Prothymosin α and its C-Terminal Immunoreactive Decapeptide Show No Evidence of Acute Toxicity: A Preliminary In Silico, In Vitro and In Vivo Investigation.

BACKGROUND: Members of the α-thymosin family have long been studied for their immunostimulating properties. Among them, the danger-associated molecular patterns (DAMPs) prothymosin α (proTα) and its C-terminal decapeptide proTα(100-109) have been shown to act as immunomodulators in vitro, due to their ability to promote T helper type 1 (Th1) responses. Recently, we verified these findings in vivo, showing that both proTα and proTα(100-109) enhance antitumor-reactive T cell-mediated responses. METHODS: In view of the eventual use of proTα and proTα(100-109) in humans, we investigated their safety profile in silico, in human leukocytes and cancer cell lines in vitro, and in immunocompetent mice in vivo, in comparison to the proTα derivative thymosin alpha 1 (Τα1), a 28-mer peptide extensively studied for its safety in clinical trials. RESULTS: In silico prediction via computational tools showed that all three peptide sequences likely are non-toxic or do not induce allergic regions. In vitro, pro- Tα, proTα(100-109) and Tα1 did not affect the viability of human cancer cell lines and healthy donor-derived leukocytes, did not promote apoptosis or alter cell cycle distribution. Furthermore, mice injected with proTα, proTα(100-109) and Tα1 at doses equivalent to the suggested dose regimen of Tα1 in humans, did not show signs of acute toxicity, whereas proTα and proTα(100-109) increased the levels of proinflammatory and Th1- type cytokines in their peripheral blood. CONCLUSION: Our preliminary findings suggest that proTα and proTα(100-109), even at high concentrations, are non-toxic in vitro and in an acute toxicity model in vivo; moreover, we show that the two peptides retain their immunomodulatory properties in vivo and, eventually, could be considered for therapeutic use in humans.

Thymosin fraction 5 does not influence urinary tract carcinogenesis by phenacetin and N-butyl-N-(4-hydroxybutyl)nitrosamine in NON/Shi mice.

The effect of thymosin fraction 5 (TF5) on the promotion and progression phases of urinary tract carcinogenesis induced by consecutive administration of phenacetin and N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) in NON/Shi mice was investigated. The study was carried out twice with a minor modification to the protocol in the second experiment. Fifty-seven male NON/Shi mice in experiment 1 and 100 mice in experiment 2 were each divided into four groups. Phenacetin was administered for 8 weeks in experiment 1 and 12 weeks in experiment 2, and subsequently BBN was given for 6 weeks in both cases, for total observation periods of 30 and 34 weeks, respectively. Sixty micrograms of TF5 per mouse was inoculated subcutaneously twice a week during (group 2) or after (group 3) BBN exposure, or both periods (group 4). Group 1 served as a control group without TF5 treatment. Histopathological examination revealed no effects on either induction of urinary tract carcinomas or distant metastasis from renal pelvic carcinomas in either experiment.

[Thymosin fraction 5. Preclinical study]. / Thymosin frakce 5. Preklinická studie.

Thymosin fraction 5 from the Research Institute for Pharmacy and Biochemistry possessed the immunomodulatory activity in performed tests. The activity is manifested mostly by the induction of the maturation and the differentiation of T cell precursors, which are released from thymus to secondary lymphoid organs. Thymosin fraction 5 causes the expression of the surface membrane markers Thy-1.2, Lyt-2 and L3T4 on the immature T lymphocytes as well. The induced cells are immunocompetent and able to exert the complete functional activity. In the intact mice thymosin fraction 5 had not pronounced effect on the functional potency of mature immunocompetent cells, but in MTA influenced mice its stimulatory effect on the proliferative response to mitogens and on the antibody production against the T-dependent antigen was demonstrated. Thymosin fraction 5 influenced positively not only the components of the specific immunity, but also the functional activity of peritoneal macrophages. The toxicity of thymosin fraction 5 was in the battery of tests in vitro and in vivo very low and therefore it can be considered to be harmless for the clinical practice.

In vitro and in vivo study of thymosin alpha1 biodegradable in situ forming poly(lactide-co-glycolide) implants.

