and left hemiparesis. Diagnostic imaging detected an infarction in the right cerebrum; lupus anticoagulant was positive. A T4N3M0 adenocarcinoma coexisted in the left lung, which was irradiated once. Two days later, the superior mesenteric artery was occluded. The bowel was widely resected but she died of hepatic infarction. The lung cancer may have triggered catastrophic antiphospholipid syndrome.

Target-cell specificity of fusogenic liposomes: membrane fusion-mediated macromolecule delivery into human blood mononuclear cells

Fusogenic liposome, a unique vector prepared by fusing ultraviolet-inactivated Sendai virus and liposome, is known to efficiently deliver content into various animal cells through membrane fusion. In this study, we examined the target-cell specificity of fusogenic liposome (FL)-mediated macromolecule delivery into human blood cells using diphtheria toxin fragment A (DTA) as a probe. Among the peripheral blood mononuclear cells (PBMC), FL was able to deliver its encapsulates into CD14+ monocytes and CD4-/CD8- T-cells, but not into CD19+ B-lymphocytes, CD4+ T-cells or CD8+ T-cells. The susceptibility of human leukemia cell lines to FL was similar to that of PBMC; the order of the reactivity was U937 (monoblastic leukemia)>MOLT4, Jurkat (T-lymphoma)>Daudi, BALL1 (B-lymphoma)>K562 (erythroblastic leukemia). Interestingly, FL showed similar binding activity to all of these leukemia cell lines. These findings indicate that, among blood cells, monocytes, monoblastic leukemia cells, CD4-/CD8- T-cells and T-lymphoma cells are preferable targets for FL-mediated macromolecule delivery. This is the first demonstration of the existence of non-permissive cells against FL. Our results also suggest that some molecules on target-cells other than the binding targets of SV-derived protein may participate in fusion between FL and cells.

Gene delivery systems using the Sendai virus

Fusogenic liposome (FL) is a delivery system that can transfer encapsulated materials into living cells directly through membrane fusion. FL is a promising approach for gene therapy because it can deliver various genetic materials much more efficiently than other non-viral vectors without damaging the cell. FL-mediated gene transfer consists of two independent membrane fusion phenomena; generation of a FL by fusing a Sendai virus (SV) particle with a simple liposome encapsulating DNA, and successive fusion of the FL with cell membrane. The former requires viral F protein but no other special molecule on the liposomal membrane, whereas the latter may require the receptor (sialic acid) and unidentified assistant molecule(s) on the cell membrane. Further analysis suggests that these assistant molecule(s), not the receptor, may control the fusion and govern the cell specificity of FL-mediated delivery. This review has described a detailed analysis of these fusion phenomena and discussed possible applications of FL-mediated gene delivery to human gene therapy.

Tumor necrosis factor alpha-mediated tumor regression by the in vivo transfer of genes into the artery that leads to tumors

We report that tumor necrosis factor (TNF) alpha induced a strong antitumor immune reaction when it was produced in arteries leading to tumors by gene transfer in vivo. We used a mouse model carrying a sarcoma-180 tumor in the right footpad and injected the fusogenic liposomes encapsulating the human TNF-alpha gene into the right femoral artery. Under this condition, human TNF-alpha was detected only in the artery leading to the tumor and in the tumor. There was a significant regression in tumor growth when the TNF-alpha gene was delivered into the right femoral artery, with 4 of 11 mice completely cured. No regression was observed when the TNF-alpha gene was delivered into the left femoral artery or into the tumor or when the luciferase gene was administered. Tumor regression was inhibited by the injection of anti-TNF-alpha, anti-CD4, or anti-CD8 monoclonal antibody, and CD8+ T cells accumulated in the tumors of TNF-alpha-treated mice. These results suggest that TNF-alpha expressed locally in the arteries leading to tumors efficiently suppresses tumor growth through reinforcement of an antitumor immune reaction. The significance of this phenomenon for cancer gene therapy was discussed.

