The chemical synthesis of the phagocytosis-stimulating tetrapeptide tuftsin (Thr-Lys-Pro-Arg) and its biological properties

A strong CD8+ T cell-stimulating supramolecular hydrogel

The development of molecules with immune stimulatory properties is crucial for cancer immunotherapy. In this work, we combined two peptide-based molecules, tuftsin (TKPR) and Nap-GDFDFDY, to develop a novel self-assembling molecule Nap-GDFDFDYTKPR (Comp.3), which has strong CD8+ T cell stimulatory properties. Comp.3 could self-assemble into nanofibers and hydrogels, which significantly improved the stability of tuftsin against enzyme digestion. The nanofibers of Comp.3 enhanced the phagocytic activity of macrophages, promoted the maturation of DCs, and stimulated the expression of cytokines. In addition, it demonstrated an excellent anti-tumor efficacy in vivo by eliciting a strong CD8+ T immune response. Taken together, our observations revealed a powerful immune stimulating nanomaterial that is a promising compound for cancer immunotherapy.

Treatment Effect of Tuftsin and Antigen Peptide Combined with Immune Cells on Colorectal Cancer

Background

The aim of this study was to investigate the effect of antigenic peptides on dendritic cell maturation and activation as well as the role of dendritic cell induced cell function. The tumor-specific cytotoxic T lymphocytes induced by activation of the dendritic cells were also evaluated.

Material/Methods

SW-480 cell lysate and peptide antigens were selected as adjuvants in dendritic cell sensitization, and tuftsin was used to induce the phagocytosis of dendritic cells. Immature dendritic cells were stimulated with the antigen and adjuvant as follows: group A was negative control; group B was SW-480 (20 μg/mL); group C was SW-480 (20 μg/mL)+tumor necrosis factor (TNF)-α (10 μg/mL); group D was SW-480 (20 μg/mL)+tuftsin (20 μg/mL); group E was antigen peptide (2 μg/mL); group F was antigen peptide (2 μg/mL)+TNF-α (10 μg/mL); group G was antigen peptide (2 μg/mL)+tuftsin (20 μg/mL). Cytotoxic T lymphocytes activation and in vitro anti-tumor effects were examined by detecting the maturation marks of dendritic cells as well as interleukin (IL)-10 and IL-12 levels secreted by dendritic cells. Cells with the strongest immunizing effects were injected into nude mice and tumor suppression status was evaluated.

Results

Group D (SW-480+tuftsin), group E (antigen peptides), group F (antigen peptide+TNF-α), and group G (antigen peptides+tuftsin) displayed significant differences compared to the control group (P<0.05). Group G (antigen peptides+tuftsin) could also promote the secretion of cytokines IL-12, as well as inhibit cytokine IL-10 secretion, compared to the other experimental groups (P<0.05). In the in vivo experiments of tumor inhibitions, antigenic polypeptide+tuftsin was the most effective (P<0.05).

Conclusions

Combination of cytotoxic T lymphocytes and T peptide therapy in treating human colorectal cancer might be used as a new treatment strategy based on adoptive cellular immunotherapy.

Tuftsin-phosphorylcholine (TPC) equally effective to methylprednisolone in ameliorating lupus nephritis in a mice model

