Sanaa S. Botros

Praziquantel: its use in control of schistosomiasis in sub-Saharan Africa and current research needs

Treatment with praziquantel (PZQ) has become virtually the sole basis of schistosomiasis control in sub-Saharan Africa and elsewhere, and the drug is reviewed here in the context of the increasing rate that it is being used for this purpose. Attention is drawn to our relative lack of knowledge about the mechanisms of action of PZQ at the molecular level, the need for more work to be done on schistosome isolates that have been collected recently from endemic areas rather than those maintained in laboratory conditions for long periods, and our reliance for experimental work mainly on Schistosoma mansoni, little work having been done on S. haematobium. There is no evidence that resistance to PZQ has been induced in African schistosomes as a result of its large-scale use on that continent to date, but there is also no assurance that PZQ and/or schistosomes are in any way unique and that resistant organisms will not be selected as a result of widespread drug usage. The failure of PZQ to produce complete cures in populations given a routine treatment should therefore solicit considerable concern. With few alternatives to PZQ currently available and/or on the horizon, methods to monitor drug-susceptibility in African schistosomes need to be devised and used to help ensure that this drug remains effective for as long a time as possible.

Praziquantel-induced tegumental damage in vitro is diminished in schistosomes derived from praziquantel-resistant infections.

The aggressive use of praziquantel to combat schistosomiasis in Egpyt raises concern about the possible emergence of resistance. Eggs from Egyptian patients with praziquantel-resistant infections (not cured by 3 doses of praziquantel) have been used to establish infection-specific schistosome isolates in mice. The response of these worms to the drug was observed in vitro, in order to determine if the isolates obtained from these resistant infections were, in fact, less responsive to praziquantel. One of the hallmark effects of praziquantel on schistosomes in vitro is a disruption of the worms outer surface, the tegument. Here, praziquantel-induced tegumental damage is observed in 3 distinct isolates, 2 derived from resistant infections and 1 from an infection cured by a single dose. The isolates from the resistant infections were less susceptible to praziquantel-induced tegumental damage in vitro, suggesting that the worms are in some way less responsive to the drug.

Stability and reproductive fitness of Schistosoma mansoni isolates with decreased sensitivity to praziquantel

These studies are focused on schistosomes derived from human infections not cured by three successive doses of praziquantel that also produced infections in mice that were significantly more difficult to cure than infections with control worms. Half (three of six) of these isolates retained their decreased response to praziquantel after multiple passages through the life-cycle in the absence of therapeutic pressure. Two of the isolates, including the one initially least sensitive to praziquantel; reverted, to a sensitivity not significantly different from controls. For example, the EE6 isolate initially required 680 mg/kg praziquantel to affect a 50% reduction in worm load in murine infections, but after only six passages through the life cycle over 5 years this was reduced to 113 mg/kg, not different from control infections. The stability of some of the isolates and the reversion of others indicates that the biological or genetic factors conferring decreased praziquantel response varies among the isolates. The three isolates that retained decreased sensitivity to praziquantel all showed compromises in reproductive fitness in the laboratory, expressed most frequently as a decreased cercarial production from snails infected with those isolates compared to controls. For example, the total cercarial production of snails infected with the EE10 isolate was only 57% that of controls. The reversion of some of the isolates to a praziquantel sensitive state and the decreased reproductive fitness of those that did not revert suggest that there is some biological cost associated with the relative praziquantel insensitivity of these worms, which could help limit the impact of such isolates in the field. Infections with the less sensitive isolates also produced significantly less circulating schistosomal antigen in mice, suggesting that a decrease in the host immune response elicited by these worms could be one of the factors contributing to the diminished praziquantel efficacy.

Activity of 9-(S)-[3-Hydroxy-2-(Phosphonomethoxy)Propyl]Adenine against Schistosomiasis mansoni in Mice

ABSTRACT The activity of the acyclic nucleotide analogue 9-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]adenine [(S)-HPMPA] against Schistosoma mansoni was investigated in mice. The compound was injected intraperitoneally, usually on two or five consecutive days, at 10 to 20 mg/kg of body weight/day. The treatment started before, at the time of, and after the onset of egg laying (oviposition) by S. mansoni. The animals were killed from 7 to 40 days after the cessation of treatment. Significant reductions in the total numbers of female and coupled worms were found. Female fecundity and both hepatic and intestinal egg loads were suppressed. These effects were more pronounced with dosing regimens launched before the time of oviposition. The complete disappearance of immature eggs and a significant reduction to the complete absence of mature eggs, with 99 to 100% of the eggs being dead, were produced. No hepatic egg-induced granulomas were present in mice treated at the time of oviposition, and the granulomas were smaller in mice treated before S. mansoni oviposition. These preliminary findings extend the knowledge of the antiparasitic properties of (S)-HPMPA.