Effect of ultrafiltration during cardiopulmonary bypass for pediatric cardiac surgery

The effect of ultrafiltration during cardiopulmonary bypass (CPB) was evaluated for correcting ventricular septal defects with associated pulmonary hypertension in patients less than 18 months old. Interleukin (IL)-6 and IL-8 concentrations in the blood, ultrafiltrate, and urine were measured. The blood IL-6 concentration increased to 128.4+/-20.2 pg/ml by the end of surgery, which is lower than the concentration seen in adult patients (273.1+/-48.2 pg/ml, p < 0.02). The blood IL-8 concentration was not significantly different than that of adults. The total amounts of excreted IL-6 in the ultrafiltrate and urine during CPB were 11.5+/-0.32 pg/kg and 0.32+/-0.07 pg/kg, respectively (p < 0.05). The total amounts of excreted IL-8 in the ultrafiltrate and urine were 4.64+/-0.69 pg/kg and 1.92+/-0.56 pg/kg, respectively (p < 0.05). No differences were seen in these values for excretion between children and adults. We conclude that ultrafiltration during CPB in pediatric patients is more effective in removing proinflammatory cytokines than in adults and more effective than renal filtration alone.

Involvement of CD4+ T cells in the development of dextran sulfate sodium-induced experimental colitis and suppressive effect of IgG on their action

1. To clarify the role of T cells in the development of dextran sulfate sodium (DSS)-induced colitis, T cells from colitis mice were primed with DSS-pulsed macrophages in vitro and then transferred into normal mice. In addition, to determine whether the target cell of immunoglobulin G (IgG) is the T cell, the extent of T cell proliferation induced by pulsed macrophages was examined after preincubation with IgG. 2. When mice receiving the primed T cells were treated with oral DSS, colitis symptoms were more severe than in animals treated with oral DSS only. This activity of primed T cells was reduced by depletion from the cells of CD4+ but not CD8+ cells. 3. The proliferation of T cells from colitis mice induced by pulsed macrophages was inhibited by T cell preincubation with homologous IgG. 4. The results suggest that CD4+ T cells play an important role in the development of DSS-induced experimental colitis and that IgG may modulate the development of colitis through interaction with pathogenic T cells.

Identification of tumor vascular antigens by monoclonal antibodies prepared from rat-tumor-derived endothelial cells

We have reported the isolation and specific in vitro properties of tumor-derived endothelial cells (TEC) from rat KMT-17 fibrosarcomas transplanted into rats. To develop antibody-based tumor vascular targeting therapy for solid tumors, we have generated monoclonal antibodies (MAbs) using passive immunization of outside-out membrane vesicles of rat epididymal-fat-pad-derived capillary endothelial cells (FCEC) followed by active immunization of those of rat TEC. The MAbs produced were screened against TEC and FCEC. Of all cultured hybridomas, 75 (3.3%) of the secreted MAbs preferentially recognized TEC. We selected a total of 7 MAbs which detected antigens highly abundant in TEC, although 5 of the 7 MAbs were weakly positive for FCEC in cell-ELISA and FACS analyses. The antigens recognized by these MAbs, with the exception of MAb TES-7, were present on endothelial cells of tumor blood vessels in KMT-17 fibrosarcoma tissues, as shown by immunohistochemical analysis. Antigens of 40- and 80-kDa were recognized by MAbs TES-1, 7, 17, 21 and 26 and by MAbs TES-23 and 27 respectively. Although the function of these antigens, which are preferentially expressed on rat tumor-derived endothelial cells, is still unknown, we believe that future studies of such antigens will help elucidate the role of endothelial cells in tumor vasculature. Our results indicate that MAbs may provide a novel tool for the development of antibody-based therapy targeting tumor vasculature.

Tryprostatin A, a specific and novel inhibitor of microtubule assembly

We have investigated the cell cycle inhibition mechanism and primary target of tryprostatin A (TPS-A) purified from Aspergillus fumigatus. TPS-A inhibited cell cycle progression of asynchronously cultured 3Y1 cells in the M phase in a dose- and time-dependent manner. In contrast, TPS-B (the demethoxy analogue of TPS-A) showed cell-cycle non-specific inhibition on cell growth even though it inhibited cell growth at lower concentrations than TPS-A. TPS-A treatment induced the reversible disruption of the cytoplasmic microtubules of 3Y1 cells as observed by indirect immunofluorescence microscopy in the range of concentrations that specifically inhibited M-phase progression. TPS-A inhibited the assembly in vitro of microtubules purified from bovine brains (40% inhibition at 250 microM); however, there was little or no effect on the self-assembly of purified tubulin when polymerization was induced by glutamate even at 250 microM TPS-A. TPS-A did not inhibit assembly promoted by taxol or by digestion of the C-terminal domain of tubulin. However, TPS-A blocked the tubulin assembly induced by inducers interacting with the C-terminal domain, microtubule-associated protein 2 (MAP2), tau and poly-(l-lysine). These results indicate that TPS-A is a novel inhibitor of MAP-dependent microtubule assembly and, through the disruption of the microtubule spindle, specifically inhibits cell cycle progression at the M phase.