The role of helminth treatment in autoimmune diseases is growing constantly. Systemic lupus erythematosus (SLE) is a multi-system autoimmune disease with challenging treatment options. Tuftsin-phosphorylcholine (TPC) is a novel helminth-based compound that modulates the host immune network. This study was conducted to evaluate the potential value of TPC in ameliorating lupus nephritis in a murine model and specifically to compare the efficacy of TPC to the existing first-line therapy for SLE: corticosteroids (methylprednisolone). Lupus-prone NZBxW/F₁ mice were treated with TPC (5 µg/mouse), methylprednisolone (MP; 5 mg/body weight) or phosphate-buffered saline (PBS) (control) three times per week once glomerulonephritis, defined as proteinuria of grade > 100 mg/dl, was established. Levels of anti-dsDNA autoantibodies were evaluated by enzyme-linked immunosorbent assay (ELISA), splenic cytokines were measured in vitro and the kidney microscopy was analysed following staining. TPC and MP treatments improved lupus nephritis significantly and prolonged survival in NZBxW/F₁ mice. TPC-treated mice showed a significantly decreased level of proteinuria (P < 0·001) and anti-dsDNA antibodies (P < 0·001) compared to PBS-treated mice. Moreover, TPC and MP inhibited the production of the proinflammatory cytokines interferon IFN-γ, interleukin IL-1β and IL-6 (P < 0·001) and enhanced expression of the anti-inflammatory cytokine IL-10 (P < 0·001). Finally, microscopy analysis of the kidneys demonstrated that TPC-treated mice maintained normal structure equally to MP-treated mice. These data indicate that the small molecule named TPC hinders lupus development in genetically lupus-prone mice equally to methylprednisolone in most of the cases. Hence, TCP may be employed as a therapeutic potential for lupus nephritis.

Gain of affinity for VEGF165 binding within the VEGFR2/NRP1 cellular complex detected by an HTRF-based binding assay

Neuroplin 1 (NRP1), a transmembrane protein interacting with Vascular Endothelial Growth Factor VEGF-A₁₆₅ (called here VEGF165) and the tyrosine kinase Receptor 2 (VEGFR2) promote angiogenesis and vascular homeostasis. In a pathophysiological context, several studies suggested that VEGFR2 and NRP1 mediate tumor development and progression. Given the involvement of the VEGF165 network in promoting tumor angiogenesis, NRP1, VEGFR2 and VEGF165 have been identified as targets for anti-angiogenic therapy. No binding assay exists to monitor specifically the binding of VEGF165 to the VEGFR2/NRP1 complex in intact cells. We established a binding assay based on the homogenous time-resolved fluorescence (HTRF®) technology. This unique binding assay enables to assess the interaction of VEGF165 with VEGFR2 or NRP1 within the VEGFR2/NRP1 complex. Ligand binding saturation experiments revealed that VEGF165 binds the VEGFR2/NRP1 complex at the cell surface with a ten to twenty-fold higher affinity compared to SNAP-VEGFR2 or SNAP-NRP1 receptors alone not engaged in the heteromeric complex. The assay allows characterizing the impact of NRP1 ligands on VEGF165 to the complex. It shows high specificity, reproducibility and robustness, making it compatible with high throughput screening (HTS) applications for identifying new VEGF165 antagonists selective for NRP1 or the VEGFR2/NRP1 complex.

Anticancer activity of tuftsin-derived T peptide in postoperative residual tumors

Immune adjuvants have been used in cancer biotherapies to stimulate immune response to tumor cells. Despite their potential as anticancer reagents, there are several impediments to their use in clinical applications. In this study, we aim to modify the existing tuftsin structure and evaluate its antitumor activity in preclinical models. We synthesized a novel tuftsin derivative, namely, the T peptide (TP), by linking four tuftsin peptides, which showed enhanced stability in vivo. We then evaluated its anticancer activity in a postoperative residual tumor model in mice, where we surgically removed most of the primary tumor from the host, a procedure mimicking clinically postoperative patients. Despite the limited effect in intact solid tumors, TP strongly inhibited relapsed growth of residual tumors in postsurgical mice. Surgical resection of tumors accelerated residual tumor growth, but TP slowed down this process significantly. Interestingly, TP showed similar effects in human xenograft residual models. As an immunomodulator, TP could synergize the functions of macrophages, thus inhibiting the growth of cocultured tumor cells in vitro. Furthermore, TP could shift the macrophages to the tumor-suppressive M1 type and mobilize them to produce elevated cytotoxic TNF-α and NO. As a result, TP effectively prolonged the survival time of tumor-resected mice. Using the postoperative residual tumor models, we provide a body of evidence showing the antitumor activity of TP, which causes no obvious toxicity. Our study highlights the potential of TP as a postoperative adjuvant in cancer therapies.

