Tuftsin: a hormone-like tetrapeptide with antimicrobial and antitumor activities

Tuftsin-Bearing Liposomes Co-Encapsulated with Doxorubicin and Curcumin Efficiently Inhibit EAC Tumor Growth in Mice

Background

Targeted multidrug-loaded delivery systems have emerged as an advanced strategy for cancer treatment. In this context, antibodies, hormones, and small peptides have been coupled to the surface of drug carriers, such as liposomes, polymeric and metallic nanoparticles loaded with drugs, as tumor-specific ligands. In the present study, we have grafted a natural macrophage stimulating peptide, tuftsin, on the surface of the liposomes (LPs) that were loaded with doxorubicin (DOX) and/or curcumin (CUR), by attaching to its C-terminus a palmitoyl residue (Thr-Lys-Pro-Arg-CO-NH-(CH₂)₂-NH-COC₁₅H₃₁, P.Tuft) to enable its grafting within the liposome’s bilayer.

Methods

The prepared drug-loaded liposomes (DOX LPs, CUR LPs, DOX-CUR LPs, P.Tuft-LPs, P.Tuft-DOX LPs, P.Tuft-CUR LPs, P.Tuft-DOX-CUR LPs) were thoroughly characterised in terms of particle size, drug content, encapsulation efficiency and structural properties using UV–visible spectroscopy, dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FTIR). The anti-cancer activity and drug toxicity of the liposomal formulations were examined on Ehrlich ascites carcinoma (EAC) tumor-induced mice model.

Results

A significant reduction in the tumor weight and volume was observed upon treating the tumor-bearing mice with palmitoyl tuftsin-grafted dual drug-loaded liposomes (P.Tuft-DOX-CUR LPs), as compared to the single drug/peptide-loaded formulation (DOX LPs, CUR LPs, DOX-CUR LPs, P.Tuft- LPs, P.Tuft-DOX LPs, P.Tuft-CUR LPs). Western blot analysis revealed that the tumor inhibition was associated with p53-mediated apoptotic pathway. Further, the biochemical and histological analysis revealed that the various liposomal preparation used in this study were non-toxic to the animals at the specified dose (10mg/kg).

Conclusion

In conclusion, we have developed a targeted liposomal formulation of P.Tuftsin-bearing liposomes co-encapsulated with effective anti-cancer drugs such as doxorubicin and curcumin. In experimental animals, tumor inhibition by P.Tuft-DOX-CUR LPs indicates the synergistic therapeutic effect of the peptide and the dual drug.

Chemical and biological properties of a supramolecular complex of tuftsin and cucurbit[7]uril

Cucurbit[7]uril (CB7) is an uncharged and water-soluble macrocyclic host. CB7 binds to doubly protonated tuftsin, which is the tetrapeptide Thr-Lys-Pro-Arg, with moderate affinity (K_a=2.1×10³M^-1). In this study, the host-guest complexation was confirmed by fluorescence titration. This affinity would allow for easy release of the peptide under physiological conditions. According to density functional theory calculations, the structural binding motif involves hydrogen bonding. The most energetically stable form had the Arg side chain inside the CB7 cavity. The effects of the tuftsin-CB7 complex on the proliferation and cytokine activity of immune cells were studied. The complex had broader spectrum immunomodulation than free peptides, and caused statistically significant (p<0,05) changes in cytokine production (tumor necrosis factor-α, interleukin-2, interferon-γ, and interleukin-10) by mononuclear cells. By contrast, the free peptide only activated tumor necrosis factor-α production.

Targeted nano-delivery of novel omega-3 conjugate against hepatocellular carcinoma: Regulating COX-2/bcl-2 expression in an animal model

The present approach enumerates the effectiveness of tuftsin tagged nano-liposome for the cytosolic transport of 2,6-di-isopropylphenol-linolenic acid conjugate against liver cancer in mice. Initially, the conjugate in its free form was examined for anticancer potential on HepG2 liver cancer cells. Induction of apoptosis and suppression of migration and adhesion of HepG2 cells confirmed the effectiveness of conjugate as an anticancer agent. After this, role of the conjugate entrapped in a nano-carrier was evaluated in animal model. The nano-formulation comprising of conjugate bearing tuftsin tagged liposome was firsly characterized and then its therapeutic effect was determined. The nano-formulation had 100-130nm size nanoparticles and showed sustained release of the conjugate in the surrounding milieu. The nano-formulation distinctly reduced the expression of COX-2, an important molecule that is vastly expressed in hepatocellular carcinoma. The utilization of in-house engineered nano-formulation was also successful in significantly up-regulating Bax and down-regulating bcl-2 gene expression eventually helping in better survival of treated mice. Histopathological analysis also revealed positive recovery of the general architecture and the violent death of cancer cells by apoptosis at tumor specific site. The site specific delivery of conjugate entrapped in tuftsin tagged liposomes was highly safe as well as efficaceous. Nano-formulation based approach showed a visible chemotherapeutic effect on liver cancer progression in experimental mice thereby making it a potential candidate for treatment of liver cancer in clinical settings.

