Serum albumin and α-1 acid glycoprotein impede the killing of Schistosoma mansoni by the tyrosine kinase inhibitor Imatinib

Abstract

In the search for new drugs and drug targets to treat the flatworm disease schistosomiasis, protein kinases (PKs) have come under particular scrutiny because of their essential roles in developmental and physiological processes in schistosome parasites. In this context the application of the anti-cancer Abl tyrosine kinase (TK) inhibitor Imatinib (Gleevec/Glivec; STI-571) to adult Schistosoma mansoni in vitro has indicated negative effects on diverse physiological processes including survival. Motivated by these in vitro findings, we performed in vivo experiments in rodent models of S. mansoni infection. Unexpectedly, Imatinib had no effect on worm burden or egg-production. We found that the blood components serum albumin (SA) and alpha-1 acid glycoprotein (AGP or orosomucoid) negated Imatinib's deleterious effects on adult S. mansoni and schistosomula (post-infective larvae) in vitro. This negative effect was partially reversed by erythromycin. AGP synthesis can increase as a consequence of inflammatory processes or infection; in addition upon infection AGP levels are 6-8 times higher in mice compared to humans. Therefore, mice and probably other rodents are poor infection models for measuring the effects of Imatinib in vivo. Accordingly, we suggest the routine evaluation of the ability of AGP and SA to block in vitro anti-schistosomal effects of small molecules like Imatinib prior to laborious and expensive animal experiments.

Keywords: Abl tyrosine kinase (Abl); Erythromycin; Imatinib (Gleevec, Glivec, STI-571); In vitro culture; Protein tyrosine kinase (PTK); Schistosoma mansoni; Serum albumin (SA); α-1 acidic glycoprotein (AGP).

Graphical abstract

Fig. 1

Influence of serum albumin on pairing stability of Imatinib-treated S. mansoni couples. S. mansoni couples were treated for up to 156 h in vitro with 0/10/50 μM Imatinib in medium with and without bovine or human serum albumin. The effect of the treatment was monitored over time (0–156 h; x-axis) analysing pairing stability (given in % values on the y-axis). (A) treatment in normal M199 medium, (B) treatment in medium with BSA (45 g/L), C: treatment in medium with HSA (45 g/L). Unexpectedly, all schistosomes treated with 10 μM Imatinib and HSA (C) had separated after 156 h of treatment, which in this specific case is unlikely to be a consequence of inhibitor treatment alone. Light grey: 0 μM Imatinib, grey: 10 μM Imatinib, dark grey: 50 μM Imatinib.

Fig. 2

Influence of alpha-1 acid glycoprotein against erythromycin addition on pairing-stability and physical integrity of Imatinib-treated S. mansoni couples. S. mansoni couples were treated for 3 days in vitro with 20 μM Imatinib in medium with and without 0.8 g/L AGP as well as with or without 20 μM erythromycin. (A) 0 μM Imatinib, M199; (B): 20 μM Imatinib, M199; (C): 0 μM Imatinib, M199 + AGP; (D): 20 μM Imatinib, M199 + AGP; (E) 0 μM Imatinib, 20 μM erythromycin, M199 + AGP; (F) 20 μM Imatinib, 20 μM erythromycin, M199 + AGP. Scale bars: 1 mm; ^∗bulges and ^#gut alterations indicating the deleterious effect of Imatinib.

Fig. 3

Influence of alpha-1 acid glycoprotein against erythromycin on egg production of Imatinib-treated S. mansoni couples. Overview of egg production of S. mansoni couples, which were treated with 20 μM Imatinib in medium with and without 0.8 g/L AGP as well as with or without 20 μM erythromycin in vitro for 3 days. (A) 0 μM Imatinib, 0 μM Imatinib/20 μM erythromycin, M199; (B) 0 μM Imatinib, 20 μM erythromycin, M199 + AGP; (C) 20 μM Imatinib, 0 μM erythromycin, M199; (D) 20 μM Imatinib, 0 μM erythromycin, M199 + AGP; (E) 20 μM Imatinib, 20 μM erythromycin, M199; (F) 20 μM Imatinib, 20 μM erythromycin, M199 + AGP. V = vitellocytes, O = oocytes; scale bars: 50 μM.

Fig. 4

In vitro effects of Imatinib on schistosomula treated additionally with BSA, AGP, and erythromycin. Newly transformed schistosomula were incubated with different concentrations of Imatinib (0, 10, 20 μM) and compared to the effects caused by the addition of BSA (45 g/L), AGP (0.8 g/L), and erythromycin (20 and 40 μM). (A) Graphical representation of the percentage of degenerate schistosomes (y-axis) in different conditions (x-axis). Normal versus “degenerate” schistosomes were counted manually in different conditions during 96 h. Error bars represent standard deviation of two independent experiments performed in duplicate. (B) Images display representative pictures of schistosomula treated with Imatinib (y-axis), with and without BSA, AGP and/or erythromycin during 96 h (x-axis).