Enhanced mucosal immune responses induced by a combined candidate mucosal vaccine based on Hepatitis A virus and Hepatitis E virus structural proteins linked to tuftsin

Hepatitis A virus (HAV) and Hepatitis E virus (HEV) are the most common causes of infectious hepatitis. These viruses are spread largely by the fecal-oral route and lead to clinically important disease in developing countries. To evaluate the potential of targeting hepatitis A and E infection simultaneously, a combined mucosal candidate vaccine was developed with the partial open reading frame 2 (ORF2) sequence (aa 368–607) of HEV (HE-ORF2) and partial virus protein 1 (VP1) sequence (aa 1–198) of HAV (HA-VP1), which included the viral neutralization epitopes. Tuftsin is an immunostimulatory peptide which can enhance the immunogenicity of a protein by targeting it to macrophages and dendritic cells. Here, we developed a novel combined protein vaccine by conjugating tuftsin to HE-ORF2 and HA-VP1 and used synthetic CpG oligodeoxynucleotides (ODNs) as the adjuvant. Subsequent experiments in BALB/c mice demonstrated that tuftsin enhanced the serum-specific IgG and IgA antibodies against HEV and HAV at the intestinal, vaginal and pulmonary interface when delivered intranasally. Moreover, mice from the intranasally immunized tuftsin group (HE-ORF2-tuftsin + HA-VP1-tuftsin + CpG) showed higher levels of IFN-γ-secreting splenocytes (Th1 response) and ratio of CD4⁺/CD8⁺ T cells than those of the no-tuftsin group (HE-ORF2 + HA-VP1 + CpG). Thus, the tuftsin group generated stronger humoral and cellular immune responses compared with the no-tuftsin group. Moreover, enhanced responses to the combined protein vaccine were obtained by intranasal immunization compared with intramuscular injection. By integrating HE-ORF2, HA-VP1 and tuftsin in a vaccine, this study validated an important concept for further development of a combined mucosal vaccine against hepatitis A and E infection.

Tuftsin signals through its receptor neuropilin-1 via the transforming growth factor beta pathway

Tuftsin (Thr-Lys-Pro-Arg) is a natural immunomodulating peptide found to stimulate phagocytosis in macrophages/microglia. Tuftsin binds to the receptor neuropilin-1 (Nrp1) on the surface of cells. Nrp1 is a single-pass transmembrane protein, but its intracellular C-terminal domain is too small to signal independently. Instead, it associates with a variety of coreceptors. Despite its long history, the pathway through which tuftsin signals has not been described. To investigate this question, we employed various inhibitors to Nrp1's coreceptors to determine which route is responsible for tuftsin signaling. We use the inhibitor EG00229, which prevents tuftsin binding to Nrp1 on the surface of microglia and reverses the anti-inflammatory M2 shift induced by tuftsin. Furthermore, we demonstrate that blockade of transforming growth factor beta (TGFβ) signaling via TβR1 disrupts the M2 shift similar to EG00229. We report that tuftsin promotes Smad3 phosphorylation and reduces Akt phosphorylation. Taken together, our data show that tuftsin signals through Nrp1 and the canonical TGFβ signaling pathway. Despite the 40-year history of the tetrapeptide tuftsin (TKPR), a macrophage and microglial activator, its mechanism of action has not been defined. Here, we report that the tuftsin-mediated anti-inflammatory M2 shift in microglia is caused specifically by tuftsin binding to the receptor neuropilin-1 (Nrp1) and signaling through TGFβ receptor-1, a coreceptor of Nrp1. We further show that tuftsin signals via the canonical TGFβ pathway and promotes TGFβ release from target cells.

