Evaluation of trypanocidal activity of combinations of anti-sleeping sickness drugs with cysteine protease inhibitors

Abstract

Chemotherapy of human African trypanosomiasis (HAT) is unsatisfactory because only a few drugs, with serious side effects and poor efficacy, are available. As drug combination regimes often achieve greater therapeutic efficacy than monotherapies, here the trypanocidal activity of the cysteine protease inhibitor K11777 in combination with current anti-HAT drugs using bloodstream forms of Trypanosoma brucei was investigated. Isobolographic analysis was used to determine the interaction between cysteine protease inhibitors (K11777, CA-074Me and CAA0225) and anti-HAT drugs (suramin, pentamidine, melarsoprol and eflornithine). Bloodstream forms of T. brucei were incubated in culture medium containing cysteine protease inhibitors or anti-HAT drugs alone or in combination at a 1:1 fixed-dose ratio. After 48 h incubation, live cells were counted, the 50% growth inhibition values determined and combination indices calculated. The general cytotoxicity of drug combinations was evaluated with human leukaemia HL-60 cells. Combinations of K11777 with suramin, pentamidine and melarsoprol showed antagonistic effects while with eflornithine a synergistic effect was observed. Whereas eflornithine antagonises with CA-074Me, an inhibitor inactivating the targeted TbCATL only under reducing conditions, it synergises with CAA0255, an inhibitor structurally related to CA-074Me which inactivates TbCATL independently of thiols. These findings indicate an essential role of thiols for the synergistic interaction between K11777 and eflornithine. Encouragingly, the K11777/eflornithine combination displayed higher trypanocidal than cytotoxic activity. The results of this study suggest that the combination of the cysteine protease inhibitor K11777 and eflornithine display promising synergistic trypanocidal activity that warrants further investigation of the drug combination as possible alternative treatment of HAT.

Expression of cysteine proteinases and cystatins in parasites and use of cysteine proteinase inhibitors in parasitic diseases. Part III: Protozoa (3): Kinetoplastids

“…The efficacy of K11777, combined with current drugs used for African trypanosomiasis, such as suramin, pentamidine, melarsoprol and eflornithine, on T. brucei bloodstream forms in vitro, was investigated. A synergistic effect was observed after treatment of K11777 with eflornithine, in contrast to antagonistic effects shown with the other drugs [224] .…”

“…Several compounds were investigated as antitrypanosomal chemotherapeutic agents through their inhibitory effects on brucipain. These included nonpeptide [216][217][218][219][220][221] and peptidomimetic [222][223][224] inhibitors. Non-peptide inhibitors: Quantitative HTS approach utilized to search for a CRZ inhibitor identified new compounds of triazine nitriles.…”

Bauerenol Acetate, the Pentacyclic Triterpenoid from Tabernaemontana longipes, is an Antitrypanosomal Agent

“…The solubility of bauerenol in DMSO was somewhat better than the acetate, and its activity on T. brucei in vitro was characterized by an IC 50 value of 2.7 µM. The antitrypanosomal activities of these compounds are much lower (1–3 order of magnitude) than clinically used antitrypanosomal drugs [ 10 ]. Also, the IC 50 values of 1 and 2 are higher than the IC 50 value (<1 µM) proposed by Nwaka and Hudson as criteria for preclinical evaluation of antitrypanosomal drug candidates [ 11 ].…”

Cysteine proteases in protozoan parasites

“…A number of studies using RNA interference (RNAi) [ 58 ] or small-molecule inhibitors in vitro [ 59 ] and in animal infection models [ 60 , 61 ] have validated these proteases as drug targets. K11777 in particular targets TbCatL: it showed synergy when combined with eflornithine and might be considered for development as a new therapy for African trypanosomiasis [ 62 ]. Other small molecules have been successfully tested against TbCatL, including dipeptide nitriles [ 63 ] and triazine nitriles [ 64 ], but their efficacy in vivo is yet to be determined.…”