In vivo preliminary investigations of the effects of the benzimidazole anthelmintic drug flubendazole on rat embryos and fetuses.

Flubendazole, in a new formulation with high systemic bioavailability, has been proposed as a macrofilaricide against filarial diseases. To investigate embryotoxic activity, the new flubendazole formulation was administered orally to Sprague Dawley rats at 2, 3.46, 6.32mg/kg/day on gestation day (GD) 9.5 and 10.5. Embryos/fetuses were evaluated on GD 11.5, 12.5 or 20. At 6.32mg/kg/day (Cmax=0.801µg/mL after single administration), flubendazole initially induced an arrest of embryonic development followed by a generalized cell death that led to 100% embryolethality by GD 12.5. At 3.46mg/kg/day (Cmax=0.539µg/mL after single administration), flubendazole markedly reduced embryonic development by GD 12.5 without causing cell death. On GD 20, 80% of fetuses showed malformations. At 2mg/kg/day (Cmax=0.389µg/mL after single administration), it did not interfere with rat embryofetal development.

Effects of the benzimidazole anthelmintic drug flubendazole on rat embryos in vitro.

Filarial diseases affect millions of people in poverty-stricken areas. In 2011, an investigation of the potential of flubendazole as a safe, highly efficacious, and field-usable macrofilaricidal drug was begun by Drug for Neglected Diseases initiative. As part of the preclinical development program, whole embryo culture was used to investigate the potential embryotoxicity of flubendazole and its metabolites, reduced and hydrolyzed flubendazole. Albendazole was included as a comparator. Flubendazole and albendazole showed similar potency in affecting rat embryonic development in vitro, inducing retardation of growth and dysmorphogenic effects at concentrations ≥0.5 µg/mL. The head, optic and otic systems, branchial arches and posterior body portion were affected. Diffuse areas of cell death were seen in various embryonic districts. The No Observed Effect Level (NOEL) was 0.25 µg/mL for both drugs. Reduced and hydrolyzed flubendazole were less embryotoxic than the parent compound, with NOELs 4-fold and >40-fold higher than that of flubendazole, respectively.

Comparative embryotoxicity of different antimalarial peroxides: in vitro study using the rat whole embryo culture model (WEC).

Three groups of compounds: (i) active peroxides (artemisinin and arterolene), (ii) inactive non-peroxidic derivatives (deoxyartemisinin and carbaOZ277) and (iii) inactive peroxide (OZ381) were tested by WEC system to provide insights into the relationship between chemical structure and embryotoxic potential, and to assess the relationship between embryotoxicity and antimalarial activity. Deoxyartemisinin, OZ381 and carbaOZ277 did not affect rat embryonic development. Artemisinin and arterolane affected primarily nucleated red blood cells (RBCs), inducing anemia and subsequent tissue damage in rat embryos, with NOELs for RBC damage at 0.1 and 0.175µg/mL, respectively. These data support the idea that only active antimalarial peroxides are able to interfere with normal embryonic development. In an attempt to establish whether and to what extent activity as antimalarials and embryotoxicity can be divorced, IC(50)s for activity in Plasmodium falciparum strains and the NOELs for RBCs were compared. From this comparison, arterolane showed a better safety margin than artemisinin.

Investigations of the effects of the antimalarial drug dihydroartemisinin (DHA) using the Frog Embryo Teratogenesis Assay-Xenopus (FETAX).