Tuftsin promotes an anti-inflammatory switch and attenuates symptoms in experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a demyelinating autoimmune disease mediated by infiltration of T cells into the central nervous system after compromise of the blood-brain barrier. We have previously shown that administration of tuftsin, a macrophage/microglial activator, dramatically improves the clinical course of experimental autoimmune encephalomyelitis (EAE), a well-established animal model for MS. Tuftsin administration correlates with upregulation of the immunosuppressive Helper-2 Tcell (Th2) cytokine transcription factor GATA-3. We now show that tuftsin-mediated microglial activation results in shifting microglia to an anti-inflammatory phenotype. Moreover, the T cell phenotype is shifted towards immunoprotection after exposure to tuftsin-treated activated microglia; specifically, downregulation of pro-inflammatory Th1 responses is triggered in conjunction with upregulation of Th2-specific responses and expansion of immunosuppressive regulatory T cells (Tregs). Finally, tuftsin-shifted T cells, delivered into animals via adoptive transfer, reverse the pathology observed in mice with established EAE. Taken together, our findings demonstrate that tuftsin decreases the proinflammatory environment of EAE and may represent a therapeutic opportunity for treatment of MS.

Microglia/macrophages promote glioma progression

Gliomas are highly aggressive and accompanied by numerous microglia/macrophages (MG/MP) in and about the tumor. Little is known about what MG/MP do in this setting, or whether modulating MG/MP activation might affect glioma progression. Here, we used a glioma-microglia in culture system to establish the effects the tumor and microglia have on each other. We assessed glioma progression in vivo after MG/MP ablation or in the setting of exaggerated MG/MP activation. We show that glioma cells activate microglia but inhibit their phagocytic activities. Local ablation of MG/MP in vivo decreased tumor size and improved survival curves. Conversely, pharmacological activation of MG/MP increased glioma size through stimulating tumor proliferation and inhibiting apoptosis. In agreement with recent reports, expression of the chemokine CCL21 is enhanced after MG/MP activation and correlates with tumor growth. Taken together, our findings demonstrate that inhibition of MG/MP activation may constitute a new and effective contribution towards suppressing glioma proliferation.

Tuftsin: on the 30-year anniversary of Victor Najjar's discovery

After a short description of the results of Victor Najjar's research on tuftsin and of the discoveries done by other authors in the early stage of tuftsin investigation, the current state of work on tuftsin is presented, based mainly on the literature published in the years 1984-1997. The presentation follows this order: the occurrence of tuftsin and retro-tuftsin sequences in proteins, their synthesis and biology, the antigenic properties of tuftsin, its influence on phagocytic cells, and other biologic activities of tuftsin, including antimicrobial, antiviral, antitumor and central effects, and the search for tuftsin superactive analogs.

Solution conformation of tuftsin

Conformation of chemically synthesized tetrapeptide tuftsin, an important immunomodulator, with the sequence Thr-Lys-Pro-Arg-OH has been studied in aqueous solution as well as in a number of organic solvents viz. trifluoroethanol (TFE), methanol and dioxane by circular dichroism (CD) spectroscopy which reveals preferential occurrence of mixture of random coil and beta-turns, that has already been predicted as bioactive conformation of this peptide.

Simulations of conformers of tuftsin and a cyclic tuftsin analog

The conformational properties of the configurational isomers of tuftsin, a linear tetrapeptide with the sequence Thr-Lys-Pro-Arg, were investigated with six 1 ns molecular dynamics simulations in explicit water and in a 1.0 m NaCl solution. The average conformation of the cis isomer is a type VI beta-turn. Our results indicate that water-peptide hydrogen bonding, in addition to intramolecular hydrogen bonds, stabilizes the cis conformer. The trans isomer is neither a beta- nor a gamma-turn. Results are compared with parallel studies on a cyclic analog of tuftsin, cyclo(Thr-Lys-Pro-Arg-Gly). The addition of salt does, not influence the backbone conformation of the peptide. Differences between the structures are confined to the side-chain orientations of the Lys and Arg residues.

Suppression of tuftsin activity by the partial sequences of adenovirus type 2 proteins

The synthesis of tuftsin inhibitor-like partial sequences of adenovirus type 2 proteins: TVPPR (1), TRPPR (2), TGPPT (3), PRPPT (4), FVPPR (5), ARPPA (6) and YGPPK (7) are described. The choice of peptides for synthesis was performed by using a simple computer-aided method for predicting antigenic determinants of proteins. For all these peptides an inhibitory activity against tuftsin was found.