MCR Synthesis of Praziquantel Derivatives

Schistosomiasis, a high volume neglected tropical disease affecting more than 200 million people worldwide, can only be effectively treated by the tetrahydroisoquinoline drug praziquantel (PZQ). Herein, we describe an efficient approach to access PZQ derivatives by the Ugi 4‐component reaction followed by the Pictet–Spengler reaction in a two‐step, one‐pot procedure. 30 novel PZQ derivatives are described based on the Ugi 4‐component reaction and an X‐ray structure of a novel derivative revealing different conformation compared with PZQ is discussed. Several analogues comparable in activity to the drug PZQ have been identified based on an in vitro Schistosoma mansoni worm viability assay.

Response of Schistosoma mansoni Isolates Having Different Drug Sensitivity to Praziquantel Over Several Life Cycle Passages with and Without Therapeutic Pressure

The stability of praziquantel (PZQ)-insusceptible S. mansoni isolates and the possible selection of PZQ-insusceptible parasites upon applying therapeutic pressure were examined over several life cycle passages (snails to mice). To test isolate stability, 3 PZQ-susceptible and 7 PZQ-insusceptible isolates were used to establish infection in mice, and they were passaged each for 2–5 life cycles. After each passage, 6 groups of mice were used to assess the PZQ dose at which the worm burden was decreased by 50% (ED50). Five of them were treated with doses of PZQ (12.5, 25, 50, 100, and 200 mg/kg for 5 days) 7 wk after infection; the last group represented infected, but untreated, controls. Possible selection of PZQ-insusceptible parasites under therapeutic pressure was examined by subjecting 1 PZQ-susceptible and 1 PZQ-insusceptible S. mansoni isolate to therapeutic pressure by PZQ for 8 passages. After the final passage, PZQ ED50 was estimated. All PZQ-susceptible S. mansoni isolates showed stable susceptibility to PZQ (mean PZQ ED50 = 85 mg/kg) over all passages. Two of the 7 PZQ-insusceptible S. mansoni isolates (S47 and ER5) showed normal sensitivity to PZQ in 1–2 passages (although not the last passage, and without a declining ED50 profile), whereas the remaining passages kept a sustained insusceptibility to the drug (mean PZQ ED50 = 217 mg/kg). Worm maturity and sex were irrelevant to variability in drug ED50 within an individual isolate over different passages, revealing the heterogeneous nature of the parasite. Therapeutic pressure for limited life cycle passages did not result in a significant increase in drug ED50. The fact that reversion of some of the PZQ-insusceptible S. mansoni isolates to normal drug-sensitive state is not long lasting and that the therapeutic pressure by PZQ in the field is not comparable with that in the laboratory (unlimited), make monitoring the response of patients to the drug in the field an integral part of schistosomiasis control measures.

IMPACT OF DRUG DOSAGE AND BRAND ON BIOAVAILABILITY AND EFFICACY OF PRAZIQUANTEL

The efficacy of two brands (brand 1 = Biltricide; Bayer AG, Leverkusen, Germany; brand 2 = Distocide; EPICO pharmaceuticals, Cairo, Egypt) of praziquantel (PZQ) in full and half doses (40 and 20 mg kg-1) monitored as percentage egg reduction and cure rate was investigated in S. mansoni infected school-children. A total of 506 school-children (8-16 years of age) were classified into three groups according to their intensity of infection, heavy [> 500 eggs per grams (epg)], moderate (100-500 epg) and light (< 100 epg), after examination three stool samples (three slides per sample) on three consecutive days. Percentage egg reduction and cure rate were monitored 4 and 10 weeks post-treatment for each dose regimen in the different test groups. Before testing the efficacy of either bran in patients, the pharmacokinetic parameters of the two brands were studied in non-infected normal volunteers. Statistical analysis of the pharmacokinetic parameters of brand 1 vs brand 2 (in a dose of 20 or 40 mg kg-1) revealed no significant difference in elimination (ke), absorption rate constant (ka), elimination half life (t1/2e), area under the time-concentration curve (Auc), serum maximum concentration (Cpmax) and time to maximum concentration (Tmax). As regards the efficacy of test drugs, statistical analysis revealed that up to 10 weeks post-treatment the two brands of PZQ in full dose were equally effective in reducing egg count as their half doses except in heavily infected cases treated with brand 2 of PZQ.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy and safety of artemether in the treatment of chronic fascioliasis in Egypt: exploratory phase-2 trials.