Synthesis of tritiated tuftsin and macrophage inhibitory tripeptide via acetylenic intermediates

Acetylenic analogues of tuftsin (Thr-Dah-Pro-Arg) and of a macrophage inhibitory tripeptide (Thr-Dah-Pro) have been synthesized by conventional procedures in solution (Dah = 2,6-diamino-4-hexynoic acid). These acetylenic derivatives are intermediates for the preparation of structurally unmodified, tritiated peptides. Catalytic tritiation of Thr-Dah-Pro-Arg and of Thr-Dah-Pro has afforded the radioactive tetra- and tripeptides with specific activities of 11.4 Ci/mmol and 37 Ci/mmol, respectively.

Tuftsin augments antitumor efficacy of liposomized etoposide against fibrosarcoma in Swiss albino mice

Anticancer drugs are generally plagued by toxic manifestations at doses necessary for control of various forms of cancer. Incorporating such drugs into liposomes not only reduces toxicity but also enhances the therapeutic index. Some antioxidants and potent immunomodulators have also been shown to impart significant antitumor activity presumably by nonspecific activation of the host immune system. In the present study, we evaluated augmentation of the antitumor activity of etoposide (ETP) by the immunomodulator tuftsin in Swiss albino mice with fibrosarcoma. The efficacies of the free form of ETP, liposomized ETP (Lip-ETP), and tuftsin-bearing liposomized ETP (Tuft-Lip-ETP) formulations were evaluated on the basis of tumor regression, effect on expression level of p53wt and p53mut, and survival of the treated animals. Tuft-Lip-ETP, when administered at a dosage of 10 mg/kg body weight/day for five days, significantly reduced tumor volume, delayed tumor growth, and also up-regulated the expression of p53wt. In contrast, although Lip-ETP delayed tumor growth, it did not decrease tumor size. The results of the present study suggest that tuftsin incorporation in drug-loaded liposomes is a promising treatment strategy for various forms of cancers, including fibrosarcoma.

Tuftsin augments antitumor efficacy of liposomized etoposide against fibrosarcoma in Swiss albino mice

Anticancer drugs are generally plagued by toxic manifestations at doses necessary for control of various forms of cancer. Incorporating such drugs into liposomes not only reduces toxicity but also enhances the therapeutic index. Some antioxidants and potent immunomodulators have also been shown to impart significant antitumor activity presumably by nonspecific activation of the host immune system. In the present study, we evaluated augmentation of the antitumor activity of etoposide (ETP) by the immunomodulator tuftsin in Swiss albino mice with fibrosarcoma. The efficacies of the free form of ETP, liposomized ETP (Lip-ETP), and tuftsin-bearing liposomized ETP (Tuft-Lip-ETP) formulations were evaluated on the basis of tumor regression, effect on expression level of p53wt and p53mut, and survival of the treated animals. Tuft-Lip-ETP, when administered at a dosage of 10 mg/kg body weight/day for five days, significantly reduced tumor volume, delayed tumor growth, and also up-regulated the expression of p53wt. In contrast, although Lip-ETP delayed tumor growth, it did not decrease tumor size. The results of the present study suggest that tuftsin incorporation in drug-loaded liposomes is a promising treatment strategy for various forms of cancers, including fibrosarcoma.

Laparoscopic hand-assisted spleen autotransplantation

BACKGROUND

Only recently has the spleen been perceived as an organ with a major immune function. This raised an interest in spleen salvage after spleen trauma and pancreatic tail resection, for the treatment of hematologic disorders and inducement tolerance for allogenic transplants. The purpose of this study was to evaluate the feasibility of a new technique for spleen transplantation: laparoscopic spleen autotransplantation in a large animal model.