Identification of tumor vascular antigens by monoclonal antibodies prepared from rat-tumor-derived endothelial cells

We have reported the isolation and specific in vitro properties of tumor-derived endothelial cells (TEC) from rat KMT-17 fibrosarcomas transplanted into rats. To develop antibody-based tumor vascular targeting therapy for solid tumors, we have generated monoclonal antibodies (MAbs) using passive immunization of outside-out membrane vesicles of rat epididymal-fat-pad-derived capillary endothelial cells (FCEC) followed by active immunization of those of rat TEC. The MAbs produced were screened against TEC and FCEC. Of all cultured hybridomas, 75 (3.3%) of the secreted MAbs preferentially recognized TEC. We selected a total of 7 MAbs which detected antigens highly abundant in TEC, although 5 of the 7 MAbs were weakly positive for FCEC in cell-ELISA and FACS analyses. The antigens recognized by these MAbs, with the exception of MAb TES-7, were present on endothelial cells of tumor blood vessels in KMT-17 fibrosarcoma tissues, as shown by immunohistochemical analysis. Antigens of 40- and 80-kDa were recognized by MAbs TES-1, 7, 17, 21 and 26 and by MAbs TES-23 and 27 respectively. Although the function of these antigens, which are preferentially expressed on rat tumor-derived endothelial cells, is still unknown, we believe that future studies of such antigens will help elucidate the role of endothelial cells in tumor vasculature. Our results indicate that MAbs may provide a novel tool for the development of antibody-based therapy targeting tumor vasculature.

Amino acids and peptides. XXXIII. A bifunctional poly(ethylene glycol) hybrid of laminin-related peptides

A novel amino acid type poly(ethylene glycol) (aaPEG) was prepared and its application as a drug-carrier was examined. The peptides, Pro-Asp-Ser-Gly-Arg (PDSGR) and Tyr-Ile-Gly-Ser-Arg (YIGSR) which are active fragments of Laminin (a cell adhesion protein), were previously reported to be inhibitors of experimental metastasis. Both peptides were conjugated with aaPEG (average molecular weight, 3,000) to prepare a bifunctional peptide-PEG hybrid. The hybrid, PDSGR-aaPEG-YIGSR, was manually prepared by the solid-phase fluorenylmethyloxycarbonyl (Fmoc) strategy. The antimetastatic activity of the peptides in mice was not lost when conjugated to form a larger aaPEG molecule. YIGSR(375 nmol) and PDSGR (375 nmol and 750 nmol) did not demonstrate antimetastatic activity, but a mixture of PDSGR (187 nnmol) and YIGSR (187 nmol) exhibited an inhibitory effect. The inhibitory effect of the hybrid (187 nmol) was more potent than that of the mixture (PDSGR and YIGSR), indicating that the inhibitory effect of the peptides was potentiated by hybrid formation with aaPEG.

Drug resistance and P-glycoprotein expression in endothelial cells of newly formed capillaries induced by tumors

The inhibitory effects of vincristine (VCR) with or without verapamil (VER) on angiogenesis in mouse subcutaneous fascia induced by mouse sarcoma 180 cells were assessed using the dorsal air sac method. VCR combined with VER had inhibitory effects on tumor-induced angiogenesis, but VCR alone did not inhibit capillarization. The chemosensitivity of human umbilical vein endothelial cells (HUVEC) and tumor-derived endothelial cells from rat KMT-17 fibrosarcoma (TEC) was examined using the microculture tetrazolium assay. VCR and taxol had strong anti-proliferative activity against HUVEC, but only weakly inhibited the proliferation of TEC. In combination with VER, VCR and Taxol inhibited the proliferation of TEC. Cisplatin, mitomycin C, and 5-fluorouracil had weakly anti-proliferative activity against both HUVEC and TEC. Expression of P-glycoprotein (P-gp) was found in TEC, but not in HUVEC using western blot analysis. These findings indicate that drug resistance and P-gp expression appeared on newly formed capillaries induced by rodents tumors.