Competition between tuftsin and HBV S-protein sequences

The syntheses of HBV S-protein partial sequences: Thr-Lys-Pro-Thr (I), Thr-Lys-Pro-Thr-Asp (II), and Thr-Lys-Pro-Thr-Asp-Gly (III) and also of pentapeptide Thr-Lys-Pro-Gly-Arg (IV), are described. For the peptides II and III inhibitory activity against tuftsin was found. Peptide IV (an analogue of tuftsin-inhibitor Thr-Lys-Pro-Pro-Arg) demonstrated a tuftsin-like activity in the phagocytosis experiments.

The characteristics of purified HL60 tuftsin receptors

The purification and characteristics of purified HL60 tuftsin receptors are described. Purification was accomplished by affinity chromatography similar to that described earlier, wherein a tuftsin analog Thr-Lys-Pro-Pro-Arg, is covalently linked at the N alpha group to a solid support. The receptor consists presumably of two subunits approximately 66 KDa and 57 KDa. The dissociation constant of the receptor complex is 4.7 X 10(-8) M with 5 X 10(4) receptors per cell. It can form oligomers with an Mr of about 560 KDa suggesting an octomeric structure, assuming the same number of each subunit is associated.

Tuftsin: its chemistry, biology, and clinical potential

Tuftsin is a tetrapeptide, Thr-Lys-Pro-Arg, which resides in the Fc-domain of the heavy chain of immunoglobulin G. The peptide originates from a specific fraction of the parent protein through enzymatic processing. Tuftsin possesses a broad spectrum of activities related primarily to the immune system function and exerts on phagocytic cells, notably on macrophages. These include potentiation of various cell functions such as phagocytosis, motility, immunogenic response, and bactericidal and tumoricidal activities. The features of tuftsin, coupled with its low toxicity, make the peptide an attractive candidate for immunotherapy. Tuftsin's capacity to augment cellular activation is mediated by specific receptors that were identified, characterized, and recently isolated from rabbit peritoneal granulocytes. Tuftsin has been chemically synthesized by a variety of techniques, some of which are adequate for large-scale preparations. A multitude of analogs have also been synthesized and extensively studied for structure-function relationships.

Tuftsin stimulates growth of HL60 cells

Many functions of monocyte/macrophage and granulocyte are activated by tuftsin; principally phagocytosis, motility, immunogenic stimulation, antibacterial and antineoplastic activities. Here it is shown that tuftsin stimulates HL60 growth to twice the control rate. The uptake of [3H]uridine and [3H]leucine in a pulse of 30 min was also double that of the control. The uptake of thymidine was not stimulated.

Splenic function: physiology and splenic hypofunction

A wide variety of disorders can result in diminished splenic function. The pathophysiology appears to be clearly defined in some instances, such as congenital asplenia and disorders of splenic vascular obstruction or congestion. In others, such as the autoimmune and GI disorders, the mechanism remains poorly defined. Further research is needed. The hyposplenia which occurs in many of these disorders has been associated with an increased risk of life-threatening, overwhelming bacterial sepsis. In other instances, this complication has not been reported. This certainly should not be interpreted to mean that it cannot occur. The risk of septicemia in hyposplenic disorders is rarely above 10 to 15%. In disorders with minimal inhibition of splenic function, the incidence of sepsis would presumably be less than the 1.5% incidence following surgical splenectomy for trauma. Considering these data, a very large number of patients would have to become asplenic before it would be likely that one would develop sepsis. Furthermore, the lack of awareness of the possibility of hyposplenia-related sepsis in many of these disorders may cause such occurrences to go unrecognized. Finally, since the risk of sepsis is probably less in hyposplenic adults as compared to children, studies on adults may underestimate the incidence of this complication in children. Many of the disorders reported to cause hyposplenia in adults have not been noted to do so in children. In instances such as celiac disease, it may take many years for the complication to manifest so that it would be unlikely for a child to manifest hyposplenia during childhood. However, in other instances, not enough children have been studied to be confident that the hyposplenia and its associated risk of sepsis are not complications that occur in children. Hyposplenia-related bacterial septicemia is a catastrophic complication. If a patient develops a disorder that is potentially associated with hyposplenia, the patient should be observed for signs of asplenia in the peripheral blood. If the technique is available, quantitation of red cell pits should be performed. If not, other studies of splenic function such as radionuclide scans should be considered, depending on the incidence of hyposplenia in that particular disorder. If evidence of asplenia develops, pneumococcal vaccine should be administered, penicillin prophylaxis should be considered, significant febrile episodes should be managed aggressively, and probably most importantly, the patient and family should be carefully educated about this complication. Most deaths from hyposplenia-related septicemia are preventable.