The purpose of this study was to develop poly(lactide-co-glycolide) (PLGA) based in situ forming implants (ISFI) for controlled release of thymosin alpha 1 (Talpha1). The ISFI was prepared by dissolving PLGA in N-methyl-2-pyrrolidone (NMP) or mixtures of NMP and triacetin. Talpha1 microparticles, prepared by spray-freeze drying method with chitosan or bovine serum albumin as a protectant, were suspended in PLGA solutions. The effects of Talpha1 pre-encapsulation, PLGA molecular weight, PLGA concentration and organic solvents composition on the in vivo Talpha1 release were evaluated by subcutaneously injecting Talpha1-loaded ISFI into Sprague-Dawley Rats. The pharmacological efficacy of Talpha1-loaded ISFI was examined using immunosuppressive BALB/c mice induced by cyclophosphamide. The ISFI composed of Talpha1 pre-encapsulated with chitosan, higher molecule-weight PLGA at higher concentration and more triacetin showed a lower initial release and a longer sustained release period. The optimal prescription of our study showed a low initial release of 29.3% (24 h), followed by a slow and continuous drug release up to 28 d in vivo. An in vitro release device was designed to mimic the in vivo release of Talpha1, and good correlation was observed between the in vitro and in vivo releases, with the linear correlation coefficient of 0.9899. Talpha1-loaded ISFI showed low cytotoxicity as tested by CCK-8 assay. Talpha1-loaded ISFI significantly increased the thymic index and spleen index of immunosuppressive mice. These results suggest that the ISFI is a suitable system for controlled release of Talpha1.

Thymosin alpha 11: a peptide related to thymosin alpha 1 isolated from calf thymosin fraction 5.

Two peptides related to thymosin alpha 1 have been isolated from preparations of calf thymosin fraction 5. One, lacking four amino acid residues at the COOH terminus, is designated des-(25-28)-thymosin alpha 1. The other, named thymosin alpha 11, contains seven additional amino acid residues at the COOH terminus. The sequence of this peptide is: AcSer-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-Ile-Thr-Thr-Lys-Asp-Leu- Lys-Glu-Lys- Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-Gly-Arg-Glu-Ala-Pro-Ala-AsnOH. Thymosin alpha 11, in doses of less than 300 ng per mouse, protects susceptible inbred murine strains against opportunistic infections with Candida albicans. It is approximately equal to 30 times as potent as thymosin fraction 5 and approximately equal in potency to thymosin alpha 1.

Phase I/II trial of thymosin fraction 5 and thymosin alpha one in HTLV-III seropositive subjects.

Forty-two male homosexuals and/or hemophiliacs with depressed helper/suppressor T-cell ratios were treated with one of three different doses of thymosin fraction 5 (TF5, 30, 60, and 120 mg), or a single dose of thymosin Alpha One (TA1, 600 micrograms), by daily subcutaneous (SQ) administration for 10 weeks, followed twice weekly for 4 weeks. No major toxicity was noted for any of the preparations tested, although three subjects treated with TF5 had to discontinue therapy because of severe local skin reactions. Of the doses and preparations tested, only 60 mg TF5 was capable of significantly improving (p less than 0.02) mean T-cell lymphoproliferative responses to alloantigens (MLR) for six HTLV-III seropositive subjects who were abnormal prior to therapy. Peripheral blood lymphocytes from subjects treated with 60 mg TF5 also exhibited a transient restoration of mean mitogen-induced interleukin-2 (IL-2) production to normal. No effects were observed with any of the four treatment regimens on absolute helper T-cell numbers, NK activity, antibody titers to HTLV-III, or in the expression of a variety of surrogate markers for acquired immunodeficiency syndrome (AIDS). Four of the six seropositive subjects treated with 60 mg TF5 exhibited a return to depressed baseline MLR, after switching to twice weekly injections. With a median follow-up time of 20 months, six cases of AIDS developed. However, none of the five subjects whose MLR improved following treatment progressed to AIDS. We recommend daily subcutaneous (SQ) administration of 60 mg (40 mg/m2) TF5 for use in combined modality trials, along with drugs capable of suppressing replication of HTLV-III.