Gene transfer vectors based on Sendai virus

A gene delivery system is a fundamental technology used in human gene therapy. In order to treat patients suffering from incurable metabolic diseases, we must be able to deliver genes efficiently in situ and induce stable gene expression in non-dividing tissue cells. However, none of the current gene transfer systems (both viral and non-viral) satisfies this goal. In order to develop a novel gene delivery system that is free from the defects of existing gene transfer vectors, we analyzed natural biological phenomena that involve gene transfer and expression, and made artificial components that mimic the functioning of these systems. Our recent results shed light on three major aspects of gene transfer and expression: (1) the direct delivery of DNA into cytoplasm using fusogenic liposomes, (2) the transfer of DNA from cytoplasm to nucleus with a nuclear localization signal, and (3) the stabilization of DNA in the nucleus as an independent replicon. The possible development of a hybrid vector by combining these components is discussed.

Enhanced in vitro percutaneous penetration of salicylate by ion pair formation with alkylamines

The apparent octanol/water partition coefficient (APC) of salicylate (SA) increased as the concentration of alkylamine (amyl, hexyl, heptyl, octyl and nonylamine) in aqueous phase increased, presumably through intermolecular ion pair formation between the negatively charged SA moiety and the alkylamine cation. The true partition coefficient (TPC) and the formation constant (Kf) of the ion pair were calculated from the partition data. The skin permeability of SA increased as the APC of SA increased, when 20-fold molar excess of alkylamine was added to the donor compartment. Permeability of ion pairs (PAB) from the aqueous phase to a shed snake skin was estimated from the permeability data assuming 1:1 ion pair. The methylene group contribution to the free energy of transfer of ion pairs from water to the shed snake skin was less than the reported value for nonionized drugs. This suggests that the ion pair is more polar by nature than nonionized molecules, even if ionic characteristics are masked to some extent by ion pair formation.

Total structures of colistin minor components

Structural characterization of the colistin (CL) components were carried out using Frit-fast atom bombardment liquid chromatography/mass spectrometry (Frit-FAB LC/MS), tandem mass spectrometry (MS/MS) and the amino acid analysis proposed by MARFEY, and the total structures of 4 minor components including the absolute configuration of the constituent amino acids were proposed. The structures of the minor components were the same as those of the main component colistin A or B except that L-leucine is replaced by L-valine or L-isoleucine.

Cell cycle arrest and antitumor activity of pironetin and its derivatives

The biological effects of pironetin and its derivatives on cell cycle progression and antitumor activity were studied. At 10-20 ng/ml, both pironetin and its demethyl derivative, NK10958P completely inhibited the cell proliferation of 3Y1 cells, however, epoxypironetin showed only a weak inhibitory activity. The cell cycle analysis revealed that these compounds arrested the cell cycle progression at the M-phase in a dose-dependent manner. These antiproliferative effects of pironetin were also observed in the range 5-25 ng/ml with several tumor cell lines. In CDF1-SLC mice bearing P388 leukemia cells, the intraperitoneal administration of 6.3 mg/kg pironetin over a 5-day period showed a moderate antitumor effect (T/C, 128%). As the chemical structure of pironetin is different from other M-phase inhibitors such as colchicine or vinblastine, pironetin will be the lead compound for a potential new antitumor drug.

[Molecular design of polymer-conjugated cytokines and its application for drug delivery systems]

In recent years, clinical application of recombinant cytokines has been expected as a novel drug for various diseases. However, cytokines have generally poor stability in vivo, so they required of very high doses to achieve sufficient clinical effect. In addition, because cytokines have pleiotropic functions, they would cause unfavourable side-effects. Therefore an drug delivery system (DDS) is necessary for clinical use, which stabilizes the cytokines and potentiates only the expected function from other unfavorable ones in vivo. Then we performed the chemical modification of cytokines with water-soluble polymers to overcome such problems as poor stability and pleiotropic activities. This approach includes some advantages that decrease renal excretion rate of proteins and prevent the degradation by proteases. This would result in prolonging the half-lives of bioactive proteins and potentiating their clinical effects. Interestingly, we found that the polymer-conjugated cytokines, that we named hybrid-cytokines, for instance, polyethylene glycol-modified interleukin-6 (PEG-IL-6), were able to increase selectively in their function of promoting platelet production, but not in other unfavourable functions. This effects were suggested for a result of the change in the systemic distribution pattern by pegylation of proteins. In this review, we proposed that the DDS using hybrid-cytokines would be able to increase the stability and regulate the spectrum of the functions of the cytokines by controlling the pharmacokinetics and pharmacodynamics in vivo. This will provide a fundamental information enabling us to design the hybrid-proteins applicable to therapeutic use.

