Authors
A I Recio-Balsells3; B A Ferreira1; E M Coser1; C Reigada2; A C Coelho1; C A Pereira2; G R Labadie3; 1 Universidade Estadual de Campinas Brazil, Brazil; 2 Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad de Buenos Aires, Instituto de Investigaciones Médicas (IDIM-UBA-CONICET)), Argentina; 3 IQUIR-CONICET, Argentina Discussion
Our group has synthesized a library of N,N'-disubstituted aliphatic diamines (N,N'-di) that displayed IC50 activities in the µM-nM range against the intracellular and extracellular stages of trypanosomatids parasites (Trypanosoma cruzi-T.c, Leishmania donovani-L.d and Trypanosoma brucei-T.b). Aiming to elucidate the mechanism of action (MoA) of these library, they were evaluated against the Trypanothione synthetase of T.c, T.b and L. infantum-L.i but only displayed low and moderate inhibition (inh<60% at 30 µM). Proven not to be the main target of these compounds.
In a new attempt to elucidate the MoA, we selected eight diamines with potent activity against T. c epimastigote and/or amastigote to define if they are inhibitors of polyamines transport. Additionally, to expand the scope as antiparasitic drug candidates, we selected nine derivatives to be tested in new World Leishmania species (L. amazoniensis-L.a., L. braziliensis-L.b. and L.i).
Preliminary results of the polyamine transport inhibition assays, showed that some derivatives decrease the internalization of putrescine in T.c epimastigotes. However, this inhibition was variable between analogs (29-69% inh at 25 µM). In particular, Tc8 (N1,N10-dibenzyldecane-1,10-diamine) was the most potent polyamine transport inhibitor (IC50=10.5 µM), and also as antichagasic (T.c epimastigotes IC50=0.60 µM).
The activities on Leishmania were below 1 µM against amastigotes (L.a. and L.i.), and seven of them, for L.b. whereas the cytotoxicity values in bone-marrow-derived macrophage (BMDM) were in the range of 0.56-3.20 µM, being more cytotoxic than for Vero cells. However, seven of the nine compounds presented selectivity index (SI) >10 for L.a., five for L.i and four for L.b (SI= EC50-BMDM/IC50-amast). Compounds L2, L5 and L6, displayed SI>10 for the three species tested (N1,N8-bis(4-(benzyloxy)benzyl)octane-1,8-diamine (L2), SI=15-22; N1,N12-dibenzyldodecane-1,12-diamine (L5), SI=14-22; N1,N12-bis(4-fluorobenzyl)dodecane-1,12-diamine (L6), S=19-57).
In conclusion, N,N'-di are promising antiparasitic compounds with potent activity against a wide range of Leishmania spp. In addition, part of the MoA could be related to the inhibition of polyamine transport. Considering the previous results on trypanothion synthetase and the results presented here, the MoA of these compounds seems to be polypharmacological, however some relevant target may be involved. 
