Bioactivity and pharmacokinetics of two human serum albumin-thymosin α1-fusion proteins, rHSA-Tα1 and rHSA-L-Tα1, expressed in recombinant Pichia pastoris

Thymosin-alpha 1 (T alpha 1) is indicated for the treatment of certain viral infections, including hepatitis B and C, and cancers, such as melanoma. In this paper, the fusion genes encoding human serum albumin (HSA) and T alpha 1 with (rHSA-L-T alpha 1) and without a linker peptide (rHSA-T alpha 1) were constructed and overexpressed in P. pastoris. Through the process of ion interaction chromatography (Q-Sepharose F.F), hydrophobic interaction chromatography (Phenyl Sepharose HP) and affinity chromatography (Blue Sepharose F.F), the purity of fusion proteins was greater than 97%. In contrast to the reactivity of normal spleen cells to Con A, the data of in vitro murine spleen lymphocytes proliferation experiment suggested that spleen cells achieved a higher degree of T cell maturation after rHSA-L-T alpha 1, rHSA-T alpha 1 and T alpha 1 treatments, respectively. Moreover, rHSA-L-T alpha 1, rHSA-T alpha 1 and T alpha 1 can also antagonize dexamethasone-induced apoptosis of thymocyte sub-populations. In hydrocortisone-induced immunosuppression mice (in vivo experiments), after subcutaneous injections with two fusion proteins and T alpha 1 for seven consecutive days, the net increment of body weight, the spleen index and the thymus index were significantly improved. Simultaneously, the increase in SOD level and the decrease in MDA level in plasma were observed. The pharmacokinetic data of rHSA-L-T alpha 1 and rHSA-T alpha 1 administered in rats showed an improved pharmacokinetic profile with a conspicuous prolonged half life. The analysis of bioactivity and pharmacokinetics suggested that fusion proteins rHSA-L-T alpha 1 and rHSA-T alpha 1 were new drug candidates.