**2. Therapeutics**

Although CD was discovered and is studied for over a century [14], the etiologic treatment is still based on solely two drugs (**Figure 1**): the nitrofuran derivative nifurtimox (NFX; Lampit®, Bayer; 5-nitrofuran(3-methyl-4-(5′-nitrofurfurylideneamine) tetrahydro-4H-1,4-tiazine-1,1-dioxide), and the 2-nitromidazole benznidazole (BZ; LAFEPE; N-benzyl-2-nitroimidazole-acetamide) [23]. Both NFX and BZ were shown to produce remarkable ultrastructural alterations in mammal cells and tissues [24, 25], which were apparently more pronounced in NFX-treated animals [26]. Therefore, experimental chemotherapy studies approaching parasites as *T. cruzi* should preferentially include ultrastructural analysis, in order to offer a subcellular compartmentation understanding to aid the antiparasitic agent mechanism(s) of action elucidation [27, 28] and ultimately leading to the understanding of cell death pathways involved [29].

*Translational Research on Chagas Disease: Focusing on Drug Combination and Repositioning DOI: http://dx.doi.org/10.5772/intechopen.104231*

#### **Figure 1.**

*Molecular structures of the nitroheterocyclic drugs employed in the treatment of Chagas disease: the 2-nitroimidazole benznidazole (A) and the 5-nitrofuran nifurtimox (B).*

The CD therapeutics remain unsatisfactory, as they are associated with adverse effects [30–32], affecting 84.8 and 95.2% of patients treated with BZ and NFX, respectively [33], which may be severe, leading to the irreversible suspension of therapy in CD, in ≈20% [34, 35], ≈30% [36, 37], 41.5% [38], and up to 50% of the cases [39, 40]. Treatment suspension using NFX was reported in 43.8% of patients [33]. In an early study based on small samples, NFX was reported to be associated to definitive treatment interruption in 75% of patients [38]. Nevertheless, treatment intolerance was reported at similar levels with the use of the two drugs, approached by the same team [34, 35], but adverse effects, including neuropsychiatric events, may be more frequently associated to NFX [33]. In addition, it was reported that among patients who had discontinued BZ treatment and were treated with NFX, 12.3% also developed adverse effects that required definitive discontinuation of therapy [39]. Nevertheless, NFX was reported to be safe as a second-line therapy in patients who discontinued BZ [41].

Most CD patients are not treated because of the insufficient diagnosis and low cure rates observed in chronically infected patients [42], although treatment may diminish the disease progression and cardiovascular events [43, 44]. In addition, the CD treatment accomplishes only a parasitological cure, and a clinical cure is hardly proved [43, 45]. Whereas the *bona fide* sterile cure or complete clearance of the infection is considered a "prerequisite" for new anti-*T. cruzi* drug candidates [46], it is usually not achieved in murine model [47, 48] or human infection as immunosuppression often leads to infection reactivation [49]. In this regard, *T. cruzi* amastigotes may persist in a dormant or quiescent form, which may protect the parasites from antiparasitic agents [50, 51].

As the dormancy state of *T. cruzi* amastigotes is associated to drug resistance [50, 51], it is desirable to develop drugs able to affect dormant parasites. The mechanisms that allow the establishment of persistence include the capacity to suppress the oxidative burst produced by phagocytes largely depending on iron-containing superoxide dismutases (FeSOD) and trypanothione-acting enzymes [52]. Thus the use of disulfiram (DSF) is of potential relevance since it can diminish glutathione levels [53, 54], and the DETC first derivative of DSF is an SOD inhibitor [55, 56].

Furthermore, DSF could target *T. cruzi* dormancy. Although the signal transduction pathways involved in this process were not completely elucidated, it is interesting that DSF is able to reverse HIV latency affecting PKC (protein kinase C), AKT (protein kinase B), PI3K (phosphoinositide 3-kinases), NF-kB (nuclear factor kappa-light-chain-enhancer of activated B cells) [57, 58], which also affect *T. cruzi* infection [59, 60] that leads to the activation of PI3K [61], whereas DSF promotes PI3K inhibition [62].

An important study [63] approached the persistent parasite elimination, but the use of higher BZ doses might pose higher risks for patients. In this regard, the polyamine and thiol synthesis *Leishmania* are associated to macrophage M2 phenotype, leading to parasite persistence [64].

### **2.1 Drug resistance**

Besides considerable severe adverse effects, one of the greatest problems of CD therapeutics is the selection of resistant parasites, impairing its effectivity, therefore causing refractory cases. BZ and NFX resistance is readily developed *in vitro* and *in vivo* [47, 65], in the former case, via different mechanisms that can act in concert [66].

Despite significant time and resources investments by innumerous research institutions over the world, only a few therapeutic candidates advanced the pipeline to treat neglected diseases such as CD [67]. It is alarming that it usually takes over 10 years to develop new drugs, whereas resistant parasites are rapidly selected. Also, there are naturally resistant *T. cruzi* strains [68–70] that express a novel ABCG-like transporter [71]. Besides extrusion pumps, *T. cruzi* resistance may involve SOD and trypanothione (*vide infra*). Therefore, there is pressing demand for the development of novel effective therapies for CD.