Amino acids and peptides. XXXI. Preparation of analogs of the laminin-related peptide YIGSR and their inhibitory effect on experimental metastasis

Analogs of a partial sequence peptide of laminin, i.e., Tyr-Ile-Gly-Ser-Arg (YIGSR) analogs and Cys-Asp-Pro-Gly-Tyr-Ile-Gly-Ser-Arg (CDPGYIGSR) analogs, were prepared by the solid-phase method and their inhibitory effects on experimental metastasis of B16-BL6 melanoma cells were examined. YIGSR analogs in which Ile was replaced by other hydrophobic amino acids (Met, Leu, Phe) were inhibitory. Cys-containing analogs of YIGSR were also prepared, but were less active than the parent peptide, YIGSR. Among them, CYIGSR was easily oxidized to form a disulfide bond. A Cys-containing YIGSR analog cyclized through a disulfide bond, cyclo(CYIGSRC)G, was prepared. The disulfide bond formation was performed on the resin by the silyl chloride-sulfoxide method and by the iodine oxidation method. The yield of the silyl chloride-sulfoxide method was much better than that of the iodine oxidation method.

Antitumor activity of tumor necrosis factor alpha conjugated with divinyl ether and maleic anhydride copolymer on solid tumors in mice

The purpose of this study is to further explore the usefulness of conjugation with functional polymeric modifiers for clinical application of bioactive proteins and to increase the therapeutic efficacy of tumor necrosis factor alpha (TNF-alpha) by conjugation in vivo. We synthesized TNF-alpha conjugated with the copolymer of divinyl ether and maleic anhydride (DIVEMA), which has intrinsic antitumor activity as a synthetic biological response modifier. The synthesis of DIVEMA-TNF-alpha could be controlled by the addition of 2,3-dimethylmaleic anhydride (DMMAn), which binds to or separates from amino groups when the pH is changed. The specific activity of DIVEMA-TNF-alpha (+) synthesized with DMMAn was hardly decreased in vitro. However, DIVEMA-TNF-alpha (-), which is conjugated without blocking by DMMAn, had a markedly diminished specific activity. DIVEMA-TNF-alpha (+) caused a dramatic hemorrhagic necrotic effect on the tumor when compared to native TNF-alpha 24 h after i.v. injection into mice bearing Sarcoma-180 solid tumors. In addition, DIVEMA-TNF-alpha (+) at a dose of only 100 Japan reference units per mouse revealed a dramatic antitumor effect that is approximately 100 times greater than native TNF-alpha and that could induce complete regression in all five mice bearing Meth-A solid tumors without any apparent side effects. Because neither DIVEMA alone nor a mixture of TNF-alpha and DIVEMA caused antitumor activity with i.v. administration, the increase in antitumor potency of TNF-alpha may be caused by the covalent conjugation with DIVEMA. DIVEMA-TNF-alpha at low dose revealed dramatic antitumor potency. Because TNF-alpha injected in vivo is extremely low-dose, concentration of intrinsic TNF-alpha in vivo is not influenced. Therefore, the cytokine network in vivo is not destroyed. These results suggest that DIVEMA is a useful polymeric modifier for conjugation of TNF-alpha to increase its antitumor activity.

Amino acids and peptides. XXXII: A bifunctional poly(ethylene glycol) hybrid of fibronectin-related peptides

An amino acid type poly(ethylene glycol) (aaPPEG) was prepared and its application to a drug carrier was examined. The peptides, Arg-Gly-Asp (RGD) and Glu-Ile-Leu-Asp-Val (EILDV) which were reported as active fragments of Fibronectin (a cell adhesion protein), were conjugated with aaPEG (molecular weight, 10,000). The hybrid, RGD-aaPEG-EILDV, was prepared by a combination of the solid-phase method and the solution method. Antiadhesive activity of the peptides was not lost by its hybrid formation with the large aaPEG molecule. A mixture of RGD (0.43 mmol) and EILDV (0.43 mmol) did not demonstrate an antiadhesive effect, but the hybrid containing 0.43 mmol of each peptide did exhibit this effect.