METHODS

Ten 35-kg pigs were used for this study. A laparoscopic hand-assisted splenectomy was first performed. The spleen was extracted through the handport to be flushed with a 4 degrees C saline solution and prepared extracorporeally. The graft was then reintroduced into the same animal's abdominal cavity, and a splenic-to-common iliac artery and vein bypass was performed laparoscopically using a 7-0 polytetrafluoroethylene running suture. The animal was killed 1 week postoperatively for histologic examination.

RESULTS

All 10 animals tolerated the procedure well. No conversion to open surgery was required. The mean operative time was 253 +/- 45 min. The mean time needed to create the artery and vein anastomoses was 116 +/- 165 min, and the mean blood loss was 190 +/- 120 ml. There was no intra- or postoperative death. Intraoperative complications included two stenosed vascular anastomoses, which were taken down and revised. Seven of the 10 spleens were histologically viable 1 week after surgery. The nonviable transplantations were attributable to a thrombosis of the common iliac artery (n = 1) or the transplant artery (n = 2).

CONCLUSIONS

Hand-assisted laparoscopic spleen autotransplantation is feasible in an animal model. This procedure could constitute an option when spleen resection is necessary for pancreatic tail resection, or when spleen preservation is important to the maintenance or restoration of an immune function.

Histone-like proteins from Atlantic cod milt: stimulatory effect on Atlantic salmon leucocytes in vivo and in vitro

This study was carried out to reveal some characteristics of cationic proteins from Atlantic cod (Gadus morhua) milt chromatin and to investigate their ability to activate Atlantic salmon (Salmo salar) macrophages. Cationic proteins extracted from cod milt chromatin were fractionated on a cation exchange chromatography column. SDS-PAGE and amino acid analyses of the resulting fractions indicated that these proteins are similar to calf thymus histones. Two cationic protein fractions were used to stimulate leucocytes from Atlantic salmon in vitro and in vivo. Increased production of superoxide, measured as reduction of nitroblue tetrazolium (NBT), was used as indication of macrophage activation. Both fractions induced elevated superoxide anion production in the macrophages after 3 and 6 days of in vitro stimulation. Intraperitoneal injection of the cationic protein fractions in Atlantic salmon (100 mg kg(-1)) four days prior to slaughtering stimulated superoxide production when assayed after one and two days of cell cultivation. In macrophages from fish slaughtered two days after injection, activation could first be seen after two days of cell cultivation.

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.

ADP-ribosylation of tuftsin suppresses its receptor-binding capacity and phagocytosis-stimulating activity to murine peritoneal macrophages

Arginine-specific ADP-ribosyltransferase present in granules of chicken polymorphonuclear leukocytes (so-called heterophils) is released into the extracellular space by stimulus of calcium ionophore A23187 or opsonized zymosan [Terashima et al. (1996) J. Biochem. 120, 1209-1215]. In the present work, we examined extracellular targets of the released transferase and identified tuftsin, a phagocytosis-stimulating tetrapeptide derived from leukokinin, as a preferential substrate of the enzyme in chicken plasma. Specific binding of FITC-tuftsin to murine peritoneal macrophages, observed under a fluorescent microscope, was impaired by ADP-ribosylation of the labelled peptide. Phagocytic assay analyzed by flow cytometry revealed that ADP-ribosylation of tuftsin decreased its phagocytosis-stimulating activity towards the macrophages. Thus, the ADP-ribosylation of tuftsin apparently decreases its biological activity and ADP-ribosylation may possibly be involved in inflammatory processes through alterations in tuftsin activity.

Effect of partially modified retro-inverso analogues derived from C-reactive protein on the induction of nitric oxide synthesis in peritoneal macrophages

