Repurposing of anticancer drugs: in vitro and in vivo activities against Schistosoma mansoni

Drugs and media

The cancer drug library used for schistosome in vitro assays was gratefully received in June 2014 from the DTP/NCI as 10 mM stock solutions
(20 ?l) in dimethyl sulfoxide (DMSO) in 96-well plates. Hit compounds were ordered
as solid compounds from DTP, and dissolved in DMSO to 10 mM stock solutions. Bosutinib
was not available from DTP and was therefore purchased from Sigma-Aldrich. For in vivo studies, solid afatinib, bosutinib, ponatinib, trametinib, and vandetanib were purchased
from AkScientific. Sunitinib was purchased from VWR as a 100 mM solution in DMSO.

Medium 199, and RPMI 1640 were purchased from Life Technologies. Heat-inactivated
fetal calf serum (FCS), penicillin, and streptomycin were purchased from LuBioScience.

Mouse infection and maintenance

Rodent experiments were authorized by the Canton Basel-Stadt, Switzerland (license
no. 2070).

Female NMRI mice, 3-weeks of age, were purchased from Charles Rivers, Germany. After
a 1-week adaptation period, mice were infected with cercariae collected from S. mansoni-infected intermediate host snails (Biomphalaria glabrata), by subcutaneous injection with 100 cercariae 12]. Mice received rodent food and water ad libitum and were maintained with a 12-h light/dark
cycle, at 22 °C and 50 % humidity.

Larval schistosome drug assay

S. mansoni cercariae were collected from S. mansoni-infected B.glabrata, and mechanically transformed to newly transformed schistosomula (NTS) 13]. After a resting period of 12–24 h (37 °C, 5 % CO
₂
), drugs were tested for NTS activity at a concentration of 33.3 ?M in Medium 199
supplemented with 5 % FCS, 200 U/ml penicillin, and 200 ?g/ml streptomycin, and prepared
in 96-well flat-bottom plates with 100 NTS per well. NTS incubated with the equivalent
volume of drug-free DMSO (0.3 %) served as control. NTS were evaluated 24, 48, and
72 h after incubation via microscopic read out (80–120× magnification; Zeiss; Germany),
using a scoring scale from 3 (normal viability, morphology, and granularity) to 0
(no motility, changed morphology, and granularity). Drugs with an activity of???50 %
after 24 h, and/or 90 % after 72 h, and a drug effect on adult schistosomes of???80 %
after 24 h and/or 90 % after 72 h at 33.3 ?M, were tested at six different concentrations
ranging from 0.14 to 33.3 ?M using a 3-fold dilution series for IC
₅₀
determination. All assays were performed in duplicate and repeated once 10].

Adult schistosome drug assay

Adult schistosomes were collected from mice with a chronic S. mansoni infection (7-week-old) by dissection of the mesenteric veins. Drugs were tested at
33.3 ?M in RPMI 1640 culture medium supplemented with 5 % FCS, 100 U/ml penicillin,
and 100 ?g/ml streptomycin, and prepared in 24-well flat-bottom plates. Three flukes
of both sexes were put into the wells, incubated at 37 °C, and 5 % CO
₂
, and scored (in the same manner as described for NTS) after 1, 24, 48, and 72 h.
Drugs revealing activity against NTS, and adult schistosomes (as explained above),
were assessed for their IC
₅₀
, using 3-fold serial dilutions resulting in five different concentrations ranging
from 0.41 to 33.3 ?M, and scored 4, 24, 48, and 72 h post incubation. IC
₅₀
determinations were performed in duplicate, and repeated once 12]. For compounds exhibiting an IC
₅₀
??33.3 ?M, IC
₅₀
s were determined using culture medium supplemented with 45 g/l bovine serum albumin
(AlbuMax® II Lipid-Rich BSA, Gibco): the physiological albumin concentration in humans
14].

Preclinical and clinical data from FDA and EMA

FDA and European Medicines Agency (EMA) data sheets were used to retrieve drug information
such as the maximal plasma concentration (C
_max
), plasma half-life (t
_1/2
), nonclinical toxicology (lethal single oral dose LD
₅₀
), indication, mechanism of action, and dosage.

In vivo adult schistosome drug assay

For oral application, the drugs were dissolved in 7 % Tween 80 and 3 % ethanol in
water (v/v/v), with the exception of sunitinib, which was used as obtained. Groups
of 4 mice harboring a chronic S. mansoni infection were treated with a single oral dose of 400 mg/kg body weight, or 200 mg/kg
for afatinib due to its low LD
₅₀
(382–763 mg/kg in mice) 15]. A control group of 8 mice was left untreated. Three weeks post treatment, the mice
were euthanized, and schistosomes residing in the mesenteric veins and the liver were
counted and sexed.

Statistics

Drug effects on schistosomes were determined with the scores of parasites exposed
to drug, and the score of the controls. For IC
₅₀
and r value (linear correlation coefficient) determination, the dose-response was
calculated with CompuSyn (version 3.0.1; ComboSyn), as described previously 10]. In vivo worm burden reductions (WBR) were calculated with the number of worms found in treated
mouse groups compared to the control group 10]. P-values were calculated using the Kruskal-Wallis test (Stats direct statistical software
version 2.8.0).