Artemisinin derivatives are effective and safe drugs for treating malaria, but they are not recommended during the first trimester of pregnancy because of resorptions and abnormalities observed in animal reproduction studies. Previous studies in rats showed that artemisinin embryotoxicity derives from the depletion of primitive red blood cells (RBCs) over a narrow critical time window (gestation Days 9-14). In order to further investigate the susceptibility of primitive RBCs to artemisinins and to establish whether this susceptibility is species-specific or inherent to the compound, we studied dihydroartemisinin (DHA), both a drug in its own right and the main metabolite of current artemisinin derivatives in use, in the Frog Embryo Teratogenesis Assay-Xenopus (FETAX). This model readily allows investigation and monitoring of primitive and definitive RBCs. Effects on frog larvae exposed to DHA for 48 h during early embryonic development, starting from 24 h post fertilization, were similar to those on rat embryos in terms of reduction in the number of primitive RBCs (clonally produced within the ventral blood island). In contrast, RBCs of older larvae (stage 47, produced at the definitive sites of hematopoiesis) were affected minimally and subsequently recovered. Compared to rat embryos, the frog larvae had no areas of necrosis but they shared similar heart defects. The mitochondrion appeared to be the main subcellular target, similar to observations in Plasmodium. These results implicate artemisinin-induced embryotoxicity through perturbation of metabolically active RBCs; whereas this mode of action does not appear to be species-specific, the stages of susceptibility varied between different species. The window of susceptibility and duration of exposure must be considered to evaluate the clinical relevance of these findings.

In vivo and in vitro investigations of the effects of the antimalarial drug dihydroartemisinin (DHA) on rat embryos.

Artemisinin derivatives are clinically effective and safe antimalarials, but are not recommended during the first trimester of pregnancy because of the resorptions and abnormalities seen in animal reproduction studies. Understanding how, when and what toxicity occurs is crucial to any assessment of clinical relevance. Previously, DHA has been shown in the rat whole embryo culture (WEC) to primarily affect primitive red blood cells (RBCs) causing subsequent tissue damage and dysmorphogenesis. To verify the primary target of DHA in vivo and to detect consequences induced by early damage on embryo development, pregnant female rats were orally treated on gestation days (GD) 9.5 and 10.5 with 7.5 or 15 mg/kg/day DHA and caesarean sectioned on GD11.5, 12.5, 13.5, 15 and 20. A parallel in vitro WEC study evaluated the role of oxidative damage and examined blood islands and primitive RBCs. In accordance with the WEC results, primitive RBCs from yolk sac hematopoiesis were the target of DHA in vivo. The resulting anemia led to cell damage, which depending on its degree, was either diffuse or focal. Embryonic response to acute anemia varied from complete recovery to malformation and death, depending on the extent of cell death. Malformations occurred only in litters with embryonic deaths. DHA induced low glutathione levels in RBCs, indicating that oxidative stress may be involved in artemisinin toxicity; effects were extremely rapid, with altered RBCs seen as early as GD10. In establishing the relevance of these findings to humans, one should consider differences in the development of rodents and humans. While yolk sac hematopoiesis occurs similarly in the two species, early placentation and extent of exposure differ. In particular, early hematopoiesis takes only 7 days in rats (during which RBCs expand in a clonal fashion) compared with 6 weeks in humans; thus the susceptible period in relation to the duration of exposure to an artemisinin-based treatment may be substantially different.

Effects of the antimalarial drug dihydroartemisinin (DHA) on rat embryos in vitro.

Artemisinin derivatives are not currently recommended for use during the first trimester of pregnancy because they cause embryo death and some abnormalities in early pregnancy in animals. We studied the effects of dihydroartemisinin (DHA) in rat whole embryo cultures (WEC). DHA was added to the culture medium for the entire 48-h culture, 1.5 h at the beginning or at the end of the culture at 0.01-2 microg/mL. DHA affected primarily red blood cells during yolk sac hematopoiesis. Higher concentrations and longer exposure inhibited angiogenesis. Tissue damage (cell deaths) and effects on embryo morphology (neural tube, branchial arches, somites and caudal region defects) were attributed to these events. The viability of severely affected embryos beyond the 48-h assay is uncertain. These results help explain findings from animal data and provide evidence that the yolk sac is highly susceptible to artemisinin compounds. Extrapolating results to pregnant women exposed in the first trimester remains difficult. Pharmacovigilance and further studies of the mechanism of damage are needed.