Combination chemotherapy of drug-resistant Trypanosoma brucei rhodesiense infections in mice using DL-alpha-difluoromethylornithine and standard trypanocides

Abstract

Combinations of DL-ot-difluoromethylornithine (DFMO; eflornithine; Ornidyl) with either suramin or melarsen oxide were found to be effective against acute laboratory model infections with Trypanosoma brucei rhodesiense. We used clinical isolates known to be resistant to these drugs when used singly. An infection with a melarsen oxide-refractory isolate was cured by a combination of low-dose DFMO (0.5% in the drinking water) plus low-dose suramin (1 mg/kg of body weight given intraperitoneally). Another strain, moderately resistant to arsenical drugs, was cured with combinations of 4% DFMO with 5 mg of melarsen oxide per kg. Furthermore, a combination of DFMO (2% in the drinking water) and suramin (20 mg/kg) provided a 100%S cure rate in a central nervous system model, although the same doses of these drugs used singly were completely ineffective. The synergism of DFMO and suramin against an acute infection was improved when suramin was given at the end of the DFMO administration. No adverse interactions were observed when high doses of DFMO combined with high doses of suramin were administered to uninfected mice. These results suggest that combinations of DFMO and suramin should be examined clinically for activity in arsenical-drugrefractory cases of East African sleeping sickness.Sleeping sickness remains a serious health problem in equatorial Africa. Major lapses in control activities have resulted from military activities in some areas so that 80% of the at-risk population is not covered by diagnostic or vector control measures (24). This is particularly true in East Africa, which has undergone recent epidemics in Uganda, north of Lake Victoria and along the Kenya-Uganda border, in Zaire, and in the Sudan (7, 26). Chemotherapy for East African sleeping sickness is unreliable: drug resistance to arsenical drugs is common (7,26), and clinical strains refractory to DL-a-difluoromethylomithine (DFMO; eflornithine; Ornidyl) and diamidines have also been documented (5,7,26). Clearly, there is a pressing need for alternatives to existing treatment methods.The newest drug to be approved by the U.S. Food and Drug Administration for use against African trypanosomiasis is DFMO. DFMO is an irreversible inhibitor of ornithine decarboxylase, a key enzyme of polyamine biosynthesis. Although this compound was originally designed as an antitumor agent, it has proven to be highly effective against Trypanosoma brucei gambiense infections (22,24,26

Discovery of Novel Orally Bioavailable Oxaborole 6-Carboxamides That Demonstrate Cure in a Murine Model of Late-Stage Central Nervous System African Trypanosomiasis

“…Evaluation of AN3520 and SCYX6759 against stage 2 CNS infections was conducted with a chronic diseaseinducing strain (TREU 667) of T. b. brucei (3,4,5). Female Swiss Webster mice were infected intraperitoneally with 1 ϫ 10 4 parasites (200 l) followed by treatment with a single 10 mg/kg i.p.…”

“…Animals were immediately removed from the cages and euthanized upon recrudescence. Animals remaining aparasitemic for at least 180 days after the end of the treatment period were considered cured (3,4,5). Brain homogenates or the blood of oxaborole-cured animals failed to generate infection when injected into naive, cyclophosphamide-immunosuppressed mice.…”

Distribution of Suramin, an Antitrypanosomal Drug, across the Blood-Brain and Blood-Cerebrospinal Fluid Interfaces in Wild-Type and P-Glycoprotein Transporter-Deficient Mice

“…If suramin does use this type of pathway to cross the brain barriers, different regional expression of the receptors may explain the ability of suramin to reach select areas of the CNS. Furthermore, coadministration of suramin with drugs that are active against the second, CNS stage, namely, melarsoprol, nifurtimox, and eflornithine, has been shown to improve cure rates (2,7,9,19,34). Inhibition by suramin of the P-glycoprotein (P-gp) transporter at the BBB, thus preventing the removal of the second-stage drug from the brain, has been put forward as a possible explanation for this observation (12,13), but this hypothesis remains untested.…”

The Distribution of Nifurtimox Across the Healthy and Trypanosome-Infected Murine Blood-Brain and Blood-Cerebrospinal Fluid Barriers

“…rhodesiense and T.b. brucei infections (Clarkson et al, 1984;Bacchi et al, 1987Bacchi et al, ,1994. We have also revealed that pentamidine (another first-stage drug) can cross the BBB, but is removed by ATP binding cassette transporters including P-glycoprotein (P-gp) and MRP (Sanderson et al, 2009).…”