Isolation and subunit composition of tuftsin receptor

Tuftsin (Thr-Lys-Pro-Arg) receptor was purified to apparent homogeneity by affinity chromatography, using a pentapeptide analog (Thr-Lys-Pro-Pro-Arg) that binds the receptor more than 4 times as avidly as tuftsin. The analog was covalently linked to a solid support (Affi-Gel 10). Rabbit peritoneal granulocyte membrane solubilized with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate was applied to the affinity column, the column was washed with 0.1 M ammonium carbonate (pH 7.9) and 0.1 M ammonium acetate (pH 5), and bound material was eluted with 20 nM tuftsin or pentapeptide. The eluate was concentrated and subjected to gel filtration; this yielded one major peak of [3H]tuftsin binding activity corresponding to approximately 500 kDa and a minor peak at approximately 250 kDa. Rechromatography of either peak resulted in the appearance of the same major and minor peaks. NaDodSO4/PAGE of the affinity-purified material under nonreducing conditions showed only two silver-staining bands. Electroblotting followed by [3H]tuftsin overlay and fluorography showed two adjacent radioactive bands corresponding in mobility to the silver-stained bands. Under reducing conditions, NaDodSO4/PAGE yielded molecular mass values 62 kDa and 52 kDa for the two tuftsin receptor subunits. Electron microscopy revealed a homogeneous population of spherical molecules with diameters of 104 A.

Defective activation of neutrophils after splenectomy

Neutrophil chemotaxis and phagocytosis in the presence of serum from 20 patients who had undergone splenectomy and from 15 healthy volunteers was studied. The mean distance migrated by normal neutrophils in the presence of serum from the patients after splenectomy was significantly less than that when normal serum was used (p less than 0.005). The percentage of neutrophils phagocytosing a yeast was also significantly reduced in the presence of serum from patients after splenectomy (p less than 0.02). In addition, when neutrophils from these patients were studied both chemotaxis and phagocytosis were enhanced in normal compared with autologous serum (p less than 0.05).

Synthesis and biological activity of [L-3,4-dehydroproline3]-tuftsin

A 3,4-dehydroproline analogue of tuftsin (L-Thr-L-Lys-L-Pro-L-Arg) was prepared by the solid phase synthetic method. Following reversed-phase high performance liquid chromatography (HPLC) purification, the analogue was compared to tuftsin for its ability to to enhance the chemotactic, bactericidal and phagocytic activities of polymorphonuclear leukocytes (PMN). Both tuftsin and [delta 3-pro3]- tuftsin elicited a similar significant chemotactic effect at a concentration of 10 micrograms/ml. A slight suppression of the chemotactic activity was observed with tuftsin at 10(-3) micrograms/ml and with [delta 3-pro3]-tuftsin at concentrations of 10(-3), 10(-2) (significant) and 10-1 micrograms/ml. Although similar bactericidal activities were observed for both peptides, PMN exposed to [delta 3-pro 3]-tuftsin exhibited increased phagocytic indicies 2-4 times that of tuftsin-treated PMN at concentrations of 0.4, 0.6 and 1.0 microgram/ml.

Antibacterial properties of tuftsin and its analogs

The antibacterial properties of tuftsin and its 11 analogs on 20 bacterial strains were investigated. Tuftsin showed a definite antibacterial effect at a minimal effective concentration of 62.5 micrograms/ml. All analogs were either less effective or lacked any activity. The bacteria used included some highly pathogenic organisms.