Proliferative effect of dextran sulfate sodium (DSS)-pulsed macrophages on T cells from mice with DSS-induced colitis and inhibition of effect by IgG

The authors have previously reported that homologous immunoglobulin (Ig)G reduces the occurrence of dextran sulfate sodium (DSS)-induced colitis, mainly by suppressing recruitment of immunocompetent cells into colitis lesions. However, the mechanisms of cell recruitment and of its suppression by IgG remain unclear. In addressing these questions, this study focused on the activation of T cells in the presence of macrophages. The authors found that [3H]-thymidine uptake of T cells from DSS-induced colitis mice, but not from normal mice, was significantly enhanced when cultured with DSS-pulsed macrophages. From the profile of cytokine production, it was suggested that T helper 1 (Th1)-type cells become predominant during stimulation. Addition of homologous IgG significantly suppressed T cell proliferation in a dose-dependent manner, while no suppressive effect was observed with heterologous IgG. Mouse IgG F(ab')2, but not Fc, fragments partially mimicked the suppressive effect of whole IgG. These findings provide evidence that Th1-type cells may play an important role in the development of DSS-induced colitis and that homologous IgG exerts its protective action at least in part through the F(ab')2 portion.

Positively charged liposome functions as an efficient immunoadjuvant in inducing immune responses to soluble proteins

To design an optimum liposome immunoadjuvant for soluble protein antigens, we investigated the relationship between liposomal surface charge and adjuvant action. Positively charged multilamellar vesicles (MLV) were taken up efficiently by macrophages, while negatively charged and neutral MLVs were hardly picked up. Consistent with this, positively charged MLVs containing soluble chicken egg albumin (OVA) functioned as a more potent inducer of antigen-specific cytotoxic T lymphocyte (CTL) responses and antibody production than negatively charged and neutral MLVs containing the same concentrations of antigens. These results indicate that the positive charge on the surface of liposomes represents an important factor for enhancing their immunoadjuvancy in the induction of antigen-specific immune responses.

Amino acids and peptides. XXX. Preparation of Arg-Gly-Asp (RGD) hybrids with poly(ethylene glycol) analogs and their antimetastatic effect

Hybrids of a fibronectin-related peptide[Arg-Gly-Asp (RGD)] with poly(ethylene glycol) (PEG) analogs were prepared by a simple and easy procedure. Two amino-PEG analogs were used as carriers for hybrid formation of the RGD. One was poly(oxyethylene)dipropylamine and the other was Jeffamine ED type, which has branched chains. RGD peptides were formed stepwise on PEG analogs by the diisopropylcarbodiimide method. The synthetic intermediates were easily purified by molecular-sieve gel chromatography and the final products were purified by molecular-sieve gel chromatography, followed by HPLC. This simple and easy preparation procedure using molecular-sieve gel chromatography for purification of synthetic intermediates is advantageous for the preparation of peptide-polymer hybrids. We found that PEG is stable to HF treatment at 0 degree C for 1 h. The inhibitory effect of the RGD hybrids on experimental metastasis of B16-BL6 was examined in mice. The Jeffamine type hybrid showed no inhibitory effect at the dose of 1 mg/mouse, but poly(oxyethylene)dipropylamine type hybrid was inhibitory at the same dose. The effect of the latter hybrid was about the same as that of 1 mg of RGD. One mg of the hybrid contains 0.18 mumol of RGD and 1 mg of RGD is 2.38 mumol. Thus it can be said that the inhibitory effect of RGD was potentiated by hybrid formation with poly(oxyethylene)diisopropylamine.

Bioconjugation of tumor necrosis factor-alpha with the copolymer of divinyl ether and maleic anhydride increasing its antitumor potency

To enhance the therapeutic usefulness of antitumor cytokines in vivo, we synthesized bioconjugated tumor necrosis factor-alpha (TNF-alpha) with divinyl ether and maleic anhydride copolymer (DIVEMA), which has intrinsic antitumor activity as a synthetic biological response modifier. The degree of modification could be controlled by the addition of 2,3-dimethylmaleic anhydride (DMMAn), which binds to amino groups of TNF-alpha by changing the pH. In addition, the specific activity of DIVEMA-TNF-alpha was hardly decreased in vitro. DIVEMA-TNF-alpha showed a marked antitumor effect compared to native TNF-alpha without any side effects such as sudden death, body-weight reduction, and decrease in platelet count on mice bearing solid tumors. These results suggest that DIVEMA is a useful polymeric modifier for-bioconjugation of TNF-alpha in order to increase its antitumor activity, and multifunctionally bioconjugated TNF-alpha may be a potentiated antitumor agent for therapeutic use.