1. The ability of three modified tetrapeptides, representing fragments of the C-reactive protein (CRP) sequence and stabilized in the first peptide bond by retro-inverso modification, to affect the secretion of nitric oxide (NO) was studied in macrophages of BALB/c mice. 2. These tetrapeptides, resembling the aminoacid sequence of tuftsin (CRP 1, H-gThr-(R,S)mLys-Pro-Leu-OH, ITF 1192; CRP II, H-gGly-(R, S)mLys-Pro-Arg-OH, ITF 1127; CRP III, H-gThr-(R,S)mLys-Pro-Gln-OH. ITF 1193), were able to induce NO synthesis by peritoneal macrophages in a dose-dependent manner; the most stimulating dose was 1000 ng ml-1 for CRP II and 100 ng ml-1 for CRP I and CRP III. NO synthesis was not strictly dependent on lipopolysaccharide (LPS) activation. 3. The enhanced effect of retro-inverso CRP-related analogues on the expression of iNOS (inducible NO synthase) was confirmed by higher levels of iNOS activity in the cytosol and by the increase in iNOS protein, as evaluated by Western blot analysis, in macrophages stimulated by CPR compared with untreated ones. 4. The production of NO by retro-inverso CRP-peptide analogues was significantly inhibited by dexamethasone (20 microM), NG-monomethyl-L-arginine (L-NMMA) (500 microM) and pyrrolidine dithiocarbamate (PDTC) (100 microM). 5. Retro-inverso CRP-peptide analogues stimulated macrophages to produce high levels of interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha) in the presence of LPS. 6. Retro-inverso CRP-peptide analogues stimulated NO synthesis by the enhancement of endogenously produced IL-1 and TNF-alpha, as the treatment of peritoneal macrophages with LPS in the presence of neutralizing anti-IL-1 and anti-TNF monoclonal antibodies (mAbs) reduced retro-inverso analogue-induced NO secretion. Data indicate a predominant role for IL-1 alpha in the induction of NO secretion by retro-inverso analogues. 7. These results suggest that retro-inverso CRP derived analogues act as costimulators of NO and cytokine synthesis in macrophages. The mechanisms by which they cause iNOS induction appear to be strongly dependent on the activation of nuclear factor-kappa B (NF-kappa B).

[Hyp3]-tuftsin ([Hyp3]-TU) synthesis and biological activity

[Hyp3]-tuftsin (Thr-Lys-Hyp-Arg) has been synthesized by the liquid-phase method. In biological investigations performed on rats antinociceptive and diuretic effects have been determined. It has been suggested that the presence of hydroxyl substituent in pyrrolidine ring of proline slightly modifies antinociceptive TU effect and is responsible for the increased diuretic [Hyp3]-TU activity.

A comparative study of [Leu1]Tuftsin and tuftsin, a natural phagocytosis-stimulating peptide

1. [Leu1]tuftsin was reported to have greater phagocytosis-stimulating activity than tuftsin (Thr-Lys-Pro-Arg). 2. However, a study on inactivation of tuftsin by polymorphonuclear leukocytes (PMNs) demonstrated that leucine aminopeptidase, an ecto-enzyme, located on PMN surface was responsible for this mechanism. 3. Since leucine aminopeptidase is known to cleave Leu more easily than Thr at the N-terminal position of peptides, this suggested to us that [Leu1]tuftsin might then be inactivated by PMNs more easily than tuftsin, and thus this analog might be less active than tuftsin. 4. In addition, many tuftsin preparations used in earlier studies were not fully active, as high-performance liquid chromatography was not available to separate out many contaminating diastereomers. 5. In view of this, we have synthesized and purified [Leu1]tuftsin and compared its phagocytosis-stimulating activity with tuftsin. 6. Our results indicate that [Leu1]tuftsin is not as active as tuftsin in stimulating phagocytosis.

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.

Specific translocation of tuftsin (Thr-Lys-Pro-Arg), a natural immunomodulating peptide, into the nuclei of human monocytes

To delineate the mechanism of growth and differentiation activities of tuftsin (Thr-Lys-Pro-Arg), we examined the translocation of tuftsin after internalization by the target cells. We found using two independent techniques, fluorescence microscopy and autoradiography, that while in human polymorphonuclear leukocytes (terminally differentiated cells) the peptide remains in the cytoplasmic compartment, in monocytes it translocates to the nucleus. The ability of tuftsin to directly interact with DNA was documented by a large increase in the melting point of bovine DNA in the presence of tuftsin. It is suggested that the translocation, processing and action of tuftsin may depend on the differentiation state and/or on the type of effector cells. Also, tuftsin has the capacity to interact directly with DNA and, therefore, may have a potential for affecting gene activity.

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.