The similarity between tuftsin (Thr-Lys-Pro-Arg) receptors and tuftsin antibody: a case of induced molecular mimicry

The characteristics of binding of tuftsin (Thr-Lys-Pro-Arg) and several of its synthetic analogues, to specific membrane receptors on rabbit polymorphonuclear granulocytes, were compared with the binding characteristics of rabbit specific antibody to tuftsin. [3H-Arg4]-tuftsin was used as the principal ligand. Six analogues were studied. Two of these, Thr-Lys-Pro and Ala-Lys-tuftsin-Glu-Ala3, showed no binding affinity either to receptor or antibody. Ala-Lys-tuftsin showed less binding than tuftsin to both acceptors. Three showed stronger binding than tuftsin. The order of binding among these was tuftsin ( [Glu]2-tuftsin ( [Pro-Pro3]-tuftsin (tuftsinyltuftsin. This same order of binding was found with both receptor and antibody.

Enhancement of endogenous xenotropic murine retrovirus expression by tuftsin

The exposure of a high-passage clone of Kirsten sarcoma virus transformed Balb/c (K-Balb) mouse cells to tuftsin (Thr-Lys-Pro-Arg) enhanced the expression of endogenous xenotropic retrovirus. The tetrapeptide increased the expression of virus that was infectious for rat, but not mouse, cells in a concentration-dependent fashion (0.001-1000 micrograms/ml). Increased virus expression could be achieved during short-term incubations (3-4 hr), with maximum enhancement occurring over longer time periods (16-18 hr). The enhancement of virus expression by tuftsin was proportional to the spontaneous release of virus. The infectivity of the enhanced virus was neutralized by goat anti-RLV gp 70 serum. Actinomycin D inhibited the induction of virus, suggesting that enhanced expression required de novo RNA synthesis. Tuftsin stimulated DNA, RNA, and protein synthesis in K-Balb cells during 16-hr incubations. Increased cellular proliferation was also seen at various time periods. The effects observed using K-Balb cells offer an opportunity to study the modulation of gene expression by tuftsin in a fibroblast culture system.

Tuftsin, a natural activator of phagocyte cells: an overview

The recognition that a small oligopeptide was responsible for the full stimulation effect of specific cytophilic gamma-globulin on blood neutrophils arose from a study of the kinetics of phagocytosis. These were unusual in that the stimulation was short lived and that preincubation of the phagocyte with the gamma-globulin rendered the latter inactive. The oligopeptide was isolated, its structure determined (Thr-Lys-Pro-Arg) and synthesized. The discovery of human mutants with tuftsin deficiency exhibiting signs and symptoms of frequent severe infection further emphasized the specific biological function of the tetrapeptide. The mutant peptide was isolated, sequenced (Thr-Glu-Pro-Arg), and synthesized. Further studies showed that tuftsin requires two enzymes for its liberation from the parent carrier gamma-globulin. One enzyme is in the spleen that cleaves distal to the arginine end, and the other, on the outer side of the plasma membrane, cleaves proximal to the threonine residue. The tetrapeptide tuftsin stimulates all functions of phagocytic cells: phagocytosis, pinocytosis, motility, immunogenic activity including processing of the antigen and augmentation of the number of antibody-forming cells, bactericidal activity, and, above all, tumoricidal activity. The latter has been shown by several laboratories.

