Fexinidazole: a potential new drug candidate for Chagas disease

Abstract

Background: New safe and effective treatments for Chagas disease (CD) are urgently needed. Current chemotherapy options for CD have significant limitations, including failure to uniformly achieve parasitological cure or prevent the chronic phase of CD, and safety and tolerability concerns. Fexinidazole, a 2-subsituted 5-nitroimidazole drug candidate rediscovered following extensive compound mining by the Drugs for Neglected Diseases initiative and currently in Phase I clinical study for the treatment of human African trypanosomiasis, was evaluated in experimental models of acute and chronic CD caused by different strains of Trypanosoma cruzi.

Methods and findings: We investigated the in vivo activity of fexinidazole against T. cruzi, using mice as hosts. The T. cruzi strains used in the study were previously characterized in murine models as susceptible (CL strain), partially resistant (Y strain), and resistant (Colombian and VL-10 strains) to the drugs currently in clinical use, benznidazole and nifurtimox. Our results demonstrated that fexinidazole was effective in suppressing parasitemia and preventing death in infected animals for all strains tested. In addition, assessment of definitive parasite clearance (cure) through parasitological, PCR, and serological methods showed cure rates of 80.0% against CL and Y strains, 88.9% against VL-10 strain, and 77.8% against Colombian strain among animals treated during acute phase, and 70% (VL-10 strain) in those treated in chronic phase. Benznidazole had a similar effect against susceptible and partially resistant T. cruzi strains. Fexinidazole treatment was also shown to reduce myocarditis in all animals infected with VL-10 or Colombian resistant T. cruzi strains, although parasite eradication was not achieved in all treated animals at the tested doses.

Conclusions: Fexinidazole is an effective oral treatment of acute and chronic experimental CD caused by benznidazole-susceptible, partially resistant, and resistant T. cruzi. These findings illustrate the potential of fexinidazole as a drug candidate for the treatment of human CD.

Figure 1. Chemical structure of fexinidazole and benznidazole.

Figure 2. Timeline of chemotherapy experiments.

Animals were inoculated with 5000 trypomastigotes of Y, CL, VL-10, or Colombian Trypanosoma cruzi strains, and treatment was started on the first day of detected parasitemia. During all treatments and up to 30 days post-treatment, parasitemia was evaluated by fresh blood examination (FBE) to determine the potential for natural reactivation of infection. Animals that did not present reactivation of parasitemia after treatment were submitted to immunosuppression consisting of three cycles of 50 mg of cyclophosphamide/kg (CY-I) of body weight for four consecutive days with intervals of three days between each cycle. Parasitemia was evaluated during the CY-I, as well as for the following 10 days after immunosuppression. Blood culture and PCR assays were performed 30 and 180 days post-treatment in mice with negative results in FBE before and after CY-I.

Figure 3. Parasitemia levels after 7 days of oral administration of fexinidazole.

Parasitemia curve obtained from 6 mice infected with 5000 trypomastigotes of T. cruzi Y strain and treated daily with doses of fexinidazole 100, 200, and 300 mg/kg of body weight (mpk) or benznidazole 100 mpk for 7 consecutive days. Arrows indicate the first and the last day of treatment. IC: infected and untreated control.

Figure 4. Anti-Trypanosoma cruzi activity of fexinidazole in mice infected with different parasite strains.

Mice were inoculated with 5000 trypomastigotes of T. cruzi CL, VL-10, or Colombian strains by intraperitoneal route and treated with fexinidazole 300 mg/kg of body weight (mpk) or benznidazole 100 mpk for 20 consecutive days. A. Parasitemia curve from mice infected with VL-10 T. cruzi strain. Arrows indicate first and last days of treatment. B. IgG antibodies in mice inoculated with CL, VL-10, or Colombian T. cruzi strains, 6 months post-treatment. C. Myocardial inflammatory cell count in mice infected with VL-10 T. cruzi strain, 6 months post-treatment. D. Myocardial inflammatory cell count in mice infected with Colombian T. cruzi strain, 6 months post-treatment. −Fex = mice with parasite negativity in fresh blood examination, blood culture, and PCR assay; +Fex or +Bz = mice positive of parasites in fresh blood examination, blood culture, and PCR assay: NIC = non-infected control; IC = infected and untreated control. * Significant difference compared to NIC; # significant difference compared to IC.

Figure 5. Effect of fexinidazole on chronic Trypanosoma cruzi infection.

Mice were inoculated with 5000 trypomastigotes of VL-10 strain by intraperitoneal route and treated with fexinidazole 300 mg/kg of body weight (mpk), or benznidazole 100 mpk for 20 days. For controls, infected and untreated (IC) and uninfected (NIC) groups were also evaluated. A. IgG antibodies in mice treated with fexinidazole or benznidazole, compared with IC control group, 6 months post-treatment. B. Myocardial inflammatory cell count in cardiac tissue of mice infected with VL-10 T. cruzi strain, 6 months post-treatment. C. Hematoxilin-eosin stained slides. −Fex = mice with parasite negativity in fresh blood examination, blood culture, and PCR assay; +Fex or +Bz = mice positive of parasites in fresh blood examination, blood culture, and PCR assay: NIC = non-infected control; IC = infected and untreated control. * Significant difference compared to NIC; # significant difference compared to IC.