Low molecular weight immunopotentiators

It has long been recognized that modulation of the immune system by various agents may have potential for the management of certain infectious and neoplastic diseases. Both natural products as well as chemically synthesized compounds have been investigated for immunotherapeutic potential. Over the years, conflicting reports on the clinical efficacy of these agents have left the early promise of immunotherapy unfulfilled. However, the manipulation of the immune system to generate a desired effect is becoming feasible as the mechanisms which regulate the immune network are better understood. Much of the early work on immunotherapy concentrated on the development of immunopotentiators, agents which enhance the host's own immune system against cancer cells or infectious pathogens. Furthermore, with the development of subunit and/or synthetic vaccines, which are often weakly immunogenic, the importance of developing agents capable of acting as adjuvants became apparent. As a result, the utility of immunopotentiators has now extended to the area of vaccines. There are a number of reviews available on immunomodulators [see Fenichel, R. L. and Chirigos, M. A. (eds) (1984), Immune Modulation Agents and Their Mechanisms, Marcel Dekker, New York]. The purpose of this article is to provide an update on low molecular weight agents capable of potentiating the immunological network. Attention will be given to those agents which have undergone significant clinical development in the areas of cancer, infectious diseases and vaccination over the past several years. These agents will be categorized as to whether they are naturally occurring or chemically synthesized.

The immunopharmacology of immunotoxicology, and immunorestoration

The first part of this paper focuses on the secondary immunodeficiencies caused by immunosuppressive drugs and environmental chemicals. The mechanism of action and the therapeutic effects of azathioprine, glucocorticosteroids, cyclophosphamide, cyclosporin A, and anticancer drugs will be discussed. The immunotoxic actions of benzene, polychlorinated and polybrominated biphenyls, tetrachlorodibenzo-paradioxin, polycyclic aromatic hydrocarbons, various insecticides, metals and abused drugs or drugs with side effects are also described. Immunorestorative approaches are discussed in the second part, based on our current knowledge of the immune system and the lymphokines and hormones involved in its function. The usefulness of thymic hormones, interleukin 2, macrophage growth factor/colony stimulating factor, and interferons as immunotherapeutic agents is considered. In addition, we address chemically defined drugs, such as levamisole, diethyldithiocarbamate, isoprinosine, muramyl dipeptides, azimexon, ciamexon, bestatin, tuftsin, and pyrimidinoles, and finally conclude that combined use of different immunostimulants may be the most effective way to treat the above mentioned immunodeficiencies.

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.

Protection of mice against Plasmodium berghei infection by a tuftsin derivative

In Plasmodium berghei infections, the mortality rate and parasitaemias were significantly reduced and the mean survival time was considerably enhanced by pretreating the animals with a tuftsin derivative, Thr-Lys-Pro-ARg-NH-(CH2)2-NHCOC15H31. This effect of the modified tuftsin was further increased upon its incorporation in the liposome bilayer. These results indicate that tuftsin and its derivatives may prove useful in enhancing nonspecific host resistance against protozoan infections.

Influence of the peptide chain length of new elongated tuftsin analogs on phagocytosis process

In this paper the synthesis of the following elongated tuftsin analogs: Arg-Thr-Lys-Pro-Arg (1), Pro-Arg-Thr-Lys-Pro-Arg(II), Lys-Pro-Arg-Thr-Lys-Pro-Arg(III) and Thr-Lys-Pro-Arg-Thr-Lys-Pro-Arg(IV) by classical and solid-phase methods are described. The obtained peptides were tested for their biological activity: restoration of the phagocytosis of defected granulocytes from blood of children with acute lymphoblastic leukemia (ALL).

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.

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.

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.

Peptide fragments from the tuftsin containing domain of immunoglobulin G synthesis and biological activity

Peptides corresponding to sequences of the Fc-portion of immunoglobulin G (IgG) surrounding and containing the tuftsin molecule were synthesized. The compounds were assayed for their ability to compete with [3H-Arg4]tuftsin in binding to mouse peritoneal macrophages and to stimulate the cell's capacity to phagocytize. Despite the sensitivity that tuftsin has demonstrated to various chemical modifications and structural alterations which usually cause reduction or total loss of biological activity, IgG-related analogs possess potent tuftsin-like activity. The activity is not caused by enzymatic breakdown and release of tuftsin. The fact that the elongated tuftsin analogs can specifically be attached to and activate macrophages may indicate a possible connection between Fc and tuftsin's receptors.

Synthesis and biological investigations of new tuftsin analogs with elongated peptide chain

In this paper the synthesis of the following elongated tuftsin analogs: Thr-Lys-Pro-Lys-Thr-Lys-Pro-Lys (I), Thr-Lys-Pro-Lys-Thr-Lys-Pro-Arg (II) and Ala-Lys-Thr-Lys-Pro-Arg-Glu-Gln (III) by the classical method is described. The compound II markedly inhibited the growth of murine sarcoma viruses (MSV).