A biochemical study of the phagocytic activities of tuftsin and its analogues

The effects of tuftsin and one of its analogues (4 [lys]-tuftsin) on phagocytosis of Staphylococcus aureus and Candida albicans were investigated in mice and rabbits. Mice were intravenously or orally administered 1-25 mg of 4 [lys]-tuftsin per kg daily for 4 to 7 days. After the mice were further treated with cyclophosphamide, they were intravenously challenged with C. albicans. More than 50% of the mice infected with C. albicans were killed within 7 days, although only 20% to 40% of those infected with the same microbes after 4 [lys]-tuftsin treatment died. A combination of 4 [lys]-tuftsin and an antibiotic was found to be somewhat more effective than either one alone. Further, pretreatment with 4 [lys]-tuftsin depressed microbial growth in the kidneys of mice bearing S-180 tumors. Rabbit peritoneal macrophages and polymorphonuclear leukocytes were harvested by intraperitoneal injection of liquid paraffin and of glycogen solution, respectively. For in vitro study of phagocytosis, rabbit macrophages of polymorphonuclear leukocytes were incubated in Hanks solution together with S. aureus and the number of survivors was determined. Enhanced engulfing activity of macrophages and increased bactericidal activity of polymorphonuclear leukocytes were shown by the in vitro phagocytosis experiments. It is expected that 4 [lys]-tuftsin will be effective against infectious disease, especially in immunocompromised hosts such as patients with malignant tumors.

New synthetic and natural tuftsin-related compounds and evaluation of their phagocytosis-stimulating activity

The preparation of large amounts of tuftsin (50 g) as well as purification by preparative HPLC are presented. Synthesis of several analogues exhibiting significant phagocytosis-stimulating activity of human PMN are described and discussed. On the other hand, the synthesis of a natural human IgG decapeptide fragment 335-344 that could be liberated from the same carrier molecule is presented. This decapeptide fragment, Thr-Ile-Ser-Lys-Ala-Lys-Gly-Gln-Pro-Arg, showed interesting activity in stimulating phagocytosis of human polymorphonuclear leukocytes.

Synthesis of an IgG fragment decapeptide exhibiting phagocytosis stimulating activity of polymorphonuclear leucocytes

Fragment 335-344 of human IgG was synthesized stepwise, using active esters of N-protected amino acids and benzotriazolyloxytris (dimethylamino)phosphonium hexafluorophosphate for coupling. This fragment could be liberated from the carrier molecule by the two specific enzymes responsible for the release of tuftsin from the same carrier molecule: tuftsin endocarboxy-peptidase cleaves at the Arg-Glu bond and leukokininase at the Lys-Thr bond. This decapeptide fragment, Thr-Ile-Ser-Lys-Ala-Lys-Gly-Gln-Pro-Arg showed significant activity in stimulating phagocytosis of human polymorphonuclear leucocytes.

Conversion of a primary amine to a labeled secondary amine by the addition of phenolic group and radioiodination

To preserve the nucleophilicity of amino compounds during conjugative radioiodination, a new method for converting primary amines to phenolic secondary amines was developed. Amino acids were used as model compounds for establishing optimal conditions for the reductive amination. In the first step of the reaction, the aldehyde group of 4-hydroxybenzaldehyde (formylphenol) was reacted reversibly with an amino group to form an imine. The irreversible attachment of formylphenol to the amino group was accomplished by reduction of the imine with sodium cyanoborohydride. The pH optimum for the reaction was 5.0. Higher temperature has favorable effects on the rate and extent of the conjugation. Phenolic derivatives of amino compounds suitable for radioiodination are produced by the reactions described.

Antitumor effect of tuftsin

Tuftsin, a physiological tetrapeptide derived from the Fc region of leukophilic IgG possesses a variety of immunopotentiating properties including the ability to act as an immunotherapeutic agent against the experimental tumors, L1210 leukemia and Cloudman S-91 melanoma. Although the mechanism of action of tuftsin in vivo is not known, several types of leukocytes have been shown to become cytotoxic effector cells following activation with tuftsin. These cells presently include macrophages, natural killer cells, and granulocytes. The possibility that tuftsin can also activate other types of effector cells have not been ruled out. We feel this small peptide has a high potential (largely unrecognized) as an antitumor immunopotentiating agent. It is naturally occurring in man and appears to be relatively non-toxic. Its exact sequence (Thr-lys-Pro-Arg) is known and it can be chemically synthesized. Methods are also available to monitor the levels of tuftsin in body fluids. These properties along with its ability to control infectious disease make this agent one of the more promising immunopotentiators.