Trypanosoma cruzi: inhibition of protein synthesis by nitrofuran SQ 18,506

Effects of trypanocidal drugs on protein biosynthesis in vitro and in vivo by Trypanosoma cruzi

Nifurtimox (NF) and benznidazole (BZ), drugs used in the treatment of Chagas' disease, did not inhibit protein biosynthesis in in vitro homologous cell-free systems isolated from Trypanosoma cruzi and Crithidia fasciculata; nevertheless, their addition to growing cultures caused polyribosomal depolymerization. On the other hand, Berenil, Antrycide and suramin, used against African trypanosomiasis, inhibited protein biosynthesis in vitro but did not affect ribosomal distribution, probably due to low permeability to the drugs. The results suggest that the inhibition by NF and BZ of protein synthesis, measured as [14C]leucine incorporation by other authors, is indirect, probably through inhibition of nucleic acid synthesis and energy metabolism.

Trypanosoma cruzi: inhibition by spirogermanium hydrochloride

Spirogermanium is an antineoplastic agent that has been shown to be useful for the treatment of a variety of solid tumors and Plasmodium falciparum infection. We found that this agent, at concentrations of 1-10 micrograms/ml, markedly inhibited the growth of epimastigotes of Trypanosoma cruzi. This inhibition of growth was seen in liver infusion tryptose cultures as well as on agar where colonial growth was inhibited markedly. Ultrastructural studies demonstrated that affected organisms were round and swollen and contained vacuoles, lamellar structures, and multivesicular bodies. Spirogermanium also significantly decreased the growth of intracellular amastigotes in myotubes. Pretreatment of myotubes with the agent protected them from infection with trypomastigotes but tachyzoites of Toxoplasma sp. readily infected pretreated cells. These data suggest that spirogermanium may be useful as a chemotherapeutic agent against T. cruzi.

Effects of beta-lapachone, a peroxide-generating quinone, on macromolecule synthesis and degradation in Trypanosoma cruzi

Incubation of Trypanosoma cruzi epimastigotes with beta-lapachone (3,4-dihydro-2,2-dimethyl-2H-naphtho[1,2-b]pyran-5,6-dione), a lipophilic o-quinone, produced inhibition of [3H]thymidine, [3H]uridine, and L-[3H]leucine incorporation into DNA, RNA, and protein, respectively. With 1.6 microM beta-lapachone, DNA synthesis was preferentially inhibited. The inhibition was irreversible, and time and concentration dependent. Other effects of beta-lapachone were (a) inhibition of 3H precursor uptake into epimastigotes, (b) exaggerated degradation of DNA, RNA, and protein, (c) increased unscheduled synthesis of DNA, and (d) increased number of strand breaks in nuclear and kinetoplast DNA. DNA damage by 1.6 microM beta-lapachone was repaired by reincubating the drug-treated epimastigotes in fresh medium for 24 h, but with 7.8 microM beta-lapachone DNA damage was irreversible. The p-quinone isomer alpha-lapachone (3,4-dihydro-2,2-dimethyl-2H-naphtho[2,3-b]pyran-5,10-dione), was less effective than beta-lapachone, especially on DNA and RNA synthesis, and did not stimulate unscheduled DNA synthesis. Since beta-lapachone redox cycling in T. cruzi generates oxygen radicals while alpha-lapachone does not (A. Boveris, R. Docampo, J. F. Turrens, and A. O. M. Stoppani (1978) Biochem. J. 175, 431-439), the summarized results support the hypothesis that oxygen radicals contribute to beta-lapachone toxicity in T. cruzi.

Effect of tingenone, a quinonoid triterpene, on growth and macromolecule biosynthesis in Trypanosoma cruzi

Tingenone and horminone, two natural quinonoid substances, inhibited the in vitro growth of Trypanosoma cruzi, 30 microM drug concentration producing total inhibition of growth. Tingenone inhibited total uptake and incorporation of [3H]thymidine, [3H]uridine, L-[3H]leucine into parasite macromolecules. Other quinonoids assayed were either less effective (abruquinone A) or even quite inactive (visminone B and ferruginin B). Investigation of several mechanisms for the cytotoxic action of tingenone pointed to the interaction with DNA as the most likely factor involved. Tingenone also inhibited the growth of Crithidia fasciculata, but the drug was significantly less active on this organism than on T. cruzi.

Effects of nitroheterocyclic drugs on macromolecule synthesis and degradation in Trypanosoma cruzi

Nifurtimox and benznidazole, two nitroheterocyclic drugs, inhibited DNA, RNA and protein synthesis, stimulated macromolecular degradation, and stimulated unscheduled DNA synthesis in Trypanosoma cruzi (Tulahuen strain). Significant differences in the mode of action of these drugs could be established and, in every case, nifurtimox was more active than benznidazole. The inhibition of macromolecular synthesis varied with drug concentration, precursor and incubation time. Nifurtimox effect was time dependent and irreversible. When assayed on macromolecular degradation, nifurtimox was more effective on DNA and protein than on RNA, while benznidazole displayed almost the same activity on DNA, RNA and protein. Labeling of RNA with [3H]uridine in the presence of nifurtimox followed atypical kinetics since, depending on incubation time and concentration, RNA degradation prevailed over RNA synthesis.

Crithidia fasciculata: a catalase-containing trypanosomatid sensitive to nitroheterocyclic drugs

Crithidia fasciculata, which contains high levels of a cytosolic catalase, is sensitive to inhibition by at least two nitroheterocyclic drugs, Nifurtimox and MK 436, both of which are also active against Trypanosoma cruzi. Drug sensitivity is not enhanced in organisms containing reduced levels of catalase. The ultrastructural lesions in T. cruzi produced by nitroheterocycles, especially the swelling and gross vacuolation of the mitochondria, are seen also in C. fasciculata. These results are not consistent with the hypothesis that the action of drugs such as Nifurtimox on T. cruzi involve hydrogen peroxide accumulation as a result of the absence of catalase.

Taxol, a microtubule stabilizing agent, blocks the replication of Trypanosoma cruzi

Taxol, an experimental antitumor agent and stabilizer of microtubules, inhibits in vitro replication of the human pathogenic hemoflagellate Trypanosoma cruzi. Micromolar concentrations of the drug prevent the completion of cell division in these organisms but allow the multiplication of cell organelles such as the nucleus, kinetoplast, and flagellum. The result is the formation of motile organisms that have extra organelles but cannot fully replicate. Division proceeds to a relatively fixed locus on the long axis of the organism, suggesting the presence of a specific affected structure or function at this site. It is postulated that taxol produces these effects by stabilizing a portion of the microtubular cytoskeleton of T. cruzi.