Background Fascioliasis is an emerging zoonotic disease of considerable veterinary and public health importance. Triclabendazole is the only available drug for treatment. Laboratory studies have documented promising fasciocidal properties of the artemisinins (e.g., artemether). Methodology We carried out two exploratory phase-2 trials to assess the efficacy and safety of oral artemether administered at (i) 6×80 mg over 3 consecutive days, and (ii) 3×200 mg within 24 h in 36 Fasciola-infected individuals in Egypt. Efficacy was determined by cure rate (CR) and egg reduction rate (ERR) based on multiple Kato-Katz thick smears before and after drug administration. Patients who remained Fasciola-positive following artemether dosing were treated with single 10 mg/kg oral triclabendazole. In case of treatment failure, triclabendazole was re-administered at 20 mg/kg in two divided doses. Principal Findings CRs achieved with 6×80 mg and 3×200 mg artemether were 35% and 6%, respectively. The corresponding ERRs were 63% and nil, respectively. Artemether was well tolerated. A high efficacy was observed with triclabendazole administered at 10 mg/kg (16 patients; CR: 67%, ERR: 94%) and 20 mg/kg (4 patients; CR: 75%, ERR: 96%). Conclusions/Significance Artemether, administered at malaria treatment regimens, shows no or only little effect against fascioliasis, and hence does not represent an alternative to triclabendazole. The role of artemether and other artemisinin derivatives as partner drug in combination chemotherapy remains to be elucidated.

Comparative efficacy and bioavailability of different praziquantel brands

This study investigates the efficacy, bioavailability and drug metabolizing enzymes mainly involved in the metabolism of the commercial brands of praziquantel (PZQ) in Egypt in comparison with the original pure powder. Mice infected with PZQ-susceptible (CD) or PZQ-insusceptible (EE2) Schistosoma mansoni isolates were divided each into seven groups, six of them received PZQ brands (Distocide, Epiquantel, Biltricide, Bilharzid, Praziquantel, and pure PZQ), while the seventh one was left as infected untreated. Seven weeks post-infection, worms were quantified and hepatic CYP450 and CYT b5 were examined. For PZQ pharmacokinetics, groups of normal mice were given the different PZQ brands and divided into subgroups, killed at 2, 5, 15, 30, 60, 90, 120,150, 180, 240 and 360 min post-dosing. Physicochemical examination revealed better dissolution rates for Biltricide, Distocide and PZQ T3A rather than Epiquantel and Bilharzid. Significant decrease in worm burden was recorded in all groups of mice regardless of the brand of PZQ used, but with better results obtained with CD isolate rather than the EE2 isolate. Biltricide and Distocide showed higher C(max) and AUC(0-6h) in normal mice, in addition to higher worm reduction with least inhibition of CYP450 and CYT b5 in EE2-infected mice. PZQ T3A, Bilharzid and Epiquantel showed, in addition to lower efficacy, higher K(el), lower t(1/2e), C(max) and AUC(0-6h). The 32-46% reduction of their bioavailability reflected on their antischistosomal efficacy and recovery of drug metabolizing enzymes. Quality of generic PZQ should include, in addition to examining the physicochemical characteristics of the brands, biological testing including efficacy and bioavailability studies.

Effect of combined low dose praziquantel and oxamniquine on different stages of schistosome maturity

Combined low doses of praziquantel and oxamniquine were tested against different stages of Schistosoma mansoni in infected Swiss albino mice. The effect of combination therapy (1/3 the curative dose of praziquantel plus 1/3 the curative dose of oxamniquine) was compared with the effect of each drug alone, in reduced or full dose. Comparison with infected untreated controls was also made. Drug effects were evaluated on different growth stages of schistosomes by administering the drugs 24 h before infection and 4 h, 1, 2, 3, 4 and 5 weeks after infection. Animals were killed 8 weeks after infection. Worm burden, distribution, tissue egg load and oogram pattern were used in assessing drug efficacy. A potentiating effect was observed in animals receiving combination therapy. The combination regimen was most effective 4 h after infection, producing 96% worm reduction; eggs were not detected in the liver or intestine. Five weeks after infection the same regimen resulted in 98% reduction in the tissue egg load.